This file documents the use of the GNU compilers.
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A GNU Manual
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You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.
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This manual documents how to use the GNU compilers, as well as their features and incompatibilities, and how to report bugs. It corresponds to the compilers version 13.3.1. The internals of the GNU compilers, including how to port them to new targets and some information about how to write front ends for new languages, are documented in a separate manual. See Introduction.
GCC stands for “GNU Compiler Collection”. GCC is an integrated distribution of compilers for several major programming languages. These languages currently include C, C++, Objective-C, Objective-C++, Fortran, Ada, D, and Go.
The abbreviation GCC has multiple meanings in common use. The current official meaning is “GNU Compiler Collection”, which refers generically to the complete suite of tools. The name historically stood for “GNU C Compiler”, and this usage is still common when the emphasis is on compiling C programs. Finally, the name is also used when speaking of the language-independent component of GCC: code shared among the compilers for all supported languages.
The language-independent component of GCC includes the majority of the optimizers, as well as the “back ends” that generate machine code for various processors.
The part of a compiler that is specific to a particular language is called the “front end”. In addition to the front ends that are integrated components of GCC, there are several other front ends that are maintained separately. These support languages such as Mercury, and COBOL. To use these, they must be built together with GCC proper.
Most of the compilers for languages other than C have their own names. The C++ compiler is G++, the Ada compiler is GNAT, and so on. When we talk about compiling one of those languages, we might refer to that compiler by its own name, or as GCC. Either is correct.
Historically, compilers for many languages, including C++ and Fortran, have been implemented as “preprocessors” which emit another high level language such as C. None of the compilers included in GCC are implemented this way; they all generate machine code directly. This sort of preprocessor should not be confused with the C preprocessor, which is an integral feature of the C, C++, Objective-C and Objective-C++ languages.
For each language compiled by GCC for which there is a standard, GCC attempts to follow one or more versions of that standard, possibly with some exceptions, and possibly with some extensions.
The original ANSI C standard (X3.159-1989) was ratified in 1989 and published in 1990. This standard was ratified as an ISO standard (ISO/IEC 9899:1990) later in 1990. There were no technical differences between these publications, although the sections of the ANSI standard were renumbered and became clauses in the ISO standard. The ANSI standard, but not the ISO standard, also came with a Rationale document. This standard, in both its forms, is commonly known as C89, or occasionally as C90, from the dates of ratification. To select this standard in GCC, use one of the options -ansi, -std=c90 or -std=iso9899:1990; to obtain all the diagnostics required by the standard, you should also specify -pedantic (or -pedantic-errors if you want them to be errors rather than warnings). See Options Controlling C Dialect.
Errors in the 1990 ISO C standard were corrected in two Technical Corrigenda published in 1994 and 1996. GCC does not support the uncorrected version.
An amendment to the 1990 standard was published in 1995. This
amendment added digraphs and __STDC_VERSION__ to the language,
but otherwise concerned the library. This amendment is commonly known
as AMD1; the amended standard is sometimes known as C94 or
C95. To select this standard in GCC, use the option
-std=iso9899:199409 (with, as for other standard versions,
-pedantic to receive all required diagnostics).
A new edition of the ISO C standard was published in 1999 as ISO/IEC 9899:1999, and is commonly known as C99. (While in development, drafts of this standard version were referred to as C9X.) GCC has substantially complete support for this standard version; see https://gcc.gnu.org/c99status.html for details. To select this standard, use -std=c99 or -std=iso9899:1999.
Errors in the 1999 ISO C standard were corrected in three Technical Corrigenda published in 2001, 2004 and 2007. GCC does not support the uncorrected version.
A fourth version of the C standard, known as C11, was published
in 2011 as ISO/IEC 9899:2011. (While in development, drafts of this
standard version were referred to as C1X.)
GCC has substantially complete support
for this standard, enabled with -std=c11 or
-std=iso9899:2011. A version with corrections integrated was
prepared in 2017 and published in 2018 as ISO/IEC 9899:2018; it is
known as C17 and is supported with -std=c17 or
-std=iso9899:2017; the corrections are also applied with
-std=c11, and the only difference between the options is the
value of __STDC_VERSION__.
A further version of the C standard, known as C2X, is under development; experimental and incomplete support for this is enabled with -std=c2x.
By default, GCC provides some extensions to the C language that, on rare occasions conflict with the C standard. See Extensions to the C Language Family. Some features that are part of the C99 standard are accepted as extensions in C90 mode, and some features that are part of the C11 standard are accepted as extensions in C90 and C99 modes. Use of the -std options listed above disables these extensions where they conflict with the C standard version selected. You may also select an extended version of the C language explicitly with -std=gnu90 (for C90 with GNU extensions), -std=gnu99 (for C99 with GNU extensions) or -std=gnu11 (for C11 with GNU extensions).
The default, if no C language dialect options are given, is -std=gnu17.
The ISO C standard defines (in clause 4) two classes of conforming
implementation. A conforming hosted implementation supports the
whole standard including all the library facilities; a conforming
freestanding implementation is only required to provide certain
library facilities: those in <float.h>, <limits.h>,
<stdarg.h>, and <stddef.h>; since AMD1, also those in
<iso646.h>; since C99, also those in <stdbool.h> and
<stdint.h>; and since C11, also those in <stdalign.h>
and <stdnoreturn.h>. In addition, complex types, added in C99, are not
required for freestanding implementations.
The standard also defines two environments for programs, a
freestanding environment, required of all implementations and
which may not have library facilities beyond those required of
freestanding implementations, where the handling of program startup
and termination are implementation-defined; and a hosted
environment, which is not required, in which all the library
facilities are provided and startup is through a function int
main (void) or int main (int, char *[]). An OS kernel is an example
of a program running in a freestanding environment;
a program using the facilities of an
operating system is an example of a program running in a hosted environment.
GCC aims towards being usable as a conforming freestanding
implementation, or as the compiler for a conforming hosted
implementation. By default, it acts as the compiler for a hosted
implementation, defining __STDC_HOSTED__ as 1 and
presuming that when the names of ISO C functions are used, they have
the semantics defined in the standard. To make it act as a conforming
freestanding implementation for a freestanding environment, use the
option -ffreestanding; it then defines
__STDC_HOSTED__ to 0 and does not make assumptions about the
meanings of function names from the standard library, with exceptions
noted below. To build an OS kernel, you may well still need to make
your own arrangements for linking and startup.
See Options Controlling C Dialect.
GCC does not provide the library facilities required only of hosted implementations, nor yet all the facilities required by C99 of freestanding implementations on all platforms. To use the facilities of a hosted environment, you need to find them elsewhere (for example, in the GNU C library). See Standard Libraries.
Most of the compiler support routines used by GCC are present in
libgcc, but there are a few exceptions. GCC requires the
freestanding environment provide memcpy, memmove,
memset and memcmp.
Finally, if __builtin_trap is used, and the target does
not implement the trap pattern, then GCC emits a call
to abort.
For references to Technical Corrigenda, Rationale documents and information concerning the history of C that is available online, see https://gcc.gnu.org/readings.html
GCC supports the original ISO C++ standard published in 1998, and the 2011, 2014, 2017 and mostly 2020 revisions.
The original ISO C++ standard was published as the ISO standard (ISO/IEC
14882:1998) and amended by a Technical Corrigenda published in 2003
(ISO/IEC 14882:2003). These standards are referred to as C++98 and
C++03, respectively. GCC implements the majority of C++98 (export
is a notable exception) and most of the changes in C++03. To select
this standard in GCC, use one of the options -ansi,
-std=c++98, or -std=c++03; to obtain all the diagnostics
required by the standard, you should also specify -pedantic (or
-pedantic-errors if you want them to be errors rather than
warnings).
A revised ISO C++ standard was published in 2011 as ISO/IEC 14882:2011, and is referred to as C++11; before its publication it was commonly referred to as C++0x. C++11 contains several changes to the C++ language, all of which have been implemented in GCC. For details see https://gcc.gnu.org/projects/cxx-status.html#cxx11. To select this standard in GCC, use the option -std=c++11.
Another revised ISO C++ standard was published in 2014 as ISO/IEC 14882:2014, and is referred to as C++14; before its publication it was sometimes referred to as C++1y. C++14 contains several further changes to the C++ language, all of which have been implemented in GCC. For details see https://gcc.gnu.org/projects/cxx-status.html#cxx14. To select this standard in GCC, use the option -std=c++14.
The C++ language was further revised in 2017 and ISO/IEC 14882:2017 was published. This is referred to as C++17, and before publication was often referred to as C++1z. GCC supports all the changes in that specification. For further details see https://gcc.gnu.org/projects/cxx-status.html#cxx17. Use the option -std=c++17 to select this variant of C++.
Another revised ISO C++ standard was published in 2020 as ISO/IEC 14882:2020, and is referred to as C++20; before its publication it was sometimes referred to as C++2a. GCC supports most of the changes in the new specification. For further details see https://gcc.gnu.org/projects/cxx-status.html#cxx20. To select this standard in GCC, use the option -std=c++20.
More information about the C++ standards is available on the ISO C++ committee's web site at http://www.open-std.org/jtc1/sc22/wg21/.
To obtain all the diagnostics required by any of the standard versions described above you should specify -pedantic or -pedantic-errors, otherwise GCC will allow some non-ISO C++ features as extensions. See Warning Options.
By default, GCC also provides some additional extensions to the C++ language that on rare occasions conflict with the C++ standard. See Options Controlling C++ Dialect. Use of the -std options listed above disables these extensions where they they conflict with the C++ standard version selected. You may also select an extended version of the C++ language explicitly with -std=gnu++98 (for C++98 with GNU extensions), or -std=gnu++11 (for C++11 with GNU extensions), or -std=gnu++14 (for C++14 with GNU extensions), or -std=gnu++17 (for C++17 with GNU extensions), or -std=gnu++20 (for C++20 with GNU extensions).
The default, if no C++ language dialect options are given, is -std=gnu++17.
GCC supports “traditional” Objective-C (also known as “Objective-C 1.0”) and contains support for the Objective-C exception and synchronization syntax. It has also support for a number of “Objective-C 2.0” language extensions, including properties, fast enumeration (only for Objective-C), method attributes and the @optional and @required keywords in protocols. GCC supports Objective-C++ and features available in Objective-C are also available in Objective-C++.
GCC by default uses the GNU Objective-C runtime library, which is part of GCC and is not the same as the Apple/NeXT Objective-C runtime library used on Apple systems. There are a number of differences documented in this manual. The options -fgnu-runtime and -fnext-runtime allow you to switch between producing output that works with the GNU Objective-C runtime library and output that works with the Apple/NeXT Objective-C runtime library.
There is no formal written standard for Objective-C or Objective-C++. The authoritative manual on traditional Objective-C (1.0) is “Object-Oriented Programming and the Objective-C Language”: https://gnustep.github.io/resources/documentation/ObjectivCBook.pdf is the original NeXTstep document.
The Objective-C exception and synchronization syntax (that is, the
keywords @try, @throw, @catch,
@finally and @synchronized) is
supported by GCC and is enabled with the option
-fobjc-exceptions. The syntax is briefly documented in this
manual and in the Objective-C 2.0 manuals from Apple.
The Objective-C 2.0 language extensions and features are automatically
enabled; they include properties (via the @property,
@synthesize and
@dynamic keywords), fast enumeration (not available in
Objective-C++), attributes for methods (such as deprecated,
noreturn, sentinel, format),
the unused attribute for method arguments, the
@package keyword for instance variables and the @optional and
@required keywords in protocols. You can disable all these
Objective-C 2.0 language extensions with the option
-fobjc-std=objc1, which causes the compiler to recognize the
same Objective-C language syntax recognized by GCC 4.0, and to produce
an error if one of the new features is used.
GCC has currently no support for non-fragile instance variables.
The authoritative manual on Objective-C 2.0 is available from Apple:
For more information concerning the history of Objective-C that is available online, see https://gcc.gnu.org/readings.html
As of the GCC 4.7.1 release, GCC supports the Go 1 language standard, described at https://go.dev/doc/go1.
GCC supports the D 2.0 programming language. The D language itself is currently defined by its reference implementation and supporting language specification, described at https://dlang.org/spec/spec.html.
See GNAT Reference Manual, for information on standard conformance and compatibility of the Ada compiler.
See Standards, for details of standards supported by GNU Fortran.
When you invoke GCC, it normally does preprocessing, compilation, assembly and linking. The “overall options” allow you to stop this process at an intermediate stage. For example, the -c option says not to run the linker. Then the output consists of object files output by the assembler. See Options Controlling the Kind of Output.
Other options are passed on to one or more stages of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them.
Most of the command-line options that you can use with GCC are useful for C programs; when an option is only useful with another language (usually C++), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages.
The usual way to run GCC is to run the executable called gcc, or machine-gcc when cross-compiling, or machine-gcc-version to run a specific version of GCC. When you compile C++ programs, you should invoke GCC as g++ instead. See Compiling C++ Programs, for information about the differences in behavior between gcc and g++ when compiling C++ programs.
The gcc program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may not be grouped: -dv is very different from ‘-d -v’.
You can mix options and other arguments. For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify -L more than once, the directories are searched in the order specified. Also, the placement of the -l option is significant.
Many options have long names starting with ‘-f’ or with ‘-W’—for example, -fmove-loop-invariants, -Wformat and so on. Most of these have both positive and negative forms; the negative form of -ffoo is -fno-foo. This manual documents only one of these two forms, whichever one is not the default.
Some options take one or more arguments typically separated either
by a space or by the equals sign (‘=’) from the option name.
Unless documented otherwise, an argument can be either numeric or
a string. Numeric arguments must typically be small unsigned decimal
or hexadecimal integers. Hexadecimal arguments must begin with
the ‘0x’ prefix. Arguments to options that specify a size
threshold of some sort may be arbitrarily large decimal or hexadecimal
integers followed by a byte size suffix designating a multiple of bytes
such as kB and KiB for kilobyte and kibibyte, respectively,
MB and MiB for megabyte and mebibyte, GB and
GiB for gigabyte and gigibyte, and so on. Such arguments are
designated by byte-size in the following text. Refer to the NIST,
IEC, and other relevant national and international standards for the full
listing and explanation of the binary and decimal byte size prefixes.
See Option Index, for an index to GCC's options.
Here is a summary of all the options, grouped by type. Explanations are in the following sections.
-c -S -E -o file
-dumpbase dumpbase -dumpbase-ext auxdropsuf
-dumpdir dumppfx -x language
-v -### --help[=class[,...]] --target-help --version
-pass-exit-codes -pipe -specs=file -wrapper
@file -ffile-prefix-map=old=new -fcanon-prefix-map
-fplugin=file -fplugin-arg-name=arg
-fdump-scos
-fdump-ada-spec[-slim] -fada-spec-parent=unit -fdump-go-spec=file
-ansi -std=standard -aux-info filename
-fno-asm
-fno-builtin -fno-builtin-function -fcond-mismatch
-ffreestanding -fgimple -fgnu-tm -fgnu89-inline -fhosted
-flax-vector-conversions -fms-extensions
-foffload=arg -foffload-options=arg
-fopenacc -fopenacc-dim=geom
-fopenmp -fopenmp-simd -fopenmp-target-simd-clone[=device-type]
-fpermitted-flt-eval-methods=standard
-fplan9-extensions -fsigned-bitfields -funsigned-bitfields
-fsigned-char -funsigned-char -fstrict-flex-arrays[=n]
-fsso-struct=endianness
-fabi-version=n -fno-access-control
-faligned-new=n -fargs-in-order=n -fchar8_t -fcheck-new
-fconstexpr-depth=n -fconstexpr-cache-depth=n
-fconstexpr-loop-limit=n -fconstexpr-ops-limit=n
-fno-elide-constructors
-fno-enforce-eh-specs
-fno-gnu-keywords
-fno-implicit-templates
-fno-implicit-inline-templates
-fno-implement-inlines
-fmodule-header[=kind] -fmodule-only -fmodules-ts
-fmodule-implicit-inline
-fno-module-lazy
-fmodule-mapper=specification
-fmodule-version-ignore
-fms-extensions
-fnew-inheriting-ctors
-fnew-ttp-matching
-fno-nonansi-builtins -fnothrow-opt -fno-operator-names
-fno-optional-diags -fpermissive
-fno-pretty-templates
-fno-rtti -fsized-deallocation
-ftemplate-backtrace-limit=n
-ftemplate-depth=n
-fno-threadsafe-statics -fuse-cxa-atexit
-fno-weak -nostdinc++
-fvisibility-inlines-hidden
-fvisibility-ms-compat
-fext-numeric-literals
-flang-info-include-translate[=header]
-flang-info-include-translate-not
-flang-info-module-cmi[=module]
-stdlib=libstdc++,libc++
-Wabi-tag -Wcatch-value -Wcatch-value=n
-Wno-class-conversion -Wclass-memaccess
-Wcomma-subscript -Wconditionally-supported
-Wno-conversion-null -Wctad-maybe-unsupported
-Wctor-dtor-privacy -Wdangling-reference
-Wno-delete-incomplete
-Wdelete-non-virtual-dtor -Wno-deprecated-array-compare
-Wdeprecated-copy -Wdeprecated-copy-dtor
-Wno-deprecated-enum-enum-conversion -Wno-deprecated-enum-float-conversion
-Weffc++ -Wno-exceptions -Wextra-semi -Wno-inaccessible-base
-Wno-inherited-variadic-ctor -Wno-init-list-lifetime
-Winvalid-constexpr -Winvalid-imported-macros
-Wno-invalid-offsetof -Wno-literal-suffix
-Wmismatched-new-delete -Wmismatched-tags
-Wmultiple-inheritance -Wnamespaces -Wnarrowing
-Wnoexcept -Wnoexcept-type -Wnon-virtual-dtor
-Wpessimizing-move -Wno-placement-new -Wplacement-new=n
-Wrange-loop-construct -Wredundant-move -Wredundant-tags
-Wreorder -Wregister
-Wstrict-null-sentinel -Wno-subobject-linkage -Wtemplates
-Wno-non-template-friend -Wold-style-cast
-Woverloaded-virtual -Wno-pmf-conversions -Wself-move -Wsign-promo
-Wsized-deallocation -Wsuggest-final-methods
-Wsuggest-final-types -Wsuggest-override
-Wno-terminate -Wuseless-cast -Wno-vexing-parse
-Wvirtual-inheritance
-Wno-virtual-move-assign -Wvolatile -Wzero-as-null-pointer-constant
-fconstant-string-class=class-name
-fgnu-runtime -fnext-runtime
-fno-nil-receivers
-fobjc-abi-version=n
-fobjc-call-cxx-cdtors
-fobjc-direct-dispatch
-fobjc-exceptions
-fobjc-gc
-fobjc-nilcheck
-fobjc-std=objc1
-fno-local-ivars
-fivar-visibility=[public|protected|private|package]
-freplace-objc-classes
-fzero-link
-gen-decls
-Wassign-intercept -Wno-property-assign-default
-Wno-protocol -Wobjc-root-class -Wselector
-Wstrict-selector-match
-Wundeclared-selector
-fmessage-length=n
-fdiagnostics-plain-output
-fdiagnostics-show-location=[once|every-line]
-fdiagnostics-color=[auto|never|always]
-fdiagnostics-urls=[auto|never|always]
-fdiagnostics-format=[text|sarif-stderr|sarif-file|json|json-stderr|json-file]
-fno-diagnostics-show-option -fno-diagnostics-show-caret
-fno-diagnostics-show-labels -fno-diagnostics-show-line-numbers
-fno-diagnostics-show-cwe
-fno-diagnostics-show-rule
-fdiagnostics-minimum-margin-width=width
-fdiagnostics-parseable-fixits -fdiagnostics-generate-patch
-fdiagnostics-show-template-tree -fno-elide-type
-fdiagnostics-path-format=[none|separate-events|inline-events]
-fdiagnostics-show-path-depths
-fno-show-column
-fdiagnostics-column-unit=[display|byte]
-fdiagnostics-column-origin=origin
-fdiagnostics-escape-format=[unicode|bytes]
-fsyntax-only -fmax-errors=n -Wpedantic
-pedantic-errors
-w -Wextra -Wall -Wabi=n
-Waddress -Wno-address-of-packed-member -Waggregate-return
-Walloc-size-larger-than=byte-size -Walloc-zero
-Walloca -Walloca-larger-than=byte-size
-Wno-aggressive-loop-optimizations
-Warith-conversion
-Warray-bounds -Warray-bounds=n -Warray-compare
-Wno-attributes -Wattribute-alias=n -Wno-attribute-alias
-Wno-attribute-warning
-Wbidi-chars=[none|unpaired|any|ucn]
-Wbool-compare -Wbool-operation
-Wno-builtin-declaration-mismatch
-Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat
-Wc11-c2x-compat
-Wc++-compat -Wc++11-compat -Wc++14-compat -Wc++17-compat
-Wc++20-compat
-Wno-c++11-extensions -Wno-c++14-extensions -Wno-c++17-extensions
-Wno-c++20-extensions -Wno-c++23-extensions
-Wcast-align -Wcast-align=strict -Wcast-function-type -Wcast-qual
-Wchar-subscripts
-Wclobbered -Wcomment
-Wno-complain-wrong-lang
-Wconversion -Wno-coverage-mismatch -Wno-cpp
-Wdangling-else -Wdangling-pointer -Wdangling-pointer=n
-Wdate-time
-Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init
-Wdisabled-optimization
-Wno-discarded-array-qualifiers -Wno-discarded-qualifiers
-Wno-div-by-zero -Wdouble-promotion
-Wduplicated-branches -Wduplicated-cond
-Wempty-body -Wno-endif-labels -Wenum-compare -Wenum-conversion
-Wenum-int-mismatch
-Werror -Werror=* -Wexpansion-to-defined -Wfatal-errors
-Wfloat-conversion -Wfloat-equal -Wformat -Wformat=2
-Wno-format-contains-nul -Wno-format-extra-args
-Wformat-nonliteral -Wformat-overflow=n
-Wformat-security -Wformat-signedness -Wformat-truncation=n
-Wformat-y2k -Wframe-address
-Wframe-larger-than=byte-size -Wno-free-nonheap-object
-Wno-if-not-aligned -Wno-ignored-attributes
-Wignored-qualifiers -Wno-incompatible-pointer-types
-Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=n
-Wno-implicit-function-declaration -Wno-implicit-int
-Winfinite-recursion
-Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context
-Wno-int-to-pointer-cast -Wno-invalid-memory-model
-Winvalid-pch -Winvalid-utf8 -Wno-unicode -Wjump-misses-init
-Wlarger-than=byte-size -Wlogical-not-parentheses -Wlogical-op
-Wlong-long -Wno-lto-type-mismatch -Wmain -Wmaybe-uninitialized
-Wmemset-elt-size -Wmemset-transposed-args
-Wmisleading-indentation -Wmissing-attributes -Wmissing-braces
-Wmissing-field-initializers -Wmissing-format-attribute
-Wmissing-include-dirs -Wmissing-noreturn -Wno-missing-profile
-Wno-multichar -Wmultistatement-macros -Wnonnull -Wnonnull-compare
-Wnormalized=[none|id|nfc|nfkc]
-Wnull-dereference -Wno-odr
-Wopenacc-parallelism
-Wopenmp-simd
-Wno-overflow -Woverlength-strings -Wno-override-init-side-effects
-Wpacked -Wno-packed-bitfield-compat -Wpacked-not-aligned -Wpadded
-Wparentheses -Wno-pedantic-ms-format
-Wpointer-arith -Wno-pointer-compare -Wno-pointer-to-int-cast
-Wno-pragmas -Wno-prio-ctor-dtor -Wredundant-decls
-Wrestrict -Wno-return-local-addr -Wreturn-type
-Wno-scalar-storage-order -Wsequence-point
-Wshadow -Wshadow=global -Wshadow=local -Wshadow=compatible-local
-Wno-shadow-ivar
-Wno-shift-count-negative -Wno-shift-count-overflow -Wshift-negative-value
-Wno-shift-overflow -Wshift-overflow=n
-Wsign-compare -Wsign-conversion
-Wno-sizeof-array-argument
-Wsizeof-array-div
-Wsizeof-pointer-div -Wsizeof-pointer-memaccess
-Wstack-protector -Wstack-usage=byte-size -Wstrict-aliasing
-Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=n
-Wstring-compare
-Wno-stringop-overflow -Wno-stringop-overread
-Wno-stringop-truncation -Wstrict-flex-arrays
-Wsuggest-attribute=[pure|const|noreturn|format|malloc]
-Wswitch -Wno-switch-bool -Wswitch-default -Wswitch-enum
-Wno-switch-outside-range -Wno-switch-unreachable -Wsync-nand
-Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs
-Wtrivial-auto-var-init -Wtsan -Wtype-limits -Wundef
-Wuninitialized -Wunknown-pragmas
-Wunsuffixed-float-constants -Wunused
-Wunused-but-set-parameter -Wunused-but-set-variable
-Wunused-const-variable -Wunused-const-variable=n
-Wunused-function -Wunused-label -Wunused-local-typedefs
-Wunused-macros
-Wunused-parameter -Wno-unused-result
-Wunused-value -Wunused-variable
-Wno-varargs -Wvariadic-macros
-Wvector-operation-performance
-Wvla -Wvla-larger-than=byte-size -Wno-vla-larger-than
-Wvolatile-register-var -Wwrite-strings
-Wxor-used-as-pow
-Wzero-length-bounds
-fanalyzer
-fanalyzer-call-summaries
-fanalyzer-checker=name
-fno-analyzer-feasibility
-fanalyzer-fine-grained
-fno-analyzer-state-merge
-fno-analyzer-state-purge
-fno-analyzer-suppress-followups
-fanalyzer-transitivity
-fno-analyzer-undo-inlining
-fanalyzer-verbose-edges
-fanalyzer-verbose-state-changes
-fanalyzer-verbosity=level
-fdump-analyzer
-fdump-analyzer-callgraph
-fdump-analyzer-exploded-graph
-fdump-analyzer-exploded-nodes
-fdump-analyzer-exploded-nodes-2
-fdump-analyzer-exploded-nodes-3
-fdump-analyzer-exploded-paths
-fdump-analyzer-feasibility
-fdump-analyzer-json
-fdump-analyzer-state-purge
-fdump-analyzer-stderr
-fdump-analyzer-supergraph
-fdump-analyzer-untracked
-Wno-analyzer-double-fclose
-Wno-analyzer-double-free
-Wno-analyzer-exposure-through-output-file
-Wno-analyzer-exposure-through-uninit-copy
-Wno-analyzer-fd-access-mode-mismatch
-Wno-analyzer-fd-double-close
-Wno-analyzer-fd-leak
-Wno-analyzer-fd-phase-mismatch
-Wno-analyzer-fd-type-mismatch
-Wno-analyzer-fd-use-after-close
-Wno-analyzer-fd-use-without-check
-Wno-analyzer-file-leak
-Wno-analyzer-free-of-non-heap
-Wno-analyzer-imprecise-fp-arithmetic
-Wno-analyzer-infinite-recursion
-Wno-analyzer-jump-through-null
-Wno-analyzer-malloc-leak
-Wno-analyzer-mismatching-deallocation
-Wno-analyzer-null-argument
-Wno-analyzer-null-dereference
-Wno-analyzer-out-of-bounds
-Wno-analyzer-possible-null-argument
-Wno-analyzer-possible-null-dereference
-Wno-analyzer-putenv-of-auto-var
-Wno-analyzer-shift-count-negative
-Wno-analyzer-shift-count-overflow
-Wno-analyzer-stale-setjmp-buffer
-Wno-analyzer-tainted-allocation-size
-Wno-analyzer-tainted-assertion
-Wno-analyzer-tainted-array-index
-Wno-analyzer-tainted-divisor
-Wno-analyzer-tainted-offset
-Wno-analyzer-tainted-size
-Wanalyzer-too-complex
-Wno-analyzer-unsafe-call-within-signal-handler
-Wno-analyzer-use-after-free
-Wno-analyzer-use-of-pointer-in-stale-stack-frame
-Wno-analyzer-use-of-uninitialized-value
-Wno-analyzer-va-arg-type-mismatch
-Wno-analyzer-va-list-exhausted
-Wno-analyzer-va-list-leak
-Wno-analyzer-va-list-use-after-va-end
-Wno-analyzer-write-to-const
-Wno-analyzer-write-to-string-literal
-Wbad-function-cast -Wmissing-declarations
-Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs
-Wold-style-declaration -Wold-style-definition
-Wstrict-prototypes -Wtraditional -Wtraditional-conversion
-Wdeclaration-after-statement -Wpointer-sign
-g -glevel -gdwarf -gdwarf-version
-gbtf -gctf -gctflevel
-ggdb -grecord-gcc-switches -gno-record-gcc-switches
-gstrict-dwarf -gno-strict-dwarf
-gas-loc-support -gno-as-loc-support
-gas-locview-support -gno-as-locview-support
-gcolumn-info -gno-column-info -gdwarf32 -gdwarf64
-gstatement-frontiers -gno-statement-frontiers
-gvariable-location-views -gno-variable-location-views
-ginternal-reset-location-views -gno-internal-reset-location-views
-ginline-points -gno-inline-points
-gvms -gz[=type]
-gsplit-dwarf -gdescribe-dies -gno-describe-dies
-fdebug-prefix-map=old=new -fdebug-types-section
-fno-eliminate-unused-debug-types
-femit-struct-debug-baseonly -femit-struct-debug-reduced
-femit-struct-debug-detailed[=spec-list]
-fno-eliminate-unused-debug-symbols -femit-class-debug-always
-fno-merge-debug-strings -fno-dwarf2-cfi-asm
-fvar-tracking -fvar-tracking-assignments
-faggressive-loop-optimizations
-falign-functions[=n[:m:[n2[:m2]]]]
-falign-jumps[=n[:m:[n2[:m2]]]]
-falign-labels[=n[:m:[n2[:m2]]]]
-falign-loops[=n[:m:[n2[:m2]]]]
-fno-allocation-dce -fallow-store-data-races
-fassociative-math -fauto-profile -fauto-profile[=path]
-fauto-inc-dec -fbranch-probabilities
-fcaller-saves
-fcombine-stack-adjustments -fconserve-stack
-fcompare-elim -fcprop-registers -fcrossjumping
-fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules
-fcx-limited-range
-fdata-sections -fdce -fdelayed-branch
-fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively
-fdevirtualize-at-ltrans -fdse
-fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects
-ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=style
-ffinite-loops
-fforward-propagate -ffp-contract=style -ffunction-sections
-fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity
-fgcse-sm -fhoist-adjacent-loads -fif-conversion
-fif-conversion2 -findirect-inlining
-finline-stringops[=fn]
-finline-functions -finline-functions-called-once -finline-limit=n
-finline-small-functions -fipa-modref -fipa-cp -fipa-cp-clone
-fipa-bit-cp -fipa-vrp -fipa-pta -fipa-profile -fipa-pure-const
-fipa-reference -fipa-reference-addressable
-fipa-stack-alignment -fipa-icf -fira-algorithm=algorithm
-flive-patching=level
-fira-region=region -fira-hoist-pressure
-fira-loop-pressure -fno-ira-share-save-slots
-fno-ira-share-spill-slots
-fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute
-fivopts -fkeep-inline-functions -fkeep-static-functions
-fkeep-static-consts -flimit-function-alignment -flive-range-shrinkage
-floop-block -floop-interchange -floop-strip-mine
-floop-unroll-and-jam -floop-nest-optimize
-floop-parallelize-all -flra-remat -flto -flto-compression-level
-flto-partition=alg -fmerge-all-constants
-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves
-fmove-loop-invariants -fmove-loop-stores -fno-branch-count-reg
-fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse
-fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole
-fno-peephole2 -fno-printf-return-value -fno-sched-interblock
-fno-sched-spec -fno-signed-zeros
-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss
-fomit-frame-pointer -foptimize-sibling-calls
-fpartial-inlining -fpeel-loops -fpredictive-commoning
-fprefetch-loop-arrays -fpreserve-control-flow -fprofile-correction
-fprofile-use -fprofile-use=path -fprofile-partial-training
-fprofile-values -fprofile-reorder-functions
-freciprocal-math -free -frename-registers -freorder-blocks
-freorder-blocks-algorithm=algorithm
-freorder-blocks-and-partition -freorder-functions
-frerun-cse-after-loop -freschedule-modulo-scheduled-loops
-frounding-math -fsave-optimization-record
-fsched2-use-superblocks -fsched-pressure
-fsched-spec-load -fsched-spec-load-dangerous
-fsched-stalled-insns-dep[=n] -fsched-stalled-insns[=n]
-fsched-group-heuristic -fsched-critical-path-heuristic
-fsched-spec-insn-heuristic -fsched-rank-heuristic
-fsched-last-insn-heuristic -fsched-dep-count-heuristic
-fschedule-fusion
-fschedule-insns -fschedule-insns2 -fsection-anchors
-fselective-scheduling -fselective-scheduling2
-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops
-fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate
-fsignaling-nans
-fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops
-fsplit-paths
-fsplit-wide-types -fsplit-wide-types-early -fssa-backprop -fssa-phiopt
-fstdarg-opt -fstore-merging -fstrict-aliasing -fipa-strict-aliasing
-fthread-jumps -ftracer -ftree-bit-ccp
-ftree-builtin-call-dce -ftree-ccp -ftree-ch
-ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts
-ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting
-ftree-loop-if-convert -ftree-loop-im
-ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns
-ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize
-ftree-loop-vectorize
-ftree-parallelize-loops=n -ftree-pre -ftree-partial-pre -ftree-pta
-ftree-reassoc -ftree-scev-cprop -ftree-sink -ftree-slsr -ftree-sra
-ftree-switch-conversion -ftree-tail-merge
-ftree-ter -ftree-vectorize -ftree-vrp -ftrivial-auto-var-init
-funconstrained-commons -funit-at-a-time -funroll-all-loops
-funroll-loops -funsafe-math-optimizations -funswitch-loops
-fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt
-fweb -fwhole-program -fwpa -fuse-linker-plugin -fzero-call-used-regs
--param name=value
-O -O0 -O1 -O2 -O3 -Os -Ofast -Og -Oz
-p -pg -fprofile-arcs --coverage -ftest-coverage
-fprofile-abs-path
-fprofile-dir=path -fprofile-generate -fprofile-generate=path
-fprofile-info-section -fprofile-info-section=name
-fprofile-note=path -fprofile-prefix-path=path
-fprofile-update=method -fprofile-filter-files=regex
-fprofile-exclude-files=regex
-fprofile-reproducible=[multithreaded|parallel-runs|serial]
-fsanitize=style -fsanitize-recover -fsanitize-recover=style
-fsanitize-trap -fsanitize-trap=style
-fasan-shadow-offset=number -fsanitize-sections=s1,s2,...
-fsanitize-undefined-trap-on-error -fbounds-check
-fcf-protection=[full|branch|return|none|check]
-fharden-compares -fharden-conditional-branches
-fharden-control-flow-redundancy -fhardcfr-skip-leaf
-fhardcfr-check-exceptions -fhardcfr-check-returning-calls
-fhardcfr-check-noreturn-calls=[always|no-xthrow|nothrow|never]
-fstack-protector -fstack-protector-all -fstack-protector-strong
-fstack-protector-explicit -fstack-check
-fstack-limit-register=reg -fstack-limit-symbol=sym
-fno-stack-limit -fsplit-stack
-fstrub=disable -fstrub=strict -fstrub=relaxed
-fstrub=all -fstrub=at-calls -fstrub=internal
-fvtable-verify=[std|preinit|none]
-fvtv-counts -fvtv-debug
-finstrument-functions -finstrument-functions-once
-finstrument-functions-exclude-function-list=sym,sym,...
-finstrument-functions-exclude-file-list=file,file,...
-fprofile-prefix-map=old=new
-Aquestion=answer
-A-question[=answer]
-C -CC -Dmacro[=defn]
-dD -dI -dM -dN -dU
-fdebug-cpp -fdirectives-only -fdollars-in-identifiers
-fexec-charset=charset -fextended-identifiers
-finput-charset=charset -flarge-source-files
-fmacro-prefix-map=old=new -fmax-include-depth=depth
-fno-canonical-system-headers -fpch-deps -fpch-preprocess
-fpreprocessed -ftabstop=width -ftrack-macro-expansion
-fwide-exec-charset=charset -fworking-directory
-H -imacros file -include file
-M -MD -MF -MG -MM -MMD -MP -MQ -MT -Mno-modules
-no-integrated-cpp -P -pthread -remap
-traditional -traditional-cpp -trigraphs
-Umacro -undef
-Wp,option -Xpreprocessor option
-Wa,option -Xassembler option
object-file-name -fuse-ld=linker -llibrary
-nostartfiles -nodefaultlibs -nolibc -nostdlib -nostdlib++
-e entry --entry=entry
-pie -pthread -r -rdynamic
-s -static -static-pie -static-libgcc -static-libstdc++
-static-libasan -static-libtsan -static-liblsan -static-libubsan
-shared -shared-libgcc -symbolic
-T script -Wl,option -Xlinker option
-u symbol -z keyword
-Bprefix -Idir -I-
-idirafter dir
-imacros file -imultilib dir
-iplugindir=dir -iprefix file
-iquote dir -isysroot dir -isystem dir
-iwithprefix dir -iwithprefixbefore dir
-Ldir -no-canonical-prefixes --no-sysroot-suffix
-nostdinc -nostdinc++ --sysroot=dir
-fcall-saved-reg -fcall-used-reg
-ffixed-reg -fexceptions
-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables
-fasynchronous-unwind-tables -fsjlj
-fno-gnu-unique
-finhibit-size-directive -fcommon -fno-ident
-fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt
-fno-jump-tables -fno-bit-tests
-frecord-gcc-switches
-freg-struct-return -fshort-enums -fshort-wchar
-fverbose-asm -fpack-struct[=n]
-fleading-underscore -ftls-model=model
-fstack-reuse=reuse_level
-ftrampolines -ftrapv -fwrapv
-fvisibility=[default|internal|hidden|protected]
-fstrict-volatile-bitfields -fsync-libcalls
-dletters -dumpspecs -dumpmachine -dumpversion
-dumpfullversion -fcallgraph-info[=su,da]
-fchecking -fchecking=n
-fdbg-cnt-list -fdbg-cnt=counter-value-list
-fdisable-ipa-pass_name
-fdisable-rtl-pass_name
-fdisable-rtl-pass-name=range-list
-fdisable-tree-pass_name
-fdisable-tree-pass-name=range-list
-fdump-debug -fdump-earlydebug
-fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links
-fdump-final-insns[=file]
-fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline
-fdump-lang-all
-fdump-lang-switch
-fdump-lang-switch-options
-fdump-lang-switch-options=filename
-fdump-passes
-fdump-rtl-pass -fdump-rtl-pass=filename
-fdump-statistics
-fdump-tree-all
-fdump-tree-switch
-fdump-tree-switch-options
-fdump-tree-switch-options=filename
-fcompare-debug[=opts] -fcompare-debug-second
-fenable-kind-pass
-fenable-kind-pass=range-list
-fira-verbose=n
-flto-report -flto-report-wpa -fmem-report-wpa
-fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report
-fopt-info -fopt-info-options[=file]
-fmultiflags -fprofile-report
-frandom-seed=string -fsched-verbose=n
-fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose
-fstats -fstack-usage -ftime-report -ftime-report-details
-fvar-tracking-assignments-toggle -gtoggle
-print-file-name=library -print-libgcc-file-name
-print-multi-directory -print-multi-lib -print-multi-os-directory
-print-prog-name=program -print-search-dirs -Q
-print-sysroot -print-sysroot-headers-suffix
-save-temps -save-temps=cwd -save-temps=obj -time[=file]
AArch64 Options
-mabi=name -mbig-endian -mlittle-endian
-mgeneral-regs-only
-mcmodel=tiny -mcmodel=small -mcmodel=large
-mstrict-align -mno-strict-align
-momit-leaf-frame-pointer
-mtls-dialect=desc -mtls-dialect=traditional
-mtls-size=size
-mfix-cortex-a53-835769 -mfix-cortex-a53-843419
-mlow-precision-recip-sqrt -mlow-precision-sqrt -mlow-precision-div
-mpc-relative-literal-loads
-msign-return-address=scope
-mbranch-protection=none|standard|pac-ret[+leaf
+b-key]|bti
-mharden-sls=opts
-march=name -mcpu=name -mtune=name
-moverride=string -mverbose-cost-dump
-mstack-protector-guard=guard -mstack-protector-guard-reg=sysreg
-mstack-protector-guard-offset=offset -mtrack-speculation
-moutline-atomics
Adapteva Epiphany Options
-mhalf-reg-file -mprefer-short-insn-regs
-mbranch-cost=num -mcmove -mnops=num -msoft-cmpsf
-msplit-lohi -mpost-inc -mpost-modify -mstack-offset=num
-mround-nearest -mlong-calls -mshort-calls -msmall16
-mfp-mode=mode -mvect-double -max-vect-align=num
-msplit-vecmove-early -m1reg-reg
AMD GCN Options
-march=gpu -mtune=gpu -mstack-size=bytes
ARC Options
-mbarrel-shifter -mjli-always
-mcpu=cpu -mA6 -mARC600 -mA7 -mARC700
-mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr
-mea -mno-mpy -mmul32x16 -mmul64 -matomic
-mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap
-mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape
-mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof
-mlong-calls -mmedium-calls -msdata -mirq-ctrl-saved
-mrgf-banked-regs -mlpc-width=width -G num
-mvolatile-cache -mtp-regno=regno
-malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc
-mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi
-mexpand-adddi -mindexed-loads -mlra -mlra-priority-none
-mlra-priority-compact -mlra-priority-noncompact -mmillicode
-mmixed-code -mq-class -mRcq -mRcw -msize-level=level
-mtune=cpu -mmultcost=num -mcode-density-frame
-munalign-prob-threshold=probability -mmpy-option=multo
-mdiv-rem -mcode-density -mll64 -mfpu=fpu -mrf16 -mbranch-index
ARM Options
-mapcs-frame -mno-apcs-frame
-mabi=name
-mapcs-stack-check -mno-apcs-stack-check
-mapcs-reentrant -mno-apcs-reentrant
-mgeneral-regs-only
-msched-prolog -mno-sched-prolog
-mlittle-endian -mbig-endian
-mbe8 -mbe32
-mfloat-abi=name
-mfp16-format=name
-mthumb-interwork -mno-thumb-interwork
-mcpu=name -march=name -mfpu=name
-mtune=name -mprint-tune-info
-mstructure-size-boundary=n
-mabort-on-noreturn
-mlong-calls -mno-long-calls
-msingle-pic-base -mno-single-pic-base
-mpic-register=reg
-mnop-fun-dllimport
-mpoke-function-name
-mthumb -marm -mflip-thumb
-mtpcs-frame -mtpcs-leaf-frame
-mcaller-super-interworking -mcallee-super-interworking
-mtp=name -mtls-dialect=dialect
-mword-relocations
-mfix-cortex-m3-ldrd
-mfix-cortex-a57-aes-1742098
-mfix-cortex-a72-aes-1655431
-munaligned-access
-mneon-for-64bits
-mslow-flash-data
-masm-syntax-unified
-mrestrict-it
-mverbose-cost-dump
-mpure-code
-mcmse
-mfix-cmse-cve-2021-35465
-mstack-protector-guard=guard -mstack-protector-guard-offset=offset
-mfdpic
-mbranch-protection=none|standard|pac-ret[+leaf]
[+bti]|bti[+pac-ret[+leaf]]
AVR Options
-mmcu=mcu -mabsdata -maccumulate-args
-mbranch-cost=cost
-mcall-prologues -mgas-isr-prologues -mint8
-mdouble=bits -mlong-double=bits
-mn_flash=size -mno-interrupts
-mmain-is-OS_task -mrelax -mrmw -mstrict-X -mtiny-stack
-mfract-convert-truncate
-mshort-calls -mskip-bug -nodevicelib -nodevicespecs
-Waddr-space-convert -Wmisspelled-isr
Blackfin Options
-mcpu=cpu[-sirevision] -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library -mno-id-shared-library -mshared-library-id=n -mleaf-id-shared-library -mno-leaf-id-shared-library -msep-data -mno-sep-data -mlong-calls -mno-long-calls -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram -micplb
C6X Options
-mbig-endian -mlittle-endian -march=cpu
-msim -msdata=sdata-type
CRIS Options
-mcpu=cpu -march=cpu
-mtune=cpu -mmax-stack-frame=n
-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects
-mstack-align -mdata-align -mconst-align
-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue
-melf -maout -sim -sim2
-mmul-bug-workaround -mno-mul-bug-workaround
C-SKY Options
-march=arch -mcpu=cpu
-mbig-endian -EB -mlittle-endian -EL
-mhard-float -msoft-float -mfpu=fpu -mdouble-float -mfdivdu
-mfloat-abi=name
-melrw -mistack -mmp -mcp -mcache -msecurity -mtrust
-mdsp -medsp -mvdsp
-mdiv -msmart -mhigh-registers -manchor
-mpushpop -mmultiple-stld -mconstpool -mstack-size -mccrt
-mbranch-cost=n -mcse-cc -msched-prolog -msim
Darwin Options
-all_load -allowable_client -arch -arch_errors_fatal
-arch_only -bind_at_load -bundle -bundle_loader
-client_name -compatibility_version -current_version
-dead_strip
-dependency-file -dylib_file -dylinker_install_name
-dynamic -dynamiclib -exported_symbols_list
-filelist -flat_namespace -force_cpusubtype_ALL
-force_flat_namespace -headerpad_max_install_names
-iframework
-image_base -init -install_name -keep_private_externs
-multi_module -multiply_defined -multiply_defined_unused
-noall_load -no_dead_strip_inits_and_terms
-nofixprebinding -nomultidefs -noprebind -noseglinkedit
-pagezero_size -prebind -prebind_all_twolevel_modules
-private_bundle -read_only_relocs -sectalign
-sectobjectsymbols -whyload -seg1addr
-sectcreate -sectobjectsymbols -sectorder
-segaddr -segs_read_only_addr -segs_read_write_addr
-seg_addr_table -seg_addr_table_filename -seglinkedit
-segprot -segs_read_only_addr -segs_read_write_addr
-single_module -static -sub_library -sub_umbrella
-twolevel_namespace -umbrella -undefined
-unexported_symbols_list -weak_reference_mismatches
-whatsloaded -F -gused -gfull -mmacosx-version-min=version
-mkernel -mone-byte-bool
DEC Alpha Options
-mno-fp-regs -msoft-float
-mieee -mieee-with-inexact -mieee-conformant
-mfp-trap-mode=mode -mfp-rounding-mode=mode
-mtrap-precision=mode -mbuild-constants
-mcpu=cpu-type -mtune=cpu-type
-mbwx -mmax -mfix -mcix
-mfloat-vax -mfloat-ieee
-mexplicit-relocs -msmall-data -mlarge-data
-msmall-text -mlarge-text
-mmemory-latency=time
eBPF Options
-mbig-endian -mlittle-endian -mkernel=version
-mframe-limit=bytes -mxbpf -mco-re -mno-co-re
-mjmpext -mjmp32 -malu32 -mcpu=version
FR30 Options
-msmall-model -mno-lsim
FT32 Options
-msim -mlra -mnodiv -mft32b -mcompress -mnopm
FRV Options
-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64
-mhard-float -msoft-float
-malloc-cc -mfixed-cc -mdword -mno-dword
-mdouble -mno-double
-mmedia -mno-media -mmuladd -mno-muladd
-mfdpic -minline-plt -mgprel-ro -multilib-library-pic
-mlinked-fp -mlong-calls -malign-labels
-mlibrary-pic -macc-4 -macc-8
-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move
-moptimize-membar -mno-optimize-membar
-mscc -mno-scc -mcond-exec -mno-cond-exec
-mvliw-branch -mno-vliw-branch
-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec
-mno-nested-cond-exec -mtomcat-stats
-mTLS -mtls
-mcpu=cpu
GNU/Linux Options
-mglibc -muclibc -mmusl -mbionic -mandroid
-tno-android-cc -tno-android-ld
H8/300 Options
-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300
HPPA Options
-march=architecture-type
-matomic-libcalls -mbig-switch
-mcaller-copies -mdisable-fpregs -mdisable-indexing
-mordered -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld
-mfixed-range=register-range
-mcoherent-ldcw -mjump-in-delay -mlinker-opt -mlong-calls
-mlong-load-store -mno-atomic-libcalls -mno-disable-fpregs
-mno-disable-indexing -mno-fast-indirect-calls -mno-gas
-mno-jump-in-delay -mno-long-load-store
-mno-portable-runtime -mno-soft-float
-mno-space-regs -msoft-float -mpa-risc-1-0
-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime
-mschedule=cpu-type -mspace-regs -msoft-mult -msio -mwsio
-munix=unix-std -nolibdld -static -threads
IA-64 Options
-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic
-mvolatile-asm-stop -mregister-names -msdata -mno-sdata
-mconstant-gp -mauto-pic -mfused-madd
-minline-float-divide-min-latency
-minline-float-divide-max-throughput
-mno-inline-float-divide
-minline-int-divide-min-latency
-minline-int-divide-max-throughput
-mno-inline-int-divide
-minline-sqrt-min-latency -minline-sqrt-max-throughput
-mno-inline-sqrt
-mdwarf2-asm -mearly-stop-bits
-mfixed-range=register-range -mtls-size=tls-size
-mtune=cpu-type -milp32 -mlp64
-msched-br-data-spec -msched-ar-data-spec -msched-control-spec
-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec
-msched-spec-ldc -msched-spec-control-ldc
-msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns
-msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path
-msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost
-msched-max-memory-insns-hard-limit -msched-max-memory-insns=max-insns
LM32 Options
-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled
-msign-extend-enabled -muser-enabled
LoongArch Options
-march=cpu-type -mtune=cpu-type -mabi=base-abi-type
-mfpu=fpu-type -msoft-float -msingle-float -mdouble-float
-mbranch-cost=n -mcheck-zero-division -mno-check-zero-division
-mcond-move-int -mno-cond-move-int
-mcond-move-float -mno-cond-move-float
-memcpy -mno-memcpy -mstrict-align -mno-strict-align
-mmax-inline-memcpy-size=n
-mexplicit-relocs -mno-explicit-relocs
-mdirect-extern-access -mno-direct-extern-access
-mcmodel=code-model -mrelax -mpass-mrelax-to-as
M32R/D Options
-m32r2 -m32rx -m32r
-mdebug
-malign-loops -mno-align-loops
-missue-rate=number
-mbranch-cost=number
-mmodel=code-size-model-type
-msdata=sdata-type
-mno-flush-func -mflush-func=name
-mno-flush-trap -mflush-trap=number
-G num
M32C Options
-mcpu=cpu -msim -memregs=number
M680x0 Options
-march=arch -mcpu=cpu -mtune=tune
-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040
-m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407
-mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020
-mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort
-mno-short -mhard-float -m68881 -msoft-float -mpcrel
-malign-int -mstrict-align -msep-data -mno-sep-data
-mshared-library-id=n -mid-shared-library -mno-id-shared-library
-mxgot -mno-xgot -mlong-jump-table-offsets
MCore Options
-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates
-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields
-m4byte-functions -mno-4byte-functions -mcallgraph-data
-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim
-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment
MicroBlaze Options
-msoft-float -mhard-float -msmall-divides -mcpu=cpu
-mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift
-mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss
-mxl-multiply-high -mxl-float-convert -mxl-float-sqrt
-mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-app-model
-mpic-data-is-text-relative
MIPS Options
-EL -EB -march=arch -mtune=arch
-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5
-mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6
-mips16 -mno-mips16 -mflip-mips16
-minterlink-compressed -mno-interlink-compressed
-minterlink-mips16 -mno-interlink-mips16
-mabi=abi -mabicalls -mno-abicalls
-mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot
-mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float
-mno-float -msingle-float -mdouble-float
-modd-spreg -mno-odd-spreg
-mabs=mode -mnan=encoding
-mdsp -mno-dsp -mdspr2 -mno-dspr2
-mmcu -mmno-mcu
-meva -mno-eva
-mvirt -mno-virt
-mxpa -mno-xpa
-mcrc -mno-crc
-mginv -mno-ginv
-mmicromips -mno-micromips
-mmsa -mno-msa
-mloongson-mmi -mno-loongson-mmi
-mloongson-ext -mno-loongson-ext
-mloongson-ext2 -mno-loongson-ext2
-mfpu=fpu-type
-msmartmips -mno-smartmips
-mpaired-single -mno-paired-single -mdmx -mno-mdmx
-mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc
-mlong64 -mlong32 -msym32 -mno-sym32
-Gnum -mlocal-sdata -mno-local-sdata
-mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt
-membedded-data -mno-embedded-data
-muninit-const-in-rodata -mno-uninit-const-in-rodata
-mcode-readable=setting
-msplit-addresses -mno-split-addresses
-mexplicit-relocs -mno-explicit-relocs
-mcheck-zero-division -mno-check-zero-division
-mdivide-traps -mdivide-breaks
-mload-store-pairs -mno-load-store-pairs
-munaligned-access -mno-unaligned-access
-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls
-mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp
-mfix-24k -mno-fix-24k
-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400
-mfix-r5900 -mno-fix-r5900
-mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000
-mfix-vr4120 -mno-fix-vr4120
-mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1
-mflush-func=func -mno-flush-func
-mbranch-cost=num -mbranch-likely -mno-branch-likely
-mcompact-branches=policy
-mfp-exceptions -mno-fp-exceptions
-mvr4130-align -mno-vr4130-align -msynci -mno-synci
-mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4
-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address
-mframe-header-opt -mno-frame-header-opt
MMIX Options
-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu
-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols
-melf -mbranch-predict -mno-branch-predict -mbase-addresses
-mno-base-addresses -msingle-exit -mno-single-exit
MN10300 Options
-mmult-bug -mno-mult-bug
-mno-am33 -mam33 -mam33-2 -mam34
-mtune=cpu-type
-mreturn-pointer-on-d0
-mno-crt0 -mrelax -mliw -msetlb
Moxie Options
-meb -mel -mmul.x -mno-crt0
MSP430 Options
-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax
-mwarn-mcu
-mcode-region= -mdata-region=
-msilicon-errata= -msilicon-errata-warn=
-mhwmult= -minrt -mtiny-printf -mmax-inline-shift=
NDS32 Options
-mbig-endian -mlittle-endian
-mreduced-regs -mfull-regs
-mcmov -mno-cmov
-mext-perf -mno-ext-perf
-mext-perf2 -mno-ext-perf2
-mext-string -mno-ext-string
-mv3push -mno-v3push
-m16bit -mno-16bit
-misr-vector-size=num
-mcache-block-size=num
-march=arch
-mcmodel=code-model
-mctor-dtor -mrelax
Nios II Options
-G num -mgpopt=option -mgpopt -mno-gpopt
-mgprel-sec=regexp -mr0rel-sec=regexp
-mel -meb
-mno-bypass-cache -mbypass-cache
-mno-cache-volatile -mcache-volatile
-mno-fast-sw-div -mfast-sw-div
-mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div
-mcustom-insn=N -mno-custom-insn
-mcustom-fpu-cfg=name
-mhal -msmallc -msys-crt0=name -msys-lib=name
-march=arch -mbmx -mno-bmx -mcdx -mno-cdx
Nvidia PTX Options
-m64 -mmainkernel -moptimize
OpenRISC Options
-mboard=name -mnewlib -mhard-mul -mhard-div
-msoft-mul -msoft-div
-msoft-float -mhard-float -mdouble-float -munordered-float
-mcmov -mror -mrori -msext -msfimm -mshftimm
-mcmodel=code-model
PDP-11 Options
-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10
-mint32 -mno-int16 -mint16 -mno-int32
-msplit -munix-asm -mdec-asm -mgnu-asm -mlra
PowerPC Options See RS/6000 and PowerPC Options.
PRU Options
-mmcu=mcu -minrt -mno-relax -mloop
-mabi=variant
RISC-V Options
-mbranch-cost=N-instruction
-mplt -mno-plt
-mabi=ABI-string
-mfdiv -mno-fdiv
-mdiv -mno-div
-misa-spec=ISA-spec-string
-march=ISA-string
-mtune=processor-string
-mpreferred-stack-boundary=num
-msmall-data-limit=N-bytes
-msave-restore -mno-save-restore
-mshorten-memrefs -mno-shorten-memrefs
-mstrict-align -mno-strict-align
-mcmodel=medlow -mcmodel=medany
-mexplicit-relocs -mno-explicit-relocs
-mrelax -mno-relax
-mriscv-attribute -mno-riscv-attribute
-malign-data=type
-mbig-endian -mlittle-endian
-mstack-protector-guard=guard -mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset
-mcsr-check -mno-csr-check
-minline-atomics -mno-inline-atomics
RL78 Options
-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs
-mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14
-m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts
RS/6000 and PowerPC Options
-mcpu=cpu-type
-mtune=cpu-type
-mcmodel=code-model
-mpowerpc64
-maltivec -mno-altivec
-mpowerpc-gpopt -mno-powerpc-gpopt
-mpowerpc-gfxopt -mno-powerpc-gfxopt
-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd
-mfprnd -mno-fprnd
-mcmpb -mno-cmpb -mhard-dfp -mno-hard-dfp
-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc
-m64 -m32 -mxl-compat -mno-xl-compat -mpe
-malign-power -malign-natural
-msoft-float -mhard-float -mmultiple -mno-multiple
-mupdate -mno-update
-mavoid-indexed-addresses -mno-avoid-indexed-addresses
-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align
-mstrict-align -mno-strict-align -mrelocatable
-mno-relocatable -mrelocatable-lib -mno-relocatable-lib
-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian
-mdynamic-no-pic -mswdiv -msingle-pic-base
-mprioritize-restricted-insns=priority
-msched-costly-dep=dependence_type
-minsert-sched-nops=scheme
-mcall-aixdesc -mcall-eabi -mcall-freebsd
-mcall-linux -mcall-netbsd -mcall-openbsd
-mcall-sysv -mcall-sysv-eabi -mcall-sysv-noeabi
-mtraceback=traceback_type
-maix-struct-return -msvr4-struct-return
-mabi=abi-type -msecure-plt -mbss-plt
-mlongcall -mno-longcall -mpltseq -mno-pltseq
-mblock-move-inline-limit=num
-mblock-compare-inline-limit=num
-mblock-compare-inline-loop-limit=num
-mno-block-ops-unaligned-vsx
-mstring-compare-inline-limit=num
-misel -mno-isel
-mvrsave -mno-vrsave
-mmulhw -mno-mulhw
-mdlmzb -mno-dlmzb
-mprototype -mno-prototype
-msim -mmvme -mads -myellowknife -memb -msdata
-msdata=opt -mreadonly-in-sdata -mvxworks -G num
-mrecip -mrecip=opt -mno-recip -mrecip-precision
-mno-recip-precision
-mveclibabi=type -mfriz -mno-friz
-mpointers-to-nested-functions -mno-pointers-to-nested-functions
-msave-toc-indirect -mno-save-toc-indirect
-mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector
-mcrypto -mno-crypto -mhtm -mno-htm
-mquad-memory -mno-quad-memory
-mquad-memory-atomic -mno-quad-memory-atomic
-mcompat-align-parm -mno-compat-align-parm
-mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware
-mgnu-attribute -mno-gnu-attribute
-mstack-protector-guard=guard -mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset -mprefixed -mno-prefixed
-mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect
-mprivileged -mno-privileged
RX Options
-m64bit-doubles -m32bit-doubles -fpu -nofpu
-mcpu=
-mbig-endian-data -mlittle-endian-data
-msmall-data
-msim -mno-sim
-mas100-syntax -mno-as100-syntax
-mrelax
-mmax-constant-size=
-mint-register=
-mpid
-mallow-string-insns -mno-allow-string-insns
-mjsr
-mno-warn-multiple-fast-interrupts
-msave-acc-in-interrupts
S/390 and zSeries Options
-mtune=cpu-type -march=cpu-type
-mhard-float -msoft-float -mhard-dfp -mno-hard-dfp
-mlong-double-64 -mlong-double-128
-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack
-msmall-exec -mno-small-exec -mmvcle -mno-mvcle
-m64 -m31 -mdebug -mno-debug -mesa -mzarch
-mhtm -mvx -mzvector
-mtpf-trace -mno-tpf-trace -mtpf-trace-skip -mno-tpf-trace-skip
-mfused-madd -mno-fused-madd
-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard
-mhotpatch=halfwords,halfwords
SH Options
-m1 -m2 -m2e
-m2a-nofpu -m2a-single-only -m2a-single -m2a
-m3 -m3e
-m4-nofpu -m4-single-only -m4-single -m4
-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al
-mb -ml -mdalign -mrelax
-mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave
-mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct
-mprefergot -musermode -multcost=number -mdiv=strategy
-mdivsi3_libfunc=name -mfixed-range=register-range
-maccumulate-outgoing-args
-matomic-model=atomic-model
-mbranch-cost=num -mzdcbranch -mno-zdcbranch
-mcbranch-force-delay-slot
-mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra
-mpretend-cmove -mtas
Solaris 2 Options
-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text
-pthreads
SPARC Options
-mcpu=cpu-type
-mtune=cpu-type
-mcmodel=code-model
-mmemory-model=mem-model
-m32 -m64 -mapp-regs -mno-app-regs
-mfaster-structs -mno-faster-structs -mflat -mno-flat
-mfpu -mno-fpu -mhard-float -msoft-float
-mhard-quad-float -msoft-quad-float
-mstack-bias -mno-stack-bias
-mstd-struct-return -mno-std-struct-return
-munaligned-doubles -mno-unaligned-doubles
-muser-mode -mno-user-mode
-mv8plus -mno-v8plus -mvis -mno-vis
-mvis2 -mno-vis2 -mvis3 -mno-vis3
-mvis4 -mno-vis4 -mvis4b -mno-vis4b
-mcbcond -mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld
-mpopc -mno-popc -msubxc -mno-subxc
-mfix-at697f -mfix-ut699 -mfix-ut700 -mfix-gr712rc
-mlra -mno-lra
System V Options
-Qy -Qn -YP,paths -Ym,dir
V850 Options
-mlong-calls -mno-long-calls -mep -mno-ep
-mprolog-function -mno-prolog-function -mspace
-mtda=n -msda=n -mzda=n
-mapp-regs -mno-app-regs
-mdisable-callt -mno-disable-callt
-mv850e2v3 -mv850e2 -mv850e1 -mv850es
-mv850e -mv850 -mv850e3v5
-mloop
-mrelax
-mlong-jumps
-msoft-float
-mhard-float
-mgcc-abi
-mrh850-abi
-mbig-switch
VAX Options
-mg -mgnu -munix -mlra
Visium Options
-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float
-mcpu=cpu-type -mtune=cpu-type -msv-mode -muser-mode
VMS Options
-mvms-return-codes -mdebug-main=prefix -mmalloc64
-mpointer-size=size
VxWorks Options
-mrtp -msmp -non-static -Bstatic -Bdynamic
-Xbind-lazy -Xbind-now
x86 Options
-mtune=cpu-type -march=cpu-type
-mtune-ctrl=feature-list -mdump-tune-features -mno-default
-mfpmath=unit
-masm=dialect -mno-fancy-math-387
-mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float
-mno-wide-multiply -mrtd -malign-double
-mpreferred-stack-boundary=num
-mincoming-stack-boundary=num
-mcld -mcx16 -msahf -mmovbe -mcrc32 -mmwait
-mrecip -mrecip=opt
-mvzeroupper -mprefer-avx128 -mprefer-vector-width=opt
-mmove-max=bits -mstore-max=bits
-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx
-mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl
-mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes
-mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd
-mptwrite -mprefetchwt1 -mclflushopt -mclwb -mxsavec -mxsaves
-msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop
-madx -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mhle -mlwp
-mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes -mwaitpkg
-mshstk -mmanual-endbr -mcet-switch -mforce-indirect-call
-mavx512vbmi2 -mavx512bf16 -menqcmd
-mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq
-mavx5124fmaps -mavx512vnni -mavx5124vnniw -mprfchw -mrdpid
-mrdseed -msgx -mavx512vp2intersect -mserialize -mtsxldtrk
-mamx-tile -mamx-int8 -mamx-bf16 -muintr -mhreset -mavxvnni
-mavx512fp16 -mavxifma -mavxvnniint8 -mavxneconvert -mcmpccxadd -mamx-fp16
-mprefetchi -mraoint -mamx-complex
-mcldemote -mms-bitfields -mno-align-stringops -minline-all-stringops
-minline-stringops-dynamically -mstringop-strategy=alg
-mkl -mwidekl
-mmemcpy-strategy=strategy -mmemset-strategy=strategy
-mpush-args -maccumulate-outgoing-args -m128bit-long-double
-m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128
-mregparm=num -msseregparm
-mveclibabi=type -mvect8-ret-in-mem
-mpc32 -mpc64 -mpc80 -mdaz-ftz -mstackrealign
-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs
-mcmodel=code-model -mabi=name -maddress-mode=mode
-m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=num
-msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv
-minstrument-return=type -mfentry-name=name -mfentry-section=name
-mavx256-split-unaligned-load -mavx256-split-unaligned-store
-malign-data=type -mstack-protector-guard=guard
-mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset
-mstack-protector-guard-symbol=symbol
-mgeneral-regs-only -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop
-mindirect-branch=choice -mfunction-return=choice
-mindirect-branch-register -mharden-sls=choice
-mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access
-munroll-only-small-loops -mlam=choice
x86 Windows Options
-mconsole -mcygwin -mno-cygwin -mdll
-mnop-fun-dllimport -mthread
-municode -mwin32 -mwindows -fno-set-stack-executable
Xstormy16 Options
-msim
Xtensa Options
-mconst16 -mno-const16
-mfused-madd -mno-fused-madd
-mforce-no-pic
-mserialize-volatile -mno-serialize-volatile
-mtext-section-literals -mno-text-section-literals
-mauto-litpools -mno-auto-litpools
-mtarget-align -mno-target-align
-mlongcalls -mno-longcalls
-mabi=abi-type
-mextra-l32r-costs=cycles
zSeries Options See S/390 and zSeries Options.
Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. GCC is capable of preprocessing and compiling several files either into several assembler input files, or into one assembler input file; then each assembler input file produces an object file, and linking combines all the object files (those newly compiled, and those specified as input) into an executable file.
For any given input file, the file name suffix determines what kind of compilation is done:
.c.i.ii.m.mi.mm.M.mii.h.cc.cp.cxx.cpp.CPP.c++.C.mm.M.mii.hh.H.hp.hxx.hpp.HPP.h++.tcc.f.for.ftn.F.FOR.fpp.FPP.FTN.f90.f95.f03.f08.F90.F95.F03.F08.go.d.di.dd.ads.adb.s.S.sxYou can specify the input language explicitly with the -x option:
-x language c c-header cpp-output
c++ c++-header c++-system-header c++-user-header c++-cpp-output
objective-c objective-c-header objective-c-cpp-output
objective-c++ objective-c++-header objective-c++-cpp-output
assembler assembler-with-cpp
ada
d
f77 f77-cpp-input f95 f95-cpp-input
go
-x noneIf you only want some of the stages of compilation, you can use -x (or filename suffixes) to tell gcc where to start, and one of the options -c, -S, or -E to say where gcc is to stop. Note that some combinations (for example, ‘-x cpp-output -E’) instruct gcc to do nothing at all.
-cBy default, the object file name for a source file is made by replacing the suffix ‘.c’, ‘.i’, ‘.s’, etc., with ‘.o’.
Unrecognized input files, not requiring compilation or assembly, are ignored.
-SBy default, the assembler file name for a source file is made by replacing the suffix ‘.c’, ‘.i’, etc., with ‘.s’.
Input files that don't require compilation are ignored.
-EInput files that don't require preprocessing are ignored.
-o fileIf -o is not specified, the default is to put an executable file in a.out, the object file for source.suffix in source.o, its assembler file in source.s, a precompiled header file in source.suffix.gch, and all preprocessed C source on standard output.
Though -o names only the primary output, it also affects the naming of auxiliary and dump outputs. See the examples below. Unless overridden, both auxiliary outputs and dump outputs are placed in the same directory as the primary output. In auxiliary outputs, the suffix of the input file is replaced with that of the auxiliary output file type; in dump outputs, the suffix of the dump file is appended to the input file suffix. In compilation commands, the base name of both auxiliary and dump outputs is that of the primary output; in compile and link commands, the primary output name, minus the executable suffix, is combined with the input file name. If both share the same base name, disregarding the suffix, the result of the combination is that base name, otherwise, they are concatenated, separated by a dash.
gcc -c foo.c ...
will use foo.o as the primary output, and place aux outputs and dumps next to it, e.g., aux file foo.dwo for -gsplit-dwarf, and dump file foo.c.???r.final for -fdump-rtl-final.
If a non-linker output file is explicitly specified, aux and dump files by default take the same base name:
gcc -c foo.c -o dir/foobar.o ...
will name aux outputs dir/foobar.* and dump outputs dir/foobar.c.*.
A linker output will instead prefix aux and dump outputs:
gcc foo.c bar.c -o dir/foobar ...
will generally name aux outputs dir/foobar-foo.* and dir/foobar-bar.*, and dump outputs dir/foobar-foo.c.* and dir/foobar-bar.c.*.
The one exception to the above is when the executable shares the base name with the single input:
gcc foo.c -o dir/foo ...
in which case aux outputs are named dir/foo.* and dump outputs named dir/foo.c.*.
The location and the names of auxiliary and dump outputs can be adjusted by the options -dumpbase, -dumpbase-ext, -dumpdir, -save-temps=cwd, and -save-temps=obj.
-dumpbase dumpbasegcc -save-temps -S foo.c
saves the (no longer) temporary preprocessed file in foo.i, and then compiles to the (implied) output file foo.s, whereas:
gcc -save-temps -dumpbase save-foo -c foo.c
preprocesses to in save-foo.i, compiles to save-foo.s (now an intermediate, thus auxiliary output), and then assembles to the (implied) output file foo.o.
Absent this option, dump and aux files take their names from the input
file, or from the (non-linker) output file, if one is explicitly
specified: dump output files (e.g. those requested by -fdump-*
options) with the input name suffix, and aux output files (those
requested by other non-dump options, e.g. -save-temps,
-gsplit-dwarf, -fcallgraph-info) without it.
Similar suffix differentiation of dump and aux outputs can be attained for explicitly-given -dumpbase basename.suf by also specifying -dumpbase-ext .suf.
If dumpbase is explicitly specified with any directory component, any dumppfx specification (e.g. -dumpdir or -save-temps=*) is ignored, and instead of appending to it, dumpbase fully overrides it:
gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \
-dumpdir pfx- -save-temps=cwd ...
creates auxiliary and dump outputs named alt/foo.*, disregarding dir/ in -o, the ./ prefix implied by -save-temps=cwd, and pfx- in -dumpdir.
When -dumpbase is specified in a command that compiles multiple inputs, or that compiles and then links, it may be combined with dumppfx, as specified under -dumpdir. Then, each input file is compiled using the combined dumppfx, and default values for dumpbase and auxdropsuf are computed for each input file:
gcc foo.c bar.c -c -dumpbase main ...
creates foo.o and bar.o as primary outputs, and avoids overwriting the auxiliary and dump outputs by using the dumpbase as a prefix, creating auxiliary and dump outputs named main-foo.* and main-bar.*.
An empty string specified as dumpbase avoids the influence of the output basename in the naming of auxiliary and dump outputs during compilation, computing default values :
gcc -c foo.c -o dir/foobar.o -dumpbase '' ...
will name aux outputs dir/foo.* and dump outputs dir/foo.c.*. Note how their basenames are taken from the input name, but the directory still defaults to that of the output.
The empty-string dumpbase does not prevent the use of the output basename for outputs during linking:
gcc foo.c bar.c -o dir/foobar -dumpbase '' -flto ...
The compilation of the source files will name auxiliary outputs dir/foo.* and dir/bar.*, and dump outputs dir/foo.c.* and dir/bar.c.*. LTO recompilation during linking will use dir/foobar. as the prefix for dumps and auxiliary files.
-dumpbase-ext auxdropsufgcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ...
creates dir/foo.o as the main output, and generates auxiliary outputs in dir/x-foo.*, taking the location of the primary output, and dropping the .c suffix from the dumpbase. Dump outputs retain the suffix: dir/x-foo.c.*.
This option is disregarded if it does not match the suffix of a specified dumpbase, except as an alternative to the executable suffix when appending the linker output base name to dumppfx, as specified below:
gcc foo.c bar.c -o main.out -dumpbase-ext .out ...
creates main.out as the primary output, and avoids overwriting the auxiliary and dump outputs by using the executable name minus auxdropsuf as a prefix, creating auxiliary outputs named main-foo.* and main-bar.* and dump outputs named main-foo.c.* and main-bar.c.*.
-dumpdir dumppfxgcc -dumpdir pfx- -c foo.c ...
creates foo.o as the primary output, and auxiliary outputs named pfx-foo.*, combining the given dumppfx with the default dumpbase derived from the default primary output, derived in turn from the input name. Dump outputs also take the input name suffix: pfx-foo.c.*.
If dumppfx is to be used as a directory name, it must end with a directory separator:
gcc -dumpdir dir/ -c foo.c -o obj/bar.o ...
creates obj/bar.o as the primary output, and auxiliary outputs named dir/bar.*, combining the given dumppfx with the default dumpbase derived from the primary output name. Dump outputs also take the input name suffix: dir/bar.c.*.
It defaults to the location of the output file, unless the output
file is a special file like /dev/null. Options
-save-temps=cwd and -save-temps=obj override this
default, just like an explicit -dumpdir option. In case
multiple such options are given, the last one prevails:
gcc -dumpdir pfx- -c foo.c -save-temps=obj ...
outputs foo.o, with auxiliary outputs named foo.* because -save-temps=* overrides the dumppfx given by the earlier -dumpdir option. It does not matter that =obj is the default for -save-temps, nor that the output directory is implicitly the current directory. Dump outputs are named foo.c.*.
When compiling from multiple input files, if -dumpbase is specified, dumpbase, minus a auxdropsuf suffix, and a dash are appended to (or override, if containing any directory components) an explicit or defaulted dumppfx, so that each of the multiple compilations gets differently-named aux and dump outputs.
gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ...
outputs auxiliary dumps to dir/pfx-main-foo.* and dir/pfx-main-bar.*, appending dumpbase- to dumppfx. Dump outputs retain the input file suffix: dir/pfx-main-foo.c.* and dir/pfx-main-bar.c.*, respectively. Contrast with the single-input compilation:
gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ...
that, applying -dumpbase to a single source, does not compute and append a separate dumpbase per input file. Its auxiliary and dump outputs go in dir/pfx-main.*.
When compiling and then linking from multiple input files, a defaulted or explicitly specified dumppfx also undergoes the dumpbase- transformation above (e.g. the compilation of foo.c and bar.c above, but without -c). If neither -dumpdir nor -dumpbase are given, the linker output base name, minus auxdropsuf, if specified, or the executable suffix otherwise, plus a dash is appended to the default dumppfx instead. Note, however, that unlike earlier cases of linking:
gcc foo.c bar.c -dumpdir dir/pfx- -o main ...
does not append the output name main to dumppfx, because -dumpdir is explicitly specified. The goal is that the explicitly-specified dumppfx may contain the specified output name as part of the prefix, if desired; only an explicitly-specified -dumpbase would be combined with it, in order to avoid simply discarding a meaningful option.
When compiling and then linking from a single input file, the linker output base name will only be appended to the default dumppfx as above if it does not share the base name with the single input file name. This has been covered in single-input linking cases above, but not with an explicit -dumpdir that inhibits the combination, even if overridden by -save-temps=*:
gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ...
Auxiliary outputs are named foo.*, and dump outputs foo.c.*, in the current working directory as ultimately requested by -save-temps=cwd.
Summing it all up for an intuitive though slightly imprecise data flow: the primary output name is broken into a directory part and a basename part; dumppfx is set to the former, unless overridden by -dumpdir or -save-temps=*, and dumpbase is set to the latter, unless overriden by -dumpbase. If there are multiple inputs or linking, this dumpbase may be combined with dumppfx and taken from each input file. Auxiliary output names for each input are formed by combining dumppfx, dumpbase minus suffix, and the auxiliary output suffix; dump output names are only different in that the suffix from dumpbase is retained.
When it comes to auxiliary and dump outputs created during LTO recompilation, a combination of dumppfx and dumpbase, as given or as derived from the linker output name but not from inputs, even in cases in which this combination would not otherwise be used as such, is passed down with a trailing period replacing the compiler-added dash, if any, as a -dumpdir option to lto-wrapper; being involved in linking, this program does not normally get any -dumpbase and -dumpbase-ext, and it ignores them.
When running sub-compilers, lto-wrapper appends LTO stage names to the received dumppfx, ensures it contains a directory component so that it overrides any -dumpdir, and passes that as -dumpbase to sub-compilers.
-v-###./-_.
This is useful for shell scripts to capture the driver-generated command lines.
--help--target-help--help={class|[^]qualifier}[,...]These are the supported qualifiers:
Thus for example to display all the undocumented target-specific switches supported by the compiler, use:
--help=target,undocumented
The sense of a qualifier can be inverted by prefixing it with the ‘^’ character, so for example to display all binary warning options (i.e., ones that are either on or off and that do not take an argument) that have a description, use:
--help=warnings,^joined,^undocumented
The argument to --help= should not consist solely of inverted qualifiers.
Combining several classes is possible, although this usually restricts the output so much that there is nothing to display. One case where it does work, however, is when one of the classes is target. For example, to display all the target-specific optimization options, use:
--help=target,optimizers
The --help= option can be repeated on the command line. Each successive use displays its requested class of options, skipping those that have already been displayed. If --help is also specified anywhere on the command line then this takes precedence over any --help= option.
If the -Q option appears on the command line before the --help= option, then the descriptive text displayed by --help= is changed. Instead of describing the displayed options, an indication is given as to whether the option is enabled, disabled or set to a specific value (assuming that the compiler knows this at the point where the --help= option is used).
Here is a truncated example from the ARM port of gcc:
% gcc -Q -mabi=2 --help=target -c
The following options are target specific:
-mabi= 2
-mabort-on-noreturn [disabled]
-mapcs [disabled]
The output is sensitive to the effects of previous command-line options, so for example it is possible to find out which optimizations are enabled at -O2 by using:
-Q -O2 --help=optimizers
Alternatively you can discover which binary optimizations are enabled by -O3 by using:
gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
diff /tmp/O2-opts /tmp/O3-opts | grep enabled
--version-pass-exit-codes-pipe-specs=file-wrappergcc -c t.c -wrapper gdb,--args
This invokes all subprograms of gcc under ‘gdb --args’, thus the invocation of cc1 is ‘gdb --args cc1 ...’.
-ffile-prefix-map=old=new-fcanon-prefix-map-fplugin=name.so-fplugin-arg-name-key=value-fdump-scos-fdump-ada-spec[-slim]-fada-spec-parent=unit-fdump-go-spec=fileconst,
type, var, and func declarations which may be a
useful way to start writing a Go interface to code written in some
other language.
@fileOptions in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively.
C++ source files conventionally use one of the suffixes ‘.C’, ‘.cc’, ‘.cpp’, ‘.CPP’, ‘.c++’, ‘.cp’, or ‘.cxx’; C++ header files often use ‘.hh’, ‘.hpp’, ‘.H’, or (for shared template code) ‘.tcc’; and preprocessed C++ files use the suffix ‘.ii’. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name gcc).
However, the use of gcc does not add the C++ library. g++ is a program that calls GCC and automatically specifies linking against the C++ library. It treats ‘.c’, ‘.h’ and ‘.i’ files as C++ source files instead of C source files unless -x is used. This program is also useful when precompiling a C header file with a ‘.h’ extension for use in C++ compilations. On many systems, g++ is also installed with the name c++.
When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs. See Options Controlling C Dialect, for explanations of options for languages related to C. See Options Controlling C++ Dialect, for explanations of options that are meaningful only for C++ programs.
The following options control the dialect of C (or languages derived from C, such as C++, Objective-C and Objective-C++) that the compiler accepts:
-ansiThis turns off certain features of GCC that are incompatible with ISO
C90 (when compiling C code), or of standard C++ (when compiling C++ code),
such as the asm and typeof keywords, and
predefined macros such as unix and vax that identify the
type of system you are using. It also enables the undesirable and
rarely used ISO trigraph feature. For the C compiler,
it disables recognition of C++ style ‘//’ comments as well as
the inline keyword.
The alternate keywords __asm__, __extension__,
__inline__ and __typeof__ continue to work despite
-ansi. You would not want to use them in an ISO C program, of
course, but it is useful to put them in header files that might be included
in compilations done with -ansi. Alternate predefined macros
such as __unix__ and __vax__ are also available, with or
without -ansi.
The -ansi option does not cause non-ISO programs to be rejected gratuitously. For that, -Wpedantic is required in addition to -ansi. See Warning Options.
The macro __STRICT_ANSI__ is predefined when the -ansi
option is used. Some header files may notice this macro and refrain
from declaring certain functions or defining certain macros that the
ISO standard doesn't call for; this is to avoid interfering with any
programs that might use these names for other things.
Functions that are normally built in but do not have semantics
defined by ISO C (such as alloca and ffs) are not built-in
functions when -ansi is used. See Other built-in functions provided by GCC, for details of the functions
affected.
-std=The compiler can accept several base standards, such as ‘c90’ or
‘c++98’, and GNU dialects of those standards, such as
‘gnu90’ or ‘gnu++98’. When a base standard is specified, the
compiler accepts all programs following that standard plus those
using GNU extensions that do not contradict it. For example,
-std=c90 turns off certain features of GCC that are
incompatible with ISO C90, such as the asm and typeof
keywords, but not other GNU extensions that do not have a meaning in
ISO C90, such as omitting the middle term of a ?:
expression. On the other hand, when a GNU dialect of a standard is
specified, all features supported by the compiler are enabled, even when
those features change the meaning of the base standard. As a result, some
strict-conforming programs may be rejected. The particular standard
is used by -Wpedantic to identify which features are GNU
extensions given that version of the standard. For example
-std=gnu90 -Wpedantic warns about C++ style ‘//’
comments, while -std=gnu99 -Wpedantic does not.
A value for this option must be provided; possible values are
__STDC_VERSION__, and so is supported to the same extent as C11.
-aux-info filenameBesides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (‘I’, ‘N’ for new or ‘O’ for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (‘C’ or ‘F’, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration.
-fno-asmasm, inline or typeof as a
keyword, so that code can use these words as identifiers. You can use
the keywords __asm__, __inline__ and __typeof__
instead. In C, -ansi implies -fno-asm.
In C++, inline is a standard keyword and is not affected by
this switch. You may want to use the -fno-gnu-keywords flag
instead, which disables typeof but not asm and
inline. In C99 mode (-std=c99 or -std=gnu99),
this switch only affects the asm and typeof keywords,
since inline is a standard keyword in ISO C99. In C2X mode
(-std=c2x or -std=gnu2x), this switch only affects
the asm keyword, since typeof is a standard keyword in
ISO C2X.
-fno-builtin-fno-builtin-functionGCC normally generates special code to handle certain built-in functions
more efficiently; for instance, calls to alloca may become single
instructions which adjust the stack directly, and calls to memcpy
may become inline copy loops. The resulting code is often both smaller
and faster, but since the function calls no longer appear as such, you
cannot set a breakpoint on those calls, nor can you change the behavior
of the functions by linking with a different library. In addition,
when a function is recognized as a built-in function, GCC may use
information about that function to warn about problems with calls to
that function, or to generate more efficient code, even if the
resulting code still contains calls to that function. For example,
warnings are given with -Wformat for bad calls to
printf when printf is built in and strlen is
known not to modify global memory.
With the -fno-builtin-function option only the built-in function function is disabled. function must not begin with ‘__builtin_’. If a function is named that is not built-in in this version of GCC, this option is ignored. There is no corresponding -fbuiltin-function option; if you wish to enable built-in functions selectively when using -fno-builtin or -ffreestanding, you may define macros such as:
#define abs(n) __builtin_abs ((n))
#define strcpy(d, s) __builtin_strcpy ((d), (s))
-fcond-mismatch-ffreestandingmain. The most obvious example is an OS kernel.
This is equivalent to -fno-hosted.
See Language Standards Supported by GCC, for details of freestanding and hosted environments.
-fgimple__GIMPLE.
This is an experimental feature that allows unit testing of GIMPLE
passes.
-fgnu-tmFor more information on GCC's support for transactional memory, See The GNU Transactional Memory Library.
Note that the transactional memory feature is not supported with non-call exceptions (-fnon-call-exceptions).
-fgnu89-inlineinline functions when in C99 mode.
See An Inline Function is As Fast As a Macro.
Using this option is roughly equivalent to adding the
gnu_inline function attribute to all inline functions
(see Function Attributes).
The option -fno-gnu89-inline explicitly tells GCC to use the
C99 semantics for inline when in C99 or gnu99 mode (i.e., it
specifies the default behavior).
This option is not supported in -std=c90 or
-std=gnu90 mode.
The preprocessor macros __GNUC_GNU_INLINE__ and
__GNUC_STDC_INLINE__ may be used to check which semantics are
in effect for inline functions. See Common Predefined Macros.
-fhostedmain has a return
type of int. Examples are nearly everything except a kernel.
This is equivalent to -fno-freestanding.
-flax-vector-conversions-fms-extensionsIn C++ code, this allows member names in structures to be similar to previous types declarations.
typedef int UOW;
struct ABC {
UOW UOW;
};
Some cases of unnamed fields in structures and unions are only accepted with this option. See Unnamed struct/union fields within structs/unions, for details.
Note that this option is off for all targets except for x86 targets using ms-abi.
-foffload=disable-foffload=default-foffload=target-listOffload targets are specified in GCC's internal target-triplet format. You can
run the compiler with -v to show the list of configured offload targets
under OFFLOAD_TARGET_NAMES.
-foffload-options=options-foffload-options=target-triplet-list=optionsTypical command lines are
-foffload-options=-lgfortran -foffload-options=-lm
-foffload-options="-lgfortran -lm" -foffload-options=nvptx-none=-latomic
-foffload-options=amdgcn-amdhsa=-march=gfx906 -foffload-options=-lm
-fopenacc#pragma acc in C/C++ and
!$acc in Fortran. When -fopenacc is specified, the
compiler generates accelerated code according to the OpenACC Application
Programming Interface v2.6 https://www.openacc.org. This option
implies -pthread, and thus is only supported on targets that
have support for -pthread.
-fopenacc-dim=geom-fopenmp#pragma omp in C/C++,
[[omp::directive(...)]] and [[omp::sequence(...)]] in C++ and
!$omp in Fortran. When -fopenmp is specified, the
compiler generates parallel code according to the OpenMP Application
Program Interface v4.5 https://www.openmp.org. This option
implies -pthread, and thus is only supported on targets that
have support for -pthread. -fopenmp implies
-fopenmp-simd.
-fopenmp-simdsimd, declare simd,
declare reduction, assume, ordered, scan,
loop directives and combined or composite directives with
simd as constituent with #pragma omp in C/C++,
[[omp::directive(...)]] and [[omp::sequence(...)]] in C++
and !$omp in Fortran. Other OpenMP directives are ignored.
-fopenmp-target-simd-clone-fopenmp-target-simd-clone=device-typedeclare simd directive, GCC also generates clones
for functions marked with the OpenMP declare target directive
that are suitable for vectorization when this option is in effect. The
device-type may be one of none, host, nohost,
and any, which correspond to keywords for the device_type
clause of the declare target directive; clones are generated for
the intersection of devices specified.
-fopenmp-target-simd-clone is equivalent to
-fopenmp-target-simd-clone=any and
-fno-openmp-target-simd-clone is equivalent to
-fopenmp-target-simd-clone=none.
At -O2 and higher (but not -Os or -Og) this optimization defaults to -fopenmp-target-simd-clone=nohost; otherwise it is disabled by default.
-fpermitted-flt-eval-methods=styleFLT_EVAL_METHOD that indicate that operations and constants with
a semantic type that is an interchange or extended format should be
evaluated to the precision and range of that type. These new values are
a superset of those permitted under C99/C11, which does not specify the
meaning of other positive values of FLT_EVAL_METHOD. As such, code
conforming to C11 may not have been written expecting the possibility of
the new values.
-fpermitted-flt-eval-methods specifies whether the compiler
should allow only the values of FLT_EVAL_METHOD specified in C99/C11,
or the extended set of values specified in ISO/IEC TS 18661-3.
style is either c11 or ts-18661-3 as appropriate.
The default when in a standards compliant mode (-std=c11 or similar) is -fpermitted-flt-eval-methods=c11. The default when in a GNU dialect (-std=gnu11 or similar) is -fpermitted-flt-eval-methods=ts-18661-3.
-fplan9-extensionsThis enables -fms-extensions, permits passing pointers to structures with anonymous fields to functions that expect pointers to elements of the type of the field, and permits referring to anonymous fields declared using a typedef. See Unnamed struct/union fields within structs/unions, for details. This is only supported for C, not C++.
-fsigned-bitfields-funsigned-bitfields-fno-signed-bitfields-fno-unsigned-bitfieldssigned or unsigned. By
default, such a bit-field is signed, because this is consistent: the
basic integer types such as int are signed types.
-fsigned-charchar be signed, like signed char.
Note that this is equivalent to -fno-unsigned-char, which is the negative form of -funsigned-char. Likewise, the option -fno-signed-char is equivalent to -funsigned-char.
-funsigned-charchar be unsigned, like unsigned char.
Each kind of machine has a default for what char should
be. It is either like unsigned char by default or like
signed char by default.
Ideally, a portable program should always use signed char or
unsigned char when it depends on the signedness of an object.
But many programs have been written to use plain char and
expect it to be signed, or expect it to be unsigned, depending on the
machines they were written for. This option, and its inverse, let you
make such a program work with the opposite default.
The type char is always a distinct type from each of
signed char or unsigned char, even though its behavior
is always just like one of those two.
-fstrict-flex-arrays-fstrict-flex-arrays=levelThe possible values of level are the same as for the
strict_flex_array attribute (see Variable Attributes).
You can control this behavior for a specific trailing array field of a
structure by using the variable attribute strict_flex_array attribute
(see Variable Attributes).
-fsso-struct=endiannessWarning: the -fsso-struct switch causes GCC to generate code that is not binary compatible with code generated without it if the specified endianness is not the native endianness of the target.
This section describes the command-line options that are only meaningful for C++ programs. You can also use most of the GNU compiler options regardless of what language your program is in. For example, you might compile a file firstClass.C like this:
g++ -g -fstrict-enums -O -c firstClass.C
In this example, only -fstrict-enums is an option meant only for C++ programs; you can use the other options with any language supported by GCC.
Some options for compiling C programs, such as -std, are also relevant for C++ programs. See Options Controlling C Dialect.
Here is a list of options that are only for compiling C++ programs:
-fabi-version=nVersion 0 refers to the version conforming most closely to the C++ ABI specification. Therefore, the ABI obtained using version 0 will change in different versions of G++ as ABI bugs are fixed.
Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.
Version 2 is the version of the C++ ABI that first appeared in G++ 3.4, and was the default through G++ 4.9.
Version 3 corrects an error in mangling a constant address as a template argument.
Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types.
Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute const/volatile on function pointer types, decltype of a plain decl, and use of a function parameter in the declaration of another parameter.
Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of C++11 scoped enums and the mangling of template argument packs, const/static_cast, prefix ++ and –, and a class scope function used as a template argument.
Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a builtin type and corrects the mangling of lambdas in default argument scope.
Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of function types with function-cv-qualifiers.
Version 9, which first appeared in G++ 5.2, corrects the alignment of
nullptr_t.
Version 10, which first appeared in G++ 6.1, adds mangling of attributes that affect type identity, such as ia32 calling convention attributes (e.g. ‘stdcall’).
Version 11, which first appeared in G++ 7, corrects the mangling of sizeof... expressions and operator names. For multiple entities with the same name within a function, that are declared in different scopes, the mangling now changes starting with the twelfth occurrence. It also implies -fnew-inheriting-ctors.
Version 12, which first appeared in G++ 8, corrects the calling conventions for empty classes on the x86_64 target and for classes with only deleted copy/move constructors. It accidentally changes the calling convention for classes with a deleted copy constructor and a trivial move constructor.
Version 13, which first appeared in G++ 8.2, fixes the accidental change in version 12.
Version 14, which first appeared in G++ 10, corrects the mangling of the nullptr expression.
Version 15, which first appeared in G++ 10.3, corrects G++ 10 ABI tag regression.
Version 16, which first appeared in G++ 11, changes the mangling of
__alignof__ to be distinct from that of alignof, and
dependent operator names.
Version 17, which first appeared in G++ 12, fixes layout of classes that inherit from aggregate classes with default member initializers in C++14 and up.
Version 18, which first appeard in G++ 13, fixes manglings of lambdas that have additional context.
See also -Wabi.
-fabi-compat-version=nWith -fabi-version=0 (the default), this defaults to 13 (GCC 8.2 compatibility). If another ABI version is explicitly selected, this defaults to 0. For compatibility with GCC versions 3.2 through 4.9, use -fabi-compat-version=2.
If this option is not provided but -Wabi=n is, that version is used for compatibility aliases. If this option is provided along with -Wabi (without the version), the version from this option is used for the warning.
-fno-access-control-faligned-newnew of types that require more
alignment than void* ::operator new(std::size_t) provides. A
numeric argument such as -faligned-new=32 can be used to
specify how much alignment (in bytes) is provided by that function,
but few users will need to override the default of
alignof(std::max_align_t).
This flag is enabled by default for -std=c++17.
-fchar8_t-fno-char8_tchar8_t as adopted for C++20. This includes
the addition of a new char8_t fundamental type, changes to the
types of UTF-8 string and character literals, new signatures for
user-defined literals, associated standard library updates, and new
__cpp_char8_t and __cpp_lib_char8_t feature test macros.
This option enables functions to be overloaded for ordinary and UTF-8 strings:
int f(const char *); // #1
int f(const char8_t *); // #2
int v1 = f("text"); // Calls #1
int v2 = f(u8"text"); // Calls #2
and introduces new signatures for user-defined literals:
int operator""_udl1(char8_t);
int v3 = u8'x'_udl1;
int operator""_udl2(const char8_t*, std::size_t);
int v4 = u8"text"_udl2;
template<typename T, T...> int operator""_udl3();
int v5 = u8"text"_udl3;
The change to the types of UTF-8 string and character literals introduces incompatibilities with ISO C++11 and later standards. For example, the following code is well-formed under ISO C++11, but is ill-formed when -fchar8_t is specified.
const char *cp = u8"xx";// error: invalid conversion from
// `const char8_t*' to `const char*'
int f(const char*);
auto v = f(u8"xx"); // error: invalid conversion from
// `const char8_t*' to `const char*'
std::string s{u8"xx"}; // error: no matching function for call to
// `std::basic_string<char>::basic_string()'
using namespace std::literals;
s = u8"xx"s; // error: conversion from
// `basic_string<char8_t>' to non-scalar
// type `basic_string<char>' requested
-fcheck-newoperator new is non-null
before attempting to modify the storage allocated. This check is
normally unnecessary because the C++ standard specifies that
operator new only returns 0 if it is declared
throw(), in which case the compiler always checks the
return value even without this option. In all other cases, when
operator new has a non-empty exception specification, memory
exhaustion is signalled by throwing std::bad_alloc. See also
‘new (nothrow)’.
-fconcepts-fconcepts-tsSome constructs that were allowed by the earlier C++ Extensions for Concepts Technical Specification, ISO 19217 (2015), but didn't make it into the standard, can additionally be enabled by -fconcepts-ts.
-fconstexpr-depth=n-fconstexpr-cache-depth=n-fconstexpr-fp-exceptconstexpr float inf = 1./0.; // OK with -fconstexpr-fp-except
-fconstexpr-loop-limit=n-fconstexpr-ops-limit=n-fcontractsOn violation of a checked contract, the violation handler is called. Users can replace the violation handler by defining
void
handle_contract_violation (const std::experimental::contract_violation&);
There are different sets of additional flags that can be used together to specify which contracts will be checked and how, for N4820 contracts, P1332 contracts, or P1429 contracts; these sets cannot be used together.
-fcontract-mode=[on|off]-fcontract-assumption-mode=[on|off]-fcontract-build-level=[off|default|audit]-fcontract-continuation-mode=[on|off]-fcontract-role=<name>:<default>,<audit>,<axiom>-fcontract-semantic=[default|audit|axiom]:<semantic>-fcontract-strict-declarations=[on|off]The possible concrete semantics for that can be specified with ‘-fcontract-role’ or ‘-fcontract-semantic’ are:
ignoreassume[[assume]].
check_never_continueneverabortstd::terminate is called.
check_maybe_continuemaybe-fcoroutines-fno-elide-constructorsIn C++17, the compiler is required to omit these temporaries, but this option still affects trivial member functions.
-fno-enforce-eh-specsNDEBUG. This does not give user code permission to throw
exceptions in violation of the exception specifications; the compiler
still optimizes based on the specifications, so throwing an
unexpected exception results in undefined behavior at run time.
-fextern-tls-init-fno-extern-tls-initthread_local and
threadprivate variables to have dynamic (runtime)
initialization. To support this, any use of such a variable goes
through a wrapper function that performs any necessary initialization.
When the use and definition of the variable are in the same
translation unit, this overhead can be optimized away, but when the
use is in a different translation unit there is significant overhead
even if the variable doesn't actually need dynamic initialization. If
the programmer can be sure that no use of the variable in a
non-defining TU needs to trigger dynamic initialization (either
because the variable is statically initialized, or a use of the
variable in the defining TU will be executed before any uses in
another TU), they can avoid this overhead with the
-fno-extern-tls-init option.
On targets that support symbol aliases, the default is -fextern-tls-init. On targets that do not support symbol aliases, the default is -fno-extern-tls-init.
-ffold-simple-inlines-fno-fold-simple-inlinesstd::move, std::forward,
std::addressof and std::as_const. In contrast to inlining, this
means no debug information will be generated for such calls. Since these
functions are rarely interesting to debug, this flag is enabled by default
unless -fno-inline is active.
-fno-gnu-keywordstypeof as a keyword, so that code can use this
word as an identifier. You can use the keyword __typeof__ instead.
This option is implied by the strict ISO C++ dialects: -ansi,
-std=c++98, -std=c++11, etc.
-fimplicit-constexpr-fno-implicit-templates-fno-implicit-inline-templates-fno-implement-inlines#pragma implementation. This causes linker
errors if these functions are not inlined everywhere they are called.
-fmodules-ts-fno-modules-ts-fmodule-header-fmodule-header=user-fmodule-header=system-fmodule-implicit-inline-fno-module-lazy-fmodule-mapper=[hostname]:port[?ident]-fmodule-mapper=|program[?ident] args...-fmodule-mapper==socket[?ident]-fmodule-mapper=<>[inout][?ident]-fmodule-mapper=<in>out[?ident]-fmodule-mapper=file[?ident]-fmodule-only-fms-extensions-fnew-inheriting-ctors-fnew-ttp-matching-fno-nonansi-builtinsffs, alloca, _exit,
index, bzero, conjf, and other related functions.
-fnothrow-optthrow() exception specification as if it were a
noexcept specification to reduce or eliminate the text size
overhead relative to a function with no exception specification. If
the function has local variables of types with non-trivial
destructors, the exception specification actually makes the
function smaller because the EH cleanups for those variables can be
optimized away. The semantic effect is that an exception thrown out of
a function with such an exception specification results in a call
to terminate rather than unexpected.
-fno-operator-namesand, bitand,
bitor, compl, not, or and xor as
synonyms as keywords.
-fno-optional-diags-fpermissive-fno-pretty-templatesvoid f(T) [with T = int]
rather than void f(int)) so that it's clear which template is
involved. When an error message refers to a specialization of a class
template, the compiler omits any template arguments that match
the default template arguments for that template. If either of these
behaviors make it harder to understand the error message rather than
easier, you can use -fno-pretty-templates to disable them.
-fno-rttidynamic_cast and typeid). If you don't use those parts
of the language, you can save some space by using this flag. Note that
exception handling uses the same information, but G++ generates it as
needed. The dynamic_cast operator can still be used for casts that
do not require run-time type information, i.e. casts to void * or to
unambiguous base classes.
Mixing code compiled with -frtti with that compiled with -fno-rtti may not work. For example, programs may fail to link if a class compiled with -fno-rtti is used as a base for a class compiled with -frtti.
-fsized-deallocation void operator delete (void *, std::size_t) noexcept;
void operator delete[] (void *, std::size_t) noexcept;
as introduced in C++14. This is useful for user-defined replacement deallocation functions that, for example, use the size of the object to make deallocation faster. Enabled by default under -std=c++14 and above. The flag -Wsized-deallocation warns about places that might want to add a definition.
-fstrict-enums-fstrong-eval-order-ftemplate-backtrace-limit=n-ftemplate-depth=n-fno-threadsafe-statics-fuse-cxa-atexit__cxa_atexit function rather than the atexit function.
This option is required for fully standards-compliant handling of static
destructors, but only works if your C library supports
__cxa_atexit.
-fno-use-cxa-get-exception-ptr__cxa_get_exception_ptr runtime routine. This
causes std::uncaught_exception to be incorrect, but is necessary
if the runtime routine is not available.
-fvisibility-inlines-hiddenThe effect of this is that GCC may, effectively, mark inline methods with
__attribute__ ((visibility ("hidden"))) so that they do not
appear in the export table of a DSO and do not require a PLT indirection
when used within the DSO. Enabling this option can have a dramatic effect
on load and link times of a DSO as it massively reduces the size of the
dynamic export table when the library makes heavy use of templates.
The behavior of this switch is not quite the same as marking the methods as hidden directly, because it does not affect static variables local to the function or cause the compiler to deduce that the function is defined in only one shared object.
You may mark a method as having a visibility explicitly to negate the effect of the switch for that method. For example, if you do want to compare pointers to a particular inline method, you might mark it as having default visibility. Marking the enclosing class with explicit visibility has no effect.
Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. See Template Instantiation.
-fvisibility-ms-compatThe flag makes these changes to GCC's linkage model:
hidden, like
-fvisibility=hidden.
In new code it is better to use -fvisibility=hidden and export those classes that are intended to be externally visible. Unfortunately it is possible for code to rely, perhaps accidentally, on the Visual Studio behavior.
Among the consequences of these changes are that static data members of the same type with the same name but defined in different shared objects are different, so changing one does not change the other; and that pointers to function members defined in different shared objects may not compare equal. When this flag is given, it is a violation of the ODR to define types with the same name differently.
-fno-weak-fext-numeric-literals (C++ and Objective-C++ only)-nostdinc++-flang-info-include-translate-flang-info-include-translate-not-flang-info-include-translate=header"user" or <system> it will be resolved to a
specific user or system header using the include path.
-flang-info-module-cmi-flang-info-module-cmi=module<> or "").
-stdlib=libstdc++,libc++-lstdc++ or -lc++ respectively,
when a C++ runtime is required for linking.
In addition, these warning options have meanings only for C++ programs:
-Wabi-tag (C++ and Objective-C++ only)-Wcomma-subscript (C++ and Objective-C++ only)( ) is not deprecated. Example:
void f(int *a, int b, int c) {
a[b,c]; // deprecated in C++20, invalid in C++23
a[(b,c)]; // OK
}
In C++23 it is valid to have comma separated expressions in a subscript when an overloaded subscript operator is found and supports the right number and types of arguments. G++ will accept the formerly valid syntax for code that is not valid in C++23 but used to be valid but deprecated in C++20 with a pedantic warning that can be disabled with -Wno-comma-subscript.
Enabled by default with -std=c++20 unless -Wno-deprecated, and with -std=c++23 regardless of -Wno-deprecated.
-Wctad-maybe-unsupported (C++ and Objective-C++ only) struct allow_ctad_t; // any name works
template <typename T> struct S {
S(T) { }
};
// Guide with incomplete parameter type will never be considered.
S(allow_ctad_t) -> S<void>;
-Wctor-dtor-privacy (C++ and Objective-C++ only)-Wdangling-reference (C++ and Objective-C++ only) int n = 1;
const int& r = std::max(n - 1, n + 1); // r is dangling
In the example above, two temporaries are created, one for each
argument, and a reference to one of the temporaries is returned.
However, both temporaries are destroyed at the end of the full
expression, so the reference r is dangling. This warning
also detects dangling references in member initializer lists:
const int& f(const int& i) { return i; }
struct S {
const int &r; // r is dangling
S() : r(f(10)) { }
};
Member functions are checked as well, but only their object argument:
struct S {
const S& self () { return *this; }
};
const S& s = S().self(); // s is dangling
Certain functions are safe in this respect, for example std::use_facet:
they take and return a reference, but they don't return one of its arguments,
which can fool the warning. Such functions can be excluded from the warning
by wrapping them in a #pragma:
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdangling-reference"
const T& foo (const T&) { ... }
#pragma GCC diagnostic pop
-Wdangling-reference also warns about code like
auto p = std::minmax(1, 2);
where std::minmax returns std::pair<const int&, const int&>, and
both references dangle after the end of the full expression that contains
the call to std::minmax.
This warning is enabled by -Wextra.
-Wdelete-non-virtual-dtor (C++ and Objective-C++ only)delete is used to destroy an instance of a class that
has virtual functions and non-virtual destructor. It is unsafe to delete
an instance of a derived class through a pointer to a base class if the
base class does not have a virtual destructor. This warning is enabled
by -Wall.
-Wdeprecated-copy (C++ and Objective-C++ only)-Wno-deprecated-enum-enum-conversion (C++ and Objective-C++ only) enum E1 { e };
enum E2 { f };
int k = f - e;
-Wdeprecated-enum-enum-conversion is enabled by default with -std=c++20. In pre-C++20 dialects, this warning can be enabled by -Wenum-conversion.
-Wno-deprecated-enum-float-conversion (C++ and Objective-C++ only) enum E1 { e };
enum E2 { f };
bool b = e <= 3.7;
-Wdeprecated-enum-float-conversion is enabled by default with -std=c++20. In pre-C++20 dialects, this warning can be enabled by -Wenum-conversion.
-Wno-init-list-lifetime (C++ and Objective-C++ only)std::initializer_list that are likely
to result in dangling pointers. Since the underlying array for an
initializer_list is handled like a normal C++ temporary object,
it is easy to inadvertently keep a pointer to the array past the end
of the array's lifetime. For example:
initializer_list, or a local
initializer_list variable, the array's lifetime ends at the end
of the return statement, so the value returned has a dangling pointer.
initializer_list, the array only
lives until the end of the enclosing full-expression, so the
initializer_list in the heap has a dangling pointer.
initializer_list variable is assigned from a
brace-enclosed initializer list, the temporary array created for the
right side of the assignment only lives until the end of the
full-expression, so at the next statement the initializer_list
variable has a dangling pointer.
// li's initial underlying array lives as long as li
std::initializer_list<int> li = { 1,2,3 };
// assignment changes li to point to a temporary array
li = { 4, 5 };
// now the temporary is gone and li has a dangling pointer
int i = li.begin()[0] // undefined behavior
begin pointer from the
initializer_list argument, this doesn't extend the lifetime of
the array, so if a class variable is constructed from a temporary
initializer_list, the pointer is left dangling by the end of
the variable declaration statement.
-Winvalid-constexprconstexpr function and function template,
there must be at least one set of function arguments in at least one
instantiation such that an invocation of the function or constructor
could be an evaluated subexpression of a core constant expression.
C++23 removed this restriction, so it's possible to have a function
or a function template marked constexpr for which no invocation
satisfies the requirements of a core constant expression.
This warning is enabled as a pedantic warning by default in C++20 and earlier. In C++23, -Winvalid-constexpr can be turned on, in which case it will be an ordinary warning. For example:
void f (int& i);
constexpr void
g (int& i)
{
// Warns by default in C++20, in C++23 only with -Winvalid-constexpr.
f(i);
}
-Winvalid-imported-macros-Wno-literal-suffix (C++ and Objective-C++ only)<inttypes.h>. For example:
#define __STDC_FORMAT_MACROS
#include <inttypes.h>
#include <stdio.h>
int main() {
int64_t i64 = 123;
printf("My int64: %" PRId64"\n", i64);
}
In this case, PRId64 is treated as a separate preprocessing token.
This option also controls warnings when a user-defined literal operator is declared with a literal suffix identifier that doesn't begin with an underscore. Literal suffix identifiers that don't begin with an underscore are reserved for future standardization.
These warnings are enabled by default.
-Wno-narrowing (C++ and Objective-C++ only)With -Wnarrowing in C++98, warn when a narrowing conversion prohibited by C++11 occurs within ‘{ }’, e.g.
int i = { 2.2 }; // error: narrowing from double to int
This flag is included in -Wall and -Wc++11-compat.
-Wnoexcept (C++ and Objective-C++ only)throw() or noexcept) but is known by
the compiler to never throw an exception.
-Wnoexcept-type (C++ and Objective-C++ only)noexcept part of a function
type changes the mangled name of a symbol relative to C++14. Enabled
by -Wabi and -Wc++17-compat.
As an example:
template <class T> void f(T t) { t(); };
void g() noexcept;
void h() { f(g); }
In C++14, f calls f<void(*)()>, but in
C++17 it calls f<void(*)()noexcept>.
-Wclass-memaccess (C++ and Objective-C++ only)memset or memcpy is an object of class type, and when writing
into such an object might bypass the class non-trivial or deleted constructor
or copy assignment, violate const-correctness or encapsulation, or corrupt
virtual table pointers. Modifying the representation of such objects may
violate invariants maintained by member functions of the class. For example,
the call to memset below is undefined because it modifies a non-trivial
class object and is, therefore, diagnosed. The safe way to either initialize
or clear the storage of objects of such types is by using the appropriate
constructor or assignment operator, if one is available.
std::string str = "abc";
memset (&str, 0, sizeof str);
The -Wclass-memaccess option is enabled by -Wall.
Explicitly casting the pointer to the class object to void * or
to a type that can be safely accessed by the raw memory function suppresses
the warning.
-Wnon-virtual-dtor (C++ and Objective-C++ only)-Wregister (C++ and Objective-C++ only)register storage class specifier, except
when it is part of the GNU Explicit Register Variables extension.
The use of the register keyword as storage class specifier has
been deprecated in C++11 and removed in C++17.
Enabled by default with -std=c++17.
-Wreorder (C++ and Objective-C++ only) struct A {
int i;
int j;
A(): j (0), i (1) { }
};
The compiler rearranges the member initializers for i
and j to match the declaration order of the members, emitting
a warning to that effect. This warning is enabled by -Wall.
-Wno-pessimizing-move (C++ and Objective-C++ only)std::move prevents copy
elision. A typical scenario when copy elision can occur is when returning in
a function with a class return type, when the expression being returned is the
name of a non-volatile automatic object, and is not a function parameter, and
has the same type as the function return type.
struct T {
...
};
T fn()
{
T t;
...
return std::move (t);
}
But in this example, the std::move call prevents copy elision.
This warning is enabled by -Wall.
-Wno-redundant-move (C++ and Objective-C++ only)std::move; that is, when
a move operation would have been performed even without the std::move
call. This happens because the compiler is forced to treat the object as if
it were an rvalue in certain situations such as returning a local variable,
where copy elision isn't applicable. Consider:
struct T {
...
};
T fn(T t)
{
...
return std::move (t);
}
Here, the std::move call is redundant. Because G++ implements Core
Issue 1579, another example is:
struct T { // convertible to U
...
};
struct U {
...
};
U fn()
{
T t;
...
return std::move (t);
}
In this example, copy elision isn't applicable because the type of the expression being returned and the function return type differ, yet G++ treats the return value as if it were designated by an rvalue.
This warning is enabled by -Wextra.
-Wrange-loop-construct (C++ and Objective-C++ only) struct S { char arr[128]; };
void fn () {
S arr[5];
for (const auto x : arr) { ... }
}
It does not warn when the type being copied is a trivially-copyable type whose size is less than 64 bytes.
This warning also warns when a loop variable in a range-based for-loop is initialized with a value of a different type resulting in a copy. For example:
void fn() {
int arr[10];
for (const double &x : arr) { ... }
}
In the example above, in every iteration of the loop a temporary value of
type double is created and destroyed, to which the reference
const double & is bound.
This warning is enabled by -Wall.
-Wredundant-tags (C++ and Objective-C++ only) struct foo;
struct foo *p; // warn that keyword struct can be eliminated
On the other hand, in this example there is no warning:
struct foo;
void foo (); // "hides" struct foo
void bar (struct foo&); // no warning, keyword struct is necessary
-Wno-subobject-linkage (C++ and Objective-C++ only)-Weffc++ (C++ and Objective-C++ only)operator= return a reference to *this.
&&, ||, or ,.
This option also enables -Wnon-virtual-dtor, which is also one of the effective C++ recommendations. However, the check is extended to warn about the lack of virtual destructor in accessible non-polymorphic bases classes too.
When selecting this option, be aware that the standard library headers do not obey all of these guidelines; use ‘grep -v’ to filter out those warnings.
-Wno-exceptions (C++ and Objective-C++ only)-Wstrict-null-sentinel (C++ and Objective-C++ only)NULL as sentinel. When
compiling only with GCC this is a valid sentinel, as NULL is defined
to __null. Although it is a null pointer constant rather than a
null pointer, it is guaranteed to be of the same size as a pointer.
But this use is not portable across different compilers.
-Wno-non-template-friend (C++ and Objective-C++ only)-Wold-style-cast (C++ and Objective-C++ only)dynamic_cast,
static_cast, reinterpret_cast, and const_cast) are
less vulnerable to unintended effects and much easier to search for.
-Woverloaded-virtual (C++ and Objective-C++ only)-Woverloaded-virtual=n struct A {
virtual void f();
};
struct B: public A {
void f(int); // does not override
};
the A class version of f is hidden in B, and code
like:
B* b;
b->f();
fails to compile.
In cases where the different signatures are not an accident, the
simplest solution is to add a using-declaration to the derived class
to un-hide the base function, e.g. add using A::f; to B.
The optional level suffix controls the behavior when all the declarations in the derived class override virtual functions in the base class, even if not all of the base functions are overridden:
struct C {
virtual void f();
virtual void f(int);
};
struct D: public C {
void f(int); // does override
}
This pattern is less likely to be a mistake; if D is only used virtually, the user might have decided that the base class semantics for some of the overloads are fine.
At level 1, this case does not warn; at level 2, it does. -Woverloaded-virtual by itself selects level 2. Level 1 is included in -Wall.
-Wno-pmf-conversions (C++ and Objective-C++ only)-Wsign-promo (C++ and Objective-C++ only)-Wtemplates (C++ and Objective-C++ only)-Wmismatched-new-delete (C++ and Objective-C++ only)operator new or operator
delete and the corresponding call to the allocation or deallocation function.
This includes invocations of C++ operator delete with pointers
returned from either mismatched forms of operator new, or from other
functions that allocate objects for which the operator delete isn't
a suitable deallocator, as well as calls to other deallocation functions
with pointers returned from operator new for which the deallocation
function isn't suitable.
For example, the delete expression in the function below is diagnosed
because it doesn't match the array form of the new expression
the pointer argument was returned from. Similarly, the call to free
is also diagnosed.
void f ()
{
int *a = new int[n];
delete a; // warning: mismatch in array forms of expressions
char *p = new char[n];
free (p); // warning: mismatch between new and free
}
The related option -Wmismatched-dealloc diagnoses mismatches
involving allocation and deallocation functions other than operator
new and operator delete.
-Wmismatched-new-delete is included in -Wall.
-Wmismatched-tags (C++ and Objective-C++ only)For example, the declaration of struct Object in the argument list
of draw triggers the warning. To avoid it, either remove the redundant
class-key struct or replace it with class to match its definition.
class Object {
public:
virtual ~Object () = 0;
};
void draw (struct Object*);
It is not wrong to declare a class with the class-key struct as
the example above shows. The -Wmismatched-tags option is intended
to help achieve a consistent style of class declarations. In code that is
intended to be portable to Windows-based compilers the warning helps prevent
unresolved references due to the difference in the mangling of symbols
declared with different class-keys. The option can be used either on its
own or in conjunction with -Wredundant-tags.
-Wmultiple-inheritance (C++ and Objective-C++ only)-Wvirtual-inheritance-Wno-virtual-move-assign-Wnamespaces-Wno-terminate (C++ and Objective-C++ only)terminate.
-Wno-vexing-parse (C++ and Objective-C++ only) void f(double a) {
int i(); // extern int i (void);
int n(int(a)); // extern int n (int);
}
Another example:
struct S { S(int); };
void f(double a) {
S x(int(a)); // extern struct S x (int);
S y(int()); // extern struct S y (int (*) (void));
S z(); // extern struct S z (void);
}
The warning will suggest options how to deal with such an ambiguity; e.g., it can suggest removing the parentheses or using braces instead.
This warning is enabled by default.
-Wno-class-conversion (C++ and Objective-C++ only)-Wvolatile (C++ and Objective-C++ only)volatile qualifier. This includes
postfix and prefix ++ and -- expressions of
volatile-qualified types, using simple assignments where the left
operand is a volatile-qualified non-class type for their value,
compound assignments where the left operand is a volatile-qualified
non-class type, volatile-qualified function return type,
volatile-qualified parameter type, and structured bindings of a
volatile-qualified type. This usage was deprecated in C++20.
Enabled by default with -std=c++20.
-Wzero-as-null-pointer-constant (C++ and Objective-C++ only)nullptr in C++11.
-Waligned-newalignof(std::max_align_t) but uses an allocation
function without an explicit alignment parameter. This option is
enabled by -Wall.
Normally this only warns about global allocation functions, but -Waligned-new=all also warns about class member allocation functions.
-Wno-placement-new-Wplacement-new=n char buf [64];
new (buf) int[64];
This warning is enabled by default.
-Wplacement-new=1new expression is not diagnosed at this level even
though it has undefined behavior according to the C++ standard because
it writes past the end of the one-element array.
struct S { int n, a[1]; };
S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
new (s->a)int [32]();
-Wplacement-new=2 struct S { int n, a[]; };
S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
new (s->a)int [32]();
-Wcatch-value-Wcatch-value=n (C++ and Objective-C++ only)-Wconditionally-supported (C++ and Objective-C++ only)-Wno-delete-incomplete (C++ and Objective-C++ only)-Wextra-semi (C++, Objective-C++ only)-Wno-inaccessible-base (C++, Objective-C++ only) struct A { int a; };
struct B : A { };
struct C : B, A { };
-Wno-inherited-variadic-ctor-Wno-invalid-offsetof (C++ and Objective-C++ only)offsetof macro to a non-POD
type. According to the 2014 ISO C++ standard, applying offsetof
to a non-standard-layout type is undefined. In existing C++ implementations,
however, offsetof typically gives meaningful results.
This flag is for users who are aware that they are
writing nonportable code and who have deliberately chosen to ignore the
warning about it.
The restrictions on offsetof may be relaxed in a future version
of the C++ standard.
-Wsized-deallocation (C++ and Objective-C++ only) void operator delete (void *) noexcept;
void operator delete[] (void *) noexcept;
without a definition of the corresponding sized deallocation function
void operator delete (void *, std::size_t) noexcept;
void operator delete[] (void *, std::size_t) noexcept;
or vice versa. Enabled by -Wextra along with -fsized-deallocation.
-Wsuggest-final-typesfinal specifier,
or, if possible,
declared in an anonymous namespace. This allows GCC to more aggressively
devirtualize the polymorphic calls. This warning is more effective with
link-time optimization,
where the information about the class hierarchy graph is
more complete.
-Wsuggest-final-methodsfinal specifier,
or, if possible, its type were
declared in an anonymous namespace or with the final specifier.
This warning is
more effective with link-time optimization, where the information about the
class hierarchy graph is more complete. It is recommended to first consider
suggestions of -Wsuggest-final-types and then rebuild with new
annotations.
-Wsuggest-overrideoverride keyword.
-Wuse-after-free-Wuse-after-free=n-Wuse-after-free=1realloc, regardless of whether or not the call resulted
in an actual reallocatio of memory. This includes double-free
calls as well as uses in arithmetic and relational expressions. Although
undefined, uses of indeterminate pointers in equality (or inequality)
expressions are not diagnosed at this level.
-Wuse-after-free=2free in the following
function is diagnosed at this level:
struct A { int refcount; void *data; };
void release (struct A *p)
{
int refcount = --p->refcount;
free (p);
if (refcount == 0)
free (p->data); // warning: p may be used after free
}
-Wuse-after-free=3realloc as
an attempt to determine whether the call resulted in relocating the object
to a different address. They are diagnosed at a separate level to aid
legacy code gradually transition to safe alternatives. For example,
the equality test in the function below is diagnosed at this level:
void adjust_pointers (int**, int);
void grow (int **p, int n)
{
int **q = (int**)realloc (p, n *= 2);
if (q == p)
return;
adjust_pointers ((int**)q, n);
}
To avoid the warning at this level, store offsets into allocated memory instead of pointers. This approach obviates needing to adjust the stored pointers after reallocation.
-Wuse-after-free=2 is included in -Wall.
-Wuseless-cast (C++ and Objective-C++ only) struct S { };
void g (S&&);
void f (S&& arg)
{
g (S(arg)); // make arg prvalue so that it can bind to S&&
}
-Wno-conversion-null (C++ and Objective-C++ only)NULL and non-pointer
types. -Wconversion-null is enabled by default.
(NOTE: This manual does not describe the Objective-C and Objective-C++ languages themselves. See Language Standards Supported by GCC, for references.)
This section describes the command-line options that are only meaningful for Objective-C and Objective-C++ programs. You can also use most of the language-independent GNU compiler options. For example, you might compile a file some_class.m like this:
gcc -g -fgnu-runtime -O -c some_class.m
In this example, -fgnu-runtime is an option meant only for Objective-C and Objective-C++ programs; you can use the other options with any language supported by GCC.
Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front-end (e.g., -Wtraditional). Similarly, Objective-C++ compilations may use C++-specific options (e.g., -Wabi).
Here is a list of options that are only for compiling Objective-C and Objective-C++ programs:
-fconstant-string-class=class-name@"...". The default
class name is NXConstantString if the GNU runtime is being used, and
NSConstantString if the NeXT runtime is being used (see below). On
Darwin (macOS, MacOS X) platforms, the -fconstant-cfstrings option, if
also present, overrides the -fconstant-string-class setting and cause
@"..." literals to be laid out as constant CoreFoundation strings.
Note that -fconstant-cfstrings is an alias for the target-specific
-mconstant-cfstrings equivalent.
-fgnu-runtime-fnext-runtime__NEXT_RUNTIME__ is predefined if (and only if) this option is
used.
-fno-nil-receivers[receiver
message:arg]) in this translation unit ensure that the receiver is
not nil. This allows for more efficient entry points in the
runtime to be used. This option is only available in conjunction with
the NeXT runtime and ABI version 0 or 1.
-fobjc-abi-version=n-fobjc-call-cxx-cdtors- (id) .cxx_construct instance method which runs
non-trivial default constructors on any such instance variables, in order,
and then return self. Similarly, check if any instance variable
is a C++ object with a non-trivial destructor, and if so, synthesize a
special - (void) .cxx_destruct method which runs
all such default destructors, in reverse order.
The - (id) .cxx_construct and - (void) .cxx_destruct
methods thusly generated only operate on instance variables
declared in the current Objective-C class, and not those inherited
from superclasses. It is the responsibility of the Objective-C
runtime to invoke all such methods in an object's inheritance
hierarchy. The - (id) .cxx_construct methods are invoked
by the runtime immediately after a new object instance is allocated;
the - (void) .cxx_destruct methods are invoked immediately
before the runtime deallocates an object instance.
As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
support for invoking the - (id) .cxx_construct and
- (void) .cxx_destruct methods.
-fobjc-direct-dispatch-fobjc-exceptions@try,
@throw, @catch, @finally and
@synchronized. This option is available with both the GNU
runtime and the NeXT runtime (but not available in conjunction with
the NeXT runtime on Mac OS X 10.2 and earlier).
-fobjc-gc-fobjc-nilcheck-fobjc-std=objc1-freplace-objc-classes-fzero-linkobjc_getClass("...") (when the name of the class is known at
compile time) with static class references that get initialized at load time,
which improves run-time performance. Specifying the -fzero-link flag
suppresses this behavior and causes calls to objc_getClass("...")
to be retained. This is useful in Zero-Link debugging mode, since it allows
for individual class implementations to be modified during program execution.
The GNU runtime currently always retains calls to objc_get_class("...")
regardless of command-line options.
-fno-local-ivars-fivar-visibility=[public|protected|private|package]-gen-decls-Wassign-intercept (Objective-C and Objective-C++ only)-Wno-property-assign-default (Objective-C and Objective-C++ only)-Wno-protocol (Objective-C and Objective-C++ only)-Wobjc-root-class (Objective-C and Objective-C++ only)NSObject (or Object) for example. When declaring
classes intended to be root classes, the warning can be suppressed by
marking their interfaces with __attribute__((objc_root_class)).
-Wselector (Objective-C and Objective-C++ only)@selector(...)
expression, and a corresponding method for that selector has been found
during compilation. Because these checks scan the method table only at
the end of compilation, these warnings are not produced if the final
stage of compilation is not reached, for example because an error is
found during compilation, or because the -fsyntax-only option is
being used.
-Wstrict-selector-match (Objective-C and Objective-C++ only)id or Class. When this flag
is off (which is the default behavior), the compiler omits such warnings
if any differences found are confined to types that share the same size
and alignment.
-Wundeclared-selector (Objective-C and Objective-C++ only)@selector(...) expression referring to an
undeclared selector is found. A selector is considered undeclared if no
method with that name has been declared before the
@selector(...) expression, either explicitly in an
@interface or @protocol declaration, or implicitly in
an @implementation section. This option always performs its
checks as soon as a @selector(...) expression is found,
while -Wselector only performs its checks in the final stage of
compilation. This also enforces the coding style convention
that methods and selectors must be declared before being used.
-print-objc-runtime-infoTraditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g. its width, ...). You can use the options described below to control the formatting algorithm for diagnostic messages, e.g. how many characters per line, how often source location information should be reported. Note that some language front ends may not honor these options.
-fmessage-length=nNote - this option also affects the display of the ‘#error’ and
‘#warning’ pre-processor directives, and the ‘deprecated’
function/type/variable attribute. It does not however affect the
‘pragma GCC warning’ and ‘pragma GCC error’ pragmas.
-fdiagnostics-plain-output -fno-diagnostics-show-caret
-fno-diagnostics-show-line-numbers
-fdiagnostics-color=never
-fdiagnostics-urls=never
-fdiagnostics-path-format=separate-events
In the future, if GCC changes the default appearance of its diagnostics, the corresponding option to disable the new behavior will be added to this list.
-fdiagnostics-show-location=once-fdiagnostics-show-location=every-line-fdiagnostics-color[=WHEN]-fno-diagnostics-colorThe colors are defined by the environment variable GCC_COLORS. Its value is a colon-separated list of capabilities and Select Graphic Rendition (SGR) substrings. SGR commands are interpreted by the terminal or terminal emulator. (See the section in the documentation of your text terminal for permitted values and their meanings as character attributes.) These substring values are integers in decimal representation and can be concatenated with semicolons. Common values to concatenate include ‘1’ for bold, ‘4’ for underline, ‘5’ for blink, ‘7’ for inverse, ‘39’ for default foreground color, ‘30’ to ‘37’ for foreground colors, ‘90’ to ‘97’ for 16-color mode foreground colors, ‘38;5;0’ to ‘38;5;255’ for 88-color and 256-color modes foreground colors, ‘49’ for default background color, ‘40’ to ‘47’ for background colors, ‘100’ to ‘107’ for 16-color mode background colors, and ‘48;5;0’ to ‘48;5;255’ for 88-color and 256-color modes background colors.
The default GCC_COLORS is
error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\
diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
type-diff=01;32:fnname=01;32:targs=35
where ‘01;31’ is bold red, ‘01;35’ is bold magenta, ‘01;36’ is bold cyan, ‘32’ is green, ‘34’ is blue, ‘01’ is bold, and ‘31’ is red. Setting GCC_COLORS to the empty string disables colors. Supported capabilities are as follows.
error=warning=note=path=range1=range2=locus=quote=fnname=targs=fixit-insert=fixit-delete=diff-filename=diff-hunk=diff-delete=diff-insert=type-diff=-fdiagnostics-urls[=WHEN]WHEN is ‘never’, ‘always’, or ‘auto’. ‘auto’ makes GCC use URL escape sequences only when the standard error is a terminal, and when not executing in an emacs shell or any graphical terminal which is known to be incompatible with this feature, see below.
The default depends on how the compiler has been configured. It can be any of the above WHEN options.
GCC can also be configured (via the --with-diagnostics-urls=auto-if-env configure-time option) so that the default is affected by environment variables. Under such a configuration, GCC defaults to using ‘auto’ if either GCC_URLS or TERM_URLS environment variables are present and non-empty in the environment of the compiler, or ‘never’ if neither are.
However, even with -fdiagnostics-urls=always the behavior is dependent on those environment variables: If GCC_URLS is set to empty or ‘no’, do not embed URLs in diagnostics. If set to ‘st’, URLs use ST escape sequences. If set to ‘bel’, the default, URLs use BEL escape sequences. Any other non-empty value enables the feature. If GCC_URLS is not set, use TERM_URLS as a fallback. Note: ST is an ANSI escape sequence, string terminator ‘ESC \’, BEL is an ASCII character, CTRL-G that usually sounds like a beep.
At this time GCC tries to detect also a few terminals that are known to not implement the URL feature, and have bugs or at least had bugs in some versions that are still in use, where the URL escapes are likely to misbehave, i.e. print garbage on the screen. That list is currently xfce4-terminal, certain known to be buggy gnome-terminal versions, the linux console, and mingw. This check can be skipped with the -fdiagnostics-urls=always.
-fno-diagnostics-show-option-fno-diagnostics-show-caret-fno-diagnostics-show-labels printf ("foo %s bar", long_i + long_j);
~^ ~~~~~~~~~~~~~~~
| |
char * long int
This option suppresses the printing of these labels (in the example above, the vertical bars and the “char *” and “long int” text).
-fno-diagnostics-show-cwe-fno-diagnostics-show-rules-fno-diagnostics-show-line-numbers-fdiagnostics-minimum-margin-width=width-fdiagnostics-parseable-fixits fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"
The location is expressed as a half-open range, expressed as a count of bytes, starting at byte 1 for the initial column. In the above example, bytes 3 through 20 of line 45 of “test.c” are to be replaced with the given string:
00000000011111111112222222222
12345678901234567890123456789
gtk_widget_showall (dlg);
^^^^^^^^^^^^^^^^^^
gtk_widget_show_all
The filename and replacement string escape backslash as “\\", tab as “\t”, newline as “\n”, double quotes as “\"”, non-printable characters as octal (e.g. vertical tab as “\013”).
An empty replacement string indicates that the given range is to be removed. An empty range (e.g. “45:3-45:3”) indicates that the string is to be inserted at the given position.
-fdiagnostics-generate-patch --- test.c
+++ test.c
@ -42,5 +42,5 @
void show_cb(GtkDialog *dlg)
{
- gtk_widget_showall(dlg);
+ gtk_widget_show_all(dlg);
}
The diff may or may not be colorized, following the same rules as for diagnostics (see -fdiagnostics-color).
-fdiagnostics-show-template-tree could not convert 'std::map<int, std::vector<double> >()'
from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
the -fdiagnostics-show-template-tree flag enables printing a tree-like structure showing the common and differing parts of the types, such as:
map<
[...],
vector<
[double != float]>>
The parts that differ are highlighted with color (“double” and “float” in this case).
-fno-elide-type could not convert 'std::map<int, std::vector<double> >()'
from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
Specifying the -fno-elide-type flag suppresses that behavior. This flag also affects the output of the -fdiagnostics-show-template-tree flag.
-fdiagnostics-path-format=KINDKIND is ‘none’, ‘separate-events’, or ‘inline-events’, the default.
‘none’ means to not print diagnostic paths.
‘separate-events’ means to print a separate “note” diagnostic for each event within the diagnostic. For example:
test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter
test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL
test.c:27:3: note: (2) when 'i < count'
test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1
‘inline-events’ means to print the events “inline” within the source code. This view attempts to consolidate the events into runs of sufficiently-close events, printing them as labelled ranges within the source.
For example, the same events as above might be printed as:
'test': events 1-3
|
| 25 | list = PyList_New(0);
| | ^~~~~~~~~~~~~
| | |
| | (1) when 'PyList_New' fails, returning NULL
| 26 |
| 27 | for (i = 0; i < count; i++) {
| | ~~~
| | |
| | (2) when 'i < count'
| 28 | item = PyLong_FromLong(random());
| 29 | PyList_Append(list, item);
| | ~~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (3) when calling 'PyList_Append', passing NULL from (1) as argument 1
|
Interprocedural control flow is shown by grouping the events by stack frame, and using indentation to show how stack frames are nested, pushed, and popped.
For example:
'test': events 1-2
|
| 133 | {
| | ^
| | |
| | (1) entering 'test'
| 134 | boxed_int *obj = make_boxed_int (i);
| | ~~~~~~~~~~~~~~~~~~
| | |
| | (2) calling 'make_boxed_int'
|
+--> 'make_boxed_int': events 3-4
|
| 120 | {
| | ^
| | |
| | (3) entering 'make_boxed_int'
| 121 | boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int));
| | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (4) calling 'wrapped_malloc'
|
+--> 'wrapped_malloc': events 5-6
|
| 7 | {
| | ^
| | |
| | (5) entering 'wrapped_malloc'
| 8 | return malloc (size);
| | ~~~~~~~~~~~~~
| | |
| | (6) calling 'malloc'
|
<-------------+
|
'test': event 7
|
| 138 | free_boxed_int (obj);
| | ^~~~~~~~~~~~~~~~~~~~
| | |
| | (7) calling 'free_boxed_int'
|
(etc)
-fdiagnostics-show-path-depthsIf this is option is provided then the stack depth will be printed for each run of events within -fdiagnostics-path-format=inline-events. If provided with -fdiagnostics-path-format=separate-events, then the stack depth and function declaration will be appended when printing each event.
This is intended for use by GCC developers and plugin developers when debugging diagnostics that report interprocedural control flow.
-fno-show-column-fdiagnostics-column-unit=UNITThe default UNIT, ‘display’, considers the number of display columns occupied by each character. This may be larger than the number of bytes required to encode the character, in the case of tab characters, or it may be smaller, in the case of multibyte characters. For example, the character “GREEK SMALL LETTER PI (U+03C0)” occupies one display column, and its UTF-8 encoding requires two bytes; the character “SLIGHTLY SMILING FACE (U+1F642)” occupies two display columns, and its UTF-8 encoding requires four bytes.
Setting UNIT to ‘byte’ changes the column number to the raw byte count in all cases, as was traditionally output by GCC prior to version 11.1.0.
-fdiagnostics-column-origin=ORIGIN-fdiagnostics-escape-format=FORMATThis option controls how such bytes should be escaped.
The default FORMAT, ‘unicode’ displays Unicode characters that are not printable ASCII in the form ‘<U+XXXX>’, and bytes that do not correspond to a Unicode character validly-encoded in UTF-8-encoded will be displayed as hexadecimal in the form ‘<XX>’.
For example, a source line containing the string ‘before’ followed by the Unicode character U+03C0 (“GREEK SMALL LETTER PI”, with UTF-8 encoding 0xCF 0x80) followed by the byte 0xBF (a stray UTF-8 trailing byte), followed by the string ‘after’ will be printed for such a diagnostic as:
before<U+03C0><BF>after
Setting FORMAT to ‘bytes’ will display all non-printable-ASCII bytes in the form ‘<XX>’, thus showing the underlying encoding of non-ASCII Unicode characters. For the example above, the following will be printed:
before<CF><80><BF>after
-fdiagnostics-format=FORMATThe default is ‘text’.
The ‘sarif-stderr’ and ‘sarif-file’ formats both emit diagnostics in SARIF Version 2.1.0 format, either to stderr, or to a file named source.sarif, respectively.
The ‘json’ format is a synonym for ‘json-stderr’. The ‘json-stderr’ and ‘json-file’ formats are identical, apart from where the JSON is emitted to - with the former, the JSON is emitted to stderr, whereas with ‘json-file’ it is written to source.gcc.json.
The emitted JSON consists of a top-level JSON array containing JSON objects representing the diagnostics. The JSON is emitted as one line, without formatting; the examples below have been formatted for clarity.
Diagnostics can have child diagnostics. For example, this error and note:
misleading-indentation.c:15:3: warning: this 'if' clause does not
guard... [-Wmisleading-indentation]
15 | if (flag)
| ^~
misleading-indentation.c:17:5: note: ...this statement, but the latter
is misleadingly indented as if it were guarded by the 'if'
17 | y = 2;
| ^
might be printed in JSON form (after formatting) like this:
[
{
"kind": "warning",
"locations": [
{
"caret": {
"display-column": 3,
"byte-column": 3,
"column": 3,
"file": "misleading-indentation.c",
"line": 15
},
"finish": {
"display-column": 4,
"byte-column": 4,
"column": 4,
"file": "misleading-indentation.c",
"line": 15
}
}
],
"message": "this \u2018if\u2019 clause does not guard...",
"option": "-Wmisleading-indentation",
"option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation",
"children": [
{
"kind": "note",
"locations": [
{
"caret": {
"display-column": 5,
"byte-column": 5,
"column": 5,
"file": "misleading-indentation.c",
"line": 17
}
}
],
"escape-source": false,
"message": "...this statement, but the latter is ..."
}
]
"escape-source": false,
"column-origin": 1,
}
]
where the note is a child of the warning.
A diagnostic has a kind. If this is warning, then there is
an option key describing the command-line option controlling the
warning.
A diagnostic can contain zero or more locations. Each location has an
optional label string and up to three positions within it: a
caret position and optional start and finish positions.
A position is described by a file name, a line number, and
three numbers indicating a column position:
display-column counts display columns, accounting for tabs and
multibyte characters.
byte-column counts raw bytes.
column is equal to one of
the previous two, as dictated by the -fdiagnostics-column-unit
option.
column-origin tag. In the remaining examples below, the extra
column number outputs have been omitted for brevity.
For example, this error:
bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' {aka
'struct s'} and 'T' {aka 'struct t'})
64 | return callee_4a () + callee_4b ();
| ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~
| | |
| | T {aka struct t}
| S {aka struct s}
has three locations. Its primary location is at the “+” token at column 23. It has two secondary locations, describing the left and right-hand sides of the expression, which have labels. It might be printed in JSON form as:
{
"children": [],
"kind": "error",
"locations": [
{
"caret": {
"column": 23, "file": "bad-binary-ops.c", "line": 64
}
},
{
"caret": {
"column": 10, "file": "bad-binary-ops.c", "line": 64
},
"finish": {
"column": 21, "file": "bad-binary-ops.c", "line": 64
},
"label": "S {aka struct s}"
},
{
"caret": {
"column": 25, "file": "bad-binary-ops.c", "line": 64
},
"finish": {
"column": 36, "file": "bad-binary-ops.c", "line": 64
},
"label": "T {aka struct t}"
}
],
"escape-source": false,
"message": "invalid operands to binary + ..."
}
If a diagnostic contains fix-it hints, it has a fixits array,
consisting of half-open intervals, similar to the output of
-fdiagnostics-parseable-fixits. For example, this diagnostic
with a replacement fix-it hint:
demo.c:8:15: error: 'struct s' has no member named 'colour'; did you
mean 'color'?
8 | return ptr->colour;
| ^~~~~~
| color
might be printed in JSON form as:
{
"children": [],
"fixits": [
{
"next": {
"column": 21,
"file": "demo.c",
"line": 8
},
"start": {
"column": 15,
"file": "demo.c",
"line": 8
},
"string": "color"
}
],
"kind": "error",
"locations": [
{
"caret": {
"column": 15,
"file": "demo.c",
"line": 8
},
"finish": {
"column": 20,
"file": "demo.c",
"line": 8
}
}
],
"escape-source": false,
"message": "\u2018struct s\u2019 has no member named ..."
}
where the fix-it hint suggests replacing the text from start up
to but not including next with string's value. Deletions
are expressed via an empty value for string, insertions by
having start equal next.
If the diagnostic has a path of control-flow events associated with it,
it has a path array of objects representing the events. Each
event object has a description string, a location object,
along with a function string and a depth number for
representing interprocedural paths. The function represents the
current function at that event, and the depth represents the
stack depth relative to some baseline: the higher, the more frames are
within the stack.
For example, the intraprocedural example shown for -fdiagnostics-path-format= might have this JSON for its path:
"path": [
{
"depth": 0,
"description": "when 'PyList_New' fails, returning NULL",
"function": "test",
"location": {
"column": 10,
"file": "test.c",
"line": 25
}
},
{
"depth": 0,
"description": "when 'i < count'",
"function": "test",
"location": {
"column": 3,
"file": "test.c",
"line": 27
}
},
{
"depth": 0,
"description": "when calling 'PyList_Append', passing NULL from (1) as argument 1",
"function": "test",
"location": {
"column": 5,
"file": "test.c",
"line": 29
}
}
]
Diagnostics have a boolean attribute escape-source, hinting whether
non-ASCII bytes should be escaped when printing the pertinent lines of
source code (true for diagnostics involving source encoding issues).
Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are risky or suggest there may have been an error.
The following language-independent options do not enable specific warnings but control the kinds of diagnostics produced by GCC.
-fsyntax-only-fmax-errors=n-w-Werror-Werror=The warning message for each controllable warning includes the option that controls the warning. That option can then be used with -Werror= and -Wno-error= as described above. (Printing of the option in the warning message can be disabled using the -fno-diagnostics-show-option flag.)
Note that specifying -Werror=foo automatically implies -Wfoo. However, -Wno-error=foo does not imply anything.
-Wfatal-errorsYou can request many specific warnings with options beginning with ‘-W’, for example -Wimplicit to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning ‘-Wno-’ to turn off warnings; for example, -Wno-implicit. This manual lists only one of the two forms, whichever is not the default. For further language-specific options also refer to C++ Dialect Options and Objective-C and Objective-C++ Dialect Options. Additional warnings can be produced by enabling the static analyzer; See Static Analyzer Options.
Some options, such as -Wall and -Wextra, turn on other options, such as -Wunused, which may turn on further options, such as -Wunused-value. The combined effect of positive and negative forms is that more specific options have priority over less specific ones, independently of their position in the command-line. For options of the same specificity, the last one takes effect. Options enabled or disabled via pragmas (see Diagnostic Pragmas) take effect as if they appeared at the end of the command-line.
When an unrecognized warning option is requested (e.g., -Wunknown-warning), GCC emits a diagnostic stating that the option is not recognized. However, if the -Wno- form is used, the behavior is slightly different: no diagnostic is produced for -Wno-unknown-warning unless other diagnostics are being produced. This allows the use of new -Wno- options with old compilers, but if something goes wrong, the compiler warns that an unrecognized option is present.
The effectiveness of some warnings depends on optimizations also being enabled. For example -Wsuggest-final-types is more effective with link-time optimization and some instances of other warnings may not be issued at all unless optimization is enabled. While optimization in general improves the efficacy of control and data flow sensitive warnings, in some cases it may also cause false positives.
-Wpedantic-pedanticValid ISO C and ISO C++ programs should compile properly with or without this option (though a rare few require -ansi or a -std option specifying the required version of ISO C). However, without this option, certain GNU extensions and traditional C and C++ features are supported as well. With this option, they are rejected.
-Wpedantic does not cause warning messages for use of the
alternate keywords whose names begin and end with ‘__’. This alternate
format can also be used to disable warnings for non-ISO ‘__intN’ types,
i.e. ‘__intN__’.
Pedantic warnings are also disabled in the expression that follows
__extension__. However, only system header files should use
these escape routes; application programs should avoid them.
See Alternate Keywords.
Some users try to use -Wpedantic to check programs for strict ISO C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not all—only those for which ISO C requires a diagnostic, and some others for which diagnostics have been added.
A feature to report any failure to conform to ISO C might be useful in some instances, but would require considerable additional work and would be quite different from -Wpedantic. We don't have plans to support such a feature in the near future.
Where the standard specified with -std represents a GNU extended dialect of C, such as ‘gnu90’ or ‘gnu99’, there is a corresponding base standard, the version of ISO C on which the GNU extended dialect is based. Warnings from -Wpedantic are given where they are required by the base standard. (It does not make sense for such warnings to be given only for features not in the specified GNU C dialect, since by definition the GNU dialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.)
-pedantic-errors-Wall-Wall turns on the following warning flags:
-Waddress
-Warray-bounds=1 (only with -O2)
-Warray-compare
-Warray-parameter=2 (C and Objective-C only)
-Wbool-compare
-Wbool-operation
-Wc++11-compat -Wc++14-compat
-Wcatch-value (C++ and Objective-C++ only)
-Wchar-subscripts
-Wcomment
-Wdangling-pointer=2
-Wduplicate-decl-specifier (C and Objective-C only)
-Wenum-compare (in C/ObjC; this is on by default in C++)
-Wenum-int-mismatch (C and Objective-C only)
-Wformat
-Wformat-overflow
-Wformat-truncation
-Wint-in-bool-context
-Wimplicit (C and Objective-C only)
-Wimplicit-int (C and Objective-C only)
-Wimplicit-function-declaration (C and Objective-C only)
-Winit-self (only for C++)
-Wlogical-not-parentheses
-Wmain (only for C/ObjC and unless -ffreestanding)
-Wmaybe-uninitialized
-Wmemset-elt-size
-Wmemset-transposed-args
-Wmisleading-indentation (only for C/C++)
-Wmismatched-dealloc
-Wmismatched-new-delete (only for C/C++)
-Wmissing-attributes
-Wmissing-braces (only for C/ObjC)
-Wmultistatement-macros
-Wnarrowing (only for C++)
-Wnonnull
-Wnonnull-compare
-Wopenmp-simd
-Wparentheses
-Wpessimizing-move (only for C++)
-Wpointer-sign
-Wrange-loop-construct (only for C++)
-Wreorder
-Wrestrict
-Wreturn-type
-Wself-move (only for C++)
-Wsequence-point
-Wsign-compare (only in C++)
-Wsizeof-array-div
-Wsizeof-pointer-div
-Wsizeof-pointer-memaccess
-Wstrict-aliasing
-Wstrict-overflow=1
-Wswitch
-Wtautological-compare
-Wtrigraphs
-Wuninitialized
-Wunknown-pragmas
-Wunused-function
-Wunused-label
-Wunused-value
-Wunused-variable
-Wuse-after-free=2
-Wvla-parameter (C and Objective-C only)
-Wvolatile-register-var
-Wzero-length-bounds
Note that some warning flags are not implied by -Wall. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled by -Wextra but many of them must be enabled individually.
-Wextra -Wclobbered
-Wcast-function-type
-Wdangling-reference (C++ only)
-Wdeprecated-copy (C++ only)
-Wempty-body
-Wenum-conversion (C only)
-Wignored-qualifiers
-Wimplicit-fallthrough=3
-Wmissing-field-initializers
-Wmissing-parameter-type (C only)
-Wold-style-declaration (C only)
-Woverride-init
-Wsign-compare (C only)
-Wstring-compare
-Wredundant-move (only for C++)
-Wtype-limits
-Wuninitialized
-Wshift-negative-value (in C++11 to C++17 and in C99 and newer)
-Wunused-parameter (only with -Wunused or -Wall)
-Wunused-but-set-parameter (only with -Wunused or -Wall)
The option -Wextra also prints warning messages for the following cases:
<, <=,
>, or >=.
register.
register.
-Wabi (C, Objective-C, C++ and Objective-C++ only)Since G++ now defaults to updating the ABI with each major release, normally -Wabi warns only about C++ ABI compatibility problems if there is a check added later in a release series for an ABI issue discovered since the initial release. -Wabi warns about more things if an older ABI version is selected (with -fabi-version=n).
-Wabi can also be used with an explicit version number to warn about C++ ABI compatibility with a particular -fabi-version level, e.g. -Wabi=2 to warn about changes relative to -fabi-version=2.
If an explicit version number is provided and -fabi-compat-version is not specified, the version number from this option is used for compatibility aliases. If no explicit version number is provided with this option, but -fabi-compat-version is specified, that version number is used for C++ ABI warnings.
Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be cases where warnings are emitted even though the code that is generated is compatible.
You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers.
Known incompatibilities in -fabi-version=2 (which was the default from GCC 3.4 to 4.9) include:
extern int N;
template <int &> struct S {};
void n (S<N>) {2}
This was fixed in -fabi-version=3.
__attribute ((vector_size)) were
mangled in a non-standard way that does not allow for overloading of
functions taking vectors of different sizes.
The mangling was changed in -fabi-version=4.
__attribute ((const)) and noreturn were mangled as type
qualifiers, and decltype of a plain declaration was folded away.
These mangling issues were fixed in -fabi-version=5.
va_arg to complain.
On most targets this does not actually affect the parameter passing
ABI, as there is no way to pass an argument smaller than int.
Also, the ABI changed the mangling of template argument packs,
const_cast, static_cast, prefix increment/decrement, and
a class scope function used as a template argument.
These issues were corrected in -fabi-version=6.
nullptr_t.
These issues were corrected in -fabi-version=7.
This was fixed in -fabi-version=8, the default for GCC 5.1.
decltype(nullptr) incorrectly had an alignment of 1, leading to
unaligned accesses. Note that this did not affect the ABI of a
function with a nullptr_t parameter, as parameters have a
minimum alignment.
This was fixed in -fabi-version=9, the default for GCC 5.2.
This was fixed in -fabi-version=10, the default for GCC 6.1.
This option also enables warnings about psABI-related changes. The known psABI changes at this point include:
long double members are
passed in memory as specified in psABI. Prior to GCC 4.4, this was not
the case. For example:
union U {
long double ld;
int i;
};
union U is now always passed in memory.
-Wno-changes-meaning (C++ and Objective-C++ only) struct A;
struct B1 { A a; typedef A A; }; // warning, 'A' changes meaning
struct B2 { A a; struct A { }; }; // error, 'A' changes meaning
By default, the B1 case is only a warning because the two declarations have the same type, while the B2 case is an error. Both diagnostics can be disabled with -Wno-changes-meaning. Alternately, the error case can be reduced to a warning with -Wno-error=changes-meaning or -fpermissive.
Both diagnostics are also suppressed by -fms-extensions.
-Wchar-subscriptschar. This is a common cause
of error, as programmers often forget that this type is signed on some
machines.
This warning is enabled by -Wall.
-Wno-coverage-mismatch-Wno-coverage-invalid-line-numberBy default, this warning is enabled and is treated as an error. -Wno-coverage-invalid-line-number can be used to disable the warning or -Wno-error=coverage-invalid-line-number can be used to disable the error.
-Wno-cpp (C, Objective-C, C++, Objective-C++ and Fortran only)#warning directives.
-Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)float is implicitly
promoted to double. CPUs with a 32-bit “single-precision”
floating-point unit implement float in hardware, but emulate
double in software. On such a machine, doing computations
using double values is much more expensive because of the
overhead required for software emulation.
It is easy to accidentally do computations with double because
floating-point literals are implicitly of type double. For
example, in:
float area(float radius)
{
return 3.14159 * radius * radius;
}
the compiler performs the entire computation with double
because the floating-point literal is a double.
-Wduplicate-decl-specifier (C and Objective-C only)const, volatile,
restrict or _Atomic specifier. This warning is enabled by
-Wall.
-Wformat-Wformat=nprintf and scanf, etc., to make sure that
the arguments supplied have types appropriate to the format string
specified, and that the conversions specified in the format string make
sense. This includes standard functions, and others specified by format
attributes (see Function Attributes), in the printf,
scanf, strftime and strfmon (an X/Open extension,
not in the C standard) families (or other target-specific families).
Which functions are checked without format attributes having been
specified depends on the standard version selected, and such checks of
functions without the attribute specified are disabled by
-ffreestanding or -fno-builtin.
The formats are checked against the format features supported by GNU
libc version 2.2. These include all ISO C90 and C99 features, as well
as features from the Single Unix Specification and some BSD and GNU
extensions. Other library implementations may not support all these
features; GCC does not support warning about features that go beyond a
particular library's limitations. However, if -Wpedantic is used
with -Wformat, warnings are given about format features not
in the selected standard version (but not for strfmon formats,
since those are not in any version of the C standard). See Options Controlling C Dialect.
-Wformat=1-Wformat-Wformat=2-Wno-format-contains-nul-Wno-format-extra-argsprintf or scanf format function. The C standard specifies
that such arguments are ignored.
Where the unused arguments lie between used arguments that are
specified with ‘$’ operand number specifications, normally
warnings are still given, since the implementation could not know what
type to pass to va_arg to skip the unused arguments. However,
in the case of scanf formats, this option suppresses the
warning if the unused arguments are all pointers, since the Single
Unix Specification says that such unused arguments are allowed.
-Wformat-overflow-Wformat-overflow=levelsprintf
and vsprintf that might overflow the destination buffer. When the
exact number of bytes written by a format directive cannot be determined
at compile-time it is estimated based on heuristics that depend on the
level argument and on optimization. While enabling optimization
will in most cases improve the accuracy of the warning, it may also
result in false positives.
-Wformat-overflow-Wformat-overflow=1sprintf
below is diagnosed because even with both a and b equal to zero,
the terminating NUL character ('\0') appended by the function
to the destination buffer will be written past its end. Increasing
the size of the buffer by a single byte is sufficient to avoid the
warning, though it may not be sufficient to avoid the overflow.
void f (int a, int b)
{
char buf [13];
sprintf (buf, "a = %i, b = %i\n", a, b);
}
-Wformat-overflow=2At level 2, the call in the example above is again diagnosed, but
this time because with a equal to a 32-bit INT_MIN the first
%i directive will write some of its digits beyond the end of
the destination buffer. To make the call safe regardless of the values
of the two variables, the size of the destination buffer must be increased
to at least 34 bytes. GCC includes the minimum size of the buffer in
an informational note following the warning.
An alternative to increasing the size of the destination buffer is to
constrain the range of formatted values. The maximum length of string
arguments can be bounded by specifying the precision in the format
directive. When numeric arguments of format directives can be assumed
to be bounded by less than the precision of their type, choosing
an appropriate length modifier to the format specifier will reduce
the required buffer size. For example, if a and b in the
example above can be assumed to be within the precision of
the short int type then using either the %hi format
directive or casting the argument to short reduces the maximum
required size of the buffer to 24 bytes.
void f (int a, int b)
{
char buf [23];
sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
}
-Wno-format-zero-length-Wformat-nonliteralva_list.
-Wformat-securityprintf and scanf functions where the
format string is not a string literal and there are no format arguments,
as in printf (foo);. This may be a security hole if the format
string came from untrusted input and contains ‘%n’. (This is
currently a subset of what -Wformat-nonliteral warns about, but
in future warnings may be added to -Wformat-security that are not
included in -Wformat-nonliteral.)
-Wformat-signedness-Wformat-truncation-Wformat-truncation=levelsnprintf
and vsnprintf that might result in output truncation. When the exact
number of bytes written by a format directive cannot be determined at
compile-time it is estimated based on heuristics that depend on
the level argument and on optimization. While enabling optimization
will in most cases improve the accuracy of the warning, it may also result
in false positives. Except as noted otherwise, the option uses the same
logic -Wformat-overflow.
-Wformat-truncation-Wformat-truncation=1-Wformat-truncation=2-Wformat-y2kstrftime
formats that may yield only a two-digit year.
-Wnonnullnonnull function attribute.
-Wnonnull is included in -Wall and -Wformat. It can be disabled with the -Wno-nonnull option.
-Wnonnull-comparenonnull
function attribute against null inside the function.
-Wnonnull-compare is included in -Wall. It can be disabled with the -Wno-nonnull-compare option.
-Wnull-dereference-Winfinite-recursionCompare with -Wanalyzer-infinite-recursion which provides a similar diagnostic, but is implemented in a different way (as part of -fanalyzer).
-Winit-self (C, C++, Objective-C and Objective-C++ only)For example, GCC warns about i being uninitialized in the
following snippet only when -Winit-self has been specified:
int f()
{
int i = i;
return i;
}
This warning is enabled by -Wall in C++.
-Wno-implicit-int (C and Objective-C only)-Wno-implicit-function-declaration (C and Objective-C only)-Wimplicit (C and Objective-C only)-Wimplicit-fallthrough-Wimplicit-fallthrough=n switch (cond)
{
case 1:
a = 1;
break;
case 2:
a = 2;
case 3:
a = 3;
break;
}
This warning does not warn when the last statement of a case cannot fall through, e.g. when there is a return statement or a call to function declared with the noreturn attribute. -Wimplicit-fallthrough= also takes into account control flow statements, such as ifs, and only warns when appropriate. E.g.
switch (cond)
{
case 1:
if (i > 3) {
bar (5);
break;
} else if (i < 1) {
bar (0);
} else
return;
default:
...
}
Since there are occasions where a switch case fall through is desirable,
GCC provides an attribute, __attribute__ ((fallthrough)), that is
to be used along with a null statement to suppress this warning that
would normally occur:
switch (cond)
{
case 1:
bar (0);
__attribute__ ((fallthrough));
default:
...
}
C++17 provides a standard way to suppress the -Wimplicit-fallthrough
warning using [[fallthrough]]; instead of the GNU attribute. In C++11
or C++14 users can use [[gnu::fallthrough]];, which is a GNU extension.
Instead of these attributes, it is also possible to add a fallthrough comment
to silence the warning. The whole body of the C or C++ style comment should
match the given regular expressions listed below. The option argument n
specifies what kind of comments are accepted:
.* regular
expression, any comment is used as fallthrough comment.
.*falls?[ \t-]*thr(ough|u).* regular expression.
-fallthrough
@fallthrough@
lint -fallthrough[ \t]*
[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?
FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?
[ \t.!]*(Else,? |Intentional(ly)? )?
Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?
[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?
fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?
-fallthrough
@fallthrough@
lint -fallthrough[ \t]*
[ \t]*FALLTHR(OUGH|U)[ \t]*
The comment needs to be followed after optional whitespace and other comments
by case or default keywords or by a user label that precedes some
case or default label.
switch (cond)
{
case 1:
bar (0);
/* FALLTHRU */
default:
...
}
The -Wimplicit-fallthrough=3 warning is enabled by -Wextra.
-Wno-if-not-aligned (C, C++, Objective-C and Objective-C++ only)warn_if_not_aligned attribute
should be issued. These warnings are enabled by default.
-Wignored-qualifiers (C and C++ only)const. For ISO C such a type qualifier has no effect,
since the value returned by a function is not an lvalue.
For C++, the warning is only emitted for scalar types or void.
ISO C prohibits qualified void return types on function
definitions, so such return types always receive a warning
even without this option.
This warning is also enabled by -Wextra.
-Wno-ignored-attributes (C and C++ only)-Wmainmain is suspicious. main should be
a function with external linkage, returning int, taking either zero
arguments, two, or three arguments of appropriate types. This warning
is enabled by default in C++ and is enabled by either -Wall
or -Wpedantic.
-Wmisleading-indentation (C and C++ only)if, else, while, and
for clauses with a guarded statement that does not use braces,
followed by an unguarded statement with the same indentation.
In the following example, the call to “bar” is misleadingly indented as if it were guarded by the “if” conditional.
if (some_condition ())
foo ();
bar (); /* Gotcha: this is not guarded by the "if". */
In the case of mixed tabs and spaces, the warning uses the -ftabstop= option to determine if the statements line up (defaulting to 8).
The warning is not issued for code involving multiline preprocessor logic such as the following example.
if (flagA)
foo (0);
#if SOME_CONDITION_THAT_DOES_NOT_HOLD
if (flagB)
#endif
foo (1);
The warning is not issued after a #line directive, since this
typically indicates autogenerated code, and no assumptions can be made
about the layout of the file that the directive references.
This warning is enabled by -Wall in C and C++.
-Wmissing-attributesalloc_align, alloc_size,
cold, const, hot, leaf, malloc,
nonnull, noreturn, nothrow, pure,
returns_nonnull, and returns_twice.
In C++, the warning is issued when an explicit specialization of a primary
template declared with attribute alloc_align, alloc_size,
assume_aligned, format, format_arg, malloc,
or nonnull is declared without it. Attributes deprecated,
error, and warning suppress the warning.
(see Function Attributes).
You can use the copy attribute to apply the same
set of attributes to a declaration as that on another declaration without
explicitly enumerating the attributes. This attribute can be applied
to declarations of functions (see Common Function Attributes),
variables (see Common Variable Attributes), or types
(see Common Type Attributes).
-Wmissing-attributes is enabled by -Wall.
For example, since the declaration of the primary function template
below makes use of both attribute malloc and alloc_size
the declaration of the explicit specialization of the template is
diagnosed because it is missing one of the attributes.
template <class T>
T* __attribute__ ((malloc, alloc_size (1)))
allocate (size_t);
template <>
void* __attribute__ ((malloc)) // missing alloc_size
allocate<void> (size_t);
-Wmissing-bracesa is not fully
bracketed, but that for b is fully bracketed.
int a[2][2] = { 0, 1, 2, 3 };
int b[2][2] = { { 0, 1 }, { 2, 3 } };
This warning is enabled by -Wall.
-Wmissing-include-dirs (C, C++, Objective-C, Objective-C++ and Fortran only)-Wno-missing-profile-Wmismatched-deallocmalloc. Unless disabled by
the -fno-builtin option the standard functions calloc,
malloc, realloc, and free, as well as the corresponding
forms of C++ operator new and operator delete are implicitly
associated as matching allocators and deallocators. In the following
example mydealloc is the deallocator for pointers returned from
myalloc.
void mydealloc (void*);
__attribute__ ((malloc (mydealloc, 1))) void*
myalloc (size_t);
void f (void)
{
void *p = myalloc (32);
// ...use p...
free (p); // warning: not a matching deallocator for myalloc
mydealloc (p); // ok
}
In C++, the related option -Wmismatched-new-delete diagnoses
mismatches involving either operator new or operator delete.
Option -Wmismatched-dealloc is included in -Wall.
-Wmultistatement-macrosif, else, for, switch, or
while, in which only the first statement is actually guarded after
the macro is expanded.
For example:
#define DOIT x++; y++
if (c)
DOIT;
will increment y unconditionally, not just when c holds.
The can usually be fixed by wrapping the macro in a do-while loop:
#define DOIT do { x++; y++; } while (0)
if (c)
DOIT;
This warning is enabled by -Wall in C and C++.
-WparenthesesAlso warn if a comparison like x<=y<=z appears; this is
equivalent to (x<=y ? 1 : 0) <= z, which is a different
interpretation from that of ordinary mathematical notation.
Also warn for dangerous uses of the GNU extension to
?: with omitted middle operand. When the condition
in the ?: operator is a boolean expression, the omitted value is
always 1. Often programmers expect it to be a value computed
inside the conditional expression instead.
For C++ this also warns for some cases of unnecessary parentheses in declarations, which can indicate an attempt at a function call instead of a declaration:
{
// Declares a local variable called mymutex.
std::unique_lock<std::mutex> (mymutex);
// User meant std::unique_lock<std::mutex> lock (mymutex);
}
This warning is enabled by -Wall.
-Wno-self-move (C++ and Objective-C++ only)std::move.
Such a std::move typically has no effect.
struct T {
...
};
void fn()
{
T t;
...
t = std::move (t);
}
This warning is enabled by -Wall.
-Wsequence-pointThe C and C++ standards define the order in which expressions in a C/C++
program are evaluated in terms of sequence points, which represent
a partial ordering between the execution of parts of the program: those
executed before the sequence point, and those executed after it. These
occur after the evaluation of a full expression (one which is not part
of a larger expression), after the evaluation of the first operand of a
&&, ||, ? : or , (comma) operator, before a
function is called (but after the evaluation of its arguments and the
expression denoting the called function), and in certain other places.
Other than as expressed by the sequence point rules, the order of
evaluation of subexpressions of an expression is not specified. All
these rules describe only a partial order rather than a total order,
since, for example, if two functions are called within one expression
with no sequence point between them, the order in which the functions
are called is not specified. However, the standards committee have
ruled that function calls do not overlap.
It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C and C++ standards specify that “Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be read only to determine the value to be stored.”. If a program breaks these rules, the results on any particular implementation are entirely unpredictable.
Examples of code with undefined behavior are a = a++;, a[n]
= b[n++] and a[i++] = i;. Some more complicated cases are not
diagnosed by this option, and it may give an occasional false positive
result, but in general it has been found fairly effective at detecting
this sort of problem in programs.
The C++17 standard will define the order of evaluation of operands in more cases: in particular it requires that the right-hand side of an assignment be evaluated before the left-hand side, so the above examples are no longer undefined. But this option will still warn about them, to help people avoid writing code that is undefined in C and earlier revisions of C++.
The standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including proposed formal definitions, may be found on the GCC readings page, at https://gcc.gnu.org/readings.html.
This warning is enabled by -Wall for C and C++.
-Wno-return-local-addr-Wreturn-typeint. Also warn about any return statement with no
return value in a function whose return type is not void
(falling off the end of the function body is considered returning
without a value).
For C only, warn about a return statement with an expression in a
function whose return type is void, unless the expression type is
also void. As a GNU extension, the latter case is accepted
without a warning unless -Wpedantic is used. Attempting
to use the return value of a non-void function other than main
that flows off the end by reaching the closing curly brace that terminates
the function is undefined.
Unlike in C, in C++, flowing off the end of a non-void function other
than main results in undefined behavior even when the value of
the function is not used.
This warning is enabled by default in C++ and by -Wall otherwise.
-Wno-shift-count-negative-Wno-shift-count-overflow-Wshift-negative-value-Wno-shift-overflow-Wshift-overflow=n-Wshift-overflow=1-Wshift-overflow=2-Wswitchswitch statement has an index of enumerated type
and lacks a case for one or more of the named codes of that
enumeration. (The presence of a default label prevents this
warning.) case labels outside the enumeration range also
provoke warnings when this option is used (even if there is a
default label).
This warning is enabled by -Wall.
-Wswitch-defaultswitch statement does not have a default
case.
-Wswitch-enumswitch statement has an index of enumerated type
and lacks a case for one or more of the named codes of that
enumeration. case labels outside the enumeration range also
provoke warnings when this option is used. The only difference
between -Wswitch and this option is that this option gives a
warning about an omitted enumeration code even if there is a
default label.
-Wno-switch-boolswitch statement has an index of boolean type
and the case values are outside the range of a boolean type.
It is possible to suppress this warning by casting the controlling
expression to a type other than bool. For example:
switch ((int) (a == 4))
{
...
}
This warning is enabled by default for C and C++ programs.
-Wno-switch-outside-rangeswitch case has a value
that is outside of its
respective type range. This warning is enabled by default for
C and C++ programs.
-Wno-switch-unreachableswitch statement contains statements between the
controlling expression and the first case label, which will never be
executed. For example:
switch (cond)
{
i = 15;
...
case 5:
...
}
-Wswitch-unreachable does not warn if the statement between the controlling expression and the first case label is just a declaration:
switch (cond)
{
int i;
...
case 5:
i = 5;
...
}
This warning is enabled by default for C and C++ programs.
-Wsync-nand (C and C++ only)__sync_fetch_and_nand and __sync_nand_and_fetch
built-in functions are used. These functions changed semantics in GCC 4.4.
-Wtrivial-auto-var-init-ftrivial-auto-var-init cannot initialize the automatic
variable. A common situation is an automatic variable that is declared
between the controlling expression and the first case label of a switch
statement.
-Wunused-but-set-parameterTo suppress this warning use the unused attribute
(see Variable Attributes).
This warning is also enabled by -Wunused together with -Wextra.
-Wunused-but-set-variableTo suppress this warning use the unused attribute
(see Variable Attributes).
This warning is also enabled by -Wunused, which is enabled by -Wall.
-Wunused-function-Wunused-labelTo suppress this warning use the unused attribute
(see Variable Attributes).
-Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)-Wunused-parameterTo suppress this warning use the unused attribute
(see Variable Attributes).
-Wno-unused-resultwarn_unused_result (see Function Attributes) does not use
its return value. The default is -Wunused-result.
-Wunused-variableTo suppress this warning use the unused attribute
(see Variable Attributes).
-Wunused-const-variable-Wunused-const-variable=n#defines.
To suppress this warning use the unused attribute
(see Variable Attributes).
-Wunused-const-variable=1-Wunused-const-variable=2-Wunused-valuevoid. This includes an expression-statement or the left-hand
side of a comma expression that contains no side effects. For example,
an expression such as x[i,j] causes a warning, while
x[(void)i,j] does not.
This warning is enabled by -Wall.
-WunusedIn order to get a warning about an unused function parameter, you must either specify -Wextra -Wunused (note that -Wall implies -Wunused), or separately specify -Wunused-parameter.
-Wuninitializedconst member appears in a class without
constructors.
In addition, passing a pointer (or in C++, a reference) to an uninitialized
object to a const-qualified argument of a built-in function known to
read the object is also diagnosed by this warning.
(-Wmaybe-uninitialized is issued for ordinary functions.)
If you want to warn about code that uses the uninitialized value of the variable in its own initializer, use the -Winit-self option.
These warnings occur for individual uninitialized elements of
structure, union or array variables as well as for variables that are
uninitialized as a whole. They do not occur for variables or elements
declared volatile. Because these warnings depend on
optimization, the exact variables or elements for which there are
warnings depend on the precise optimization options and version of GCC
used.
Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed.
In C++, this warning also warns about using uninitialized objects in
member-initializer-lists. For example, GCC warns about b being
uninitialized in the following snippet:
struct A {
int a;
int b;
A() : a(b) { }
};
-Wno-invalid-memory-modelmemory_order enumeration. For example, since the
__atomic_store and __atomic_store_n built-ins are only
defined for the relaxed, release, and sequentially consistent memory
orders the following code is diagnosed:
void store (int *i)
{
__atomic_store_n (i, 0, memory_order_consume);
}
-Winvalid-memory-model is enabled by default.
-Wmaybe-uninitializedIn addition, passing a pointer (or in C++, a reference) to an uninitialized
object to a const-qualified function argument is also diagnosed by
this warning. (-Wuninitialized is issued for built-in functions
known to read the object.) Annotating the function with attribute
access (none) indicates that the argument isn't used to access
the object and avoids the warning (see Common Function Attributes).
These warnings are only possible in optimizing compilation, because otherwise GCC does not keep track of the state of variables.
These warnings are made optional because GCC may not be able to determine when the code is correct in spite of appearing to have an error. Here is one example of how this can happen:
{
int x;
switch (y)
{
case 1: x = 1;
break;
case 2: x = 4;
break;
case 3: x = 5;
}
foo (x);
}
If the value of y is always 1, 2 or 3, then x is
always initialized, but GCC doesn't know this. To suppress the
warning, you need to provide a default case with assert(0) or
similar code.
This option also warns when a non-volatile automatic variable might be
changed by a call to longjmp.
The compiler sees only the calls to setjmp. It cannot know
where longjmp will be called; in fact, a signal handler could
call it at any point in the code. As a result, you may get a warning
even when there is in fact no problem because longjmp cannot
in fact be called at the place that would cause a problem.
Some spurious warnings can be avoided if you declare all the functions
you use that never return as noreturn. See Function Attributes.
This warning is enabled by -Wall or -Wextra.
-Wunknown-pragmas#pragma directive is encountered that is not understood by
GCC. If this command-line option is used, warnings are even issued
for unknown pragmas in system header files. This is not the case if
the warnings are only enabled by the -Wall command-line option.
-Wno-pragmas-Wno-prio-ctor-dtormain is called or after it returns. The priority values must be
greater than 100 as the compiler reserves priority values between 0–100 for
the implementation.
-Wstrict-aliasing-Wstrict-aliasing=nLevel 1: Most aggressive, quick, least accurate. Possibly useful when higher levels do not warn but -fstrict-aliasing still breaks the code, as it has very few false negatives. However, it has many false positives. Warns for all pointer conversions between possibly incompatible types, even if never dereferenced. Runs in the front end only.
Level 2: Aggressive, quick, not too precise. May still have many false positives (not as many as level 1 though), and few false negatives (but possibly more than level 1). Unlike level 1, it only warns when an address is taken. Warns about incomplete types. Runs in the front end only.
Level 3 (default for -Wstrict-aliasing):
Should have very few false positives and few false
negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
Takes care of the common pun+dereference pattern in the front end:
*(int*)&some_float.
If optimization is enabled, it also runs in the back end, where it deals
with multiple statement cases using flow-sensitive points-to information.
Only warns when the converted pointer is dereferenced.
Does not warn about incomplete types.
-Wstrict-overflow-Wstrict-overflow=nAn optimization that assumes that signed overflow does not occur is perfectly safe if the values of the variables involved are such that overflow never does, in fact, occur. Therefore this warning can easily give a false positive: a warning about code that is not actually a problem. To help focus on important issues, several warning levels are defined. No warnings are issued for the use of undefined signed overflow when estimating how many iterations a loop requires, in particular when determining whether a loop will be executed at all.
-Wstrict-overflow=1x + 1 > x to 1. This level of
-Wstrict-overflow is enabled by -Wall; higher levels
are not, and must be explicitly requested.
-Wstrict-overflow=2abs (x) >= 0. This can only be
simplified when signed integer overflow is undefined, because
abs (INT_MIN) overflows to INT_MIN, which is less than
zero. -Wstrict-overflow (with no level) is the same as
-Wstrict-overflow=2.
-Wstrict-overflow=3x + 1 > 1 is simplified to x > 0.
-Wstrict-overflow=4(x * 10) / 5 is simplified to x * 2.
-Wstrict-overflow=5x + 2 > y is
simplified to x + 1 >= y. This is reported only at the
highest warning level because this simplification applies to many
comparisons, so this warning level gives a very large number of
false positives.
-Wstring-comparestrcmp and strncmp whose result is
determined to be either zero or non-zero in tests for such equality
owing to the length of one argument being greater than the size of
the array the other argument is stored in (or the bound in the case
of strncmp). Such calls could be mistakes. For example,
the call to strcmp below is diagnosed because its result is
necessarily non-zero irrespective of the contents of the array a.
extern char a[4];
void f (char *d)
{
strcpy (d, "string");
...
if (0 == strcmp (a, d)) // cannot be true
puts ("a and d are the same");
}
-Wstring-compare is enabled by -Wextra.
-Wno-stringop-overflow-Wstringop-overflow-Wstringop-overflow=typememcpy and
strcpy that are determined to overflow the destination buffer. The
optional argument is one greater than the type of Object Size Checking to
perform to determine the size of the destination. See Object Size Checking.
The argument is meaningful only for functions that operate on character arrays
but not for raw memory functions like memcpy which always make use
of Object Size type-0. The option also warns for calls that specify a size
in excess of the largest possible object or at most SIZE_MAX / 2 bytes.
The option produces the best results with optimization enabled but can detect
a small subset of simple buffer overflows even without optimization in
calls to the GCC built-in functions like __builtin_memcpy that
correspond to the standard functions. In any case, the option warns about
just a subset of buffer overflows detected by the corresponding overflow
checking built-ins. For example, the option issues a warning for
the strcpy call below because it copies at least 5 characters
(the string "blue" including the terminating NUL) into the buffer
of size 4.
enum Color { blue, purple, yellow };
const char* f (enum Color clr)
{
static char buf [4];
const char *str;
switch (clr)
{
case blue: str = "blue"; break;
case purple: str = "purple"; break;
case yellow: str = "yellow"; break;
}
return strcpy (buf, str); // warning here
}
Option -Wstringop-overflow=2 is enabled by default.
-Wstringop-overflow-Wstringop-overflow=1_FORTIFY_SOURCE macro
is defined to a non-zero value.
-Wstringop-overflow=2-Wstringop-overflow=3-Wstringop-overflow=4-Wno-stringop-overreadmemchr, or
strcpy that are determined to read past the end of the source
sequence.
Option -Wstringop-overread is enabled by default.
-Wno-stringop-truncationstrncat,
strncpy, and stpncpy that may either truncate the copied string
or leave the destination unchanged.
In the following example, the call to strncat specifies a bound that
is less than the length of the source string. As a result, the copy of
the source will be truncated and so the call is diagnosed. To avoid the
warning use bufsize - strlen (buf) - 1) as the bound.
void append (char *buf, size_t bufsize)
{
strncat (buf, ".txt", 3);
}
As another example, the following call to strncpy results in copying
to d just the characters preceding the terminating NUL, without
appending the NUL to the end. Assuming the result of strncpy is
necessarily a NUL-terminated string is a common mistake, and so the call
is diagnosed. To avoid the warning when the result is not expected to be
NUL-terminated, call memcpy instead.
void copy (char *d, const char *s)
{
strncpy (d, s, strlen (s));
}
In the following example, the call to strncpy specifies the size
of the destination buffer as the bound. If the length of the source
string is equal to or greater than this size the result of the copy will
not be NUL-terminated. Therefore, the call is also diagnosed. To avoid
the warning, specify sizeof buf - 1 as the bound and set the last
element of the buffer to NUL.
void copy (const char *s)
{
char buf[80];
strncpy (buf, s, sizeof buf);
...
}
In situations where a character array is intended to store a sequence
of bytes with no terminating NUL such an array may be annotated
with attribute nonstring to avoid this warning. Such arrays,
however, are not suitable arguments to functions that expect
NUL-terminated strings. To help detect accidental misuses of
such arrays GCC issues warnings unless it can prove that the use is
safe. See Common Variable Attributes.
-Wstrict-flex-arraysstrict_flex_array (level)
attribute attached to the trailing array field of a structure if it's
available, otherwise according to the level of the option
-fstrict-flex-arrays=level.
This option is effective only when level is bigger than 0. Otherwise, it will be ignored with a warning.
when level=1, warnings will be issued for a trailing array reference of a structure that have 2 or more elements if the trailing array is referenced as a flexible array member.
when level=2, in addition to level=1, additional warnings will be issued for a trailing one-element array reference of a structure if the array is referenced as a flexible array member.
when level=3, in addition to level=2, additional warnings will be issued for a trailing zero-length array reference of a structure if the array is referenced as a flexible array member.
-Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]-Wsuggest-attribute=pure-Wsuggest-attribute=const-Wsuggest-attribute=noreturn-Wmissing-noreturn-Wsuggest-attribute=mallocpure, const or noreturn or malloc. The compiler
only warns for functions visible in other compilation units or (in the case of
pure and const) if it cannot prove that the function returns
normally. A function returns normally if it doesn't contain an infinite loop or
return abnormally by throwing, calling abort or trapping. This analysis
requires option -fipa-pure-const, which is enabled by default at
-O and higher. Higher optimization levels improve the accuracy
of the analysis.
-Wsuggest-attribute=format-Wmissing-format-attributeformat
attributes. Note these are only possible candidates, not absolute ones.
GCC guesses that function pointers with format attributes that
are used in assignment, initialization, parameter passing or return
statements should have a corresponding format attribute in the
resulting type. I.e. the left-hand side of the assignment or
initialization, the type of the parameter variable, or the return type
of the containing function respectively should also have a format
attribute to avoid the warning.
GCC also warns about function definitions that might be
candidates for format attributes. Again, these are only
possible candidates. GCC guesses that format attributes
might be appropriate for any function that calls a function like
vprintf or vscanf, but this might not always be the
case, and some functions for which format attributes are
appropriate may not be detected.
-Wsuggest-attribute=coldcold attribute. This
is based on static detection and generally only warns about functions which
always leads to a call to another cold function such as wrappers of
C++ throw or fatal error reporting functions leading to abort.
-Walloc-zeroalloc_size that specify zero bytes, including those to the built-in
forms of the functions aligned_alloc, alloca, calloc,
malloc, and realloc. Because the behavior of these functions
when called with a zero size differs among implementations (and in the case
of realloc has been deprecated) relying on it may result in subtle
portability bugs and should be avoided.
-Walloc-size-larger-than=byte-sizealloc_size
that attempt to allocate objects larger than the specified number of bytes,
or where the result of the size computation in an integer type with infinite
precision would exceed the value of ‘PTRDIFF_MAX’ on the target.
-Walloc-size-larger-than=‘PTRDIFF_MAX’ is enabled by default.
Warnings controlled by the option can be disabled either by specifying
byte-size of ‘SIZE_MAX’ or more or by
-Wno-alloc-size-larger-than.
See Function Attributes.
-Wno-alloc-size-larger-than-Wallocaalloca in the source.
-Walloca-larger-than=byte-sizealloca with an integer argument whose
value is either zero, or that is not bounded by a controlling predicate
that limits its value to at most byte-size. It also warns for calls
to alloca where the bound value is unknown. Arguments of non-integer
types are considered unbounded even if they appear to be constrained to
the expected range.
For example, a bounded case of alloca could be:
void func (size_t n)
{
void *p;
if (n <= 1000)
p = alloca (n);
else
p = malloc (n);
f (p);
}
In the above example, passing -Walloca-larger-than=1000 would not
issue a warning because the call to alloca is known to be at most
1000 bytes. However, if -Walloca-larger-than=500 were passed,
the compiler would emit a warning.
Unbounded uses, on the other hand, are uses of alloca with no
controlling predicate constraining its integer argument. For example:
void func ()
{
void *p = alloca (n);
f (p);
}
If -Walloca-larger-than=500 were passed, the above would trigger
a warning, but this time because of the lack of bounds checking.
Note, that even seemingly correct code involving signed integers could cause a warning:
void func (signed int n)
{
if (n < 500)
{
p = alloca (n);
f (p);
}
}
In the above example, n could be negative, causing a larger than
expected argument to be implicitly cast into the alloca call.
This option also warns when alloca is used in a loop.
-Walloca-larger-than=‘PTRDIFF_MAX’ is enabled by default but is usually only effective when -ftree-vrp is active (default for -O2 and above).
See also -Wvla-larger-than=‘byte-size’.
-Wno-alloca-larger-than-Warith-conversion void f (char c, int i)
{
c = c + i; // warns with -Wconversion
c = c + 1; // only warns with -Warith-conversion
}
-Warray-bounds-Warray-bounds=nBy default, the trailing array of a structure will be treated as a flexible array member by -Warray-bounds or -Warray-bounds=n if it is declared as either a flexible array member per C99 standard onwards (‘[]’), a GCC zero-length array extension (‘[0]’), or an one-element array (‘[1]’). As a result, out of bounds subscripts or offsets into zero-length arrays or one-element arrays are not warned by default.
You can add the option -fstrict-flex-arrays or -fstrict-flex-arrays=level to control how this option treat trailing array of a structure as a flexible array member:
when level<=1, no change to the default behavior.
when level=2, additional warnings will be issued for out of bounds subscripts or offsets into one-element arrays;
when level=3, in addition to level=2, additional warnings will be issued for out of bounds subscripts or offsets into zero-length arrays.
-Warray-bounds=1-Warray-bounds=2-Warray-compare int arr1[5];
int arr2[5];
bool same = arr1 == arr2;
-Warray-compare is enabled by -Wall.
-Warray-parameter-Warray-parameter=nIf the first function declaration uses the array form the bound specified
in the array is assumed to be the minimum number of elements expected to
be provided in calls to the function and the maximum number of elements
accessed by it. Failing to provide arguments of sufficient size or accessing
more than the maximum number of elements may be diagnosed by warnings such
as -Warray-bounds. At level 1 the warning diagnoses inconsistencies
involving array parameters declared using the T[static N] form.
For example, the warning triggers for the following redeclarations because
the first one allows an array of any size to be passed to f while
the second one with the keyword static specifies that the array
argument must have at least four elements.
void f (int[static 4]);
void f (int[]); // warning (inconsistent array form)
void g (void)
{
int *p = (int *)malloc (4);
f (p); // warning (array too small)
...
}
At level 2 the warning also triggers for redeclarations involving any other inconsistency in array or pointer argument forms denoting array sizes. Pointers and arrays of unspecified bound are considered equivalent and do not trigger a warning.
void g (int*);
void g (int[]); // no warning
void g (int[8]); // warning (inconsistent array bound)
-Warray-parameter=2 is included in -Wall. The -Wvla-parameter option triggers warnings for similar inconsistencies involving Variable Length Array arguments.
-Wattribute-alias=n-Wno-attribute-aliasalias and similar attributes whose
target is incompatible with the type of the alias.
See Declaring Attributes of Functions.
-Wattribute-alias=1-Wattribute-alias=2Attributes considered include alloc_align, alloc_size,
cold, const, hot, leaf, malloc,
nonnull, noreturn, nothrow, pure,
returns_nonnull, and returns_twice.
-Wattribute-alias is equivalent to -Wattribute-alias=1. This is the default. You can disable these warnings with either -Wno-attribute-alias or -Wattribute-alias=0.
-Wbidi-chars=[none|unpaired|any|ucn]There are three levels of warning supported by GCC. The default is -Wbidi-chars=unpaired, which warns about improperly terminated bidi contexts. -Wbidi-chars=none turns the warning off. -Wbidi-chars=any warns about any use of bidirectional control characters.
By default, this warning does not warn about UCNs. It is, however, possible to turn on such checking by using -Wbidi-chars=unpaired,ucn or -Wbidi-chars=any,ucn. Using -Wbidi-chars=ucn is valid, and is equivalent to -Wbidi-chars=unpaired,ucn, if no previous -Wbidi-chars=any was specified.
-Wbool-comparetrue/false. For instance, the following comparison is
always false:
int n = 5;
...
if ((n > 1) == 2) { ... }
This warning is enabled by -Wall.
-Wbool-operationThis warning is enabled by -Wall.
-Wduplicated-branches if (p != NULL)
return 0;
else
return 0;
It doesn't warn when both branches contain just a null statement. This warning also warn for conditional operators:
int i = x ? *p : *p;
-Wduplicated-cond if (p->q != NULL) { ... }
else if (p->q != NULL) { ... }
-Wframe-address-Wno-discarded-qualifiers (C and Objective-C only)const char * variable is
passed to a function that takes a char * parameter. This option
can be used to suppress such a warning.
-Wno-discarded-array-qualifiers (C and Objective-C only)const int (*)[] variable is passed to a function that
takes a int (*)[] parameter. This option can be used to
suppress such a warning.
-Wno-incompatible-pointer-types (C and Objective-C only)-Wno-int-conversion (C and Objective-C only)-Wzero-length-boundsFor example, the first two stores in function bad are diagnosed
because the array elements overlap the subsequent members b and
c. The third store is diagnosed by -Warray-bounds
because it is beyond the bounds of the enclosing object.
struct X { int a[0]; int b, c; };
struct X x;
void bad (void)
{
x.a[0] = 0; // -Wzero-length-bounds
x.a[1] = 1; // -Wzero-length-bounds
x.a[2] = 2; // -Warray-bounds
}
Option -Wzero-length-bounds is enabled by -Warray-bounds.
-Wno-div-by-zero-Wsystem-headers-Wtautological-compare int i = 1;
...
if (i > i) { ... }
This warning also warns about bitwise comparisons that always evaluate to true or false, for instance:
if ((a & 16) == 10) { ... }
will always be false.
This warning is enabled by -Wall.
-Wtrampolines-Wfloat-equalThe idea behind this is that sometimes it is convenient (for the programmer) to consider floating-point values as approximations to infinitely precise real numbers. If you are doing this, then you need to compute (by analyzing the code, or in some other way) the maximum or likely maximum error that the computation introduces, and allow for it when performing comparisons (and when producing output, but that's a different problem). In particular, instead of testing for equality, you should check to see whether the two values have ranges that overlap; and this is done with the relational operators, so equality comparisons are probably mistaken.
-Wtraditional (C and Objective-C only)#pragma not understood by traditional C by indenting them. Some
traditional implementations do not recognize #elif, so this option
suggests avoiding it altogether.
<limits.h>.
Use of these macros in user code might normally lead to spurious
warnings, however GCC's integrated preprocessor has enough context to
avoid warning in these cases.
switch statement has an operand of type long.
static function declaration follows a static one.
This construct is not accepted by some traditional C compilers.
__STDC__ to avoid missing
initializer warnings and relies on default initialization to zero in the
traditional C case.
PARAMS and
VPARAMS. This warning is also bypassed for nested functions
because that feature is already a GCC extension and thus not relevant to
traditional C compatibility.
-Wtraditional-conversion (C and Objective-C only)-Wdeclaration-after-statement (C and Objective-C only)-Wshadow-Wno-shadow-ivar (Objective-C only)-Wshadow=global-Wshadow=local-Wshadow=compatible-local for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
{
for (int i = 0; i < N; ++i)
{
...
}
...
}
Since the two variable i in the example above have incompatible types,
enabling only -Wshadow=compatible-local does not emit a warning.
Because their types are incompatible, if a programmer accidentally uses one
in place of the other, type checking is expected to catch that and emit an
error or warning. Use of this flag instead of -Wshadow=local can
possibly reduce the number of warnings triggered by intentional shadowing.
Note that this also means that shadowing const char *i by
char *i does not emit a warning.
This warning is also enabled by -Wshadow=local.
-Wlarger-than=byte-sizeAlso warn for calls to bounded functions such as memchr or
strnlen that specify a bound greater than the largest possible
object, which is ‘PTRDIFF_MAX’ bytes by default. These warnings
can only be disabled by -Wno-larger-than.
-Wno-larger-than-Wframe-larger-than=byte-sizealloca, variable-length arrays, or related constructs
is not included by the compiler when determining
whether or not to issue a warning.
-Wframe-larger-than=‘PTRDIFF_MAX’ is enabled by default.
Warnings controlled by the option can be disabled either by specifying
byte-size of ‘SIZE_MAX’ or more or by
-Wno-frame-larger-than.
-Wno-frame-larger-than-Wfree-nonheap-objectstpcpy returns a pointer to the terminating nul character and
not to the beginning of the object, the call to free below is
diagnosed.
void f (char *p)
{
p = stpcpy (p, "abc");
// ...
free (p); // warning
}
-Wfree-nonheap-object is included in -Wall.
-Wstack-usage=byte-sizealloca, variable-length arrays, or related
constructs is included by the compiler when determining whether or not to
issue a warning.
The message is in keeping with the output of -fstack-usage.
warning: stack usage is 1120 bytes
warning: stack usage might be 1648 bytes
warning: stack usage might be unbounded
-Wstack-usage=‘PTRDIFF_MAX’ is enabled by default. Warnings controlled by the option can be disabled either by specifying byte-size of ‘SIZE_MAX’ or more or by -Wno-stack-usage.
-Wno-stack-usage-Wunsafe-loop-optimizations-Wno-pedantic-ms-format (MinGW targets only)printf / scanf format
width specifiers I32, I64, and I used on Windows targets,
which depend on the MS runtime.
-Wpointer-arithvoid. GNU C assigns these types a size of 1, for
convenience in calculations with void * pointers and pointers
to functions. In C++, warn also when an arithmetic operation involves
NULL. This warning is also enabled by -Wpedantic.
-Wno-pointer-compare const char *p = foo ();
if (p == '\0')
return 42;
Note that the code above is invalid in C++11.
This warning is enabled by default.
-WtsanThreadSanitizer does not support std::atomic_thread_fence and
can report false positives.
This warning is enabled by default.
-Wtype-limits< or >=. This warning is also enabled by
-Wextra.
-Wabsolute-value (C and Objective-C only)abs(3.14) triggers the warning because the
appropriate function to call to compute the absolute value of a double
argument is fabs. The option also triggers warnings when the
argument in a call to such a function has an unsigned type. This
warning can be suppressed with an explicit type cast and it is also
enabled by -Wextra.
-Wcomment-Wcomments-WtrigraphsThis option is implied by -Wall. If -Wall is not given, this option is still enabled unless trigraphs are enabled. To get trigraph conversion without warnings, but get the other -Wall warnings, use ‘-trigraphs -Wall -Wno-trigraphs’.
-Wundef#if directive.
Such identifiers are replaced with zero.
-Wexpansion-to-defined-Wunused-macrosBuilt-in macros, macros defined on the command line, and macros defined in include files are not warned about.
Note: If a macro is actually used, but only used in skipped conditional blocks, then the preprocessor reports it as unused. To avoid the warning in such a case, you might improve the scope of the macro's definition by, for example, moving it into the first skipped block. Alternatively, you could provide a dummy use with something like:
#if defined the_macro_causing_the_warning
#endif
-Wno-endif-labels#else or an #endif are followed by text.
This sometimes happens in older programs with code of the form
#if FOO
...
#else FOO
...
#endif FOO
The second and third FOO should be in comments.
This warning is on by default.
-Wbad-function-cast (C and Objective-C only)-Wc90-c99-compat (C and Objective-C only)long long
type, bool type, compound literals, designated initializers, and so
on. This option is independent of the standards mode. Warnings are disabled
in the expression that follows __extension__.
-Wc99-c11-compat (C and Objective-C only)_Atomic type qualifier, _Thread_local storage-class specifier,
_Alignas specifier, Alignof operator, _Generic keyword,
and so on. This option is independent of the standards mode. Warnings are
disabled in the expression that follows __extension__.
-Wc11-c2x-compat (C and Objective-C only)_Static_assert,
use of ‘[[]]’ syntax for attributes, use of decimal
floating-point types, and so on. This option is independent of the
standards mode. Warnings are disabled in the expression that follows
__extension__.
-Wc++-compat (C and Objective-C only)void * to a pointer to non-void type.
-Wc++11-compat (C++ and Objective-C++ only)-Wc++14-compat (C++ and Objective-C++ only)-Wc++17-compat (C++ and Objective-C++ only)-Wc++20-compat (C++ and Objective-C++ only)-Wno-c++11-extensions (C++ and Objective-C++ only)-Wno-c++14-extensions (C++ and Objective-C++ only)-Wno-c++17-extensions (C++ and Objective-C++ only)-Wno-c++20-extensions (C++ and Objective-C++ only)-Wno-c++23-extensions (C++ and Objective-C++ only)-Wcast-qualconst char * is cast
to an ordinary char *.
Also warn when making a cast that introduces a type qualifier in an
unsafe way. For example, casting char ** to const char **
is unsafe, as in this example:
/* p is char ** value. */
const char **q = (const char **) p;
/* Assignment of readonly string to const char * is OK. */
*q = "string";
/* Now char** pointer points to read-only memory. */
**p = 'b';
-Wcast-alignchar * is cast to
an int * on machines where integers can only be accessed at
two- or four-byte boundaries.
-Wcast-align=strictchar * is cast to
an int * regardless of the target machine.
-Wcast-function-typeint vs. long
on ILP32 targets. Likewise type qualifiers are ignored. The function
type void (*) (void) is special and matches everything, which can
be used to suppress this warning.
In a cast involving pointer to member types this warning warns whenever
the type cast is changing the pointer to member type.
This warning is enabled by -Wextra.
-Wwrite-stringsconst
char[length] so that copying the address of one into a
non-const char * pointer produces a warning. These
warnings help you find at compile time code that can try to write
into a string constant, but only if you have been very careful about
using const in declarations and prototypes. Otherwise, it is
just a nuisance. This is why we did not make -Wall request
these warnings.
When compiling C++, warn about the deprecated conversion from string
literals to char *. This warning is enabled by default for C++
programs.
-Wclobberedlongjmp or
vfork. This warning is also enabled by -Wextra.
-Wno-complain-wrong-lang$ g++ -fno-rtti a.cc b.f90
The driver g++ invokes the C++ front end to compile a.cc and the Fortran front end to compile b.f90. The latter front end diagnoses ‘f951: Warning: command-line option '-fno-rtti' is valid for C++/D/ObjC++ but not for Fortran’, which may be disabled with -Wno-complain-wrong-lang.
-Wconversionabs (x) when
x is double; conversions between signed and unsigned,
like unsigned ui = -1; and conversions to smaller types, like
sqrtf (M_PI). Do not warn for explicit casts like abs
((int) x) and ui = (unsigned) -1, or if the value is not
changed by the conversion like in abs (2.0). Warnings about
conversions between signed and unsigned integers can be disabled by
using -Wno-sign-conversion.
For C++, also warn for confusing overload resolution for user-defined
conversions; and conversions that never use a type conversion
operator: conversions to void, the same type, a base class or a
reference to them. Warnings about conversions between signed and
unsigned integers are disabled by default in C++ unless
-Wsign-conversion is explicitly enabled.
Warnings about conversion from arithmetic on a small type back to that type are only given with -Warith-conversion.
-Wdangling-elseif statement an else branch belongs. Here is an example of
such a case:
{
if (a)
if (b)
foo ();
else
bar ();
}
In C/C++, every else branch belongs to the innermost possible
if statement, which in this example is if (b). This is
often not what the programmer expected, as illustrated in the above
example by indentation the programmer chose. When there is the
potential for this confusion, GCC issues a warning when this flag
is specified. To eliminate the warning, add explicit braces around
the innermost if statement so there is no way the else
can belong to the enclosing if. The resulting code
looks like this:
{
if (a)
{
if (b)
foo ();
else
bar ();
}
}
This warning is enabled by -Wparentheses.
-Wdangling-pointer-Wdangling-pointer=n-Wdangling-pointer=1 int f (int c1, int c2, x)
{
char *p = strchr ((char[]){ c1, c2 }, c3);
// warning: dangling pointer to a compound literal
return p ? *p : 'x';
}
In the following function the store of the address of the local variable
x in the escaped pointer *p also triggers the warning.
void g (int **p)
{
int x = 7;
// warning: storing the address of a local variable in *p
*p = &x;
}
-Wdangling-pointer=2For example, because the array a in the following function is out of scope when the pointer s that was set to point is used, the warning triggers at this level.
void f (char *s)
{
if (!s)
{
char a[12] = "tmpname";
s = a;
}
// warning: dangling pointer to a may be used
strcat (s, ".tmp");
...
}
-Wdangling-pointer=2 is included in -Wall.
-Wdate-time__TIME__, __DATE__ or __TIMESTAMP__
are encountered as they might prevent bit-wise-identical reproducible
compilations.
-Wempty-bodyif, else or do
while statement. This warning is also enabled by -Wextra.
-Wno-endif-labels#else and #endif.
-Wenum-compare-Wenum-conversion-Wenum-int-mismatch (C and Objective-C only) enum E { l = -1, z = 0, g = 1 };
int foo(void);
enum E foo(void);
In C, an enumerated type is compatible with char, a signed
integer type, or an unsigned integer type. However, since the choice
of the underlying type of an enumerated type is implementation-defined,
such mismatches may cause portability issues. In C++, such mismatches
are an error. In C, this warning is enabled by -Wall and
-Wc++-compat.
-Wjump-misses-init (C, Objective-C only)goto statement or a switch statement jumps
forward across the initialization of a variable, or jumps backward to a
label after the variable has been initialized. This only warns about
variables that are initialized when they are declared. This warning is
only supported for C and Objective-C; in C++ this sort of branch is an
error in any case.
-Wjump-misses-init is included in -Wc++-compat. It can be disabled with the -Wno-jump-misses-init option.
-Wsign-compare-Wsign-conversion-Wfloat-conversion-Wno-scalar-storage-order-Wsizeof-array-div int fn ()
{
int arr[10];
return sizeof (arr) / sizeof (short);
}
This warning is enabled by -Wall.
-Wsizeof-pointer-divsizeof (ptr) / sizeof (ptr[0]) if ptr is
not an array, but a pointer. This warning is enabled by -Wall.
-Wsizeof-pointer-memaccesssizeof. This warning triggers for
example for memset (ptr, 0, sizeof (ptr)); if ptr is not
an array, but a pointer, and suggests a possible fix, or about
memcpy (&foo, ptr, sizeof (&foo));. -Wsizeof-pointer-memaccess
also warns about calls to bounded string copy functions like strncat
or strncpy that specify as the bound a sizeof expression of
the source array. For example, in the following function the call to
strncat specifies the size of the source string as the bound. That
is almost certainly a mistake and so the call is diagnosed.
void make_file (const char *name)
{
char path[PATH_MAX];
strncpy (path, name, sizeof path - 1);
strncat (path, ".text", sizeof ".text");
...
}
The -Wsizeof-pointer-memaccess option is enabled by -Wall.
-Wno-sizeof-array-argumentsizeof operator is applied to a parameter that is
declared as an array in a function definition. This warning is enabled by
default for C and C++ programs.
-Wmemset-elt-sizememset built-in function, if the
first argument references an array, and the third argument is a number
equal to the number of elements, but not equal to the size of the array
in memory. This indicates that the user has omitted a multiplication by
the element size. This warning is enabled by -Wall.
-Wmemset-transposed-argsmemset built-in function where
the second argument is not zero and the third argument is zero. For
example, the call memset (buf, sizeof buf, 0) is diagnosed because
memset (buf, 0, sizeof buf) was meant instead. The diagnostic
is only emitted if the third argument is a literal zero. Otherwise, if
it is an expression that is folded to zero, or a cast of zero to some
type, it is far less likely that the arguments have been mistakenly
transposed and no warning is emitted. This warning is enabled
by -Wall.
-Waddress void f (void);
void g (void)
{
if (!f) // warning: expression evaluates to false
abort ();
}
comparisons of a pointer to a string literal, such as in
void f (const char *x)
{
if (x == "abc") // warning: expression evaluates to false
puts ("equal");
}
and tests of the results of pointer addition or subtraction for equality to null, such as in
void f (const int *p, int i)
{
return p + i == NULL;
}
Such uses typically indicate a programmer error: the address of most
functions and objects necessarily evaluates to true (the exception are
weak symbols), so their use in a conditional might indicate missing
parentheses in a function call or a missing dereference in an array
expression. The subset of the warning for object pointers can be
suppressed by casting the pointer operand to an integer type such
as intptr_t or uintptr_t.
Comparisons against string literals result in unspecified behavior
and are not portable, and suggest the intent was to call strcmp.
The warning is suppressed if the suspicious expression is the result
of macro expansion.
-Waddress warning is enabled by -Wall.
-Wno-address-of-packed-member-Wlogical-op extern int a;
if (a < 0 && a < 0) { ... }
-Wlogical-not-parentheses int a;
...
if (!a > 1) { ... }
It is possible to suppress the warning by wrapping the LHS into parentheses:
if ((!a) > 1) { ... }
This warning is enabled by -Wall.
-Waggregate-return-Wno-aggressive-loop-optimizations-Wno-attributes__attribute__ is used, such as
unrecognized attributes, function attributes applied to variables,
etc. This does not stop errors for incorrect use of supported
attributes.
Additionally, using -Wno-attributes=, it is possible to suppress warnings about unknown scoped attributes (in C++11 and C2X). For example, -Wno-attributes=vendor::attr disables warning about the following declaration:
[[vendor::attr]] void f();
It is also possible to disable warning about all attributes in a namespace using -Wno-attributes=vendor:: which prevents warning about both of these declarations:
[[vendor::safe]] void f();
[[vendor::unsafe]] void f2();
Note that -Wno-attributes= does not imply -Wno-attributes.
-Wno-builtin-declaration-mismatchFor example, the call to memset below is diagnosed by the warning
because the function expects a value of type size_t as its argument
but the type of 32 is int. With -Wextra,
the declaration of the function is diagnosed as well.
extern void* memset ();
void f (void *d)
{
memset (d, '\0', 32);
}
-Wno-builtin-macro-redefined__TIMESTAMP__, __TIME__,
__DATE__, __FILE__, and __BASE_FILE__.
-Wstrict-prototypes (C and Objective-C only)-Wold-style-declaration (C and Objective-C only)static are not the first things in a declaration. This warning
is also enabled by -Wextra.
-Wold-style-definition (C and Objective-C only)-Wmissing-parameter-type (C and Objective-C only) void foo(bar) { }
This warning is also enabled by -Wextra.
-Wmissing-prototypes (C and Objective-C only)-Wmissing-declarations-Wmissing-field-initializersx.h is implicitly zero:
struct s { int f, g, h; };
struct s x = { 3, 4 };
This option does not warn about designated initializers, so the following modification does not trigger a warning:
struct s { int f, g, h; };
struct s x = { .f = 3, .g = 4 };
In C this option does not warn about the universal zero initializer ‘{ 0 }’:
struct s { int f, g, h; };
struct s x = { 0 };
Likewise, in C++ this option does not warn about the empty { } initializer, for example:
struct s { int f, g, h; };
s x = { };
This warning is included in -Wextra. To get other -Wextra warnings without this one, use -Wextra -Wno-missing-field-initializers.
-Wno-missing-requires bool satisfied = requires { C<T> };
Here ‘satisfied’ will be true if ‘C<T>’ is a valid expression, which it is for all T. Presumably the user meant to write
bool satisfied = requires { requires C<T> };
so ‘satisfied’ is only true if concept ‘C’ is satisfied for type ‘T’.
This warning can be disabled with -Wno-missing-requires.
-Wno-missing-template-keywordtemplate
keyword if the parent object is dependent and the member being named is a
template.
template <class X>
void DoStuff (X x)
{
x.template DoSomeOtherStuff<X>(); // Good.
x.DoMoreStuff<X>(); // Warning, x is dependent.
}
In rare cases it is possible to get false positives. To silence this, wrap the expression in parentheses. For example, the following is treated as a template, even where m and N are integers:
void NotATemplate (my_class t)
{
int N = 5;
bool test = t.m < N > (0); // Treated as a template.
test = (t.m < N) > (0); // Same meaning, but not treated as a template.
}
This warning can be disabled with -Wno-missing-template-keyword.
-Wno-multichar-Wnormalized=[none|id|nfc|nfkc]There are four levels of warning supported by GCC. The default is -Wnormalized=nfc, which warns about any identifier that is not in the ISO 10646 “C” normalized form, NFC. NFC is the recommended form for most uses. It is equivalent to -Wnormalized.
Unfortunately, there are some characters allowed in identifiers by ISO C and ISO C++ that, when turned into NFC, are not allowed in identifiers. That is, there's no way to use these symbols in portable ISO C or C++ and have all your identifiers in NFC. -Wnormalized=id suppresses the warning for these characters. It is hoped that future versions of the standards involved will correct this, which is why this option is not the default.
You can switch the warning off for all characters by writing -Wnormalized=none or -Wno-normalized. You should only do this if you are using some other normalization scheme (like “D”), because otherwise you can easily create bugs that are literally impossible to see.
Some characters in ISO 10646 have distinct meanings but look identical
in some fonts or display methodologies, especially once formatting has
been applied. For instance \u207F, “SUPERSCRIPT LATIN SMALL
LETTER N”, displays just like a regular n that has been
placed in a superscript. ISO 10646 defines the NFKC
normalization scheme to convert all these into a standard form as
well, and GCC warns if your code is not in NFKC if you use
-Wnormalized=nfkc. This warning is comparable to warning
about every identifier that contains the letter O because it might be
confused with the digit 0, and so is not the default, but may be
useful as a local coding convention if the programming environment
cannot be fixed to display these characters distinctly.
-Wno-attribute-warningwarning attribute. By default, this warning is
enabled. -Wno-attribute-warning can be used to disable the
warning or -Wno-error=attribute-warning can be used to
disable the error when compiled with -Werror flag.
-Wno-deprecated-Wno-deprecated-declarationsdeprecated
attribute.
-Wno-overflow-Wno-odr-Wopenacc-parallelism-Wopenmp-simd-Woverride-init (C and Objective-C only)This warning is included in -Wextra. To get other -Wextra warnings without this one, use -Wextra -Wno-override-init.
-Wno-override-init-side-effects (C and Objective-C only)-Wpackedf.x in struct bar
is misaligned even though struct bar does not itself
have the packed attribute:
struct foo {
int x;
char a, b, c, d;
} __attribute__((packed));
struct bar {
char z;
struct foo f;
};
-Wnopacked-bitfield-compatpacked attribute
on bit-fields of type char. This was fixed in GCC 4.4 but
the change can lead to differences in the structure layout. GCC
informs you when the offset of such a field has changed in GCC 4.4.
For example there is no longer a 4-bit padding between field a
and b in this structure:
struct foo
{
char a:4;
char b:8;
} __attribute__ ((packed));
This warning is enabled by default. Use -Wno-packed-bitfield-compat to disable this warning.
-Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only)struct S, like, warning: alignment 1 of
'struct S' is less than 8, in this code:
struct __attribute__ ((aligned (8))) S8 { char a[8]; };
struct __attribute__ ((packed)) S {
struct S8 s8;
};
This warning is enabled by -Wall.
-Wpadded-Wredundant-decls-Wrestrictrestrict-qualified parameter
(or, in C++, a __restrict-qualified parameter) is aliased by another
argument, or when copies between such objects overlap. For example,
the call to the strcpy function below attempts to truncate the string
by replacing its initial characters with the last four. However, because
the call writes the terminating NUL into a[4], the copies overlap and
the call is diagnosed.
void foo (void)
{
char a[] = "abcd1234";
strcpy (a, a + 4);
...
}
The -Wrestrict option detects some instances of simple overlap even without optimization but works best at -O2 and above. It is included in -Wall.
-Wnested-externs (C and Objective-C only)extern declaration is encountered within a function.
-WinlineThe compiler uses a variety of heuristics to determine whether or not to inline a function. For example, the compiler takes into account the size of the function being inlined and the amount of inlining that has already been done in the current function. Therefore, seemingly insignificant changes in the source program can cause the warnings produced by -Winline to appear or disappear.
-Winterference-sizestd::hardware_destructive_interference_size
without specifying its value with --param destructive-interference-size.
Also warn about questionable values for that option.
This variable is intended to be used for controlling class layout, to avoid false sharing in concurrent code:
struct independent_fields {
alignas(std::hardware_destructive_interference_size)
std::atomic<int> one;
alignas(std::hardware_destructive_interference_size)
std::atomic<int> two;
};
Here ‘one’ and ‘two’ are intended to be far enough apart that stores to one won't require accesses to the other to reload the cache line.
By default, --param destructive-interference-size and --param constructive-interference-size are set based on the current -mtune option, typically to the L1 cache line size for the particular target CPU, sometimes to a range if tuning for a generic target. So all translation units that depend on ABI compatibility for the use of these variables must be compiled with the same -mtune (or -mcpu).
If ABI stability is important, such as if the use is in a header for a library, you should probably not use the hardware interference size variables at all. Alternatively, you can force a particular value with --param.
If you are confident that your use of the variable does not affect ABI outside a single build of your project, you can turn off the warning with -Wno-interference-size.
-Wint-in-bool-contextif (a <= b ? 2 : 3). Or left shifting of signed
integers in boolean context, like for (a = 0; 1 << a; a++);. Likewise
for all kinds of multiplications regardless of the data type.
This warning is enabled by -Wall.
-Wno-int-to-pointer-cast-Wno-pointer-to-int-cast (C and Objective-C only)-Winvalid-pch-Winvalid-utf8-Wno-unicode-Wlong-longlong long type is used. This is enabled by either
-Wpedantic or -Wtraditional in ISO C90 and C++98
modes. To inhibit the warning messages, use -Wno-long-long.
-Wvariadic-macros-Wno-varargsva_start. These warnings are enabled by default.
-Wvector-operation-performancepiecewise, which means that the
scalar operation is performed on every vector element;
in parallel, which means that the vector operation is implemented
using scalars of wider type, which normally is more performance efficient;
and as a single scalar, which means that vector fits into a
scalar type.
-Wvla-Wvla-larger-than=byte-sizeNote that GCC may optimize small variable-length arrays of a known value into plain arrays, so this warning may not get triggered for such arrays.
-Wvla-larger-than=‘PTRDIFF_MAX’ is enabled by default but is typically only effective when -ftree-vrp is active (default for -O2 and above).
See also -Walloca-larger-than=byte-size.
-Wno-vla-larger-than-Wvla-parameterIf the first function declaration uses the VLA form the bound specified in the array is assumed to be the minimum number of elements expected to be provided in calls to the function and the maximum number of elements accessed by it. Failing to provide arguments of sufficient size or accessing more than the maximum number of elements may be diagnosed.
For example, the warning triggers for the following redeclarations because
the first one allows an array of any size to be passed to f while
the second one specifies that the array argument must have at least n
elements. In addition, calling f with the associated VLA bound
parameter in excess of the actual VLA bound triggers a warning as well.
void f (int n, int[n]);
// warning: argument 2 previously declared as a VLA
void f (int, int[]);
void g (int n)
{
if (n > 4)
return;
int a[n];
// warning: access to a by f may be out of bounds
f (sizeof a, a);
...
}
-Wvla-parameter is included in -Wall. The -Warray-parameter option triggers warnings for similar problems involving ordinary array arguments.
-Wvolatile-register-var-Wxor-used-as-pow (C, C++, Objective-C and Objective-C++ only)^, the exclusive or operator, where it appears
the user meant exponentiation. Specifically, the warning occurs when the
left-hand side is the decimal constant 2 or 10 and the right-hand side
is also a decimal constant.
In C and C++, ^ means exclusive or, whereas in some other languages
(e.g. TeX and some versions of BASIC) it means exponentiation.
This warning is enabled by default. It can be silenced by converting one of the operands to hexadecimal.
-Wdisabled-optimization-Wpointer-sign (C and Objective-C only)-Wstack-protector-Woverlength-stringsThe limit applies after string constant concatenation, and does not count the trailing NUL. In C90, the limit was 509 characters; in C99, it was raised to 4095. C++98 does not specify a normative minimum maximum, so we do not diagnose overlength strings in C++.
This option is implied by -Wpedantic, and can be disabled with -Wno-overlength-strings.
-Wunsuffixed-float-constants (C and Objective-C only)FLOAT_CONST_DECIMAL64 pragma
from the decimal floating-point extension to C99.
-Wno-lto-type-mismatch-Wno-designated-init (C and Objective-C only)designated_init
attribute.
-fanalyzerThis analysis is much more expensive than other GCC warnings.
In technical terms, it performs coverage-guided symbolic execution of the code being compiled. It is neither sound nor complete: it can have false positives and false negatives. It is a bug-finding tool, rather than a tool for proving program correctness.
The analyzer is only suitable for use on C code in this release.
Enabling this option effectively enables the following warnings:
-Wanalyzer-allocation-size
-Wanalyzer-deref-before-check
-Wanalyzer-double-fclose
-Wanalyzer-double-free
-Wanalyzer-exposure-through-output-file
-Wanalyzer-exposure-through-uninit-copy
-Wanalyzer-fd-access-mode-mismatch
-Wanalyzer-fd-double-close
-Wanalyzer-fd-leak
-Wanalyzer-fd-phase-mismatch
-Wanalyzer-fd-type-mismatch
-Wanalyzer-fd-use-after-close
-Wanalyzer-fd-use-without-check
-Wanalyzer-file-leak
-Wanalyzer-free-of-non-heap
-Wanalyzer-imprecise-fp-arithmetic
-Wanalyzer-infinite-recursion
-Wanalyzer-jump-through-null
-Wanalyzer-malloc-leak
-Wanalyzer-mismatching-deallocation
-Wanalyzer-null-argument
-Wanalyzer-null-dereference
-Wanalyzer-out-of-bounds
-Wanalyzer-possible-null-argument
-Wanalyzer-possible-null-dereference
-Wanalyzer-putenv-of-auto-var
-Wanalyzer-shift-count-negative
-Wanalyzer-shift-count-overflow
-Wanalyzer-stale-setjmp-buffer
-Wanalyzer-unsafe-call-within-signal-handler
-Wanalyzer-use-after-free
-Wanalyzer-use-of-pointer-in-stale-stack-frame
-Wanalyzer-use-of-uninitialized-value
-Wanalyzer-va-arg-type-mismatch
-Wanalyzer-va-list-exhausted
-Wanalyzer-va-list-leak
-Wanalyzer-va-list-use-after-va-end
-Wanalyzer-write-to-const
-Wanalyzer-write-to-string-literal
This option is only available if GCC was configured with analyzer support enabled.
-Wanalyzer-too-complexBy default, the analysis silently stops if the code is too complicated for the analyzer to fully explore and it reaches an internal limit. The -Wanalyzer-too-complex option warns if this occurs.
-Wno-analyzer-allocation-sizeThis diagnostic warns for paths through the code in which a pointer to
a buffer is assigned to point at a buffer with a size that is not a
multiple of sizeof (*pointer).
-Wno-analyzer-deref-before-checkThis diagnostic warns for paths through the code in which a pointer
is checked for NULL *after* it has already been
dereferenced, suggesting that the pointer could have been NULL.
Such cases suggest that the check for NULL is either redundant,
or that it needs to be moved to before the pointer is dereferenced.
This diagnostic also considers values passed to a function argument
marked with __attribute__((nonnull)) as requiring a non-NULL
value, and thus will complain if such values are checked for NULL
after returning from such a function call.
This diagnostic is unlikely to be reported when any level of optimization is enabled, as GCC's optimization logic will typically consider such checks for NULL as being redundant, and optimize them away before the analyzer "sees" them. Hence optimization should be disabled when attempting to trigger this diagnostic.
-Wno-analyzer-double-fcloseThis diagnostic warns for paths through the code in which a FILE *
can have fclose called on it more than once.
-Wno-analyzer-double-freeThis diagnostic warns for paths through the code in which a pointer
can have a deallocator called on it more than once, either free,
or a deallocator referenced by attribute malloc.
See CWE-415: Double Free.
-Wno-analyzer-exposure-through-output-fileThis diagnostic warns for paths through the code in which a security-sensitive value is written to an output file (such as writing a password to a log file).
-Wanalyzer-exposure-through-uninit-copyThis diagnostic warns for “infoleaks” - paths through the code in which uninitialized values are copied across a security boundary (such as code within an OS kernel that copies a partially-initialized struct on the stack to user space).
See CWE-200: Exposure of Sensitive Information to an Unauthorized Actor.
-Wno-analyzer-fd-access-mode-mismatchThis diagnostic warns for paths through code in which a
read on a write-only file descriptor is attempted, or vice versa.
This diagnostic also warns for code paths in a which a function with attribute
fd_arg_read (N) is called with a file descriptor opened with
O_WRONLY at referenced argument N or a function with attribute
fd_arg_write (N) is called with a file descriptor opened with
O_RDONLY at referenced argument N.
-Wno-analyzer-fd-double-closeThis diagnostic warns for paths through code in which a file descriptor can be closed more than once.
-Wno-analyzer-fd-leakThis diagnostic warns for paths through code in which an open file descriptor is leaked.
See CWE-775: Missing Release of File Descriptor or Handle after Effective Lifetime.
-Wno-analyzer-fd-phase-mismatchThis diagnostic warns for paths through code in which an operation is
attempted in the wrong phase of a file descriptor's lifetime.
For example, it will warn on attempts to call accept on a stream
socket that has not yet had listen successfully called on it.
See CWE-666: Operation on Resource in Wrong Phase of Lifetime.
-Wno-analyzer-fd-type-mismatchThis diagnostic warns for paths through code in which an
operation is attempted on the wrong type of file descriptor.
For example, it will warn on attempts to use socket operations
on a file descriptor obtained via open, or when attempting
to use a stream socket operation on a datagram socket.
-Wno-analyzer-fd-use-after-closeThis diagnostic warns for paths through code in which a read or write is called on a closed file descriptor.
This diagnostic also warns for paths through code in which
a function with attribute fd_arg (N) or fd_arg_read (N)
or fd_arg_write (N) is called with a closed file descriptor at
referenced argument N.
-Wno-analyzer-fd-use-without-checkThis diagnostic warns for paths through code in which a file descriptor is used without being checked for validity.
This diagnostic also warns for paths through code in which
a function with attribute fd_arg (N) or fd_arg_read (N)
or fd_arg_write (N) is called with a file descriptor, at referenced
argument N, without being checked for validity.
-Wno-analyzer-file-leakThis diagnostic warns for paths through the code in which a
<stdio.h> FILE * stream object is leaked.
See CWE-775: Missing Release of File Descriptor or Handle after Effective Lifetime.
-Wno-analyzer-free-of-non-heapThis diagnostic warns for paths through the code in which free
is called on a non-heap pointer (e.g. an on-stack buffer, or a global).
-Wno-analyzer-imprecise-fp-arithmeticThis diagnostic warns for paths through the code in which floating-point arithmetic is used in locations where precise computation is needed. This diagnostic only warns on use of floating-point operands inside the calculation of an allocation size at the moment.
-Wno-analyzer-infinite-recursionThis diagnostics warns for paths through the code which appear to lead to infinite recursion.
Specifically, when the analyzer "sees" a recursive call, it will compare the state of memory at the entry to the new frame with that at the entry to the previous frame of that function on the stack. The warning is issued if nothing in memory appears to be changing; any changes observed to parameters or globals are assumed to lead to termination of the recursion and thus suppress the warning.
This diagnostic is likely to miss cases of infinite recursion that are convered to iteration by the optimizer before the analyzer "sees" them. Hence optimization should be disabled when attempting to trigger this diagnostic.
Compare with -Winfinite-recursion, which provides a similar diagnostic, but is implemented in a different way.
-Wno-analyzer-jump-through-nullThis diagnostic warns for paths through the code in which a NULL
function pointer is called.
-Wno-analyzer-malloc-leakThis diagnostic warns for paths through the code in which a
pointer allocated via an allocator is leaked: either malloc,
or a function marked with attribute malloc.
See CWE-401: Missing Release of Memory after Effective Lifetime.
-Wno-analyzer-mismatching-deallocationThis diagnostic warns for paths through the code in which the
wrong deallocation function is called on a pointer value, based on
which function was used to allocate the pointer value. The diagnostic
will warn about mismatches between free, scalar delete
and vector delete[], and those marked as allocator/deallocator
pairs using attribute malloc.
-Wno-analyzer-out-of-boundsThis diagnostic warns for paths through the code in which a buffer is definitely read or written out-of-bounds. The diagnostic applies for cases where the analyzer is able to determine a constant offset and for accesses past the end of a buffer, also a constant capacity. Further, the diagnostic does limited checking for accesses past the end when the offset as well as the capacity is symbolic.
See CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer.
-Wno-analyzer-possible-null-argumentThis diagnostic warns for paths through the code in which a
possibly-NULL value is passed to a function argument marked
with __attribute__((nonnull)) as requiring a non-NULL
value.
See CWE-690: Unchecked Return Value to NULL Pointer Dereference.
-Wno-analyzer-possible-null-dereferenceThis diagnostic warns for paths through the code in which a possibly-NULL value is dereferenced.
See CWE-690: Unchecked Return Value to NULL Pointer Dereference.
-Wno-analyzer-null-argumentThis diagnostic warns for paths through the code in which a
value known to be NULL is passed to a function argument marked
with __attribute__((nonnull)) as requiring a non-NULL
value.
-Wno-analyzer-null-dereferenceThis diagnostic warns for paths through the code in which a value known to be NULL is dereferenced.
-Wno-analyzer-putenv-of-auto-varThis diagnostic warns for paths through the code in which a
call to putenv is passed a pointer to an automatic variable
or an on-stack buffer.
See POS34-C. Do not call putenv() with a pointer to an automatic variable as the argument.
-Wno-analyzer-shift-count-negativeThis diagnostic warns for paths through the code in which a shift is attempted with a negative count. It is analogous to the -Wshift-count-negative diagnostic implemented in the C/C++ front ends, but is implemented based on analyzing interprocedural paths, rather than merely parsing the syntax tree. However, the analyzer does not prioritize detection of such paths, so false negatives are more likely relative to other warnings.
-Wno-analyzer-shift-count-overflowThis diagnostic warns for paths through the code in which a shift is attempted with a count greater than or equal to the precision of the operand's type. It is analogous to the -Wshift-count-overflow diagnostic implemented in the C/C++ front ends, but is implemented based on analyzing interprocedural paths, rather than merely parsing the syntax tree. However, the analyzer does not prioritize detection of such paths, so false negatives are more likely relative to other warnings.
-Wno-analyzer-stale-setjmp-bufferThis diagnostic warns for paths through the code in which
longjmp is called to rewind to a jmp_buf relating
to a setjmp call in a function that has returned.
When setjmp is called on a jmp_buf to record a rewind
location, it records the stack frame. The stack frame becomes invalid
when the function containing the setjmp call returns. Attempting
to rewind to it via longjmp would reference a stack frame that
no longer exists, and likely lead to a crash (or worse).
-Wno-analyzer-tainted-allocation-sizeThis diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as the size of an allocation without being sanitized, so that an attacker could inject an excessively large allocation and potentially cause a denial of service attack.
-Wno-analyzer-tainted-assertionThis diagnostic warns for paths through the code in which a value
that could be under an attacker's control is used as part of a
condition without being first sanitized, and that condition guards a
call to a function marked with attribute noreturn
(such as the function __builtin_unreachable). Such functions
typically indicate abnormal termination of the program, such as for
assertion failure handlers. For example:
assert (some_tainted_value < SOME_LIMIT);
In such cases:
NDEBUG,
an attacker could inject data that subverts the process, since it
presumably violates a precondition that is being assumed by the code.
Note that when assertion-checking is disabled, the assertions are typically removed by the preprocessor before the analyzer has a chance to "see" them, so this diagnostic can only generate warnings on builds in which assertion-checking is enabled.
For the purpose of this warning, any function marked with attribute
noreturn is considered as a possible assertion failure
handler, including __builtin_unreachable. Note that these functions
are sometimes removed by the optimizer before the analyzer "sees" them.
Hence optimization should be disabled when attempting to trigger this
diagnostic.
See CWE-617: Reachable Assertion.
The warning can also report problematic constructions such as
switch (some_tainted_value) {
case 0:
/* [...etc; various valid cases omitted...] */
break;
default:
__builtin_unreachable (); /* BUG: attacker can trigger this */
}
despite the above not being an assertion failure, strictly speaking.
-Wno-analyzer-tainted-array-indexThis diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as the index of an array access without being sanitized, so that an attacker could inject an out-of-bounds access.
-Wno-analyzer-tainted-divisorThis diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as the divisor in a division or modulus operation without being sanitized, so that an attacker could inject a division-by-zero.
-Wno-analyzer-tainted-offsetThis diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as a pointer offset without being sanitized, so that an attacker could inject an out-of-bounds access.
-Wno-analyzer-tainted-sizeThis diagnostic warns for paths through the code in which a value
that could be under an attacker's control is used as the size of
an operation such as memset without being sanitized, so that an
attacker could inject an out-of-bounds access.
-Wno-analyzer-unsafe-call-within-signal-handlerThis diagnostic warns for paths through the code in which a
function known to be async-signal-unsafe (such as fprintf) is
called from a signal handler.
See CWE-479: Signal Handler Use of a Non-reentrant Function.
-Wno-analyzer-use-after-freeThis diagnostic warns for paths through the code in which a
pointer is used after a deallocator is called on it: either free,
or a deallocator referenced by attribute malloc.
-Wno-analyzer-use-of-pointer-in-stale-stack-frameThis diagnostic warns for paths through the code in which a pointer is dereferenced that points to a variable in a stale stack frame.
-Wno-analyzer-va-arg-type-mismatchThis diagnostic warns for interprocedural paths through the code for which
the analyzer detects an attempt to use va_arg to extract a value
passed to a variadic call, but uses a type that does not match that of
the expression passed to the call.
-Wno-analyzer-va-list-exhaustedThis diagnostic warns for interprocedural paths through the code for which
the analyzer detects an attempt to use va_arg to access the next
value passed to a variadic call, but all of the values in the
va_list have already been consumed.
See CWE-685: Function Call With Incorrect Number of Arguments.
-Wno-analyzer-va-list-leakThis diagnostic warns for interprocedural paths through the code for which
the analyzer detects that va_start or va_copy has been called
on a va_list without a corresponding call to va_end.
-Wno-analyzer-va-list-use-after-va-endThis diagnostic warns for interprocedural paths through the code for which
the analyzer detects an attempt to use a va_list after
va_end has been called on it.
va_list.
-Wno-analyzer-write-to-constThis diagnostic warns for paths through the code in which the analyzer
detects an attempt to write through a pointer to a const object.
However, the analyzer does not prioritize detection of such paths, so
false negatives are more likely relative to other warnings.
-Wno-analyzer-write-to-string-literalThis diagnostic warns for paths through the code in which the analyzer detects an attempt to write through a pointer to a string literal. However, the analyzer does not prioritize detection of such paths, so false negatives are more likely relative to other warnings.
-Wno-analyzer-use-of-uninitialized-valueThis diagnostic warns for paths through the code in which an uninitialized value is used.
The analyzer has hardcoded knowledge about the behavior of the following memory-management functions:
alloca
__builtin_alloc,
__builtin_alloc_with_align, __builtin_calloc,
__builtin_free, __builtin_malloc, __builtin_memcpy,
__builtin_memcpy_chk, __builtin_memset,
__builtin_memset_chk, __builtin_realloc,
__builtin_stack_restore, and __builtin_stack_save
calloc
free
malloc
memset
operator delete
operator delete []
operator new
operator new []
realloc
strdup
strndup
of the following functions for working with file descriptors:
open
close
creat
dup, dup2 and dup3
isatty
pipe, and pipe2
read
write
socket, bind, listen, accept, and connect
of the following functions for working with <stdio.h> streams:
__builtin_fprintf,
__builtin_fprintf_unlocked, __builtin_fputc,
__builtin_fputc_unlocked, __builtin_fputs,
__builtin_fputs_unlocked, __builtin_fwrite,
__builtin_fwrite_unlocked, __builtin_printf,
__builtin_printf_unlocked, __builtin_putc,
__builtin_putchar, __builtin_putchar_unlocked,
__builtin_putc_unlocked, __builtin_puts,
__builtin_puts_unlocked, __builtin_vfprintf, and
__builtin_vprintf
fopen
fclose
ferror
fgets
fgets_unlocked
fileno
fread
getc
getchar
fprintf
printf
fwrite
and of the following functions:
__builtin_expect,
__builtin_expect_with_probability, __builtin_strchr,
__builtin_strcpy, __builtin_strcpy_chk,
__builtin_strlen, __builtin_va_copy, and
__builtin_va_start
error and error_at_line
getpass
longjmp
putenv
setjmp
siglongjmp
signal
sigsetjmp
strchr
strlen
In addition, various functions with an __analyzer_ prefix have
special meaning to the analyzer, described in the GCC Internals manual.
Pertinent parameters for controlling the exploration are:
The following options control the analyzer.
-fanalyzer-call-summariesIf enabled, call summaries are only used for functions with more than one call site, and that are sufficiently complicated (as per --param analyzer-min-snodes-for-call-summary=value).
-fanalyzer-checker=nameSome checkers are disabled by default (even with -fanalyzer),
such as the taint checker that implements
-Wanalyzer-tainted-array-index, and this option is required
to enable them.
Note: currently, -fanalyzer-checker=taint disables the following warnings from -fanalyzer:
-Wanalyzer-deref-before-check
-Wanalyzer-double-fclose
-Wanalyzer-double-free
-Wanalyzer-exposure-through-output-file
-Wanalyzer-fd-access-mode-mismatch
-Wanalyzer-fd-double-close
-Wanalyzer-fd-leak
-Wanalyzer-fd-use-after-close
-Wanalyzer-fd-use-without-check
-Wanalyzer-file-leak
-Wanalyzer-free-of-non-heap
-Wanalyzer-malloc-leak
-Wanalyzer-mismatching-deallocation
-Wanalyzer-null-argument
-Wanalyzer-null-dereference
-Wanalyzer-possible-null-argument
-Wanalyzer-possible-null-dereference
-Wanalyzer-unsafe-call-within-signal-handler
-Wanalyzer-use-after-free
-Wanalyzer-va-list-leak
-Wanalyzer-va-list-use-after-va-end
-fno-analyzer-feasibilityBy default the analyzer verifies that there is a feasible control flow path for each diagnostic it emits: that the conditions that hold are not mutually exclusive. Diagnostics for which no feasible path can be found are rejected. This filtering can be suppressed with -fno-analyzer-feasibility, for debugging issues in this code.
-fanalyzer-fine-grainedInternally the analyzer builds an “exploded graph” that combines control flow graphs with data flow information.
By default, an edge in this graph can contain the effects of a run of multiple statements within a basic block. With -fanalyzer-fine-grained, each statement gets its own edge.
-fanalyzer-show-duplicate-count-fno-analyzer-state-mergeBy default the analyzer attempts to simplify analysis by merging sufficiently similar states at each program point as it builds its “exploded graph”. With -fno-analyzer-state-merge this merging can be suppressed, for debugging state-handling issues.
-fno-analyzer-state-purgeBy default the analyzer attempts to simplify analysis by purging aspects of state at a program point that appear to no longer be relevant e.g. the values of locals that aren't accessed later in the function and which aren't relevant to leak analysis.
With -fno-analyzer-state-purge this purging of state can be suppressed, for debugging state-handling issues.
-fno-analyzer-suppress-followupsBy default the analyzer will stop exploring an execution path after encountering certain diagnostics, in order to avoid potentially issuing a cascade of follow-up diagnostics.
The diagnostics that terminate analysis along a path are:
With -fno-analyzer-suppress-followups the analyzer will continue to explore such paths even after such diagnostics, which may be helpful for debugging issues in the analyzer, or for microbenchmarks for detecting undefined behavior.
-fanalyzer-transitivity-fno-analyzer-undo-inlining-fanalyzer runs relatively late compared to other code analysis tools, and some optimizations have already been applied to the code. In particular function inlining may have occurred, leading to the interprocedural execution paths emitted by the analyzer containing function frames that don't correspond to those in the original source code.
By default the analyzer attempts to reconstruct the original function frames, and to emit events showing the inlined calls.
With -fno-analyzer-undo-inlining this attempt to reconstruct
the original frame information can be be disabled, which may be of help
when debugging issues in the analyzer.
-fanalyzer-verbose-edges-fanalyzer-verbose-state-changes-fanalyzer-verbosity=levelThe level can be one of:
free diagnostic,
both calls to free will be shown.
This level is the default.
-fdump-analyzer-fdump-analyzer-stderr-fdump-analyzer-callgraph-fdump-analyzer-exploded-graph-fdump-analyzer-exploded-nodes-fdump-analyzer-exploded-nodes-2-fdump-analyzer-exploded-nodes-3-fdump-analyzer-exploded-paths-fdump-analyzer-feasibility-fdump-analyzer-json-fdump-analyzer-state-purge-fdump-analyzer-supergraph-fdump-analyzer-untrackedTo tell GCC to emit extra information for use by a debugger, in almost all cases you need only to add -g to your other options. Some debug formats can co-exist (like DWARF with CTF) when each of them is enabled explicitly by adding the respective command line option to your other options.
GCC allows you to use -g with -O. The shortcuts taken by optimized code may occasionally be surprising: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values are already at hand; some statements may execute in different places because they have been moved out of loops. Nevertheless it is possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs.
If you are not using some other optimization option, consider using -Og (see Optimize Options) with -g. With no -O option at all, some compiler passes that collect information useful for debugging do not run at all, so that -Og may result in a better debugging experience.
-gOn most systems that use stabs format, -g enables use of extra debugging information that only GDB can use; this extra information makes debugging work better in GDB but probably makes other debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use -gvms (see below).
-ggdb-gdwarf-gdwarf-versionNote that with DWARF Version 2, some ports require and always use some non-conflicting DWARF 3 extensions in the unwind tables.
Version 4 may require GDB 7.0 and -fvar-tracking-assignments for maximum benefit. Version 5 requires GDB 8.0 or higher.
GCC no longer supports DWARF Version 1, which is substantially different than Version 2 and later. For historical reasons, some other DWARF-related options such as -fno-dwarf2-cfi-asm) retain a reference to DWARF Version 2 in their names, but apply to all currently-supported versions of DWARF.
-gbtf-gctf-gctflevelCTF debug information can be generated along with DWARF debug information when both of the debug formats are enabled explicitly via their respective command line options.
Level 0 produces no CTF debug information at all. Thus, -gctf0 negates -gctf.
Level 1 produces CTF information for tracebacks only. This includes callsite information, but does not include type information.
Level 2 produces type information for entities (functions, data objects etc.) at file-scope or global-scope only.
-gvms-glevel-ggdblevel-gvmslevelLevel 0 produces no debug information at all. Thus, -g0 negates -g.
Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, and line number tables, but no information about local variables.
Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use -g3.
If you use multiple -g options, with or without level numbers, the last such option is the one that is effective.
-gdwarf does not accept a concatenated debug level, to avoid confusion with -gdwarf-level. Instead use an additional -glevel option to change the debug level for DWARF.
-fno-eliminate-unused-debug-symbols-femit-class-debug-always-fno-merge-debug-strings-fdebug-prefix-map=old=new-fvar-trackingIt is enabled by default when compiling with optimization (-Os, -O, -O2, ...), debugging information (-g) and the debug info format supports it.
-fvar-tracking-assignmentsIt can be enabled even if var-tracking is disabled, in which case annotations are created and maintained, but discarded at the end. By default, this flag is enabled together with -fvar-tracking, except when selective scheduling is enabled.
-gsplit-dwarf-gdwarf32-gdwarf64-gdescribe-dies-gpubnames.debug_pubnames and .debug_pubtypes sections.
-ggnu-pubnames.debug_pubnames and .debug_pubtypes sections in a format
suitable for conversion into a GDB index. This option is only useful
with a linker that can produce GDB index version 7.
-fdebug-types-section.debug_types section instead of making them part of the
.debug_info section. It is more efficient to put them in a separate
comdat section since the linker can then remove duplicates.
But not all DWARF consumers support .debug_types sections yet
and on some objects .debug_types produces larger instead of smaller
debugging information.
-grecord-gcc-switches-gno-record-gcc-switches-gstrict-dwarf-gno-strict-dwarf-gas-loc-support.loc directives.
It may then use them for the assembler to generate DWARF2+ line number
tables.
This is generally desirable, because assembler-generated line-number tables are a lot more compact than those the compiler can generate itself.
This option will be enabled by default if, at GCC configure time, the assembler was found to support such directives.
-gno-as-loc-support-gas-locview-supportview assignment
and reset assertion checking in .loc directives.
This option will be enabled by default if, at GCC configure time, the
assembler was found to support them.
-gno-as-locview-support-gcolumn-info-gno-column-info-gstatement-frontiers-gno-statement-frontiersis_stmt
markers in the line number table. This is enabled by default when
compiling with optimization (-Os, -O1, -O2,
...), and outputting DWARF 2 debug information at the normal level.
-gvariable-location-views-gvariable-location-views=incompat5-gno-variable-location-viewsThis is enabled by default when outputting DWARF 2 debug information at the normal level, as long as there is assembler support, -fvar-tracking-assignments is enabled and -gstrict-dwarf is not. When assembler support is not available, this may still be enabled, but it will force GCC to output internal line number tables, and if -ginternal-reset-location-views is not enabled, that will most certainly lead to silently mismatching location views.
There is a proposed representation for view numbers that is not backward compatible with the location list format introduced in DWARF 5, that can be enabled with -gvariable-location-views=incompat5. This option may be removed in the future, is only provided as a reference implementation of the proposed representation. Debug information consumers are not expected to support this extended format, and they would be rendered unable to decode location lists using it.
-ginternal-reset-location-views-gno-internal-reset-location-viewsview number mismatch. This is only enabled
on ports that define a reliable estimation function.
-ginline-points-gno-inline-points-gz[=type]-femit-struct-debug-baseonlyThis option substantially reduces the size of debugging information, but at significant potential loss in type information to the debugger. See -femit-struct-debug-reduced for a less aggressive option. See -femit-struct-debug-detailed for more detailed control.
This option works only with DWARF debug output.
-femit-struct-debug-reducedThis option significantly reduces the size of debugging information, with some potential loss in type information to the debugger. See -femit-struct-debug-baseonly for a more aggressive option. See -femit-struct-debug-detailed for more detailed control.
This option works only with DWARF debug output.
-femit-struct-debug-detailed[=spec-list]This option is a detailed version of -femit-struct-debug-reduced and -femit-struct-debug-baseonly, which serves for most needs.
A specification has the syntax
[‘dir:’|‘ind:’][‘ord:’|‘gen:’](‘any’|‘sys’|‘base’|‘none’)
The optional first word limits the specification to structs that are used directly (‘dir:’) or used indirectly (‘ind:’). A struct type is used directly when it is the type of a variable, member. Indirect uses arise through pointers to structs. That is, when use of an incomplete struct is valid, the use is indirect. An example is ‘struct one direct; struct two * indirect;’.
The optional second word limits the specification to ordinary structs (‘ord:’) or generic structs (‘gen:’). Generic structs are a bit complicated to explain. For C++, these are non-explicit specializations of template classes, or non-template classes within the above. Other programming languages have generics, but -femit-struct-debug-detailed does not yet implement them.
The third word specifies the source files for those structs for which the compiler should emit debug information. The values ‘none’ and ‘any’ have the normal meaning. The value ‘base’ means that the base of name of the file in which the type declaration appears must match the base of the name of the main compilation file. In practice, this means that when compiling foo.c, debug information is generated for types declared in that file and foo.h, but not other header files. The value ‘sys’ means those types satisfying ‘base’ or declared in system or compiler headers.
You may need to experiment to determine the best settings for your application.
The default is -femit-struct-debug-detailed=all.
This option works only with DWARF debug output.
-fno-dwarf2-cfi-asm.eh_frame section
instead of using GAS .cfi_* directives.
-fno-eliminate-unused-debug-typesThese options control various sorts of optimizations.
Without any optimization option, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you expect from the source code.
Turning on optimization flags makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program.
The compiler performs optimization based on the knowledge it has of the program. Compiling multiple files at once to a single output file mode allows the compiler to use information gained from all of the files when compiling each of them.
Not all optimizations are controlled directly by a flag. Only optimizations that have a flag are listed in this section.
Most optimizations are completely disabled at -O0 or if an -O level is not set on the command line, even if individual optimization flags are specified. Similarly, -Og suppresses many optimization passes.
Depending on the target and how GCC was configured, a slightly different set of optimizations may be enabled at each -O level than those listed here. You can invoke GCC with -Q --help=optimizers to find out the exact set of optimizations that are enabled at each level. See Overall Options, for examples.
-O-O1With -O, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time.
-O turns on the following optimization flags:
-fauto-inc-dec
-fbranch-count-reg
-fcombine-stack-adjustments
-fcompare-elim
-fcprop-registers
-fdce
-fdefer-pop
-fdelayed-branch
-fdse
-fforward-propagate
-fguess-branch-probability
-fif-conversion
-fif-conversion2
-finline-functions-called-once
-fipa-modref
-fipa-profile
-fipa-pure-const
-fipa-reference
-fipa-reference-addressable
-fmerge-constants
-fmove-loop-invariants
-fmove-loop-stores
-fomit-frame-pointer
-freorder-blocks
-fshrink-wrap
-fshrink-wrap-separate
-fsplit-wide-types
-fssa-backprop
-fssa-phiopt
-ftree-bit-ccp
-ftree-ccp
-ftree-ch
-ftree-coalesce-vars
-ftree-copy-prop
-ftree-dominator-opts
-ftree-dse
-ftree-forwprop
-ftree-fre
-ftree-phiprop
-ftree-pta
-ftree-scev-cprop
-ftree-sink
-ftree-slsr
-ftree-sra
-ftree-ter
-funit-at-a-time
-O2-O2 turns on all optimization flags specified by -O1. It also turns on the following optimization flags:
-falign-functions -falign-jumps
-falign-labels -falign-loops
-fcaller-saves
-fcode-hoisting
-fcrossjumping
-fcse-follow-jumps -fcse-skip-blocks
-fdelete-null-pointer-checks
-fdevirtualize -fdevirtualize-speculatively
-fexpensive-optimizations
-ffinite-loops
-fgcse -fgcse-lm
-fhoist-adjacent-loads
-finline-functions
-finline-small-functions
-findirect-inlining
-fipa-bit-cp -fipa-cp -fipa-icf
-fipa-ra -fipa-sra -fipa-vrp
-fisolate-erroneous-paths-dereference
-flra-remat
-foptimize-sibling-calls
-foptimize-strlen
-fpartial-inlining
-fpeephole2
-freorder-blocks-algorithm=stc
-freorder-blocks-and-partition -freorder-functions
-frerun-cse-after-loop
-fschedule-insns -fschedule-insns2
-fsched-interblock -fsched-spec
-fstore-merging
-fstrict-aliasing
-fthread-jumps
-ftree-builtin-call-dce
-ftree-loop-vectorize
-ftree-pre
-ftree-slp-vectorize
-ftree-switch-conversion -ftree-tail-merge
-ftree-vrp
-fvect-cost-model=very-cheap
Please note the warning under -fgcse about invoking -O2 on programs that use computed gotos.
-O3 -fgcse-after-reload
-fipa-cp-clone
-floop-interchange
-floop-unroll-and-jam
-fpeel-loops
-fpredictive-commoning
-fsplit-loops
-fsplit-paths
-ftree-loop-distribution
-ftree-partial-pre
-funswitch-loops
-fvect-cost-model=dynamic
-fversion-loops-for-strides
-O0-Os -falign-functions -falign-jumps
-falign-labels -falign-loops
-fprefetch-loop-arrays -freorder-blocks-algorithm=stc
It also enables -finline-functions, causes the compiler to tune for code size rather than execution speed, and performs further optimizations designed to reduce code size.
-Ofast-OgLike -O0, -Og completely disables a number of optimization passes so that individual options controlling them have no effect. Otherwise -Og enables all -O1 optimization flags except for those that may interfere with debugging:
-fbranch-count-reg -fdelayed-branch
-fdse -fif-conversion -fif-conversion2
-finline-functions-called-once
-fmove-loop-invariants -fmove-loop-stores -fssa-phiopt
-ftree-bit-ccp -ftree-dse -ftree-pta -ftree-sra
-OzIf you use multiple -O options, with or without level numbers, the last such option is the one that is effective.
Options of the form -fflag specify machine-independent flags. Most flags have both positive and negative forms; the negative form of -ffoo is -fno-foo. In the table below, only one of the forms is listed—the one you typically use. You can figure out the other form by either removing ‘no-’ or adding it.
The following options control specific optimizations. They are either activated by -O options or are related to ones that are. You can use the following flags in the rare cases when “fine-tuning” of optimizations to be performed is desired.
-fno-defer-pop-fforward-propagateThis option is enabled by default at optimization levels -O1, -O2, -O3, -Os.
-ffp-contract=styleThe default is -ffp-contract=fast.
-fomit-frame-pointerOn some targets this flag has no effect because the standard calling sequence always uses a frame pointer, so it cannot be omitted.
Note that -fno-omit-frame-pointer doesn't guarantee the frame pointer is used in all functions. Several targets always omit the frame pointer in leaf functions.
Enabled by default at -O1 and higher.
-foptimize-sibling-callsEnabled at levels -O2, -O3, -Os.
-foptimize-strlenstrlen,
strchr or strcpy) and
their _FORTIFY_SOURCE counterparts into faster alternatives.
Enabled at levels -O2, -O3.
-finline-stringops[=fn]memset)
inline, even when the length is variable or big enough as to require
looping. This is most useful along with -ffreestanding and
-fno-builtin.
In some circumstances, it enables the compiler to generate code that takes advantage of known alignment and length multipliers, but even then it may be less efficient than optimized runtime implementations, and grow code size so much that even a less performant but shared implementation runs faster due to better use of code caches. This option is disabled by default.
-fno-inlinealways_inline attribute. This is the default when not
optimizing.
Single functions can be exempted from inlining by marking them
with the noinline attribute.
-finline-small-functionsEnabled at levels -O2, -O3, -Os.
-findirect-inliningEnabled at levels -O2, -O3, -Os.
-finline-functionsIf all calls to a given function are integrated, and the function is
declared static, then the function is normally not output as
assembler code in its own right.
Enabled at levels -O2, -O3, -Os. Also enabled by -fprofile-use and -fauto-profile.
-finline-functions-called-oncestatic functions called once for inlining into their
caller even if they are not marked inline. If a call to a given
function is integrated, then the function is not output as assembler code
in its own right.
Enabled at levels -O1, -O2, -O3 and -Os, but not -Og.
-fearly-inliningalways_inline and functions whose body seems
smaller than the function call overhead early before doing
-fprofile-generate instrumentation and real inlining pass. Doing so
makes profiling significantly cheaper and usually inlining faster on programs
having large chains of nested wrapper functions.
Enabled by default.
-fipa-sraEnabled at levels -O2, -O3 and -Os.
-finline-limit=nInlining is actually controlled by a number of parameters, which may be specified individually by using --param name=value. The -finline-limit=n option sets some of these parameters as follows:
max-inline-insns-singlemax-inline-insns-autoSee below for a documentation of the individual parameters controlling inlining and for the defaults of these parameters.
Note: there may be no value to -finline-limit that results in default behavior.
Note: pseudo instruction represents, in this particular context, an abstract measurement of function's size. In no way does it represent a count of assembly instructions and as such its exact meaning might change from one release to an another.
-fno-keep-inline-dllexportdllexport
attribute or declspec. See Declaring Attributes of Functions.
-fkeep-inline-functionsstatic functions that are declared inline
into the object file, even if the function has been inlined into all
of its callers. This switch does not affect functions using the
extern inline extension in GNU C90. In C++, emit any and all
inline functions into the object file.
-fkeep-static-functionsstatic functions into the object file, even if the function
is never used.
-fkeep-static-constsstatic const when optimization isn't turned
on, even if the variables aren't referenced.
GCC enables this option by default. If you want to force the compiler to check if a variable is referenced, regardless of whether or not optimization is turned on, use the -fno-keep-static-consts option.
-fmerge-constantsThis option is the default for optimized compilation if the assembler and linker support it. Use -fno-merge-constants to inhibit this behavior.
Enabled at levels -O1, -O2, -O3, -Os.
-fmerge-all-constantsThis option implies -fmerge-constants. In addition to -fmerge-constants this considers e.g. even constant initialized arrays or initialized constant variables with integral or floating-point types. Languages like C or C++ require each variable, including multiple instances of the same variable in recursive calls, to have distinct locations, so using this option results in non-conforming behavior.
-fmodulo-sched-fmodulo-sched-allow-regmoves-fno-branch-count-regThe default is -fbranch-count-reg at -O1 and higher, except for -Og.
-fno-function-cseThis option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used.
The default is -ffunction-cse
-fno-zero-initialized-in-bssThis option turns off this behavior because some programs explicitly rely on variables going to the data section—e.g., so that the resulting executable can find the beginning of that section and/or make assumptions based on that.
The default is -fzero-initialized-in-bss.
-fthread-jumpsEnabled at levels -O1, -O2, -O3, -Os.
-fsplit-wide-typeslong
long on a 32-bit system, split the registers apart and allocate them
independently. This normally generates better code for those types,
but may make debugging more difficult.
Enabled at levels -O1, -O2, -O3, -Os.
-fsplit-wide-types-earlyThis is the default on some targets.
-fcse-follow-jumpsif statement with an
else clause, CSE follows the jump when the condition
tested is false.
Enabled at levels -O2, -O3, -Os.
-fcse-skip-blocksif statement with no else clause,
-fcse-skip-blocks causes CSE to follow the jump around the
body of the if.
Enabled at levels -O2, -O3, -Os.
-frerun-cse-after-loopEnabled at levels -O2, -O3, -Os.
-fgcseNote: When compiling a program using computed gotos, a GCC extension, you may get better run-time performance if you disable the global common subexpression elimination pass by adding -fno-gcse to the command line.
Enabled at levels -O2, -O3, -Os.
-fgcse-lmEnabled by default when -fgcse is enabled.
-fgcse-smNot enabled at any optimization level.
-fgcse-lasNot enabled at any optimization level.
-fgcse-after-reloadEnabled by -O3, -fprofile-use and -fauto-profile.
-faggressive-loop-optimizations-funconstrained-commons-fcrossjumpingEnabled at levels -O2, -O3, -Os.
-fauto-inc-dec-fdce-fdse-fif-conversionEnabled at levels -O1, -O2, -O3, -Os, but not with -Og.
-fif-conversion2Enabled at levels -O1, -O2, -O3, -Os, but not with -Og.
-fdeclone-ctor-dtorEnabled by -Os.
-fdelete-null-pointer-checksNote however that in some environments this assumption is not true. Use -fno-delete-null-pointer-checks to disable this optimization for programs that depend on that behavior.
This option is enabled by default on most targets. On Nios II ELF, it defaults to off. On AVR and MSP430, this option is completely disabled.
Passes that use the dataflow information are enabled independently at different optimization levels.
-fdevirtualize-fdevirtualize-speculatively-fdevirtualize-at-ltrans-fexpensive-optimizationsEnabled at levels -O2, -O3, -Os.
-freeEnabled for Alpha, AArch64 and x86 at levels -O2, -O3, -Os.
-fno-lifetime-dse-flive-range-shrinkage-fira-algorithm=algorithm-fira-region=region-fira-hoist-pressureThis option is enabled at level -Os for all targets.
-fira-loop-pressureThis option is enabled at level -O3 for some targets.
-fno-ira-share-save-slots-fno-ira-share-spill-slots-flra-rematEnabled at levels -O2, -O3, -Os.
-fdelayed-branchEnabled at levels -O1, -O2, -O3, -Os, but not at -Og.
-fschedule-insnsEnabled at levels -O2, -O3.
-fschedule-insns2Enabled at levels -O2, -O3, -Os.
-fno-sched-interblock-fno-sched-spec-fsched-pressure-fsched-spec-load-fsched-spec-load-dangerous-fsched-stalled-insns-fsched-stalled-insns=n-fsched-stalled-insns-dep-fsched-stalled-insns-dep=n-fsched2-use-superblocksThis only makes sense when scheduling after register allocation, i.e. with -fschedule-insns2 or at -O2 or higher.
-fsched-group-heuristic-fsched-critical-path-heuristic-fsched-spec-insn-heuristic-fsched-rank-heuristic-fsched-last-insn-heuristic-fsched-dep-count-heuristic-freschedule-modulo-scheduled-loops-fselective-scheduling-fselective-scheduling2-fsel-sched-pipelining-fsel-sched-pipelining-outer-loops-fsemantic-interposition-fshrink-wrap-fshrink-wrap-separate-fcaller-savesThis option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead.
Enabled at levels -O2, -O3, -Os.
-fcombine-stack-adjustmentsEnabled by default at -O1 and higher.
-fipa-raEnabled at levels -O2, -O3, -Os, however the option is disabled if generated code will be instrumented for profiling (-p, or -pg) or if callee's register usage cannot be known exactly (this happens on targets that do not expose prologues and epilogues in RTL).
-fconserve-stack-ftree-reassoc-fcode-hoisting-ftree-pre-ftree-partial-pre-ftree-forwprop-ftree-fre-ftree-phiprop-fhoist-adjacent-loads-ftree-copy-prop-fipa-pure-const-fipa-reference-fipa-reference-addressable-fipa-stack-alignment-fipa-pta-fipa-profilecold, noreturn, static constructors or destructors) are
identified. Cold functions and loop less parts of functions executed once are
then optimized for size.
Enabled by default at -O1 and higher.
-fipa-modref-fipa-cp-fipa-cp-clone-fipa-bit-cp-fipa-vrp-fipa-icfAlthough the behavior is similar to the Gold Linker's ICF optimization, GCC ICF works on different levels and thus the optimizations are not same - there are equivalences that are found only by GCC and equivalences found only by Gold.
This flag is enabled by default at -O2 and -Os.
-flive-patching=levelIf the compiler's optimization uses a function's body or information extracted from its body to optimize/change another function, the latter is called an impacted function of the former. If a function is patched, its impacted functions should be patched too.
The impacted functions are determined by the compiler's interprocedural optimizations. For example, a caller is impacted when inlining a function into its caller, cloning a function and changing its caller to call this new clone, or extracting a function's pureness/constness information to optimize its direct or indirect callers, etc.
Usually, the more IPA optimizations enabled, the larger the number of impacted functions for each function. In order to control the number of impacted functions and more easily compute the list of impacted function, IPA optimizations can be partially enabled at two different levels.
The level argument should be one of the following:
-flive-patching=inline-clone disables the following optimization flags:
-fwhole-program -fipa-pta -fipa-reference -fipa-ra
-fipa-icf -fipa-icf-functions -fipa-icf-variables
-fipa-bit-cp -fipa-vrp -fipa-pure-const
-fipa-reference-addressable
-fipa-stack-alignment -fipa-modref
In addition to all the flags that -flive-patching=inline-clone disables, -flive-patching=inline-only-static disables the following additional optimization flags:
-fipa-cp-clone -fipa-sra -fpartial-inlining -fipa-cp
When -flive-patching is specified without any value, the default value is inline-clone.
This flag is disabled by default.
Note that -flive-patching is not supported with link-time optimization (-flto).
-fisolate-erroneous-paths-dereference-fisolate-erroneous-paths-attributereturns_nonnull or nonnull
attribute. Isolate those paths from the main control flow and turn the
statement with erroneous or undefined behavior into a trap. This is not
currently enabled, but may be enabled by -O2 in the future.
-ftree-sink-ftree-bit-ccp-ftree-ccp-fssa-backprop-fssa-phiopt-ftree-switch-conversion-ftree-tail-merge-ftree-dce-ftree-builtin-call-dceerrno but are otherwise free of side effects. This flag is
enabled by default at -O2 and higher if -Os is not also
specified.
-ffinite-loopsThis option is enabled by default at -O2 for C++ with -std=c++11 or higher.
-ftree-dominator-opts-ftree-dse-ftree-ch-ftree-loop-optimize-ftree-loop-linear-floop-strip-mine-floop-block-fgraphite-identity-floop-nest-optimize-floop-parallelize-all-ftree-coalesce-vars-ftree-loop-if-convert-ftree-loop-distribution DO I = 1, N
A(I) = B(I) + C
D(I) = E(I) * F
ENDDO
is transformed to
DO I = 1, N
A(I) = B(I) + C
ENDDO
DO I = 1, N
D(I) = E(I) * F
ENDDO
This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile.
-ftree-loop-distribute-patternsThis pass distributes the initialization loops and generates a call to memset zero. For example, the loop
DO I = 1, N
A(I) = 0
B(I) = A(I) + I
ENDDO
is transformed to
DO I = 1, N
A(I) = 0
ENDDO
DO I = 1, N
B(I) = A(I) + I
ENDDO
and the initialization loop is transformed into a call to memset zero. This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile.
-floop-interchange for (int i = 0; i < N; i++)
for (int j = 0; j < N; j++)
for (int k = 0; k < N; k++)
c[i][j] = c[i][j] + a[i][k]*b[k][j];
is transformed to
for (int i = 0; i < N; i++)
for (int k = 0; k < N; k++)
for (int j = 0; j < N; j++)
c[i][j] = c[i][j] + a[i][k]*b[k][j];
This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile.
-floop-unroll-and-jam-ftree-loop-im-ftree-loop-ivcanon-ftree-scev-cprop-fivopts-ftree-parallelize-loops=n-ftree-pta-ftree-sra-fstore-merging-ftree-ter-ftree-slsr-ftree-vectorize-ftree-loop-vectorize-ftree-slp-vectorize-ftrivial-auto-var-init=choiceswitch statement. Using -Wtrivial-auto-var-init to report all
such cases.
The three values of choice are:
The default is ‘uninitialized’.
Note that the initializer values, whether ‘zero’ or ‘pattern’,
refer to data representation (in memory or machine registers), rather
than to their interpretation as numerical values. This distinction may
be important in languages that support types with biases or implicit
multipliers, and with such extensions as ‘hardbool’ (see Type Attributes). For example, a variable that uses 8 bits to represent
(biased) quantities in the range 160..400 will be initialized
with the bit patterns 0x00 or 0xFE, depending on
choice, whether or not these representations stand for values in
that range, and even if they do, the interpretation of the value held by
the variable will depend on the bias. A ‘hardbool’ variable that
uses say 0X5A and 0xA5 for false and true,
respectively, will trap with either ‘choice’ of trivial
initializer, i.e., ‘zero’ initialization will not convert to the
representation for false, even if it would for a static
variable of the same type. This means the initializer pattern doesn't
generally depend on the type of the initialized variable. One notable
exception is that (non-hardened) boolean variables that fit in registers
are initialized with false (zero), even when ‘pattern’ is
requested.
You can control this behavior for a specific variable by using the variable
attribute uninitialized (see Variable Attributes).
-fvect-cost-model=modelThe default cost model depends on other optimization flags and is either ‘dynamic’ or ‘cheap’.
-fsimd-cost-model=model-ftree-vrp-fsplit-paths-fsplit-ivs-in-unrollerA combination of -fweb and CSE is often sufficient to obtain the same effect. However, that is not reliable in cases where the loop body is more complicated than a single basic block. It also does not work at all on some architectures due to restrictions in the CSE pass.
This optimization is enabled by default.
-fvariable-expansion-in-unrollerThis optimization is enabled by default for PowerPC targets, but disabled by default otherwise.
-fpartial-inliningEnabled at levels -O2, -O3, -Os.
-fpredictive-commoningThis option is enabled at level -O3. It is also enabled by -fprofile-use and -fauto-profile.
-fprefetch-loop-arraysThis option may generate better or worse code; results are highly dependent on the structure of loops within the source code.
Disabled at level -Os.
-fno-printf-return-valuesprintf, snprintf, vsprintf, and
vsnprintf (but not printf of fprintf). This
transformation allows GCC to optimize or even eliminate branches based
on the known return value of these functions called with arguments that
are either constant, or whose values are known to be in a range that
makes determining the exact return value possible. For example, when
-fprintf-return-value is in effect, both the branch and the
body of the if statement (but not the call to snprint)
can be optimized away when i is a 32-bit or smaller integer
because the return value is guaranteed to be at most 8.
char buf[9];
if (snprintf (buf, "%08x", i) >= sizeof buf)
...
The -fprintf-return-value option relies on other optimizations and yields best results with -O2 and above. It works in tandem with the -Wformat-overflow and -Wformat-truncation options. The -fprintf-return-value option is enabled by default.
-fno-peephole-fno-peephole2-fpeephole is enabled by default. -fpeephole2 enabled at levels -O2, -O3, -Os.
-fno-guess-branch-probabilityGCC uses heuristics to guess branch probabilities if they are
not provided by profiling feedback (-fprofile-arcs). These
heuristics are based on the control flow graph. If some branch probabilities
are specified by __builtin_expect, then the heuristics are
used to guess branch probabilities for the rest of the control flow graph,
taking the __builtin_expect info into account. The interactions
between the heuristics and __builtin_expect can be complex, and in
some cases, it may be useful to disable the heuristics so that the effects
of __builtin_expect are easier to understand.
It is also possible to specify expected probability of the expression
with __builtin_expect_with_probability built-in function.
The default is -fguess-branch-probability at levels -O, -O2, -O3, -Os.
-freorder-blocksEnabled at levels -O1, -O2, -O3, -Os.
-freorder-blocks-algorithm=algorithmThe default is ‘simple’ at levels -O1, -Os, and ‘stc’ at levels -O2, -O3.
-freorder-blocks-and-partitionThis optimization is automatically turned off in the presence of exception handling or unwind tables (on targets using setjump/longjump or target specific scheme), for linkonce sections, for functions with a user-defined section attribute and on any architecture that does not support named sections. When -fsplit-stack is used this option is not enabled by default (to avoid linker errors), but may be enabled explicitly (if using a working linker).
Enabled for x86 at levels -O2, -O3, -Os.
-freorder-functions.text.hot for most frequently executed functions and
.text.unlikely for unlikely executed functions. Reordering is done by
the linker so object file format must support named sections and linker must
place them in a reasonable way.
This option isn't effective unless you either provide profile feedback
(see -fprofile-arcs for details) or manually annotate functions with
hot or cold attributes (see Common Function Attributes).
Enabled at levels -O2, -O3, -Os.
-fstrict-aliasingunsigned int can alias an int, but not a
void* or a double. A character type may alias any other
type.
Pay special attention to code like this:
union a_union {
int i;
double d;
};
int f() {
union a_union t;
t.d = 3.0;
return t.i;
}
The practice of reading from a different union member than the one most recently written to (called “type-punning”) is common. Even with -fstrict-aliasing, type-punning is allowed, provided the memory is accessed through the union type. So, the code above works as expected. See Structures unions enumerations and bit-fields implementation. However, this code might not:
int f() {
union a_union t;
int* ip;
t.d = 3.0;
ip = &t.i;
return *ip;
}
Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior, even if the cast uses a union type, e.g.:
int f() {
double d = 3.0;
return ((union a_union *) &d)->i;
}
The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.
-fipa-strict-aliasingThe -fipa-strict-aliasing option is enabled by default and is effective only in combination with -fstrict-aliasing.
-falign-functions-falign-functions=n-falign-functions=n:m-falign-functions=n:m:n2-falign-functions=n:m:n2:m2If m is not specified, it defaults to n.
Examples: -falign-functions=32 aligns functions to the next 32-byte boundary, -falign-functions=24 aligns to the next 32-byte boundary only if this can be done by skipping 23 bytes or less, -falign-functions=32:7 aligns to the next 32-byte boundary only if this can be done by skipping 6 bytes or less.
The second pair of n2:m2 values allows you to specify a secondary alignment: -falign-functions=64:7:32:3 aligns to the next 64-byte boundary if this can be done by skipping 6 bytes or less, otherwise aligns to the next 32-byte boundary if this can be done by skipping 2 bytes or less. If m2 is not specified, it defaults to n2.
Some assemblers only support this flag when n is a power of two; in that case, it is rounded up.
-fno-align-functions and -falign-functions=1 are equivalent and mean that functions are not aligned.
If n is not specified or is zero, use a machine-dependent default. The maximum allowed n option value is 65536.
Enabled at levels -O2, -O3.
-flimit-function-alignment-falign-labels-falign-labels=n-falign-labels=n:m-falign-labels=n:m:n2-falign-labels=n:m:n2:m2Parameters of this option are analogous to the -falign-functions option. -fno-align-labels and -falign-labels=1 are equivalent and mean that labels are not aligned.
If -falign-loops or -falign-jumps are applicable and are greater than this value, then their values are used instead.
If n is not specified or is zero, use a machine-dependent default which is very likely to be ‘1’, meaning no alignment. The maximum allowed n option value is 65536.
Enabled at levels -O2, -O3.
-falign-loops-falign-loops=n-falign-loops=n:m-falign-loops=n:m:n2-falign-loops=n:m:n2:m2If -falign-labels is greater than this value, then its value is used instead.
Parameters of this option are analogous to the -falign-functions option. -fno-align-loops and -falign-loops=1 are equivalent and mean that loops are not aligned. The maximum allowed n option value is 65536.
If n is not specified or is zero, use a machine-dependent default.
Enabled at levels -O2, -O3.
-falign-jumps-falign-jumps=n-falign-jumps=n:m-falign-jumps=n:m:n2-falign-jumps=n:m:n2:m2If -falign-labels is greater than this value, then its value is used instead.
Parameters of this option are analogous to the -falign-functions option. -fno-align-jumps and -falign-jumps=1 are equivalent and mean that loops are not aligned.
If n is not specified or is zero, use a machine-dependent default. The maximum allowed n option value is 65536.
Enabled at levels -O2, -O3.
-fno-allocation-dce-fallow-store-data-racesExamples of optimizations enabled by -fallow-store-data-races include hoisting or if-conversions that may cause a value that was already in memory to be re-written with that same value. Such re-writing is safe in a single threaded context but may be unsafe in a multi-threaded context. Note that on some processors, if-conversions may be required in order to enable vectorization.
Enabled at level -Ofast.
-funit-at-a-timeEnabled by default.
-fno-toplevel-reorderasm
statements. Output them in the same order that they appear in the
input file. When this option is used, unreferenced static variables
are not removed. This option is intended to support existing code
that relies on a particular ordering. For new code, it is better to
use attributes when possible.
-ftoplevel-reorder is the default at -O1 and higher, and also at -O0 if -fsection-anchors is explicitly requested. Additionally -fno-toplevel-reorder implies -fno-section-anchors.
-funreachable-traps__builtin_unreachable into traps, instead of using them for
optimization. This also affects any such calls implicitly generated
by the compiler.
This option has the same effect as -fsanitize=unreachable -fsanitize-trap=unreachable, but does not affect the values of those options. If -fsanitize=unreachable is enabled, that option takes priority over this one.
This option is enabled by default at -O0 and -Og.
-fwebEnabled by default with -funroll-loops.
-fwhole-programmain
and those merged by attribute externally_visible become static functions
and in effect are optimized more aggressively by interprocedural optimizers.
With -flto this option has a limited use. In most cases the precise list of symbols used or exported from the binary is known the resolution info passed to the link-time optimizer by the linker plugin. It is still useful if no linker plugin is used or during incremental link step when final code is produced (with -flto -flinker-output=nolto-rel).
-flto[=n]To use the link-time optimizer, -flto and optimization options should be specified at compile time and during the final link. It is recommended that you compile all the files participating in the same link with the same options and also specify those options at link time. For example:
gcc -c -O2 -flto foo.c
gcc -c -O2 -flto bar.c
gcc -o myprog -flto -O2 foo.o bar.o
The first two invocations to GCC save a bytecode representation of GIMPLE into special ELF sections inside foo.o and bar.o. The final invocation reads the GIMPLE bytecode from foo.o and bar.o, merges the two files into a single internal image, and compiles the result as usual. Since both foo.o and bar.o are merged into a single image, this causes all the interprocedural analyses and optimizations in GCC to work across the two files as if they were a single one. This means, for example, that the inliner is able to inline functions in bar.o into functions in foo.o and vice-versa.
Another (simpler) way to enable link-time optimization is:
gcc -o myprog -flto -O2 foo.c bar.c
The above generates bytecode for foo.c and bar.c, merges them together into a single GIMPLE representation and optimizes them as usual to produce myprog.
The important thing to keep in mind is that to enable link-time optimizations you need to use the GCC driver to perform the link step. GCC automatically performs link-time optimization if any of the objects involved were compiled with the -flto command-line option. You can always override the automatic decision to do link-time optimization by passing -fno-lto to the link command.
To make whole program optimization effective, it is necessary to make certain whole program assumptions. The compiler needs to know what functions and variables can be accessed by libraries and runtime outside of the link-time optimized unit. When supported by the linker, the linker plugin (see -fuse-linker-plugin) passes information to the compiler about used and externally visible symbols. When the linker plugin is not available, -fwhole-program should be used to allow the compiler to make these assumptions, which leads to more aggressive optimization decisions.
When a file is compiled with -flto without -fuse-linker-plugin, the generated object file is larger than a regular object file because it contains GIMPLE bytecodes and the usual final code (see -ffat-lto-objects). This means that object files with LTO information can be linked as normal object files; if -fno-lto is passed to the linker, no interprocedural optimizations are applied. Note that when -fno-fat-lto-objects is enabled the compile stage is faster but you cannot perform a regular, non-LTO link on them.
When producing the final binary, GCC only applies link-time optimizations to those files that contain bytecode. Therefore, you can mix and match object files and libraries with GIMPLE bytecodes and final object code. GCC automatically selects which files to optimize in LTO mode and which files to link without further processing.
Generally, options specified at link time override those specified at compile time, although in some cases GCC attempts to infer link-time options from the settings used to compile the input files.
If you do not specify an optimization level option -O at link time, then GCC uses the highest optimization level used when compiling the object files. Note that it is generally ineffective to specify an optimization level option only at link time and not at compile time, for two reasons. First, compiling without optimization suppresses compiler passes that gather information needed for effective optimization at link time. Second, some early optimization passes can be performed only at compile time and not at link time.
There are some code generation flags preserved by GCC when generating bytecodes, as they need to be used during the final link. Currently, the following options and their settings are taken from the first object file that explicitly specifies them: -fcommon, -fexceptions, -fnon-call-exceptions, -fgnu-tm and all the -m target flags.
The following options -fPIC, -fpic, -fpie and -fPIE are combined based on the following scheme:
-fPIC + -fpic = -fpic -fPIC + -fno-pic = -fno-pic -fpic/-fPIC + (no option) = (no option) -fPIC + -fPIE = -fPIE -fpic + -fPIE = -fpie -fPIC/-fpic + -fpie = -fpie
Certain ABI-changing flags are required to match in all compilation units, and trying to override this at link time with a conflicting value is ignored. This includes options such as -freg-struct-return and -fpcc-struct-return.
Other options such as -ffp-contract, -fno-strict-overflow, -fwrapv, -fno-trapv or -fno-strict-aliasing are passed through to the link stage and merged conservatively for conflicting translation units. Specifically -fno-strict-overflow, -fwrapv and -fno-trapv take precedence; and for example -ffp-contract=off takes precedence over -ffp-contract=fast. You can override them at link time.
Diagnostic options such as -Wstringop-overflow are passed through to the link stage and their setting matches that of the compile-step at function granularity. Note that this matters only for diagnostics emitted during optimization. Note that code transforms such as inlining can lead to warnings being enabled or disabled for regions if code not consistent with the setting at compile time.
When you need to pass options to the assembler via -Wa or -Xassembler make sure to either compile such translation units with -fno-lto or consistently use the same assembler options on all translation units. You can alternatively also specify assembler options at LTO link time.
To enable debug info generation you need to supply -g at compile time. If any of the input files at link time were built with debug info generation enabled the link will enable debug info generation as well. Any elaborate debug info settings like the dwarf level -gdwarf-5 need to be explicitly repeated at the linker command line and mixing different settings in different translation units is discouraged.
If LTO encounters objects with C linkage declared with incompatible types in separate translation units to be linked together (undefined behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be issued. The behavior is still undefined at run time. Similar diagnostics may be raised for other languages.
Another feature of LTO is that it is possible to apply interprocedural optimizations on files written in different languages:
gcc -c -flto foo.c
g++ -c -flto bar.cc
gfortran -c -flto baz.f90
g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
Notice that the final link is done with g++ to get the C++ runtime libraries and -lgfortran is added to get the Fortran runtime libraries. In general, when mixing languages in LTO mode, you should use the same link command options as when mixing languages in a regular (non-LTO) compilation.
If object files containing GIMPLE bytecode are stored in a library archive, say libfoo.a, it is possible to extract and use them in an LTO link if you are using a linker with plugin support. To create static libraries suitable for LTO, use gcc-ar and gcc-ranlib instead of ar and ranlib; to show the symbols of object files with GIMPLE bytecode, use gcc-nm. Those commands require that ar, ranlib and nm have been compiled with plugin support. At link time, use the flag -fuse-linker-plugin to ensure that the library participates in the LTO optimization process:
gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
With the linker plugin enabled, the linker extracts the needed GIMPLE files from libfoo.a and passes them on to the running GCC to make them part of the aggregated GIMPLE image to be optimized.
If you are not using a linker with plugin support and/or do not enable the linker plugin, then the objects inside libfoo.a are extracted and linked as usual, but they do not participate in the LTO optimization process. In order to make a static library suitable for both LTO optimization and usual linkage, compile its object files with -flto -ffat-lto-objects.
Link-time optimizations do not require the presence of the whole program to operate. If the program does not require any symbols to be exported, it is possible to combine -flto and -fwhole-program to allow the interprocedural optimizers to use more aggressive assumptions which may lead to improved optimization opportunities. Use of -fwhole-program is not needed when linker plugin is active (see -fuse-linker-plugin).
The current implementation of LTO makes no attempt to generate bytecode that is portable between different types of hosts. The bytecode files are versioned and there is a strict version check, so bytecode files generated in one version of GCC do not work with an older or newer version of GCC.
Link-time optimization does not work well with generation of debugging information on systems other than those using a combination of ELF and DWARF.
If you specify the optional n, the optimization and code generation done at link time is executed in parallel using n parallel jobs by utilizing an installed make program. The environment variable MAKE may be used to override the program used.
You can also specify -flto=jobserver to use GNU make's job server mode to determine the number of parallel jobs. This is useful when the Makefile calling GCC is already executing in parallel. You must prepend a ‘+’ to the command recipe in the parent Makefile for this to work. This option likely only works if MAKE is GNU make. Even without the option value, GCC tries to automatically detect a running GNU make's job server.
Use -flto=auto to use GNU make's job server, if available, or otherwise fall back to autodetection of the number of CPU threads present in your system.
-flto-partition=alg-flto-compression-level=n-fuse-linker-pluginThis option enables the extraction of object files with GIMPLE bytecode out of library archives. This improves the quality of optimization by exposing more code to the link-time optimizer. This information specifies what symbols can be accessed externally (by non-LTO object or during dynamic linking). Resulting code quality improvements on binaries (and shared libraries that use hidden visibility) are similar to -fwhole-program. See -flto for a description of the effect of this flag and how to use it.
This option is enabled by default when LTO support in GCC is enabled and GCC was configured for use with a linker supporting plugins (GNU ld 2.21 or newer or gold).
-ffat-lto-objects-fno-fat-lto-objects improves compilation time over plain LTO, but requires the complete toolchain to be aware of LTO. It requires a linker with linker plugin support for basic functionality. Additionally, nm, ar and ranlib need to support linker plugins to allow a full-featured build environment (capable of building static libraries etc). GCC provides the gcc-ar, gcc-nm, gcc-ranlib wrappers to pass the right options to these tools. With non fat LTO makefiles need to be modified to use them.
Note that modern binutils provide plugin auto-load mechanism. Installing the linker plugin into $libdir/bfd-plugins has the same effect as usage of the command wrappers (gcc-ar, gcc-nm and gcc-ranlib).
The default is -fno-fat-lto-objects on targets with linker plugin support.
-fcompare-elimThis pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete.
Enabled at levels -O1, -O2, -O3, -Os.
-fcprop-registersEnabled at levels -O1, -O2, -O3, -Os.
-fprofile-correctionThis option is enabled by -fauto-profile.
-fprofile-partial-training-fprofile-use all portions of programs not executed during train
run are optimized agressively for size rather than speed. In some cases it is
not practical to train all possible hot paths in the program. (For
example, program may contain functions specific for a given hardware and
trianing may not cover all hardware configurations program is run on.) With
-fprofile-partial-training profile feedback will be ignored for all
functions not executed during the train run leading them to be optimized as if
they were compiled without profile feedback. This leads to better performance
when train run is not representative but also leads to significantly bigger
code.
-fprofile-use-fprofile-use=path -fbranch-probabilities -fprofile-values
-funroll-loops -fpeel-loops -ftracer -fvpt
-finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp
-fpredictive-commoning -fsplit-loops -funswitch-loops
-fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize
-fvect-cost-model=dynamic -ftree-loop-distribute-patterns
-fprofile-reorder-functions
Before you can use this option, you must first generate profiling information. See Instrumentation Options, for information about the -fprofile-generate option.
By default, GCC emits an error message if the feedback profiles do not match the source code. This error can be turned into a warning by using -Wno-error=coverage-mismatch. Note this may result in poorly optimized code. Additionally, by default, GCC also emits a warning message if the feedback profiles do not exist (see -Wmissing-profile).
If path is specified, GCC looks at the path to find the profile feedback data files. See -fprofile-dir.
-fauto-profile-fauto-profile=path -fbranch-probabilities -fprofile-values
-funroll-loops -fpeel-loops -ftracer -fvpt
-finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp
-fpredictive-commoning -fsplit-loops -funswitch-loops
-fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize
-fvect-cost-model=dynamic -ftree-loop-distribute-patterns
-fprofile-correction
path is the name of a file containing AutoFDO profile information. If omitted, it defaults to fbdata.afdo in the current directory.
Producing an AutoFDO profile data file requires running your program with the perf utility on a supported GNU/Linux target system. For more information, see https://perf.wiki.kernel.org/.
E.g.
perf record -e br_inst_retired:near_taken -b -o perf.data \
-- your_program
Then use the create_gcov tool to convert the raw profile data to a format that can be used by GCC. You must also supply the unstripped binary for your program to this tool. See https://github.com/google/autofdo.
E.g.
create_gcov --binary=your_program.unstripped --profile=perf.data \
--gcov=profile.afdo
-fpreserve-control-flowThe following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness. All must be specifically enabled.
-ffloat-storeThis option prevents undesirable excess precision on machines such as
the 68000 where the floating registers (of the 68881) keep more
precision than a double is supposed to have. Similarly for the
x86 architecture. For most programs, the excess precision does only
good, but a few programs rely on the precise definition of IEEE floating
point. Use -ffloat-store for such programs, after modifying
them to store all pertinent intermediate computations into variables.
-fexcess-precision=style-fexcess-precision=standard is not implemented for languages other than C or C++. On the x86, it has no effect if -mfpmath=sse or -mfpmath=sse+387 is specified; in the former case, IEEE semantics apply without excess precision, and in the latter, rounding is unpredictable.
-ffast-mathThis option causes the preprocessor macro __FAST_MATH__ to be defined.
This option is not turned on by any -O option besides -Ofast since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications.
-fno-math-errnoerrno after calling math functions that are executed
with a single instruction, e.g., sqrt. A program that relies on
IEEE exceptions for math error handling may want to use this flag
for speed while maintaining IEEE arithmetic compatibility.
This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications.
The default is -fmath-errno.
On Darwin systems, the math library never sets errno. There is
therefore no reason for the compiler to consider the possibility that
it might, and -fno-math-errno is the default.
-funsafe-math-optimizationsThis option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. Enables -fno-signed-zeros, -fno-trapping-math, -fassociative-math and -freciprocal-math.
The default is -fno-unsafe-math-optimizations.
-fassociative-math(x + 2**52) - 2**52. May also reorder floating-point comparisons
and thus may not be used when ordered comparisons are required.
This option requires that both -fno-signed-zeros and
-fno-trapping-math be in effect. Moreover, it doesn't make
much sense with -frounding-math. For Fortran the option
is automatically enabled when both -fno-signed-zeros and
-fno-trapping-math are in effect.
The default is -fno-associative-math.
-freciprocal-mathx / y
can be replaced with x * (1/y), which is useful if (1/y)
is subject to common subexpression elimination. Note that this loses
precision and increases the number of flops operating on the value.
The default is -fno-reciprocal-math.
-ffinite-math-onlyThis option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications.
The default is -fno-finite-math-only.
-fno-signed-zerosThe default is -fsigned-zeros.
-fno-trapping-mathThis option should never be turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions.
The default is -ftrapping-math.
Future versions of GCC may provide finer control of this setting
using C99's FENV_ACCESS pragma. This command-line option
will be used along with -frounding-math to specify the
default state for FENV_ACCESS.
-frounding-mathThe default is -fno-rounding-math.
This option is experimental and does not currently guarantee to
disable all GCC optimizations that are affected by rounding mode.
Future versions of GCC may provide finer control of this setting
using C99's FENV_ACCESS pragma. This command-line option
will be used along with -ftrapping-math to specify the
default state for FENV_ACCESS.
-fsignaling-nansThis option causes the preprocessor macro __SUPPORT_SNAN__ to
be defined.
The default is -fno-signaling-nans.
This option is experimental and does not currently guarantee to disable all GCC optimizations that affect signaling NaN behavior.
-fno-fp-int-builtin-inexactceil, floor,
round and trunc, and their float and long
double variants, to generate code that raises the “inexact”
floating-point exception for noninteger arguments. ISO C99 and C11
allow these functions to raise the “inexact” exception, but ISO/IEC
TS 18661-1:2014, the C bindings to IEEE 754-2008, as integrated into
ISO C2X, does not allow these functions to do so.
The default is -ffp-int-builtin-inexact, allowing the exception to be raised, unless C2X or a later C standard is selected. This option does nothing unless -ftrapping-math is in effect.
Even if -fno-fp-int-builtin-inexact is used, if the functions generate a call to a library function then the “inexact” exception may be raised if the library implementation does not follow TS 18661.
-fsingle-precision-constant-fcx-limited-rangeNaN
+ I*NaN, with an attempt to rescue the situation in that case. The
default is -fno-cx-limited-range, but is enabled by
-ffast-math.
This option controls the default setting of the ISO C99
CX_LIMITED_RANGE pragma. Nevertheless, the option applies to
all languages.
-fcx-fortran-rulesNaN
+ I*NaN, with an attempt to rescue the situation in that case.
The default is -fno-cx-fortran-rules.
The following options control optimizations that may improve performance, but are not enabled by any -O options. This section includes experimental options that may produce broken code.
-fbranch-probabilitiesWith -fbranch-probabilities, GCC puts a ‘REG_BR_PROB’ note on each ‘JUMP_INSN’ and ‘CALL_INSN’. These can be used to improve optimization. Currently, they are only used in one place: in reorg.cc, instead of guessing which path a branch is most likely to take, the ‘REG_BR_PROB’ values are used to exactly determine which path is taken more often.
Enabled by -fprofile-use and -fauto-profile.
-fprofile-valuesWith -fbranch-probabilities, it reads back the data gathered from profiling values of expressions for usage in optimizations.
Enabled by -fprofile-generate, -fprofile-use, and -fauto-profile.
-fprofile-reorder-functionsEnabled with -fprofile-use.
-fvptWith -fbranch-probabilities, it reads back the data gathered and actually performs the optimizations based on them. Currently the optimizations include specialization of division operations using the knowledge about the value of the denominator.
Enabled with -fprofile-use and -fauto-profile.
-frename-registersEnabled by default with -funroll-loops.
-fschedule-fusionEnabled at levels -O2, -O3, -Os.
-ftracerEnabled by -fprofile-use and -fauto-profile.
-funroll-loopsEnabled by -fprofile-use and -fauto-profile.
-funroll-all-loops-fpeel-loopsEnabled by -O3, -fprofile-use, and -fauto-profile.
-fmove-loop-invariants-fmove-loop-stores-fsplit-loopsEnabled by -fprofile-use and -fauto-profile.
-funswitch-loopsEnabled by -fprofile-use and -fauto-profile.
-fversion-loops-for-strides for (int i = 0; i < n; ++i)
x[i * stride] = ...;
becomes:
if (stride == 1)
for (int i = 0; i < n; ++i)
x[i] = ...;
else
for (int i = 0; i < n; ++i)
x[i * stride] = ...;
This is particularly useful for assumed-shape arrays in Fortran where (for example) it allows better vectorization assuming contiguous accesses. This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile.
-ffunction-sections-fdata-sectionsUse these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space. Most systems using the ELF object format have linkers with such optimizations. On AIX, the linker rearranges sections (CSECTs) based on the call graph. The performance impact varies.
Together with a linker garbage collection (linker --gc-sections option) these options may lead to smaller statically-linked executables (after stripping).
On ELF/DWARF systems these options do not degenerate the quality of the debug information. There could be issues with other object files/debug info formats.
Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker create larger object and executable files and are also slower. These options affect code generation. They prevent optimizations by the compiler and assembler using relative locations inside a translation unit since the locations are unknown until link time. An example of such an optimization is relaxing calls to short call instructions.
-fstdarg-opt-fsection-anchorsFor example, the implementation of the following function foo:
static int a, b, c;
int foo (void) { return a + b + c; }
usually calculates the addresses of all three variables, but if you compile it with -fsection-anchors, it accesses the variables from a common anchor point instead. The effect is similar to the following pseudocode (which isn't valid C):
int foo (void)
{
register int *xr = &x;
return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
}
Not all targets support this option.
-fzero-call-used-regs=choiceThe possible values of choice are the same as for the
zero_call_used_regs attribute (see Function Attributes).
The default is ‘skip’.
You can control this behavior for a specific function by using the function
attribute zero_call_used_regs (see Function Attributes).
--param name=valueThe names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases.
In order to get the minimal, maximal and default values of a parameter, use the --help=param -Q options.
In each case, the value is an integer. The following choices of name are recognized for all targets:
predictable-branch-outcomemax-rtl-if-conversion-insnsmax-rtl-if-conversion-predictable-costmax-crossjump-edgesmin-crossjump-insnsmax-grow-copy-bb-insnsmax-goto-duplication-insnsmax-delay-slot-insn-searchmax-delay-slot-live-searchmax-gcse-memorykB that can be allocated in
order to perform the global common subexpression elimination
optimization. If more memory than specified is required, the
optimization is not done.
max-gcse-insertion-ratiomax-pending-list-lengthmax-modulo-backtrack-attemptsmax-inline-functions-called-once-loop-depthmax-inline-functions-called-once-insnsmax-inline-insns-singlemax-inline-insns-automax-inline-insns-smallmax-inline-insns-sizeuninlined-function-insnsuninlined-function-timeinline-heuristics-hint-percentuninlined-thunk-insnsuninlined-thunk-timeinline-min-speeduplarge-function-insnslarge-function-growthlarge-unit-insnslazy-modulesinline-unit-growthipa-cp-unit-growthipa-cp-large-unit-insnslarge-stack-framelarge-stack-frame-growthmax-inline-insns-recursivemax-inline-insns-recursive-auto--param max-inline-insns-recursive applies to functions
declared inline.
For functions not declared inline, recursive inlining
happens only when -finline-functions (included in -O3) is
enabled; --param max-inline-insns-recursive-auto applies instead.
max-inline-recursive-depthmax-inline-recursive-depth-auto--param max-inline-recursive-depth applies to functions
declared inline. For functions not declared inline, recursive inlining
happens only when -finline-functions (included in -O3) is
enabled; --param max-inline-recursive-depth-auto applies instead.
min-inline-recursive-probabilityWhen profile feedback is available (see -fprofile-generate) the actual
recursion depth can be guessed from the probability that function recurses
via a given call expression. This parameter limits inlining only to call
expressions whose probability exceeds the given threshold (in percents).
early-inlining-insnsmax-early-inliner-iterationscomdat-sharing-probabilitymodref-max-basesmodref-max-refsmodref-max-accessesmodref-max-testsmodref-max-depthmodref-max-escape-pointsmodref-max-adjustmentsprofile-func-internal-idmin-vect-loop-boundgcse-cost-distance-ratiogcse-unrestricted-costmax-hoist-depthmax-tail-merge-comparisonsmax-tail-merge-iterationsstore-merging-allow-unalignedmax-stores-to-mergemax-store-chains-to-trackmax-stores-to-trackmax-unrolled-insnsmax-average-unrolled-insnsmax-unroll-timesmax-peeled-insnsmax-peel-timesmax-peel-branchesmax-completely-peeled-insnsmax-completely-peel-timesmax-completely-peel-loop-nest-depthmax-unswitch-insnsmax-unswitch-depthlim-expensivemin-loop-cond-split-probiv-consider-all-candidates-boundiv-max-considered-usesiv-always-prune-cand-set-boundavg-loop-niterdse-max-object-sizedse-max-alias-queries-per-storescev-max-expr-sizescev-max-expr-complexitymax-tree-if-conversion-phi-argsvect-max-layout-candidatesvect-max-version-for-alignment-checksvect-max-version-for-alias-checksvect-max-peeling-for-alignmentmax-iterations-to-trackhot-bb-count-fractionhot-bb-count-ws-permillehot-bb-frequency-fractionunlikely-bb-count-fractionmax-predicted-iterationsbuiltin-expect-probabilitybuiltin-string-cmp-inline-lengthalign-thresholdalign-loop-iterationstracer-dynamic-coveragetracer-dynamic-coverage-feedbackThe tracer-dynamic-coverage-feedback parameter
is used only when profile
feedback is available. The real profiles (as opposed to statically estimated
ones) are much less balanced allowing the threshold to be larger value.
tracer-max-code-growthtracer-min-branch-ratiotracer-min-branch-probabilitytracer-min-branch-probability-feedbackSimilarly to tracer-dynamic-coverage two parameters are
provided. tracer-min-branch-probability-feedback is used for
compilation with profile feedback and tracer-min-branch-probability
compilation without. The value for compilation with profile feedback
needs to be more conservative (higher) in order to make tracer
effective.
stack-clash-protection-guard-sizestack-clash-protection-probe-intervalmax-cse-path-lengthmax-cse-insnsggc-min-expandThe default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
RAM >= 1GB. If getrlimit is available, the notion of “RAM” is
the smallest of actual RAM and RLIMIT_DATA or RLIMIT_AS. If
GCC is not able to calculate RAM on a particular platform, the lower
bound of 30% is used. Setting this parameter and
ggc-min-heapsize to zero causes a full collection to occur at
every opportunity. This is extremely slow, but can be useful for
debugging.
ggc-min-heapsizeThe default is the smaller of RAM/8, RLIMIT_RSS, or a limit that
tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
with a lower bound of 4096 (four megabytes) and an upper bound of
131072 (128 megabytes). If GCC is not able to calculate RAM on a
particular platform, the lower bound is used. Setting this parameter
very large effectively disables garbage collection. Setting this
parameter and ggc-min-expand to zero causes a full collection
to occur at every opportunity.
max-reload-search-insnsmax-cselib-memory-locationsmax-sched-ready-insnsmax-sched-region-blocksmax-pipeline-region-blocksmax-sched-region-insnsmax-pipeline-region-insnsmin-spec-probmax-sched-extend-regions-itersmax-sched-insn-conflict-delaysched-spec-prob-cutoffsched-state-edge-prob-cutoffsched-mem-true-dep-costselsched-max-lookaheadselsched-max-sched-timesselsched-insns-to-renamesms-min-scmax-last-value-rtlmax-combine-insnsinteger-share-limitssp-buffer-sizemin-size-for-stack-sharingmax-jump-thread-duplication-stmtsmax-jump-thread-pathsmax-fields-for-field-sensitiveprefetch-latencysimultaneous-prefetchesl1-cache-line-sizel1-cache-sizel2-cache-sizeprefetch-dynamic-stridesSet to 1 if the prefetch hints should be issued for non-constant
strides. Set to 0 if prefetch hints should be issued only for strides that
are known to be constant and below prefetch-minimum-stride.
prefetch-minimum-strideThis setting is useful for processors that have hardware prefetchers, in which case there may be conflicts between the hardware prefetchers and the software prefetchers. If the hardware prefetchers have a maximum stride they can handle, it should be used here to improve the use of software prefetchers.
A value of -1 means we don't have a threshold and therefore prefetch hints can be issued for any constant stride.
This setting is only useful for strides that are known and constant.
destructive-interference-sizeconstructive-interference-sizestd::hardware_destructive_interference_size and
std::hardware_constructive_interference_size. The destructive
interference size is the minimum recommended offset between two
independent concurrently-accessed objects; the constructive
interference size is the maximum recommended size of contiguous memory
accessed together. Typically both will be the size of an L1 cache
line for the target, in bytes. For a generic target covering a range of L1
cache line sizes, typically the constructive interference size will be
the small end of the range and the destructive size will be the large
end.
The destructive interference size is intended to be used for layout, and thus has ABI impact. The default value is not expected to be stable, and on some targets varies with -mtune, so use of this variable in a context where ABI stability is important, such as the public interface of a library, is strongly discouraged; if it is used in that context, users can stabilize the value using this option.
The constructive interference size is less sensitive, as it is typically only used in a ‘static_assert’ to make sure that a type fits within a cache line.
See also -Winterference-size.
loop-interchange-max-num-stmtsloop-interchange-stride-ratiomin-insn-to-prefetch-ratioprefetch-min-insn-to-mem-ratiouse-canonical-typesswitch-conversion-max-branch-ratiomax-partial-antic-lengthrpo-vn-max-loop-depthsccvn-max-alias-queries-per-accessira-max-loops-numira-max-conflict-table-sizeira-loop-reserved-regsira-consider-dup-in-all-altsira-simple-lra-insn-thresholdlra-inheritance-ebb-probability-cutoffloop-invariant-max-bbs-in-looploop-max-datarefs-for-datadepsmax-vartrack-sizemax-vartrack-expr-depthmax-debug-marker-countmin-nondebug-insn-uidipa-sra-deref-prob-thresholdipa-sra-ptr-growth-factoripa-sra-ptrwrap-growth-factoripa-sra-max-replacementssra-max-scalarization-size-Ospeedsra-max-scalarization-size-Osizesra-max-propagationstm-max-aggregate-sizegraphite-max-nb-scop-paramshardcfr-max-blockshardcfr-max-inline-blocksloop-block-tile-sizeipa-jump-function-lookupsipa-cp-value-list-sizeipa-cp-eval-thresholdipa-cp-max-recursive-depthipa-cp-min-recursive-probabilityipa-cp-profile-count-baseipa-cp-recursive-freq-factoripa-cp-recursion-penaltyipa-cp-single-call-penaltyipa-max-agg-itemsipa-cp-loop-hint-bonusipa-max-loop-predicatesipa-max-aa-stepsipa-max-switch-predicate-boundsipa-max-param-expr-opslto-partitionslto-min-partitionlto-max-partitionlto-max-streaming-parallelismcxx-max-namespaces-for-diagnostic-helpsink-frequency-thresholdmax-stores-to-sinkcase-values-thresholdjump-table-max-growth-ratio-for-sizejump-table-max-growth-ratio-for-speedtree-reassoc-widthsched-pressure-algorithmThe default choice depends on the target.
max-slsr-cand-scanasan-globalsasan-stackasan-instrument-readsasan-instrument-writesasan-memintrinasan-use-after-returnNote: By default the check is disabled at run time. To enable it,
add detect_stack_use_after_return=1 to the environment variable
ASAN_OPTIONS.
asan-instrumentation-with-call-thresholdasan-kernel-mem-intrinsic-prefixmemcpy, memset and memmove
with ‘__asan_’ or ‘__hwasan_’
for -fsanitize=kernel-address or ‘-fsanitize=kernel-hwaddress’,
respectively.
hwasan-instrument-stackhwasan-random-frame-taghwasan-instrument-allocashwasan-instrument-readshwasan-instrument-writeshwasan-instrument-mem-intrinsicsuse-after-scope-direct-emission-thresholdtsan-distinguish-volatiletsan-instrument-func-entry-exitmax-fsm-thread-path-insnsthreader-debugparloops-chunk-sizeparloops-scheduleparloops-min-per-threadmax-ssa-name-query-depthmax-speculative-devirt-maydefsevrp-sparse-thresholdranger-debugevrp-switch-limitunroll-jam-min-percentunroll-jam-max-unrollmax-rtl-if-conversion-unpredictable-costmax-variable-expansions-in-unrollerpartial-inlining-entry-probabilitymax-tracked-strlensgcse-after-reload-partial-fractiongcse-after-reload-critical-fractionmax-loop-header-insnsvect-epilogues-nomaskvect-partial-vector-usagevect-inner-loop-cost-factorvect-induction-floatavoid-fma-max-bitssms-loop-average-count-thresholdsms-dfa-historygraphite-allow-codegen-errorssms-max-ii-factorlra-max-considered-reload-pseudosmax-pow-sqrt-depthmax-dse-active-local-storesasan-instrument-allocasmax-iterations-computation-costmax-isl-operationsgraphite-max-arrays-per-scopmax-vartrack-reverse-op-sizefsm-scale-path-stmtsuninit-control-dep-attemptsuninit-max-chain-lenuninit-max-num-chainssched-autopref-queue-depthloop-versioning-max-inner-insnsloop-versioning-max-outer-insnsssa-name-def-chain-limitstore-merging-max-sizehash-table-verification-limitmax-find-base-term-valuesanalyzer-max-enodes-per-program-pointanalyzer-max-constraintsanalyzer-min-snodes-for-call-summaryanalyzer-max-enodes-for-full-dumpanalyzer-max-recursion-depthanalyzer-max-svalue-depthanalyzer-max-infeasible-edgesgimple-fe-computed-hot-bb-thresholdanalyzer-bb-explosion-factorranger-logical-depthranger-recompute-depthrelation-block-limitmin-pagesizeopenacc-kernelsopenacc-privatizationThe following choices of name are available on AArch64 targets:
aarch64-sve-compare-costsUsing unpacked vectors includes storing smaller elements in larger
containers and accessing elements with extending loads and truncating
stores.
aarch64-float-recp-precisionaarch64-double-recp-precisionaarch64-autovec-preferenceaarch64-loop-vect-issue-rate-nitersaarch64-vect-unroll-limitThe following choices of name are available on i386 and x86_64 targets:
x86-stlf-window-ninsnsx86-stv-max-visitsGCC supports a number of command-line options that control adding run-time instrumentation to the code it normally generates. For example, one purpose of instrumentation is collect profiling statistics for use in finding program hot spots, code coverage analysis, or profile-guided optimizations. Another class of program instrumentation is adding run-time checking to detect programming errors like invalid pointer dereferences or out-of-bounds array accesses, as well as deliberately hostile attacks such as stack smashing or C++ vtable hijacking. There is also a general hook which can be used to implement other forms of tracing or function-level instrumentation for debug or program analysis purposes.
-p-pgYou can use the function attribute no_instrument_function to
suppress profiling of individual functions when compiling with these options.
See Common Function Attributes.
-fprofile-arcsWhen the compiled program exits it saves this data to a file called auxname.gcda for each source file. The data may be used for profile-directed optimizations (-fbranch-probabilities), or for test coverage analysis (-ftest-coverage). Each object file's auxname is generated from the name of the output file, if explicitly specified and it is not the final executable, otherwise it is the basename of the source file. In both cases any suffix is removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda for output file specified as -o dir/foo.o).
Note that if a command line directly links source files, the corresponding
.gcda files will be prefixed with the unsuffixed name of the output file.
E.g. gcc a.c b.c -o binary would generate binary-a.gcda and
binary-b.gcda files.
See Cross-profiling.
--coveragefork calls are
detected and correctly handled without double counting.
Moreover, an object file can be recompiled multiple times and the corresponding .gcda file merges as long as the source file and the compiler options are unchanged.
With -fprofile-arcs, for each function of your program GCC creates a program flow graph, then finds a spanning tree for the graph. Only arcs that are not on the spanning tree have to be instrumented: the compiler adds code to count the number of times that these arcs are executed. When an arc is the only exit or only entrance to a block, the instrumentation code can be added to the block; otherwise, a new basic block must be created to hold the instrumentation code.
-ftest-coverage-fprofile-abs-path-fprofile-dir=pathWhen an executable is run in a massive parallel environment, it is recommended to save profile to different folders. That can be done with variables in path that are exported during run-time:
%p%q{VAR}-fprofile-generate-fprofile-generate=pathThe following options are enabled: -fprofile-arcs, -fprofile-values, -finline-functions, and -fipa-bit-cp.
If path is specified, GCC looks at the path to find the profile feedback data files. See -fprofile-dir.
To optimize the program based on the collected profile information, use -fprofile-use. See Optimize Options, for more information.
-fprofile-info-section-fprofile-info-section=name.gcov_info. A pointer to the
profile information generated by -fprofile-arcs is placed in the
specified section for each translation unit. This option disables the profile
information registration through a constructor and it disables the profile
information processing through a destructor. This option is not intended to be
used in hosted environments such as GNU/Linux. It targets freestanding
environments (for example embedded systems) with limited resources which do not
support constructors/destructors or the C library file I/O.
The linker could collect the input sections in a continuous memory block and define start and end symbols. A GNU linker script example which defines a linker output section follows:
.gcov_info :
{
PROVIDE (__gcov_info_start = .);
KEEP (*(.gcov_info))
PROVIDE (__gcov_info_end = .);
}
The program could dump the profiling information registered in this linker set for example like this:
#include <gcov.h>
#include <stdio.h>
#include <stdlib.h>
extern const struct gcov_info *const __gcov_info_start[];
extern const struct gcov_info *const __gcov_info_end[];
static void
dump (const void *d, unsigned n, void *arg)
{
const unsigned char *c = d;
for (unsigned i = 0; i < n; ++i)
printf ("%02x", c[i]);
}
static void
filename (const char *f, void *arg)
{
__gcov_filename_to_gcfn (f, dump, arg );
}
static void *
allocate (unsigned length, void *arg)
{
return malloc (length);
}
static void
dump_gcov_info (void)
{
const struct gcov_info *const *info = __gcov_info_start;
const struct gcov_info *const *end = __gcov_info_end;
/* Obfuscate variable to prevent compiler optimizations. */
__asm__ ("" : "+r" (info));
while (info != end)
{
void *arg = NULL;
__gcov_info_to_gcda (*info, filename, dump, allocate, arg);
putchar ('\n');
++info;
}
}
int
main (void)
{
dump_gcov_info ();
return 0;
}
The merge-stream subcommand of gcov-tool may be used to
deserialize the data stream generated by the __gcov_filename_to_gcfn and
__gcov_info_to_gcda functions and merge the profile information into
.gcda files on the host filesystem.
-fprofile-note=path-fprofile-prefix-path=path-fprofile-prefix-map=old=new-fprofile-update=methodWarning: When an application does not properly join all threads (or creates an detached thread), a profile file can be still corrupted.
Using ‘prefer-atomic’ would be transformed either to ‘atomic’, when supported by a target, or to ‘single’ otherwise. The GCC driver automatically selects ‘prefer-atomic’ when -pthread is present in the command line.
-fprofile-filter-files=regexFor example, -fprofile-filter-files=main\.c;module.*\.c will instrument only main.c and all C files starting with 'module'.
-fprofile-exclude-files=regexFor example, -fprofile-exclude-files=/usr/.* will prevent instrumentation of all files that are located in the /usr/ folder.
-fprofile-reproducible=[multithreaded|parallel-runs|serial]-fprofile-generate. This makes it possible to rebuild program
with same outcome which is useful, for example, for distribution
packages.
With -fprofile-reproducible=serial the profile gathered by
-fprofile-generate is reproducible provided the trained program
behaves the same at each invocation of the train run, it is not
multi-threaded and profile data streaming is always done in the same
order. Note that profile streaming happens at the end of program run but
also before fork function is invoked.
Note that it is quite common that execution counts of some part of
programs depends, for example, on length of temporary file names or
memory space randomization (that may affect hash-table collision rate).
Such non-reproducible part of programs may be annotated by
no_instrument_function function attribute. gcov-dump with
-l can be used to dump gathered data and verify that they are
indeed reproducible.
With -fprofile-reproducible=parallel-runs collected profile
stays reproducible regardless the order of streaming of the data into
gcda files. This setting makes it possible to run multiple instances of
instrumented program in parallel (such as with make -j). This
reduces quality of gathered data, in particular of indirect call
profiling.
-fsanitize=addresshelp=1,
the available options are shown at startup of the instrumented program. See
https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags
for a list of supported options.
The option cannot be combined with -fsanitize=thread or
-fsanitize=hwaddress. Note that the only target
-fsanitize=hwaddress is currently supported on is AArch64.
To get more accurate stack traces, it is possible to use options such as -O0, -O1, or -Og (which, for instance, prevent most function inlining), -fno-optimize-sibling-calls (which prevents optimizing sibling and tail recursive calls; this option is implicit for -O0, -O1, or -Og), or -fno-ipa-icf (which disables Identical Code Folding for functions). Since multiple runs of the program may yield backtraces with different addresses due to ASLR (Address Space Layout Randomization), it may be desirable to turn ASLR off. On Linux, this can be achieved with ‘setarch `uname -m` -R ./prog’.
-fsanitize=kernel-address-fsanitize=hwaddresshelp=1,
the available options are shown at startup of the instrumented program.
The option cannot be combined with -fsanitize=thread or
-fsanitize=address, and is currently only available on AArch64.
-fsanitize=kernel-hwaddressNote: This option has different defaults to the -fsanitize=hwaddress. Instrumenting the stack and alloca calls are not on by default but are still possible by specifying the command-line options --param hwasan-instrument-stack=1 and --param hwasan-instrument-allocas=1 respectively. Using a random frame tag is not implemented for kernel instrumentation.
-fsanitize=pointer-comparedetect_invalid_pointer_pairs=2 to the environment variable
ASAN_OPTIONS. Using detect_invalid_pointer_pairs=1 detects
invalid operation only when both pointers are non-null.
-fsanitize=pointer-subtractdetect_invalid_pointer_pairs=2 to the environment variable
ASAN_OPTIONS. Using detect_invalid_pointer_pairs=1 detects
invalid operation only when both pointers are non-null.
-fsanitize=shadow-call-stackCurrently it only supports the aarch64 platform. It is specifically designed for linux kernels that enable the CONFIG_SHADOW_CALL_STACK option. For the user space programs, runtime support is not currently provided in libc and libgcc. Users who want to use this feature in user space need to provide their own support for the runtime. It should be noted that this may cause the ABI rules to be broken.
On aarch64, the instrumentation makes use of the platform register x18.
This generally means that any code that may run on the same thread as code
compiled with ShadowCallStack must be compiled with the flag
-ffixed-x18, otherwise functions compiled without
-ffixed-x18 might clobber x18 and so corrupt the shadow
stack pointer.
Also, because there is no userspace runtime support, code compiled with ShadowCallStack cannot use exception handling. Use -fno-exceptions to turn off exceptions.
See https://clang.llvm.org/docs/ShadowCallStack.html for more details.
-fsanitize=threadNote that sanitized atomic builtins cannot throw exceptions when operating on invalid memory addresses with non-call exceptions (-fnon-call-exceptions).
-fsanitize=leakmalloc
and other allocator functions. See
https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer for more
details. The run-time behavior can be influenced using the
LSAN_OPTIONS environment variable.
The option cannot be combined with -fsanitize=thread.
-fsanitize=undefined-fsanitize=shift-fsanitize=shift-exponent-fsanitize=shift-base-fsanitize=integer-divide-by-zero-fsanitize=unreachable__builtin_unreachable
call into a diagnostics message call instead. When reaching the
__builtin_unreachable call, the behavior is undefined.
-fsanitize=vla-bound-fsanitize=null-fsanitize=return-fsanitize=signed-integer-overflow+, *, and both unary and binary -
does not overflow in the signed arithmetics. This also detects
INT_MIN / -1 signed division. Note, integer promotion
rules must be taken into account. That is, the following is not an
overflow:
signed char a = SCHAR_MAX;
a++;
-fsanitize=bounds-fstrict-flex-arrays or -fstrict-flex-arrays=
options or strict_flex_array attributes say they shouldn't be treated
like flexible array member-like arrays.
-fsanitize=bounds-strict-fsanitize=alignment-fsanitize=object-size__builtin_dynamic_object_size function. Various out of bounds
pointer accesses are detected.
-fsanitize=float-divide-by-zero-fsanitize=float-cast-overflowFE_INVALID exceptions enabled.
-fsanitize=nonnull-attributenonnull function attribute.
-fsanitize=returns-nonnull-attributereturns_nonnull function attribute, to detect returning
of null values from such functions.
-fsanitize=bool-fsanitize=enum-fsanitize=vptr-fsanitize=pointer-overflow-fsanitize=builtin__builtin_ctz
or __builtin_clz invokes undefined behavior and is diagnosed
by this option.
Note that sanitizers tend to increase the rate of false positive warnings, most notably those around -Wmaybe-uninitialized. We recommend against combining -Werror and [the use of] sanitizers.
While -ftrapv causes traps for signed overflows to be emitted, -fsanitize=undefined gives a diagnostic message. This currently works only for the C family of languages.
-fno-sanitize=all-fasan-shadow-offset=number-fsanitize-sections=s1,s2,...-fsanitize-recover[=opts]Currently this feature only works for -fsanitize=undefined (and its suboptions except for -fsanitize=unreachable and -fsanitize=return), -fsanitize=float-cast-overflow, -fsanitize=float-divide-by-zero, -fsanitize=bounds-strict, -fsanitize=kernel-address and -fsanitize=address. For these sanitizers error recovery is turned on by default, except -fsanitize=address, for which this feature is experimental. -fsanitize-recover=all and -fno-sanitize-recover=all is also accepted, the former enables recovery for all sanitizers that support it, the latter disables recovery for all sanitizers that support it.
Even if a recovery mode is turned on the compiler side, it needs to be also
enabled on the runtime library side, otherwise the failures are still fatal.
The runtime library defaults to halt_on_error=0 for
ThreadSanitizer and UndefinedBehaviorSanitizer, while default value for
AddressSanitizer is halt_on_error=1. This can be overridden through
setting the halt_on_error flag in the corresponding environment variable.
Syntax without an explicit opts parameter is deprecated. It is equivalent to specifying an opts list of:
undefined,float-cast-overflow,float-divide-by-zero,bounds-strict
-fsanitize-address-use-after-scope-fsanitize-trap[=opts]__builtin_trap rather than a libubsan
library routine. If this option is enabled for certain sanitizer,
it takes precedence over the -fsanitizer-recover= for that
sanitizer, __builtin_trap will be emitted and be fatal regardless
of whether recovery is enabled or disabled using -fsanitize-recover=.
The advantage of this is that the libubsan library is not needed
and is not linked in, so this is usable even in freestanding environments.
Currently this feature works with -fsanitize=undefined (and its suboptions
except for -fsanitize=vptr), -fsanitize=float-cast-overflow,
-fsanitize=float-divide-by-zero and
-fsanitize=bounds-strict. -fsanitize-trap=all can be also
specified, which enables it for undefined suboptions,
-fsanitize=float-cast-overflow,
-fsanitize=float-divide-by-zero and
-fsanitize=bounds-strict.
If -fsanitize-trap=undefined or -fsanitize-trap=all is used
and -fsanitize=vptr is enabled on the command line, the
instrumentation is silently ignored as the instrumentation always needs
libubsan support, -fsanitize-trap=vptr is not allowed.
-fsanitize-undefined-trap-on-error-fsanitize-coverage=trace-pc__sanitizer_cov_trace_pc into every basic block.
-fsanitize-coverage=trace-cmp__sanitizer_cov_trace_cmp1,
__sanitizer_cov_trace_cmp2, __sanitizer_cov_trace_cmp4 or
__sanitizer_cov_trace_cmp8 for integral comparison with both operands
variable or __sanitizer_cov_trace_const_cmp1,
__sanitizer_cov_trace_const_cmp2,
__sanitizer_cov_trace_const_cmp4 or
__sanitizer_cov_trace_const_cmp8 for integral comparison with one
operand constant, __sanitizer_cov_trace_cmpf or
__sanitizer_cov_trace_cmpd for float or double comparisons and
__sanitizer_cov_trace_switch for switch statements.
-fcf-protection=[full|branch|return|none|check]The value branch tells the compiler to implement checking of
validity of control-flow transfer at the point of indirect branch
instructions, i.e. call/jmp instructions. The value return
implements checking of validity at the point of returning from a
function. The value full is an alias for specifying both
branch and return. The value none turns off
instrumentation.
The value check is used for the final link with link-time
optimization (LTO). An error is issued if LTO object files are
compiled with different -fcf-protection values. The
value check is ignored at the compile time.
The macro __CET__ is defined when -fcf-protection is
used. The first bit of __CET__ is set to 1 for the value
branch and the second bit of __CET__ is set to 1 for
the return.
You can also use the nocf_check attribute to identify
which functions and calls should be skipped from instrumentation
(see Function Attributes).
Currently the x86 GNU/Linux target provides an implementation based on Intel Control-flow Enforcement Technology (CET) which works for i686 processor or newer.
-fharden-compares__builtin_trap if the results do not
match. Use with ‘-fharden-conditional-branches’ to cover all
conditionals.
-fharden-conditional-branches__builtin_trap if the result is
unexpected. Use with ‘-fharden-compares’ to cover all
conditionals.
-fharden-control-flow-redundancyVerification takes place before returns, before mandatory tail calls (see below) and, optionally, before escaping exceptions with -fhardcfr-check-exceptions, before returning calls with -fhardcfr-check-returning-calls, and before noreturn calls with -fhardcfr-check-noreturn-calls). Tuning options --param hardcfr-max-blocks and --param hardcfr-max-inline-blocks are available.
Tail call optimization takes place too late to affect control flow redundancy, but calls annotated as mandatory tail calls by language front-ends, and any calls marked early enough as potential tail calls would also have verification issued before the call, but these possibilities are merely theoretical, as these conditions can only be met when using custom compiler plugins.
-fhardcfr-skip-leaf-fhardcfr-check-exceptions-fhardcfr-check-returning-callsThis option is enabled by default whenever sibling call optimizations are enabled (see -foptimize-sibling-calls), but it can be enabled (or disabled, using its negated form) explicitly, regardless of the optimizations.
-fhardcfr-check-noreturn-calls=[always|no-xthrow|nothrow|never]noreturn calls, either all of them (always), those that
aren't expected to return control to the caller through an exception
(no-xthrow, the default), those that may not return control to
the caller through an exception either (nothrow), or none of
them (never).
Checking before a noreturn function that may return control to
the caller through an exception may cause checking to be performed more
than once, if the exception is caught in the caller, whether by a
handler or a cleanup. When -fhardcfr-check-exceptions is also
enabled, the compiler will avoid associating a noreturn call with
the implicitly-added cleanup handler, since it would be redundant with
the check performed before the call, but other handlers or cleanups in
the function, if activated, will modify the recorded execution path and
check it again when another checkpoint is hit. The checkpoint may even
be another noreturn call, so checking may end up performed
multiple times.
Various optimizers may cause calls to be marked as noreturn
and/or nothrow, even in the absence of the corresponding
attributes, which may affect the placement of checks before calls, as
well as the addition of implicit cleanup handlers for them. This
unpredictability, and the fact that raising and reraising exceptions
frequently amounts to implicitly calling noreturn functions, have
made no-xthrow the default setting for this option: it excludes
from the noreturn treatment only internal functions used to
(re)raise exceptions, that are not affected by these optimizations.
-fstack-protectoralloca, and
functions with buffers larger than or equal to 8 bytes. The guards are
initialized when a function is entered and then checked when the function
exits. If a guard check fails, an error message is printed and the program
exits. Only variables that are actually allocated on the stack are
considered, optimized away variables or variables allocated in registers
don't count.
-fstack-protector-all-fstack-protector-strong-fstack-protector-explicitstack_protect attribute.
-fstack-checkNote that this switch does not actually cause checking to be done; the operating system or the language runtime must do that. The switch causes generation of code to ensure that they see the stack being extended.
You can additionally specify a string parameter: ‘no’ means no checking, ‘generic’ means force the use of old-style checking, ‘specific’ means use the best checking method and is equivalent to bare -fstack-check.
Old-style checking is a generic mechanism that requires no specific target support in the compiler but comes with the following drawbacks:
Note that old-style stack checking is also the fallback method for ‘specific’ if no target support has been added in the compiler.
‘-fstack-check=’ is designed for Ada's needs to detect infinite recursion and stack overflows. ‘specific’ is an excellent choice when compiling Ada code. It is not generally sufficient to protect against stack-clash attacks. To protect against those you want ‘-fstack-clash-protection’.
-fstack-clash-protectionMost targets do not fully support stack clash protection. However, on those targets -fstack-clash-protection will protect dynamic stack allocations. -fstack-clash-protection may also provide limited protection for static stack allocations if the target supports -fstack-check=specific.
-fstack-limit-register=reg-fstack-limit-symbol=sym-fno-stack-limitFor instance, if the stack starts at absolute address ‘0x80000000’ and grows downwards, you can use the flags -fstack-limit-symbol=__stack_limit and -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of 128KB. Note that this may only work with the GNU linker.
You can locally override stack limit checking by using the
no_stack_limit function attribute (see Function Attributes).
-fsplit-stackWhen code compiled with -fsplit-stack calls code compiled without -fsplit-stack, there may not be much stack space available for the latter code to run. If compiling all code, including library code, with -fsplit-stack is not an option, then the linker can fix up these calls so that the code compiled without -fsplit-stack always has a large stack. Support for this is implemented in the gold linker in GNU binutils release 2.21 and later.
-fstrub=disablestrub attributes.
See See Common Type Attributes.
-fstrub=strictstrub mode disabled, and apply
strictly the restriction that only functions associated with
strub-callable modes (at-calls, callable and
always_inline internal) are callable by functions
with strub-enabled modes (at-calls and internal).
-fstrub=relaxedstrub) setting, namely,
strub is only enabled as required by strub attributes
associated with function and data types. Relaxed means that
strub contexts are only prevented from calling functions explicitly
associated with strub mode disabled. This option is only
useful to override other -fstrub=* options that precede it in
the command line.
-fstrub=at-callsat-calls strub mode where viable. The primary use
of this option is for testing. It exercises the strub machinery
in scenarios strictly local to a translation unit. This strub
mode modifies function interfaces, so any function that is visible to
other translation units, or that has its address taken, will not
be affected by this option. Optimization options may also affect
viability. See the strub attribute documentation for details on
viability and eligibility requirements.
-fstrub=internalinternal strub mode where viable. The primary use
of this option is for testing. This option is intended to exercise
thoroughly parts of the strub machinery that implement the less
efficient, but interface-preserving strub mode. Functions that
would not be affected by this option are quite uncommon.
-fstrub=allstrub mode where viable. When both strub modes are
viable, at-calls is preferred. -fdump-ipa-strubm adds
function attributes that tell which mode was selected for each function.
The primary use of this option is for testing, to exercise thoroughly
the strub machinery.
-fvtable-verify=[std|preinit|none]This option causes run-time data structures to be built at program startup,
which are used for verifying the vtable pointers.
The options ‘std’ and ‘preinit’
control the timing of when these data structures are built. In both cases the
data structures are built before execution reaches main. Using
-fvtable-verify=std causes the data structures to be built after
shared libraries have been loaded and initialized.
-fvtable-verify=preinit causes them to be built before shared
libraries have been loaded and initialized.
If this option appears multiple times in the command line with different values specified, ‘none’ takes highest priority over both ‘std’ and ‘preinit’; ‘preinit’ takes priority over ‘std’.
-fvtv-debugNote: This feature appends data to the log file. If you want a fresh log file, be sure to delete any existing one.
-fvtv-countsNote: This feature appends data to the log files. To get fresh log files, be sure to delete any existing ones.
-finstrument-functions__builtin_return_address does not work beyond the current
function, so the call site information may not be available to the
profiling functions otherwise.)
void __cyg_profile_func_enter (void *this_fn,
void *call_site);
void __cyg_profile_func_exit (void *this_fn,
void *call_site);
The first argument is the address of the start of the current function, which may be looked up exactly in the symbol table.
This instrumentation is also done for functions expanded inline in other
functions. The profiling calls indicate where, conceptually, the
inline function is entered and exited. This means that addressable
versions of such functions must be available. If all your uses of a
function are expanded inline, this may mean an additional expansion of
code size. If you use extern inline in your C code, an
addressable version of such functions must be provided. (This is
normally the case anyway, but if you get lucky and the optimizer always
expands the functions inline, you might have gotten away without
providing static copies.)
A function may be given the attribute no_instrument_function, in
which case this instrumentation is not done. This can be used, for
example, for the profiling functions listed above, high-priority
interrupt routines, and any functions from which the profiling functions
cannot safely be called (perhaps signal handlers, if the profiling
routines generate output or allocate memory).
See Common Function Attributes.
-finstrument-functions-onceThe definition of once for the purpose of this option is a little
vague because the implementation is not protected against data races.
As a result, the implementation only guarantees that the profiling
functions are called at least once per process and at most
once per thread, but the calls are always paired, that is to say, if a
thread calls the first function, then it will call the second function,
unless it never reaches the exit of the instrumented function.
-finstrument-functions-exclude-file-list=file,file,...For example:
-finstrument-functions-exclude-file-list=/bits/stl,include/sys
excludes any inline function defined in files whose pathnames contain /bits/stl or include/sys.
If, for some reason, you want to include letter ‘,’ in one of sym, write ‘\,’. For example, -finstrument-functions-exclude-file-list='\,\,tmp' (note the single quote surrounding the option).
-finstrument-functions-exclude-function-list=sym,sym,...vector<int> blah(const vector<int> &), not the
internal mangled name (e.g., _Z4blahRSt6vectorIiSaIiEE). The
match is done on substrings: if the sym parameter is a substring
of the function name, it is considered to be a match. For C99 and C++
extended identifiers, the function name must be given in UTF-8, not
using universal character names.
-fpatchable-function-entry=N[,M]0 so the
function entry points to the address just at the first NOP.
The NOP instructions reserve extra space which can be used to patch in
any desired instrumentation at run time, provided that the code segment
is writable. The amount of space is controllable indirectly via
the number of NOPs; the NOP instruction used corresponds to the instruction
emitted by the internal GCC back-end interface gen_nop. This behavior
is target-specific and may also depend on the architecture variant and/or
other compilation options.
For run-time identification, the starting addresses of these areas,
which correspond to their respective function entries minus M,
are additionally collected in the __patchable_function_entries
section of the resulting binary.
Note that the value of __attribute__ ((patchable_function_entry
(N,M))) takes precedence over command-line option
-fpatchable-function-entry=N,M. This can be used to increase
the area size or to remove it completely on a single function.
If N=0, no pad location is recorded.
The NOP instructions are inserted at—and maybe before, depending on M—the function entry address, even before the prologue. On PowerPC with the ELFv2 ABI, for a function with dual entry points, the local entry point is this function entry address.
The maximum value of N and M is 65535. On PowerPC with the ELFv2 ABI, for a function with dual entry points, the supported values for M are 0, 2, 6 and 14.
These options control the C preprocessor, which is run on each C source file before actual compilation.
If you use the -E option, nothing is done except preprocessing. Some of these options make sense only together with -E because they cause the preprocessor output to be unsuitable for actual compilation.
In addition to the options listed here, there are a number of options to control search paths for include files documented in Directory Options. Options to control preprocessor diagnostics are listed in Warning Options.
-D name1.
-D name=definitionIf you are invoking the preprocessor from a shell or shell-like program you may need to use the shell's quoting syntax to protect characters such as spaces that have a meaning in the shell syntax.
If you wish to define a function-like macro on the command line, write its argument list with surrounding parentheses before the equals sign (if any). Parentheses are meaningful to most shells, so you should quote the option. With sh and csh, -D'name(args...)=definition' works.
-D and -U options are processed in the order they are given on the command line. All -imacros file and -include file options are processed after all -D and -U options.
-U name-include file#include "file" appeared as the first
line of the primary source file. However, the first directory searched
for file is the preprocessor's working directory instead of
the directory containing the main source file. If not found there, it
is searched for in the remainder of the #include "..." search
chain as normal.
If multiple -include options are given, the files are included in the order they appear on the command line.
-imacros fileAll files specified by -imacros are processed before all files specified by -include.
-undef-pthread-MUnless specified explicitly (with -MT or -MQ), the object file name consists of the name of the source file with any suffix replaced with object file suffix and with any leading directory parts removed. If there are many included files then the rule is split into several lines using ‘\’-newline. The rule has no commands.
This option does not suppress the preprocessor's debug output, such as -dM. To avoid mixing such debug output with the dependency rules you should explicitly specify the dependency output file with -MF, or use an environment variable like DEPENDENCIES_OUTPUT (see Environment Variables). Debug output is still sent to the regular output stream as normal.
Passing -M to the driver implies -E, and suppresses warnings with an implicit -w.
-MMThis implies that the choice of angle brackets or double quotes in an ‘#include’ directive does not in itself determine whether that header appears in -MM dependency output.
-MF fileWhen used with the driver options -MD or -MMD, -MF overrides the default dependency output file.
If file is -, then the dependencies are written to stdout.
-MG#include directive without prepending any path. -MG
also suppresses preprocessed output, as a missing header file renders
this useless.
This feature is used in automatic updating of makefiles.
-Mno-modules-MPThis is typical output:
test.o: test.c test.h
test.h:
-MT targetAn -MT option sets the target to be exactly the string you specify. If you want multiple targets, you can specify them as a single argument to -MT, or use multiple -MT options.
For example, -MT '$(objpfx)foo.o' might give
$(objpfx)foo.o: foo.c
-MQ target$$(objpfx)foo.o: foo.c
The default target is automatically quoted, as if it were given with -MQ.
-MDIf -MD is used in conjunction with -E, any -o switch is understood to specify the dependency output file (see -MF), but if used without -E, each -o is understood to specify a target object file.
Since -E is not implied, -MD can be used to generate a dependency output file as a side effect of the compilation process.
-MMD-fpreprocessed-fpreprocessed is implicit if the input file has one of the extensions ‘.i’, ‘.ii’ or ‘.mi’. These are the extensions that GCC uses for preprocessed files created by -save-temps.
-fdirectives-onlyThe option's behavior depends on the -E and -fpreprocessed options.
With -E, preprocessing is limited to the handling of directives
such as #define, #ifdef, and #error. Other
preprocessor operations, such as macro expansion and trigraph
conversion are not performed. In addition, the -dD option is
implicitly enabled.
With -fpreprocessed, predefinition of command line and most
builtin macros is disabled. Macros such as __LINE__, which are
contextually dependent, are handled normally. This enables compilation of
files previously preprocessed with -E -fdirectives-only.
With both -E and -fpreprocessed, the rules for
-fpreprocessed take precedence. This enables full preprocessing of
files previously preprocessed with -E -fdirectives-only.
-fdollars-in-identifiers-fextended-identifiers-fno-canonical-system-headers-fmax-include-depth=depth-ftabstop=width-ftrack-macro-expansion[=level]Note that -ftrack-macro-expansion=2 is activated by default.
-fmacro-prefix-map=old=new__FILE__ and __BASE_FILE__ macros as if the
files resided in directory new instead. This can be used
to change an absolute path to a relative path by using . for
new which can result in more reproducible builds that are
location independent. This option also affects
__builtin_FILE() during compilation. See also
-ffile-prefix-map and -fcanon-prefix-map.
-fexec-charset=charseticonv library routine.
-fwide-exec-charset=charsetwchar_t and the
big-endian or little-endian byte order being used for code generation. As
with -fexec-charset, charset can be any encoding supported
by the system's iconv library routine; however, you will have
problems with encodings that do not fit exactly in wchar_t.
-finput-charset=charseticonv library routine.
-fpch-deps-fpch-preprocess#pragma,
#pragma GCC pch_preprocess "filename" in the output to mark
the place where the precompiled header was found, and its filename.
When -fpreprocessed is in use, GCC recognizes this #pragma
and loads the PCH.
This option is off by default, because the resulting preprocessed output is only really suitable as input to GCC. It is switched on by -save-temps.
You should not write this #pragma in your own code, but it is
safe to edit the filename if the PCH file is available in a different
location. The filename may be absolute or it may be relative to GCC's
current directory.
-fworking-directory#line directives are emitted whatsoever.
-A predicate=answer-A -predicate=answer-CYou should be prepared for side effects when using -C; it causes the preprocessor to treat comments as tokens in their own right. For example, comments appearing at the start of what would be a directive line have the effect of turning that line into an ordinary source line, since the first token on the line is no longer a ‘#’.
-CCIn addition to the side effects of the -C option, the -CC option causes all C++-style comments inside a macro to be converted to C-style comments. This is to prevent later use of that macro from inadvertently commenting out the remainder of the source line.
The -CC option is generally used to support lint comments.
-P-traditional-traditional-cppNote that GCC does not otherwise attempt to emulate a pre-standard C compiler, and these options are only supported with the -E switch, or when invoking CPP explicitly.
-trigraphsThe nine trigraphs and their replacements are
Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
Replacement: [ ] { } # \ ^ | ~
By default, GCC ignores trigraphs, but in standard-conforming modes it converts them. See the -std and -ansi options.
-remap-H-dletters-dMtouch foo.h; cpp -dM foo.h
shows all the predefined macros.
If you use -dM without the -E option, -dM is interpreted as a synonym for -fdump-rtl-mach. See Developer Options.
-dD-dN-dI-dU-fdebug-cppWhen used from GCC without -E, this option has no effect.
-Wp,option-Xpreprocessor optionIf you want to pass an option that takes an argument, you must use -Xpreprocessor twice, once for the option and once for the argument.
-no-integrated-cpp-flarge-source-filesSpecifically, GCC normally tracks both column numbers and line numbers within source files and it normally prints both of these numbers in diagnostics. However, once it has processed a certain number of source lines, it stops tracking column numbers and only tracks line numbers. This means that diagnostics for later lines do not include column numbers. It also means that options like -Wmisleading-indentation cease to work at that point, although the compiler prints a note if this happens. Passing -flarge-source-files significantly increases the number of source lines that GCC can process before it stops tracking columns.
You can pass options to the assembler.
-Wa,option-Xassembler optionIf you want to pass an option that takes an argument, you must use -Xassembler twice, once for the option and once for the argument.
These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step.
-c-S-E-flinker-output=typeIf type is ‘exec’, code generation produces a static binary. In this case -fpic and -fpie are both disabled.
If type is ‘dyn’, code generation produces a shared library. In this case -fpic or -fPIC is preserved, but not enabled automatically. This allows to build shared libraries without position-independent code on architectures where this is possible, i.e. on x86.
If type is ‘pie’, code generation produces an -fpie executable. This results in similar optimizations as ‘exec’ except that -fpie is not disabled if specified at compilation time.
If type is ‘rel’, the compiler assumes that incremental linking is done. The sections containing intermediate code for link-time optimization are merged, pre-optimized, and output to the resulting object file. In addition, if -ffat-lto-objects is specified, binary code is produced for future non-LTO linking. The object file produced by incremental linking is smaller than a static library produced from the same object files. At link time the result of incremental linking also loads faster than a static library assuming that the majority of objects in the library are used.
Finally ‘nolto-rel’ configures the compiler for incremental linking where code generation is forced, a final binary is produced, and the intermediate code for later link-time optimization is stripped. When multiple object files are linked together the resulting code is better optimized than with link-time optimizations disabled (for example, cross-module inlining happens), but most of benefits of whole program optimizations are lost.
During the incremental link (by -r) the linker plugin defaults to rel. With current interfaces to GNU Binutils it is however not possible to incrementally link LTO objects and non-LTO objects into a single mixed object file. If any of object files in incremental link cannot be used for link-time optimization, the linker plugin issues a warning and uses ‘nolto-rel’. To maintain whole program optimization, it is recommended to link such objects into static library instead. Alternatively it is possible to use H.J. Lu's binutils with support for mixed objects.
-fuse-ld=bfd-fuse-ld=gold-fuse-ld=lld-fuse-ld=mold-llibrary-l libraryThe -l option is passed directly to the linker by GCC. Refer to your linker documentation for exact details. The general description below applies to the GNU linker.
The linker searches a standard list of directories for the library. The directories searched include several standard system directories plus any that you specify with -L.
Static libraries are archives of object files, and have file names like liblibrary.a. Some targets also support shared libraries, which typically have names like liblibrary.so. If both static and shared libraries are found, the linker gives preference to linking with the shared library unless the -static option is used.
It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, ‘foo.o -lz bar.o’ searches library ‘z’ after file foo.o but before bar.o. If bar.o refers to functions in ‘z’, those functions may not be loaded.
-lobjc-nostartfiles-nodefaultlibsThe compiler may generate calls to memcmp,
memset, memcpy and memmove.
These entries are usually resolved by entries in
libc. These entry points should be supplied through some other
mechanism when this option is specified.
-nolibc-nostdlibThe compiler may generate calls to memcmp, memset,
memcpy and memmove.
These entries are usually resolved by entries in
libc. These entry points should be supplied through some other
mechanism when this option is specified.
One of the standard libraries bypassed by -nostdlib and
-nodefaultlibs is libgcc.a, a library of internal subroutines
which GCC uses to overcome shortcomings of particular machines, or special
needs for some languages.
(See Interfacing to GCC Output,
for more discussion of libgcc.a.)
In most cases, you need libgcc.a even when you want to avoid
other standard libraries. In other words, when you specify -nostdlib
or -nodefaultlibs you should usually specify -lgcc as well.
This ensures that you have no unresolved references to internal GCC
library subroutines.
(An example of such an internal subroutine is __main, used to ensure C++
constructors are called; see collect2.)
-nostdlib++-e entry--entry=entry-pie-no-pie-static-pie-pthread-r-rdynamicdlopen or to allow obtaining backtraces
from within a program.
-s-static-shared-shared-libgcc-static-libgccThere are several situations in which an application should use the shared libgcc instead of the static version. The most common of these is when the application wishes to throw and catch exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should use the shared libgcc.
Therefore, the G++ driver automatically adds -shared-libgcc whenever you build a shared library or a main executable, because C++ programs typically use exceptions, so this is the right thing to do.
If, instead, you use the GCC driver to create shared libraries, you may find that they are not always linked with the shared libgcc. If GCC finds, at its configuration time, that you have a non-GNU linker or a GNU linker that does not support option --eh-frame-hdr, it links the shared version of libgcc into shared libraries by default. Otherwise, it takes advantage of the linker and optimizes away the linking with the shared version of libgcc, linking with the static version of libgcc by default. This allows exceptions to propagate through such shared libraries, without incurring relocation costs at library load time.
However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ driver, or using the option -shared-libgcc, such that it is linked with the shared libgcc.
-static-libasan-static-libtsan-static-liblsan-static-libubsan-static-libstdc++-symbolic-T script-Xlinker optionIf you want to pass an option that takes a separate argument, you must use -Xlinker twice, once for the option and once for the argument. For example, to pass -assert definitions, you must write -Xlinker -assert -Xlinker definitions. It does not work to write -Xlinker "-assert definitions", because this passes the entire string as a single argument, which is not what the linker expects.
When using the GNU linker, it is usually more convenient to pass arguments to linker options using the option=value syntax than as separate arguments. For example, you can specify -Xlinker -Map=output.map rather than -Xlinker -Map -Xlinker output.map. Other linkers may not support this syntax for command-line options.
-Wl,option-u symbol-z keywordThese options specify directories to search for header files, for libraries and for parts of the compiler:
-I dir-iquote dir-isystem dir-idirafter dir$SYSROOT, then the ‘=’
or $SYSROOT is replaced by the sysroot prefix; see
--sysroot and -isysroot.
Directories specified with -iquote apply only to the quote
form of the directive, #include "file".
Directories specified with -I, -isystem,
or -idirafter apply to lookup for both the
#include "file" and
#include <file> directives.
You can specify any number or combination of these options on the command line to search for header files in several directories. The lookup order is as follows:
You can use -I to override a system header file, substituting your own version, since these directories are searched before the standard system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files; use -isystem for that.
The -isystem and -idirafter options also mark the directory as a system directory, so that it gets the same special treatment that is applied to the standard system directories.
If a standard system include directory, or a directory specified with
-isystem, is also specified with -I, the -I
option is ignored. The directory is still searched but as a
system directory at its normal position in the system include chain.
This is to ensure that GCC's procedure to fix buggy system headers and
the ordering for the #include_next directive are not inadvertently
changed.
If you really need to change the search order for system directories,
use the -nostdinc and/or -isystem options.
-I-Any directories specified with -I
options before -I- are searched only for headers requested with
#include "file"; they are not searched for
#include <file>. If additional directories are
specified with -I options after the -I-, those
directories are searched for all ‘#include’ directives.
In addition, -I- inhibits the use of the directory of the current
file directory as the first search directory for #include "file". There is no way to override this effect of -I-.
-iprefix prefix-iwithprefix dir-iwithprefixbefore dir-isysroot dir-imultilib dir-nostdinc-nostdinc++-iplugindir=dir-Ldir-BprefixThe compiler driver program runs one or more of the subprograms cpp, cc1, as and ld. It tries prefix as a prefix for each program it tries to run, both with and without ‘machine/version/’ for the corresponding target machine and compiler version.
For each subprogram to be run, the compiler driver first tries the -B prefix, if any. If that name is not found, or if -B is not specified, the driver tries two standard prefixes, /usr/lib/gcc/ and /usr/local/lib/gcc/. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your PATH environment variable.
The compiler checks to see if the path provided by -B refers to a directory, and if necessary it adds a directory separator character at the end of the path.
-B prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into -L options for the linker. They also apply to include files in the preprocessor, because the compiler translates these options into -isystem options for the preprocessor. In this case, the compiler appends ‘include’ to the prefix.
The runtime support file libgcc.a can also be searched for using the -B prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means.
Another way to specify a prefix much like the -B prefix is to use the environment variable GCC_EXEC_PREFIX. See Environment Variables.
As a special kludge, if the path provided by -B is [dir/]stageN/, where N is a number in the range 0 to 9, then it is replaced by [dir/]include. This is to help with boot-strapping the compiler.
-no-canonical-prefixes--sysroot=dirIf you use both this option and the -isysroot option, then the --sysroot option applies to libraries, but the -isysroot option applies to header files.
The GNU linker (beginning with version 2.16) has the necessary support for this option. If your linker does not support this option, the header file aspect of --sysroot still works, but the library aspect does not.
--no-sysroot-suffixThese machine-independent options control the interface conventions used in code generation.
Most of them have both positive and negative forms; the negative form of -ffoo is -fno-foo. In the table below, only one of the forms is listed—the one that is not the default. You can figure out the other form by either removing ‘no-’ or adding it.
-fstack-reuse=reuse-levelFor example,
int *p;
{
int local1;
p = &local1;
local1 = 10;
....
}
{
int local2;
local2 = 20;
...
}
if (*p == 10) // out of scope use of local1
{
}
Another example:
struct A
{
A(int k) : i(k), j(k) { }
int i;
int j;
};
A *ap;
void foo(const A& ar)
{
ap = &ar;
}
void bar()
{
foo(A(10)); // temp object's lifetime ends when foo returns
{
A a(20);
....
}
ap->i+= 10; // ap references out of scope temp whose space
// is reused with a. What is the value of ap->i?
}
The lifetime of a compiler generated temporary is well defined by the C++ standard. When a lifetime of a temporary ends, and if the temporary lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. However some of the legacy code relies on the behavior of older compilers in which temporaries' stack space is not reused, the aggressive stack reuse can lead to runtime errors. This option is used to control the temporary stack reuse optimization.
-ftrapv-fwrapv-fwrapv-pointer-fstrict-overflow-fexceptions-fnon-call-exceptionsSIGALRM. This enables
-fexceptions.
-fdelete-dead-exceptionspure or const attributes.
This option is enabled by default for the Ada and C++ compilers, as permitted by
the language specifications.
Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels.
-funwind-tables-fasynchronous-unwind-tables-fno-gnu-uniqueSTB_GNU_UNIQUE binding to make sure that definitions
of template static data members and static local variables in inline
functions are unique even in the presence of RTLD_LOCAL; this
is necessary to avoid problems with a library used by two different
RTLD_LOCAL plugins depending on a definition in one of them and
therefore disagreeing with the other one about the binding of the
symbol. But this causes dlclose to be ignored for affected
DSOs; if your program relies on reinitialization of a DSO via
dlclose and dlopen, you can use
-fno-gnu-unique.
-fsjlj-fpcc-struct-returnstruct and union values in memory like
longer ones, rather than in registers. This convention is less
efficient, but it has the advantage of allowing intercallability between
GCC-compiled files and files compiled with other compilers, particularly
the Portable C Compiler (pcc).
The precise convention for returning structures in memory depends on the target configuration macros.
Short structures and unions are those whose size and alignment match that of some integer type.
Warning: code compiled with the -fpcc-struct-return switch is not binary compatible with code compiled with the -freg-struct-return switch. Use it to conform to a non-default application binary interface.
-freg-struct-returnstruct and union values in registers when possible.
This is more efficient for small structures than
-fpcc-struct-return.
If you specify neither -fpcc-struct-return nor -freg-struct-return, GCC defaults to whichever convention is standard for the target. If there is no standard convention, GCC defaults to -fpcc-struct-return, except on targets where GCC is the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative.
Warning: code compiled with the -freg-struct-return switch is not binary compatible with code compiled with the -fpcc-struct-return switch. Use it to conform to a non-default application binary interface.
-fshort-enumsenum type only as many bytes as it needs for the
declared range of possible values. Specifically, the enum type
is equivalent to the smallest integer type that has enough room.
Warning: the -fshort-enums switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface.
-fshort-wcharwchar_t to be short
unsigned int instead of the default for the target. This option is
useful for building programs to run under WINE.
Warning: the -fshort-wchar switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface.
-fcommonextern keyword, which do not allocate storage.
The default is -fno-common, which specifies that the compiler places uninitialized global variables in the BSS section of the object file. This inhibits the merging of tentative definitions by the linker so you get a multiple-definition error if the same variable is accidentally defined in more than one compilation unit.
The -fcommon places uninitialized global variables in a common block. This allows the linker to resolve all tentative definitions of the same variable in different compilation units to the same object, or to a non-tentative definition. This behavior is inconsistent with C++, and on many targets implies a speed and code size penalty on global variable references. It is mainly useful to enable legacy code to link without errors.
-fno-ident#ident directive.
-finhibit-size-directive.size assembler directive, or anything else that
would cause trouble if the function is split in the middle, and the
two halves are placed at locations far apart in memory. This option is
used when compiling crtstuff.c; you should not need to use it
for anything else.
-fverbose-asm-fno-verbose-asm, the default, causes the extra information to be omitted and is useful when comparing two assembler files.
The added comments include:
For example, given this C source file:
int test (int n)
{
int i;
int total = 0;
for (i = 0; i < n; i++)
total += i * i;
return total;
}
compiling to (x86_64) assembly via -S and emitting the result direct to stdout via -o -
gcc -S test.c -fverbose-asm -Os -o -
gives output similar to this:
.file "test.c"
# GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
[...snip...]
# options passed:
[...snip...]
.text
.globl test
.type test, @function
test:
.LFB0:
.cfi_startproc
# test.c:4: int total = 0;
xorl %eax, %eax # <retval>
# test.c:6: for (i = 0; i < n; i++)
xorl %edx, %edx # i
.L2:
# test.c:6: for (i = 0; i < n; i++)
cmpl %edi, %edx # n, i
jge .L5 #,
# test.c:7: total += i * i;
movl %edx, %ecx # i, tmp92
imull %edx, %ecx # i, tmp92
# test.c:6: for (i = 0; i < n; i++)
incl %edx # i
# test.c:7: total += i * i;
addl %ecx, %eax # tmp92, <retval>
jmp .L2 #
.L5:
# test.c:10: }
ret
.cfi_endproc
.LFE0:
.size test, .-test
.ident "GCC: (GNU) 7.0.0 20160809 (experimental)"
.section .note.GNU-stack,"",@progbits
The comments are intended for humans rather than machines and hence the precise format of the comments is subject to change.
-frecord-gcc-switches-fpicPosition-independent code requires special support, and therefore works only on certain machines. For the x86, GCC supports PIC for System V but not for the Sun 386i. Code generated for the IBM RS/6000 is always position-independent.
When this flag is set, the macros __pic__ and __PIC__
are defined to 1.
-fPICPosition-independent code requires special support, and therefore works only on certain machines.
When this flag is set, the macros __pic__ and __PIC__
are defined to 2.
-fpie-fPIE-fpie and -fPIE both define the macros
__pie__ and __PIE__. The macros have the value 1
for -fpie and 2 for -fPIE.
-fno-pltAlternatively, the function attribute noplt can be used to avoid calls
through the PLT for specific external functions.
In position-dependent code, a few targets also convert calls to functions that are marked to not use the PLT to use the GOT instead.
-fno-jump-tables-fno-bit-tests-ffixed-regreg must be the name of a register. The register names accepted
are machine-specific and are defined in the REGISTER_NAMES
macro in the machine description macro file.
This flag does not have a negative form, because it specifies a three-way choice.
-fcall-used-regIt is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces disastrous results.
This flag does not have a negative form, because it specifies a three-way choice.
-fcall-saved-regIt is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces disastrous results.
A different sort of disaster results from the use of this flag for a register in which function values may be returned.
This flag does not have a negative form, because it specifies a three-way choice.
-fpack-struct[=n]Warning: the -fpack-struct switch causes GCC to generate code that is not binary compatible with code generated without that switch. Additionally, it makes the code suboptimal. Use it to conform to a non-default application binary interface.
-fleading-underscoreWarning: the -fleading-underscore switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Not all targets provide complete support for this switch.
-ftls-model=modelThe default without -fpic is ‘initial-exec’; with -fpic the default is ‘global-dynamic’.
-ftrampolinesA trampoline is a small piece of code that is created at run time on the stack when the address of a nested function is taken, and is used to call the nested function indirectly. Therefore, it requires the stack to be made executable in order for the program to work properly.
-fno-trampolines is enabled by default on a language by language basis to let the compiler avoid generating them, if it computes that this is safe, and replace them with descriptors. Descriptors are made up of data only, but the generated code must be prepared to deal with them. As of this writing, -fno-trampolines is enabled by default only for Ada.
Moreover, code compiled with -ftrampolines and code compiled with -fno-trampolines are not binary compatible if nested functions are present. This option must therefore be used on a program-wide basis and be manipulated with extreme care.
For languages other than Ada, the -ftrampolines and
-fno-trampolines options currently have no effect, and
trampolines are always generated on platforms that need them
for nested functions.
-fvisibility=[default|internal|hidden|protected]Despite the nomenclature, ‘default’ always means public; i.e., available to be linked against from outside the shared object. ‘protected’ and ‘internal’ are pretty useless in real-world usage so the only other commonly used option is ‘hidden’. The default if -fvisibility isn't specified is ‘default’, i.e., make every symbol public.
A good explanation of the benefits offered by ensuring ELF
symbols have the correct visibility is given by “How To Write
Shared Libraries” by Ulrich Drepper (which can be found at
https://www.akkadia.org/drepper/)—however a superior
solution made possible by this option to marking things hidden when
the default is public is to make the default hidden and mark things
public. This is the norm with DLLs on Windows and with -fvisibility=hidden
and __attribute__ ((visibility("default"))) instead of
__declspec(dllexport) you get almost identical semantics with
identical syntax. This is a great boon to those working with
cross-platform projects.
For those adding visibility support to existing code, you may find
#pragma GCC visibility of use. This works by you enclosing
the declarations you wish to set visibility for with (for example)
#pragma GCC visibility push(hidden) and
#pragma GCC visibility pop.
Bear in mind that symbol visibility should be viewed as
part of the API interface contract and thus all new code should
always specify visibility when it is not the default; i.e., declarations
only for use within the local DSO should always be marked explicitly
as hidden as so to avoid PLT indirection overheads—making this
abundantly clear also aids readability and self-documentation of the code.
Note that due to ISO C++ specification requirements, operator new and
operator delete must always be of default visibility.
Be aware that headers from outside your project, in particular system
headers and headers from any other library you use, may not be
expecting to be compiled with visibility other than the default. You
may need to explicitly say #pragma GCC visibility push(default)
before including any such headers.
extern declarations are not affected by -fvisibility, so
a lot of code can be recompiled with -fvisibility=hidden with
no modifications. However, this means that calls to extern
functions with no explicit visibility use the PLT, so it is more
effective to use __attribute ((visibility)) and/or
#pragma GCC visibility to tell the compiler which extern
declarations should be treated as hidden.
Note that -fvisibility does affect C++ vague linkage entities. This means that, for instance, an exception class that is be thrown between DSOs must be explicitly marked with default visibility so that the ‘type_info’ nodes are unified between the DSOs.
An overview of these techniques, their benefits and how to use them is at https://gcc.gnu.org/wiki/Visibility.
-fstrict-volatile-bitfieldsunsigned short (assuming short
is 16 bits on these targets) to force GCC to use 16-bit accesses
instead of, perhaps, a more efficient 32-bit access.
If this option is disabled, the compiler uses the most efficient instruction. In the previous example, that might be a 32-bit load instruction, even though that accesses bytes that do not contain any portion of the bit-field, or memory-mapped registers unrelated to the one being updated.
In some cases, such as when the packed attribute is applied to a
structure field, it may not be possible to access the field with a single
read or write that is correctly aligned for the target machine. In this
case GCC falls back to generating multiple accesses rather than code that
will fault or truncate the result at run time.
Note: Due to restrictions of the C/C++11 memory model, write accesses are not allowed to touch non bit-field members. It is therefore recommended to define all bits of the field's type as bit-field members.
The default value of this option is determined by the application binary interface for the target processor.
-fsync-libcalls__sync
family of functions may be used to implement the C++11 __atomic
family of functions.
The default value of this option is enabled, thus the only useful form of the option is -fno-sync-libcalls. This option is used in the implementation of the libatomic runtime library.
This section describes command-line options that are primarily of interest to GCC developers, including options to support compiler testing and investigation of compiler bugs and compile-time performance problems. This includes options that produce debug dumps at various points in the compilation; that print statistics such as memory use and execution time; and that print information about GCC's configuration, such as where it searches for libraries. You should rarely need to use any of these options for ordinary compilation and linking tasks.
Many developer options that cause GCC to dump output to a file take an optional ‘=filename’ suffix. You can specify ‘stdout’ or ‘-’ to dump to standard output, and ‘stderr’ for standard error.
If ‘=filename’ is omitted, a default dump file name is constructed by concatenating the base dump file name, a pass number, phase letter, and pass name. The base dump file name is the name of output file produced by the compiler if explicitly specified and not an executable; otherwise it is the source file name. The pass number is determined by the order passes are registered with the compiler's pass manager. This is generally the same as the order of execution, but passes registered by plugins, target-specific passes, or passes that are otherwise registered late are numbered higher than the pass named ‘final’, even if they are executed earlier. The phase letter is one of ‘i’ (inter-procedural analysis), ‘l’ (language-specific), ‘r’ (RTL), or ‘t’ (tree). The files are created in the directory of the output file.
-fcallgraph-info-fcallgraph-info=MARKERSsu marker is specified, the callgraph is
decorated with stack usage information; it is equivalent to
-fstack-usage. When the da marker is specified, the
callgraph is decorated with information about dynamically allocated
objects.
When compiling with -flto, no callgraph information is output along with the object file. At LTO link time, -fcallgraph-info may generate multiple callgraph information files next to intermediate LTO output files.
-dletters-fdump-rtl-pass-fdump-rtl-pass=filenameSome -dletters switches have different meaning when -E is used for preprocessing. See Preprocessor Options, for information about preprocessor-specific dump options.
Debug dumps can be enabled with a -fdump-rtl switch or some -d option letters. Here are the possible letters for use in pass and letters, and their meanings:
-fdump-rtl-alignments-fdump-rtl-asmcons-fdump-rtl-auto_inc_dec-fdump-rtl-barriers-fdump-rtl-bbpart-fdump-rtl-bbro-fdump-rtl-btl1-fdump-rtl-btl2-fdump-rtl-bypass-fdump-rtl-combine-fdump-rtl-compgotos-fdump-rtl-ce1-fdump-rtl-ce2-fdump-rtl-ce3-fdump-rtl-cprop_hardreg-fdump-rtl-csa-fdump-rtl-cse1-fdump-rtl-cse2-fdump-rtl-dce-fdump-rtl-dbr-fdump-rtl-dce1-fdump-rtl-dce2-fdump-rtl-eh-fdump-rtl-eh_ranges-fdump-rtl-expand-fdump-rtl-fwprop1-fdump-rtl-fwprop2-fdump-rtl-gcse1-fdump-rtl-gcse2-fdump-rtl-init-regs-fdump-rtl-initvals-fdump-rtl-into_cfglayout-fdump-rtl-ira-fdump-rtl-jump-fdump-rtl-loop2-fdump-rtl-mach-fdump-rtl-mode_sw-fdump-rtl-rnreg-fdump-rtl-outof_cfglayout-fdump-rtl-peephole2-fdump-rtl-postreload-fdump-rtl-pro_and_epilogue-fdump-rtl-sched1-fdump-rtl-sched2-fdump-rtl-ree-fdump-rtl-seqabstr-fdump-rtl-shorten-fdump-rtl-sibling-fdump-rtl-split1-fdump-rtl-split2-fdump-rtl-split3-fdump-rtl-split4-fdump-rtl-split5-fdump-rtl-sms-fdump-rtl-stack-fdump-rtl-subreg1-fdump-rtl-subreg2-fdump-rtl-unshare-fdump-rtl-vartrack-fdump-rtl-vregs-fdump-rtl-web-fdump-rtl-regclass-fdump-rtl-subregs_of_mode_init-fdump-rtl-subregs_of_mode_finish-fdump-rtl-dfinit-fdump-rtl-dfinish-da-fdump-rtl-all-dA-dD-dH-dp-dP-dx-fdump-debug-fdump-earlydebug-fdump-noaddr-freport-bug-fdump-unnumbered-fdump-unnumbered-links-fdump-ipa-switch-fdump-ipa-switch-optionsstrub modes, and recording the selections as
function attributes.
strub transformations: interface changes, function wrapping,
and insertion of builtin calls for stack scrubbing and watermarking.
Additionally, the options -optimized, -missed, -note, and -all can be provided, with the same meaning as for -fopt-info, defaulting to -optimized.
For example, -fdump-ipa-inline-optimized-missed will emit information on callsites that were inlined, along with callsites that were not inlined.
By default, the dump will contain messages about successful optimizations (equivalent to -optimized) together with low-level details about the analysis.
-fdump-lang-fdump-lang-all-fdump-lang-switch-fdump-lang-switch-options-fdump-lang-switch-options=filename-fdump-passes-fdump-statistics-option-fdump-tree-all-fdump-tree-switch-fdump-tree-switch-options-fdump-tree-switch-options=filenameDECL_ASSEMBLER_NAME has been set for a given decl, use that
in the dump instead of DECL_NAME. Its primary use is ease of
use working backward from mangled names in the assembly file.
When dumping pretty-printed trees, this option inhibits dumping the bodies of control structures.
When dumping RTL, print the RTL in slim (condensed) form instead of
the default LISP-like representation.
This option currently only works for RTL dumps, and the RTL is always
dumped in slim form.
DECL_UID) for each variable.
To determine what tree dumps are available or find the dump for a pass of interest follow the steps below.
tree-evrp, tree-vrp1, and
tree-vrp2 correspond to the three Value Range Propagation passes.
The number at the end distinguishes distinct invocations of the same pass.
-fopt-info-fopt-info-options-fopt-info-options=filenameThe options can be divided into three groups:
The following options control which kinds of messages should be emitted:
The following option controls the dump verbosity:
One or more of the following option keywords can be used to describe a group of optimizations:
If options is omitted, it defaults to ‘optimized-optall’, which means to dump messages about successful optimizations from all the passes, omitting messages that are treated as “internals”.
If the filename is provided, then the dumps from all the applicable optimizations are concatenated into the filename. Otherwise the dump is output onto stderr. Though multiple -fopt-info options are accepted, only one of them can include a filename. If other filenames are provided then all but the first such option are ignored.
Note that the output filename is overwritten in case of multiple translation units. If a combined output from multiple translation units is desired, stderr should be used instead.
In the following example, the optimization info is output to stderr:
gcc -O3 -fopt-info
This example:
gcc -O3 -fopt-info-missed=missed.all
outputs missed optimization report from all the passes into missed.all, and this one:
gcc -O2 -ftree-vectorize -fopt-info-vec-missed
prints information about missed optimization opportunities from vectorization passes on stderr. Note that -fopt-info-vec-missed is equivalent to -fopt-info-missed-vec. The order of the optimization group names and message types listed after -fopt-info does not matter.
As another example,
gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
outputs information about missed optimizations as well as optimized locations from all the inlining passes into inline.txt.
Finally, consider:
gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
Here the two output filenames vec.miss and loop.opt are in conflict since only one output file is allowed. In this case, only the first option takes effect and the subsequent options are ignored. Thus only vec.miss is produced which contains dumps from the vectorizer about missed opportunities.
-fsave-optimization-recordThis option is experimental and the format of the data within the compressed JSON file is subject to change.
It is roughly equivalent to a machine-readable version of -fopt-info-all, as a collection of messages with source file, line number and column number, with the following additional data for each message:
Additionally, some messages are logically nested within other messages, reflecting implementation details of the optimization passes.
-fsched-verbose=nFor n greater than zero, -fsched-verbose outputs the same information as -fdump-rtl-sched1 and -fdump-rtl-sched2. For n greater than one, it also output basic block probabilities, detailed ready list information and unit/insn info. For n greater than two, it includes RTL at abort point, control-flow and regions info. And for n over four, -fsched-verbose also includes dependence info.
-fenable-kind-pass-fdisable-kind-pass=range-list-fdisable-ipa-pass-fdisable-rtl-pass-fdisable-rtl-pass=range-list-fdisable-tree-pass-fdisable-tree-pass=range-list-fenable-ipa-pass-fenable-rtl-pass-fenable-rtl-pass=range-list-fenable-tree-pass-fenable-tree-pass=range-listHere are some examples showing uses of these options.
# disable ccp1 for all functions
-fdisable-tree-ccp1
# disable complete unroll for function whose cgraph node uid is 1
-fenable-tree-cunroll=1
# disable gcse2 for functions at the following ranges [1,1],
# [300,400], and [400,1000]
# disable gcse2 for functions foo and foo2
-fdisable-rtl-gcse2=foo,foo2
# disable early inlining
-fdisable-tree-einline
# disable ipa inlining
-fdisable-ipa-inline
# enable tree full unroll
-fenable-tree-unroll
-fchecking-fchecking=n-frandom-seed=stringThe string can either be a number (decimal, octal or hex) or an arbitrary string (in which case it's converted to a number by computing CRC32).
The string should be different for every file you compile.
-save-tempsWhen used in combination with the -x command-line option, -save-temps is sensible enough to avoid overwriting an input source file with the same extension as an intermediate file. The corresponding intermediate file may be obtained by renaming the source file before using -save-temps.
-save-temps=cwd-save-temps=obj-time[=file]Without the specification of an output file, the output looks like this:
# cc1 0.12 0.01
# as 0.00 0.01
The first number on each line is the “user time”, that is time spent executing the program itself. The second number is “system time”, time spent executing operating system routines on behalf of the program. Both numbers are in seconds.
With the specification of an output file, the output is appended to the named file, and it looks like this:
0.12 0.01 cc1 options
0.00 0.01 as options
The “user time” and the “system time” are moved before the program name, and the options passed to the program are displayed, so that one can later tell what file was being compiled, and with which options.
-fdump-final-insns[=file].), the name
of the dump file is determined by appending .gkd to the
dump base name, see -dumpbase.
-fcompare-debug[=opts]If the equal sign is omitted, the default -gtoggle is used.
The environment variable GCC_COMPARE_DEBUG, if defined, non-empty and nonzero, implicitly enables -fcompare-debug. If GCC_COMPARE_DEBUG is defined to a string starting with a dash, then it is used for opts, otherwise the default -gtoggle is used.
-fcompare-debug=, with the equal sign but without opts, is equivalent to -fno-compare-debug, which disables the dumping of the final representation and the second compilation, preventing even GCC_COMPARE_DEBUG from taking effect.
To verify full coverage during -fcompare-debug testing, set GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC rejects as an invalid option in any actual compilation (rather than preprocessing, assembly or linking). To get just a warning, setting GCC_COMPARE_DEBUG to ‘-w%n-fcompare-debug not overridden’ will do.
-fcompare-debug-second.gk additional extension during the second compilation, to avoid
overwriting those generated by the first.
When this option is passed to the compiler driver, it causes the first compilation to be skipped, which makes it useful for little other than debugging the compiler proper.
-gtoggle-fvar-tracking-assignments-toggle-Q-ftime-report-ftime-report-details-fira-verbose=n-flto-reportDisabled by default.
-flto-report-wpa-fmem-report-fmem-report-wpa-fpre-ipa-mem-report-fpost-ipa-mem-report-fmultiflagsTFLAGS to be used to build
target libraries with options different from those the compiler is
configured to use by default, through the use of specs (see Spec Files) set up by compiler internals, by the target, or by builders at
configure time.
Like TFLAGS, this allows the target libraries to be built for
portable baseline environments, while the compiler defaults to more
demanding ones. That's useful because users can easily override the
defaults the compiler is configured to use to build their own programs,
if the defaults are not ideal for their target environment, whereas
rebuilding the runtime libraries is usually not as easy or desirable.
Unlike TFLAGS, the use of specs enables different flags to be
selected for different multilibs. The way to accomplish that is to
build with ‘make TFLAGS=-fmultiflags’, after configuring
‘--with-specs=%{fmultiflags:...}’.
This option is discarded by the driver once it's done processing driver self spec.
It is also useful to check that TFLAGS are being used to build
all target libraries, by configuring a non-bootstrap compiler
‘--with-specs='%{!fmultiflags:%emissing TFLAGS}'’ and building
the compiler and target libraries.
-fprofile-report-fstack-usagestatic, dynamic, bounded.
The qualifier static means that the function manipulates the stack
statically: a fixed number of bytes are allocated for the frame on function
entry and released on function exit; no stack adjustments are otherwise made
in the function. The second field is this fixed number of bytes.
The qualifier dynamic means that the function manipulates the stack
dynamically: in addition to the static allocation described above, stack
adjustments are made in the body of the function, for example to push/pop
arguments around function calls. If the qualifier bounded is also
present, the amount of these adjustments is bounded at compile time and
the second field is an upper bound of the total amount of stack used by
the function. If it is not present, the amount of these adjustments is
not bounded at compile time and the second field only represents the
bounded part.
-fstats-fdbg-cnt-list-fdbg-cnt=counter-value-listdbg_cnt(dce) returns true only for second, third, fourth, tenth and
eleventh invocation.
For dbg_cnt(tail_call) true is returned for first 10 invocations.
-print-file-name=library-print-multi-directory-print-multi-lib-print-multi-os-directory-print-multiarch-print-prog-name=program-print-libgcc-file-nameThis is useful when you use -nostdlib or -nodefaultlibs but you do want to link with libgcc.a. You can do:
gcc -nostdlib files... `gcc -print-libgcc-file-name`
-print-search-dirsThis is useful when gcc prints the error message ‘installation problem, cannot exec cpp0: No such file or directory’. To resolve this you either need to put cpp0 and the other compiler components where gcc expects to find them, or you can set the environment variable GCC_EXEC_PREFIX to the directory where you installed them. Don't forget the trailing ‘/’. See Environment Variables.
-print-sysroot-print-sysroot-headers-suffix-dumpmachine-dumpversion3.0, 6.3.0 or 7)—and don't do
anything else. This is the compiler version used in filesystem paths and
specs. Depending on how the compiler has been configured it can be just
a single number (major version), two numbers separated by a dot (major and
minor version) or three numbers separated by dots (major, minor and patchlevel
version).
-dumpfullversion-dumpspecsEach target machine supported by GCC can have its own options—for example, to allow you to compile for a particular processor variant or ABI, or to control optimizations specific to that machine. By convention, the names of machine-specific options start with ‘-m’.
Some configurations of the compiler also support additional target-specific options, usually for compatibility with other compilers on the same platform.
These options are defined for AArch64 implementations:
-mabi=nameThe default depends on the specific target configuration. Note that the LP64 and ILP32 ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries.
-mbig-endian-mgeneral-regs-only-mlittle-endian-mcmodel=tiny-mcmodel=small-mcmodel=large-mstrict-align-mno-strict-align-momit-leaf-frame-pointer-mno-omit-leaf-frame-pointer-mstack-protector-guard=guard-mstack-protector-guard-reg=reg-mstack-protector-guard-offset=offsetWith the latter choice the options -mstack-protector-guard-reg=reg and -mstack-protector-guard-offset=offset furthermore specify which system register to use as base register for reading the canary, and from what offset from that base register. There is no default register or offset as this is entirely for use within the Linux kernel.
-mtls-dialect=desc-mtls-dialect=traditional-mtls-size=size-mfix-cortex-a53-835769-mno-fix-cortex-a53-835769-mfix-cortex-a53-843419-mno-fix-cortex-a53-843419-mlow-precision-recip-sqrt-mno-low-precision-recip-sqrt-mlow-precision-sqrt-mno-low-precision-sqrt-mlow-precision-div-mno-low-precision-div-mtrack-speculation-mno-track-speculation__builtin_speculation_safe_copy to permit a more efficient code
sequence to be generated.
-moutline-atomics-mno-outline-atomicsThis option is only applicable when compiling for the base ARMv8.0 instruction set. If using a later revision, e.g. -march=armv8.1-a or -march=armv8-a+lse, the ARMv8.1-Atomics instructions will be used directly. The same applies when using -mcpu= when the selected cpu supports the ‘lse’ feature. This option is on by default.
-march=nameThe table below summarizes the permissible values for arch and the features that they enable by default:
| arch value | Architecture | Includes by default
|
|---|---|---|
| ‘armv8-a’ | Armv8-A | ‘+fp’, ‘+simd’
|
| ‘armv8.1-a’ | Armv8.1-A | ‘armv8-a’, ‘+crc’, ‘+lse’, ‘+rdma’
|
| ‘armv8.2-a’ | Armv8.2-A | ‘armv8.1-a’
|
| ‘armv8.3-a’ | Armv8.3-A | ‘armv8.2-a’, ‘+pauth’
|
| ‘armv8.4-a’ | Armv8.4-A | ‘armv8.3-a’, ‘+flagm’, ‘+fp16fml’, ‘+dotprod’
|
| ‘armv8.5-a’ | Armv8.5-A | ‘armv8.4-a’, ‘+sb’, ‘+ssbs’, ‘+predres’
|
| ‘armv8.6-a’ | Armv8.6-A | ‘armv8.5-a’, ‘+bf16’, ‘+i8mm’
|
| ‘armv8.7-a’ | Armv8.7-A | ‘armv8.6-a’, ‘+ls64’
|
| ‘armv8.8-a’ | Armv8.8-a | ‘armv8.7-a’, ‘+mops’
|
| ‘armv9-a’ | Armv9-A | ‘armv8.5-a’, ‘+sve’, ‘+sve2’
|
| ‘armv9.1-a’ | Armv9.1-A | ‘armv9-a’, ‘+bf16’, ‘+i8mm’
|
| ‘armv9.2-a’ | Armv9.2-A | ‘armv9.1-a’, ‘+ls64’
|
| ‘armv9.3-a’ | Armv9.3-A | ‘armv9.2-a’, ‘+mops’
|
| ‘armv8-r’ | Armv8-R | ‘armv8-r’
|
The value ‘native’ is available on native AArch64 GNU/Linux and causes the compiler to pick the architecture of the host system. This option has no effect if the compiler is unable to recognize the architecture of the host system,
The permissible values for feature are listed in the sub-section on -march and -mcpu Feature Modifiers. Where conflicting feature modifiers are specified, the right-most feature is used.
GCC uses name to determine what kind of instructions it can emit when generating assembly code. If -march is specified without either of -mtune or -mcpu also being specified, the code is tuned to perform well across a range of target processors implementing the target architecture.
-mtune=nameThe values ‘cortex-a57.cortex-a53’, ‘cortex-a72.cortex-a53’, ‘cortex-a73.cortex-a35’, ‘cortex-a73.cortex-a53’, ‘cortex-a75.cortex-a55’, ‘cortex-a76.cortex-a55’ specify that GCC should tune for a big.LITTLE system.
The value ‘neoverse-512tvb’ specifies that GCC should tune for Neoverse cores that (a) implement SVE and (b) have a total vector bandwidth of 512 bits per cycle. In other words, the option tells GCC to tune for Neoverse cores that can execute 4 128-bit Advanced SIMD arithmetic instructions a cycle and that can execute an equivalent number of SVE arithmetic instructions per cycle (2 for 256-bit SVE, 4 for 128-bit SVE). This is more general than tuning for a specific core like Neoverse V1 but is more specific than the default tuning described below.
Additionally on native AArch64 GNU/Linux systems the value ‘native’ tunes performance to the host system. This option has no effect if the compiler is unable to recognize the processor of the host system.
Where none of -mtune=, -mcpu= or -march= are specified, the code is tuned to perform well across a range of target processors.
This option cannot be suffixed by feature modifiers.
-mcpu=nameGCC uses name to determine what kind of instructions it can emit when generating assembly code (as if by -march) and to determine the target processor for which to tune for performance (as if by -mtune). Where this option is used in conjunction with -march or -mtune, those options take precedence over the appropriate part of this option.
-mcpu=neoverse-512tvb is special in that it does not refer to a specific core, but instead refers to all Neoverse cores that (a) implement SVE and (b) have a total vector bandwidth of 512 bits a cycle. Unless overridden by -march, -mcpu=neoverse-512tvb generates code that can run on a Neoverse V1 core, since Neoverse V1 is the first Neoverse core with these properties. Unless overridden by -mtune, -mcpu=neoverse-512tvb tunes code in the same way as for -mtune=neoverse-512tvb.
-moverride=stringThis option is only intended to be useful when developing GCC.
-mverbose-cost-dump-mpc-relative-literal-loads-mno-pc-relative-literal-loads-msign-return-address=scope-mbranch-protection=none|standard|pac-ret[+leaf+b-key]|bti-mharden-sls=opts-msve-vector-bits=bitsGCC supports two forms of SVE code generation: “vector-length agnostic” output that works with any size of vector register and “vector-length specific” output that allows GCC to make assumptions about the vector length when it is useful for optimization reasons. The possible values of ‘bits’ are: ‘scalable’, ‘128’, ‘256’, ‘512’, ‘1024’ and ‘2048’. Specifying ‘scalable’ selects vector-length agnostic output. At present ‘-msve-vector-bits=128’ also generates vector-length agnostic output for big-endian targets. All other values generate vector-length specific code. The behavior of these values may change in future releases and no value except ‘scalable’ should be relied on for producing code that is portable across different hardware SVE vector lengths.
The default is ‘-msve-vector-bits=scalable’, which produces vector-length agnostic code.
Feature modifiers used with -march and -mcpu can be any of the following and their inverses nofeature:
memcpy,
memmove, memset. This option is enabled by default for
-march=armv8.8-a
Feature crypto implies aes, sha2, and simd, which implies fp. Conversely, nofp implies nosimd, which implies nocrypto, noaes and nosha2.
These ‘-m’ options are defined for Adapteva Epiphany:
-mhalf-reg-filer32...r63.
That allows code to run on hardware variants that lack these registers.
-mprefer-short-insn-regs-mbranch-cost=num-mcmove-mnops=num-mno-soft-cmpsffsub instruction
and test the flags. This is faster than a software comparison, but can
get incorrect results in the presence of NaNs, or when two different small
numbers are compared such that their difference is calculated as zero.
The default is -msoft-cmpsf, which uses slower, but IEEE-compliant,
software comparisons.
-mstack-offset=numsp+0...sp+7
can be used by leaf functions without stack allocation.
Values other than ‘8’ or ‘16’ are untested and unlikely to work.
Note also that this option changes the ABI; compiling a program with a
different stack offset than the libraries have been compiled with
generally does not work.
This option can be useful if you want to evaluate if a different stack
offset would give you better code, but to actually use a different stack
offset to build working programs, it is recommended to configure the
toolchain with the appropriate --with-stack-offset=num option.
-mno-round-nearest-mlong-callsb / bl instructions, and therefore load the
function address into a register before performing a (otherwise direct) call.
This is the default.
-mshort-callsb / bl instructions, so use these instructions
for direct calls. The default is -mlong-calls.
-msmall16-mfp-mode=modemode can be set to one the following values:
The default is -mfp-mode=caller
-mno-split-lohi-mno-postinc-mno-postmodify-mnovect-double-max-vect-align=num-msplit-vecmove-early-m1reg-regThese options are defined specifically for the AMD GCN port.
-march=gpu-mtune=gpu-msram-ecc=on-msram-ecc=off-msram-ecc=any-mstack-size=bytes-mxnackThe following options control the architecture variant for which code is being compiled:
-mbarrel-shifter-mjli-always-mcpu=cpunorm instructions enabled.
norm and 32x16-bit multiply
instructions enabled.
norm and mul64-family
instructions enabled.
norm instructions enabled.
norm and 32x16-bit multiply
instructions enabled.
norm and mul64-family
instructions enabled.
-mdpfp-mdpfp-compact-mdpfp-fast-mno-dpfp-lrsrlr and sr instructions from using FPX extension
aux registers.
-meadivaw, adds, subs, and sat16 are
supported. Only valid for -mcpu=ARC700.
-mno-mpympy-family instructions for ARC700. This option is
deprecated.
-mmul32x16-mmul64mul64 and mulu64 instructions.
Only valid for -mcpu=ARC600.
-mnormnorm instructions. This is the default if -mcpu=ARC700
is in effect.
-mspfp-mspfp-compact-mspfp-fast-msimd-msoft-float-mswapswap instructions.
-matomic-mdiv-remdiv and rem instructions for ARCv2 cores.
-mcode-density-mll64-mtp-regno=regno-mmpy-option=multompyw and mpyuw.
mpy, mpyu, mpym, mpymu, and mpy_s.
mpy,
mpyu, mpym, mpymu, and mpy_s.
mpy,
mpyu, mpym, mpymu, and mpy_s.
mpy,
mpyu, mpym, mpymu, and mpy_s.
mpy,
mpyu, mpym, mpymu, and mpy_s.
This option is only available for ARCv2 cores.
-mfpu=fpu-mirq-ctrl-saved=register-range, blink, lp_countr0, the upper limit is fp register.
blink and lp_count are optional. This option is only
valid for ARC EM and ARC HS cores.
-mrgf-banked-regs=number-mlpc-width=widthlp_count register. Valid values for
width are 8, 16, 20, 24, 28 and 32 bits. The default width is
fixed to 32 bits. If the width is less than 32, the compiler does not
attempt to transform loops in your program to use the zero-delay loop
mechanism unless it is known that the lp_count register can
hold the required loop-counter value. Depending on the width
specified, the compiler and run-time library might continue to use the
loop mechanism for various needs. This option defines macro
__ARC_LPC_WIDTH__ with the value of width.
-mrf16__ARC_RF16__
preprocessor macro.
-mbranch-indexbi or bih instructions to implement jump
tables.
The following options are passed through to the assembler, and also define preprocessor macro symbols.
-mdsp-packa__Xdsp_packa. This option is
deprecated.
-mdvbf__Xdvbf. This
option is deprecated.
-mlock__Xlock.
-mmac-d16__Xxmac_d16. This option is deprecated.
-mmac-24__Xxmac_24. This option is deprecated.
-mrtsc__Xrtsc. This option is deprecated.
-mswape__Xswape.
-mtelephony__Xtelephony. This option is deprecated.
-mxy__Xxy.
The following options control how the assembly code is annotated:
-misize-mannotate-alignThe following options are passed through to the linker:
-marclinuxarclinux emulation.
This option is enabled by default in tool chains built for
arc-linux-uclibc and arceb-linux-uclibc targets
when profiling is not requested.
-marclinux_profarclinux_prof emulation. This option is enabled by default in
tool chains built for arc-linux-uclibc and
arceb-linux-uclibc targets when profiling is requested.
The following options control the semantics of generated code:
-mlong-calls-mmedium-callsarc-linux-uclibc and arceb-linux-uclibc targets.
-G num-mno-sdataarc-linux-uclibc and arceb-linux-uclibc
targets.
-mvolatile-cache-mno-volatile-cacheThe following options fine tune code generation:
-malign-call-mauto-modify-reg-mbbit-peephole-mno-brccbrcc) instructions.
It has no effect on
generation of these instructions driven by the combiner pass.
-mcase-vector-pcrel-mcompact-casesicasesi pattern. This is the default for -Os,
and only available for ARCv1 cores. This option is deprecated.
-mno-cond-execDue to delay slot scheduling and interactions between operand numbers, literal sizes, instruction lengths, and the support for conditional execution, the target-independent pass to generate conditional execution is often lacking, so the ARC port has kept a special pass around that tries to find more conditional execution generation opportunities after register allocation, branch shortening, and delay slot scheduling have been done. This pass generally, but not always, improves performance and code size, at the cost of extra compilation time, which is why there is an option to switch it off. If you have a problem with call instructions exceeding their allowable offset range because they are conditionalized, you should consider using -mmedium-calls instead.
-mearly-cbranchsicbranchsi pattern.
-mexpand-adddiadddi3 and subdi3 at RTL generation time into
add.f, adc etc. This option is deprecated.
-mindexed-loads-mlra-mlra-priority-none-mlra-priority-compact-mlra-priority-noncompact-mmillicode-mcode-density-frameenter and leave
instructions. These instructions are only valid for CPUs with
code-density feature.
-mmixed-code-mq-class-mRcq-mRcw-msize-level=levelThis defaults to ‘3’ when -Os is in effect. Otherwise, the behavior when this is not set is equivalent to level ‘1’.
-mtune=cpuSupported values for cpu are
dbnz instruction.
-mmultcost=num-munalign-prob-threshold=probabilityThe following options are maintained for backward compatibility, but are now deprecated and will be removed in a future release:
-margonaut-mbig-endian-EBarceb-elf32 and arceb-linux-uclibc targets,
for which big endian is the default.
-mlittle-endian-ELarc-elf32 and arc-linux-uclibc targets,
for which little endian is the default.
-mbarrel_shifter-mdpfp_compact-mdpfp_fast-mdsp_packa-mEA-mmac_24-mmac_d16-mspfp_compact-mspfp_fast-mtune=cpu-multcost=numThese ‘-m’ options are defined for the ARM port:
-mabi=name-mapcs-frame-mapcs-mthumb-interwork-mno-sched-prolog-mfloat-abi=nameSpecifying ‘soft’ causes GCC to generate output containing library calls for floating-point operations. ‘softfp’ allows the generation of code using hardware floating-point instructions, but still uses the soft-float calling conventions. ‘hard’ allows generation of floating-point instructions and uses FPU-specific calling conventions.
The default depends on the specific target configuration. Note that the hard-float and soft-float ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries.
-mgeneral-regs-only-mlittle-endian-mbig-endian-mbe8-mbe32-march=name[+extension...]Permissible names are: ‘armv4t’, ‘armv5t’, ‘armv5te’, ‘armv6’, ‘armv6j’, ‘armv6k’, ‘armv6kz’, ‘armv6t2’, ‘armv6z’, ‘armv6zk’, ‘armv7’, ‘armv7-a’, ‘armv7ve’, ‘armv8-a’, ‘armv8.1-a’, ‘armv8.2-a’, ‘armv8.3-a’, ‘armv8.4-a’, ‘armv8.5-a’, ‘armv8.6-a’, ‘armv9-a’, ‘armv7-r’, ‘armv8-r’, ‘armv6-m’, ‘armv6s-m’, ‘armv7-m’, ‘armv7e-m’, ‘armv8-m.base’, ‘armv8-m.main’, ‘armv8.1-m.main’, ‘armv9-a’, ‘iwmmxt’ and ‘iwmmxt2’.
Additionally, the following architectures, which lack support for the Thumb execution state, are recognized but support is deprecated: ‘armv4’.
Many of the architectures support extensions. These can be added by appending ‘+extension’ to the architecture name. Extension options are processed in order and capabilities accumulate. An extension will also enable any necessary base extensions upon which it depends. For example, the ‘+crypto’ extension will always enable the ‘+simd’ extension. The exception to the additive construction is for extensions that are prefixed with ‘+no...’: these extensions disable the specified option and any other extensions that may depend on the presence of that extension.
For example, ‘-march=armv7-a+simd+nofp+vfpv4’ is equivalent to writing ‘-march=armv7-a+vfpv4’ since the ‘+simd’ option is entirely disabled by the ‘+nofp’ option that follows it.
Most extension names are generically named, but have an effect that is dependent upon the architecture to which it is applied. For example, the ‘+simd’ option can be applied to both ‘armv7-a’ and ‘armv8-a’ architectures, but will enable the original ARMv7-A Advanced SIMD (Neon) extensions for ‘armv7-a’ and the ARMv8-A variant for ‘armv8-a’.
The table below lists the supported extensions for each architecture. Architectures not mentioned do not support any extensions.
-march=native causes the compiler to auto-detect the architecture of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect.
-mtune=nameAdditionally, this option can specify that GCC should tune the performance of the code for a big.LITTLE system. Permissible names are: ‘cortex-a15.cortex-a7’, ‘cortex-a17.cortex-a7’, ‘cortex-a57.cortex-a53’, ‘cortex-a72.cortex-a53’, ‘cortex-a72.cortex-a35’, ‘cortex-a73.cortex-a53’, ‘cortex-a75.cortex-a55’, ‘cortex-a76.cortex-a55’.
-mtune=generic-arch specifies that GCC should tune the performance for a blend of processors within architecture arch. The aim is to generate code that run well on the current most popular processors, balancing between optimizations that benefit some CPUs in the range, and avoiding performance pitfalls of other CPUs. The effects of this option may change in future GCC versions as CPU models come and go.
-mtune permits the same extension options as -mcpu, but the extension options do not affect the tuning of the generated code.
-mtune=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect.
-mcpu=name[+extension...]Many of the supported CPUs implement optional architectural extensions. Where this is so the architectural extensions are normally enabled by default. If implementations that lack the extension exist, then the extension syntax can be used to disable those extensions that have been omitted. For floating-point and Advanced SIMD (Neon) instructions, the settings of the options -mfloat-abi and -mfpu must also be considered: floating-point and Advanced SIMD instructions will only be used if -mfloat-abi is not set to ‘soft’; and any setting of -mfpu other than ‘auto’ will override the available floating-point and SIMD extension instructions.
For example, ‘cortex-a9’ can be found in three major configurations: integer only, with just a floating-point unit or with floating-point and Advanced SIMD. The default is to enable all the instructions, but the extensions ‘+nosimd’ and ‘+nofp’ can be used to disable just the SIMD or both the SIMD and floating-point instructions respectively.
Permissible names for this option are the same as those for -mtune.
The following extension options are common to the listed CPUs:
Additionally the ‘generic-armv7-a’ pseudo target defaults to VFPv3 with 16 double-precision registers. It supports the following extension options: ‘mp’, ‘sec’, ‘vfpv3-d16’, ‘vfpv3’, ‘vfpv3-d16-fp16’, ‘vfpv3-fp16’, ‘vfpv4-d16’, ‘vfpv4’, ‘neon’, ‘neon-vfpv3’, ‘neon-fp16’, ‘neon-vfpv4’. The meanings are the same as for the extensions to -march=armv7-a.
-mcpu=generic-arch is also permissible, and is equivalent to -march=arch -mtune=generic-arch. See -mtune for more information.
-mcpu=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect.
-mfpu=nameThe setting ‘auto’ is the default and is special. It causes the compiler to select the floating-point and Advanced SIMD instructions based on the settings of -mcpu and -march.
If the selected floating-point hardware includes the NEON extension (e.g. -mfpu=neon), note that floating-point operations are not generated by GCC's auto-vectorization pass unless -funsafe-math-optimizations is also specified. This is because NEON hardware does not fully implement the IEEE 754 standard for floating-point arithmetic (in particular denormal values are treated as zero), so the use of NEON instructions may lead to a loss of precision.
You can also set the fpu name at function level by using the target("fpu=") function attributes (see ARM Function Attributes) or pragmas (see Function Specific Option Pragmas).
-mfp16-format=name__fp16 half-precision floating-point type.
Permissible names are ‘none’, ‘ieee’, and ‘alternative’;
the default is ‘none’, in which case the __fp16 type is not
defined. See Half-Precision, for more information.
-mstructure-size-boundary=nSpecifying a larger number can produce faster, more efficient code, but can also increase the size of the program. Different values are potentially incompatible. Code compiled with one value cannot necessarily expect to work with code or libraries compiled with another value, if they exchange information using structures or unions.
This option is deprecated.
-mabort-on-noreturnabort at the end of a
noreturn function. It is executed if the function tries to
return.
-mlong-calls-mno-long-callsEven if this switch is enabled, not all function calls are turned
into long calls. The heuristic is that static functions, functions
that have the short_call attribute, functions that are inside
the scope of a #pragma no_long_calls directive, and functions whose
definitions have already been compiled within the current compilation
unit are not turned into long calls. The exceptions to this rule are
that weak function definitions, functions with the long_call
attribute or the section attribute, and functions that are within
the scope of a #pragma long_calls directive are always
turned into long calls.
This feature is not enabled by default. Specifying
-mno-long-calls restores the default behavior, as does
placing the function calls within the scope of a #pragma
long_calls_off directive. Note these switches have no effect on how
the compiler generates code to handle function calls via function
pointers.
-msingle-pic-base-mpic-register=reg-mpic-data-is-text-relative-mpoke-function-name t0
.ascii "arm_poke_function_name", 0
.align
t1
.word 0xff000000 + (t1 - t0)
arm_poke_function_name
mov ip, sp
stmfd sp!, {fp, ip, lr, pc}
sub fp, ip, #4
When performing a stack backtrace, code can inspect the value of
pc stored at fp + 0. If the trace function then looks at
location pc - 12 and the top 8 bits are set, then we know that
there is a function name embedded immediately preceding this location
and has length ((pc[-3]) & 0xff000000).
-mthumb-marmYou can also override the ARM and Thumb mode for each function
by using the target("thumb") and target("arm") function attributes
(see ARM Function Attributes) or pragmas (see Function Specific Option Pragmas).
-mflip-thumb-mtpcs-frame-mtpcs-leaf-frame-mcallee-super-interworking-mcaller-super-interworking-mtp=name__aeabi_read_tp,
‘cp15’, which fetches the thread pointer from cp15 directly
(supported in the arm6k architecture), and ‘auto’, which uses the
best available method for the selected processor. The default setting is
‘auto’.
-mtls-dialect=dialect-mword-relocations-mfix-cortex-m3-ldrdldrd instructions
with overlapping destination and base registers are used. This option avoids
generating these instructions. This option is enabled by default when
-mcpu=cortex-m3 is specified.
-mfix-cortex-a57-aes-1742098-mno-fix-cortex-a57-aes-1742098-mfix-cortex-a72-aes-1655431-mno-fix-cortex-a72-aes-1655431-munaligned-access-mno-unaligned-accessThe ARM attribute Tag_CPU_unaligned_access is set in the
generated object file to either true or false, depending upon the
setting of this option. If unaligned access is enabled then the
preprocessor symbol __ARM_FEATURE_UNALIGNED is also
defined.
-mneon-for-64bits-mslow-flash-data-masm-syntax-unified-mrestrict-it-mprint-tune-info-mverbose-cost-dump-mpure-codeSHF_ARM_PURECODE. This option
is only available when generating non-pic code for M-profile targets.
-mcmse-mfix-cmse-cve-2021-35465VLLDM instruction
in some M-profile devices when using CMSE (CVE-2021-365465). This option is
enabled by default when the option -mcpu= is used with
cortex-m33, cortex-m35p, cortex-m55, cortex-m85
or star-mc1. The option -mno-fix-cmse-cve-2021-35465 can be used
to disable the mitigation.
-mstack-protector-guard=guard-mstack-protector-guard-offset=offset-mfdpic-mno-fdpicarm-*-uclinuxfdpiceabi targets, this option is on by default
and implies -fPIE if none of the PIC/PIE-related options is
provided. On other targets, it only enables the FDPIC-specific code
generation features, and the user should explicitly provide the
PIC/PIE-related options as needed.
Note that static linking is not supported because it would still involve the dynamic linker when the program self-relocates. If such behavior is acceptable, use -static and -Wl,-dynamic-linker options.
The opposite -mno-fdpic option is useful (and required) to
build the Linux kernel using the same (arm-*-uclinuxfdpiceabi)
toolchain as the one used to build the userland programs.
-mbranch-protection=none|standard|pac-ret[+leaf][+bti]|bti[+pac-ret[+leaf]]If the ‘+pacbti’ architecture extension is not enabled, then all branch protection and return address signing operations are constrained to use only the instructions defined in the architectural-NOP space. The generated code will remain backwards-compatible with earlier versions of the architecture, but the additional security can be enabled at run time on processors that support the ‘PACBTI’ extension.
Branch target enforcement using BTI can only be enabled at runtime if all code in the application has been compiled with at least ‘-mbranch-protection=bti’.
Any setting other than ‘none’ is supported only on armv8-m.main or later.
The default is to generate code without branch protection or return address signing.
These options are defined for AVR implementations:
-mmcu=mcuavr2.
The following AVR devices and ISAs are supported.
Note: A complete device support consists of
startup code crtmcu.o, a device header avr/io*.h,
a device library libmcu.a and a
device-specs file
specs-mcu. Only the latter is provided by the compiler
according the supported mcus below. The rest is supported
by AVR-LibC, or by means of
atpack files
from the hardware manufacturer.
avr2attiny22, attiny26, at90s2313, at90s2323, at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90c8534, at90s8515, at90s8535.
avr25MOVW instruction.
attiny13, attiny13a, attiny24, attiny24a, attiny25, attiny261, attiny261a, attiny2313, attiny2313a, attiny43u, attiny44, attiny44a, attiny45, attiny48, attiny441, attiny461, attiny461a, attiny4313, attiny84, attiny84a, attiny85, attiny87, attiny88, attiny828, attiny841, attiny861, attiny861a, ata5272, ata6616c, at86rf401.
avr3at76c711, at43usb355.
avr31atmega103, at43usb320.
avr35MOVW instruction.
attiny167, attiny1634, atmega8u2, atmega16u2, atmega32u2, ata5505, ata6617c, ata664251, at90usb82, at90usb162.
avr4atmega48, atmega48a, atmega48p, atmega48pa, atmega48pb, atmega8, atmega8a, atmega8hva, atmega88, atmega88a, atmega88p, atmega88pa, atmega88pb, atmega8515, atmega8535, ata5795, ata6285, ata6286, ata6289, ata6612c, at90pwm1, at90pwm2, at90pwm2b, at90pwm3, at90pwm3b, at90pwm81.
avr5atmega16, atmega16a, atmega16hva, atmega16hva2, atmega16hvb, atmega16hvbrevb, atmega16m1, atmega16u4, atmega161, atmega162, atmega163, atmega164a, atmega164p, atmega164pa, atmega165, atmega165a, atmega165p, atmega165pa, atmega168, atmega168a, atmega168p, atmega168pa, atmega168pb, atmega169, atmega169a, atmega169p, atmega169pa, atmega32, atmega32a, atmega32c1, atmega32hvb, atmega32hvbrevb, atmega32m1, atmega32u4, atmega32u6, atmega323, atmega324a, atmega324p, atmega324pa, atmega324pb, atmega325, atmega325a, atmega325p, atmega325pa, atmega328, atmega328p, atmega328pb, atmega329, atmega329a, atmega329p, atmega329pa, atmega3250, atmega3250a, atmega3250p, atmega3250pa, atmega3290, atmega3290a, atmega3290p, atmega3290pa, atmega406, atmega64, atmega64a, atmega64c1, atmega64hve, atmega64hve2, atmega64m1, atmega64rfr2, atmega640, atmega644, atmega644a, atmega644p, atmega644pa, atmega644rfr2, atmega645, atmega645a, atmega645p, atmega649, atmega649a, atmega649p, atmega6450, atmega6450a, atmega6450p, atmega6490, atmega6490a, atmega6490p, ata5790, ata5790n, ata5791, ata6613c, ata6614q, ata5782, ata5831, ata8210, ata8510, ata5787, ata5835, ata5700m322, ata5702m322, at90pwm161, at90pwm216, at90pwm316, at90can32, at90can64, at90scr100, at90usb646, at90usb647, at94k, m3000.
avr51atmega128, atmega128a, atmega128rfa1, atmega128rfr2, atmega1280, atmega1281, atmega1284, atmega1284p, atmega1284rfr2, at90can128, at90usb1286, at90usb1287.
avr6atmega256rfr2, atmega2560, atmega2561, atmega2564rfr2.
avrxmega2atxmega8e5, atxmega16a4, atxmega16a4u, atxmega16c4, atxmega16d4, atxmega16e5, atxmega32a4, atxmega32a4u, atxmega32c3, atxmega32c4, atxmega32d3, atxmega32d4, atxmega32e5, avr64da28, avr64da32, avr64da48, avr64da64, avr64db28, avr64db32, avr64db48, avr64db64, avr64dd14, avr64dd20, avr64dd28, avr64dd32, avr64du28, avr64du32, avr64ea28, avr64ea32, avr64ea48, avr64sd28, avr64sd32, avr64sd48.
avrxmega3attiny202, attiny204, attiny212, attiny214, attiny402, attiny404, attiny406, attiny412, attiny414, attiny416, attiny416auto, attiny417, attiny424, attiny426, attiny427, attiny804, attiny806, attiny807, attiny814, attiny816, attiny817, attiny824, attiny826, attiny827, attiny1604, attiny1606, attiny1607, attiny1614, attiny1616, attiny1617, attiny1624, attiny1626, attiny1627, attiny3214, attiny3216, attiny3217, attiny3224, attiny3226, attiny3227, atmega808, atmega809, atmega1608, atmega1609, atmega3208, atmega3209, atmega4808, atmega4809, avr16dd14, avr16dd20, avr16dd28, avr16dd32, avr16du14, avr16du20, avr16du28, avr16du32, avr16ea28, avr16ea32, avr16ea48, avr16eb14, avr16eb20, avr16eb28, avr16eb32, avr32da28, avr32da32, avr32da48, avr32db28, avr32db32, avr32db48, avr32dd14, avr32dd20, avr32dd28, avr32dd32, avr32du14, avr32du20, avr32du28, avr32du32, avr32ea28, avr32ea32, avr32ea48, avr32sd20, avr32sd28, avr32sd32.
avrxmega4atxmega64a3, atxmega64a3u, atxmega64a4u, atxmega64b1, atxmega64b3, atxmega64c3, atxmega64d3, atxmega64d4, avr128da28, avr128da32, avr128da48, avr128da64, avr128db28, avr128db32, avr128db48, avr128db64.
avrxmega5atxmega64a1, atxmega64a1u.
avrxmega6atxmega128a3, atxmega128a3u, atxmega128b1, atxmega128b3, atxmega128c3, atxmega128d3, atxmega128d4, atxmega192a3, atxmega192a3u, atxmega192c3, atxmega192d3, atxmega256a3, atxmega256a3b, atxmega256a3bu, atxmega256a3u, atxmega256c3, atxmega256d3, atxmega384c3, atxmega384d3.
avrxmega7atxmega128a1, atxmega128a1u, atxmega128a4u.
avrtinyattiny4, attiny5, attiny9, attiny10, attiny102, attiny104, attiny20, attiny40.
avr1attiny11, attiny12, attiny15, attiny28, at90s1200.
-mabsdataabsdata
variable attribute.
-maccumulate-argsPopping the arguments after the function call can be expensive on AVR so that accumulating the stack space might lead to smaller executables because arguments need not be removed from the stack after such a function call.
This option can lead to reduced code size for functions that perform several calls to functions that get their arguments on the stack like calls to printf-like functions.
-mbranch-cost=cost-mcall-prologues-mdouble=bits-mlong-double=bitsdouble or long double type,
respectively. Possible values for bits are 32 and 64.
Whether or not a specific value for bits is allowed depends on
the --with-double= and --with-long-double=
configure options,
and the same applies for the default values of the options.
-mgas-isr-prologues__gcc_isr pseudo
instruction supported by GNU Binutils.
If this option is on, the feature can still be disabled for individual
ISRs by means of the no_gccisr
function attribute. This feature is activated per default
if optimization is on (but not with -Og, see Optimize Options),
and if GNU Binutils support PR21683.
-mint8int to be 8-bit integer. This affects the sizes of all types: a
char is 1 byte, an int is 1 byte, a long is 2 bytes,
and long long is 4 bytes. Please note that this option does not
conform to the C standards, but it results in smaller code
size.
-mmain-is-OS_taskmain. The effect is the same like
attaching attribute OS_task
to main. It is activated per default if optimization is on.
-mno-interrupts-mrelaxCALL resp. JMP instruction by the shorter
RCALL resp. RJMP instruction if applicable.
Setting -mrelax just adds the --mlink-relax option to
the assembler's command line and the --relax option to the
linker's command line.
Jump relaxing is performed by the linker because jump offsets are not known before code is located. Therefore, the assembler code generated by the compiler is the same, but the instructions in the executable may differ from instructions in the assembler code.
Relaxing must be turned on if linker stubs are needed, see the
section on EIND and linker stubs below.
-mstrict-XX in a way proposed by the hardware. This means
that X is only used in indirect, post-increment or
pre-decrement addressing.
Without this option, the X register may be used in the same way
as Y or Z which then is emulated by additional
instructions.
For example, loading a value with X+const addressing with a
small non-negative const < 64 to a register Rn is
performed as
adiw r26, const ; X += const
ld Rn, X ; Rn = *X
sbiw r26, const ; X -= const
-mtiny-stack-mfract-convert-truncate-nodeviceliblib<mcu>.a.
-nodevicespecsThis option can also serve as a replacement for the older way of
specifying custom device-specs files that needed -B some-path to point to a directory
which contains a folder named device-specs which contains a specs file named
specs-mcu, where mcu was specified by -mmcu=mcu.
-Waddr-space-convert-Wmisspelled-isrEIND and Devices with More Than 128 Ki Bytes of FlashPointers in the implementation are 16 bits wide. The address of a function or label is represented as word address so that indirect jumps and calls can target any code address in the range of 64 Ki words.
In order to facilitate indirect jump on devices with more than 128 Ki
bytes of program memory space, there is a special function register called
EIND that serves as most significant part of the target address
when EICALL or EIJMP instructions are used.
Indirect jumps and calls on these devices are handled as follows by the compiler and are subject to some limitations:
EIND.
EIND implicitly in EICALL/EIJMP
instructions or might read EIND directly in order to emulate an
indirect call/jump by means of a RET instruction.
EIND never changes during the startup
code or during the application. In particular, EIND is not
saved/restored in function or interrupt service routine
prologue/epilogue.
EIND = 0.
If code is supposed to work for a setup with EIND != 0, a custom
linker script has to be used in order to place the sections whose
name start with .trampolines into the segment where EIND
points to.
EIND.
Notice that startup code is a blend of code from libgcc and AVR-LibC.
For the impact of AVR-LibC on EIND, see the
AVR-LibC user manual.
EIND
early, for example by means of initialization code located in
section .init3. Such code runs prior to general startup code
that initializes RAM and calls constructors, but after the bit
of startup code from AVR-LibC that sets EIND to the segment
where the vector table is located.
#include <avr/io.h>
static void
__attribute__((section(".init3"),naked,used,no_instrument_function))
init3_set_eind (void)
{
__asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
"out %i0,r24" :: "n" (&EIND) : "r24","memory");
}
The __trampolines_start symbol is defined in the linker script.
gs modifier
(short for generate stubs) like so:
LDI r24, lo8(gs(func))
LDI r25, hi8(gs(func))
gs modifiers for code labels in the
following situations:
gs() modifier explained above.
int main (void)
{
/* Call function at word address 0x2 */
return ((int(*)(void)) 0x2)();
}
Instead, a stub has to be set up, i.e. the function has to be called
through a symbol (func_4 in the example):
int main (void)
{
extern int func_4 (void);
/* Call function at byte address 0x4 */
return func_4();
}
and the application be linked with -Wl,--defsym,func_4=0x4.
Alternatively, func_4 can be defined in the linker script.
RAMPD, RAMPX, RAMPY and RAMPZ Special Function RegistersSome AVR devices support memories larger than the 64 KiB range
that can be accessed with 16-bit pointers. To access memory locations
outside this 64 KiB range, the content of a RAMP
register is used as high part of the address:
The X, Y, Z address register is concatenated
with the RAMPX, RAMPY, RAMPZ special function
register, respectively, to get a wide address. Similarly,
RAMPD is used together with direct addressing.
RAMP special function
registers with zero.
__flash is used, then RAMPZ is set
as needed before the operation.
RAMPZ to accomplish an operation, RAMPZ
is reset to zero after the operation.
RAMP register, the ISR
prologue/epilogue saves/restores that SFR and initializes it with
zero in case the ISR code might (implicitly) use it.
RAMP registers,
you must reset it to zero after the access.
GCC defines several built-in macros so that the user code can test for the presence or absence of features. Almost any of the following built-in macros are deduced from device capabilities and thus triggered by the -mmcu= command-line option.
For even more AVR-specific built-in macros see AVR Named Address Spaces and AVR Built-in Functions.
__AVR_ARCH__2, 25, 3, 31, 35,
4, 5, 51, 6
for mcu=avr2, avr25, avr3, avr31,
avr35, avr4, avr5, avr51, avr6,
respectively and
100,
102, 103, 104,
105, 106, 107
for mcu=avrtiny,
avrxmega2, avrxmega3, avrxmega4,
avrxmega5, avrxmega6, avrxmega7, respectively.
If mcu specifies a device, this built-in macro is set
accordingly. For example, with -mmcu=atmega8 the macro is
defined to 4.
__AVR_Device____AVR_ATmega8__, -mmcu=attiny261a defines
__AVR_ATtiny261A__, etc.
The built-in macros' names follow
the scheme __AVR_Device__ where Device is
the device name as from the AVR user manual. The difference between
Device in the built-in macro and device in
-mmcu=device is that the latter is always lowercase.
If device is not a device but only a core architecture like
‘avr51’, this macro is not defined.
__AVR_DEVICE_NAME__atmega8.
If device is not a device but only a core architecture like
‘avr51’, this macro is not defined.
__AVR_XMEGA____AVR_HAVE_ADIW__ADIW and SBIW instructions.
__AVR_HAVE_ELPM__ELPM instruction.
__AVR_HAVE_ELPMX__ELPM Rn,Z and ELPM
Rn,Z+ instructions.
__AVR_HAVE_LPMX__LPM Rn,Z and
LPM Rn,Z+ instructions.
__AVR_HAVE_MOVW__MOVW instruction to perform 16-bit
register-register moves.
__AVR_HAVE_MUL____AVR_HAVE_JMP_CALL__JMP and CALL instructions.
This is the case for devices with more than 8 KiB of program
memory.
__AVR_HAVE_EIJMP_EICALL____AVR_3_BYTE_PC__EIJMP and EICALL instructions.
This is the case for devices with more than 128 KiB of program memory.
This also means that the program counter
(PC) is 3 bytes wide.
__AVR_2_BYTE_PC____AVR_HAVE_8BIT_SP____AVR_HAVE_16BIT_SP____AVR_HAVE_SPH____AVR_SP8____AVR_HAVE_RAMPD____AVR_HAVE_RAMPX____AVR_HAVE_RAMPY____AVR_HAVE_RAMPZ__RAMPD, RAMPX, RAMPY,
RAMPZ special function register, respectively.
__NO_INTERRUPTS____AVR_ERRATA_SKIP____AVR_ERRATA_SKIP_JMP_CALL__SBRS, SBRC, SBIS, SBIC and CPSE.
The second macro is only defined if __AVR_HAVE_JMP_CALL__ is also
set.
__AVR_ISA_RMW____AVR_SFR_OFFSET__=offsetIN, OUT, SBI, etc. may use a different
address as if addressed by an instruction to access RAM like LD
or STS. This offset depends on the device architecture and has
to be subtracted from the RAM address in order to get the
respective I/O address.
__AVR_SHORT_CALLS____AVR_PM_BASE_ADDRESS__=addrLD*
instructions. The flash memory is seen in the data address space
at an offset of __AVR_PM_BASE_ADDRESS__. If this macro
is not defined, this feature is not available. If defined,
the address space is linear and there is no need to put
.rodata into RAM. This is handled by the default linker
description file, and is currently available for
avrtiny and avrxmega3. Even more convenient,
there is no need to use address spaces like __flash or
features like attribute progmem and pgm_read_*.
__WITH_AVRLIBC____HAVE_DOUBLE_MULTILIB____HAVE_DOUBLE32____HAVE_DOUBLE64____DEFAULT_DOUBLE__double if -mdouble= is not set.
To test the layout of double in a program, use the built-in
macro __SIZEOF_DOUBLE__.
__HAVE_LONG_DOUBLE32____HAVE_LONG_DOUBLE64____HAVE_LONG_DOUBLE_MULTILIB____DEFAULT_LONG_DOUBLE__long double instead of double.
__WITH_DOUBLE_COMPARISON__--with-double-comparison={tristate|bool|libf7}
configure option
and is defined to 2 or 3.
__WITH_LIBF7_LIBGCC____WITH_LIBF7_MATH____WITH_LIBF7_MATH_SYMBOLS__--with-libf7={libgcc|math|math-symbols}
configure option.
The following options are used internally by the compiler and to communicate between device specs files and the compiler proper. You don't need to set these options by hand, in particular they are not optimization options. Using these options in the wrong way may lead to sub-optimal or wrong code. They are documented for completeness, and in order to get a better understanding of device specs files.
-mn-flash=num__flashN address spaces are available.
-mrmwXCH, LAC, LAS and LAT.
-mshort-callsRJMP and RCALL can target the whole
program memory. This option is used for multilib generation and selection
for the devices from architecture avrxmega3.
-mskip-bugCPSE, SBRS,
SBRC, SBIS, SBIC) over 32-bit instructions.
-msp8avr2 and avr25.
These architectures mix devices with and without SPH.
-mcpu=cpu[-sirevision]The optional sirevision specifies the silicon revision of the target
Blackfin processor. Any workarounds available for the targeted silicon revision
are enabled. If sirevision is ‘none’, no workarounds are enabled.
If sirevision is ‘any’, all workarounds for the targeted processor
are enabled. The __SILICON_REVISION__ macro is defined to two
hexadecimal digits representing the major and minor numbers in the silicon
revision. If sirevision is ‘none’, the __SILICON_REVISION__
is not defined. If sirevision is ‘any’, the
__SILICON_REVISION__ is defined to be 0xffff.
If this optional sirevision is not used, GCC assumes the latest known
silicon revision of the targeted Blackfin processor.
GCC defines a preprocessor macro for the specified cpu. For the ‘bfin-elf’ toolchain, this option causes the hardware BSP provided by libgloss to be linked in if -msim is not given.
Without this option, ‘bf532’ is used as the processor by default.
Note that support for ‘bf561’ is incomplete. For ‘bf561’, only the preprocessor macro is defined.
-msim-momit-leaf-frame-pointer-mspecld-anomaly__WORKAROUND_SPECULATIVE_LOADS is defined.
-mno-specld-anomaly-mcsync-anomaly__WORKAROUND_SPECULATIVE_SYNCS is defined.
-mno-csync-anomaly-mlow64k-mno-low64k-mstack-check-l1-mid-shared-library-mno-id-shared-library-mleaf-id-shared-library-mno-leaf-id-shared-library-mshared-library-id=n-msep-data-mno-sep-data-mlong-calls-mno-long-callsThis feature is not enabled by default. Specifying -mno-long-calls restores the default behavior. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers.
-mfast-fp-minline-plt-mmulticore__BFIN_MULTICORE.
It can only be used with -mcpu=bf561[-sirevision].
This option can be used with -mcorea or -mcoreb, which
selects the one-application-per-core programming model. Without
-mcorea or -mcoreb, the single-application/dual-core
programming model is used. In this model, the main function of Core B
should be named as coreb_main.
If this option is not used, the single-core application programming model is used.
-mcorea__BFIN_COREA is defined.
This option can only be used in conjunction with -mmulticore.
-mcoreb__BFIN_COREB is defined. When this option is used, coreb_main
should be used instead of main.
This option can only be used in conjunction with -mmulticore.
-msdram__BFIN_SDRAM is defined.
The loader should initialize SDRAM before loading the application.
-micplb-march=name-mbig-endian-mlittle-endian-msim-msdata=default.neardata section,
which is pointed to by register B14. Put small uninitialized
global and static data in the .bss section, which is adjacent
to the .neardata section. Put small read-only data into the
.rodata section. The corresponding sections used for large
pieces of data are .fardata, .far and .const.
-msdata=allB14 register to
access them.
-msdata=none.fardata section, and all uninitialized data in the
.far section. Put all constant data into the .const
section.
These options are defined specifically for the CRIS ports.
-march=architecture-type-mcpu=architecture-type-mtune=architecture-type-mmax-stack-frame=n-metrax4-metrax100-mmul-bug-workaround-mno-mul-bug-workaroundmuls and mulu instructions for CPU
models where it applies. This option is disabled by default.
-mpdebug-mcc-init-mno-side-effects-mstack-align-mno-stack-align-mdata-align-mno-data-align-mconst-align-mno-const-align-m32-bit-m16-bit-m8-bit-mno-prologue-epilogue-mprologue-epilogue-melf-sim-sim2GCC supports these options when compiling for C-SKY V2 processors.
-march=arch-mcpu=cpu-mbig-endian-EB-mlittle-endian-EL-mfloat-abi=nameSpecifying ‘soft’ causes GCC to generate output containing library calls for floating-point operations. ‘softfp’ allows the generation of code using hardware floating-point instructions, but still uses the soft-float calling conventions. ‘hard’ allows generation of floating-point instructions and uses FPU-specific calling conventions.
The default depends on the specific target configuration. Note that the hard-float and soft-float ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries.
-mhard-float-msoft-float-mdouble-float-mno-double-float-mfdivdu-mno-fdivdufrecipd, fsqrtd, and fdivd instructions.
This is the default except when compiling for CK803.
-mfpu=fpu-melrw-mno-elrwlrw instruction. This option defaults to on
for CK801 and off otherwise.
-mistack-mno-istackThe -mistack option is required to handle the
interrupt and isr function attributes
(see C-SKY Function Attributes).
-mmp-mcp-mcache-msecurity-mtrust-mdsp-medsp-mvdsp-mdiv-mno-div-msmart-mno-smart-mhigh-registers-mno-high-registers-manchor-mno-anchor-mpushpop-mno-pushpoppush and pop instructions. This option
defaults to on.
-mmultiple-stld-mstm-mno-multiple-stld-mno-stmstm and ldm instructions. This option
isn't supported on CK801 but is enabled by default on other processors.
-mconstpool-mno-constpool-mstack-size-mno-stack-size.stack_size directives for each function in the assembly
output. This option defaults to off.
-mccrt-mno-ccrt-mbranch-cost=nn instructions. The default is 1.
-msched-prolog-mno-sched-prolog-msimThese options are defined for all architectures running the Darwin operating system.
FSF GCC on Darwin does not create “fat” object files; it creates an object file for the single architecture that GCC was built to target. Apple's GCC on Darwin does create “fat” files if multiple -arch options are used; it does so by running the compiler or linker multiple times and joining the results together with lipo.
The subtype of the file created (like ‘ppc7400’ or ‘ppc970’ or ‘i686’) is determined by the flags that specify the ISA that GCC is targeting, like -mcpu or -march. The -force_cpusubtype_ALL option can be used to override this.
The Darwin tools vary in their behavior when presented with an ISA mismatch. The assembler, as, only permits instructions to be used that are valid for the subtype of the file it is generating, so you cannot put 64-bit instructions in a ‘ppc750’ object file. The linker for shared libraries, /usr/bin/libtool, fails and prints an error if asked to create a shared library with a less restrictive subtype than its input files (for instance, trying to put a ‘ppc970’ object file in a ‘ppc7400’ library). The linker for executables, ld, quietly gives the executable the most restrictive subtype of any of its input files.
-FdirA framework directory is a directory with frameworks in it. A
framework is a directory with a Headers and/or
PrivateHeaders directory contained directly in it that ends
in .framework. The name of a framework is the name of this
directory excluding the .framework. Headers associated with
the framework are found in one of those two directories, with
Headers being searched first. A subframework is a framework
directory that is in a framework's Frameworks directory.
Includes of subframework headers can only appear in a header of a
framework that contains the subframework, or in a sibling subframework
header. Two subframeworks are siblings if they occur in the same
framework. A subframework should not have the same name as a
framework; a warning is issued if this is violated. Currently a
subframework cannot have subframeworks; in the future, the mechanism
may be extended to support this. The standard frameworks can be found
in /System/Library/Frameworks and
/Library/Frameworks. An example include looks like
#include <Framework/header.h>, where Framework denotes
the name of the framework and header.h is found in the
PrivateHeaders or Headers directory.
-iframeworkdir-gused-gfull-fconstant-cfstrings-mconstant-cfstrings@"..."
literals to be laid out as constant CoreFoundation strings.
-mmacosx-version-min=version12,
10.12, and 10.5.8.
If the compiler was built to use the system's headers by default, then the default for this option is the system version on which the compiler is running, otherwise the default is to make choices that are compatible with as many systems and code bases as possible.
-mkernel-mone-byte-boolbool so that sizeof(bool)==1.
By default sizeof(bool) is 4 when compiling for
Darwin/PowerPC and 1 when compiling for Darwin/x86, so this
option has no effect on x86.
Warning: The -mone-byte-bool switch causes GCC to generate code that is not binary compatible with code generated without that switch. Using this switch may require recompiling all other modules in a program, including system libraries. Use this switch to conform to a non-default data model.
-mfix-and-continue-ffix-and-continue-findirect-data-all_load-arch_errors_fatal-bind_at_load-bundle-bundle_loader executable-dynamiclib-force_cpusubtype_ALL-allowable_client client_name-client_name-compatibility_version-current_version-dead_strip-dependency-file-dylib_file-dylinker_install_name-dynamic-exported_symbols_list-filelist-flat_namespace-force_flat_namespace-headerpad_max_install_names-image_base-init-install_name-keep_private_externs-multi_module-multiply_defined-multiply_defined_unused-noall_load-no_dead_strip_inits_and_terms-nofixprebinding-nomultidefs-noprebind-noseglinkedit-pagezero_size-prebind-prebind_all_twolevel_modules-private_bundle-read_only_relocs-sectalign-sectobjectsymbols-whyload-seg1addr-sectcreate-sectobjectsymbols-sectorder-segaddr-segs_read_only_addr-segs_read_write_addr-seg_addr_table-seg_addr_table_filename-seglinkedit-segprot-segs_read_only_addr-segs_read_write_addr-single_module-static-sub_library-sub_umbrella-twolevel_namespace-umbrella-undefined-unexported_symbols_list-weak_reference_mismatches-whatsloadedThese ‘-m’ options are defined for the DEC Alpha implementations:
-mno-soft-float-msoft-floatNote that Alpha implementations without floating-point operations are required to have floating-point registers.
-mfp-reg-mno-fp-regs$0 instead of $f0. This is a non-standard calling sequence,
so any function with a floating-point argument or return value called by code
compiled with -mno-fp-regs must also be compiled with that
option.
A typical use of this option is building a kernel that does not use, and hence need not save and restore, any floating-point registers.
-mieee_IEEE_FP is
defined during compilation. The resulting code is less efficient but is
able to correctly support denormalized numbers and exceptional IEEE
values such as not-a-number and plus/minus infinity. Other Alpha
compilers call this option -ieee_with_no_inexact.
-mieee-with-inexact_IEEE_FP, _IEEE_FP_EXACT is defined as a preprocessor
macro. On some Alpha implementations the resulting code may execute
significantly slower than the code generated by default. Since there is
very little code that depends on the inexact-flag, you should
normally not specify this option. Other Alpha compilers call this
option -ieee_with_inexact.
-mfp-trap-mode=trap-mode-mfp-rounding-mode=rounding-mode-mtrap-precision=trap-precisionOther Alpha compilers provide the equivalent options called -scope_safe and -resumption_safe.
-mieee-conformant-mbuild-constantsUse this option to require GCC to construct all integer constants using code, even if it takes more instructions (the maximum is six).
You typically use this option to build a shared library dynamic loader. Itself a shared library, it must relocate itself in memory before it can find the variables and constants in its own data segment.
-mbwx-mno-bwx-mcix-mno-cix-mfix-mno-fix-mmax-mno-max-mfloat-vax-mfloat-ieee-mexplicit-relocs-mno-explicit-relocs-msmall-data-mlarge-data.sdata and .sbss sections) and are accessed via
16-bit relocations off of the $gp register. This limits the
size of the small data area to 64KB, but allows the variables to be
directly accessed via a single instruction.
The default is -mlarge-data. With this option the data area
is limited to just below 2GB. Programs that require more than 2GB of
data must use malloc or mmap to allocate the data in the
heap instead of in the program's data segment.
When generating code for shared libraries, -fpic implies -msmall-data and -fPIC implies -mlarge-data.
-msmall-text-mlarge-text$gp value, and thus reduce the number of instructions
required for a function call from 4 to 1.
The default is -mlarge-text.
-mcpu=cpu_typeSupported values for cpu_type are
Native toolchains also support the value ‘native’, which selects the best architecture option for the host processor. -mcpu=native has no effect if GCC does not recognize the processor.
-mtune=cpu_typeNative toolchains also support the value ‘native’, which selects the best architecture option for the host processor. -mtune=native has no effect if GCC does not recognize the processor.
-mmemory-latency=timeValid options for time are
-mframe-limit=bytes-mkernel=version-mbig-endian-mlittle-endian-mjmpext-mjmp32-malu32-mcpu=versionSupported values for version are:
-mco-re-mno-co-re-mxbpfThese options are defined specifically for the FR30 port.
-msmall-model-mno-lsimThese options are defined specifically for the FT32 port.
-msim-mlra-mnodiv-mft32b-mcompress-mnopm-mgpr-32-mgpr-64-mfpr-32-mfpr-64-mhard-float-msoft-float-malloc-cc-mfixed-ccicc0 and fcc0.
-mdword-mno-dword-mdouble-mno-double-mmedia-mno-media-mmuladd-mno-muladd-mfdpic-minline-plt-mTLS-mtls-mgprel-roGPREL relocations in the FDPIC ABI for data
that is known to be in read-only sections. It's enabled by default,
except for -fpic or -fpie: even though it may help
make the global offset table smaller, it trades 1 instruction for 4.
With -fPIC or -fPIE, it trades 3 instructions for 4,
one of which may be shared by multiple symbols, and it avoids the need
for a GOT entry for the referenced symbol, so it's more likely to be a
win. If it is not, -mno-gprel-ro can be used to disable it.
-multilib-library-pic-mlinked-fp-mlong-calls-malign-labels-mlibrary-pic-macc-4-macc-8-mpack-mno-pack-mno-eflags-mcond-moveThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-mno-cond-moveThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-msccThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-mno-sccThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-mcond-execThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-mno-cond-execThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-mvliw-branchThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-mno-vliw-branchThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-mmulti-cond-exec&& and || in conditional execution
(default).
This switch is mainly for debugging the compiler and will likely be removed in a future version.
-mno-multi-cond-exec&& and || in conditional execution.
This switch is mainly for debugging the compiler and will likely be removed in a future version.
-mnested-cond-execThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-mno-nested-cond-execThis switch is mainly for debugging the compiler and will likely be removed in a future version.
-moptimize-membarmembar instructions from the
compiler-generated code. It is enabled by default.
-mno-optimize-membarmembar
instructions from the generated code.
-mtomcat-stats-mcpu=cpuThese ‘-m’ options are defined for GNU/Linux targets:
-mglibc-muclibc-mmusl-mbionic-mandroidWhen compiling, this option enables -mbionic, -fPIC,
-fno-exceptions and -fno-rtti by default. When linking,
this option makes the GCC driver pass Android-specific options to the linker.
Finally, this option causes the preprocessor macro __ANDROID__
to be defined.
-tno-android-cc-tno-android-ldThese ‘-m’ options are defined for the H8/300 implementations:
-mrelaxld and the H8/300, for a fuller description.
-mh-ms-mn-ms2600-mexr-mno-exr-mint32int data 32 bits by default.
-malign-300These ‘-m’ options are defined for the HPPA family of computers:
-march=architecture-type-mpa-risc-1-0-mpa-risc-1-1-mpa-risc-2-0-matomic-libcallsBoth the sync and libatomic libcall implementations use locking. As a result, processor stores are not atomic with respect to other atomic operations. Processor loads up to DImode are atomic with respect to other atomic operations provided they are implemented as a single access.
The PA-RISC architecture does not support any atomic operations in
hardware except for the ldcw instruction. Thus, all atomic
support is implemented using sync and atomic libcalls. Sync libcall
support is in libgcc.a. Atomic libcall support is in
libatomic.
This option generates __atomic_exchange calls for atomic stores.
It also provides special handling for atomic DImode accesses on 32-bit
targets.
-mbig-switch-mcaller-copies-mcoherent-ldcw-mdisable-fpregs-msoft-float.
-mdisable-indexing-mfast-indirect-callsThis option does not work in the presence of shared libraries or nested functions.
-mfixed-range=register-range-mgas-mgnu-ld-mhp-ld-mlinker-opt-mlong-callsDistances are measured from the beginning of functions when using the -ffunction-sections option, or when using the -mgas and -mno-portable-runtime options together under HP-UX with the SOM linker.
It is normally not desirable to use this option as it degrades performance. However, it may be useful in large applications, particularly when partial linking is used to build the application.
The types of long calls used depends on the capabilities of the assembler and linker, and the type of code being generated. The impact on systems that support long absolute calls, and long pic symbol-difference or pc-relative calls should be relatively small. However, an indirect call is used on 32-bit ELF systems in pic code and it is quite long.
-mlong-load-store-mjump-in-delay-mno-space-regsSuch code is suitable for level 0 PA systems and kernels.
-mordered-mportable-runtime-mschedule=cpu-type-msio_SIO, for server IO. The default is
-mwsio. This generates the predefines, __hp9000s700,
__hp9000s700__ and _WSIO, for workstation IO. These
options are available under HP-UX and HI-UX.
-msoft-float-msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this to work.
-msoft-multThis disables the use of the xmpyu instruction.
-munix=unix-std-munix=93 provides the same predefines as GCC 3.3 and 3.4.
-munix=95 provides additional predefines for XOPEN_UNIX
and _XOPEN_SOURCE_EXTENDED, and the startfile unix95.o.
-munix=98 provides additional predefines for _XOPEN_UNIX,
_XOPEN_SOURCE_EXTENDED, _INCLUDE__STDC_A1_SOURCE and
_INCLUDE_XOPEN_SOURCE_500, and the startfile unix98.o.
It is important to note that this option changes the interfaces for various library routines. It also affects the operational behavior of the C library. Thus, extreme care is needed in using this option.
Library code that is intended to operate with more than one UNIX
standard must test, set and restore the variable __xpg4_extended_mask
as appropriate. Most GNU software doesn't provide this capability.
-nolibdld-staticOn HP-UX 10 and later, the GCC driver adds the necessary options to link with libdld.sl when the -static option is specified. This causes the resulting binary to be dynamic. On the 64-bit port, the linkers generate dynamic binaries by default in any case. The -nolibdld option can be used to prevent the GCC driver from adding these link options.
-threadsThese are the ‘-m’ options defined for the Intel IA-64 architecture.
-mbig-endian-mlittle-endian-mgnu-as-mno-gnu-as-mgnu-ld-mno-gnu-ld-mno-pic-mvolatile-asm-stop-mno-volatile-asm-stop-mregister-names-mno-register-names-mno-sdata-msdata-mconstant-gp-mauto-pic-minline-float-divide-min-latency-minline-float-divide-max-throughput-mno-inline-float-divide-minline-int-divide-min-latency-minline-int-divide-max-throughput-mno-inline-int-divide-minline-sqrt-min-latency-minline-sqrt-max-throughput-mno-inline-sqrtsqrt.
-mfused-madd-mno-fused-madd-mno-dwarf2-asm-mdwarf2-asm-mearly-stop-bits-mno-early-stop-bits-mfixed-range=register-range-mtls-size=tls-size-mtune=cpu-type-milp32-mlp64-mno-sched-br-data-spec-msched-br-data-specld.a instructions and
the corresponding check instructions (ld.c / chk.a).
The default setting is disabled.
-msched-ar-data-spec-mno-sched-ar-data-specld.a instructions and
the corresponding check instructions (ld.c / chk.a).
The default setting is enabled.
-mno-sched-control-spec-msched-control-specld.s instructions and
the corresponding check instructions chk.s.
The default setting is disabled.
-msched-br-in-data-spec-mno-sched-br-in-data-spec-msched-ar-in-data-spec-mno-sched-ar-in-data-spec-msched-in-control-spec-mno-sched-in-control-spec-mno-sched-prefer-non-data-spec-insns-msched-prefer-non-data-spec-insns-mno-sched-prefer-non-control-spec-insns-msched-prefer-non-control-spec-insns-mno-sched-count-spec-in-critical-path-msched-count-spec-in-critical-path-msched-spec-ldc-msched-control-spec-ldc-msched-stop-bits-after-every-cycle-msched-fp-mem-deps-zero-cost-msel-sched-dont-check-control-spec-msched-max-memory-insns=max-insns-msched-max-memory-insns-hard-limitThese -m options are defined for the LatticeMico32 architecture:
-mbarrel-shift-enabled-mdivide-enabled-mmultiply-enabled-msign-extend-enabled-muser-enabledThese command-line options are defined for LoongArch targets:
-march=cpu-typeThe choices for cpu-type are:
-mtune=cpu-type-mabi=base-abi-type-mfpu=fpu-type-msoft-float-msingle-float-mdouble-float-mbranch-cost=n-mcheck-zero-division-mno-check-zero-divison-mcond-move-int-mno-cond-move-int-mcond-move-float-mno-cond-move-float-mmemcpy-mno-memcpymemcpy for non-trivial block moves.
The default is -mno-memcpy, which allows GCC to inline most
constant-sized copies. Setting optimization level to -Os also
forces the use of memcpy, but -mno-memcpy may override this
behavior if explicitly specified, regardless of the order these options on
the command line.
-mstrict-align-mno-strict-align-msmall-data-limit=number-mmax-inline-memcpy-size=nmemcpy or structure copies)
less than or equal to n bytes. The default value of n is 1024.
-mcmodel=code-modelnormal.
-mexplicit-relocs-mno-explicit-relocs-mrelax:
-mexplicit-relocs if the assembler supports relocation operators
but -mrelax is not enabled, -mno-explicit-relocs otherwise.
-mdirect-extern-access-mno-direct-extern-accessWith -mdirect-extern-access, GOT is not used and all external
symbols are PC-relatively addressed. It is only suitable for
environments where no dynamic link is performed, like firmwares, OS
kernels, executables linked with -static or -static-pie.
-mdirect-extern-access is not compatible with -fPIC or
-fpic.
-mrelax-mno-relax.align directives and conditional branch instructions in the
assembly code outputted by GCC may be rejected by the assembler because
of a relocation overflow), -mno-relax otherwise.
-mpass-mrelax-to-as-mno-pass-mrelax-to-as-mcpu=name-msim-memregs=numberThese -m options are defined for Renesas M32R/D architectures:
-m32r2-m32rx-m32r-mmodel=smallld24 instruction), and assume all subroutines
are reachable with the bl instruction.
This is the default.
The addressability of a particular object can be set with the
model attribute.
-mmodel=mediumseth/add3 instructions to load their addresses), and
assume all subroutines are reachable with the bl instruction.
-mmodel=largeseth/add3 instructions to load their addresses), and
assume subroutines may not be reachable with the bl instruction
(the compiler generates the much slower seth/add3/jl
instruction sequence).
-msdata=none.data, .bss, or .rodata (unless the
section attribute has been specified).
This is the default.
The small data area consists of sections .sdata and .sbss.
Objects may be explicitly put in the small data area with the
section attribute using one of these sections.
-msdata=sdata-msdata=use-G numAll modules should be compiled with the same -G num value. Compiling with different values of num may or may not work; if it doesn't the linker gives an error message—incorrect code is not generated.
-mdebug-malign-loops-mno-align-loops-missue-rate=number-mbranch-cost=number-mflush-trap=number-mno-flush-trap-mflush-func=name-mno-flush-funcThese are the ‘-m’ options defined for M680x0 and ColdFire processors. The default settings depend on which architecture was selected when the compiler was configured; the defaults for the most common choices are given below.
-march=archGCC defines a macro __mcfarch__ whenever it is generating
code for a ColdFire target. The arch in this macro is one of the
-march arguments given above.
When used together, -march and -mtune select code that runs on a family of similar processors but that is optimized for a particular microarchitecture.
-mcpu=cpu| Family | ‘-mcpu’ arguments
|
|---|---|
| ‘51’ | ‘51’ ‘51ac’ ‘51ag’ ‘51cn’ ‘51em’ ‘51je’ ‘51jf’ ‘51jg’ ‘51jm’ ‘51mm’ ‘51qe’ ‘51qm’
|
| ‘5206’ | ‘5202’ ‘5204’ ‘5206’
|
| ‘5206e’ | ‘5206e’
|
| ‘5208’ | ‘5207’ ‘5208’
|
| ‘5211a’ | ‘5210a’ ‘5211a’
|
| ‘5213’ | ‘5211’ ‘5212’ ‘5213’
|
| ‘5216’ | ‘5214’ ‘5216’
|
| ‘52235’ | ‘52230’ ‘52231’ ‘52232’ ‘52233’ ‘52234’ ‘52235’
|
| ‘5225’ | ‘5224’ ‘5225’
|
| ‘52259’ | ‘52252’ ‘52254’ ‘52255’ ‘52256’ ‘52258’ ‘52259’
|
| ‘5235’ | ‘5232’ ‘5233’ ‘5234’ ‘5235’ ‘523x’
|
| ‘5249’ | ‘5249’
|
| ‘5250’ | ‘5250’
|
| ‘5271’ | ‘5270’ ‘5271’
|
| ‘5272’ | ‘5272’
|
| ‘5275’ | ‘5274’ ‘5275’
|
| ‘5282’ | ‘5280’ ‘5281’ ‘5282’ ‘528x’
|
| ‘53017’ | ‘53011’ ‘53012’ ‘53013’ ‘53014’ ‘53015’ ‘53016’ ‘53017’
|
| ‘5307’ | ‘5307’
|
| ‘5329’ | ‘5327’ ‘5328’ ‘5329’ ‘532x’
|
| ‘5373’ | ‘5372’ ‘5373’ ‘537x’
|
| ‘5407’ | ‘5407’
|
| ‘5475’ | ‘5470’ ‘5471’ ‘5472’ ‘5473’ ‘5474’ ‘5475’ ‘547x’ ‘5480’ ‘5481’ ‘5482’ ‘5483’ ‘5484’ ‘5485’
|
-mcpu=cpu overrides -march=arch if arch is compatible with cpu. Other combinations of -mcpu and -march are rejected.
GCC defines the macro __mcf_cpu_cpu when ColdFire target
cpu is selected. It also defines __mcf_family_family,
where the value of family is given by the table above.
-mtune=tuneYou can also use -mtune=68020-40 for code that needs to run relatively well on 68020, 68030 and 68040 targets. -mtune=68020-60 is similar but includes 68060 targets as well. These two options select the same tuning decisions as -m68020-40 and -m68020-60 respectively.
GCC defines the macros __mcarch and __mcarch__
when tuning for 680x0 architecture arch. It also defines
mcarch unless either -ansi or a non-GNU -std
option is used. If GCC is tuning for a range of architectures,
as selected by -mtune=68020-40 or -mtune=68020-60,
it defines the macros for every architecture in the range.
GCC also defines the macro __muarch__ when tuning for
ColdFire microarchitecture uarch, where uarch is one
of the arguments given above.
-m68000-mc68000Use this option for microcontrollers with a 68000 or EC000 core, including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
-m68010-m68020-mc68020-m68030-m68040This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. Use this option if your 68040 does not have code to emulate those instructions.
-m68060This option inhibits the use of 68020 and 68881/68882 instructions that have to be emulated by software on the 68060. Use this option if your 68060 does not have code to emulate those instructions.
-mcpu32Use this option for microcontrollers with a CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360.
-m5200Use this option for microcontroller with a 5200 core, including the MCF5202, MCF5203, MCF5204 and MCF5206.
-m5206e-m528x-m5307-m5407-mcfv4e-m68020-40The option is equivalent to -march=68020 -mtune=68020-40.
-m68020-60The option is equivalent to -march=68020 -mtune=68020-60.
-mhard-float-m68881__HAVE_68881__ on M680x0 targets and __mcffpu__
on ColdFire targets.
-msoft-float-mdiv-mno-divGCC defines the macro __mcfhwdiv__ when this option is enabled.
-mshortint to be 16 bits wide, like short int.
Additionally, parameters passed on the stack are also aligned to a
16-bit boundary even on targets whose API mandates promotion to 32-bit.
-mno-shortint to be 16 bits wide. This is the default.
-mnobitfield-mno-bitfield-mbitfield-mrtdrtd
instruction, which pops their arguments while returning. This
saves one instruction in the caller since there is no need to pop
the arguments there.
This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including printf);
otherwise incorrect code is generated for calls to those
functions.
In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.)
The rtd instruction is supported by the 68010, 68020, 68030,
68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
The default is -mno-rtd.
-malign-int-mno-align-intint, long, long long,
float, double, and long double variables on a 32-bit
boundary (-malign-int) or a 16-bit boundary (-mno-align-int).
Aligning variables on 32-bit boundaries produces code that runs somewhat
faster on processors with 32-bit busses at the expense of more memory.
Warning: if you use the -malign-int switch, GCC aligns structures containing the above types differently than most published application binary interface specifications for the m68k.
Use the pc-relative addressing mode of the 68000 directly, instead of using a global offset table. At present, this option implies -fpic, allowing at most a 16-bit offset for pc-relative addressing. -fPIC is not presently supported with -mpcrel, though this could be supported for 68020 and higher processors.
-mno-strict-align-mstrict-align-msep-data-mno-sep-data-mid-shared-library-mno-id-shared-library-mshared-library-id=n-mxgot-mno-xgotGCC normally uses a single instruction to load values from the GOT. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as:
relocation truncated to fit: R_68K_GOT16O foobar
If this happens, you should recompile your code with -mxgot. It should then work with very large GOTs. However, code generated with -mxgot is less efficient, since it takes 4 instructions to fetch the value of a global symbol.
Note that some linkers, including newer versions of the GNU linker, can create multiple GOTs and sort GOT entries. If you have such a linker, you should only need to use -mxgot when compiling a single object file that accesses more than 8192 GOT entries. Very few do.
These options have no effect unless GCC is generating position-independent code.
-mlong-jump-table-offsetsswitch tables. The default is to use
16-bit offsets.
These are the ‘-m’ options defined for the Motorola M*Core processors.
-mhardlit-mno-hardlit-mdiv-mno-div-mrelax-immediate-mno-relax-immediate-mwide-bitfields-mno-wide-bitfieldsint-sized.
-m4byte-functions-mno-4byte-functions-mcallgraph-data-mno-callgraph-data-mslow-bytes-mno-slow-bytes-mlittle-endian-mbig-endian-m210-m340-mno-lsim-mstack-increment=size-msoft-float-mhard-float-mmemcpymemcpy.
-mno-clearbss-mcpu=cpu-type-mxl-soft-mul-mxl-soft-div-mxl-barrel-shift-mxl-pattern-compare-msmall-divides-mxl-stack-check-mxl-gp-opt.sdata/.sbss sections.
-mxl-multiply-high-mxl-float-convert-mxl-float-sqrt-mbig-endian-mlittle-endian-mxl-reorder-mxl-mode-app-modelOption -xl-mode-app-model is a deprecated alias for -mxl-mode-app-model.
-mpic-data-is-text-relative-EB-EL-march=archThe native Linux/GNU toolchain also supports the value ‘native’, which selects the best architecture option for the host processor. -march=native has no effect if GCC does not recognize the processor.
In processor names, a final ‘000’ can be abbreviated as ‘k’ (for example, -march=r2k). Prefixes are optional, and ‘vr’ may be written ‘r’.
Names of the form ‘nf2_1’ refer to processors with FPUs clocked at half the rate of the core, names of the form ‘nf1_1’ refer to processors with FPUs clocked at the same rate as the core, and names of the form ‘nf3_2’ refer to processors with FPUs clocked a ratio of 3:2 with respect to the core. For compatibility reasons, ‘nf’ is accepted as a synonym for ‘nf2_1’ while ‘nx’ and ‘bfx’ are accepted as synonyms for ‘nf1_1’.
GCC defines two macros based on the value of this option. The first
is _MIPS_ARCH, which gives the name of target architecture, as
a string. The second has the form _MIPS_ARCH_foo,
where foo is the capitalized value of _MIPS_ARCH.
For example, -march=r2000 sets _MIPS_ARCH
to "r2000" and defines the macro _MIPS_ARCH_R2000.
Note that the _MIPS_ARCH macro uses the processor names given
above. In other words, it has the full prefix and does not
abbreviate ‘000’ as ‘k’. In the case of ‘from-abi’,
the macro names the resolved architecture (either "mips1" or
"mips3"). It names the default architecture when no
-march option is given.
-mtune=archWhen this option is not used, GCC optimizes for the processor specified by -march. By using -march and -mtune together, it is possible to generate code that runs on a family of processors, but optimize the code for one particular member of that family.
-mtune defines the macros _MIPS_TUNE and
_MIPS_TUNE_foo, which work in the same way as the
-march ones described above.
-mips1-mips2-mips3-mips4-mips32-mips32r3-mips32r5-mips32r6-mips64-mips64r2-mips64r3-mips64r5-mips64r6-mips16-mno-mips16MIPS16 code generation can also be controlled on a per-function basis
by means of mips16 and nomips16 attributes.
See Function Attributes, for more information.
-mflip-mips16-minterlink-compressed-mno-interlink-compressedFor example, code using the standard ISA encoding cannot jump directly to MIPS16 or microMIPS code; it must either use a call or an indirect jump. -minterlink-compressed therefore disables direct jumps unless GCC knows that the target of the jump is not compressed.
-minterlink-mips16-mno-interlink-mips16-mabi=32-mabi=o64-mabi=n32-mabi=64-mabi=eabiNote that the EABI has a 32-bit and a 64-bit variant. GCC normally generates 64-bit code when you select a 64-bit architecture, but you can use -mgp32 to get 32-bit code instead.
For information about the O64 ABI, see https://gcc.gnu.org/projects/mipso64-abi.html.
GCC supports a variant of the o32 ABI in which floating-point registers
are 64 rather than 32 bits wide. You can select this combination with
-mabi=32 -mfp64. This ABI relies on the mthc1
and mfhc1 instructions and is therefore only supported for
MIPS32R2, MIPS32R3 and MIPS32R5 processors.
The register assignments for arguments and return values remain the same, but each scalar value is passed in a single 64-bit register rather than a pair of 32-bit registers. For example, scalar floating-point values are returned in ‘$f0’ only, not a ‘$f0’/‘$f1’ pair. The set of call-saved registers also remains the same in that the even-numbered double-precision registers are saved.
Two additional variants of the o32 ABI are supported to enable
a transition from 32-bit to 64-bit registers. These are FPXX
(-mfpxx) and FP64A (-mfp64 -mno-odd-spreg).
The FPXX extension mandates that all code must execute correctly
when run using 32-bit or 64-bit registers. The code can be interlinked
with either FP32 or FP64, but not both.
The FP64A extension is similar to the FP64 extension but forbids the
use of odd-numbered single-precision registers. This can be used
in conjunction with the FRE mode of FPUs in MIPS32R5
processors and allows both FP32 and FP64A code to interlink and
run in the same process without changing FPU modes.
-mabicalls-mno-abicalls-mshared-mno-sharedAll -mabicalls code has traditionally been position-independent, regardless of options like -fPIC and -fpic. However, as an extension, the GNU toolchain allows executables to use absolute accesses for locally-binding symbols. It can also use shorter GP initialization sequences and generate direct calls to locally-defined functions. This mode is selected by -mno-shared.
-mno-shared depends on binutils 2.16 or higher and generates objects that can only be linked by the GNU linker. However, the option does not affect the ABI of the final executable; it only affects the ABI of relocatable objects. Using -mno-shared generally makes executables both smaller and quicker.
-mshared is the default.
-mplt-mno-pltYou can make -mplt the default by configuring GCC with --with-mips-plt. The default is -mno-plt otherwise.
-mxgot-mno-xgotGCC normally uses a single instruction to load values from the GOT. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as:
relocation truncated to fit: R_MIPS_GOT16 foobar
If this happens, you should recompile your code with -mxgot. This works with very large GOTs, although the code is also less efficient, since it takes three instructions to fetch the value of a global symbol.
Note that some linkers can create multiple GOTs. If you have such a linker, you should only need to use -mxgot when a single object file accesses more than 64k's worth of GOT entries. Very few do.
These options have no effect unless GCC is generating position independent code.
-mgp32-mgp64-mfp32-mfp64-mfpxx-mhard-float-msoft-float-mno-floatprintf formats).
If code compiled with -mno-float accidentally contains
floating-point operations, it is likely to suffer a link-time
or run-time failure.
-msingle-float-mdouble-float-modd-spreg-mno-odd-spreg-mabs=2008-mabs=legacyabs.fmt and
neg.fmt machine instructions.
By default or when -mabs=legacy is used the legacy treatment is selected. In this case these instructions are considered arithmetic and avoided where correct operation is required and the input operand might be a NaN. A longer sequence of instructions that manipulate the sign bit of floating-point datum manually is used instead unless the -ffinite-math-only option has also been specified.
The -mabs=2008 option selects the IEEE 754-2008 treatment. In this case these instructions are considered non-arithmetic and therefore operating correctly in all cases, including in particular where the input operand is a NaN. These instructions are therefore always used for the respective operations.
-mnan=2008-mnan=legacyThe -mnan=legacy option selects the legacy encoding. In this case quiet NaNs (qNaNs) are denoted by the first bit of their trailing significand field being 0, whereas signaling NaNs (sNaNs) are denoted by the first bit of their trailing significand field being 1.
The -mnan=2008 option selects the IEEE 754-2008 encoding. In this case qNaNs are denoted by the first bit of their trailing significand field being 1, whereas sNaNs are denoted by the first bit of their trailing significand field being 0.
The default is -mnan=legacy unless GCC has been configured with --with-nan=2008.
-mllsc-mno-llsc-mllsc is useful if the runtime environment can emulate the instructions and -mno-llsc can be useful when compiling for nonstandard ISAs. You can make either option the default by configuring GCC with --with-llsc and --without-llsc respectively. --with-llsc is the default for some configurations; see the installation documentation for details.
-mdsp-mno-dsp__mips_dsp. It also defines
__mips_dsp_rev to 1.
-mdspr2-mno-dspr2__mips_dsp and __mips_dspr2.
It also defines __mips_dsp_rev to 2.
-msmartmips-mno-smartmips-mpaired-single-mno-paired-single-mdmx-mno-mdmx-mips3d-mno-mips3d-mmicromips-mno-micromipsMicroMIPS code generation can also be controlled on a per-function basis
by means of micromips and nomicromips attributes.
See Function Attributes, for more information.
-mmt-mno-mt-mmcu-mno-mcu-meva-mno-eva-mvirt-mno-virt-mxpa-mno-xpa-mcrc-mno-crc-mginv-mno-ginv-mloongson-mmi-mno-loongson-mmi-mloongson-ext-mno-loongson-ext-mloongson-ext2-mno-loongson-ext2-mlong64long types to be 64 bits wide. See -mlong32 for
an explanation of the default and the way that the pointer size is
determined.
-mlong32long, int, and pointer types to be 32 bits wide.
The default size of ints, longs and pointers depends on
the ABI. All the supported ABIs use 32-bit ints. The n64 ABI
uses 64-bit longs, as does the 64-bit EABI; the others use
32-bit longs. Pointers are the same size as longs,
or the same size as integer registers, whichever is smaller.
-msym32-mno-sym32-G numThe default -G option depends on the configuration.
-mlocal-sdata-mno-local-sdataIf the linker complains that an application is using too much small data, you might want to try rebuilding the less performance-critical parts with -mno-local-sdata. You might also want to build large libraries with -mno-local-sdata, so that the libraries leave more room for the main program.
-mextern-sdata-mno-extern-sdataIf you compile a module Mod with -mextern-sdata -G
num -mgpopt, and Mod references a variable Var
that is no bigger than num bytes, you must make sure that Var
is placed in a small data section. If Var is defined by another
module, you must either compile that module with a high-enough
-G setting or attach a section attribute to Var's
definition. If Var is common, you must link the application
with a high-enough -G setting.
The easiest way of satisfying these restrictions is to compile and link every module with the same -G option. However, you may wish to build a library that supports several different small data limits. You can do this by compiling the library with the highest supported -G setting and additionally using -mno-extern-sdata to stop the library from making assumptions about externally-defined data.
-mgpopt-mno-gpopt-mno-gpopt is useful for cases where the $gp register
might not hold the value of _gp. For example, if the code is
part of a library that might be used in a boot monitor, programs that
call boot monitor routines pass an unknown value in $gp.
(In such situations, the boot monitor itself is usually compiled
with -G0.)
-mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.
-membedded-data-mno-embedded-data-muninit-const-in-rodata-mno-uninit-const-in-rodataconst variables in the read-only data section.
This option is only meaningful in conjunction with -membedded-data.
-mcode-readable=setting-mcode-readable=yes-mcode-readable=pcrel-mcode-readable=no-msplit-addresses-mno-split-addresses%hi() and %lo() assembler
relocation operators. This option has been superseded by
-mexplicit-relocs but is retained for backwards compatibility.
-mexplicit-relocs-mno-explicit-relocs-mexplicit-relocs is the default if GCC was configured to use an assembler that supports relocation operators.
-mcheck-zero-division-mno-check-zero-divisionThe default is -mcheck-zero-division.
-mdivide-traps-mdivide-breaksSIGFPE). Use -mdivide-traps to
allow conditional traps on architectures that support them and
-mdivide-breaks to force the use of breaks.
The default is usually -mdivide-traps, but this can be overridden at configure time using --with-divide=breaks. Divide-by-zero checks can be completely disabled using -mno-check-zero-division.
-mload-store-pairs-mno-load-store-pairs-munaligned-access-mno-unaligned-access-mmemcpy-mno-memcpymemcpy for non-trivial block
moves. The default is -mno-memcpy, which allows GCC to inline
most constant-sized copies.
-mlong-calls-mno-long-callsjal instruction. Calling
functions using jal is more efficient but requires the caller
and callee to be in the same 256 megabyte segment.
This option has no effect on abicalls code. The default is -mno-long-calls.
-mmad-mno-madmad, madu and mul
instructions, as provided by the R4650 ISA.
-mimadd-mno-imaddmadd and msub integer
instructions. The default is -mimadd on architectures
that support madd and msub except for the 74k
architecture where it was found to generate slower code.
-mfused-madd-mno-fused-maddOn the R8000 CPU when multiply-accumulate instructions are used, the intermediate product is calculated to infinite precision and is not subject to the FCSR Flush to Zero bit. This may be undesirable in some circumstances. On other processors the result is numerically identical to the equivalent computation using separate multiply, add, subtract and negate instructions.
-nocpp-mfix-24k-mno-fix-24k-mfix-r4000-mno-fix-r4000-mfix-r4400-mno-fix-r4400-mfix-r10000-mno-fix-r10000ll/sc sequences may not behave atomically on revisions
prior to 3.0. They may deadlock on revisions 2.6 and earlier.
This option can only be used if the target architecture supports branch-likely instructions. -mfix-r10000 is the default when -march=r10000 is used; -mno-fix-r10000 is the default otherwise.
-mfix-r5900-mno-fix-r5900nop instruction there
instead. The short loop bug under certain conditions causes loops to
execute only once or twice, due to a hardware bug in the R5900 chip. The
workaround is implemented by the assembler rather than by GCC.
-mfix-rm7000-mno-fix-rm7000dmult/dmultu errata. The
workarounds are implemented by the assembler rather than by GCC.
-mfix-vr4120-mno-fix-vr4120dmultu does not always produce the correct result.
div and ddiv do not always produce the correct result if one
of the operands is negative.
mips64vr*-elf configurations.
Other VR4120 errata require a NOP to be inserted between certain pairs of instructions. These errata are handled by the assembler, not by GCC itself.
-mfix-vr4130mflo/mfhi errata. The
workarounds are implemented by the assembler rather than by GCC,
although GCC avoids using mflo and mfhi if the
VR4130 macc, macchi, dmacc and dmacchi
instructions are available instead.
-mfix-sb1-mno-fix-sb1-mr10k-cache-barrier=settingIn common with many processors, the R10K tries to predict the outcome of a conditional branch and speculatively executes instructions from the “taken” branch. It later aborts these instructions if the predicted outcome is wrong. However, on the R10K, even aborted instructions can have side effects.
This problem only affects kernel stores and, depending on the system, kernel loads. As an example, a speculatively-executed store may load the target memory into cache and mark the cache line as dirty, even if the store itself is later aborted. If a DMA operation writes to the same area of memory before the “dirty” line is flushed, the cached data overwrites the DMA-ed data. See the R10K processor manual for a full description, including other potential problems.
One workaround is to insert cache barrier instructions before every memory access that might be speculatively executed and that might have side effects even if aborted. -mr10k-cache-barrier=setting controls GCC's implementation of this workaround. It assumes that aborted accesses to any byte in the following regions does not have side effects:
It is the kernel's responsibility to ensure that speculative accesses to these regions are indeed safe.
If the input program contains a function declaration such as:
void foo (void);
then the implementation of foo must allow j foo and
jal foo to be executed speculatively. GCC honors this
restriction for functions it compiles itself. It expects non-GCC
functions (such as hand-written assembly code) to do the same.
The option has three forms:
-mr10k-cache-barrier=load-store-mr10k-cache-barrier=store-mr10k-cache-barrier=none-mflush-func=func-mno-flush-func_flush_func, that is, the address of the
memory range for which the cache is being flushed, the size of the
memory range, and the number 3 (to flush both caches). The default
depends on the target GCC was configured for, but commonly is either
_flush_func or __cpu_flush.
mbranch-cost=num-mbranch-likely-mno-branch-likely-mcompact-branches=never-mcompact-branches=optimal-mcompact-branches=alwaysThe -mcompact-branches=never option ensures that compact branch instructions will never be generated.
The -mcompact-branches=always option ensures that a compact branch instruction will be generated if available for MIPS Release 6 onwards. If a compact branch instruction is not available (or pre-R6), a delay slot form of the branch will be used instead.
If it is used for MIPS16/microMIPS targets, it will be just ignored now. The behaviour for MIPS16/microMIPS may change in future, since they do have some compact branch instructions.
The -mcompact-branches=optimal option will cause a delay slot branch to be used if one is available in the current ISA and the delay slot is successfully filled. If the delay slot is not filled, a compact branch will be chosen if one is available.
-mfp-exceptions-mno-fp-exceptionsFor instance, on the SB-1, if FP exceptions are disabled, and we are emitting 64-bit code, then we can use both FP pipes. Otherwise, we can only use one FP pipe.
-mvr4130-align-mno-vr4130-alignThis option only has an effect when optimizing for the VR4130. It normally makes code faster, but at the expense of making it bigger. It is enabled by default at optimization level -O3.
-msynci-mno-syncisynci instructions on
architectures that support it. The synci instructions (if
enabled) are generated when __builtin___clear_cache is
compiled.
This option defaults to -mno-synci, but the default can be overridden by configuring GCC with --with-synci.
When compiling code for single processor systems, it is generally safe
to use synci. However, on many multi-core (SMP) systems, it
does not invalidate the instruction caches on all cores and may lead
to undefined behavior.
-mrelax-pic-calls-mno-relax-pic-calls$25 into direct calls. This is only possible if the linker can
resolve the destination at link time and if the destination is within
range for a direct call.
-mrelax-pic-calls is the default if GCC was configured to use
an assembler and a linker that support the .reloc assembly
directive and -mexplicit-relocs is in effect. With
-mno-explicit-relocs, this optimization can be performed by the
assembler and the linker alone without help from the compiler.
-mmcount-ra-address-mno-mcount-ra-address_mcount to modify the
calling function's return address. When enabled, this option extends
the usual _mcount interface with a new ra-address
parameter, which has type intptr_t * and is passed in register
$12. _mcount can then modify the return address by
doing both of the following:
$31.
*ra-address,
if ra-address is nonnull.
The default is -mno-mcount-ra-address.
-mframe-header-opt-mno-frame-header-optThis optimization is off by default at all optimization levels.
-mlxc1-sxc1-mno-lxc1-sxc1lwxc1,
swxc1, ldxc1, sdxc1 instructions. Enabled by default.
-mmadd4-mno-madd4madd.s,
madd.d and related instructions. Enabled by default.
These options are defined for the MMIX:
-mlibfuncs-mno-libfuncs-mepsilon-mno-epsilonrE epsilon register.
-mabi=mmixware-mabi=gnu$0 and up, as opposed to
the GNU ABI which uses global registers $231 and up.
-mzero-extend-mno-zero-extend-mknuthdiv-mno-knuthdiv-mtoplevel-symbols-mno-toplevel-symbolsPREFIX assembly directive.
-melf-mbranch-predict-mno-branch-predict-mbase-addresses-mno-base-addresses-msingle-exit-mno-single-exitThese -m options are defined for Matsushita MN10300 architectures:
-mmult-bug-mno-mult-bug-mam33-mno-am33-mam33-2-mam34-mtune=cpu-type-mreturn-pointer-on-d0a0 and d0. Otherwise, the pointer is returned
only in a0, and attempts to call such functions without a prototype
result in errors. Note that this option is on by default; use
-mno-return-pointer-on-d0 to disable it.
-mno-crt0-mrelaxThis option makes symbolic debugging impossible.
-mliw__LIW__.
-mno-liw__NO_LIW__.
-msetlb__SETLB__.
-mno-setlb__NO_SETLB__.
-meb-mel-mmul.x-mno-crt0These options are defined for the MSP430:
-masm-hex-mmcu=The option also sets the ISA to use. If the MCU name is one that is known to only support the 430 ISA then that is selected, otherwise the 430X ISA is selected. A generic MCU name of ‘msp430’ can also be used to select the 430 ISA. Similarly the generic ‘msp430x’ MCU name selects the 430X ISA.
In addition an MCU-specific linker script is added to the linker
command line. The script's name is the name of the MCU with
.ld appended. Thus specifying -mmcu=xxx on the gcc
command line defines the C preprocessor symbol __XXX__ and
cause the linker to search for a script called xxx.ld.
The ISA and hardware multiply supported for the different MCUs is hard-coded into GCC. However, an external ‘devices.csv’ file can be used to extend device support beyond those that have been hard-coded.
GCC searches for the ‘devices.csv’ file using the following methods in the given precedence order, where the first method takes precendence over the second which takes precedence over the third.
-I and -L-I and -L on the command line.
-mwarn-mcu-mno-warn-mcu-mcpu=-msim-mlargesize_t).
-msmallsize_t).
-mrelaxmhwmult=auto is the default setting.
Hardware multiplies are normally performed by calling a library routine. This saves space in the generated code. When compiling at -O3 or higher however the hardware multiplier is invoked inline. This makes for bigger, but faster code.
The hardware multiply routines disable interrupts whilst running and restore the previous interrupt state when they finish. This makes them safe to use inside interrupt handlers as well as in normal code.
-minrt-mtiny-printfprintf and puts library functions.
The ‘tiny’ implementations of these functions are not reentrant, so
must be used with caution in multi-threaded applications.
Support for streams has been removed and the string to be printed will
always be sent to stdout via the write syscall. The string is not
buffered before it is sent to write.
This option requires Newlib Nano IO, so GCC must be configured with ‘--enable-newlib-nano-formatted-io’.
-mmax-inline-shift=This only affects cases where a shift by multiple positions cannot be completed with a single instruction (e.g. all shifts >1 on the 430 ISA).
Shifts of a 32-bit value are at least twice as costly, so the value passed for this option is divided by 2 and the resulting value used instead.
-mcode-region=-mdata-region=lower, upper, either or
section attributes. Possible values are lower,
upper, either or any. The first three behave
like the corresponding attribute. The fourth possible value -
any - is the default. It leaves placement entirely up to the
linker script and how it assigns the standard sections
(.text, .data, etc) to the memory regions.
-msilicon-errata=-msilicon-errata-warn=-mwarn-devices-csv-mno-warn-devices-csvThese options are defined for NDS32 implementations:
-mbig-endian-mlittle-endian-mreduced-regs-mfull-regs-mcmov-mno-cmov-mext-perf-mno-ext-perf-mext-perf2-mno-ext-perf2-mext-string-mno-ext-string-mv3push-mno-v3push-m16-bit-mno-16-bit-misr-vector-size=num-mcache-block-size=num-march=arch-mcmodel=code-model-mctor-dtor-mrelaxThese are the options defined for the Altera Nios II processor.
-G num-mgpopt=option-mgpopt-mno-gpoptsection
attribute.
-mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is equivalent to -mgpopt=none.
The default is -mgpopt except when -fpic or -fPIC is specified to generate position-independent code. Note that the Nios II ABI does not permit GP-relative accesses from shared libraries.
You may need to specify -mno-gpopt explicitly when building programs that include large amounts of small data, including large GOT data sections. In this case, the 16-bit offset for GP-relative addressing may not be large enough to allow access to the entire small data section.
-mgprel-sec=regexpsection attributes on variable declarations
(see Common Variable Attributes) and a custom linker script.
The regexp is a POSIX Extended Regular Expression.
This option does not affect the behavior of the -G option, and
the specified sections are in addition to the standard .sdata
and .sbss small-data sections that are recognized by -mgpopt.
-mr0rel-sec=regexpr0; that is, in the low 32K or high 32K
of the 32-bit address space. It is most useful in conjunction with
section attributes on variable declarations
(see Common Variable Attributes) and a custom linker script.
The regexp is a POSIX Extended Regular Expression.
In contrast to the use of GP-relative addressing for small data, zero-based addressing is never generated by default and there are no conventional section names used in standard linker scripts for sections in the low or high areas of memory.
-mel-meb-march=archThe preprocessor macro __nios2_arch__ is available to programs,
with value 1 or 2, indicating the targeted ISA level.
-mbypass-cache-mno-bypass-cache-mno-cache-volatile-mcache-volatile-mno-fast-sw-div-mfast-sw-div-mno-hw-mul-mhw-mul-mno-hw-mulx-mhw-mulx-mno-hw-div-mhw-divmul, mulx and div family of
instructions by the compiler. The default is to emit mul
and not emit div and mulx.
-mbmx-mno-bmx-mcdx-mno-cdx-mcustom-insn=N-mno-custom-insnThe following values of insn are supported. Except as otherwise noted, floating-point operations are expected to be implemented with normal IEEE 754 semantics and correspond directly to the C operators or the equivalent GCC built-in functions (see Other Builtins).
Single-precision floating point:
Double-precision floating point:
Conversions:
__builtin_lroundf function when
-fno-math-errno is used.
In addition, all of the following transfer instructions for internal registers X and Y must be provided to use any of the double-precision floating-point instructions. Custom instructions taking two double-precision source operands expect the first operand in the 64-bit register X. The other operand (or only operand of a unary operation) is given to the custom arithmetic instruction with the least significant half in source register src1 and the most significant half in src2. A custom instruction that returns a double-precision result returns the most significant 32 bits in the destination register and the other half in 32-bit register Y. GCC automatically generates the necessary code sequences to write register X and/or read register Y when double-precision floating-point instructions are used.
Note that you can gain more local control over generation of Nios II custom
instructions by using the target("custom-insn=N")
and target("no-custom-insn") function attributes
(see Function Attributes)
or pragmas (see Function Specific Option Pragmas).
-mcustom-fpu-cfg=name-mcustom-fpu-cfg=60-1 is equivalent to:
-mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-fsingle-precision-constant
-mcustom-fpu-cfg=60-2 is equivalent to:
-mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-mcustom-fdivs=255
-fsingle-precision-constant
-mcustom-fpu-cfg=72-3 is equivalent to:
-mcustom-floatus=243
-mcustom-fixsi=244
-mcustom-floatis=245
-mcustom-fcmpgts=246
-mcustom-fcmples=249
-mcustom-fcmpeqs=250
-mcustom-fcmpnes=251
-mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-mcustom-fdivs=255
-fsingle-precision-constant
-mcustom-fpu-cfg=fph2 is equivalent to:
-mcustom-fabss=224
-mcustom-fnegs=225
-mcustom-fcmpnes=226
-mcustom-fcmpeqs=227
-mcustom-fcmpges=228
-mcustom-fcmpgts=229
-mcustom-fcmples=230
-mcustom-fcmplts=231
-mcustom-fmaxs=232
-mcustom-fmins=233
-mcustom-round=248
-mcustom-fixsi=249
-mcustom-floatis=250
-mcustom-fsqrts=251
-mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-mcustom-fdivs=255
Custom instruction assignments given by individual -mcustom-insn= options override those given by -mcustom-fpu-cfg=, regardless of the order of the options on the command line.
Note that you can gain more local control over selection of a FPU
configuration by using the target("custom-fpu-cfg=name")
function attribute (see Function Attributes)
or pragma (see Function Specific Option Pragmas).
The name fph2 is an abbreviation for Nios II Floating Point Hardware 2 Component. Please note that the custom instructions enabled by -mcustom-fmins=233 and -mcustom-fmaxs=234 are only generated if -ffinite-math-only is specified. The custom instruction enabled by -mcustom-round=248 is only generated if -fno-math-errno is specified. In contrast to the other configurations, -fsingle-precision-constant is not set.
These additional ‘-m’ options are available for the Altera Nios II ELF (bare-metal) target:
-mhal-msmallc-msys-crt0=startfile-msys-lib=systemlibread and write.
This option is typically used to link with a library provided by a HAL BSP.
These options are defined for Nvidia PTX:
-m64-march=architecture-stringThis option sets the value of the preprocessor macro
__PTX_SM__; for instance, for ‘sm_35’, it has the value
‘350’.
-misa=architecture-string-march-map=architecture-string-mptx=version-stringThis option sets the values of the preprocessor macros
__PTX_ISA_VERSION_MAJOR__ and __PTX_ISA_VERSION_MINOR__;
for instance, for ‘3.1’ the macros have the values ‘3’ and
‘1’, respectively.
-mmainkernel-moptimize-msoft-stack.local memory
directly for stack storage. Instead, a per-warp stack pointer is
maintained explicitly. This enables variable-length stack allocation (with
variable-length arrays or alloca), and when global memory is used for
underlying storage, makes it possible to access automatic variables from other
threads, or with atomic instructions. This code generation variant is used
for OpenMP offloading, but the option is exposed on its own for the purpose
of testing the compiler; to generate code suitable for linking into programs
using OpenMP offloading, use option -mgomp.
-muniform-simtint __nvptx_uni[] stores all-zeros or
all-ones bitmasks for each warp, indicating current mode (0 outside of SIMD
regions). Each thread can bitwise-and the bitmask at position tid.y
with current lane index to compute the master lane index.
-mgompThese options are defined for OpenRISC:
-mboard=nameor1ksim.
-mnewlib-msoft-div-mhard-divl.div, l.divu) instructions.
This default is hardware divide.
-msoft-mul-mhard-mull.mul, l.muli) instructions.
This default is hardware multiply.
-msoft-float-mhard-float-mdouble-float-munordered-floatlf.sfun*) instructions. By default
functions from libgcc are used to perform unordered floating point
compare and set flag operations.
-mcmovl.cmov) instructions. By
default the equivalent will be generated using set and branch.
-mrorl.ror) instructions. By default
functions from libgcc are used to perform rotate right operations.
-mroril.rori) instructions.
By default functions from libgcc are used to perform rotate right with
immediate operations.
-msextl.ext*) instructions. By default
memory loads are used to perform sign extension.
-msfimml.sf*i)
instructions. By default extra instructions will be generated to store the
immediate to a register first.
-mshftimml.srai, l.srli,
l.slli) instructions. By default extra instructions will be generated
to store the immediate to a register first.
-mcmodel=small-mcmodel=largeThese options are defined for the PDP-11:
-mfpu-msoft-float-mac0-mno-ac0-m40-m45-m10-mint16-mno-int32int. This is the default.
-mint32-mno-int16int.
-msplit-munix-asm-mdec-asm-mgnu-asm-mlraThese are listed under See RS/6000 and PowerPC Options.
These command-line options are defined for PRU target:
-minrt-mmcu=mcu-mno-relax-mloop-mabi=variantThe current -mabi=ti implementation simply raises a compile error when any of the above code constructs is detected. As a consequence the standard C library cannot be built and it is omitted when linking with -mabi=ti.
Relaxation is a GNU feature and for safety reasons is disabled when using -mabi=ti. The TI toolchain does not emit relocations for QBBx instructions, so the GNU linker cannot adjust them when shortening adjacent LDI32 pseudo instructions.
These command-line options are defined for RISC-V targets:
-mbranch-cost=n-mplt-mno-plt-mabi=ABI-stringThe default for this argument is system dependent, users who want a specific calling convention should specify one explicitly. The valid calling conventions are: ‘ilp32’, ‘ilp32f’, ‘ilp32d’, ‘lp64’, ‘lp64f’, and ‘lp64d’. Some calling conventions are impossible to implement on some ISAs: for example, ‘-march=rv32if -mabi=ilp32d’ is invalid because the ABI requires 64-bit values be passed in F registers, but F registers are only 32 bits wide. There is also the ‘ilp32e’ ABI that can only be used with the ‘rv32e’ architecture. This ABI is not well specified at present, and is subject to change.
-mfdiv-mno-fdiv-mdiv-mno-div-misa-spec=ISA-spec-string2.22019060820191213-march=ISA-stringWhen -march= is not specified, use the setting from -mcpu.
If both -march and -mcpu= are not specified, the default for this argument is system dependent, users who want a specific architecture extensions should specify one explicitly.
-mcpu=processor-string-mtune=processor-stringWhen -mtune= is not specified, use the setting from -mcpu, the default is ‘rocket’ if both are not specified.
The ‘size’ choice is not intended for use by end-users. This is used when -Os is specified. It overrides the instruction cost info provided by -mtune=, but does not override the pipeline info. This helps reduce code size while still giving good performance.
-mpreferred-stack-boundary=numWarning: If you use this switch, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules.
-msmall-data-limit=n-msave-restore-mno-save-restore-minline-atomics-mno-inline-atomics-mshorten-memrefs-mno-shorten-memrefs-mstrict-align-mno-strict-align-mcmodel=medlow-mcmodel=medanyThe code generated by the medium-any code model is position-independent, but is
not guaranteed to function correctly when linked into position-independent
executables or libraries.
-mexplicit-relocs-mno-exlicit-relocs-mrelax-mno-relax-mriscv-attribute-mno-riscv-attribute-mcsr-check-mno-csr-check-malign-data=type-mbig-endian-mlittle-endian-mstack-protector-guard=guard-mstack-protector-guard-reg=reg-mstack-protector-guard-offset=offsetWith the latter choice the options -mstack-protector-guard-reg=reg and -mstack-protector-guard-offset=offset furthermore specify which register to use as base register for reading the canary, and from what offset from that base register. There is no default register or offset as this is entirely for use within the Linux kernel.
-msim-mmul=none-mmul=g10-mmul=g13-mmul=g14-mmul=rl78none, which uses software for both
multiplication and division. This is the default. The g13
value is for the hardware multiply/divide peripheral found on the
RL78/G13 (S2 core) targets. The g14 value selects the use of
the multiplication and division instructions supported by the RL78/G14
(S3 core) parts. The value rl78 is an alias for g14 and
the value mg10 is an alias for none.
In addition a C preprocessor macro is defined, based upon the setting
of this option. Possible values are: __RL78_MUL_NONE__,
__RL78_MUL_G13__ or __RL78_MUL_G14__.
-mcpu=g10-mcpu=g13-mcpu=g14-mcpu=rl78If this option is set it also selects the type of hardware multiply support to use, unless this is overridden by an explicit -mmul=none option on the command line. Thus specifying -mcpu=g13 enables the use of the G13 hardware multiply peripheral and specifying -mcpu=g10 disables the use of hardware multiplications altogether.
Note, although the RL78/G14 core is the default target, specifying -mcpu=g14 or -mcpu=rl78 on the command line does change the behavior of the toolchain since it also enables G14 hardware multiply support. If these options are not specified on the command line then software multiplication routines will be used even though the code targets the RL78 core. This is for backwards compatibility with older toolchains which did not have hardware multiply and divide support.
In addition a C preprocessor macro is defined, based upon the setting
of this option. Possible values are: __RL78_G10__,
__RL78_G13__ or __RL78_G14__.
-mg10-mg13-mg14-mrl78-mallregsr24..r31 are reserved for use in interrupt handlers.
With this option enabled these registers can be used in ordinary
functions as well.
-m64bit-doubles-m32bit-doublesdouble data type be 64 bits (-m64bit-doubles)
or 32 bits (-m32bit-doubles) in size. The default is
-m32bit-doubles.
-msave-mduc-in-interrupts-mno-save-mduc-in-interruptsThese ‘-m’ options are defined for the IBM RS/6000 and PowerPC:
-mpowerpc-gpopt-mno-powerpc-gpopt-mpowerpc-gfxopt-mno-powerpc-gfxopt-mpowerpc64-mno-powerpc64-mmfcrf-mno-mfcrf-mpopcntb-mno-popcntb-mpopcntd-mno-popcntd-mfprnd-mno-fprnd-mcmpb-mno-cmpb-mhard-dfp-mno-hard-dfpSpecifying -mpowerpc-gpopt allows GCC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying -mpowerpc-gfxopt allows GCC to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select.
The -mmfcrf option allows GCC to generate the move from condition register field instruction implemented on the POWER4 processor and other processors that support the PowerPC V2.01 architecture. The -mpopcntb option allows GCC to generate the popcount and double-precision FP reciprocal estimate instruction implemented on the POWER5 processor and other processors that support the PowerPC V2.02 architecture. The -mpopcntd option allows GCC to generate the popcount instruction implemented on the POWER7 processor and other processors that support the PowerPC V2.06 architecture. The -mfprnd option allows GCC to generate the FP round to integer instructions implemented on the POWER5+ processor and other processors that support the PowerPC V2.03 architecture. The -mcmpb option allows GCC to generate the compare bytes instruction implemented on the POWER6 processor and other processors that support the PowerPC V2.05 architecture. The -mhard-dfp option allows GCC to generate the decimal floating-point instructions implemented on some POWER processors.
The -mpowerpc64 option allows GCC to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to -mno-powerpc64.
-mcpu=cpu_type-mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure 32-bit PowerPC (either endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes.
Specifying ‘native’ as cpu type detects and selects the architecture option that corresponds to the host processor of the system performing the compilation. -mcpu=native has no effect if GCC does not recognize the processor.
The other options specify a specific processor. Code generated under those options runs best on that processor, and may not run at all on others.
The -mcpu options automatically enable or disable the following options:
-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple
-mpopcntb -mpopcntd -mpowerpc64
-mpowerpc-gpopt -mpowerpc-gfxopt
-mmulhw -mdlmzb -mmfpgpr -mvsx
-mcrypto -mhtm -mpower8-fusion -mpower8-vector
-mquad-memory -mquad-memory-atomic -mfloat128
-mfloat128-hardware -mprefixed -mpcrel -mmma
-mrop-protect
The particular options set for any particular CPU varies between compiler versions, depending on what setting seems to produce optimal code for that CPU; it doesn't necessarily reflect the actual hardware's capabilities. If you wish to set an individual option to a particular value, you may specify it after the -mcpu option, like -mcpu=970 -mno-altivec.
On AIX, the -maltivec and -mpowerpc64 options are not enabled or disabled by the -mcpu option at present because AIX does not have full support for these options. You may still enable or disable them individually if you're sure it'll work in your environment.
-mtune=cpu_type-mcmodel=small-mcmodel=medium-mcmodel=large-maltivec-mno-altivecWhen -maltivec is used, the element order for AltiVec intrinsics
such as vec_splat, vec_extract, and vec_insert
match array element order corresponding to the endianness of the
target. That is, element zero identifies the leftmost element in a
vector register when targeting a big-endian platform, and identifies
the rightmost element in a vector register when targeting a
little-endian platform.
-mvrsave-mno-vrsave-msecure-plt.plt and .got sections.
This is a PowerPC
32-bit SYSV ABI option.
-mbss-plt.plt section that ld.so
fills in, and
requires .plt and .got
sections that are both writable and executable.
This is a PowerPC 32-bit SYSV ABI option.
-misel-mno-isel-mvsx-mno-vsx-mcrypto-mno-crypto-mhtm-mno-htm-mpower8-fusion-mno-power8-fusion-mpower8-vector-mno-power8-vector-mquad-memory-mno-quad-memory-mquad-memory-atomic-mno-quad-memory-atomic-mfloat128-mno-float128The VSX instruction set (-mvsx) must be enabled to use the IEEE 128-bit floating point support. The IEEE 128-bit floating point is only supported on Linux.
The default for -mfloat128 is enabled on PowerPC Linux systems using the VSX instruction set, and disabled on other systems.
If you use the ISA 3.0 instruction set (-mpower9-vector or -mcpu=power9) on a 64-bit system, the IEEE 128-bit floating point support will also enable the generation of ISA 3.0 IEEE 128-bit floating point instructions. Otherwise, if you do not specify to generate ISA 3.0 instructions or you are targeting a 32-bit big endian system, IEEE 128-bit floating point will be done with software emulation.
-mfloat128-hardware-mno-float128-hardwareThe default for -mfloat128-hardware is enabled on PowerPC Linux systems using the ISA 3.0 instruction set, and disabled on other systems.
-m32-m64-mfull-toc-mno-fp-in-toc-mno-sum-in-toc-mminimal-tocIf you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options. -mno-fp-in-toc prevents GCC from putting floating-point constants in the TOC and -mno-sum-in-toc forces GCC to generate code to calculate the sum of an address and a constant at run time instead of putting that sum into the TOC. You may specify one or both of these options. Each causes GCC to produce very slightly slower and larger code at the expense of conserving TOC space.
If you still run out of space in the TOC even when you specify both of these options, specify -mminimal-toc instead. This option causes GCC to make only one TOC entry for every file. When you specify this option, GCC produces code that is slower and larger but which uses extremely little TOC space. You may wish to use this option only on files that contain less frequently-executed code.
-maix64-maix32long type, and the infrastructure needed to support them.
Specifying -maix64 implies -mpowerpc64,
while -maix32 disables the 64-bit ABI and
implies -mno-powerpc64. GCC defaults to -maix32.
-mxl-compat-mno-xl-compatThe AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. IBM XL compilers access floating-point arguments that do not fit in the RSA from the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by IBM XL compilers without optimization.
-mpe-malign-natural-malign-powerOn 64-bit Darwin, natural alignment is the default, and -malign-power is not supported.
-msoft-float-mhard-float-mmultiple-mno-multiple-mupdate-mno-update-mavoid-indexed-addresses-mno-avoid-indexed-addresses-mfused-madd-mno-fused-madd-mmulhw-mno-mulhw-mdlmzb-mno-dlmzb-mno-bit-align-mbit-alignFor example, by default a structure containing nothing but 8
unsigned bit-fields of length 1 is aligned to a 4-byte
boundary and has a size of 4 bytes. By using -mno-bit-align,
the structure is aligned to a 1-byte boundary and is 1 byte in
size.
-mno-strict-align-mstrict-align-mrelocatable-mno-relocatable.got2 and 4-byte locations listed in the .fixup section,
a table of 32-bit addresses generated by this option. For this to
work, all objects linked together must be compiled with
-mrelocatable or -mrelocatable-lib.
-mrelocatable code aligns the stack to an 8-byte boundary.
-mrelocatable-lib-mno-relocatable-lib.fixup section to allow static executables to be relocated at
run time, but -mrelocatable-lib does not use the smaller stack
alignment of -mrelocatable. Objects compiled with
-mrelocatable-lib may be linked with objects compiled with
any combination of the -mrelocatable options.
-mno-toc-mtoc-mlittle-mlittle-endian-mbig-mbig-endian-mdynamic-no-pic-msingle-pic-base-mprioritize-restricted-insns=priority-msched-costly-dep=dependence_type-minsert-sched-nops=scheme-mcall-sysv-mcall-sysv-eabi-mcall-eabi-mcall-sysv-noeabi-mcall-aixdesc-mcall-linux-mcall-freebsd-mcall-netbsd-mcall-openbsd-mtraceback=traceback_type-maix-struct-return-msvr4-struct-return-mabi=abi-type-mabi=ibmlongdouble-mabi=ieeelongdouble-mabi=elfv1-mabi=elfv2-mgnu-attribute-mno-gnu-attribute-mprototype-mno-prototypeCR) to
indicate whether floating-point values are passed in the floating-point
registers in case the function takes variable arguments. With
-mprototype, only calls to prototyped variable argument functions
set or clear the bit.
-msim-mmvme-mads-myellowknife-mvxworks-membPPC_EMB bit in the ELF flags
header to indicate that ‘eabi’ extended relocations are used.
-meabi-mno-eabi__eabi is called from main to set up the EABI
environment, and the -msdata option can use both r2 and
r13 to point to two separate small data areas. Selecting
-mno-eabi means that the stack is aligned to a 16-byte boundary,
no EABI initialization function is called from main, and the
-msdata option only uses r13 to point to a single
small data area. The -meabi option is on by default if you
configured GCC using one of the ‘powerpc*-*-eabi*’ options.
-msdata=eabiconst global and static data in the .sdata2 section, which
is pointed to by register r2. Put small initialized
non-const global and static data in the .sdata section,
which is pointed to by register r13. Put small uninitialized
global and static data in the .sbss section, which is adjacent to
the .sdata section. The -msdata=eabi option is
incompatible with the -mrelocatable option. The
-msdata=eabi option also sets the -memb option.
-msdata=sysv.sdata section, which is pointed to by register
r13. Put small uninitialized global and static data in the
.sbss section, which is adjacent to the .sdata section.
The -msdata=sysv option is incompatible with the
-mrelocatable option.
-msdata=default-msdata-msdata=data.sdata section. Put small uninitialized global
data in the .sbss section. Do not use register r13
to address small data however. This is the default behavior unless
other -msdata options are used.
-msdata=none-mno-sdata.data section, and all uninitialized data in the
.bss section.
-mreadonly-in-sdata.sdata section as well. This is the
default.
-mblock-move-inline-limit=nummemcpy or structure
copies) less than or equal to num bytes. The minimum value for
num is 32 bytes on 32-bit targets and 64 bytes on 64-bit
targets. The default value is target-specific.
-mblock-compare-inline-limit=nummemcmp or structure compares) less than or equal to num
bytes. If num is 0, all inline expansion (non-loop and loop) of
block compare is disabled. The default value is target-specific.
-mblock-compare-inline-loop-limit=nummemcmp
is called to compare the remainder of the block. The default value is
target-specific.
-mstring-compare-inline-limit=numstrcmp or strncmp will
take care of the rest of the comparison. The default is 64 bytes.
-G num-mregnames-mno-regnames-mlongcall-mno-longcallshortcall function attribute, or by #pragma
longcall(0).
Some linkers are capable of detecting out-of-range calls and generating glue code on the fly. On these systems, long calls are unnecessary and generate slower code. As of this writing, the AIX linker can do this, as can the GNU linker for PowerPC/64. It is planned to add this feature to the GNU linker for 32-bit PowerPC systems as well.
On PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU linkers, GCC can generate long calls using an inline PLT call sequence (see -mpltseq). PowerPC with -mbss-plt and PowerPC64 ELFv1 (big-endian) do not support inline PLT calls.
On Darwin/PPC systems, #pragma longcall generates jbsr
callee, L42, plus a branch island (glue code). The two target
addresses represent the callee and the branch island. The
Darwin/PPC linker prefers the first address and generates a bl
callee if the PPC bl instruction reaches the callee directly;
otherwise, the linker generates bl L42 to call the branch
island. The branch island is appended to the body of the
calling function; it computes the full 32-bit address of the callee
and jumps to it.
On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct call, and the Darwin linker decides whether to use or discard it.
In the future, GCC may ignore all longcall specifications when the linker is known to generate glue.
-mpltseq-mno-pltseq-mtls-markers-mno-tls-markers__tls_get_addr with a relocation
specifying the function argument. The relocation allows the linker to
reliably associate function call with argument setup instructions for
TLS optimization, which in turn allows GCC to better schedule the
sequence.
-mrecip-mno-recip-mrecip=opt! to invert the option:
So, for example, -mrecip=all,!rsqrtd enables
all of the reciprocal estimate instructions, except for the
FRSQRTE, XSRSQRTEDP, and XVRSQRTEDP instructions
which handle the double-precision reciprocal square root calculations.
-mrecip-precision-mno-recip-precision-mveclibabi=typeacosd2, acosf4,
acoshd2, acoshf4, asind2, asinf4,
asinhd2, asinhf4, atan2d2, atan2f4,
atand2, atanf4, atanhd2, atanhf4,
cbrtd2, cbrtf4, cosd2, cosf4,
coshd2, coshf4, erfcd2, erfcf4,
erfd2, erff4, exp2d2, exp2f4,
expd2, expf4, expm1d2, expm1f4,
hypotd2, hypotf4, lgammad2, lgammaf4,
log10d2, log10f4, log1pd2, log1pf4,
log2d2, log2f4, logd2, logf4,
powd2, powf4, sind2, sinf4, sinhd2,
sinhf4, sqrtd2, sqrtf4, tand2,
tanf4, tanhd2, and tanhf4 when generating code
for power7. Both -ftree-vectorize and
-funsafe-math-optimizations must also be enabled. The MASS
libraries must be specified at link time.
-mfriz-mno-frizfriz instruction when the
-funsafe-math-optimizations option is used to optimize
rounding of floating-point values to 64-bit integer and back to floating
point. The friz instruction does not return the same value if
the floating-point number is too large to fit in an integer.
-mpointers-to-nested-functions-mno-pointers-to-nested-functionsr11) when calling through a pointer on AIX and 64-bit Linux
systems where a function pointer points to a 3-word descriptor giving
the function address, TOC value to be loaded in register r2, and
static chain value to be loaded in register r11. The
-mpointers-to-nested-functions is on by default. You cannot
call through pointers to nested functions or pointers
to functions compiled in other languages that use the static chain if
you use -mno-pointers-to-nested-functions.
-msave-toc-indirect-mno-save-toc-indirect-mcompat-align-parm-mno-compat-align-parmOlder versions of GCC (prior to 4.9.0) incorrectly did not align a structure parameter on a 128-bit boundary when that structure contained a member requiring 128-bit alignment. This is corrected in more recent versions of GCC. This option may be used to generate code that is compatible with functions compiled with older versions of GCC.
The -mno-compat-align-parm option is the default.
-mstack-protector-guard=guard-mstack-protector-guard-reg=reg-mstack-protector-guard-offset=offset-mstack-protector-guard-symbol=symbolWith the latter choice the options -mstack-protector-guard-reg=reg and -mstack-protector-guard-offset=offset furthermore specify which register to use as base register for reading the canary, and from what offset from that base register. The default for those is as specified in the relevant ABI. -mstack-protector-guard-symbol=symbol overrides the offset with a symbol reference to a canary in the TLS block.
-mpcrel-mno-pcrel-mprefixed-mno-prefixed-mmma-mno-mma-mrop-protect-mno-rop-protect-mprivileged-mno-privileged-mblock-ops-unaligned-vsx-mno-block-ops-unaligned-vsxmemcpy and memmove.
--param rs6000-vect-unroll-limit=These command-line options are defined for RX targets:
-m64bit-doubles-m32bit-doublesdouble data type be 64 bits (-m64bit-doubles)
or 32 bits (-m32bit-doubles) in size. The default is
-m32bit-doubles. Note RX floating-point hardware only
works on 32-bit values, which is why the default is
-m32bit-doubles.
-fpu-nofpuFloating-point instructions are only generated for 32-bit floating-point values, however, so the FPU hardware is not used for doubles if the -m64bit-doubles option is used.
Note If the -fpu option is enabled then -funsafe-math-optimizations is also enabled automatically. This is because the RX FPU instructions are themselves unsafe.
-mcpu=nameThe only difference between ‘RX600’ and ‘RX610’ is that the
‘RX610’ does not support the MVTIPL instruction.
The ‘RX200’ series does not have a hardware floating-point unit and so -nofpu is enabled by default when this type is selected.
-mbig-endian-data-mlittle-endian-data-msmall-data-limit=Nr13) is reserved for use pointing to this
area, so it is no longer available for use by the compiler. This
could result in slower and/or larger code if variables are pushed onto
the stack instead of being held in this register.
Note, common variables (variables that have not been initialized) and constants are not placed into the small data area as they are assigned to other sections in the output executable.
The default value is zero, which disables this feature. Note, this feature is not enabled by default with higher optimization levels (-O2 etc) because of the potentially detrimental effects of reserving a register. It is up to the programmer to experiment and discover whether this feature is of benefit to their program. See the description of the -mpid option for a description of how the actual register to hold the small data area pointer is chosen.
-msim-mno-sim-mas100-syntax-mno-as100-syntax-mmax-constant-size=NThe value N can be between 0 and 4. A value of 0 (the default) or 4 means that constants of any size are allowed.
-mrelax-mint-register=Nr13 is reserved for the exclusive use
of fast interrupt handlers. A value of 2 reserves r13 and
r12. A value of 3 reserves r13, r12 and
r11, and a value of 4 reserves r13 through r10.
A value of 0, the default, does not reserve any registers.
-msave-acc-in-interrupts-mpid-mno-pidNote, using this feature reserves a register, usually r13, for
the constant data base address. This can result in slower and/or
larger code, especially in complicated functions.
The actual register chosen to hold the constant data base address
depends upon whether the -msmall-data-limit and/or the
-mint-register command-line options are enabled. Starting
with register r13 and proceeding downwards, registers are
allocated first to satisfy the requirements of -mint-register,
then -mpid and finally -msmall-data-limit. Thus it
is possible for the small data area register to be r8 if both
-mint-register=4 and -mpid are specified on the
command line.
By default this feature is not enabled. The default can be restored via the -mno-pid command-line option.
-mno-warn-multiple-fast-interrupts-mwarn-multiple-fast-interrupts-mallow-string-insns-mno-allow-string-insnsSMOVF, SCMPU, SMOVB, SMOVU, SUNTIL
SWHILE and also the RMPA instruction. These
instructions may prefetch data, which is not safe to do if accessing
an I/O register. (See section 12.2.7 of the RX62N Group User's Manual
for more information).
The default is to allow these instructions, but it is not possible for GCC to reliably detect all circumstances where a string instruction might be used to access an I/O register, so their use cannot be disabled automatically. Instead it is reliant upon the programmer to use the -mno-allow-string-insns option if their program accesses I/O space.
When the instructions are enabled GCC defines the C preprocessor
symbol __RX_ALLOW_STRING_INSNS__, otherwise it defines the
symbol __RX_DISALLOW_STRING_INSNS__.
-mjsr-mno-jsrJSR instructions to access functions.
This option can be used when code size exceeds the range of BSR
instructions. Note that -mno-jsr does not mean to not use
JSR but instead means that any type of branch may be used.
Note: The generic GCC command-line option -ffixed-reg
has special significance to the RX port when used with the
interrupt function attribute. This attribute indicates a
function intended to process fast interrupts. GCC ensures
that it only uses the registers r10, r11, r12
and/or r13 and only provided that the normal use of the
corresponding registers have been restricted via the
-ffixed-reg or -mint-register command-line
options.
These are the ‘-m’ options defined for the S/390 and zSeries architecture.
-mhard-float-msoft-float-mhard-dfp-mno-hard-dfp-mlong-double-64-mlong-double-128long double type. A size
of 64 bits makes the long double type equivalent to the double
type. This is the default.
-mbackchain-mno-backchainIn general, code compiled with -mbackchain is call-compatible with code compiled with -mno-backchain; however, use of the backchain for debugging purposes usually requires that the whole binary is built with -mbackchain. Note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float.
The default is to not maintain the backchain.
-mpacked-stack-mno-packed-stackAs long as the stack frame backchain is not used, code generated with -mpacked-stack is call-compatible with code generated with -mno-packed-stack. Note that some non-FSF releases of GCC 2.95 for S/390 or zSeries generated code that uses the stack frame backchain at run time, not just for debugging purposes. Such code is not call-compatible with code compiled with -mpacked-stack. Also, note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float.
The default is to not use the packed stack layout.
-msmall-exec-mno-small-execbras instruction
to do subroutine calls.
This only works reliably if the total executable size does not
exceed 64k. The default is to use the basr instruction instead,
which does not have this limitation.
-m64-m31-mzarch-mesa-mhtm-mno-htm-mvx-mno-vx-mzvector-mno-zvector-mmvcle-mno-mvclemvcle instruction
to perform block moves. When -mno-mvcle is specified,
use a mvc loop instead. This is the default unless optimizing for
size.
-mdebug-mno-debug-march=cpu-typeThe default is -march=z900.
Specifying ‘native’ as cpu type can be used to select the best architecture option for the host processor. -march=native has no effect if GCC does not recognize the processor.
-mtune=cpu-type-mtpf-trace-mno-tpf-trace-mtpf-trace-skip-mno-tpf-trace-skip-mfused-madd-mno-fused-madd-mwarn-framesize=framesize-mwarn-dynamicstackalloca or uses dynamically-sized
arrays. This is generally a bad idea with a limited stack size.
-mstack-guard=stack-guard-mstack-size=stack-size-mhotpatch=pre-halfwords,post-halfwordsIf both arguments are zero, hotpatching is disabled.
This option can be overridden for individual functions with the
hotpatch attribute.
These ‘-m’ options are defined for the SH implementations:
-m1-m2-m2e-m2a-nofpu-m2a-single-only-m2a-single-m2a-m3-m3e-m4-nofpu-m4-single-only-m4-single-m4-m4-100-m4-100-nofpu-m4-100-single-m4-100-single-only-m4-200-m4-200-nofpu-m4-200-single-m4-200-single-only-m4-300-m4-300-nofpu-m4-300-single-m4-300-single-only-m4-340-m4-500-m4a-nofpu-m4a-single-only-m4a-single-m4a-m4al-mb-ml-mdalign-mrelax-mbigtableswitch tables. The default is to use
16-bit offsets.
-mbitops-mfmovdfmovd. Check -mdalign for
alignment constraints.
-mrenesas-mno-renesas-mnomacsaveMAC register as call-clobbered, even if
-mrenesas is given.
-mieee-mno-ieee-minline-ic_invalidateicbi
instruction.
If the selected code generation option does not allow the use of the icbi
instruction, and -musermode is not in effect, the inlined code
manipulates the instruction cache address array directly with an associative
write. This not only requires privileged mode at run time, but it also
fails if the cache line had been mapped via the TLB and has become unmapped.
-misize-mpadstruct-matomic-model=modelsh*-*-linux*.
sh*-*-linux* and SH3* or SH4*. When the target is SH4A,
this option also partially utilizes the hardware atomic instructions
movli.l and movco.l to create more efficient code, unless
‘strict’ is specified.
SR.IMASK = 1111. This model works only when the program runs
in privileged mode and is only suitable for single-core systems. Additional
support from the interrupt/exception handling code of the system is not
required. This model is enabled by default when the target is
sh*-*-linux* and SH1* or SH2*.
movli.l and movco.l
instructions only. This is only available on SH4A and is suitable for
multi-core systems. Since the hardware instructions support only 32 bit atomic
variables access to 8 or 16 bit variables is emulated with 32 bit accesses.
Code compiled with this option is also compatible with other software
atomic model interrupt/exception handling systems if executed on an SH4A
system. Additional support from the interrupt/exception handling code of the
system is not required for this model.
-mtastas.b opcode for __atomic_test_and_set.
Notice that depending on the particular hardware and software configuration
this can degrade overall performance due to the operand cache line flushes
that are implied by the tas.b instruction. On multi-core SH4A
processors the tas.b instruction must be used with caution since it
can result in data corruption for certain cache configurations.
-mprefergot-musermode-mno-usermodesh*-*-linux*. If the target is SH1* or SH2*
-musermode has no effect, since there is no user mode.
-multcost=number-mdiv=strategydiv1 to perform the operation. Division by zero calculates an
unspecified result and does not trap. This is the default except for SH4,
SH2A and SHcompact.
call-div1.
div1 instruction with case distinction for larger divisors. Division
by zero calculates an unspecified result and does not trap. This is the default
for SH4. Specifying this for targets that do not have dynamic shift
instructions defaults to call-div1.
When a division strategy has not been specified the default strategy is
selected based on the current target. For SH2A the default strategy is to
use the divs and divu instructions instead of library function
calls.
-maccumulate-outgoing-args-mdivsi3_libfunc=name-mfixed-range=register-range-mbranch-cost=num-mzdcbranch-mno-zdcbranchbt and bf are fast. If -mzdcbranch is specified, the
compiler prefers zero displacement branch code sequences. This is
enabled by default when generating code for SH4 and SH4A. It can be explicitly
disabled by specifying -mno-zdcbranch.
-mcbranch-force-delay-slotnop if a suitable instruction cannot be found. By default
this option is disabled. It can be enabled to work around hardware bugs as
found in the original SH7055.
-mfused-madd-mno-fused-madd-mfsca-mno-fscafsca instruction for sine
and cosine approximations. The option -mfsca must be used in
combination with -funsafe-math-optimizations. It is enabled by default
when generating code for SH4A. Using -mno-fsca disables sine and cosine
approximations even if -funsafe-math-optimizations is in effect.
-mfsrra-mno-fsrrafsrra instruction for
reciprocal square root approximations. The option -mfsrra must be used
in combination with -funsafe-math-optimizations and
-ffinite-math-only. It is enabled by default when generating code for
SH4A. Using -mno-fsrra disables reciprocal square root approximations
even if -funsafe-math-optimizations and -ffinite-math-only are
in effect.
-mpretend-cmove-mfdpicThese ‘-m’ options are supported on Solaris 2:
-mclear-hwcap-mimpure-text-mimpure-text suppresses the “relocations remain against allocatable but non-writable sections” linker error message. However, the necessary relocations trigger copy-on-write, and the shared object is not actually shared across processes. Instead of using -mimpure-text, you should compile all source code with -fpic or -fPIC.
These switches are supported in addition to the above on Solaris 2:
-pthreadsThese ‘-m’ options are supported on the SPARC:
-mno-app-regs-mapp-regsTo be fully SVR4 ABI-compliant at the cost of some performance loss, specify -mno-app-regs. You should compile libraries and system software with this option.
-mflat-mno-flatWith -mno-flat (the default), the compiler generates save/restore instructions (except for leaf functions). This is the normal operating mode.
-mfpu-mhard-float-mno-fpu-msoft-float-msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this to work.
-mhard-quad-float-msoft-quad-floatAs of this writing, there are no SPARC implementations that have hardware support for the quad-word floating-point instructions. They all invoke a trap handler for one of these instructions, and then the trap handler emulates the effect of the instruction. Because of the trap handler overhead, this is much slower than calling the ABI library routines. Thus the -msoft-quad-float option is the default.
-mno-unaligned-doubles-munaligned-doublesWith -munaligned-doubles, GCC assumes that doubles have 8-byte alignment only if they are contained in another type, or if they have an absolute address. Otherwise, it assumes they have 4-byte alignment. Specifying this option avoids some rare compatibility problems with code generated by other compilers. It is not the default because it results in a performance loss, especially for floating-point code.
-muser-mode-mno-user-modecasa instruction emitted for the LEON3 processor. This
is the default.
-mfaster-structs-mno-faster-structsldd and std instructions for copies in structure
assignment, in place of twice as many ld and st pairs.
However, the use of this changed alignment directly violates the SPARC
ABI. Thus, it's intended only for use on targets where the developer
acknowledges that their resulting code is not directly in line with
the rules of the ABI.
-mstd-struct-return-mno-std-struct-returnThe default is -mno-std-struct-return. This option has no effect in 64-bit mode.
-mlra-mno-lra-mcpu=cpu_typeNative Solaris and GNU/Linux toolchains also support the value ‘native’, which selects the best architecture option for the host processor. -mcpu=native has no effect if GCC does not recognize the processor.
Default instruction scheduling parameters are used for values that select an architecture and not an implementation. These are ‘v7’, ‘v8’, ‘sparclite’, ‘sparclet’, ‘v9’.
Here is a list of each supported architecture and their supported implementations.
By default (unless configured otherwise), GCC generates code for the V7 variant of the SPARC architecture. With -mcpu=cypress, the compiler additionally optimizes it for the Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series. This is also appropriate for the older SPARCStation 1, 2, IPX etc.
With -mcpu=v8, GCC generates code for the V8 variant of the SPARC architecture. The only difference from V7 code is that the compiler emits the integer multiply and integer divide instructions which exist in SPARC-V8 but not in SPARC-V7. With -mcpu=supersparc, the compiler additionally optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000 series.
With -mcpu=sparclite, GCC generates code for the SPARClite variant of
the SPARC architecture. This adds the integer multiply, integer divide step
and scan (ffs) instructions which exist in SPARClite but not in SPARC-V7.
With -mcpu=f930, the compiler additionally optimizes it for the
Fujitsu MB86930 chip, which is the original SPARClite, with no FPU. With
-mcpu=f934, the compiler additionally optimizes it for the Fujitsu
MB86934 chip, which is the more recent SPARClite with FPU.
With -mcpu=sparclet, GCC generates code for the SPARClet variant of
the SPARC architecture. This adds the integer multiply, multiply/accumulate,
integer divide step and scan (ffs) instructions which exist in SPARClet
but not in SPARC-V7. With -mcpu=tsc701, the compiler additionally
optimizes it for the TEMIC SPARClet chip.
With -mcpu=v9, GCC generates code for the V9 variant of the SPARC architecture. This adds 64-bit integer and floating-point move instructions, 3 additional floating-point condition code registers and conditional move instructions. With -mcpu=ultrasparc, the compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi chips. With -mcpu=ultrasparc3, the compiler additionally optimizes it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With -mcpu=niagara, the compiler additionally optimizes it for Sun UltraSPARC T1 chips. With -mcpu=niagara2, the compiler additionally optimizes it for Sun UltraSPARC T2 chips. With -mcpu=niagara3, the compiler additionally optimizes it for Sun UltraSPARC T3 chips. With -mcpu=niagara4, the compiler additionally optimizes it for Sun UltraSPARC T4 chips. With -mcpu=niagara7, the compiler additionally optimizes it for Oracle SPARC M7 chips. With -mcpu=m8, the compiler additionally optimizes it for Oracle M8 chips.
-mtune=cpu_typeThe same values for -mcpu=cpu_type can be used for -mtune=cpu_type, but the only useful values are those that select a particular CPU implementation. Those are ‘cypress’, ‘supersparc’, ‘hypersparc’, ‘leon’, ‘leon3’, ‘leon3v7’, ‘leon5’, ‘f930’, ‘f934’, ‘sparclite86x’, ‘tsc701’, ‘ultrasparc’, ‘ultrasparc3’, ‘niagara’, ‘niagara2’, ‘niagara3’, ‘niagara4’, ‘niagara7’ and ‘m8’. With native Solaris and GNU/Linux toolchains, ‘native’ can also be used.
-mv8plus-mno-v8plus-mvis-mno-vis-mvis2-mno-vis2-mvis3-mno-vis3-mvis4-mno-vis4-mvis4b-mno-vis4b-mcbcond-mno-cbcond-mfmaf-mno-fmaf-mfsmuld-mno-fsmuld-mpopc-mno-popc-msubxc-mno-subxc-mfix-at697f-mfix-ut699-mfix-ut700-mfix-gr712rcThese ‘-m’ options are supported in addition to the above on SPARC-V9 processors in 64-bit environments:
-m32-m64-mcmodel=which-mmemory-model=mem-modelThese memory models are formally defined in Appendix D of the SPARC-V9
architecture manual, as set in the processor's PSTATE.MM field.
-mstack-bias-mno-stack-biasThese additional options are available on System V Release 4 for compatibility with other compilers on those systems:
-G-Qy.ident assembler directive in the output.
-Qn.ident directives to the output file (this is
the default).
-YP,dirs-Ym,dirThese ‘-m’ options are defined for V850 implementations:
-mlong-calls-mno-long-calls-mno-ep-mepep register, and
use the shorter sld and sst instructions. The -mep
option is on by default if you optimize.
-mno-prolog-function-mprolog-function-mspace-mtda=nep points to. The tiny data
area can hold up to 256 bytes in total (128 bytes for byte references).
-msda=ngp points to. The small data
area can hold up to 64 kilobytes.
-mzda=n-mv850-mv850e3v5__v850e3v5__ is defined if this option is used.
-mv850e2v4-mv850e2v3__v850e2v3__ is defined if this option is used.
-mv850e2__v850e2__ is defined if this option is used.
-mv850e1__v850e1__ and __v850e__ are defined if
this option is used.
-mv850es-mv850e__v850e__ is defined if this option is used.
If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor -mv850e2v3 nor -mv850e3v5 are defined then a default target processor is chosen and the relevant ‘__v850*__’ preprocessor constant is defined.
The preprocessor constants __v850 and __v851__ are always
defined, regardless of which processor variant is the target.
-mdisable-callt-mno-disable-calltCALLT instruction for the
v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850
architecture.
This option is enabled by default when the RH850 ABI is
in use (see -mrh850-abi), and disabled by default when the
GCC ABI is in use. If CALLT instructions are being generated
then the C preprocessor symbol __V850_CALLT__ is defined.
-mrelax-mno-relax-mlong-jumps-mno-long-jumps-msoft-float-mhard-float__FPU_OK__ is defined, otherwise the symbol
__NO_FPU__ is defined.
-mloop-mrh850-abi-mghsWhen this version of the ABI is enabled the C preprocessor symbol
__V850_RH850_ABI__ is defined.
-mgcc-abir10.
When this version of the ABI is enabled the C preprocessor symbol
__V850_GCC_ABI__ is defined.
-m8byte-align-mno-8byte-aligndouble and long long types to be
aligned on 8-byte boundaries. The default is to restrict the
alignment of all objects to at most 4-bytes. When
-m8byte-align is in effect the C preprocessor symbol
__V850_8BYTE_ALIGN__ is defined.
-mbig-switch-mapp-regs-mno-app-regsThese ‘-m’ options are defined for the VAX:
-munixaobleq and so on)
that the Unix assembler for the VAX cannot handle across long
ranges.
-mgnu-mg-mlra-mno-lra-mdebug-msim-mfpu-mhard-float-mno-fpu-msoft-float-msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this to work.
-mcpu=cpu_type‘mcm’ is a synonym of ‘gr5’ present for backward compatibility.
By default (unless configured otherwise), GCC generates code for the GR5 variant of the Visium architecture.
With -mcpu=gr6, GCC generates code for the GR6 variant of the Visium architecture. The only difference from GR5 code is that the compiler will generate block move instructions.
-mtune=cpu_type-msv-mode-muser-modeThese ‘-m’ options are defined for the VMS implementations:
-mvms-return-codesmain. The default is to return POSIX-style
condition (e.g. error) codes.
-mdebug-main=prefix-mmalloc64-mpointer-size=sizepragma pointer_size.
The options in this section are defined for all VxWorks targets. Options specific to the target hardware are listed with the other options for that target.
-mrtp__RTP__.
-msmp-non-static-Bstatic-Bdynamic-Xbind-lazy-Xbind-nowThese ‘-m’ options are defined for the x86 family of computers.
-march=cpu-typeThe choices for cpu-type are:
Since these cpu-type values do not have a corresponding
-mtune setting, using -march with these values enables
generic tuning. Specific tuning can be enabled using the
-mtune=other-cpu-type option with an appropriate
other-cpu-type value.
-march=lujiazui
for performance reasons.
-mtune=cpu-typeThe choices for cpu-type are the same as for -march. In addition, -mtune supports 2 extra choices for cpu-type:
As new processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this option will change to reflect the processors that are most common at the time that version of GCC is released.
There is no -march=generic option because -march
indicates the instruction set the compiler can use, and there is no
generic instruction set applicable to all processors. In contrast,
-mtune indicates the processor (or, in this case, collection of
processors) for which the code is optimized.
As new Intel processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this option will change to reflect the most current Intel processors at the time that version of GCC is released.
There is no -march=intel option because -march indicates the instruction set the compiler can use, and there is no common instruction set applicable to all processors. In contrast, -mtune indicates the processor (or, in this case, collection of processors) for which the code is optimized.
-mcpu=cpu-type-mfpmath=unitThis is the default choice for non-Darwin x86-32 targets.
For the x86-32 compiler, you must use -march=cpu-type, -msse or -msse2 switches to enable SSE extensions and make this option effective. For the x86-64 compiler, these extensions are enabled by default.
The resulting code should be considerably faster in the majority of cases and avoid the numerical instability problems of 387 code, but may break some existing code that expects temporaries to be 80 bits.
This is the default choice for the x86-64 compiler, Darwin x86-32 targets,
and the default choice for x86-32 targets with the SSE2 instruction set
when -ffast-math is enabled.
-masm=dialectasm (see Basic Asm) and
extended asm (see Extended Asm). Supported choices (in dialect
order) are ‘att’ or ‘intel’. The default is ‘att’. Darwin does
not support ‘intel’.
-mieee-fp-mno-ieee-fp-m80387-mhard-float-mno-80387-msoft-floatWarning: the requisite libraries are not part of GCC. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation.
On machines where a function returns floating-point results in the 80387 register stack, some floating-point opcodes may be emitted even if -msoft-float is used.
-mno-fp-ret-in-387The usual calling convention has functions return values of types
float and double in an FPU register, even if there
is no FPU. The idea is that the operating system should emulate
an FPU.
The option -mno-fp-ret-in-387 causes such values to be returned in ordinary CPU registers instead.
-mno-fancy-math-387sin, cos and
sqrt instructions for the 387. Specify this option to avoid
generating those instructions.
This option is overridden when -march
indicates that the target CPU always has an FPU and so the
instruction does not need emulation. These
instructions are not generated unless you also use the
-funsafe-math-optimizations switch.
-malign-double-mno-align-doubledouble, long double, and
long long variables on a two-word boundary or a one-word
boundary. Aligning double variables on a two-word boundary
produces code that runs somewhat faster on a Pentium at the
expense of more memory.
On x86-64, -malign-double is enabled by default.
Warning: if you use the -malign-double switch, structures containing the above types are aligned differently than the published application binary interface specifications for the x86-32 and are not binary compatible with structures in code compiled without that switch.
-m96bit-long-double-m128bit-long-doublelong double type. The x86-32
application binary interface specifies the size to be 96 bits,
so -m96bit-long-double is the default in 32-bit mode.
Modern architectures (Pentium and newer) prefer long double
to be aligned to an 8- or 16-byte boundary. In arrays or structures
conforming to the ABI, this is not possible. So specifying
-m128bit-long-double aligns long double
to a 16-byte boundary by padding the long double with an additional
32-bit zero.
In the x86-64 compiler, -m128bit-long-double is the default choice as
its ABI specifies that long double is aligned on 16-byte boundary.
Notice that neither of these options enable any extra precision over the x87
standard of 80 bits for a long double.
Warning: if you override the default value for your target ABI, this
changes the size of
structures and arrays containing long double variables,
as well as modifying the function calling convention for functions taking
long double. Hence they are not binary-compatible
with code compiled without that switch.
-mlong-double-64-mlong-double-80-mlong-double-128long double type. A size
of 64 bits makes the long double type equivalent to the double
type. This is the default for 32-bit Bionic C library. A size
of 128 bits makes the long double type equivalent to the
__float128 type. This is the default for 64-bit Bionic C library.
Warning: if you override the default value for your target ABI, this
changes the size of
structures and arrays containing long double variables,
as well as modifying the function calling convention for functions taking
long double. Hence they are not binary-compatible
with code compiled without that switch.
-malign-data=type-mlarge-data-threshold=threshold-mrtdret num
instruction, which pops their arguments while returning. This saves one
instruction in the caller since there is no need to pop the arguments
there.
You can specify that an individual function is called with this calling
sequence with the function attribute stdcall. You can also
override the -mrtd option by using the function attribute
cdecl. See Function Attributes.
Warning: this calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including printf);
otherwise incorrect code is generated for calls to those
functions.
In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.)
-mregparm=numregparm.
See Function Attributes.
Warning: if you use this switch, and num is nonzero, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules.
-msseregparmsseregparm.
See Function Attributes.
Warning: if you use this switch then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules.
-mvect8-ret-in-mem-mpc32-mpc64-mpc80Setting the rounding of floating-point operations to less than the default 80 bits can speed some programs by 2% or more. Note that some mathematical libraries assume that extended-precision (80-bit) floating-point operations are enabled by default; routines in such libraries could suffer significant loss of accuracy, typically through so-called “catastrophic cancellation”, when this option is used to set the precision to less than extended precision.
-mdaz-ftz-mstackrealignforce_align_arg_pointer,
applicable to individual functions.
-mpreferred-stack-boundary=numWarning: When generating code for the x86-64 architecture with SSE extensions disabled, -mpreferred-stack-boundary=3 can be used to keep the stack boundary aligned to 8 byte boundary. Since x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and intended to be used in controlled environment where stack space is important limitation. This option leads to wrong code when functions compiled with 16 byte stack alignment (such as functions from a standard library) are called with misaligned stack. In this case, SSE instructions may lead to misaligned memory access traps. In addition, variable arguments are handled incorrectly for 16 byte aligned objects (including x87 long double and __int128), leading to wrong results. You must build all modules with -mpreferred-stack-boundary=3, including any libraries. This includes the system libraries and startup modules.
-mincoming-stack-boundary=numOn Pentium and Pentium Pro, double and long double values
should be aligned to an 8-byte boundary (see -malign-double) or
suffer significant run time performance penalties. On Pentium III, the
Streaming SIMD Extension (SSE) data type __m128 may not work
properly if it is not 16-byte aligned.
To ensure proper alignment of this values on the stack, the stack boundary must be as aligned as that required by any value stored on the stack. Further, every function must be generated such that it keeps the stack aligned. Thus calling a function compiled with a higher preferred stack boundary from a function compiled with a lower preferred stack boundary most likely misaligns the stack. It is recommended that libraries that use callbacks always use the default setting.
This extra alignment does consume extra stack space, and generally increases code size. Code that is sensitive to stack space usage, such as embedded systems and operating system kernels, may want to reduce the preferred alignment to -mpreferred-stack-boundary=2.
-mmmx-msse-msse2-msse3-mssse3-msse4-msse4a-msse4.1-msse4.2-mavx-mavx2-mavx512f-mavx512pf-mavx512er-mavx512cd-mavx512vl-mavx512bw-mavx512dq-mavx512ifma-mavx512vbmi-msha-maes-mpclmul-mclflushopt-mclwb-mfsgsbase-mptwrite-mrdrnd-mf16c-mfma-mpconfig-mwbnoinvd-mfma4-mprfchw-mrdpid-mprefetchwt1-mrdseed-msgx-mxop-mlwp-m3dnow-m3dnowa-mpopcnt-mabm-madx-mbmi-mbmi2-mlzcnt-mfxsr-mxsave-mxsaveopt-mxsavec-mxsaves-mrtm-mhle-mtbm-mmwaitx-mclzero-mpku-mavx512vbmi2-mavx512bf16-mavx512fp16-mgfni-mvaes-mwaitpkg-mvpclmulqdq-mavx512bitalg-mmovdiri-mmovdir64b-menqcmd-muintr-mtsxldtrk-mavx512vpopcntdq-mavx512vp2intersect-mavx5124fmaps-mavx512vnni-mavxvnni-mavx5124vnniw-mcldemote-mserialize-mamx-tile-mamx-int8-mamx-bf16-mhreset-mkl-mwidekl-mavxifma-mavxvnniint8-mavxneconvert-mcmpccxadd-mamx-fp16-mprefetchi-mraoint-mamx-complexThese extensions are also available as built-in functions: see x86 Built-in Functions, for details of the functions enabled and disabled by these switches.
To generate SSE/SSE2 instructions automatically from floating-point code (as opposed to 387 instructions), see -mfpmath=sse.
GCC depresses SSEx instructions when -mavx is used. Instead, it generates new AVX instructions or AVX equivalence for all SSEx instructions when needed.
These options enable GCC to use these extended instructions in generated code, even without -mfpmath=sse. Applications that perform run-time CPU detection must compile separate files for each supported architecture, using the appropriate flags. In particular, the file containing the CPU detection code should be compiled without these options.
-mdump-tune-features-mtune-ctrl=feature-list-mno-default-mcldcld instruction in the prologue
of functions that use string instructions. String instructions depend on
the DF flag to select between autoincrement or autodecrement mode. While the
ABI specifies the DF flag to be cleared on function entry, some operating
systems violate this specification by not clearing the DF flag in their
exception dispatchers. The exception handler can be invoked with the DF flag
set, which leads to wrong direction mode when string instructions are used.
This option can be enabled by default on 32-bit x86 targets by configuring
GCC with the --enable-cld configure option. Generation of cld
instructions can be suppressed with the -mno-cld compiler option
in this case.
-mvzerouppervzeroupper instruction
before a transfer of control flow out of the function to minimize
the AVX to SSE transition penalty as well as remove unnecessary zeroupper
intrinsics.
-mprefer-avx128-mprefer-vector-width=opt-mmove-max=bits-mstore-max=bits-mcx16CMPXCHG16B instructions in 64-bit
code to implement compare-and-exchange operations on 16-byte aligned 128-bit
objects. This is useful for atomic updates of data structures exceeding one
machine word in size. The compiler uses this instruction to implement
__sync Builtins. However, for __atomic Builtins operating on
128-bit integers, a library call is always used.
-msahfSAHF instructions in 64-bit code.
Early Intel Pentium 4 CPUs with Intel 64 support,
prior to the introduction of Pentium 4 G1 step in December 2005,
lacked the LAHF and SAHF instructions
which are supported by AMD64.
These are load and store instructions, respectively, for certain status flags.
In 64-bit mode, the SAHF instruction is used to optimize fmod,
drem, and remainder built-in functions;
see Other Builtins for details.
-mmovbemovbe instruction to implement
__builtin_bswap32 and __builtin_bswap64.
-mshstk-mcrc32__builtin_ia32_crc32qi,
__builtin_ia32_crc32hi, __builtin_ia32_crc32si and
__builtin_ia32_crc32di to generate the crc32 machine instruction.
-mmwait__builtin_ia32_monitor,
and __builtin_ia32_mwait to generate the monitor and
mwait machine instructions.
-mrecipRCPSS and RSQRTSS instructions
(and their vectorized variants RCPPS and RSQRTPS)
with an additional Newton-Raphson step
to increase precision instead of DIVSS and SQRTSS
(and their vectorized
variants) for single-precision floating-point arguments. These instructions
are generated only when -funsafe-math-optimizations is enabled
together with -ffinite-math-only and -fno-trapping-math.
Note that while the throughput of the sequence is higher than the throughput
of the non-reciprocal instruction, the precision of the sequence can be
decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
Note that GCC implements 1.0f/sqrtf(x) in terms of RSQRTSS
(or RSQRTPS) already with -ffast-math (or the above option
combination), and doesn't need -mrecip.
Also note that GCC emits the above sequence with additional Newton-Raphson step
for vectorized single-float division and vectorized sqrtf(x)
already with -ffast-math (or the above option combination), and
doesn't need -mrecip.
-mrecip=optSo, for example, -mrecip=all,!sqrt enables all of the reciprocal approximations, except for square root.
-mveclibabi=typeGCC currently emits calls to vmldExp2,
vmldLn2, vmldLog102, vmldPow2,
vmldTanh2, vmldTan2, vmldAtan2, vmldAtanh2,
vmldCbrt2, vmldSinh2, vmldSin2, vmldAsinh2,
vmldAsin2, vmldCosh2, vmldCos2, vmldAcosh2,
vmldAcos2, vmlsExp4, vmlsLn4,
vmlsLog104, vmlsPow4, vmlsTanh4, vmlsTan4,
vmlsAtan4, vmlsAtanh4, vmlsCbrt4, vmlsSinh4,
vmlsSin4, vmlsAsinh4, vmlsAsin4, vmlsCosh4,
vmlsCos4, vmlsAcosh4 and vmlsAcos4 for corresponding
function type when -mveclibabi=svml is used, and __vrd2_sin,
__vrd2_cos, __vrd2_exp, __vrd2_log, __vrd2_log2,
__vrd2_log10, __vrs4_sinf, __vrs4_cosf,
__vrs4_expf, __vrs4_logf, __vrs4_log2f,
__vrs4_log10f and __vrs4_powf for the corresponding function type
when -mveclibabi=acml is used.
-mabi=namems_abi and sysv_abi.
See Function Attributes.
-mforce-indirect-call-mmanual-endbrcf_check
function attribute. This is useful when used with the option
-fcf-protection=branch to control ENDBR insertion at the
function entry.
-mcet-switch-mcall-ms2sysv-xlogues-mtls-dialect=type-mpush-args-mno-push-args-maccumulate-outgoing-args-mthreads-mms-bitfields-mno-ms-bitfieldsIf packed is used on a structure, or if bit-fields are used,
it may be that the Microsoft ABI lays out the structure differently
than the way GCC normally does. Particularly when moving packed
data between functions compiled with GCC and the native Microsoft compiler
(either via function call or as data in a file), it may be necessary to access
either format.
This option is enabled by default for Microsoft Windows targets. This behavior can also be controlled locally by use of variable or type attributes. For more information, see x86 Variable Attributes and x86 Type Attributes.
The Microsoft structure layout algorithm is fairly simple with the exception of the bit-field packing. The padding and alignment of members of structures and whether a bit-field can straddle a storage-unit boundary are determine by these rules:
aligned attribute or the pack pragma),
whichever is less. For structures, unions, and arrays,
the alignment requirement is the largest alignment requirement of its members.
Every object is allocated an offset so that:
offset % alignment_requirement == 0
MSVC interprets zero-length bit-fields in the following ways:
For example:
struct
{
unsigned long bf_1 : 12;
unsigned long : 0;
unsigned long bf_2 : 12;
} t1;
The size of t1 is 8 bytes with the zero-length bit-field. If the
zero-length bit-field were removed, t1's size would be 4 bytes.
foo, and the
alignment of the zero-length bit-field is greater than the member that follows it,
bar, bar is aligned as the type of the zero-length bit-field.
For example:
struct
{
char foo : 4;
short : 0;
char bar;
} t2;
struct
{
char foo : 4;
short : 0;
double bar;
} t3;
For t2, bar is placed at offset 2, rather than offset 1.
Accordingly, the size of t2 is 4. For t3, the zero-length
bit-field does not affect the alignment of bar or, as a result, the size
of the structure.
Taking this into account, it is important to note the following:
t2 has a size of 4 bytes, since the zero-length bit-field follows a
normal bit-field, and is of type short.
struct
{
char foo : 6;
long : 0;
} t4;
Here, t4 takes up 4 bytes.
struct
{
char foo;
long : 0;
char bar;
} t5;
Here, t5 takes up 2 bytes.
-mno-align-stringops-minline-all-stringopsmemcpy and memset for short lengths.
The option enables inline expansion of strlen for all
pointer alignments.
-minline-stringops-dynamically-mstringop-strategy=algrep prefix of the specified size.
-mmemcpy-strategy=strategy__builtin_memcpy
should be inlined and what inline algorithm to use when the expected size
of the copy operation is known. strategy
is a comma-separated list of alg:max_size:dest_align triplets.
alg is specified in -mstringop-strategy, max_size specifies
the max byte size with which inline algorithm alg is allowed. For the last
triplet, the max_size must be -1. The max_size of the triplets
in the list must be specified in increasing order. The minimal byte size for
alg is 0 for the first triplet and max_size + 1 of the
preceding range.
-mmemset-strategy=strategy__builtin_memset expansion.
-momit-leaf-frame-pointer-mtls-direct-seg-refs-mno-tls-direct-seg-refs%gs for 32-bit, %fs for 64-bit),
or whether the thread base pointer must be added. Whether or not this
is valid depends on the operating system, and whether it maps the
segment to cover the entire TLS area.
For systems that use the GNU C Library, the default is on.
-msse2avx-mno-sse2avx-mfentry-mno-fentryms_hook_prologue
isn't possible at the moment for -mfentry and -pg.
-mrecord-mcount-mno-record-mcount-mnop-mcount-mno-nop-mcount-minstrument-return=type-mrecord-return-mno-record-return-mfentry-name=name-mfentry-section=name-mskip-rax-setup-mno-skip-rax-setupWarning: Since RAX register is used to avoid unnecessarily saving vector registers on stack when passing variable arguments, the impacts of this option are callees may waste some stack space, misbehave or jump to a random location. GCC 4.4 or newer don't have those issues, regardless the RAX register value.
-m8bit-idiv-mno-8bit-idiv-mavx256-split-unaligned-load-mavx256-split-unaligned-store-mstack-protector-guard=guard-mstack-protector-guard-reg=reg-mstack-protector-guard-offset=offsetWith the latter choice the options
-mstack-protector-guard-reg=reg and
-mstack-protector-guard-offset=offset furthermore specify
which segment register (%fs or %gs) to use as base register
for reading the canary, and from what offset from that base register.
The default for those is as specified in the relevant ABI.
-mgeneral-regs-only-mrelax-cmpxchg-loopCMPXCHG instruction, and using the PAUSE instruction
to save CPU power when restarting the loop.
-mindirect-branch=choiceindirect_branch. See Function Attributes.
Note that -mcmodel=large is incompatible with -mindirect-branch=thunk and -mindirect-branch=thunk-extern since the thunk function may not be reachable in the large code model.
Note that -mindirect-branch=thunk-extern is compatible with -fcf-protection=branch since the external thunk can be made to enable control-flow check.
-mfunction-return=choicefunction_return.
See Function Attributes.
Note that -mindirect-return=thunk-extern is compatible with -fcf-protection=branch since the external thunk can be made to enable control-flow check.
Note that -mcmodel=large is incompatible with -mfunction-return=thunk and -mfunction-return=thunk-extern since the thunk function may not be reachable in the large code model.
-mindirect-branch-register-mharden-sls=choice-mindirect-branch-cs-prefixThese ‘-m’ switches are supported in addition to the above on x86-64 processors in 64-bit environments.
-m32-m64-mx32-m16-miamcuint, long, and pointer types
to 32 bits, and
generates code that runs in 32-bit mode.
The -m64 option sets int to 32 bits and long and pointer
types to 64 bits, and generates code for the x86-64 architecture.
For Darwin only the -m64 option also turns off the -fno-pic
and -mdynamic-no-pic options.
The -mx32 option sets int, long, and pointer types
to 32 bits, and
generates code for the x86-64 architecture.
The -m16 option is the same as -m32, except for that
it outputs the .code16gcc assembly directive at the beginning of
the assembly output so that the binary can run in 16-bit mode.
The -miamcu option generates code which conforms to Intel MCU psABI. It requires the -m32 option to be turned on.
-mno-red-zone-mcmodel=small-mcmodel=kernel-mcmodel=medium-mcmodel=large-maddress-mode=long-maddress-mode=short-mneeded-mno-needed-mno-direct-extern-accessWarning: shared libraries compiled with -mno-direct-extern-access and executable compiled with -mdirect-extern-access may not be binary compatible if protected symbols are used in shared libraries and executable.
-munroll-only-small-loops-mlam=choiceThese additional options are available for Microsoft Windows targets:
-mconsole-mdll-mnop-fun-dllimportdllimport attribute should be ignored.
-mthreads-municodeUNICODE preprocessor macro to be predefined, and
chooses Unicode-capable runtime startup code.
-mwin32-mwindows-fno-set-stack-executable-fwritable-relocated-rdata.data
section. This is a necessary for older runtimes not supporting
modification of .rdata sections for pseudo-relocation.
-mpe-aligned-commonsSee also under x86 Options for standard options.
These options are defined for Xstormy16:
-msimThese options are supported for Xtensa targets:
-mconst16-mno-const16CONST16 instructions for loading
constant values. The CONST16 instruction is currently not a
standard option from Tensilica. When enabled, CONST16
instructions are always used in place of the standard L32R
instructions. The use of CONST16 is enabled by default only if
the L32R instruction is not available.
-mfused-madd-mno-fused-madd-mserialize-volatile-mno-serialize-volatileMEMW instructions before
volatile memory references to guarantee sequential consistency.
The default is -mserialize-volatile. Use
-mno-serialize-volatile to omit the MEMW instructions.
-mforce-no-pic-mtext-section-literals-mno-text-section-literals-mauto-litpools-mno-auto-litpools.literal directives and loads literals into registers with
MOVI instructions instead of L32R to let the assembler
do relaxation and place literals as necessary. This option allows
assembler to create several literal pools per function and assemble
very big functions, which may not be possible with
-mtext-section-literals.
-mtarget-align-mno-target-alignLOOP, which the
assembler always aligns, either by widening density instructions or
by inserting NOP instructions.
-mlongcalls-mno-longcallsCALL
instruction into an L32R followed by a CALLX instruction.
The default is -mno-longcalls. This option should be used in
programs where the call target can potentially be out of range. This
option is implemented in the assembler, not the compiler, so the
assembly code generated by GCC still shows direct call
instructions—look at the disassembled object code to see the actual
instructions. Note that the assembler uses an indirect call for
every cross-file call, not just those that really are out of range.
-mabi=name-mabi=call0a2 through a7, registers a12 through a15 are
caller-saved, and register a15 may be used as a frame pointer.
When this version of the ABI is enabled the C preprocessor symbol
__XTENSA_CALL0_ABI__ is defined.
-mabi=windoweda10 through a15, and called function rotates register window
by 8 registers on entry so that its arguments are found in registers
a2 through a7. Register a7 may be used as a frame
pointer. Register window is rotated 8 registers back upon return.
When this version of the ABI is enabled the C preprocessor symbol
__XTENSA_WINDOWED_ABI__ is defined.
-mextra-l32r-costs=nL32R
instructions, in clock cycles. This affects, when optimizing for speed,
whether loading a constant from literal pool using L32R or
synthesizing the constant from a small one with a couple of arithmetic
instructions. The default value is 0.
These are listed under See S/390 and zSeries Options.
gcc is a driver program. It performs its job by invoking a sequence of other programs to do the work of compiling, assembling and linking. GCC interprets its command-line parameters and uses these to deduce which programs it should invoke, and which command-line options it ought to place on their command lines. This behavior is controlled by spec strings. In most cases there is one spec string for each program that GCC can invoke, but a few programs have multiple spec strings to control their behavior. The spec strings built into GCC can be overridden by using the -specs= command-line switch to specify a spec file.
Spec files are plain-text files that are used to construct spec strings. They consist of a sequence of directives separated by blank lines. The type of directive is determined by the first non-whitespace character on the line, which can be one of the following:
%command%include <file>%include_noerr <file>%rename old_name new_name*[spec_name]:[suffix]: .ZZ:
z-compile -input %i
This says that any input file whose name ends in ‘.ZZ’ should be passed to the program ‘z-compile’, which should be invoked with the command-line switch -input and with the result of performing the ‘%i’ substitution. (See below.)
As an alternative to providing a spec string, the text following a suffix directive can be one of the following:
@language .ZZ:
@c++
Says that .ZZ files are, in fact, C++ source files.
#namename compiler not installed on this system.
GCC already has an extensive list of suffixes built into it. This directive adds an entry to the end of the list of suffixes, but since the list is searched from the end backwards, it is effectively possible to override earlier entries using this technique.
GCC has the following spec strings built into it. Spec files can override these strings or create their own. Note that individual targets can also add their own spec strings to this list.
asm Options to pass to the assembler
asm_final Options to pass to the assembler post-processor
cpp Options to pass to the C preprocessor
cc1 Options to pass to the C compiler
cc1plus Options to pass to the C++ compiler
endfile Object files to include at the end of the link
link Options to pass to the linker
lib Libraries to include on the command line to the linker
libgcc Decides which GCC support library to pass to the linker
linker Sets the name of the linker
predefines Defines to be passed to the C preprocessor
signed_char Defines to pass to CPP to say whether char is signed
by default
startfile Object files to include at the start of the link
Here is a small example of a spec file:
%rename lib old_lib
*lib:
--start-group -lgcc -lc -leval1 --end-group %(old_lib)
This example renames the spec called ‘lib’ to ‘old_lib’ and then overrides the previous definition of ‘lib’ with a new one. The new definition adds in some extra command-line options before including the text of the old definition.
Spec strings are a list of command-line options to be passed to their corresponding program. In addition, the spec strings can contain ‘%’-prefixed sequences to substitute variable text or to conditionally insert text into the command line. Using these constructs it is possible to generate quite complex command lines.
Here is a table of all defined ‘%’-sequences for spec strings. Note that spaces are not generated automatically around the results of expanding these sequences. Therefore you can concatenate them together or combine them with constant text in a single argument.
%%%"%i%b%B%d%gsuffix%usuffix%Usuffix%jsuffixHOST_BIT_BUCKET, if any, and if it is
writable, and if -save-temps is not used;
otherwise, substitute the name
of a temporary file, just like ‘%u’. This temporary file is not
meant for communication between processes, but rather as a junk
disposal mechanism.
%|suffix%msuffixX}’
construct: see for example gcc/fortran/lang-specs.h.
%.SUFFIX%w%V%o%O%I%s%T%estr%nstr%(name)%x{option}%X%Y%Z%Mmultilib_os_dir.
%Rtarget_system_root and target_sysroot_suffix.
%aasm spec. This is used to compute the
switches to be passed to the assembler.
%Aasm_final spec. This is a spec string for
passing switches to an assembler post-processor, if such a program is
needed.
%llink spec. This is the spec for computing the
command line passed to the linker. Typically it makes use of the
‘%L %G %S %D and %E’ sequences.
%D%Llib spec. This is a spec string for deciding which
libraries are included on the command line to the linker.
%Glibgcc spec. This is a spec string for deciding
which GCC support library is included on the command line to the linker.
%Sstartfile spec. This is a spec for deciding which
object files are the first ones passed to the linker. Typically
this might be a file named crt0.o.
%Eendfile spec. This is a spec string that specifies
the last object files that are passed to the linker.
%Ccpp spec. This is used to construct the arguments
to be passed to the C preprocessor.
%1cc1 spec. This is used to construct the options to be
passed to the actual C compiler (cc1).
%2cc1plus spec. This is used to construct the options to be
passed to the actual C++ compiler (cc1plus).
%*%<S-S from the command line. Note—this
command is position dependent. ‘%’ commands in the spec string
before this one see -S, ‘%’ commands in the spec string
after this one do not.
%<S*-S.
%>S-S in the GCC command line.
%:function(args)The following built-in spec functions are provided:
getenvgetenv spec function takes two arguments: an environment
variable name and a string. If the environment variable is not
defined, a fatal error is issued. Otherwise, the return value is the
value of the environment variable concatenated with the string. For
example, if TOPDIR is defined as /path/to/top, then:
%:getenv(TOPDIR /include)
expands to /path/to/top/include.
if-existsif-exists spec function takes one argument, an absolute
pathname to a file. If the file exists, if-exists returns the
pathname. Here is a small example of its usage:
*startfile:
crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
if-exists-elseif-exists-else spec function is similar to the if-exists
spec function, except that it takes two arguments. The first argument is
an absolute pathname to a file. If the file exists, if-exists-else
returns the pathname. If it does not exist, it returns the second argument.
This way, if-exists-else can be used to select one file or another,
based on the existence of the first. Here is a small example of its usage:
*startfile:
crt0%O%s %:if-exists(crti%O%s) \
%:if-exists-else(crtbeginT%O%s crtbegin%O%s)
if-exists-then-elseif-exists-then-else spec function takes at least two arguments
and an optional third one. The first argument is an absolute pathname to a
file. If the file exists, the function returns the second argument.
If the file does not exist, the function returns the third argument if there
is one, or NULL otherwise. This can be used to expand one text, or optionally
another, based on the existence of a file. Here is a small example of its
usage:
-l%:if-exists-then-else(%:getenv(VSB_DIR rtnet.h) rtnet net)
sanitizesanitize spec function takes no arguments. It returns non-NULL if
any address, thread or undefined behavior sanitizers are active.
%{%:sanitize(address):-funwind-tables}
replace-outfilereplace-outfile spec function takes two arguments. It looks for the
first argument in the outfiles array and replaces it with the second argument. Here
is a small example of its usage:
%{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)}
remove-outfileremove-outfile spec function takes one argument. It looks for the
first argument in the outfiles array and removes it. Here is a small example
its usage:
%:remove-outfile(-lm)
version-compareversion-compare spec function takes four or five arguments of the following
form:
<comparison-op> <arg1> [<arg2>] <switch> <result>
It returns result if the comparison evaluates to true, and NULL if it doesn't.
The supported comparison-op values are:
>=switch is a later (or same) version than arg1
!>>=
<switch is an earlier version than arg1
!<<
><switch is arg1 or later, and earlier than arg2
<>switch is earlier than arg1, or is arg2 or later
If the switch is not present at all, the condition is false unless the first character
of the comparison-op is !.
%:version-compare(>= 10.3 mmacosx-version-min= -lmx)
The above example would add -lmx if -mmacosx-version-min=10.3.9 was
passed.
includeinclude spec function behaves much like %include, with the advantage
that it can be nested inside a spec and thus be conditionalized. It takes one argument,
the filename, and looks for it in the startfile path. It always returns NULL.
%{static-libasan|static:%:include(libsanitizer.spec)%(link_libasan)}
pass-through-libspass-through-libs spec function takes any number of arguments. It
finds any -l options and any non-options ending in .a (which it
assumes are the names of linker input library archive files) and returns a
result containing all the found arguments each prepended by
-plugin-opt=-pass-through= and joined by spaces. This list is
intended to be passed to the LTO linker plugin.
%:pass-through-libs(%G %L %G)
print-asm-headerprint-asm-header function takes no arguments and simply
prints a banner like:
Assembler options
=================
Use "-Wa,OPTION" to pass "OPTION" to the assembler.
It is used to separate compiler options from assembler options
in the --target-help output.
gtgt spec function takes two or more arguments. It returns "" (the
empty string) if the second-to-last argument is greater than the last argument, and NULL
otherwise. The following example inserts the link_gomp spec if the last
-ftree-parallelize-loops= option given on the command line is greater than 1:
%{%:gt(%{ftree-parallelize-loops=*:%*} 1):%:include(libgomp.spec)%(link_gomp)}
debug-level-gtdebug-level-gt spec function takes one argument and returns "" (the
empty string) if debug_info_level is greater than the specified number, and NULL
otherwise.
%{%:debug-level-gt(0):%{gdwarf*:--gdwarf2}}
%{S}-S switch, if that switch is given to GCC.
If that switch is not specified, this substitutes nothing. Note that
the leading dash is omitted when specifying this option, and it is
automatically inserted if the substitution is performed. Thus the spec
string ‘%{foo}’ matches the command-line option -foo
and outputs the command-line option -foo.
%W{S}S} but mark last argument supplied within as a file to be
deleted on failure.
%@{S}S} but puts the result into a FILE and substitutes
@FILE if an @file argument has been supplied.
%{S*}-S, but which also take an argument. This is used for
switches like -o, -D, -I, etc.
GCC considers -o foo as being
one switch whose name starts with ‘o’. %{o*} substitutes this
text, including the space. Thus two arguments are generated.
%{S*&T*}S*}, but preserve order of S and T options
(the order of S and T in the spec is not significant).
There can be any number of ampersand-separated variables; for each the
wild card is optional. Useful for CPP as ‘%{D*&U*&A*}’.
%{S:X}X, if the -S switch is given to GCC.
%{!S:X}X, if the -S switch is not given to GCC.
%{S*:X}X if one or more switches whose names start with
-S are specified to GCC. Normally X is substituted only
once, no matter how many such switches appeared. However, if %*
appears somewhere in X, then X is substituted once
for each matching switch, with the %* replaced by the part of
that switch matching the *.
If %* appears as the last part of a spec sequence then a space
is added after the end of the last substitution. If there is more
text in the sequence, however, then a space is not generated. This
allows the %* substitution to be used as part of a larger
string. For example, a spec string like this:
%{mcu=*:--script=%*/memory.ld}
when matching an option like -mcu=newchip produces:
--script=newchip/memory.ld
%{.S:X}X, if processing a file with suffix S.
%{!.S:X}X, if not processing a file with suffix S.
%{,S:X}X, if processing a file for language S.
%{!,S:X}X, if not processing a file for language S.
%{S|P:X}X if either -S or -P is given to
GCC. This may be combined with ‘!’, ‘.’, ‘,’, and
* sequences as well, although they have a stronger binding than
the ‘|’. If %* appears in X, all of the
alternatives must be starred, and only the first matching alternative
is substituted.
For example, a spec string like this:
%{.c:-foo} %{!.c:-bar} %{.c|d:-baz} %{!.c|d:-boggle}
outputs the following command-line options from the following input command-line options:
fred.c -foo -baz
jim.d -bar -boggle
-d fred.c -foo -baz -boggle
-d jim.d -bar -baz -boggle
%{%:function(args):X}X is substituted, if it returns
NULL, it isn't substituted.
%{S:X; T:Y; :D}S is given to GCC, substitutes X; else if T is
given to GCC, substitutes Y; else substitutes D. There can
be as many clauses as you need. This may be combined with .,
,, !, |, and * as needed.
The switch matching text S in a ‘%{S}’, ‘%{S:X}’
or similar construct can use a backslash to ignore the special meaning
of the character following it, thus allowing literal matching of a
character that is otherwise specially treated. For example,
‘%{std=iso9899\:1999:X}’ substitutes X if the
-std=iso9899:1999 option is given.
The conditional text X in a ‘%{S:X}’ or similar
construct may contain other nested ‘%’ constructs or spaces, or
even newlines. They are processed as usual, as described above.
Trailing white space in X is ignored. White space may also
appear anywhere on the left side of the colon in these constructs,
except between . or * and the corresponding word.
The -O, -f, -m, and -W switches are
handled specifically in these constructs. If another value of
-O or the negated form of a -f, -m, or
-W switch is found later in the command line, the earlier
switch value is ignored, except with {S*} where S is
just one letter, which passes all matching options.
The character ‘|’ at the beginning of the predicate text is used to indicate that a command should be piped to the following command, but only if -pipe is specified.
It is built into GCC which switches take arguments and which do not. (You might think it would be useful to generalize this to allow each compiler's spec to say which switches take arguments. But this cannot be done in a consistent fashion. GCC cannot even decide which input files have been specified without knowing which switches take arguments, and it must know which input files to compile in order to tell which compilers to run).
GCC also knows implicitly that arguments starting in -l are to be treated as compiler output files, and passed to the linker in their proper position among the other output files.
This section describes several environment variables that affect how GCC operates. Some of them work by specifying directories or prefixes to use when searching for various kinds of files. Some are used to specify other aspects of the compilation environment.
Note that you can also specify places to search using options such as -B, -I and -L (see Directory Options). These take precedence over places specified using environment variables, which in turn take precedence over those specified by the configuration of GCC. See Controlling the Compilation Driver gcc.
The LC_CTYPE environment variable specifies character classification. GCC uses it to determine the character boundaries in a string; this is needed for some multibyte encodings that contain quote and escape characters that are otherwise interpreted as a string end or escape.
The LC_MESSAGES environment variable specifies the language to use in diagnostic messages.
If the LC_ALL environment variable is set, it overrides the value of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES default to the value of the LANG environment variable. If none of these variables are set, GCC defaults to traditional C English behavior.
If GCC_EXEC_PREFIX is not set, GCC attempts to figure out an appropriate prefix to use based on the pathname it is invoked with.
If GCC cannot find the subprogram using the specified prefix, it tries looking in the usual places for the subprogram.
The default value of GCC_EXEC_PREFIX is
prefix/lib/gcc/ where prefix is the prefix to
the installed compiler. In many cases prefix is the value
of prefix when you ran the configure script.
Other prefixes specified with -B take precedence over this prefix.
This prefix is also used for finding files such as crt0.o that are used for linking.
In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with ‘/usr/local/lib/gcc’ (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with -Bfoo/, GCC searches foo/bar just before it searches the standard directory /usr/local/lib/bar. If a standard directory begins with the configured prefix then the value of prefix is replaced by GCC_EXEC_PREFIX when looking for header files.
If LANG is not defined, or if it has some other value, then the
compiler uses mblen and mbtowc as defined by the default locale to
recognize and translate multibyte characters.
fixits-v1, but columns are expressed as display columns,
as per -fdiagnostics-column-unit=display.
Some additional environment variables affect the behavior of the preprocessor.
PATH_SEPARATOR, is target-dependent and
determined at GCC build time. For Microsoft Windows-based targets it is a
semicolon, and for almost all other targets it is a colon.
CPATH specifies a list of directories to be searched as if specified with -I, but after any paths given with -I options on the command line. This environment variable is used regardless of which language is being preprocessed.
The remaining environment variables apply only when preprocessing the particular language indicated. Each specifies a list of directories to be searched as if specified with -isystem, but after any paths given with -isystem options on the command line.
In all these variables, an empty element instructs the compiler to
search its current working directory. Empty elements can appear at the
beginning or end of a path. For instance, if the value of
CPATH is :/special/include, that has the same
effect as ‘-I. -I/special/include’.
The value of DEPENDENCIES_OUTPUT can be just a file name, in which case the Make rules are written to that file, guessing the target name from the source file name. Or the value can have the form ‘file target’, in which case the rules are written to file file using target as the target name.
In other words, this environment variable is equivalent to combining the options -MM and -MF (see Preprocessor Options), with an optional -MT switch too.
__DATE__
and __TIME__ macros, so that the embedded timestamps become
reproducible.
The value of SOURCE_DATE_EPOCH must be a UNIX timestamp,
defined as the number of seconds (excluding leap seconds) since
01 Jan 1970 00:00:00 represented in ASCII; identical to the output of
date +%s on GNU/Linux and other systems that support the
%s extension in the date command.
The value should be a known timestamp such as the last modification time of the source or package and it should be set by the build process.
Often large projects have many header files that are included in every source file. The time the compiler takes to process these header files over and over again can account for nearly all of the time required to build the project. To make builds faster, GCC allows you to precompile a header file.
To create a precompiled header file, simply compile it as you would any other file, if necessary using the -x option to make the driver treat it as a C or C++ header file. You may want to use a tool like make to keep the precompiled header up-to-date when the headers it contains change.
A precompiled header file is searched for when #include is
seen in the compilation. As it searches for the included file
(see Search Path) the
compiler looks for a precompiled header in each directory just before it
looks for the include file in that directory. The name searched for is
the name specified in the #include with ‘.gch’ appended. If
the precompiled header file cannot be used, it is ignored.
For instance, if you have #include "all.h", and you have
all.h.gch in the same directory as all.h, then the
precompiled header file is used if possible, and the original
header is used otherwise.
Alternatively, you might decide to put the precompiled header file in a
directory and use -I to ensure that directory is searched
before (or instead of) the directory containing the original header.
Then, if you want to check that the precompiled header file is always
used, you can put a file of the same name as the original header in this
directory containing an #error command.
This also works with -include. So yet another way to use precompiled headers, good for projects not designed with precompiled header files in mind, is to simply take most of the header files used by a project, include them from another header file, precompile that header file, and -include the precompiled header. If the header files have guards against multiple inclusion, they are skipped because they've already been included (in the precompiled header).
If you need to precompile the same header file for different languages, targets, or compiler options, you can instead make a directory named like all.h.gch, and put each precompiled header in the directory, perhaps using -o. It doesn't matter what you call the files in the directory; every precompiled header in the directory is considered. The first precompiled header encountered in the directory that is valid for this compilation is used; they're searched in no particular order.
There are many other possibilities, limited only by your imagination, good sense, and the constraints of your build system.
A precompiled header file can be used only when these conditions apply:
The -D option is one way to define a macro before a
precompiled header is included; using a #define can also do it.
There are also some options that define macros implicitly, like
-O and -Wdeprecated; the same rule applies to macros
defined this way.
-fexceptions
-fmessage-length= -fpreprocessed -fsched-interblock
-fsched-spec -fsched-spec-load -fsched-spec-load-dangerous
-fsched-verbose=number -fschedule-insns -fvisibility=
-pedantic-errors
For all of these except the last, the compiler automatically ignores the precompiled header if the conditions aren't met. If you find an option combination that doesn't work and doesn't cause the precompiled header to be ignored, please consider filing a bug report, see Bugs.
If you do use differing options when generating and using the precompiled header, the actual behavior is a mixture of the behavior for the options. For instance, if you use -g to generate the precompiled header but not when using it, you may or may not get debugging information for routines in the precompiled header.
Modules are a C++20 language feature. As the name suggests, they provides a modular compilation system, intending to provide both faster builds and better library isolation. The “Merging Modules” paper https://wg21.link/p1103, provides the easiest to read set of changes to the standard, although it does not capture later changes.
G++'s modules support is not complete. Other than bugs, the known missing pieces are:
Modular compilation is not enabled with just the -std=c++20 option. You must explicitly enable it with the -fmodules-ts option. It is independent of the language version selected, although in pre-C++20 versions, it is of course an extension.
No new source file suffixes are required or supported. If you wish to use a non-standard suffix (see Overall Options), you also need to provide a -x c++ option too.2
Compiling a module interface unit produces an additional output (to the assembly or object file), called a Compiled Module Interface (CMI). This encodes the exported declarations of the module. Importing a module reads in the CMI. The import graph is a Directed Acyclic Graph (DAG). You must build imports before the importer.
Header files may themselves be compiled to header units, which are a transitional ability aiming at faster compilation. The -fmodule-header option is used to enable this, and implies the -fmodules-ts option. These CMIs are named by the fully resolved underlying header file, and thus may be a complete pathname containing subdirectories. If the header file is found at an absolute pathname, the CMI location is still relative to a CMI root directory.
As header files often have no suffix, you commonly have to specify a -x option to tell the compiler the source is a header file. You may use -x c++-header, -x c++-user-header or -x c++-system-header. When used in conjunction with -fmodules-ts, these all imply an appropriate -fmodule-header option. The latter two variants use the user or system include path to search for the file specified. This allows you to, for instance, compile standard library header files as header units, without needing to know exactly where they are installed. Specifying the language as one of these variants also inhibits output of the object file, as header files have no associated object file.
The -fmodule-only option disables generation of the associated object file for compiling a module interface. Only the CMI is generated. This option is implied when using the -fmodule-header option.
The -flang-info-include-translate and -flang-info-include-translate-not options notes whether include translation occurs or not. With no argument, the first will note all include translation. The second will note all non-translations of include files not known to intentionally be textual. With an argument, queries about include translation of a header files with that particular trailing pathname are noted. You may repeat this form to cover several different header files. This option may be helpful in determining whether include translation is happening—if it is working correctly, it behaves as if it isn't there at all.
The -flang-info-module-cmi option can be used to determine where the compiler is reading a CMI from. Without the option, the compiler is silent when such a read is successful. This option has an optional argument, which will restrict the notification to just the set of named modules or header units specified.
The -Winvalid-imported-macros option causes all imported macros to be resolved at the end of compilation. Without this, imported macros are only resolved when expanded or (re)defined. This option detects conflicting import definitions for all macros.
For details of the -fmodule-mapper family of options, see C++ Module Mapper.
A module mapper provides a server or file that the compiler queries to determine the mapping between module names and CMI files. It is also used to build CMIs on demand. Mapper functionality is in its infancy and is intended for experimentation with build system interactions.
You can specify a mapper with the -fmodule-mapper=val option or CXX_MODULE_MAPPER environment variable. The value may have one of the following forms:
:port[?ident]=socket[?ident]|program[?ident] [args...]@g++-mapper-server.
<>[?ident]<>inout[?ident]<in>out[?ident]?ident]As shown, an optional ident may suffix the first word of the option, indicated by a ‘?’ prefix. The value is used in the initial handshake with the module server, or to specify a prefix on mapping file lines. In the server case, the main source file name is used if no ident is specified. In the file case, all non-blank lines are significant, unless a value is specified, in which case only lines beginning with ident are significant. The ident must be separated by whitespace from the module name. Be aware that ‘<’, ‘>’, ‘?’, and ‘|’ characters are often significant to the shell, and therefore may need quoting.
The mapper is connected to or loaded lazily, when the first module mapping is required. The networking protocols are only supported on hosts that provide networking. If no mapper is specified a default is provided.
A project-specific mapper is expected to be provided by the build system that invokes the compiler. It is not expected that a general-purpose server is provided for all compilations. As such, the server will know the build configuration, the compiler it invoked, and the environment (such as working directory) in which that is operating. As it may parallelize builds, several compilations may connect to the same socket.
The default mapper generates CMI files in a ‘gcm.cache’ directory. CMI files have a ‘.gcm’ suffix. The module unit name is used directly to provide the basename. Header units construct a relative path using the underlying header file name. If the path is already relative, a ‘,’ directory is prepended. Internal ‘..’ components are translated to ‘,,’. No attempt is made to canonicalize these filenames beyond that done by the preprocessor's include search algorithm, as in general it is ambiguous when symbolic links are present.
The mapper protocol was published as “A Module Mapper” https://wg21.link/p1184. The implementation is provided by libcody, https://github.com/urnathan/libcody, which specifies the canonical protocol definition. A proof of concept server implementation embedded in make was described in ”Make Me A Module”, https://wg21.link/p1602.
Modules affect preprocessing because of header units and include translation. Some uses of the preprocessor as a separate step either do not produce a correct output, or require CMIs to be available.
Header units import macros. These macros can affect later conditional inclusion, which therefore can cascade to differing import sets. When preprocessing, it is necessary to load the CMI. If a header unit is unavailable, the preprocessor issues a warning and continue (when not just preprocessing, an error is emitted). Detecting such imports requires preprocessor tokenization of the input stream to phase 4 (macro expansion).
Include translation converts #include, #include_next and
#import directives to internal import declarations.
Whether a particular directive is translated is controlled by the
module mapper. Header unit names are canonicalized during
preprocessing.
Dependency information can be emitted for macro import, extending the functionality of -MD and -MMD options. Detection of import declarations also requires phase 4 preprocessing, and thus requires full preprocessing (or compilation).
The -M, -MM and -E -fdirectives-only options halt preprocessing before phase 4.
The -save-temps option uses -fdirectives-only for preprocessing, and preserve the macro definitions in the preprocessed output. Usually you also want to use this option when explicitly preprocessing a header-unit, or consuming such preprocessed output:
g++ -fmodules-ts -E -fdirectives-only my-header.hh -o my-header.ii
g++ -x c++-header -fmodules-ts -fpreprocessed -fdirectives-only my-header.ii
CMIs are an additional artifact when compiling named module interfaces, partitions or header units. These are read when importing. CMI contents are implementation-specific, and in GCC's case tied to the compiler version. Consider them a rebuildable cache artifact, not a distributable object.
When creating an output CMI, any missing directory components are created in a manner that is safe for concurrent builds creating multiple, different, CMIs within a common subdirectory tree.
CMI contents are written to a temporary file, which is then atomically renamed. Observers either see old contents (if there is an existing file), or complete new contents. They do not observe the CMI during its creation. This is unlike object file writing, which may be observed by an external process.
CMIs are read in lazily, if the host OS provides mmap
functionality. Generally blocks are read when name lookup or template
instantiation occurs. To inhibit this, the -fno-module-lazy
option may be used.
The --param lazy-modules=n parameter controls the limit on the number of concurrently open module files during lazy loading. Should more modules be imported, an LRU algorithm is used to determine which files to close—until that file is needed again. This limit may be exceeded with deep module dependency hierarchies. With large code bases there may be more imports than the process limit of file descriptors. By default, the limit is a few less than the per-process file descriptor hard limit, if that is determinable.3
GCC CMIs use ELF32 as an architecture-neutral encapsulation mechanism.
You may use readelf to inspect them, although section
contents are largely undecipherable. There is a section named
.gnu.c++.README, which contains human-readable text. Other
than the first line, each line consists of tag: value
tuples.
> readelf -p.gnu.c++.README gcm.cache/foo.gcm
String dump of section '.gnu.c++.README':
[ 0] GNU C++ primary module interface
[ 21] compiler: 11.0.0 20201116 (experimental) [c++-modules revision 20201116-0454]
[ 6f] version: 2020/11/16-04:54
[ 89] module: foo
[ 95] source: c_b.ii
[ a4] dialect: C++20/coroutines
[ be] cwd: /data/users/nathans/modules/obj/x86_64/gcc
[ ee] repository: gcm.cache
[ 104] buildtime: 2020/11/16 15:03:21 UTC
[ 127] localtime: 2020/11/16 07:03:21 PST
[ 14a] export: foo:part1 foo-part1.gcm
Amongst other things, this lists the source that was built, C++
dialect used and imports of the module.4 The timestamp is the same value as that
provided by the __DATE__ & __TIME__ macros, and may be
explicitly specified with the environment variable
SOURCE_DATE_EPOCH. For further details
see Environment Variables.
A set of related CMIs may be copied, provided the relative pathnames are preserved.
The .gnu.c++.README contents do not affect CMI integrity, and
it may be removed or altered. The section numbering of the sections
whose names do not begin with .gnu.c++., or are not the string
section is significant and must not be altered.
A conforming implementation of ISO C is required to document its choice of behavior in each of the areas that are designated “implementation defined”. The following lists all such areas, along with the section numbers from the ISO/IEC 9899:1990, ISO/IEC 9899:1999 and ISO/IEC 9899:2011 standards. Some areas are only implementation-defined in one version of the standard.
Some choices depend on the externally determined ABI for the platform (including standard character encodings) which GCC follows; these are listed as “determined by ABI” below. See Binary Compatibility, and https://gcc.gnu.org/readings.html. Some choices are documented in the preprocessor manual. See Implementation-defined behavior. Some choices are made by the library and operating system (or other environment when compiling for a freestanding environment); refer to their documentation for details.
Diagnostics consist of all the output sent to stderr by GCC.
The behavior of most of these points are dependent on the implementation of the C library, and are not defined by GCC itself.
For internal names, all characters are significant. For external names, the number of significant characters are defined by the linker; for almost all targets, all characters are significant.
This is a property of the linker. C99 and C11 require that case distinctions are always significant in identifiers with external linkage and systems without this property are not supported by GCC.
Determined by ABI.
Determined by ABI.
Determined by ABI.
char object into which has been stored any
character other than a member of the basic execution character set
(C90 6.1.2.5, C99 and C11 6.2.5).
Determined by ABI.
signed char or unsigned char has the same
range, representation, and behavior as “plain” char (C90
6.1.2.5, C90 6.2.1.1, C99 and C11 6.2.5, C99 and C11 6.3.1.1).
Determined by ABI. The options -funsigned-char and -fsigned-char change the default. See Options Controlling C Dialect.
Determined by ABI.
Such tokens may not be concatenated.
wchar_t, char16_t, and
char32_t where the corresponding standard encoding macro
(__STDC_ISO_10646__, __STDC_UTF_16__, or
__STDC_UTF_32__) is not defined (C11 6.10.8.2).
See Implementation-defined behavior. char16_t and
char32_t literals are always encoded in UTF-16 and UTF-32
respectively.
GCC does not support any extended integer types.
GCC supports only two's complement integer types, and all bit patterns are ordinary values.
GCC does not support any extended integer types.
For conversion to a type of width N, the value is reduced modulo 2^N to be within range of the type; no signal is raised.
Bitwise operators act on the representation of the value including both the sign and value bits, where the sign bit is considered immediately above the highest-value value bit. Signed ‘>>’ acts on negative numbers by sign extension.
As an extension to the C language, GCC does not use the latitude given in C99 and C11 only to treat certain aspects of signed ‘<<’ as undefined. However, -fsanitize=shift (and -fsanitize=undefined) will diagnose such cases. They are also diagnosed where constant expressions are required.
GCC always follows the C99 and C11 requirement that the result of division is truncated towards zero.
<math.h> and <complex.h> that return floating-point
results (C90, C99 and C11 5.2.4.2.2).
The accuracy is unknown.
FLT_ROUNDS
(C90, C99 and C11 5.2.4.2.2).
GCC does not use such values.
FLT_EVAL_METHOD (C99 and C11 5.2.4.2.2).
GCC does not use such values.
C99 Annex F is followed.
C99 Annex F is followed.
C99 Annex F is followed.
FP_CONTRACT pragma (C99 and C11 6.5).
Expressions are currently only contracted if -ffp-contract=fast, -funsafe-math-optimizations or -ffast-math are used. This is subject to change.
FENV_ACCESS pragma (C99 and C11
7.6.1).
This pragma is not implemented, but the default is to “off” unless -frounding-math is used and -fno-trapping-math is not in which case it is “on”.
This is dependent on the implementation of the C library, and is not defined by GCC itself.
FP_CONTRACT pragma (C99 and C11
7.12.2).
This pragma is not implemented. Expressions are currently only contracted if -ffp-contract=fast, -funsafe-math-optimizations or -ffast-math are used. This is subject to change.
This is dependent on the implementation of the C library, and is not defined by GCC itself.
This is dependent on the implementation of the C library, and is not defined by GCC itself.
A cast from pointer to integer discards most-significant bits if the pointer representation is larger than the integer type, sign-extends5 if the pointer representation is smaller than the integer type, otherwise the bits are unchanged.
A cast from integer to pointer discards most-significant bits if the pointer representation is smaller than the integer type, extends according to the signedness of the integer type if the pointer representation is larger than the integer type, otherwise the bits are unchanged.
When casting from pointer to integer and back again, the resulting pointer must reference the same object as the original pointer, otherwise the behavior is undefined. That is, one may not use integer arithmetic to avoid the undefined behavior of pointer arithmetic as proscribed in C99 and C11 6.5.6/8.
The value is as specified in the standard and the type is determined by the ABI.
register
storage-class specifier are effective (C90 6.5.1, C99 and C11 6.7.1).
The register specifier affects code generation only in these ways:
register
storage-class specifier; if register is specified, the variable
may have a shorter lifespan than the code would indicate and may never
be placed in memory.
setjmp doesn't save the registers in
all circumstances. In those cases, GCC doesn't allocate any variables
in registers unless they are marked register.
GCC will not inline any functions if the -fno-inline option is used or if -O0 is used. Otherwise, GCC may still be unable to inline a function for many reasons; the -Winline option may be used to determine if a function has not been inlined and why not.
The relevant bytes of the representation of the object are treated as an object of the type used for the access. See Type-punning. This may be a trap representation.
int bit-field is treated as a
signed int bit-field or as an unsigned int bit-field
(C90 6.5.2, C90 6.5.2.1, C99 and C11 6.7.2, C99 and C11 6.7.2.1).
By default it is treated as signed int but this may be changed
by the -funsigned-bitfields option.
_Bool, signed int,
and unsigned int (C99 and C11 6.7.2.1).
Other integer types, such as long int, and enumerated types are
permitted even in strictly conforming mode.
Atomic types are not permitted for bit-fields.
Determined by ABI.
Determined by ABI.
Determined by ABI.
Normally, the type is unsigned int if there are no negative
values in the enumeration, otherwise int. If
-fshort-enums is specified, then if there are negative values
it is the first of signed char, short and int
that can represent all the values, otherwise it is the first of
unsigned char, unsigned short and unsigned int
that can represent all the values.
On some targets, -fshort-enums is the default; this is determined by the ABI.
Such an object is normally accessed by pointers and used for accessing hardware. In most expressions, it is intuitively obvious what is a read and what is a write. For example
volatile int *dst = somevalue;
volatile int *src = someothervalue;
*dst = *src;
will cause a read of the volatile object pointed to by src and store the
value into the volatile object pointed to by dst. There is no
guarantee that these reads and writes are atomic, especially for objects
larger than int.
However, if the volatile storage is not being modified, and the value of the volatile storage is not used, then the situation is less obvious. For example
volatile int *src = somevalue;
*src;
According to the C standard, such an expression is an rvalue whose type
is the unqualified version of its original type, i.e. int. Whether
GCC interprets this as a read of the volatile object being pointed to or
only as a request to evaluate the expression for its side effects depends
on this type.
If it is a scalar type, or on most targets an aggregate type whose only member object is of a scalar type, or a union type whose member objects are of scalar types, the expression is interpreted by GCC as a read of the volatile object; in the other cases, the expression is only evaluated for its side effects.
When an object of an aggregate type, with the same size and alignment as a
scalar type S, is the subject of a volatile access by an assignment
expression or an atomic function, the access to it is performed as if the
object's declared type were volatile S.
GCC is only limited by available memory.
case values in a switch
statement (C90 6.6.4.2).
GCC is only limited by available memory.
See Implementation-defined behavior, for details of these aspects of implementation-defined behavior.
#pragma directives where header name
preprocessing tokens are recognized (C11 6.4, C11 6.4.7).
#include directive are combined into a header
name (C90 6.8.2, C99 and C11 6.10.2).
#include processing (C90 6.8.2, C99
and C11 6.10.2).
STDC #pragma
directive (C90 6.8.6, C99 and C11 6.10.6).
See Pragmas, for details of pragmas accepted by GCC on all targets. See Pragmas Accepted by GCC, for details of target-specific pragmas.
__DATE__ and __TIME__ when
respectively, the date and time of translation are not available (C90
6.8.8, C99 6.10.8, C11 6.10.8.1).
The behavior of most of these points are dependent on the implementation of the C library, and are not defined by GCC itself.
NULL expands
(C90 7.1.6, C99 7.17, C11 7.19).
In <stddef.h>, NULL expands to ((void *)0). GCC
does not provide the other headers which define NULL and some
library implementations may use other definitions in those headers.
<float.h>, <limits.h>, and <stdint.h>
(C90, C99 and C11 5.2.4.2, C99 7.18.2, C99 7.18.3, C11 7.20.2, C11 7.20.3).
Determined by ABI.
Such accesses are supported, subject to the same requirements for synchronization for concurrent accesses as for concurrent accesses to any object.
Determined by ABI.
Extended alignments up to 2^28 (bytes) are supported for objects of automatic storage duration. Alignments supported for objects of static and thread storage duration are determined by the ABI.
Valid alignments are powers of 2 up to and including 2^28.
sizeof and _Alignof
operators (C90 6.3.3.4, C99 and C11 6.5.3.4).
Determined by ABI.
The behavior of these points are dependent on the implementation of the C library, and are not defined by GCC itself.
A conforming implementation of ISO C++ is required to document its choice of behavior in each of the areas that are designated “implementation defined”. The following lists all such areas, along with the section numbers from the ISO/IEC 14882:1998 and ISO/IEC 14882:2003 standards. Some areas are only implementation-defined in one version of the standard.
Some choices depend on the externally determined ABI for the platform (including standard character encodings) which GCC follows; these are listed as “determined by ABI” below. See Binary Compatibility, and https://gcc.gnu.org/readings.html. Some choices are documented in the preprocessor manual. See Implementation-defined behavior. Some choices are documented in the corresponding document for the C language. See C Implementation. Some choices are made by the library and operating system (or other environment when compiling for a freestanding environment); refer to their documentation for details.
Each implementation shall include documentation that identifies all conditionally-supported constructs that it does not support (C++0x 1.4).
Such argument passing is supported, using the same pass-by-invisible-reference approach used for normal function arguments of such types.
The stack is not unwound before std::terminate is called.
GNU C provides several language features not found in ISO standard C.
(The -pedantic option directs GCC to print a warning message if
any of these features is used.) To test for the availability of these
features in conditional compilation, check for a predefined macro
__GNUC__, which is always defined under GCC.
These extensions are available in C and Objective-C. Most of them are also available in C++. See Extensions to the C++ Language, for extensions that apply only to C++.
Some features that are in ISO C99 but not C90 or C++ are also, as extensions, accepted by GCC in C90 mode and in C++.
A compound statement enclosed in parentheses may appear as an expression in GNU C. This allows you to use loops, switches, and local variables within an expression.
Recall that a compound statement is a sequence of statements surrounded by braces; in this construct, parentheses go around the braces. For example:
({ int y = foo (); int z;
if (y > 0) z = y;
else z = - y;
z; })
is a valid (though slightly more complex than necessary) expression
for the absolute value of foo ().
The last thing in the compound statement should be an expression
followed by a semicolon; the value of this subexpression serves as the
value of the entire construct. (If you use some other kind of statement
last within the braces, the construct has type void, and thus
effectively no value.)
This feature is especially useful in making macro definitions “safe” (so that they evaluate each operand exactly once). For example, the “maximum” function is commonly defined as a macro in standard C as follows:
#define max(a,b) ((a) > (b) ? (a) : (b))
But this definition computes either a or b twice, with bad
results if the operand has side effects. In GNU C, if you know the
type of the operands (here taken as int), you can avoid this
problem by defining the macro as follows:
#define maxint(a,b) \
({int _a = (a), _b = (b); _a > _b ? _a : _b; })
Note that introducing variable declarations (as we do in maxint) can
cause variable shadowing, so while this example using the max macro
produces correct results:
int _a = 1, _b = 2, c;
c = max (_a, _b);
this example using maxint will not:
int _a = 1, _b = 2, c;
c = maxint (_a, _b);
This problem may for instance occur when we use this pattern recursively, like so:
#define maxint3(a, b, c) \
({int _a = (a), _b = (b), _c = (c); maxint (maxint (_a, _b), _c); })
Embedded statements are not allowed in constant expressions, such as the value of an enumeration constant, the width of a bit-field, or the initial value of a static variable.
If you don't know the type of the operand, you can still do this, but you
must use typeof or __auto_type (see Typeof).
In G++, the result value of a statement expression undergoes array and
function pointer decay, and is returned by value to the enclosing
expression. For instance, if A is a class, then
A a;
({a;}).Foo ()
constructs a temporary A object to hold the result of the
statement expression, and that is used to invoke Foo.
Therefore the this pointer observed by Foo is not the
address of a.
In a statement expression, any temporaries created within a statement are destroyed at that statement's end. This makes statement expressions inside macros slightly different from function calls. In the latter case temporaries introduced during argument evaluation are destroyed at the end of the statement that includes the function call. In the statement expression case they are destroyed during the statement expression. For instance,
#define macro(a) ({__typeof__(a) b = (a); b + 3; })
template<typename T> T function(T a) { T b = a; return b + 3; }
void foo ()
{
macro (X ());
function (X ());
}
has different places where temporaries are destroyed. For the
macro case, the temporary X is destroyed just after
the initialization of b. In the function case that
temporary is destroyed when the function returns.
These considerations mean that it is probably a bad idea to use statement expressions of this form in header files that are designed to work with C++. (Note that some versions of the GNU C Library contained header files using statement expressions that lead to precisely this bug.)
Jumping into a statement expression with goto or using a
switch statement outside the statement expression with a
case or default label inside the statement expression is
not permitted. Jumping into a statement expression with a computed
goto (see Labels as Values) has undefined behavior.
Jumping out of a statement expression is permitted, but if the
statement expression is part of a larger expression then it is
unspecified which other subexpressions of that expression have been
evaluated except where the language definition requires certain
subexpressions to be evaluated before or after the statement
expression. A break or continue statement inside of
a statement expression used in while, do or for
loop or switch statement condition
or for statement init or increment expressions jumps to an
outer loop or switch statement if any (otherwise it is an error),
rather than to the loop or switch statement in whose condition
or init or increment expression it appears.
In any case, as with a function call, the evaluation of a
statement expression is not interleaved with the evaluation of other
parts of the containing expression. For example,
foo (), (({ bar1 (); goto a; 0; }) + bar2 ()), baz();
calls foo and bar1 and does not call baz but
may or may not call bar2. If bar2 is called, it is
called after foo and before bar1.
GCC allows you to declare local labels in any nested block
scope. A local label is just like an ordinary label, but you can
only reference it (with a goto statement, or by taking its
address) within the block in which it is declared.
A local label declaration looks like this:
__label__ label;
or
__label__ label1, label2, /* ... */;
Local label declarations must come at the beginning of the block, before any ordinary declarations or statements.
The label declaration defines the label name, but does not define
the label itself. You must do this in the usual way, with
label:, within the statements of the statement expression.
The local label feature is useful for complex macros. If a macro
contains nested loops, a goto can be useful for breaking out of
them. However, an ordinary label whose scope is the whole function
cannot be used: if the macro can be expanded several times in one
function, the label is multiply defined in that function. A
local label avoids this problem. For example:
#define SEARCH(value, array, target) \
do { \
__label__ found; \
typeof (target) _SEARCH_target = (target); \
typeof (*(array)) *_SEARCH_array = (array); \
int i, j; \
int value; \
for (i = 0; i < max; i++) \
for (j = 0; j < max; j++) \
if (_SEARCH_array[i][j] == _SEARCH_target) \
{ (value) = i; goto found; } \
(value) = -1; \
found:; \
} while (0)
This could also be written using a statement expression:
#define SEARCH(array, target) \
({ \
__label__ found; \
typeof (target) _SEARCH_target = (target); \
typeof (*(array)) *_SEARCH_array = (array); \
int i, j; \
int value; \
for (i = 0; i < max; i++) \
for (j = 0; j < max; j++) \
if (_SEARCH_array[i][j] == _SEARCH_target) \
{ value = i; goto found; } \
value = -1; \
found: \
value; \
})
Local label declarations also make the labels they declare visible to nested functions, if there are any. See Nested Functions, for details.
You can get the address of a label defined in the current function
(or a containing function) with the unary operator ‘&&’. The
value has type void *. This value is a constant and can be used
wherever a constant of that type is valid. For example:
void *ptr;
/* ... */
ptr = &&foo;
To use these values, you need to be able to jump to one. This is done
with the computed goto statement6, goto *exp;. For example,
goto *ptr;
Any expression of type void * is allowed.
One way of using these constants is in initializing a static array that serves as a jump table:
static void *array[] = { &&foo, &&bar, &&hack };
Then you can select a label with indexing, like this:
goto *array[i];
Note that this does not check whether the subscript is in bounds—array indexing in C never does that.
Such an array of label values serves a purpose much like that of the
switch statement. The switch statement is cleaner, so
use that rather than an array unless the problem does not fit a
switch statement very well.
Another use of label values is in an interpreter for threaded code. The labels within the interpreter function can be stored in the threaded code for super-fast dispatching.
You may not use this mechanism to jump to code in a different function. If you do that, totally unpredictable things happen. The best way to avoid this is to store the label address only in automatic variables and never pass it as an argument.
An alternate way to write the above example is
static const int array[] = { &&foo - &&foo, &&bar - &&foo,
&&hack - &&foo };
goto *(&&foo + array[i]);
This is more friendly to code living in shared libraries, as it reduces the number of dynamic relocations that are needed, and by consequence, allows the data to be read-only. This alternative with label differences is not supported for the AVR target, please use the first approach for AVR programs.
The &&foo expressions for the same label might have different
values if the containing function is inlined or cloned. If a program
relies on them being always the same,
__attribute__((__noinline__,__noclone__)) should be used to
prevent inlining and cloning. If &&foo is used in a static
variable initializer, inlining and cloning is forbidden.
A nested function is a function defined inside another function. Nested functions are supported as an extension in GNU C, but are not supported by GNU C++.
The nested function's name is local to the block where it is defined.
For example, here we define a nested function named square, and
call it twice:
foo (double a, double b)
{
double square (double z) { return z * z; }
return square (a) + square (b);
}
The nested function can access all the variables of the containing
function that are visible at the point of its definition. This is
called lexical scoping. For example, here we show a nested
function which uses an inherited variable named offset:
bar (int *array, int offset, int size)
{
int access (int *array, int index)
{ return array[index + offset]; }
int i;
/* ... */
for (i = 0; i < size; i++)
/* ... */ access (array, i) /* ... */
}
Nested function definitions are permitted within functions in the places where variable definitions are allowed; that is, in any block, mixed with the other declarations and statements in the block.
It is possible to call the nested function from outside the scope of its name by storing its address or passing the address to another function:
hack (int *array, int size)
{
void store (int index, int value)
{ array[index] = value; }
intermediate (store, size);
}
Here, the function intermediate receives the address of
store as an argument. If intermediate calls store,
the arguments given to store are used to store into array.
But this technique works only so long as the containing function
(hack, in this example) does not exit.
If you try to call the nested function through its address after the containing function exits, all hell breaks loose. If you try to call it after a containing scope level exits, and if it refers to some of the variables that are no longer in scope, you may be lucky, but it's not wise to take the risk. If, however, the nested function does not refer to anything that has gone out of scope, you should be safe.
GCC implements taking the address of a nested function using a technique called trampolines. This technique was described in Lexical Closures for C++ (Thomas M. Breuel, USENIX C++ Conference Proceedings, October 17-21, 1988).
A nested function can jump to a label inherited from a containing
function, provided the label is explicitly declared in the containing
function (see Local Labels). Such a jump returns instantly to the
containing function, exiting the nested function that did the
goto and any intermediate functions as well. Here is an example:
bar (int *array, int offset, int size)
{
__label__ failure;
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
int i;
/* ... */
for (i = 0; i < size; i++)
/* ... */ access (array, i) /* ... */
/* ... */
return 0;
/* Control comes here from access
if it detects an error. */
failure:
return -1;
}
A nested function always has no linkage. Declaring one with
extern or static is erroneous. If you need to declare the nested function
before its definition, use auto (which is otherwise meaningless
for function declarations).
bar (int *array, int offset, int size)
{
__label__ failure;
auto int access (int *, int);
/* ... */
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
/* ... */
}
GCC provides the built-in functions __builtin_setjmp and
__builtin_longjmp which are similar to, but not interchangeable
with, the C library functions setjmp and longjmp.
The built-in versions are used internally by GCC's libraries
to implement exception handling on some targets. You should use the
standard C library functions declared in <setjmp.h> in user code
instead of the builtins.
The built-in versions of these functions use GCC's normal mechanisms to save and restore registers using the stack on function entry and exit. The jump buffer argument buf holds only the information needed to restore the stack frame, rather than the entire set of saved register values.
An important caveat is that GCC arranges to save and restore only
those registers known to the specific architecture variant being
compiled for. This can make __builtin_setjmp and
__builtin_longjmp more efficient than their library
counterparts in some cases, but it can also cause incorrect and
mysterious behavior when mixing with code that uses the full register
set.
You should declare the jump buffer argument buf to the built-in functions as:
#include <stdint.h>
intptr_t buf[5];
This function saves the current stack context in buf.
__builtin_setjmpreturns 0 when returning directly, and 1 when returning from__builtin_longjmpusing the same buf.
This function restores the stack context in buf, saved by a previous call to
__builtin_setjmp. After__builtin_longjmpis finished, the program resumes execution as if the matching__builtin_setjmpreturns the value val, which must be 1.Because
__builtin_longjmpdepends on the function return mechanism to restore the stack context, it cannot be called from the same function calling__builtin_setjmpto initialize buf. It can only be called from a function called (directly or indirectly) from the function calling__builtin_setjmp.
Using the built-in functions described below, you can record the arguments a function received, and call another function with the same arguments, without knowing the number or types of the arguments.
You can also record the return value of that function call, and later return that value, without knowing what data type the function tried to return (as long as your caller expects that data type).
However, these built-in functions may interact badly with some sophisticated features or other extensions of the language. It is, therefore, not recommended to use them outside very simple functions acting as mere forwarders for their arguments.
This built-in function returns a pointer to data describing how to perform a call with the same arguments as are passed to the current function.
The function saves the arg pointer register, structure value address, and all registers that might be used to pass arguments to a function into a block of memory allocated on the stack. Then it returns the address of that block.
This built-in function invokes function with a copy of the parameters described by arguments and size.
The value of arguments should be the value returned by
__builtin_apply_args. The argument size specifies the size of the stack argument data, in bytes.This function returns a pointer to data describing how to return whatever value is returned by function. The data is saved in a block of memory allocated on the stack.
It is not always simple to compute the proper value for size. The value is used by
__builtin_applyto compute the amount of data that should be pushed on the stack and copied from the incoming argument area.
This built-in function returns the value described by result from the containing function. You should specify, for result, a value returned by
__builtin_apply.
This built-in function represents all anonymous arguments of an inline function. It can be used only in inline functions that are always inlined, never compiled as a separate function, such as those using
__attribute__ ((__always_inline__))or__attribute__ ((__gnu_inline__))extern inline functions. It must be only passed as last argument to some other function with variable arguments. This is useful for writing small wrapper inlines for variable argument functions, when using preprocessor macros is undesirable. For example:extern int myprintf (FILE *f, const char *format, ...); extern inline __attribute__ ((__gnu_inline__)) int myprintf (FILE *f, const char *format, ...) { int r = fprintf (f, "myprintf: "); if (r < 0) return r; int s = fprintf (f, format, __builtin_va_arg_pack ()); if (s < 0) return s; return r + s; }
This built-in function returns the number of anonymous arguments of an inline function. It can be used only in inline functions that are always inlined, never compiled as a separate function, such as those using
__attribute__ ((__always_inline__))or__attribute__ ((__gnu_inline__))extern inline functions. For example following does link- or run-time checking of open arguments for optimized code:#ifdef __OPTIMIZE__ extern inline __attribute__((__gnu_inline__)) int myopen (const char *path, int oflag, ...) { if (__builtin_va_arg_pack_len () > 1) warn_open_too_many_arguments (); if (__builtin_constant_p (oflag)) { if ((oflag & O_CREAT) != 0 && __builtin_va_arg_pack_len () < 1) { warn_open_missing_mode (); return __open_2 (path, oflag); } return open (path, oflag, __builtin_va_arg_pack ()); } if (__builtin_va_arg_pack_len () < 1) return __open_2 (path, oflag); return open (path, oflag, __builtin_va_arg_pack ()); } #endif
typeof
Another way to refer to the type of an expression is with typeof.
The syntax of using of this keyword looks like sizeof, but the
construct acts semantically like a type name defined with typedef.
There are two ways of writing the argument to typeof: with an
expression or with a type. Here is an example with an expression:
typeof (x[0](1))
This assumes that x is an array of pointers to functions;
the type described is that of the values of the functions.
Here is an example with a typename as the argument:
typeof (int *)
Here the type described is that of pointers to int.
If you are writing a header file that must work when included in ISO C
programs, write __typeof__ instead of typeof.
See Alternate Keywords.
A typeof construct can be used anywhere a typedef name can be
used. For example, you can use it in a declaration, in a cast, or inside
of sizeof or typeof.
The operand of typeof is evaluated for its side effects if and
only if it is an expression of variably modified type or the name of
such a type.
typeof is often useful in conjunction with
statement expressions (see Statement Exprs).
Here is how the two together can
be used to define a safe “maximum” macro which operates on any
arithmetic type and evaluates each of its arguments exactly once:
#define max(a,b) \
({ typeof (a) _a = (a); \
typeof (b) _b = (b); \
_a > _b ? _a : _b; })
The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within the
expressions that are substituted for a and b. Eventually we
hope to design a new form of declaration syntax that allows you to declare
variables whose scopes start only after their initializers; this will be a
more reliable way to prevent such conflicts.
Some more examples of the use of typeof:
y with the type of what x points to.
typeof (*x) y;
y as an array of such values.
typeof (*x) y[4];
y as an array of pointers to characters:
typeof (typeof (char *)[4]) y;
It is equivalent to the following traditional C declaration:
char *y[4];
To see the meaning of the declaration using typeof, and why it
might be a useful way to write, rewrite it with these macros:
#define pointer(T) typeof(T *)
#define array(T, N) typeof(T [N])
Now the declaration can be rewritten this way:
array (pointer (char), 4) y;
Thus, array (pointer (char), 4) is the type of arrays of 4
pointers to char.
In GNU C, but not GNU C++, you may also declare the type of a variable
as __auto_type. In that case, the declaration must declare
only one variable, whose declarator must just be an identifier, the
declaration must be initialized, and the type of the variable is
determined by the initializer; the name of the variable is not in
scope until after the initializer. (In C++, you should use C++11
auto for this purpose.) Using __auto_type, the
“maximum” macro above could be written as:
#define max(a,b) \
({ __auto_type _a = (a); \
__auto_type _b = (b); \
_a > _b ? _a : _b; })
Using __auto_type instead of typeof has two advantages:
__auto_type, but twice if
typeof is used.
The middle operand in a conditional expression may be omitted. Then if the first operand is nonzero, its value is the value of the conditional expression.
Therefore, the expression
x ? : y
has the value of x if that is nonzero; otherwise, the value of
y.
This example is perfectly equivalent to
x ? x : y
In this simple case, the ability to omit the middle operand is not especially useful. When it becomes useful is when the first operand does, or may (if it is a macro argument), contain a side effect. Then repeating the operand in the middle would perform the side effect twice. Omitting the middle operand uses the value already computed without the undesirable effects of recomputing it.
As an extension the integer scalar type __int128 is supported for
targets which have an integer mode wide enough to hold 128 bits.
Simply write __int128 for a signed 128-bit integer, or
unsigned __int128 for an unsigned 128-bit integer. There is no
support in GCC for expressing an integer constant of type __int128
for targets with long long integer less than 128 bits wide.
ISO C99 and ISO C++11 support data types for integers that are at least
64 bits wide, and as an extension GCC supports them in C90 and C++98 modes.
Simply write long long int for a signed integer, or
unsigned long long int for an unsigned integer. To make an
integer constant of type long long int, add the suffix ‘LL’
to the integer. To make an integer constant of type unsigned long
long int, add the suffix ‘ULL’ to the integer.
You can use these types in arithmetic like any other integer types. Addition, subtraction, and bitwise boolean operations on these types are open-coded on all types of machines. Multiplication is open-coded if the machine supports a fullword-to-doubleword widening multiply instruction. Division and shifts are open-coded only on machines that provide special support. The operations that are not open-coded use special library routines that come with GCC.
There may be pitfalls when you use long long types for function
arguments without function prototypes. If a function
expects type int for its argument, and you pass a value of type
long long int, confusion results because the caller and the
subroutine disagree about the number of bytes for the argument.
Likewise, if the function expects long long int and you pass
int. The best way to avoid such problems is to use prototypes.
ISO C99 supports complex floating data types, and as an extension GCC
supports them in C90 mode and in C++. GCC also supports complex integer data
types which are not part of ISO C99. You can declare complex types
using the keyword _Complex. As an extension, the older GNU
keyword __complex__ is also supported.
For example, ‘_Complex double x;’ declares x as a
variable whose real part and imaginary part are both of type
double. ‘_Complex short int y;’ declares y to
have real and imaginary parts of type short int; this is not
likely to be useful, but it shows that the set of complex types is
complete.
To write a constant with a complex data type, use the suffix ‘i’ or
‘j’ (either one; they are equivalent). For example, 2.5fi
has type _Complex float and 3i has type
_Complex int. Such a constant always has a pure imaginary
value, but you can form any complex value you like by adding one to a
real constant. This is a GNU extension; if you have an ISO C99
conforming C library (such as the GNU C Library), and want to construct complex
constants of floating type, you should include <complex.h> and
use the macros I or _Complex_I instead.
The ISO C++14 library also defines the ‘i’ suffix, so C++14 code that includes the ‘<complex>’ header cannot use ‘i’ for the GNU extension. The ‘j’ suffix still has the GNU meaning.
GCC can handle both implicit and explicit casts between the _Complex
types and other _Complex types as casting both the real and imaginary
parts to the scalar type.
GCC can handle implicit and explicit casts from a scalar type to a _Complex
type and where the imaginary part will be considered zero.
The C front-end can handle implicit and explicit casts from a _Complex type
to a scalar type where the imaginary part will be ignored. In C++ code, this cast
is considered illformed and G++ will error out.
GCC provides a built-in function __builtin_complex will can be used to
construct a complex value.
GCC has a few extensions which can be used to extract the real
and the imaginary part of the complex-valued expression. Note
these expressions are lvalues if the exp is an lvalue.
These expressions operands have the type of a complex type
which might get prompoted to a complex type from a scalar type.
E.g. __real__ (int)x is the same as casting to
_Complex int before __real__ is done.
| Expression | Description
|
|---|---|
__real__ exp
| Extract the real part of exp.
|
__imag__ exp
| Extract the imaginary part of exp.
|
For values of floating point, you should use the ISO C99
functions, declared in <complex.h> and also provided as
built-in functions by GCC.
| Expression | float | double | long double
|
|---|---|---|---|
__real__ exp
| crealf | creal | creall
|
__imag__ exp
| cimagf | cimag | cimagl
|
The operator ‘~’ performs complex conjugation when used on a value
with a complex type. This is a GNU extension; for values of
floating type, you should use the ISO C99 functions conjf,
conj and conjl, declared in <complex.h> and also
provided as built-in functions by GCC. Note unlike the __real__
and __imag__ operators, this operator will not do an implicit cast
to the complex type because the ‘~’ is already a normal operator.
GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice versa). Only the DWARF
debug info format can represent this, so use of DWARF is recommended.
If you are using the stabs debug info format, GCC describes a noncontiguous
complex variable as if it were two separate variables of noncomplex type.
If the variable's actual name is foo, the two fictitious
variables are named foo$real and foo$imag. You can
examine and set these two fictitious variables with your debugger.
The built-in function
__builtin_complexis provided for use in implementing the ISO C11 macrosCMPLXF,CMPLXandCMPLXL. real and imag must have the same type, a real binary floating-point type, and the result has the corresponding complex type with real and imaginary parts real and imag. Unlike ‘real + I * imag’, this works even when infinities, NaNs and negative zeros are involved.
ISO/IEC TS 18661-3:2015 defines C support for additional floating
types _Floatn and _Floatnx, and GCC supports
these type names; the set of types supported depends on the target
architecture.
Constants with these types use suffixes fn or
Fn and fnx or Fnx. These type
names can be used together with _Complex to declare complex
types.
As an extension, GNU C and GNU C++ support additional floating types, which are not supported by all targets.
__float128 is available on i386, x86_64, IA-64, and
hppa HP-UX, as well as on PowerPC GNU/Linux targets that enable
the vector scalar (VSX) instruction set. __float128 supports
the 128-bit floating type. On i386, x86_64, PowerPC, and IA-64
other than HP-UX, __float128 is an alias for _Float128.
On hppa and IA-64 HP-UX, __float128 is an alias for long
double.
__float80 is available on the i386, x86_64, and IA-64
targets, and supports the 80-bit (XFmode) floating type. It is
an alias for the type name _Float64x on these targets.
__ibm128 is available on PowerPC targets, and provides
access to the IBM extended double format which is the current format
used for long double. When long double transitions to
__float128 on PowerPC in the future, __ibm128 will remain
for use in conversions between the two types.
Support for these additional types includes the arithmetic operators:
add, subtract, multiply, divide; unary arithmetic operators;
relational operators; equality operators; and conversions to and from
integer and other floating types. Use a suffix ‘w’ or ‘W’
in a literal constant of type __float80 or type
__ibm128. Use a suffix ‘q’ or ‘Q’ for __float128.
In order to use _Float128, __float128, and __ibm128
on PowerPC Linux systems, you must use the -mfloat128 option. It is
expected in future versions of GCC that _Float128 and __float128
will be enabled automatically.
The _Float128 type is supported on all systems where
__float128 is supported or where long double has the
IEEE binary128 format. The _Float64x type is supported on all
systems where __float128 is supported. The _Float32
type is supported on all systems supporting IEEE binary32; the
_Float64 and _Float32x types are supported on all systems
supporting IEEE binary64. The _Float16 type is supported on AArch64
systems by default, on ARM systems when the IEEE format for 16-bit
floating-point types is selected with -mfp16-format=ieee and,
for both C and C++, on x86 systems with SSE2 enabled. GCC does not currently
support _Float128x on any systems.
On the i386, x86_64, IA-64, and HP-UX targets, you can declare complex
types using the corresponding internal complex type, XCmode for
__float80 type and TCmode for __float128 type:
typedef _Complex float __attribute__((mode(TC))) _Complex128;
typedef _Complex float __attribute__((mode(XC))) _Complex80;
On the PowerPC Linux VSX targets, you can declare complex types using
the corresponding internal complex type, KCmode for
__float128 type and ICmode for __ibm128 type:
typedef _Complex float __attribute__((mode(KC))) _Complex_float128;
typedef _Complex float __attribute__((mode(IC))) _Complex_ibm128;
On ARM and AArch64 targets, GCC supports half-precision (16-bit) floating
point via the __fp16 type defined in the ARM C Language Extensions.
On ARM systems, you must enable this type explicitly with the
-mfp16-format command-line option in order to use it.
On x86 targets with SSE2 enabled, GCC supports half-precision (16-bit)
floating point via the _Float16 type. For C++, x86 provides a builtin
type named _Float16 which contains same data format as C.
ARM targets support two incompatible representations for half-precision floating-point values. You must choose one of the representations and use it consistently in your program.
Specifying -mfp16-format=ieee selects the IEEE 754-2008 format. This format can represent normalized values in the range of 2^-14 to 65504. There are 11 bits of significand precision, approximately 3 decimal digits.
Specifying -mfp16-format=alternative selects the ARM alternative format. This representation is similar to the IEEE format, but does not support infinities or NaNs. Instead, the range of exponents is extended, so that this format can represent normalized values in the range of 2^-14 to 131008.
The GCC port for AArch64 only supports the IEEE 754-2008 format, and does not require use of the -mfp16-format command-line option.
The __fp16 type may only be used as an argument to intrinsics defined
in <arm_fp16.h>, or as a storage format. For purposes of
arithmetic and other operations, __fp16 values in C or C++
expressions are automatically promoted to float.
The ARM target provides hardware support for conversions between
__fp16 and float values
as an extension to VFP and NEON (Advanced SIMD), and from ARMv8-A provides
hardware support for conversions between __fp16 and double
values. GCC generates code using these hardware instructions if you
compile with options to select an FPU that provides them;
for example, -mfpu=neon-fp16 -mfloat-abi=softfp,
in addition to the -mfp16-format option to select
a half-precision format.
Language-level support for the __fp16 data type is
independent of whether GCC generates code using hardware floating-point
instructions. In cases where hardware support is not specified, GCC
implements conversions between __fp16 and other types as library
calls.
It is recommended that portable code use the _Float16 type defined
by ISO/IEC TS 18661-3:2015. See Floating Types.
On x86 targets with SSE2 enabled, without -mavx512fp16,
all operations will be emulated by software emulation and the float
instructions. The default behavior for FLT_EVAL_METHOD is to keep the
intermediate result of the operation as 32-bit precision. This may lead to
inconsistent behavior between software emulation and AVX512-FP16 instructions.
Using -fexcess-precision=16 will force round back after each operation.
Using -mavx512fp16 will generate AVX512-FP16 instructions instead of
software emulation. The default behavior of FLT_EVAL_METHOD is to round
after each operation. The same is true with -fexcess-precision=standard
and -mfpmath=sse. If there is no -mfpmath=sse,
-fexcess-precision=standard alone does the same thing as before,
It is useful for code that does not have _Float16 and runs on the x87
FPU.
As an extension, GNU C supports decimal floating types as defined in the N1312 draft of ISO/IEC WDTR24732. Support for decimal floating types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. Not all targets support decimal floating types.
The decimal floating types are _Decimal32, _Decimal64, and
_Decimal128. They use a radix of ten, unlike the floating types
float, double, and long double whose radix is not
specified by the C standard but is usually two.
Support for decimal floating types includes the arithmetic operators
add, subtract, multiply, divide; unary arithmetic operators;
relational operators; equality operators; and conversions to and from
integer and other floating types. Use a suffix ‘df’ or
‘DF’ in a literal constant of type _Decimal32, ‘dd’
or ‘DD’ for _Decimal64, and ‘dl’ or ‘DL’ for
_Decimal128.
GCC support of decimal float as specified by the draft technical report is incomplete:
__STDC_DEC_FP__ to indicate that the implementation conforms to
the technical report.
Types _Decimal32, _Decimal64, and _Decimal128
are supported by the DWARF debug information format.
ISO C99 and ISO C++17 support floating-point numbers written not only in
the usual decimal notation, such as 1.55e1, but also numbers such as
0x1.fp3 written in hexadecimal format. As a GNU extension, GCC
supports this in C90 mode (except in some cases when strictly
conforming) and in C++98, C++11 and C++14 modes. In that format the
‘0x’ hex introducer and the ‘p’ or ‘P’ exponent field are
mandatory. The exponent is a decimal number that indicates the power of
2 by which the significant part is multiplied. Thus ‘0x1.f’ is
1 15/16,
‘p3’ multiplies it by 8, and the value of 0x1.fp3
is the same as 1.55e1.
Unlike for floating-point numbers in the decimal notation the exponent
is always required in the hexadecimal notation. Otherwise the compiler
would not be able to resolve the ambiguity of, e.g., 0x1.f. This
could mean 1.0f or 1.9375 since ‘f’ is also the
extension for floating-point constants of type float.
As an extension, GNU C supports fixed-point types as defined in the N1169 draft of ISO/IEC DTR 18037. Support for fixed-point types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. Not all targets support fixed-point types.
The fixed-point types are
short _Fract,
_Fract,
long _Fract,
long long _Fract,
unsigned short _Fract,
unsigned _Fract,
unsigned long _Fract,
unsigned long long _Fract,
_Sat short _Fract,
_Sat _Fract,
_Sat long _Fract,
_Sat long long _Fract,
_Sat unsigned short _Fract,
_Sat unsigned _Fract,
_Sat unsigned long _Fract,
_Sat unsigned long long _Fract,
short _Accum,
_Accum,
long _Accum,
long long _Accum,
unsigned short _Accum,
unsigned _Accum,
unsigned long _Accum,
unsigned long long _Accum,
_Sat short _Accum,
_Sat _Accum,
_Sat long _Accum,
_Sat long long _Accum,
_Sat unsigned short _Accum,
_Sat unsigned _Accum,
_Sat unsigned long _Accum,
_Sat unsigned long long _Accum.
Fixed-point data values contain fractional and optional integral parts. The format of fixed-point data varies and depends on the target machine.
Support for fixed-point types includes:
++, --)
+, -, !)
+, -, *, /)
<<, >>)
<, <=, >=, >)
==, !=)
+=, -=, *=, /=,
<<=, >>=)
Use a suffix in a fixed-point literal constant:
short _Fract and
_Sat short _Fract
_Fract and _Sat _Fract
long _Fract and
_Sat long _Fract
long long _Fract and
_Sat long long _Fract
unsigned short _Fract and
_Sat unsigned short _Fract
unsigned _Fract and
_Sat unsigned _Fract
unsigned long _Fract and
_Sat unsigned long _Fract
unsigned long long _Fract
and _Sat unsigned long long _Fract
short _Accum and
_Sat short _Accum
_Accum and _Sat _Accum
long _Accum and
_Sat long _Accum
long long _Accum and
_Sat long long _Accum
unsigned short _Accum and
_Sat unsigned short _Accum
unsigned _Accum and
_Sat unsigned _Accum
unsigned long _Accum and
_Sat unsigned long _Accum
unsigned long long _Accum
and _Sat unsigned long long _Accum
GCC support of fixed-point types as specified by the draft technical report is incomplete:
Fixed-point types are supported by the DWARF debug information format.
As an extension, GNU C supports named address spaces as defined in the N1275 draft of ISO/IEC DTR 18037. Support for named address spaces in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. At present, only the AVR, M32C, PRU, RL78, and x86 targets support address spaces other than the generic address space.
Address space identifiers may be used exactly like any other C type
qualifier (e.g., const or volatile). See the N1275
document for more details.
On the AVR target, there are several address spaces that can be used
in order to put read-only data into the flash memory and access that
data by means of the special instructions LPM or ELPM
needed to read from flash.
Devices belonging to avrtiny and avrxmega3 can access
flash memory by means of LD* instructions because the flash
memory is mapped into the RAM address space. There is no need
for language extensions like __flash or attribute
progmem.
The default linker description files for these devices cater for that
feature and .rodata stays in flash: The compiler just generates
LD* instructions, and the linker script adds core specific
offsets to all .rodata symbols: 0x4000 in the case of
avrtiny and 0x8000 in the case of avrxmega3.
See AVR Options for a list of respective devices.
For devices not in avrtiny or avrxmega3,
any data including read-only data is located in RAM (the generic
address space) because flash memory is not visible in the RAM address
space. In order to locate read-only data in flash memory and
to generate the right instructions to access this data without
using (inline) assembler code, special address spaces are needed.
__flash__flash qualifier locates data in the
.progmem.data section. Data is read using the LPM
instruction. Pointers to this address space are 16 bits wide.
__flash1__flash2__flash3__flash4__flash5.progmemN.data where N refers to
address space __flashN.
The compiler sets the RAMPZ segment register appropriately
before reading data by means of the ELPM instruction.
__memxRAMPZ set according to the high byte of the address.
See __builtin_avr_flash_segment.
Objects in this address space are located in .progmemx.data.
Example
char my_read (const __flash char ** p)
{
/* p is a pointer to RAM that points to a pointer to flash.
The first indirection of p reads that flash pointer
from RAM and the second indirection reads a char from this
flash address. */
return **p;
}
/* Locate array[] in flash memory */
const __flash int array[] = { 3, 5, 7, 11, 13, 17, 19 };
int i = 1;
int main (void)
{
/* Return 17 by reading from flash memory */
return array[array[i]];
}
For each named address space supported by avr-gcc there is an equally named but uppercase built-in macro defined. The purpose is to facilitate testing if respective address space support is available or not:
#ifdef __FLASH
const __flash int var = 1;
int read_var (void)
{
return var;
}
#else
#include <avr/pgmspace.h> /* From AVR-LibC */
const int var PROGMEM = 1;
int read_var (void)
{
return (int) pgm_read_word (&var);
}
#endif /* __FLASH */
Notice that attribute progmem
locates data in flash but
accesses to these data read from generic address space, i.e.
from RAM,
so that you need special accessors like pgm_read_byte
from AVR-LibC
together with attribute progmem.
Limitations and caveats
__flash or __flashN address spaces
shows undefined behavior. The only address space that
supports reading across the 64 KiB flash segment boundaries is
__memx.
__flashN address spaces
you must arrange your linker script to locate the
.progmemN.data sections according to your needs.
const, i.e. as read-only data.
This still applies if the data in one of these address
spaces like software version number or calibration lookup table are intended to
be changed after load time by, say, a boot loader. In this case
the right qualification is const volatile so that the compiler
must not optimize away known values or insert them
as immediates into operands of instructions.
pfoo
located in static storage with a 24-bit address:
extern const __memx char foo;
const __memx void *pfoo = &foo;
progmem is supported but works differently,
see AVR Variable Attributes.
On the M32C target, with the R8C and M16C CPU variants, variables
qualified with __far are accessed using 32-bit addresses in
order to access memory beyond the first 64 Ki bytes. If
__far is used with the M32CM or M32C CPU variants, it has no
effect.
On the PRU target, variables qualified with __regio_symbol are
aliases used to access the special I/O CPU registers. They must be
declared as extern because such variables will not be allocated in
any data memory. They must also be marked as volatile, and can
only be 32-bit integer types. The only names those variables can have
are __R30 and __R31, representing respectively the
R30 and R31 special I/O CPU registers. Hence the following
example is the only valid usage of __regio_symbol:
extern volatile __regio_symbol uint32_t __R30;
extern volatile __regio_symbol uint32_t __R31;
On the RL78 target, variables qualified with __far are accessed
with 32-bit pointers (20-bit addresses) rather than the default 16-bit
addresses. Non-far variables are assumed to appear in the topmost
64 KiB of the address space.
On the x86 target, variables may be declared as being relative
to the %fs or %gs segments.
__seg_fs__seg_gsThe respective segment base must be set via some method specific to
the operating system. Rather than require an expensive system call
to retrieve the segment base, these address spaces are not considered
to be subspaces of the generic (flat) address space. This means that
explicit casts are required to convert pointers between these address
spaces and the generic address space. In practice the application
should cast to uintptr_t and apply the segment base offset
that it installed previously.
The preprocessor symbols __SEG_FS and __SEG_GS are
defined when these address spaces are supported.
Declaring zero-length arrays is allowed in GNU C as an extension. A zero-length array can be useful as the last element of a structure that is really a header for a variable-length object:
struct line {
int length;
char contents[0];
};
struct line *thisline = (struct line *)
malloc (sizeof (struct line) + this_length);
thisline->length = this_length;
Although the size of a zero-length array is zero, an array member of this kind may increase the size of the enclosing type as a result of tail padding. The offset of a zero-length array member from the beginning of the enclosing structure is the same as the offset of an array with one or more elements of the same type. The alignment of a zero-length array is the same as the alignment of its elements.
Declaring zero-length arrays in other contexts, including as interior members of structure objects or as non-member objects, is discouraged. Accessing elements of zero-length arrays declared in such contexts is undefined and may be diagnosed.
In the absence of the zero-length array extension, in ISO C90
the contents array in the example above would typically be declared
to have a single element. Unlike a zero-length array which only contributes
to the size of the enclosing structure for the purposes of alignment,
a one-element array always occupies at least as much space as a single
object of the type. Although using one-element arrays this way is
discouraged, GCC handles accesses to trailing one-element array members
analogously to zero-length arrays.
The preferred mechanism to declare variable-length types like
struct line above is the ISO C99 flexible array member,
with slightly different syntax and semantics:
contents[] without
the 0.
sizeof
operator may not be applied. As a quirk of the original implementation
of zero-length arrays, sizeof evaluates to zero.
struct that is otherwise non-empty.
Non-empty initialization of zero-length arrays is treated like any case where there are more initializer elements than the array holds, in that a suitable warning about “excess elements in array” is given, and the excess elements (all of them, in this case) are ignored.
GCC allows static initialization of flexible array members.
This is equivalent to defining a new structure containing the original
structure followed by an array of sufficient size to contain the data.
E.g. in the following, f1 is constructed as if it were declared
like f2.
struct f1 {
int x; int y[];
} f1 = { 1, { 2, 3, 4 } };
struct f2 {
struct f1 f1; int data[3];
} f2 = { { 1 }, { 2, 3, 4 } };
The convenience of this extension is that f1 has the desired
type, eliminating the need to consistently refer to f2.f1.
This has symmetry with normal static arrays, in that an array of
unknown size is also written with [].
Of course, this extension only makes sense if the extra data comes at the end of a top-level object, as otherwise we would be overwriting data at subsequent offsets. To avoid undue complication and confusion with initialization of deeply nested arrays, we simply disallow any non-empty initialization except when the structure is the top-level object. For example:
struct foo { int x; int y[]; };
struct bar { struct foo z; };
struct foo a = { 1, { 2, 3, 4 } }; // Valid.
struct bar b = { { 1, { 2, 3, 4 } } }; // Invalid.
struct bar c = { { 1, { } } }; // Valid.
struct foo d[1] = { { 1, { 2, 3, 4 } } }; // Invalid.
GCC permits a C structure to have no members:
struct empty {
};
The structure has size zero. In C++, empty structures are part
of the language. G++ treats empty structures as if they had a single
member of type char.
Variable-length automatic arrays are allowed in ISO C99, and as an extension GCC accepts them in C90 mode and in C++. These arrays are declared like any other automatic arrays, but with a length that is not a constant expression. The storage is allocated at the point of declaration and deallocated when the block scope containing the declaration exits. For example:
FILE *
concat_fopen (char *s1, char *s2, char *mode)
{
char str[strlen (s1) + strlen (s2) + 1];
strcpy (str, s1);
strcat (str, s2);
return fopen (str, mode);
}
Jumping or breaking out of the scope of the array name deallocates the storage. Jumping into the scope is not allowed; you get an error message for it.
As an extension, GCC accepts variable-length arrays as a member of a structure or a union. For example:
void
foo (int n)
{
struct S { int x[n]; };
}
You can use the function alloca to get an effect much like
variable-length arrays. The function alloca is available in
many other C implementations (but not in all). On the other hand,
variable-length arrays are more elegant.
There are other differences between these two methods. Space allocated
with alloca exists until the containing function returns.
The space for a variable-length array is deallocated as soon as the array
name's scope ends, unless you also use alloca in this scope.
You can also use variable-length arrays as arguments to functions:
struct entry
tester (int len, char data[len][len])
{
/* ... */
}
The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
sizeof.
If you want to pass the array first and the length afterward, you can use a forward declaration in the parameter list—another GNU extension.
struct entry
tester (int len; char data[len][len], int len)
{
/* ... */
}
The ‘int len’ before the semicolon is a parameter forward
declaration, and it serves the purpose of making the name len
known when the declaration of data is parsed.
You can write any number of such parameter forward declarations in the parameter list. They can be separated by commas or semicolons, but the last one must end with a semicolon, which is followed by the “real” parameter declarations. Each forward declaration must match a “real” declaration in parameter name and data type. ISO C99 does not support parameter forward declarations.
In the ISO C standard of 1999, a macro can be declared to accept a variable number of arguments much as a function can. The syntax for defining the macro is similar to that of a function. Here is an example:
#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)
Here ‘...’ is a variable argument. In the invocation of
such a macro, it represents the zero or more tokens until the closing
parenthesis that ends the invocation, including any commas. This set of
tokens replaces the identifier __VA_ARGS__ in the macro body
wherever it appears. See the CPP manual for more information.
GCC has long supported variadic macros, and used a different syntax that allowed you to give a name to the variable arguments just like any other argument. Here is an example:
#define debug(format, args...) fprintf (stderr, format, args)
This is in all ways equivalent to the ISO C example above, but arguably more readable and descriptive.
GNU CPP has two further variadic macro extensions, and permits them to be used with either of the above forms of macro definition.
In standard C, you are not allowed to leave the variable argument out entirely; but you are allowed to pass an empty argument. For example, this invocation is invalid in ISO C, because there is no comma after the string:
debug ("A message")
GNU CPP permits you to completely omit the variable arguments in this way. In the above examples, the compiler would complain, though since the expansion of the macro still has the extra comma after the format string.
To help solve this problem, CPP behaves specially for variable arguments used with the token paste operator, ‘##’. If instead you write
#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)
and if the variable arguments are omitted or empty, the ‘##’ operator causes the preprocessor to remove the comma before it. If you do provide some variable arguments in your macro invocation, GNU CPP does not complain about the paste operation and instead places the variable arguments after the comma. Just like any other pasted macro argument, these arguments are not macro expanded.
The preprocessor treatment of escaped newlines is more relaxed than that specified by the C90 standard, which requires the newline to immediately follow a backslash. GCC's implementation allows whitespace in the form of spaces, horizontal and vertical tabs, and form feeds between the backslash and the subsequent newline. The preprocessor issues a warning, but treats it as a valid escaped newline and combines the two lines to form a single logical line. This works within comments and tokens, as well as between tokens. Comments are not treated as whitespace for the purposes of this relaxation, since they have not yet been replaced with spaces.
In ISO C99, arrays that are not lvalues still decay to pointers, and may be subscripted, although they may not be modified or used after the next sequence point and the unary ‘&’ operator may not be applied to them. As an extension, GNU C allows such arrays to be subscripted in C90 mode, though otherwise they do not decay to pointers outside C99 mode. For example, this is valid in GNU C though not valid in C90:
struct foo {int a[4];};
struct foo f();
bar (int index)
{
return f().a[index];
}
void- and Function-Pointers
In GNU C, addition and subtraction operations are supported on pointers to
void and on pointers to functions. This is done by treating the
size of a void or of a function as 1.
A consequence of this is that sizeof is also allowed on void
and on function types, and returns 1.
The option -Wpointer-arith requests a warning if these extensions are used.
Standard C requires that pointer types used with va_arg in
functions with variable argument lists either must be compatible with
that of the actual argument, or that one type must be a pointer to
void and the other a pointer to a character type. GNU C
implements the POSIX XSI extension that additionally permits the use
of va_arg with a pointer type to receive arguments of any other
pointer type.
In particular, in GNU C ‘va_arg (ap, void *)’ can safely be used to consume an argument of any pointer type.
In GNU C, pointers to arrays with qualifiers work similar to pointers
to other qualified types. For example, a value of type int (*)[5]
can be used to initialize a variable of type const int (*)[5].
These types are incompatible in ISO C because the const qualifier
is formally attached to the element type of the array and not the
array itself.
extern void
transpose (int N, int M, double out[M][N], const double in[N][M]);
double x[3][2];
double y[2][3];
...
transpose(3, 2, y, x);
As in standard C++ and ISO C99, the elements of an aggregate initializer for an automatic variable are not required to be constant expressions in GNU C. Here is an example of an initializer with run-time varying elements:
foo (float f, float g)
{
float beat_freqs[2] = { f-g, f+g };
/* ... */
}
A compound literal looks like a cast of a brace-enclosed aggregate initializer list. Its value is an object of the type specified in the cast, containing the elements specified in the initializer. Unlike the result of a cast, a compound literal is an lvalue. ISO C99 and later support compound literals. As an extension, GCC supports compound literals also in C90 mode and in C++, although as explained below, the C++ semantics are somewhat different.
Usually, the specified type of a compound literal is a structure. Assume
that struct foo and structure are declared as shown:
struct foo {int a; char b[2];} structure;
Here is an example of constructing a struct foo with a compound literal:
structure = ((struct foo) {x + y, 'a', 0});
This is equivalent to writing the following:
{
struct foo temp = {x + y, 'a', 0};
structure = temp;
}
You can also construct an array, though this is dangerous in C++, as explained below. If all the elements of the compound literal are (made up of) simple constant expressions suitable for use in initializers of objects of static storage duration, then the compound literal can be coerced to a pointer to its first element and used in such an initializer, as shown here:
char **foo = (char *[]) { "x", "y", "z" };
Compound literals for scalar types and union types are also allowed. In
the following example the variable i is initialized to the value
2, the result of incrementing the unnamed object created by
the compound literal.
int i = ++(int) { 1 };
As a GNU extension, GCC allows initialization of objects with static storage duration by compound literals (which is not possible in ISO C99 because the initializer is not a constant). It is handled as if the object were initialized only with the brace-enclosed list if the types of the compound literal and the object match. The elements of the compound literal must be constant. If the object being initialized has array type of unknown size, the size is determined by the size of the compound literal.
static struct foo x = (struct foo) {1, 'a', 'b'};
static int y[] = (int []) {1, 2, 3};
static int z[] = (int [3]) {1};
The above lines are equivalent to the following:
static struct foo x = {1, 'a', 'b'};
static int y[] = {1, 2, 3};
static int z[] = {1, 0, 0};
In C, a compound literal designates an unnamed object with static or
automatic storage duration. In C++, a compound literal designates a
temporary object that only lives until the end of its full-expression.
As a result, well-defined C code that takes the address of a subobject
of a compound literal can be undefined in C++, so G++ rejects
the conversion of a temporary array to a pointer. For instance, if
the array compound literal example above appeared inside a function,
any subsequent use of foo in C++ would have undefined behavior
because the lifetime of the array ends after the declaration of foo.
As an optimization, G++ sometimes gives array compound literals longer
lifetimes: when the array either appears outside a function or has
a const-qualified type. If foo and its initializer had
elements of type char *const rather than char *, or if
foo were a global variable, the array would have static storage
duration. But it is probably safest just to avoid the use of array
compound literals in C++ code.
Standard C90 requires the elements of an initializer to appear in a fixed order, the same as the order of the elements in the array or structure being initialized.
In ISO C99 you can give the elements in any order, specifying the array indices or structure field names they apply to, and GNU C allows this as an extension in C90 mode as well. This extension is not implemented in GNU C++.
To specify an array index, write ‘[index] =’ before the element value. For example,
int a[6] = { [4] = 29, [2] = 15 };
is equivalent to
int a[6] = { 0, 0, 15, 0, 29, 0 };
The index values must be constant expressions, even if the array being initialized is automatic.
An alternative syntax for this that has been obsolete since GCC 2.5 but GCC still accepts is to write ‘[index]’ before the element value, with no ‘=’.
To initialize a range of elements to the same value, write ‘[first ... last] = value’. This is a GNU extension. For example,
int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };
If the value in it has side effects, the side effects happen only once, not for each initialized field by the range initializer.
Note that the length of the array is the highest value specified plus one.
In a structure initializer, specify the name of a field to initialize with ‘.fieldname =’ before the element value. For example, given the following structure,
struct point { int x, y; };
the following initialization
struct point p = { .y = yvalue, .x = xvalue };
is equivalent to
struct point p = { xvalue, yvalue };
Another syntax that has the same meaning, obsolete since GCC 2.5, is ‘fieldname:’, as shown here:
struct point p = { y: yvalue, x: xvalue };
Omitted fields are implicitly initialized the same as for objects that have static storage duration.
The ‘[index]’ or ‘.fieldname’ is known as a designator. You can also use a designator (or the obsolete colon syntax) when initializing a union, to specify which element of the union should be used. For example,
union foo { int i; double d; };
union foo f = { .d = 4 };
converts 4 to a double to store it in the union using
the second element. By contrast, casting 4 to type union foo
stores it into the union as the integer i, since it is
an integer. See Cast to Union.
You can combine this technique of naming elements with ordinary C initialization of successive elements. Each initializer element that does not have a designator applies to the next consecutive element of the array or structure. For example,
int a[6] = { [1] = v1, v2, [4] = v4 };
is equivalent to
int a[6] = { 0, v1, v2, 0, v4, 0 };
Labeling the elements of an array initializer is especially useful
when the indices are characters or belong to an enum type.
For example:
int whitespace[256]
= { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };
You can also write a series of ‘.fieldname’ and ‘[index]’ designators before an ‘=’ to specify a nested subobject to initialize; the list is taken relative to the subobject corresponding to the closest surrounding brace pair. For example, with the ‘struct point’ declaration above:
struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };
If the same field is initialized multiple times, or overlapping fields of a union are initialized, the value from the last initialization is used. When a field of a union is itself a structure, the entire structure from the last field initialized is used. If any previous initializer has side effect, it is unspecified whether the side effect happens or not. Currently, GCC discards the side-effecting initializer expressions and issues a warning.
You can specify a range of consecutive values in a single case label,
like this:
case low ... high:
This has the same effect as the proper number of individual case
labels, one for each integer value from low to high, inclusive.
This feature is especially useful for ranges of ASCII character codes:
case 'A' ... 'Z':
Be careful: Write spaces around the ..., for otherwise
it may be parsed wrong when you use it with integer values. For example,
write this:
case 1 ... 5:
rather than this:
case 1...5:
A cast to a union type is a C extension not available in C++. It looks
just like ordinary casts with the constraint that the type specified is
a union type. You can specify the type either with the union
keyword or with a typedef name that refers to a union. The result
of a cast to a union is a temporary rvalue of the union type with a member
whose type matches that of the operand initialized to the value of
the operand. The effect of a cast to a union is similar to a compound
literal except that it yields an rvalue like standard casts do.
See Compound Literals.
Expressions that may be cast to the union type are those whose type matches at least one of the members of the union. Thus, given the following union and variables:
union foo { int i; double d; };
int x;
double y;
union foo z;
both x and y can be cast to type union foo and
the following assignments
z = (union foo) x;
z = (union foo) y;
are shorthand equivalents of these
z = (union foo) { .i = x };
z = (union foo) { .d = y };
However, (union foo) FLT_MAX; is not a valid cast because the union
has no member of type float.
Using the cast as the right-hand side of an assignment to a variable of union type is equivalent to storing in a member of the union with the same type
union foo u;
/* ... */
u = (union foo) x == u.i = x
u = (union foo) y == u.d = y
You can also use the union cast as a function argument:
void hack (union foo);
/* ... */
hack ((union foo) x);
ISO C99 and ISO C++ allow declarations and code to be freely mixed within compound statements. ISO C2X allows labels to be placed before declarations and at the end of a compound statement. As an extension, GNU C also allows all this in C90 mode. For example, you could do:
int i;
/* ... */
i++;
int j = i + 2;
Each identifier is visible from where it is declared until the end of the enclosing block.
In GNU C and C++, you can use function attributes to specify certain
function properties that may help the compiler optimize calls or
check code more carefully for correctness. For example, you
can use attributes to specify that a function never returns
(noreturn), returns a value depending only on the values of
its arguments (const), or has printf-style arguments
(format).
You can also use attributes to control memory placement, code generation options or call/return conventions within the function being annotated. Many of these attributes are target-specific. For example, many targets support attributes for defining interrupt handler functions, which typically must follow special register usage and return conventions. Such attributes are described in the subsection for each target. However, a considerable number of attributes are supported by most, if not all targets. Those are described in the Common Function Attributes section.
Function attributes are introduced by the __attribute__ keyword
in the declaration of a function, followed by an attribute specification
enclosed in double parentheses. You can specify multiple attributes in
a declaration by separating them by commas within the double parentheses
or by immediately following one attribute specification with another.
See Attribute Syntax, for the exact rules on attribute syntax and
placement. Compatible attribute specifications on distinct declarations
of the same function are merged. An attribute specification that is not
compatible with attributes already applied to a declaration of the same
function is ignored with a warning.
Some function attributes take one or more arguments that refer to
the function's parameters by their positions within the function parameter
list. Such attribute arguments are referred to as positional arguments.
Unless specified otherwise, positional arguments that specify properties
of parameters with pointer types can also specify the same properties of
the implicit C++ this argument in non-static member functions, and
of parameters of reference to a pointer type. For ordinary functions,
position one refers to the first parameter on the list. In C++ non-static
member functions, position one refers to the implicit this pointer.
The same restrictions and effects apply to function attributes used with
ordinary functions or C++ member functions.
GCC also supports attributes on
variable declarations (see Variable Attributes),
labels (see Label Attributes),
enumerators (see Enumerator Attributes),
statements (see Statement Attributes),
types (see Type Attributes),
and on field declarations (for tainted_args).
There is some overlap between the purposes of attributes and pragmas
(see Pragmas Accepted by GCC). It has been
found convenient to use __attribute__ to achieve a natural
attachment of attributes to their corresponding declarations, whereas
#pragma is of use for compatibility with other compilers
or constructs that do not naturally form part of the grammar.
In addition to the attributes documented here, GCC plugins may provide their own attributes.
The following attributes are supported on most targets.
access (access-mode, ref-index)access (access-mode, ref-index, size-index)access attribute enables the detection of invalid or unsafe
accesses by functions to which they apply or their callers, as well as
write-only accesses to objects that are never read from. Such accesses
may be diagnosed by warnings such as -Wstringop-overflow,
-Wuninitialized, -Wunused, and others.
The access attribute specifies that a function to whose by-reference
arguments the attribute applies accesses the referenced object according to
access-mode. The access-mode argument is required and must be
one of four names: read_only, read_write, write_only,
or none. The remaining two are positional arguments.
The required ref-index positional argument denotes a function
argument of pointer (or in C++, reference) type that is subject to
the access. The same pointer argument can be referenced by at most one
distinct access attribute.
The optional size-index positional argument denotes a function
argument of integer type that specifies the maximum size of the access.
The size is the number of elements of the type referenced by ref-index,
or the number of bytes when the pointer type is void*. When no
size-index argument is specified, the pointer argument must be either
null or point to a space that is suitably aligned and large for at least one
object of the referenced type (this implies that a past-the-end pointer is
not a valid argument). The actual size of the access may be less but it
must not be more.
The read_only access mode specifies that the pointer to which it
applies is used to read the referenced object but not write to it. Unless
the argument specifying the size of the access denoted by size-index
is zero, the referenced object must be initialized. The mode implies
a stronger guarantee than the const qualifier which, when cast away
from a pointer, does not prevent the pointed-to object from being modified.
Examples of the use of the read_only access mode is the argument to
the puts function, or the second and third arguments to
the memcpy function.
__attribute__ ((access (read_only, 1)))
int puts (const char*);
__attribute__ ((access (read_only, 2, 3)))
void* memcpy (void*, const void*, size_t);
The read_write access mode applies to arguments of pointer types
without the const qualifier. It specifies that the pointer to which
it applies is used to both read and write the referenced object. Unless
the argument specifying the size of the access denoted by size-index
is zero, the object referenced by the pointer must be initialized. An example
of the use of the read_write access mode is the first argument to
the strcat function.
__attribute__ ((access (read_write, 1), access (read_only, 2)))
char* strcat (char*, const char*);
The write_only access mode applies to arguments of pointer types
without the const qualifier. It specifies that the pointer to which
it applies is used to write to the referenced object but not read from it.
The object referenced by the pointer need not be initialized. An example
of the use of the write_only access mode is the first argument to
the strcpy function, or the first two arguments to the fgets
function.
__attribute__ ((access (write_only, 1), access (read_only, 2)))
char* strcpy (char*, const char*);
__attribute__ ((access (write_only, 1, 2), access (read_write, 3)))
int fgets (char*, int, FILE*);
The access mode none specifies that the pointer to which it applies
is not used to access the referenced object at all. Unless the pointer is
null the pointed-to object must exist and have at least the size as denoted
by the size-index argument. When the optional size-index
argument is omitted for an argument of void* type the actual pointer
agument is ignored. The referenced object need not be initialized.
The mode is intended to be used as a means to help validate the expected
object size, for example in functions that call __builtin_object_size.
See Object Size Checking.
Note that the access attribute merely specifies how an object
referenced by the pointer argument can be accessed; it does not imply that
an access will happen. Also, the access attribute does not
imply the attribute nonnull; it may be appropriate to add both attributes
at the declaration of a function that unconditionally manipulates a buffer via
a pointer argument. See the nonnull attribute for more information and
caveats.
alias ("target")alias attribute causes the declaration to be emitted as an alias
for another symbol, which must have been previously declared with the same
type, and for variables, also the same size and alignment. Declaring an alias
with a different type than the target is undefined and may be diagnosed. As
an example, the following declarations:
void __f () { /* Do something. */; }
void f () __attribute__ ((weak, alias ("__f")));
define ‘f’ to be a weak alias for ‘__f’. In C++, the mangled name for the target must be used. It is an error if ‘__f’ is not defined in the same translation unit.
This attribute requires assembler and object file support, and may not be available on all targets.
alignedaligned (alignment)aligned attribute specifies a minimum alignment for
the first instruction of the function, measured in bytes. When specified,
alignment must be an integer constant power of 2. Specifying no
alignment argument implies the ideal alignment for the target.
The __alignof__ operator can be used to determine what that is
(see Alignment). The attribute has no effect when a definition for
the function is not provided in the same translation unit.
The attribute cannot be used to decrease the alignment of a function previously declared with a more restrictive alignment; only to increase it. Attempts to do otherwise are diagnosed. Some targets specify a minimum default alignment for functions that is greater than 1. On such targets, specifying a less restrictive alignment is silently ignored. Using the attribute overrides the effect of the -falign-functions (see Optimize Options) option for this function.
Note that the effectiveness of aligned attributes may be
limited by inherent limitations in the system linker
and/or object file format. On some systems, the
linker is only able to arrange for functions to be aligned up to a
certain maximum alignment. (For some linkers, the maximum supported
alignment may be very very small.) See your linker documentation for
further information.
The aligned attribute can also be used for variables and fields
(see Variable Attributes.)
alloc_align (position)alloc_align attribute may be applied to a function that
returns a pointer and takes at least one argument of an integer or
enumerated type.
It indicates that the returned pointer is aligned on a boundary given
by the function argument at position. Meaningful alignments are
powers of 2 greater than one. GCC uses this information to improve
pointer alignment analysis.
The function parameter denoting the allocated alignment is specified by one constant integer argument whose number is the argument of the attribute. Argument numbering starts at one.
For instance,
void* my_memalign (size_t, size_t) __attribute__ ((alloc_align (1)));
declares that my_memalign returns memory with minimum alignment
given by parameter 1.
alloc_size (position)alloc_size (position-1, position-2)alloc_size attribute may be applied to a function that
returns a pointer and takes at least one argument of an integer or
enumerated type.
It indicates that the returned pointer points to memory whose size is
given by the function argument at position-1, or by the product
of the arguments at position-1 and position-2. Meaningful
sizes are positive values less than PTRDIFF_MAX. GCC uses this
information to improve the results of __builtin_object_size.
The function parameter(s) denoting the allocated size are specified by one or two integer arguments supplied to the attribute. The allocated size is either the value of the single function argument specified or the product of the two function arguments specified. Argument numbering starts at one for ordinary functions, and at two for C++ non-static member functions.
For instance,
void* my_calloc (size_t, size_t) __attribute__ ((alloc_size (1, 2)));
void* my_realloc (void*, size_t) __attribute__ ((alloc_size (2)));
declares that my_calloc returns memory of the size given by
the product of parameter 1 and 2 and that my_realloc returns memory
of the size given by parameter 2.
always_inlineartificialassume_aligned (alignment)assume_aligned (alignment, offset)assume_aligned attribute may be applied to a function that
returns a pointer. It indicates that the returned pointer is aligned
on a boundary given by alignment. If the attribute has two
arguments, the second argument is misalignment offset. Meaningful
values of alignment are powers of 2 greater than one. Meaningful
values of offset are greater than zero and less than alignment.
For instance
void* my_alloc1 (size_t) __attribute__((assume_aligned (16)));
void* my_alloc2 (size_t) __attribute__((assume_aligned (32, 8)));
declares that my_alloc1 returns 16-byte aligned pointers and
that my_alloc2 returns a pointer whose value modulo 32 is equal
to 8.
coldcold attribute on functions is used to inform the compiler that
the function is unlikely to be executed. The function is optimized for
size rather than speed and on many targets it is placed into a special
subsection of the text section so all cold functions appear close together,
improving code locality of non-cold parts of program. The paths leading
to calls of cold functions within code are marked as unlikely by the branch
prediction mechanism. It is thus useful to mark functions used to handle
unlikely conditions, such as perror, as cold to improve optimization
of hot functions that do call marked functions in rare occasions.
When profile feedback is available, via -fprofile-use, cold functions are automatically detected and this attribute is ignored.
constconst attribute allows GCC to avoid emitting
some calls in repeated invocations of the function with the same argument
values.
For example,
int square (int) __attribute__ ((const));
tells GCC that subsequent calls to function square with the same
argument value can be replaced by the result of the first call regardless
of the statements in between.
The const attribute prohibits a function from reading objects
that affect its return value between successive invocations. However,
functions declared with the attribute can safely read objects that do
not change their return value, such as non-volatile constants.
The const attribute imposes greater restrictions on a function's
definition than the similar pure attribute. Declaring the same
function with both the const and the pure attribute is
diagnosed. Because a const function cannot have any observable side
effects it does not make sense for it to return void. Declaring
such a function is diagnosed.
Note that a function that has pointer arguments and examines the data
pointed to must not be declared const if the pointed-to
data might change between successive invocations of the function. In
general, since a function cannot distinguish data that might change
from data that cannot, const functions should never take pointer or,
in C++, reference arguments. Likewise, a function that calls a non-const
function usually must not be const itself.
constructordestructorconstructor (priority)destructor (priority)constructor attribute causes the function to be called
automatically before execution enters main (). Similarly, the
destructor attribute causes the function to be called
automatically after main () completes or exit () is
called. Functions with these attributes are useful for
initializing data that is used implicitly during the execution of
the program.
On some targets the attributes also accept an integer argument to
specify a priority to control the order in which constructor and
destructor functions are run. A constructor
with a smaller priority number runs before a constructor with a larger
priority number; the opposite relationship holds for destructors. Note
that priorities 0-100 are reserved. So, if you have a constructor that
allocates a resource and a destructor that deallocates the same
resource, both functions typically have the same priority. The
priorities for constructor and destructor functions are the same as
those specified for namespace-scope C++ objects (see C++ Attributes).
However, at present, the order in which constructors for C++ objects
with static storage duration and functions decorated with attribute
constructor are invoked is unspecified. In mixed declarations,
attribute init_priority can be used to impose a specific ordering.
Using the argument forms of the constructor and destructor
attributes on targets where the feature is not supported is rejected with
an error.
copycopy (function)copy attribute applies the set of attributes with which
function has been declared to the declaration of the function
to which the attribute is applied. The attribute is designed for
libraries that define aliases or function resolvers that are expected
to specify the same set of attributes as their targets. The copy
attribute can be used with functions, variables, or types. However,
the kind of symbol to which the attribute is applied (either function
or variable) must match the kind of symbol to which the argument refers.
The copy attribute copies only syntactic and semantic attributes
but not attributes that affect a symbol's linkage or visibility such as
alias, visibility, or weak. The deprecated
and target_clones attribute are also not copied.
See Common Type Attributes.
See Common Variable Attributes.
For example, the StrongAlias macro below makes use of the alias
and copy attributes to define an alias named alloc for function
allocate declared with attributes alloc_size, malloc, and
nothrow. Thanks to the __typeof__ operator the alias has
the same type as the target function. As a result of the copy
attribute the alias also shares the same attributes as the target.
#define StrongAlias(TargetFunc, AliasDecl) \
extern __typeof__ (TargetFunc) AliasDecl \
__attribute__ ((alias (#TargetFunc), copy (TargetFunc)));
extern __attribute__ ((alloc_size (1), malloc, nothrow))
void* allocate (size_t);
StrongAlias (allocate, alloc);
deprecateddeprecated (msg)deprecated attribute results in a warning if the function
is used anywhere in the source file. This is useful when identifying
functions that are expected to be removed in a future version of a
program. The warning also includes the location of the declaration
of the deprecated function, to enable users to easily find further
information about why the function is deprecated, or what they should
do instead. Note that the warnings only occurs for uses:
int old_fn () __attribute__ ((deprecated));
int old_fn ();
int (*fn_ptr)() = old_fn;
results in a warning on line 3 but not line 2. The optional msg argument, which must be a string, is printed in the warning if present.
The deprecated attribute can also be used for variables and
types (see Variable Attributes, see Type Attributes.)
The message attached to the attribute is affected by the setting of the -fmessage-length option.
unavailableunavailable (msg)unavailable attribute results in an error if the function
is used anywhere in the source file. This is useful when identifying
functions that have been removed from a particular variation of an
interface. Other than emitting an error rather than a warning, the
unavailable attribute behaves in the same manner as
deprecated.
The unavailable attribute can also be used for variables and
types (see Variable Attributes, see Type Attributes.)
error ("message")warning ("message")error or warning attribute
is used on a function declaration and a call to such a function
is not eliminated through dead code elimination or other optimizations,
an error or warning (respectively) that includes message is diagnosed.
This is useful
for compile-time checking, especially together with __builtin_constant_p
and inline functions where checking the inline function arguments is not
possible through extern char [(condition) ? 1 : -1]; tricks.
While it is possible to leave the function undefined and thus invoke
a link failure (to define the function with
a message in .gnu.warning* section),
when using these attributes the problem is diagnosed
earlier and with exact location of the call even in presence of inline
functions or when not emitting debugging information.
expected_throwThis hint is mostly ignored by the compiler. The only effect is when
it's applied to noreturn functions and
‘-fharden-control-flow-redundancy’ is enabled, and
‘-fhardcfr-check-noreturn-calls=not-always’ is not overridden.
externally_visibleIf -fwhole-program is used together with -flto and
gold is used as the linker plugin,
externally_visible attributes are automatically added to functions
(not variable yet due to a current gold issue)
that are accessed outside of LTO objects according to resolution file
produced by gold.
For other linkers that cannot generate resolution file,
explicit externally_visible attributes are still necessary.
fd_argfd_arg (N)fd_arg attribute may be applied to a function that takes an open
file descriptor at referenced argument N.
It indicates that the passed filedescriptor must not have been closed. Therefore, when the analyzer is enabled with -fanalyzer, the analyzer may emit a -Wanalyzer-fd-use-after-close diagnostic if it detects a code path in which a function with this attribute is called with a closed file descriptor.
The attribute also indicates that the file descriptor must have been checked for validity before usage. Therefore, analyzer may emit -Wanalyzer-fd-use-without-check diagnostic if it detects a code path in which a function with this attribute is called with a file descriptor that has not been checked for validity.
fd_arg_readfd_arg_read (N)fd_arg_read is identical to fd_arg, but with the additional
requirement that it might read from the file descriptor, and thus, the file
descriptor must not have been opened as write-only.
The analyzer may emit a -Wanalyzer-access-mode-mismatch
diagnostic if it detects a code path in which a function with this
attribute is called on a file descriptor opened with O_WRONLY.
fd_arg_writefd_arg_write (N)fd_arg_write is identical to fd_arg_read except that the
analyzer may emit a -Wanalyzer-access-mode-mismatch diagnostic if
it detects a code path in which a function with this attribute is called on a
file descriptor opened with O_RDONLY.
flattennoinline and similar are not
inlined. Whether the function itself is considered for inlining depends
on its size and the current inlining parameters.
format (archetype, string-index, first-to-check)format attribute specifies that a function takes printf,
scanf, strftime or strfmon style arguments that
should be type-checked against a format string. For example, the
declaration:
extern int
my_printf (void *my_object, const char *my_format, ...)
__attribute__ ((format (printf, 2, 3)));
causes the compiler to check the arguments in calls to my_printf
for consistency with the printf style format string argument
my_format.
The parameter archetype determines how the format string is
interpreted, and should be printf, scanf, strftime,
gnu_printf, gnu_scanf, gnu_strftime or
strfmon. (You can also use __printf__,
__scanf__, __strftime__ or __strfmon__.) On
MinGW targets, ms_printf, ms_scanf, and
ms_strftime are also present.
archetype values such as printf refer to the formats accepted
by the system's C runtime library,
while values prefixed with ‘gnu_’ always refer
to the formats accepted by the GNU C Library. On Microsoft Windows
targets, values prefixed with ‘ms_’ refer to the formats accepted by the
msvcrt.dll library.
The parameter string-index
specifies which argument is the format string argument (starting
from 1), while first-to-check is the number of the first
argument to check against the format string. For functions
where the arguments are not available to be checked (such as
vprintf), specify the third parameter as zero. In this case the
compiler only checks the format string for consistency. For
strftime formats, the third parameter is required to be zero.
Since non-static C++ methods have an implicit this argument, the
arguments of such methods should be counted from two, not one, when
giving values for string-index and first-to-check.
In the example above, the format string (my_format) is the second
argument of the function my_print, and the arguments to check
start with the third argument, so the correct parameters for the format
attribute are 2 and 3.
The format attribute allows you to identify your own functions
that take format strings as arguments, so that GCC can check the
calls to these functions for errors. The compiler always (unless
-ffreestanding or -fno-builtin is used) checks formats
for the standard library functions printf, fprintf,
sprintf, scanf, fscanf, sscanf, strftime,
vprintf, vfprintf and vsprintf whenever such
warnings are requested (using -Wformat), so there is no need to
modify the header file stdio.h. In C99 mode, the functions
snprintf, vsnprintf, vscanf, vfscanf and
vsscanf are also checked. Except in strictly conforming C
standard modes, the X/Open function strfmon is also checked as
are printf_unlocked and fprintf_unlocked.
See Options Controlling C Dialect.
For Objective-C dialects, NSString (or __NSString__) is
recognized in the same context. Declarations including these format attributes
are parsed for correct syntax, however the result of checking of such format
strings is not yet defined, and is not carried out by this version of the
compiler.
The target may also provide additional types of format checks. See Format Checks Specific to Particular Target Machines.
format_arg (string-index)format_arg attribute specifies that a function takes one or
more format strings for a printf, scanf, strftime or
strfmon style function and modifies it (for example, to translate
it into another language), so the result can be passed to a
printf, scanf, strftime or strfmon style
function (with the remaining arguments to the format function the same
as they would have been for the unmodified string). Multiple
format_arg attributes may be applied to the same function, each
designating a distinct parameter as a format string. For example, the
declaration:
extern char *
my_dgettext (char *my_domain, const char *my_format)
__attribute__ ((format_arg (2)));
causes the compiler to check the arguments in calls to a printf,
scanf, strftime or strfmon type function, whose
format string argument is a call to the my_dgettext function, for
consistency with the format string argument my_format. If the
format_arg attribute had not been specified, all the compiler
could tell in such calls to format functions would be that the format
string argument is not constant; this would generate a warning when
-Wformat-nonliteral is used, but the calls could not be checked
without the attribute.
In calls to a function declared with more than one format_arg
attribute, each with a distinct argument value, the corresponding
actual function arguments are checked against all format strings
designated by the attributes. This capability is designed to support
the GNU ngettext family of functions.
The parameter string-index specifies which argument is the format
string argument (starting from one). Since non-static C++ methods have
an implicit this argument, the arguments of such methods should
be counted from two.
The format_arg attribute allows you to identify your own
functions that modify format strings, so that GCC can check the
calls to printf, scanf, strftime or strfmon
type function whose operands are a call to one of your own function.
The compiler always treats gettext, dgettext, and
dcgettext in this manner except when strict ISO C support is
requested by -ansi or an appropriate -std option, or
-ffreestanding or -fno-builtin
is used. See Options Controlling C Dialect.
For Objective-C dialects, the format-arg attribute may refer to an
NSString reference for compatibility with the format attribute
above.
The target may also allow additional types in format-arg attributes.
See Format Checks Specific to Particular Target Machines.
gnu_inlineinline keyword. It directs GCC to treat the function
as if it were defined in gnu90 mode even when compiling in C99 or
gnu99 mode.
If the function is declared extern, then this definition of the
function is used only for inlining. In no case is the function
compiled as a standalone function, not even if you take its address
explicitly. Such an address becomes an external reference, as if you
had only declared the function, and had not defined it. This has
almost the effect of a macro. The way to use this is to put a
function definition in a header file with this attribute, and put
another copy of the function, without extern, in a library
file. The definition in the header file causes most calls to the
function to be inlined. If any uses of the function remain, they
refer to the single copy in the library. Note that the two
definitions of the functions need not be precisely the same, although
if they do not have the same effect your program may behave oddly.
In C, if the function is neither extern nor static, then
the function is compiled as a standalone function, as well as being
inlined where possible.
This is how GCC traditionally handled functions declared
inline. Since ISO C99 specifies a different semantics for
inline, this function attribute is provided as a transition
measure and as a useful feature in its own right. This attribute is
available in GCC 4.1.3 and later. It is available if either of the
preprocessor macros __GNUC_GNU_INLINE__ or
__GNUC_STDC_INLINE__ are defined. See An Inline Function is As Fast As a Macro.
In C++, this attribute does not depend on extern in any way,
but it still requires the inline keyword to enable its special
behavior.
hothot attribute on a function is used to inform the compiler that
the function is a hot spot of the compiled program. The function is
optimized more aggressively and on many targets it is placed into a special
subsection of the text section so all hot functions appear close together,
improving locality.
When profile feedback is available, via -fprofile-use, hot functions are automatically detected and this attribute is ignored.
ifunc ("resolver")ifunc attribute is used to mark a function as an indirect
function using the STT_GNU_IFUNC symbol type extension to the ELF
standard. This allows the resolution of the symbol value to be
determined dynamically at load time, and an optimized version of the
routine to be selected for the particular processor or other system
characteristics determined then. To use this attribute, first define
the implementation functions available, and a resolver function that
returns a pointer to the selected implementation function. The
implementation functions' declarations must match the API of the
function being implemented. The resolver should be declared to
be a function taking no arguments and returning a pointer to
a function of the same type as the implementation. For example:
void *my_memcpy (void *dst, const void *src, size_t len)
{
...
return dst;
}
static void * (*resolve_memcpy (void))(void *, const void *, size_t)
{
return my_memcpy; // we will just always select this routine
}
The exported header file declaring the function the user calls would contain:
extern void *memcpy (void *, const void *, size_t);
allowing the user to call memcpy as a regular function, unaware of
the actual implementation. Finally, the indirect function needs to be
defined in the same translation unit as the resolver function:
void *memcpy (void *, const void *, size_t)
__attribute__ ((ifunc ("resolve_memcpy")));
In C++, the ifunc attribute takes a string that is the mangled name
of the resolver function. A C++ resolver for a non-static member function
of class C should be declared to return a pointer to a non-member
function taking pointer to C as the first argument, followed by
the same arguments as of the implementation function. G++ checks
the signatures of the two functions and issues
a -Wattribute-alias warning for mismatches. To suppress a warning
for the necessary cast from a pointer to the implementation member function
to the type of the corresponding non-member function use
the -Wno-pmf-conversions option. For example:
class S
{
private:
int debug_impl (int);
int optimized_impl (int);
typedef int Func (S*, int);
static Func* resolver ();
public:
int interface (int);
};
int S::debug_impl (int) { /* ... */ }
int S::optimized_impl (int) { /* ... */ }
S::Func* S::resolver ()
{
int (S::*pimpl) (int)
= getenv ("DEBUG") ? &S::debug_impl : &S::optimized_impl;
// Cast triggers -Wno-pmf-conversions.
return reinterpret_cast<Func*>(pimpl);
}
int S::interface (int) __attribute__ ((ifunc ("_ZN1S8resolverEv")));
Indirect functions cannot be weak. Binutils version 2.20.1 or higher
and GNU C Library version 2.11.1 are required to use this feature.
interruptinterrupt_handlerleaflongjmp into the unit. Leaf functions
might still call functions from other compilation units and thus they
are not necessarily leaf in the sense that they contain no function
calls at all.
The attribute is intended for library functions to improve dataflow
analysis. The compiler takes the hint that any data not escaping the
current compilation unit cannot be used or modified by the leaf
function. For example, the sin function is a leaf function, but
qsort is not.
Note that leaf functions might indirectly run a signal handler defined
in the current compilation unit that uses static variables. Similarly,
when lazy symbol resolution is in effect, leaf functions might invoke
indirect functions whose resolver function or implementation function is
defined in the current compilation unit and uses static variables. There
is no standard-compliant way to write such a signal handler, resolver
function, or implementation function, and the best that you can do is to
remove the leaf attribute or mark all such static variables
volatile. Lastly, for ELF-based systems that support symbol
interposition, care should be taken that functions defined in the
current compilation unit do not unexpectedly interpose other symbols
based on the defined standards mode and defined feature test macros;
otherwise an inadvertent callback would be added.
The attribute has no effect on functions defined within the current compilation unit. This is to allow easy merging of multiple compilation units into one, for example, by using the link-time optimization. For this reason the attribute is not allowed on types to annotate indirect calls.
mallocmalloc (deallocator)malloc (deallocator, ptr-index)malloc indicates that a function is malloc-like,
i.e., that the pointer P returned by the function cannot alias any
other pointer valid when the function returns, and moreover no
pointers to valid objects occur in any storage addressed by P. In
addition, GCC predicts that a function with the attribute returns
non-null in most cases.
Independently, the form of the attribute with one or two arguments
associates deallocator as a suitable deallocation function for
pointers returned from the malloc-like function. ptr-index
denotes the positional argument to which when the pointer is passed in
calls to deallocator has the effect of deallocating it.
Using the attribute with no arguments is designed to improve optimization
by relying on the aliasing property it implies. Functions like malloc
and calloc have this property because they return a pointer to
uninitialized or zeroed-out, newly obtained storage. However, functions
like realloc do not have this property, as they may return pointers
to storage containing pointers to existing objects. Additionally, since
all such functions are assumed to return null only infrequently, callers
can be optimized based on that assumption.
Associating a function with a deallocator helps detect calls to
mismatched allocation and deallocation functions and diagnose them under
the control of options such as -Wmismatched-dealloc. It also
makes it possible to diagnose attempts to deallocate objects that were not
allocated dynamically, by -Wfree-nonheap-object. To indicate
that an allocation function both satisifies the nonaliasing property and
has a deallocator associated with it, both the plain form of the attribute
and the one with the deallocator argument must be used. The same
function can be both an allocator and a deallocator. Since inlining one
of the associated functions but not the other could result in apparent
mismatches, this form of attribute malloc is not accepted on inline
functions. For the same reason, using the attribute prevents both
the allocation and deallocation functions from being expanded inline.
For example, besides stating that the functions return pointers that do
not alias any others, the following declarations make fclose
a suitable deallocator for pointers returned from all functions except
popen, and pclose as the only suitable deallocator for
pointers returned from popen. The deallocator functions must
be declared before they can be referenced in the attribute.
int fclose (FILE*);
int pclose (FILE*);
__attribute__ ((malloc, malloc (fclose, 1)))
FILE* fdopen (int, const char*);
__attribute__ ((malloc, malloc (fclose, 1)))
FILE* fopen (const char*, const char*);
__attribute__ ((malloc, malloc (fclose, 1)))
FILE* fmemopen(void *, size_t, const char *);
__attribute__ ((malloc, malloc (pclose, 1)))
FILE* popen (const char*, const char*);
__attribute__ ((malloc, malloc (fclose, 1)))
FILE* tmpfile (void);
The warnings guarded by -fanalyzer respect allocation and
deallocation pairs marked with the malloc. In particular:
__attribute__ ((returns_nonnull)) to suppress these warnings.
For example:
char *xstrdup (const char *)
__attribute__((malloc (free), returns_nonnull));
The analyzer assumes that deallocators can gracefully handle the null
pointer. If this is not the case, the deallocator can be marked with
__attribute__((nonnull)) so that -fanalyzer can emit
a -Wanalyzer-possible-null-argument diagnostic for code paths
in which the deallocator is called with null.
no_icfno_instrument_functionno_profile_instrument_functionno_profile_instrument_function attribute on functions is used
to inform the compiler that it should not process any profile feedback based
optimization code instrumentation.
no_reorderno_reorder
against each other or top level assembler statements the executable.
The actual order in the program will depend on the linker command
line. Static variables marked like this are also not removed.
This has a similar effect
as the -fno-toplevel-reorder option, but only applies to the
marked symbols.
no_sanitize ("sanitize_option")no_sanitize attribute on functions is used
to inform the compiler that it should not do sanitization of any option
mentioned in sanitize_option. A list of values acceptable by
the -fsanitize option can be provided.
void __attribute__ ((no_sanitize ("alignment", "object-size")))
f () { /* Do something. */; }
void __attribute__ ((no_sanitize ("alignment,object-size")))
g () { /* Do something. */; }
no_sanitize_addressno_address_safety_analysisno_sanitize_address attribute on functions is used
to inform the compiler that it should not instrument memory accesses
in the function when compiling with the -fsanitize=address option.
The no_address_safety_analysis is a deprecated alias of the
no_sanitize_address attribute, new code should use
no_sanitize_address.
no_sanitize_threadno_sanitize_thread attribute on functions is used
to inform the compiler that it should not instrument memory accesses
in the function when compiling with the -fsanitize=thread option.
no_sanitize_undefinedno_sanitize_undefined attribute on functions is used
to inform the compiler that it should not check for undefined behavior
in the function when compiling with the -fsanitize=undefined option.
no_sanitize_coverageno_sanitize_coverage attribute on functions is used
to inform the compiler that it should not do coverage-guided
fuzzing code instrumentation (-fsanitize-coverage).
no_split_stackno_split_stack attribute do not have that prologue, and thus
may run with only a small amount of stack space available.
no_stack_limitnoclonenoinline asm ("");
(see Extended Asm) in the called function, to serve as a special side effect.
noipanoinline, noclone and
no_icf attributes. However, this attribute is not equivalent
to a combination of other attributes, because its purpose is to suppress
existing and future optimizations employing interprocedural analysis,
including those that do not have an attribute suitable for disabling
them individually. This attribute is supported mainly for the purpose
of testing the compiler.
nonnullnonnull (arg-index, ...)nonnull attribute may be applied to a function that takes at
least one argument of a pointer type. It indicates that the referenced
arguments must be non-null pointers. For instance, the declaration:
extern void *
my_memcpy (void *dest, const void *src, size_t len)
__attribute__((nonnull (1, 2)));
informs the compiler that, in calls to my_memcpy, arguments
dest and src must be non-null.
The attribute has an effect both on functions calls and function definitions.
For function calls:
For function definitions:
nonnull parameters cannot be null. This can
currently not be disabled other than by removing the nonnull
attribute.
If no arg-index is given to the nonnull attribute,
all pointer arguments are marked as non-null. To illustrate, the
following declaration is equivalent to the previous example:
extern void *
my_memcpy (void *dest, const void *src, size_t len)
__attribute__((nonnull));
nopltnoplt attribute is the counterpart to option -fno-plt.
Calls to functions marked with this attribute in position-independent code
do not use the PLT.
/* Externally defined function foo. */
int foo () __attribute__ ((noplt));
int
main (/* ... */)
{
/* ... */
foo ();
/* ... */
}
The noplt attribute on function foo
tells the compiler to assume that
the function foo is externally defined and that the call to
foo must avoid the PLT
in position-independent code.
In position-dependent code, a few targets also convert calls to functions that are marked to not use the PLT to use the GOT instead.
noreturnabort and exit,
cannot return. GCC knows this automatically. Some programs define
their own functions that never return. You can declare them
noreturn to tell the compiler this fact. For example,
void fatal () __attribute__ ((noreturn));
void
fatal (/* ... */)
{
/* ... */ /* Print error message. */ /* ... */
exit (1);
}
The noreturn keyword tells the compiler to assume that
fatal cannot return. It can then optimize without regard to what
would happen if fatal ever did return. This makes slightly
better code. More importantly, it helps avoid spurious warnings of
uninitialized variables.
The noreturn keyword does not affect the exceptional path when that
applies: a noreturn-marked function may still return to the caller
by throwing an exception or calling longjmp.
In order to preserve backtraces, GCC will never turn calls to
noreturn functions into tail calls.
Do not assume that registers saved by the calling function are
restored before calling the noreturn function.
It does not make sense for a noreturn function to have a return
type other than void.
nothrownothrow attribute is used to inform the compiler that a
function cannot throw an exception. For example, most functions in
the standard C library can be guaranteed not to throw an exception
with the notable exceptions of qsort and bsearch that
take function pointer arguments.
optimize (level, ...)optimize (string, ...)optimize attribute is used to specify that a function is to
be compiled with different optimization options than specified on the
command line. The optimize attribute arguments of a function behave
as if appended to the command-line.
Valid arguments are constant non-negative integers and
strings. Each numeric argument specifies an optimization level.
Each string argument consists of one or more comma-separated
substrings. Each substring that begins with the letter O refers
to an optimization option such as -O0 or -Os. Other
substrings are taken as suffixes to the -f prefix jointly
forming the name of an optimization option. See Optimize Options.
‘#pragma GCC optimize’ can be used to set optimization options for more than one function. See Function Specific Option Pragmas, for details about the pragma.
Providing multiple strings as arguments separated by commas to specify multiple options is equivalent to separating the option suffixes with a comma (‘,’) within a single string. Spaces are not permitted within the strings.
Not every optimization option that starts with the -f prefix
specified by the attribute necessarily has an effect on the function.
The optimize attribute should be used for debugging purposes only.
It is not suitable in production code.
patchable_function_entryThe patchable_function_entry function attribute can be used to
change the number of NOPs to any desired value. The two-value syntax
is the same as for the command-line switch
-fpatchable-function-entry=N,M, generating N NOPs, with
the function entry point before the Mth NOP instruction.
M defaults to 0 if omitted e.g. function entry point is before
the first NOP.
If patchable function entries are enabled globally using the command-line
option -fpatchable-function-entry=N,M, then you must disable
instrumentation on all functions that are part of the instrumentation
framework with the attribute patchable_function_entry (0)
to prevent recursion.
purepure attribute allows GCC to avoid emitting some calls in repeated
invocations of the function with the same argument values.
The pure attribute prohibits a function from modifying the state
of the program that is observable by means other than inspecting
the function's return value. However, functions declared with the pure
attribute can safely read any non-volatile objects, and modify the value of
objects in a way that does not affect their return value or the observable
state of the program.
For example,
int hash (char *) __attribute__ ((pure));
tells GCC that subsequent calls to the function hash with the same
string can be replaced by the result of the first call provided the state
of the program observable by hash, including the contents of the array
itself, does not change in between. Even though hash takes a non-const
pointer argument it must not modify the array it points to, or any other object
whose value the rest of the program may depend on. However, the caller may
safely change the contents of the array between successive calls to
the function (doing so disables the optimization). The restriction also
applies to member objects referenced by the this pointer in C++
non-static member functions.
Some common examples of pure functions are strlen or memcmp.
Interesting non-pure functions are functions with infinite loops or those
depending on volatile memory or other system resource, that may change between
consecutive calls (such as the standard C feof function in
a multithreading environment).
The pure attribute imposes similar but looser restrictions on
a function's definition than the const attribute: pure
allows the function to read any non-volatile memory, even if it changes
in between successive invocations of the function. Declaring the same
function with both the pure and the const attribute is
diagnosed. Because a pure function cannot have any observable side
effects it does not make sense for such a function to return void.
Declaring such a function is diagnosed.
returns_nonnullreturns_nonnull attribute specifies that the function
return value should be a non-null pointer. For instance, the declaration:
extern void *
mymalloc (size_t len) __attribute__((returns_nonnull));
lets the compiler optimize callers based on the knowledge that the return value will never be null.
returns_twicereturns_twice attribute tells the compiler that a function may
return more than one time. The compiler ensures that all registers
are dead before calling such a function and emits a warning about
the variables that may be clobbered after the second return from the
function. Examples of such functions are setjmp and vfork.
The longjmp-like counterpart of such function, if any, might need
to be marked with the noreturn attribute.
section ("section-name")text section.
Sometimes, however, you need additional sections, or you need certain
particular functions to appear in special sections. The section
attribute specifies that a function lives in a particular section.
For example, the declaration:
extern void foobar (void) __attribute__ ((section ("bar")));
puts the function foobar in the bar section.
Some file formats do not support arbitrary sections so the section
attribute is not available on all platforms.
If you need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.
sentinelsentinel (position)NULL. The attribute is only valid on
variadic functions. By default, the sentinel is expected to be the last
argument of the function call. If the optional position argument
is specified to the attribute, the sentinel must be located at
position counting backwards from the end of the argument list.
__attribute__ ((sentinel))
is equivalent to
__attribute__ ((sentinel(0)))
The attribute is automatically set with a position of 0 for the built-in
functions execl and execlp. The built-in function
execle has the attribute set with a position of 1.
A valid NULL in this context is defined as zero with any object
pointer type. If your system defines the NULL macro with
an integer type then you need to add an explicit cast. During
installation GCC replaces the system <stddef.h> header with
a copy that redefines NULL appropriately.
The warnings for missing or incorrect sentinels are enabled with -Wformat.
simdsimd("mask")The optional argument mask may have the value
notinbranch or inbranch,
and instructs the compiler to generate non-masked or masked
clones correspondingly. By default, all clones are generated.
If the attribute is specified and #pragma omp declare simd is
present on a declaration and the -fopenmp or -fopenmp-simd
switch is specified, then the attribute is ignored.
stack_protectno_stack_protectortarget (string, ...)target attribute
to specify that a function is to
be compiled with different target options than specified on the
command line. The original target command-line options are ignored.
One or more strings can be provided as arguments.
Each string consists of one or more comma-separated suffixes to
the -m prefix jointly forming the name of a machine-dependent
option. See Machine-Dependent Options.
The target attribute can be used for instance to have a function
compiled with a different ISA (instruction set architecture) than the
default. ‘#pragma GCC target’ can be used to specify target-specific
options for more than one function. See Function Specific Option Pragmas,
for details about the pragma.
For instance, on an x86, you could declare one function with the
target("sse4.1,arch=core2") attribute and another with
target("sse4a,arch=amdfam10"). This is equivalent to
compiling the first function with -msse4.1 and
-march=core2 options, and the second function with
-msse4a and -march=amdfam10 options. It is up to you
to make sure that a function is only invoked on a machine that
supports the particular ISA it is compiled for (for example by using
cpuid on x86 to determine what feature bits and architecture
family are used).
int core2_func (void) __attribute__ ((__target__ ("arch=core2")));
int sse3_func (void) __attribute__ ((__target__ ("sse3")));
Providing multiple strings as arguments separated by commas to specify multiple options is equivalent to separating the option suffixes with a comma (‘,’) within a single string. Spaces are not permitted within the strings.
The options supported are specific to each target; refer to x86 Function Attributes, PowerPC Function Attributes, ARM Function Attributes, AArch64 Function Attributes, Nios II Function Attributes, and S/390 Function Attributes for details.
symver ("name2@nodename")nodename portion should be the name of a
node specified in the version script supplied to the linker when building a
shared library. Versioned symbol must be defined and must be exported with
default visibility.
__attribute__ ((__symver__ ("foo@VERS_1"))) int
foo_v1 (void)
{
}
Will produce a .symver foo_v1, foo@VERS_1 directive in the assembler
output.
One can also define multiple version for a given symbol (starting from binutils 2.35).
__attribute__ ((__symver__ ("foo@VERS_2"), __symver__ ("foo@VERS_3")))
int symver_foo_v1 (void)
{
}
This example creates a symbol name symver_foo_v1
which will be version VERS_2 and VERS_3 of foo.
If you have an older release of binutils, then symbol alias needs to be used:
__attribute__ ((__symver__ ("foo@VERS_2")))
int foo_v1 (void)
{
return 0;
}
__attribute__ ((__symver__ ("foo@VERS_3")))
__attribute__ ((alias ("foo_v1")))
int symver_foo_v1 (void);
Finally if the parameter is "name2@@nodename" then in
addition to creating a symbol version (as if
"name2@nodename" was used) the version will be also used
to resolve name2 by the linker.
tainted_argstainted_args attribute is used to specify that a function is called
in a way that requires sanitization of its arguments, such as a system
call in an operating system kernel. Such a function can be considered part
of the “attack surface” of the program. The attribute can be used both
on function declarations, and on field declarations containing function
pointers. In the latter case, any function used as an initializer of
such a callback field will be treated as being called with tainted
arguments.
The analyzer will pay particular attention to such functions when both -fanalyzer and -fanalyzer-checker=taint are supplied, potentially issuing warnings guarded by -Wanalyzer-tainted-allocation-size, -Wanalyzer-tainted-array-index, -Wanalyzer-tainted-divisor, -Wanalyzer-tainted-offset, and -Wanalyzer-tainted-size.
target_clones (options)target_clones attribute is used to specify that a function
be cloned into multiple versions compiled with different target options
than specified on the command line. The supported options and restrictions
are the same as for target attribute.
For instance, on an x86, you could compile a function with
target_clones("sse4.1,avx"). GCC creates two function clones,
one compiled with -msse4.1 and another with -mavx.
On a PowerPC, you can compile a function with
target_clones("cpu=power9,default"). GCC will create two
function clones, one compiled with -mcpu=power9 and another
with the default options. GCC must be configured to use GLIBC 2.23 or
newer in order to use the target_clones attribute.
It also creates a resolver function (see
the ifunc attribute above) that dynamically selects a clone
suitable for current architecture. The resolver is created only if there
is a usage of a function with target_clones attribute.
Note that any subsequent call of a function without target_clone
from a target_clone caller will not lead to copying
(target clone) of the called function.
If you want to enforce such behaviour,
we recommend declaring the calling function with the flatten attribute?
unusedusedWhen applied to a member function of a C++ class template, the attribute also means that the function is instantiated if the class itself is instantiated.
retainsection attribute, or the -ffunction-sections
option), will be placed in new, unique sections.
This additional functionality requires Binutils version 2.36 or later.
visibility ("visibility_type")There are four supported visibility_type values: default, hidden, protected or internal visibility.
void __attribute__ ((visibility ("protected")))
f () { /* Do something. */; }
int i __attribute__ ((visibility ("hidden")));
The possible values of visibility_type correspond to the visibility settings in the ELF gABI.
defaultOn ELF, default visibility means that the declaration is visible to other modules and, in shared libraries, means that the declared entity may be overridden.
On Darwin, default visibility means that the declaration is visible to other modules.
Default visibility corresponds to “external linkage” in the language.
hiddeninternalprotectedAll visibilities are supported on many, but not all, ELF targets (supported when the assembler supports the ‘.visibility’ pseudo-op). Default visibility is supported everywhere. Hidden visibility is supported on Darwin targets.
The visibility attribute should be applied only to declarations that would otherwise have external linkage. The attribute should be applied consistently, so that the same entity should not be declared with different settings of the attribute.
In C++, the visibility attribute applies to types as well as functions and objects, because in C++ types have linkage. A class must not have greater visibility than its non-static data member types and bases, and class members default to the visibility of their class. Also, a declaration without explicit visibility is limited to the visibility of its type.
In C++, you can mark member functions and static member variables of a class with the visibility attribute. This is useful if you know a particular method or static member variable should only be used from one shared object; then you can mark it hidden while the rest of the class has default visibility. Care must be taken to avoid breaking the One Definition Rule; for example, it is usually not useful to mark an inline method as hidden without marking the whole class as hidden.
A C++ namespace declaration can also have the visibility attribute.
namespace nspace1 __attribute__ ((visibility ("protected")))
{ /* Do something. */; }
This attribute applies only to the particular namespace body, not to other definitions of the same namespace; it is equivalent to using ‘#pragma GCC visibility’ before and after the namespace definition (see Visibility Pragmas).
In C++, if a template argument has limited visibility, this restriction is implicitly propagated to the template instantiation. Otherwise, template instantiations and specializations default to the visibility of their template.
If both the template and enclosing class have explicit visibility, the visibility from the template is used.
warn_unused_resultwarn_unused_result attribute causes a warning to be emitted
if a caller of the function with this attribute does not use its
return value. This is useful for functions where not checking
the result is either a security problem or always a bug, such as
realloc.
int fn () __attribute__ ((warn_unused_result));
int foo ()
{
if (fn () < 0) return -1;
fn ();
return 0;
}
results in warning on line 5.
weakweak attribute causes a declaration of an external symbol
to be emitted as a weak symbol rather than a global. This is primarily
useful in defining library functions that can be overridden in user code,
though it can also be used with non-function declarations. The overriding
symbol must have the same type as the weak symbol. In addition, if it
designates a variable it must also have the same size and alignment as
the weak symbol. Weak symbols are supported for ELF targets, and also
for a.out targets when using the GNU assembler and linker.
weakrefweakref ("target")weakref attribute marks a declaration as a weak reference.
Without arguments, it should be accompanied by an alias attribute
naming the target symbol. Alternatively, target may be given as
an argument to weakref itself, naming the target definition of
the alias. The target must have the same type as the declaration.
In addition, if it designates a variable it must also have the same size
and alignment as the declaration. In either form of the declaration
weakref implicitly marks the declared symbol as weak. Without
a target given as an argument to weakref or to alias,
weakref is equivalent to weak (in that case the declaration
may be extern).
/* Given the declaration: */
extern int y (void);
/* the following... */
static int x (void) __attribute__ ((weakref ("y")));
/* is equivalent to... */
static int x (void) __attribute__ ((weakref, alias ("y")));
/* or, alternatively, to... */
static int x (void) __attribute__ ((weakref));
static int x (void) __attribute__ ((alias ("y")));
A weak reference is an alias that does not by itself require a
definition to be given for the target symbol. If the target symbol is
only referenced through weak references, then it becomes a weak
undefined symbol. If it is directly referenced, however, then such
strong references prevail, and a definition is required for the
symbol, not necessarily in the same translation unit.
The effect is equivalent to moving all references to the alias to a
separate translation unit, renaming the alias to the aliased symbol,
declaring it as weak, compiling the two separate translation units and
performing a link with relocatable output (i.e. ld -r) on them.
A declaration to which weakref is attached and that is associated
with a named target must be static.
zero_call_used_regs ("choice")zero_call_used_regs attribute causes the compiler to zero
a subset of all call-used registers7 at function return.
This is used to increase program security by either mitigating
Return-Oriented Programming (ROP) attacks or preventing information leakage
through registers.
In order to satisfy users with different security needs and control the run-time overhead at the same time, the choice parameter provides a flexible way to choose the subset of the call-used registers to be zeroed. The four basic values of choice are:
In addition to these three basic choices, it is possible to modify ‘used’, ‘all’, and ‘leafy’ as follows:
The modifiers can be used individually or together. If they are used together, they must appear in the order above.
The full list of choices is therefore:
skipusedused-gprused-argused-gpr-argallall-gprall-argall-gpr-argleafyleafy-gprleafy-argleafy-gpr-argOf this list, ‘used-arg’, ‘used-gpr-arg’, ‘all-arg’, ‘all-gpr-arg’, ‘leafy-arg’, and ‘leafy-gpr-arg’ are mainly used for ROP mitigation.
The default for the attribute is controlled by -fzero-call-used-regs.
The following target-specific function attributes are available for the AArch64 target. For the most part, these options mirror the behavior of similar command-line options (see AArch64 Options), but on a per-function basis.
general-regs-onlyfix-cortex-a53-835769no-fix-cortex-a53-835769.
This corresponds to the behavior of the command line options
-mfix-cortex-a53-835769 and -mno-fix-cortex-a53-835769.
cmodel=strict-alignno-strict-alignstrict-align indicates that the compiler should not assume that unaligned
memory references are handled by the system. To allow the compiler to assume
that aligned memory references are handled by the system, the inverse attribute
no-strict-align can be specified. The behavior is same as for the
command-line option -mstrict-align and -mno-strict-align.
omit-leaf-frame-pointerno-omit-leaf-frame-pointer can be specified. These attributes have
the same behavior as the command-line options -momit-leaf-frame-pointer
and -mno-omit-leaf-frame-pointer.
tls-dialect=arch=tune=cpu=sign-return-addressnone. This
attribute is deprecated. The branch-protection attribute should
be used instead.
branch-protectionnone.
outline-atomicsThe above target attributes can be specified as follows:
__attribute__((target("attr-string")))
int
f (int a)
{
return a + 5;
}
where attr-string is one of the attribute strings specified above.
Additionally, the architectural extension string may be specified on its own. This can be used to turn on and off particular architectural extensions without having to specify a particular architecture version or core. Example:
__attribute__((target("+crc+nocrypto")))
int
foo (int a)
{
return a + 5;
}
In this example target("+crc+nocrypto") enables the crc
extension and disables the crypto extension for the function foo
without modifying an existing -march= or -mcpu option.
Multiple target function attributes can be specified by separating them with a comma. For example:
__attribute__((target("arch=armv8-a+crc+crypto,tune=cortex-a53")))
int
foo (int a)
{
return a + 5;
}
is valid and compiles function foo for ARMv8-A with crc
and crypto extensions and tunes it for cortex-a53.
Specifying target attributes on individual functions or performing link-time optimization across translation units compiled with different target options can affect function inlining rules:
In particular, a caller function can inline a callee function only if the
architectural features available to the callee are a subset of the features
available to the caller.
For example: A function foo compiled with -march=armv8-a+crc,
or tagged with the equivalent arch=armv8-a+crc attribute,
can inline a function bar compiled with -march=armv8-a+nocrc
because the all the architectural features that function bar requires
are available to function foo. Conversely, function bar cannot
inline function foo.
Additionally inlining a function compiled with -mstrict-align into a
function compiled without -mstrict-align is not allowed.
However, inlining a function compiled without -mstrict-align into a
function compiled with -mstrict-align is allowed.
Note that CPU tuning options and attributes such as the -mcpu=,
-mtune= do not inhibit inlining unless the CPU specified by the
-mcpu= option or the cpu= attribute conflicts with the
architectural feature rules specified above.
These function attributes are supported by the AMD GCN back end:
amdgpu_hsa_kernelThis attribute is implicitly applied to any function named main, using
default parameters.
Kernel functions may return an integer value, which will be written to a conventional place within the HSA "kernargs" region.
The attribute parameters configure what values are passed into the kernel function by the GPU drivers, via the initial register state. Some values are used by the compiler, and therefore forced on. Enabling other options may break assumptions in the compiler and/or run-time libraries.
private_segment_bufferenable_sgpr_private_segment_buffer flag. Always on (required to
locate the stack).
dispatch_ptrenable_sgpr_dispatch_ptr flag. Always on (required to locate the
launch dimensions).
queue_ptrenable_sgpr_queue_ptr flag. Always on (required to convert address
spaces).
kernarg_segment_ptrenable_sgpr_kernarg_segment_ptr flag. Always on (required to
locate the kernel arguments, "kernargs").
dispatch_idenable_sgpr_dispatch_id flag.
flat_scratch_initenable_sgpr_flat_scratch_init flag.
private_segment_sizeenable_sgpr_private_segment_size flag.
grid_workgroup_count_Xenable_sgpr_grid_workgroup_count_x flag. Always on (required to
use OpenACC/OpenMP).
grid_workgroup_count_Yenable_sgpr_grid_workgroup_count_y flag.
grid_workgroup_count_Zenable_sgpr_grid_workgroup_count_z flag.
workgroup_id_Xenable_sgpr_workgroup_id_x flag.
workgroup_id_Yenable_sgpr_workgroup_id_y flag.
workgroup_id_Zenable_sgpr_workgroup_id_z flag.
workgroup_infoenable_sgpr_workgroup_info flag.
private_segment_wave_offsetenable_sgpr_private_segment_wave_byte_offset flag. Always on
(required to locate the stack).
work_item_id_Xenable_vgpr_workitem_id parameter. Always on (can't be disabled).
work_item_id_Yenable_vgpr_workitem_id parameter. Always on (required to enable
vectorization.)
work_item_id_Zenable_vgpr_workitem_id parameter. Always on (required to use
OpenACC/OpenMP).
These function attributes are supported by the ARC back end:
interruptOn the ARC, you must specify the kind of interrupt to be handled in a parameter to the interrupt attribute like this:
void f () __attribute__ ((interrupt ("ilink1")));
Permissible values for this parameter are: ilink1 and
ilink2 for ARCv1 architecture, and ilink and
firq for ARCv2 architecture.
long_callmedium_callshort_call#pragma long_calls settings.
For ARC, a function marked with the long_call attribute is
always called using register-indirect jump-and-link instructions,
thereby enabling the called function to be placed anywhere within the
32-bit address space. A function marked with the medium_call
attribute will always be close enough to be called with an unconditional
branch-and-link instruction, which has a 25-bit offset from
the call site. A function marked with the short_call
attribute will always be close enough to be called with a conditional
branch-and-link instruction, which has a 21-bit offset from
the call site.
jli_alwaysjli
instruction. The jli instruction makes use of a table stored
into .jlitab section, which holds the location of the functions
which are addressed using this instruction.
jli_fixedjli table is known and given as an attribute parameter.
secure_callsjli table needs to be passed as argument.
nakedasm statements
can safely be included in naked functions (see Basic Asm). While
using extended asm or a mixture of basic asm and C code
may appear to work, they cannot be depended upon to work reliably and
are not supported.
These function attributes are supported for ARM targets:
general-regs-onlyinterruptYou can specify the kind of interrupt to be handled by adding an optional parameter to the interrupt attribute like this:
void f () __attribute__ ((interrupt ("IRQ")));
Permissible values for this parameter are: IRQ, FIQ,
SWI, ABORT and UNDEF.
On ARMv7-M the interrupt type is ignored, and the attribute means the function may be called with a word-aligned stack pointer.
isrinterrupt attribute above.
long_callshort_call#pragma long_calls settings. For ARM, the
long_call attribute indicates that the function might be far
away from the call site and require a different (more expensive)
calling sequence. The short_call attribute always places
the offset to the function from the call site into the ‘BL’
instruction directly.
nakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
pcspcs attribute can be used to control the calling convention
used for a function on ARM. The attribute takes an argument that specifies
the calling convention to use.
When compiling using the AAPCS ABI (or a variant of it) then valid
values for the argument are "aapcs" and "aapcs-vfp". In
order to use a variant other than "aapcs" then the compiler must
be permitted to use the appropriate co-processor registers (i.e., the
VFP registers must be available in order to use "aapcs-vfp").
For example,
/* Argument passed in r0, and result returned in r0+r1. */
double f2d (float) __attribute__((pcs("aapcs")));
Variadic functions always use the "aapcs" calling convention and
the compiler rejects attempts to specify an alternative.
target (options)On ARM, the following options are allowed:
Functions from different modes can be inlined in the caller's mode.
The above target attributes can be specified as follows:
__attribute__((target("arch=armv8-a+crc")))
int
f (int a)
{
return a + 5;
}
Additionally, the architectural extension string may be specified on its own. This can be used to turn on and off particular architectural extensions without having to specify a particular architecture version or core. Example:
__attribute__((target("+crc+nocrypto")))
int
foo (int a)
{
return a + 5;
}
In this example target("+crc+nocrypto") enables the crc
extension and disables the crypto extension for the function foo
without modifying an existing -march= or -mcpu option.
These function attributes are supported by the AVR back end:
interruptOn the AVR, the hardware globally disables interrupts when an
interrupt is executed. The first instruction of an interrupt handler
declared with this attribute is a SEI instruction to
re-enable interrupts. See also the signal function attribute
that does not insert a SEI instruction. If both signal and
interrupt are specified for the same function, signal
is silently ignored.
nakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
no_gccisr__gcc_isr pseudo instructions in a function with
the interrupt or signal attribute aka. interrupt
service routine (ISR).
Use this attribute if the preamble of the ISR prologue should always read
push __zero_reg__
push __tmp_reg__
in __tmp_reg__, __SREG__
push __tmp_reg__
clr __zero_reg__
and accordingly for the postamble of the epilogue — no matter whether the mentioned registers are actually used in the ISR or not. Situations where you might want to use this attribute include:
SREG other than the
I-flag by writing to the memory location of SREG.
__gcc_isr generation for the whole compilation unit,
there is option -mno-gas-isr-prologues, see AVR Options.
OS_mainOS_taskOS_main or OS_task attribute
do not save/restore any call-saved register in their prologue/epilogue.
The OS_main attribute can be used when there is
guarantee that interrupts are disabled at the time when the function
is entered. This saves resources when the stack pointer has to be
changed to set up a frame for local variables.
The OS_task attribute can be used when there is no
guarantee that interrupts are disabled at that time when the function
is entered like for, e.g. task functions in a multi-threading operating
system. In that case, changing the stack pointer register is
guarded by save/clear/restore of the global interrupt enable flag.
The differences to the naked function attribute are:
naked functions do not have a return instruction whereas
OS_main and OS_task functions have a RET or
RETI return instruction.
naked functions do not set up a frame for local variables
or a frame pointer whereas OS_main and OS_task do this
as needed.
signalSee also the interrupt function attribute.
The AVR hardware globally disables interrupts when an interrupt is executed.
Interrupt handler functions defined with the signal attribute
do not re-enable interrupts. It is save to enable interrupts in a
signal handler. This “save” only applies to the code
generated by the compiler and not to the IRQ layout of the
application which is responsibility of the application.
If both signal and interrupt are specified for the same
function, signal is silently ignored.
These function attributes are supported by the Blackfin back end:
exception_handlerinterrupt_handlerkspisuspinterrupt_handler, exception_handler
or nmi_handler, code is generated to load the stack pointer
from the USP register in the function prologue.
l1_text.l1.text.
With -mfdpic, function calls with a such function as the callee
or caller uses inlined PLT.
l2.l2.text. With -mfdpic, callers of such functions use
an inlined PLT.
longcallshortcalllongcall attribute
indicates that the function might be far away from the call site and
require a different (more expensive) calling sequence. The
shortcall attribute indicates that the function is always close
enough for the shorter calling sequence to be used. These attributes
override the -mlongcall switch.
nestinginterrupt_handler,
exception_handler or nmi_handler to indicate that the function
entry code should enable nested interrupts or exceptions.
nmi_handlersaveallThese function attributes are supported by the BPF back end:
kernel_helper int bpf_probe_read (void *dst, int size, const void *unsafe_ptr)
__attribute__ ((kernel_helper (4)));
These function attributes are supported by the C-SKY back end:
interruptisrUse of these options requires the -mistack command-line option to enable support for the necessary interrupt stack instructions. They are ignored with a warning otherwise. See C-SKY Options.
nakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
These function attributes are supported by the Epiphany back end:
disinterruptforwarder_sectioninterruptOn Epiphany targets one or more optional parameters can be added like this:
void __attribute__ ((interrupt ("dma0, dma1"))) universal_dma_handler ();
Permissible values for these parameters are: reset,
software_exception, page_miss,
timer0, timer1, message,
dma0, dma1, wand and swi.
Multiple parameters indicate that multiple entries in the interrupt
vector table should be initialized for this function, i.e. for each
parameter name, a jump to the function is emitted in
the section ivt_entry_name. The parameter(s) may be omitted
entirely, in which case no interrupt vector table entry is provided.
Note that interrupts are enabled inside the function
unless the disinterrupt attribute is also specified.
The following examples are all valid uses of these attributes on Epiphany targets:
void __attribute__ ((interrupt)) universal_handler ();
void __attribute__ ((interrupt ("dma1"))) dma1_handler ();
void __attribute__ ((interrupt ("dma0, dma1")))
universal_dma_handler ();
void __attribute__ ((interrupt ("timer0"), disinterrupt))
fast_timer_handler ();
void __attribute__ ((interrupt ("dma0, dma1"),
forwarder_section ("tramp")))
external_dma_handler ();
long_callshort_call#pragma long_calls settings.
These function attributes are available for H8/300 targets:
function_vectorinterrupt_handlersaveallThese function attributes are supported on IA-64 targets:
syscall_linkageversion_id extern int foo () __attribute__((version_id ("20040821")));
Calls to foo are mapped to calls to foo{20040821}.
These function attributes are supported by the M32C back end:
bank_switchfast_interruptinterrupt attribute, except that freit is used to return
instead of reit.
function_vectorfunction_vector attribute declares a
special page subroutine call function. Use of this attribute reduces
the code size by 2 bytes for each call generated to the
subroutine. The argument to the attribute is the vector number entry
from the special page vector table which contains the 16 low-order
bits of the subroutine's entry address. Each vector table has special
page number (18 to 255) that is used in jsrs instructions.
Jump addresses of the routines are generated by adding 0x0F0000 (in
case of M16C targets) or 0xFF0000 (in case of M32C targets), to the
2-byte addresses set in the vector table. Therefore you need to ensure
that all the special page vector routines should get mapped within the
address range 0x0F0000 to 0x0FFFFF (for M16C) and 0xFF0000 to 0xFFFFFF
(for M32C).
In the following example 2 bytes are saved for each call to
function foo.
void foo (void) __attribute__((function_vector(0x18)));
void foo (void)
{
}
void bar (void)
{
foo();
}
If functions are defined in one file and are called in another file, then be sure to write this declaration in both files.
This attribute is ignored for R8C target.
interruptThese function attributes are supported by the M32R/D back end:
interruptmodel (model-name)small, medium, or
large, representing each of the code models.
Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the ld24 instruction), and are
callable with the bl instruction.
Medium model objects may live anywhere in the 32-bit address space (the
compiler generates seth/add3 instructions to load their addresses),
and are callable with the bl instruction.
Large model objects may live anywhere in the 32-bit address space (the
compiler generates seth/add3 instructions to load their addresses),
and may not be reachable with the bl instruction (the compiler
generates the much slower seth/add3/jl instruction sequence).
These function attributes are supported by the m68k back end:
interruptinterrupt_handlerinterrupt_threadsleep
instruction. This attribute is available only on fido.
These function attributes are supported by the MCORE back end:
nakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
These function attributes are supported on MicroBlaze targets:
save_volatilesbreak_handlerbreak_handler is done through
the rtbd instead of rtsd.
void f () __attribute__ ((break_handler));
interrupt_handlerfast_interruptfast_interrupt attribute to indicate handlers
used in low-latency interrupt mode, and interrupt_handler for
interrupts that do not use low-latency handlers. In both cases, GCC
emits appropriate prologue code and generates a return from the handler
using rtid instead of rtsd.
The following attributes are available on Microsoft Windows and Symbian OS targets.
dllexportdllexport attribute causes the compiler to provide a global
pointer to a pointer in a DLL, so that it can be referenced with the
dllimport attribute. On Microsoft Windows targets, the pointer
name is formed by combining _imp__ and the function or variable
name.
You can use __declspec(dllexport) as a synonym for
__attribute__ ((dllexport)) for compatibility with other
compilers.
On systems that support the visibility attribute, this
attribute also implies “default” visibility. It is an error to
explicitly specify any other visibility.
GCC's default behavior is to emit all inline functions with the
dllexport attribute. Since this can cause object file-size bloat,
you can use -fno-keep-inline-dllexport, which tells GCC to
ignore the attribute for inlined functions unless the
-fkeep-inline-functions flag is used instead.
The attribute is ignored for undefined symbols.
When applied to C++ classes, the attribute marks defined non-inlined member functions and static data members as exports. Static consts initialized in-class are not marked unless they are also defined out-of-class.
For Microsoft Windows targets there are alternative methods for
including the symbol in the DLL's export table such as using a
.def file with an EXPORTS section or, with GNU ld, using
the --export-all linker flag.
dllimportdllimport
attribute causes the compiler to reference a function or variable via
a global pointer to a pointer that is set up by the DLL exporting the
symbol. The attribute implies extern. On Microsoft Windows
targets, the pointer name is formed by combining _imp__ and the
function or variable name.
You can use __declspec(dllimport) as a synonym for
__attribute__ ((dllimport)) for compatibility with other
compilers.
On systems that support the visibility attribute, this
attribute also implies “default” visibility. It is an error to
explicitly specify any other visibility.
Currently, the attribute is ignored for inlined functions. If the
attribute is applied to a symbol definition, an error is reported.
If a symbol previously declared dllimport is later defined, the
attribute is ignored in subsequent references, and a warning is emitted.
The attribute is also overridden by a subsequent declaration as
dllexport.
When applied to C++ classes, the attribute marks non-inlined member functions and static data members as imports. However, the attribute is ignored for virtual methods to allow creation of vtables using thunks.
On the SH Symbian OS target the dllimport attribute also has
another affect—it can cause the vtable and run-time type information
for a class to be exported. This happens when the class has a
dllimported constructor or a non-inline, non-pure virtual function
and, for either of those two conditions, the class also has an inline
constructor or destructor and has a key function that is defined in
the current translation unit.
For Microsoft Windows targets the use of the dllimport
attribute on functions is not necessary, but provides a small
performance benefit by eliminating a thunk in the DLL. The use of the
dllimport attribute on imported variables can be avoided by passing the
--enable-auto-import switch to the GNU linker. As with
functions, using the attribute for a variable eliminates a thunk in
the DLL.
One drawback to using this attribute is that a pointer to a
variable marked as dllimport cannot be used as a constant
address. However, a pointer to a function with the
dllimport attribute can be used as a constant initializer; in
this case, the address of a stub function in the import lib is
referenced. On Microsoft Windows targets, the attribute can be disabled
for functions by setting the -mnop-fun-dllimport flag.
These function attributes are supported by the MIPS back end:
interrupteic. When interrupts are non-masked then the requested Interrupt
Priority Level (IPL) is copied to the current IPL which has the effect of only
enabling higher priority interrupts. To use vectored interrupt mode use
the argument vector=[sw0|sw1|hw0|hw1|hw2|hw3|hw4|hw5], this will change
the behavior of the non-masked interrupt support and GCC will arrange to mask
all interrupts from sw0 up to and including the specified interrupt vector.
You can use the following attributes to modify the behavior of an interrupt handler:
use_shadow_register_setintstack is
supported to indicate that the shadow register set contains a valid stack
pointer.
keep_interrupts_maskeduse_debug_exception_returnderet instruction. Interrupt handlers that don't
have this attribute return using eret instead.
You can use any combination of these attributes, as shown below:
void __attribute__ ((interrupt)) v0 ();
void __attribute__ ((interrupt, use_shadow_register_set)) v1 ();
void __attribute__ ((interrupt, keep_interrupts_masked)) v2 ();
void __attribute__ ((interrupt, use_debug_exception_return)) v3 ();
void __attribute__ ((interrupt, use_shadow_register_set,
keep_interrupts_masked)) v4 ();
void __attribute__ ((interrupt, use_shadow_register_set,
use_debug_exception_return)) v5 ();
void __attribute__ ((interrupt, keep_interrupts_masked,
use_debug_exception_return)) v6 ();
void __attribute__ ((interrupt, use_shadow_register_set,
keep_interrupts_masked,
use_debug_exception_return)) v7 ();
void __attribute__ ((interrupt("eic"))) v8 ();
void __attribute__ ((interrupt("vector=hw3"))) v9 ();
long_callshort_callnearfarlong_call and far attributes are
synonyms, and cause the compiler to always call
the function by first loading its address into a register, and then using
the contents of that register. The short_call and near
attributes are synonyms, and have the opposite
effect; they specify that non-PIC calls should be made using the more
efficient jal instruction.
mips16nomips16mips16 and nomips16
function attributes to locally select or turn off MIPS16 code generation.
A function with the mips16 attribute is emitted as MIPS16 code,
while MIPS16 code generation is disabled for functions with the
nomips16 attribute. These attributes override the
-mips16 and -mno-mips16 options on the command line
(see MIPS Options).
When compiling files containing mixed MIPS16 and non-MIPS16 code, the
preprocessor symbol __mips16 reflects the setting on the command line,
not that within individual functions. Mixed MIPS16 and non-MIPS16 code
may interact badly with some GCC extensions such as __builtin_apply
(see Constructing Calls).
micromips, MIPSnomicromips, MIPSmicromips and nomicromips
function attributes to locally select or turn off microMIPS code generation.
A function with the micromips attribute is emitted as microMIPS code,
while microMIPS code generation is disabled for functions with the
nomicromips attribute. These attributes override the
-mmicromips and -mno-micromips options on the command line
(see MIPS Options).
When compiling files containing mixed microMIPS and non-microMIPS code, the
preprocessor symbol __mips_micromips reflects the setting on the
command line,
not that within individual functions. Mixed microMIPS and non-microMIPS code
may interact badly with some GCC extensions such as __builtin_apply
(see Constructing Calls).
nocompressionnocompression function attribute
to locally turn off MIPS16 and microMIPS code generation. This attribute
overrides the -mips16 and -mmicromips options on the
command line (see MIPS Options).
use_hazard_barrier_returnThese function attributes are supported by the MSP430 back end:
criticalnaked, reentrant or interrupt attributes.
The MSP430 hardware ensures that interrupts are disabled on entry to
interrupt functions, and restores the previous interrupt state
on exit. The critical attribute is therefore redundant on
interrupt functions.
interruptYou can provide an argument to the interrupt
attribute which specifies a name or number. If the argument is a
number it indicates the slot in the interrupt vector table (0 - 31) to
which this handler should be assigned. If the argument is a name it
is treated as a symbolic name for the vector slot. These names should
match up with appropriate entries in the linker script. By default
the names watchdog for vector 26, nmi for vector 30 and
reset for vector 31 are recognized.
nakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
reentrantnaked
or critical attributes. They can have the interrupt
attribute.
wakeuploweruppereitherThe attributes work in conjunction with a linker script that has been
augmented to specify where to place sections with a .lower and
a .upper prefix. So, for example, as well as placing the
.data section, the script also specifies the placement of a
.lower.data and a .upper.data section. The intention
is that lower sections are placed into a small but easier to
access memory region and the upper sections are placed into a larger, but
slower to access, region.
The either attribute is special. It tells the linker to place
the object into the corresponding lower section if there is
room for it. If there is insufficient room then the object is placed
into the corresponding upper section instead. Note that the
placement algorithm is not very sophisticated. It does not attempt to
find an optimal packing of the lower sections. It just makes
one pass over the objects and does the best that it can. Using the
-ffunction-sections and -fdata-sections command-line
options can help the packing, however, since they produce smaller,
easier to pack regions.
These function attributes are supported by the NDS32 back end:
exceptioninterruptnestednot_nestednested_readyPSW.GIE
(global interrupt enable) is set. This allows interrupt service routine to
finish some short critical code before enabling interrupts.
save_allpartial_savenakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
resetnmiwarmThese function attributes are supported by the Nios II back end:
target (options)When compiling for Nios II, the following options are allowed:
These function attributes are supported by the Nvidia PTX back end:
kernelKernel functions must have void return type.
These function attributes are supported by the PowerPC back end:
longcallshortcalllongcall attribute
indicates that the function might be far away from the call site and
require a different (more expensive) calling sequence. The
shortcall attribute indicates that the function is always close
enough for the shorter calling sequence to be used. These attributes
override both the -mlongcall switch and
the #pragma longcall setting.
See RS/6000 and PowerPC Options, for more information on whether long calls are necessary.
target (options)On the PowerPC, the following options are allowed:
friz instruction when the
-funsafe-math-optimizations option is used to optimize
rounding a floating-point value to 64-bit integer and back to floating
point. The friz instruction does not return the same value if
the floating-point number is too large to fit in an integer.
target("cpu=power7") attribute when
generating 32-bit code, VSX and AltiVec instructions are not generated
unless you use the -mabi=altivec option on the command line.
target("tune=TUNE") attribute and
you do specify the target("cpu=CPU") attribute,
compilation tunes for the CPU architecture, and not the
default tuning specified on the command line.
On the PowerPC, the inliner does not inline a function that has different target options than the caller, unless the callee has a subset of the target options of the caller.
These function attributes are supported by the RISC-V back end:
nakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
interruptYou can specify the kind of interrupt to be handled by adding an optional parameter to the interrupt attribute like this:
void f (void) __attribute__ ((interrupt ("user")));
Permissible values for this parameter are user, supervisor,
and machine. If there is no parameter, then it defaults to
machine.
These function attributes are supported by the RL78 back end:
interruptbrk_interruptUse brk_interrupt instead of interrupt for
handlers intended to be used with the BRK opcode (i.e. those
that must end with RETB instead of RETI).
nakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
These function attributes are supported by the RX back end:
fast_interruptinterrupt attribute, except that freit is used to return
instead of reit.
interruptOn RX and RL78 targets, you may specify one or more vector numbers as arguments
to the attribute, as well as naming an alternate table name.
Parameters are handled sequentially, so one handler can be assigned to
multiple entries in multiple tables. One may also pass the magic
string "$default" which causes the function to be used for any
unfilled slots in the current table.
This example shows a simple assignment of a function to one vector in the default table (note that preprocessor macros may be used for chip-specific symbolic vector names):
void __attribute__ ((interrupt (5))) txd1_handler ();
This example assigns a function to two slots in the default table
(using preprocessor macros defined elsewhere) and makes it the default
for the dct table:
void __attribute__ ((interrupt (RXD1_VECT,RXD2_VECT,"dct","$default")))
txd1_handler ();
nakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
vectorinterrupt attribute, including its
parameters, but does not make the function an interrupt-handler type
function (i.e. it retains the normal C function calling ABI). See the
interrupt attribute for a description of its arguments.
These function attributes are supported on the S/390:
hotpatch (halfwords-before-function-label,halfwords-after-function-label)hotpatch attribute takes precedence. The first of the
two arguments specifies the number of halfwords to be added before
the function label. A second argument can be used to specify the
number of halfwords to be added after the function label. For
both arguments the maximum allowed value is 1000000.
If both arguments are zero, hotpatching is disabled.
target (options)On S/390, the following options are supported:
The options work exactly like the S/390 specific command line options (without the prefix -m) except that they do not change any feature macros. For example,
target("no-vx")
does not undefine the __VEC__ macro.
These function attributes are supported on the SH family of processors:
function_vectorIn an application, for a function being called once, this attribute saves at least 8 bytes of code; and if other successive calls are being made to the same function, it saves 2 bytes of code per each of these calls.
interrupt_handlernosave_low_regsinterrupt_handler
function should not save and restore registers R0..R7. This can be used on SH3*
and SH4* targets that have a second R0..R7 register bank for non-reentrant
interrupt handlers.
renesasresbankinterrupt_handler
routines. Saving to the bank is performed automatically after the CPU
accepts an interrupt that uses a register bank.
The nineteen 32-bit registers comprising general register R0 to R14, control register GBR, and system registers MACH, MACL, and PR and the vector table address offset are saved into a register bank. Register banks are stacked in first-in last-out (FILO) sequence. Restoration from the bank is executed by issuing a RESBANK instruction.
sp_switchinterrupt_handler
function should switch to an alternate stack. It expects a string
argument that names a global variable holding the address of the
alternate stack.
void *alt_stack;
void f () __attribute__ ((interrupt_handler,
sp_switch ("alt_stack")));
trap_exitinterrupt_handler to return using
trapa instead of rte. This attribute expects an integer
argument specifying the trap number to be used.
trapa_handlerinterrupt_handler
but it does not save and restore all registers.
See Microsoft Windows Function Attributes, for discussion of the
dllexport and dllimport attributes.
The V850 back end supports these function attributes:
interruptinterrupt_handlerThese function attributes are supported by the Visium back end:
interruptThese function attributes are supported by the x86 back end:
cdeclcdecl attribute causes the compiler to
assume that the calling function pops off the stack space used to
pass arguments. This is
useful to override the effects of the -mrtd switch.
fastcallfastcall attribute causes the compiler to
pass the first argument (if of integral type) in the register ECX and
the second argument (if of integral type) in the register EDX. Subsequent
and other typed arguments are passed on the stack. The called function
pops the arguments off the stack. If the number of arguments is variable all
arguments are pushed on the stack.
thiscallthiscall attribute causes the compiler to
pass the first argument (if of integral type) in the register ECX.
Subsequent and other typed arguments are passed on the stack. The called
function pops the arguments off the stack.
If the number of arguments is variable all arguments are pushed on the
stack.
The thiscall attribute is intended for C++ non-static member functions.
As a GCC extension, this calling convention can be used for C functions
and for static member methods.
ms_abisysv_abims_abi attribute tells the compiler to use the Microsoft ABI,
while the sysv_abi attribute tells the compiler to use the System V
ELF ABI, which is used on GNU/Linux and other systems. The default is to use
the Microsoft ABI when targeting Windows. On all other systems, the default
is the System V ELF ABI.
Note, the ms_abi attribute for Microsoft Windows 64-bit targets currently
requires the -maccumulate-outgoing-args option.
callee_pop_aggregate_return (number)The default x86-32 ABI assumes that the callee pops the stack for hidden pointer. However, on x86-32 Microsoft Windows targets, the compiler assumes that the caller pops the stack for hidden pointer.
ms_hook_prologuenakedasm statements can safely be included in naked functions
(see Basic Asm). While using extended asm or a mixture of
basic asm and C code may appear to work, they cannot be
depended upon to work reliably and are not supported.
regparm (number)regparm attribute causes the compiler to
pass arguments number one to number if they are of integral type
in registers EAX, EDX, and ECX instead of on the stack. Functions that
take a variable number of arguments continue to be passed all of their
arguments on the stack.
Beware that on some ELF systems this attribute is unsuitable for global functions in shared libraries with lazy binding (which is the default). Lazy binding sends the first call via resolving code in the loader, which might assume EAX, EDX and ECX can be clobbered, as per the standard calling conventions. Solaris 8 is affected by this. Systems with the GNU C Library version 2.1 or higher and FreeBSD are believed to be safe since the loaders there save EAX, EDX and ECX. (Lazy binding can be disabled with the linker or the loader if desired, to avoid the problem.)
sseregparmsseregparm attribute
causes the compiler to pass up to 3 floating-point arguments in
SSE registers instead of on the stack. Functions that take a
variable number of arguments continue to pass all of their
floating-point arguments on the stack.
force_align_arg_pointerforce_align_arg_pointer attribute may be
applied to individual function definitions, generating an alternate
prologue and epilogue that realigns the run-time stack if necessary.
This supports mixing legacy codes that run with a 4-byte aligned stack
with modern codes that keep a 16-byte stack for SSE compatibility.
stdcallstdcall attribute causes the compiler to
assume that the called function pops off the stack space used to
pass arguments, unless it takes a variable number of arguments.
no_caller_saved_registersno_caller_saved_registers attribute.
interruptIRET instruction, instead of the
RET instruction, is used to return from interrupt handlers. All
registers, except for the EFLAGS register which is restored by the
IRET instruction, are preserved by the compiler. Since GCC
doesn't preserve SSE, MMX nor x87 states, the GCC option
-mgeneral-regs-only should be used to compile interrupt and
exception handlers.
Any interruptible-without-stack-switch code must be compiled with -mno-red-zone since interrupt handlers can and will, because of the hardware design, touch the red zone.
An interrupt handler must be declared with a mandatory pointer argument:
struct interrupt_frame;
__attribute__ ((interrupt))
void
f (struct interrupt_frame *frame)
{
}
and you must define struct interrupt_frame as described in the
processor's manual.
Exception handlers differ from interrupt handlers because the system
pushes an error code on the stack. An exception handler declaration is
similar to that for an interrupt handler, but with a different mandatory
function signature. The compiler arranges to pop the error code off the
stack before the IRET instruction.
#ifdef __x86_64__
typedef unsigned long long int uword_t;
#else
typedef unsigned int uword_t;
#endif
struct interrupt_frame;
__attribute__ ((interrupt))
void
f (struct interrupt_frame *frame, uword_t error_code)
{
...
}
Exception handlers should only be used for exceptions that push an error code; you should use an interrupt handler in other cases. The system will crash if the wrong kind of handler is used.
target (options)On the x86, the following options are allowed:
sin, cos, and
sqrt instructions on the 387 floating-point unit.
target("fpmath=sse,387") option as
target("fpmath=sse+387") because the comma would separate
different options.
prefer-vector-width attribute informs the
compiler to use OPT-bit vector width in instructions
instead of the default on the selected platform.
Valid OPT values are:
On the x86, the inliner does not inline a
function that has different target options than the caller, unless the
callee has a subset of the target options of the caller. For example
a function declared with target("sse3") can inline a function
with target("sse2"), since -msse3 implies -msse2.
indirect_branch("choice")indirect_branch attribute causes the compiler
to convert indirect call and jump with choice. ‘keep’
keeps indirect call and jump unmodified. ‘thunk’ converts indirect
call and jump to call and return thunk. ‘thunk-inline’ converts
indirect call and jump to inlined call and return thunk.
‘thunk-extern’ converts indirect call and jump to external call
and return thunk provided in a separate object file.
function_return("choice")function_return attribute causes the compiler
to convert function return with choice. ‘keep’ keeps function
return unmodified. ‘thunk’ converts function return to call and
return thunk. ‘thunk-inline’ converts function return to inlined
call and return thunk. ‘thunk-extern’ converts function return to
external call and return thunk provided in a separate object file.
nocf_checknocf_check attribute on a function is used to inform the
compiler that the function's prologue should not be instrumented when
compiled with the -fcf-protection=branch option. The
compiler assumes that the function's address is a valid target for a
control-flow transfer.
The nocf_check attribute on a type of pointer to function is
used to inform the compiler that a call through the pointer should
not be instrumented when compiled with the
-fcf-protection=branch option. The compiler assumes
that the function's address from the pointer is a valid target for
a control-flow transfer. A direct function call through a function
name is assumed to be a safe call thus direct calls are not
instrumented by the compiler.
The nocf_check attribute is applied to an object's type.
In case of assignment of a function address or a function pointer to
another pointer, the attribute is not carried over from the right-hand
object's type; the type of left-hand object stays unchanged. The
compiler checks for nocf_check attribute mismatch and reports
a warning in case of mismatch.
{
int foo (void) __attribute__(nocf_check);
void (*foo1)(void) __attribute__(nocf_check);
void (*foo2)(void);
/* foo's address is assumed to be valid. */
int
foo (void)
/* This call site is not checked for control-flow
validity. */
(*foo1)();
/* A warning is issued about attribute mismatch. */
foo1 = foo2;
/* This call site is still not checked. */
(*foo1)();
/* This call site is checked. */
(*foo2)();
/* A warning is issued about attribute mismatch. */
foo2 = foo1;
/* This call site is still checked. */
(*foo2)();
return 0;
}
cf_checkcf_check attribute on a function is used to inform the
compiler that ENDBR instruction should be placed at the function
entry when -fcf-protection=branch is enabled.
indirect_returnindirect_return attribute can be applied to a function,
as well as variable or type of function pointer to inform the
compiler that the function may return via indirect branch.
fentry_name("name")fentry_name attribute sets the function to
call on function entry when function instrumentation is enabled
with -pg -mfentry. When name is nop then a 5 byte
nop sequence is generated.
fentry_section("name")fentry_section attribute sets the name
of the section to record function entry instrumentation calls in when
enabled with -pg -mrecord-mcount
nodirect_extern_accessThese function attributes are supported by the Xstormy16 back end:
interrupt
The keyword __attribute__ allows you to specify special properties
of variables, function parameters, or structure, union, and, in C++, class
members. This __attribute__ keyword is followed by an attribute
specification enclosed in double parentheses. Some attributes are currently
defined generically for variables. Other attributes are defined for
variables on particular target systems. Other attributes are available
for functions (see Function Attributes), labels (see Label Attributes),
enumerators (see Enumerator Attributes), statements
(see Statement Attributes), and for types (see Type Attributes).
Other front ends might define more attributes
(see Extensions to the C++ Language).
See Attribute Syntax, for details of the exact syntax for using attributes.
The following attributes are supported on most targets.
alias ("target")alias variable attribute causes the declaration to be emitted
as an alias for another symbol known as an alias target. Except
for top-level qualifiers the alias target must have the same type as
the alias. For instance, the following
int var_target;
extern int __attribute__ ((alias ("var_target"))) var_alias;
defines var_alias to be an alias for the var_target variable.
It is an error if the alias target is not defined in the same translation unit as the alias.
Note that in the absence of the attribute GCC assumes that distinct declarations with external linkage denote distinct objects. Using both the alias and the alias target to access the same object is undefined in a translation unit without a declaration of the alias with the attribute.
This attribute requires assembler and object file support, and may not be available on all targets.
alignedaligned (alignment)aligned attribute specifies a minimum alignment for the variable
or structure field, measured in bytes. When specified, alignment must
be an integer constant power of 2. Specifying no alignment argument
implies the maximum alignment for the target, which is often, but by no
means always, 8 or 16 bytes.
For example, the declaration:
int x __attribute__ ((aligned (16))) = 0;
causes the compiler to allocate the global variable x on a
16-byte boundary. On a 68040, this could be used in conjunction with
an asm expression to access the move16 instruction which
requires 16-byte aligned operands.
You can also specify the alignment of structure fields. For example, to
create a double-word aligned int pair, you could write:
struct foo { int x[2] __attribute__ ((aligned (8))); };
This is an alternative to creating a union with a double member,
which forces the union to be double-word aligned.
As in the preceding examples, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given variable or structure field. Alternatively, you can leave out the alignment factor and just ask the compiler to align a variable or field to the default alignment for the target architecture you are compiling for. The default alignment is sufficient for all scalar types, but may not be enough for all vector types on a target that supports vector operations. The default alignment is fixed for a particular target ABI.
GCC also provides a target specific macro __BIGGEST_ALIGNMENT__,
which is the largest alignment ever used for any data type on the
target machine you are compiling for. For example, you could write:
short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__)));
The compiler automatically sets the alignment for the declared
variable or field to __BIGGEST_ALIGNMENT__. Doing this can
often make copy operations more efficient, because the compiler can
use whatever instructions copy the biggest chunks of memory when
performing copies to or from the variables or fields that you have
aligned this way. Note that the value of __BIGGEST_ALIGNMENT__
may change depending on command-line options.
When used on a struct, or struct member, the aligned attribute can
only increase the alignment; in order to decrease it, the packed
attribute must be specified as well. When used as part of a typedef, the
aligned attribute can both increase and decrease alignment, and
specifying the packed attribute generates a warning.
Note that the effectiveness of aligned attributes for static
variables may be limited by inherent limitations in the system linker
and/or object file format. On some systems, the linker is
only able to arrange for variables to be aligned up to a certain maximum
alignment. (For some linkers, the maximum supported alignment may
be very very small.) If your linker is only able to align variables
up to a maximum of 8-byte alignment, then specifying aligned(16)
in an __attribute__ still only provides you with 8-byte
alignment. See your linker documentation for further information.
Stack variables are not affected by linker restrictions; GCC can properly align them on any target.
The aligned attribute can also be used for functions
(see Common Function Attributes.)
warn_if_not_aligned (alignment) struct foo
{
int i1;
int i2;
unsigned long long x __attribute__ ((warn_if_not_aligned (16)));
};
causes the compiler to issue an warning on struct foo, like
‘warning: alignment 8 of 'struct foo' is less than 16’.
The compiler also issues a warning, like ‘warning: 'x' offset
8 in 'struct foo' isn't aligned to 16’, when the structure field has
the misaligned offset:
struct __attribute__ ((aligned (16))) foo
{
int i1;
int i2;
unsigned long long x __attribute__ ((warn_if_not_aligned (16)));
};
This warning can be disabled by -Wno-if-not-aligned.
The warn_if_not_aligned attribute can also be used for types
(see Common Type Attributes.)
strict_flex_array (level)strict_flex_array attribute should be attached to the trailing
array field of a structure. It controls when to treat the trailing array
field of a structure as a flexible array member for the purposes of accessing
the elements of such an array.
level must be an integer betwen 0 to 3.
level=0 is the least strict level, all trailing arrays of structures are treated as flexible array members. level=3 is the strictest level, only when the trailing array is declared as a flexible array member per C99 standard onwards (‘[]’), it is treated as a flexible array member.
There are two more levels in between 0 and 3, which are provided to support older codes that use GCC zero-length array extension (‘[0]’) or one-element array as flexible array members (‘[1]’): When level is 1, the trailing array is treated as a flexible array member when it is declared as either ‘[]’, ‘[0]’, or ‘[1]’; When level is 2, the trailing array is treated as a flexible array member when it is declared as either ‘[]’, or ‘[0]’.
This attribute can be used with or without the -fstrict-flex-arrays. When both the attribute and the option present at the same time, the level of the strictness for the specific trailing array field is determined by the attribute.
alloc_size (position)alloc_size (position-1, position-2)alloc_size variable attribute may be applied to the declaration
of a pointer to a function that returns a pointer and takes at least one
argument of an integer type. It indicates that the returned pointer points
to an object whose size is given by the function argument at position,
or by the product of the arguments at position-1 and position-2.
Meaningful sizes are positive values less than PTRDIFF_MAX. Other
sizes are diagnosed when detected. GCC uses this information to improve
the results of __builtin_object_size.
For instance, the following declarations
typedef __attribute__ ((alloc_size (1, 2))) void*
(*calloc_ptr) (size_t, size_t);
typedef __attribute__ ((alloc_size (1))) void*
(*malloc_ptr) (size_t);
specify that calloc_ptr is a pointer of a function that, like
the standard C function calloc, returns an object whose size
is given by the product of arguments 1 and 2, and similarly, that
malloc_ptr, like the standard C function malloc,
returns an object whose size is given by argument 1 to the function.
cleanup (cleanup_function)cleanup attribute runs a function when the variable goes
out of scope. This attribute can only be applied to auto function
scope variables; it may not be applied to parameters or variables
with static storage duration. The function must take one parameter,
a pointer to a type compatible with the variable. The return value
of the function (if any) is ignored.
If -fexceptions is enabled, then cleanup_function
is run during the stack unwinding that happens during the
processing of the exception. Note that the cleanup attribute
does not allow the exception to be caught, only to perform an action.
It is undefined what happens if cleanup_function does not
return normally.
commonnocommoncommon attribute requests GCC to place a variable in
“common” storage. The nocommon attribute requests the
opposite—to allocate space for it directly.
These attributes override the default chosen by the -fno-common and -fcommon flags respectively.
copycopy (variable)copy attribute applies the set of attributes with which
variable has been declared to the declaration of the variable
to which the attribute is applied. The attribute is designed for
libraries that define aliases that are expected to specify the same
set of attributes as the aliased symbols. The copy attribute
can be used with variables, functions or types. However, the kind
of symbol to which the attribute is applied (either varible or
function) must match the kind of symbol to which the argument refers.
The copy attribute copies only syntactic and semantic attributes
but not attributes that affect a symbol's linkage or visibility such as
alias, visibility, or weak. The deprecated
attribute is also not copied. See Common Function Attributes.
See Common Type Attributes.
deprecateddeprecated (msg)deprecated attribute results in a warning if the variable
is used anywhere in the source file. This is useful when identifying
variables that are expected to be removed in a future version of a
program. The warning also includes the location of the declaration
of the deprecated variable, to enable users to easily find further
information about why the variable is deprecated, or what they should
do instead. Note that the warning only occurs for uses:
extern int old_var __attribute__ ((deprecated));
extern int old_var;
int new_fn () { return old_var; }
results in a warning on line 3 but not line 2. The optional msg argument, which must be a string, is printed in the warning if present.
The deprecated attribute can also be used for functions and
types (see Common Function Attributes,
see Common Type Attributes).
The message attached to the attribute is affected by the setting of the -fmessage-length option.
unavailableunavailable (msg)unavailable attribute indicates that the variable so marked
is not available, if it is used anywhere in the source file. It behaves
in the same manner as the deprecated attribute except that the
compiler will emit an error rather than a warning.
It is expected that items marked as deprecated will eventually be
withdrawn from interfaces, and then become unavailable. This attribute
allows for marking them appropriately.
The unavailable attribute can also be used for functions and
types (see Common Function Attributes,
see Common Type Attributes).
mode (mode)See Machine Modes,
for a list of the possible keywords for mode.
You may also specify a mode of byte or __byte__ to
indicate the mode corresponding to a one-byte integer, word or
__word__ for the mode of a one-word integer, and pointer
or __pointer__ for the mode used to represent pointers.
nonstringnonstring variable attribute specifies that an object or member
declaration with type array of char, signed char, or
unsigned char, or pointer to such a type is intended to store
character arrays that do not necessarily contain a terminating NUL.
This is useful in detecting uses of such arrays or pointers with functions
that expect NUL-terminated strings, and to avoid warnings when such
an array or pointer is used as an argument to a bounded string manipulation
function such as strncpy. For example, without the attribute, GCC
will issue a warning for the strncpy call below because it may
truncate the copy without appending the terminating NUL character.
Using the attribute makes it possible to suppress the warning. However,
when the array is declared with the attribute the call to strlen is
diagnosed because when the array doesn't contain a NUL-terminated
string the call is undefined. To copy, compare, of search non-string
character arrays use the memcpy, memcmp, memchr,
and other functions that operate on arrays of bytes. In addition,
calling strnlen and strndup with such arrays is safe
provided a suitable bound is specified, and not diagnosed.
struct Data
{
char name [32] __attribute__ ((nonstring));
};
int f (struct Data *pd, const char *s)
{
strncpy (pd->name, s, sizeof pd->name);
...
return strlen (pd->name); // unsafe, gets a warning
}
packedpacked attribute specifies that a structure member should have
the smallest possible alignment—one bit for a bit-field and one byte
otherwise, unless a larger value is specified with the aligned
attribute. The attribute does not apply to non-member objects.
For example in the structure below, the member array x is packed
so that it immediately follows a with no intervening padding:
struct foo
{
char a;
int x[2] __attribute__ ((packed));
};
Note: The 4.1, 4.2 and 4.3 series of GCC ignore the
packed attribute on bit-fields of type char. This has
been fixed in GCC 4.4 but the change can lead to differences in the
structure layout. See the documentation of
-Wpacked-bitfield-compat for more information.
section ("section-name")data and bss. Sometimes, however, you need additional sections,
or you need certain particular variables to appear in special sections,
for example to map to special hardware. The section
attribute specifies that a variable (or function) lives in a particular
section. For example, this small program uses several specific section names:
struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
int init_data __attribute__ ((section ("INITDATA")));
main()
{
/* Initialize stack pointer */
init_sp (stack + sizeof (stack));
/* Initialize initialized data */
memcpy (&init_data, &data, &edata - &data);
/* Turn on the serial ports */
init_duart (&a);
init_duart (&b);
}
Use the section attribute with
global variables and not local variables,
as shown in the example.
You may use the section attribute with initialized or
uninitialized global variables but the linker requires
each object be defined once, with the exception that uninitialized
variables tentatively go in the common (or bss) section
and can be multiply “defined”. Using the section attribute
changes what section the variable goes into and may cause the
linker to issue an error if an uninitialized variable has multiple
definitions. You can force a variable to be initialized with the
-fno-common flag or the nocommon attribute.
Some file formats do not support arbitrary sections so the section
attribute is not available on all platforms.
If you need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.
tls_model ("tls_model")tls_model attribute sets thread-local storage model
(see Thread-Local) of a particular __thread variable,
overriding -ftls-model= command-line switch on a per-variable
basis.
The tls_model argument should be one of global-dynamic,
local-dynamic, initial-exec or local-exec.
Not all targets support this attribute.
unusedusedWhen applied to a static data member of a C++ class template, the attribute also means that the member is instantiated if the class itself is instantiated.
retainsection attribute, or the -fdata-sections option),
will be placed in new, unique sections.
This additional functionality requires Binutils version 2.36 or later.
uninitialized-ftrivial-auto-var-init presents.
With the option -ftrivial-auto-var-init, all the automatic variables
that do not have explicit initializers will be initialized by the compiler.
These additional compiler initializations might incur run-time overhead,
sometimes dramatically. This attribute can be used to mark some variables
to be excluded from such automatical initialization in order to reduce runtime
overhead.
This attribute has no effect when the option -ftrivial-auto-var-init
does not present.
vector_size (bytes)int foo __attribute__ ((vector_size (16)));
causes the compiler to set the mode for foo, to be 16 bytes,
divided into int sized units. Assuming a 32-bit int,
foo's type is a vector of four units of four bytes each, and
the corresponding mode of foo is V4SI.
See Vector Extensions, for details of manipulating vector variables.
This attribute is only applicable to integral and floating scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct.
Aggregates with this attribute are invalid, even if they are of the same size as a corresponding scalar. For example, the declaration:
struct S { int a; };
struct S __attribute__ ((vector_size (16))) foo;
is invalid even if the size of the structure is the same as the size of
the int.
visibility ("visibility_type")visibility attribute is described in
Common Function Attributes.
weakweak attribute is described in
Common Function Attributes.
noinitnoinit attribute will not be initialized by
the C runtime startup code, or the program loader. Not initializing
data in this way can reduce program startup times.
This attribute is specific to ELF targets and relies on the linker
script to place sections with the .noinit prefix in the right
location.
persistentpersistent attribute will not be initialized by
the C runtime startup code, but will be initialized by the program
loader. This enables the value of the variable to ‘persist’
between processor resets.
This attribute is specific to ELF targets and relies on the linker
script to place the sections with the .persistent prefix in the
right location. Specifically, some type of non-volatile, writeable
memory is required.
objc_nullability (nullability kind) (Objective-C and Objective-C++ only)nil value. In most cases, the
attribute is intended to be an internal representation for property and
method nullability (specified by language keywords); it is not recommended
to use it directly.
When nullability kind is "unspecified" or 0, nothing is
known about the conditions in which the pointer might be nil. Making
this state specific serves to avoid false positives in diagnostics.
When nullability kind is "nonnull" or 1, the pointer has
no meaning if it is nil and thus the compiler is free to emit
diagnostics if it can be determined that the value will be nil.
When nullability kind is "nullable" or 2, the pointer might
be nil and carry meaning as such.
When nullability kind is "resettable" or 3 (used only in
the context of property attribute lists) this describes the case in which a
property setter may take the value nil (which perhaps causes the
property to be reset in some manner to a default) but for which the property
getter will never validly return nil.
auxaux attribute is used to directly access the ARC's
auxiliary register space from C. The auxilirary register number is
given via attribute argument.
progmemprogmem attribute is used on the AVR to place read-only
data in the non-volatile program memory (flash). The progmem
attribute accomplishes this by putting respective variables into a
section whose name starts with .progmem.
This attribute works similar to the section attribute
but adds additional checking.
progmem affects the location
of the data but not how this data is accessed.
In order to read data located with the progmem attribute
(inline) assembler must be used.
/* Use custom macros from AVR-LibC */
#include <avr/pgmspace.h>
/* Locate var in flash memory */
const int var[2] PROGMEM = { 1, 2 };
int read_var (int i)
{
/* Access var[] by accessor macro from avr/pgmspace.h */
return (int) pgm_read_word (& var[i]);
}
AVR is a Harvard architecture processor and data and read-only data normally resides in the data memory (RAM).
See also the AVR Named Address Spaces section for
an alternate way to locate and access data in flash memory.
progmem or
__flash qualifier at all.
Just use standard C / C++. The compiler will generate LD*
instructions. As flash memory is visible in the RAM address range,
and the default linker script does not locate .rodata in
RAM, no special features are needed in order not to waste RAM for
read-only data or to read from flash. You might even get slightly better
performance by
avoiding progmem and __flash. This applies to devices from
families avrtiny and avrxmega3, see AVR Options for
an overview.
0x4000
to the addresses of objects and declarations in progmem and locates
the objects in flash memory, namely in section .progmem.data.
The offset is needed because the flash memory is visible in the RAM
address space starting at address 0x4000.
Data in progmem can be accessed by means of ordinary C code,
no special functions or macros are needed.
/* var is located in flash memory */
extern const int var[2] __attribute__((progmem));
int read_var (int i)
{
return var[i];
}
Please notice that on these devices, there is no need for progmem
at all.
ioio (addr)io attribute are used to address
memory-mapped peripherals in the io address range.
If an address is specified, the variable
is assigned that address, and the value is interpreted as an
address in the data address space.
Example:
volatile int porta __attribute__((io (0x22)));
The address specified in the address in the data address range.
Otherwise, the variable it is not assigned an address, but the compiler will still use in/out instructions where applicable, assuming some other module assigns an address in the io address range. Example:
extern volatile int porta __attribute__((io));
io_lowio_low (addr)io attribute, but additionally it informs the
compiler that the object lies in the lower half of the I/O area,
allowing the use of cbi, sbi, sbic and sbis
instructions.
addressaddress (addr)address attribute are used to address
memory-mapped peripherals that may lie outside the io address range.
volatile int porta __attribute__((address (0x600)));
absdataabsdata attribute can
be accessed by the LDS and STS instructions which take
absolute addresses.
0x40...0xbf accessible by
LDS and STS. One way to achieve this as an
appropriate linker description file.
LDS
and STS, there is currently (Binutils 2.26) just an unspecific
warning like
module.cc:(.text+0x1c): warning: internal error: out of range error
See also the -mabsdata command-line option.
Three attributes are currently defined for the Blackfin.
l1_datal1_data_Al1_data_Bl1_data attribute are put into the specific section
named .l1.data. Those with l1_data_A attribute are put into
the specific section named .l1.data.A. Those with l1_data_B
attribute are put into the specific section named .l1.data.B.
l2l2 attribute are put into the specific section
named .l2.data.
These variable attributes are available for H8/300 targets:
eightbit_dataYou must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.
tiny_dataThe IA-64 back end supports the following variable attribute:
model (model-name)small, indicating addressability via “small” (22-bit)
addresses (so that their addresses can be loaded with the addl
instruction). Caveat: such addressing is by definition not position
independent and hence this attribute must not be used for objects
defined by shared libraries.
One attribute is currently defined for the LoongArch.
model("name")section attribute and/or a linker script will locate this object
specially. Currently the only supported values of name are
normal and extreme.
One attribute is currently defined for the M32R/D.
model (model-name)small, medium,
or large, representing each of the code models.
Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the ld24 instruction).
Medium and large model objects may live anywhere in the 32-bit address space
(the compiler generates seth/add3 instructions to load their
addresses).
You can use these attributes on Microsoft Windows targets. x86 Variable Attributes for additional Windows compatibility attributes available on all x86 targets.
dllimportdllexportdllimport and dllexport attributes are described in
Microsoft Windows Function Attributes.
selectanyselectany attribute causes an initialized global variable to
have link-once semantics. When multiple definitions of the variable are
encountered by the linker, the first is selected and the remainder are
discarded. Following usage by the Microsoft compiler, the linker is told
not to warn about size or content differences of the multiple
definitions.
Although the primary usage of this attribute is for POD types, the attribute can also be applied to global C++ objects that are initialized by a constructor. In this case, the static initialization and destruction code for the object is emitted in each translation defining the object, but the calls to the constructor and destructor are protected by a link-once guard variable.
The selectany attribute is only available on Microsoft Windows
targets. You can use __declspec (selectany) as a synonym for
__attribute__ ((selectany)) for compatibility with other
compilers.
sharedshared and marking the section
shareable:
int foo __attribute__((section ("shared"), shared)) = 0;
int
main()
{
/* Read and write foo. All running
copies see the same value. */
return 0;
}
You may only use the shared attribute along with section
attribute with a fully-initialized global definition because of the way
linkers work. See section attribute for more information.
The shared attribute is only available on Microsoft Windows.
uppereitherlowerIf -mdata-region={upper,either,none} has been passed, or
the section attribute is applied to a variable, the compiler will
generate 430X instructions to handle it. This is because the compiler has
to assume that the variable could get placed in the upper memory region
(above address 0xFFFF). Marking the variable with the lower attribute
informs the compiler that the variable will be placed in lower memory so it
is safe to use 430 instructions to handle it.
In the case of the section attribute, the section name given
will be used, and the .lower prefix will not be added.
These variable attributes are supported by the Nvidia PTX back end:
shared.shared memory space.
This memory space is private to each cooperative thread array; only threads
within one thread block refer to the same instance of the variable.
The runtime does not initialize variables in this memory space.
Three attributes currently are defined for PowerPC configurations:
altivec, ms_struct and gcc_struct.
For full documentation of the struct attributes please see the documentation in x86 Variable Attributes.
For documentation of altivec attribute please see the
documentation in PowerPC Type Attributes.
The RL78 back end supports the saddr variable attribute. This
specifies placement of the corresponding variable in the SADDR area,
which can be accessed more efficiently than the default memory region.
These variable attributes are supported by the V850 back end:
sdatdazdaTwo attributes are currently defined for x86 configurations:
ms_struct and gcc_struct.
ms_structgcc_structpacked is used on a structure, or if bit-fields are used,
it may be that the Microsoft ABI lays out the structure differently
than the way GCC normally does. Particularly when moving packed
data between functions compiled with GCC and the native Microsoft compiler
(either via function call or as data in a file), it may be necessary to access
either format.
The ms_struct and gcc_struct attributes correspond
to the -mms-bitfields and -mno-ms-bitfields
command-line options, respectively;
see x86 Options, for details of how structure layout is affected.
See x86 Type Attributes, for information about the corresponding
attributes on types.
One attribute is currently defined for xstormy16 configurations:
below100.
below100below100 attribute (BELOW100 is
allowed also), GCC places the variable in the first 0x100 bytes of
memory and use special opcodes to access it. Such variables are
placed in either the .bss_below100 section or the
.data_below100 section.
The keyword __attribute__ allows you to specify various special
properties of types. Some type attributes apply only to structure and
union types, and in C++, also class types, while others can apply to
any type defined via a typedef declaration. Unless otherwise
specified, the same restrictions and effects apply to attributes regardless
of whether a type is a trivial structure or a C++ class with user-defined
constructors, destructors, or a copy assignment.
Other attributes are defined for functions (see Function Attributes), labels (see Label Attributes), enumerators (see Enumerator Attributes), statements (see Statement Attributes), and for variables (see Variable Attributes).
The __attribute__ keyword is followed by an attribute specification
enclosed in double parentheses.
You may specify type attributes in an enum, struct or union type
declaration or definition by placing them immediately after the
struct, union or enum keyword. You can also place
them just past the closing curly brace of the definition, but this is less
preferred because logically the type should be fully defined at
the closing brace.
You can also include type attributes in a typedef declaration.
See Attribute Syntax, for details of the exact syntax for using
attributes.
The following type attributes are supported on most targets.
alignedaligned (alignment)aligned attribute specifies a minimum alignment (in bytes) for
variables of the specified type. When specified, alignment must be
a power of 2. Specifying no alignment argument implies the maximum
alignment for the target, which is often, but by no means always, 8 or 16
bytes. For example, the declarations:
struct __attribute__ ((aligned (8))) S { short f[3]; };
typedef int more_aligned_int __attribute__ ((aligned (8)));
force the compiler to ensure (as far as it can) that each variable whose
type is struct S or more_aligned_int is allocated and
aligned at least on a 8-byte boundary. On a SPARC, having all
variables of type struct S aligned to 8-byte boundaries allows
the compiler to use the ldd and std (doubleword load and
store) instructions when copying one variable of type struct S to
another, thus improving run-time efficiency.
Note that the alignment of any given struct or union type
is required by the ISO C standard to be at least a perfect multiple of
the lowest common multiple of the alignments of all of the members of
the struct or union in question. This means that you can
effectively adjust the alignment of a struct or union
type by attaching an aligned attribute to any one of the members
of such a type, but the notation illustrated in the example above is a
more obvious, intuitive, and readable way to request the compiler to
adjust the alignment of an entire struct or union type.
As in the preceding example, you can explicitly specify the alignment
(in bytes) that you wish the compiler to use for a given struct
or union type. Alternatively, you can leave out the alignment factor
and just ask the compiler to align a type to the maximum
useful alignment for the target machine you are compiling for. For
example, you could write:
struct __attribute__ ((aligned)) S { short f[3]; };
Whenever you leave out the alignment factor in an aligned
attribute specification, the compiler automatically sets the alignment
for the type to the largest alignment that is ever used for any data
type on the target machine you are compiling for. Doing this can often
make copy operations more efficient, because the compiler can use
whatever instructions copy the biggest chunks of memory when performing
copies to or from the variables that have types that you have aligned
this way.
In the example above, if the size of each short is 2 bytes, then
the size of the entire struct S type is 6 bytes. The smallest
power of two that is greater than or equal to that is 8, so the
compiler sets the alignment for the entire struct S type to 8
bytes.
Note that although you can ask the compiler to select a time-efficient alignment for a given type and then declare only individual stand-alone objects of that type, the compiler's ability to select a time-efficient alignment is primarily useful only when you plan to create arrays of variables having the relevant (efficiently aligned) type. If you declare or use arrays of variables of an efficiently-aligned type, then it is likely that your program also does pointer arithmetic (or subscripting, which amounts to the same thing) on pointers to the relevant type, and the code that the compiler generates for these pointer arithmetic operations is often more efficient for efficiently-aligned types than for other types.
Note that the effectiveness of aligned attributes may be limited
by inherent limitations in your linker. On many systems, the linker is
only able to arrange for variables to be aligned up to a certain maximum
alignment. (For some linkers, the maximum supported alignment may
be very very small.) If your linker is only able to align variables
up to a maximum of 8-byte alignment, then specifying aligned (16)
in an __attribute__ still only provides you with 8-byte
alignment. See your linker documentation for further information.
When used on a struct, or struct member, the aligned attribute can
only increase the alignment; in order to decrease it, the packed
attribute must be specified as well. When used as part of a typedef, the
aligned attribute can both increase and decrease alignment, and
specifying the packed attribute generates a warning.
warn_if_not_aligned (alignment) typedef unsigned long long __u64
__attribute__((aligned (4), warn_if_not_aligned (8)));
struct foo
{
int i1;
int i2;
__u64 x;
};
causes the compiler to issue an warning on struct foo, like
‘warning: alignment 4 of 'struct foo' is less than 8’.
It is used to define struct foo in such a way that
struct foo has the same layout and the structure field x
has the same alignment when __u64 is aligned at either 4 or
8 bytes. Align struct foo to 8 bytes:
struct __attribute__ ((aligned (8))) foo
{
int i1;
int i2;
__u64 x;
};
silences the warning. The compiler also issues a warning, like ‘warning: 'x' offset 12 in 'struct foo' isn't aligned to 8’, when the structure field has the misaligned offset:
struct __attribute__ ((aligned (8))) foo
{
int i1;
int i2;
int i3;
__u64 x;
};
This warning can be disabled by -Wno-if-not-aligned.
alloc_size (position)alloc_size (position-1, position-2)alloc_size type attribute may be applied to the definition
of a type of a function that returns a pointer and takes at least one
argument of an integer type. It indicates that the returned pointer
points to an object whose size is given by the function argument at
position-1, or by the product of the arguments at position-1
and position-2. Meaningful sizes are positive values less than
PTRDIFF_MAX. Other sizes are disagnosed when detected. GCC uses
this information to improve the results of __builtin_object_size.
For instance, the following declarations
typedef __attribute__ ((alloc_size (1, 2))) void*
calloc_type (size_t, size_t);
typedef __attribute__ ((alloc_size (1))) void*
malloc_type (size_t);
specify that calloc_type is a type of a function that, like
the standard C function calloc, returns an object whose size
is given by the product of arguments 1 and 2, and that
malloc_type, like the standard C function malloc,
returns an object whose size is given by argument 1 to the function.
copycopy (expression)copy attribute applies the set of attributes with which
the type of the expression has been declared to the declaration
of the type to which the attribute is applied. The attribute is
designed for libraries that define aliases that are expected to
specify the same set of attributes as the aliased symbols.
The copy attribute can be used with types, variables, or
functions. However, the kind of symbol to which the attribute is
applied (either varible or function) must match the kind of symbol
to which the argument refers.
The copy attribute copies only syntactic and semantic attributes
but not attributes that affect a symbol's linkage or visibility such as
alias, visibility, or weak. The deprecated
attribute is also not copied. See Common Function Attributes.
See Common Variable Attributes.
For example, suppose struct A below is defined in some third
party library header to have the alignment requirement N and
to force a warning whenever a variable of the type is not so aligned
due to attribute packed. Specifying the copy attribute
on the definition on the unrelated struct B has the effect of
copying all relevant attributes from the type referenced by the pointer
expression to struct B.
struct __attribute__ ((aligned (N), warn_if_not_aligned (N)))
A { /* ... */ };
struct __attribute__ ((copy ( (struct A *)0)) B { /* ... */ };
deprecateddeprecated (msg)deprecated attribute results in a warning if the type
is used anywhere in the source file. This is useful when identifying
types that are expected to be removed in a future version of a program.
If possible, the warning also includes the location of the declaration
of the deprecated type, to enable users to easily find further
information about why the type is deprecated, or what they should do
instead. Note that the warnings only occur for uses and then only
if the type is being applied to an identifier that itself is not being
declared as deprecated.
typedef int T1 __attribute__ ((deprecated));
T1 x;
typedef T1 T2;
T2 y;
typedef T1 T3 __attribute__ ((deprecated));
T3 z __attribute__ ((deprecated));
results in a warning on line 2 and 3 but not lines 4, 5, or 6. No warning is issued for line 4 because T2 is not explicitly deprecated. Line 5 has no warning because T3 is explicitly deprecated. Similarly for line 6. The optional msg argument, which must be a string, is printed in the warning if present. Control characters in the string will be replaced with escape sequences, and if the -fmessage-length option is set to 0 (its default value) then any newline characters will be ignored.
The deprecated attribute can also be used for functions and
variables (see Function Attributes, see Variable Attributes.)
The message attached to the attribute is affected by the setting of the -fmessage-length option.
unavailableunavailable (msg)unavailable attribute behaves in the same manner as the
deprecated one, but emits an error rather than a warning. It is
used to indicate that a (perhaps previously deprecated) type is
no longer usable.
The unavailable attribute can also be used for functions and
variables (see Function Attributes, see Variable Attributes.)
designated_initGCC emits warnings based on this attribute by default; use -Wno-designated-init to suppress them.
hardboolhardbool (false_value)hardbool (false_value, true_value)false and true. Underneath, it is
actually an enumerate type, but its observable behavior is like that of
_Bool, except for the strict internal representations, verified
by runtime checks.
If true_value is omitted, the bitwise negation of false_value is used. If false_value is omitted, zero is used. The named representation values must be different when converted to the original integral type. Narrower bitfields are rejected if the representations become indistinguishable.
Values of such types automatically decay to _Bool, at which
point, the selected representation values are mapped to the
corresponding _Bool values. When the represented value is not
determined, at compile time, to be either false_value or
true_value, runtime verification calls __builtin_trap if it
is neither. This is what makes them hardened boolean types.
When converting scalar types to such hardened boolean types, implicitly
or explicitly, behavior corresponds to a conversion to _Bool,
followed by a mapping from false and true to
false_value and true_value, respectively.
typedef char __attribute__ ((__hardbool__ (0x5a))) hbool;
hbool first = 0; /* False, stored as (char)0x5a. */
hbool second = !first; /* True, stored as ~(char)0x5a. */
static hbool zeroinit; /* False, stored as (char)0x5a. */
auto hbool uninit; /* Undefined, may trap. */
When zero-initializing a variable or field of hardened boolean type
(presumably held in static storage) the implied zero initializer gets
converted to _Bool, and then to the hardened boolean type, so
that the initial value is the hardened representation for false.
Using that value is well defined. This is not the case when
variables and fields of such types are uninitialized (presumably held in
automatic or dynamic storage): their values are indeterminate, and using
them invokes undefined behavior. Using them may trap or not, depending
on the bits held in the storage (re)used for the variable, if any, and
on optimizations the compiler may perform on the grounds that using
uninitialized values invokes undefined behavior.
Users of -ftrivial-auto-var-init should be aware that the bit
patterns used as initializers are not converted to
hardbool types, so using a hardbool variable that is
implicitly initialized by the -ftrivial-auto-var-init may trap
if the representations values chosen for false and true do
not match the initializer.
Since this is a language extension only available in C, interoperation with other languages may pose difficulties. It should interoperate with Ada Booleans defined with the same size and equivalent representation clauses, and with enumerations or other languages' integral types that correspond to C's chosen integral type.
may_aliasNote that an object of a type with this attribute does not have any special semantics.
Example of use:
typedef short __attribute__ ((__may_alias__)) short_a;
int
main (void)
{
int a = 0x12345678;
short_a *b = (short_a *) &a;
b[1] = 0;
if (a == 0x12345678)
abort();
exit(0);
}
If you replaced short_a with short in the variable
declaration, the above program would abort when compiled with
-fstrict-aliasing, which is on by default at -O2 or
above.
mode (mode)See Machine Modes,
for a list of the possible keywords for mode.
You may also specify a mode of byte or __byte__ to
indicate the mode corresponding to a one-byte integer, word or
__word__ for the mode of a one-word integer, and pointer
or __pointer__ for the mode used to represent pointers.
packedstruct, union, or C++ class
type definition, specifies that each of its members (other than zero-width
bit-fields) is placed to minimize the memory required. This is equivalent
to specifying the packed attribute on each of the members.
When attached to an enum definition, the packed attribute
indicates that the smallest integral type should be used.
Specifying the -fshort-enums flag on the command line
is equivalent to specifying the packed
attribute on all enum definitions.
In the following example struct my_packed_struct's members are
packed closely together, but the internal layout of its s member
is not packed—to do that, struct my_unpacked_struct needs to
be packed too.
struct my_unpacked_struct
{
char c;
int i;
};
struct __attribute__ ((__packed__)) my_packed_struct
{
char c;
int i;
struct my_unpacked_struct s;
};
You may only specify the packed attribute on the definition
of an enum, struct, union, or class,
not on a typedef that does not also define the enumerated type,
structure, union, or class.
scalar_storage_order ("endianness")union or a struct, this attribute sets
the storage order, aka endianness, of the scalar fields of the type, as
well as the array fields whose component is scalar. The supported
endiannesses are big-endian and little-endian. The attribute
has no effects on fields which are themselves a union, a struct
or an array whose component is a union or a struct, and it is
possible for these fields to have a different scalar storage order than the
enclosing type.
Note that neither pointer nor vector fields are considered scalar fields in this context, so the attribute has no effects on these fields.
This attribute is supported only for targets that use a uniform default scalar storage order (fortunately, most of them), i.e. targets that store the scalars either all in big-endian or all in little-endian.
Additional restrictions are enforced for types with the reverse scalar storage order with regard to the scalar storage order of the target:
union or a
struct with reverse scalar storage order is not permitted and yields
an error.
union or a struct with reverse scalar storage order is
permitted but yields a warning, unless -Wno-scalar-storage-order
is specified.
union or a struct with reverse
scalar storage order is permitted.
These restrictions exist because the storage order attribute is lost when the address of a scalar or the address of an array with scalar component is taken, so storing indirectly through this address generally does not work. The second case is nevertheless allowed to be able to perform a block copy from or to the array.
Moreover, the use of type punning or aliasing to toggle the storage order is not supported; that is to say, if a given scalar object can be accessed through distinct types that assign a different storage order to it, then the behavior is undefined.
transparent_unionunion type definition, indicates
that any function parameter having that union type causes calls to that
function to be treated in a special way.
First, the argument corresponding to a transparent union type can be of
any type in the union; no cast is required. Also, if the union contains
a pointer type, the corresponding argument can be a null pointer
constant or a void pointer expression; and if the union contains a void
pointer type, the corresponding argument can be any pointer expression.
If the union member type is a pointer, qualifiers like const on
the referenced type must be respected, just as with normal pointer
conversions.
Second, the argument is passed to the function using the calling conventions of the first member of the transparent union, not the calling conventions of the union itself. All members of the union must have the same machine representation; this is necessary for this argument passing to work properly.
Transparent unions are designed for library functions that have multiple
interfaces for compatibility reasons. For example, suppose the
wait function must accept either a value of type int * to
comply with POSIX, or a value of type union wait * to comply with
the 4.1BSD interface. If wait's parameter were void *,
wait would accept both kinds of arguments, but it would also
accept any other pointer type and this would make argument type checking
less useful. Instead, <sys/wait.h> might define the interface
as follows:
typedef union __attribute__ ((__transparent_union__))
{
int *__ip;
union wait *__up;
} wait_status_ptr_t;
pid_t wait (wait_status_ptr_t);
This interface allows either int * or union wait *
arguments to be passed, using the int * calling convention.
The program can call wait with arguments of either type:
int w1 () { int w; return wait (&w); }
int w2 () { union wait w; return wait (&w); }
With this interface, wait's implementation might look like this:
pid_t wait (wait_status_ptr_t p)
{
return waitpid (-1, p.__ip, 0);
}
strubstrub modes for
specific functions, or implicitly, by means of strub variables.
Being a type attribute, it attaches to types, even when specified in function and variable declarations. When applied to function types, it takes an optional string argument. When applied to a pointer-to-function type, if the optional argument is given, it gets propagated to the function type.
/* A strub variable. */
int __attribute__ ((strub)) var;
/* A strub variable that happens to be a pointer. */
__attribute__ ((strub)) int *strub_ptr_to_int;
/* A pointer type that may point to a strub variable. */
typedef int __attribute__ ((strub)) *ptr_to_strub_int_type;
/* A declaration of a strub function. */
extern int __attribute__ ((strub)) foo (void);
/* A pointer to that strub function. */
int __attribute__ ((strub ("at-calls"))) (*ptr_to_strub_fn)(void) = foo;
A function associated with at-calls strub mode
(strub("at-calls"), or just strub) undergoes interface
changes. Its callers are adjusted to match the changes, and to scrub
(overwrite with zeros) the stack space used by the called function after
it returns. The interface change makes the function type incompatible
with an unadorned but otherwise equivalent type, so every
declaration and every type that may be used to call the function must be
associated with this strub mode.
A function associated with internal strub mode
(strub("internal")) retains an unmodified, type-compatible
interface, but it may be turned into a wrapper that calls the wrapped
body using a custom interface. The wrapper then scrubs the stack space
used by the wrapped body. Though the wrapped body has its stack space
scrubbed, the wrapper does not, so arguments and return values may
remain unscrubbed even when such a function is called by another
function that enables strub. This is why, when compiling with
-fstrub=strict, a strub context is not allowed to call
internal strub functions.
/* A declaration of an internal-strub function. */
extern int __attribute__ ((strub ("internal"))) bar (void);
int __attribute__ ((strub))
baz (void)
{
/* Ok, foo was declared above as an at-calls strub function. */
foo ();
/* Not allowed in strict mode, otherwise allowed. */
bar ();
}
An automatically-allocated variable associated with the strub
attribute causes the (immediately) enclosing function to have
strub enabled.
A statically-allocated variable associated with the strub
attribute causes functions that read it, through its strub
data type, to have strub enabled. Reading data by dereferencing
a pointer to a strub data type has the same effect. Note: The
attribute does not carry over from a composite type to the types of its
components, so the intended effect may not be obtained with non-scalar
types.
When selecting a strub-enabled mode for a function that is not
explicitly associated with one, because of strub variables or
data pointers, the function must satisfy internal mode viability
requirements (see below), even when at-calls mode is also viable
and, being more efficient, ends up selected as an optimization.
/* zapme is implicitly strub-enabled because of strub variables.
Optimization may change its strub mode, but not the requirements. */
static int
zapme (int i)
{
/* A local strub variable enables strub. */
int __attribute__ ((strub)) lvar;
/* Reading strub data through a pointer-to-strub enables strub. */
lvar = * (ptr_to_strub_int_type) &i;
/* Writing to a global strub variable does not enable strub. */
var = lvar;
/* Reading from a global strub variable enables strub. */
return var;
}
A strub context is the body (as opposed to the interface) of a
function that has strub enabled, be it explicitly, by
at-calls or internal mode, or implicitly, due to
strub variables or command-line options.
A function of a type associated with the disabled strub
mode (strub("disabled") will not have its own stack space
scrubbed. Such functions cannot be called from within
strub contexts.
In order to enable a function to be called from within strub
contexts without having its stack space scrubbed, associate it with the
callable strub mode (strub("callable")).
When a function is not assigned a strub mode, explicitly or
implicitly, the mode defaults to callable, except when compiling
with -fstrub=strict, that causes strub mode to default
to disabled.
extern int __attribute__ ((strub ("callable"))) bac (void);
extern int __attribute__ ((strub ("disabled"))) bad (void);
/* Implicitly disabled with -fstrub=strict, otherwise callable. */
extern int bah (void);
int __attribute__ ((strub))
bal (void)
{
/* Not allowed, bad is not strub-callable. */
bad ();
/* Ok, bac is strub-callable. */
bac ();
/* Not allowed with -fstrub=strict, otherwise allowed. */
bah ();
}
Function types marked callable and disabled are not
mutually compatible types, but the underlying interfaces are compatible,
so it is safe to convert pointers between them, and to use such pointers
or alternate declarations to call them. Interfaces are also
interchangeable between them and internal (but not
at-calls!), but adding internal to a pointer type will not
cause the pointed-to function to perform stack scrubbing.
void __attribute__ ((strub))
bap (void)
{
/* Assign a callable function to pointer-to-disabled.
Flagged as not quite compatible with -Wpedantic. */
int __attribute__ ((strub ("disabled"))) (*d_p) (void) = bac;
/* Not allowed: calls disabled type in a strub context. */
d_p ();
/* Assign a disabled function to pointer-to-callable.
Flagged as not quite compatible with -Wpedantic. */
int __attribute__ ((strub ("callable"))) (*c_p) (void) = bad;
/* Ok, safe. */
c_p ();
/* Assign an internal function to pointer-to-callable.
Flagged as not quite compatible with -Wpedantic. */
c_p = bar;
/* Ok, safe. */
c_p ();
/* Assign an at-calls function to pointer-to-callable.
Flaggged as incompatible. */
c_p = bal;
/* The call through an interface-incompatible type will not use the
modified interface expected by the at-calls function, so it is
likely to misbehave at runtime. */
c_p ();
}
Strub contexts are never inlined into non-strub contexts.
When an internal-strub function is split up, the wrapper can
often be inlined, but the wrapped body never is. A function
marked as always_inline, even if explicitly assigned
internal strub mode, will not undergo wrapping, so its body gets
inlined as required.
inline int __attribute__ ((strub ("at-calls")))
inl_atc (void)
{
/* This body may get inlined into strub contexts. */
}
inline int __attribute__ ((strub ("internal")))
inl_int (void)
{
/* This body NEVER gets inlined, though its wrapper may. */
}
inline int __attribute__ ((strub ("internal"), always_inline))
inl_int_ali (void)
{
/* No internal wrapper, so this body ALWAYS gets inlined,
but it cannot be called from non-strub contexts. */
}
void __attribute__ ((strub ("disabled")))
bat (void)
{
/* Not allowed, cannot inline into a non-strub context. */
inl_int_ali ();
}
Some -fstrub=* command line options enable strub modes
implicitly where viable. A strub mode is only viable for a
function if the function is eligible for that mode, and if other
conditions, detailed below, are satisfied. If it's not eligible for a
mode, attempts to explicitly associate it with that mode are rejected
with an error message. If it is eligible, that mode may be assigned
explicitly through this attribute, but implicit assignment through
command-line options may involve additional viability requirements.
A function is ineligible for at-calls strub mode if a
different strub mode is explicitly requested, if attribute
noipa is present, or if it calls __builtin_apply_args.
At-calls strub mode, if not requested through the function
type, is only viable for an eligible function if the function is not
visible to other translation units, if it doesn't have its address
taken, and if it is never called with a function type overrider.
/* bar is eligible for at-calls strub mode,
but not viable for that mode because it is visible to other units.
It is eligible and viable for internal strub mode. */
void bav () {}
/* setp is eligible for at-calls strub mode,
but not viable for that mode because its address is taken.
It is eligible and viable for internal strub mode. */
void setp (void) { static void (*p)(void); = setp; }
A function is ineligible for internal strub mode if a
different strub mode is explicitly requested, or if attribute
noipa is present. For an always_inline function, meeting
these requirements is enough to make it eligible. Any function that has
attribute noclone, that uses such extensions as non-local labels,
computed gotos, alternate variable argument passing interfaces,
__builtin_next_arg, or __builtin_return_address, or that
takes too many (about 64Ki) arguments is ineligible, unless it is
always_inline. For internal strub mode, all
eligible functions are viable.
/* flop is not eligible, thus not viable, for at-calls strub mode.
Likewise for internal strub mode. */
__attribute__ ((noipa)) void flop (void) {}
/* flip is eligible and viable for at-calls strub mode.
It would be ineligible for internal strub mode, because of noclone,
if it weren't for always_inline. With always_inline, noclone is not
an obstacle, so it is also eligible and viable for internal strub mode. */
inline __attribute__ ((noclone, always_inline)) void flip (void) {}
unusedunion or a struct),
this attribute means that variables of that type are meant to appear
possibly unused. GCC does not produce a warning for any variables of
that type, even if the variable appears to do nothing. This is often
the case with lock or thread classes, which are usually defined and then
not referenced, but contain constructors and destructors that have
nontrivial bookkeeping functions.
vector_size (bytes) typedef __attribute__ ((vector_size (32))) int int_vec32_t ;
typedef __attribute__ ((vector_size (32))) int* int_vec32_ptr_t;
typedef __attribute__ ((vector_size (32))) int int_vec32_arr3_t[3];
define int_vec32_t to be a 32-byte vector type composed of int
sized units. With int having a size of 4 bytes, the type defines
a vector of eight units, four bytes each. The mode of variables of type
int_vec32_t is V8SI. int_vec32_ptr_t is then defined
to be a pointer to such a vector type, and int_vec32_arr3_t to be
an array of three such vectors. See Vector Extensions, for details of
manipulating objects of vector types.
This attribute is only applicable to integral and floating scalar types. In function declarations the attribute applies to the function return type.
For example, the following:
__attribute__ ((vector_size (16))) float get_flt_vec16 (void);
declares get_flt_vec16 to be a function returning a 16-byte vector
with the base type float.
visibilityNote that the type visibility is applied to vague linkage entities associated with the class (vtable, typeinfo node, etc.). In particular, if a class is thrown as an exception in one shared object and caught in another, the class must have default visibility. Otherwise the two shared objects are unable to use the same typeinfo node and exception handling will break.
objc_root_class (Objective-C and Objective-C++ only)To specify multiple attributes, separate them by commas within the double parentheses: for example, ‘__attribute__ ((aligned (16), packed))’.
Declaring objects with uncached allows you to exclude
data-cache participation in load and store operations on those objects
without involving the additional semantic implications of
volatile. The .di instruction suffix is used for all
loads and stores of data declared uncached.
On those ARM targets that support dllimport (such as Symbian
OS), you can use the notshared attribute to indicate that the
virtual table and other similar data for a class should not be
exported from a DLL. For example:
class __declspec(notshared) C {
public:
__declspec(dllimport) C();
virtual void f();
}
__declspec(dllexport)
C::C() {}
In this code, C::C is exported from the current DLL, but the
virtual table for C is not exported. (You can use
__attribute__ instead of __declspec if you prefer, but
most Symbian OS code uses __declspec.)
BPF Compile Once - Run Everywhere (CO-RE) support. When attached to a
struct or union type definition, indicates that CO-RE
relocation information should be generated for any access to a variable
of that type. The behavior is equivalent to the programmer manually
wrapping every such access with __builtin_preserve_access_index.
Three attributes currently are defined for PowerPC configurations:
altivec, ms_struct and gcc_struct.
For full documentation of the ms_struct and gcc_struct
attributes please see the documentation in x86 Type Attributes.
The altivec attribute allows one to declare AltiVec vector data
types supported by the AltiVec Programming Interface Manual. The
attribute requires an argument to specify one of three vector types:
vector__, pixel__ (always followed by unsigned short),
and bool__ (always followed by unsigned).
__attribute__((altivec(vector__)))
__attribute__((altivec(pixel__))) unsigned short
__attribute__((altivec(bool__))) unsigned
These attributes mainly are intended to support the __vector,
__pixel, and __bool AltiVec keywords.
Two attributes are currently defined for x86 configurations:
ms_struct and gcc_struct.
ms_structgcc_structpacked is used on a structure, or if bit-fields are used
it may be that the Microsoft ABI packs them differently
than GCC normally packs them. Particularly when moving packed
data between functions compiled with GCC and the native Microsoft compiler
(either via function call or as data in a file), it may be necessary to access
either format.
The ms_struct and gcc_struct attributes correspond
to the -mms-bitfields and -mno-ms-bitfields
command-line options, respectively;
see x86 Options, for details of how structure layout is affected.
See x86 Variable Attributes, for information about the corresponding
attributes on variables.
GCC allows attributes to be set on C labels. See Attribute Syntax, for details of the exact syntax for using attributes. Other attributes are available for functions (see Function Attributes), variables (see Variable Attributes), enumerators (see Enumerator Attributes), statements (see Statement Attributes), and for types (see Type Attributes). A label attribute followed by a declaration appertains to the label and not the declaration.
This example uses the cold label attribute to indicate the
ErrorHandling branch is unlikely to be taken and that the
ErrorHandling label is unused:
asm goto ("some asm" : : : : NoError);
/* This branch (the fall-through from the asm) is less commonly used */
ErrorHandling:
__attribute__((cold, unused)); /* Semi-colon is required here */
printf("error\n");
return 0;
NoError:
printf("no error\n");
return 1;
unused#ifdef conditional.
hothot attribute on a label is used to inform the compiler that
the path following the label is more likely than paths that are not so
annotated. This attribute is used in cases where __builtin_expect
cannot be used, for instance with computed goto or asm goto.
coldcold attribute on labels is used to inform the compiler that
the path following the label is unlikely to be executed. This attribute
is used in cases where __builtin_expect cannot be used, for instance
with computed goto or asm goto.
GCC allows attributes to be set on enumerators. See Attribute Syntax, for details of the exact syntax for using attributes. Other attributes are available for functions (see Function Attributes), variables (see Variable Attributes), labels (see Label Attributes), statements (see Statement Attributes), and for types (see Type Attributes).
This example uses the deprecated enumerator attribute to indicate the
oldval enumerator is deprecated:
enum E {
oldval __attribute__((deprecated)),
newval
};
int
fn (void)
{
return oldval;
}
deprecateddeprecated attribute results in a warning if the enumerator
is used anywhere in the source file. This is useful when identifying
enumerators that are expected to be removed in a future version of a
program. The warning also includes the location of the declaration
of the deprecated enumerator, to enable users to easily find further
information about why the enumerator is deprecated, or what they should
do instead. Note that the warnings only occurs for uses.
unavailableunavailable attribute results in an error if the enumerator
is used anywhere in the source file. In other respects it behaves in the
same manner as the deprecated attribute.
GCC allows attributes to be set on null statements. See Attribute Syntax, for details of the exact syntax for using attributes. Other attributes are available for functions (see Function Attributes), variables (see Variable Attributes), labels (see Label Attributes), enumerators (see Enumerator Attributes), and for types (see Type Attributes).
fallthroughfallthrough attribute with a null statement serves as a
fallthrough statement. It hints to the compiler that a statement
that falls through to another case label, or user-defined label
in a switch statement is intentional and thus the
-Wimplicit-fallthrough warning must not trigger. The
fallthrough attribute may appear at most once in each attribute
list, and may not be mixed with other attributes. It can only
be used in a switch statement (the compiler will issue an error
otherwise), after a preceding statement and before a logically
succeeding case label, or user-defined label.
This example uses the fallthrough statement attribute to indicate that
the -Wimplicit-fallthrough warning should not be emitted:
switch (cond)
{
case 1:
bar (1);
__attribute__((fallthrough));
case 2:
...
}
assumeassume attribute with a null statement serves as portable
assumption. It should have a single argument, a conditional expression,
which is not evaluated. If the argument would evaluate to true
at the point where it appears, it has no effect, otherwise there
is undefined behavior. This is a GNU variant of the ISO C++23
standard assume attribute, but it can be used in any version of
both C and C++.
int
foo (int x, int y)
{
__attribute__((assume(x == 42)));
__attribute__((assume(++y == 43)));
return x + y;
}
y is not actually incremented and the compiler can but does not
have to optimize it to just return 42 + 42;.
This section describes the syntax with which __attribute__ may be
used, and the constructs to which attribute specifiers bind, for the C
language. Some details may vary for C++ and Objective-C. Because of
limitations in the grammar for attributes, some forms described here
may not be successfully parsed in all cases.
There are some problems with the semantics of attributes in C++. For
example, there are no manglings for attributes, although they may affect
code generation, so problems may arise when attributed types are used in
conjunction with templates or overloading. Similarly, typeid
does not distinguish between types with different attributes. Support
for attributes in C++ may be restricted in future to attributes on
declarations only, but not on nested declarators.
See Function Attributes, for details of the semantics of attributes applying to functions. See Variable Attributes, for details of the semantics of attributes applying to variables. See Type Attributes, for details of the semantics of attributes applying to structure, union and enumerated types. See Label Attributes, for details of the semantics of attributes applying to labels. See Enumerator Attributes, for details of the semantics of attributes applying to enumerators. See Statement Attributes, for details of the semantics of attributes applying to statements.
An attribute specifier is of the form
__attribute__ ((attribute-list)). An attribute list
is a possibly empty comma-separated sequence of attributes, where
each attribute is one of the following:
unused, or a reserved
word such as const).
mode attributes use this form.
format attributes use this form.
format_arg attributes use this form with the list being a single
integer constant expression, and alias attributes use this form
with the list being a single string constant.
An attribute specifier list is a sequence of one or more attribute specifiers, not separated by any other tokens.
You may optionally specify attribute names with ‘__’
preceding and following the name.
This allows you to use them in header files without
being concerned about a possible macro of the same name. For example,
you may use the attribute name __noreturn__ instead of noreturn.
In GNU C, an attribute specifier list may appear after the colon following a
label, other than a case or default label. GNU C++ only permits
attributes on labels if the attribute specifier is immediately
followed by a semicolon (i.e., the label applies to an empty
statement). If the semicolon is missing, C++ label attributes are
ambiguous, as it is permissible for a declaration, which could begin
with an attribute list, to be labelled in C++. Declarations cannot be
labelled in C90 or C99, so the ambiguity does not arise there.
In GNU C, an attribute specifier list may appear as part of an enumerator.
The attribute goes after the enumeration constant, before =, if
present. The optional attribute in the enumerator appertains to the
enumeration constant. It is not possible to place the attribute after
the constant expression, if present.
In GNU C, an attribute specifier list may appear as part of a null statement. The attribute goes before the semicolon.
An attribute specifier list may appear as part of a struct,
union or enum specifier. It may go either immediately
after the struct, union or enum keyword, or after
the closing brace. The former syntax is preferred.
Where attribute specifiers follow the closing brace, they are considered
to relate to the structure, union or enumerated type defined, not to any
enclosing declaration the type specifier appears in, and the type
defined is not complete until after the attribute specifiers.
Otherwise, an attribute specifier appears as part of a declaration, counting declarations of unnamed parameters and type names, and relates to that declaration (which may be nested in another declaration, for example in the case of a parameter declaration), or to a particular declarator within a declaration. Where an attribute specifier is applied to a parameter declared as a function or an array, it should apply to the function or array rather than the pointer to which the parameter is implicitly converted, but this is not yet correctly implemented.
Any list of specifiers and qualifiers at the start of a declaration may
contain attribute specifiers, whether or not such a list may in that
context contain storage class specifiers. (Some attributes, however,
are essentially in the nature of storage class specifiers, and only make
sense where storage class specifiers may be used; for example,
section.) There is one necessary limitation to this syntax: the
first old-style parameter declaration in a function definition cannot
begin with an attribute specifier, because such an attribute applies to
the function instead by syntax described below (which, however, is not
yet implemented in this case). In some other cases, attribute
specifiers are permitted by this grammar but not yet supported by the
compiler. All attribute specifiers in this place relate to the
declaration as a whole. In the obsolescent usage where a type of
int is implied by the absence of type specifiers, such a list of
specifiers and qualifiers may be an attribute specifier list with no
other specifiers or qualifiers.
At present, the first parameter in a function prototype must have some
type specifier that is not an attribute specifier; this resolves an
ambiguity in the interpretation of void f(int
(__attribute__((foo)) x)), but is subject to change. At present, if
the parentheses of a function declarator contain only attributes then
those attributes are ignored, rather than yielding an error or warning
or implying a single parameter of type int, but this is subject to
change.
An attribute specifier list may appear immediately before a declarator (other than the first) in a comma-separated list of declarators in a declaration of more than one identifier using a single list of specifiers and qualifiers. Such attribute specifiers apply only to the identifier before whose declarator they appear. For example, in
__attribute__((noreturn)) void d0 (void),
__attribute__((format(printf, 1, 2))) d1 (const char *, ...),
d2 (void);
the noreturn attribute applies to all the functions
declared; the format attribute only applies to d1.
An attribute specifier list may appear immediately before the comma,
= or semicolon terminating the declaration of an identifier other
than a function definition. Such attribute specifiers apply
to the declared object or function. Where an
assembler name for an object or function is specified (see Asm Labels), the attribute must follow the asm
specification.
An attribute specifier list may, in future, be permitted to appear after the declarator in a function definition (before any old-style parameter declarations or the function body).
Attribute specifiers may be mixed with type qualifiers appearing inside
the [] of a parameter array declarator, in the C99 construct by
which such qualifiers are applied to the pointer to which the array is
implicitly converted. Such attribute specifiers apply to the pointer,
not to the array, but at present this is not implemented and they are
ignored.
An attribute specifier list may appear at the start of a nested
declarator. At present, there are some limitations in this usage: the
attributes correctly apply to the declarator, but for most individual
attributes the semantics this implies are not implemented.
When attribute specifiers follow the * of a pointer
declarator, they may be mixed with any type qualifiers present.
The following describes the formal semantics of this syntax. It makes the
most sense if you are familiar with the formal specification of
declarators in the ISO C standard.
Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration T
D1, where T contains declaration specifiers that specify a type
Type (such as int) and D1 is a declarator that
contains an identifier ident. The type specified for ident
for derived declarators whose type does not include an attribute
specifier is as in the ISO C standard.
If D1 has the form ( attribute-specifier-list D ),
and the declaration T D specifies the type
“derived-declarator-type-list Type” for ident, then
T D1 specifies the type “derived-declarator-type-list
attribute-specifier-list Type” for ident.
If D1 has the form *
type-qualifier-and-attribute-specifier-list D, and the
declaration T D specifies the type
“derived-declarator-type-list Type” for ident, then
T D1 specifies the type “derived-declarator-type-list
type-qualifier-and-attribute-specifier-list pointer to Type” for
ident.
For example,
void (__attribute__((noreturn)) ****f) (void);
specifies the type “pointer to pointer to pointer to pointer to
non-returning function returning void”. As another example,
char *__attribute__((aligned(8))) *f;
specifies the type “pointer to 8-byte-aligned pointer to char”.
Note again that this does not work with most attributes; for example,
the usage of ‘aligned’ and ‘noreturn’ attributes given above
is not yet supported.
For compatibility with existing code written for compiler versions that did not implement attributes on nested declarators, some laxity is allowed in the placing of attributes. If an attribute that only applies to types is applied to a declaration, it is treated as applying to the type of that declaration. If an attribute that only applies to declarations is applied to the type of a declaration, it is treated as applying to that declaration; and, for compatibility with code placing the attributes immediately before the identifier declared, such an attribute applied to a function return type is treated as applying to the function type, and such an attribute applied to an array element type is treated as applying to the array type. If an attribute that only applies to function types is applied to a pointer-to-function type, it is treated as applying to the pointer target type; if such an attribute is applied to a function return type that is not a pointer-to-function type, it is treated as applying to the function type.
GNU C extends ISO C to allow a function prototype to override a later old-style non-prototype definition. Consider the following example:
/* Use prototypes unless the compiler is old-fashioned. */ #ifdef __STDC__ #define P(x) x #else #define P(x) () #endif /* Prototype function declaration. */ int isroot P((uid_t)); /* Old-style function definition. */ int isroot (x) /* ??? lossage here ??? */ uid_t x; { return x == 0; }
Suppose the type uid_t happens to be short. ISO C does
not allow this example, because subword arguments in old-style
non-prototype definitions are promoted. Therefore in this example the
function definition's argument is really an int, which does not
match the prototype argument type of short.
This restriction of ISO C makes it hard to write code that is portable
to traditional C compilers, because the programmer does not know
whether the uid_t type is short, int, or
long. Therefore, in cases like these GNU C allows a prototype
to override a later old-style definition. More precisely, in GNU C, a
function prototype argument type overrides the argument type specified
by a later old-style definition if the former type is the same as the
latter type before promotion. Thus in GNU C the above example is
equivalent to the following:
int isroot (uid_t);
int
isroot (uid_t x)
{
return x == 0;
}
GNU C++ does not support old-style function definitions, so this extension is irrelevant.
In GNU C, you may use C++ style comments, which start with ‘//’ and continue until the end of the line. Many other C implementations allow such comments, and they are included in the 1999 C standard. However, C++ style comments are not recognized if you specify an -std option specifying a version of ISO C before C99, or -ansi (equivalent to -std=c90).
In GNU C, you may normally use dollar signs in identifier names. This is because many traditional C implementations allow such identifiers. However, dollar signs in identifiers are not supported on a few target machines, typically because the target assembler does not allow them.
You can use the sequence ‘\e’ in a string or character constant to stand for the ASCII character <ESC>.
The keyword __alignof__ determines the alignment requirement of
a function, object, or a type, or the minimum alignment usually required
by a type. Its syntax is just like sizeof and C11 _Alignof.
For example, if the target machine requires a double value to be
aligned on an 8-byte boundary, then __alignof__ (double) is 8.
This is true on many RISC machines. On more traditional machine
designs, __alignof__ (double) is 4 or even 2.
Some machines never actually require alignment; they allow references to any
data type even at an odd address. For these machines, __alignof__
reports the smallest alignment that GCC gives the data type, usually as
mandated by the target ABI.
If the operand of __alignof__ is an lvalue rather than a type,
its value is the required alignment for its type, taking into account
any minimum alignment specified by attribute aligned
(see Common Variable Attributes). For example, after this
declaration:
struct foo { int x; char y; } foo1;
the value of __alignof__ (foo1.y) is 1, even though its actual
alignment is probably 2 or 4, the same as __alignof__ (int).
It is an error to ask for the alignment of an incomplete type other
than void.
If the operand of the __alignof__ expression is a function,
the expression evaluates to the alignment of the function which may
be specified by attribute aligned (see Common Function Attributes).
By declaring a function inline, you can direct GCC to make calls to that function faster. One way GCC can achieve this is to integrate that function's code into the code for its callers. This makes execution faster by eliminating the function-call overhead; in addition, if any of the actual argument values are constant, their known values may permit simplifications at compile time so that not all of the inline function's code needs to be included. The effect on code size is less predictable; object code may be larger or smaller with function inlining, depending on the particular case. You can also direct GCC to try to integrate all “simple enough” functions into their callers with the option -finline-functions.
GCC implements three different semantics of declaring a function
inline. One is available with -std=gnu89 or
-fgnu89-inline or when gnu_inline attribute is present
on all inline declarations, another when
-std=c99,
-std=gnu99 or an option for a later C version is used
(without -fgnu89-inline), and the third
is used when compiling C++.
To declare a function inline, use the inline keyword in its
declaration, like this:
static inline int
inc (int *a)
{
return (*a)++;
}
If you are writing a header file to be included in ISO C90 programs, write
__inline__ instead of inline. See Alternate Keywords.
The three types of inlining behave similarly in two important cases:
when the inline keyword is used on a static function,
like the example above, and when a function is first declared without
using the inline keyword and then is defined with
inline, like this:
extern int inc (int *a);
inline int
inc (int *a)
{
return (*a)++;
}
In both of these common cases, the program behaves the same as if you
had not used the inline keyword, except for its speed.
When a function is both inline and static, if all calls to the
function are integrated into the caller, and the function's address is
never used, then the function's own assembler code is never referenced.
In this case, GCC does not actually output assembler code for the
function, unless you specify the option -fkeep-inline-functions.
If there is a nonintegrated call, then the function is compiled to
assembler code as usual. The function must also be compiled as usual if
the program refers to its address, because that cannot be inlined.
Note that certain usages in a function definition can make it unsuitable
for inline substitution. Among these usages are: variadic functions,
use of alloca, use of computed goto (see Labels as Values),
use of nonlocal goto, use of nested functions, use of setjmp, use
of __builtin_longjmp and use of __builtin_return or
__builtin_apply_args. Using -Winline warns when a
function marked inline could not be substituted, and gives the
reason for the failure.
As required by ISO C++, GCC considers member functions defined within
the body of a class to be marked inline even if they are
not explicitly declared with the inline keyword. You can
override this with -fno-default-inline; see Options Controlling C++ Dialect.
GCC does not inline any functions when not optimizing unless you specify the ‘always_inline’ attribute for the function, like this:
/* Prototype. */
inline void foo (const char) __attribute__((always_inline));
The remainder of this section is specific to GNU C90 inlining.
When an inline function is not static, then the compiler must assume
that there may be calls from other source files; since a global symbol can
be defined only once in any program, the function must not be defined in
the other source files, so the calls therein cannot be integrated.
Therefore, a non-static inline function is always compiled on its
own in the usual fashion.
If you specify both inline and extern in the function
definition, then the definition is used only for inlining. In no case
is the function compiled on its own, not even if you refer to its
address explicitly. Such an address becomes an external reference, as
if you had only declared the function, and had not defined it.
This combination of inline and extern has almost the
effect of a macro. The way to use it is to put a function definition in
a header file with these keywords, and put another copy of the
definition (lacking inline and extern) in a library file.
The definition in the header file causes most calls to the function
to be inlined. If any uses of the function remain, they refer to
the single copy in the library.
C has the concept of volatile objects. These are normally accessed by pointers and used for accessing hardware or inter-thread communication. The standard encourages compilers to refrain from optimizations concerning accesses to volatile objects, but leaves it implementation defined as to what constitutes a volatile access. The minimum requirement is that at a sequence point all previous accesses to volatile objects have stabilized and no subsequent accesses have occurred. Thus an implementation is free to reorder and combine volatile accesses that occur between sequence points, but cannot do so for accesses across a sequence point. The use of volatile does not allow you to violate the restriction on updating objects multiple times between two sequence points.
Accesses to non-volatile objects are not ordered with respect to volatile accesses. You cannot use a volatile object as a memory barrier to order a sequence of writes to non-volatile memory. For instance:
int *ptr = something;
volatile int vobj;
*ptr = something;
vobj = 1;
Unless *ptr and vobj can be aliased, it is not guaranteed that the write to *ptr occurs by the time the update of vobj happens. If you need this guarantee, you must use a stronger memory barrier such as:
int *ptr = something;
volatile int vobj;
*ptr = something;
asm volatile ("" : : : "memory");
vobj = 1;
A scalar volatile object is read when it is accessed in a void context:
volatile int *src = somevalue;
*src;
Such expressions are rvalues, and GCC implements this as a read of the volatile object being pointed to.
Assignments are also expressions and have an rvalue. However when assigning to a scalar volatile, the volatile object is not reread, regardless of whether the assignment expression's rvalue is used or not. If the assignment's rvalue is used, the value is that assigned to the volatile object. For instance, there is no read of vobj in all the following cases:
int obj;
volatile int vobj;
vobj = something;
obj = vobj = something;
obj ? vobj = onething : vobj = anotherthing;
obj = (something, vobj = anotherthing);
If you need to read the volatile object after an assignment has occurred, you must use a separate expression with an intervening sequence point.
As bit-fields are not individually addressable, volatile bit-fields may be implicitly read when written to, or when adjacent bit-fields are accessed. Bit-field operations may be optimized such that adjacent bit-fields are only partially accessed, if they straddle a storage unit boundary. For these reasons it is unwise to use volatile bit-fields to access hardware.
The asm keyword allows you to embed assembler instructions
within C code. GCC provides two forms of inline asm
statements. A basic asm statement is one with no
operands (see Basic Asm), while an extended asm
statement (see Extended Asm) includes one or more operands.
The extended form is preferred for mixing C and assembly language
within a function, but to include assembly language at
top level you must use basic asm.
You can also use the asm keyword to override the assembler name
for a C symbol, or to place a C variable in a specific register.
A basic asm statement has the following syntax:
asm asm-qualifiers ( AssemblerInstructions )
For the C language, the asm keyword is a GNU extension.
When writing C code that can be compiled with -ansi and the
-std options that select C dialects without GNU extensions, use
__asm__ instead of asm (see Alternate Keywords). For
the C++ language, asm is a standard keyword, but __asm__
can be used for code compiled with -fno-asm.
volatilevolatile qualifier has no effect.
All basic asm blocks are implicitly volatile.
inlineinline qualifier, then for inlining purposes the size
of the asm statement is taken as the smallest size possible (see Size of an asm).
You may place multiple assembler instructions together in a single asm
string, separated by the characters normally used in assembly code for the
system. A combination that works in most places is a newline to break the
line, plus a tab character (written as ‘\n\t’).
Some assemblers allow semicolons as a line separator. However,
note that some assembler dialects use semicolons to start a comment.
Using extended asm (see Extended Asm) typically produces
smaller, safer, and more efficient code, and in most cases it is a
better solution than basic asm. However, there are two
situations where only basic asm can be used:
asm statements have to be inside a C
function, so to write inline assembly language at file scope (“top-level”),
outside of C functions, you must use basic asm.
You can use this technique to emit assembler directives,
define assembly language macros that can be invoked elsewhere in the file,
or write entire functions in assembly language.
Basic asm statements outside of functions may not use any
qualifiers.
naked attribute also require basic asm
(see Function Attributes).
Safely accessing C data and calling functions from basic asm is more
complex than it may appear. To access C data, it is better to use extended
asm.
Do not expect a sequence of asm statements to remain perfectly
consecutive after compilation. If certain instructions need to remain
consecutive in the output, put them in a single multi-instruction asm
statement. Note that GCC's optimizers can move asm statements
relative to other code, including across jumps.
asm statements may not perform jumps into other asm statements.
GCC does not know about these jumps, and therefore cannot take
account of them when deciding how to optimize. Jumps from asm to C
labels are only supported in extended asm.
Under certain circumstances, GCC may duplicate (or remove duplicates of) your assembly code when optimizing. This can lead to unexpected duplicate symbol errors during compilation if your assembly code defines symbols or labels.
Warning: The C standards do not specify semantics for asm,
making it a potential source of incompatibilities between compilers. These
incompatibilities may not produce compiler warnings/errors.
GCC does not parse basic asm's AssemblerInstructions, which
means there is no way to communicate to the compiler what is happening
inside them. GCC has no visibility of symbols in the asm and may
discard them as unreferenced. It also does not know about side effects of
the assembler code, such as modifications to memory or registers. Unlike
some compilers, GCC assumes that no changes to general purpose registers
occur. This assumption may change in a future release.
To avoid complications from future changes to the semantics and the
compatibility issues between compilers, consider replacing basic asm
with extended asm. See
How to convert from basic asm to extended asm for information about how to perform this
conversion.
The compiler copies the assembler instructions in a basic asm
verbatim to the assembly language output file, without
processing dialects or any of the ‘%’ operators that are available with
extended asm. This results in minor differences between basic
asm strings and extended asm templates. For example, to refer to
registers you might use ‘%eax’ in basic asm and
‘%%eax’ in extended asm.
On targets such as x86 that support multiple assembler dialects,
all basic asm blocks use the assembler dialect specified by the
-masm command-line option (see x86 Options).
Basic asm provides no
mechanism to provide different assembler strings for different dialects.
For basic asm with non-empty assembler string GCC assumes
the assembler block does not change any general purpose registers,
but it may read or write any globally accessible variable.
Here is an example of basic asm for i386:
/* Note that this code will not compile with -masm=intel */
#define DebugBreak() asm("int $3")
With extended asm you can read and write C variables from
assembler and perform jumps from assembler code to C labels.
Extended asm syntax uses colons (‘:’) to delimit
the operand parameters after the assembler template:
asm asm-qualifiers ( AssemblerTemplate
: OutputOperands
[ : InputOperands
[ : Clobbers ] ])
asm asm-qualifiers ( AssemblerTemplate
: OutputOperands
: InputOperands
: Clobbers
: GotoLabels)
where in the last form, asm-qualifiers contains goto (and in the
first form, not).
The asm keyword is a GNU extension.
When writing code that can be compiled with -ansi and the
various -std options, use __asm__ instead of
asm (see Alternate Keywords).
volatileasm statements is to manipulate input
values to produce output values. However, your asm statements may
also produce side effects. If so, you may need to use the volatile
qualifier to disable certain optimizations. See Volatile.
inlineinline qualifier, then for inlining purposes the size
of the asm statement is taken as the smallest size possible
(see Size of an asm).
gotoasm statement may
perform a jump to one of the labels listed in the GotoLabels.
See GotoLabels.
goto form of asm, this section contains
the list of all C labels to which the code in the
AssemblerTemplate may jump.
See GotoLabels.
asm statements may not perform jumps into other asm statements,
only to the listed GotoLabels.
GCC's optimizers do not know about other jumps; therefore they cannot take
account of them when deciding how to optimize.
The total number of input + output + goto operands is limited to 30.
The asm statement allows you to include assembly instructions directly
within C code. This may help you to maximize performance in time-sensitive
code or to access assembly instructions that are not readily available to C
programs.
Note that extended asm statements must be inside a function. Only
basic asm may be outside functions (see Basic Asm).
Functions declared with the naked attribute also require basic
asm (see Function Attributes).
While the uses of asm are many and varied, it may help to think of an
asm statement as a series of low-level instructions that convert input
parameters to output parameters. So a simple (if not particularly useful)
example for i386 using asm might look like this:
int src = 1;
int dst;
asm ("mov %1, %0\n\t"
"add $1, %0"
: "=r" (dst)
: "r" (src));
printf("%d\n", dst);
This code copies src to dst and add 1 to dst.
GCC's optimizers sometimes discard asm statements if they determine
there is no need for the output variables. Also, the optimizers may move
code out of loops if they believe that the code will always return the same
result (i.e. none of its input values change between calls). Using the
volatile qualifier disables these optimizations. asm statements
that have no output operands and asm goto statements,
are implicitly volatile.
This i386 code demonstrates a case that does not use (or require) the
volatile qualifier. If it is performing assertion checking, this code
uses asm to perform the validation. Otherwise, dwRes is
unreferenced by any code. As a result, the optimizers can discard the
asm statement, which in turn removes the need for the entire
DoCheck routine. By omitting the volatile qualifier when it
isn't needed you allow the optimizers to produce the most efficient code
possible.
void DoCheck(uint32_t dwSomeValue)
{
uint32_t dwRes;
// Assumes dwSomeValue is not zero.
asm ("bsfl %1,%0"
: "=r" (dwRes)
: "r" (dwSomeValue)
: "cc");
assert(dwRes > 3);
}
The next example shows a case where the optimizers can recognize that the input
(dwSomeValue) never changes during the execution of the function and can
therefore move the asm outside the loop to produce more efficient code.
Again, using the volatile qualifier disables this type of optimization.
void do_print(uint32_t dwSomeValue)
{
uint32_t dwRes;
for (uint32_t x=0; x < 5; x++)
{
// Assumes dwSomeValue is not zero.
asm ("bsfl %1,%0"
: "=r" (dwRes)
: "r" (dwSomeValue)
: "cc");
printf("%u: %u %u\n", x, dwSomeValue, dwRes);
}
}
The following example demonstrates a case where you need to use the
volatile qualifier.
It uses the x86 rdtsc instruction, which reads
the computer's time-stamp counter. Without the volatile qualifier,
the optimizers might assume that the asm block will always return the
same value and therefore optimize away the second call.
uint64_t msr;
asm volatile ( "rdtsc\n\t" // Returns the time in EDX:EAX.
"shl $32, %%rdx\n\t" // Shift the upper bits left.
"or %%rdx, %0" // 'Or' in the lower bits.
: "=a" (msr)
:
: "rdx");
printf("msr: %llx\n", msr);
// Do other work...
// Reprint the timestamp
asm volatile ( "rdtsc\n\t" // Returns the time in EDX:EAX.
"shl $32, %%rdx\n\t" // Shift the upper bits left.
"or %%rdx, %0" // 'Or' in the lower bits.
: "=a" (msr)
:
: "rdx");
printf("msr: %llx\n", msr);
GCC's optimizers do not treat this code like the non-volatile code in the earlier examples. They do not move it out of loops or omit it on the assumption that the result from a previous call is still valid.
Note that the compiler can move even volatile asm instructions relative
to other code, including across jump instructions. For example, on many
targets there is a system register that controls the rounding mode of
floating-point operations. Setting it with a volatile asm statement,
as in the following PowerPC example, does not work reliably.
asm volatile("mtfsf 255, %0" : : "f" (fpenv));
sum = x + y;
The compiler may move the addition back before the volatile asm
statement. To make it work as expected, add an artificial dependency to
the asm by referencing a variable in the subsequent code, for
example:
asm volatile ("mtfsf 255,%1" : "=X" (sum) : "f" (fpenv));
sum = x + y;
Under certain circumstances, GCC may duplicate (or remove duplicates of) your
assembly code when optimizing. This can lead to unexpected duplicate symbol
errors during compilation if your asm code defines symbols or labels.
Using ‘%=’
(see AssemblerTemplate) may help resolve this problem.
An assembler template is a literal string containing assembler instructions. The compiler replaces tokens in the template that refer to inputs, outputs, and goto labels, and then outputs the resulting string to the assembler. The string can contain any instructions recognized by the assembler, including directives. GCC does not parse the assembler instructions themselves and does not know what they mean or even whether they are valid assembler input. However, it does count the statements (see Size of an asm).
You may place multiple assembler instructions together in a single asm
string, separated by the characters normally used in assembly code for the
system. A combination that works in most places is a newline to break the
line, plus a tab character to move to the instruction field (written as
‘\n\t’).
Some assemblers allow semicolons as a line separator. However, note
that some assembler dialects use semicolons to start a comment.
Do not expect a sequence of asm statements to remain perfectly
consecutive after compilation, even when you are using the volatile
qualifier. If certain instructions need to remain consecutive in the output,
put them in a single multi-instruction asm statement.
Accessing data from C programs without using input/output operands (such as by using global symbols directly from the assembler template) may not work as expected. Similarly, calling functions directly from an assembler template requires a detailed understanding of the target assembler and ABI.
Since GCC does not parse the assembler template, it has no visibility of any symbols it references. This may result in GCC discarding those symbols as unreferenced unless they are also listed as input, output, or goto operands.
In addition to the tokens described by the input, output, and goto operands, these tokens have special meanings in the assembler template:
asm
statement in the entire compilation. This option is useful when creating local
labels and referring to them multiple times in a single template that
generates multiple assembler instructions.
asm templatesOn targets such as x86, GCC supports multiple assembler dialects. The -masm option controls which dialect GCC uses as its default for inline assembler. The target-specific documentation for the -masm option contains the list of supported dialects, as well as the default dialect if the option is not specified. This information may be important to understand, since assembler code that works correctly when compiled using one dialect will likely fail if compiled using another. See x86 Options.
If your code needs to support multiple assembler dialects (for example, if you are writing public headers that need to support a variety of compilation options), use constructs of this form:
{ dialect0 | dialect1 | dialect2... }
This construct outputs dialect0
when using dialect #0 to compile the code,
dialect1 for dialect #1, etc. If there are fewer alternatives within the
braces than the number of dialects the compiler supports, the construct
outputs nothing.
For example, if an x86 compiler supports two dialects (‘att’, ‘intel’), an assembler template such as this:
"bt{l %[Offset],%[Base] | %[Base],%[Offset]}; jc %l2"
is equivalent to one of
"btl %[Offset],%[Base] ; jc %l2" /* att dialect */ "bt %[Base],%[Offset]; jc %l2" /* intel dialect */
Using that same compiler, this code:
"xchg{l}\t{%%}ebx, %1"
corresponds to either
"xchgl\t%%ebx, %1" /* att dialect */ "xchg\tebx, %1" /* intel dialect */
There is no support for nesting dialect alternatives.
An asm statement has zero or more output operands indicating the names
of C variables modified by the assembler code.
In this i386 example, old (referred to in the template string as
%0) and *Base (as %1) are outputs and Offset
(%2) is an input:
bool old;
__asm__ ("btsl %2,%1\n\t" // Turn on zero-based bit #Offset in Base.
"sbb %0,%0" // Use the CF to calculate old.
: "=r" (old), "+rm" (*Base)
: "Ir" (Offset)
: "cc");
return old;
Operands are separated by commas. Each operand has this format:
[ [asmSymbolicName] ] constraint (cvariablename)
asm statement
that contains the definition. Any valid C variable name is acceptable,
including names already defined in the surrounding code. No two operands
within the same asm statement can use the same symbolic name.
When not using an asmSymbolicName, use the (zero-based) position
of the operand
in the list of operands in the assembler template. For example if there are
three output operands, use ‘%0’ in the template to refer to the first,
‘%1’ for the second, and ‘%2’ for the third.
Output constraints must begin with either ‘=’ (a variable overwriting an
existing value) or ‘+’ (when reading and writing). When using
‘=’, do not assume the location contains the existing value
on entry to the asm, except
when the operand is tied to an input; see Input Operands.
After the prefix, there must be one or more additional constraints
(see Constraints) that describe where the value resides. Common
constraints include ‘r’ for register and ‘m’ for memory.
When you list more than one possible location (for example, "=rm"),
the compiler chooses the most efficient one based on the current context.
If you list as many alternates as the asm statement allows, you permit
the optimizers to produce the best possible code.
If you must use a specific register, but your Machine Constraints do not
provide sufficient control to select the specific register you want,
local register variables may provide a solution (see Local Register Variables).
When the compiler selects the registers to use to represent the output operands, it does not use any of the clobbered registers (see Clobbers and Scratch Registers).
Output operand expressions must be lvalues. The compiler cannot check whether
the operands have data types that are reasonable for the instruction being
executed. For output expressions that are not directly addressable (for
example a bit-field), the constraint must allow a register. In that case, GCC
uses the register as the output of the asm, and then stores that
register into the output.
Operands using the ‘+’ constraint modifier count as two operands
(that is, both as input and output) towards the total maximum of 30 operands
per asm statement.
Use the ‘&’ constraint modifier (see Modifiers) on all output operands that must not overlap an input. Otherwise, GCC may allocate the output operand in the same register as an unrelated input operand, on the assumption that the assembler code consumes its inputs before producing outputs. This assumption may be false if the assembler code actually consists of more than one instruction.
The same problem can occur if one output parameter (a) allows a register
constraint and another output parameter (b) allows a memory constraint.
The code generated by GCC to access the memory address in b can contain
registers which might be shared by a, and GCC considers those
registers to be inputs to the asm. As above, GCC assumes that such input
registers are consumed before any outputs are written. This assumption may
result in incorrect behavior if the asm statement writes to a
before using
b. Combining the ‘&’ modifier with the register constraint on a
ensures that modifying a does not affect the address referenced by
b. Otherwise, the location of b
is undefined if a is modified before using b.
asm supports operand modifiers on operands (for example ‘%k2’
instead of simply ‘%2’). Generic Operand modifiers lists the modifiers that are available
on all targets. Other modifiers are hardware dependent.
For example, the list of supported modifiers for x86 is found at
x86 Operand modifiers.
If the C code that follows the asm makes no use of any of the output
operands, use volatile for the asm statement to prevent the
optimizers from discarding the asm statement as unneeded
(see Volatile).
This code makes no use of the optional asmSymbolicName. Therefore it
references the first output operand as %0 (were there a second, it
would be %1, etc). The number of the first input operand is one greater
than that of the last output operand. In this i386 example, that makes
Mask referenced as %1:
uint32_t Mask = 1234;
uint32_t Index;
asm ("bsfl %1, %0"
: "=r" (Index)
: "r" (Mask)
: "cc");
That code overwrites the variable Index (‘=’),
placing the value in a register (‘r’).
Using the generic ‘r’ constraint instead of a constraint for a specific
register allows the compiler to pick the register to use, which can result
in more efficient code. This may not be possible if an assembler instruction
requires a specific register.
The following i386 example uses the asmSymbolicName syntax.
It produces the
same result as the code above, but some may consider it more readable or more
maintainable since reordering index numbers is not necessary when adding or
removing operands. The names aIndex and aMask
are only used in this example to emphasize which
names get used where.
It is acceptable to reuse the names Index and Mask.
uint32_t Mask = 1234;
uint32_t Index;
asm ("bsfl %[aMask], %[aIndex]"
: [aIndex] "=r" (Index)
: [aMask] "r" (Mask)
: "cc");
Here are some more examples of output operands.
uint32_t c = 1;
uint32_t d;
uint32_t *e = &c;
asm ("mov %[e], %[d]"
: [d] "=rm" (d)
: [e] "rm" (*e));
Here, d may either be in a register or in memory. Since the compiler
might already have the current value of the uint32_t location
pointed to by e
in a register, you can enable it to choose the best location
for d by specifying both constraints.
Some targets have a special register that holds the “flags” for the
result of an operation or comparison. Normally, the contents of that
register are either unmodifed by the asm, or the asm statement is
considered to clobber the contents.
On some targets, a special form of output operand exists by which
conditions in the flags register may be outputs of the asm. The set of
conditions supported are target specific, but the general rule is that
the output variable must be a scalar integer, and the value is boolean.
When supported, the target defines the preprocessor symbol
__GCC_ASM_FLAG_OUTPUTS__.
Because of the special nature of the flag output operands, the constraint may not include alternatives.
Most often, the target has only one flags register, and thus is an implied
operand of many instructions. In this case, the operand should not be
referenced within the assembler template via %0 etc, as there's
no corresponding text in the assembly language.
ConditionHolds.
eqnecshscclomiplvsvchilsgeltgtleThe flag output constraints are not supported in thumb1 mode.
jcc or
setcc.
aaebbecezggelleopsnanaenbnbencnengngenlnlenonpnsnzInput operands make values from C variables and expressions available to the assembly code.
Operands are separated by commas. Each operand has this format:
[ [asmSymbolicName] ] constraint (cexpression)
asm statement
that contains the definition. Any valid C variable name is acceptable,
including names already defined in the surrounding code. No two operands
within the same asm statement can use the same symbolic name.
When not using an asmSymbolicName, use the (zero-based) position
of the operand
in the list of operands in the assembler template. For example if there are
two output operands and three inputs,
use ‘%2’ in the template to refer to the first input operand,
‘%3’ for the second, and ‘%4’ for the third.
Input constraint strings may not begin with either ‘=’ or ‘+’. When you list more than one possible location (for example, ‘"irm"’), the compiler chooses the most efficient one based on the current context. If you must use a specific register, but your Machine Constraints do not provide sufficient control to select the specific register you want, local register variables may provide a solution (see Local Register Variables).
Input constraints can also be digits (for example, "0"). This indicates
that the specified input must be in the same place as the output constraint
at the (zero-based) index in the output constraint list.
When using asmSymbolicName syntax for the output operands,
you may use these names (enclosed in brackets ‘[]’) instead of digits.
asm statement
as input. The enclosing parentheses are a required part of the syntax.
When the compiler selects the registers to use to represent the input operands, it does not use any of the clobbered registers (see Clobbers and Scratch Registers).
If there are no output operands but there are input operands, place two consecutive colons where the output operands would go:
__asm__ ("some instructions"
: /* No outputs. */
: "r" (Offset / 8));
Warning: Do not modify the contents of input-only operands
(except for inputs tied to outputs). The compiler assumes that on exit from
the asm statement these operands contain the same values as they
had before executing the statement.
It is not possible to use clobbers
to inform the compiler that the values in these inputs are changing. One
common work-around is to tie the changing input variable to an output variable
that never gets used. Note, however, that if the code that follows the
asm statement makes no use of any of the output operands, the GCC
optimizers may discard the asm statement as unneeded
(see Volatile).
asm supports operand modifiers on operands (for example ‘%k2’
instead of simply ‘%2’). Generic Operand modifiers lists the modifiers that are available
on all targets. Other modifiers are hardware dependent.
For example, the list of supported modifiers for x86 is found at
x86 Operand modifiers.
In this example using the fictitious combine instruction, the
constraint "0" for input operand 1 says that it must occupy the same
location as output operand 0. Only input operands may use numbers in
constraints, and they must each refer to an output operand. Only a number (or
the symbolic assembler name) in the constraint can guarantee that one operand
is in the same place as another. The mere fact that foo is the value of
both operands is not enough to guarantee that they are in the same place in
the generated assembler code.
asm ("combine %2, %0"
: "=r" (foo)
: "0" (foo), "g" (bar));
Here is an example using symbolic names.
asm ("cmoveq %1, %2, %[result]"
: [result] "=r"(result)
: "r" (test), "r" (new), "[result]" (old));
While the compiler is aware of changes to entries listed in the output
operands, the inline asm code may modify more than just the outputs. For
example, calculations may require additional registers, or the processor may
overwrite a register as a side effect of a particular assembler instruction.
In order to inform the compiler of these changes, list them in the clobber
list. Clobber list items are either register names or the special clobbers
(listed below). Each clobber list item is a string constant
enclosed in double quotes and separated by commas.
Clobber descriptions may not in any way overlap with an input or output
operand. For example, you may not have an operand describing a register class
with one member when listing that register in the clobber list. Variables
declared to live in specific registers (see Explicit Register Variables) and used
as asm input or output operands must have no part mentioned in the
clobber description. In particular, there is no way to specify that input
operands get modified without also specifying them as output operands.
When the compiler selects which registers to use to represent input and output operands, it does not use any of the clobbered registers. As a result, clobbered registers are available for any use in the assembler code.
Another restriction is that the clobber list should not contain the
stack pointer register. This is because the compiler requires the
value of the stack pointer to be the same after an asm
statement as it was on entry to the statement. However, previous
versions of GCC did not enforce this rule and allowed the stack
pointer to appear in the list, with unclear semantics. This behavior
is deprecated and listing the stack pointer may become an error in
future versions of GCC.
Here is a realistic example for the VAX showing the use of clobbered registers:
asm volatile ("movc3 %0, %1, %2"
: /* No outputs. */
: "g" (from), "g" (to), "g" (count)
: "r0", "r1", "r2", "r3", "r4", "r5", "memory");
Also, there are two special clobber arguments:
"cc""cc" clobber indicates that the assembler code modifies the flags
register. On some machines, GCC represents the condition codes as a specific
hardware register; "cc" serves to name this register.
On other machines, condition code handling is different,
and specifying "cc" has no effect. But
it is valid no matter what the target.
"memory""memory" clobber tells the compiler that the assembly code
performs memory
reads or writes to items other than those listed in the input and output
operands (for example, accessing the memory pointed to by one of the input
parameters). To ensure memory contains correct values, GCC may need to flush
specific register values to memory before executing the asm. Further,
the compiler does not assume that any values read from memory before an
asm remain unchanged after that asm; it reloads them as
needed.
Using the "memory" clobber effectively forms a read/write
memory barrier for the compiler.
Note that this clobber does not prevent the processor from doing
speculative reads past the asm statement. To prevent that, you need
processor-specific fence instructions.
Flushing registers to memory has performance implications and may be an issue for time-sensitive code. You can provide better information to GCC to avoid this, as shown in the following examples. At a minimum, aliasing rules allow GCC to know what memory doesn't need to be flushed.
Here is a fictitious sum of squares instruction, that takes two
pointers to floating point values in memory and produces a floating
point register output.
Notice that x, and y both appear twice in the asm
parameters, once to specify memory accessed, and once to specify a
base register used by the asm. You won't normally be wasting a
register by doing this as GCC can use the same register for both
purposes. However, it would be foolish to use both %1 and
%3 for x in this asm and expect them to be the
same. In fact, %3 may well not be a register. It might be a
symbolic memory reference to the object pointed to by x.
asm ("sumsq %0, %1, %2"
: "+f" (result)
: "r" (x), "r" (y), "m" (*x), "m" (*y));
Here is a fictitious *z++ = *x++ * *y++ instruction.
Notice that the x, y and z pointer registers
must be specified as input/output because the asm modifies
them.
asm ("vecmul %0, %1, %2"
: "+r" (z), "+r" (x), "+r" (y), "=m" (*z)
: "m" (*x), "m" (*y));
An x86 example where the string memory argument is of unknown length.
asm("repne scasb"
: "=c" (count), "+D" (p)
: "m" (*(const char (*)[]) p), "0" (-1), "a" (0));
If you know the above will only be reading a ten byte array then you
could instead use a memory input like:
"m" (*(const char (*)[10]) p).
Here is an example of a PowerPC vector scale implemented in assembly,
complete with vector and condition code clobbers, and some initialized
offset registers that are unchanged by the asm.
void
dscal (size_t n, double *x, double alpha)
{
asm ("/* lots of asm here */"
: "+m" (*(double (*)[n]) x), "+&r" (n), "+b" (x)
: "d" (alpha), "b" (32), "b" (48), "b" (64),
"b" (80), "b" (96), "b" (112)
: "cr0",
"vs32","vs33","vs34","vs35","vs36","vs37","vs38","vs39",
"vs40","vs41","vs42","vs43","vs44","vs45","vs46","vs47");
}
Rather than allocating fixed registers via clobbers to provide scratch
registers for an asm statement, an alternative is to define a
variable and make it an early-clobber output as with a2 and
a3 in the example below. This gives the compiler register
allocator more freedom. You can also define a variable and make it an
output tied to an input as with a0 and a1, tied
respectively to ap and lda. Of course, with tied
outputs your asm can't use the input value after modifying the
output register since they are one and the same register. What's
more, if you omit the early-clobber on the output, it is possible that
GCC might allocate the same register to another of the inputs if GCC
could prove they had the same value on entry to the asm. This
is why a1 has an early-clobber. Its tied input, lda
might conceivably be known to have the value 16 and without an
early-clobber share the same register as %11. On the other
hand, ap can't be the same as any of the other inputs, so an
early-clobber on a0 is not needed. It is also not desirable in
this case. An early-clobber on a0 would cause GCC to allocate
a separate register for the "m" (*(const double (*)[]) ap)
input. Note that tying an input to an output is the way to set up an
initialized temporary register modified by an asm statement.
An input not tied to an output is assumed by GCC to be unchanged, for
example "b" (16) below sets up %11 to 16, and GCC might
use that register in following code if the value 16 happened to be
needed. You can even use a normal asm output for a scratch if
all inputs that might share the same register are consumed before the
scratch is used. The VSX registers clobbered by the asm
statement could have used this technique except for GCC's limit on the
number of asm parameters.
static void
dgemv_kernel_4x4 (long n, const double *ap, long lda,
const double *x, double *y, double alpha)
{
double *a0;
double *a1;
double *a2;
double *a3;
__asm__
(
/* lots of asm here */
"#n=%1 ap=%8=%12 lda=%13 x=%7=%10 y=%0=%2 alpha=%9 o16=%11\n"
"#a0=%3 a1=%4 a2=%5 a3=%6"
:
"+m" (*(double (*)[n]) y),
"+&r" (n), // 1
"+b" (y), // 2
"=b" (a0), // 3
"=&b" (a1), // 4
"=&b" (a2), // 5
"=&b" (a3) // 6
:
"m" (*(const double (*)[n]) x),
"m" (*(const double (*)[]) ap),
"d" (alpha), // 9
"r" (x), // 10
"b" (16), // 11
"3" (ap), // 12
"4" (lda) // 13
:
"cr0",
"vs32","vs33","vs34","vs35","vs36","vs37",
"vs40","vs41","vs42","vs43","vs44","vs45","vs46","vs47"
);
}
asm goto allows assembly code to jump to one or more C labels. The
GotoLabels section in an asm goto statement contains
a comma-separated
list of all C labels to which the assembler code may jump. GCC assumes that
asm execution falls through to the next statement (if this is not the
case, consider using the __builtin_unreachable intrinsic after the
asm statement). Optimization of asm goto may be improved by
using the hot and cold label attributes (see Label Attributes).
If the assembler code does modify anything, use the "memory" clobber
to force the
optimizers to flush all register values to memory and reload them if
necessary after the asm statement.
Also note that an asm goto statement is always implicitly
considered volatile.
Be careful when you set output operands inside asm goto only on
some possible control flow paths. If you don't set up the output on
given path and never use it on this path, it is okay. Otherwise, you
should use ‘+’ constraint modifier meaning that the operand is
input and output one. With this modifier you will have the correct
values on all possible paths from the asm goto.
To reference a label in the assembler template, prefix it with
‘%l’ (lowercase ‘L’) followed by its (zero-based) position
in GotoLabels plus the number of input and output operands.
Output operand with constraint modifier ‘+’ is counted as two
operands because it is considered as one output and one input operand.
For example, if the asm has three inputs, one output operand
with constraint modifier ‘+’ and one output operand with
constraint modifier ‘=’ and references two labels, refer to the
first label as ‘%l6’ and the second as ‘%l7’).
Alternately, you can reference labels using the actual C label name
enclosed in brackets. For example, to reference a label named
carry, you can use ‘%l[carry]’. The label must still be
listed in the GotoLabels section when using this approach. It
is better to use the named references for labels as in this case you
can avoid counting input and output operands and special treatment of
output operands with constraint modifier ‘+’.
Here is an example of asm goto for i386:
asm goto (
"btl %1, %0\n\t"
"jc %l2"
: /* No outputs. */
: "r" (p1), "r" (p2)
: "cc"
: carry);
return 0;
carry:
return 1;
The following example shows an asm goto that uses a memory clobber.
int frob(int x)
{
int y;
asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
: /* No outputs. */
: "r"(x), "r"(&y)
: "r5", "memory"
: error);
return y;
error:
return -1;
}
The following example shows an asm goto that uses an output.
int foo(int count)
{
asm goto ("dec %0; jb %l[stop]"
: "+r" (count)
:
:
: stop);
return count;
stop:
return 0;
}
The following artificial example shows an asm goto that sets
up an output only on one path inside the asm goto. Usage of
constraint modifier = instead of + would be wrong as
factor is used on all paths from the asm goto.
int foo(int inp)
{
int factor = 0;
asm goto ("cmp %1, 10; jb %l[lab]; mov 2, %0"
: "+r" (factor)
: "r" (inp)
:
: lab);
lab:
return inp * factor; /* return 2 * inp or 0 if inp < 10 */
}
The following table shows the modifiers supported by all targets and their effects:
| Modifier | Description | Example
|
|---|---|---|
c
| Require a constant operand and print the constant expression with no punctuation. | %c0
|
n
| Like ‘%c’ except that the value of the constant is negated before printing. | %n0
|
a
| Substitute a memory reference, with the actual operand treated as the address. This may be useful when outputting a “load address” instruction, because often the assembler syntax for such an instruction requires you to write the operand as if it were a memory reference. | %a0
|
l
| Print the label name with no punctuation. | %l0
|
References to input, output, and goto operands in the assembler template
of extended asm statements can use
modifiers to affect the way the operands are formatted in
the code output to the assembler. For example, the
following code uses the ‘h’ and ‘b’ modifiers for x86:
uint16_t num;
asm volatile ("xchg %h0, %b0" : "+a" (num) );
These modifiers generate this assembler code:
xchg %ah, %al
The rest of this discussion uses the following code for illustrative purposes.
int main()
{
int iInt = 1;
top:
asm volatile goto ("some assembler instructions here"
: /* No outputs. */
: "q" (iInt), "X" (sizeof(unsigned char) + 1), "i" (42)
: /* No clobbers. */
: top);
}
With no modifiers, this is what the output from the operands would be for the ‘att’ and ‘intel’ dialects of assembler:
| Operand | ‘att’ | ‘intel’
|
|---|---|---|
%0
| %eax
| eax
|
%1
| $2
| 2
|
%3
| $.L3
| OFFSET FLAT:.L3
|
%4
| $8
| 8
|
%5
| %xmm0
| xmm0
|
%7
| $0
| 0
|
The table below shows the list of supported modifiers and their effects.
| Modifier | Description | Operand | ‘att’ | ‘intel’
|
|---|---|---|---|---|
A
| Print an absolute memory reference. | %A0
| *%rax
| rax
|
b
| Print the QImode name of the register. | %b0
| %al
| al
|
B
| print the opcode suffix of b. | %B0
| b
|
|
c
| Require a constant operand and print the constant expression with no punctuation. | %c1
| 2
| 2
|
d
| print duplicated register operand for AVX instruction. | %d5
| %xmm0, %xmm0
| xmm0, xmm0
|
E
| Print the address in Double Integer (DImode) mode (8 bytes) when the target is 64-bit. Otherwise mode is unspecified (VOIDmode). | %E1
| %(rax)
| [rax]
|
g
| Print the V16SFmode name of the register. | %g0
| %zmm0
| zmm0
|
h
| Print the QImode name for a “high” register. | %h0
| %ah
| ah
|
H
| Add 8 bytes to an offsettable memory reference. Useful when accessing the high 8 bytes of SSE values. For a memref in (%rax), it generates | %H0
| 8(%rax)
| 8[rax]
|
k
| Print the SImode name of the register. | %k0
| %eax
| eax
|
l
| Print the label name with no punctuation. | %l3
| .L3
| .L3
|
L
| print the opcode suffix of l. | %L0
| l
|
|
N
| print maskz. | %N7
| {z}
| {z}
|
p
| Print raw symbol name (without syntax-specific prefixes). | %p2
| 42
| 42
|
P
| If used for a function, print the PLT suffix and generate PIC code.
For example, emit foo@PLT instead of 'foo' for the function
foo(). If used for a constant, drop all syntax-specific prefixes and
issue the bare constant. See p above.
| |||
q
| Print the DImode name of the register. | %q0
| %rax
| rax
|
Q
| print the opcode suffix of q. | %Q0
| q
|
|
R
| print embedded rounding and sae. | %R4
| {rn-sae},
| , {rn-sae}
|
r
| print only sae. | %r4
| {sae},
| , {sae}
|
s
| print a shift double count, followed by the assemblers argument delimiterprint the opcode suffix of s. | %s1
| $2,
| 2,
|
S
| print the opcode suffix of s. | %S0
| s
|
|
t
| print the V8SFmode name of the register. | %t5
| %ymm0
| ymm0
|
T
| print the opcode suffix of t. | %T0
| t
|
|
V
| print naked full integer register name without %. | %V0
| eax
| eax
|
w
| Print the HImode name of the register. | %w0
| %ax
| ax
|
W
| print the opcode suffix of w. | %W0
| w
|
|
x
| print the V4SFmode name of the register. | %x5
| %xmm0
| xmm0
|
y
| print "st(0)" instead of "st" as a register. | %y6
| %st(0)
| st(0)
|
z
| Print the opcode suffix for the size of the current integer operand (one of b/w/l/q).
| %z0
| l
|
|
Z
| Like z, with special suffixes for x87 instructions.
|
asm OperandsOn x86 targets, there are several rules on the usage of stack-like registers
in the operands of an asm. These rules apply only to the operands
that are stack-like registers:
asm, it is
necessary to know which are implicitly popped by the asm, and
which must be explicitly popped by GCC.
An input register that is implicitly popped by the asm must be
explicitly clobbered, unless it is constrained to match an
output operand.
asm, it is
necessary to know how to adjust the stack to compensate for the pop.
If any non-popped input is closer to the top of the reg-stack than
the implicitly popped register, it would not be possible to know what the
stack looked like—it's not clear how the rest of the stack “slides
up”.
All implicitly popped input registers must be closer to the top of the reg-stack than any input that is not implicitly popped.
It is possible that if an input dies in an asm, the compiler might
use the input register for an output reload. Consider this example:
asm ("foo" : "=t" (a) : "f" (b));
This code says that input b is not popped by the asm, and that
the asm pushes a result onto the reg-stack, i.e., the stack is one
deeper after the asm than it was before. But, it is possible that
reload may think that it can use the same register for both the input and
the output.
To prevent this from happening, if any input operand uses the ‘f’ constraint, all output register constraints must use the ‘&’ early-clobber modifier.
The example above is correctly written as:
asm ("foo" : "=&t" (a) : "f" (b));
Output operands must specifically indicate which register an output
appears in after an asm. ‘=f’ is not allowed: the operand
constraints must select a class with a single register.
asm, and are pushed by the asm.
It makes no sense to push anywhere but the top of the reg-stack.
Output operands must start at the top of the reg-stack: output operands may not “skip” a register.
asm statements may need extra stack space for internal
calculations. This can be guaranteed by clobbering stack registers
unrelated to the inputs and outputs.
This asm
takes one input, which is internally popped, and produces two outputs.
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));
This asm takes two inputs, which are popped by the fyl2xp1 opcode,
and replaces them with one output. The st(1) clobber is necessary
for the compiler to know that fyl2xp1 pops both inputs.
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");
The list below describes the supported modifiers and their effects for MSP430.
| Modifier | Description
|
|---|---|
A | Select low 16-bits of the constant/register/memory operand.
|
B | Select high 16-bits of the constant/register/memory
operand.
|
C | Select bits 32-47 of the constant/register/memory operand.
|
D | Select bits 48-63 of the constant/register/memory operand.
|
H | Equivalent to B (for backwards compatibility).
|
I | Print the inverse (logical NOT) of the constant
value.
|
J | Print an integer without a # prefix.
|
L | Equivalent to A (for backwards compatibility).
|
O | Offset of the current frame from the top of the stack.
|
Q | Use the A instruction postfix.
|
R | Inverse of condition code, for unsigned comparisons.
|
W | Subtract 16 from the constant value.
|
X | Use the X instruction postfix.
|
Y | Subtract 4 from the constant value.
|
Z | Subtract 1 from the constant value.
|
b | Append .B, .W or .A to the
instruction, depending on the mode.
|
d | Offset 1 byte of a memory reference or constant value.
|
e | Offset 3 bytes of a memory reference or constant value.
|
f | Offset 5 bytes of a memory reference or constant value.
|
g | Offset 7 bytes of a memory reference or constant value.
|
p | Print the value of 2, raised to the power of the given
constant. Used to select the specified bit position.
|
r | Inverse of condition code, for signed comparisons.
|
x | Equivialent to X, but only for pointers.
|
The list below describes the supported modifiers and their effects for LoongArch.
| Modifier | Description
|
|---|---|
d | Same as c.
|
i | Print the character ”i” if the operand is not a register.
|
m | Same as c, but the printed value is operand - 1.
|
X | Print a constant integer operand in hexadecimal.
|
z | Print the operand in its unmodified form, followed by a comma.
|
asm Operands
Here are specific details on what constraint letters you can use with
asm operands.
Constraints can say whether
an operand may be in a register, and which kinds of register; whether the
operand can be a memory reference, and which kinds of address; whether the
operand may be an immediate constant, and which possible values it may
have. Constraints can also require two operands to match.
Side-effects aren't allowed in operands of inline asm, unless
‘<’ or ‘>’ constraints are used, because there is no guarantee
that the side effects will happen exactly once in an instruction that can update
the addressing register.
The simplest kind of constraint is a string full of letters, each of which describes one kind of operand that is permitted. Here are the letters that are allowed:
TARGET_MEM_CONSTRAINT macro.
For example, an address which is constant is offsettable; so is an address that is the sum of a register and a constant (as long as a slightly larger constant is also within the range of address-offsets supported by the machine); but an autoincrement or autodecrement address is not offsettable. More complicated indirect/indexed addresses may or may not be offsettable depending on the other addressing modes that the machine supports.
Note that in an output operand which can be matched by another operand, the constraint letter ‘o’ is valid only when accompanied by both ‘<’ (if the target machine has predecrement addressing) and ‘>’ (if the target machine has preincrement addressing).
asm this constraint is only
allowed if the operand is used exactly once in an instruction that can
handle the side effects. Not using an operand with ‘<’ in constraint
string in the inline asm pattern at all or using it in multiple
instructions isn't valid, because the side effects wouldn't be performed
or would be performed more than once. Furthermore, on some targets
the operand with ‘<’ in constraint string must be accompanied by
special instruction suffixes like %U0 instruction suffix on PowerPC
or %P0 on IA-64.
asm the same restrictions
as for ‘<’ apply.
const_double) is
allowed, but only if the target floating point format is the same as
that of the host machine (on which the compiler is running).
const_double or
const_vector) is allowed.
This might appear strange; if an insn allows a constant operand with a value not known at compile time, it certainly must allow any known value. So why use ‘s’ instead of ‘i’? Sometimes it allows better code to be generated.
For example, on the 68000 in a fullword instruction it is possible to use an immediate operand; but if the immediate value is between −128 and 127, better code results from loading the value into a register and using the register. This is because the load into the register can be done with a ‘moveq’ instruction. We arrange for this to happen by defining the letter ‘K’ to mean “any integer outside the range −128 to 127”, and then specifying ‘Ks’ in the operand constraints.
This number is allowed to be more than a single digit. If multiple digits are encountered consecutively, they are interpreted as a single decimal integer. There is scant chance for ambiguity, since to-date it has never been desirable that ‘10’ be interpreted as matching either operand 1 or operand 0. Should this be desired, one can use multiple alternatives instead.
This is called a matching constraint and what it really means is
that the assembler has only a single operand that fills two roles
which asm distinguishes. For example, an add instruction uses
two input operands and an output operand, but on most CISC
machines an add instruction really has only two operands, one of them an
input-output operand:
addl #35,r12
Matching constraints are used in these circumstances. More precisely, the two operands that match must include one input-only operand and one output-only operand. Moreover, the digit must be a smaller number than the number of the operand that uses it in the constraint.
‘p’ in the constraint must be accompanied by address_operand
as the predicate in the match_operand. This predicate interprets
the mode specified in the match_operand as the mode of the memory
reference for which the address would be valid.
Sometimes a single instruction has multiple alternative sets of possible operands. For example, on the 68000, a logical-or instruction can combine register or an immediate value into memory, or it can combine any kind of operand into a register; but it cannot combine one memory location into another.
These constraints are represented as multiple alternatives. An alternative can be described by a series of letters for each operand. The overall constraint for an operand is made from the letters for this operand from the first alternative, a comma, the letters for this operand from the second alternative, a comma, and so on until the last alternative. All operands for a single instruction must have the same number of alternatives.
So the first alternative for the 68000's logical-or could be written as
"+m" (output) : "ir" (input). The second could be "+r"
(output): "irm" (input). However, the fact that two memory locations
cannot be used in a single instruction prevents simply using "+rm"
(output) : "irm" (input). Using multi-alternatives, this might be
written as "+m,r" (output) : "ir,irm" (input). This describes
all the available alternatives to the compiler, allowing it to choose
the most efficient one for the current conditions.
There is no way within the template to determine which alternative was
chosen. However you may be able to wrap your asm statements with
builtins such as __builtin_constant_p to achieve the desired results.
Here are constraint modifier characters.
When the compiler fixes up the operands to satisfy the constraints, it needs to know which operands are read by the instruction and which are written by it. ‘=’ identifies an operand which is only written; ‘+’ identifies an operand that is both read and written; all other operands are assumed to only be read.
If you specify ‘=’ or ‘+’ in a constraint, you put it in the first character of the constraint string.
‘&’ applies only to the alternative in which it is written. In constraints with multiple alternatives, sometimes one alternative requires ‘&’ while others do not. See, for example, the ‘movdf’ insn of the 68000.
An operand which is read by the instruction can be tied to an earlyclobber operand if its only use as an input occurs before the early result is written. Adding alternatives of this form often allows GCC to produce better code when only some of the read operands can be affected by the earlyclobber. See, for example, the ‘mulsi3’ insn of the ARM.
Furthermore, if the earlyclobber operand is also a read/write operand, then that operand is written only after it's used.
‘&’ does not obviate the need to write ‘=’ or ‘+’. As earlyclobber operands are always written, a read-only earlyclobber operand is ill-formed and will be rejected by the compiler.
GCC can only handle one commutative pair in an asm; if you use more, the compiler may fail. Note that you need not use the modifier if the two alternatives are strictly identical; this would only waste time in the reload pass.
Whenever possible, you should use the general-purpose constraint letters
in asm arguments, since they will convey meaning more readily to
people reading your code. Failing that, use the constraint letters
that usually have very similar meanings across architectures. The most
commonly used constraints are ‘m’ and ‘r’ (for memory and
general-purpose registers respectively; see Simple Constraints), and
‘I’, usually the letter indicating the most common
immediate-constant format.
Each architecture defines additional constraints. These constraints
are used by the compiler itself for instruction generation, as well as
for asm statements; therefore, some of the constraints are not
particularly useful for asm. Here is a summary of some of the
machine-dependent constraints available on some particular machines;
it includes both constraints that are useful for asm and
constraints that aren't. The compiler source file mentioned in the
table heading for each architecture is the definitive reference for
the meanings of that architecture's constraints.
kSP)
wxw, but restricted to registers 0 to 15 inclusive.
yw, but restricted to registers 0 to 7 inclusive.
UplP0 to P7)
UpaP0 to P15)
IADD
instruction
JSUB
instruction (once negated)
KLMMOV
pseudo instruction. The MOV may be assembled to one of several different
machine instructions depending on the value
NMOV
pseudo instruction
SYZUshQUmpIJKfLABCDADBUunspec
Ysymbol_ref or label_ref
vSgSDSSSmSvcacscVeRBbuffer_* instructions
RFflat_* instructions
RSs_* instructions
RLds_* LDS instructions
RGds_* GDS instructions
RDds_* instructions
RMglobal_* instructions
qr0-r3,
r12-r15. This constraint can only match when the -mq
option is in effect.
er0-r3, r12-r15, sp.
This constraint can only match when the -mq
option is in effect.
DD0, D1.
ICalKLCnLCmLMOPHhr8-r15.
klr0-r7. In ARM state this
is an alias for the r constraint.
ts0-s31. Used for 32 bit values.
wd0-d31 and the appropriate
subset d0-d15 based on command line options.
Used for 64 bit values only. Not valid for Thumb1.
yzGIJKLMQasm statements)
RSUvUyUqladwebqtxyzIJKLMNOPGQadzqnA, then the register P0.
DWeABbvfcCtkuxywKshKuhKs7Ku7Ku5Ks4Ks3Ku3PnPAPBM1M2JLHQabcylhvzQWU16KLCm1Cl1Cr1Cali, except that for position independent code,
no symbols / expressions needing relocations are allowed.
CsyRcsRscRctRgsRraRccSraCfmUNSPEC_FP_MODE.
aACC_REGS (acc0 to acc7).
bEVEN_ACC_REGS (acc0 to acc7).
cCC_REGS (fcc0 to fcc3 and
icc0 to icc3).
dGPR_REGS (gr0 to gr63).
eEVEN_REGS (gr0 to gr63).
Odd registers are excluded not in the class but through the use of a machine
mode larger than 4 bytes.
fFPR_REGS (fr0 to fr63).
hFEVEN_REGS (fr0 to fr63).
Odd registers are excluded not in the class but through the use of a machine
mode larger than 4 bytes.
lLR_REG (the lr register).
qQUAD_REGS (gr2 to gr63).
Register numbers not divisible by 4 are excluded not in the class but through
the use of a machine mode larger than 8 bytes.
tICC_REGS (icc0 to icc3).
uFCC_REGS (fcc0 to fcc3).
vICR_REGS (cc4 to cc7).
wFCR_REGS (cc0 to cc3).
xQUAD_FPR_REGS (fr0 to fr63).
Register numbers not divisible by 4 are excluded not in the class but through
the use of a machine mode larger than 8 bytes.
zSPR_REGS (lcr and lr).
AQUAD_ACC_REGS (acc0 to acc7).
BACCG_REGS (accg0 to accg7).
CCR_REGS (cc0 to cc7).
GIJLMNOPABWefOIwxLSbKAafqxyZIJKzdepi instruction
LMNldil instruction
OPand operations in depi
and extru instructions
SUGAlo_sum data-linkage-table memory operand
QRTWar0 to r3 for addl instruction
bcdefmGIJKLMNOPdep instruction
QRshladd instruction
SRspRfbRsbRcrRclR0wR1wR2wR3wR02R13RdiRhlR23RaaRawRalRqiRadRsiRhiRhcRraRflRmmRpiRpaIs3IS1IS2IU2In4In5In6IM2IlbIlwSdSaSiSsSfSsS1fklmst.w and ld.w.
IKZBZCll.w and sc.w.
dr0 to r31).
zrmsr, $fcc1 to $fcc7).
dr unless
generating MIPS16 code, in which case the MIPS16 register set is used.
fhhi register. This constraint is no longer supported.
llo register. Use this register to store values that are
no bigger than a word.
xhi and lo registers. Use this register
to store doubleword values.
c$25 for -mabicalls.
v$3. Do not use this constraint in new code;
it is retained only for compatibility with glibc.
yr; retained for backwards compatibility.
zIJKLlui.
Mlui, addiu
or ori.
NOPGRZCll and sc.
ZDprefetch instruction, or for any other
instruction with the same addressing mode as prefetch.
adfIJKLMNOPRGSTQUWCsCiC0CjCmvqCapswCmvzCmvsApAcABWINR12R13KLMYaYlYswldhtkIu03In03Iu04Is05Iu05In05Ip05Iu06Iu08Iu09Is10Is11Is15Iu15Ic15Ie15It15Ii15Is16Is17Is19Is20IhigIzebIzehIxlsIx11IbmsIfexU33U45U37IJKLMz to use r0
instead of 0 in the assembly output.
NPSgp
as a 16-bit immediate to re-create their 32-bit value.
UvwIKMl.movhi)
OadDfGhIJKLMNOQRrr0...r31.
br, but r0 is not allowed, so
r1...r31.
ff0...f31.
df nowadays;
historically f was for single-precision and d was for
double-precision floating point.
vv0...v31.
wavs0...vs63. This is either an
FPR (vs0...vs31 are f0...f31) or a VR
(vs32...vs63 are v0...v31).
When using wa, you should use the %x output modifier, so that
the correct register number is printed. For example:
asm ("xvadddp %x0,%x1,%x2"
: "=wa" (v1)
: "wa" (v2), "wa" (v3));
You should not use %x for v operands:
asm ("xsaddqp %0,%1,%2"
: "=v" (v1)
: "v" (v2), "v" (v3));
cctr.
llr.
xcr0.
ycr0...cr7.
IJL instead
for SImode constants).
KLeIePeQlxvkq instruction.
mm does not allow addresses that update the base register.
If the < or > constraint is also used, they are allowed and
therefore on PowerPC targets in that case it is only safe
to use m<> in an asm statement if that asm statement
accesses the operand exactly once. The asm statement must also
use %U<opno> as a placeholder for the “update” flag in the
corresponding load or store instruction. For example:
asm ("st%U0 %1,%0" : "=m<>" (mem) : "r" (val));
is correct but:
asm ("st %1,%0" : "=m<>" (mem) : "r" (val));
is not.
QZaIJLTZInt3Int8JKLMNOPQbiQscWabWbcBC as a base register, with an optional offset.
WcaAX, BC, DE, or HL for the address, for calls.
WcvWd2DE as a base register, with an optional offset.
WdeDE as a base register, without any offset.
WfrWh1HL as a base register, with an optional one-byte offset.
WhbHL as a base register, with B or C as the index register.
WhlHL as a base register, without any offset.
Ws1SP as a base register, with an optional one-byte offset.
YAAX register.
BBC register.
DDE register.
RA through L registers.
SSP register.
THL register.
Z08WR8 register.
Z10WR10 register.
ZintR24 to R31).
aA register.
bB register.
cC register.
dD register.
eE register.
hH register.
lL register.
vwPSW register.
xX register.
fIJKASvrvdvmQSymbolInt08Sint08Sint16Sint24Uint04acdfIJKL(0..4095)(−524288..524287)MN0..9:H,Q:D,S,H:0,F:QRSTUWYfecdbhCADIJKsethi instruction)
Lmovcc instructions (11-bit
signed immediate)
Mmovrcc instructions (10-bit
signed immediate)
NSImode
OGHPQRSTUWwYabABCDaDbIu4Iu5In5Is5I5xIuBIsBIsCJcJsQRZbmdb
cmdc
flr29, r30 and r31
tr1
ur2
vr3
GJKLMOPRa, b, c, d,
si, di, bp, sp).
ql. In 32-bit mode, a,
b, c, and d; in 64-bit mode, any integer register.
Qh: a, b,
c, and d.
aa register.
bb register.
cc register.
dd register.
Ssi register.
Ddi register.
Aa and d registers. This class is used for instructions
that return double word results in the ax:dx register pair. Single
word values will be allocated either in ax or dx.
For example on i386 the following implements rdtsc:
unsigned long long rdtsc (void)
{
unsigned long long tick;
__asm__ __volatile__("rdtsc":"=A"(tick));
return tick;
}
This is not correct on x86-64 as it would allocate tick in either ax
or dx. You have to use the following variant instead:
unsigned long long rdtsc (void)
{
unsigned int tickl, tickh;
__asm__ __volatile__("rdtsc":"=a"(tickl),"=d"(tickh));
return ((unsigned long long)tickh << 32)|tickl;
}
Uft%st(0)).
u%st(1)).
yxv%xmm0-%xmm31).
Yz%xmm0).
IJKL0xFF or 0xFFFF, for andsi as a zero-extending move.
Mlea instruction).
Nin and out
instructions).
GCeWeVOIDmode immediate operands).
WzVOIDmode immediate operands).
Wde constraint.
ZTvTsabcdetyzIJKLMNOPQRSTUZabAIJKL
You can specify the name to be used in the assembler code for a C
function or variable by writing the asm (or __asm__)
keyword after the declarator.
It is up to you to make sure that the assembler names you choose do not
conflict with any other assembler symbols, or reference registers.
This sample shows how to specify the assembler name for data:
int foo asm ("myfoo") = 2;
This specifies that the name to be used for the variable foo in
the assembler code should be ‘myfoo’ rather than the usual
‘_foo’.
On systems where an underscore is normally prepended to the name of a C variable, this feature allows you to define names for the linker that do not start with an underscore.
GCC does not support using this feature with a non-static local variable since such variables do not have assembler names. If you are trying to put the variable in a particular register, see Explicit Register Variables.
To specify the assembler name for functions, write a declaration for the
function before its definition and put asm there, like this:
int func (int x, int y) asm ("MYFUNC");
int func (int x, int y)
{
/* ... */
This specifies that the name to be used for the function func in
the assembler code should be MYFUNC.
GNU C allows you to associate specific hardware registers with C variables. In almost all cases, allowing the compiler to assign registers produces the best code. However under certain unusual circumstances, more precise control over the variable storage is required.
Both global and local variables can be associated with a register. The consequences of performing this association are very different between the two, as explained in the sections below.
You can define a global register variable and associate it with a specified register like this:
register int *foo asm ("r12");
Here r12 is the name of the register that should be used. Note that
this is the same syntax used for defining local register variables, but for
a global variable the declaration appears outside a function. The
register keyword is required, and cannot be combined with
static. The register name must be a valid register name for the
target platform.
Do not use type qualifiers such as const and volatile, as
the outcome may be contrary to expectations. In particular, using the
volatile qualifier does not fully prevent the compiler from
optimizing accesses to the register.
Registers are a scarce resource on most systems and allowing the compiler to manage their usage usually results in the best code. However, under special circumstances it can make sense to reserve some globally. For example this may be useful in programs such as programming language interpreters that have a couple of global variables that are accessed very often.
After defining a global register variable, for the current compilation unit:
Note that these points only apply to code that is compiled with the definition. The behavior of code that is merely linked in (for example code from libraries) is not affected.
If you want to recompile source files that do not actually use your global register variable so they do not use the specified register for any other purpose, you need not actually add the global register declaration to their source code. It suffices to specify the compiler option -ffixed-reg (see Code Gen Options) to reserve the register.
Global register variables cannot have initial values, because an executable file has no means to supply initial contents for a register.
When selecting a register, choose one that is normally saved and restored by function calls on your machine. This ensures that code which is unaware of this reservation (such as library routines) will restore it before returning.
On machines with register windows, be sure to choose a global register that is not affected magically by the function call mechanism.
When calling routines that are not aware of the reservation, be
cautious if those routines call back into code which uses them. As an
example, if you call the system library version of qsort, it may
clobber your registers during execution, but (if you have selected
appropriate registers) it will restore them before returning. However
it will not restore them before calling qsort's comparison
function. As a result, global values will not reliably be available to
the comparison function unless the qsort function itself is rebuilt.
Similarly, it is not safe to access the global register variables from signal handlers or from more than one thread of control. Unless you recompile them specially for the task at hand, the system library routines may temporarily use the register for other things. Furthermore, since the register is not reserved exclusively for the variable, accessing it from handlers of asynchronous signals may observe unrelated temporary values residing in the register.
On most machines, longjmp restores to each global register
variable the value it had at the time of the setjmp. On some
machines, however, longjmp does not change the value of global
register variables. To be portable, the function that called setjmp
should make other arrangements to save the values of the global register
variables, and to restore them in a longjmp. This way, the same
thing happens regardless of what longjmp does.
You can define a local register variable and associate it with a specified register like this:
register int *foo asm ("r12");
Here r12 is the name of the register that should be used. Note
that this is the same syntax used for defining global register variables,
but for a local variable the declaration appears within a function. The
register keyword is required, and cannot be combined with
static. The register name must be a valid register name for the
target platform.
Do not use type qualifiers such as const and volatile, as
the outcome may be contrary to expectations. In particular, when the
const qualifier is used, the compiler may substitute the
variable with its initializer in asm statements, which may cause
the corresponding operand to appear in a different register.
As with global register variables, it is recommended that you choose a register that is normally saved and restored by function calls on your machine, so that calls to library routines will not clobber it.
The only supported use for this feature is to specify registers
for input and output operands when calling Extended asm
(see Extended Asm). This may be necessary if the constraints for a
particular machine don't provide sufficient control to select the desired
register. To force an operand into a register, create a local variable
and specify the register name after the variable's declaration. Then use
the local variable for the asm operand and specify any constraint
letter that matches the register:
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = ...;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
Warning: In the above example, be aware that a register (for example
r0) can be call-clobbered by subsequent code, including function
calls and library calls for arithmetic operators on other variables (for
example the initialization of p2). In this case, use temporary
variables for expressions between the register assignments:
int t1 = ...;
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = t1;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
Defining a register variable does not reserve the register. Other than
when invoking the Extended asm, the contents of the specified
register are not guaranteed. For this reason, the following uses
are explicitly not supported. If they appear to work, it is only
happenstance, and may stop working as intended due to (seemingly)
unrelated changes in surrounding code, or even minor changes in the
optimization of a future version of gcc:
asm
asm without using input
or output operands.
Some developers use Local Register Variables in an attempt to improve gcc's allocation of registers, especially in large functions. In this case the register name is essentially a hint to the register allocator. While in some instances this can generate better code, improvements are subject to the whims of the allocator/optimizers. Since there are no guarantees that your improvements won't be lost, this usage of Local Register Variables is discouraged.
On the MIPS platform, there is related use for local register variables with slightly different characteristics (see Defining coprocessor specifics for MIPS targets).
asmSome targets require that GCC track the size of each instruction used
in order to generate correct code. Because the final length of the
code produced by an asm statement is only known by the
assembler, GCC must make an estimate as to how big it will be. It
does this by counting the number of instructions in the pattern of the
asm and multiplying that by the length of the longest
instruction supported by that processor. (When working out the number
of instructions, it assumes that any occurrence of a newline or of
whatever statement separator character is supported by the assembler —
typically ‘;’ — indicates the end of an instruction.)
Normally, GCC's estimate is adequate to ensure that correct code is generated, but it is possible to confuse the compiler if you use pseudo instructions or assembler macros that expand into multiple real instructions, or if you use assembler directives that expand to more space in the object file than is needed for a single instruction. If this happens then the assembler may produce a diagnostic saying that a label is unreachable.
This size is also used for inlining decisions. If you use asm inline
instead of just asm, then for inlining purposes the size of the asm
is taken as the minimum size, ignoring how many instructions GCC thinks it is.
-ansi and the various -std options disable certain
keywords. This causes trouble when you want to use GNU C extensions, or
a general-purpose header file that should be usable by all programs,
including ISO C programs. The keywords asm, typeof and
inline are not available in programs compiled with
-ansi or -std (although inline can be used in a
program compiled with -std=c99 or a later standard). The
ISO C99 keyword
restrict is only available when -std=gnu99 (which will
eventually be the default) or -std=c99 (or the equivalent
-std=iso9899:1999), or an option for a later standard
version, is used.
The way to solve these problems is to put ‘__’ at the beginning and
end of each problematical keyword. For example, use __asm__
instead of asm, and __inline__ instead of inline.
Other C compilers won't accept these alternative keywords; if you want to compile with another compiler, you can define the alternate keywords as macros to replace them with the customary keywords. It looks like this:
#ifndef __GNUC__
#define __asm__ asm
#endif
-pedantic and other options cause warnings for many GNU C extensions.
You can
prevent such warnings within one expression by writing
__extension__ before the expression. __extension__ has no
effect aside from this.
enum TypesYou can define an enum tag without specifying its possible values.
This results in an incomplete type, much like what you get if you write
struct foo without describing the elements. A later declaration
that does specify the possible values completes the type.
You cannot allocate variables or storage using the type while it is incomplete. However, you can work with pointers to that type.
This extension may not be very useful, but it makes the handling of
enum more consistent with the way struct and union
are handled.
This extension is not supported by GNU C++.
GCC provides three magic constants that hold the name of the current
function as a string. In C++11 and later modes, all three are treated
as constant expressions and can be used in constexpr constexts.
The first of these constants is __func__, which is part of
the C99 standard:
The identifier __func__ is implicitly declared by the translator
as if, immediately following the opening brace of each function
definition, the declaration
static const char __func__[] = "function-name";
appeared, where function-name is the name of the lexically-enclosing
function. This name is the unadorned name of the function. As an
extension, at file (or, in C++, namespace scope), __func__
evaluates to the empty string.
__FUNCTION__ is another name for __func__, provided for
backward compatibility with old versions of GCC.
In C, __PRETTY_FUNCTION__ is yet another name for
__func__, except that at file scope (or, in C++, namespace scope),
it evaluates to the string "top level". In addition, in C++,
__PRETTY_FUNCTION__ contains the signature of the function as
well as its bare name. For example, this program:
extern "C" int printf (const char *, ...);
class a {
public:
void sub (int i)
{
printf ("__FUNCTION__ = %s\n", __FUNCTION__);
printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
}
};
int
main (void)
{
a ax;
ax.sub (0);
return 0;
}
gives this output:
__FUNCTION__ = sub
__PRETTY_FUNCTION__ = void a::sub(int)
These identifiers are variables, not preprocessor macros, and may not
be used to initialize char arrays or be concatenated with string
literals.
These functions may be used to get information about the callers of a function.
This function returns the return address of the current function, or of one of its callers. The level argument is number of frames to scan up the call stack. A value of
0yields the return address of the current function, a value of1yields the return address of the caller of the current function, and so forth. When inlining the expected behavior is that the function returns the address of the function that is returned to. To work around this behavior use thenoinlinefunction attribute.The level argument must be a constant integer.
On some machines it may be impossible to determine the return address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function returns an unspecified value. In addition,
__builtin_frame_addressmay be used to determine if the top of the stack has been reached.Additional post-processing of the returned value may be needed, see
__builtin_extract_return_addr.The stored representation of the return address in memory may be different from the address returned by
__builtin_return_address. For example, on AArch64 the stored address may be mangled with return address signing whereas the address returned by__builtin_return_addressis not.Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program. As a result, calls that are considered unsafe are diagnosed when the -Wframe-address option is in effect. Such calls should only be made in debugging situations.
On targets where code addresses are representable as
void *,void *addr = __builtin_extract_return_addr (__builtin_return_address (0));gives the code address where the current function would return. For example, such an address may be used with
dladdror other interfaces that work with code addresses.
The address as returned by
__builtin_return_addressmay have to be fed through this function to get the actual encoded address. For example, on the 31-bit S/390 platform the highest bit has to be masked out, or on SPARC platforms an offset has to be added for the true next instruction to be executed.If no fixup is needed, this function simply passes through addr.
This function does the reverse of
__builtin_extract_return_addr.
This function is similar to
__builtin_return_address, but it returns the address of the function frame rather than the return address of the function. Calling__builtin_frame_addresswith a value of0yields the frame address of the current function, a value of1yields the frame address of the caller of the current function, and so forth.The frame is the area on the stack that holds local variables and saved registers. The frame address is normally the address of the first word pushed on to the stack by the function. However, the exact definition depends upon the processor and the calling convention. If the processor has a dedicated frame pointer register, and the function has a frame, then
__builtin_frame_addressreturns the value of the frame pointer register.On some machines it may be impossible to determine the frame address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function returns
0if the first frame pointer is properly initialized by the startup code.Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program. As a result, calls that are considered unsafe are diagnosed when the -Wframe-address option is in effect. Such calls should only be made in debugging situations.
This function returns the stack pointer register, offset by
STACK_ADDRESS_OFFSETif that's defined.Conceptually, the returned address returned by this built-in function is the boundary between the stack area allocated for use by its caller, and the area that could be modified by a function call, that the caller could safely zero-out before or after (but not during) the call sequence.
Arguments for a callee may be preallocated as part of the caller's stack frame, or allocated on a per-call basis, depending on the target, so they may be on either side of this boundary.
Even if the stack pointer is biased, the result is not. The register save area on SPARC is regarded as modifiable by calls, rather than as allocated for use by the caller function, since it is never in use while the caller function itself is running.
Red zones that only leaf functions could use are also regarded as modifiable by calls, rather than as allocated for use by the caller. This is only theoretical, since leaf functions do not issue calls, but a constant offset makes this built-in function more predictable.
Stack scrubbing involves cooperation between a strub context,
i.e., a function whose stack frame is to be zeroed-out, and its callers.
The caller initializes a stack watermark, the strub context
updates the watermark according to its stack use, and the caller zeroes
it out once it regains control, whether by the callee's returning or by
an exception.
Each of these steps is performed by a different builtin function call.
Calls to these builtins are introduced automatically, in response to
strub attributes and command-line options; they are not expected
to be explicitly called by source code.
The functions that implement the builtins are available in libgcc but, depending on optimization levels, they are expanded internally, adjusted to account for inlining, and sometimes combined/deferred (e.g. passing the caller-supplied watermark on to callees, refraining from erasing stack areas that the caller will) to enable tail calls and to optimize for code size.
This function initializes a stack watermark variable with the current top of the stack. A call to this builtin function is introduced before entering a
strubcontext. It remains as a function call if optimization is not enabled.
This function updates a stack watermark variable with the current top of the stack, if it tops the previous watermark. A call to this builtin function is inserted within
strubcontexts, whenever additional stack space may have been used. It remains as a function call at optimization levels lower than 2.
This function overwrites the memory area between the current top of the stack, and the watermarked address. A call to this builtin function is inserted after leaving a
strubcontext. It remains as a function call at optimization levels lower than 3, and it is guarded by a condition at level 2.
On some targets, the instruction set contains SIMD vector instructions which operate on multiple values contained in one large register at the same time. For example, on the x86 the MMX, 3DNow! and SSE extensions can be used this way.
The first step in using these extensions is to provide the necessary data
types. This should be done using an appropriate typedef:
typedef int v4si __attribute__ ((vector_size (16)));
The int type specifies the base type, while the attribute specifies
the vector size for the variable, measured in bytes. For example, the
declaration above causes the compiler to set the mode for the v4si
type to be 16 bytes wide and divided into int sized units. For
a 32-bit int this means a vector of 4 units of 4 bytes, and the
corresponding mode of foo is V4SI.
The vector_size attribute is only applicable to integral and
floating scalars, although arrays, pointers, and function return values
are allowed in conjunction with this construct. Only sizes that are
positive power-of-two multiples of the base type size are currently allowed.
All the basic integer types can be used as base types, both as signed
and as unsigned: char, short, int, long,
long long. In addition, float and double can be
used to build floating-point vector types.
Specifying a combination that is not valid for the current architecture
causes GCC to synthesize the instructions using a narrower mode.
For example, if you specify a variable of type V4SI and your
architecture does not allow for this specific SIMD type, GCC
produces code that uses 4 SIs.
The types defined in this manner can be used with a subset of normal C
operations. Currently, GCC allows using the following operators
on these types: +, -, *, /, unary minus, ^, |, &, ~, %.
The operations behave like C++ valarrays. Addition is defined as
the addition of the corresponding elements of the operands. For
example, in the code below, each of the 4 elements in a is
added to the corresponding 4 elements in b and the resulting
vector is stored in c.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a, b, c;
c = a + b;
Subtraction, multiplication, division, and the logical operations operate in a similar manner. Likewise, the result of using the unary minus or complement operators on a vector type is a vector whose elements are the negative or complemented values of the corresponding elements in the operand.
It is possible to use shifting operators <<, >> on
integer-type vectors. The operation is defined as following: {a0,
a1, ..., an} >> {b0, b1, ..., bn} == {a0 >> b0, a1 >> b1,
..., an >> bn}. Vector operands must have the same number of
elements.
For convenience, it is allowed to use a binary vector operation where one operand is a scalar. In that case the compiler transforms the scalar operand into a vector where each element is the scalar from the operation. The transformation happens only if the scalar could be safely converted to the vector-element type. Consider the following code.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a, b, c;
long l;
a = b + 1; /* a = b + {1,1,1,1}; */
a = 2 * b; /* a = {2,2,2,2} * b; */
a = l + a; /* Error, cannot convert long to int. */
Vectors can be subscripted as if the vector were an array with the same number of elements and base type. Out of bound accesses invoke undefined behavior at run time. Warnings for out of bound accesses for vector subscription can be enabled with -Warray-bounds.
Vector comparison is supported with standard comparison
operators: ==, !=, <, <=, >, >=. Comparison operands can be
vector expressions of integer-type or real-type. Comparison between
integer-type vectors and real-type vectors are not supported. The
result of the comparison is a vector of the same width and number of
elements as the comparison operands with a signed integral element
type.
Vectors are compared element-wise producing 0 when comparison is false and -1 (constant of the appropriate type where all bits are set) otherwise. Consider the following example.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a = {1,2,3,4};
v4si b = {3,2,1,4};
v4si c;
c = a > b; /* The result would be {0, 0,-1, 0} */
c = a == b; /* The result would be {0,-1, 0,-1} */
In C++, the ternary operator ?: is available. a?b:c, where
b and c are vectors of the same type and a is an
integer vector with the same number of elements of the same size as b
and c, computes all three arguments and creates a vector
{a[0]?b[0]:c[0], a[1]?b[1]:c[1], ...}. Note that unlike in
OpenCL, a is thus interpreted as a != 0 and not a < 0.
As in the case of binary operations, this syntax is also accepted when
one of b or c is a scalar that is then transformed into a
vector. If both b and c are scalars and the type of
true?b:c has the same size as the element type of a, then
b and c are converted to a vector type whose elements have
this type and with the same number of elements as a.
In C++, the logic operators !, &&, || are available for vectors.
!v is equivalent to v == 0, a && b is equivalent to
a!=0 & b!=0 and a || b is equivalent to a!=0 | b!=0.
For mixed operations between a scalar s and a vector v,
s && v is equivalent to s?v!=0:0 (the evaluation is
short-circuit) and v && s is equivalent to v!=0 & (s?-1:0).
Vector shuffling is available using functions
__builtin_shuffle (vec, mask) and
__builtin_shuffle (vec0, vec1, mask).
Both functions construct a permutation of elements from one or two
vectors and return a vector of the same type as the input vector(s).
The mask is an integral vector with the same width (W)
and element count (N) as the output vector.
The elements of the input vectors are numbered in memory ordering of vec0 beginning at 0 and vec1 beginning at N. The elements of mask are considered modulo N in the single-operand case and modulo 2*N in the two-operand case.
Consider the following example,
typedef int v4si __attribute__ ((vector_size (16)));
v4si a = {1,2,3,4};
v4si b = {5,6,7,8};
v4si mask1 = {0,1,1,3};
v4si mask2 = {0,4,2,5};
v4si res;
res = __builtin_shuffle (a, mask1); /* res is {1,2,2,4} */
res = __builtin_shuffle (a, b, mask2); /* res is {1,5,3,6} */
Note that __builtin_shuffle is intentionally semantically
compatible with the OpenCL shuffle and shuffle2 functions.
You can declare variables and use them in function calls and returns, as well as in assignments and some casts. You can specify a vector type as a return type for a function. Vector types can also be used as function arguments. It is possible to cast from one vector type to another, provided they are of the same size (in fact, you can also cast vectors to and from other datatypes of the same size).
You cannot operate between vectors of different lengths or different signedness without a cast.
Vector shuffling is available using the
__builtin_shufflevector (vec1, vec2, index...)
function. vec1 and vec2 must be expressions with
vector type with a compatible element type. The result of
__builtin_shufflevector is a vector with the same element type
as vec1 and vec2 but that has an element count equal to
the number of indices specified.
The index arguments are a list of integers that specify the elements indices of the first two vectors that should be extracted and returned in a new vector. These element indices are numbered sequentially starting with the first vector, continuing into the second vector. An index of -1 can be used to indicate that the corresponding element in the returned vector is a don't care and can be freely chosen to optimized the generated code sequence performing the shuffle operation.
Consider the following example,
typedef int v4si __attribute__ ((vector_size (16)));
typedef int v8si __attribute__ ((vector_size (32)));
v8si a = {1,-2,3,-4,5,-6,7,-8};
v4si b = __builtin_shufflevector (a, a, 0, 2, 4, 6); /* b is {1,3,5,7} */
v4si c = {-2,-4,-6,-8};
v8si d = __builtin_shufflevector (c, b, 4, 0, 5, 1, 6, 2, 7, 3); /* d is a */
Vector conversion is available using the
__builtin_convertvector (vec, vectype)
function. vec must be an expression with integral or floating
vector type and vectype an integral or floating vector type with the
same number of elements. The result has vectype type and value of
a C cast of every element of vec to the element type of vectype.
Consider the following example,
typedef int v4si __attribute__ ((vector_size (16)));
typedef float v4sf __attribute__ ((vector_size (16)));
typedef double v4df __attribute__ ((vector_size (32)));
typedef unsigned long long v4di __attribute__ ((vector_size (32)));
v4si a = {1,-2,3,-4};
v4sf b = {1.5f,-2.5f,3.f,7.f};
v4di c = {1ULL,5ULL,0ULL,10ULL};
v4sf d = __builtin_convertvector (a, v4sf); /* d is {1.f,-2.f,3.f,-4.f} */
/* Equivalent of:
v4sf d = { (float)a[0], (float)a[1], (float)a[2], (float)a[3] }; */
v4df e = __builtin_convertvector (a, v4df); /* e is {1.,-2.,3.,-4.} */
v4df f = __builtin_convertvector (b, v4df); /* f is {1.5,-2.5,3.,7.} */
v4si g = __builtin_convertvector (f, v4si); /* g is {1,-2,3,7} */
v4si h = __builtin_convertvector (c, v4si); /* h is {1,5,0,10} */
Sometimes it is desirable to write code using a mix of generic vector
operations (for clarity) and machine-specific vector intrinsics (to
access vector instructions that are not exposed via generic built-ins).
On x86, intrinsic functions for integer vectors typically use the same
vector type __m128i irrespective of how they interpret the vector,
making it necessary to cast their arguments and return values from/to
other vector types. In C, you can make use of a union type:
#include <immintrin.h>
typedef unsigned char u8x16 __attribute__ ((vector_size (16)));
typedef unsigned int u32x4 __attribute__ ((vector_size (16)));
typedef union {
__m128i mm;
u8x16 u8;
u32x4 u32;
} v128;
for variables that can be used with both built-in operators and x86 intrinsics:
v128 x, y = { 0 };
memcpy (&x, ptr, sizeof x);
y.u8 += 0x80;
x.mm = _mm_adds_epu8 (x.mm, y.mm);
x.u32 &= 0xffffff;
/* Instead of a variable, a compound literal may be used to pass the
return value of an intrinsic call to a function expecting the union: */
v128 foo (v128);
x = foo ((v128) {_mm_adds_epu8 (x.mm, y.mm)});
offsetof
GCC implements for both C and C++ a syntactic extension to implement
the offsetof macro.
primary:
"__builtin_offsetof" "(" typename "," offsetof_member_designator ")"
offsetof_member_designator:
identifier
| offsetof_member_designator "." identifier
| offsetof_member_designator "[" expr "]"
This extension is sufficient such that
#define offsetof(type, member) __builtin_offsetof (type, member)
is a suitable definition of the offsetof macro. In C++, type
may be dependent. In either case, member may consist of a single
identifier, or a sequence of member accesses and array references.
__sync Built-in Functions for Atomic Memory AccessThe following built-in functions are intended to be compatible with those described in the Intel Itanium Processor-specific Application Binary Interface, section 7.4. As such, they depart from normal GCC practice by not using the ‘__builtin_’ prefix and also by being overloaded so that they work on multiple types.
The definition given in the Intel documentation allows only for the use of
the types int, long, long long or their unsigned
counterparts. GCC allows any scalar type that is 1, 2, 4 or 8 bytes in
size other than the C type _Bool or the C++ type bool.
Operations on pointer arguments are performed as if the operands were
of the uintptr_t type. That is, they are not scaled by the size
of the type to which the pointer points.
These functions are implemented in terms of the ‘__atomic’ builtins (see __atomic Builtins). They should not be used for new code which should use the ‘__atomic’ builtins instead.
Not all operations are supported by all target processors. If a particular operation cannot be implemented on the target processor, a warning is generated and a call to an external function is generated. The external function carries the same name as the built-in version, with an additional suffix ‘_n’ where n is the size of the data type.
In most cases, these built-in functions are considered a full barrier. That is, no memory operand is moved across the operation, either forward or backward. Further, instructions are issued as necessary to prevent the processor from speculating loads across the operation and from queuing stores after the operation.
All of the routines are described in the Intel documentation to take “an optional list of variables protected by the memory barrier”. It's not clear what is meant by that; it could mean that only the listed variables are protected, or it could mean a list of additional variables to be protected. The list is ignored by GCC which treats it as empty. GCC interprets an empty list as meaning that all globally accessible variables should be protected.
These built-in functions perform the operation suggested by the name, and returns the value that had previously been in memory. That is, operations on integer operands have the following semantics. Operations on pointer arguments are performed as if the operands were of the
uintptr_ttype. That is, they are not scaled by the size of the type to which the pointer points.{ tmp = *ptr; *ptr op= value; return tmp; } { tmp = *ptr; *ptr = ~(tmp & value); return tmp; } // nandThe object pointed to by the first argument must be of integer or pointer type. It must not be a boolean type.
Note: GCC 4.4 and later implement
__sync_fetch_and_nandas*ptr = ~(tmp & value)instead of*ptr = ~tmp & value.
These built-in functions perform the operation suggested by the name, and return the new value. That is, operations on integer operands have the following semantics. Operations on pointer operands are performed as if the operand's type were
uintptr_t.{ *ptr op= value; return *ptr; } { *ptr = ~(*ptr & value); return *ptr; } // nandThe same constraints on arguments apply as for the corresponding
__sync_op_and_fetchbuilt-in functions.Note: GCC 4.4 and later implement
__sync_nand_and_fetchas*ptr = ~(*ptr & value)instead of*ptr = ~*ptr & value.
These built-in functions perform an atomic compare and swap. That is, if the current value of
*ptr is oldval, then write newval into*ptr.The “bool” version returns
trueif the comparison is successful and newval is written. The “val” version returns the contents of*ptr before the operation.
This built-in function issues a full memory barrier.
This built-in function, as described by Intel, is not a traditional test-and-set operation, but rather an atomic exchange operation. It writes value into
*ptr, and returns the previous contents of*ptr.Many targets have only minimal support for such locks, and do not support a full exchange operation. In this case, a target may support reduced functionality here by which the only valid value to store is the immediate constant 1. The exact value actually stored in
*ptr is implementation defined.This built-in function is not a full barrier, but rather an acquire barrier. This means that references after the operation cannot move to (or be speculated to) before the operation, but previous memory stores may not be globally visible yet, and previous memory loads may not yet be satisfied.
This built-in function releases the lock acquired by
__sync_lock_test_and_set. Normally this means writing the constant 0 to*ptr.This built-in function is not a full barrier, but rather a release barrier. This means that all previous memory stores are globally visible, and all previous memory loads have been satisfied, but following memory reads are not prevented from being speculated to before the barrier.
The following built-in functions approximately match the requirements for the C++11 memory model. They are all identified by being prefixed with ‘__atomic’ and most are overloaded so that they work with multiple types.
These functions are intended to replace the legacy ‘__sync’ builtins. The main difference is that the memory order that is requested is a parameter to the functions. New code should always use the ‘__atomic’ builtins rather than the ‘__sync’ builtins.
Note that the ‘__atomic’ builtins assume that programs will conform to the C++11 memory model. In particular, they assume that programs are free of data races. See the C++11 standard for detailed requirements.
The ‘__atomic’ builtins can be used with any integral scalar or pointer type that is 1, 2, 4, or 8 bytes in length. 16-byte integral types are also allowed if ‘__int128’ (see __int128) is supported by the architecture.
The four non-arithmetic functions (load, store, exchange, and compare_exchange) all have a generic version as well. This generic version works on any data type. It uses the lock-free built-in function if the specific data type size makes that possible; otherwise, an external call is left to be resolved at run time. This external call is the same format with the addition of a ‘size_t’ parameter inserted as the first parameter indicating the size of the object being pointed to. All objects must be the same size.
There are 6 different memory orders that can be specified. These map to the C++11 memory orders with the same names, see the C++11 standard or the GCC wiki on atomic synchronization for detailed definitions. Individual targets may also support additional memory orders for use on specific architectures. Refer to the target documentation for details of these.
An atomic operation can both constrain code motion and be mapped to hardware instructions for synchronization between threads (e.g., a fence). To which extent this happens is controlled by the memory orders, which are listed here in approximately ascending order of strength. The description of each memory order is only meant to roughly illustrate the effects and is not a specification; see the C++11 memory model for precise semantics.
__ATOMIC_RELAXED__ATOMIC_CONSUME__ATOMIC_ACQUIRE
memory order because of a deficiency in C++11's semantics for
memory_order_consume.
__ATOMIC_ACQUIRE__ATOMIC_RELEASE__ATOMIC_ACQ_REL__ATOMIC_ACQUIRE and
__ATOMIC_RELEASE.
__ATOMIC_SEQ_CST__ATOMIC_SEQ_CST operations.
Note that in the C++11 memory model, fences (e.g., ‘__atomic_thread_fence’) take effect in combination with other atomic operations on specific memory locations (e.g., atomic loads); operations on specific memory locations do not necessarily affect other operations in the same way.
Target architectures are encouraged to provide their own patterns for each of the atomic built-in functions. If no target is provided, the original non-memory model set of ‘__sync’ atomic built-in functions are used, along with any required synchronization fences surrounding it in order to achieve the proper behavior. Execution in this case is subject to the same restrictions as those built-in functions.
If there is no pattern or mechanism to provide a lock-free instruction sequence, a call is made to an external routine with the same parameters to be resolved at run time.
When implementing patterns for these built-in functions, the memory order
parameter can be ignored as long as the pattern implements the most
restrictive __ATOMIC_SEQ_CST memory order. Any of the other memory
orders execute correctly with this memory order but they may not execute as
efficiently as they could with a more appropriate implementation of the
relaxed requirements.
Note that the C++11 standard allows for the memory order parameter to be
determined at run time rather than at compile time. These built-in
functions map any run-time value to __ATOMIC_SEQ_CST rather
than invoke a runtime library call or inline a switch statement. This is
standard compliant, safe, and the simplest approach for now.
The memory order parameter is a signed int, but only the lower 16 bits are reserved for the memory order. The remainder of the signed int is reserved for target use and should be 0. Use of the predefined atomic values ensures proper usage.
This built-in function implements an atomic load operation. It returns the contents of
*ptr.The valid memory order variants are
__ATOMIC_RELAXED,__ATOMIC_SEQ_CST,__ATOMIC_ACQUIRE, and__ATOMIC_CONSUME.
This is the generic version of an atomic load. It returns the contents of
*ptr in*ret.
This built-in function implements an atomic store operation. It writes val into
*ptr.The valid memory order variants are
__ATOMIC_RELAXED,__ATOMIC_SEQ_CST, and__ATOMIC_RELEASE.
This is the generic version of an atomic store. It stores the value of
*val into*ptr.
This built-in function implements an atomic exchange operation. It writes val into
*ptr, and returns the previous contents of*ptr.All memory order variants are valid.
This is the generic version of an atomic exchange. It stores the contents of
*val into*ptr. The original value of*ptr is copied into*ret.
This built-in function implements an atomic compare and exchange operation. This compares the contents of
*ptr with the contents of*expected. If equal, the operation is a read-modify-write operation that writes desired into*ptr. If they are not equal, the operation is a read and the current contents of*ptr are written into*expected. weak istruefor weak compare_exchange, which may fail spuriously, andfalsefor the strong variation, which never fails spuriously. Many targets only offer the strong variation and ignore the parameter. When in doubt, use the strong variation.If desired is written into
*ptr thentrueis returned and memory is affected according to the memory order specified by success_memorder. There are no restrictions on what memory order can be used here.Otherwise,
falseis returned and memory is affected according to failure_memorder. This memory order cannot be__ATOMIC_RELEASEnor__ATOMIC_ACQ_REL. It also cannot be a stronger order than that specified by success_memorder.
This built-in function implements the generic version of
__atomic_compare_exchange. The function is virtually identical to__atomic_compare_exchange_n, except the desired value is also a pointer.
These built-in functions perform the operation suggested by the name, and return the result of the operation. Operations on pointer arguments are performed as if the operands were of the
uintptr_ttype. That is, they are not scaled by the size of the type to which the pointer points.{ *ptr op= val; return *ptr; } { *ptr = ~(*ptr & val); return *ptr; } // nandThe object pointed to by the first argument must be of integer or pointer type. It must not be a boolean type. All memory orders are valid.
These built-in functions perform the operation suggested by the name, and return the value that had previously been in
*ptr. Operations on pointer arguments are performed as if the operands were of theuintptr_ttype. That is, they are not scaled by the size of the type to which the pointer points.{ tmp = *ptr; *ptr op= val; return tmp; } { tmp = *ptr; *ptr = ~(*ptr & val); return tmp; } // nandThe same constraints on arguments apply as for the corresponding
__atomic_op_fetchbuilt-in functions. All memory orders are valid.
This built-in function performs an atomic test-and-set operation on the byte at
*ptr. The byte is set to some implementation defined nonzero “set” value and the return value istrueif and only if the previous contents were “set”. It should be only used for operands of typeboolorchar. For other types only part of the value may be set.All memory orders are valid.
This built-in function performs an atomic clear operation on
*ptr. After the operation,*ptr contains 0. It should be only used for operands of typeboolorcharand in conjunction with__atomic_test_and_set. For other types it may only clear partially. If the type is notboolprefer using__atomic_store.The valid memory order variants are
__ATOMIC_RELAXED,__ATOMIC_SEQ_CST, and__ATOMIC_RELEASE.
This built-in function acts as a synchronization fence between threads based on the specified memory order.
All memory orders are valid.
This built-in function acts as a synchronization fence between a thread and signal handlers based in the same thread.
All memory orders are valid.
This built-in function returns
trueif objects of size bytes always generate lock-free atomic instructions for the target architecture. size must resolve to a compile-time constant and the result also resolves to a compile-time constant.ptr is an optional pointer to the object that may be used to determine alignment. A value of 0 indicates typical alignment should be used. The compiler may also ignore this parameter.
if (__atomic_always_lock_free (sizeof (long long), 0))
This built-in function returns
trueif objects of size bytes always generate lock-free atomic instructions for the target architecture. If the built-in function is not known to be lock-free, a call is made to a runtime routine named__atomic_is_lock_free.ptr is an optional pointer to the object that may be used to determine alignment. A value of 0 indicates typical alignment should be used. The compiler may also ignore this parameter.
The following built-in functions allow performing simple arithmetic operations together with checking whether the operations overflowed.
These built-in functions promote the first two operands into infinite precision signed type and perform addition on those promoted operands. The result is then cast to the type the third pointer argument points to and stored there. If the stored result is equal to the infinite precision result, the built-in functions return
false, otherwise they returntrue. As the addition is performed in infinite signed precision, these built-in functions have fully defined behavior for all argument values.The first built-in function allows arbitrary integral types for operands and the result type must be pointer to some integral type other than enumerated or boolean type, the rest of the built-in functions have explicit integer types.
The compiler will attempt to use hardware instructions to implement these built-in functions where possible, like conditional jump on overflow after addition, conditional jump on carry etc.
These built-in functions are similar to the add overflow checking built-in functions above, except they perform subtraction, subtract the second argument from the first one, instead of addition.
These built-in functions are similar to the add overflow checking built-in functions above, except they perform multiplication, instead of addition.
The following built-in functions allow checking if simple arithmetic operation would overflow.
These built-in functions are similar to
__builtin_add_overflow,__builtin_sub_overflow, or__builtin_mul_overflow, except that they don't store the result of the arithmetic operation anywhere and the last argument is not a pointer, but some expression with integral type other than enumerated or boolean type.The built-in functions promote the first two operands into infinite precision signed type and perform addition on those promoted operands. The result is then cast to the type of the third argument. If the cast result is equal to the infinite precision result, the built-in functions return
false, otherwise they returntrue. The value of the third argument is ignored, just the side effects in the third argument are evaluated, and no integral argument promotions are performed on the last argument. If the third argument is a bit-field, the type used for the result cast has the precision and signedness of the given bit-field, rather than precision and signedness of the underlying type.For example, the following macro can be used to portably check, at compile-time, whether or not adding two constant integers will overflow, and perform the addition only when it is known to be safe and not to trigger a -Woverflow warning.
#define INT_ADD_OVERFLOW_P(a, b) \ __builtin_add_overflow_p (a, b, (__typeof__ ((a) + (b))) 0) enum { A = INT_MAX, B = 3, C = INT_ADD_OVERFLOW_P (A, B) ? 0 : A + B, D = __builtin_add_overflow_p (1, SCHAR_MAX, (signed char) 0) };The compiler will attempt to use hardware instructions to implement these built-in functions where possible, like conditional jump on overflow after addition, conditional jump on carry etc.
The x86 architecture supports additional memory ordering flags to mark critical sections for hardware lock elision. These must be specified in addition to an existing memory order to atomic intrinsics.
__ATOMIC_HLE_ACQUIRE__ATOMIC_ACQUIRE or stronger.
__ATOMIC_HLE_RELEASE__ATOMIC_RELEASE or stronger.
When a lock acquire fails, it is required for good performance to abort
the transaction quickly. This can be done with a _mm_pause.
#include <immintrin.h> // For _mm_pause
int lockvar;
/* Acquire lock with lock elision */
while (__atomic_exchange_n(&lockvar, 1, __ATOMIC_ACQUIRE|__ATOMIC_HLE_ACQUIRE))
_mm_pause(); /* Abort failed transaction */
...
/* Free lock with lock elision */
__atomic_store_n(&lockvar, 0, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE);
GCC implements a limited buffer overflow protection mechanism that can prevent some buffer overflow attacks by determining the sizes of objects into which data is about to be written and preventing the writes when the size isn't sufficient. The built-in functions described below yield the best results when used together and when optimization is enabled. For example, to detect object sizes across function boundaries or to follow pointer assignments through non-trivial control flow they rely on various optimization passes enabled with -O2. However, to a limited extent, they can be used without optimization as well.
is a built-in construct that returns a constant number of bytes from ptr to the end of the object ptr pointer points to (if known at compile time). To determine the sizes of dynamically allocated objects the function relies on the allocation functions called to obtain the storage to be declared with the
alloc_sizeattribute (see Common Function Attributes).__builtin_object_sizenever evaluates its arguments for side effects. If there are any side effects in them, it returns(size_t) -1for type 0 or 1 and(size_t) 0for type 2 or 3. If there are multiple objects ptr can point to and all of them are known at compile time, the returned number is the maximum of remaining byte counts in those objects if type & 2 is 0 and minimum if nonzero. If it is not possible to determine which objects ptr points to at compile time,__builtin_object_sizeshould return(size_t) -1for type 0 or 1 and(size_t) 0for type 2 or 3.type is an integer constant from 0 to 3. If the least significant bit is clear, objects are whole variables, if it is set, a closest surrounding subobject is considered the object a pointer points to. The second bit determines if maximum or minimum of remaining bytes is computed.
struct V { char buf1[10]; int b; char buf2[10]; } var; char *p = &var.buf1[1], *q = &var.b; /* Here the object p points to is var. */ assert (__builtin_object_size (p, 0) == sizeof (var) - 1); /* The subobject p points to is var.buf1. */ assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1); /* The object q points to is var. */ assert (__builtin_object_size (q, 0) == (char *) (&var + 1) - (char *) &var.b); /* The subobject q points to is var.b. */ assert (__builtin_object_size (q, 1) == sizeof (var.b));
is similar to
__builtin_object_sizein that it returns a number of bytes from ptr to the end of the object ptr pointer points to, except that the size returned may not be a constant. This results in successful evaluation of object size estimates in a wider range of use cases and can be more precise than__builtin_object_size, but it incurs a performance penalty since it may add a runtime overhead on size computation. Semantics of type as well as return values in case it is not possible to determine which objects ptr points to at compile time are the same as in the case of__builtin_object_size.
Hardening of function calls using the _FORTIFY_SOURCE macro is
one of the key uses of the object size checking built-in functions. To
make implementation of these features more convenient and improve
optimization and diagnostics, there are built-in functions added for
many common string operation functions, e.g., for memcpy
__builtin___memcpy_chk built-in is provided. This built-in has
an additional last argument, which is the number of bytes remaining in
the object the dest argument points to or (size_t) -1 if
the size is not known.
The built-in functions are optimized into the normal string functions
like memcpy if the last argument is (size_t) -1 or if
it is known at compile time that the destination object will not
be overflowed. If the compiler can determine at compile time that the
object will always be overflowed, it issues a warning.
The intended use can be e.g.
#undef memcpy
#define bos0(dest) __builtin_object_size (dest, 0)
#define memcpy(dest, src, n) \
__builtin___memcpy_chk (dest, src, n, bos0 (dest))
char *volatile p;
char buf[10];
/* It is unknown what object p points to, so this is optimized
into plain memcpy - no checking is possible. */
memcpy (p, "abcde", n);
/* Destination is known and length too. It is known at compile
time there will be no overflow. */
memcpy (&buf[5], "abcde", 5);
/* Destination is known, but the length is not known at compile time.
This will result in __memcpy_chk call that can check for overflow
at run time. */
memcpy (&buf[5], "abcde", n);
/* Destination is known and it is known at compile time there will
be overflow. There will be a warning and __memcpy_chk call that
will abort the program at run time. */
memcpy (&buf[6], "abcde", 5);
Such built-in functions are provided for memcpy, mempcpy,
memmove, memset, strcpy, stpcpy, strncpy,
strcat and strncat.
The added flag argument is passed unchanged to
__sprintf_chketc. functions and can contain implementation specific flags on what additional security measures the checking function might take, such as handling%ndifferently.The os argument is the object size s points to, like in the other built-in functions. There is a small difference in the behavior though, if os is
(size_t) -1, the built-in functions are optimized into the non-checking functions only if flag is 0, otherwise the checking function is called with os argument set to(size_t) -1.In addition to this, there are checking built-in functions
__builtin___printf_chk,__builtin___vprintf_chk,__builtin___fprintf_chkand__builtin___vfprintf_chk. These have just one additional argument, flag, right before format string fmt. If the compiler is able to optimize them tofputcetc. functions, it does, otherwise the checking function is called and the flag argument passed to it.
GCC provides a large number of built-in functions other than the ones mentioned above. Some of these are for internal use in the processing of exceptions or variable-length argument lists and are not documented here because they may change from time to time; we do not recommend general use of these functions.
The remaining functions are provided for optimization purposes.
With the exception of built-ins that have library equivalents such as the standard C library functions discussed below, or that expand to library calls, GCC built-in functions are always expanded inline and thus do not have corresponding entry points and their address cannot be obtained. Attempting to use them in an expression other than a function call results in a compile-time error.
GCC includes built-in versions of many of the functions in the standard
C library. These functions come in two forms: one whose names start with
the __builtin_ prefix, and the other without. Both forms have the
same type (including prototype), the same address (when their address is
taken), and the same meaning as the C library functions even if you specify
the -fno-builtin option see C Dialect Options). Many of these
functions are only optimized in certain cases; if they are not optimized in
a particular case, a call to the library function is emitted.
Outside strict ISO C mode (-ansi, -std=c90,
-std=c99 or -std=c11), the functions
_exit, alloca, bcmp, bzero,
dcgettext, dgettext, dremf, dreml,
drem, exp10f, exp10l, exp10, ffsll,
ffsl, ffs, fprintf_unlocked,
fputs_unlocked, gammaf, gammal, gamma,
gammaf_r, gammal_r, gamma_r, gettext,
index, isascii, j0f, j0l, j0,
j1f, j1l, j1, jnf, jnl, jn,
lgammaf_r, lgammal_r, lgamma_r, mempcpy,
pow10f, pow10l, pow10, printf_unlocked,
rindex, roundeven, roundevenf, roundevenl,
scalbf, scalbl, scalb,
signbit, signbitf, signbitl, signbitd32,
signbitd64, signbitd128, significandf,
significandl, significand, sincosf,
sincosl, sincos, stpcpy, stpncpy,
strcasecmp, strdup, strfmon, strncasecmp,
strndup, strnlen, toascii, y0f, y0l,
y0, y1f, y1l, y1, ynf, ynl and
yn
may be handled as built-in functions.
All these functions have corresponding versions
prefixed with __builtin_, which may be used even in strict C90
mode.
The ISO C99 functions
_Exit, acoshf, acoshl, acosh, asinhf,
asinhl, asinh, atanhf, atanhl, atanh,
cabsf, cabsl, cabs, cacosf, cacoshf,
cacoshl, cacosh, cacosl, cacos,
cargf, cargl, carg, casinf, casinhf,
casinhl, casinh, casinl, casin,
catanf, catanhf, catanhl, catanh,
catanl, catan, cbrtf, cbrtl, cbrt,
ccosf, ccoshf, ccoshl, ccosh, ccosl,
ccos, cexpf, cexpl, cexp, cimagf,
cimagl, cimag, clogf, clogl, clog,
conjf, conjl, conj, copysignf, copysignl,
copysign, cpowf, cpowl, cpow, cprojf,
cprojl, cproj, crealf, creall, creal,
csinf, csinhf, csinhl, csinh, csinl,
csin, csqrtf, csqrtl, csqrt, ctanf,
ctanhf, ctanhl, ctanh, ctanl, ctan,
erfcf, erfcl, erfc, erff, erfl,
erf, exp2f, exp2l, exp2, expm1f,
expm1l, expm1, fdimf, fdiml, fdim,
fmaf, fmal, fmaxf, fmaxl, fmax,
fma, fminf, fminl, fmin, hypotf,
hypotl, hypot, ilogbf, ilogbl, ilogb,
imaxabs, isblank, iswblank, lgammaf,
lgammal, lgamma, llabs, llrintf, llrintl,
llrint, llroundf, llroundl, llround,
log1pf, log1pl, log1p, log2f, log2l,
log2, logbf, logbl, logb, lrintf,
lrintl, lrint, lroundf, lroundl,
lround, nearbyintf, nearbyintl, nearbyint,
nextafterf, nextafterl, nextafter,
nexttowardf, nexttowardl, nexttoward,
remainderf, remainderl, remainder, remquof,
remquol, remquo, rintf, rintl, rint,
roundf, roundl, round, scalblnf,
scalblnl, scalbln, scalbnf, scalbnl,
scalbn, snprintf, tgammaf, tgammal,
tgamma, truncf, truncl, trunc,
vfscanf, vscanf, vsnprintf and vsscanf
are handled as built-in functions
except in strict ISO C90 mode (-ansi or -std=c90).
There are also built-in versions of the ISO C99 functions
acosf, acosl, asinf, asinl, atan2f,
atan2l, atanf, atanl, ceilf, ceill,
cosf, coshf, coshl, cosl, expf,
expl, fabsf, fabsl, floorf, floorl,
fmodf, fmodl, frexpf, frexpl, ldexpf,
ldexpl, log10f, log10l, logf, logl,
modfl, modff, powf, powl, sinf,
sinhf, sinhl, sinl, sqrtf, sqrtl,
tanf, tanhf, tanhl and tanl
that are recognized in any mode since ISO C90 reserves these names for
the purpose to which ISO C99 puts them. All these functions have
corresponding versions prefixed with __builtin_.
There are also built-in functions __builtin_fabsfn,
__builtin_fabsfnx, __builtin_copysignfn and
__builtin_copysignfnx, corresponding to the TS 18661-3
functions fabsfn, fabsfnx,
copysignfn and copysignfnx, for supported
types _Floatn and _Floatnx.
There are also GNU extension functions clog10, clog10f and
clog10l which names are reserved by ISO C99 for future use.
All these functions have versions prefixed with __builtin_.
The ISO C94 functions
iswalnum, iswalpha, iswcntrl, iswdigit,
iswgraph, iswlower, iswprint, iswpunct,
iswspace, iswupper, iswxdigit, towlower and
towupper
are handled as built-in functions
except in strict ISO C90 mode (-ansi or -std=c90).
The ISO C90 functions
abort, abs, acos, asin, atan2,
atan, calloc, ceil, cosh, cos,
exit, exp, fabs, floor, fmod,
fprintf, fputs, free, frexp, fscanf,
isalnum, isalpha, iscntrl, isdigit,
isgraph, islower, isprint, ispunct,
isspace, isupper, isxdigit, tolower,
toupper, labs, ldexp, log10, log,
malloc, memchr, memcmp, memcpy,
memset, modf, pow, printf, putchar,
puts, realloc, scanf, sinh, sin,
snprintf, sprintf, sqrt, sscanf, strcat,
strchr, strcmp, strcpy, strcspn,
strlen, strncat, strncmp, strncpy,
strpbrk, strrchr, strspn, strstr,
tanh, tan, vfprintf, vprintf and vsprintf
are all recognized as built-in functions unless
-fno-builtin is specified (or -fno-builtin-function
is specified for an individual function). All of these functions have
corresponding versions prefixed with __builtin_.
GCC provides built-in versions of the ISO C99 floating-point comparison
macros that avoid raising exceptions for unordered operands. They have
the same names as the standard macros ( isgreater,
isgreaterequal, isless, islessequal,
islessgreater, and isunordered) , with __builtin_
prefixed. We intend for a library implementor to be able to simply
#define each standard macro to its built-in equivalent.
In the same fashion, GCC provides fpclassify, isfinite,
isinf_sign, isnormal and signbit built-ins used with
__builtin_ prefixed. The isinf and isnan
built-in functions appear both with and without the __builtin_ prefix.
With -ffinite-math-only option the isinf and isnan
built-in functions will always return 0.
GCC provides built-in versions of the ISO C99 floating-point rounding and
exceptions handling functions fegetround, feclearexcept and
feraiseexcept. They may not be available for all targets, and because
they need close interaction with libc internal values, they may not be available
for all target libcs, but in all cases they will gracefully fallback to libc
calls. These built-in functions appear both with and without the
__builtin_ prefix.
The
__builtin_allocafunction must be called at block scope. The function allocates an object size bytes large on the stack of the calling function. The object is aligned on the default stack alignment boundary for the target determined by the__BIGGEST_ALIGNMENT__macro. The__builtin_allocafunction returns a pointer to the first byte of the allocated object. The lifetime of the allocated object ends just before the calling function returns to its caller. This is so even when__builtin_allocais called within a nested block.For example, the following function allocates eight objects of
nbytes each on the stack, storing a pointer to each in consecutive elements of the arraya. It then passes the array to functiongwhich can safely use the storage pointed to by each of the array elements.void f (unsigned n) { void *a [8]; for (int i = 0; i != 8; ++i) a [i] = __builtin_alloca (n); g (a, n); // safe }Since the
__builtin_allocafunction doesn't validate its argument it is the responsibility of its caller to make sure the argument doesn't cause it to exceed the stack size limit. The__builtin_allocafunction is provided to make it possible to allocate on the stack arrays of bytes with an upper bound that may be computed at run time. Since C99 Variable Length Arrays offer similar functionality under a portable, more convenient, and safer interface they are recommended instead, in both C99 and C++ programs where GCC provides them as an extension. See Variable Length, for details.
The
__builtin_alloca_with_alignfunction must be called at block scope. The function allocates an object size bytes large on the stack of the calling function. The allocated object is aligned on the boundary specified by the argument alignment whose unit is given in bits (not bytes). The size argument must be positive and not exceed the stack size limit. The alignment argument must be a constant integer expression that evaluates to a power of 2 greater than or equal toCHAR_BITand less than some unspecified maximum. Invocations with other values are rejected with an error indicating the valid bounds. The function returns a pointer to the first byte of the allocated object. The lifetime of the allocated object ends at the end of the block in which the function was called. The allocated storage is released no later than just before the calling function returns to its caller, but may be released at the end of the block in which the function was called.For example, in the following function the call to
gis unsafe because whenoveralignis non-zero, the space allocated by__builtin_alloca_with_alignmay have been released at the end of theifstatement in which it was called.void f (unsigned n, bool overalign) { void *p; if (overalign) p = __builtin_alloca_with_align (n, 64 /* bits */); else p = __builtin_alloc (n); g (p, n); // unsafe }Since the
__builtin_alloca_with_alignfunction doesn't validate its size argument it is the responsibility of its caller to make sure the argument doesn't cause it to exceed the stack size limit. The__builtin_alloca_with_alignfunction is provided to make it possible to allocate on the stack overaligned arrays of bytes with an upper bound that may be computed at run time. Since C99 Variable Length Arrays offer the same functionality under a portable, more convenient, and safer interface they are recommended instead, in both C99 and C++ programs where GCC provides them as an extension. See Variable Length, for details.
Similar to
__builtin_alloca_with_alignbut takes an extra argument specifying an upper bound for size in case its value cannot be computed at compile time, for use by -fstack-usage, -Wstack-usage and -Walloca-larger-than. max_size must be a constant integer expression, it has no effect on code generation and no attempt is made to check its compatibility with size.
The
__builtin_has_attributefunction evaluates to an integer constant expression equal totrueif the symbol or type referenced by the type-or-expression argument has been declared with the attribute referenced by the second argument. For an type-or-expression argument that does not reference a symbol, since attributes do not apply to expressions the built-in consider the type of the argument. Neither argument is evaluated. The type-or-expression argument is subject to the same restrictions as the argument totypeof(see Typeof). The attribute argument is an attribute name optionally followed by a comma-separated list of arguments enclosed in parentheses. Both forms of attribute names—with and without double leading and trailing underscores—are recognized. See Attribute Syntax, for details. When no attribute arguments are specified for an attribute that expects one or more arguments the function returnstrueif type-or-expression has been declared with the attribute regardless of the attribute argument values. Arguments provided for an attribute that expects some are validated and matched up to the provided number. The function returnstrueif all provided arguments match. For example, the first call to the function below evaluates totruebecausexis declared with thealignedattribute but the second call evaluates tofalsebecausexis declaredaligned (8)and notaligned (4).__attribute__ ((aligned (8))) int x; _Static_assert (__builtin_has_attribute (x, aligned), "aligned"); _Static_assert (!__builtin_has_attribute (x, aligned (4)), "aligned (4)");Due to a limitation the
__builtin_has_attributefunction returnsfalsefor themodeattribute even if the type or variable referenced by the type-or-expression argument was declared with one. The function is also not supported with labels, and in C with enumerators.Note that unlike the
__has_attributepreprocessor operator which is suitable for use in#ifpreprocessing directives__builtin_has_attributeis an intrinsic function that is not recognized in such contexts.
This built-in function can be used to help mitigate against unsafe speculative execution. type may be any integral type or any pointer type.
- If the CPU is not speculatively executing the code, then val is returned.
- If the CPU is executing speculatively then either:
- The function may cause execution to pause until it is known that the code is no-longer being executed speculatively (in which case val can be returned, as above); or
- The function may use target-dependent speculation tracking state to cause failval to be returned when it is known that speculative execution has incorrectly predicted a conditional branch operation.
The second argument, failval, is optional and defaults to zero if omitted.
GCC defines the preprocessor macro
__HAVE_BUILTIN_SPECULATION_SAFE_VALUEfor targets that have been updated to support this builtin.The built-in function can be used where a variable appears to be used in a safe way, but the CPU, due to speculative execution may temporarily ignore the bounds checks. Consider, for example, the following function:
int array[500]; int f (unsigned untrusted_index) { if (untrusted_index < 500) return array[untrusted_index]; return 0; }If the function is called repeatedly with
untrusted_indexless than the limit of 500, then a branch predictor will learn that the block of code that returns a value stored inarraywill be executed. If the function is subsequently called with an out-of-range value it will still try to execute that block of code first until the CPU determines that the prediction was incorrect (the CPU will unwind any incorrect operations at that point). However, depending on how the result of the function is used, it might be possible to leave traces in the cache that can reveal what was stored at the out-of-bounds location. The built-in function can be used to provide some protection against leaking data in this way by changing the code to:int array[500]; int f (unsigned untrusted_index) { if (untrusted_index < 500) return array[__builtin_speculation_safe_value (untrusted_index)]; return 0; }The built-in function will either cause execution to stall until the conditional branch has been fully resolved, or it may permit speculative execution to continue, but using 0 instead of
untrusted_valueif that exceeds the limit.If accessing any memory location is potentially unsafe when speculative execution is incorrect, then the code can be rewritten as
int array[500]; int f (unsigned untrusted_index) { if (untrusted_index < 500) return *__builtin_speculation_safe_value (&array[untrusted_index], NULL); return 0; }which will cause a
NULLpointer to be used for the unsafe case.
You can use the built-in function
__builtin_types_compatible_pto determine whether two types are the same.This built-in function returns 1 if the unqualified versions of the types type1 and type2 (which are types, not expressions) are compatible, 0 otherwise. The result of this built-in function can be used in integer constant expressions.
This built-in function ignores top level qualifiers (e.g.,
const,volatile). For example,intis equivalent toconst int.The type
int[]andint[5]are compatible. On the other hand,intandchar *are not compatible, even if the size of their types, on the particular architecture are the same. Also, the amount of pointer indirection is taken into account when determining similarity. Consequently,short *is not similar toshort **. Furthermore, two types that are typedefed are considered compatible if their underlying types are compatible.An
enumtype is not considered to be compatible with anotherenumtype even if both are compatible with the same integer type; this is what the C standard specifies. For example,enum {foo, bar}is not similar toenum {hot, dog}.You typically use this function in code whose execution varies depending on the arguments' types. For example:
#define foo(x) \ ({ \ typeof (x) tmp = (x); \ if (__builtin_types_compatible_p (typeof (x), long double)) \ tmp = foo_long_double (tmp); \ else if (__builtin_types_compatible_p (typeof (x), double)) \ tmp = foo_double (tmp); \ else if (__builtin_types_compatible_p (typeof (x), float)) \ tmp = foo_float (tmp); \ else \ abort (); \ tmp; \ })Note: This construct is only available for C.
The call_exp expression must be a function call, and the pointer_exp expression must be a pointer. The pointer_exp is passed to the function call in the target's static chain location. The result of builtin is the result of the function call.
Note: This builtin is only available for C. This builtin can be used to call Go closures from C.
You can use the built-in function
__builtin_choose_exprto evaluate code depending on the value of a constant expression. This built-in function returns exp1 if const_exp, which is an integer constant expression, is nonzero. Otherwise it returns exp2.This built-in function is analogous to the ‘? :’ operator in C, except that the expression returned has its type unaltered by promotion rules. Also, the built-in function does not evaluate the expression that is not chosen. For example, if const_exp evaluates to
true, exp2 is not evaluated even if it has side effects.This built-in function can return an lvalue if the chosen argument is an lvalue.
If exp1 is returned, the return type is the same as exp1's type. Similarly, if exp2 is returned, its return type is the same as exp2.
Example:
#define foo(x) \ __builtin_choose_expr ( \ __builtin_types_compatible_p (typeof (x), double), \ foo_double (x), \ __builtin_choose_expr ( \ __builtin_types_compatible_p (typeof (x), float), \ foo_float (x), \ /* The void expression results in a compile-time error \ when assigning the result to something. */ \ (void)0))Note: This construct is only available for C. Furthermore, the unused expression (exp1 or exp2 depending on the value of const_exp) may still generate syntax errors. This may change in future revisions.
The built-in function
__builtin_tgmath, available only for C and Objective-C, calls a function determined according to the rules of<tgmath.h>macros. It is intended to be used in implementations of that header, so that expansions of macros from that header only expand each of their arguments once, to avoid problems when calls to such macros are nested inside the arguments of other calls to such macros; in addition, it results in better diagnostics for invalid calls to<tgmath.h>macros than implementations using other GNU C language features. For example, thepowtype-generic macro might be defined as:#define pow(a, b) __builtin_tgmath (powf, pow, powl, \ cpowf, cpow, cpowl, a, b)The arguments to
__builtin_tgmathare at least two pointers to functions, followed by the arguments to the type-generic macro (which will be passed as arguments to the selected function). All the pointers to functions must be pointers to prototyped functions, none of which may have variable arguments, and all of which must have the same number of parameters; the number of parameters of the first function determines how many arguments to__builtin_tgmathare interpreted as function pointers, and how many as the arguments to the called function.The types of the specified functions must all be different, but related to each other in the same way as a set of functions that may be selected between by a macro in
<tgmath.h>. This means that the functions are parameterized by a floating-point type t, different for each such function. The function return types may all be the same type, or they may be t for each function, or they may be the real type corresponding to t for each function (if some of the types t are complex). Likewise, for each parameter position, the type of the parameter in that position may always be the same type, or may be t for each function (this case must apply for at least one parameter position), or may be the real type corresponding to t for each function.The standard rules for
<tgmath.h>macros are used to find a common type u from the types of the arguments for parameters whose types vary between the functions; complex integer types (a GNU extension) are treated like the complex type corresponding to the real floating type that would be chosen for the corresponding real integer type. If the function return types vary, or are all the same integer type, the function called is the one for which t is u, and it is an error if there is no such function. If the function return types are all the same floating-point type, the type-generic macro is taken to be one of those from TS 18661 that rounds the result to a narrower type; if there is a function for which t is u, it is called, and otherwise the first function, if any, for which t has at least the range and precision of u is called, and it is an error if there is no such function.
You can use the built-in function
__builtin_constant_pto determine if a value is known to be constant at compile time and hence that GCC can perform constant-folding on expressions involving that value. The argument of the function is the value to test. The function returns the integer 1 if the argument is known to be a compile-time constant and 0 if it is not known to be a compile-time constant. A return of 0 does not indicate that the value is not a constant, but merely that GCC cannot prove it is a constant with the specified value of the -O option.You typically use this function in an embedded application where memory is a critical resource. If you have some complex calculation, you may want it to be folded if it involves constants, but need to call a function if it does not. For example:
#define Scale_Value(X) \ (__builtin_constant_p (X) \ ? ((X) * SCALE + OFFSET) : Scale (X))You may use this built-in function in either a macro or an inline function. However, if you use it in an inlined function and pass an argument of the function as the argument to the built-in, GCC never returns 1 when you call the inline function with a string constant or compound literal (see Compound Literals) and does not return 1 when you pass a constant numeric value to the inline function unless you specify the -O option.
You may also use
__builtin_constant_pin initializers for static data. For instance, you can writestatic const int table[] = { __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1, /* ... */ };This is an acceptable initializer even if EXPRESSION is not a constant expression, including the case where
__builtin_constant_preturns 1 because EXPRESSION can be folded to a constant but EXPRESSION contains operands that are not otherwise permitted in a static initializer (for example,0 && foo ()). GCC must be more conservative about evaluating the built-in in this case, because it has no opportunity to perform optimization.
The
__builtin_is_constant_evaluatedfunction is available only in C++. The built-in is intended to be used by implementations of thestd::is_constant_evaluatedC++ function. Programs should make use of the latter function rather than invoking the built-in directly.The main use case of the built-in is to determine whether a
constexprfunction is being called in aconstexprcontext. A call to the function evaluates to a core constant expression with the valuetrueif and only if it occurs within the evaluation of an expression or conversion that is manifestly constant-evaluated as defined in the C++ standard. Manifestly constant-evaluated contexts include constant-expressions, the conditions ofconstexpr ifstatements, constraint-expressions, and initializers of variables usable in constant expressions. For more details refer to the latest revision of the C++ standard.
The built-in function
__builtin_clear_paddingfunction clears padding bits inside of the object representation of object pointed by ptr, which has to be a pointer. The value representation of the object is not affected. The type of the object is assumed to be the type the pointer points to. Inside of a union, the only cleared bits are bits that are padding bits for all the union members.This built-in-function is useful if the padding bits of an object might have intederminate values and the object representation needs to be bitwise compared to some other object, for example for atomic operations.
For C++, ptr argument type should be pointer to trivially-copyable type, unless the argument is address of a variable or parameter, because otherwise it isn't known if the type isn't just a base class whose padding bits are reused or laid out differently in a derived class.
The
__builtin_bit_castfunction is available only in C++. The built-in is intended to be used by implementations of thestd::bit_castC++ template function. Programs should make use of the latter function rather than invoking the built-in directly.This built-in function allows reinterpreting the bits of the arg argument as if it had type type. type and the type of the arg argument need to be trivially copyable types with the same size. When manifestly constant-evaluated, it performs extra diagnostics required for
std::bit_castand returns a constant expression if arg is a constant expression. For more details refer to the latest revision of the C++ standard.
You may use
__builtin_expectto provide the compiler with branch prediction information. In general, you should prefer to use actual profile feedback for this (-fprofile-arcs), as programmers are notoriously bad at predicting how their programs actually perform. However, there are applications in which this data is hard to collect.The return value is the value of exp, which should be an integral expression. The semantics of the built-in are that it is expected that exp == c. For example:
if (__builtin_expect (x, 0)) foo ();indicates that we do not expect to call
foo, since we expectxto be zero. Since you are limited to integral expressions for exp, you should use constructions such asif (__builtin_expect (ptr != NULL, 1)) foo (*ptr);when testing pointer or floating-point values.
For the purposes of branch prediction optimizations, the probability that a
__builtin_expectexpression istrueis controlled by GCC'sbuiltin-expect-probabilityparameter, which defaults to 90%.You can also use
__builtin_expect_with_probabilityto explicitly assign a probability value to individual expressions. If the built-in is used in a loop construct, the provided probability will influence the expected number of iterations made by loop optimizations.
(long exp, long c, double probability)
This function has the same semantics as
__builtin_expect, but the caller provides the expected probability that exp == c. The last argument, probability, is a floating-point value in the range 0.0 to 1.0, inclusive. The probability argument must be constant floating-point expression.
This function causes the program to exit abnormally. GCC implements this function by using a target-dependent mechanism (such as intentionally executing an illegal instruction) or by calling
abort. The mechanism used may vary from release to release so you should not rely on any particular implementation.
If control flow reaches the point of the
__builtin_unreachable, the program is undefined. It is useful in situations where the compiler cannot deduce the unreachability of the code.One such case is immediately following an
asmstatement that either never terminates, or one that transfers control elsewhere and never returns. In this example, without the__builtin_unreachable, GCC issues a warning that control reaches the end of a non-void function. It also generates code to return after theasm.int f (int c, int v) { if (c) { return v; } else { asm("jmp error_handler"); __builtin_unreachable (); } }Because the
asmstatement unconditionally transfers control out of the function, control never reaches the end of the function body. The__builtin_unreachableis in fact unreachable and communicates this fact to the compiler.Another use for
__builtin_unreachableis following a call a function that never returns but that is not declared__attribute__((noreturn)), as in this example:void function_that_never_returns (void); int g (int c) { if (c) { return 1; } else { function_that_never_returns (); __builtin_unreachable (); } }
This built-in inhibits re-association of the floating-point expression expr with expressions consuming the return value of the built-in. The expression expr itself can be reordered, and the whole expression expr can be reordered with operands after the barrier. The barrier is only relevant when
-fassociative-mathis active, since otherwise floating-point is not treated as associative.float x0 = a + b - b; float x1 = __builtin_assoc_barrier(a + b) - b;means that, with
-fassociative-math,x0can be optimized tox0 = abutx1cannot.
This function returns its first argument, and allows the compiler to assume that the returned pointer is at least align bytes aligned. This built-in can have either two or three arguments, if it has three, the third argument should have integer type, and if it is nonzero means misalignment offset. For example:
void *x = __builtin_assume_aligned (arg, 16);means that the compiler can assume
x, set toarg, is at least 16-byte aligned, while:void *x = __builtin_assume_aligned (arg, 32, 8);means that the compiler can assume for
x, set toarg, that(char *) x - 8is 32-byte aligned.
This function is the equivalent of the preprocessor
__LINE__macro and returns a constant integer expression that evaluates to the line number of the invocation of the built-in. When used as a C++ default argument for a function F, it returns the line number of the call to F.
This function is the equivalent of the
__FUNCTION__symbol and returns an address constant pointing to the name of the function from which the built-in was invoked, or the empty string if the invocation is not at function scope. When used as a C++ default argument for a function F, it returns the name of F's caller or the empty string if the call was not made at function scope.
This function is the equivalent of the preprocessor
__FILE__macro and returns an address constant pointing to the file name containing the invocation of the built-in, or the empty string if the invocation is not at function scope. When used as a C++ default argument for a function F, it returns the file name of the call to F or the empty string if the call was not made at function scope.For example, in the following, each call to function
foowill print a line similar to"file.c:123: foo: message"with the name of the file and the line number of theprintfcall, the name of the functionfoo, followed by the wordmessage.const char* function (const char *func = __builtin_FUNCTION ()) { return func; } void foo (void) { printf ("%s:%i: %s: message\n", file (), line (), function ()); }
This function is used to flush the processor's instruction cache for the region of memory between begin inclusive and end exclusive. Some targets require that the instruction cache be flushed, after modifying memory containing code, in order to obtain deterministic behavior.
If the target does not require instruction cache flushes,
__builtin___clear_cachehas no effect. Otherwise either instructions are emitted in-line to clear the instruction cache or a call to the__clear_cachefunction in libgcc is made.
This function is used to minimize cache-miss latency by moving data into a cache before it is accessed. You can insert calls to
__builtin_prefetchinto code for which you know addresses of data in memory that is likely to be accessed soon. If the target supports them, data prefetch instructions are generated. If the prefetch is done early enough before the access then the data will be in the cache by the time it is accessed.The value of addr is the address of the memory to prefetch. There are two optional arguments, rw and locality. The value of rw is a compile-time constant one or zero; one means that the prefetch is preparing for a write to the memory address and zero, the default, means that the prefetch is preparing for a read. The value locality must be a compile-time constant integer between zero and three. A value of zero means that the data has no temporal locality, so it need not be left in the cache after the access. A value of three means that the data has a high degree of temporal locality and should be left in all levels of cache possible. Values of one and two mean, respectively, a low or moderate degree of temporal locality. The default is three.
for (i = 0; i < n; i++) { a[i] = a[i] + b[i]; __builtin_prefetch (&a[i+j], 1, 1); __builtin_prefetch (&b[i+j], 0, 1); /* ... */ }Data prefetch does not generate faults if addr is invalid, but the address expression itself must be valid. For example, a prefetch of
p->nextdoes not fault ifp->nextis not a valid address, but evaluation faults ifpis not a valid address.If the target does not support data prefetch, the address expression is evaluated if it includes side effects but no other code is generated and GCC does not issue a warning.
Returns a constant size estimate of an object pointed to by ptr. See Object Size Checking, for a detailed description of the function.
Similar to
__builtin_object_sizeexcept that the return value need not be a constant. See Object Size Checking, for a detailed description of the function.
Returns a positive infinity, if supported by the floating-point format, else
DBL_MAX. This function is suitable for implementing the ISO C macroHUGE_VAL.
Similar to
__builtin_huge_val, except the return type isfloat.
Similar to
__builtin_huge_val, except the return type islong double.
Similar to
__builtin_huge_val, except the return type is_Floatn.
Similar to
__builtin_huge_val, except the return type is_Floatnx.
This built-in implements the C99 fpclassify functionality. The first five int arguments should be the target library's notion of the possible FP classes and are used for return values. They must be constant values and they must appear in this order:
FP_NAN,FP_INFINITE,FP_NORMAL,FP_SUBNORMALandFP_ZERO. The ellipsis is for exactly one floating-point value to classify. GCC treats the last argument as type-generic, which means it does not do default promotion from float to double.
Similar to
__builtin_huge_val, except a warning is generated if the target floating-point format does not support infinities.
Similar to
__builtin_inf, except the return type is_Decimal32.
Similar to
__builtin_inf, except the return type is_Decimal64.
Similar to
__builtin_inf, except the return type is_Decimal128.
Similar to
__builtin_inf, except the return type isfloat. This function is suitable for implementing the ISO C99 macroINFINITY.
Similar to
__builtin_inf, except the return type islong double.
Similar to
__builtin_inf, except the return type is_Floatn.
Similar to
__builtin_inf, except the return type is_Floatnx.
Similar to
isinf, except the return value is -1 for an argument of-Infand 1 for an argument of+Inf. Note while the parameter list is an ellipsis, this function only accepts exactly one floating-point argument. GCC treats this parameter as type-generic, which means it does not do default promotion from float to double.
This is an implementation of the ISO C99 function
nan.Since ISO C99 defines this function in terms of
strtod, which we do not implement, a description of the parsing is in order. The string is parsed as bystrtol; that is, the base is recognized by leading ‘0’ or ‘0x’ prefixes. The number parsed is placed in the significand such that the least significant bit of the number is at the least significant bit of the significand. The number is truncated to fit the significand field provided. The significand is forced to be a quiet NaN.This function, if given a string literal all of which would have been consumed by
strtol, is evaluated early enough that it is considered a compile-time constant.
Similar to
__builtin_nan, except the return type is_Decimal32.
Similar to
__builtin_nan, except the return type is_Decimal64.
Similar to
__builtin_nan, except the return type is_Decimal128.
Similar to
__builtin_nan, except the return type isfloat.
Similar to
__builtin_nan, except the return type islong double.
Similar to
__builtin_nan, except the return type is_Floatn.
Similar to
__builtin_nan, except the return type is_Floatnx.
Similar to
__builtin_nan, except the significand is forced to be a signaling NaN. Thenansfunction is proposed by WG14 N965.
Similar to
__builtin_nans, except the return type is_Decimal32.
Similar to
__builtin_nans, except the return type is_Decimal64.
Similar to
__builtin_nans, except the return type is_Decimal128.
Similar to
__builtin_nans, except the return type isfloat.
Similar to
__builtin_nans, except the return type islong double.
Similar to
__builtin_nans, except the return type is_Floatn.
Similar to
__builtin_nans, except the return type is_Floatnx.
Return non-zero if the argument is a signaling NaN and zero otherwise. Note while the parameter list is an ellipsis, this function only accepts exactly one floating-point argument. GCC treats this parameter as type-generic, which means it does not do default promotion from float to double. This built-in function can work even without the non-default
-fsignaling-nansoption, although if a signaling NaN is computed, stored or passed as argument to some function other than this built-in in the current translation unit, it is safer to use-fsignaling-nans. With-ffinite-math-onlyoption this built-in function will always return 0.
Returns one plus the index of the least significant 1-bit of x, or if x is zero, returns zero.
Returns the number of leading 0-bits in x, starting at the most significant bit position. If x is 0, the result is undefined.
Returns the number of trailing 0-bits in x, starting at the least significant bit position. If x is 0, the result is undefined.
Returns the number of leading redundant sign bits in x, i.e. the number of bits following the most significant bit that are identical to it. There are no special cases for 0 or other values.
Returns the parity of x, i.e. the number of 1-bits in x modulo 2.
Similar to
__builtin_ffs, except the argument type islong.
Similar to
__builtin_clz, except the argument type isunsigned long.
Similar to
__builtin_ctz, except the argument type isunsigned long.
Similar to
__builtin_clrsb, except the argument type islong.
Similar to
__builtin_popcount, except the argument type isunsigned long.
Similar to
__builtin_parity, except the argument type isunsigned long.
Similar to
__builtin_ffs, except the argument type islong long.
Similar to
__builtin_clz, except the argument type isunsigned long long.
Similar to
__builtin_ctz, except the argument type isunsigned long long.
Similar to
__builtin_clrsb, except the argument type islong long.
Similar to
__builtin_popcount, except the argument type isunsigned long long.
Similar to
__builtin_parity, except the argument type isunsigned long long.
Returns the first argument raised to the power of the second. Unlike the
powfunction no guarantees about precision and rounding are made.
Returns x with the order of the bytes reversed; for example,
0xaabbbecomes0xbbaa. Byte here always means exactly 8 bits.
Similar to
__builtin_bswap16, except the argument and return types are 32-bit.
Similar to
__builtin_bswap32, except the argument and return types are 64-bit.
Similar to
__builtin_bswap64, except the argument and return types are 128-bit. Only supported on targets when 128-bit types are supported.
On targets where the user visible pointer size is smaller than the size of an actual hardware address this function returns the extended user pointer. Targets where this is true included ILP32 mode on x86_64 or Aarch64. This function is mainly useful when writing inline assembly code.
Returns the openacc gang, worker or vector id depending on whether x is 0, 1 or 2.
Returns the openacc gang, worker or vector size depending on whether x is 0, 1 or 2.
On some target machines, GCC supports many built-in functions specific to those machines. Generally these generate calls to specific machine instructions, but allow the compiler to schedule those calls.
These built-in functions are available for the AArch64 family of processors.
unsigned int __builtin_aarch64_get_fpcr ();
void __builtin_aarch64_set_fpcr (unsigned int);
unsigned int __builtin_aarch64_get_fpsr ();
void __builtin_aarch64_set_fpsr (unsigned int);
unsigned long long __builtin_aarch64_get_fpcr64 ();
void __builtin_aarch64_set_fpcr64 (unsigned long long);
unsigned long long __builtin_aarch64_get_fpsr64 ();
void __builtin_aarch64_set_fpsr64 (unsigned long long);
These built-in functions are available for the Alpha family of processors, depending on the command-line switches used.
The following built-in functions are always available. They all generate the machine instruction that is part of the name.
long __builtin_alpha_implver (void);
long __builtin_alpha_rpcc (void);
long __builtin_alpha_amask (long);
long __builtin_alpha_cmpbge (long, long);
long __builtin_alpha_extbl (long, long);
long __builtin_alpha_extwl (long, long);
long __builtin_alpha_extll (long, long);
long __builtin_alpha_extql (long, long);
long __builtin_alpha_extwh (long, long);
long __builtin_alpha_extlh (long, long);
long __builtin_alpha_extqh (long, long);
long __builtin_alpha_insbl (long, long);
long __builtin_alpha_inswl (long, long);
long __builtin_alpha_insll (long, long);
long __builtin_alpha_insql (long, long);
long __builtin_alpha_inswh (long, long);
long __builtin_alpha_inslh (long, long);
long __builtin_alpha_insqh (long, long);
long __builtin_alpha_mskbl (long, long);
long __builtin_alpha_mskwl (long, long);
long __builtin_alpha_mskll (long, long);
long __builtin_alpha_mskql (long, long);
long __builtin_alpha_mskwh (long, long);
long __builtin_alpha_msklh (long, long);
long __builtin_alpha_mskqh (long, long);
long __builtin_alpha_umulh (long, long);
long __builtin_alpha_zap (long, long);
long __builtin_alpha_zapnot (long, long);
The following built-in functions are always with -mmax
or -mcpu=cpu where cpu is pca56 or
later. They all generate the machine instruction that is part
of the name.
long __builtin_alpha_pklb (long);
long __builtin_alpha_pkwb (long);
long __builtin_alpha_unpkbl (long);
long __builtin_alpha_unpkbw (long);
long __builtin_alpha_minub8 (long, long);
long __builtin_alpha_minsb8 (long, long);
long __builtin_alpha_minuw4 (long, long);
long __builtin_alpha_minsw4 (long, long);
long __builtin_alpha_maxub8 (long, long);
long __builtin_alpha_maxsb8 (long, long);
long __builtin_alpha_maxuw4 (long, long);
long __builtin_alpha_maxsw4 (long, long);
long __builtin_alpha_perr (long, long);
The following built-in functions are always with -mcix
or -mcpu=cpu where cpu is ev67 or
later. They all generate the machine instruction that is part
of the name.
long __builtin_alpha_cttz (long);
long __builtin_alpha_ctlz (long);
long __builtin_alpha_ctpop (long);
The following built-in functions are available on systems that use the OSF/1
PALcode. Normally they invoke the rduniq and wruniq
PAL calls, but when invoked with -mtls-kernel, they invoke
rdval and wrval.
void *__builtin_thread_pointer (void);
void __builtin_set_thread_pointer (void *);
These built-in functions are available for the Altera Nios II family of processors.
The following built-in functions are always available. They all generate the machine instruction that is part of the name.
int __builtin_ldbio (volatile const void *);
int __builtin_ldbuio (volatile const void *);
int __builtin_ldhio (volatile const void *);
int __builtin_ldhuio (volatile const void *);
int __builtin_ldwio (volatile const void *);
void __builtin_stbio (volatile void *, int);
void __builtin_sthio (volatile void *, int);
void __builtin_stwio (volatile void *, int);
void __builtin_sync (void);
int __builtin_rdctl (int);
int __builtin_rdprs (int, int);
void __builtin_wrctl (int, int);
void __builtin_flushd (volatile void *);
void __builtin_flushda (volatile void *);
int __builtin_wrpie (int);
void __builtin_eni (int);
int __builtin_ldex (volatile const void *);
int __builtin_stex (volatile void *, int);
int __builtin_ldsex (volatile const void *);
int __builtin_stsex (volatile void *, int);
The following built-in functions are always available. They
all generate a Nios II Custom Instruction. The name of the
function represents the types that the function takes and
returns. The letter before the n is the return type
or void if absent. The n represents the first parameter
to all the custom instructions, the custom instruction number.
The two letters after the n represent the up to two
parameters to the function.
The letters represent the following data types:
<no letter>void for return type and no parameter for parameter types.
iint for return type and parameter type
ffloat for return type and parameter type
pvoid * for return type and parameter type
And the function names are:
void __builtin_custom_n (void);
void __builtin_custom_ni (int);
void __builtin_custom_nf (float);
void __builtin_custom_np (void *);
void __builtin_custom_nii (int, int);
void __builtin_custom_nif (int, float);
void __builtin_custom_nip (int, void *);
void __builtin_custom_nfi (float, int);
void __builtin_custom_nff (float, float);
void __builtin_custom_nfp (float, void *);
void __builtin_custom_npi (void *, int);
void __builtin_custom_npf (void *, float);
void __builtin_custom_npp (void *, void *);
int __builtin_custom_in (void);
int __builtin_custom_ini (int);
int __builtin_custom_inf (float);
int __builtin_custom_inp (void *);
int __builtin_custom_inii (int, int);
int __builtin_custom_inif (int, float);
int __builtin_custom_inip (int, void *);
int __builtin_custom_infi (float, int);
int __builtin_custom_inff (float, float);
int __builtin_custom_infp (float, void *);
int __builtin_custom_inpi (void *, int);
int __builtin_custom_inpf (void *, float);
int __builtin_custom_inpp (void *, void *);
float __builtin_custom_fn (void);
float __builtin_custom_fni (int);
float __builtin_custom_fnf (float);
float __builtin_custom_fnp (void *);
float __builtin_custom_fnii (int, int);
float __builtin_custom_fnif (int, float);
float __builtin_custom_fnip (int, void *);
float __builtin_custom_fnfi (float, int);
float __builtin_custom_fnff (float, float);
float __builtin_custom_fnfp (float, void *);
float __builtin_custom_fnpi (void *, int);
float __builtin_custom_fnpf (void *, float);
float __builtin_custom_fnpp (void *, void *);
void * __builtin_custom_pn (void);
void * __builtin_custom_pni (int);
void * __builtin_custom_pnf (float);
void * __builtin_custom_pnp (void *);
void * __builtin_custom_pnii (int, int);
void * __builtin_custom_pnif (int, float);
void * __builtin_custom_pnip (int, void *);
void * __builtin_custom_pnfi (float, int);
void * __builtin_custom_pnff (float, float);
void * __builtin_custom_pnfp (float, void *);
void * __builtin_custom_pnpi (void *, int);
void * __builtin_custom_pnpf (void *, float);
void * __builtin_custom_pnpp (void *, void *);
The following built-in functions are provided for ARC targets. The built-ins generate the corresponding assembly instructions. In the examples given below, the generated code often requires an operand or result to be in a register. Where necessary further code will be generated to ensure this is true, but for brevity this is not described in each case.
Note: Using a built-in to generate an instruction not supported by a target may cause problems. At present the compiler is not guaranteed to detect such misuse, and as a result an internal compiler error may be generated.
Return 1 if val is known to have the byte alignment given by alignval, otherwise return 0. Note that this is different from
__alignof__(*(char *)val) >= alignvalbecause __alignof__ sees only the type of the dereference, whereas __builtin_arc_align uses alignment information from the pointer as well as from the pointed-to type. The information available will depend on optimization level.
The operand is the number of a register to be read. Generates:
mov dest, rregnowhere the value in dest will be the result returned from the built-in.
The first operand is the number of a register to be written, the second operand is a compile time constant to write into that register. Generates:
mov rregno, val
Only available if either -mcpu=ARC700 or -meA is set. Generates:
divaw dest, a, bwhere the value in dest will be the result returned from the built-in.
The operand, auxv, is the address of an auxiliary register and must be a compile time constant. Generates:
lr dest, [auxr]Where the value in dest will be the result returned from the built-in.
Only available with -mmul64. Generates:
mul64 a, b
Only available with -mmul64. Generates:
mulu64 a, b
Only valid if the ‘norm’ instruction is available through the -mnorm option or by default with -mcpu=ARC700. Generates:
norm dest, srcWhere the value in dest will be the result returned from the built-in.
Only valid if the ‘normw’ instruction is available through the -mnorm option or by default with -mcpu=ARC700. Generates:
normw dest, srcWhere the value in dest will be the result returned from the built-in.
The first argument, val, is a compile time constant to be written to the register, the second argument, auxr, is the address of an auxiliary register. Generates:
sr val, [auxr]
Only valid with -mswap. Generates:
swap dest, srcWhere the value in dest will be the result returned from the built-in.
Only available with -mcpu=ARC700. Generates:
sync
Only available with -mcpu=ARC700. Generates:
trap_s c
Only available with -mcpu=ARC700. Generates:
unimp_s
The instructions generated by the following builtins are not considered as candidates for scheduling. They are not moved around by the compiler during scheduling, and thus can be expected to appear where they are put in the C code:
__builtin_arc_brk()
__builtin_arc_core_read()
__builtin_arc_core_write()
__builtin_arc_flag()
__builtin_arc_lr()
__builtin_arc_sleep()
__builtin_arc_sr()
__builtin_arc_swi()
SIMD builtins provided by the compiler can be used to generate the
vector instructions. This section describes the available builtins
and their usage in programs. With the -msimd option, the
compiler provides 128-bit vector types, which can be specified using
the vector_size attribute. The header file arc-simd.h
can be included to use the following predefined types:
typedef int __v4si __attribute__((vector_size(16)));
typedef short __v8hi __attribute__((vector_size(16)));
These types can be used to define 128-bit variables. The built-in functions listed in the following section can be used on these variables to generate the vector operations.
For all builtins, __builtin_arc_someinsn, the header file
arc-simd.h also provides equivalent macros called
_someinsn that can be used for programming ease and
improved readability. The following macros for DMA control are also
provided:
#define _setup_dma_in_channel_reg _vdiwr
#define _setup_dma_out_channel_reg _vdowr
The following is a complete list of all the SIMD built-ins provided for ARC, grouped by calling signature.
The following take two __v8hi arguments and return a
__v8hi result:
__v8hi __builtin_arc_vaddaw (__v8hi, __v8hi);
__v8hi __builtin_arc_vaddw (__v8hi, __v8hi);
__v8hi __builtin_arc_vand (__v8hi, __v8hi);
__v8hi __builtin_arc_vandaw (__v8hi, __v8hi);
__v8hi __builtin_arc_vavb (__v8hi, __v8hi);
__v8hi __builtin_arc_vavrb (__v8hi, __v8hi);
__v8hi __builtin_arc_vbic (__v8hi, __v8hi);
__v8hi __builtin_arc_vbicaw (__v8hi, __v8hi);
__v8hi __builtin_arc_vdifaw (__v8hi, __v8hi);
__v8hi __builtin_arc_vdifw (__v8hi, __v8hi);
__v8hi __builtin_arc_veqw (__v8hi, __v8hi);
__v8hi __builtin_arc_vh264f (__v8hi, __v8hi);
__v8hi __builtin_arc_vh264ft (__v8hi, __v8hi);
__v8hi __builtin_arc_vh264fw (__v8hi, __v8hi);
__v8hi __builtin_arc_vlew (__v8hi, __v8hi);
__v8hi __builtin_arc_vltw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmaxaw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmaxw (__v8hi, __v8hi);
__v8hi __builtin_arc_vminaw (__v8hi, __v8hi);
__v8hi __builtin_arc_vminw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr1aw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr1w (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr2aw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr2w (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr3aw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr3w (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr4aw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr4w (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr5aw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr5w (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr6aw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr6w (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr7aw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmr7w (__v8hi, __v8hi);
__v8hi __builtin_arc_vmrb (__v8hi, __v8hi);
__v8hi __builtin_arc_vmulaw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmulfaw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmulfw (__v8hi, __v8hi);
__v8hi __builtin_arc_vmulw (__v8hi, __v8hi);
__v8hi __builtin_arc_vnew (__v8hi, __v8hi);
__v8hi __builtin_arc_vor (__v8hi, __v8hi);
__v8hi __builtin_arc_vsubaw (__v8hi, __v8hi);
__v8hi __builtin_arc_vsubw (__v8hi, __v8hi);
__v8hi __builtin_arc_vsummw (__v8hi, __v8hi);
__v8hi __builtin_arc_vvc1f (__v8hi, __v8hi);
__v8hi __builtin_arc_vvc1ft (__v8hi, __v8hi);
__v8hi __builtin_arc_vxor (__v8hi, __v8hi);
__v8hi __builtin_arc_vxoraw (__v8hi, __v8hi);
The following take one __v8hi and one int argument and return a
__v8hi result:
__v8hi __builtin_arc_vbaddw (__v8hi, int);
__v8hi __builtin_arc_vbmaxw (__v8hi, int);
__v8hi __builtin_arc_vbminw (__v8hi, int);
__v8hi __builtin_arc_vbmulaw (__v8hi, int);
__v8hi __builtin_arc_vbmulfw (__v8hi, int);
__v8hi __builtin_arc_vbmulw (__v8hi, int);
__v8hi __builtin_arc_vbrsubw (__v8hi, int);
__v8hi __builtin_arc_vbsubw (__v8hi, int);
The following take one __v8hi argument and one int argument which
must be a 3-bit compile time constant indicating a register number
I0-I7. They return a __v8hi result.
__v8hi __builtin_arc_vasrw (__v8hi, const int);
__v8hi __builtin_arc_vsr8 (__v8hi, const int);
__v8hi __builtin_arc_vsr8aw (__v8hi, const int);
The following take one __v8hi argument and one int
argument which must be a 6-bit compile time constant. They return a
__v8hi result.
__v8hi __builtin_arc_vasrpwbi (__v8hi, const int);
__v8hi __builtin_arc_vasrrpwbi (__v8hi, const int);
__v8hi __builtin_arc_vasrrwi (__v8hi, const int);
__v8hi __builtin_arc_vasrsrwi (__v8hi, const int);
__v8hi __builtin_arc_vasrwi (__v8hi, const int);
__v8hi __builtin_arc_vsr8awi (__v8hi, const int);
__v8hi __builtin_arc_vsr8i (__v8hi, const int);
The following take one __v8hi argument and one int argument which
must be a 8-bit compile time constant. They return a __v8hi
result.
__v8hi __builtin_arc_vd6tapf (__v8hi, const int);
__v8hi __builtin_arc_vmvaw (__v8hi, const int);
__v8hi __builtin_arc_vmvw (__v8hi, const int);
__v8hi __builtin_arc_vmvzw (__v8hi, const int);
The following take two int arguments, the second of which which
must be a 8-bit compile time constant. They return a __v8hi
result:
__v8hi __builtin_arc_vmovaw (int, const int);
__v8hi __builtin_arc_vmovw (int, const int);
__v8hi __builtin_arc_vmovzw (int, const int);
The following take a single __v8hi argument and return a
__v8hi result:
__v8hi __builtin_arc_vabsaw (__v8hi);
__v8hi __builtin_arc_vabsw (__v8hi);
__v8hi __builtin_arc_vaddsuw (__v8hi);
__v8hi __builtin_arc_vexch1 (__v8hi);
__v8hi __builtin_arc_vexch2 (__v8hi);
__v8hi __builtin_arc_vexch4 (__v8hi);
__v8hi __builtin_arc_vsignw (__v8hi);
__v8hi __builtin_arc_vupbaw (__v8hi);
__v8hi __builtin_arc_vupbw (__v8hi);
__v8hi __builtin_arc_vupsbaw (__v8hi);
__v8hi __builtin_arc_vupsbw (__v8hi);
The following take two int arguments and return no result:
void __builtin_arc_vdirun (int, int);
void __builtin_arc_vdorun (int, int);
The following take two int arguments and return no result. The
first argument must a 3-bit compile time constant indicating one of
the DR0-DR7 DMA setup channels:
void __builtin_arc_vdiwr (const int, int);
void __builtin_arc_vdowr (const int, int);
The following take an int argument and return no result:
void __builtin_arc_vendrec (int);
void __builtin_arc_vrec (int);
void __builtin_arc_vrecrun (int);
void __builtin_arc_vrun (int);
The following take a __v8hi argument and two int
arguments and return a __v8hi result. The second argument must
be a 3-bit compile time constants, indicating one the registers I0-I7,
and the third argument must be an 8-bit compile time constant.
Note: Although the equivalent hardware instructions do not take
an SIMD register as an operand, these builtins overwrite the relevant
bits of the __v8hi register provided as the first argument with
the value loaded from the [Ib, u8] location in the SDM.
__v8hi __builtin_arc_vld32 (__v8hi, const int, const int);
__v8hi __builtin_arc_vld32wh (__v8hi, const int, const int);
__v8hi __builtin_arc_vld32wl (__v8hi, const int, const int);
__v8hi __builtin_arc_vld64 (__v8hi, const int, const int);
The following take two int arguments and return a __v8hi
result. The first argument must be a 3-bit compile time constants,
indicating one the registers I0-I7, and the second argument must be an
8-bit compile time constant.
__v8hi __builtin_arc_vld128 (const int, const int);
__v8hi __builtin_arc_vld64w (const int, const int);
The following take a __v8hi argument and two int
arguments and return no result. The second argument must be a 3-bit
compile time constants, indicating one the registers I0-I7, and the
third argument must be an 8-bit compile time constant.
void __builtin_arc_vst128 (__v8hi, const int, const int);
void __builtin_arc_vst64 (__v8hi, const int, const int);
The following take a __v8hi argument and three int
arguments and return no result. The second argument must be a 3-bit
compile-time constant, identifying the 16-bit sub-register to be
stored, the third argument must be a 3-bit compile time constants,
indicating one the registers I0-I7, and the fourth argument must be an
8-bit compile time constant.
void __builtin_arc_vst16_n (__v8hi, const int, const int, const int);
void __builtin_arc_vst32_n (__v8hi, const int, const int, const int);
These built-in functions are available for the ARM family of processors when the -mcpu=iwmmxt switch is used:
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef char v8qi __attribute__ ((vector_size (8)));
int __builtin_arm_getwcgr0 (void);
void __builtin_arm_setwcgr0 (int);
int __builtin_arm_getwcgr1 (void);
void __builtin_arm_setwcgr1 (int);
int __builtin_arm_getwcgr2 (void);
void __builtin_arm_setwcgr2 (int);
int __builtin_arm_getwcgr3 (void);
void __builtin_arm_setwcgr3 (int);
int __builtin_arm_textrmsb (v8qi, int);
int __builtin_arm_textrmsh (v4hi, int);
int __builtin_arm_textrmsw (v2si, int);
int __builtin_arm_textrmub (v8qi, int);
int __builtin_arm_textrmuh (v4hi, int);
int __builtin_arm_textrmuw (v2si, int);
v8qi __builtin_arm_tinsrb (v8qi, int, int);
v4hi __builtin_arm_tinsrh (v4hi, int, int);
v2si __builtin_arm_tinsrw (v2si, int, int);
long long __builtin_arm_tmia (long long, int, int);
long long __builtin_arm_tmiabb (long long, int, int);
long long __builtin_arm_tmiabt (long long, int, int);
long long __builtin_arm_tmiaph (long long, int, int);
long long __builtin_arm_tmiatb (long long, int, int);
long long __builtin_arm_tmiatt (long long, int, int);
int __builtin_arm_tmovmskb (v8qi);
int __builtin_arm_tmovmskh (v4hi);
int __builtin_arm_tmovmskw (v2si);
long long __builtin_arm_waccb (v8qi);
long long __builtin_arm_wacch (v4hi);
long long __builtin_arm_waccw (v2si);
v8qi __builtin_arm_waddb (v8qi, v8qi);
v8qi __builtin_arm_waddbss (v8qi, v8qi);
v8qi __builtin_arm_waddbus (v8qi, v8qi);
v4hi __builtin_arm_waddh (v4hi, v4hi);
v4hi __builtin_arm_waddhss (v4hi, v4hi);
v4hi __builtin_arm_waddhus (v4hi, v4hi);
v2si __builtin_arm_waddw (v2si, v2si);
v2si __builtin_arm_waddwss (v2si, v2si);
v2si __builtin_arm_waddwus (v2si, v2si);
v8qi __builtin_arm_walign (v8qi, v8qi, int);
long long __builtin_arm_wand(long long, long long);
long long __builtin_arm_wandn (long long, long long);
v8qi __builtin_arm_wavg2b (v8qi, v8qi);
v8qi __builtin_arm_wavg2br (v8qi, v8qi);
v4hi __builtin_arm_wavg2h (v4hi, v4hi);
v4hi __builtin_arm_wavg2hr (v4hi, v4hi);
v8qi __builtin_arm_wcmpeqb (v8qi, v8qi);
v4hi __builtin_arm_wcmpeqh (v4hi, v4hi);
v2si __builtin_arm_wcmpeqw (v2si, v2si);
v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi);
v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi);
v2si __builtin_arm_wcmpgtsw (v2si, v2si);
v8qi __builtin_arm_wcmpgtub (v8qi, v8qi);
v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi);
v2si __builtin_arm_wcmpgtuw (v2si, v2si);
long long __builtin_arm_wmacs (long long, v4hi, v4hi);
long long __builtin_arm_wmacsz (v4hi, v4hi);
long long __builtin_arm_wmacu (long long, v4hi, v4hi);
long long __builtin_arm_wmacuz (v4hi, v4hi);
v4hi __builtin_arm_wmadds (v4hi, v4hi);
v4hi __builtin_arm_wmaddu (v4hi, v4hi);
v8qi __builtin_arm_wmaxsb (v8qi, v8qi);
v4hi __builtin_arm_wmaxsh (v4hi, v4hi);
v2si __builtin_arm_wmaxsw (v2si, v2si);
v8qi __builtin_arm_wmaxub (v8qi, v8qi);
v4hi __builtin_arm_wmaxuh (v4hi, v4hi);
v2si __builtin_arm_wmaxuw (v2si, v2si);
v8qi __builtin_arm_wminsb (v8qi, v8qi);
v4hi __builtin_arm_wminsh (v4hi, v4hi);
v2si __builtin_arm_wminsw (v2si, v2si);
v8qi __builtin_arm_wminub (v8qi, v8qi);
v4hi __builtin_arm_wminuh (v4hi, v4hi);
v2si __builtin_arm_wminuw (v2si, v2si);
v4hi __builtin_arm_wmulsm (v4hi, v4hi);
v4hi __builtin_arm_wmulul (v4hi, v4hi);
v4hi __builtin_arm_wmulum (v4hi, v4hi);
long long __builtin_arm_wor (long long, long long);
v2si __builtin_arm_wpackdss (long long, long long);
v2si __builtin_arm_wpackdus (long long, long long);
v8qi __builtin_arm_wpackhss (v4hi, v4hi);
v8qi __builtin_arm_wpackhus (v4hi, v4hi);
v4hi __builtin_arm_wpackwss (v2si, v2si);
v4hi __builtin_arm_wpackwus (v2si, v2si);
long long __builtin_arm_wrord (long long, long long);
long long __builtin_arm_wrordi (long long, int);
v4hi __builtin_arm_wrorh (v4hi, long long);
v4hi __builtin_arm_wrorhi (v4hi, int);
v2si __builtin_arm_wrorw (v2si, long long);
v2si __builtin_arm_wrorwi (v2si, int);
v2si __builtin_arm_wsadb (v2si, v8qi, v8qi);
v2si __builtin_arm_wsadbz (v8qi, v8qi);
v2si __builtin_arm_wsadh (v2si, v4hi, v4hi);
v2si __builtin_arm_wsadhz (v4hi, v4hi);
v4hi __builtin_arm_wshufh (v4hi, int);
long long __builtin_arm_wslld (long long, long long);
long long __builtin_arm_wslldi (long long, int);
v4hi __builtin_arm_wsllh (v4hi, long long);
v4hi __builtin_arm_wsllhi (v4hi, int);
v2si __builtin_arm_wsllw (v2si, long long);
v2si __builtin_arm_wsllwi (v2si, int);
long long __builtin_arm_wsrad (long long, long long);
long long __builtin_arm_wsradi (long long, int);
v4hi __builtin_arm_wsrah (v4hi, long long);
v4hi __builtin_arm_wsrahi (v4hi, int);
v2si __builtin_arm_wsraw (v2si, long long);
v2si __builtin_arm_wsrawi (v2si, int);
long long __builtin_arm_wsrld (long long, long long);
long long __builtin_arm_wsrldi (long long, int);
v4hi __builtin_arm_wsrlh (v4hi, long long);
v4hi __builtin_arm_wsrlhi (v4hi, int);
v2si __builtin_arm_wsrlw (v2si, long long);
v2si __builtin_arm_wsrlwi (v2si, int);
v8qi __builtin_arm_wsubb (v8qi, v8qi);
v8qi __builtin_arm_wsubbss (v8qi, v8qi);
v8qi __builtin_arm_wsubbus (v8qi, v8qi);
v4hi __builtin_arm_wsubh (v4hi, v4hi);
v4hi __builtin_arm_wsubhss (v4hi, v4hi);
v4hi __builtin_arm_wsubhus (v4hi, v4hi);
v2si __builtin_arm_wsubw (v2si, v2si);
v2si __builtin_arm_wsubwss (v2si, v2si);
v2si __builtin_arm_wsubwus (v2si, v2si);
v4hi __builtin_arm_wunpckehsb (v8qi);
v2si __builtin_arm_wunpckehsh (v4hi);
long long __builtin_arm_wunpckehsw (v2si);
v4hi __builtin_arm_wunpckehub (v8qi);
v2si __builtin_arm_wunpckehuh (v4hi);
long long __builtin_arm_wunpckehuw (v2si);
v4hi __builtin_arm_wunpckelsb (v8qi);
v2si __builtin_arm_wunpckelsh (v4hi);
long long __builtin_arm_wunpckelsw (v2si);
v4hi __builtin_arm_wunpckelub (v8qi);
v2si __builtin_arm_wunpckeluh (v4hi);
long long __builtin_arm_wunpckeluw (v2si);
v8qi __builtin_arm_wunpckihb (v8qi, v8qi);
v4hi __builtin_arm_wunpckihh (v4hi, v4hi);
v2si __builtin_arm_wunpckihw (v2si, v2si);
v8qi __builtin_arm_wunpckilb (v8qi, v8qi);
v4hi __builtin_arm_wunpckilh (v4hi, v4hi);
v2si __builtin_arm_wunpckilw (v2si, v2si);
long long __builtin_arm_wxor (long long, long long);
long long __builtin_arm_wzero ();
GCC implements extensions for C as described in the ARM C Language Extensions (ACLE) specification, which can be found at https://developer.arm.com/documentation/ihi0053/latest/.
As a part of ACLE, GCC implements extensions for Advanced SIMD as described in the ARM C Language Extensions Specification. The complete list of Advanced SIMD intrinsics can be found at https://developer.arm.com/documentation/ihi0073/latest/. The built-in intrinsics for the Advanced SIMD extension are available when NEON is enabled.
Currently, ARM and AArch64 back ends do not support ACLE 2.0 fully. Both back ends support CRC32 intrinsics and the ARM back end supports the Coprocessor intrinsics, all from arm_acle.h. The ARM back end's 16-bit floating-point Advanced SIMD intrinsics currently comply to ACLE v1.1. AArch64's back end does not have support for 16-bit floating point Advanced SIMD intrinsics yet.
See ARM Options and AArch64 Options for more information on the availability of extensions.
These built-in functions are available for the ARM family of processors with floating-point unit.
unsigned int __builtin_arm_get_fpscr ();
void __builtin_arm_set_fpscr (unsigned int);
GCC implements the ARMv8-M Security Extensions as described in the ARMv8-M Security Extensions: Requirements on Development Tools Engineering Specification, which can be found at https://developer.arm.com/documentation/ecm0359818/latest/.
As part of the Security Extensions GCC implements two new function attributes:
cmse_nonsecure_entry and cmse_nonsecure_call.
As part of the Security Extensions GCC implements the intrinsics below. FPTR is used here to mean any function pointer type.
cmse_address_info_t cmse_TT (void *);
cmse_address_info_t cmse_TT_fptr (FPTR);
cmse_address_info_t cmse_TTT (void *);
cmse_address_info_t cmse_TTT_fptr (FPTR);
cmse_address_info_t cmse_TTA (void *);
cmse_address_info_t cmse_TTA_fptr (FPTR);
cmse_address_info_t cmse_TTAT (void *);
cmse_address_info_t cmse_TTAT_fptr (FPTR);
void * cmse_check_address_range (void *, size_t, int);
typeof(p) cmse_nsfptr_create (FPTR p);
intptr_t cmse_is_nsfptr (FPTR);
int cmse_nonsecure_caller (void);
For each built-in function for AVR, there is an equally named,
uppercase built-in macro defined. That way users can easily query if
or if not a specific built-in is implemented or not. For example, if
__builtin_avr_nop is available the macro
__BUILTIN_AVR_NOP is defined to 1 and undefined otherwise.
void __builtin_avr_nop (void)void __builtin_avr_sei (void)void __builtin_avr_cli (void)void __builtin_avr_sleep (void)void __builtin_avr_wdr (void)unsigned char __builtin_avr_swap (unsigned char)unsigned int __builtin_avr_fmul (unsigned char, unsigned char)int __builtin_avr_fmuls (char, char)int __builtin_avr_fmulsu (char, unsigned char)nop, sei, cli, sleep,
wdr, swap, fmul, fmuls
resp. fmulsu. The three fmul* built-ins are implemented
as library call if no hardware multiplier is available.
void __builtin_avr_delay_cycles (unsigned long ticks)char __builtin_avr_flash_segment (const __memx void*)__memx and returns
the number of the flash segment (the 64 KiB chunk) where the address
points to. Counting starts at 0.
If the address does not point to flash memory, return -1.
uint8_t __builtin_avr_insert_bits (uint32_t map, uint8_t bits, uint8_t val)0xf,
then the n-th bit of val is returned unaltered.
0xe,
then the n-th result bit is undefined.
One typical use case for this built-in is adjusting input and output values to non-contiguous port layouts. Some examples:
// same as val, bits is unused
__builtin_avr_insert_bits (0xffffffff, bits, val);
// same as bits, val is unused
__builtin_avr_insert_bits (0x76543210, bits, val);
// same as rotating bits by 4
__builtin_avr_insert_bits (0x32107654, bits, 0);
// high nibble of result is the high nibble of val
// low nibble of result is the low nibble of bits
__builtin_avr_insert_bits (0xffff3210, bits, val);
// reverse the bit order of bits
__builtin_avr_insert_bits (0x01234567, bits, 0);
void __builtin_avr_nops (unsigned count)NOP instructions.
The number of instructions must be a compile-time integer constant.
There are many more AVR-specific built-in functions that are used to
implement the ISO/IEC TR 18037 “Embedded C” fixed-point functions of
section 7.18a.6. You don't need to use these built-ins directly.
Instead, use the declarations as supplied by the stdfix.h header
with GNU-C99:
#include <stdfix.h>
// Re-interpret the bit representation of unsigned 16-bit
// integer uval as Q-format 0.16 value.
unsigned fract get_bits (uint_ur_t uval)
{
return urbits (uval);
}
Currently, there are two Blackfin-specific built-in functions. These are
used for generating CSYNC and SSYNC machine insns without
using inline assembly; by using these built-in functions the compiler can
automatically add workarounds for hardware errata involving these
instructions. These functions are named as follows:
void __builtin_bfin_csync (void);
void __builtin_bfin_ssync (void);
The following built-in functions are available for eBPF targets.
Load a byte from the
struct sk_buffpacket data pointed by the register%r6and return it.
Load 16 bits from the
struct sk_buffpacket data pointed by the register%r6and return it.
Load 32 bits from the
struct sk_buffpacket data pointed by the register%r6and return it.
BPF Compile Once-Run Everywhere (CO-RE) support. Instruct GCC to generate CO-RE relocation records for any accesses to aggregate data structures (struct, union, array types) in expr. This builtin is otherwise transparent, the return value is whatever expr evaluates to. It is also overloaded: expr may be of any type (not necessarily a pointer), the return type is the same. Has no effect if
-mco-reis not in effect (either specified or implied).
BPF Compile Once-Run Everywhere (CO-RE) support. This builtin is used to extract information to aid in struct/union relocations. expr is an access to a field of a struct or union. Depending on kind, different information is returned to the program. A CO-RE relocation for the access in expr with kind kind is recorded if
-mco-reis in effect.The following values are supported for kind:
FIELD_BYTE_OFFSET = 0- The returned value is the offset, in bytes, of the field from the beginning of the containing structure. For bit-fields, this is the byte offset of the containing word.
FIELD_BYTE_SIZE = 1- The returned value is the size, in bytes, of the field. For bit-fields, this is the size in bytes of the containing word.
FIELD_EXISTENCE = 2- The returned value is 1 if the field exists, 0 otherwise. Always 1 at compile time.
FIELD_SIGNEDNESS = 3- The returned value is 1 if the field is signed, 0 otherwise.
FIELD_LSHIFT_U64 = 4FIELD_RSHIFT_U64 = 5- The returned value is the number of bits of left- or right-shifting (respectively) needed in order to recover the original value of the field, after it has been loaded by a read of
FIELD_BYTE_SIZEbytes into an unsigned 64-bit value. Primarily useful for reading bit-field values from structures that may change between kernel versions.Note that the return value is a constant which is known at compile time. If the field has a variable offset then
FIELD_BYTE_OFFSET,FIELD_LSHIFT_U64, andFIELD_RSHIFT_U64are not supported. Similarly, if the field has a variable size thenFIELD_BYTE_SIZE,FIELD_LSHIFT_U64, andFIELD_RSHIFT_U64are not supported.For example,
__builtin_preserve_field_infocan be used to reliably extract bit-field values from a structure that may change between kernel versions:struct S { short a; int x:7; int y:5; }; int read_y (struct S *arg) { unsigned long long val; unsigned int offset = __builtin_preserve_field_info (arg->y, FIELD_BYTE_OFFSET); unsigned int size = __builtin_preserve_field_info (arg->y, FIELD_BYTE_SIZE); /* Read size bytes from arg + offset into val. */ bpf_probe_read (&val, size, arg + offset); val <<= __builtin_preserve_field_info (arg->y, FIELD_LSHIFT_U64); if (__builtin_preserve_field_info (arg->y, FIELD_SIGNEDNESS)) val = ((long long) val >> __builtin_preserve_field_info (arg->y, FIELD_RSHIFT_U64)); else val >>= __builtin_preserve_field_info (arg->y, FIELD_RSHIFT_U64); return val; }
GCC provides many FR-V-specific built-in functions. In general,
these functions are intended to be compatible with those described
by FR-V Family, Softune C/C++ Compiler Manual (V6), Fujitsu
Semiconductor. The two exceptions are __MDUNPACKH and
__MBTOHE, the GCC forms of which pass 128-bit values by
pointer rather than by value.
Most of the functions are named after specific FR-V instructions. Such functions are said to be “directly mapped” and are summarized here in tabular form.
The arguments to the built-in functions can be divided into three groups: register numbers, compile-time constants and run-time values. In order to make this classification clear at a glance, the arguments and return values are given the following pseudo types:
| Pseudo type | Real C type | Constant? | Description
|
|---|---|---|---|
uh | unsigned short | No | an unsigned halfword
|
uw1 | unsigned int | No | an unsigned word
|
sw1 | int | No | a signed word
|
uw2 | unsigned long long | No | an unsigned doubleword
|
sw2 | long long | No | a signed doubleword
|
const | int | Yes | an integer constant
|
acc | int | Yes | an ACC register number
|
iacc | int | Yes | an IACC register number
|
These pseudo types are not defined by GCC, they are simply a notational convenience used in this manual.
Arguments of type uh, uw1, sw1, uw2
and sw2 are evaluated at run time. They correspond to
register operands in the underlying FR-V instructions.
const arguments represent immediate operands in the underlying
FR-V instructions. They must be compile-time constants.
acc arguments are evaluated at compile time and specify the number
of an accumulator register. For example, an acc argument of 2
selects the ACC2 register.
iacc arguments are similar to acc arguments but specify the
number of an IACC register. See see Other Built-in Functions
for more details.
The functions listed below map directly to FR-V I-type instructions.
| Function prototype | Example usage | Assembly output
|
|---|---|---|
sw1 __ADDSS (sw1, sw1)
| c = __ADDSS (a, b)
| ADDSS a,b,c
|
sw1 __SCAN (sw1, sw1)
| c = __SCAN (a, b)
| SCAN a,b,c
|
sw1 __SCUTSS (sw1)
| b = __SCUTSS (a)
| SCUTSS a,b
|
sw1 __SLASS (sw1, sw1)
| c = __SLASS (a, b)
| SLASS a,b,c
|
void __SMASS (sw1, sw1)
| __SMASS (a, b)
| SMASS a,b
|
void __SMSSS (sw1, sw1)
| __SMSSS (a, b)
| SMSSS a,b
|
void __SMU (sw1, sw1)
| __SMU (a, b)
| SMU a,b
|
sw2 __SMUL (sw1, sw1)
| c = __SMUL (a, b)
| SMUL a,b,c
|
sw1 __SUBSS (sw1, sw1)
| c = __SUBSS (a, b)
| SUBSS a,b,c
|
uw2 __UMUL (uw1, uw1)
| c = __UMUL (a, b)
| UMUL a,b,c
|
The functions listed below map directly to FR-V M-type instructions.
| Function prototype | Example usage | Assembly output
|
|---|---|---|
uw1 __MABSHS (sw1)
| b = __MABSHS (a)
| MABSHS a,b
|
void __MADDACCS (acc, acc)
| __MADDACCS (b, a)
| MADDACCS a,b
|
sw1 __MADDHSS (sw1, sw1)
| c = __MADDHSS (a, b)
| MADDHSS a,b,c
|
uw1 __MADDHUS (uw1, uw1)
| c = __MADDHUS (a, b)
| MADDHUS a,b,c
|
uw1 __MAND (uw1, uw1)
| c = __MAND (a, b)
| MAND a,b,c
|
void __MASACCS (acc, acc)
| __MASACCS (b, a)
| MASACCS a,b
|
uw1 __MAVEH (uw1, uw1)
| c = __MAVEH (a, b)
| MAVEH a,b,c
|
uw2 __MBTOH (uw1)
| b = __MBTOH (a)
| MBTOH a,b
|
void __MBTOHE (uw1 *, uw1)
| __MBTOHE (&b, a)
| MBTOHE a,b
|
void __MCLRACC (acc)
| __MCLRACC (a)
| MCLRACC a
|
void __MCLRACCA (void)
| __MCLRACCA ()
| MCLRACCA
|
uw1 __Mcop1 (uw1, uw1)
| c = __Mcop1 (a, b)
| Mcop1 a,b,c
|
uw1 __Mcop2 (uw1, uw1)
| c = __Mcop2 (a, b)
| Mcop2 a,b,c
|
uw1 __MCPLHI (uw2, const)
| c = __MCPLHI (a, b)
| MCPLHI a,#b,c
|
uw1 __MCPLI (uw2, const)
| c = __MCPLI (a, b)
| MCPLI a,#b,c
|
void __MCPXIS (acc, sw1, sw1)
| __MCPXIS (c, a, b)
| MCPXIS a,b,c
|
void __MCPXIU (acc, uw1, uw1)
| __MCPXIU (c, a, b)
| MCPXIU a,b,c
|
void __MCPXRS (acc, sw1, sw1)
| __MCPXRS (c, a, b)
| MCPXRS a,b,c
|
void __MCPXRU (acc, uw1, uw1)
| __MCPXRU (c, a, b)
| MCPXRU a,b,c
|
uw1 __MCUT (acc, uw1)
| c = __MCUT (a, b)
| MCUT a,b,c
|
uw1 __MCUTSS (acc, sw1)
| c = __MCUTSS (a, b)
| MCUTSS a,b,c
|
void __MDADDACCS (acc, acc)
| __MDADDACCS (b, a)
| MDADDACCS a,b
|
void __MDASACCS (acc, acc)
| __MDASACCS (b, a)
| MDASACCS a,b
|
uw2 __MDCUTSSI (acc, const)
| c = __MDCUTSSI (a, b)
| MDCUTSSI a,#b,c
|
uw2 __MDPACKH (uw2, uw2)
| c = __MDPACKH (a, b)
| MDPACKH a,b,c
|
uw2 __MDROTLI (uw2, const)
| c = __MDROTLI (a, b)
| MDROTLI a,#b,c
|
void __MDSUBACCS (acc, acc)
| __MDSUBACCS (b, a)
| MDSUBACCS a,b
|
void __MDUNPACKH (uw1 *, uw2)
| __MDUNPACKH (&b, a)
| MDUNPACKH a,b
|
uw2 __MEXPDHD (uw1, const)
| c = __MEXPDHD (a, b)
| MEXPDHD a,#b,c
|
uw1 __MEXPDHW (uw1, const)
| c = __MEXPDHW (a, b)
| MEXPDHW a,#b,c
|
uw1 __MHDSETH (uw1, const)
| c = __MHDSETH (a, b)
| MHDSETH a,#b,c
|
sw1 __MHDSETS (const)
| b = __MHDSETS (a)
| MHDSETS #a,b
|
uw1 __MHSETHIH (uw1, const)
| b = __MHSETHIH (b, a)
| MHSETHIH #a,b
|
sw1 __MHSETHIS (sw1, const)
| b = __MHSETHIS (b, a)
| MHSETHIS #a,b
|
uw1 __MHSETLOH (uw1, const)
| b = __MHSETLOH (b, a)
| MHSETLOH #a,b
|
sw1 __MHSETLOS (sw1, const)
| b = __MHSETLOS (b, a)
| MHSETLOS #a,b
|
uw1 __MHTOB (uw2)
| b = __MHTOB (a)
| MHTOB a,b
|
void __MMACHS (acc, sw1, sw1)
| __MMACHS (c, a, b)
| MMACHS a,b,c
|
void __MMACHU (acc, uw1, uw1)
| __MMACHU (c, a, b)
| MMACHU a,b,c
|
void __MMRDHS (acc, sw1, sw1)
| __MMRDHS (c, a, b)
| MMRDHS a,b,c
|
void __MMRDHU (acc, uw1, uw1)
| __MMRDHU (c, a, b)
| MMRDHU a,b,c
|
void __MMULHS (acc, sw1, sw1)
| __MMULHS (c, a, b)
| MMULHS a,b,c
|
void __MMULHU (acc, uw1, uw1)
| __MMULHU (c, a, b)
| MMULHU a,b,c
|
void __MMULXHS (acc, sw1, sw1)
| __MMULXHS (c, a, b)
| MMULXHS a,b,c
|
void __MMULXHU (acc, uw1, uw1)
| __MMULXHU (c, a, b)
| MMULXHU a,b,c
|
uw1 __MNOT (uw1)
| b = __MNOT (a)
| MNOT a,b
|
uw1 __MOR (uw1, uw1)
| c = __MOR (a, b)
| MOR a,b,c
|
uw1 __MPACKH (uh, uh)
| c = __MPACKH (a, b)
| MPACKH a,b,c
|
sw2 __MQADDHSS (sw2, sw2)
| c = __MQADDHSS (a, b)
| MQADDHSS a,b,c
|
uw2 __MQADDHUS (uw2, uw2)
| c = __MQADDHUS (a, b)
| MQADDHUS a,b,c
|
void __MQCPXIS (acc, sw2, sw2)
| __MQCPXIS (c, a, b)
| MQCPXIS a,b,c
|
void __MQCPXIU (acc, uw2, uw2)
| __MQCPXIU (c, a, b)
| MQCPXIU a,b,c
|
void __MQCPXRS (acc, sw2, sw2)
| __MQCPXRS (c, a, b)
| MQCPXRS a,b,c
|
void __MQCPXRU (acc, uw2, uw2)
| __MQCPXRU (c, a, b)
| MQCPXRU a,b,c
|
sw2 __MQLCLRHS (sw2, sw2)
| c = __MQLCLRHS (a, b)
| MQLCLRHS a,b,c
|
sw2 __MQLMTHS (sw2, sw2)
| c = __MQLMTHS (a, b)
| MQLMTHS a,b,c
|
void __MQMACHS (acc, sw2, sw2)
| __MQMACHS (c, a, b)
| MQMACHS a,b,c
|
void __MQMACHU (acc, uw2, uw2)
| __MQMACHU (c, a, b)
| MQMACHU a,b,c
|
void __MQMACXHS (acc, sw2, sw2)
| __MQMACXHS (c, a, b)
| MQMACXHS a,b,c
|
void __MQMULHS (acc, sw2, sw2)
| __MQMULHS (c, a, b)
| MQMULHS a,b,c
|
void __MQMULHU (acc, uw2, uw2)
| __MQMULHU (c, a, b)
| MQMULHU a,b,c
|
void __MQMULXHS (acc, sw2, sw2)
| __MQMULXHS (c, a, b)
| MQMULXHS a,b,c
|
void __MQMULXHU (acc, uw2, uw2)
| __MQMULXHU (c, a, b)
| MQMULXHU a,b,c
|
sw2 __MQSATHS (sw2, sw2)
| c = __MQSATHS (a, b)
| MQSATHS a,b,c
|
uw2 __MQSLLHI (uw2, int)
| c = __MQSLLHI (a, b)
| MQSLLHI a,b,c
|
sw2 __MQSRAHI (sw2, int)
| c = __MQSRAHI (a, b)
| MQSRAHI a,b,c
|
sw2 __MQSUBHSS (sw2, sw2)
| c = __MQSUBHSS (a, b)
| MQSUBHSS a,b,c
|
uw2 __MQSUBHUS (uw2, uw2)
| c = __MQSUBHUS (a, b)
| MQSUBHUS a,b,c
|
void __MQXMACHS (acc, sw2, sw2)
| __MQXMACHS (c, a, b)
| MQXMACHS a,b,c
|
void __MQXMACXHS (acc, sw2, sw2)
| __MQXMACXHS (c, a, b)
| MQXMACXHS a,b,c
|
uw1 __MRDACC (acc)
| b = __MRDACC (a)
| MRDACC a,b
|
uw1 __MRDACCG (acc)
| b = __MRDACCG (a)
| MRDACCG a,b
|
uw1 __MROTLI (uw1, const)
| c = __MROTLI (a, b)
| MROTLI a,#b,c
|
uw1 __MROTRI (uw1, const)
| c = __MROTRI (a, b)
| MROTRI a,#b,c
|
sw1 __MSATHS (sw1, sw1)
| c = __MSATHS (a, b)
| MSATHS a,b,c
|
uw1 __MSATHU (uw1, uw1)
| c = __MSATHU (a, b)
| MSATHU a,b,c
|
uw1 __MSLLHI (uw1, const)
| c = __MSLLHI (a, b)
| MSLLHI a,#b,c
|
sw1 __MSRAHI (sw1, const)
| c = __MSRAHI (a, b)
| MSRAHI a,#b,c
|
uw1 __MSRLHI (uw1, const)
| c = __MSRLHI (a, b)
| MSRLHI a,#b,c
|
void __MSUBACCS (acc, acc)
| __MSUBACCS (b, a)
| MSUBACCS a,b
|
sw1 __MSUBHSS (sw1, sw1)
| c = __MSUBHSS (a, b)
| MSUBHSS a,b,c
|
uw1 __MSUBHUS (uw1, uw1)
| c = __MSUBHUS (a, b)
| MSUBHUS a,b,c
|
void __MTRAP (void)
| __MTRAP ()
| MTRAP
|
uw2 __MUNPACKH (uw1)
| b = __MUNPACKH (a)
| MUNPACKH a,b
|
uw1 __MWCUT (uw2, uw1)
| c = __MWCUT (a, b)
| MWCUT a,b,c
|
void __MWTACC (acc, uw1)
| __MWTACC (b, a)
| MWTACC a,b
|
void __MWTACCG (acc, uw1)
| __MWTACCG (b, a)
| MWTACCG a,b
|
uw1 __MXOR (uw1, uw1)
| c = __MXOR (a, b)
| MXOR a,b,c
|
This sections describes built-in functions related to read and write
instructions to access memory. These functions generate
membar instructions to flush the I/O load and stores where
appropriate, as described in Fujitsu's manual described above.
unsigned char __builtin_read8 (void *data)unsigned short __builtin_read16 (void *data)unsigned long __builtin_read32 (void *data)unsigned long long __builtin_read64 (void *data)
void __builtin_write8 (void *data, unsigned char datum)void __builtin_write16 (void *data, unsigned short datum)void __builtin_write32 (void *data, unsigned long datum)void __builtin_write64 (void *data, unsigned long long datum)This section describes built-in functions that are not named after a specific FR-V instruction.
sw2 __IACCreadll (iacc reg)sw1 __IACCreadl (iacc reg)void __IACCsetll (iacc reg, sw2 x)void __IACCsetl (iacc reg, sw1 x)void __data_prefetch0 (const void *x)dcpl instruction to load the contents of address x
into the data cache.
void __data_prefetch (const void *x)nldub instruction to load the contents of address x
into the data cache. The instruction is issued in slot I1.
These built-in functions are available for LoongArch.
Data Type Description:
imm0_31, a compile-time constant in range 0 to 31;
imm0_16383, a compile-time constant in range 0 to 16383;
imm0_32767, a compile-time constant in range 0 to 32767;
imm_n2048_2047, a compile-time constant in range -2048 to 2047;
The intrinsics provided are listed below:
unsigned int __builtin_loongarch_movfcsr2gr (imm0_31)
void __builtin_loongarch_movgr2fcsr (imm0_31, unsigned int)
void __builtin_loongarch_cacop_d (imm0_31, unsigned long int, imm_n2048_2047)
unsigned int __builtin_loongarch_cpucfg (unsigned int)
void __builtin_loongarch_asrtle_d (long int, long int)
void __builtin_loongarch_asrtgt_d (long int, long int)
long int __builtin_loongarch_lddir_d (long int, imm0_31)
void __builtin_loongarch_ldpte_d (long int, imm0_31)
int __builtin_loongarch_crc_w_b_w (char, int)
int __builtin_loongarch_crc_w_h_w (short, int)
int __builtin_loongarch_crc_w_w_w (int, int)
int __builtin_loongarch_crc_w_d_w (long int, int)
int __builtin_loongarch_crcc_w_b_w (char, int)
int __builtin_loongarch_crcc_w_h_w (short, int)
int __builtin_loongarch_crcc_w_w_w (int, int)
int __builtin_loongarch_crcc_w_d_w (long int, int)
unsigned int __builtin_loongarch_csrrd_w (imm0_16383)
unsigned int __builtin_loongarch_csrwr_w (unsigned int, imm0_16383)
unsigned int __builtin_loongarch_csrxchg_w (unsigned int, unsigned int, imm0_16383)
unsigned long int __builtin_loongarch_csrrd_d (imm0_16383)
unsigned long int __builtin_loongarch_csrwr_d (unsigned long int, imm0_16383)
unsigned long int __builtin_loongarch_csrxchg_d (unsigned long int, unsigned long int, imm0_16383)
unsigned char __builtin_loongarch_iocsrrd_b (unsigned int)
unsigned short __builtin_loongarch_iocsrrd_h (unsigned int)
unsigned int __builtin_loongarch_iocsrrd_w (unsigned int)
unsigned long int __builtin_loongarch_iocsrrd_d (unsigned int)
void __builtin_loongarch_iocsrwr_b (unsigned char, unsigned int)
void __builtin_loongarch_iocsrwr_h (unsigned short, unsigned int)
void __builtin_loongarch_iocsrwr_w (unsigned int, unsigned int)
void __builtin_loongarch_iocsrwr_d (unsigned long int, unsigned int)
void __builtin_loongarch_dbar (imm0_32767)
void __builtin_loongarch_ibar (imm0_32767)
void __builtin_loongarch_syscall (imm0_32767)
void __builtin_loongarch_break (imm0_32767)
Note:Since the control register is divided into 32-bit and 64-bit, but the access instruction is not distinguished. So GCC renames the control instructions when implementing intrinsics.
Take the csrrd instruction as an example, built-in functions are implemented as follows:
__builtin_loongarch_csrrd_w // When reading the 32-bit control register use.
__builtin_loongarch_csrrd_d // When reading the 64-bit control register use.
For the convenience of use, the built-in functions are encapsulated,
the encapsulated functions and __drdtime_t, __rdtime_t are
defined in the larchintrin.h. So if you call the following
function you need to include larchintrin.h.
typedef struct drdtime{
unsigned long dvalue;
unsigned long dtimeid;
} __drdtime_t;
typedef struct rdtime{
unsigned int value;
unsigned int timeid;
} __rdtime_t;
__drdtime_t __rdtime_d (void)
__rdtime_t __rdtimel_w (void)
__rdtime_t __rdtimeh_w (void)
unsigned int __movfcsr2gr (imm0_31)
void __movgr2fcsr (imm0_31, unsigned int)
void __cacop_d (imm0_31, unsigned long, imm_n2048_2047)
unsigned int __cpucfg (unsigned int)
void __asrtle_d (long int, long int)
void __asrtgt_d (long int, long int)
long int __lddir_d (long int, imm0_31)
void __ldpte_d (long int, imm0_31)
int __crc_w_b_w (char, int)
int __crc_w_h_w (short, int)
int __crc_w_w_w (int, int)
int __crc_w_d_w (long int, int)
int __crcc_w_b_w (char, int)
int __crcc_w_h_w (short, int)
int __crcc_w_w_w (int, int)
int __crcc_w_d_w (long int, int)
unsigned int __csrrd_w (imm0_16383)
unsigned int __csrwr_w (unsigned int, imm0_16383)
unsigned int __csrxchg_w (unsigned int, unsigned int, imm0_16383)
unsigned long __csrrd_d (imm0_16383)
unsigned long __csrwr_d (unsigned long, imm0_16383)
unsigned long __csrxchg_d (unsigned long, unsigned long, imm0_16383)
unsigned char __iocsrrd_b (unsigned int)
unsigned short __iocsrrd_h (unsigned int)
unsigned int __iocsrrd_w (unsigned int)
unsigned long __iocsrrd_d (unsigned int)
void __iocsrwr_b (unsigned char, unsigned int)
void __iocsrwr_h (unsigned short, unsigned int)
void __iocsrwr_w (unsigned int, unsigned int)
void __iocsrwr_d (unsigned long, unsigned int)
void __dbar (imm0_32767)
void __ibar (imm0_32767)
void __syscall (imm0_32767)
void __break (imm0_32767)
Returns the value that is currently set in the ‘tp’ register.
void * __builtin_thread_pointer (void)
The MIPS DSP Application-Specific Extension (ASE) includes new instructions that are designed to improve the performance of DSP and media applications. It provides instructions that operate on packed 8-bit/16-bit integer data, Q7, Q15 and Q31 fractional data.
GCC supports MIPS DSP operations using both the generic vector extensions (see Vector Extensions) and a collection of MIPS-specific built-in functions. Both kinds of support are enabled by the -mdsp command-line option.
Revision 2 of the ASE was introduced in the second half of 2006. This revision adds extra instructions to the original ASE, but is otherwise backwards-compatible with it. You can select revision 2 using the command-line option -mdspr2; this option implies -mdsp.
The SCOUNT and POS bits of the DSP control register are global. The WRDSP, EXTPDP, EXTPDPV and MTHLIP instructions modify the SCOUNT and POS bits. During optimization, the compiler does not delete these instructions and it does not delete calls to functions containing these instructions.
At present, GCC only provides support for operations on 32-bit
vectors. The vector type associated with 8-bit integer data is
usually called v4i8, the vector type associated with Q7
is usually called v4q7, the vector type associated with 16-bit
integer data is usually called v2i16, and the vector type
associated with Q15 is usually called v2q15. They can be
defined in C as follows:
typedef signed char v4i8 __attribute__ ((vector_size(4)));
typedef signed char v4q7 __attribute__ ((vector_size(4)));
typedef short v2i16 __attribute__ ((vector_size(4)));
typedef short v2q15 __attribute__ ((vector_size(4)));
v4i8, v4q7, v2i16 and v2q15 values are
initialized in the same way as aggregates. For example:
v4i8 a = {1, 2, 3, 4};
v4i8 b;
b = (v4i8) {5, 6, 7, 8};
v2q15 c = {0x0fcb, 0x3a75};
v2q15 d;
d = (v2q15) {0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15};
Note: The CPU's endianness determines the order in which values
are packed. On little-endian targets, the first value is the least
significant and the last value is the most significant. The opposite
order applies to big-endian targets. For example, the code above
sets the lowest byte of a to 1 on little-endian targets
and 4 on big-endian targets.
Note: Q7, Q15 and Q31 values must be initialized with their integer
representation. As shown in this example, the integer representation
of a Q7 value can be obtained by multiplying the fractional value by
0x1.0p7. The equivalent for Q15 values is to multiply by
0x1.0p15. The equivalent for Q31 values is to multiply by
0x1.0p31.
The table below lists the v4i8 and v2q15 operations for which
hardware support exists. a and b are v4i8 values,
and c and d are v2q15 values.
| C code | MIPS instruction
|
|---|---|
a + b | addu.qb
|
c + d | addq.ph
|
a - b | subu.qb
|
c - d | subq.ph
|
The table below lists the v2i16 operation for which
hardware support exists for the DSP ASE REV 2. e and f are
v2i16 values.
| C code | MIPS instruction
|
|---|---|
e * f | mul.ph
|
It is easier to describe the DSP built-in functions if we first define the following types:
typedef int q31;
typedef int i32;
typedef unsigned int ui32;
typedef long long a64;
q31 and i32 are actually the same as int, but we
use q31 to indicate a Q31 fractional value and i32 to
indicate a 32-bit integer value. Similarly, a64 is the same as
long long, but we use a64 to indicate values that are
placed in one of the four DSP accumulators ($ac0,
$ac1, $ac2 or $ac3).
Also, some built-in functions prefer or require immediate numbers as parameters, because the corresponding DSP instructions accept both immediate numbers and register operands, or accept immediate numbers only. The immediate parameters are listed as follows.
imm0_3: 0 to 3.
imm0_7: 0 to 7.
imm0_15: 0 to 15.
imm0_31: 0 to 31.
imm0_63: 0 to 63.
imm0_255: 0 to 255.
imm_n32_31: -32 to 31.
imm_n512_511: -512 to 511.
The following built-in functions map directly to a particular MIPS DSP instruction. Please refer to the architecture specification for details on what each instruction does.
v2q15 __builtin_mips_addq_ph (v2q15, v2q15);
v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15);
q31 __builtin_mips_addq_s_w (q31, q31);
v4i8 __builtin_mips_addu_qb (v4i8, v4i8);
v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8);
v2q15 __builtin_mips_subq_ph (v2q15, v2q15);
v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15);
q31 __builtin_mips_subq_s_w (q31, q31);
v4i8 __builtin_mips_subu_qb (v4i8, v4i8);
v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8);
i32 __builtin_mips_addsc (i32, i32);
i32 __builtin_mips_addwc (i32, i32);
i32 __builtin_mips_modsub (i32, i32);
i32 __builtin_mips_raddu_w_qb (v4i8);
v2q15 __builtin_mips_absq_s_ph (v2q15);
q31 __builtin_mips_absq_s_w (q31);
v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15);
v2q15 __builtin_mips_precrq_ph_w (q31, q31);
v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31);
v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15);
q31 __builtin_mips_preceq_w_phl (v2q15);
q31 __builtin_mips_preceq_w_phr (v2q15);
v2q15 __builtin_mips_precequ_ph_qbl (v4i8);
v2q15 __builtin_mips_precequ_ph_qbr (v4i8);
v2q15 __builtin_mips_precequ_ph_qbla (v4i8);
v2q15 __builtin_mips_precequ_ph_qbra (v4i8);
v2q15 __builtin_mips_preceu_ph_qbl (v4i8);
v2q15 __builtin_mips_preceu_ph_qbr (v4i8);
v2q15 __builtin_mips_preceu_ph_qbla (v4i8);
v2q15 __builtin_mips_preceu_ph_qbra (v4i8);
v4i8 __builtin_mips_shll_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shll_qb (v4i8, i32);
v2q15 __builtin_mips_shll_ph (v2q15, imm0_15);
v2q15 __builtin_mips_shll_ph (v2q15, i32);
v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15);
v2q15 __builtin_mips_shll_s_ph (v2q15, i32);
q31 __builtin_mips_shll_s_w (q31, imm0_31);
q31 __builtin_mips_shll_s_w (q31, i32);
v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shrl_qb (v4i8, i32);
v2q15 __builtin_mips_shra_ph (v2q15, imm0_15);
v2q15 __builtin_mips_shra_ph (v2q15, i32);
v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15);
v2q15 __builtin_mips_shra_r_ph (v2q15, i32);
q31 __builtin_mips_shra_r_w (q31, imm0_31);
q31 __builtin_mips_shra_r_w (q31, i32);
v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15);
v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15);
v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15);
q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15);
q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15);
a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8);
a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8);
a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8);
a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8);
a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31);
a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31);
a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15);
a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15);
a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15);
a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15);
i32 __builtin_mips_bitrev (i32);
i32 __builtin_mips_insv (i32, i32);
v4i8 __builtin_mips_repl_qb (imm0_255);
v4i8 __builtin_mips_repl_qb (i32);
v2q15 __builtin_mips_repl_ph (imm_n512_511);
v2q15 __builtin_mips_repl_ph (i32);
void __builtin_mips_cmpu_eq_qb (v4i8, v4i8);
void __builtin_mips_cmpu_lt_qb (v4i8, v4i8);
void __builtin_mips_cmpu_le_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8);
void __builtin_mips_cmp_eq_ph (v2q15, v2q15);
void __builtin_mips_cmp_lt_ph (v2q15, v2q15);
void __builtin_mips_cmp_le_ph (v2q15, v2q15);
v4i8 __builtin_mips_pick_qb (v4i8, v4i8);
v2q15 __builtin_mips_pick_ph (v2q15, v2q15);
v2q15 __builtin_mips_packrl_ph (v2q15, v2q15);
i32 __builtin_mips_extr_w (a64, imm0_31);
i32 __builtin_mips_extr_w (a64, i32);
i32 __builtin_mips_extr_r_w (a64, imm0_31);
i32 __builtin_mips_extr_s_h (a64, i32);
i32 __builtin_mips_extr_rs_w (a64, imm0_31);
i32 __builtin_mips_extr_rs_w (a64, i32);
i32 __builtin_mips_extr_s_h (a64, imm0_31);
i32 __builtin_mips_extr_r_w (a64, i32);
i32 __builtin_mips_extp (a64, imm0_31);
i32 __builtin_mips_extp (a64, i32);
i32 __builtin_mips_extpdp (a64, imm0_31);
i32 __builtin_mips_extpdp (a64, i32);
a64 __builtin_mips_shilo (a64, imm_n32_31);
a64 __builtin_mips_shilo (a64, i32);
a64 __builtin_mips_mthlip (a64, i32);
void __builtin_mips_wrdsp (i32, imm0_63);
i32 __builtin_mips_rddsp (imm0_63);
i32 __builtin_mips_lbux (void *, i32);
i32 __builtin_mips_lhx (void *, i32);
i32 __builtin_mips_lwx (void *, i32);
a64 __builtin_mips_ldx (void *, i32); /* MIPS64 only */
i32 __builtin_mips_bposge32 (void);
a64 __builtin_mips_madd (a64, i32, i32);
a64 __builtin_mips_maddu (a64, ui32, ui32);
a64 __builtin_mips_msub (a64, i32, i32);
a64 __builtin_mips_msubu (a64, ui32, ui32);
a64 __builtin_mips_mult (i32, i32);
a64 __builtin_mips_multu (ui32, ui32);
The following built-in functions map directly to a particular MIPS DSP REV 2 instruction. Please refer to the architecture specification for details on what each instruction does.
v4q7 __builtin_mips_absq_s_qb (v4q7);
v2i16 __builtin_mips_addu_ph (v2i16, v2i16);
v2i16 __builtin_mips_addu_s_ph (v2i16, v2i16);
v4i8 __builtin_mips_adduh_qb (v4i8, v4i8);
v4i8 __builtin_mips_adduh_r_qb (v4i8, v4i8);
i32 __builtin_mips_append (i32, i32, imm0_31);
i32 __builtin_mips_balign (i32, i32, imm0_3);
i32 __builtin_mips_cmpgdu_eq_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgdu_lt_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgdu_le_qb (v4i8, v4i8);
a64 __builtin_mips_dpa_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dps_w_ph (a64, v2i16, v2i16);
v2i16 __builtin_mips_mul_ph (v2i16, v2i16);
v2i16 __builtin_mips_mul_s_ph (v2i16, v2i16);
q31 __builtin_mips_mulq_rs_w (q31, q31);
v2q15 __builtin_mips_mulq_s_ph (v2q15, v2q15);
q31 __builtin_mips_mulq_s_w (q31, q31);
a64 __builtin_mips_mulsa_w_ph (a64, v2i16, v2i16);
v4i8 __builtin_mips_precr_qb_ph (v2i16, v2i16);
v2i16 __builtin_mips_precr_sra_ph_w (i32, i32, imm0_31);
v2i16 __builtin_mips_precr_sra_r_ph_w (i32, i32, imm0_31);
i32 __builtin_mips_prepend (i32, i32, imm0_31);
v4i8 __builtin_mips_shra_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shra_r_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shra_qb (v4i8, i32);
v4i8 __builtin_mips_shra_r_qb (v4i8, i32);
v2i16 __builtin_mips_shrl_ph (v2i16, imm0_15);
v2i16 __builtin_mips_shrl_ph (v2i16, i32);
v2i16 __builtin_mips_subu_ph (v2i16, v2i16);
v2i16 __builtin_mips_subu_s_ph (v2i16, v2i16);
v4i8 __builtin_mips_subuh_qb (v4i8, v4i8);
v4i8 __builtin_mips_subuh_r_qb (v4i8, v4i8);
v2q15 __builtin_mips_addqh_ph (v2q15, v2q15);
v2q15 __builtin_mips_addqh_r_ph (v2q15, v2q15);
q31 __builtin_mips_addqh_w (q31, q31);
q31 __builtin_mips_addqh_r_w (q31, q31);
v2q15 __builtin_mips_subqh_ph (v2q15, v2q15);
v2q15 __builtin_mips_subqh_r_ph (v2q15, v2q15);
q31 __builtin_mips_subqh_w (q31, q31);
q31 __builtin_mips_subqh_r_w (q31, q31);
a64 __builtin_mips_dpax_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dpsx_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dpaqx_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpaqx_sa_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpsqx_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpsqx_sa_w_ph (a64, v2q15, v2q15);
The MIPS64 architecture includes a number of instructions that operate on pairs of single-precision floating-point values. Each pair is packed into a 64-bit floating-point register, with one element being designated the “upper half” and the other being designated the “lower half”.
GCC supports paired-single operations using both the generic vector extensions (see Vector Extensions) and a collection of MIPS-specific built-in functions. Both kinds of support are enabled by the -mpaired-single command-line option.
The vector type associated with paired-single values is usually
called v2sf. It can be defined in C as follows:
typedef float v2sf __attribute__ ((vector_size (8)));
v2sf values are initialized in the same way as aggregates.
For example:
v2sf a = {1.5, 9.1};
v2sf b;
float e, f;
b = (v2sf) {e, f};
Note: The CPU's endianness determines which value is stored in
the upper half of a register and which value is stored in the lower half.
On little-endian targets, the first value is the lower one and the second
value is the upper one. The opposite order applies to big-endian targets.
For example, the code above sets the lower half of a to
1.5 on little-endian targets and 9.1 on big-endian targets.
GCC provides intrinsics to access the SIMD instructions provided by the
ST Microelectronics Loongson-2E and -2F processors. These intrinsics,
available after inclusion of the loongson.h header file,
operate on the following 64-bit vector types:
uint8x8_t, a vector of eight unsigned 8-bit integers;
uint16x4_t, a vector of four unsigned 16-bit integers;
uint32x2_t, a vector of two unsigned 32-bit integers;
int8x8_t, a vector of eight signed 8-bit integers;
int16x4_t, a vector of four signed 16-bit integers;
int32x2_t, a vector of two signed 32-bit integers.
The intrinsics provided are listed below; each is named after the machine instruction to which it corresponds, with suffixes added as appropriate to distinguish intrinsics that expand to the same machine instruction yet have different argument types. Refer to the architecture documentation for a description of the functionality of each instruction.
int16x4_t packsswh (int32x2_t s, int32x2_t t);
int8x8_t packsshb (int16x4_t s, int16x4_t t);
uint8x8_t packushb (uint16x4_t s, uint16x4_t t);
uint32x2_t paddw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t paddh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t paddb_u (uint8x8_t s, uint8x8_t t);
int32x2_t paddw_s (int32x2_t s, int32x2_t t);
int16x4_t paddh_s (int16x4_t s, int16x4_t t);
int8x8_t paddb_s (int8x8_t s, int8x8_t t);
uint64_t paddd_u (uint64_t s, uint64_t t);
int64_t paddd_s (int64_t s, int64_t t);
int16x4_t paddsh (int16x4_t s, int16x4_t t);
int8x8_t paddsb (int8x8_t s, int8x8_t t);
uint16x4_t paddush (uint16x4_t s, uint16x4_t t);
uint8x8_t paddusb (uint8x8_t s, uint8x8_t t);
uint64_t pandn_ud (uint64_t s, uint64_t t);
uint32x2_t pandn_uw (uint32x2_t s, uint32x2_t t);
uint16x4_t pandn_uh (uint16x4_t s, uint16x4_t t);
uint8x8_t pandn_ub (uint8x8_t s, uint8x8_t t);
int64_t pandn_sd (int64_t s, int64_t t);
int32x2_t pandn_sw (int32x2_t s, int32x2_t t);
int16x4_t pandn_sh (int16x4_t s, int16x4_t t);
int8x8_t pandn_sb (int8x8_t s, int8x8_t t);
uint16x4_t pavgh (uint16x4_t s, uint16x4_t t);
uint8x8_t pavgb (uint8x8_t s, uint8x8_t t);
uint32x2_t pcmpeqw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t pcmpeqh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t pcmpeqb_u (uint8x8_t s, uint8x8_t t);
int32x2_t pcmpeqw_s (int32x2_t s, int32x2_t t);
int16x4_t pcmpeqh_s (int16x4_t s, int16x4_t t);
int8x8_t pcmpeqb_s (int8x8_t s, int8x8_t t);
uint32x2_t pcmpgtw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t pcmpgth_u (uint16x4_t s, uint16x4_t t);
uint8x8_t pcmpgtb_u (uint8x8_t s, uint8x8_t t);
int32x2_t pcmpgtw_s (int32x2_t s, int32x2_t t);
int16x4_t pcmpgth_s (int16x4_t s, int16x4_t t);
int8x8_t pcmpgtb_s (int8x8_t s, int8x8_t t);
uint16x4_t pextrh_u (uint16x4_t s, int field);
int16x4_t pextrh_s (int16x4_t s, int field);
uint16x4_t pinsrh_0_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_1_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_2_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_3_u (uint16x4_t s, uint16x4_t t);
int16x4_t pinsrh_0_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_1_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_2_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_3_s (int16x4_t s, int16x4_t t);
int32x2_t pmaddhw (int16x4_t s, int16x4_t t);
int16x4_t pmaxsh (int16x4_t s, int16x4_t t);
uint8x8_t pmaxub (uint8x8_t s, uint8x8_t t);
int16x4_t pminsh (int16x4_t s, int16x4_t t);
uint8x8_t pminub (uint8x8_t s, uint8x8_t t);
uint8x8_t pmovmskb_u (uint8x8_t s);
int8x8_t pmovmskb_s (int8x8_t s);
uint16x4_t pmulhuh (uint16x4_t s, uint16x4_t t);
int16x4_t pmulhh (int16x4_t s, int16x4_t t);
int16x4_t pmullh (int16x4_t s, int16x4_t t);
int64_t pmuluw (uint32x2_t s, uint32x2_t t);
uint8x8_t pasubub (uint8x8_t s, uint8x8_t t);
uint16x4_t biadd (uint8x8_t s);
uint16x4_t psadbh (uint8x8_t s, uint8x8_t t);
uint16x4_t pshufh_u (uint16x4_t dest, uint16x4_t s, uint8_t order);
int16x4_t pshufh_s (int16x4_t dest, int16x4_t s, uint8_t order);
uint16x4_t psllh_u (uint16x4_t s, uint8_t amount);
int16x4_t psllh_s (int16x4_t s, uint8_t amount);
uint32x2_t psllw_u (uint32x2_t s, uint8_t amount);
int32x2_t psllw_s (int32x2_t s, uint8_t amount);
uint16x4_t psrlh_u (uint16x4_t s, uint8_t amount);
int16x4_t psrlh_s (int16x4_t s, uint8_t amount);
uint32x2_t psrlw_u (uint32x2_t s, uint8_t amount);
int32x2_t psrlw_s (int32x2_t s, uint8_t amount);
uint16x4_t psrah_u (uint16x4_t s, uint8_t amount);
int16x4_t psrah_s (int16x4_t s, uint8_t amount);
uint32x2_t psraw_u (uint32x2_t s, uint8_t amount);
int32x2_t psraw_s (int32x2_t s, uint8_t amount);
uint32x2_t psubw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t psubh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t psubb_u (uint8x8_t s, uint8x8_t t);
int32x2_t psubw_s (int32x2_t s, int32x2_t t);
int16x4_t psubh_s (int16x4_t s, int16x4_t t);
int8x8_t psubb_s (int8x8_t s, int8x8_t t);
uint64_t psubd_u (uint64_t s, uint64_t t);
int64_t psubd_s (int64_t s, int64_t t);
int16x4_t psubsh (int16x4_t s, int16x4_t t);
int8x8_t psubsb (int8x8_t s, int8x8_t t);
uint16x4_t psubush (uint16x4_t s, uint16x4_t t);
uint8x8_t psubusb (uint8x8_t s, uint8x8_t t);
uint32x2_t punpckhwd_u (uint32x2_t s, uint32x2_t t);
uint16x4_t punpckhhw_u (uint16x4_t s, uint16x4_t t);
uint8x8_t punpckhbh_u (uint8x8_t s, uint8x8_t t);
int32x2_t punpckhwd_s (int32x2_t s, int32x2_t t);
int16x4_t punpckhhw_s (int16x4_t s, int16x4_t t);
int8x8_t punpckhbh_s (int8x8_t s, int8x8_t t);
uint32x2_t punpcklwd_u (uint32x2_t s, uint32x2_t t);
uint16x4_t punpcklhw_u (uint16x4_t s, uint16x4_t t);
uint8x8_t punpcklbh_u (uint8x8_t s, uint8x8_t t);
int32x2_t punpcklwd_s (int32x2_t s, int32x2_t t);
int16x4_t punpcklhw_s (int16x4_t s, int16x4_t t);
int8x8_t punpcklbh_s (int8x8_t s, int8x8_t t);
The table below lists the v2sf operations for which hardware
support exists. a, b and c are v2sf
values and x is an integral value.
| C code | MIPS instruction
|
|---|---|
a + b | add.ps
|
a - b | sub.ps
|
-a | neg.ps
|
a * b | mul.ps
|
a * b + c | madd.ps
|
a * b - c | msub.ps
|
-(a * b + c) | nmadd.ps
|
-(a * b - c) | nmsub.ps
|
x ? a : b | movn.ps/movz.ps
|
Note that the multiply-accumulate instructions can be disabled
using the command-line option -mno-fused-madd.
The following paired-single functions map directly to a particular MIPS instruction. Please refer to the architecture specification for details on what each instruction does.
v2sf __builtin_mips_pll_ps (v2sf, v2sf)pll.ps).
v2sf __builtin_mips_pul_ps (v2sf, v2sf)pul.ps).
v2sf __builtin_mips_plu_ps (v2sf, v2sf)plu.ps).
v2sf __builtin_mips_puu_ps (v2sf, v2sf)puu.ps).
v2sf __builtin_mips_cvt_ps_s (float, float)cvt.ps.s).
float __builtin_mips_cvt_s_pl (v2sf)cvt.s.pl).
float __builtin_mips_cvt_s_pu (v2sf)cvt.s.pu).
v2sf __builtin_mips_abs_ps (v2sf)abs.ps).
v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int)alnv.ps).
Note: The value of the third parameter must be 0 or 4 modulo 8, otherwise the result is unpredictable. Please read the instruction description for details.
The following multi-instruction functions are also available.
In each case, cond can be any of the 16 floating-point conditions:
f, un, eq, ueq, olt, ult,
ole, ule, sf, ngle, seq, ngl,
lt, nge, le or ngt.
v2sf __builtin_mips_movt_c_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)v2sf __builtin_mips_movf_c_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)c.cond.ps,
movt.ps/movf.ps).
The movt functions return the value x computed by:
c.cond.ps cc,a,b
mov.ps x,c
movt.ps x,d,cc
The movf functions are similar but use movf.ps instead
of movt.ps.
int __builtin_mips_upper_c_cond_ps (v2sf a, v2sf b)int __builtin_mips_lower_c_cond_ps (v2sf a, v2sf b)c.cond.ps,
bc1t/bc1f).
These functions compare a and b using c.cond.ps
and return either the upper or lower half of the result. For example:
v2sf a, b;
if (__builtin_mips_upper_c_eq_ps (a, b))
upper_halves_are_equal ();
else
upper_halves_are_unequal ();
if (__builtin_mips_lower_c_eq_ps (a, b))
lower_halves_are_equal ();
else
lower_halves_are_unequal ();
The MIPS-3D Application-Specific Extension (ASE) includes additional paired-single instructions that are designed to improve the performance of 3D graphics operations. Support for these instructions is controlled by the -mips3d command-line option.
The functions listed below map directly to a particular MIPS-3D instruction. Please refer to the architecture specification for more details on what each instruction does.
v2sf __builtin_mips_addr_ps (v2sf, v2sf)addr.ps).
v2sf __builtin_mips_mulr_ps (v2sf, v2sf)mulr.ps).
v2sf __builtin_mips_cvt_pw_ps (v2sf)cvt.pw.ps).
v2sf __builtin_mips_cvt_ps_pw (v2sf)cvt.ps.pw).
float __builtin_mips_recip1_s (float)double __builtin_mips_recip1_d (double)v2sf __builtin_mips_recip1_ps (v2sf)recip1.fmt).
float __builtin_mips_recip2_s (float, float)double __builtin_mips_recip2_d (double, double)v2sf __builtin_mips_recip2_ps (v2sf, v2sf)recip2.fmt).
float __builtin_mips_rsqrt1_s (float)double __builtin_mips_rsqrt1_d (double)v2sf __builtin_mips_rsqrt1_ps (v2sf)rsqrt1.fmt).
float __builtin_mips_rsqrt2_s (float, float)double __builtin_mips_rsqrt2_d (double, double)v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf)rsqrt2.fmt).
The following multi-instruction functions are also available.
In each case, cond can be any of the 16 floating-point conditions:
f, un, eq, ueq, olt, ult,
ole, ule, sf, ngle, seq,
ngl, lt, nge, le or ngt.
int __builtin_mips_cabs_cond_s (float a, float b)int __builtin_mips_cabs_cond_d (double a, double b)cabs.cond.fmt,
bc1t/bc1f).
These functions compare a and b using cabs.cond.s
or cabs.cond.d and return the result as a boolean value.
For example:
float a, b;
if (__builtin_mips_cabs_eq_s (a, b))
true ();
else
false ();
int __builtin_mips_upper_cabs_cond_ps (v2sf a, v2sf b)int __builtin_mips_lower_cabs_cond_ps (v2sf a, v2sf b)cabs.cond.ps,
bc1t/bc1f).
These functions compare a and b using cabs.cond.ps
and return either the upper or lower half of the result. For example:
v2sf a, b;
if (__builtin_mips_upper_cabs_eq_ps (a, b))
upper_halves_are_equal ();
else
upper_halves_are_unequal ();
if (__builtin_mips_lower_cabs_eq_ps (a, b))
lower_halves_are_equal ();
else
lower_halves_are_unequal ();
v2sf __builtin_mips_movt_cabs_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)v2sf __builtin_mips_movf_cabs_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)cabs.cond.ps,
movt.ps/movf.ps).
The movt functions return the value x computed by:
cabs.cond.ps cc,a,b
mov.ps x,c
movt.ps x,d,cc
The movf functions are similar but use movf.ps instead
of movt.ps.
int __builtin_mips_any_c_cond_ps (v2sf a, v2sf b)int __builtin_mips_all_c_cond_ps (v2sf a, v2sf b)int __builtin_mips_any_cabs_cond_ps (v2sf a, v2sf b)int __builtin_mips_all_cabs_cond_ps (v2sf a, v2sf b)c.cond.ps/cabs.cond.ps,
bc1any2t/bc1any2f).
These functions compare a and b using c.cond.ps
or cabs.cond.ps. The any forms return true if either
result is true and the all forms return true if both results are true.
For example:
v2sf a, b;
if (__builtin_mips_any_c_eq_ps (a, b))
one_is_true ();
else
both_are_false ();
if (__builtin_mips_all_c_eq_ps (a, b))
both_are_true ();
else
one_is_false ();
int __builtin_mips_any_c_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)int __builtin_mips_all_c_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)int __builtin_mips_any_cabs_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)int __builtin_mips_all_cabs_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)c.cond.ps/cabs.cond.ps,
bc1any4t/bc1any4f).
These functions use c.cond.ps or cabs.cond.ps
to compare a with b and to compare c with d.
The any forms return true if any of the four results are true
and the all forms return true if all four results are true.
For example:
v2sf a, b, c, d;
if (__builtin_mips_any_c_eq_4s (a, b, c, d))
some_are_true ();
else
all_are_false ();
if (__builtin_mips_all_c_eq_4s (a, b, c, d))
all_are_true ();
else
some_are_false ();
GCC provides intrinsics to access the SIMD instructions provided by the
MSA MIPS SIMD Architecture. The interface is made available by including
<msa.h> and using -mmsa -mhard-float -mfp64 -mnan=2008.
For each __builtin_msa_*, there is a shortened name of the intrinsic,
__msa_*.
MSA implements 128-bit wide vector registers, operating on 8-, 16-, 32- and
64-bit integer, 16- and 32-bit fixed-point, or 32- and 64-bit floating point
data elements. The following vectors typedefs are included in msa.h:
v16i8, a vector of sixteen signed 8-bit integers;
v16u8, a vector of sixteen unsigned 8-bit integers;
v8i16, a vector of eight signed 16-bit integers;
v8u16, a vector of eight unsigned 16-bit integers;
v4i32, a vector of four signed 32-bit integers;
v4u32, a vector of four unsigned 32-bit integers;
v2i64, a vector of two signed 64-bit integers;
v2u64, a vector of two unsigned 64-bit integers;
v4f32, a vector of four 32-bit floats;
v2f64, a vector of two 64-bit doubles.
Instructions and corresponding built-ins may have additional restrictions and/or input/output values manipulated:
imm0_1, an integer literal in range 0 to 1;
imm0_3, an integer literal in range 0 to 3;
imm0_7, an integer literal in range 0 to 7;
imm0_15, an integer literal in range 0 to 15;
imm0_31, an integer literal in range 0 to 31;
imm0_63, an integer literal in range 0 to 63;
imm0_255, an integer literal in range 0 to 255;
imm_n16_15, an integer literal in range -16 to 15;
imm_n512_511, an integer literal in range -512 to 511;
imm_n1024_1022, an integer literal in range -512 to 511 left
shifted by 1 bit, i.e., -1024, -1022, ..., 1020, 1022;
imm_n2048_2044, an integer literal in range -512 to 511 left
shifted by 2 bits, i.e., -2048, -2044, ..., 2040, 2044;
imm_n4096_4088, an integer literal in range -512 to 511 left
shifted by 3 bits, i.e., -4096, -4088, ..., 4080, 4088;
imm1_4, an integer literal in range 1 to 4;
i32, i64, u32, u64, f32, f64, defined as follows:
{
typedef int i32;
#if __LONG_MAX__ == __LONG_LONG_MAX__
typedef long i64;
#else
typedef long long i64;
#endif
typedef unsigned int u32;
#if __LONG_MAX__ == __LONG_LONG_MAX__
typedef unsigned long u64;
#else
typedef unsigned long long u64;
#endif
typedef double f64;
typedef float f32;
}
The intrinsics provided are listed below; each is named after the machine instruction.
v16i8 __builtin_msa_add_a_b (v16i8, v16i8);
v8i16 __builtin_msa_add_a_h (v8i16, v8i16);
v4i32 __builtin_msa_add_a_w (v4i32, v4i32);
v2i64 __builtin_msa_add_a_d (v2i64, v2i64);
v16i8 __builtin_msa_adds_a_b (v16i8, v16i8);
v8i16 __builtin_msa_adds_a_h (v8i16, v8i16);
v4i32 __builtin_msa_adds_a_w (v4i32, v4i32);
v2i64 __builtin_msa_adds_a_d (v2i64, v2i64);
v16i8 __builtin_msa_adds_s_b (v16i8, v16i8);
v8i16 __builtin_msa_adds_s_h (v8i16, v8i16);
v4i32 __builtin_msa_adds_s_w (v4i32, v4i32);
v2i64 __builtin_msa_adds_s_d (v2i64, v2i64);
v16u8 __builtin_msa_adds_u_b (v16u8, v16u8);
v8u16 __builtin_msa_adds_u_h (v8u16, v8u16);
v4u32 __builtin_msa_adds_u_w (v4u32, v4u32);
v2u64 __builtin_msa_adds_u_d (v2u64, v2u64);
v16i8 __builtin_msa_addv_b (v16i8, v16i8);
v8i16 __builtin_msa_addv_h (v8i16, v8i16);
v4i32 __builtin_msa_addv_w (v4i32, v4i32);
v2i64 __builtin_msa_addv_d (v2i64, v2i64);
v16i8 __builtin_msa_addvi_b (v16i8, imm0_31);
v8i16 __builtin_msa_addvi_h (v8i16, imm0_31);
v4i32 __builtin_msa_addvi_w (v4i32, imm0_31);
v2i64 __builtin_msa_addvi_d (v2i64, imm0_31);
v16u8 __builtin_msa_and_v (v16u8, v16u8);
v16u8 __builtin_msa_andi_b (v16u8, imm0_255);
v16i8 __builtin_msa_asub_s_b (v16i8, v16i8);
v8i16 __builtin_msa_asub_s_h (v8i16, v8i16);
v4i32 __builtin_msa_asub_s_w (v4i32, v4i32);
v2i64 __builtin_msa_asub_s_d (v2i64, v2i64);
v16u8 __builtin_msa_asub_u_b (v16u8, v16u8);
v8u16 __builtin_msa_asub_u_h (v8u16, v8u16);
v4u32 __builtin_msa_asub_u_w (v4u32, v4u32);
v2u64 __builtin_msa_asub_u_d (v2u64, v2u64);
v16i8 __builtin_msa_ave_s_b (v16i8, v16i8);
v8i16 __builtin_msa_ave_s_h (v8i16, v8i16);
v4i32 __builtin_msa_ave_s_w (v4i32, v4i32);
v2i64 __builtin_msa_ave_s_d (v2i64, v2i64);
v16u8 __builtin_msa_ave_u_b (v16u8, v16u8);
v8u16 __builtin_msa_ave_u_h (v8u16, v8u16);
v4u32 __builtin_msa_ave_u_w (v4u32, v4u32);
v2u64 __builtin_msa_ave_u_d (v2u64, v2u64);
v16i8 __builtin_msa_aver_s_b (v16i8, v16i8);
v8i16 __builtin_msa_aver_s_h (v8i16, v8i16);
v4i32 __builtin_msa_aver_s_w (v4i32, v4i32);
v2i64 __builtin_msa_aver_s_d (v2i64, v2i64);
v16u8 __builtin_msa_aver_u_b (v16u8, v16u8);
v8u16 __builtin_msa_aver_u_h (v8u16, v8u16);
v4u32 __builtin_msa_aver_u_w (v4u32, v4u32);
v2u64 __builtin_msa_aver_u_d (v2u64, v2u64);
v16u8 __builtin_msa_bclr_b (v16u8, v16u8);
v8u16 __builtin_msa_bclr_h (v8u16, v8u16);
v4u32 __builtin_msa_bclr_w (v4u32, v4u32);
v2u64 __builtin_msa_bclr_d (v2u64, v2u64);
v16u8 __builtin_msa_bclri_b (v16u8, imm0_7);
v8u16 __builtin_msa_bclri_h (v8u16, imm0_15);
v4u32 __builtin_msa_bclri_w (v4u32, imm0_31);
v2u64 __builtin_msa_bclri_d (v2u64, imm0_63);
v16u8 __builtin_msa_binsl_b (v16u8, v16u8, v16u8);
v8u16 __builtin_msa_binsl_h (v8u16, v8u16, v8u16);
v4u32 __builtin_msa_binsl_w (v4u32, v4u32, v4u32);
v2u64 __builtin_msa_binsl_d (v2u64, v2u64, v2u64);
v16u8 __builtin_msa_binsli_b (v16u8, v16u8, imm0_7);
v8u16 __builtin_msa_binsli_h (v8u16, v8u16, imm0_15);
v4u32 __builtin_msa_binsli_w (v4u32, v4u32, imm0_31);
v2u64 __builtin_msa_binsli_d (v2u64, v2u64, imm0_63);
v16u8 __builtin_msa_binsr_b (v16u8, v16u8, v16u8);
v8u16 __builtin_msa_binsr_h (v8u16, v8u16, v8u16);
v4u32 __builtin_msa_binsr_w (v4u32, v4u32, v4u32);
v2u64 __builtin_msa_binsr_d (v2u64, v2u64, v2u64);
v16u8 __builtin_msa_binsri_b (v16u8, v16u8, imm0_7);
v8u16 __builtin_msa_binsri_h (v8u16, v8u16, imm0_15);
v4u32 __builtin_msa_binsri_w (v4u32, v4u32, imm0_31);
v2u64 __builtin_msa_binsri_d (v2u64, v2u64, imm0_63);
v16u8 __builtin_msa_bmnz_v (v16u8, v16u8, v16u8);
v16u8 __builtin_msa_bmnzi_b (v16u8, v16u8, imm0_255);
v16u8 __builtin_msa_bmz_v (v16u8, v16u8, v16u8);
v16u8 __builtin_msa_bmzi_b (v16u8, v16u8, imm0_255);
v16u8 __builtin_msa_bneg_b (v16u8, v16u8);
v8u16 __builtin_msa_bneg_h (v8u16, v8u16);
v4u32 __builtin_msa_bneg_w (v4u32, v4u32);
v2u64 __builtin_msa_bneg_d (v2u64, v2u64);
v16u8 __builtin_msa_bnegi_b (v16u8, imm0_7);
v8u16 __builtin_msa_bnegi_h (v8u16, imm0_15);
v4u32 __builtin_msa_bnegi_w (v4u32, imm0_31);
v2u64 __builtin_msa_bnegi_d (v2u64, imm0_63);
i32 __builtin_msa_bnz_b (v16u8);
i32 __builtin_msa_bnz_h (v8u16);
i32 __builtin_msa_bnz_w (v4u32);
i32 __builtin_msa_bnz_d (v2u64);
i32 __builtin_msa_bnz_v (v16u8);
v16u8 __builtin_msa_bsel_v (v16u8, v16u8, v16u8);
v16u8 __builtin_msa_bseli_b (v16u8, v16u8, imm0_255);
v16u8 __builtin_msa_bset_b (v16u8, v16u8);
v8u16 __builtin_msa_bset_h (v8u16, v8u16);
v4u32 __builtin_msa_bset_w (v4u32, v4u32);
v2u64 __builtin_msa_bset_d (v2u64, v2u64);
v16u8 __builtin_msa_bseti_b (v16u8, imm0_7);
v8u16 __builtin_msa_bseti_h (v8u16, imm0_15);
v4u32 __builtin_msa_bseti_w (v4u32, imm0_31);
v2u64 __builtin_msa_bseti_d (v2u64, imm0_63);
i32 __builtin_msa_bz_b (v16u8);
i32 __builtin_msa_bz_h (v8u16);
i32 __builtin_msa_bz_w (v4u32);
i32 __builtin_msa_bz_d (v2u64);
i32 __builtin_msa_bz_v (v16u8);
v16i8 __builtin_msa_ceq_b (v16i8, v16i8);
v8i16 __builtin_msa_ceq_h (v8i16, v8i16);
v4i32 __builtin_msa_ceq_w (v4i32, v4i32);
v2i64 __builtin_msa_ceq_d (v2i64, v2i64);
v16i8 __builtin_msa_ceqi_b (v16i8, imm_n16_15);
v8i16 __builtin_msa_ceqi_h (v8i16, imm_n16_15);
v4i32 __builtin_msa_ceqi_w (v4i32, imm_n16_15);
v2i64 __builtin_msa_ceqi_d (v2i64, imm_n16_15);
i32 __builtin_msa_cfcmsa (imm0_31);
v16i8 __builtin_msa_cle_s_b (v16i8, v16i8);
v8i16 __builtin_msa_cle_s_h (v8i16, v8i16);
v4i32 __builtin_msa_cle_s_w (v4i32, v4i32);
v2i64 __builtin_msa_cle_s_d (v2i64, v2i64);
v16i8 __builtin_msa_cle_u_b (v16u8, v16u8);
v8i16 __builtin_msa_cle_u_h (v8u16, v8u16);
v4i32 __builtin_msa_cle_u_w (v4u32, v4u32);
v2i64 __builtin_msa_cle_u_d (v2u64, v2u64);
v16i8 __builtin_msa_clei_s_b (v16i8, imm_n16_15);
v8i16 __builtin_msa_clei_s_h (v8i16, imm_n16_15);
v4i32 __builtin_msa_clei_s_w (v4i32, imm_n16_15);
v2i64 __builtin_msa_clei_s_d (v2i64, imm_n16_15);
v16i8 __builtin_msa_clei_u_b (v16u8, imm0_31);
v8i16 __builtin_msa_clei_u_h (v8u16, imm0_31);
v4i32 __builtin_msa_clei_u_w (v4u32, imm0_31);
v2i64 __builtin_msa_clei_u_d (v2u64, imm0_31);
v16i8 __builtin_msa_clt_s_b (v16i8, v16i8);
v8i16 __builtin_msa_clt_s_h (v8i16, v8i16);
v4i32 __builtin_msa_clt_s_w (v4i32, v4i32);
v2i64 __builtin_msa_clt_s_d (v2i64, v2i64);
v16i8 __builtin_msa_clt_u_b (v16u8, v16u8);
v8i16 __builtin_msa_clt_u_h (v8u16, v8u16);
v4i32 __builtin_msa_clt_u_w (v4u32, v4u32);
v2i64 __builtin_msa_clt_u_d (v2u64, v2u64);
v16i8 __builtin_msa_clti_s_b (v16i8, imm_n16_15);
v8i16 __builtin_msa_clti_s_h (v8i16, imm_n16_15);
v4i32 __builtin_msa_clti_s_w (v4i32, imm_n16_15);
v2i64 __builtin_msa_clti_s_d (v2i64, imm_n16_15);
v16i8 __builtin_msa_clti_u_b (v16u8, imm0_31);
v8i16 __builtin_msa_clti_u_h (v8u16, imm0_31);
v4i32 __builtin_msa_clti_u_w (v4u32, imm0_31);
v2i64 __builtin_msa_clti_u_d (v2u64, imm0_31);
i32 __builtin_msa_copy_s_b (v16i8, imm0_15);
i32 __builtin_msa_copy_s_h (v8i16, imm0_7);
i32 __builtin_msa_copy_s_w (v4i32, imm0_3);
i64 __builtin_msa_copy_s_d (v2i64, imm0_1);
u32 __builtin_msa_copy_u_b (v16i8, imm0_15);
u32 __builtin_msa_copy_u_h (v8i16, imm0_7);
u32 __builtin_msa_copy_u_w (v4i32, imm0_3);
u64 __builtin_msa_copy_u_d (v2i64, imm0_1);
void __builtin_msa_ctcmsa (imm0_31, i32);
v16i8 __builtin_msa_div_s_b (v16i8, v16i8);
v8i16 __builtin_msa_div_s_h (v8i16, v8i16);
v4i32 __builtin_msa_div_s_w (v4i32, v4i32);
v2i64 __builtin_msa_div_s_d (v2i64, v2i64);
v16u8 __builtin_msa_div_u_b (v16u8, v16u8);
v8u16 __builtin_msa_div_u_h (v8u16, v8u16);
v4u32 __builtin_msa_div_u_w (v4u32, v4u32);
v2u64 __builtin_msa_div_u_d (v2u64, v2u64);
v8i16 __builtin_msa_dotp_s_h (v16i8, v16i8);
v4i32 __builtin_msa_dotp_s_w (v8i16, v8i16);
v2i64 __builtin_msa_dotp_s_d (v4i32, v4i32);
v8u16 __builtin_msa_dotp_u_h (v16u8, v16u8);
v4u32 __builtin_msa_dotp_u_w (v8u16, v8u16);
v2u64 __builtin_msa_dotp_u_d (v4u32, v4u32);
v8i16 __builtin_msa_dpadd_s_h (v8i16, v16i8, v16i8);
v4i32 __builtin_msa_dpadd_s_w (v4i32, v8i16, v8i16);
v2i64 __builtin_msa_dpadd_s_d (v2i64, v4i32, v4i32);
v8u16 __builtin_msa_dpadd_u_h (v8u16, v16u8, v16u8);
v4u32 __builtin_msa_dpadd_u_w (v4u32, v8u16, v8u16);
v2u64 __builtin_msa_dpadd_u_d (v2u64, v4u32, v4u32);
v8i16 __builtin_msa_dpsub_s_h (v8i16, v16i8, v16i8);
v4i32 __builtin_msa_dpsub_s_w (v4i32, v8i16, v8i16);
v2i64 __builtin_msa_dpsub_s_d (v2i64, v4i32, v4i32);
v8i16 __builtin_msa_dpsub_u_h (v8i16, v16u8, v16u8);
v4i32 __builtin_msa_dpsub_u_w (v4i32, v8u16, v8u16);
v2i64 __builtin_msa_dpsub_u_d (v2i64, v4u32, v4u32);
v4f32 __builtin_msa_fadd_w (v4f32, v4f32);
v2f64 __builtin_msa_fadd_d (v2f64, v2f64);
v4i32 __builtin_msa_fcaf_w (v4f32, v4f32);
v2i64 __builtin_msa_fcaf_d (v2f64, v2f64);
v4i32 __builtin_msa_fceq_w (v4f32, v4f32);
v2i64 __builtin_msa_fceq_d (v2f64, v2f64);
v4i32 __builtin_msa_fclass_w (v4f32);
v2i64 __builtin_msa_fclass_d (v2f64);
v4i32 __builtin_msa_fcle_w (v4f32, v4f32);
v2i64 __builtin_msa_fcle_d (v2f64, v2f64);
v4i32 __builtin_msa_fclt_w (v4f32, v4f32);
v2i64 __builtin_msa_fclt_d (v2f64, v2f64);
v4i32 __builtin_msa_fcne_w (v4f32, v4f32);
v2i64 __builtin_msa_fcne_d (v2f64, v2f64);
v4i32 __builtin_msa_fcor_w (v4f32, v4f32);
v2i64 __builtin_msa_fcor_d (v2f64, v2f64);
v4i32 __builtin_msa_fcueq_w (v4f32, v4f32);
v2i64 __builtin_msa_fcueq_d (v2f64, v2f64);
v4i32 __builtin_msa_fcule_w (v4f32, v4f32);
v2i64 __builtin_msa_fcule_d (v2f64, v2f64);
v4i32 __builtin_msa_fcult_w (v4f32, v4f32);
v2i64 __builtin_msa_fcult_d (v2f64, v2f64);
v4i32 __builtin_msa_fcun_w (v4f32, v4f32);
v2i64 __builtin_msa_fcun_d (v2f64, v2f64);
v4i32 __builtin_msa_fcune_w (v4f32, v4f32);
v2i64 __builtin_msa_fcune_d (v2f64, v2f64);
v4f32 __builtin_msa_fdiv_w (v4f32, v4f32);
v2f64 __builtin_msa_fdiv_d (v2f64, v2f64);
v8i16 __builtin_msa_fexdo_h (v4f32, v4f32);
v4f32 __builtin_msa_fexdo_w (v2f64, v2f64);
v4f32 __builtin_msa_fexp2_w (v4f32, v4i32);
v2f64 __builtin_msa_fexp2_d (v2f64, v2i64);
v4f32 __builtin_msa_fexupl_w (v8i16);
v2f64 __builtin_msa_fexupl_d (v4f32);
v4f32 __builtin_msa_fexupr_w (v8i16);
v2f64 __builtin_msa_fexupr_d (v4f32);
v4f32 __builtin_msa_ffint_s_w (v4i32);
v2f64 __builtin_msa_ffint_s_d (v2i64);
v4f32 __builtin_msa_ffint_u_w (v4u32);
v2f64 __builtin_msa_ffint_u_d (v2u64);
v4f32 __builtin_msa_ffql_w (v8i16);
v2f64 __builtin_msa_ffql_d (v4i32);
v4f32 __builtin_msa_ffqr_w (v8i16);
v2f64 __builtin_msa_ffqr_d (v4i32);
v16i8 __builtin_msa_fill_b (i32);
v8i16 __builtin_msa_fill_h (i32);
v4i32 __builtin_msa_fill_w (i32);
v2i64 __builtin_msa_fill_d (i64);
v4f32 __builtin_msa_flog2_w (v4f32);
v2f64 __builtin_msa_flog2_d (v2f64);
v4f32 __builtin_msa_fmadd_w (v4f32, v4f32, v4f32);
v2f64 __builtin_msa_fmadd_d (v2f64, v2f64, v2f64);
v4f32 __builtin_msa_fmax_w (v4f32, v4f32);
v2f64 __builtin_msa_fmax_d (v2f64, v2f64);
v4f32 __builtin_msa_fmax_a_w (v4f32, v4f32);
v2f64 __builtin_msa_fmax_a_d (v2f64, v2f64);
v4f32 __builtin_msa_fmin_w (v4f32, v4f32);
v2f64 __builtin_msa_fmin_d (v2f64, v2f64);
v4f32 __builtin_msa_fmin_a_w (v4f32, v4f32);
v2f64 __builtin_msa_fmin_a_d (v2f64, v2f64);
v4f32 __builtin_msa_fmsub_w (v4f32, v4f32, v4f32);
v2f64 __builtin_msa_fmsub_d (v2f64, v2f64, v2f64);
v4f32 __builtin_msa_fmul_w (v4f32, v4f32);
v2f64 __builtin_msa_fmul_d (v2f64, v2f64);
v4f32 __builtin_msa_frint_w (v4f32);
v2f64 __builtin_msa_frint_d (v2f64);
v4f32 __builtin_msa_frcp_w (v4f32);
v2f64 __builtin_msa_frcp_d (v2f64);
v4f32 __builtin_msa_frsqrt_w (v4f32);
v2f64 __builtin_msa_frsqrt_d (v2f64);
v4i32 __builtin_msa_fsaf_w (v4f32, v4f32);
v2i64 __builtin_msa_fsaf_d (v2f64, v2f64);
v4i32 __builtin_msa_fseq_w (v4f32, v4f32);
v2i64 __builtin_msa_fseq_d (v2f64, v2f64);
v4i32 __builtin_msa_fsle_w (v4f32, v4f32);
v2i64 __builtin_msa_fsle_d (v2f64, v2f64);
v4i32 __builtin_msa_fslt_w (v4f32, v4f32);
v2i64 __builtin_msa_fslt_d (v2f64, v2f64);
v4i32 __builtin_msa_fsne_w (v4f32, v4f32);
v2i64 __builtin_msa_fsne_d (v2f64, v2f64);
v4i32 __builtin_msa_fsor_w (v4f32, v4f32);
v2i64 __builtin_msa_fsor_d (v2f64, v2f64);
v4f32 __builtin_msa_fsqrt_w (v4f32);
v2f64 __builtin_msa_fsqrt_d (v2f64);
v4f32 __builtin_msa_fsub_w (v4f32, v4f32);
v2f64 __builtin_msa_fsub_d (v2f64, v2f64);
v4i32 __builtin_msa_fsueq_w (v4f32, v4f32);
v2i64 __builtin_msa_fsueq_d (v2f64, v2f64);
v4i32 __builtin_msa_fsule_w (v4f32, v4f32);
v2i64 __builtin_msa_fsule_d (v2f64, v2f64);
v4i32 __builtin_msa_fsult_w (v4f32, v4f32);
v2i64 __builtin_msa_fsult_d (v2f64, v2f64);
v4i32 __builtin_msa_fsun_w (v4f32, v4f32);
v2i64 __builtin_msa_fsun_d (v2f64, v2f64);
v4i32 __builtin_msa_fsune_w (v4f32, v4f32);
v2i64 __builtin_msa_fsune_d (v2f64, v2f64);
v4i32 __builtin_msa_ftint_s_w (v4f32);
v2i64 __builtin_msa_ftint_s_d (v2f64);
v4u32 __builtin_msa_ftint_u_w (v4f32);
v2u64 __builtin_msa_ftint_u_d (v2f64);
v8i16 __builtin_msa_ftq_h (v4f32, v4f32);
v4i32 __builtin_msa_ftq_w (v2f64, v2f64);
v4i32 __builtin_msa_ftrunc_s_w (v4f32);
v2i64 __builtin_msa_ftrunc_s_d (v2f64);
v4u32 __builtin_msa_ftrunc_u_w (v4f32);
v2u64 __builtin_msa_ftrunc_u_d (v2f64);
v8i16 __builtin_msa_hadd_s_h (v16i8, v16i8);
v4i32 __builtin_msa_hadd_s_w (v8i16, v8i16);
v2i64 __builtin_msa_hadd_s_d (v4i32, v4i32);
v8u16 __builtin_msa_hadd_u_h (v16u8, v16u8);
v4u32 __builtin_msa_hadd_u_w (v8u16, v8u16);
v2u64 __builtin_msa_hadd_u_d (v4u32, v4u32);
v8i16 __builtin_msa_hsub_s_h (v16i8, v16i8);
v4i32 __builtin_msa_hsub_s_w (v8i16, v8i16);
v2i64 __builtin_msa_hsub_s_d (v4i32, v4i32);
v8i16 __builtin_msa_hsub_u_h (v16u8, v16u8);
v4i32 __builtin_msa_hsub_u_w (v8u16, v8u16);
v2i64 __builtin_msa_hsub_u_d (v4u32, v4u32);
v16i8 __builtin_msa_ilvev_b (v16i8, v16i8);
v8i16 __builtin_msa_ilvev_h (v8i16, v8i16);
v4i32 __builtin_msa_ilvev_w (v4i32, v4i32);
v2i64 __builtin_msa_ilvev_d (v2i64, v2i64);
v16i8 __builtin_msa_ilvl_b (v16i8, v16i8);
v8i16 __builtin_msa_ilvl_h (v8i16, v8i16);
v4i32 __builtin_msa_ilvl_w (v4i32, v4i32);
v2i64 __builtin_msa_ilvl_d (v2i64, v2i64);
v16i8 __builtin_msa_ilvod_b (v16i8, v16i8);
v8i16 __builtin_msa_ilvod_h (v8i16, v8i16);
v4i32 __builtin_msa_ilvod_w (v4i32, v4i32);
v2i64 __builtin_msa_ilvod_d (v2i64, v2i64);
v16i8 __builtin_msa_ilvr_b (v16i8, v16i8);
v8i16 __builtin_msa_ilvr_h (v8i16, v8i16);
v4i32 __builtin_msa_ilvr_w (v4i32, v4i32);
v2i64 __builtin_msa_ilvr_d (v2i64, v2i64);
v16i8 __builtin_msa_insert_b (v16i8, imm0_15, i32);
v8i16 __builtin_msa_insert_h (v8i16, imm0_7, i32);
v4i32 __builtin_msa_insert_w (v4i32, imm0_3, i32);
v2i64 __builtin_msa_insert_d (v2i64, imm0_1, i64);
v16i8 __builtin_msa_insve_b (v16i8, imm0_15, v16i8);
v8i16 __builtin_msa_insve_h (v8i16, imm0_7, v8i16);
v4i32 __builtin_msa_insve_w (v4i32, imm0_3, v4i32);
v2i64 __builtin_msa_insve_d (v2i64, imm0_1, v2i64);
v16i8 __builtin_msa_ld_b (const void *, imm_n512_511);
v8i16 __builtin_msa_ld_h (const void *, imm_n1024_1022);
v4i32 __builtin_msa_ld_w (const void *, imm_n2048_2044);
v2i64 __builtin_msa_ld_d (const void *, imm_n4096_4088);
v16i8 __builtin_msa_ldi_b (imm_n512_511);
v8i16 __builtin_msa_ldi_h (imm_n512_511);
v4i32 __builtin_msa_ldi_w (imm_n512_511);
v2i64 __builtin_msa_ldi_d (imm_n512_511);
v8i16 __builtin_msa_madd_q_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_madd_q_w (v4i32, v4i32, v4i32);
v8i16 __builtin_msa_maddr_q_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_maddr_q_w (v4i32, v4i32, v4i32);
v16i8 __builtin_msa_maddv_b (v16i8, v16i8, v16i8);
v8i16 __builtin_msa_maddv_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_maddv_w (v4i32, v4i32, v4i32);
v2i64 __builtin_msa_maddv_d (v2i64, v2i64, v2i64);
v16i8 __builtin_msa_max_a_b (v16i8, v16i8);
v8i16 __builtin_msa_max_a_h (v8i16, v8i16);
v4i32 __builtin_msa_max_a_w (v4i32, v4i32);
v2i64 __builtin_msa_max_a_d (v2i64, v2i64);
v16i8 __builtin_msa_max_s_b (v16i8, v16i8);
v8i16 __builtin_msa_max_s_h (v8i16, v8i16);
v4i32 __builtin_msa_max_s_w (v4i32, v4i32);
v2i64 __builtin_msa_max_s_d (v2i64, v2i64);
v16u8 __builtin_msa_max_u_b (v16u8, v16u8);
v8u16 __builtin_msa_max_u_h (v8u16, v8u16);
v4u32 __builtin_msa_max_u_w (v4u32, v4u32);
v2u64 __builtin_msa_max_u_d (v2u64, v2u64);
v16i8 __builtin_msa_maxi_s_b (v16i8, imm_n16_15);
v8i16 __builtin_msa_maxi_s_h (v8i16, imm_n16_15);
v4i32 __builtin_msa_maxi_s_w (v4i32, imm_n16_15);
v2i64 __builtin_msa_maxi_s_d (v2i64, imm_n16_15);
v16u8 __builtin_msa_maxi_u_b (v16u8, imm0_31);
v8u16 __builtin_msa_maxi_u_h (v8u16, imm0_31);
v4u32 __builtin_msa_maxi_u_w (v4u32, imm0_31);
v2u64 __builtin_msa_maxi_u_d (v2u64, imm0_31);
v16i8 __builtin_msa_min_a_b (v16i8, v16i8);
v8i16 __builtin_msa_min_a_h (v8i16, v8i16);
v4i32 __builtin_msa_min_a_w (v4i32, v4i32);
v2i64 __builtin_msa_min_a_d (v2i64, v2i64);
v16i8 __builtin_msa_min_s_b (v16i8, v16i8);
v8i16 __builtin_msa_min_s_h (v8i16, v8i16);
v4i32 __builtin_msa_min_s_w (v4i32, v4i32);
v2i64 __builtin_msa_min_s_d (v2i64, v2i64);
v16u8 __builtin_msa_min_u_b (v16u8, v16u8);
v8u16 __builtin_msa_min_u_h (v8u16, v8u16);
v4u32 __builtin_msa_min_u_w (v4u32, v4u32);
v2u64 __builtin_msa_min_u_d (v2u64, v2u64);
v16i8 __builtin_msa_mini_s_b (v16i8, imm_n16_15);
v8i16 __builtin_msa_mini_s_h (v8i16, imm_n16_15);
v4i32 __builtin_msa_mini_s_w (v4i32, imm_n16_15);
v2i64 __builtin_msa_mini_s_d (v2i64, imm_n16_15);
v16u8 __builtin_msa_mini_u_b (v16u8, imm0_31);
v8u16 __builtin_msa_mini_u_h (v8u16, imm0_31);
v4u32 __builtin_msa_mini_u_w (v4u32, imm0_31);
v2u64 __builtin_msa_mini_u_d (v2u64, imm0_31);
v16i8 __builtin_msa_mod_s_b (v16i8, v16i8);
v8i16 __builtin_msa_mod_s_h (v8i16, v8i16);
v4i32 __builtin_msa_mod_s_w (v4i32, v4i32);
v2i64 __builtin_msa_mod_s_d (v2i64, v2i64);
v16u8 __builtin_msa_mod_u_b (v16u8, v16u8);
v8u16 __builtin_msa_mod_u_h (v8u16, v8u16);
v4u32 __builtin_msa_mod_u_w (v4u32, v4u32);
v2u64 __builtin_msa_mod_u_d (v2u64, v2u64);
v16i8 __builtin_msa_move_v (v16i8);
v8i16 __builtin_msa_msub_q_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_msub_q_w (v4i32, v4i32, v4i32);
v8i16 __builtin_msa_msubr_q_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_msubr_q_w (v4i32, v4i32, v4i32);
v16i8 __builtin_msa_msubv_b (v16i8, v16i8, v16i8);
v8i16 __builtin_msa_msubv_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_msubv_w (v4i32, v4i32, v4i32);
v2i64 __builtin_msa_msubv_d (v2i64, v2i64, v2i64);
v8i16 __builtin_msa_mul_q_h (v8i16, v8i16);
v4i32 __builtin_msa_mul_q_w (v4i32, v4i32);
v8i16 __builtin_msa_mulr_q_h (v8i16, v8i16);
v4i32 __builtin_msa_mulr_q_w (v4i32, v4i32);
v16i8 __builtin_msa_mulv_b (v16i8, v16i8);
v8i16 __builtin_msa_mulv_h (v8i16, v8i16);
v4i32 __builtin_msa_mulv_w (v4i32, v4i32);
v2i64 __builtin_msa_mulv_d (v2i64, v2i64);
v16i8 __builtin_msa_nloc_b (v16i8);
v8i16 __builtin_msa_nloc_h (v8i16);
v4i32 __builtin_msa_nloc_w (v4i32);
v2i64 __builtin_msa_nloc_d (v2i64);
v16i8 __builtin_msa_nlzc_b (v16i8);
v8i16 __builtin_msa_nlzc_h (v8i16);
v4i32 __builtin_msa_nlzc_w (v4i32);
v2i64 __builtin_msa_nlzc_d (v2i64);
v16u8 __builtin_msa_nor_v (v16u8, v16u8);
v16u8 __builtin_msa_nori_b (v16u8, imm0_255);
v16u8 __builtin_msa_or_v (v16u8, v16u8);
v16u8 __builtin_msa_ori_b (v16u8, imm0_255);
v16i8 __builtin_msa_pckev_b (v16i8, v16i8);
v8i16 __builtin_msa_pckev_h (v8i16, v8i16);
v4i32 __builtin_msa_pckev_w (v4i32, v4i32);
v2i64 __builtin_msa_pckev_d (v2i64, v2i64);
v16i8 __builtin_msa_pckod_b (v16i8, v16i8);
v8i16 __builtin_msa_pckod_h (v8i16, v8i16);
v4i32 __builtin_msa_pckod_w (v4i32, v4i32);
v2i64 __builtin_msa_pckod_d (v2i64, v2i64);
v16i8 __builtin_msa_pcnt_b (v16i8);
v8i16 __builtin_msa_pcnt_h (v8i16);
v4i32 __builtin_msa_pcnt_w (v4i32);
v2i64 __builtin_msa_pcnt_d (v2i64);
v16i8 __builtin_msa_sat_s_b (v16i8, imm0_7);
v8i16 __builtin_msa_sat_s_h (v8i16, imm0_15);
v4i32 __builtin_msa_sat_s_w (v4i32, imm0_31);
v2i64 __builtin_msa_sat_s_d (v2i64, imm0_63);
v16u8 __builtin_msa_sat_u_b (v16u8, imm0_7);
v8u16 __builtin_msa_sat_u_h (v8u16, imm0_15);
v4u32 __builtin_msa_sat_u_w (v4u32, imm0_31);
v2u64 __builtin_msa_sat_u_d (v2u64, imm0_63);
v16i8 __builtin_msa_shf_b (v16i8, imm0_255);
v8i16 __builtin_msa_shf_h (v8i16, imm0_255);
v4i32 __builtin_msa_shf_w (v4i32, imm0_255);
v16i8 __builtin_msa_sld_b (v16i8, v16i8, i32);
v8i16 __builtin_msa_sld_h (v8i16, v8i16, i32);
v4i32 __builtin_msa_sld_w (v4i32, v4i32, i32);
v2i64 __builtin_msa_sld_d (v2i64, v2i64, i32);
v16i8 __builtin_msa_sldi_b (v16i8, v16i8, imm0_15);
v8i16 __builtin_msa_sldi_h (v8i16, v8i16, imm0_7);
v4i32 __builtin_msa_sldi_w (v4i32, v4i32, imm0_3);
v2i64 __builtin_msa_sldi_d (v2i64, v2i64, imm0_1);
v16i8 __builtin_msa_sll_b (v16i8, v16i8);
v8i16 __builtin_msa_sll_h (v8i16, v8i16);
v4i32 __builtin_msa_sll_w (v4i32, v4i32);
v2i64 __builtin_msa_sll_d (v2i64, v2i64);
v16i8 __builtin_msa_slli_b (v16i8, imm0_7);
v8i16 __builtin_msa_slli_h (v8i16, imm0_15);
v4i32 __builtin_msa_slli_w (v4i32, imm0_31);
v2i64 __builtin_msa_slli_d (v2i64, imm0_63);
v16i8 __builtin_msa_splat_b (v16i8, i32);
v8i16 __builtin_msa_splat_h (v8i16, i32);
v4i32 __builtin_msa_splat_w (v4i32, i32);
v2i64 __builtin_msa_splat_d (v2i64, i32);
v16i8 __builtin_msa_splati_b (v16i8, imm0_15);
v8i16 __builtin_msa_splati_h (v8i16, imm0_7);
v4i32 __builtin_msa_splati_w (v4i32, imm0_3);
v2i64 __builtin_msa_splati_d (v2i64, imm0_1);
v16i8 __builtin_msa_sra_b (v16i8, v16i8);
v8i16 __builtin_msa_sra_h (v8i16, v8i16);
v4i32 __builtin_msa_sra_w (v4i32, v4i32);
v2i64 __builtin_msa_sra_d (v2i64, v2i64);
v16i8 __builtin_msa_srai_b (v16i8, imm0_7);
v8i16 __builtin_msa_srai_h (v8i16, imm0_15);
v4i32 __builtin_msa_srai_w (v4i32, imm0_31);
v2i64 __builtin_msa_srai_d (v2i64, imm0_63);
v16i8 __builtin_msa_srar_b (v16i8, v16i8);
v8i16 __builtin_msa_srar_h (v8i16, v8i16);
v4i32 __builtin_msa_srar_w (v4i32, v4i32);
v2i64 __builtin_msa_srar_d (v2i64, v2i64);
v16i8 __builtin_msa_srari_b (v16i8, imm0_7);
v8i16 __builtin_msa_srari_h (v8i16, imm0_15);
v4i32 __builtin_msa_srari_w (v4i32, imm0_31);
v2i64 __builtin_msa_srari_d (v2i64, imm0_63);
v16i8 __builtin_msa_srl_b (v16i8, v16i8);
v8i16 __builtin_msa_srl_h (v8i16, v8i16);
v4i32 __builtin_msa_srl_w (v4i32, v4i32);
v2i64 __builtin_msa_srl_d (v2i64, v2i64);
v16i8 __builtin_msa_srli_b (v16i8, imm0_7);
v8i16 __builtin_msa_srli_h (v8i16, imm0_15);
v4i32 __builtin_msa_srli_w (v4i32, imm0_31);
v2i64 __builtin_msa_srli_d (v2i64, imm0_63);
v16i8 __builtin_msa_srlr_b (v16i8, v16i8);
v8i16 __builtin_msa_srlr_h (v8i16, v8i16);
v4i32 __builtin_msa_srlr_w (v4i32, v4i32);
v2i64 __builtin_msa_srlr_d (v2i64, v2i64);
v16i8 __builtin_msa_srlri_b (v16i8, imm0_7);
v8i16 __builtin_msa_srlri_h (v8i16, imm0_15);
v4i32 __builtin_msa_srlri_w (v4i32, imm0_31);
v2i64 __builtin_msa_srlri_d (v2i64, imm0_63);
void __builtin_msa_st_b (v16i8, void *, imm_n512_511);
void __builtin_msa_st_h (v8i16, void *, imm_n1024_1022);
void __builtin_msa_st_w (v4i32, void *, imm_n2048_2044);
void __builtin_msa_st_d (v2i64, void *, imm_n4096_4088);
v16i8 __builtin_msa_subs_s_b (v16i8, v16i8);
v8i16 __builtin_msa_subs_s_h (v8i16, v8i16);
v4i32 __builtin_msa_subs_s_w (v4i32, v4i32);
v2i64 __builtin_msa_subs_s_d (v2i64, v2i64);
v16u8 __builtin_msa_subs_u_b (v16u8, v16u8);
v8u16 __builtin_msa_subs_u_h (v8u16, v8u16);
v4u32 __builtin_msa_subs_u_w (v4u32, v4u32);
v2u64 __builtin_msa_subs_u_d (v2u64, v2u64);
v16u8 __builtin_msa_subsus_u_b (v16u8, v16i8);
v8u16 __builtin_msa_subsus_u_h (v8u16, v8i16);
v4u32 __builtin_msa_subsus_u_w (v4u32, v4i32);
v2u64 __builtin_msa_subsus_u_d (v2u64, v2i64);
v16i8 __builtin_msa_subsuu_s_b (v16u8, v16u8);
v8i16 __builtin_msa_subsuu_s_h (v8u16, v8u16);
v4i32 __builtin_msa_subsuu_s_w (v4u32, v4u32);
v2i64 __builtin_msa_subsuu_s_d (v2u64, v2u64);
v16i8 __builtin_msa_subv_b (v16i8, v16i8);
v8i16 __builtin_msa_subv_h (v8i16, v8i16);
v4i32 __builtin_msa_subv_w (v4i32, v4i32);
v2i64 __builtin_msa_subv_d (v2i64, v2i64);
v16i8 __builtin_msa_subvi_b (v16i8, imm0_31);
v8i16 __builtin_msa_subvi_h (v8i16, imm0_31);
v4i32 __builtin_msa_subvi_w (v4i32, imm0_31);
v2i64 __builtin_msa_subvi_d (v2i64, imm0_31);
v16i8 __builtin_msa_vshf_b (v16i8, v16i8, v16i8);
v8i16 __builtin_msa_vshf_h (v8i16, v8i16, v8i16);
v4i32 __builtin_msa_vshf_w (v4i32, v4i32, v4i32);
v2i64 __builtin_msa_vshf_d (v2i64, v2i64, v2i64);
v16u8 __builtin_msa_xor_v (v16u8, v16u8);
v16u8 __builtin_msa_xori_b (v16u8, imm0_255);
GCC provides other MIPS-specific built-in functions:
void __builtin_mips_cache (int op, const volatile void *addr)___GCC_HAVE_BUILTIN_MIPS_CACHE
when this function is available.
unsigned int __builtin_mips_get_fcsr (void)void __builtin_mips_set_fcsr (unsigned int value)__builtin_mips_set_fcsr can be used to change any bit of the
register except the condition codes, which GCC assumes are preserved.
GCC provides a couple of special builtin functions to aid in the writing of interrupt handlers in C.
__bic_SR_register_on_exit (int mask)__bis_SR_register_on_exit (int mask)__delay_cycles (long long cycles)These built-in functions are available for the NDS32 target:
Insert an ISYNC instruction into the instruction stream where addr is an instruction address for serialization.
Insert an ISB instruction into the instruction stream.
Return the content of a system register which is mapped by sr.
Return the content of a user space register which is mapped by usr.
Move the value to a system register which is mapped by sr.
Move the value to a user space register which is mapped by usr.
This section describes PowerPC built-in functions that do not require the inclusion of any special header files to declare prototypes or provide macro definitions. The sections that follow describe additional PowerPC built-in functions.
This function is a
nopon the PowerPC platform and is included solely to maintain API compatibility with the x86 builtins.
This function returns a value of
1if the run-time CPU is of type cpuname and returns0otherwiseThe
__builtin_cpu_isfunction requires GLIBC 2.23 or newer which exports the hardware capability bits. GCC defines the macro__BUILTIN_CPU_SUPPORTS__if the__builtin_cpu_supportsbuilt-in function is fully supported.If GCC was configured to use a GLIBC before 2.23, the built-in function
__builtin_cpu_isalways returns a 0 and the compiler issues a warning.The following CPU names can be detected:
- ‘power10’
- IBM POWER10 Server CPU.
- ‘power9’
- IBM POWER9 Server CPU.
- ‘power8’
- IBM POWER8 Server CPU.
- ‘power7’
- IBM POWER7 Server CPU.
- ‘power6x’
- IBM POWER6 Server CPU (RAW mode).
- ‘power6’
- IBM POWER6 Server CPU (Architected mode).
- ‘power5+’
- IBM POWER5+ Server CPU.
- ‘power5’
- IBM POWER5 Server CPU.
- ‘ppc970’
- IBM 970 Server CPU (ie, Apple G5).
- ‘power4’
- IBM POWER4 Server CPU.
- ‘ppca2’
- IBM A2 64-bit Embedded CPU
- ‘ppc476’
- IBM PowerPC 476FP 32-bit Embedded CPU.
- ‘ppc464’
- IBM PowerPC 464 32-bit Embedded CPU.
- ‘ppc440’
- PowerPC 440 32-bit Embedded CPU.
- ‘ppc405’
- PowerPC 405 32-bit Embedded CPU.
- ‘ppc-cell-be’
- IBM PowerPC Cell Broadband Engine Architecture CPU.
Here is an example:
#ifdef __BUILTIN_CPU_SUPPORTS__ if (__builtin_cpu_is ("power8")) { do_power8 (); // POWER8 specific implementation. } else #endif { do_generic (); // Generic implementation. }
This function returns a value of
1if the run-time CPU supports the HWCAP feature feature and returns0otherwise.The
__builtin_cpu_supportsfunction requires GLIBC 2.23 or newer which exports the hardware capability bits. GCC defines the macro__BUILTIN_CPU_SUPPORTS__if the__builtin_cpu_supportsbuilt-in function is fully supported.If GCC was configured to use a GLIBC before 2.23, the built-in function
__builtin_cpu_supportsalways returns a 0 and the compiler issues a warning.The following features can be detected:
- ‘4xxmac’
- 4xx CPU has a Multiply Accumulator.
- ‘altivec’
- CPU has a SIMD/Vector Unit.
- ‘arch_2_05’
- CPU supports ISA 2.05 (eg, POWER6)
- ‘arch_2_06’
- CPU supports ISA 2.06 (eg, POWER7)
- ‘arch_2_07’
- CPU supports ISA 2.07 (eg, POWER8)
- ‘arch_3_00’
- CPU supports ISA 3.0 (eg, POWER9)
- ‘arch_3_1’
- CPU supports ISA 3.1 (eg, POWER10)
- ‘archpmu’
- CPU supports the set of compatible performance monitoring events.
- ‘booke’
- CPU supports the Embedded ISA category.
- ‘cellbe’
- CPU has a CELL broadband engine.
- ‘darn’
- CPU supports the
darn(deliver a random number) instruction.- ‘dfp’
- CPU has a decimal floating point unit.
- ‘dscr’
- CPU supports the data stream control register.
- ‘ebb’
- CPU supports event base branching.
- ‘efpdouble’
- CPU has a SPE double precision floating point unit.
- ‘efpsingle’
- CPU has a SPE single precision floating point unit.
- ‘fpu’
- CPU has a floating point unit.
- ‘htm’
- CPU has hardware transaction memory instructions.
- ‘htm-nosc’
- Kernel aborts hardware transactions when a syscall is made.
- ‘htm-no-suspend’
- CPU supports hardware transaction memory but does not support the
tsuspend.instruction.- ‘ic_snoop’
- CPU supports icache snooping capabilities.
- ‘ieee128’
- CPU supports 128-bit IEEE binary floating point instructions.
- ‘isel’
- CPU supports the integer select instruction.
- ‘mma’
- CPU supports the matrix-multiply assist instructions.
- ‘mmu’
- CPU has a memory management unit.
- ‘notb’
- CPU does not have a timebase (eg, 601 and 403gx).
- ‘pa6t’
- CPU supports the PA Semi 6T CORE ISA.
- ‘power4’
- CPU supports ISA 2.00 (eg, POWER4)
- ‘power5’
- CPU supports ISA 2.02 (eg, POWER5)
- ‘power5+’
- CPU supports ISA 2.03 (eg, POWER5+)
- ‘power6x’
- CPU supports ISA 2.05 (eg, POWER6) extended opcodes mffgpr and mftgpr.
- ‘ppc32’
- CPU supports 32-bit mode execution.
- ‘ppc601’
- CPU supports the old POWER ISA (eg, 601)
- ‘ppc64’
- CPU supports 64-bit mode execution.
- ‘ppcle’
- CPU supports a little-endian mode that uses address swizzling.
- ‘scv’
- Kernel supports system call vectored.
- ‘smt’
- CPU support simultaneous multi-threading.
- ‘spe’
- CPU has a signal processing extension unit.
- ‘tar’
- CPU supports the target address register.
- ‘true_le’
- CPU supports true little-endian mode.
- ‘ucache’
- CPU has unified I/D cache.
- ‘vcrypto’
- CPU supports the vector cryptography instructions.
- ‘vsx’
- CPU supports the vector-scalar extension.
Here is an example:
#ifdef __BUILTIN_CPU_SUPPORTS__ if (__builtin_cpu_supports ("fpu")) { asm("fadd %0,%1,%2" : "=d"(dst) : "d"(src1), "d"(src2)); } else #endif { dst = __fadd (src1, src2); // Software FP addition function. }
The following built-in functions are also available on all PowerPC processors:
uint64_t __builtin_ppc_get_timebase ();
unsigned long __builtin_ppc_mftb ();
double __builtin_unpack_ibm128 (__ibm128, int);
__ibm128 __builtin_pack_ibm128 (double, double);
double __builtin_mffs (void);
void __builtin_mtfsf (const int, double);
void __builtin_mtfsb0 (const int);
void __builtin_mtfsb1 (const int);
void __builtin_set_fpscr_rn (int);
The __builtin_ppc_get_timebase and __builtin_ppc_mftb
functions generate instructions to read the Time Base Register. The
__builtin_ppc_get_timebase function may generate multiple
instructions and always returns the 64 bits of the Time Base Register.
The __builtin_ppc_mftb function always generates one instruction and
returns the Time Base Register value as an unsigned long, throwing away
the most significant word on 32-bit environments. The __builtin_mffs
return the value of the FPSCR register. Note, ISA 3.0 supports the
__builtin_mffsl() which permits software to read the control and
non-sticky status bits in the FSPCR without the higher latency associated with
accessing the sticky status bits. The __builtin_mtfsf takes a constant
8-bit integer field mask and a double precision floating point argument
and generates the mtfsf (extended mnemonic) instruction to write new
values to selected fields of the FPSCR. The
__builtin_mtfsb0 and __builtin_mtfsb1 take the bit to change
as an argument. The valid bit range is between 0 and 31. The builtins map to
the mtfsb0 and mtfsb1 instructions which take the argument and
add 32. Hence these instructions only modify the FPSCR[32:63] bits by
changing the specified bit to a zero or one respectively. The
__builtin_set_fpscr_rn builtin allows changing both of the floating
point rounding mode bits. The argument is a 2-bit value. The argument can
either be a const int or stored in a variable. The builtin uses
the ISA 3.0
instruction mffscrn if available, otherwise it reads the FPSCR, masks
the current rounding mode bits out and OR's in the new value.
The basic built-in functions described in this section are available on the PowerPC family of processors starting with ISA 2.05 or later. Unless specific options are explicitly disabled on the command line, specifying option -mcpu=power6 has the effect of enabling the -mpowerpc64, -mpowerpc-gpopt, -mpowerpc-gfxopt, -mmfcrf, -mpopcntb, -mfprnd, -mcmpb, -mhard-dfp, and -mrecip-precision options. Specify the -maltivec option explicitly in combination with the above options if desired.
The following functions require option -mcmpb.
unsigned long long __builtin_cmpb (unsigned long long int, unsigned long long int);
unsigned int __builtin_cmpb (unsigned int, unsigned int);
The __builtin_cmpb function
performs a byte-wise compare on the contents of its two arguments,
returning the result of the byte-wise comparison as the returned
value. For each byte comparison, the corresponding byte of the return
value holds 0xff if the input bytes are equal and 0 if the input bytes
are not equal. If either of the arguments to this built-in function
is wider than 32 bits, the function call expands into the form that
expects unsigned long long int arguments
which is only available on 64-bit targets.
The following built-in functions are available when hardware decimal floating point (-mhard-dfp) is available:
void __builtin_set_fpscr_drn(int);
_Decimal64 __builtin_ddedpd (int, _Decimal64);
_Decimal128 __builtin_ddedpdq (int, _Decimal128);
_Decimal64 __builtin_denbcd (int, _Decimal64);
_Decimal128 __builtin_denbcdq (int, _Decimal128);
_Decimal64 __builtin_diex (long long, _Decimal64);
_Decimal128 _builtin_diexq (long long, _Decimal128);
_Decimal64 __builtin_dscli (_Decimal64, int);
_Decimal128 __builtin_dscliq (_Decimal128, int);
_Decimal64 __builtin_dscri (_Decimal64, int);
_Decimal128 __builtin_dscriq (_Decimal128, int);
long long __builtin_dxex (_Decimal64);
long long __builtin_dxexq (_Decimal128);
_Decimal128 __builtin_pack_dec128 (unsigned long long, unsigned long long);
unsigned long long __builtin_unpack_dec128 (_Decimal128, int);
The __builtin_set_fpscr_drn builtin allows changing the three decimal
floating point rounding mode bits. The argument is a 3-bit value. The
argument can either be a const int or the value can be stored in
a variable.
The builtin uses the ISA 3.0 instruction mffscdrn if available.
Otherwise the builtin reads the FPSCR, masks the current decimal rounding
mode bits out and OR's in the new value.
The following functions require -mhard-float, -mpowerpc-gfxopt, and -mpopcntb options.
double __builtin_recipdiv (double, double);
float __builtin_recipdivf (float, float);
double __builtin_rsqrt (double);
float __builtin_rsqrtf (float);
The vec_rsqrt, __builtin_rsqrt, and
__builtin_rsqrtf functions generate multiple instructions to
implement the reciprocal sqrt functionality using reciprocal sqrt
estimate instructions.
The __builtin_recipdiv, and __builtin_recipdivf
functions generate multiple instructions to implement division using
the reciprocal estimate instructions.
The following functions require -mhard-float and -mmultiple options.
The __builtin_unpack_longdouble function takes a
long double argument and a compile time constant of 0 or 1. If
the constant is 0, the first double within the
long double is returned, otherwise the second double
is returned. The __builtin_unpack_longdouble function is only
available if long double uses the IBM extended double
representation.
The __builtin_pack_longdouble function takes two double
arguments and returns a long double value that combines the two
arguments. The __builtin_pack_longdouble function is only
available if long double uses the IBM extended double
representation.
The __builtin_unpack_ibm128 function takes a __ibm128
argument and a compile time constant of 0 or 1. If the constant is 0,
the first double within the __ibm128 is returned,
otherwise the second double is returned.
The __builtin_pack_ibm128 function takes two double
arguments and returns a __ibm128 value that combines the two
arguments.
Additional built-in functions are available for the 64-bit PowerPC
family of processors, for efficient use of 128-bit floating point
(__float128) values.
The basic built-in functions described in this section are available on the PowerPC family of processors starting with ISA 2.05 or later. Unless specific options are explicitly disabled on the command line, specifying option -mcpu=power7 has the effect of enabling all the same options as for -mcpu=power6 in addition to the -maltivec, -mpopcntd, and -mvsx options.
The following basic built-in functions require -mpopcntd:
unsigned int __builtin_addg6s (unsigned int, unsigned int);
long long __builtin_bpermd (long long, long long);
unsigned int __builtin_cbcdtd (unsigned int);
unsigned int __builtin_cdtbcd (unsigned int);
long long __builtin_divde (long long, long long);
unsigned long long __builtin_divdeu (unsigned long long, unsigned long long);
int __builtin_divwe (int, int);
unsigned int __builtin_divweu (unsigned int, unsigned int);
vector __int128 __builtin_pack_vector_int128 (long long, long long);
void __builtin_rs6000_speculation_barrier (void);
long long __builtin_unpack_vector_int128 (vector __int128, signed char);
Of these, the __builtin_divde and __builtin_divdeu functions
require a 64-bit environment.
The following basic built-in functions, which are also supported on x86 targets, require -mfloat128.
__float128 __builtin_fabsq (__float128);
__float128 __builtin_copysignq (__float128, __float128);
__float128 __builtin_infq (void);
__float128 __builtin_huge_valq (void);
__float128 __builtin_nanq (void);
__float128 __builtin_nansq (void);
__float128 __builtin_sqrtf128 (__float128);
__float128 __builtin_fmaf128 (__float128, __float128, __float128);
The basic built-in functions described in this section are available on the PowerPC family of processors starting with ISA 2.07 or later. Unless specific options are explicitly disabled on the command line, specifying option -mcpu=power8 has the effect of enabling all the same options as for -mcpu=power7 in addition to the -mpower8-fusion, -mpower8-vector, -mcrypto, -mhtm, -mquad-memory, and -mquad-memory-atomic options.
This section intentionally empty.
The basic built-in functions described in this section are available on the PowerPC family of processors starting with ISA 3.0 or later. Unless specific options are explicitly disabled on the command line, specifying option -mcpu=power9 has the effect of enabling all the same options as for -mcpu=power8 in addition to the -misel option.
The following built-in functions are available on Linux 64-bit systems that use the ISA 3.0 instruction set (-mcpu=power9):
Perform a 128-bit IEEE floating point add using round to odd as the rounding mode.
Perform a 128-bit IEEE floating point subtract using round to odd as the rounding mode.
Perform a 128-bit IEEE floating point multiply using round to odd as the rounding mode.
Perform a 128-bit IEEE floating point divide using round to odd as the rounding mode.
Perform a 128-bit IEEE floating point square root using round to odd as the rounding mode.
Perform a 128-bit IEEE floating point fused multiply and add operation using round to odd as the rounding mode.
Convert a 128-bit IEEE floating point value to
doubleusing round to odd as the rounding mode.
The following additional built-in functions are also available for the PowerPC family of processors, starting with ISA 3.0 or later:
The
__builtin_darnand__builtin_darn_rawfunctions require a 64-bit environment supporting ISA 3.0 or later. The__builtin_darnfunction provides a 64-bit conditioned random number. The__builtin_darn_rawfunction provides a 64-bit raw random number. The__builtin_darn_32function provides a 32-bit conditioned random number.
The following additional built-in functions are also available for the PowerPC family of processors, starting with ISA 3.0 or later:
int __builtin_byte_in_set (unsigned char u, unsigned long long set);
int __builtin_byte_in_range (unsigned char u, unsigned int range);
int __builtin_byte_in_either_range (unsigned char u, unsigned int ranges);
int __builtin_dfp_dtstsfi_lt (unsigned int comparison, _Decimal64 value);
int __builtin_dfp_dtstsfi_lt (unsigned int comparison, _Decimal128 value);
int __builtin_dfp_dtstsfi_lt_dd (unsigned int comparison, _Decimal64 value);
int __builtin_dfp_dtstsfi_lt_td (unsigned int comparison, _Decimal128 value);
int __builtin_dfp_dtstsfi_gt (unsigned int comparison, _Decimal64 value);
int __builtin_dfp_dtstsfi_gt (unsigned int comparison, _Decimal128 value);
int __builtin_dfp_dtstsfi_gt_dd (unsigned int comparison, _Decimal64 value);
int __builtin_dfp_dtstsfi_gt_td (unsigned int comparison, _Decimal128 value);
int __builtin_dfp_dtstsfi_eq (unsigned int comparison, _Decimal64 value);
int __builtin_dfp_dtstsfi_eq (unsigned int comparison, _Decimal128 value);
int __builtin_dfp_dtstsfi_eq_dd (unsigned int comparison, _Decimal64 value);
int __builtin_dfp_dtstsfi_eq_td (unsigned int comparison, _Decimal128 value);
int __builtin_dfp_dtstsfi_ov (unsigned int comparison, _Decimal64 value);
int __builtin_dfp_dtstsfi_ov (unsigned int comparison, _Decimal128 value);
int __builtin_dfp_dtstsfi_ov_dd (unsigned int comparison, _Decimal64 value);
int __builtin_dfp_dtstsfi_ov_td (unsigned int comparison, _Decimal128 value);
double __builtin_mffsl(void);
The __builtin_byte_in_set function requires a
64-bit environment supporting ISA 3.0 or later. This function returns
a non-zero value if and only if its u argument exactly equals one of
the eight bytes contained within its 64-bit set argument.
The __builtin_byte_in_range and
__builtin_byte_in_either_range require an environment
supporting ISA 3.0 or later. For these two functions, the
range argument is encoded as 4 bytes, organized as
hi_1:lo_1:hi_2:lo_2.
The __builtin_byte_in_range function returns a
non-zero value if and only if its u argument is within the
range bounded between lo_2 and hi_2 inclusive.
The __builtin_byte_in_either_range function returns non-zero if
and only if its u argument is within either the range bounded
between lo_1 and hi_1 inclusive or the range bounded
between lo_2 and hi_2 inclusive.
The __builtin_dfp_dtstsfi_lt function returns a non-zero value
if and only if the number of signficant digits of its value argument
is less than its comparison argument. The
__builtin_dfp_dtstsfi_lt_dd and
__builtin_dfp_dtstsfi_lt_td functions behave similarly, but
require that the type of the value argument be
__Decimal64 and __Decimal128 respectively.
The __builtin_dfp_dtstsfi_gt function returns a non-zero value
if and only if the number of signficant digits of its value argument
is greater than its comparison argument. The
__builtin_dfp_dtstsfi_gt_dd and
__builtin_dfp_dtstsfi_gt_td functions behave similarly, but
require that the type of the value argument be
__Decimal64 and __Decimal128 respectively.
The __builtin_dfp_dtstsfi_eq function returns a non-zero value
if and only if the number of signficant digits of its value argument
equals its comparison argument. The
__builtin_dfp_dtstsfi_eq_dd and
__builtin_dfp_dtstsfi_eq_td functions behave similarly, but
require that the type of the value argument be
__Decimal64 and __Decimal128 respectively.
The __builtin_dfp_dtstsfi_ov function returns a non-zero value
if and only if its value argument has an undefined number of
significant digits, such as when value is an encoding of NaN.
The __builtin_dfp_dtstsfi_ov_dd and
__builtin_dfp_dtstsfi_ov_td functions behave similarly, but
require that the type of the value argument be
__Decimal64 and __Decimal128 respectively.
The __builtin_mffsl uses the ISA 3.0 mffsl instruction to read
the FPSCR. The instruction is a lower latency version of the mffs
instruction. If the mffsl instruction is not available, then the
builtin uses the older mffs instruction to read the FPSCR.
The basic built-in functions described in this section are available on the PowerPC family of processors starting with ISA 3.1. Unless specific options are explicitly disabled on the command line, specifying option -mcpu=power10 has the effect of enabling all the same options as for -mcpu=power9.
The following built-in functions are available on Linux 64-bit systems that use a future architecture instruction set (-mcpu=power10):
Perform a 64-bit centrifuge operation, as if implemented by the
cfugedinstruction.
Perform a 64-bit count leading zeros operation under mask, as if implemented by the
cntlzdminstruction.
Perform a 64-bit count trailing zeros operation under mask, as if implemented by the
cnttzdminstruction.
Perform a 64-bit parallel bits deposit operation, as if implemented by the
pdepdinstruction.
Perform a 64-bit parallel bits extract operation, as if implemented by the
pextdinstruction.
Load (and sign extend) to an __int128 vector, as if implemented by the ISA 3.1
lxvrbx,lxvrhx,lxvrwx, andlxvrdxinstructions.
Truncate and store the rightmost element of a vector, as if implemented by the ISA 3.1
stxvrbx,stxvrhx,stxvrwx, andstxvrdxinstructions.
GCC provides an interface for the PowerPC family of processors to access
the AltiVec operations described in Motorola's AltiVec Programming
Interface Manual. The interface is made available by including
<altivec.h> and using -maltivec and
-mabi=altivec. The interface supports the following vector
types.
vector unsigned char
vector signed char
vector bool char
vector unsigned short
vector signed short
vector bool short
vector pixel
vector unsigned int
vector signed int
vector bool int
vector float
GCC's implementation of the high-level language interface available from C and C++ code differs from Motorola's documentation in several ways.
signed or unsigned is omitted, the signedness of the
vector type is the default signedness of the base type. The default
varies depending on the operating system, so a portable program should
always specify the signedness.
__vector,
vector, __pixel, pixel, __bool and
bool. When compiling ISO C, the context-sensitive substitution
of the keywords vector, pixel and bool is
disabled. To use them, you must include <altivec.h> instead.
typedef name as the type specifier for a
vector type, but only under the following circumstances:
__vector instead of vector; for example,
typedef signed short int16;
__vector int16 data;
vector in keyword-and-predefine mode; for example,
typedef signed short int16;
vector int16 data;
Note that keyword-and-predefine mode is enabled by disabling GNU
extensions (e.g., by using -std=c11) and including
<altivec.h>.
vec_add ((vector signed int){1, 2, 3, 4}, foo);
Since vec_add is a macro, the vector constant in the example
is treated as four separate arguments. Wrap the entire argument in
parentheses for this to work.
Note: Only the <altivec.h> interface is supported.
Internally, GCC uses built-in functions to achieve the functionality in
the aforementioned header file, but they are not supported and are
subject to change without notice.
GCC complies with the Power Vector Intrinsic Programming Reference (PVIPR), which may be found at https://openpowerfoundation.org/?resource_lib=power-vector-intrinsic-programming-reference. Chapter 4 of this document fully documents the vector API interfaces that must be provided by compliant compilers. Programmers should preferentially use the interfaces described therein. However, historically GCC has provided additional interfaces for access to vector instructions. These are briefly described below. Where the PVIPR provides a portable interface, other functions in GCC that provide the same capabilities should be considered deprecated.
The PVIPR documents the following overloaded functions:
vec_abs
| vec_absd
| vec_abss
|
vec_add
| vec_addc
| vec_adde
|
vec_addec
| vec_adds
| vec_all_eq
|
vec_all_ge
| vec_all_gt
| vec_all_in
|
vec_all_le
| vec_all_lt
| vec_all_nan
|
vec_all_ne
| vec_all_nge
| vec_all_ngt
|
vec_all_nle
| vec_all_nlt
| vec_all_numeric
|
vec_and
| vec_andc
| vec_any_eq
|
vec_any_ge
| vec_any_gt
| vec_any_le
|
vec_any_lt
| vec_any_nan
| vec_any_ne
|
vec_any_nge
| vec_any_ngt
| vec_any_nle
|
vec_any_nlt
| vec_any_numeric
| vec_any_out
|
vec_avg
| vec_bperm
| vec_ceil
|
vec_cipher_be
| vec_cipherlast_be
| vec_cmpb
|
vec_cmpeq
| vec_cmpge
| vec_cmpgt
|
vec_cmple
| vec_cmplt
| vec_cmpne
|
vec_cmpnez
| vec_cntlz
| vec_cntlz_lsbb
|
vec_cnttz
| vec_cnttz_lsbb
| vec_cpsgn
|
vec_ctf
| vec_cts
| vec_ctu
|
vec_div
| vec_double
| vec_doublee
|
vec_doubleh
| vec_doublel
| vec_doubleo
|
vec_eqv
| vec_expte
| vec_extract
|
vec_extract_exp
| vec_extract_fp32_from_shorth
| vec_extract_fp32_from_shortl
|
vec_extract_sig
| vec_extract_4b
| vec_first_match_index
|
vec_first_match_or_eos_index
| vec_first_mismatch_index
| vec_first_mismatch_or_eos_index
|
vec_float
| vec_float2
| vec_floate
|
vec_floato
| vec_floor
| vec_gb
|
vec_insert
| vec_insert_exp
| vec_insert4b
|
vec_ld
| vec_lde
| vec_ldl
|
vec_loge
| vec_madd
| vec_madds
|
vec_max
| vec_mergee
| vec_mergeh
|
vec_mergel
| vec_mergeo
| vec_mfvscr
|
vec_min
| vec_mradds
| vec_msub
|
vec_msum
| vec_msums
| vec_mtvscr
|
vec_mul
| vec_mule
| vec_mulo
|
vec_nabs
| vec_nand
| vec_ncipher_be
|
vec_ncipherlast_be
| vec_nearbyint
| vec_neg
|
vec_nmadd
| vec_nmsub
| vec_nor
|
vec_or
| vec_orc
| vec_pack
|
vec_pack_to_short_fp32
| vec_packpx
| vec_packs
|
vec_packsu
| vec_parity_lsbb
| vec_perm
|
vec_permxor
| vec_pmsum_be
| vec_popcnt
|
vec_re
| vec_recipdiv
| vec_revb
|
vec_reve
| vec_rint
| vec_rl
|
vec_rlmi
| vec_rlnm
| vec_round
|
vec_rsqrt
| vec_rsqrte
| vec_sbox_be
|
vec_sel
| vec_shasigma_be
| vec_signed
|
vec_signed2
| vec_signede
| vec_signedo
|
vec_sl
| vec_sld
| vec_sldw
|
vec_sll
| vec_slo
| vec_slv
|
vec_splat
| vec_splat_s8
| vec_splat_s16
|
vec_splat_s32
| vec_splat_u8
| vec_splat_u16
|
vec_splat_u32
| vec_splats
| vec_sqrt
|
vec_sr
| vec_sra
| vec_srl
|
vec_sro
| vec_srv
| vec_st
|
vec_ste
| vec_stl
| vec_sub
|
vec_subc
| vec_sube
| vec_subec
|
vec_subs
| vec_sum2s
| vec_sum4s
|
vec_sums
| vec_test_data_class
| vec_trunc
|
vec_unpackh
| vec_unpackl
| vec_unsigned
|
vec_unsigned2
| vec_unsignede
| vec_unsignedo
|
vec_xl
| vec_xl_be
| vec_xl_len
|
vec_xl_len_r
| vec_xor
| vec_xst
|
vec_xst_be
| vec_xst_len
| vec_xst_len_r
|
The following interfaces are supported for the generic and specific AltiVec operations and the AltiVec predicates. In cases where there is a direct mapping between generic and specific operations, only the generic names are shown here, although the specific operations can also be used.
Arguments that are documented as const int require literal
integral values within the range required for that operation.
Only functions excluded from the PVIPR are listed here.
void vec_dss (const int);
void vec_dssall (void);
void vec_dst (const vector unsigned char *, int, const int);
void vec_dst (const vector signed char *, int, const int);
void vec_dst (const vector bool char *, int, const int);
void vec_dst (const vector unsigned short *, int, const int);
void vec_dst (const vector signed short *, int, const int);
void vec_dst (const vector bool short *, int, const int);
void vec_dst (const vector pixel *, int, const int);
void vec_dst (const vector unsigned int *, int, const int);
void vec_dst (const vector signed int *, int, const int);
void vec_dst (const vector bool int *, int, const int);
void vec_dst (const vector float *, int, const int);
void vec_dst (const unsigned char *, int, const int);
void vec_dst (const signed char *, int, const int);
void vec_dst (const unsigned short *, int, const int);
void vec_dst (const short *, int, const int);
void vec_dst (const unsigned int *, int, const int);
void vec_dst (const int *, int, const int);
void vec_dst (const float *, int, const int);
void vec_dstst (const vector unsigned char *, int, const int);
void vec_dstst (const vector signed char *, int, const int);
void vec_dstst (const vector bool char *, int, const int);
void vec_dstst (const vector unsigned short *, int, const int);
void vec_dstst (const vector signed short *, int, const int);
void vec_dstst (const vector bool short *, int, const int);
void vec_dstst (const vector pixel *, int, const int);
void vec_dstst (const vector unsigned int *, int, const int);
void vec_dstst (const vector signed int *, int, const int);
void vec_dstst (const vector bool int *, int, const int);
void vec_dstst (const vector float *, int, const int);
void vec_dstst (const unsigned char *, int, const int);
void vec_dstst (const signed char *, int, const int);
void vec_dstst (const unsigned short *, int, const int);
void vec_dstst (const short *, int, const int);
void vec_dstst (const unsigned int *, int, const int);
void vec_dstst (const int *, int, const int);
void vec_dstst (const unsigned long *, int, const int);
void vec_dstst (const long *, int, const int);
void vec_dstst (const float *, int, const int);
void vec_dststt (const vector unsigned char *, int, const int);
void vec_dststt (const vector signed char *, int, const int);
void vec_dststt (const vector bool char *, int, const int);
void vec_dststt (const vector unsigned short *, int, const int);
void vec_dststt (const vector signed short *, int, const int);
void vec_dststt (const vector bool short *, int, const int);
void vec_dststt (const vector pixel *, int, const int);
void vec_dststt (const vector unsigned int *, int, const int);
void vec_dststt (const vector signed int *, int, const int);
void vec_dststt (const vector bool int *, int, const int);
void vec_dststt (const vector float *, int, const int);
void vec_dststt (const unsigned char *, int, const int);
void vec_dststt (const signed char *, int, const int);
void vec_dststt (const unsigned short *, int, const int);
void vec_dststt (const short *, int, const int);
void vec_dststt (const unsigned int *, int, const int);
void vec_dststt (const int *, int, const int);
void vec_dststt (const float *, int, const int);
void vec_dstt (const vector unsigned char *, int, const int);
void vec_dstt (const vector signed char *, int, const int);
void vec_dstt (const vector bool char *, int, const int);
void vec_dstt (const vector unsigned short *, int, const int);
void vec_dstt (const vector signed short *, int, const int);
void vec_dstt (const vector bool short *, int, const int);
void vec_dstt (const vector pixel *, int, const int);
void vec_dstt (const vector unsigned int *, int, const int);
void vec_dstt (const vector signed int *, int, const int);
void vec_dstt (const vector bool int *, int, const int);
void vec_dstt (const vector float *, int, const int);
void vec_dstt (const unsigned char *, int, const int);
void vec_dstt (const signed char *, int, const int);
void vec_dstt (const unsigned short *, int, const int);
void vec_dstt (const short *, int, const int);
void vec_dstt (const unsigned int *, int, const int);
void vec_dstt (const int *, int, const int);
void vec_dstt (const float *, int, const int);
vector signed char vec_lvebx (int, char *);
vector unsigned char vec_lvebx (int, unsigned char *);
vector signed short vec_lvehx (int, short *);
vector unsigned short vec_lvehx (int, unsigned short *);
vector float vec_lvewx (int, float *);
vector signed int vec_lvewx (int, int *);
vector unsigned int vec_lvewx (int, unsigned int *);
vector unsigned char vec_lvsl (int, const unsigned char *);
vector unsigned char vec_lvsl (int, const signed char *);
vector unsigned char vec_lvsl (int, const unsigned short *);
vector unsigned char vec_lvsl (int, const short *);
vector unsigned char vec_lvsl (int, const unsigned int *);
vector unsigned char vec_lvsl (int, const int *);
vector unsigned char vec_lvsl (int, const float *);
vector unsigned char vec_lvsr (int, const unsigned char *);
vector unsigned char vec_lvsr (int, const signed char *);
vector unsigned char vec_lvsr (int, const unsigned short *);
vector unsigned char vec_lvsr (int, const short *);
vector unsigned char vec_lvsr (int, const unsigned int *);
vector unsigned char vec_lvsr (int, const int *);
vector unsigned char vec_lvsr (int, const float *);
void vec_stvebx (vector signed char, int, signed char *);
void vec_stvebx (vector unsigned char, int, unsigned char *);
void vec_stvebx (vector bool char, int, signed char *);
void vec_stvebx (vector bool char, int, unsigned char *);
void vec_stvehx (vector signed short, int, short *);
void vec_stvehx (vector unsigned short, int, unsigned short *);
void vec_stvehx (vector bool short, int, short *);
void vec_stvehx (vector bool short, int, unsigned short *);
void vec_stvewx (vector float, int, float *);
void vec_stvewx (vector signed int, int, int *);
void vec_stvewx (vector unsigned int, int, unsigned int *);
void vec_stvewx (vector bool int, int, int *);
void vec_stvewx (vector bool int, int, unsigned int *);
vector float vec_vaddfp (vector float, vector float);
vector signed char vec_vaddsbs (vector bool char, vector signed char);
vector signed char vec_vaddsbs (vector signed char, vector bool char);
vector signed char vec_vaddsbs (vector signed char, vector signed char);
vector signed short vec_vaddshs (vector bool short, vector signed short);
vector signed short vec_vaddshs (vector signed short, vector bool short);
vector signed short vec_vaddshs (vector signed short, vector signed short);
vector signed int vec_vaddsws (vector bool int, vector signed int);
vector signed int vec_vaddsws (vector signed int, vector bool int);
vector signed int vec_vaddsws (vector signed int, vector signed int);
vector signed char vec_vaddubm (vector bool char, vector signed char);
vector signed char vec_vaddubm (vector signed char, vector bool char);
vector signed char vec_vaddubm (vector signed char, vector signed char);
vector unsigned char vec_vaddubm (vector bool char, vector unsigned char);
vector unsigned char vec_vaddubm (vector unsigned char, vector bool char);
vector unsigned char vec_vaddubm (vector unsigned char, vector unsigned char);
vector unsigned char vec_vaddubs (vector bool char, vector unsigned char);
vector unsigned char vec_vaddubs (vector unsigned char, vector bool char);
vector unsigned char vec_vaddubs (vector unsigned char, vector unsigned char);
vector signed short vec_vadduhm (vector bool short, vector signed short);
vector signed short vec_vadduhm (vector signed short, vector bool short);
vector signed short vec_vadduhm (vector signed short, vector signed short);
vector unsigned short vec_vadduhm (vector bool short, vector unsigned short);
vector unsigned short vec_vadduhm (vector unsigned short, vector bool short);
vector unsigned short vec_vadduhm (vector unsigned short, vector unsigned short);
vector unsigned short vec_vadduhs (vector bool short, vector unsigned short);
vector unsigned short vec_vadduhs (vector unsigned short, vector bool short);
vector unsigned short vec_vadduhs (vector unsigned short, vector unsigned short);
vector signed int vec_vadduwm (vector bool int, vector signed int);
vector signed int vec_vadduwm (vector signed int, vector bool int);
vector signed int vec_vadduwm (vector signed int, vector signed int);
vector unsigned int vec_vadduwm (vector bool int, vector unsigned int);
vector unsigned int vec_vadduwm (vector unsigned int, vector bool int);
vector unsigned int vec_vadduwm (vector unsigned int, vector unsigned int);
vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
vector unsigned int vec_vadduws (vector unsigned int, vector unsigned int);
vector signed char vec_vavgsb (vector signed char, vector signed char);
vector signed short vec_vavgsh (vector signed short, vector signed short);
vector signed int vec_vavgsw (vector signed int, vector signed int);
vector unsigned char vec_vavgub (vector unsigned char, vector unsigned char);
vector unsigned short vec_vavguh (vector unsigned short, vector unsigned short);
vector unsigned int vec_vavguw (vector unsigned int, vector unsigned int);
vector float vec_vcfsx (vector signed int, const int);
vector float vec_vcfux (vector unsigned int, const int);
vector bool int vec_vcmpeqfp (vector float, vector float);
vector bool char vec_vcmpequb (vector signed char, vector signed char);
vector bool char vec_vcmpequb (vector unsigned char, vector unsigned char);
vector bool short vec_vcmpequh (vector signed short, vector signed short);
vector bool short vec_vcmpequh (vector unsigned short, vector unsigned short);
vector bool int vec_vcmpequw (vector signed int, vector signed int);
vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);
vector bool int vec_vcmpgtfp (vector float, vector float);
vector bool char vec_vcmpgtsb (vector signed char, vector signed char);
vector bool short vec_vcmpgtsh (vector signed short, vector signed short);
vector bool int vec_vcmpgtsw (vector signed int, vector signed int);
vector bool char vec_vcmpgtub (vector unsigned char, vector unsigned char);
vector bool short vec_vcmpgtuh (vector unsigned short, vector unsigned short);
vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);
vector float vec_vmaxfp (vector float, vector float);
vector signed char vec_vmaxsb (vector bool char, vector signed char);
vector signed char vec_vmaxsb (vector signed char, vector bool char);
vector signed char vec_vmaxsb (vector signed char, vector signed char);
vector signed short vec_vmaxsh (vector bool short, vector signed short);
vector signed short vec_vmaxsh (vector signed short, vector bool short);
vector signed short vec_vmaxsh (vector signed short, vector signed short);
vector signed int vec_vmaxsw (vector bool int, vector signed int);
vector signed int vec_vmaxsw (vector signed int, vector bool int);
vector signed int vec_vmaxsw (vector signed int, vector signed int);
vector unsigned char vec_vmaxub (vector bool char, vector unsigned char);
vector unsigned char vec_vmaxub (vector unsigned char, vector bool char);
vector unsigned char vec_vmaxub (vector unsigned char, vector unsigned char);
vector unsigned short vec_vmaxuh (vector bool short, vector unsigned short);
vector unsigned short vec_vmaxuh (vector unsigned short, vector bool short);
vector unsigned short vec_vmaxuh (vector unsigned short, vector unsigned short);
vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
vector unsigned int vec_vmaxuw (vector unsigned int, vector unsigned int);
vector float vec_vminfp (vector float, vector float);
vector signed char vec_vminsb (vector bool char, vector signed char);
vector signed char vec_vminsb (vector signed char, vector bool char);
vector signed char vec_vminsb (vector signed char, vector signed char);
vector signed short vec_vminsh (vector bool short, vector signed short);
vector signed short vec_vminsh (vector signed short, vector bool short);
vector signed short vec_vminsh (vector signed short, vector signed short);
vector signed int vec_vminsw (vector bool int, vector signed int);
vector signed int vec_vminsw (vector signed int, vector bool int);
vector signed int vec_vminsw (vector signed int, vector signed int);
vector unsigned char vec_vminub (vector bool char, vector unsigned char);
vector unsigned char vec_vminub (vector unsigned char, vector bool char);
vector unsigned char vec_vminub (vector unsigned char, vector unsigned char);
vector unsigned short vec_vminuh (vector bool short, vector unsigned short);
vector unsigned short vec_vminuh (vector unsigned short, vector bool short);
vector unsigned short vec_vminuh (vector unsigned short, vector unsigned short);
vector unsigned int vec_vminuw (vector bool int, vector unsigned int);
vector unsigned int vec_vminuw (vector unsigned int, vector bool int);
vector unsigned int vec_vminuw (vector unsigned int, vector unsigned int);
vector bool char vec_vmrghb (vector bool char, vector bool char);
vector signed char vec_vmrghb (vector signed char, vector signed char);
vector unsigned char vec_vmrghb (vector unsigned char, vector unsigned char);
vector bool short vec_vmrghh (vector bool short, vector bool short);
vector signed short vec_vmrghh (vector signed short, vector signed short);
vector unsigned short vec_vmrghh (vector unsigned short, vector unsigned short);
vector pixel vec_vmrghh (vector pixel, vector pixel);
vector float vec_vmrghw (vector float, vector float);
vector bool int vec_vmrghw (vector bool int, vector bool int);
vector signed int vec_vmrghw (vector signed int, vector signed int);
vector unsigned int vec_vmrghw (vector unsigned int, vector unsigned int);
vector bool char vec_vmrglb (vector bool char, vector bool char);
vector signed char vec_vmrglb (vector signed char, vector signed char);
vector unsigned char vec_vmrglb (vector unsigned char, vector unsigned char);
vector bool short vec_vmrglh (vector bool short, vector bool short);
vector signed short vec_vmrglh (vector signed short, vector signed short);
vector unsigned short vec_vmrglh (vector unsigned short, vector unsigned short);
vector pixel vec_vmrglh (vector pixel, vector pixel);
vector float vec_vmrglw (vector float, vector float);
vector signed int vec_vmrglw (vector signed int, vector signed int);
vector unsigned int vec_vmrglw (vector unsigned int, vector unsigned int);
vector bool int vec_vmrglw (vector bool int, vector bool int);
vector signed int vec_vmsummbm (vector signed char, vector unsigned char,
vector signed int);
vector signed int vec_vmsumshm (vector signed short, vector signed short,
vector signed int);
vector signed int vec_vmsumshs (vector signed short, vector signed short,
vector signed int);
vector unsigned int vec_vmsumubm (vector unsigned char, vector unsigned char,
vector unsigned int);
vector unsigned int vec_vmsumuhm (vector unsigned short, vector unsigned short,
vector unsigned int);
vector unsigned int vec_vmsumuhs (vector unsigned short, vector unsigned short,
vector unsigned int);
vector signed short vec_vmulesb (vector signed char, vector signed char);
vector signed int vec_vmulesh (vector signed short, vector signed short);
vector unsigned short vec_vmuleub (vector unsigned char, vector unsigned char);
vector unsigned int vec_vmuleuh (vector unsigned short, vector unsigned short);
vector signed short vec_vmulosb (vector signed char, vector signed char);
vector signed int vec_vmulosh (vector signed short, vector signed short);
vector unsigned short vec_vmuloub (vector unsigned char, vector unsigned char);
vector unsigned int vec_vmulouh (vector unsigned short, vector unsigned short);
vector signed char vec_vpkshss (vector signed short, vector signed short);
vector unsigned char vec_vpkshus (vector signed short, vector signed short);
vector signed short vec_vpkswss (vector signed int, vector signed int);
vector unsigned short vec_vpkswus (vector signed int, vector signed int);
vector bool char vec_vpkuhum (vector bool short, vector bool short);
vector signed char vec_vpkuhum (vector signed short, vector signed short);
vector unsigned char vec_vpkuhum (vector unsigned short, vector unsigned short);
vector unsigned char vec_vpkuhus (vector unsigned short, vector unsigned short);
vector bool short vec_vpkuwum (vector bool int, vector bool int);
vector signed short vec_vpkuwum (vector signed int, vector signed int);
vector unsigned short vec_vpkuwum (vector unsigned int, vector unsigned int);
vector unsigned short vec_vpkuwus (vector unsigned int, vector unsigned int);
vector signed char vec_vrlb (vector signed char, vector unsigned char);
vector unsigned char vec_vrlb (vector unsigned char, vector unsigned char);
vector signed short vec_vrlh (vector signed short, vector unsigned short);
vector unsigned short vec_vrlh (vector unsigned short, vector unsigned short);
vector signed int vec_vrlw (vector signed int, vector unsigned int);
vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int);
vector signed char vec_vslb (vector signed char, vector unsigned char);
vector unsigned char vec_vslb (vector unsigned char, vector unsigned char);
vector signed short vec_vslh (vector signed short, vector unsigned short);
vector unsigned short vec_vslh (vector unsigned short, vector unsigned short);
vector signed int vec_vslw (vector signed int, vector unsigned int);
vector unsigned int vec_vslw (vector unsigned int, vector unsigned int);
vector signed char vec_vspltb (vector signed char, const int);
vector unsigned char vec_vspltb (vector unsigned char, const int);
vector bool char vec_vspltb (vector bool char, const int);
vector bool short vec_vsplth (vector bool short, const int);
vector signed short vec_vsplth (vector signed short, const int);
vector unsigned short vec_vsplth (vector unsigned short, const int);
vector pixel vec_vsplth (vector pixel, const int);
vector float vec_vspltw (vector float, const int);
vector signed int vec_vspltw (vector signed int, const int);
vector unsigned int vec_vspltw (vector unsigned int, const int);
vector bool int vec_vspltw (vector bool int, const int);
vector signed char vec_vsrab (vector signed char, vector unsigned char);
vector unsigned char vec_vsrab (vector unsigned char, vector unsigned char);
vector signed short vec_vsrah (vector signed short, vector unsigned short);
vector unsigned short vec_vsrah (vector unsigned short, vector unsigned short);
vector signed int vec_vsraw (vector signed int, vector unsigned int);
vector unsigned int vec_vsraw (vector unsigned int, vector unsigned int);
vector signed char vec_vsrb (vector signed char, vector unsigned char);
vector unsigned char vec_vsrb (vector unsigned char, vector unsigned char);
vector signed short vec_vsrh (vector signed short, vector unsigned short);
vector unsigned short vec_vsrh (vector unsigned short, vector unsigned short);
vector signed int vec_vsrw (vector signed int, vector unsigned int);
vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int);
vector float vec_vsubfp (vector float, vector float);
vector signed char vec_vsubsbs (vector bool char, vector signed char);
vector signed char vec_vsubsbs (vector signed char, vector bool char);
vector signed char vec_vsubsbs (vector signed char, vector signed char);
vector signed short vec_vsubshs (vector bool short, vector signed short);
vector signed short vec_vsubshs (vector signed short, vector bool short);
vector signed short vec_vsubshs (vector signed short, vector signed short);
vector signed int vec_vsubsws (vector bool int, vector signed int);
vector signed int vec_vsubsws (vector signed int, vector bool int);
vector signed int vec_vsubsws (vector signed int, vector signed int);
vector signed char vec_vsububm (vector bool char, vector signed char);
vector signed char vec_vsububm (vector signed char, vector bool char);
vector signed char vec_vsububm (vector signed char, vector signed char);
vector unsigned char vec_vsububm (vector bool char, vector unsigned char);
vector unsigned char vec_vsububm (vector unsigned char, vector bool char);
vector unsigned char vec_vsububm (vector unsigned char, vector unsigned char);
vector unsigned char vec_vsububs (vector bool char, vector unsigned char);
vector unsigned char vec_vsububs (vector unsigned char, vector bool char);
vector unsigned char vec_vsububs (vector unsigned char, vector unsigned char);
vector signed short vec_vsubuhm (vector bool short, vector signed short);
vector signed short vec_vsubuhm (vector signed short, vector bool short);
vector signed short vec_vsubuhm (vector signed short, vector signed short);
vector unsigned short vec_vsubuhm (vector bool short, vector unsigned short);
vector unsigned short vec_vsubuhm (vector unsigned short, vector bool short);
vector unsigned short vec_vsubuhm (vector unsigned short, vector unsigned short);
vector unsigned short vec_vsubuhs (vector bool short, vector unsigned short);
vector unsigned short vec_vsubuhs (vector unsigned short, vector bool short);
vector unsigned short vec_vsubuhs (vector unsigned short, vector unsigned short);
vector signed int vec_vsubuwm (vector bool int, vector signed int);
vector signed int vec_vsubuwm (vector signed int, vector bool int);
vector signed int vec_vsubuwm (vector signed int, vector signed int);
vector unsigned int vec_vsubuwm (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuwm (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuwm (vector unsigned int, vector unsigned int);
vector unsigned int vec_vsubuws (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuws (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuws (vector unsigned int, vector unsigned int);
vector signed int vec_vsum4sbs (vector signed char, vector signed int);
vector signed int vec_vsum4shs (vector signed short, vector signed int);
vector unsigned int vec_vsum4ubs (vector unsigned char, vector unsigned int);
vector unsigned int vec_vupkhpx (vector pixel);
vector bool short vec_vupkhsb (vector bool char);
vector signed short vec_vupkhsb (vector signed char);
vector bool int vec_vupkhsh (vector bool short);
vector signed int vec_vupkhsh (vector signed short);
vector unsigned int vec_vupklpx (vector pixel);
vector bool short vec_vupklsb (vector bool char);
vector signed short vec_vupklsb (vector signed char);
vector bool int vec_vupklsh (vector bool short);
vector signed int vec_vupklsh (vector signed short);
The AltiVec built-in functions described in this section are available on the PowerPC family of processors starting with ISA 2.06 or later. These are normally enabled by adding -mvsx to the command line.
When -mvsx is used, the following additional vector types are implemented.
vector unsigned __int128
vector signed __int128
vector unsigned long long int
vector signed long long int
vector double
The long long types are only implemented for 64-bit code generation.
Only functions excluded from the PVIPR are listed here.
void vec_dst (const unsigned long *, int, const int);
void vec_dst (const long *, int, const int);
void vec_dststt (const unsigned long *, int, const int);
void vec_dststt (const long *, int, const int);
void vec_dstt (const unsigned long *, int, const int);
void vec_dstt (const long *, int, const int);
vector unsigned char vec_lvsl (int, const unsigned long *);
vector unsigned char vec_lvsl (int, const long *);
vector unsigned char vec_lvsr (int, const unsigned long *);
vector unsigned char vec_lvsr (int, const long *);
vector unsigned char vec_lvsl (int, const double *);
vector unsigned char vec_lvsr (int, const double *);
vector double vec_vsx_ld (int, const vector double *);
vector double vec_vsx_ld (int, const double *);
vector float vec_vsx_ld (int, const vector float *);
vector float vec_vsx_ld (int, const float *);
vector bool int vec_vsx_ld (int, const vector bool int *);
vector signed int vec_vsx_ld (int, const vector signed int *);
vector signed int vec_vsx_ld (int, const int *);
vector signed int vec_vsx_ld (int, const long *);
vector unsigned int vec_vsx_ld (int, const vector unsigned int *);
vector unsigned int vec_vsx_ld (int, const unsigned int *);
vector unsigned int vec_vsx_ld (int, const unsigned long *);
vector bool short vec_vsx_ld (int, const vector bool short *);
vector pixel vec_vsx_ld (int, const vector pixel *);
vector signed short vec_vsx_ld (int, const vector signed short *);
vector signed short vec_vsx_ld (int, const short *);
vector unsigned short vec_vsx_ld (int, const vector unsigned short *);
vector unsigned short vec_vsx_ld (int, const unsigned short *);
vector bool char vec_vsx_ld (int, const vector bool char *);
vector signed char vec_vsx_ld (int, const vector signed char *);
vector signed char vec_vsx_ld (int, const signed char *);
vector unsigned char vec_vsx_ld (int, const vector unsigned char *);
vector unsigned char vec_vsx_ld (int, const unsigned char *);
void vec_vsx_st (vector double, int, vector double *);
void vec_vsx_st (vector double, int, double *);
void vec_vsx_st (vector float, int, vector float *);
void vec_vsx_st (vector float, int, float *);
void vec_vsx_st (vector signed int, int, vector signed int *);
void vec_vsx_st (vector signed int, int, int *);
void vec_vsx_st (vector unsigned int, int, vector unsigned int *);
void vec_vsx_st (vector unsigned int, int, unsigned int *);
void vec_vsx_st (vector bool int, int, vector bool int *);
void vec_vsx_st (vector bool int, int, unsigned int *);
void vec_vsx_st (vector bool int, int, int *);
void vec_vsx_st (vector signed short, int, vector signed short *);
void vec_vsx_st (vector signed short, int, short *);
void vec_vsx_st (vector unsigned short, int, vector unsigned short *);
void vec_vsx_st (vector unsigned short, int, unsigned short *);
void vec_vsx_st (vector bool short, int, vector bool short *);
void vec_vsx_st (vector bool short, int, unsigned short *);
void vec_vsx_st (vector pixel, int, vector pixel *);
void vec_vsx_st (vector pixel, int, unsigned short *);
void vec_vsx_st (vector pixel, int, short *);
void vec_vsx_st (vector bool short, int, short *);
void vec_vsx_st (vector signed char, int, vector signed char *);
void vec_vsx_st (vector signed char, int, signed char *);
void vec_vsx_st (vector unsigned char, int, vector unsigned char *);
void vec_vsx_st (vector unsigned char, int, unsigned char *);
void vec_vsx_st (vector bool char, int, vector bool char *);
void vec_vsx_st (vector bool char, int, unsigned char *);
void vec_vsx_st (vector bool char, int, signed char *);
vector double vec_xxpermdi (vector double, vector double, const int);
vector float vec_xxpermdi (vector float, vector float, const int);
vector long long vec_xxpermdi (vector long long, vector long long, const int);
vector unsigned long long vec_xxpermdi (vector unsigned long long,
vector unsigned long long, const int);
vector int vec_xxpermdi (vector int, vector int, const int);
vector unsigned int vec_xxpermdi (vector unsigned int,
vector unsigned int, const int);
vector short vec_xxpermdi (vector short, vector short, const int);
vector unsigned short vec_xxpermdi (vector unsigned short,
vector unsigned short, const int);
vector signed char vec_xxpermdi (vector signed char, vector signed char,
const int);
vector unsigned char vec_xxpermdi (vector unsigned char,
vector unsigned char, const int);
vector double vec_xxsldi (vector double, vector double, int);
vector float vec_xxsldi (vector float, vector float, int);
vector long long vec_xxsldi (vector long long, vector long long, int);
vector unsigned long long vec_xxsldi (vector unsigned long long,
vector unsigned long long, int);
vector int vec_xxsldi (vector int, vector int, int);
vector unsigned int vec_xxsldi (vector unsigned int, vector unsigned int, int);
vector short vec_xxsldi (vector short, vector short, int);
vector unsigned short vec_xxsldi (vector unsigned short,
vector unsigned short, int);
vector signed char vec_xxsldi (vector signed char, vector signed char, int);
vector unsigned char vec_xxsldi (vector unsigned char,
vector unsigned char, int);
Note that the ‘vec_ld’ and ‘vec_st’ built-in functions always generate the AltiVec ‘LVX’ and ‘STVX’ instructions even if the VSX instruction set is available. The ‘vec_vsx_ld’ and ‘vec_vsx_st’ built-in functions always generate the VSX ‘LXVD2X’, ‘LXVW4X’, ‘STXVD2X’, and ‘STXVW4X’ instructions.
If the ISA 2.07 additions to the vector/scalar (power8-vector) instruction set are available, the following additional functions are available for both 32-bit and 64-bit targets. For 64-bit targets, you can use vector long instead of vector long long, vector bool long instead of vector bool long long, and vector unsigned long instead of vector unsigned long long.
Only functions excluded from the PVIPR are listed here.
vector long long vec_vaddudm (vector long long, vector long long);
vector long long vec_vaddudm (vector bool long long, vector long long);
vector long long vec_vaddudm (vector long long, vector bool long long);
vector unsigned long long vec_vaddudm (vector unsigned long long,
vector unsigned long long);
vector unsigned long long vec_vaddudm (vector bool unsigned long long,
vector unsigned long long);
vector unsigned long long vec_vaddudm (vector unsigned long long,
vector bool unsigned long long);
vector long long vec_vclz (vector long long);
vector unsigned long long vec_vclz (vector unsigned long long);
vector int vec_vclz (vector int);
vector unsigned int vec_vclz (vector int);
vector short vec_vclz (vector short);
vector unsigned short vec_vclz (vector unsigned short);
vector signed char vec_vclz (vector signed char);
vector unsigned char vec_vclz (vector unsigned char);
vector signed char vec_vclzb (vector signed char);
vector unsigned char vec_vclzb (vector unsigned char);
vector long long vec_vclzd (vector long long);
vector unsigned long long vec_vclzd (vector unsigned long long);
vector short vec_vclzh (vector short);
vector unsigned short vec_vclzh (vector unsigned short);
vector int vec_vclzw (vector int);
vector unsigned int vec_vclzw (vector int);
vector signed char vec_vgbbd (vector signed char);
vector unsigned char vec_vgbbd (vector unsigned char);
vector long long vec_vmaxsd (vector long long, vector long long);
vector unsigned long long vec_vmaxud (vector unsigned long long,
unsigned vector long long);
vector long long vec_vminsd (vector long long, vector long long);
vector unsigned long long vec_vminud (vector long long, vector long long);
vector int vec_vpksdss (vector long long, vector long long);
vector unsigned int vec_vpksdss (vector long long, vector long long);
vector unsigned int vec_vpkudus (vector unsigned long long,
vector unsigned long long);
vector int vec_vpkudum (vector long long, vector long long);
vector unsigned int vec_vpkudum (vector unsigned long long,
vector unsigned long long);
vector bool int vec_vpkudum (vector bool long long, vector bool long long);
vector long long vec_vpopcnt (vector long long);
vector unsigned long long vec_vpopcnt (vector unsigned long long);
vector int vec_vpopcnt (vector int);
vector unsigned int vec_vpopcnt (vector int);
vector short vec_vpopcnt (vector short);
vector unsigned short vec_vpopcnt (vector unsigned short);
vector signed char vec_vpopcnt (vector signed char);
vector unsigned char vec_vpopcnt (vector unsigned char);
vector signed char vec_vpopcntb (vector signed char);
vector unsigned char vec_vpopcntb (vector unsigned char);
vector long long vec_vpopcntd (vector long long);
vector unsigned long long vec_vpopcntd (vector unsigned long long);
vector short vec_vpopcnth (vector short);
vector unsigned short vec_vpopcnth (vector unsigned short);
vector int vec_vpopcntw (vector int);
vector unsigned int vec_vpopcntw (vector int);
vector long long vec_vrld (vector long long, vector unsigned long long);
vector unsigned long long vec_vrld (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsld (vector long long, vector unsigned long long);
vector long long vec_vsld (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsrad (vector long long, vector unsigned long long);
vector unsigned long long vec_vsrad (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsrd (vector long long, vector unsigned long long);
vector unsigned long long char vec_vsrd (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsubudm (vector long long, vector long long);
vector long long vec_vsubudm (vector bool long long, vector long long);
vector long long vec_vsubudm (vector long long, vector bool long long);
vector unsigned long long vec_vsubudm (vector unsigned long long,
vector unsigned long long);
vector unsigned long long vec_vsubudm (vector bool long long,
vector unsigned long long);
vector unsigned long long vec_vsubudm (vector unsigned long long,
vector bool long long);
vector long long vec_vupkhsw (vector int);
vector unsigned long long vec_vupkhsw (vector unsigned int);
vector long long vec_vupklsw (vector int);
vector unsigned long long vec_vupklsw (vector int);
If the ISA 2.07 additions to the vector/scalar (power8-vector) instruction set are available, the following additional functions are available for 64-bit targets. New vector types (vector __int128 and vector __uint128) are available to hold the __int128 and __uint128 types to use these builtins.
The normal vector extract, and set operations work on vector __int128 and vector __uint128 types, but the index value must be 0.
Only functions excluded from the PVIPR are listed here.
vector __int128 vec_vaddcuq (vector __int128, vector __int128);
vector __uint128 vec_vaddcuq (vector __uint128, vector __uint128);
vector __int128 vec_vadduqm (vector __int128, vector __int128);
vector __uint128 vec_vadduqm (vector __uint128, vector __uint128);
vector __int128 vec_vaddecuq (vector __int128, vector __int128,
vector __int128);
vector __uint128 vec_vaddecuq (vector __uint128, vector __uint128,
vector __uint128);
vector __int128 vec_vaddeuqm (vector __int128, vector __int128,
vector __int128);
vector __uint128 vec_vaddeuqm (vector __uint128, vector __uint128,
vector __uint128);
vector __int128 vec_vsubecuq (vector __int128, vector __int128,
vector __int128);
vector __uint128 vec_vsubecuq (vector __uint128, vector __uint128,
vector __uint128);
vector __int128 vec_vsubeuqm (vector __int128, vector __int128,
vector __int128);
vector __uint128 vec_vsubeuqm (vector __uint128, vector __uint128,
vector __uint128);
vector __int128 vec_vsubcuq (vector __int128, vector __int128);
vector __uint128 vec_vsubcuq (vector __uint128, vector __uint128);
__int128 vec_vsubuqm (__int128, __int128);
__uint128 vec_vsubuqm (__uint128, __uint128);
vector __int128 __builtin_bcdadd (vector __int128, vector __int128, const int);
vector unsigned char __builtin_bcdadd (vector unsigned char, vector unsigned char,
const int);
int __builtin_bcdadd_lt (vector __int128, vector __int128, const int);
int __builtin_bcdadd_lt (vector unsigned char, vector unsigned char, const int);
int __builtin_bcdadd_eq (vector __int128, vector __int128, const int);
int __builtin_bcdadd_eq (vector unsigned char, vector unsigned char, const int);
int __builtin_bcdadd_gt (vector __int128, vector __int128, const int);
int __builtin_bcdadd_gt (vector unsigned char, vector unsigned char, const int);
int __builtin_bcdadd_ov (vector __int128, vector __int128, const int);
int __builtin_bcdadd_ov (vector unsigned char, vector unsigned char, const int);
vector __int128 __builtin_bcdsub (vector __int128, vector __int128, const int);
vector unsigned char __builtin_bcdsub (vector unsigned char, vector unsigned char,
const int);
int __builtin_bcdsub_lt (vector __int128, vector __int128, const int);
int __builtin_bcdsub_lt (vector unsigned char, vector unsigned char, const int);
int __builtin_bcdsub_eq (vector __int128, vector __int128, const int);
int __builtin_bcdsub_eq (vector unsigned char, vector unsigned char, const int);
int __builtin_bcdsub_gt (vector __int128, vector __int128, const int);
int __builtin_bcdsub_gt (vector unsigned char, vector unsigned char, const int);
int __builtin_bcdsub_ov (vector __int128, vector __int128, const int);
int __builtin_bcdsub_ov (vector unsigned char, vector unsigned char, const int);
The following additional built-in functions are also available for the PowerPC family of processors, starting with ISA 3.0 (-mcpu=power9) or later.
Only instructions excluded from the PVIPR are listed here.
unsigned int scalar_extract_exp (double source);
unsigned long long int scalar_extract_exp (__ieee128 source);
unsigned long long int scalar_extract_sig (double source);
unsigned __int128 scalar_extract_sig (__ieee128 source);
double scalar_insert_exp (unsigned long long int significand,
unsigned long long int exponent);
double scalar_insert_exp (double significand, unsigned long long int exponent);
ieee_128 scalar_insert_exp (unsigned __int128 significand,
unsigned long long int exponent);
ieee_128 scalar_insert_exp (ieee_128 significand, unsigned long long int exponent);
int scalar_cmp_exp_gt (double arg1, double arg2);
int scalar_cmp_exp_lt (double arg1, double arg2);
int scalar_cmp_exp_eq (double arg1, double arg2);
int scalar_cmp_exp_unordered (double arg1, double arg2);
bool scalar_test_data_class (float source, const int condition);
bool scalar_test_data_class (double source, const int condition);
bool scalar_test_data_class (__ieee128 source, const int condition);
bool scalar_test_neg (float source);
bool scalar_test_neg (double source);
bool scalar_test_neg (__ieee128 source);
The scalar_extract_exp and scalar_extract_sig
functions require a 64-bit environment supporting ISA 3.0 or later.
The scalar_extract_exp and scalar_extract_sig built-in
functions return the significand and the biased exponent value
respectively of their source arguments.
When supplied with a 64-bit source argument, the
result returned by scalar_extract_sig has
the 0x0010000000000000 bit set if the
function's source argument is in normalized form.
Otherwise, this bit is set to 0.
When supplied with a 128-bit source argument, the
0x00010000000000000000000000000000 bit of the result is
treated similarly.
Note that the sign of the significand is not represented in the result
returned from the scalar_extract_sig function. Use the
scalar_test_neg function to test the sign of its double
argument.
The scalar_insert_exp
functions require a 64-bit environment supporting ISA 3.0 or later.
When supplied with a 64-bit first argument, the
scalar_insert_exp built-in function returns a double-precision
floating point value that is constructed by assembling the values of its
significand and exponent arguments. The sign of the
result is copied from the most significant bit of the
significand argument. The significand and exponent components
of the result are composed of the least significant 11 bits of the
exponent argument and the least significant 52 bits of the
significand argument respectively.
When supplied with a 128-bit first argument, the
scalar_insert_exp built-in function returns a quad-precision
ieee floating point value. The sign bit of the result is copied from
the most significant bit of the significand argument.
The significand and exponent components of the result are composed of
the least significant 15 bits of the exponent argument and the
least significant 112 bits of the significand argument respectively.
The scalar_cmp_exp_gt, scalar_cmp_exp_lt,
scalar_cmp_exp_eq, and scalar_cmp_exp_unordered built-in
functions return a non-zero value if arg1 is greater than, less
than, equal to, or not comparable to arg2 respectively. The
arguments are not comparable if one or the other equals NaN (not a
number).
The scalar_test_data_class built-in function returns 1
if any of the condition tests enabled by the value of the
condition variable are true, and 0 otherwise. The
condition argument must be a compile-time constant integer with
value not exceeding 127. The
condition argument is encoded as a bitmask with each bit
enabling the testing of a different condition, as characterized by the
following:
0x40 Test for NaN
0x20 Test for +Infinity
0x10 Test for -Infinity
0x08 Test for +Zero
0x04 Test for -Zero
0x02 Test for +Denormal
0x01 Test for -Denormal
The scalar_test_neg built-in function returns 1 if its
source argument holds a negative value, 0 otherwise.
The following built-in functions are also available for the PowerPC family of processors, starting with ISA 3.0 or later (-mcpu=power9). These string functions are described separately in order to group the descriptions closer to the function prototypes.
Only functions excluded from the PVIPR are listed here.
int vec_all_nez (vector signed char, vector signed char);
int vec_all_nez (vector unsigned char, vector unsigned char);
int vec_all_nez (vector signed short, vector signed short);
int vec_all_nez (vector unsigned short, vector unsigned short);
int vec_all_nez (vector signed int, vector signed int);
int vec_all_nez (vector unsigned int, vector unsigned int);
int vec_any_eqz (vector signed char, vector signed char);
int vec_any_eqz (vector unsigned char, vector unsigned char);
int vec_any_eqz (vector signed short, vector signed short);
int vec_any_eqz (vector unsigned short, vector unsigned short);
int vec_any_eqz (vector signed int, vector signed int);
int vec_any_eqz (vector unsigned int, vector unsigned int);
signed char vec_xlx (unsigned int index, vector signed char data);
unsigned char vec_xlx (unsigned int index, vector unsigned char data);
signed short vec_xlx (unsigned int index, vector signed short data);
unsigned short vec_xlx (unsigned int index, vector unsigned short data);
signed int vec_xlx (unsigned int index, vector signed int data);
unsigned int vec_xlx (unsigned int index, vector unsigned int data);
float vec_xlx (unsigned int index, vector float data);
signed char vec_xrx (unsigned int index, vector signed char data);
unsigned char vec_xrx (unsigned int index, vector unsigned char data);
signed short vec_xrx (unsigned int index, vector signed short data);
unsigned short vec_xrx (unsigned int index, vector unsigned short data);
signed int vec_xrx (unsigned int index, vector signed int data);
unsigned int vec_xrx (unsigned int index, vector unsigned int data);
float vec_xrx (unsigned int index, vector float data);
The vec_all_nez, vec_any_eqz, and vec_cmpnez
perform pairwise comparisons between the elements at the same
positions within their two vector arguments.
The vec_all_nez function returns a
non-zero value if and only if all pairwise comparisons are not
equal and no element of either vector argument contains a zero.
The vec_any_eqz function returns a
non-zero value if and only if at least one pairwise comparison is equal
or if at least one element of either vector argument contains a zero.
The vec_cmpnez function returns a vector of the same type as
its two arguments, within which each element consists of all ones to
denote that either the corresponding elements of the incoming arguments are
not equal or that at least one of the corresponding elements contains
zero. Otherwise, the element of the returned vector contains all zeros.
The vec_xlx and vec_xrx functions extract the single
element selected by the index argument from the vector
represented by the data argument. The index argument
always specifies a byte offset, regardless of the size of the vector
element. With vec_xlx, index is the offset of the first
byte of the element to be extracted. With vec_xrx, index
represents the last byte of the element to be extracted, measured
from the right end of the vector. In other words, the last byte of
the element to be extracted is found at position (15 - index).
There is no requirement that index be a multiple of the vector
element size. However, if the size of the vector element added to
index is greater than 15, the content of the returned value is
undefined.
The following functions are also available if the ISA 3.0 instruction set additions (-mcpu=power9) are available.
Only functions excluded from the PVIPR are listed here.
vector long long vec_vctz (vector long long);
vector unsigned long long vec_vctz (vector unsigned long long);
vector int vec_vctz (vector int);
vector unsigned int vec_vctz (vector int);
vector short vec_vctz (vector short);
vector unsigned short vec_vctz (vector unsigned short);
vector signed char vec_vctz (vector signed char);
vector unsigned char vec_vctz (vector unsigned char);
vector signed char vec_vctzb (vector signed char);
vector unsigned char vec_vctzb (vector unsigned char);
vector long long vec_vctzd (vector long long);
vector unsigned long long vec_vctzd (vector unsigned long long);
vector short vec_vctzh (vector short);
vector unsigned short vec_vctzh (vector unsigned short);
vector int vec_vctzw (vector int);
vector unsigned int vec_vctzw (vector int);
vector int vec_vprtyb (vector int);
vector unsigned int vec_vprtyb (vector unsigned int);
vector long long vec_vprtyb (vector long long);
vector unsigned long long vec_vprtyb (vector unsigned long long);
vector int vec_vprtybw (vector int);
vector unsigned int vec_vprtybw (vector unsigned int);
vector long long vec_vprtybd (vector long long);
vector unsigned long long vec_vprtybd (vector unsigned long long);
On 64-bit targets, if the ISA 3.0 additions (-mcpu=power9) are available:
vector long vec_vprtyb (vector long);
vector unsigned long vec_vprtyb (vector unsigned long);
vector __int128 vec_vprtyb (vector __int128);
vector __uint128 vec_vprtyb (vector __uint128);
vector long vec_vprtybd (vector long);
vector unsigned long vec_vprtybd (vector unsigned long);
vector __int128 vec_vprtybq (vector __int128);
vector __uint128 vec_vprtybd (vector __uint128);
The following built-in functions are available for the PowerPC family of processors, starting with ISA 3.0 or later (-mcpu=power9).
Only functions excluded from the PVIPR are listed here.
__vector unsigned char
vec_absdb (__vector unsigned char arg1, __vector unsigned char arg2);
__vector unsigned short
vec_absdh (__vector unsigned short arg1, __vector unsigned short arg2);
__vector unsigned int
vec_absdw (__vector unsigned int arg1, __vector unsigned int arg2);
The vec_absd, vec_absdb, vec_absdh, and
vec_absdw built-in functions each computes the absolute
differences of the pairs of vector elements supplied in its two vector
arguments, placing the absolute differences into the corresponding
elements of the vector result.
The following built-in functions are available for the PowerPC family of processors, starting with ISA 3.0 or later (-mcpu=power9):
vector unsigned int vec_vrlnm (vector unsigned int, vector unsigned int);
vector unsigned long long vec_vrlnm (vector unsigned long long,
vector unsigned long long);
The result of vec_vrlnm is obtained by rotating each element
of the first argument vector left and ANDing it with a mask. The
second argument vector contains the mask beginning in bits 11:15,
the mask end in bits 19:23, and the shift count in bits 27:31,
of each element.
If the cryptographic instructions are enabled (-mcrypto or -mcpu=power8), the following builtins are enabled.
Only functions excluded from the PVIPR are listed here.
vector unsigned long long __builtin_crypto_vsbox (vector unsigned long long);
vector unsigned long long __builtin_crypto_vcipher (vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vcipherlast
(vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vncipher (vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vncipherlast (vector unsigned long long,
vector unsigned long long);
vector unsigned char __builtin_crypto_vpermxor (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector unsigned short __builtin_crypto_vpermxor (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector unsigned int __builtin_crypto_vpermxor (vector unsigned int,
vector unsigned int,
vector unsigned int);
vector unsigned long long __builtin_crypto_vpermxor (vector unsigned long long,
vector unsigned long long,
vector unsigned long long);
vector unsigned char __builtin_crypto_vpmsumb (vector unsigned char,
vector unsigned char);
vector unsigned short __builtin_crypto_vpmsumh (vector unsigned short,
vector unsigned short);
vector unsigned int __builtin_crypto_vpmsumw (vector unsigned int,
vector unsigned int);
vector unsigned long long __builtin_crypto_vpmsumd (vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vshasigmad (vector unsigned long long,
int, int);
vector unsigned int __builtin_crypto_vshasigmaw (vector unsigned int, int, int);
The second argument to __builtin_crypto_vshasigmad and __builtin_crypto_vshasigmaw must be a constant integer that is 0 or 1. The third argument to these built-in functions must be a constant integer in the range of 0 to 15.
The following sign extension builtins are provided:
vector signed int vec_signexti (vector signed char a);
vector signed long long vec_signextll (vector signed char a);
vector signed int vec_signexti (vector signed short a);
vector signed long long vec_signextll (vector signed short a);
vector signed long long vec_signextll (vector signed int a);
vector signed long long vec_signextq (vector signed long long a);
Each element of the result is produced by sign-extending the element of the input vector that would fall in the least significant portion of the result element. For example, a sign-extension of a vector signed char to a vector signed long long will sign extend the rightmost byte of each doubleword.
The following additional built-in functions are also available for the PowerPC family of processors, starting with ISA 3.1 (-mcpu=power10):
vector unsigned long long int
vec_cfuge (vector unsigned long long int, vector unsigned long long int);
Perform a vector centrifuge operation, as if implemented by the
vcfuged instruction.
vector unsigned long long int
vec_cntlzm (vector unsigned long long int, vector unsigned long long int);
Perform a vector count leading zeros under bit mask operation, as if
implemented by the vclzdm instruction.
vector unsigned long long int
vec_cnttzm (vector unsigned long long int, vector unsigned long long int);
Perform a vector count trailing zeros under bit mask operation, as if
implemented by the vctzdm instruction.
vector signed char
vec_clrl (vector signed char a, unsigned int n);
vector unsigned char
vec_clrl (vector unsigned char a, unsigned int n);
Clear the left-most (16 - n) bytes of vector argument a, as if
implemented by the vclrlb instruction on a big-endian target
and by the vclrrb instruction on a little-endian target. A
value of n that is greater than 16 is treated as if it equaled 16.
vector signed char
vec_clrr (vector signed char a, unsigned int n);
vector unsigned char
vec_clrr (vector unsigned char a, unsigned int n);
Clear the right-most (16 - n) bytes of vector argument a, as if
implemented by the vclrrb instruction on a big-endian target
and by the vclrlb instruction on a little-endian target. A
value of n that is greater than 16 is treated as if it equaled 16.
vector unsigned long long int
vec_gnb (vector unsigned __int128, const unsigned char);
Perform a 128-bit vector gather operation, as if implemented by the
vgnb instruction. The second argument must be a literal
integer value between 2 and 7 inclusive.
Vector Extract
vector unsigned long long int
vec_extractl (vector unsigned char, vector unsigned char, unsigned int);
vector unsigned long long int
vec_extractl (vector unsigned short, vector unsigned short, unsigned int);
vector unsigned long long int
vec_extractl (vector unsigned int, vector unsigned int, unsigned int);
vector unsigned long long int
vec_extractl (vector unsigned long long, vector unsigned long long, unsigned int);
Extract an element from two concatenated vectors starting at the given byte index
in natural-endian order, and place it zero-extended in doubleword 1 of the result
according to natural element order. If the byte index is out of range for the
data type, the intrinsic will be rejected.
For little-endian, this output will match the placement by the hardware
instruction, i.e., dword[0] in RTL notation. For big-endian, an additional
instruction is needed to move it from the "left" doubleword to the "right" one.
For little-endian, semantics matching the vextdubvrx,
vextduhvrx, vextduwvrx instruction will be generated, while for
big-endian, semantics matching the vextdubvlx, vextduhvlx,
vextduwvlx instructions
will be generated. Note that some fairly anomalous results can be generated if
the byte index is not aligned on an element boundary for the element being
extracted. This is a limitation of the bi-endian vector programming model is
consistent with the limitation on vec_perm.
vector unsigned long long int
vec_extracth (vector unsigned char, vector unsigned char, unsigned int);
vector unsigned long long int
vec_extracth (vector unsigned short, vector unsigned short,
unsigned int);
vector unsigned long long int
vec_extracth (vector unsigned int, vector unsigned int, unsigned int);
vector unsigned long long int
vec_extracth (vector unsigned long long, vector unsigned long long,
unsigned int);
Extract an element from two concatenated vectors starting at the given byte
index. The index is based on big endian order for a little endian system.
Similarly, the index is based on little endian order for a big endian system.
The extraced elements are zero-extended and put in doubleword 1
according to natural element order. If the byte index is out of range for the
data type, the intrinsic will be rejected. For little-endian, this output
will match the placement by the hardware instruction (vextdubvrx, vextduhvrx,
vextduwvrx, vextddvrx) i.e., dword[0] in RTL
notation. For big-endian, an additional instruction is needed to move it
from the "left" doubleword to the "right" one. For little-endian, semantics
matching the vextdubvlx, vextduhvlx, vextduwvlx
instructions will be generated, while for big-endian, semantics matching the
vextdubvrx, vextduhvrx, vextduwvrx instructions will
be generated. Note that some fairly anomalous
results can be generated if the byte index is not aligned on the
element boundary for the element being extracted. This is a
limitation of the bi-endian vector programming model consistent with the
limitation on vec_perm.
vector unsigned long long int
vec_pdep (vector unsigned long long int, vector unsigned long long int);
Perform a vector parallel bits deposit operation, as if implemented by
the vpdepd instruction.
Vector Insert
vector unsigned char
vec_insertl (unsigned char, vector unsigned char, unsigned int);
vector unsigned short
vec_insertl (unsigned short, vector unsigned short, unsigned int);
vector unsigned int
vec_insertl (unsigned int, vector unsigned int, unsigned int);
vector unsigned long long
vec_insertl (unsigned long long, vector unsigned long long,
unsigned int);
vector unsigned char
vec_insertl (vector unsigned char, vector unsigned char, unsigned int;
vector unsigned short
vec_insertl (vector unsigned short, vector unsigned short,
unsigned int);
vector unsigned int
vec_insertl (vector unsigned int, vector unsigned int, unsigned int);
Let src be the first argument, when the first argument is a scalar, or the
rightmost element of the left doubleword of the first argument, when the first
argument is a vector. Insert the source into the destination at the position
given by the third argument, using natural element order in the second
argument. The rest of the second argument is unchanged. If the byte
index is greater than 14 for halfwords, greater than 12 for words, or
greater than 8 for doublewords the result is undefined. For little-endian,
the generated code will be semantically equivalent to vins[bhwd]rx
instructions. Similarly for big-endian it will be semantically equivalent
to vins[bhwd]lx. Note that some fairly anomalous results can be
generated if the byte index is not aligned on an element boundary for the
type of element being inserted.
vector unsigned char
vec_inserth (unsigned char, vector unsigned char, unsigned int);
vector unsigned short
vec_inserth (unsigned short, vector unsigned short, unsigned int);
vector unsigned int
vec_inserth (unsigned int, vector unsigned int, unsigned int);
vector unsigned long long
vec_inserth (unsigned long long, vector unsigned long long,
unsigned int);
vector unsigned char
vec_inserth (vector unsigned char, vector unsigned char, unsigned int);
vector unsigned short
vec_inserth (vector unsigned short, vector unsigned short,
unsigned int);
vector unsigned int
vec_inserth (vector unsigned int, vector unsigned int, unsigned int);
Let src be the first argument, when the first argument is a scalar, or the
rightmost element of the first argument, when the first argument is a vector.
Insert src into the second argument at the position identified by the third
argument, using opposite element order in the second argument, and leaving the
rest of the second argument unchanged. If the byte index is greater than 14
for halfwords, 12 for words, or 8 for doublewords, the intrinsic will be
rejected. Note that the underlying hardware instruction uses the same register
for the second argument and the result.
For little-endian, the code generation will be semantically equivalent to
vins[bhwd]lx, while for big-endian it will be semantically equivalent to
vins[bhwd]rx.
Note that some fairly anomalous results can be generated if the byte index is
not aligned on an element boundary for the sort of element being inserted.
Vector Replace Element
vector signed int vec_replace_elt (vector signed int, signed int,
const int);
vector unsigned int vec_replace_elt (vector unsigned int,
unsigned int, const int);
vector float vec_replace_elt (vector float, float, const int);
vector signed long long vec_replace_elt (vector signed long long,
signed long long, const int);
vector unsigned long long vec_replace_elt (vector unsigned long long,
unsigned long long, const int);
vector double rec_replace_elt (vector double, double, const int);
The third argument (constrained to [0,3]) identifies the natural-endian element number of the first argument that will be replaced by the second argument to produce the result. The other elements of the first argument will remain unchanged in the result.
If it's desirable to insert a word at an unaligned position, use vec_replace_unaligned instead.
vector unsigned char vec_replace_unaligned (vector unsigned char,
signed int, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
unsigned int, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
float, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
signed long long, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
unsigned long long, const int);
vector unsigned char vec_replace_unaligned (vector unsigned char,
double, const int);
The second argument replaces a portion of the first argument to produce the result, with the rest of the first argument unchanged in the result. The third argument identifies the byte index (using left-to-right, or big-endian order) where the high-order byte of the second argument will be placed, with the remaining bytes of the second argument placed naturally "to the right" of the high-order byte.
The programmer is responsible for understanding the endianness issues involved with the first argument and the result. Vector Shift Left Double Bit Immediate
vector signed char vec_sldb (vector signed char, vector signed char,
const unsigned int);
vector unsigned char vec_sldb (vector unsigned char,
vector unsigned char, const unsigned int);
vector signed short vec_sldb (vector signed short, vector signed short,
const unsigned int);
vector unsigned short vec_sldb (vector unsigned short,
vector unsigned short, const unsigned int);
vector signed int vec_sldb (vector signed int, vector signed int,
const unsigned int);
vector unsigned int vec_sldb (vector unsigned int, vector unsigned int,
const unsigned int);
vector signed long long vec_sldb (vector signed long long,
vector signed long long, const unsigned int);
vector unsigned long long vec_sldb (vector unsigned long long,
vector unsigned long long, const unsigned int);
Shift the combined input vectors left by the amount specified by the low-order three bits of the third argument, and return the leftmost remaining 128 bits. Code using this instruction must be endian-aware.
Vector Shift Right Double Bit Immediate
vector signed char vec_srdb (vector signed char, vector signed char,
const unsigned int);
vector unsigned char vec_srdb (vector unsigned char, vector unsigned char,
const unsigned int);
vector signed short vec_srdb (vector signed short, vector signed short,
const unsigned int);
vector unsigned short vec_srdb (vector unsigned short, vector unsigned short,
const unsigned int);
vector signed int vec_srdb (vector signed int, vector signed int,
const unsigned int);
vector unsigned int vec_srdb (vector unsigned int, vector unsigned int,
const unsigned int);
vector signed long long vec_srdb (vector signed long long,
vector signed long long, const unsigned int);
vector unsigned long long vec_srdb (vector unsigned long long,
vector unsigned long long, const unsigned int);
Shift the combined input vectors right by the amount specified by the low-order three bits of the third argument, and return the remaining 128 bits. Code using this built-in must be endian-aware.
vector signed int vec_splati (const signed int);
vector float vec_splati (const float);
Splat a 32-bit immediate into a vector of words.
vector double vec_splatid (const float);
Convert a single precision floating-point value to double-precision and splat the result to a vector of double-precision floats.
vector signed int vec_splati_ins (vector signed int,
const unsigned int, const signed int);
vector unsigned int vec_splati_ins (vector unsigned int,
const unsigned int, const unsigned int);
vector float vec_splati_ins (vector float, const unsigned int,
const float);
Argument 2 must be either 0 or 1. Splat the value of argument 3 into the word identified by argument 2 of each doubleword of argument 1 and return the result. The other words of argument 1 are unchanged.
vector signed char vec_blendv (vector signed char, vector signed char,
vector unsigned char);
vector unsigned char vec_blendv (vector unsigned char,
vector unsigned char, vector unsigned char);
vector signed short vec_blendv (vector signed short,
vector signed short, vector unsigned short);
vector unsigned short vec_blendv (vector unsigned short,
vector unsigned short, vector unsigned short);
vector signed int vec_blendv (vector signed int, vector signed int,
vector unsigned int);
vector unsigned int vec_blendv (vector unsigned int,
vector unsigned int, vector unsigned int);
vector signed long long vec_blendv (vector signed long long,
vector signed long long, vector unsigned long long);
vector unsigned long long vec_blendv (vector unsigned long long,
vector unsigned long long, vector unsigned long long);
vector float vec_blendv (vector float, vector float,
vector unsigned int);
vector double vec_blendv (vector double, vector double,
vector unsigned long long);
Blend the first and second argument vectors according to the sign bits of the
corresponding elements of the third argument vector. This is similar to the
vsel and xxsel instructions but for bigger elements.
vector signed char vec_permx (vector signed char, vector signed char,
vector unsigned char, const int);
vector unsigned char vec_permx (vector unsigned char,
vector unsigned char, vector unsigned char, const int);
vector signed short vec_permx (vector signed short,
vector signed short, vector unsigned char, const int);
vector unsigned short vec_permx (vector unsigned short,
vector unsigned short, vector unsigned char, const int);
vector signed int vec_permx (vector signed int, vector signed int,
vector unsigned char, const int);
vector unsigned int vec_permx (vector unsigned int,
vector unsigned int, vector unsigned char, const int);
vector signed long long vec_permx (vector signed long long,
vector signed long long, vector unsigned char, const int);
vector unsigned long long vec_permx (vector unsigned long long,
vector unsigned long long, vector unsigned char, const int);
vector float (vector float, vector float, vector unsigned char,
const int);
vector double (vector double, vector double, vector unsigned char,
const int);
Perform a partial permute of the first two arguments, which form a 32-byte section of an emulated vector up to 256 bytes wide, using the partial permute control vector in the third argument. The fourth argument (constrained to values of 0-7) identifies which 32-byte section of the emulated vector is contained in the first two arguments.
vector unsigned long long int
vec_pext (vector unsigned long long int, vector unsigned long long int);
Perform a vector parallel bit extract operation, as if implemented by
the vpextd instruction.
vector unsigned char vec_stril (vector unsigned char);
vector signed char vec_stril (vector signed char);
vector unsigned short vec_stril (vector unsigned short);
vector signed short vec_stril (vector signed short);
Isolate the left-most non-zero elements of the incoming vector argument,
replacing all elements to the right of the left-most zero element
found within the argument with zero. The typical implementation uses
the vstribl or vstrihl instruction on big-endian targets
and uses the vstribr or vstrihr instruction on
little-endian targets.
int vec_stril_p (vector unsigned char);
int vec_stril_p (vector signed char);
int short vec_stril_p (vector unsigned short);
int vec_stril_p (vector signed short);
Return a non-zero value if and only if the argument contains a zero
element. The typical implementation uses
the vstribl. or vstrihl. instruction on big-endian targets
and uses the vstribr. or vstrihr. instruction on
little-endian targets. Choose this built-in to check for presence of
zero element if the same argument is also passed to vec_stril.
vector unsigned char vec_strir (vector unsigned char);
vector signed char vec_strir (vector signed char);
vector unsigned short vec_strir (vector unsigned short);
vector signed short vec_strir (vector signed short);
Isolate the right-most non-zero elements of the incoming vector argument,
replacing all elements to the left of the right-most zero element
found within the argument with zero. The typical implementation uses
the vstribr or vstrihr instruction on big-endian targets
and uses the vstribl or vstrihl instruction on
little-endian targets.
int vec_strir_p (vector unsigned char);
int vec_strir_p (vector signed char);
int short vec_strir_p (vector unsigned short);
int vec_strir_p (vector signed short);
Return a non-zero value if and only if the argument contains a zero
element. The typical implementation uses
the vstribr. or vstrihr. instruction on big-endian targets
and uses the vstribl. or vstrihl. instruction on
little-endian targets. Choose this built-in to check for presence of
zero element if the same argument is also passed to vec_strir.
vector unsigned char
vec_ternarylogic (vector unsigned char, vector unsigned char,
vector unsigned char, const unsigned int);
vector unsigned short
vec_ternarylogic (vector unsigned short, vector unsigned short,
vector unsigned short, const unsigned int);
vector unsigned int
vec_ternarylogic (vector unsigned int, vector unsigned int,
vector unsigned int, const unsigned int);
vector unsigned long long int
vec_ternarylogic (vector unsigned long long int, vector unsigned long long int,
vector unsigned long long int, const unsigned int);
vector unsigned __int128
vec_ternarylogic (vector unsigned __int128, vector unsigned __int128,
vector unsigned __int128, const unsigned int);
Perform a 128-bit vector evaluate operation, as if implemented by the
xxeval instruction. The fourth argument must be a literal
integer value between 0 and 255 inclusive.
vector unsigned char vec_genpcvm (vector unsigned char, const int);
vector unsigned short vec_genpcvm (vector unsigned short, const int);
vector unsigned int vec_genpcvm (vector unsigned int, const int);
vector unsigned int vec_genpcvm (vector unsigned long long int,
const int);
Vector Integer Multiply/Divide/Modulo
vector signed int
vec_mulh (vector signed int a, vector signed int b);
vector unsigned int
vec_mulh (vector unsigned int a, vector unsigned int b);
For each integer value i from 0 to 3, do the following. The integer
value in word element i of a is multiplied by the integer value in word
element i of b. The high-order 32 bits of the 64-bit product are placed
into word element i of the vector returned.
vector signed long long
vec_mulh (vector signed long long a, vector signed long long b);
vector unsigned long long
vec_mulh (vector unsigned long long a, vector unsigned long long b);
For each integer value i from 0 to 1, do the following. The integer
value in doubleword element i of a is multiplied by the integer value in
doubleword element i of b. The high-order 64 bits of the 128-bit product
are placed into doubleword element i of the vector returned.
vector unsigned long long
vec_mul (vector unsigned long long a, vector unsigned long long b);
vector signed long long
vec_mul (vector signed long long a, vector signed long long b);
For each integer value i from 0 to 1, do the following. The integer
value in doubleword element i of a is multiplied by the integer value in
doubleword element i of b. The low-order 64 bits of the 128-bit product
are placed into doubleword element i of the vector returned.
vector signed int
vec_div (vector signed int a, vector signed int b);
vector unsigned int
vec_div (vector unsigned int a, vector unsigned int b);
For each integer value i from 0 to 3, do the following. The integer in
word element i of a is divided by the integer in word element i
of b. The unique integer quotient is placed into the word element i of
the vector returned. If an attempt is made to perform any of the divisions
<anything> ÷ 0 then the quotient is undefined.
vector signed long long
vec_div (vector signed long long a, vector signed long long b);
vector unsigned long long
vec_div (vector unsigned long long a, vector unsigned long long b);
For each integer value i from 0 to 1, do the following. The integer in
doubleword element i of a is divided by the integer in doubleword
element i of b. The unique integer quotient is placed into the
doubleword element i of the vector returned. If an attempt is made to
perform any of the divisions 0x8000_0000_0000_0000 ÷ -1 or <anything> ÷ 0 then
the quotient is undefined.
vector signed int
vec_dive (vector signed int a, vector signed int b);
vector unsigned int
vec_dive (vector unsigned int a, vector unsigned int b);
For each integer value i from 0 to 3, do the following. The integer in
word element i of a is shifted left by 32 bits, then divided by the
integer in word element i of b. The unique integer quotient is placed
into the word element i of the vector returned. If the quotient cannot
be represented in 32 bits, or if an attempt is made to perform any of the
divisions <anything> ÷ 0 then the quotient is undefined.
vector signed long long
vec_dive (vector signed long long a, vector signed long long b);
vector unsigned long long
vec_dive (vector unsigned long long a, vector unsigned long long b);
For each integer value i from 0 to 1, do the following. The integer in
doubleword element i of a is shifted left by 64 bits, then divided by
the integer in doubleword element i of b. The unique integer quotient is
placed into the doubleword element i of the vector returned. If the
quotient cannot be represented in 64 bits, or if an attempt is made to perform
<anything> ÷ 0 then the quotient is undefined.
vector signed int
vec_mod (vector signed int a, vector signed int b);
vector unsigned int
vec_mod (vector unsigned int a, vector unsigned int b);
For each integer value i from 0 to 3, do the following. The integer in
word element i of a is divided by the integer in word element i
of b. The unique integer remainder is placed into the word element i of
the vector returned. If an attempt is made to perform any of the divisions
0x8000_0000 ÷ -1 or <anything> ÷ 0 then the remainder is undefined.
vector signed long long
vec_mod (vector signed long long a, vector signed long long b);
vector unsigned long long
vec_mod (vector unsigned long long a, vector unsigned long long b);
For each integer value i from 0 to 1, do the following. The integer in
doubleword element i of a is divided by the integer in doubleword
element i of b. The unique integer remainder is placed into the
doubleword element i of the vector returned. If an attempt is made to
perform <anything> ÷ 0 then the remainder is undefined.
Generate PCV from specified Mask size, as if implemented by the
xxgenpcvbm, xxgenpcvhm, xxgenpcvwm instructions, where
immediate value is either 0, 1, 2 or 3.
vector unsigned __int128 vec_rl (vector unsigned __int128 A,
vector unsigned __int128 B);
vector signed __int128 vec_rl (vector signed __int128 A,
vector unsigned __int128 B);
Result value: Each element of R is obtained by rotating the corresponding element of A left by the number of bits specified by the corresponding element of B.
vector unsigned __int128 vec_rlmi (vector unsigned __int128,
vector unsigned __int128, vector unsigned __int128);
vector signed __int128 vec_rlmi (vector signed __int128,
vector signed __int128, vector unsigned __int128);
Returns the result of rotating the first input and inserting it under mask into the second input. The first bit in the mask, the last bit in the mask are obtained from the two 7-bit fields bits [108:115] and bits [117:123] respectively of the second input. The shift is obtained from the third input in the 7-bit field [125:131] where all bits counted from zero at the left.
vector unsigned __int128 vec_rlnm (vector unsigned __int128,
vector unsigned __int128, vector unsigned __int128);
vector signed __int128 vec_rlnm (vector signed __int128,
vector unsigned __int128, vector unsigned __int128);
Returns the result of rotating the first input and ANDing it with a mask. The first bit in the mask and the last bit in the mask are obtained from the two 7-bit fields bits [117:123] and bits [125:131] respectively of the second input. The shift is obtained from the third input in the 7-bit field bits [125:131] where all bits counted from zero at the left.
vector unsigned __int128 vec_sl(vector unsigned __int128 A, vector unsigned __int128 B);
vector signed __int128 vec_sl(vector signed __int128 A, vector unsigned __int128 B);
Result value: Each element of R is obtained by shifting the corresponding element of A left by the number of bits specified by the corresponding element of B.
vector unsigned __int128 vec_sr(vector unsigned __int128 A, vector unsigned __int128 B);
vector signed __int128 vec_sr(vector signed __int128 A, vector unsigned __int128 B);
Result value: Each element of R is obtained by shifting the corresponding element of A right by the number of bits specified by the corresponding element of B.
vector unsigned __int128 vec_sra(vector unsigned __int128 A, vector unsigned __int128 B);
vector signed __int128 vec_sra(vector signed __int128 A, vector unsigned __int128 B);
Result value: Each element of R is obtained by arithmetic shifting the corresponding element of A right by the number of bits specified by the corresponding element of B.
vector unsigned __int128 vec_mule (vector unsigned long long,
vector unsigned long long);
vector signed __int128 vec_mule (vector signed long long,
vector signed long long);
Returns a vector containing a 128-bit integer result of multiplying the even doubleword elements of the two inputs.
vector unsigned __int128 vec_mulo (vector unsigned long long,
vector unsigned long long);
vector signed __int128 vec_mulo (vector signed long long,
vector signed long long);
Returns a vector containing a 128-bit integer result of multiplying the odd doubleword elements of the two inputs.
vector unsigned __int128 vec_div (vector unsigned __int128,
vector unsigned __int128);
vector signed __int128 vec_div (vector signed __int128,
vector signed __int128);
Returns the result of dividing the first operand by the second operand. An attempt to divide any value by zero or to divide the most negative signed 128-bit integer by negative one results in an undefined value.
vector unsigned __int128 vec_dive (vector unsigned __int128,
vector unsigned __int128);
vector signed __int128 vec_dive (vector signed __int128,
vector signed __int128);
The result is produced by shifting the first input left by 128 bits and dividing by the second. If an attempt is made to divide by zero or the result is larger than 128 bits, the result is undefined.
vector unsigned __int128 vec_mod (vector unsigned __int128,
vector unsigned __int128);
vector signed __int128 vec_mod (vector signed __int128,
vector signed __int128);
The result is the modulo result of dividing the first input by the second input.
The following builtins perform 128-bit vector comparisons. The
vec_all_xx, vec_any_xx, and vec_cmpxx, where xx is
one of the operations eq, ne, gt, lt, ge, le perform pairwise
comparisons between the elements at the same positions within their two vector
arguments. The vec_all_xxfunction returns a non-zero value if and only
if all pairwise comparisons are true. The vec_any_xx function returns
a non-zero value if and only if at least one pairwise comparison is true. The
vec_cmpxxfunction returns a vector of the same type as its two
arguments, within which each element consists of all ones to denote that
specified logical comparison of the corresponding elements was true.
Otherwise, the element of the returned vector contains all zeros.
vector bool __int128 vec_cmpeq (vector signed __int128, vector signed __int128);
vector bool __int128 vec_cmpeq (vector unsigned __int128, vector unsigned __int128);
vector bool __int128 vec_cmpne (vector signed __int128, vector signed __int128);
vector bool __int128 vec_cmpne (vector unsigned __int128, vector unsigned __int128);
vector bool __int128 vec_cmpgt (vector signed __int128, vector signed __int128);
vector bool __int128 vec_cmpgt (vector unsigned __int128, vector unsigned __int128);
vector bool __int128 vec_cmplt (vector signed __int128, vector signed __int128);
vector bool __int128 vec_cmplt (vector unsigned __int128, vector unsigned __int128);
vector bool __int128 vec_cmpge (vector signed __int128, vector signed __int128);
vector bool __int128 vec_cmpge (vector unsigned __int128, vector unsigned __int128);
vector bool __int128 vec_cmple (vector signed __int128, vector signed __int128);
vector bool __int128 vec_cmple (vector unsigned __int128, vector unsigned __int128);
int vec_all_eq (vector signed __int128, vector signed __int128);
int vec_all_eq (vector unsigned __int128, vector unsigned __int128);
int vec_all_ne (vector signed __int128, vector signed __int128);
int vec_all_ne (vector unsigned __int128, vector unsigned __int128);
int vec_all_gt (vector signed __int128, vector signed __int128);
int vec_all_gt (vector unsigned __int128, vector unsigned __int128);
int vec_all_lt (vector signed __int128, vector signed __int128);
int vec_all_lt (vector unsigned __int128, vector unsigned __int128);
int vec_all_ge (vector signed __int128, vector signed __int128);
int vec_all_ge (vector unsigned __int128, vector unsigned __int128);
int vec_all_le (vector signed __int128, vector signed __int128);
int vec_all_le (vector unsigned __int128, vector unsigned __int128);
int vec_any_eq (vector signed __int128, vector signed __int128);
int vec_any_eq (vector unsigned __int128, vector unsigned __int128);
int vec_any_ne (vector signed __int128, vector signed __int128);
int vec_any_ne (vector unsigned __int128, vector unsigned __int128);
int vec_any_gt (vector signed __int128, vector signed __int128);
int vec_any_gt (vector unsigned __int128, vector unsigned __int128);
int vec_any_lt (vector signed __int128, vector signed __int128);
int vec_any_lt (vector unsigned __int128, vector unsigned __int128);
int vec_any_ge (vector signed __int128, vector signed __int128);
int vec_any_ge (vector unsigned __int128, vector unsigned __int128);
int vec_any_le (vector signed __int128, vector signed __int128);
int vec_any_le (vector unsigned __int128, vector unsigned __int128);
GCC provides two interfaces for accessing the Hardware Transactional Memory (HTM) instructions available on some of the PowerPC family of processors (eg, POWER8). The two interfaces come in a low level interface, consisting of built-in functions specific to PowerPC and a higher level interface consisting of inline functions that are common between PowerPC and S/390.
The following low level built-in functions are available with -mhtm or -mcpu=CPU where CPU is `power8' or later. They all generate the machine instruction that is part of the name.
The HTM builtins (with the exception of __builtin_tbegin) return
the full 4-bit condition register value set by their associated hardware
instruction. The header file htmintrin.h defines some macros that can
be used to decipher the return value. The __builtin_tbegin builtin
returns a simple true or false value depending on whether a transaction was
successfully started or not. The arguments of the builtins match exactly the
type and order of the associated hardware instruction's operands, except for
the __builtin_tcheck builtin, which does not take any input arguments.
Refer to the ISA manual for a description of each instruction's operands.
unsigned int __builtin_tbegin (unsigned int);
unsigned int __builtin_tend (unsigned int);
unsigned int __builtin_tabort (unsigned int);
unsigned int __builtin_tabortdc (unsigned int, unsigned int, unsigned int);
unsigned int __builtin_tabortdci (unsigned int, unsigned int, int);
unsigned int __builtin_tabortwc (unsigned int, unsigned int, unsigned int);
unsigned int __builtin_tabortwci (unsigned int, unsigned int, int);
unsigned int __builtin_tcheck (void);
unsigned int __builtin_treclaim (unsigned int);
unsigned int __builtin_trechkpt (void);
unsigned int __builtin_tsr (unsigned int);
In addition to the above HTM built-ins, we have added built-ins for some common extended mnemonics of the HTM instructions:
unsigned int __builtin_tendall (void);
unsigned int __builtin_tresume (void);
unsigned int __builtin_tsuspend (void);
Note that the semantics of the above HTM builtins are required to mimic
the locking semantics used for critical sections. Builtins that are used
to create a new transaction or restart a suspended transaction must have
lock acquisition like semantics while those builtins that end or suspend a
transaction must have lock release like semantics. Specifically, this must
mimic lock semantics as specified by C++11, for example: Lock acquisition is
as-if an execution of __atomic_exchange_n(&globallock,1,__ATOMIC_ACQUIRE)
that returns 0, and lock release is as-if an execution of
__atomic_store(&globallock,0,__ATOMIC_RELEASE), with globallock being an
implicit implementation-defined lock used for all transactions. The HTM
instructions associated with with the builtins inherently provide the
correct acquisition and release hardware barriers required. However,
the compiler must also be prohibited from moving loads and stores across
the builtins in a way that would violate their semantics. This has been
accomplished by adding memory barriers to the associated HTM instructions
(which is a conservative approach to provide acquire and release semantics).
Earlier versions of the compiler did not treat the HTM instructions as
memory barriers. A __TM_FENCE__ macro has been added, which can
be used to determine whether the current compiler treats HTM instructions
as memory barriers or not. This allows the user to explicitly add memory
barriers to their code when using an older version of the compiler.
The following set of built-in functions are available to gain access to the HTM specific special purpose registers.
unsigned long __builtin_get_texasr (void);
unsigned long __builtin_get_texasru (void);
unsigned long __builtin_get_tfhar (void);
unsigned long __builtin_get_tfiar (void);
void __builtin_set_texasr (unsigned long);
void __builtin_set_texasru (unsigned long);
void __builtin_set_tfhar (unsigned long);
void __builtin_set_tfiar (unsigned long);
Example usage of these low level built-in functions may look like:
#include <htmintrin.h>
int num_retries = 10;
while (1)
{
if (__builtin_tbegin (0))
{
/* Transaction State Initiated. */
if (is_locked (lock))
__builtin_tabort (0);
... transaction code...
__builtin_tend (0);
break;
}
else
{
/* Transaction State Failed. Use locks if the transaction
failure is "persistent" or we've tried too many times. */
if (num_retries-- <= 0
|| _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
{
acquire_lock (lock);
... non transactional fallback path...
release_lock (lock);
break;
}
}
}
One final built-in function has been added that returns the value of
the 2-bit Transaction State field of the Machine Status Register (MSR)
as stored in CR0.
unsigned long __builtin_ttest (void)
This built-in can be used to determine the current transaction state using the following code example:
#include <htmintrin.h>
unsigned char tx_state = _HTM_STATE (__builtin_ttest ());
if (tx_state == _HTM_TRANSACTIONAL)
{
/* Code to use in transactional state. */
}
else if (tx_state == _HTM_NONTRANSACTIONAL)
{
/* Code to use in non-transactional state. */
}
else if (tx_state == _HTM_SUSPENDED)
{
/* Code to use in transaction suspended state. */
}
The following high level HTM interface is made available by including
<htmxlintrin.h> and using -mhtm or -mcpu=CPU
where CPU is `power8' or later. This interface is common between PowerPC
and S/390, allowing users to write one HTM source implementation that
can be compiled and executed on either system.
long __TM_simple_begin (void);
long __TM_begin (void* const TM_buff);
long __TM_end (void);
void __TM_abort (void);
void __TM_named_abort (unsigned char const code);
void __TM_resume (void);
void __TM_suspend (void);
long __TM_is_user_abort (void* const TM_buff);
long __TM_is_named_user_abort (void* const TM_buff, unsigned char *code);
long __TM_is_illegal (void* const TM_buff);
long __TM_is_footprint_exceeded (void* const TM_buff);
long __TM_nesting_depth (void* const TM_buff);
long __TM_is_nested_too_deep(void* const TM_buff);
long __TM_is_conflict(void* const TM_buff);
long __TM_is_failure_persistent(void* const TM_buff);
long __TM_failure_address(void* const TM_buff);
long long __TM_failure_code(void* const TM_buff);
Using these common set of HTM inline functions, we can create a more portable version of the HTM example in the previous section that will work on either PowerPC or S/390:
#include <htmxlintrin.h>
int num_retries = 10;
TM_buff_type TM_buff;
while (1)
{
if (__TM_begin (TM_buff) == _HTM_TBEGIN_STARTED)
{
/* Transaction State Initiated. */
if (is_locked (lock))
__TM_abort ();
... transaction code...
__TM_end ();
break;
}
else
{
/* Transaction State Failed. Use locks if the transaction
failure is "persistent" or we've tried too many times. */
if (num_retries-- <= 0
|| __TM_is_failure_persistent (TM_buff))
{
acquire_lock (lock);
... non transactional fallback path...
release_lock (lock);
break;
}
}
}
ISA 3.0 of the PowerPC added new atomic memory operation (amo)
instructions. GCC provides support for these instructions in 64-bit
environments. All of the functions are declared in the include file
amo.h.
The functions supported are:
#include <amo.h>
uint32_t amo_lwat_add (uint32_t *, uint32_t);
uint32_t amo_lwat_xor (uint32_t *, uint32_t);
uint32_t amo_lwat_ior (uint32_t *, uint32_t);
uint32_t amo_lwat_and (uint32_t *, uint32_t);
uint32_t amo_lwat_umax (uint32_t *, uint32_t);
uint32_t amo_lwat_umin (uint32_t *, uint32_t);
uint32_t amo_lwat_swap (uint32_t *, uint32_t);
int32_t amo_lwat_sadd (int32_t *, int32_t);
int32_t amo_lwat_smax (int32_t *, int32_t);
int32_t amo_lwat_smin (int32_t *, int32_t);
int32_t amo_lwat_sswap (int32_t *, int32_t);
uint64_t amo_ldat_add (uint64_t *, uint64_t);
uint64_t amo_ldat_xor (uint64_t *, uint64_t);
uint64_t amo_ldat_ior (uint64_t *, uint64_t);
uint64_t amo_ldat_and (uint64_t *, uint64_t);
uint64_t amo_ldat_umax (uint64_t *, uint64_t);
uint64_t amo_ldat_umin (uint64_t *, uint64_t);
uint64_t amo_ldat_swap (uint64_t *, uint64_t);
int64_t amo_ldat_sadd (int64_t *, int64_t);
int64_t amo_ldat_smax (int64_t *, int64_t);
int64_t amo_ldat_smin (int64_t *, int64_t);
int64_t amo_ldat_sswap (int64_t *, int64_t);
void amo_stwat_add (uint32_t *, uint32_t);
void amo_stwat_xor (uint32_t *, uint32_t);
void amo_stwat_ior (uint32_t *, uint32_t);
void amo_stwat_and (uint32_t *, uint32_t);
void amo_stwat_umax (uint32_t *, uint32_t);
void amo_stwat_umin (uint32_t *, uint32_t);
void amo_stwat_sadd (int32_t *, int32_t);
void amo_stwat_smax (int32_t *, int32_t);
void amo_stwat_smin (int32_t *, int32_t);
void amo_stdat_add (uint64_t *, uint64_t);
void amo_stdat_xor (uint64_t *, uint64_t);
void amo_stdat_ior (uint64_t *, uint64_t);
void amo_stdat_and (uint64_t *, uint64_t);
void amo_stdat_umax (uint64_t *, uint64_t);
void amo_stdat_umin (uint64_t *, uint64_t);
void amo_stdat_sadd (int64_t *, int64_t);
void amo_stdat_smax (int64_t *, int64_t);
void amo_stdat_smin (int64_t *, int64_t);
ISA 3.1 of the PowerPC added new Matrix-Multiply Assist (MMA) instructions.
GCC provides support for these instructions through the following built-in
functions which are enabled with the -mmma option. The vec_t type
below is defined to be a normal vector unsigned char type. The uint2, uint4
and uint8 parameters are 2-bit, 4-bit and 8-bit unsigned integer constants
respectively. The compiler will verify that they are constants and that
their values are within range.
The built-in functions supported are:
void __builtin_mma_xvi4ger8 (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvi8ger4 (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvi16ger2 (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvi16ger2s (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf16ger2 (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvbf16ger2 (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf32ger (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvi4ger8pp (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvi8ger4pp (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvi8ger4spp(__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvi16ger2pp (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvi16ger2spp (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf16ger2pp (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf16ger2pn (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf16ger2np (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf16ger2nn (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvbf16ger2pp (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvbf16ger2pn (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvbf16ger2np (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvbf16ger2nn (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf32gerpp (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf32gerpn (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf32gernp (__vector_quad *, vec_t, vec_t);
void __builtin_mma_xvf32gernn (__vector_quad *, vec_t, vec_t);
void __builtin_mma_pmxvi4ger8 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint8);
void __builtin_mma_pmxvi4ger8pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint8);
void __builtin_mma_pmxvi8ger4 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint4);
void __builtin_mma_pmxvi8ger4pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint4);
void __builtin_mma_pmxvi8ger4spp(__vector_quad *, vec_t, vec_t, uint4, uint4, uint4);
void __builtin_mma_pmxvi16ger2 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvi16ger2s (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvf16ger2 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvbf16ger2 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvi16ger2pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvi16ger2spp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvf16ger2pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvf16ger2pn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvf16ger2np (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvf16ger2nn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvbf16ger2pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvbf16ger2pn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvbf16ger2np (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvbf16ger2nn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2);
void __builtin_mma_pmxvf32ger (__vector_quad *, vec_t, vec_t, uint4, uint4);
void __builtin_mma_pmxvf32gerpp (__vector_quad *, vec_t, vec_t, uint4, uint4);
void __builtin_mma_pmxvf32gerpn (__vector_quad *, vec_t, vec_t, uint4, uint4);
void __builtin_mma_pmxvf32gernp (__vector_quad *, vec_t, vec_t, uint4, uint4);
void __builtin_mma_pmxvf32gernn (__vector_quad *, vec_t, vec_t, uint4, uint4);
void __builtin_mma_xvf64ger (__vector_quad *, __vector_pair, vec_t);
void __builtin_mma_xvf64gerpp (__vector_quad *, __vector_pair, vec_t);
void __builtin_mma_xvf64gerpn (__vector_quad *, __vector_pair, vec_t);
void __builtin_mma_xvf64gernp (__vector_quad *, __vector_pair, vec_t);
void __builtin_mma_xvf64gernn (__vector_quad *, __vector_pair, vec_t);
void __builtin_mma_pmxvf64ger (__vector_quad *, __vector_pair, vec_t, uint4, uint2);
void __builtin_mma_pmxvf64gerpp (__vector_quad *, __vector_pair, vec_t, uint4, uint2);
void __builtin_mma_pmxvf64gerpn (__vector_quad *, __vector_pair, vec_t, uint4, uint2);
void __builtin_mma_pmxvf64gernp (__vector_quad *, __vector_pair, vec_t, uint4, uint2);
void __builtin_mma_pmxvf64gernn (__vector_quad *, __vector_pair, vec_t, uint4, uint2);
void __builtin_mma_xxmtacc (__vector_quad *);
void __builtin_mma_xxmfacc (__vector_quad *);
void __builtin_mma_xxsetaccz (__vector_quad *);
void __builtin_mma_build_acc (__vector_quad *, vec_t, vec_t, vec_t, vec_t);
void __builtin_mma_disassemble_acc (void *, __vector_quad *);
void __builtin_vsx_build_pair (__vector_pair *, vec_t, vec_t);
void __builtin_vsx_disassemble_pair (void *, __vector_pair *);
vec_t __builtin_vsx_xvcvspbf16 (vec_t);
vec_t __builtin_vsx_xvcvbf16spn (vec_t);
__vector_pair __builtin_vsx_lxvp (size_t, __vector_pair *);
void __builtin_vsx_stxvp (__vector_pair, size_t, __vector_pair *);
GCC provides a couple of special builtin functions to aid in utilizing special PRU instructions.
The built-in functions supported are:
This inserts an instruction sequence that takes exactly cycles cycles (between 0 and 0xffffffff) to complete. The inserted sequence may use jumps, loops, or no-ops, and does not interfere with any other instructions. Note that cycles must be a compile-time constant integer - that is, you must pass a number, not a variable that may be optimized to a constant later. The number of cycles delayed by this builtin is exact.
This inserts a HALT instruction to stop processor execution.
This inserts LMBD instruction to calculate the left-most bit with value bitval in value wordval. Only the least significant bit of bitval is taken into account.
These built-in functions are available for the RISC-V family of processors.
Returns the value that is currently set in the ‘tp’ register.
Generates the
pause(hint) machine instruction. This implies the Xgnuzihintpausestate extension, which redefines thepauseinstruction to change architectural state.
GCC supports vector intrinsics as specified in version 0.11 of the RISC-V vector intrinsic specification, which is available at the following link: https://github.com/riscv-non-isa/rvv-intrinsic-doc/tree/v0.11.x. All of these functions are declared in the include file riscv_vector.h.
GCC supports some of the RX instructions which cannot be expressed in the C programming language via the use of built-in functions. The following functions are supported:
Generates the
clrpswmachine instruction to clear the specified bit in the processor status word.
Generates the
intmachine instruction to generate an interrupt with the specified value.
Generates the
machimachine instruction to add the result of multiplying the top 16 bits of the two arguments into the accumulator.
Generates the
maclomachine instruction to add the result of multiplying the bottom 16 bits of the two arguments into the accumulator.
Generates the
mulhimachine instruction to place the result of multiplying the top 16 bits of the two arguments into the accumulator.
Generates the
mullomachine instruction to place the result of multiplying the bottom 16 bits of the two arguments into the accumulator.
Generates the
mvfachimachine instruction to read the top 32 bits of the accumulator.
Generates the
mvfacmimachine instruction to read the middle 32 bits of the accumulator.
Generates the
mvfcmachine instruction which reads the control register specified in its argument and returns its value.
Generates the
mvtachimachine instruction to set the top 32 bits of the accumulator.
Generates the
mvtaclomachine instruction to set the bottom 32 bits of the accumulator.
Generates the
mvtcmachine instruction which sets control register numberregtoval.
Generates the
mvtiplmachine instruction set the interrupt priority level.
Generates the
racwmachine instruction to round the accumulator according to the specified mode.
Generates the
revwmachine instruction which swaps the bytes in the argument so that bits 0–7 now occupy bits 8–15 and vice versa, and also bits 16–23 occupy bits 24–31 and vice versa.
Generates the
rmpamachine instruction which initiates a repeated multiply and accumulate sequence.
Generates the
roundmachine instruction which returns the floating-point argument rounded according to the current rounding mode set in the floating-point status word register.
Generates the
satmachine instruction which returns the saturated value of the argument.
Generates the
setpswmachine instruction to set the specified bit in the processor status word.
Generates the
tbeginmachine instruction starting a non-constrained hardware transaction. If the parameter is non-NULL the memory area is used to store the transaction diagnostic buffer and will be passed as first operand totbegin. This buffer can be defined using thestruct __htm_tdbC struct defined inhtmintrin.hand must reside on a double-word boundary. The second tbegin operand is set to0xff0c. This enables save/restore of all GPRs and disables aborts for FPR and AR manipulations inside the transaction body. The condition code set by the tbegin instruction is returned as integer value. The tbegin instruction by definition overwrites the content of all FPRs. The compiler will generate code which saves and restores the FPRs. For soft-float code it is recommended to used the*_nofloatvariant. In order to prevent a TDB from being written it is required to pass a constant zero value as parameter. Passing a zero value through a variable is not sufficient. Although modifications of access registers inside the transaction will not trigger an transaction abort it is not supported to actually modify them. Access registers do not get saved when entering a transaction. They will have undefined state when reaching the abort code.
Macros for the possible return codes of tbegin are defined in the
htmintrin.h header file:
tbeginhas been executed as part of normal processing. The transaction body is supposed to be executed.
The transaction was aborted due to an indeterminate condition which might be persistent.
The transaction aborted due to a transient failure. The transaction should be re-executed in that case.
The transaction aborted due to a persistent failure. Re-execution under same circumstances will not be productive.
The
_HTM_FIRST_USER_ABORT_CODEdefined inhtmintrin.hspecifies the first abort code which can be used for__builtin_tabort. Values below this threshold are reserved for machine use.
The
struct __htm_tdbdefined inhtmintrin.hdescribes the structure of the transaction diagnostic block as specified in the Principles of Operation manual chapter 5-91.
Same as
__builtin_tbeginbut without FPR saves and restores. Using this variant in code making use of FPRs will leave the FPRs in undefined state when entering the transaction abort handler code.
In addition to
__builtin_tbegina loop for transient failures is generated. If tbegin returns a condition code of 2 the transaction will be retried as often as specified in the second argument. The perform processor assist instruction is used to tell the CPU about the number of fails so far.
Same as
__builtin_tbegin_retrybut without FPR saves and restores. Using this variant in code making use of FPRs will leave the FPRs in undefined state when entering the transaction abort handler code.
Generates the
tbegincmachine instruction starting a constrained hardware transaction. The second operand is set to0xff08.
Generates the
tendmachine instruction finishing a transaction and making the changes visible to other threads. The condition code generated by tend is returned as integer value.
Generates the
tabortmachine instruction with the specified abort code. Abort codes from 0 through 255 are reserved and will result in an error message.
Generates the
ppa rX,rY,1machine instruction. Where the integer parameter is loaded into rX and a value of zero is loaded into rY. The integer parameter specifies the number of times the transaction repeatedly aborted.
Generates the
etndmachine instruction. The current nesting depth is returned as integer value. For a nesting depth of 0 the code is not executed as part of an transaction.
Generates the
ntstgmachine instruction. The second argument is written to the first arguments location. The store operation will not be rolled-back in case of an transaction abort.
The following built-in functions are supported on the SH1, SH2, SH3 and SH4 families of processors:
Sets the ‘GBR’ register to the specified value ptr. This is usually used by system code that manages threads and execution contexts. The compiler normally does not generate code that modifies the contents of ‘GBR’ and thus the value is preserved across function calls. Changing the ‘GBR’ value in user code must be done with caution, since the compiler might use ‘GBR’ in order to access thread local variables.
Returns the value that is currently set in the ‘GBR’ register. Memory loads and stores that use the thread pointer as a base address are turned into ‘GBR’ based displacement loads and stores, if possible. For example:
struct my_tcb { int a, b, c, d, e; }; int get_tcb_value (void) { // Generate ‘mov.l @(8,gbr),r0’ instruction return ((my_tcb*)__builtin_thread_pointer ())->c; }
Returns the value that is currently set in the ‘FPSCR’ register.
Sets the ‘FPSCR’ register to the specified value val, while preserving the current values of the FR, SZ and PR bits.
GCC supports SIMD operations on the SPARC using both the generic vector extensions (see Vector Extensions) as well as built-in functions for the SPARC Visual Instruction Set (VIS). When you use the -mvis switch, the VIS extension is exposed as the following built-in functions:
typedef int v1si __attribute__ ((vector_size (4)));
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef short v2hi __attribute__ ((vector_size (4)));
typedef unsigned char v8qi __attribute__ ((vector_size (8)));
typedef unsigned char v4qi __attribute__ ((vector_size (4)));
void __builtin_vis_write_gsr (int64_t);
int64_t __builtin_vis_read_gsr (void);
void * __builtin_vis_alignaddr (void *, long);
void * __builtin_vis_alignaddrl (void *, long);
int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
v2si __builtin_vis_faligndatav2si (v2si, v2si);
v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);
v4hi __builtin_vis_fexpand (v4qi);
v4hi __builtin_vis_fmul8x16 (v4qi, v4hi);
v4hi __builtin_vis_fmul8x16au (v4qi, v2hi);
v4hi __builtin_vis_fmul8x16al (v4qi, v2hi);
v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi);
v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi);
v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi);
v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi);
v4qi __builtin_vis_fpack16 (v4hi);
v8qi __builtin_vis_fpack32 (v2si, v8qi);
v2hi __builtin_vis_fpackfix (v2si);
v8qi __builtin_vis_fpmerge (v4qi, v4qi);
int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);
long __builtin_vis_edge8 (void *, void *);
long __builtin_vis_edge8l (void *, void *);
long __builtin_vis_edge16 (void *, void *);
long __builtin_vis_edge16l (void *, void *);
long __builtin_vis_edge32 (void *, void *);
long __builtin_vis_edge32l (void *, void *);
long __builtin_vis_fcmple16 (v4hi, v4hi);
long __builtin_vis_fcmple32 (v2si, v2si);
long __builtin_vis_fcmpne16 (v4hi, v4hi);
long __builtin_vis_fcmpne32 (v2si, v2si);
long __builtin_vis_fcmpgt16 (v4hi, v4hi);
long __builtin_vis_fcmpgt32 (v2si, v2si);
long __builtin_vis_fcmpeq16 (v4hi, v4hi);
long __builtin_vis_fcmpeq32 (v2si, v2si);
v4hi __builtin_vis_fpadd16 (v4hi, v4hi);
v2hi __builtin_vis_fpadd16s (v2hi, v2hi);
v2si __builtin_vis_fpadd32 (v2si, v2si);
v1si __builtin_vis_fpadd32s (v1si, v1si);
v4hi __builtin_vis_fpsub16 (v4hi, v4hi);
v2hi __builtin_vis_fpsub16s (v2hi, v2hi);
v2si __builtin_vis_fpsub32 (v2si, v2si);
v1si __builtin_vis_fpsub32s (v1si, v1si);
long __builtin_vis_array8 (long, long);
long __builtin_vis_array16 (long, long);
long __builtin_vis_array32 (long, long);
When you use the -mvis2 switch, the VIS version 2.0 built-in functions also become available:
long __builtin_vis_bmask (long, long);
int64_t __builtin_vis_bshuffledi (int64_t, int64_t);
v2si __builtin_vis_bshufflev2si (v2si, v2si);
v4hi __builtin_vis_bshufflev2si (v4hi, v4hi);
v8qi __builtin_vis_bshufflev2si (v8qi, v8qi);
long __builtin_vis_edge8n (void *, void *);
long __builtin_vis_edge8ln (void *, void *);
long __builtin_vis_edge16n (void *, void *);
long __builtin_vis_edge16ln (void *, void *);
long __builtin_vis_edge32n (void *, void *);
long __builtin_vis_edge32ln (void *, void *);
When you use the -mvis3 switch, the VIS version 3.0 built-in functions also become available:
void __builtin_vis_cmask8 (long);
void __builtin_vis_cmask16 (long);
void __builtin_vis_cmask32 (long);
v4hi __builtin_vis_fchksm16 (v4hi, v4hi);
v4hi __builtin_vis_fsll16 (v4hi, v4hi);
v4hi __builtin_vis_fslas16 (v4hi, v4hi);
v4hi __builtin_vis_fsrl16 (v4hi, v4hi);
v4hi __builtin_vis_fsra16 (v4hi, v4hi);
v2si __builtin_vis_fsll16 (v2si, v2si);
v2si __builtin_vis_fslas16 (v2si, v2si);
v2si __builtin_vis_fsrl16 (v2si, v2si);
v2si __builtin_vis_fsra16 (v2si, v2si);
long __builtin_vis_pdistn (v8qi, v8qi);
v4hi __builtin_vis_fmean16 (v4hi, v4hi);
int64_t __builtin_vis_fpadd64 (int64_t, int64_t);
int64_t __builtin_vis_fpsub64 (int64_t, int64_t);
v4hi __builtin_vis_fpadds16 (v4hi, v4hi);
v2hi __builtin_vis_fpadds16s (v2hi, v2hi);
v4hi __builtin_vis_fpsubs16 (v4hi, v4hi);
v2hi __builtin_vis_fpsubs16s (v2hi, v2hi);
v2si __builtin_vis_fpadds32 (v2si, v2si);
v1si __builtin_vis_fpadds32s (v1si, v1si);
v2si __builtin_vis_fpsubs32 (v2si, v2si);
v1si __builtin_vis_fpsubs32s (v1si, v1si);
long __builtin_vis_fucmple8 (v8qi, v8qi);
long __builtin_vis_fucmpne8 (v8qi, v8qi);
long __builtin_vis_fucmpgt8 (v8qi, v8qi);
long __builtin_vis_fucmpeq8 (v8qi, v8qi);
float __builtin_vis_fhadds (float, float);
double __builtin_vis_fhaddd (double, double);
float __builtin_vis_fhsubs (float, float);
double __builtin_vis_fhsubd (double, double);
float __builtin_vis_fnhadds (float, float);
double __builtin_vis_fnhaddd (double, double);
int64_t __builtin_vis_umulxhi (int64_t, int64_t);
int64_t __builtin_vis_xmulx (int64_t, int64_t);
int64_t __builtin_vis_xmulxhi (int64_t, int64_t);
When you use the -mvis4 switch, the VIS version 4.0 built-in functions also become available:
v8qi __builtin_vis_fpadd8 (v8qi, v8qi);
v8qi __builtin_vis_fpadds8 (v8qi, v8qi);
v8qi __builtin_vis_fpaddus8 (v8qi, v8qi);
v4hi __builtin_vis_fpaddus16 (v4hi, v4hi);
v8qi __builtin_vis_fpsub8 (v8qi, v8qi);
v8qi __builtin_vis_fpsubs8 (v8qi, v8qi);
v8qi __builtin_vis_fpsubus8 (v8qi, v8qi);
v4hi __builtin_vis_fpsubus16 (v4hi, v4hi);
long __builtin_vis_fpcmple8 (v8qi, v8qi);
long __builtin_vis_fpcmpgt8 (v8qi, v8qi);
long __builtin_vis_fpcmpule16 (v4hi, v4hi);
long __builtin_vis_fpcmpugt16 (v4hi, v4hi);
long __builtin_vis_fpcmpule32 (v2si, v2si);
long __builtin_vis_fpcmpugt32 (v2si, v2si);
v8qi __builtin_vis_fpmax8 (v8qi, v8qi);
v4hi __builtin_vis_fpmax16 (v4hi, v4hi);
v2si __builtin_vis_fpmax32 (v2si, v2si);
v8qi __builtin_vis_fpmaxu8 (v8qi, v8qi);
v4hi __builtin_vis_fpmaxu16 (v4hi, v4hi);
v2si __builtin_vis_fpmaxu32 (v2si, v2si);
v8qi __builtin_vis_fpmin8 (v8qi, v8qi);
v4hi __builtin_vis_fpmin16 (v4hi, v4hi);
v2si __builtin_vis_fpmin32 (v2si, v2si);
v8qi __builtin_vis_fpminu8 (v8qi, v8qi);
v4hi __builtin_vis_fpminu16 (v4hi, v4hi);
v2si __builtin_vis_fpminu32 (v2si, v2si);
When you use the -mvis4b switch, the VIS version 4.0B built-in functions also become available:
v8qi __builtin_vis_dictunpack8 (double, int);
v4hi __builtin_vis_dictunpack16 (double, int);
v2si __builtin_vis_dictunpack32 (double, int);
long __builtin_vis_fpcmple8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmpgt8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmpeq8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmpne8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmple16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmpgt16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmpeq16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmpne16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmple32shl (v2si, v2si, int);
long __builtin_vis_fpcmpgt32shl (v2si, v2si, int);
long __builtin_vis_fpcmpeq32shl (v2si, v2si, int);
long __builtin_vis_fpcmpne32shl (v2si, v2si, int);
long __builtin_vis_fpcmpule8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmpugt8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmpule16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmpugt16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmpule32shl (v2si, v2si, int);
long __builtin_vis_fpcmpugt32shl (v2si, v2si, int);
long __builtin_vis_fpcmpde8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmpde16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmpde32shl (v2si, v2si, int);
long __builtin_vis_fpcmpur8shl (v8qi, v8qi, int);
long __builtin_vis_fpcmpur16shl (v4hi, v4hi, int);
long __builtin_vis_fpcmpur32shl (v2si, v2si, int);
GCC provides intrinsics to access certain instructions of the TI C6X
processors. These intrinsics, listed below, are available after
inclusion of the c6x_intrinsics.h header file. They map directly
to C6X instructions.
int _sadd (int, int);
int _ssub (int, int);
int _sadd2 (int, int);
int _ssub2 (int, int);
long long _mpy2 (int, int);
long long _smpy2 (int, int);
int _add4 (int, int);
int _sub4 (int, int);
int _saddu4 (int, int);
int _smpy (int, int);
int _smpyh (int, int);
int _smpyhl (int, int);
int _smpylh (int, int);
int _sshl (int, int);
int _subc (int, int);
int _avg2 (int, int);
int _avgu4 (int, int);
int _clrr (int, int);
int _extr (int, int);
int _extru (int, int);
int _abs (int);
int _abs2 (int);
These built-in functions are available for the x86-32 and x86-64 family of computers, depending on the command-line switches used.
If you specify command-line switches such as -msse, the compiler could use the extended instruction sets even if the built-ins are not used explicitly in the program. For this reason, applications that perform run-time CPU detection must compile separate files for each supported architecture, using the appropriate flags. In particular, the file containing the CPU detection code should be compiled without these options.
The following machine modes are available for use with MMX built-in functions
(see Vector Extensions): V2SI for a vector of two 32-bit integers,
V4HI for a vector of four 16-bit integers, and V8QI for a
vector of eight 8-bit integers. Some of the built-in functions operate on
MMX registers as a whole 64-bit entity, these use V1DI as their mode.
If 3DNow! extensions are enabled, V2SF is used as a mode for a vector
of two 32-bit floating-point values.
If SSE extensions are enabled, V4SF is used for a vector of four 32-bit
floating-point values. Some instructions use a vector of four 32-bit
integers, these use V4SI. Finally, some instructions operate on an
entire vector register, interpreting it as a 128-bit integer, these use mode
TI.
The x86-32 and x86-64 family of processors use additional built-in
functions for efficient use of TF (__float128) 128-bit
floating point and TC 128-bit complex floating-point values.
The following floating-point built-in functions are always available:
Copies the sign of y into x and returns the new value of x.
Similar to
__builtin_inf, except the return type is__float128.
Similar to
__builtin_huge_val, except the return type is__float128.
Similar to
__builtin_nan, except the return type is__float128.
Similar to
__builtin_nans, except the return type is__float128.
The following built-in function is always available.
Generates the
pausemachine instruction with a compiler memory barrier.
The following built-in functions are always available and can be used to check the target platform type.
This function runs the CPU detection code to check the type of CPU and the features supported. This built-in function needs to be invoked along with the built-in functions to check CPU type and features,
__builtin_cpu_isand__builtin_cpu_supports, only when used in a function that is executed before any constructors are called. The CPU detection code is automatically executed in a very high priority constructor.For example, this function has to be used in
ifuncresolvers that check for CPU type using the built-in functions__builtin_cpu_isand__builtin_cpu_supports, or in constructors on targets that don't support constructor priority.static void (*resolve_memcpy (void)) (void) { // ifunc resolvers fire before constructors, explicitly call the init // function. __builtin_cpu_init (); if (__builtin_cpu_supports ("ssse3")) return ssse3_memcpy; // super fast memcpy with ssse3 instructions. else return default_memcpy; } void *memcpy (void *, const void *, size_t) __attribute__ ((ifunc ("resolve_memcpy")));
This function returns a positive integer if the run-time CPU is of type cpuname and returns
0otherwise. The following CPU names can be detected:
- ‘amd’
- AMD CPU.
- ‘intel’
- Intel CPU.
- ‘atom’
- Intel Atom CPU.
- ‘slm’
- Intel Silvermont CPU.
- ‘core2’
- Intel Core 2 CPU.
- ‘corei7’
- Intel Core i7 CPU.
- ‘nehalem’
- Intel Core i7 Nehalem CPU.
- ‘westmere’
- Intel Core i7 Westmere CPU.
- ‘sandybridge’
- Intel Core i7 Sandy Bridge CPU.
- ‘ivybridge’
- Intel Core i7 Ivy Bridge CPU.
- ‘haswell’
- Intel Core i7 Haswell CPU.
- ‘broadwell’
- Intel Core i7 Broadwell CPU.
- ‘skylake’
- Intel Core i7 Skylake CPU.
- ‘skylake-avx512’
- Intel Core i7 Skylake AVX512 CPU.
- ‘cannonlake’
- Intel Core i7 Cannon Lake CPU.
- ‘icelake-client’
- Intel Core i7 Ice Lake Client CPU.
- ‘icelake-server’
- Intel Core i7 Ice Lake Server CPU.
- ‘cascadelake’
- Intel Core i7 Cascadelake CPU.
- ‘tigerlake’
- Intel Core i7 Tigerlake CPU.
- ‘cooperlake’
- Intel Core i7 Cooperlake CPU.
- ‘sapphirerapids’
- Intel Core i7 sapphirerapids CPU.
- ‘alderlake’
- Intel Core i7 Alderlake CPU.
- ‘rocketlake’
- Intel Core i7 Rocketlake CPU.
- ‘graniterapids’
- Intel Core i7 graniterapids CPU.
- ‘graniterapids-d’
- Intel Core i7 graniterapids D CPU.
- ‘bonnell’
- Intel Atom Bonnell CPU.
- ‘silvermont’
- Intel Atom Silvermont CPU.
- ‘goldmont’
- Intel Atom Goldmont CPU.
- ‘goldmont-plus’
- Intel Atom Goldmont Plus CPU.
- ‘tremont’
- Intel Atom Tremont CPU.
- ‘sierraforest’
- Intel Atom Sierra Forest CPU.
- ‘grandridge’
- Intel Atom Grand Ridge CPU.
- ‘knl’
- Intel Knights Landing CPU.
- ‘knm’
- Intel Knights Mill CPU.
- ‘lujiazui’
- ZHAOXIN lujiazui CPU.
- ‘amdfam10h’
- AMD Family 10h CPU.
- ‘barcelona’
- AMD Family 10h Barcelona CPU.
- ‘shanghai’
- AMD Family 10h Shanghai CPU.
- ‘istanbul’
- AMD Family 10h Istanbul CPU.
- ‘btver1’
- AMD Family 14h CPU.
- ‘amdfam15h’
- AMD Family 15h CPU.
- ‘bdver1’
- AMD Family 15h Bulldozer version 1.
- ‘bdver2’
- AMD Family 15h Bulldozer version 2.
- ‘bdver3’
- AMD Family 15h Bulldozer version 3.
- ‘bdver4’
- AMD Family 15h Bulldozer version 4.
- ‘btver2’
- AMD Family 16h CPU.
- ‘amdfam17h’
- AMD Family 17h CPU.
- ‘znver1’
- AMD Family 17h Zen version 1.
- ‘znver2’
- AMD Family 17h Zen version 2.
- ‘amdfam19h’
- AMD Family 19h CPU.
- ‘znver3’
- AMD Family 19h Zen version 3.
- ‘znver4’
- AMD Family 19h Zen version 4.
- ‘znver5’
- AMD Family 1ah Zen version 5.
Here is an example:
if (__builtin_cpu_is ("corei7")) { do_corei7 (); // Core i7 specific implementation. } else { do_generic (); // Generic implementation. }
This function returns a positive integer if the run-time CPU supports feature and returns
0otherwise. The following features can be detected:
- ‘cmov’
- CMOV instruction.
- ‘mmx’
- MMX instructions.
- ‘popcnt’
- POPCNT instruction.
- ‘sse’
- SSE instructions.
- ‘sse2’
- SSE2 instructions.
- ‘sse3’
- SSE3 instructions.
- ‘ssse3’
- SSSE3 instructions.
- ‘sse4.1’
- SSE4.1 instructions.
- ‘sse4.2’
- SSE4.2 instructions.
- ‘avx’
- AVX instructions.
- ‘avx2’
- AVX2 instructions.
- ‘sse4a’
- SSE4A instructions.
- ‘fma4’
- FMA4 instructions.
- ‘xop’
- XOP instructions.
- ‘fma’
- FMA instructions.
- ‘avx512f’
- AVX512F instructions.
- ‘bmi’
- BMI instructions.
- ‘bmi2’
- BMI2 instructions.
- ‘aes’
- AES instructions.
- ‘pclmul’
- PCLMUL instructions.
- ‘avx512vl’
- AVX512VL instructions.
- ‘avx512bw’
- AVX512BW instructions.
- ‘avx512dq’
- AVX512DQ instructions.
- ‘avx512cd’
- AVX512CD instructions.
- ‘avx512er’
- AVX512ER instructions.
- ‘avx512pf’
- AVX512PF instructions.
- ‘avx512vbmi’
- AVX512VBMI instructions.
- ‘avx512ifma’
- AVX512IFMA instructions.
- ‘avx5124vnniw’
- AVX5124VNNIW instructions.
- ‘avx5124fmaps’
- AVX5124FMAPS instructions.
- ‘avx512vpopcntdq’
- AVX512VPOPCNTDQ instructions.
- ‘avx512vbmi2’
- AVX512VBMI2 instructions.
- ‘gfni’
- GFNI instructions.
- ‘vpclmulqdq’
- VPCLMULQDQ instructions.
- ‘avx512vnni’
- AVX512VNNI instructions.
- ‘avx512bitalg’
- AVX512BITALG instructions.
- ‘x86-64’
- Baseline x86-64 microarchitecture level (as defined in x86-64 psABI).
- ‘x86-64-v2’
- x86-64-v2 microarchitecture level.
- ‘x86-64-v3’
- x86-64-v3 microarchitecture level.
- ‘x86-64-v4’
- x86-64-v4 microarchitecture level.
Here is an example:
if (__builtin_cpu_supports ("popcnt")) { asm("popcnt %1,%0" : "=r"(count) : "rm"(n) : "cc"); } else { count = generic_countbits (n); //generic implementation. }
The following built-in functions are made available by -mmmx. All of them generate the machine instruction that is part of the name.
v8qi __builtin_ia32_paddb (v8qi, v8qi);
v4hi __builtin_ia32_paddw (v4hi, v4hi);
v2si __builtin_ia32_paddd (v2si, v2si);
v8qi __builtin_ia32_psubb (v8qi, v8qi);
v4hi __builtin_ia32_psubw (v4hi, v4hi);
v2si __builtin_ia32_psubd (v2si, v2si);
v8qi __builtin_ia32_paddsb (v8qi, v8qi);
v4hi __builtin_ia32_paddsw (v4hi, v4hi);
v8qi __builtin_ia32_psubsb (v8qi, v8qi);
v4hi __builtin_ia32_psubsw (v4hi, v4hi);
v8qi __builtin_ia32_paddusb (v8qi, v8qi);
v4hi __builtin_ia32_paddusw (v4hi, v4hi);
v8qi __builtin_ia32_psubusb (v8qi, v8qi);
v4hi __builtin_ia32_psubusw (v4hi, v4hi);
v4hi __builtin_ia32_pmullw (v4hi, v4hi);
v4hi __builtin_ia32_pmulhw (v4hi, v4hi);
di __builtin_ia32_pand (di, di);
di __builtin_ia32_pandn (di,di);
di __builtin_ia32_por (di, di);
di __builtin_ia32_pxor (di, di);
v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi);
v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi);
v2si __builtin_ia32_pcmpeqd (v2si, v2si);
v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi);
v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi);
v2si __builtin_ia32_pcmpgtd (v2si, v2si);
v8qi __builtin_ia32_punpckhbw (v8qi, v8qi);
v4hi __builtin_ia32_punpckhwd (v4hi, v4hi);
v2si __builtin_ia32_punpckhdq (v2si, v2si);
v8qi __builtin_ia32_punpcklbw (v8qi, v8qi);
v4hi __builtin_ia32_punpcklwd (v4hi, v4hi);
v2si __builtin_ia32_punpckldq (v2si, v2si);
v8qi __builtin_ia32_packsswb (v4hi, v4hi);
v4hi __builtin_ia32_packssdw (v2si, v2si);
v8qi __builtin_ia32_packuswb (v4hi, v4hi);
v4hi __builtin_ia32_psllw (v4hi, v4hi);
v2si __builtin_ia32_pslld (v2si, v2si);
v1di __builtin_ia32_psllq (v1di, v1di);
v4hi __builtin_ia32_psrlw (v4hi, v4hi);
v2si __builtin_ia32_psrld (v2si, v2si);
v1di __builtin_ia32_psrlq (v1di, v1di);
v4hi __builtin_ia32_psraw (v4hi, v4hi);
v2si __builtin_ia32_psrad (v2si, v2si);
v4hi __builtin_ia32_psllwi (v4hi, int);
v2si __builtin_ia32_pslldi (v2si, int);
v1di __builtin_ia32_psllqi (v1di, int);
v4hi __builtin_ia32_psrlwi (v4hi, int);
v2si __builtin_ia32_psrldi (v2si, int);
v1di __builtin_ia32_psrlqi (v1di, int);
v4hi __builtin_ia32_psrawi (v4hi, int);
v2si __builtin_ia32_psradi (v2si, int);
The following built-in functions are made available either with -msse, or with -m3dnowa. All of them generate the machine instruction that is part of the name.
v4hi __builtin_ia32_pmulhuw (v4hi, v4hi);
v8qi __builtin_ia32_pavgb (v8qi, v8qi);
v4hi __builtin_ia32_pavgw (v4hi, v4hi);
v1di __builtin_ia32_psadbw (v8qi, v8qi);
v8qi __builtin_ia32_pmaxub (v8qi, v8qi);
v4hi __builtin_ia32_pmaxsw (v4hi, v4hi);
v8qi __builtin_ia32_pminub (v8qi, v8qi);
v4hi __builtin_ia32_pminsw (v4hi, v4hi);
int __builtin_ia32_pmovmskb (v8qi);
void __builtin_ia32_maskmovq (v8qi, v8qi, char *);
void __builtin_ia32_movntq (di *, di);
void __builtin_ia32_sfence (void);
The following built-in functions are available when -msse is used. All of them generate the machine instruction that is part of the name.
int __builtin_ia32_comieq (v4sf, v4sf);
int __builtin_ia32_comineq (v4sf, v4sf);
int __builtin_ia32_comilt (v4sf, v4sf);
int __builtin_ia32_comile (v4sf, v4sf);
int __builtin_ia32_comigt (v4sf, v4sf);
int __builtin_ia32_comige (v4sf, v4sf);
int __builtin_ia32_ucomieq (v4sf, v4sf);
int __builtin_ia32_ucomineq (v4sf, v4sf);
int __builtin_ia32_ucomilt (v4sf, v4sf);
int __builtin_ia32_ucomile (v4sf, v4sf);
int __builtin_ia32_ucomigt (v4sf, v4sf);
int __builtin_ia32_ucomige (v4sf, v4sf);
v4sf __builtin_ia32_addps (v4sf, v4sf);
v4sf __builtin_ia32_subps (v4sf, v4sf);
v4sf __builtin_ia32_mulps (v4sf, v4sf);
v4sf __builtin_ia32_divps (v4sf, v4sf);
v4sf __builtin_ia32_addss (v4sf, v4sf);
v4sf __builtin_ia32_subss (v4sf, v4sf);
v4sf __builtin_ia32_mulss (v4sf, v4sf);
v4sf __builtin_ia32_divss (v4sf, v4sf);
v4sf __builtin_ia32_cmpeqps (v4sf, v4sf);
v4sf __builtin_ia32_cmpltps (v4sf, v4sf);
v4sf __builtin_ia32_cmpleps (v4sf, v4sf);
v4sf __builtin_ia32_cmpgtps (v4sf, v4sf);
v4sf __builtin_ia32_cmpgeps (v4sf, v4sf);
v4sf __builtin_ia32_cmpunordps (v4sf, v4sf);
v4sf __builtin_ia32_cmpneqps (v4sf, v4sf);
v4sf __builtin_ia32_cmpnltps (v4sf, v4sf);
v4sf __builtin_ia32_cmpnleps (v4sf, v4sf);
v4sf __builtin_ia32_cmpngtps (v4sf, v4sf);
v4sf __builtin_ia32_cmpngeps (v4sf, v4sf);
v4sf __builtin_ia32_cmpordps (v4sf, v4sf);
v4sf __builtin_ia32_cmpeqss (v4sf, v4sf);
v4sf __builtin_ia32_cmpltss (v4sf, v4sf);
v4sf __builtin_ia32_cmpless (v4sf, v4sf);
v4sf __builtin_ia32_cmpunordss (v4sf, v4sf);
v4sf __builtin_ia32_cmpneqss (v4sf, v4sf);
v4sf __builtin_ia32_cmpnltss (v4sf, v4sf);
v4sf __builtin_ia32_cmpnless (v4sf, v4sf);
v4sf __builtin_ia32_cmpordss (v4sf, v4sf);
v4sf __builtin_ia32_maxps (v4sf, v4sf);
v4sf __builtin_ia32_maxss (v4sf, v4sf);
v4sf __builtin_ia32_minps (v4sf, v4sf);
v4sf __builtin_ia32_minss (v4sf, v4sf);
v4sf __builtin_ia32_andps (v4sf, v4sf);
v4sf __builtin_ia32_andnps (v4sf, v4sf);
v4sf __builtin_ia32_orps (v4sf, v4sf);
v4sf __builtin_ia32_xorps (v4sf, v4sf);
v4sf __builtin_ia32_movss (v4sf, v4sf);
v4sf __builtin_ia32_movhlps (v4sf, v4sf);
v4sf __builtin_ia32_movlhps (v4sf, v4sf);
v4sf __builtin_ia32_unpckhps (v4sf, v4sf);
v4sf __builtin_ia32_unpcklps (v4sf, v4sf);
v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si);
v4sf __builtin_ia32_cvtsi2ss (v4sf, int);
v2si __builtin_ia32_cvtps2pi (v4sf);
int __builtin_ia32_cvtss2si (v4sf);
v2si __builtin_ia32_cvttps2pi (v4sf);
int __builtin_ia32_cvttss2si (v4sf);
v4sf __builtin_ia32_rcpps (v4sf);
v4sf __builtin_ia32_rsqrtps (v4sf);
v4sf __builtin_ia32_sqrtps (v4sf);
v4sf __builtin_ia32_rcpss (v4sf);
v4sf __builtin_ia32_rsqrtss (v4sf);
v4sf __builtin_ia32_sqrtss (v4sf);
v4sf __builtin_ia32_shufps (v4sf, v4sf, int);
void __builtin_ia32_movntps (float *, v4sf);
int __builtin_ia32_movmskps (v4sf);
The following built-in functions are available when -msse is used.
Generates the
movupsmachine instruction as a load from memory.
Generates the
movupsmachine instruction as a store to memory.
Generates the
movssmachine instruction as a load from memory.
Generates the
movhpsmachine instruction as a load from memory.
Generates the
movlpsmachine instruction as a load from memory
Generates the
movhpsmachine instruction as a store to memory.
Generates the
movlpsmachine instruction as a store to memory.
The following built-in functions are available when -msse2 is used. All of them generate the machine instruction that is part of the name.
int __builtin_ia32_comisdeq (v2df, v2df);
int __builtin_ia32_comisdlt (v2df, v2df);
int __builtin_ia32_comisdle (v2df, v2df);
int __builtin_ia32_comisdgt (v2df, v2df);
int __builtin_ia32_comisdge (v2df, v2df);
int __builtin_ia32_comisdneq (v2df, v2df);
int __builtin_ia32_ucomisdeq (v2df, v2df);
int __builtin_ia32_ucomisdlt (v2df, v2df);
int __builtin_ia32_ucomisdle (v2df, v2df);
int __builtin_ia32_ucomisdgt (v2df, v2df);
int __builtin_ia32_ucomisdge (v2df, v2df);
int __builtin_ia32_ucomisdneq (v2df, v2df);
v2df __builtin_ia32_cmpeqpd (v2df, v2df);
v2df __builtin_ia32_cmpltpd (v2df, v2df);
v2df __builtin_ia32_cmplepd (v2df, v2df);
v2df __builtin_ia32_cmpgtpd (v2df, v2df);
v2df __builtin_ia32_cmpgepd (v2df, v2df);
v2df __builtin_ia32_cmpunordpd (v2df, v2df);
v2df __builtin_ia32_cmpneqpd (v2df, v2df);
v2df __builtin_ia32_cmpnltpd (v2df, v2df);
v2df __builtin_ia32_cmpnlepd (v2df, v2df);
v2df __builtin_ia32_cmpngtpd (v2df, v2df);
v2df __builtin_ia32_cmpngepd (v2df, v2df);
v2df __builtin_ia32_cmpordpd (v2df, v2df);
v2df __builtin_ia32_cmpeqsd (v2df, v2df);
v2df __builtin_ia32_cmpltsd (v2df, v2df);
v2df __builtin_ia32_cmplesd (v2df, v2df);
v2df __builtin_ia32_cmpunordsd (v2df, v2df);
v2df __builtin_ia32_cmpneqsd (v2df, v2df);
v2df __builtin_ia32_cmpnltsd (v2df, v2df);
v2df __builtin_ia32_cmpnlesd (v2df, v2df);
v2df __builtin_ia32_cmpordsd (v2df, v2df);
v2di __builtin_ia32_paddq (v2di, v2di);
v2di __builtin_ia32_psubq (v2di, v2di);
v2df __builtin_ia32_addpd (v2df, v2df);
v2df __builtin_ia32_subpd (v2df, v2df);
v2df __builtin_ia32_mulpd (v2df, v2df);
v2df __builtin_ia32_divpd (v2df, v2df);
v2df __builtin_ia32_addsd (v2df, v2df);
v2df __builtin_ia32_subsd (v2df, v2df);
v2df __builtin_ia32_mulsd (v2df, v2df);
v2df __builtin_ia32_divsd (v2df, v2df);
v2df __builtin_ia32_minpd (v2df, v2df);
v2df __builtin_ia32_maxpd (v2df, v2df);
v2df __builtin_ia32_minsd (v2df, v2df);
v2df __builtin_ia32_maxsd (v2df, v2df);
v2df __builtin_ia32_andpd (v2df, v2df);
v2df __builtin_ia32_andnpd (v2df, v2df);
v2df __builtin_ia32_orpd (v2df, v2df);
v2df __builtin_ia32_xorpd (v2df, v2df);
v2df __builtin_ia32_movsd (v2df, v2df);
v2df __builtin_ia32_unpckhpd (v2df, v2df);
v2df __builtin_ia32_unpcklpd (v2df, v2df);
v16qi __builtin_ia32_paddb128 (v16qi, v16qi);
v8hi __builtin_ia32_paddw128 (v8hi, v8hi);
v4si __builtin_ia32_paddd128 (v4si, v4si);
v2di __builtin_ia32_paddq128 (v2di, v2di);
v16qi __builtin_ia32_psubb128 (v16qi, v16qi);
v8hi __builtin_ia32_psubw128 (v8hi, v8hi);
v4si __builtin_ia32_psubd128 (v4si, v4si);
v2di __builtin_ia32_psubq128 (v2di, v2di);
v8hi __builtin_ia32_pmullw128 (v8hi, v8hi);
v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi);
v2di __builtin_ia32_pand128 (v2di, v2di);
v2di __builtin_ia32_pandn128 (v2di, v2di);
v2di __builtin_ia32_por128 (v2di, v2di);
v2di __builtin_ia32_pxor128 (v2di, v2di);
v16qi __builtin_ia32_pavgb128 (v16qi, v16qi);
v8hi __builtin_ia32_pavgw128 (v8hi, v8hi);
v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi);
v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi);
v4si __builtin_ia32_pcmpeqd128 (v4si, v4si);
v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi);
v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi);
v4si __builtin_ia32_pcmpgtd128 (v4si, v4si);
v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi);
v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi);
v16qi __builtin_ia32_pminub128 (v16qi, v16qi);
v8hi __builtin_ia32_pminsw128 (v8hi, v8hi);
v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi);
v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi);
v4si __builtin_ia32_punpckhdq128 (v4si, v4si);
v2di __builtin_ia32_punpckhqdq128 (v2di, v2di);
v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi);
v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi);
v4si __builtin_ia32_punpckldq128 (v4si, v4si);
v2di __builtin_ia32_punpcklqdq128 (v2di, v2di);
v16qi __builtin_ia32_packsswb128 (v8hi, v8hi);
v8hi __builtin_ia32_packssdw128 (v4si, v4si);
v16qi __builtin_ia32_packuswb128 (v8hi, v8hi);
v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi);
void __builtin_ia32_maskmovdqu (v16qi, v16qi);
v2df __builtin_ia32_loadupd (double *);
void __builtin_ia32_storeupd (double *, v2df);
v2df __builtin_ia32_loadhpd (v2df, double const *);
v2df __builtin_ia32_loadlpd (v2df, double const *);
int __builtin_ia32_movmskpd (v2df);
int __builtin_ia32_pmovmskb128 (v16qi);
void __builtin_ia32_movnti (int *, int);
void __builtin_ia32_movnti64 (long long int *, long long int);
void __builtin_ia32_movntpd (double *, v2df);
void __builtin_ia32_movntdq (v2df *, v2df);
v4si __builtin_ia32_pshufd (v4si, int);
v8hi __builtin_ia32_pshuflw (v8hi, int);
v8hi __builtin_ia32_pshufhw (v8hi, int);
v2di __builtin_ia32_psadbw128 (v16qi, v16qi);
v2df __builtin_ia32_sqrtpd (v2df);
v2df __builtin_ia32_sqrtsd (v2df);
v2df __builtin_ia32_shufpd (v2df, v2df, int);
v2df __builtin_ia32_cvtdq2pd (v4si);
v4sf __builtin_ia32_cvtdq2ps (v4si);
v4si __builtin_ia32_cvtpd2dq (v2df);
v2si __builtin_ia32_cvtpd2pi (v2df);
v4sf __builtin_ia32_cvtpd2ps (v2df);
v4si __builtin_ia32_cvttpd2dq (v2df);
v2si __builtin_ia32_cvttpd2pi (v2df);
v2df __builtin_ia32_cvtpi2pd (v2si);
int __builtin_ia32_cvtsd2si (v2df);
int __builtin_ia32_cvttsd2si (v2df);
long long __builtin_ia32_cvtsd2si64 (v2df);
long long __builtin_ia32_cvttsd2si64 (v2df);
v4si __builtin_ia32_cvtps2dq (v4sf);
v2df __builtin_ia32_cvtps2pd (v4sf);
v4si __builtin_ia32_cvttps2dq (v4sf);
v2df __builtin_ia32_cvtsi2sd (v2df, int);
v2df __builtin_ia32_cvtsi642sd (v2df, long long);
v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df);
v2df __builtin_ia32_cvtss2sd (v2df, v4sf);
void __builtin_ia32_clflush (const void *);
void __builtin_ia32_lfence (void);
void __builtin_ia32_mfence (void);
v16qi __builtin_ia32_loaddqu (const char *);
void __builtin_ia32_storedqu (char *, v16qi);
v1di __builtin_ia32_pmuludq (v2si, v2si);
v2di __builtin_ia32_pmuludq128 (v4si, v4si);
v8hi __builtin_ia32_psllw128 (v8hi, v8hi);
v4si __builtin_ia32_pslld128 (v4si, v4si);
v2di __builtin_ia32_psllq128 (v2di, v2di);
v8hi __builtin_ia32_psrlw128 (v8hi, v8hi);
v4si __builtin_ia32_psrld128 (v4si, v4si);
v2di __builtin_ia32_psrlq128 (v2di, v2di);
v8hi __builtin_ia32_psraw128 (v8hi, v8hi);
v4si __builtin_ia32_psrad128 (v4si, v4si);
v2di __builtin_ia32_pslldqi128 (v2di, int);
v8hi __builtin_ia32_psllwi128 (v8hi, int);
v4si __builtin_ia32_pslldi128 (v4si, int);
v2di __builtin_ia32_psllqi128 (v2di, int);
v2di __builtin_ia32_psrldqi128 (v2di, int);
v8hi __builtin_ia32_psrlwi128 (v8hi, int);
v4si __builtin_ia32_psrldi128 (v4si, int);
v2di __builtin_ia32_psrlqi128 (v2di, int);
v8hi __builtin_ia32_psrawi128 (v8hi, int);
v4si __builtin_ia32_psradi128 (v4si, int);
v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi);
v2di __builtin_ia32_movq128 (v2di);
The following built-in functions are available when -msse3 is used. All of them generate the machine instruction that is part of the name.
v2df __builtin_ia32_addsubpd (v2df, v2df);
v4sf __builtin_ia32_addsubps (v4sf, v4sf);
v2df __builtin_ia32_haddpd (v2df, v2df);
v4sf __builtin_ia32_haddps (v4sf, v4sf);
v2df __builtin_ia32_hsubpd (v2df, v2df);
v4sf __builtin_ia32_hsubps (v4sf, v4sf);
v16qi __builtin_ia32_lddqu (char const *);
void __builtin_ia32_monitor (void *, unsigned int, unsigned int);
v4sf __builtin_ia32_movshdup (v4sf);
v4sf __builtin_ia32_movsldup (v4sf);
void __builtin_ia32_mwait (unsigned int, unsigned int);
The following built-in functions are available when -mssse3 is used. All of them generate the machine instruction that is part of the name.
v2si __builtin_ia32_phaddd (v2si, v2si);
v4hi __builtin_ia32_phaddw (v4hi, v4hi);
v4hi __builtin_ia32_phaddsw (v4hi, v4hi);
v2si __builtin_ia32_phsubd (v2si, v2si);
v4hi __builtin_ia32_phsubw (v4hi, v4hi);
v4hi __builtin_ia32_phsubsw (v4hi, v4hi);
v4hi __builtin_ia32_pmaddubsw (v8qi, v8qi);
v4hi __builtin_ia32_pmulhrsw (v4hi, v4hi);
v8qi __builtin_ia32_pshufb (v8qi, v8qi);
v8qi __builtin_ia32_psignb (v8qi, v8qi);
v2si __builtin_ia32_psignd (v2si, v2si);
v4hi __builtin_ia32_psignw (v4hi, v4hi);
v1di __builtin_ia32_palignr (v1di, v1di, int);
v8qi __builtin_ia32_pabsb (v8qi);
v2si __builtin_ia32_pabsd (v2si);
v4hi __builtin_ia32_pabsw (v4hi);
The following built-in functions are available when -mssse3 is used. All of them generate the machine instruction that is part of the name.
v4si __builtin_ia32_phaddd128 (v4si, v4si);
v8hi __builtin_ia32_phaddw128 (v8hi, v8hi);
v8hi __builtin_ia32_phaddsw128 (v8hi, v8hi);
v4si __builtin_ia32_phsubd128 (v4si, v4si);
v8hi __builtin_ia32_phsubw128 (v8hi, v8hi);
v8hi __builtin_ia32_phsubsw128 (v8hi, v8hi);
v8hi __builtin_ia32_pmaddubsw128 (v16qi, v16qi);
v8hi __builtin_ia32_pmulhrsw128 (v8hi, v8hi);
v16qi __builtin_ia32_pshufb128 (v16qi, v16qi);
v16qi __builtin_ia32_psignb128 (v16qi, v16qi);
v4si __builtin_ia32_psignd128 (v4si, v4si);
v8hi __builtin_ia32_psignw128 (v8hi, v8hi);
v2di __builtin_ia32_palignr128 (v2di, v2di, int);
v16qi __builtin_ia32_pabsb128 (v16qi);
v4si __builtin_ia32_pabsd128 (v4si);
v8hi __builtin_ia32_pabsw128 (v8hi);
The following built-in functions are available when -msse4.1 is used. All of them generate the machine instruction that is part of the name.
v2df __builtin_ia32_blendpd (v2df, v2df, const int);
v4sf __builtin_ia32_blendps (v4sf, v4sf, const int);
v2df __builtin_ia32_blendvpd (v2df, v2df, v2df);
v4sf __builtin_ia32_blendvps (v4sf, v4sf, v4sf);
v2df __builtin_ia32_dppd (v2df, v2df, const int);
v4sf __builtin_ia32_dpps (v4sf, v4sf, const int);
v4sf __builtin_ia32_insertps128 (v4sf, v4sf, const int);
v2di __builtin_ia32_movntdqa (v2di *);
v16qi __builtin_ia32_mpsadbw128 (v16qi, v16qi, const int);
v8hi __builtin_ia32_packusdw128 (v4si, v4si);
v16qi __builtin_ia32_pblendvb128 (v16qi, v16qi, v16qi);
v8hi __builtin_ia32_pblendw128 (v8hi, v8hi, const int);
v2di __builtin_ia32_pcmpeqq (v2di, v2di);
v8hi __builtin_ia32_phminposuw128 (v8hi);
v16qi __builtin_ia32_pmaxsb128 (v16qi, v16qi);
v4si __builtin_ia32_pmaxsd128 (v4si, v4si);
v4si __builtin_ia32_pmaxud128 (v4si, v4si);
v8hi __builtin_ia32_pmaxuw128 (v8hi, v8hi);
v16qi __builtin_ia32_pminsb128 (v16qi, v16qi);
v4si __builtin_ia32_pminsd128 (v4si, v4si);
v4si __builtin_ia32_pminud128 (v4si, v4si);
v8hi __builtin_ia32_pminuw128 (v8hi, v8hi);
v4si __builtin_ia32_pmovsxbd128 (v16qi);
v2di __builtin_ia32_pmovsxbq128 (v16qi);
v8hi __builtin_ia32_pmovsxbw128 (v16qi);
v2di __builtin_ia32_pmovsxdq128 (v4si);
v4si __builtin_ia32_pmovsxwd128 (v8hi);
v2di __builtin_ia32_pmovsxwq128 (v8hi);
v4si __builtin_ia32_pmovzxbd128 (v16qi);
v2di __builtin_ia32_pmovzxbq128 (v16qi);
v8hi __builtin_ia32_pmovzxbw128 (v16qi);
v2di __builtin_ia32_pmovzxdq128 (v4si);
v4si __builtin_ia32_pmovzxwd128 (v8hi);
v2di __builtin_ia32_pmovzxwq128 (v8hi);
v2di __builtin_ia32_pmuldq128 (v4si, v4si);
v4si __builtin_ia32_pmulld128 (v4si, v4si);
int __builtin_ia32_ptestc128 (v2di, v2di);
int __builtin_ia32_ptestnzc128 (v2di, v2di);
int __builtin_ia32_ptestz128 (v2di, v2di);
v2df __builtin_ia32_roundpd (v2df, const int);
v4sf __builtin_ia32_roundps (v4sf, const int);
v2df __builtin_ia32_roundsd (v2df, v2df, const int);
v4sf __builtin_ia32_roundss (v4sf, v4sf, const int);
The following built-in functions are available when -msse4.1 is used.
Generates the
insertpsmachine instruction.
Generates the
pextrbmachine instruction.
Generates the
pinsrbmachine instruction.
Generates the
pinsrdmachine instruction.
Generates the
pinsrqmachine instruction in 64bit mode.
The following built-in functions are changed to generate new SSE4.1 instructions when -msse4.1 is used.
Generates the
extractpsmachine instruction.
Generates the
pextrdmachine instruction.
Generates the
pextrqmachine instruction in 64bit mode.
The following built-in functions are available when -msse4.2 is used. All of them generate the machine instruction that is part of the name.
v16qi __builtin_ia32_pcmpestrm128 (v16qi, int, v16qi, int, const int);
int __builtin_ia32_pcmpestri128 (v16qi, int, v16qi, int, const int);
int __builtin_ia32_pcmpestria128 (v16qi, int, v16qi, int, const int);
int __builtin_ia32_pcmpestric128 (v16qi, int, v16qi, int, const int);
int __builtin_ia32_pcmpestrio128 (v16qi, int, v16qi, int, const int);
int __builtin_ia32_pcmpestris128 (v16qi, int, v16qi, int, const int);
int __builtin_ia32_pcmpestriz128 (v16qi, int, v16qi, int, const int);
v16qi __builtin_ia32_pcmpistrm128 (v16qi, v16qi, const int);
int __builtin_ia32_pcmpistri128 (v16qi, v16qi, const int);
int __builtin_ia32_pcmpistria128 (v16qi, v16qi, const int);
int __builtin_ia32_pcmpistric128 (v16qi, v16qi, const int);
int __builtin_ia32_pcmpistrio128 (v16qi, v16qi, const int);
int __builtin_ia32_pcmpistris128 (v16qi, v16qi, const int);
int __builtin_ia32_pcmpistriz128 (v16qi, v16qi, const int);
v2di __builtin_ia32_pcmpgtq (v2di, v2di);
The following built-in functions are available when -msse4.2 is used.
Generates the
crc32bmachine instruction.
Generates the
crc32wmachine instruction.
Generates the
crc32lmachine instruction.
Generates the
crc32qmachine instruction.
The following built-in functions are changed to generate new SSE4.2 instructions when -msse4.2 is used.
Generates the
popcntlmachine instruction.
Generates the
popcntlorpopcntqmachine instruction, depending on the size ofunsigned long.
Generates the
popcntqmachine instruction.
The following built-in functions are available when -mavx is used. All of them generate the machine instruction that is part of the name.
v4df __builtin_ia32_addpd256 (v4df,v4df);
v8sf __builtin_ia32_addps256 (v8sf,v8sf);
v4df __builtin_ia32_addsubpd256 (v4df,v4df);
v8sf __builtin_ia32_addsubps256 (v8sf,v8sf);
v4df __builtin_ia32_andnpd256 (v4df,v4df);
v8sf __builtin_ia32_andnps256 (v8sf,v8sf);
v4df __builtin_ia32_andpd256 (v4df,v4df);
v8sf __builtin_ia32_andps256 (v8sf,v8sf);
v4df __builtin_ia32_blendpd256 (v4df,v4df,int);
v8sf __builtin_ia32_blendps256 (v8sf,v8sf,int);
v4df __builtin_ia32_blendvpd256 (v4df,v4df,v4df);
v8sf __builtin_ia32_blendvps256 (v8sf,v8sf,v8sf);
v2df __builtin_ia32_cmppd (v2df,v2df,int);
v4df __builtin_ia32_cmppd256 (v4df,v4df,int);
v4sf __builtin_ia32_cmpps (v4sf,v4sf,int);
v8sf __builtin_ia32_cmpps256 (v8sf,v8sf,int);
v2df __builtin_ia32_cmpsd (v2df,v2df,int);
v4sf __builtin_ia32_cmpss (v4sf,v4sf,int);
v4df __builtin_ia32_cvtdq2pd256 (v4si);
v8sf __builtin_ia32_cvtdq2ps256 (v8si);
v4si __builtin_ia32_cvtpd2dq256 (v4df);
v4sf __builtin_ia32_cvtpd2ps256 (v4df);
v8si __builtin_ia32_cvtps2dq256 (v8sf);
v4df __builtin_ia32_cvtps2pd256 (v4sf);
v4si __builtin_ia32_cvttpd2dq256 (v4df);
v8si __builtin_ia32_cvttps2dq256 (v8sf);
v4df __builtin_ia32_divpd256 (v4df,v4df);
v8sf __builtin_ia32_divps256 (v8sf,v8sf);
v8sf __builtin_ia32_dpps256 (v8sf,v8sf,int);
v4df __builtin_ia32_haddpd256 (v4df,v4df);
v8sf __builtin_ia32_haddps256 (v8sf,v8sf);
v4df __builtin_ia32_hsubpd256 (v4df,v4df);
v8sf __builtin_ia32_hsubps256 (v8sf,v8sf);
v32qi __builtin_ia32_lddqu256 (pcchar);
v32qi __builtin_ia32_loaddqu256 (pcchar);
v4df __builtin_ia32_loadupd256 (pcdouble);
v8sf __builtin_ia32_loadups256 (pcfloat);
v2df __builtin_ia32_maskloadpd (pcv2df,v2df);
v4df __builtin_ia32_maskloadpd256 (pcv4df,v4df);
v4sf __builtin_ia32_maskloadps (pcv4sf,v4sf);
v8sf __builtin_ia32_maskloadps256 (pcv8sf,v8sf);
void __builtin_ia32_maskstorepd (pv2df,v2df,v2df);
void __builtin_ia32_maskstorepd256 (pv4df,v4df,v4df);
void __builtin_ia32_maskstoreps (pv4sf,v4sf,v4sf);
void __builtin_ia32_maskstoreps256 (pv8sf,v8sf,v8sf);
v4df __builtin_ia32_maxpd256 (v4df,v4df);
v8sf __builtin_ia32_maxps256 (v8sf,v8sf);
v4df __builtin_ia32_minpd256 (v4df,v4df);
v8sf __builtin_ia32_minps256 (v8sf,v8sf);
v4df __builtin_ia32_movddup256 (v4df);
int __builtin_ia32_movmskpd256 (v4df);
int __builtin_ia32_movmskps256 (v8sf);
v8sf __builtin_ia32_movshdup256 (v8sf);
v8sf __builtin_ia32_movsldup256 (v8sf);
v4df __builtin_ia32_mulpd256 (v4df,v4df);
v8sf __builtin_ia32_mulps256 (v8sf,v8sf);
v4df __builtin_ia32_orpd256 (v4df,v4df);
v8sf __builtin_ia32_orps256 (v8sf,v8sf);
v2df __builtin_ia32_pd_pd256 (v4df);
v4df __builtin_ia32_pd256_pd (v2df);
v4sf __builtin_ia32_ps_ps256 (v8sf);
v8sf __builtin_ia32_ps256_ps (v4sf);
int __builtin_ia32_ptestc256 (v4di,v4di,ptest);
int __builtin_ia32_ptestnzc256 (v4di,v4di,ptest);
int __builtin_ia32_ptestz256 (v4di,v4di,ptest);
v8sf __builtin_ia32_rcpps256 (v8sf);
v4df __builtin_ia32_roundpd256 (v4df,int);
v8sf __builtin_ia32_roundps256 (v8sf,int);
v8sf __builtin_ia32_rsqrtps_nr256 (v8sf);
v8sf __builtin_ia32_rsqrtps256 (v8sf);
v4df __builtin_ia32_shufpd256 (v4df,v4df,int);
v8sf __builtin_ia32_shufps256 (v8sf,v8sf,int);
v4si __builtin_ia32_si_si256 (v8si);
v8si __builtin_ia32_si256_si (v4si);
v4df __builtin_ia32_sqrtpd256 (v4df);
v8sf __builtin_ia32_sqrtps_nr256 (v8sf);
v8sf __builtin_ia32_sqrtps256 (v8sf);
void __builtin_ia32_storedqu256 (pchar,v32qi);
void __builtin_ia32_storeupd256 (pdouble,v4df);
void __builtin_ia32_storeups256 (pfloat,v8sf);
v4df __builtin_ia32_subpd256 (v4df,v4df);
v8sf __builtin_ia32_subps256 (v8sf,v8sf);
v4df __builtin_ia32_unpckhpd256 (v4df,v4df);
v8sf __builtin_ia32_unpckhps256 (v8sf,v8sf);
v4df __builtin_ia32_unpcklpd256 (v4df,v4df);
v8sf __builtin_ia32_unpcklps256 (v8sf,v8sf);
v4df __builtin_ia32_vbroadcastf128_pd256 (pcv2df);
v8sf __builtin_ia32_vbroadcastf128_ps256 (pcv4sf);
v4df __builtin_ia32_vbroadcastsd256 (pcdouble);
v4sf __builtin_ia32_vbroadcastss (pcfloat);
v8sf __builtin_ia32_vbroadcastss256 (pcfloat);
v2df __builtin_ia32_vextractf128_pd256 (v4df,int);
v4sf __builtin_ia32_vextractf128_ps256 (v8sf,int);
v4si __builtin_ia32_vextractf128_si256 (v8si,int);
v4df __builtin_ia32_vinsertf128_pd256 (v4df,v2df,int);
v8sf __builtin_ia32_vinsertf128_ps256 (v8sf,v4sf,int);
v8si __builtin_ia32_vinsertf128_si256 (v8si,v4si,int);
v4df __builtin_ia32_vperm2f128_pd256 (v4df,v4df,int);
v8sf __builtin_ia32_vperm2f128_ps256 (v8sf,v8sf,int);
v8si __builtin_ia32_vperm2f128_si256 (v8si,v8si,int);
v2df __builtin_ia32_vpermil2pd (v2df,v2df,v2di,int);
v4df __builtin_ia32_vpermil2pd256 (v4df,v4df,v4di,int);
v4sf __builtin_ia32_vpermil2ps (v4sf,v4sf,v4si,int);
v8sf __builtin_ia32_vpermil2ps256 (v8sf,v8sf,v8si,int);
v2df __builtin_ia32_vpermilpd (v2df,int);
v4df __builtin_ia32_vpermilpd256 (v4df,int);
v4sf __builtin_ia32_vpermilps (v4sf,int);
v8sf __builtin_ia32_vpermilps256 (v8sf,int);
v2df __builtin_ia32_vpermilvarpd (v2df,v2di);
v4df __builtin_ia32_vpermilvarpd256 (v4df,v4di);
v4sf __builtin_ia32_vpermilvarps (v4sf,v4si);
v8sf __builtin_ia32_vpermilvarps256 (v8sf,v8si);
int __builtin_ia32_vtestcpd (v2df,v2df,ptest);
int __builtin_ia32_vtestcpd256 (v4df,v4df,ptest);
int __builtin_ia32_vtestcps (v4sf,v4sf,ptest);
int __builtin_ia32_vtestcps256 (v8sf,v8sf,ptest);
int __builtin_ia32_vtestnzcpd (v2df,v2df,ptest);
int __builtin_ia32_vtestnzcpd256 (v4df,v4df,ptest);
int __builtin_ia32_vtestnzcps (v4sf,v4sf,ptest);
int __builtin_ia32_vtestnzcps256 (v8sf,v8sf,ptest);
int __builtin_ia32_vtestzpd (v2df,v2df,ptest);
int __builtin_ia32_vtestzpd256 (v4df,v4df,ptest);
int __builtin_ia32_vtestzps (v4sf,v4sf,ptest);
int __builtin_ia32_vtestzps256 (v8sf,v8sf,ptest);
void __builtin_ia32_vzeroall (void);
void __builtin_ia32_vzeroupper (void);
v4df __builtin_ia32_xorpd256 (v4df,v4df);
v8sf __builtin_ia32_xorps256 (v8sf,v8sf);
The following built-in functions are available when -mavx2 is used. All of them generate the machine instruction that is part of the name.
v32qi __builtin_ia32_mpsadbw256 (v32qi,v32qi,int);
v32qi __builtin_ia32_pabsb256 (v32qi);
v16hi __builtin_ia32_pabsw256 (v16hi);
v8si __builtin_ia32_pabsd256 (v8si);
v16hi __builtin_ia32_packssdw256 (v8si,v8si);
v32qi __builtin_ia32_packsswb256 (v16hi,v16hi);
v16hi __builtin_ia32_packusdw256 (v8si,v8si);
v32qi __builtin_ia32_packuswb256 (v16hi,v16hi);
v32qi __builtin_ia32_paddb256 (v32qi,v32qi);
v16hi __builtin_ia32_paddw256 (v16hi,v16hi);
v8si __builtin_ia32_paddd256 (v8si,v8si);
v4di __builtin_ia32_paddq256 (v4di,v4di);
v32qi __builtin_ia32_paddsb256 (v32qi,v32qi);
v16hi __builtin_ia32_paddsw256 (v16hi,v16hi);
v32qi __builtin_ia32_paddusb256 (v32qi,v32qi);
v16hi __builtin_ia32_paddusw256 (v16hi,v16hi);
v4di __builtin_ia32_palignr256 (v4di,v4di,int);
v4di __builtin_ia32_andsi256 (v4di,v4di);
v4di __builtin_ia32_andnotsi256 (v4di,v4di);
v32qi __builtin_ia32_pavgb256 (v32qi,v32qi);
v16hi __builtin_ia32_pavgw256 (v16hi,v16hi);
v32qi __builtin_ia32_pblendvb256 (v32qi,v32qi,v32qi);
v16hi __builtin_ia32_pblendw256 (v16hi,v16hi,int);
v32qi __builtin_ia32_pcmpeqb256 (v32qi,v32qi);
v16hi __builtin_ia32_pcmpeqw256 (v16hi,v16hi);
v8si __builtin_ia32_pcmpeqd256 (c8si,v8si);
v4di __builtin_ia32_pcmpeqq256 (v4di,v4di);
v32qi __builtin_ia32_pcmpgtb256 (v32qi,v32qi);
v16hi __builtin_ia32_pcmpgtw256 (16hi,v16hi);
v8si __builtin_ia32_pcmpgtd256 (v8si,v8si);
v4di __builtin_ia32_pcmpgtq256 (v4di,v4di);
v16hi __builtin_ia32_phaddw256 (v16hi,v16hi);
v8si __builtin_ia32_phaddd256 (v8si,v8si);
v16hi __builtin_ia32_phaddsw256 (v16hi,v16hi);
v16hi __builtin_ia32_phsubw256 (v16hi,v16hi);
v8si __builtin_ia32_phsubd256 (v8si,v8si);
v16hi __builtin_ia32_phsubsw256 (v16hi,v16hi);
v32qi __builtin_ia32_pmaddubsw256 (v32qi,v32qi);
v16hi __builtin_ia32_pmaddwd256 (v16hi,v16hi);
v32qi __builtin_ia32_pmaxsb256 (v32qi,v32qi);
v16hi __builtin_ia32_pmaxsw256 (v16hi,v16hi);
v8si __builtin_ia32_pmaxsd256 (v8si,v8si);
v32qi __builtin_ia32_pmaxub256 (v32qi,v32qi);
v16hi __builtin_ia32_pmaxuw256 (v16hi,v16hi);
v8si __builtin_ia32_pmaxud256 (v8si,v8si);
v32qi __builtin_ia32_pminsb256 (v32qi,v32qi);
v16hi __builtin_ia32_pminsw256 (v16hi,v16hi);
v8si __builtin_ia32_pminsd256 (v8si,v8si);
v32qi __builtin_ia32_pminub256 (v32qi,v32qi);
v16hi __builtin_ia32_pminuw256 (v16hi,v16hi);
v8si __builtin_ia32_pminud256 (v8si,v8si);
int __builtin_ia32_pmovmskb256 (v32qi);
v16hi __builtin_ia32_pmovsxbw256 (v16qi);
v8si __builtin_ia32_pmovsxbd256 (v16qi);
v4di __builtin_ia32_pmovsxbq256 (v16qi);
v8si __builtin_ia32_pmovsxwd256 (v8hi);
v4di __builtin_ia32_pmovsxwq256 (v8hi);
v4di __builtin_ia32_pmovsxdq256 (v4si);
v16hi __builtin_ia32_pmovzxbw256 (v16qi);
v8si __builtin_ia32_pmovzxbd256 (v16qi);
v4di __builtin_ia32_pmovzxbq256 (v16qi);
v8si __builtin_ia32_pmovzxwd256 (v8hi);
v4di __builtin_ia32_pmovzxwq256 (v8hi);
v4di __builtin_ia32_pmovzxdq256 (v4si);
v4di __builtin_ia32_pmuldq256 (v8si,v8si);
v16hi __builtin_ia32_pmulhrsw256 (v16hi, v16hi);
v16hi __builtin_ia32_pmulhuw256 (v16hi,v16hi);
v16hi __builtin_ia32_pmulhw256 (v16hi,v16hi);
v16hi __builtin_ia32_pmullw256 (v16hi,v16hi);
v8si __builtin_ia32_pmulld256 (v8si,v8si);
v4di __builtin_ia32_pmuludq256 (v8si,v8si);
v4di __builtin_ia32_por256 (v4di,v4di);
v16hi __builtin_ia32_psadbw256 (v32qi,v32qi);
v32qi __builtin_ia32_pshufb256 (v32qi,v32qi);
v8si __builtin_ia32_pshufd256 (v8si,int);
v16hi __builtin_ia32_pshufhw256 (v16hi,int);
v16hi __builtin_ia32_pshuflw256 (v16hi,int);
v32qi __builtin_ia32_psignb256 (v32qi,v32qi);
v16hi __builtin_ia32_psignw256 (v16hi,v16hi);
v8si __builtin_ia32_psignd256 (v8si,v8si);
v4di __builtin_ia32_pslldqi256 (v4di,int);
v16hi __builtin_ia32_psllwi256 (16hi,int);
v16hi __builtin_ia32_psllw256(v16hi,v8hi);
v8si __builtin_ia32_pslldi256 (v8si,int);
v8si __builtin_ia32_pslld256(v8si,v4si);
v4di __builtin_ia32_psllqi256 (v4di,int);
v4di __builtin_ia32_psllq256(v4di,v2di);
v16hi __builtin_ia32_psrawi256 (v16hi,int);
v16hi __builtin_ia32_psraw256 (v16hi,v8hi);
v8si __builtin_ia32_psradi256 (v8si,int);
v8si __builtin_ia32_psrad256 (v8si,v4si);
v4di __builtin_ia32_psrldqi256 (v4di, int);
v16hi __builtin_ia32_psrlwi256 (v16hi,int);
v16hi __builtin_ia32_psrlw256 (v16hi,v8hi);
v8si __builtin_ia32_psrldi256 (v8si,int);
v8si __builtin_ia32_psrld256 (v8si,v4si);
v4di __builtin_ia32_psrlqi256 (v4di,int);
v4di __builtin_ia32_psrlq256(v4di,v2di);
v32qi __builtin_ia32_psubb256 (v32qi,v32qi);
v32hi __builtin_ia32_psubw256 (v16hi,v16hi);
v8si __builtin_ia32_psubd256 (v8si,v8si);
v4di __builtin_ia32_psubq256 (v4di,v4di);
v32qi __builtin_ia32_psubsb256 (v32qi,v32qi);
v16hi __builtin_ia32_psubsw256 (v16hi,v16hi);
v32qi __builtin_ia32_psubusb256 (v32qi,v32qi);
v16hi __builtin_ia32_psubusw256 (v16hi,v16hi);
v32qi __builtin_ia32_punpckhbw256 (v32qi,v32qi);
v16hi __builtin_ia32_punpckhwd256 (v16hi,v16hi);
v8si __builtin_ia32_punpckhdq256 (v8si,v8si);
v4di __builtin_ia32_punpckhqdq256 (v4di,v4di);
v32qi __builtin_ia32_punpcklbw256 (v32qi,v32qi);
v16hi __builtin_ia32_punpcklwd256 (v16hi,v16hi);
v8si __builtin_ia32_punpckldq256 (v8si,v8si);
v4di __builtin_ia32_punpcklqdq256 (v4di,v4di);
v4di __builtin_ia32_pxor256 (v4di,v4di);
v4di __builtin_ia32_movntdqa256 (pv4di);
v4sf __builtin_ia32_vbroadcastss_ps (v4sf);
v8sf __builtin_ia32_vbroadcastss_ps256 (v4sf);
v4df __builtin_ia32_vbroadcastsd_pd256 (v2df);
v4di __builtin_ia32_vbroadcastsi256 (v2di);
v4si __builtin_ia32_pblendd128 (v4si,v4si);
v8si __builtin_ia32_pblendd256 (v8si,v8si);
v32qi __builtin_ia32_pbroadcastb256 (v16qi);
v16hi __builtin_ia32_pbroadcastw256 (v8hi);
v8si __builtin_ia32_pbroadcastd256 (v4si);
v4di __builtin_ia32_pbroadcastq256 (v2di);
v16qi __builtin_ia32_pbroadcastb128 (v16qi);
v8hi __builtin_ia32_pbroadcastw128 (v8hi);
v4si __builtin_ia32_pbroadcastd128 (v4si);
v2di __builtin_ia32_pbroadcastq128 (v2di);
v8si __builtin_ia32_permvarsi256 (v8si,v8si);
v4df __builtin_ia32_permdf256 (v4df,int);
v8sf __builtin_ia32_permvarsf256 (v8sf,v8sf);
v4di __builtin_ia32_permdi256 (v4di,int);
v4di __builtin_ia32_permti256 (v4di,v4di,int);
v4di __builtin_ia32_extract128i256 (v4di,int);
v4di __builtin_ia32_insert128i256 (v4di,v2di,int);
v8si __builtin_ia32_maskloadd256 (pcv8si,v8si);
v4di __builtin_ia32_maskloadq256 (pcv4di,v4di);
v4si __builtin_ia32_maskloadd (pcv4si,v4si);
v2di __builtin_ia32_maskloadq (pcv2di,v2di);
void __builtin_ia32_maskstored256 (pv8si,v8si,v8si);
void __builtin_ia32_maskstoreq256 (pv4di,v4di,v4di);
void __builtin_ia32_maskstored (pv4si,v4si,v4si);
void __builtin_ia32_maskstoreq (pv2di,v2di,v2di);
v8si __builtin_ia32_psllv8si (v8si,v8si);
v4si __builtin_ia32_psllv4si (v4si,v4si);
v4di __builtin_ia32_psllv4di (v4di,v4di);
v2di __builtin_ia32_psllv2di (v2di,v2di);
v8si __builtin_ia32_psrav8si (v8si,v8si);
v4si __builtin_ia32_psrav4si (v4si,v4si);
v8si __builtin_ia32_psrlv8si (v8si,v8si);
v4si __builtin_ia32_psrlv4si (v4si,v4si);
v4di __builtin_ia32_psrlv4di (v4di,v4di);
v2di __builtin_ia32_psrlv2di (v2di,v2di);
v2df __builtin_ia32_gathersiv2df (v2df, pcdouble,v4si,v2df,int);
v4df __builtin_ia32_gathersiv4df (v4df, pcdouble,v4si,v4df,int);
v2df __builtin_ia32_gatherdiv2df (v2df, pcdouble,v2di,v2df,int);
v4df __builtin_ia32_gatherdiv4df (v4df, pcdouble,v4di,v4df,int);
v4sf __builtin_ia32_gathersiv4sf (v4sf, pcfloat,v4si,v4sf,int);
v8sf __builtin_ia32_gathersiv8sf (v8sf, pcfloat,v8si,v8sf,int);
v4sf __builtin_ia32_gatherdiv4sf (v4sf, pcfloat,v2di,v4sf,int);
v4sf __builtin_ia32_gatherdiv4sf256 (v4sf, pcfloat,v4di,v4sf,int);
v2di __builtin_ia32_gathersiv2di (v2di, pcint64,v4si,v2di,int);
v4di __builtin_ia32_gathersiv4di (v4di, pcint64,v4si,v4di,int);
v2di __builtin_ia32_gatherdiv2di (v2di, pcint64,v2di,v2di,int);
v4di __builtin_ia32_gatherdiv4di (v4di, pcint64,v4di,v4di,int);
v4si __builtin_ia32_gathersiv4si (v4si, pcint,v4si,v4si,int);
v8si __builtin_ia32_gathersiv8si (v8si, pcint,v8si,v8si,int);
v4si __builtin_ia32_gatherdiv4si (v4si, pcint,v2di,v4si,int);
v4si __builtin_ia32_gatherdiv4si256 (v4si, pcint,v4di,v4si,int);
The following built-in functions are available when -maes is used. All of them generate the machine instruction that is part of the name.
v2di __builtin_ia32_aesenc128 (v2di, v2di);
v2di __builtin_ia32_aesenclast128 (v2di, v2di);
v2di __builtin_ia32_aesdec128 (v2di, v2di);
v2di __builtin_ia32_aesdeclast128 (v2di, v2di);
v2di __builtin_ia32_aeskeygenassist128 (v2di, const int);
v2di __builtin_ia32_aesimc128 (v2di);
The following built-in function is available when -mpclmul is used.
Generates the
pclmulqdqmachine instruction.
The following built-in function is available when -mfsgsbase is used. All of them generate the machine instruction that is part of the name.
unsigned int __builtin_ia32_rdfsbase32 (void);
unsigned long long __builtin_ia32_rdfsbase64 (void);
unsigned int __builtin_ia32_rdgsbase32 (void);
unsigned long long __builtin_ia32_rdgsbase64 (void);
void _writefsbase_u32 (unsigned int);
void _writefsbase_u64 (unsigned long long);
void _writegsbase_u32 (unsigned int);
void _writegsbase_u64 (unsigned long long);
The following built-in function is available when -mrdrnd is used. All of them generate the machine instruction that is part of the name.
unsigned int __builtin_ia32_rdrand16_step (unsigned short *);
unsigned int __builtin_ia32_rdrand32_step (unsigned int *);
unsigned int __builtin_ia32_rdrand64_step (unsigned long long *);
The following built-in function is available when -mptwrite is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_ptwrite32 (unsigned);
void __builtin_ia32_ptwrite64 (unsigned long long);
The following built-in functions are available when -msse4a is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_movntsd (double *, v2df);
void __builtin_ia32_movntss (float *, v4sf);
v2di __builtin_ia32_extrq (v2di, v16qi);
v2di __builtin_ia32_extrqi (v2di, const unsigned int, const unsigned int);
v2di __builtin_ia32_insertq (v2di, v2di);
v2di __builtin_ia32_insertqi (v2di, v2di, const unsigned int, const unsigned int);
The following built-in functions are available when -mxop is used.
v2df __builtin_ia32_vfrczpd (v2df);
v4sf __builtin_ia32_vfrczps (v4sf);
v2df __builtin_ia32_vfrczsd (v2df);
v4sf __builtin_ia32_vfrczss (v4sf);
v4df __builtin_ia32_vfrczpd256 (v4df);
v8sf __builtin_ia32_vfrczps256 (v8sf);
v2di __builtin_ia32_vpcmov (v2di, v2di, v2di);
v2di __builtin_ia32_vpcmov_v2di (v2di, v2di, v2di);
v4si __builtin_ia32_vpcmov_v4si (v4si, v4si, v4si);
v8hi __builtin_ia32_vpcmov_v8hi (v8hi, v8hi, v8hi);
v16qi __builtin_ia32_vpcmov_v16qi (v16qi, v16qi, v16qi);
v2df __builtin_ia32_vpcmov_v2df (v2df, v2df, v2df);
v4sf __builtin_ia32_vpcmov_v4sf (v4sf, v4sf, v4sf);
v4di __builtin_ia32_vpcmov_v4di256 (v4di, v4di, v4di);
v8si __builtin_ia32_vpcmov_v8si256 (v8si, v8si, v8si);
v16hi __builtin_ia32_vpcmov_v16hi256 (v16hi, v16hi, v16hi);
v32qi __builtin_ia32_vpcmov_v32qi256 (v32qi, v32qi, v32qi);
v4df __builtin_ia32_vpcmov_v4df256 (v4df, v4df, v4df);
v8sf __builtin_ia32_vpcmov_v8sf256 (v8sf, v8sf, v8sf);
v16qi __builtin_ia32_vpcomeqb (v16qi, v16qi);
v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi);
v4si __builtin_ia32_vpcomeqd (v4si, v4si);
v2di __builtin_ia32_vpcomeqq (v2di, v2di);
v16qi __builtin_ia32_vpcomequb (v16qi, v16qi);
v4si __builtin_ia32_vpcomequd (v4si, v4si);
v2di __builtin_ia32_vpcomequq (v2di, v2di);
v8hi __builtin_ia32_vpcomequw (v8hi, v8hi);
v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi);
v16qi __builtin_ia32_vpcomfalseb (v16qi, v16qi);
v4si __builtin_ia32_vpcomfalsed (v4si, v4si);
v2di __builtin_ia32_vpcomfalseq (v2di, v2di);
v16qi __builtin_ia32_vpcomfalseub (v16qi, v16qi);
v4si __builtin_ia32_vpcomfalseud (v4si, v4si);
v2di __builtin_ia32_vpcomfalseuq (v2di, v2di);
v8hi __builtin_ia32_vpcomfalseuw (v8hi, v8hi);
v8hi __builtin_ia32_vpcomfalsew (v8hi, v8hi);
v16qi __builtin_ia32_vpcomgeb (v16qi, v16qi);
v4si __builtin_ia32_vpcomged (v4si, v4si);
v2di __builtin_ia32_vpcomgeq (v2di, v2di);
v16qi __builtin_ia32_vpcomgeub (v16qi, v16qi);
v4si __builtin_ia32_vpcomgeud (v4si, v4si);
v2di __builtin_ia32_vpcomgeuq (v2di, v2di);
v8hi __builtin_ia32_vpcomgeuw (v8hi, v8hi);
v8hi __builtin_ia32_vpcomgew (v8hi, v8hi);
v16qi __builtin_ia32_vpcomgtb (v16qi, v16qi);
v4si __builtin_ia32_vpcomgtd (v4si, v4si);
v2di __builtin_ia32_vpcomgtq (v2di, v2di);
v16qi __builtin_ia32_vpcomgtub (v16qi, v16qi);
v4si __builtin_ia32_vpcomgtud (v4si, v4si);
v2di __builtin_ia32_vpcomgtuq (v2di, v2di);
v8hi __builtin_ia32_vpcomgtuw (v8hi, v8hi);
v8hi __builtin_ia32_vpcomgtw (v8hi, v8hi);
v16qi __builtin_ia32_vpcomleb (v16qi, v16qi);
v4si __builtin_ia32_vpcomled (v4si, v4si);
v2di __builtin_ia32_vpcomleq (v2di, v2di);
v16qi __builtin_ia32_vpcomleub (v16qi, v16qi);
v4si __builtin_ia32_vpcomleud (v4si, v4si);
v2di __builtin_ia32_vpcomleuq (v2di, v2di);
v8hi __builtin_ia32_vpcomleuw (v8hi, v8hi);
v8hi __builtin_ia32_vpcomlew (v8hi, v8hi);
v16qi __builtin_ia32_vpcomltb (v16qi, v16qi);
v4si __builtin_ia32_vpcomltd (v4si, v4si);
v2di __builtin_ia32_vpcomltq (v2di, v2di);
v16qi __builtin_ia32_vpcomltub (v16qi, v16qi);
v4si __builtin_ia32_vpcomltud (v4si, v4si);
v2di __builtin_ia32_vpcomltuq (v2di, v2di);
v8hi __builtin_ia32_vpcomltuw (v8hi, v8hi);
v8hi __builtin_ia32_vpcomltw (v8hi, v8hi);
v16qi __builtin_ia32_vpcomneb (v16qi, v16qi);
v4si __builtin_ia32_vpcomned (v4si, v4si);
v2di __builtin_ia32_vpcomneq (v2di, v2di);
v16qi __builtin_ia32_vpcomneub (v16qi, v16qi);
v4si __builtin_ia32_vpcomneud (v4si, v4si);
v2di __builtin_ia32_vpcomneuq (v2di, v2di);
v8hi __builtin_ia32_vpcomneuw (v8hi, v8hi);
v8hi __builtin_ia32_vpcomnew (v8hi, v8hi);
v16qi __builtin_ia32_vpcomtrueb (v16qi, v16qi);
v4si __builtin_ia32_vpcomtrued (v4si, v4si);
v2di __builtin_ia32_vpcomtrueq (v2di, v2di);
v16qi __builtin_ia32_vpcomtrueub (v16qi, v16qi);
v4si __builtin_ia32_vpcomtrueud (v4si, v4si);
v2di __builtin_ia32_vpcomtrueuq (v2di, v2di);
v8hi __builtin_ia32_vpcomtrueuw (v8hi, v8hi);
v8hi __builtin_ia32_vpcomtruew (v8hi, v8hi);
v4si __builtin_ia32_vphaddbd (v16qi);
v2di __builtin_ia32_vphaddbq (v16qi);
v8hi __builtin_ia32_vphaddbw (v16qi);
v2di __builtin_ia32_vphadddq (v4si);
v4si __builtin_ia32_vphaddubd (v16qi);
v2di __builtin_ia32_vphaddubq (v16qi);
v8hi __builtin_ia32_vphaddubw (v16qi);
v2di __builtin_ia32_vphaddudq (v4si);
v4si __builtin_ia32_vphadduwd (v8hi);
v2di __builtin_ia32_vphadduwq (v8hi);
v4si __builtin_ia32_vphaddwd (v8hi);
v2di __builtin_ia32_vphaddwq (v8hi);
v8hi __builtin_ia32_vphsubbw (v16qi);
v2di __builtin_ia32_vphsubdq (v4si);
v4si __builtin_ia32_vphsubwd (v8hi);
v4si __builtin_ia32_vpmacsdd (v4si, v4si, v4si);
v2di __builtin_ia32_vpmacsdqh (v4si, v4si, v2di);
v2di __builtin_ia32_vpmacsdql (v4si, v4si, v2di);
v4si __builtin_ia32_vpmacssdd (v4si, v4si, v4si);
v2di __builtin_ia32_vpmacssdqh (v4si, v4si, v2di);
v2di __builtin_ia32_vpmacssdql (v4si, v4si, v2di);
v4si __builtin_ia32_vpmacsswd (v8hi, v8hi, v4si);
v8hi __builtin_ia32_vpmacssww (v8hi, v8hi, v8hi);
v4si __builtin_ia32_vpmacswd (v8hi, v8hi, v4si);
v8hi __builtin_ia32_vpmacsww (v8hi, v8hi, v8hi);
v4si __builtin_ia32_vpmadcsswd (v8hi, v8hi, v4si);
v4si __builtin_ia32_vpmadcswd (v8hi, v8hi, v4si);
v16qi __builtin_ia32_vpperm (v16qi, v16qi, v16qi);
v16qi __builtin_ia32_vprotb (v16qi, v16qi);
v4si __builtin_ia32_vprotd (v4si, v4si);
v2di __builtin_ia32_vprotq (v2di, v2di);
v8hi __builtin_ia32_vprotw (v8hi, v8hi);
v16qi __builtin_ia32_vpshab (v16qi, v16qi);
v4si __builtin_ia32_vpshad (v4si, v4si);
v2di __builtin_ia32_vpshaq (v2di, v2di);
v8hi __builtin_ia32_vpshaw (v8hi, v8hi);
v16qi __builtin_ia32_vpshlb (v16qi, v16qi);
v4si __builtin_ia32_vpshld (v4si, v4si);
v2di __builtin_ia32_vpshlq (v2di, v2di);
v8hi __builtin_ia32_vpshlw (v8hi, v8hi);
The following built-in functions are available when -mfma4 is used. All of them generate the machine instruction that is part of the name.
v2df __builtin_ia32_vfmaddpd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfmaddps (v4sf, v4sf, v4sf);
v2df __builtin_ia32_vfmaddsd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfmaddss (v4sf, v4sf, v4sf);
v2df __builtin_ia32_vfmsubpd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfmsubps (v4sf, v4sf, v4sf);
v2df __builtin_ia32_vfmsubsd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfmsubss (v4sf, v4sf, v4sf);
v2df __builtin_ia32_vfnmaddpd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfnmaddps (v4sf, v4sf, v4sf);
v2df __builtin_ia32_vfnmaddsd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfnmaddss (v4sf, v4sf, v4sf);
v2df __builtin_ia32_vfnmsubpd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfnmsubps (v4sf, v4sf, v4sf);
v2df __builtin_ia32_vfnmsubsd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfnmsubss (v4sf, v4sf, v4sf);
v2df __builtin_ia32_vfmaddsubpd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfmaddsubps (v4sf, v4sf, v4sf);
v2df __builtin_ia32_vfmsubaddpd (v2df, v2df, v2df);
v4sf __builtin_ia32_vfmsubaddps (v4sf, v4sf, v4sf);
v4df __builtin_ia32_vfmaddpd256 (v4df, v4df, v4df);
v8sf __builtin_ia32_vfmaddps256 (v8sf, v8sf, v8sf);
v4df __builtin_ia32_vfmsubpd256 (v4df, v4df, v4df);
v8sf __builtin_ia32_vfmsubps256 (v8sf, v8sf, v8sf);
v4df __builtin_ia32_vfnmaddpd256 (v4df, v4df, v4df);
v8sf __builtin_ia32_vfnmaddps256 (v8sf, v8sf, v8sf);
v4df __builtin_ia32_vfnmsubpd256 (v4df, v4df, v4df);
v8sf __builtin_ia32_vfnmsubps256 (v8sf, v8sf, v8sf);
v4df __builtin_ia32_vfmaddsubpd256 (v4df, v4df, v4df);
v8sf __builtin_ia32_vfmaddsubps256 (v8sf, v8sf, v8sf);
v4df __builtin_ia32_vfmsubaddpd256 (v4df, v4df, v4df);
v8sf __builtin_ia32_vfmsubaddps256 (v8sf, v8sf, v8sf);
The following built-in functions are available when -mlwp is used.
void __builtin_ia32_llwpcb16 (void *);
void __builtin_ia32_llwpcb32 (void *);
void __builtin_ia32_llwpcb64 (void *);
void * __builtin_ia32_llwpcb16 (void);
void * __builtin_ia32_llwpcb32 (void);
void * __builtin_ia32_llwpcb64 (void);
void __builtin_ia32_lwpval16 (unsigned short, unsigned int, unsigned short);
void __builtin_ia32_lwpval32 (unsigned int, unsigned int, unsigned int);
void __builtin_ia32_lwpval64 (unsigned __int64, unsigned int, unsigned int);
unsigned char __builtin_ia32_lwpins16 (unsigned short, unsigned int, unsigned short);
unsigned char __builtin_ia32_lwpins32 (unsigned int, unsigned int, unsigned int);
unsigned char __builtin_ia32_lwpins64 (unsigned __int64, unsigned int, unsigned int);
The following built-in functions are available when -mbmi is used. All of them generate the machine instruction that is part of the name.
unsigned int __builtin_ia32_bextr_u32(unsigned int, unsigned int);
unsigned long long __builtin_ia32_bextr_u64 (unsigned long long, unsigned long long);
The following built-in functions are available when -mbmi2 is used. All of them generate the machine instruction that is part of the name.
unsigned int _bzhi_u32 (unsigned int, unsigned int);
unsigned int _pdep_u32 (unsigned int, unsigned int);
unsigned int _pext_u32 (unsigned int, unsigned int);
unsigned long long _bzhi_u64 (unsigned long long, unsigned long long);
unsigned long long _pdep_u64 (unsigned long long, unsigned long long);
unsigned long long _pext_u64 (unsigned long long, unsigned long long);
The following built-in functions are available when -mlzcnt is used. All of them generate the machine instruction that is part of the name.
unsigned short __builtin_ia32_lzcnt_u16(unsigned short);
unsigned int __builtin_ia32_lzcnt_u32(unsigned int);
unsigned long long __builtin_ia32_lzcnt_u64 (unsigned long long);
The following built-in functions are available when -mfxsr is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_fxsave (void *);
void __builtin_ia32_fxrstor (void *);
void __builtin_ia32_fxsave64 (void *);
void __builtin_ia32_fxrstor64 (void *);
The following built-in functions are available when -mxsave is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_xsave (void *, long long);
void __builtin_ia32_xrstor (void *, long long);
void __builtin_ia32_xsave64 (void *, long long);
void __builtin_ia32_xrstor64 (void *, long long);
The following built-in functions are available when -mxsaveopt is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_xsaveopt (void *, long long);
void __builtin_ia32_xsaveopt64 (void *, long long);
The following built-in functions are available when -mtbm is used. Both of them generate the immediate form of the bextr machine instruction.
unsigned int __builtin_ia32_bextri_u32 (unsigned int,
const unsigned int);
unsigned long long __builtin_ia32_bextri_u64 (unsigned long long,
const unsigned long long);
The following built-in functions are available when -m3dnow is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_femms (void);
v8qi __builtin_ia32_pavgusb (v8qi, v8qi);
v2si __builtin_ia32_pf2id (v2sf);
v2sf __builtin_ia32_pfacc (v2sf, v2sf);
v2sf __builtin_ia32_pfadd (v2sf, v2sf);
v2si __builtin_ia32_pfcmpeq (v2sf, v2sf);
v2si __builtin_ia32_pfcmpge (v2sf, v2sf);
v2si __builtin_ia32_pfcmpgt (v2sf, v2sf);
v2sf __builtin_ia32_pfmax (v2sf, v2sf);
v2sf __builtin_ia32_pfmin (v2sf, v2sf);
v2sf __builtin_ia32_pfmul (v2sf, v2sf);
v2sf __builtin_ia32_pfrcp (v2sf);
v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf);
v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf);
v2sf __builtin_ia32_pfrsqrt (v2sf);
v2sf __builtin_ia32_pfsub (v2sf, v2sf);
v2sf __builtin_ia32_pfsubr (v2sf, v2sf);
v2sf __builtin_ia32_pi2fd (v2si);
v4hi __builtin_ia32_pmulhrw (v4hi, v4hi);
The following built-in functions are available when -m3dnowa is used. All of them generate the machine instruction that is part of the name.
v2si __builtin_ia32_pf2iw (v2sf);
v2sf __builtin_ia32_pfnacc (v2sf, v2sf);
v2sf __builtin_ia32_pfpnacc (v2sf, v2sf);
v2sf __builtin_ia32_pi2fw (v2si);
v2sf __builtin_ia32_pswapdsf (v2sf);
v2si __builtin_ia32_pswapdsi (v2si);
The following built-in functions are available when -mrtm is used They are used for restricted transactional memory. These are the internal low level functions. Normally the functions in x86 transactional memory intrinsics should be used instead.
int __builtin_ia32_xbegin ();
void __builtin_ia32_xend ();
void __builtin_ia32_xabort (status);
int __builtin_ia32_xtest ();
The following built-in functions are available when -mmwaitx is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_monitorx (void *, unsigned int, unsigned int);
void __builtin_ia32_mwaitx (unsigned int, unsigned int, unsigned int);
The following built-in functions are available when -mclzero is used. All of them generate the machine instruction that is part of the name.
void __builtin_i32_clzero (void *);
The following built-in functions are available when -mpku is used. They generate reads and writes to PKRU.
void __builtin_ia32_wrpkru (unsigned int);
unsigned int __builtin_ia32_rdpkru ();
The following built-in functions are available when -mshstk option is used. They support shadow stack machine instructions from Intel Control-flow Enforcement Technology (CET). Each built-in function generates the machine instruction that is part of the function's name. These are the internal low-level functions. Normally the functions in x86 control-flow protection intrinsics should be used instead.
unsigned int __builtin_ia32_rdsspd (void);
unsigned long long __builtin_ia32_rdsspq (void);
void __builtin_ia32_incsspd (unsigned int);
void __builtin_ia32_incsspq (unsigned long long);
void __builtin_ia32_saveprevssp(void);
void __builtin_ia32_rstorssp(void *);
void __builtin_ia32_wrssd(unsigned int, void *);
void __builtin_ia32_wrssq(unsigned long long, void *);
void __builtin_ia32_wrussd(unsigned int, void *);
void __builtin_ia32_wrussq(unsigned long long, void *);
void __builtin_ia32_setssbsy(void);
void __builtin_ia32_clrssbsy(void *);
These hardware transactional memory intrinsics for x86 allow you to use memory transactions with RTM (Restricted Transactional Memory). This support is enabled with the -mrtm option. For using HLE (Hardware Lock Elision) see x86 specific memory model extensions for transactional memory instead.
A memory transaction commits all changes to memory in an atomic way, as visible to other threads. If the transaction fails it is rolled back and all side effects discarded.
Generally there is no guarantee that a memory transaction ever succeeds and suitable fallback code always needs to be supplied.
Start a RTM (Restricted Transactional Memory) transaction. Returns
_XBEGIN_STARTEDwhen the transaction started successfully (note this is not 0, so the constant has to be explicitly tested).If the transaction aborts, all side effects are undone and an abort code encoded as a bit mask is returned. The following macros are defined:
— Macro: _XABORT_EXPLICIT
Transaction was explicitly aborted with
_xabort. The parameter passed to_xabortis available with_XABORT_CODE(status).There is no guarantee any transaction ever succeeds, so there always needs to be a valid fallback path.
Commit the current transaction. When no transaction is active this faults. All memory side effects of the transaction become visible to other threads in an atomic manner.
Return a nonzero value if a transaction is currently active, otherwise 0.
Abort the current transaction. When no transaction is active this is a no-op. The status is an 8-bit constant; its value is encoded in the return value from
_xbegin.
Here is an example showing handling for _XABORT_RETRY
and a fallback path for other failures:
#include <immintrin.h>
int n_tries, max_tries;
unsigned status = _XABORT_EXPLICIT;
...
for (n_tries = 0; n_tries < max_tries; n_tries++)
{
status = _xbegin ();
if (status == _XBEGIN_STARTED || !(status & _XABORT_RETRY))
break;
}
if (status == _XBEGIN_STARTED)
{
... transaction code...
_xend ();
}
else
{
... non-transactional fallback path...
}
Note that, in most cases, the transactional and non-transactional code must synchronize together to ensure consistency.
Get the current value of shadow stack pointer if shadow stack support from Intel CET is enabled in the hardware or
0otherwise. Theret_typeisunsigned long longfor 64-bit targets andunsigned intfor 32-bit targets.
Increment the current shadow stack pointer by the size specified by the function argument. The argument is masked to a byte value for security reasons, so to increment by more than 255 bytes you must call the function multiple times.
The shadow stack unwind code looks like:
#include <immintrin.h>
/* Unwind the shadow stack for EH. */
#define _Unwind_Frames_Extra(x) \
do \
{ \
_Unwind_Word ssp = _get_ssp (); \
if (ssp != 0) \
{ \
_Unwind_Word tmp = (x); \
while (tmp > 255) \
{ \
_inc_ssp (tmp); \
tmp -= 255; \
} \
_inc_ssp (tmp); \
} \
} \
while (0)
This code runs unconditionally on all 64-bit processors. For 32-bit processors the code runs on those that support multi-byte NOP instructions.
For some target machines, GCC supports additional options to the format attribute (see Declaring Attributes of Functions).
Solaris targets support the cmn_err (or __cmn_err__) format
check. cmn_err accepts a subset of the standard printf
conversions, and the two-argument %b conversion for displaying
bit-fields. See the Solaris man page for cmn_err for more information.
In addition to the full set of format archetypes (attribute format style
arguments such as printf, scanf, strftime, and
strfmon), Darwin targets also support the CFString (or
__CFString__) archetype in the format attribute.
Declarations with this archetype are parsed for correct syntax
and argument types. However, parsing of the format string itself and
validating arguments against it in calls to such functions is currently
not performed.
Additionally, CFStringRefs (defined by the CoreFoundation headers) may
also be used as format arguments. Note that the relevant headers are only likely to be
available on Darwin (OSX) installations. On such installations, the XCode and system
documentation provide descriptions of CFString, CFStringRefs and
associated functions.
GCC supports several types of pragmas, primarily in order to compile code originally written for other compilers. Note that in general we do not recommend the use of pragmas; See Function Attributes, for further explanation.
The GNU C preprocessor recognizes several pragmas in addition to the compiler pragmas documented here. Refer to the CPP manual for more information.
The pragmas defined by the AArch64 target correspond to the AArch64 target function attributes. They can be specified as below:
#pragma GCC target("string")
where string can be any string accepted as an AArch64 target
attribute. See AArch64 Function Attributes, for more details
on the permissible values of string.
The ARM target defines pragmas for controlling the default addition of
long_call and short_call attributes to functions.
See Function Attributes, for information about the effects of these
attributes.
long_callslong_call attribute.
no_long_callsshort_call attribute.
long_calls_offlong_call or short_call attributes of
subsequent functions.
GCC memregs number-memregs= for the current
file. Use with care! This pragma must be before any function in the
file, and mixing different memregs values in different objects may
make them incompatible. This pragma is useful when a
performance-critical function uses a memreg for temporary values,
as it may allow you to reduce the number of memregs used.
ADDRESS name address1234H numeric syntax is not supported (use 0x1234
instead). Example:
#pragma ADDRESS port3 0x103
char port3;
ctable_entry index constant_address /* will compile to "sbco Rx, 2, 0x10, 4" */
#pragma ctable_entry 2 0x4802a000
*(unsigned int *)0x4802a010 = val;
The RS/6000 and PowerPC targets define one pragma for controlling
whether or not the longcall attribute is added to function
declarations by default. This pragma overrides the -mlongcall
option, but not the longcall and shortcall attributes.
See RS/6000 and PowerPC Options, for more information about when long
calls are and are not necessary.
longcall (1)longcall attribute to all subsequent function
declarations.
longcall (0)longcall attribute to subsequent function
declarations.
The pragmas defined by the S/390 target correspond to the S/390 target function attributes and some the additional options:
Note that options of the pragma, unlike options of the target
attribute, do change the value of preprocessor macros like
__VEC__. They can be specified as below:
#pragma GCC target("string[,string]...")
#pragma GCC target("string"[,"string"]...)
The following pragmas are available for all architectures running the Darwin operating system. These are useful for compatibility with other Mac OS compilers.
mark tokens...options align=alignmentmac68k, to emulate m68k alignment, or
power, to emulate PowerPC alignment. Uses of this pragma nest
properly; to restore the previous setting, use reset for the
alignment.
segment tokens...unused (var [, var]...)unused attribute, except that this pragma may appear
anywhere within the variables' scopes.
The Solaris target supports #pragma redefine_extname
(see Symbol-Renaming Pragmas). It also supports additional
#pragma directives for compatibility with the system compiler.
align alignment (variable [, variable]...)aligned attribute see Variable Attributes). Macro expansion occurs on the arguments to this pragma
when compiling C and Objective-C. It does not currently occur when
compiling C++, but this is a bug which may be fixed in a future
release.
fini (function [, function]...).fini section.
init (function [, function]...)main) or during shared module loading, by
adding a call to the .init section.
GCC supports a #pragma directive that changes the name used in
assembly for a given declaration. While this pragma is supported on all
platforms, it is intended primarily to provide compatibility with the
Solaris system headers. This effect can also be achieved using the asm
labels extension (see Asm Labels).
redefine_extname oldname newname__PRAGMA_REDEFINE_EXTNAME
is defined if this pragma is available (currently on all platforms).
This pragma and the asm labels extension interact in a complicated
manner. Here are some corner cases you may want to be aware of:
asm label feature does not have this restriction.
asm labels do not have this restriction.
#pragma redefine_extname is
always the C-language name.
For compatibility with Microsoft Windows compilers, GCC supports a
set of #pragma directives that change the maximum alignment of
members of structures (other than zero-width bit-fields), unions, and
classes subsequently defined. The n value below always is required
to be a small power of two and specifies the new alignment in bytes.
#pragma pack(n) simply sets the new alignment.
#pragma pack() sets the alignment to the one that was in
effect when compilation started (see also command-line option
-fpack-struct[=n] see Code Gen Options).
#pragma pack(push[,n]) pushes the current alignment
setting on an internal stack and then optionally sets the new alignment.
#pragma pack(pop) restores the alignment setting to the one
saved at the top of the internal stack (and removes that stack entry).
Note that #pragma pack([n]) does not influence this internal
stack; thus it is possible to have #pragma pack(push) followed by
multiple #pragma pack(n) instances and finalized by a single
#pragma pack(pop).
Some targets, e.g. x86 and PowerPC, support the #pragma ms_struct
directive which lays out structures and unions subsequently defined as the
documented __attribute__ ((ms_struct)).
#pragma ms_struct on turns on the Microsoft layout.
#pragma ms_struct off turns off the Microsoft layout.
#pragma ms_struct reset goes back to the default layout.
Most targets also support the #pragma scalar_storage_order directive
which lays out structures and unions subsequently defined as the documented
__attribute__ ((scalar_storage_order)).
#pragma scalar_storage_order big-endian sets the storage order
of the scalar fields to big-endian.
#pragma scalar_storage_order little-endian sets the storage order
of the scalar fields to little-endian.
#pragma scalar_storage_order default goes back to the endianness
that was in effect when compilation started (see also command-line option
-fsso-struct=endianness see C Dialect Options).
For compatibility with SVR4, GCC supports a set of #pragma
directives for declaring symbols to be weak, and defining weak
aliases.
#pragma weak symbol#pragma weak symbol1 = symbol2GCC allows the user to selectively enable or disable certain types of diagnostics, and change the kind of the diagnostic. For example, a project's policy might require that all sources compile with -Werror but certain files might have exceptions allowing specific types of warnings. Or, a project might selectively enable diagnostics and treat them as errors depending on which preprocessor macros are defined.
#pragma GCC diagnostic kind optionkind is ‘error’ to treat this diagnostic as an error, ‘warning’ to treat it like a warning (even if -Werror is in effect), or ‘ignored’ if the diagnostic is to be ignored. option is a double quoted string that matches the command-line option.
#pragma GCC diagnostic warning "-Wformat"
#pragma GCC diagnostic error "-Wformat"
#pragma GCC diagnostic ignored "-Wformat"
Note that these pragmas override any command-line options. GCC keeps
track of the location of each pragma, and issues diagnostics according
to the state as of that point in the source file. Thus, pragmas occurring
after a line do not affect diagnostics caused by that line.
#pragma GCC diagnostic push#pragma GCC diagnostic poppush, and restore to that point at each pop. If a
pop has no matching push, the command-line options are
restored.
#pragma GCC diagnostic error "-Wuninitialized"
foo(a); /* error is given for this one */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wuninitialized"
foo(b); /* no diagnostic for this one */
#pragma GCC diagnostic pop
foo(c); /* error is given for this one */
#pragma GCC diagnostic pop
foo(d); /* depends on command-line options */
#pragma GCC diagnostic ignored_attributes#pragma GCC diagnostic ignored_attributes "vendor::attr" disables
warning about the following declaration:
[[vendor::attr]] void f();
whereas #pragma GCC diagnostic ignored_attributes "vendor::" prevents
warning about both of these declarations:
[[vendor::safe]] void f();
[[vendor::unsafe]] void f2();
GCC also offers a simple mechanism for printing messages during compilation.
#pragma message string#pragma message "Compiling " __FILE__ "..."
string may be parenthesized, and is printed with location information. For example,
#define DO_PRAGMA(x) _Pragma (#x)
#define TODO(x) DO_PRAGMA(message ("TODO - " #x))
TODO(Remember to fix this)
prints ‘/tmp/file.c:4: note: #pragma message: TODO - Remember to fix this’.
#pragma GCC error messageNewlines can be included in the string by using the ‘\n’ escape sequence. They will be displayed as newlines even if the -fmessage-length option is set to zero.
The error is only generated if the pragma is present in the code after pre-processing has been completed. It does not matter however if the code containing the pragma is unreachable:
#if 0
#pragma GCC error "this error is not seen"
#endif
void foo (void)
{
return;
#pragma GCC error "this error is seen"
}
#pragma GCC warning message#pragma GCC visibility push(visibility)#pragma GCC visibility popIn C++, ‘#pragma GCC visibility’ affects only namespace-scope declarations. Class members and template specializations are not affected; if you want to override the visibility for a particular member or instantiation, you must use an attribute.
For compatibility with Microsoft Windows compilers, GCC supports ‘#pragma push_macro("macro_name")’ and ‘#pragma pop_macro("macro_name")’.
#pragma push_macro("macro_name")#pragma pop_macro("macro_name")For example:
#define X 1
#pragma push_macro("X")
#undef X
#define X -1
#pragma pop_macro("X")
int x [X];
In this example, the definition of X as 1 is saved by #pragma
push_macro and restored by #pragma pop_macro.
#pragma GCC target (string, ...)target(string)
attribute for each string argument. The parentheses around
the strings in the pragma are optional. See Function Attributes,
for more information about the target attribute and the attribute
syntax.
The #pragma GCC target pragma is presently implemented for
x86, ARM, AArch64, PowerPC, S/390, and Nios II targets only.
#pragma GCC optimize (string, ...)optimize(string)
attribute for each string argument. The parentheses around
the strings in the pragma are optional. See Function Attributes,
for more information about the optimize attribute and the attribute
syntax.
#pragma GCC push_options#pragma GCC pop_options#pragma GCC reset_options#pragma GCC target and
#pragma GCC optimize to use the default switches as specified
on the command line.
#pragma GCC ivdepFor example, the compiler can only unconditionally vectorize the following loop with the pragma:
void foo (int n, int *a, int *b, int *c)
{
int i, j;
#pragma GCC ivdep
for (i = 0; i < n; ++i)
a[i] = b[i] + c[i];
}
In this example, using the restrict qualifier had the same
effect. In the following example, that would not be possible. Assume
k < -m or k >= m. Only with the pragma, the compiler knows
that it can unconditionally vectorize the following loop:
void ignore_vec_dep (int *a, int k, int c, int m)
{
#pragma GCC ivdep
for (int i = 0; i < m; i++)
a[i] = a[i + k] * c;
}
#pragma GCC unroll nfor, while or do
loop or a #pragma GCC ivdep, and applies only to the loop that follows.
n is an integer constant expression specifying the unrolling factor.
The values of 0 and 1 block any unrolling of the loop.
As permitted by ISO C11 and for compatibility with other compilers, GCC allows you to define a structure or union that contains, as fields, structures and unions without names. For example:
struct {
int a;
union {
int b;
float c;
};
int d;
} foo;
In this example, you are able to access members of the unnamed
union with code like ‘foo.b’. Note that only unnamed structs and
unions are allowed, you may not have, for example, an unnamed
int.
You must never create such structures that cause ambiguous field definitions. For example, in this structure:
struct {
int a;
struct {
int a;
};
} foo;
it is ambiguous which a is being referred to with ‘foo.a’.
The compiler gives errors for such constructs.
Unless -fms-extensions is used, the unnamed field must be a
structure or union definition without a tag (for example, ‘struct
{ int a; };’). If -fms-extensions is used, the field may
also be a definition with a tag such as ‘struct foo { int a;
};’, a reference to a previously defined structure or union such as
‘struct foo;’, or a reference to a typedef name for a
previously defined structure or union type.
The option -fplan9-extensions enables -fms-extensions as well as two other extensions. First, a pointer to a structure is automatically converted to a pointer to an anonymous field for assignments and function calls. For example:
struct s1 { int a; };
struct s2 { struct s1; };
extern void f1 (struct s1 *);
void f2 (struct s2 *p) { f1 (p); }
In the call to f1 inside f2, the pointer p is
converted into a pointer to the anonymous field.
Second, when the type of an anonymous field is a typedef for a
struct or union, code may refer to the field using the
name of the typedef.
typedef struct { int a; } s1;
struct s2 { s1; };
s1 f1 (struct s2 *p) { return p->s1; }
These usages are only permitted when they are not ambiguous.
Thread-local storage (TLS) is a mechanism by which variables are allocated such that there is one instance of the variable per extant thread. The runtime model GCC uses to implement this originates in the IA-64 processor-specific ABI, but has since been migrated to other processors as well. It requires significant support from the linker (ld), dynamic linker (ld.so), and system libraries (libc.so and libpthread.so), so it is not available everywhere.
At the user level, the extension is visible with a new storage
class keyword: __thread. For example:
__thread int i;
extern __thread struct state s;
static __thread char *p;
The __thread specifier may be used alone, with the extern
or static specifiers, but with no other storage class specifier.
When used with extern or static, __thread must appear
immediately after the other storage class specifier.
The __thread specifier may be applied to any global, file-scoped
static, function-scoped static, or static data member of a class. It may
not be applied to block-scoped automatic or non-static data member.
When the address-of operator is applied to a thread-local variable, it is evaluated at run time and returns the address of the current thread's instance of that variable. An address so obtained may be used by any thread. When a thread terminates, any pointers to thread-local variables in that thread become invalid.
No static initialization may refer to the address of a thread-local variable.
In C++, if an initializer is present for a thread-local variable, it must be a constant-expression, as defined in 5.19.2 of the ANSI/ISO C++ standard.
See ELF Handling For Thread-Local Storage for a detailed explanation of the four thread-local storage addressing models, and how the runtime is expected to function.
The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that document the exact semantics of the language extension.
Add new text after paragraph 1
Within either execution environment, a thread is a flow of control within a program. It is implementation defined whether or not there may be more than one thread associated with a program. It is implementation defined how threads beyond the first are created, the name and type of the function called at thread startup, and how threads may be terminated. However, objects with thread storage duration shall be initialized before thread startup.
Add new text before paragraph 3
An object whose identifier is declared with the storage-class
specifier __thread has thread storage duration.
Its lifetime is the entire execution of the thread, and its
stored value is initialized only once, prior to thread startup.
Add __thread.
Add __thread to the list of storage class specifiers in
paragraph 1.
Change paragraph 2 to
With the exception of__thread, at most one storage-class specifier may be given [...]. The__threadspecifier may be used alone, or immediately followingexternorstatic.
Add new text after paragraph 6
The declaration of an identifier for a variable that has block scope that specifies__threadshall also specify eitherexternorstatic.The
__threadspecifier shall be used only with variables.
The following are a set of changes to ISO/IEC 14882:1998 (aka C++98) that document the exact semantics of the language extension.
New text after paragraph 4
A thread is a flow of control within the abstract machine. It is implementation defined whether or not there may be more than one thread.
New text after paragraph 7
It is unspecified whether additional action must be taken to ensure when and whether side effects are visible to other threads.
Add __thread.
Add after paragraph 5
The thread that begins execution at themainfunction is called the main thread. It is implementation defined how functions beginning threads other than the main thread are designated or typed. A function so designated, as well as themainfunction, is called a thread startup function. It is implementation defined what happens if a thread startup function returns. It is implementation defined what happens to other threads when any thread callsexit.
Add after paragraph 4
The storage for an object of thread storage duration shall be statically initialized before the first statement of the thread startup function. An object of thread storage duration shall not require dynamic initialization.
Add after paragraph 3
The type of an object with thread storage duration shall not have a non-trivial destructor, nor shall it be an array type whose elements (directly or indirectly) have non-trivial destructors.
Add “thread storage duration” to the list in paragraph 1.
Change paragraph 2
Thread, static, and automatic storage durations are associated with objects introduced by declarations [...].
Add __thread to the list of specifiers in paragraph 3.
New section before [basic.stc.static]
The keyword__threadapplied to a non-local object gives the object thread storage duration.A local variable or class data member declared both
staticand__threadgives the variable or member thread storage duration.
Change paragraph 1
All objects that have neither thread storage duration, dynamic storage duration nor are local [...].
Add __thread to the list in paragraph 1.
Change paragraph 1
With the exception of__thread, at most one storage-class-specifier shall appear in a given decl-specifier-seq. The__threadspecifier may be used alone, or immediately following theexternorstaticspecifiers. [...]
Add after paragraph 5
The __thread specifier can be applied only to the names of objects
and to anonymous unions.
Add after paragraph 6
Non-staticmembers shall not be__thread.
Integer constants can be written as binary constants, consisting of a sequence of ‘0’ and ‘1’ digits, prefixed by ‘0b’ or ‘0B’. This is particularly useful in environments that operate a lot on the bit level (like microcontrollers).
The following statements are identical:
i = 42;
i = 0x2a;
i = 052;
i = 0b101010;
The type of these constants follows the same rules as for octal or hexadecimal integer constants, so suffixes like ‘L’ or ‘UL’ can be applied.
The GNU compiler provides these extensions to the C++ language (and you
can also use most of the C language extensions in your C++ programs). If you
want to write code that checks whether these features are available, you can
test for the GNU compiler the same way as for C programs: check for a
predefined macro __GNUC__. You can also use __GNUG__ to
test specifically for GNU C++ (see Predefined Macros).
The C++ standard differs from the C standard in its treatment of volatile objects. It fails to specify what constitutes a volatile access, except to say that C++ should behave in a similar manner to C with respect to volatiles, where possible. However, the different lvalueness of expressions between C and C++ complicate the behavior. G++ behaves the same as GCC for volatile access, See Volatiles, for a description of GCC's behavior.
The C and C++ language specifications differ when an object is accessed in a void context:
volatile int *src = somevalue;
*src;
The C++ standard specifies that such expressions do not undergo lvalue to rvalue conversion, and that the type of the dereferenced object may be incomplete. The C++ standard does not specify explicitly that it is lvalue to rvalue conversion that is responsible for causing an access. There is reason to believe that it is, because otherwise certain simple expressions become undefined. However, because it would surprise most programmers, G++ treats dereferencing a pointer to volatile object of complete type as GCC would do for an equivalent type in C. When the object has incomplete type, G++ issues a warning; if you wish to force an error, you must force a conversion to rvalue with, for instance, a static cast.
When using a reference to volatile, G++ does not treat equivalent expressions as accesses to volatiles, but instead issues a warning that no volatile is accessed. The rationale for this is that otherwise it becomes difficult to determine where volatile access occur, and not possible to ignore the return value from functions returning volatile references. Again, if you wish to force a read, cast the reference to an rvalue.
G++ implements the same behavior as GCC does when assigning to a volatile object—there is no reread of the assigned-to object, the assigned rvalue is reused. Note that in C++ assignment expressions are lvalues, and if used as an lvalue, the volatile object is referred to. For instance, vref refers to vobj, as expected, in the following example:
volatile int vobj;
volatile int &vref = vobj = something;
As with the C front end, G++ understands the C99 feature of restricted pointers,
specified with the __restrict__, or __restrict type
qualifier. Because you cannot compile C++ by specifying the -std=c99
language flag, restrict is not a keyword in C++.
In addition to allowing restricted pointers, you can specify restricted references, which indicate that the reference is not aliased in the local context.
void fn (int *__restrict__ rptr, int &__restrict__ rref)
{
/* ... */
}
In the body of fn, rptr points to an unaliased integer and
rref refers to a (different) unaliased integer.
You may also specify whether a member function's this pointer is
unaliased by using __restrict__ as a member function qualifier.
void T::fn () __restrict__
{
/* ... */
}
Within the body of T::fn, this has the effective
definition T *__restrict__ const this. Notice that the
interpretation of a __restrict__ member function qualifier is
different to that of const or volatile qualifier, in that it
is applied to the pointer rather than the object. This is consistent with
other compilers that implement restricted pointers.
As with all outermost parameter qualifiers, __restrict__ is
ignored in function definition matching. This means you only need to
specify __restrict__ in a function definition, rather than
in a function prototype as well.
There are several constructs in C++ that require space in the object file but are not clearly tied to a single translation unit. We say that these constructs have “vague linkage”. Typically such constructs are emitted wherever they are needed, though sometimes we can be more clever.
Local static variables and string constants used in an inline function are also considered to have vague linkage, since they must be shared between all inlined and out-of-line instances of the function.
Note: If the chosen key method is later defined as inline, the vtable is still emitted in every translation unit that defines it. Make sure that any inline virtuals are declared inline in the class body, even if they are not defined there.
type_info objectsWhen used with GNU ld version 2.8 or later on an ELF system such as GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of these constructs will be discarded at link time. This is known as COMDAT support.
On targets that don't support COMDAT, but do support weak symbols, GCC uses them. This way one copy overrides all the others, but the unused copies still take up space in the executable.
For targets that do not support either COMDAT or weak symbols, most entities with vague linkage are emitted as local symbols to avoid duplicate definition errors from the linker. This does not happen for local statics in inlines, however, as having multiple copies almost certainly breaks things.
See Declarations and Definitions in One Header, for another way to control placement of these constructs.
#pragma interface and #pragma implementation provide the
user with a way of explicitly directing the compiler to emit entities
with vague linkage (and debugging information) in a particular
translation unit.
Note: These #pragmas have been superceded as of GCC 2.7.2
by COMDAT support and the “key method” heuristic
mentioned in Vague Linkage. Using them can actually cause your
program to grow due to unnecessary out-of-line copies of inline
functions.
#pragma interface#pragma interface "subdir/objects.h"The second form of this directive is useful for the case where you have multiple headers with the same name in different directories. If you use this form, you must specify the same string to ‘#pragma implementation’.
#pragma implementation#pragma implementation "objects.h"If you use ‘#pragma implementation’ with no argument, it applies to an include file with the same basename8 as your source file. For example, in allclass.cc, giving just ‘#pragma implementation’ by itself is equivalent to ‘#pragma implementation "allclass.h"’.
Use the string argument if you want a single implementation file to include code from multiple header files. (You must also use ‘#include’ to include the header file; ‘#pragma implementation’ only specifies how to use the file—it doesn't actually include it.)
There is no way to split up the contents of a single header file into multiple implementation files.
‘#pragma implementation’ and ‘#pragma interface’ also have an effect on function inlining.
If you define a class in a header file marked with ‘#pragma
interface’, the effect on an inline function defined in that class is
similar to an explicit extern declaration—the compiler emits
no code at all to define an independent version of the function. Its
definition is used only for inlining with its callers.
Conversely, when you include the same header file in a main source file that declares it as ‘#pragma implementation’, the compiler emits code for the function itself; this defines a version of the function that can be found via pointers (or by callers compiled without inlining). If all calls to the function can be inlined, you can avoid emitting the function by compiling with -fno-implement-inlines. If any calls are not inlined, you will get linker errors.
C++ templates were the first language feature to require more intelligence from the environment than was traditionally found on a UNIX system. Somehow the compiler and linker have to make sure that each template instance occurs exactly once in the executable if it is needed, and not at all otherwise. There are two basic approaches to this problem, which are referred to as the Borland model and the Cfront model.
G++ implements the Borland model on targets where the linker supports it, including ELF targets (such as GNU/Linux), Mac OS X and Microsoft Windows. Otherwise G++ implements neither automatic model.
You have the following options for dealing with template instantiations:
Duplicate instances of a template can be avoided by defining an explicit
instantiation in one object file, and preventing the compiler from doing
implicit instantiations in any other object files by using an explicit
instantiation declaration, using the extern template syntax:
extern template int max (int, int);
This syntax is defined in the C++ 2011 standard, but has been supported by G++ and other compilers since well before 2011.
Explicit instantiations can be used for the largest or most frequently duplicated instances, without having to know exactly which other instances are used in the rest of the program. You can scatter the explicit instantiations throughout your program, perhaps putting them in the translation units where the instances are used or the translation units that define the templates themselves; you can put all of the explicit instantiations you need into one big file; or you can create small files like
#include "Foo.h"
#include "Foo.cc"
template class Foo<int>;
template ostream& operator <<
(ostream&, const Foo<int>&);
for each of the instances you need, and create a template instantiation library from those.
This is the simplest option, but also offers flexibility and fine-grained control when necessary. It is also the most portable alternative and programs using this approach will work with most modern compilers.
If you are using Cfront-model code, you can probably get away with not using -fno-implicit-templates when compiling files that don't ‘#include’ the member template definitions.
If you use one big file to do the instantiations, you may want to compile it without -fno-implicit-templates so you get all of the instances required by your explicit instantiations (but not by any other files) without having to specify them as well.
In addition to forward declaration of explicit instantiations
(with extern), G++ has extended the template instantiation
syntax to support instantiation of the compiler support data for a
template class (i.e. the vtable) without instantiating any of its
members (with inline), and instantiation of only the static data
members of a template class, without the support data or member
functions (with static):
inline template class Foo<int>;
static template class Foo<int>;
In C++, pointer to member functions (PMFs) are implemented using a wide pointer of sorts to handle all the possible call mechanisms; the PMF needs to store information about how to adjust the ‘this’ pointer, and if the function pointed to is virtual, where to find the vtable, and where in the vtable to look for the member function. If you are using PMFs in an inner loop, you should really reconsider that decision. If that is not an option, you can extract the pointer to the function that would be called for a given object/PMF pair and call it directly inside the inner loop, to save a bit of time.
Note that you still pay the penalty for the call through a function pointer; on most modern architectures, such a call defeats the branch prediction features of the CPU. This is also true of normal virtual function calls.
The syntax for this extension is
extern A a;
extern int (A::*fp)();
typedef int (*fptr)(A *);
fptr p = (fptr)(a.*fp);
For PMF constants (i.e. expressions of the form ‘&Klasse::Member’), no object is needed to obtain the address of the function. They can be converted to function pointers directly:
fptr p1 = (fptr)(&A::foo);
You must specify -Wno-pmf-conversions to use this extension.
Some attributes only make sense for C++ programs.
abi_tag ("tag", ...)abi_tag attribute can be applied to a function, variable, or class
declaration. It modifies the mangled name of the entity to
incorporate the tag name, in order to distinguish the function or
class from an earlier version with a different ABI; perhaps the class
has changed size, or the function has a different return type that is
not encoded in the mangled name.
The attribute can also be applied to an inline namespace, but does not affect the mangled name of the namespace; in this case it is only used for -Wabi-tag warnings and automatic tagging of functions and variables. Tagging inline namespaces is generally preferable to tagging individual declarations, but the latter is sometimes necessary, such as when only certain members of a class need to be tagged.
The argument can be a list of strings of arbitrary length. The strings are sorted on output, so the order of the list is unimportant.
A redeclaration of an entity must not add new ABI tags, since doing so would change the mangled name.
The ABI tags apply to a name, so all instantiations and specializations of a template have the same tags. The attribute will be ignored if applied to an explicit specialization or instantiation.
The -Wabi-tag flag enables a warning about a class which does not have all the ABI tags used by its subobjects and virtual functions; for users with code that needs to coexist with an earlier ABI, using this option can help to find all affected types that need to be tagged.
When a type involving an ABI tag is used as the type of a variable or return type of a function where that tag is not already present in the signature of the function, the tag is automatically applied to the variable or function. -Wabi-tag also warns about this situation; this warning can be avoided by explicitly tagging the variable or function or moving it into a tagged inline namespace.
init_priority (priority)init_priority attribute by specifying a relative priority,
a constant integral expression currently bounded between 101 and 65535
inclusive. Lower numbers indicate a higher priority.
In the following example, A would normally be created before
B, but the init_priority attribute reverses that order:
Some_Class A __attribute__ ((init_priority (2000)));
Some_Class B __attribute__ ((init_priority (543)));
Note that the particular values of priority do not matter; only their relative ordering.
warn_unusedThis attribute is appropriate for types which just represent a value,
such as std::string; it is not appropriate for types which
control a resource, such as std::lock_guard.
This attribute is also accepted in C, but it is unnecessary because C does not have constructors or destructors.
With the GNU C++ front end, for x86 targets, you may specify multiple versions of a function, where each function is specialized for a specific target feature. At runtime, the appropriate version of the function is automatically executed depending on the characteristics of the execution platform. Here is an example.
__attribute__ ((target ("default")))
int foo ()
{
// The default version of foo.
return 0;
}
__attribute__ ((target ("sse4.2")))
int foo ()
{
// foo version for SSE4.2
return 1;
}
__attribute__ ((target ("arch=atom")))
int foo ()
{
// foo version for the Intel ATOM processor
return 2;
}
__attribute__ ((target ("arch=amdfam10")))
int foo ()
{
// foo version for the AMD Family 0x10 processors.
return 3;
}
int main ()
{
int (*p)() = &foo;
assert ((*p) () == foo ());
return 0;
}
In the above example, four versions of function foo are created. The first version of foo with the target attribute "default" is the default version. This version gets executed when no other target specific version qualifies for execution on a particular platform. A new version of foo is created by using the same function signature but with a different target string. Function foo is called or a pointer to it is taken just like a regular function. GCC takes care of doing the dispatching to call the right version at runtime. Refer to the GCC wiki on Function Multiversioning for more details.
The C++ front end implements syntactic extensions that allow compile-time determination of various characteristics of a type (or of a pair of types).
If type is
const-qualified or is a reference type then the trait isfalse. Otherwise if__has_trivial_assign (type)istruethen the trait istrue, else if type is a cv-qualified class or union type with copy assignment operators that are known not to throw an exception then the trait istrue, else it isfalse. Requires: type shall be a complete type, (possibly cv-qualified)void, or an array of unknown bound.
If
__has_trivial_copy (type)istruethen the trait istrue, else if type is a cv-qualified class or union type with copy constructors that are known not to throw an exception then the trait istrue, else it isfalse. Requires: type shall be a complete type, (possibly cv-qualified)void, or an array of unknown bound.
If
__has_trivial_constructor (type)istruethen the trait istrue, else if type is a cv class or union type (or array thereof) with a default constructor that is known not to throw an exception then the trait istrue, else it isfalse. Requires: type shall be a complete type, (possibly cv-qualified)void, or an array of unknown bound.
If type is
const- qualified or is a reference type then the trait isfalse. Otherwise if__is_trivial (type)istruethen the trait istrue, else if type is a cv-qualified class or union type with a trivial copy assignment ([class.copy]) then the trait istrue, else it isfalse. Requires: type shall be a complete type, (possibly cv-qualified)void, or an array of unknown bound.
If
__is_trivial (type)istrueor type is a reference type then the trait istrue, else if type is a cv class or union type with a trivial copy constructor ([class.copy]) then the trait istrue, else it isfalse. Requires: type shall be a complete type, (possibly cv-qualified)void, or an array of unknown bound.
If
__is_trivial (type)istruethen the trait istrue, else if type is a cv-qualified class or union type (or array thereof) with a trivial default constructor ([class.ctor]) then the trait istrue, else it isfalse. Requires: type shall be a complete type, (possibly cv-qualified)void, or an array of unknown bound.
If
__is_trivial (type)istrueor type is a reference type then the trait istrue, else if type is a cv class or union type (or array thereof) with a trivial destructor ([class.dtor]) then the trait istrue, else it isfalse. Requires: type shall be a complete type, (possibly cv-qualified)void, or an array of unknown bound.
If type is a class type with a virtual destructor ([class.dtor]) then the trait is
true, else it isfalse. Requires: If type is a non-union class type, it shall be a complete type.
If type is an abstract class ([class.abstract]) then the trait is
true, else it isfalse. Requires: If type is a non-union class type, it shall be a complete type.
If type is an aggregate type ([dcl.init.aggr]) the trait is
true, else it isfalse. Requires: If type is a class type, it shall be a complete type.
If base_type is a base class of derived_type ([class.derived]) then the trait is
true, otherwise it isfalse. Top-level cv-qualifications of base_type and derived_type are ignored. For the purposes of this trait, a class type is considered is own base. Requires: if__is_class (base_type)and__is_class (derived_type)aretrueand base_type and derived_type are not the same type (disregarding cv-qualifiers), derived_type shall be a complete type. A diagnostic is produced if this requirement is not met.
If type is a cv-qualified class type, and not a union type ([basic.compound]) the trait is
true, else it isfalse.
If
__is_class (type)isfalsethen the trait isfalse. Otherwise type is considered empty if and only if: type has no non-static data members, or all non-static data members, if any, are bit-fields of length 0, and type has no virtual members, and type has no virtual base classes, and type has no base classes base_type for which__is_empty (base_type)isfalse. Requires: If type is a non-union class type, it shall be a complete type.
If type is a cv enumeration type ([basic.compound]) the trait is
true, else it isfalse.
If type is a class or union type marked
final, then the trait istrue, else it isfalse. Requires: If type is a class type, it shall be a complete type.
If type is a literal type ([basic.types]) the trait is
true, else it isfalse. Requires: type shall be a complete type, (possibly cv-qualified)void, or an array of unknown bound.
If type is a cv POD type ([basic.types]) then the trait is
true, else it isfalse. Requires: type shall be a complete type, (possibly cv-qualified)void, or an array of unknown bound.
If type is a polymorphic class ([class.virtual]) then the trait is
true, else it isfalse. Requires: If type is a non-union class type, it shall be a complete type.
If type is a standard-layout type ([basic.types]) the trait is
true, else it isfalse. Requires: type shall be a complete type, an array of complete types, or (possibly cv-qualified)void.
If type is a trivial type ([basic.types]) the trait is
true, else it isfalse. Requires: type shall be a complete type, an array of complete types, or (possibly cv-qualified)void.
If type is a cv union type ([basic.compound]) the trait is
true, else it isfalse.
The underlying type of type. Requires: type shall be an enumeration type ([dcl.enum]).
When used as the pattern of a pack expansion within a template definition, expands to a template argument pack containing integers from
0to length-1. This is provided for efficient implementation ofstd::make_integer_sequence.
C++ concepts provide much-improved support for generic programming. In particular, they allow the specification of constraints on template arguments. The constraints are used to extend the usual overloading and partial specialization capabilities of the language, allowing generic data structures and algorithms to be “refined” based on their properties rather than their type names.
The following keywords are reserved for concepts.
assumesassume(n > 0).
axiomforallforall (int n) n + 0 == n).
conceptrequiresThe front end also exposes a number of internal mechanism that can be used to simplify the writing of type traits. Note that some of these traits are likely to be removed in the future.
A binary type trait:
truewhenever the type1 and type2 refer to the same type.
In the past, the GNU C++ compiler was extended to experiment with new features, at a time when the C++ language was still evolving. Now that the C++ standard is complete, some of those features are superseded by superior alternatives. Using the old features might cause a warning in some cases that the feature will be dropped in the future. In other cases, the feature might be gone already.
G++ allows a virtual function returning ‘void *’ to be overridden by one returning a different pointer type. This extension to the covariant return type rules is now deprecated and will be removed from a future version.
The use of default arguments in function pointers, function typedefs and other places where they are not permitted by the standard is deprecated and will be removed from a future version of G++.
G++ allows floating-point literals to appear in integral constant expressions, e.g. ‘ enum E { e = int(2.2 * 3.7) } ’ This extension is deprecated and will be removed from a future version.
G++ allows static data members of const floating-point type to be declared with an initializer in a class definition. The standard only allows initializers for static members of const integral types and const enumeration types so this extension has been deprecated and will be removed from a future version.
G++ allows attributes to follow a parenthesized direct initializer, e.g. ‘ int f (0) __attribute__ ((something)); ’ This extension has been ignored since G++ 3.3 and is deprecated.
G++ allows anonymous structs and unions to have members that are not public non-static data members (i.e. fields). These extensions are deprecated.
Now that there is a definitive ISO standard C++, G++ has a specification to adhere to. The C++ language evolved over time, and features that used to be acceptable in previous drafts of the standard, such as the ARM [Annotated C++ Reference Manual], are no longer accepted. In order to allow compilation of C++ written to such drafts, G++ contains some backwards compatibilities. All such backwards compatibility features are liable to disappear in future versions of G++. They should be considered deprecated. See Deprecated Features.
Implicit C languageextern "C" {...}
scope to set the language. On such systems, all system header files are
implicitly scoped inside a C language scope. Such headers must
correctly prototype function argument types, there is no leeway for
() to indicate an unspecified set of arguments.
This document is meant to describe some of the GNU Objective-C features. It is not intended to teach you Objective-C. There are several resources on the Internet that present the language.
This section is specific for the GNU Objective-C runtime. If you are using a different runtime, you can skip it.
The GNU Objective-C runtime provides an API that allows you to interact with the Objective-C runtime system, querying the live runtime structures and even manipulating them. This allows you for example to inspect and navigate classes, methods and protocols; to define new classes or new methods, and even to modify existing classes or protocols.
If you are using a “Foundation” library such as GNUstep-Base, this library will provide you with a rich set of functionality to do most of the inspection tasks, and you probably will only need direct access to the GNU Objective-C runtime API to define new classes or methods.
The GNU Objective-C runtime provides an API which is similar to the one provided by the “Objective-C 2.0” Apple/NeXT Objective-C runtime. The API is documented in the public header files of the GNU Objective-C runtime:
id, Class
and BOOL. You have to include this header to do almost
anything with Objective-C.
class_getName(), declared in
objc/runtime.h.
@synchronized() syntax, allowing
you to emulate an Objective-C @synchronized() block in plain
C/C++ code.
objc_mutex_lock(), which provide a
platform-independent set of threading functions.
The header files contain detailed documentation for each function in the GNU Objective-C runtime API.
The GNU Objective-C runtime used to provide a different API, which we
call the “traditional” GNU Objective-C runtime API. Functions
belonging to this API are easy to recognize because they use a
different naming convention, such as class_get_super_class()
(traditional API) instead of class_getSuperclass() (modern
API). Software using this API includes the file
objc/objc-api.h where it is declared.
Starting with GCC 4.7.0, the traditional GNU runtime API is no longer available.
+load: Executing Code before mainThis section is specific for the GNU Objective-C runtime. If you are using a different runtime, you can skip it.
The GNU Objective-C runtime provides a way that allows you to execute
code before the execution of the program enters the main
function. The code is executed on a per-class and a per-category basis,
through a special class method +load.
This facility is very useful if you want to initialize global variables
which can be accessed by the program directly, without sending a message
to the class first. The usual way to initialize global variables, in the
+initialize method, might not be useful because
+initialize is only called when the first message is sent to a
class object, which in some cases could be too late.
Suppose for example you have a FileStream class that declares
Stdin, Stdout and Stderr as global variables, like
below:
FileStream *Stdin = nil;
FileStream *Stdout = nil;
FileStream *Stderr = nil;
@implementation FileStream
+ (void)initialize
{
Stdin = [[FileStream new] initWithFd:0];
Stdout = [[FileStream new] initWithFd:1];
Stderr = [[FileStream new] initWithFd:2];
}
/* Other methods here */
@end
In this example, the initialization of Stdin, Stdout and
Stderr in +initialize occurs too late. The programmer can
send a message to one of these objects before the variables are actually
initialized, thus sending messages to the nil object. The
+initialize method which actually initializes the global
variables is not invoked until the first message is sent to the class
object. The solution would require these variables to be initialized
just before entering main.
The correct solution of the above problem is to use the +load
method instead of +initialize:
@implementation FileStream
+ (void)load
{
Stdin = [[FileStream new] initWithFd:0];
Stdout = [[FileStream new] initWithFd:1];
Stderr = [[FileStream new] initWithFd:2];
}
/* Other methods here */
@end
The +load is a method that is not overridden by categories. If a
class and a category of it both implement +load, both methods are
invoked. This allows some additional initializations to be performed in
a category.
This mechanism is not intended to be a replacement for +initialize.
You should be aware of its limitations when you decide to use it
instead of +initialize.
+load+load is to be used only as a last resort. Because it is
executed very early, most of the Objective-C runtime machinery will
not be ready when +load is executed; hence +load works
best for executing C code that is independent on the Objective-C
runtime.
The +load implementation in the GNU runtime guarantees you the
following things:
+load implementation of all super classes of a class are
executed before the +load of that class is executed;
+load implementation of a class is executed before the
+load implementation of any category.
In particular, the following things, even if they can work in a particular case, are not guaranteed:
@"this is a
constant string");
You should make no assumptions about receiving +load in sibling
classes when you write +load of a class. The order in which
sibling classes receive +load is not guaranteed.
The order in which +load and +initialize are called could
be problematic if this matters. If you don't allocate objects inside
+load, it is guaranteed that +load is called before
+initialize. If you create an object inside +load the
+initialize method of object's class is invoked even if
+load was not invoked. Note if you explicitly call +load
on a class, +initialize will be called first. To avoid possible
problems try to implement only one of these methods.
The +load method is also invoked when a bundle is dynamically
loaded into your running program. This happens automatically without any
intervening operation from you. When you write bundles and you need to
write +load you can safely create and send messages to objects whose
classes already exist in the running program. The same restrictions as
above apply to classes defined in bundle.
This is an advanced section. Type encodings are used extensively by the compiler and by the runtime, but you generally do not need to know about them to use Objective-C.
The Objective-C compiler generates type encodings for all the types. These type encodings are used at runtime to find out information about selectors and methods and about objects and classes.
The types are encoded in the following way:
_Bool
| B
|
char
| c
|
unsigned char
| C
|
short
| s
|
unsigned short
| S
|
int
| i
|
unsigned int
| I
|
long
| l
|
unsigned long
| L
|
long long
| q
|
unsigned long long
| Q
|
float
| f
|
double
| d
|
long double
| D
|
void
| v
|
id
| @
|
Class
| #
|
SEL
| :
|
char*
| *
|
enum
| an enum is encoded exactly as the integer type that the compiler uses for it, which depends on the enumeration
values. Often the compiler users unsigned int, which is then encoded as I.
|
| unknown type | ?
|
| Complex types | j followed by the inner type. For example _Complex double is encoded as "jd".
|
| bit-fields | b followed by the starting position of the bit-field, the type of the bit-field and the size of the bit-field (the bit-fields encoding was changed from the NeXT's compiler encoding, see below)
|
The encoding of bit-fields has changed to allow bit-fields to be properly handled by the runtime functions that compute sizes and alignments of types that contain bit-fields. The previous encoding contained only the size of the bit-field. Using only this information it is not possible to reliably compute the size occupied by the bit-field. This is very important in the presence of the Boehm's garbage collector because the objects are allocated using the typed memory facility available in this collector. The typed memory allocation requires information about where the pointers are located inside the object.
The position in the bit-field is the position, counting in bits, of the bit closest to the beginning of the structure.
The non-atomic types are encoded as follows:
| pointers | ‘^’ followed by the pointed type.
|
| arrays | ‘[’ followed by the number of elements in the array followed by the type of the elements followed by ‘]’
|
| structures | ‘{’ followed by the name of the structure (or ‘?’ if the structure is unnamed), the ‘=’ sign, the type of the members and by ‘}’
|
| unions | ‘(’ followed by the name of the structure (or ‘?’ if the union is unnamed), the ‘=’ sign, the type of the members followed by ‘)’
|
| vectors | ‘![’ followed by the vector_size (the number of bytes composing the vector) followed by a comma, followed by the alignment (in bytes) of the vector, followed by the type of the elements followed by ‘]’
|
Here are some types and their encodings, as they are generated by the compiler on an i386 machine:
| Objective-C type | Compiler encoding
|
|---|---|
int a[10]; | [10i]
|
struct {
int i;
float f[3];
int a:3;
int b:2;
char c;
}
| {?=i[3f]b128i3b131i2c}
|
int a __attribute__ ((vector_size (16))); | ![16,16i] (alignment depends on the machine)
|
In addition to the types the compiler also encodes the type specifiers. The table below describes the encoding of the current Objective-C type specifiers:
| Specifier | Encoding
|
|---|---|
const
| r
|
in
| n
|
inout
| N
|
out
| o
|
bycopy
| O
|
byref
| R
|
oneway
| V
|
The type specifiers are encoded just before the type. Unlike types however, the type specifiers are only encoded when they appear in method argument types.
Note how const interacts with pointers:
| Objective-C type | Compiler encoding
|
|---|---|
const int | ri
|
const int* | ^ri
|
int *const | r^i
|
const int* is a pointer to a const int, and so is
encoded as ^ri. int* const, instead, is a const
pointer to an int, and so is encoded as r^i.
Finally, there is a complication when encoding const char *
versus char * const. Because char * is encoded as
* and not as ^c, there is no way to express the fact
that r applies to the pointer or to the pointee.
Hence, it is assumed as a convention that r* means const
char * (since it is what is most often meant), and there is no way to
encode char *const. char *const would simply be encoded
as *, and the const is lost.
Unfortunately, historically GCC used to have a number of bugs in its encoding code. The NeXT runtime expects GCC to emit type encodings in this historical format (compatible with GCC-3.3), so when using the NeXT runtime, GCC will introduce on purpose a number of incorrect encodings:
enums are always encoded as 'i' (int) even if they are actually
unsigned or long.
In addition to that, the NeXT runtime uses a different encoding for
bitfields. It encodes them as b followed by the size, without
a bit offset or the underlying field type.
@encodeGNU Objective-C supports the @encode syntax that allows you to
create a type encoding from a C/Objective-C type. For example,
@encode(int) is compiled by the compiler into "i".
@encode does not support type qualifiers other than
const. For example, @encode(const char*) is valid and
is compiled into "r*", while @encode(bycopy char *) is
invalid and will cause a compilation error.
This section documents the encoding of method types, which is rarely needed to use Objective-C. You should skip it at a first reading; the runtime provides functions that will work on methods and can walk through the list of parameters and interpret them for you. These functions are part of the public “API” and are the preferred way to interact with method signatures from user code.
But if you need to debug a problem with method signatures and need to know how they are implemented (i.e., the “ABI”), read on.
Methods have their “signature” encoded and made available to the runtime. The “signature” encodes all the information required to dynamically build invocations of the method at runtime: return type and arguments.
The “signature” is a null-terminated string, composed of the following:
int would have i here.
self and the
method selector _cmd).
For example, a method with no arguments and returning int would
have the signature i8@0:4 if the size of a pointer is 4. The
signature is interpreted as follows: the i is the return type
(an int), the 8 is the total size of the parameters in
bytes (two pointers each of size 4), the @0 is the first
parameter (an object at byte offset 0) and :4 is the
second parameter (a SEL at byte offset 4).
You can easily find more examples by running the “strings” program
on an Objective-C object file compiled by GCC. You'll see a lot of
strings that look very much like i8@0:4. They are signatures
of Objective-C methods.
This section is specific for the GNU Objective-C runtime. If you are using a different runtime, you can skip it.
Support for garbage collection with the GNU runtime has been added by using a powerful conservative garbage collector, known as the Boehm-Demers-Weiser conservative garbage collector.
To enable the support for it you have to configure the compiler using an additional argument, --enable-objc-gc. This will build the boehm-gc library, and build an additional runtime library which has several enhancements to support the garbage collector. The new library has a new name, libobjc_gc.a to not conflict with the non-garbage-collected library.
When the garbage collector is used, the objects are allocated using the so-called typed memory allocation mechanism available in the Boehm-Demers-Weiser collector. This mode requires precise information on where pointers are located inside objects. This information is computed once per class, immediately after the class has been initialized.
There is a new runtime function class_ivar_set_gcinvisible()
which can be used to declare a so-called weak pointer
reference. Such a pointer is basically hidden for the garbage collector;
this can be useful in certain situations, especially when you want to
keep track of the allocated objects, yet allow them to be
collected. This kind of pointers can only be members of objects, you
cannot declare a global pointer as a weak reference. Every type which is
a pointer type can be declared a weak pointer, including id,
Class and SEL.
Here is an example of how to use this feature. Suppose you want to implement a class whose instances hold a weak pointer reference; the following class does this:
@interface WeakPointer : Object
{
const void* weakPointer;
}
- initWithPointer:(const void*)p;
- (const void*)weakPointer;
@end
@implementation WeakPointer
+ (void)initialize
{
if (self == objc_lookUpClass ("WeakPointer"))
class_ivar_set_gcinvisible (self, "weakPointer", YES);
}
- initWithPointer:(const void*)p
{
weakPointer = p;
return self;
}
- (const void*)weakPointer
{
return weakPointer;
}
@end
Weak pointers are supported through a new type character specifier
represented by the ‘!’ character. The
class_ivar_set_gcinvisible() function adds or removes this
specifier to the string type description of the instance variable named
as argument.
GNU Objective-C provides constant string objects that are generated directly by the compiler. You declare a constant string object by prefixing a C constant string with the character ‘@’:
id myString = @"this is a constant string object";
The constant string objects are by default instances of the
NXConstantString class which is provided by the GNU Objective-C
runtime. To get the definition of this class you must include the
objc/NXConstStr.h header file.
User defined libraries may want to implement their own constant string
class. To be able to support them, the GNU Objective-C compiler provides
a new command line options -fconstant-string-class=class-name.
The provided class should adhere to a strict structure, the same
as NXConstantString's structure:
@interface MyConstantStringClass
{
Class isa;
char *c_string;
unsigned int len;
}
@end
NXConstantString inherits from Object; user class
libraries may choose to inherit the customized constant string class
from a different class than Object. There is no requirement in
the methods the constant string class has to implement, but the final
ivar layout of the class must be the compatible with the given
structure.
When the compiler creates the statically allocated constant string
object, the c_string field will be filled by the compiler with
the string; the length field will be filled by the compiler with
the string length; the isa pointer will be filled with
NULL by the compiler, and it will later be fixed up automatically
at runtime by the GNU Objective-C runtime library to point to the class
which was set by the -fconstant-string-class option when the
object file is loaded (if you wonder how it works behind the scenes, the
name of the class to use, and the list of static objects to fixup, are
stored by the compiler in the object file in a place where the GNU
runtime library will find them at runtime).
As a result, when a file is compiled with the -fconstant-string-class option, all the constant string objects will be instances of the class specified as argument to this option. It is possible to have multiple compilation units referring to different constant string classes, neither the compiler nor the linker impose any restrictions in doing this.
compatibility_aliasThe keyword @compatibility_alias allows you to define a class name
as equivalent to another class name. For example:
@compatibility_alias WOApplication GSWApplication;
tells the compiler that each time it encounters WOApplication as
a class name, it should replace it with GSWApplication (that is,
WOApplication is just an alias for GSWApplication).
There are some constraints on how this can be used—
WOApplication (the alias) must not be an existing class;
GSWApplication (the real class) must be an existing class.
GNU Objective-C provides exception support built into the language, as in the following example:
@try {
...
@throw expr;
...
}
@catch (AnObjCClass *exc) {
...
@throw expr;
...
@throw;
...
}
@catch (AnotherClass *exc) {
...
}
@catch (id allOthers) {
...
}
@finally {
...
@throw expr;
...
}
The @throw statement may appear anywhere in an Objective-C or
Objective-C++ program; when used inside of a @catch block, the
@throw may appear without an argument (as shown above), in
which case the object caught by the @catch will be rethrown.
Note that only (pointers to) Objective-C objects may be thrown and
caught using this scheme. When an object is thrown, it will be caught
by the nearest @catch clause capable of handling objects of
that type, analogously to how catch blocks work in C++ and
Java. A @catch(id ...) clause (as shown above) may also
be provided to catch any and all Objective-C exceptions not caught by
previous @catch clauses (if any).
The @finally clause, if present, will be executed upon exit
from the immediately preceding @try ... @catch section.
This will happen regardless of whether any exceptions are thrown,
caught or rethrown inside the @try ... @catch section,
analogously to the behavior of the finally clause in Java.
There are several caveats to using the new exception mechanism:
NS_HANDLER-style idioms provided by the
NSException class, the new exceptions can only be used on Mac
OS X 10.3 (Panther) and later systems, due to additional functionality
needed in the NeXT Objective-C runtime.
@throw an exception
from Objective-C and catch it in C++, or vice versa
(i.e., throw ... @catch).
GNU Objective-C provides support for synchronized blocks:
@synchronized (ObjCClass *guard) {
...
}
Upon entering the @synchronized block, a thread of execution
shall first check whether a lock has been placed on the corresponding
guard object by another thread. If it has, the current thread
shall wait until the other thread relinquishes its lock. Once
guard becomes available, the current thread will place its own
lock on it, execute the code contained in the @synchronized
block, and finally relinquish the lock (thereby making guard
available to other threads).
Unlike Java, Objective-C does not allow for entire methods to be
marked @synchronized. Note that throwing exceptions out of
@synchronized blocks is allowed, and will cause the guarding
object to be unlocked properly.
Because of the interactions between synchronization and exception
handling, you can only use @synchronized when compiling with
exceptions enabled, that is with the command line option
-fobjc-exceptions.
GNU Objective-C provides support for the fast enumeration syntax:
id array = ...;
id object;
for (object in array)
{
/* Do something with 'object' */
}
array needs to be an Objective-C object (usually a collection
object, for example an array, a dictionary or a set) which implements
the “Fast Enumeration Protocol” (see below). If you are using a
Foundation library such as GNUstep Base or Apple Cocoa Foundation, all
collection objects in the library implement this protocol and can be
used in this way.
The code above would iterate over all objects in array. For
each of them, it assigns it to object, then executes the
Do something with 'object' statements.
Here is a fully worked-out example using a Foundation library (which
provides the implementation of NSArray, NSString and
NSLog):
NSArray *array = [NSArray arrayWithObjects: @"1", @"2", @"3", nil];
NSString *object;
for (object in array)
NSLog (@"Iterating over %@", object);
A c99-like declaration syntax is also allowed:
id array = ...;
for (id object in array)
{
/* Do something with 'object' */
}
this is completely equivalent to:
id array = ...;
{
id object;
for (object in array)
{
/* Do something with 'object' */
}
}
but can save some typing.
Note that the option -std=c99 is not required to allow this syntax in Objective-C.
Here is a more technical description with the gory details. Consider the code
for (object expression in collection expression)
{
statements
}
here is what happens when you run it:
for (object in [NSDictionary
keyEnumerator]) ....
nil and the loop
immediately terminates.
break and continue
commands, which will abort the iteration or skip to the next loop
iteration as expected.
nil. This allows
you to determine whether the iteration finished because a break
command was used (in which case object expression will remain
set to the last object that was iterated over) or because it iterated
over all the objects (in which case object expression will be
set to nil).
objc_enumerationMutation, a runtime
function that normally aborts the program but which can be customized
by Foundation libraries via objc_set_mutation_handler to do
something different, such as raising an exception.
If you want your own collection object to be usable with fast enumeration, you need to have it implement the method
- (unsigned long) countByEnumeratingWithState: (NSFastEnumerationState *)state
objects: (id *)objects
count: (unsigned long)len;
where NSFastEnumerationState must be defined in your code as follows:
typedef struct
{
unsigned long state;
id *itemsPtr;
unsigned long *mutationsPtr;
unsigned long extra[5];
} NSFastEnumerationState;
If no NSFastEnumerationState is defined in your code, the
compiler will automatically replace NSFastEnumerationState *
with struct __objcFastEnumerationState *, where that type is
silently defined by the compiler in an identical way. This can be
confusing and we recommend that you define
NSFastEnumerationState (as shown above) instead.
The method is called repeatedly during a fast enumeration to retrieve batches of objects. Each invocation of the method should retrieve the next batch of objects.
The return value of the method is the number of objects in the current
batch; this should not exceed len, which is the maximum size of
a batch as requested by the caller. The batch itself is returned in
the itemsPtr field of the NSFastEnumerationState struct.
To help with returning the objects, the objects array is a C
array preallocated by the caller (on the stack) of size len.
In many cases you can put the objects you want to return in that
objects array, then do itemsPtr = objects. But you
don't have to; if your collection already has the objects to return in
some form of C array, it could return them from there instead.
The state and extra fields of the
NSFastEnumerationState structure allows your collection object
to keep track of the state of the enumeration. In a simple array
implementation, state may keep track of the index of the last
object that was returned, and extra may be unused.
The mutationsPtr field of the NSFastEnumerationState is
used to keep track of mutations. It should point to a number; before
working on each object, the fast enumeration loop will check that this
number has not changed. If it has, a mutation has happened and the
fast enumeration will abort. So, mutationsPtr could be set to
point to some sort of version number of your collection, which is
increased by one every time there is a change (for example when an
object is added or removed). Or, if you are content with less strict
mutation checks, it could point to the number of objects in your
collection or some other value that can be checked to perform an
approximate check that the collection has not been mutated.
Finally, note how we declared the len argument and the return
value to be of type unsigned long. They could also be declared
to be of type unsigned int and everything would still work.
This section is specific for the GNU Objective-C runtime. If you are using a different runtime, you can skip it.
The implementation of messaging in the GNU Objective-C runtime is designed to be portable, and so is based on standard C.
Sending a message in the GNU Objective-C runtime is composed of two
separate steps. First, there is a call to the lookup function,
objc_msg_lookup () (or, in the case of messages to super,
objc_msg_lookup_super ()). This runtime function takes as
argument the receiver and the selector of the method to be called; it
returns the IMP, that is a pointer to the function implementing
the method. The second step of method invocation consists of casting
this pointer function to the appropriate function pointer type, and
calling the function pointed to it with the right arguments.
For example, when the compiler encounters a method invocation such as
[object init], it compiles it into a call to
objc_msg_lookup (object, @selector(init)) followed by a cast
of the returned value to the appropriate function pointer type, and
then it calls it.
If objc_msg_lookup() does not find a suitable method
implementation, because the receiver does not implement the required
method, it tries to see if the class can dynamically register the
method.
To do so, the runtime checks if the class of the receiver implements the method
+ (BOOL) resolveInstanceMethod: (SEL)selector;
in the case of an instance method, or
+ (BOOL) resolveClassMethod: (SEL)selector;
in the case of a class method. If the class implements it, the
runtime invokes it, passing as argument the selector of the original
method, and if it returns YES, the runtime tries the lookup
again, which could now succeed if a matching method was added
dynamically by +resolveInstanceMethod: or
+resolveClassMethod:.
This allows classes to dynamically register methods (by adding them to
the class using class_addMethod) when they are first called.
To do so, a class should implement +resolveInstanceMethod: (or,
depending on the case, +resolveClassMethod:) and have it
recognize the selectors of methods that can be registered dynamically
at runtime, register them, and return YES. It should return
NO for methods that it does not dynamically registered at
runtime.
If +resolveInstanceMethod: (or +resolveClassMethod:) is
not implemented or returns NO, the runtime then tries the
forwarding hook.
Support for +resolveInstanceMethod: and
resolveClassMethod: was added to the GNU Objective-C runtime in
GCC version 4.6.
The GNU Objective-C runtime provides a hook, called
__objc_msg_forward2, which is called by
objc_msg_lookup() when it cannot find a method implementation in
the runtime tables and after calling +resolveInstanceMethod:
and +resolveClassMethod: has been attempted and did not succeed
in dynamically registering the method.
To configure the hook, you set the global variable
__objc_msg_forward2 to a function with the same argument and
return types of objc_msg_lookup(). When
objc_msg_lookup() cannot find a method implementation, it
invokes the hook function you provided to get a method implementation
to return. So, in practice __objc_msg_forward2 allows you to
extend objc_msg_lookup() by adding some custom code that is
called to do a further lookup when no standard method implementation
can be found using the normal lookup.
This hook is generally reserved for “Foundation” libraries such as
GNUstep Base, which use it to implement their high-level method
forwarding API, typically based around the forwardInvocation:
method. So, unless you are implementing your own “Foundation”
library, you should not set this hook.
In a typical forwarding implementation, the __objc_msg_forward2
hook function determines the argument and return type of the method
that is being looked up, and then creates a function that takes these
arguments and has that return type, and returns it to the caller.
Creating this function is non-trivial and is typically performed using
a dedicated library such as libffi.
The forwarding method implementation thus created is returned by
objc_msg_lookup() and is executed as if it was a normal method
implementation. When the forwarding method implementation is called,
it is usually expected to pack all arguments into some sort of object
(typically, an NSInvocation in a “Foundation” library), and
hand it over to the programmer (forwardInvocation:) who is then
allowed to manipulate the method invocation using a high-level API
provided by the “Foundation” library. For example, the programmer
may want to examine the method invocation arguments and name and
potentially change them before forwarding the method invocation to one
or more local objects (performInvocation:) or even to remote
objects (by using Distributed Objects or some other mechanism). When
all this completes, the return value is passed back and must be
returned correctly to the original caller.
Note that the GNU Objective-C runtime currently provides no support
for method forwarding or method invocations other than the
__objc_msg_forward2 hook.
If the forwarding hook does not exist or returns NULL, the
runtime currently attempts forwarding using an older, deprecated API,
and if that fails, it aborts the program. In future versions of the
GNU Objective-C runtime, the runtime will immediately abort.
Binary compatibility encompasses several related concepts:
The application binary interface implemented by a C or C++ compiler affects code generation and runtime support for:
In addition, the application binary interface implemented by a C++ compiler affects code generation and runtime support for:
Some GCC compilation options cause the compiler to generate code that does not conform to the platform's default ABI. Other options cause different program behavior for implementation-defined features that are not covered by an ABI. These options are provided for consistency with other compilers that do not follow the platform's default ABI or the usual behavior of implementation-defined features for the platform. Be very careful about using such options.
Most platforms have a well-defined ABI that covers C code, but ABIs that cover C++ functionality are not yet common.
Starting with GCC 3.2, GCC binary conventions for C++ are based on a written, vendor-neutral C++ ABI that was designed to be specific to 64-bit Itanium but also includes generic specifications that apply to any platform. This C++ ABI is also implemented by other compiler vendors on some platforms, notably GNU/Linux and BSD systems. We have tried hard to provide a stable ABI that will be compatible with future GCC releases, but it is possible that we will encounter problems that make this difficult. Such problems could include different interpretations of the C++ ABI by different vendors, bugs in the ABI, or bugs in the implementation of the ABI in different compilers. GCC's -Wabi switch warns when G++ generates code that is probably not compatible with the C++ ABI.
The C++ library used with a C++ compiler includes the Standard C++ Library, with functionality defined in the C++ Standard, plus language runtime support. The runtime support is included in a C++ ABI, but there is no formal ABI for the Standard C++ Library. Two implementations of that library are interoperable if one follows the de-facto ABI of the other and if they are both built with the same compiler, or with compilers that conform to the same ABI for C++ compiler and runtime support.
When G++ and another C++ compiler conform to the same C++ ABI, but the implementations of the Standard C++ Library that they normally use do not follow the same ABI for the Standard C++ Library, object files built with those compilers can be used in the same program only if they use the same C++ library. This requires specifying the location of the C++ library header files when invoking the compiler whose usual library is not being used. The location of GCC's C++ header files depends on how the GCC build was configured, but can be seen by using the G++ -v option. With default configuration options for G++ 3.3 the compile line for a different C++ compiler needs to include
-Igcc_install_directory/include/c++/3.3
Similarly, compiling code with G++ that must use a C++ library other than the GNU C++ library requires specifying the location of the header files for that other library.
The most straightforward way to link a program to use a particular C++ library is to use a C++ driver that specifies that C++ library by default. The g++ driver, for example, tells the linker where to find GCC's C++ library (libstdc++) plus the other libraries and startup files it needs, in the proper order.
If a program must use a different C++ library and it's not possible to do the final link using a C++ driver that uses that library by default, it is necessary to tell g++ the location and name of that library. It might also be necessary to specify different startup files and other runtime support libraries, and to suppress the use of GCC's support libraries with one or more of the options -nostdlib, -nostartfiles, and -nodefaultlibs.
gcov is a tool you can use in conjunction with GCC to test code coverage in your programs.
gcov is a test coverage program. Use it in concert with GCC to analyze your programs to help create more efficient, faster running code and to discover untested parts of your program. You can use gcov as a profiling tool to help discover where your optimization efforts will best affect your code. You can also use gcov along with the other profiling tool, gprof, to assess which parts of your code use the greatest amount of computing time.
Profiling tools help you analyze your code's performance. Using a profiler such as gcov or gprof, you can find out some basic performance statistics, such as:
Once you know these things about how your code works when compiled, you can look at each module to see which modules should be optimized. gcov helps you determine where to work on optimization.
Software developers also use coverage testing in concert with testsuites, to make sure software is actually good enough for a release. Testsuites can verify that a program works as expected; a coverage program tests to see how much of the program is exercised by the testsuite. Developers can then determine what kinds of test cases need to be added to the testsuites to create both better testing and a better final product.
You should compile your code without optimization if you plan to use gcov because the optimization, by combining some lines of code into one function, may not give you as much information as you need to look for `hot spots' where the code is using a great deal of computer time. Likewise, because gcov accumulates statistics by line (at the lowest resolution), it works best with a programming style that places only one statement on each line. If you use complicated macros that expand to loops or to other control structures, the statistics are less helpful—they only report on the line where the macro call appears. If your complex macros behave like functions, you can replace them with inline functions to solve this problem.
gcov creates a logfile called sourcefile.gcov which indicates how many times each line of a source file sourcefile.c has executed. You can use these logfiles along with gprof to aid in fine-tuning the performance of your programs. gprof gives timing information you can use along with the information you get from gcov.
gcov works only on code compiled with GCC. It is not compatible with any other profiling or test coverage mechanism.
gcov [options] files
gcov accepts the following options:
-a--all-blocks-b--branch-probabilities-c--branch-counts-d--display-progress-f--function-summaries-h--help-j--json-formatStructure of the JSON is following:
{
"current_working_directory": "foo/bar",
"data_file": "a.out",
"format_version": "1",
"gcc_version": "11.1.1 20210510"
"files": ["$file"]
}
Fields of the root element have following semantics:
Each file has the following form:
{
"file": "a.c",
"functions": ["$function"],
"lines": ["$line"]
}
Fields of the file element have following semantics:
Each function has the following form:
{
"blocks": 2,
"blocks_executed": 2,
"demangled_name": "foo",
"end_column": 1,
"end_line": 4,
"execution_count": 1,
"name": "foo",
"start_column": 5,
"start_line": 1
}
Fields of the function element have following semantics:
Note that line numbers and column numbers number from 1. In the current implementation, start_line and start_column do not include any template parameters and the leading return type but that this is likely to be fixed in the future.
Each line has the following form:
{
"branches": ["$branch"],
"count": 2,
"line_number": 15,
"unexecuted_block": false,
"function_name": "foo",
}
Branches are present only with -b option. Fields of the line element have following semantics:
Each branch has the following form:
{
"count": 11,
"fallthrough": true,
"throw": false
}
Fields of the branch element have following semantics:
-H--human-readable-k--use-colors-l--long-file-names-m--demangled-names-n--no-output-o directory|file--object-directory directory--object-file file-p--preserve-paths-q--use-hotness-colors-r--relative-only-s directory--source-prefix directory-t--stdout-u--unconditional-branches-v--version-w--verbose-x--hash-filenamesgcov should be run with the current directory the same as that when you invoked the compiler. Otherwise it will not be able to locate the source files. gcov produces files called mangledname.gcov in the current directory. These contain the coverage information of the source file they correspond to. One .gcov file is produced for each source (or header) file containing code, which was compiled to produce the data files. The mangledname part of the output file name is usually simply the source file name, but can be something more complicated if the ‘-l’ or ‘-p’ options are given. Refer to those options for details.
If you invoke gcov with multiple input files, the contributions from each input file are summed. Typically you would invoke it with the same list of files as the final link of your executable.
The .gcov files contain the ‘:’ separated fields along with program source code. The format is
execution_count:line_number:source line text
Additional block information may succeed each line, when requested by command line option. The execution_count is ‘-’ for lines containing no code. Unexecuted lines are marked ‘#####’ or ‘=====’, depending on whether they are reachable by non-exceptional paths or only exceptional paths such as C++ exception handlers, respectively. Given the ‘-a’ option, unexecuted blocks are marked ‘$$$$$’ or ‘%%%%%’, depending on whether a basic block is reachable via non-exceptional or exceptional paths. Executed basic blocks having a statement with zero execution_count end with ‘*’ character and are colored with magenta color with the -k option. This functionality is not supported in Ada.
Note that GCC can completely remove the bodies of functions that are not needed – for instance if they are inlined everywhere. Such functions are marked with ‘-’, which can be confusing. Use the -fkeep-inline-functions and -fkeep-static-functions options to retain these functions and allow gcov to properly show their execution_count.
Some lines of information at the start have line_number of zero. These preamble lines are of the form
-:0:tag:value
The ordering and number of these preamble lines will be augmented as gcov development progresses — do not rely on them remaining unchanged. Use tag to locate a particular preamble line.
The additional block information is of the form
tag information
The information is human readable, but designed to be simple enough for machine parsing too.
When printing percentages, 0% and 100% are only printed when the values are exactly 0% and 100% respectively. Other values which would conventionally be rounded to 0% or 100% are instead printed as the nearest non-boundary value.
When using gcov, you must first compile your program with a special GCC option ‘--coverage’. This tells the compiler to generate additional information needed by gcov (basically a flow graph of the program) and also includes additional code in the object files for generating the extra profiling information needed by gcov. These additional files are placed in the directory where the object file is located.
Running the program will cause profile output to be generated. For each source file compiled with -fprofile-arcs, an accompanying .gcda file will be placed in the object file directory.
Running gcov with your program's source file names as arguments will now produce a listing of the code along with frequency of execution for each line. For example, if your program is called tmp.cpp, this is what you see when you use the basic gcov facility:
$ g++ --coverage tmp.cpp -c
$ g++ --coverage tmp.o
$ a.out
$ gcov tmp.cpp -m
File 'tmp.cpp'
Lines executed:92.86% of 14
Creating 'tmp.cpp.gcov'
The file tmp.cpp.gcov contains output from gcov. Here is a sample:
-: 0:Source:tmp.cpp
-: 0:Working directory:/home/gcc/testcase
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:template<class T>
-: 4:class Foo
-: 5:{
-: 6: public:
1*: 7: Foo(): b (1000) {}
------------------
Foo<char>::Foo():
#####: 7: Foo(): b (1000) {}
------------------
Foo<int>::Foo():
1: 7: Foo(): b (1000) {}
------------------
2*: 8: void inc () { b++; }
------------------
Foo<char>::inc():
#####: 8: void inc () { b++; }
------------------
Foo<int>::inc():
2: 8: void inc () { b++; }
------------------
-: 9:
-: 10: private:
-: 11: int b;
-: 12:};
-: 13:
-: 14:template class Foo<int>;
-: 15:template class Foo<char>;
-: 16:
-: 17:int
1: 18:main (void)
-: 19:{
-: 20: int i, total;
1: 21: Foo<int> counter;
-: 22:
1: 23: counter.inc();
1: 24: counter.inc();
1: 25: total = 0;
-: 26:
11: 27: for (i = 0; i < 10; i++)
10: 28: total += i;
-: 29:
1*: 30: int v = total > 100 ? 1 : 2;
-: 31:
1: 32: if (total != 45)
#####: 33: printf ("Failure\n");
-: 34: else
1: 35: printf ("Success\n");
1: 36: return 0;
-: 37:}
Note that line 7 is shown in the report multiple times. First occurrence presents total number of execution of the line and the next two belong to instances of class Foo constructors. As you can also see, line 30 contains some unexecuted basic blocks and thus execution count has asterisk symbol.
When you use the -a option, you will get individual block counts, and the output looks like this:
-: 0:Source:tmp.cpp
-: 0:Working directory:/home/gcc/testcase
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:template<class T>
-: 4:class Foo
-: 5:{
-: 6: public:
1*: 7: Foo(): b (1000) {}
------------------
Foo<char>::Foo():
#####: 7: Foo(): b (1000) {}
------------------
Foo<int>::Foo():
1: 7: Foo(): b (1000) {}
------------------
2*: 8: void inc () { b++; }
------------------
Foo<char>::inc():
#####: 8: void inc () { b++; }
------------------
Foo<int>::inc():
2: 8: void inc () { b++; }
------------------
-: 9:
-: 10: private:
-: 11: int b;
-: 12:};
-: 13:
-: 14:template class Foo<int>;
-: 15:template class Foo<char>;
-: 16:
-: 17:int
1: 18:main (void)
-: 19:{
-: 20: int i, total;
1: 21: Foo<int> counter;
1: 21-block 0
-: 22:
1: 23: counter.inc();
1: 23-block 0
1: 24: counter.inc();
1: 24-block 0
1: 25: total = 0;
-: 26:
11: 27: for (i = 0; i < 10; i++)
1: 27-block 0
11: 27-block 1
10: 28: total += i;
10: 28-block 0
-: 29:
1*: 30: int v = total > 100 ? 1 : 2;
1: 30-block 0
%%%%%: 30-block 1
1: 30-block 2
-: 31:
1: 32: if (total != 45)
1: 32-block 0
#####: 33: printf ("Failure\n");
%%%%%: 33-block 0
-: 34: else
1: 35: printf ("Success\n");
1: 35-block 0
1: 36: return 0;
1: 36-block 0
-: 37:}
In this mode, each basic block is only shown on one line – the last line of the block. A multi-line block will only contribute to the execution count of that last line, and other lines will not be shown to contain code, unless previous blocks end on those lines. The total execution count of a line is shown and subsequent lines show the execution counts for individual blocks that end on that line. After each block, the branch and call counts of the block will be shown, if the -b option is given.
Because of the way GCC instruments calls, a call count can be shown after a line with no individual blocks. As you can see, line 33 contains a basic block that was not executed.
When you use the -b option, your output looks like this:
-: 0:Source:tmp.cpp
-: 0:Working directory:/home/gcc/testcase
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:template<class T>
-: 4:class Foo
-: 5:{
-: 6: public:
1*: 7: Foo(): b (1000) {}
------------------
Foo<char>::Foo():
function Foo<char>::Foo() called 0 returned 0% blocks executed 0%
#####: 7: Foo(): b (1000) {}
------------------
Foo<int>::Foo():
function Foo<int>::Foo() called 1 returned 100% blocks executed 100%
1: 7: Foo(): b (1000) {}
------------------
2*: 8: void inc () { b++; }
------------------
Foo<char>::inc():
function Foo<char>::inc() called 0 returned 0% blocks executed 0%
#####: 8: void inc () { b++; }
------------------
Foo<int>::inc():
function Foo<int>::inc() called 2 returned 100% blocks executed 100%
2: 8: void inc () { b++; }
------------------
-: 9:
-: 10: private:
-: 11: int b;
-: 12:};
-: 13:
-: 14:template class Foo<int>;
-: 15:template class Foo<char>;
-: 16:
-: 17:int
function main called 1 returned 100% blocks executed 81%
1: 18:main (void)
-: 19:{
-: 20: int i, total;
1: 21: Foo<int> counter;
call 0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
-: 22:
1: 23: counter.inc();
call 0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
1: 24: counter.inc();
call 0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
1: 25: total = 0;
-: 26:
11: 27: for (i = 0; i < 10; i++)
branch 0 taken 91% (fallthrough)
branch 1 taken 9%
10: 28: total += i;
-: 29:
1*: 30: int v = total > 100 ? 1 : 2;
branch 0 taken 0% (fallthrough)
branch 1 taken 100%
-: 31:
1: 32: if (total != 45)
branch 0 taken 0% (fallthrough)
branch 1 taken 100%
#####: 33: printf ("Failure\n");
call 0 never executed
branch 1 never executed
branch 2 never executed
-: 34: else
1: 35: printf ("Success\n");
call 0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
1: 36: return 0;
-: 37:}
For each function, a line is printed showing how many times the function is called, how many times it returns and what percentage of the function's blocks were executed.
For each basic block, a line is printed after the last line of the basic block describing the branch or call that ends the basic block. There can be multiple branches and calls listed for a single source line if there are multiple basic blocks that end on that line. In this case, the branches and calls are each given a number. There is no simple way to map these branches and calls back to source constructs. In general, though, the lowest numbered branch or call will correspond to the leftmost construct on the source line.
For a branch, if it was executed at least once, then a percentage indicating the number of times the branch was taken divided by the number of times the branch was executed will be printed. Otherwise, the message “never executed” is printed.
For a call, if it was executed at least once, then a percentage
indicating the number of times the call returned divided by the number
of times the call was executed will be printed. This will usually be
100%, but may be less for functions that call exit or longjmp,
and thus may not return every time they are called.
The execution counts are cumulative. If the example program were executed again without removing the .gcda file, the count for the number of times each line in the source was executed would be added to the results of the previous run(s). This is potentially useful in several ways. For example, it could be used to accumulate data over a number of program runs as part of a test verification suite, or to provide more accurate long-term information over a large number of program runs.
The data in the .gcda files is saved immediately before the program exits. For each source file compiled with -fprofile-arcs, the profiling code first attempts to read in an existing .gcda file; if the file doesn't match the executable (differing number of basic block counts) it will ignore the contents of the file. It then adds in the new execution counts and finally writes the data to the file.
gcov can genuinely perform decision coverage by using option -b (i.e. showing that each branch was taken). But you can even go further, showing that each individual subcondition is covered and can modify the global decision. For example:
int is_cond (int a, int b, int c)
{
return (a >= 0) || (b == 0 && c != 0);
}
You have to write testcases (the minimum is 4 here) to show that each argument can make the function return 0.
In principle, you can achieve this result with gcov by using a
particular coding style: always use short-circuit boolean operators.
This is a very natural coding style in C as the boolean operators
|| and && are short-circuit operators.
A consequence of the short-circuit operator is that a decision is made for each individual subcondition. With a properly written test harness, the result of ‘gcov -b -c’ on the previous example can be:
-: 1:int is_cond (int a, int b, int c)
function is_cond called 4 returned 100% blocks executed 100%
4: 2:{
4: 3: return (a >= 0) || (b == 0 && c != 0);
branch 0 taken 3 (fallthrough)
branch 1 taken 1
branch 2 taken 2 (fallthrough)
branch 3 taken 1
branch 4 taken 1 (fallthrough)
branch 5 taken 1
-: 4:}
There are 3 decisions and thus 6 branches (1 for the true path and one for the false path). And with the 4 tests all the branches are taken.
By default, the GCC optimizers may defeat this approach by performing transformations that break the low-level control flow representativity of the source-level control flow. -fpreserve-control-flow can be passed on the command line to disable these transformations.
If you plan to use gcov to help optimize your code, you must first compile your program with a special GCC option ‘--coverage’. Aside from that, you can use any other GCC options; but if you want to prove that every single line in your program was executed, you should not compile with optimization at the same time. On some machines the optimizer can eliminate some simple code lines by combining them with other lines. For example, code like this:
if (a != b)
c = 1;
else
c = 0;
can be compiled into one instruction on some machines. In this case, there is no way for gcov to calculate separate execution counts for each line because there isn't separate code for each line. Hence the gcov output looks like this if you compiled the program with optimization:
100: 12:if (a != b)
100: 13: c = 1;
100: 14:else
100: 15: c = 0;
The output shows that this block of code, combined by optimization, executed 100 times. In one sense this result is correct, because there was only one instruction representing all four of these lines. However, the output does not indicate how many times the result was 0 and how many times the result was 1.
Inlineable functions can create unexpected line counts. Line counts are shown for the source code of the inlineable function, but what is shown depends on where the function is inlined, or if it is not inlined at all.
If the function is not inlined, the compiler must emit an out of line copy of the function, in any object file that needs it. If fileA.o and fileB.o both contain out of line bodies of a particular inlineable function, they will also both contain coverage counts for that function. When fileA.o and fileB.o are linked together, the linker will, on many systems, select one of those out of line bodies for all calls to that function, and remove or ignore the other. Unfortunately, it will not remove the coverage counters for the unused function body. Hence when instrumented, all but one use of that function will show zero counts.
If the function is inlined in several places, the block structure in each location might not be the same. For instance, a condition might now be calculable at compile time in some instances. Because the coverage of all the uses of the inline function will be shown for the same source lines, the line counts themselves might seem inconsistent.
Long-running applications can use the __gcov_reset and __gcov_dump
facilities to restrict profile collection to the program region of
interest. Calling __gcov_reset(void) will clear all run-time profile
counters to zero, and calling __gcov_dump(void) will cause the profile
information collected at that point to be dumped to .gcda output files.
Instrumented applications use a static destructor with priority 99
to invoke the __gcov_dump function. Thus __gcov_dump
is executed after all user defined static destructors,
as well as handlers registered with atexit.
If an executable loads a dynamic shared object via dlopen functionality, -Wl,--dynamic-list-data is needed to dump all profile data.
Profiling run-time library reports various errors related to profile manipulation and profile saving. Errors are printed into standard error output or ‘GCOV_ERROR_FILE’ file, if environment variable is used. In order to terminate immediately after an errors occurs set ‘GCOV_EXIT_AT_ERROR’ environment variable. That can help users to find profile clashing which leads to a misleading profile.
gcov uses two files for profiling. The names of these files are derived from the original object file by substituting the file suffix with either .gcno, or .gcda. The files contain coverage and profile data stored in a platform-independent format. The .gcno files are placed in the same directory as the object file. By default, the .gcda files are also stored in the same directory as the object file, but the GCC -fprofile-dir option may be used to store the .gcda files in a separate directory.
The .gcno notes file is generated when the source file is compiled with the GCC -ftest-coverage option. It contains information to reconstruct the basic block graphs and assign source line numbers to blocks.
The .gcda count data file is generated when a program containing object files built with the GCC -fprofile-arcs option is executed. A separate .gcda file is created for each object file compiled with this option. It contains arc transition counts, value profile counts, and some summary information.
It is not recommended to access the coverage files directly. Consumers should use the intermediate format that is provided by gcov tool via --json-format option.
Running the program will cause profile output to be generated. For each source file compiled with -fprofile-arcs, an accompanying .gcda file will be placed in the object file directory. That implicitly requires running the program on the same system as it was built or having the same absolute directory structure on the target system. The program will try to create the needed directory structure, if it is not already present.
To support cross-profiling, a program compiled with -fprofile-arcs can relocate the data files based on two environment variables:
Note: If GCOV_PREFIX_STRIP is set without GCOV_PREFIX is undefined, then a relative path is made out of the hardwired absolute paths.
For example, if the object file /user/build/foo.o was built with -fprofile-arcs, the final executable will try to create the data file /user/build/foo.gcda when running on the target system. This will fail if the corresponding directory does not exist and it is unable to create it. This can be overcome by, for example, setting the environment as ‘GCOV_PREFIX=/target/run’ and ‘GCOV_PREFIX_STRIP=1’. Such a setting will name the data file /target/run/build/foo.gcda.
You must move the data files to the expected directory tree in order to use them for profile directed optimizations (-fprofile-use), or to use the gcov tool.
In case your application runs in a hosted environment such as GNU/Linux, then this section is likely not relevant to you. This section is intended for application developers targeting freestanding environments (for example embedded systems) with limited resources. In particular, systems or test cases which do not support constructors/destructors or the C library file I/O. In this section, the target system runs your application instrumented for profiling or test coverage. You develop and analyze your application on the host system. We now provide an overview how profiling and test coverage can be obtained in this scenario followed by a tutorial which can be exercised on the host system. Finally, some system initialization caveats are listed.
For an application instrumented for profiling or test coverage, the compiler
generates some global data structures which are updated by instrumentation code
while the application runs. These data structures are called the gcov
information. Normally, when the application exits, the gcov information is
stored to .gcda files. There is one file per translation unit
instrumented for profiling or test coverage. The function
__gcov_exit(), which stores the gcov information to a file, is called by
a global destructor function for each translation unit instrumented for
profiling or test coverage. It runs at process exit. In a global constructor
function, the __gcov_init() function is called to register the gcov
information of a translation unit in a global list. In some situations, this
procedure does not work. Firstly, if you want to profile the global
constructor or exit processing of an operating system, the compiler generated
functions may conflict with the test objectives. Secondly, you may want to
test early parts of the system initialization or abnormal program behaviour
which do not allow a global constructor or exit processing. Thirdly, you need
a filesystem to store the files.
The -fprofile-info-section GCC option enables you to use profiling and
test coverage in freestanding environments. This option disables the use of
global constructors and destructors for the gcov information. Instead, a
pointer to the gcov information is stored in a special linker input section for
each translation unit which is compiled with this option. By default, the
section name is .gcov_info. The gcov information is statically
initialized. The pointers to the gcov information from all translation units
of an executable can be collected by the linker in a contiguous memory block.
For the GNU linker, the below linker script output section definition can be
used to achieve this:
.gcov_info :
{
PROVIDE (__gcov_info_start = .);
KEEP (*(.gcov_info))
PROVIDE (__gcov_info_end = .);
}
The linker will provide two global symbols, __gcov_info_start and
__gcov_info_end, which define the start and end of the array of pointers
to gcov information blocks, respectively. The KEEP () directive is
required to prevent a garbage collection of the pointers. They are not
directly referenced by anything in the executable. The section may be placed
in a read-only memory area.
In order to transfer the profiling and test coverage data from the target to
the host system, the application has to provide a function to produce a
reliable in order byte stream from the target to the host. The byte stream may
be compressed and encoded using error detection and correction codes to meet
application-specific requirements. The GCC provided libgcov target
library provides two functions, __gcov_info_to_gcda() and
__gcov_filename_to_gcfn(), to generate a byte stream from a gcov
information bock. The functions are declared in #include <gcov.h>. The
byte stream can be deserialized by the merge-stream subcommand of the
gcov-tool to create or update .gcda files in the host
filesystem for the instrumented application.
This tutorial should be exercised on the host system. We will build a program instrumented for test coverage. The program runs an application and dumps the gcov information to stderr encoded as a printable character stream. The application simply decodes such character streams from stdin and writes the decoded character stream to stdout (warning: this is binary data). The decoded character stream is consumed by the merge-stream subcommand of the gcov-tool to create or update the .gcda files.
To get started, create an empty directory. Change into the new directory. Then you will create the following three files in this directory
Firstly, create the header file app.h with the following content:
static const unsigned char a = 'a';
static inline unsigned char *
encode (unsigned char c, unsigned char buf[2])
{
buf[0] = c % 16 + a;
buf[1] = (c / 16) % 16 + a;
return buf;
}
extern void application (void);
Secondly, create the source file app.c with the following content:
#include "app.h"
#include <stdio.h>
/* The application reads a character stream encoded by encode() from stdin,
decodes it, and writes the decoded characters to stdout. Characters other
than the 16 characters 'a' to 'p' are ignored. */
static int can_decode (unsigned char c)
{
return (unsigned char)(c - a) < 16;
}
void
application (void)
{
int first = 1;
int i;
unsigned char c;
while ((i = fgetc (stdin)) != EOF)
{
unsigned char x = (unsigned char)i;
if (can_decode (x))
{
if (first)
c = x - a;
else
fputc (c + 16 * (x - a), stdout);
first = !first;
}
else
first = 1;
}
}
Thirdly, create the source file main.c with the following content:
#include "app.h"
#include <gcov.h>
#include <stdio.h>
#include <stdlib.h>
/* The start and end symbols are provided by the linker script. We use the
array notation to avoid issues with a potential small-data area. */
extern const struct gcov_info *const __gcov_info_start[];
extern const struct gcov_info *const __gcov_info_end[];
/* This function shall produce a reliable in order byte stream to transfer the
gcov information from the target to the host system. */
static void
dump (const void *d, unsigned n, void *arg)
{
(void)arg;
const unsigned char *c = d;
unsigned char buf[2];
for (unsigned i = 0; i < n; ++i)
fwrite (encode (c[i], buf), sizeof (buf), 1, stderr);
}
/* The filename is serialized to a gcfn data stream by the
__gcov_filename_to_gcfn() function. The gcfn data is used by the
"merge-stream" subcommand of the "gcov-tool" to figure out the filename
associated with the gcov information. */
static void
filename (const char *f, void *arg)
{
__gcov_filename_to_gcfn (f, dump, arg);
}
/* The __gcov_info_to_gcda() function may have to allocate memory under
certain conditions. Simply try it out if it is needed for your application
or not. */
static void *
allocate (unsigned length, void *arg)
{
(void)arg;
return malloc (length);
}
/* Dump the gcov information of all translation units. */
static void
dump_gcov_info (void)
{
const struct gcov_info *const *info = __gcov_info_start;
const struct gcov_info *const *end = __gcov_info_end;
/* Obfuscate variable to prevent compiler optimizations. */
__asm__ ("" : "+r" (info));
while (info != end)
{
void *arg = NULL;
__gcov_info_to_gcda (*info, filename, dump, allocate, arg);
fputc ('\n', stderr);
++info;
}
}
/* The main() function just runs the application and then dumps the gcov
information to stderr. */
int
main (void)
{
application ();
dump_gcov_info ();
return 0;
}
If we compile app.c with test coverage and no extra profiling options,
then a global constructor (_sub_I_00100_0 here, it may have a different
name in your environment) and destructor (_sub_D_00100_1) is used to
register and dump the gcov information, respectively. We also see undefined
references to __gcov_init and __gcov_exit:
$ gcc --coverage -c app.c
$ nm app.o
0000000000000000 r a
0000000000000030 T application
0000000000000000 t can_decode
U fgetc
U fputc
0000000000000000 b __gcov0.application
0000000000000038 b __gcov0.can_decode
0000000000000000 d __gcov_.application
00000000000000c0 d __gcov_.can_decode
U __gcov_exit
U __gcov_init
U __gcov_merge_add
U stdin
U stdout
0000000000000161 t _sub_D_00100_1
0000000000000151 t _sub_I_00100_0
Compile app.c and main.c with test coverage and
-fprofile-info-section. Now, a read-only pointer size object is
present in the .gcov_info section and there are no undefined references
to __gcov_init and __gcov_exit:
$ gcc --coverage -fprofile-info-section -c main.c
$ gcc --coverage -fprofile-info-section -c app.c
$ objdump -h app.o
app.o: file format elf64-x86-64
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000151 0000000000000000 0000000000000000 00000040 2**0
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
1 .data 00000100 0000000000000000 0000000000000000 000001a0 2**5
CONTENTS, ALLOC, LOAD, RELOC, DATA
2 .bss 00000040 0000000000000000 0000000000000000 000002a0 2**5
ALLOC
3 .rodata 0000003c 0000000000000000 0000000000000000 000002a0 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .gcov_info 00000008 0000000000000000 0000000000000000 000002e0 2**3
CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
5 .comment 0000004e 0000000000000000 0000000000000000 000002e8 2**0
CONTENTS, READONLY
6 .note.GNU-stack 00000000 0000000000000000 0000000000000000 00000336 2**0
CONTENTS, READONLY
7 .eh_frame 00000058 0000000000000000 0000000000000000 00000338 2**3
CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
We have to customize the program link procedure so that all the
.gcov_info linker input sections are placed in a contiguous memory block
with a begin and end symbol. Firstly, get the default linker script using the
following commands (we assume a GNU linker):
$ ld --verbose | sed '1,/^===/d' | sed '/^===/d' > linkcmds
Secondly, open the file linkcmds with a text editor and place the linker
output section definition from the overview after the .rodata section
definition. Link the program executable using the customized linker script:
$ gcc --coverage main.o app.o -T linkcmds -Wl,-Map,app.map
In the linker map file app.map, we see that the linker placed the
read-only pointer size objects of our objects files main.o and
app.o into a contiguous memory block and provided the symbols
__gcov_info_start and __gcov_info_end:
$ grep -C 1 "\.gcov_info" app.map
.gcov_info 0x0000000000403ac0 0x10
0x0000000000403ac0 PROVIDE (__gcov_info_start = .)
*(.gcov_info)
.gcov_info 0x0000000000403ac0 0x8 main.o
.gcov_info 0x0000000000403ac8 0x8 app.o
0x0000000000403ad0 PROVIDE (__gcov_info_end = .)
Make sure no .gcda files are present. Run the program with nothing to decode and dump stderr to the file gcda-0.txt (first run). Run the program to decode gcda-0.txt and send it to the gcov-tool using the merge-stream subcommand to create the .gcda files (second run). Run gcov to produce a report for app.c. We see that the first run with nothing to decode results in a partially covered application:
$ rm -f app.gcda main.gcda
$ echo "" | ./a.out 2>gcda-0.txt
$ ./a.out <gcda-0.txt 2>gcda-1.txt | gcov-tool merge-stream
$ gcov -bc app.c
File 'app.c'
Lines executed:69.23% of 13
Branches executed:66.67% of 6
Taken at least once:50.00% of 6
Calls executed:66.67% of 3
Creating 'app.c.gcov'
Lines executed:69.23% of 13
Run the program to decode gcda-1.txt and send it to the gcov-tool using the merge-stream subcommand to update the .gcda files. Run gcov to produce a report for app.c. Since the second run decoded the gcov information of the first run, we have now a fully covered application:
$ ./a.out <gcda-1.txt 2>gcda-2.txt | gcov-tool merge-stream
$ gcov -bc app.c
File 'app.c'
Lines executed:100.00% of 13
Branches executed:100.00% of 6
Taken at least once:100.00% of 6
Calls executed:100.00% of 3
Creating 'app.c.gcov'
Lines executed:100.00% of 13
The gcov information of a translation unit consists of several global data
structures. For example, the instrumented code may update program flow graph
edge counters in a zero-initialized data structure. It is safe to run
instrumented code before the zero-initialized data is cleared to zero. The
coverage information obtained before the zero-initialized data is cleared to
zero is unusable. Dumping the gcov information using
__gcov_info_to_gcda() before the zero-initialized data is cleared to
zero or the initialized data is loaded, is undefined behaviour. Clearing the
zero-initialized data to zero through a function instrumented for profiling or
test coverage is undefined behaviour, since it may produce inconsistent program
flow graph edge counters for example.
gcov-tool is a tool you can use in conjunction with GCC to manipulate or process gcda profile files offline.
gcov-tool is an offline tool to process gcc's gcda profile files.
Current gcov-tool supports the following functionalities:
Examples of the use cases for this tool are:
Note that for the merging operation, this profile generated offline may contain slight different values from the online merged profile. Here are a list of typical differences:
gcov-tool [global-options] SUB_COMMAND [sub_command-options] profile_dir
gcov-tool accepts the following options:
-h--help-v--versionmerge-o directory--output directory-v--verbose-w w1,w2--weight w1,w2merge-streamFor the generation of a gcfn and gcda data stream on the target
system, please have a look at the __gcov_filename_to_gcfn() and
__gcov_info_to_gcda() functions declared in #include <gcov.h>.
-v--verbose-w w1,w2--weight w1,w2rewrite-n long_long_value--normalize <long_long_value>-o directory--output directory-s float_or_simple-frac_value--scale float_or_simple-frac_value-v--verboseoverlap-f--function-F--fullname-h--hotonly-o--object-t float--hot_threshold <float>-v--verbosegcov-dump is a tool you can use in conjunction with GCC to dump content of gcda and gcno profile files offline.
Usage: gcov-dump [OPTION] ... gcovfiles
gcov-dump accepts the following options:
-h--help-l--long-p--positions-r--raw-s--stable-v--versionlto-dump is a tool you can use in conjunction with GCC to dump link time optimization object files.
Usage: lto-dump [OPTION] ... objfiles
lto-dump accepts the following options:
-list-demangle-defined-only-print-value-name-sort-size-sort-reverse-sort-no-sort-symbol=-objects-type-stats-tree-stats-gimple-stats-dump-level=-dump-body=-helpThis section describes known problems that affect users of GCC. Most of these are not GCC bugs per se—if they were, we would fix them. But the result for a user may be like the result of a bug.
Some of these problems are due to bugs in other software, some are missing features that are too much work to add, and some are places where people's opinions differ as to what is best.
fixincludes script interacts badly with automounters; if the
directory of system header files is automounted, it tends to be
unmounted while fixincludes is running. This would seem to be a
bug in the automounter. We don't know any good way to work around it.
This section lists various difficulties encountered in using GCC together with other compilers or with the assemblers, linkers, libraries and debuggers on certain systems.
An area where the difference is most apparent is name mangling. The use of different name mangling is intentional, to protect you from more subtle problems. Compilers differ as to many internal details of C++ implementation, including: how class instances are laid out, how multiple inheritance is implemented, and how virtual function calls are handled. If the name encoding were made the same, your programs would link against libraries provided from other compilers—but the programs would then crash when run. Incompatible libraries are then detected at link time, rather than at run time.
double on an 8-byte
boundary, and it expects every double to be so aligned. The Sun
compiler usually gives double values 8-byte alignment, with one
exception: function arguments of type double may not be aligned.
As a result, if a function compiled with Sun CC takes the address of an
argument of type double and passes this pointer of type
double * to a function compiled with GCC, dereferencing the
pointer may cause a fatal signal.
One way to solve this problem is to compile your entire program with GCC.
Another solution is to modify the function that is compiled with
Sun CC to copy the argument into a local variable; local variables
are always properly aligned. A third solution is to modify the function
that uses the pointer to dereference it via the following function
access_double instead of directly with ‘*’:
inline double
access_double (double *unaligned_ptr)
{
union d2i { double d; int i[2]; };
union d2i *p = (union d2i *) unaligned_ptr;
union d2i u;
u.i[0] = p->i[0];
u.i[1] = p->i[1];
return u.d;
}
Storing into the pointer can be done likewise with the same union.
malloc function in the libmalloc.a library
may allocate memory that is only 4 byte aligned. Since GCC on the
SPARC assumes that doubles are 8 byte aligned, this may result in a
fatal signal if doubles are stored in memory allocated by the
libmalloc.a library.
The solution is to not use the libmalloc.a library. Use instead
malloc and related functions from libc.a; they do not have
this problem.
alloca or variable-size arrays. This is because GCC doesn't
generate HP-UX unwind descriptors for such functions. It may even be
impossible to generate them.
(warning) Use of GR3 when
frame >= 8192 may cause conflict.
These warnings are harmless and can be safely ignored.
There are several noteworthy incompatibilities between GNU C and K&R (non-ISO) versions of C.
One consequence is that you cannot call mktemp with a string
constant argument. The function mktemp always alters the
string its argument points to.
Another consequence is that sscanf does not work on some very
old systems when passed a string constant as its format control string
or input. This is because sscanf incorrectly tries to write
into the string constant. Likewise fscanf and scanf.
The solution to these problems is to change the program to use
char-array variables with initialization strings for these
purposes instead of string constants.
-2147483648 is positive.
This is because 2147483648 cannot fit in the type int, so
(following the ISO C rules) its data type is unsigned long int.
Negating this value yields 2147483648 again.
#define foo(a) "a"
will produce output "a" regardless of what the argument a is.
setjmp and longjmp, the only automatic
variables guaranteed to remain valid are those declared
volatile. This is a consequence of automatic register
allocation. Consider this function:
jmp_buf j;
foo ()
{
int a, b;
a = fun1 ();
if (setjmp (j))
return a;
a = fun2 ();
/* longjmp (j) may occur in fun3. */
return a + fun3 ();
}
Here a may or may not be restored to its first value when the
longjmp occurs. If a is allocated in a register, then
its first value is restored; otherwise, it keeps the last value stored
in it.
If you use the -W option with the -O option, you will get a warning when GCC thinks such a problem might be possible.
foobar (
#define luser
hack)
ISO C does not permit such a construct.
In some other C compilers, an extern declaration affects all the
rest of the file even if it happens within a block.
long, etc., with a typedef name,
as shown here:
typedef int foo;
typedef long foo bar;
In ISO C, this is not allowed: long and other type modifiers
require an explicit int.
typedef int foo;
typedef foo foo;
#if 0
You can't expect this to work.
#endif
The best solution to such a problem is to put the text into an actual C comment delimited by ‘/*...*/’.
time, so it did not matter what type your program declared it to
return. But in systems with ISO C headers, time is declared to
return time_t, and if that is not the same as long, then
‘long time ();’ is erroneous.
The solution is to change your program to use appropriate system headers
(<time.h> on systems with ISO C headers) and not to declare
time if the system header files declare it, or failing that to
use time_t as the return type of time.
float, PCC converts it to
a double. GCC actually returns a float. If you are concerned
with PCC compatibility, you should declare your functions to return
double; you might as well say what you mean.
The method used by GCC is as follows: a structure or union which is
1, 2, 4 or 8 bytes long is returned like a scalar. A structure or union
with any other size is stored into an address supplied by the caller
(usually in a special, fixed register, but on some machines it is passed
on the stack). The target hook TARGET_STRUCT_VALUE_RTX
tells GCC where to pass this address.
By contrast, PCC on most target machines returns structures and unions of any size by copying the data into an area of static storage, and then returning the address of that storage as if it were a pointer value. The caller must copy the data from that memory area to the place where the value is wanted. GCC does not use this method because it is slower and nonreentrant.
On some newer machines, PCC uses a reentrant convention for all structure and union returning. GCC on most of these machines uses a compatible convention when returning structures and unions in memory, but still returns small structures and unions in registers.
You can tell GCC to use a compatible convention for all structure and union returning with the option -fpcc-struct-return.
A preprocessing token is a preprocessing number if it begins with a digit and is followed by letters, underscores, digits, periods and ‘e+’, ‘e-’, ‘E+’, ‘E-’, ‘p+’, ‘p-’, ‘P+’, or ‘P-’ character sequences. (In strict C90 mode, the sequences ‘p+’, ‘p-’, ‘P+’ and ‘P-’ cannot appear in preprocessing numbers.)
To make the above program fragment valid, place whitespace in front of the minus sign. This whitespace will end the preprocessing number.
GCC needs to install corrected versions of some system header files. This is because most target systems have some header files that won't work with GCC unless they are changed. Some have bugs, some are incompatible with ISO C, and some depend on special features of other compilers.
Installing GCC automatically creates and installs the fixed header
files, by running a program called fixincludes. Normally, you
don't need to pay attention to this. But there are cases where it
doesn't do the right thing automatically.
The programs that fix the header files do not understand this special way of using symbolic links; therefore, the directory of fixed header files is good only for the machine model used to build it.
It is possible to make separate sets of fixed header files for the different machine models, and arrange a structure of symbolic links so as to use the proper set, but you'll have to do this by hand.
GCC by itself attempts to be a conforming freestanding implementation. See Language Standards Supported by GCC, for details of what this means. Beyond the library facilities required of such an implementation, the rest of the C library is supplied by the vendor of the operating system. If that C library doesn't conform to the C standards, then your programs might get warnings (especially when using -Wall) that you don't expect.
For example, the sprintf function on SunOS 4.1.3 returns
char * while the C standard says that sprintf returns an
int. The fixincludes program could make the prototype for
this function match the Standard, but that would be wrong, since the
function will still return char *.
If you need a Standard compliant library, then you need to find one, as
GCC does not provide one. The GNU C library (called glibc)
provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for
GNU/Linux and HURD-based GNU systems; no recent version of it supports
other systems, though some very old versions did. Version 2.2 of the
GNU C library includes nearly complete C99 support. You could also ask
your operating system vendor if newer libraries are available.
These problems are perhaps regrettable, but we don't know any practical way around them.
This occurs because sometimes GCC optimizes the variable out of existence. There is no way to tell the debugger how to compute the value such a variable “would have had”, and it is not clear that would be desirable anyway. So GCC simply does not mention the eliminated variable when it writes debugging information.
You have to expect a certain amount of disagreement between the executable and your source code, when you use optimization.
int foo (struct mumble *);
struct mumble { ... };
int foo (struct mumble *x)
{ ... }
This code really is erroneous, because the scope of struct
mumble in the prototype is limited to the argument list containing it.
It does not refer to the struct mumble defined with file scope
immediately below—they are two unrelated types with similar names in
different scopes.
But in the definition of foo, the file-scope type is used
because that is available to be inherited. Thus, the definition and
the prototype do not match, and you get an error.
This behavior may seem silly, but it's what the ISO standard specifies.
It is easy enough for you to make your code work by moving the
definition of struct mumble above the prototype. It's not worth
being incompatible with ISO C just to avoid an error for the example
shown above.
If you care about controlling the amount of memory that is accessed, use volatile but do not use bit-fields.
If new system header files are installed, nothing automatically arranges to update the corrected header files. They can be updated using the mkheaders script installed in libexecdir/gcc/target/version/install-tools/.
double in memory.
Compiled code moves values between memory and floating point registers
at its convenience, and moving them into memory truncates them.
You can partially avoid this problem by using the -ffloat-store option (see Optimize Options).
C++ is a complex language and an evolving one, and its standard definition (the ISO C++ standard) was only recently completed. As a result, your C++ compiler may occasionally surprise you, even when its behavior is correct. This section discusses some areas that frequently give rise to questions of this sort.
When a class has static data members, it is not enough to declare the static member; you must also define it. For example:
class Foo
{
...
void method();
static int bar;
};
This declaration only establishes that the class Foo has an
int named Foo::bar, and a member function named
Foo::method. But you still need to define both
method and bar elsewhere. According to the ISO
standard, you must supply an initializer in one (and only one) source
file, such as:
int Foo::bar = 0;
Other C++ compilers may not correctly implement the standard behavior. As a result, when you switch to g++ from one of these compilers, you may discover that a program that appeared to work correctly in fact does not conform to the standard: g++ reports as undefined symbols any static data members that lack definitions.
The C++ standard prescribes that all names that are not dependent on template parameters are bound to their present definitions when parsing a template function or class.9 Only names that are dependent are looked up at the point of instantiation. For example, consider
void foo(double);
struct A {
template <typename T>
void f () {
foo (1); // 1
int i = N; // 2
T t;
t.bar(); // 3
foo (t); // 4
}
static const int N;
};
Here, the names foo and N appear in a context that does
not depend on the type of T. The compiler will thus require that
they are defined in the context of use in the template, not only before
the point of instantiation, and will here use ::foo(double) and
A::N, respectively. In particular, it will convert the integer
value to a double when passing it to ::foo(double).
Conversely, bar and the call to foo in the fourth marked
line are used in contexts that do depend on the type of T, so
they are only looked up at the point of instantiation, and you can
provide declarations for them after declaring the template, but before
instantiating it. In particular, if you instantiate A::f<int>,
the last line will call an overloaded ::foo(int) if one was
provided, even if after the declaration of struct A.
This distinction between lookup of dependent and non-dependent names is called two-stage (or dependent) name lookup. G++ implements it since version 3.4.
Two-stage name lookup sometimes leads to situations with behavior different from non-template codes. The most common is probably this:
template <typename T> struct Base {
int i;
};
template <typename T> struct Derived : public Base<T> {
int get_i() { return i; }
};
In get_i(), i is not used in a dependent context, so the
compiler will look for a name declared at the enclosing namespace scope
(which is the global scope here). It will not look into the base class,
since that is dependent and you may declare specializations of
Base even after declaring Derived, so the compiler cannot
really know what i would refer to. If there is no global
variable i, then you will get an error message.
In order to make it clear that you want the member of the base class,
you need to defer lookup until instantiation time, at which the base
class is known. For this, you need to access i in a dependent
context, by either using this->i (remember that this is of
type Derived<T>*, so is obviously dependent), or using
Base<T>::i. Alternatively, Base<T>::i might be brought
into scope by a using-declaration.
Another, similar example involves calling member functions of a base class:
template <typename T> struct Base {
int f();
};
template <typename T> struct Derived : Base<T> {
int g() { return f(); };
};
Again, the call to f() is not dependent on template arguments
(there are no arguments that depend on the type T, and it is also
not otherwise specified that the call should be in a dependent context).
Thus a global declaration of such a function must be available, since
the one in the base class is not visible until instantiation time. The
compiler will consequently produce the following error message:
x.cc: In member function `int Derived<T>::g()':
x.cc:6: error: there are no arguments to `f' that depend on a template
parameter, so a declaration of `f' must be available
x.cc:6: error: (if you use `-fpermissive', G++ will accept your code, but
allowing the use of an undeclared name is deprecated)
To make the code valid either use this->f(), or
Base<T>::f(). Using the -fpermissive flag will also let
the compiler accept the code, by marking all function calls for which no
declaration is visible at the time of definition of the template for
later lookup at instantiation time, as if it were a dependent call.
We do not recommend using -fpermissive to work around invalid
code, and it will also only catch cases where functions in base classes
are called, not where variables in base classes are used (as in the
example above).
Note that some compilers (including G++ versions prior to 3.4) get these examples wrong and accept above code without an error. Those compilers do not implement two-stage name lookup correctly.
It is dangerous to use pointers or references to portions of a
temporary object. The compiler may very well delete the object before
you expect it to, leaving a pointer to garbage. The most common place
where this problem crops up is in classes like string classes,
especially ones that define a conversion function to type char *
or const char *—which is one reason why the standard
string class requires you to call the c_str member
function. However, any class that returns a pointer to some internal
structure is potentially subject to this problem.
For example, a program may use a function strfunc that returns
string objects, and another function charfunc that
operates on pointers to char:
string strfunc ();
void charfunc (const char *);
void
f ()
{
const char *p = strfunc().c_str();
...
charfunc (p);
...
charfunc (p);
}
In this situation, it may seem reasonable to save a pointer to the C
string returned by the c_str member function and use that rather
than call c_str repeatedly. However, the temporary string
created by the call to strfunc is destroyed after p is
initialized, at which point p is left pointing to freed memory.
Code like this may run successfully under some other compilers, particularly obsolete cfront-based compilers that delete temporaries along with normal local variables. However, the GNU C++ behavior is standard-conforming, so if your program depends on late destruction of temporaries it is not portable.
The safe way to write such code is to give the temporary a name, which forces it to remain until the end of the scope of the name. For example:
const string& tmp = strfunc ();
charfunc (tmp.c_str ());
When a base class is virtual, only one subobject of the base class belongs to each full object. Also, the constructors and destructors are invoked only once, and called from the most-derived class. However, such objects behave unspecified when being assigned. For example:
struct Base{
char *name;
Base(const char *n) : name(strdup(n)){}
Base& operator= (const Base& other){
free (name);
name = strdup (other.name);
return *this;
}
};
struct A:virtual Base{
int val;
A():Base("A"){}
};
struct B:virtual Base{
int bval;
B():Base("B"){}
};
struct Derived:public A, public B{
Derived():Base("Derived"){}
};
void func(Derived &d1, Derived &d2)
{
d1 = d2;
}
The C++ standard specifies that ‘Base::Base’ is only called once when constructing or copy-constructing a Derived object. It is unspecified whether ‘Base::operator=’ is called more than once when the implicit copy-assignment for Derived objects is invoked (as it is inside ‘func’ in the example).
G++ implements the “intuitive” algorithm for copy-assignment: assign all
direct bases, then assign all members. In that algorithm, the virtual
base subobject can be encountered more than once. In the example, copying
proceeds in the following order: ‘name’ (via strdup),
‘val’, ‘name’ again, and ‘bval’.
If application code relies on copy-assignment, a user-defined copy-assignment operator removes any uncertainties. With such an operator, the application can define whether and how the virtual base subobject is assigned.
This section lists changes that people frequently request, but which we do not make because we think GCC is better without them.
Such a feature would work only occasionally—only for calls that appear in the same file as the called function, following the definition. The only way to check all calls reliably is to add a prototype for the function. But adding a prototype eliminates the motivation for this feature. So the feature is not worthwhile.
Shift count operands are probably signed more often than unsigned. Warning about this would cause far more annoyance than good.
Such assignments must be very common; warning about them would cause more annoyance than good.
C contains many standard functions that return a value that most
programs choose to ignore. One obvious example is printf.
Warning about this practice only leads the defensive programmer to
clutter programs with dozens of casts to void. Such casts are
required so frequently that they become visual noise. Writing those
casts becomes so automatic that they no longer convey useful
information about the intentions of the programmer. For functions
where the return value should never be ignored, use the
warn_unused_result function attribute (see Function Attributes).
This would cause storage layout to be incompatible with most other C compilers. And it doesn't seem very important, given that you can get the same result in other ways. The case where it matters most is when the enumeration-valued object is inside a structure, and in that case you can specify a field width explicitly.
The ISO C standard leaves it up to the implementation whether a bit-field
declared plain int is signed or not. This in effect creates two
alternative dialects of C.
The GNU C compiler supports both dialects; you can specify the signed dialect with -fsigned-bitfields and the unsigned dialect with -funsigned-bitfields. However, this leaves open the question of which dialect to use by default.
Currently, the preferred dialect makes plain bit-fields signed, because
this is simplest. Since int is the same as signed int in
every other context, it is cleanest for them to be the same in bit-fields
as well.
Some computer manufacturers have published Application Binary Interface standards which specify that plain bit-fields should be unsigned. It is a mistake, however, to say anything about this issue in an ABI. This is because the handling of plain bit-fields distinguishes two dialects of C. Both dialects are meaningful on every type of machine. Whether a particular object file was compiled using signed bit-fields or unsigned is of no concern to other object files, even if they access the same bit-fields in the same data structures.
A given program is written in one or the other of these two dialects. The program stands a chance to work on most any machine if it is compiled with the proper dialect. It is unlikely to work at all if compiled with the wrong dialect.
Many users appreciate the GNU C compiler because it provides an environment that is uniform across machines. These users would be inconvenienced if the compiler treated plain bit-fields differently on certain machines.
Occasionally users write programs intended only for a particular machine type. On these occasions, the users would benefit if the GNU C compiler were to support by default the same dialect as the other compilers on that machine. But such applications are rare. And users writing a program to run on more than one type of machine cannot possibly benefit from this kind of compatibility.
This is why GCC does and will treat plain bit-fields in the same fashion on all types of machines (by default).
There are some arguments for making bit-fields unsigned by default on all machines. If, for example, this becomes a universal de facto standard, it would make sense for GCC to go along with it. This is something to be considered in the future.
(Of course, users strongly concerned about portability should indicate explicitly in each bit-field whether it is signed or not. In this way, they write programs which have the same meaning in both C dialects.)
__STDC__ when -ansi is not used.
Currently, GCC defines __STDC__ unconditionally. This provides
good results in practice.
Programmers normally use conditionals on __STDC__ to ask whether
it is safe to use certain features of ISO C, such as function
prototypes or ISO token concatenation. Since plain gcc supports
all the features of ISO C, the correct answer to these questions is
“yes”.
Some users try to use __STDC__ to check for the availability of
certain library facilities. This is actually incorrect usage in an ISO
C program, because the ISO C standard says that a conforming
freestanding implementation should define __STDC__ even though it
does not have the library facilities. ‘gcc -ansi -pedantic’ is a
conforming freestanding implementation, and it is therefore required to
define __STDC__, even though it does not come with an ISO C
library.
Sometimes people say that defining __STDC__ in a compiler that
does not completely conform to the ISO C standard somehow violates the
standard. This is illogical. The standard is a standard for compilers
that claim to support ISO C, such as ‘gcc -ansi’—not for other
compilers such as plain gcc. Whatever the ISO C standard says
is relevant to the design of plain gcc without -ansi only
for pragmatic reasons, not as a requirement.
GCC normally defines __STDC__ to be 1, and in addition
defines __STRICT_ANSI__ if you specify the -ansi option,
or a -std option for strict conformance to some version of ISO C.
On some hosts, system include files use a different convention, where
__STDC__ is normally 0, but is 1 if the user specifies strict
conformance to the C Standard. GCC follows the host convention when
processing system include files, but when processing user files it follows
the usual GNU C convention.
__STDC__ in C++.
Programs written to compile with C++-to-C translators get the
value of __STDC__ that goes with the C compiler that is
subsequently used. These programs must test __STDC__
to determine what kind of C preprocessor that compiler uses:
whether they should concatenate tokens in the ISO C fashion
or in the traditional fashion.
These programs work properly with GNU C++ if __STDC__ is defined.
They would not work otherwise.
In addition, many header files are written to provide prototypes in ISO
C but not in traditional C. Many of these header files can work without
change in C++ provided __STDC__ is defined. If __STDC__
is not defined, they will all fail, and will all need to be changed to
test explicitly for C++ as well.
Historically, GCC has not deleted “empty” loops under the assumption that the most likely reason you would put one in a program is to have a delay, so deleting them will not make real programs run any faster.
However, the rationale here is that optimization of a nonempty loop cannot produce an empty one. This held for carefully written C compiled with less powerful optimizers but is not always the case for carefully written C++ or with more powerful optimizers. Thus GCC will remove operations from loops whenever it can determine those operations are not externally visible (apart from the time taken to execute them, of course). In case the loop can be proved to be finite, GCC will also remove the loop itself.
Be aware of this when performing timing tests, for instance the
following loop can be completely removed, provided
some_expression can provably not change any global state.
{
int sum = 0;
int ix;
for (ix = 0; ix != 10000; ix++)
sum += some_expression;
}
Even though sum is accumulated in the loop, no use is made of
that summation, so the accumulation can be removed.
It is never safe to depend on the order of evaluation of side effects. For example, a function call like this may very well behave differently from one compiler to another:
void func (int, int);
int i = 2;
func (i++, i++);
There is no guarantee (in either the C or the C++ standard language
definitions) that the increments will be evaluated in any particular
order. Either increment might happen first. func might get the
arguments ‘2, 3’, or it might get ‘3, 2’, or even ‘2, 2’.
Some ISO C testsuites report failure when the compiler does not produce an error message for a certain program.
ISO C requires a “diagnostic” message for certain kinds of invalid programs, but a warning is defined by GCC to count as a diagnostic. If GCC produces a warning but not an error, that is correct ISO C support. If testsuites call this “failure”, they should be run with the GCC option -pedantic-errors, which will turn these warnings into errors.
The GNU compiler can produce two kinds of diagnostics: errors and warnings. Each kind has a different purpose:
Warnings may indicate danger points where you should check to make sure that your program really does what you intend; or the use of obsolete features; or the use of nonstandard features of GNU C or C++. Many warnings are issued only if you ask for them, with one of the -W options (for instance, -Wall requests a variety of useful warnings).
GCC always tries to compile your program if possible; it never gratuitously rejects a program whose meaning is clear merely because (for instance) it fails to conform to a standard. In some cases, however, the C and C++ standards specify that certain extensions are forbidden, and a diagnostic must be issued by a conforming compiler. The -pedantic option tells GCC to issue warnings in such cases; -pedantic-errors says to make them errors instead. This does not mean that all non-ISO constructs get warnings or errors.
See Options to Request or Suppress Warnings, for more detail on these and related command-line options.
Your bug reports play an essential role in making GCC reliable.
When you encounter a problem, the first thing to do is to see if it is already known. See Trouble. If it isn't known, then you should report the problem.
If you are not sure whether you have found a bug, here are some guidelines:
asm statement), that is a compiler bug, unless the
compiler reports errors (not just warnings) which would ordinarily
prevent the assembler from being run.
However, you must double-check to make sure, because you may have a program whose behavior is undefined, which happened by chance to give the desired results with another C or C++ compiler.
For example, in many nonoptimizing compilers, you can write ‘x;’
at the end of a function instead of ‘return x;’, with the same
results. But the value of the function is undefined if return
is omitted; it is not a bug when GCC produces different results.
Problems often result from expressions with two increment operators,
as in f (*p++, *p++). Your previous compiler might have
interpreted that expression the way you intended; GCC might
interpret it another way. Neither compiler is wrong. The bug is
in your code.
After you have localized the error to a single source line, it should be easy to check for these things. If your program is correct and well defined, you have found a compiler bug.
Bugs should be reported to the bug database at mailto:support@adacore.com.
If you need help installing, using or changing GCC, there are two ways to find it:
For further information, see https://gcc.gnu.org/faq.html#support.
If you would like to help pretest GCC releases to assure they work well, current development sources are available via Git (see https://gcc.gnu.org/git.html). Source and binary snapshots are also available for FTP; see https://gcc.gnu.org/snapshots.html.
If you would like to work on improvements to GCC, please read the advice at these URLs:
https://gcc.gnu.org/contribute.html
https://gcc.gnu.org/contributewhy.html
for information on how to make useful contributions and avoid duplication of effort. Suggested projects are listed at https://gcc.gnu.org/projects/.
If you want to have more free software a few years from now, it makes sense for you to help encourage people to contribute funds for its development. The most effective approach known is to encourage commercial redistributors to donate.
Users of free software systems can boost the pace of development by encouraging for-a-fee distributors to donate part of their selling price to free software developers—the Free Software Foundation, and others.
The way to convince distributors to do this is to demand it and expect it from them. So when you compare distributors, judge them partly by how much they give to free software development. Show distributors they must compete to be the one who gives the most.
To make this approach work, you must insist on numbers that you can compare, such as, “We will donate ten dollars to the Frobnitz project for each disk sold.” Don't be satisfied with a vague promise, such as “A portion of the profits are donated,” since it doesn't give a basis for comparison.
Even a precise fraction “of the profits from this disk” is not very meaningful, since creative accounting and unrelated business decisions can greatly alter what fraction of the sales price counts as profit. If the price you pay is $50, ten percent of the profit is probably less than a dollar; it might be a few cents, or nothing at all.
Some redistributors do development work themselves. This is useful too; but to keep everyone honest, you need to inquire how much they do, and what kind. Some kinds of development make much more long-term difference than others. For example, maintaining a separate version of a program contributes very little; maintaining the standard version of a program for the whole community contributes much. Easy new ports contribute little, since someone else would surely do them; difficult ports such as adding a new CPU to the GNU Compiler Collection contribute more; major new features or packages contribute the most.
By establishing the idea that supporting further development is “the proper thing to do” when distributing free software for a fee, we can assure a steady flow of resources into making more free software.
Copyright © 1994 Free Software Foundation, Inc.
Verbatim copying and redistribution of this section is permitted
without royalty; alteration is not permitted.
The GNU Project was launched in 1984 to develop a complete Unix-like operating system which is free software: the GNU system. (GNU is a recursive acronym for “GNU's Not Unix”; it is pronounced “guh-NEW”.) Variants of the GNU operating system, which use the kernel Linux, are now widely used; though these systems are often referred to as “Linux”, they are more accurately called GNU/Linux systems.
For more information, see:
https://www.gnu.org/
https://www.gnu.org/gnu/linux-and-gnu.html
Copyright © 2007 Free Software Foundation, Inc. https://www.fsf.org
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
The GNU General Public License is a free, copyleft license for software and other kinds of works.
The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a program–to make sure it remains free software for all its users. We, the Free Software Foundation, use the GNU General Public License for most of our software; it applies also to any other work released this way by its authors. You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for them if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs, and that you know you can do these things.
To protect your rights, we need to prevent others from denying you these rights or asking you to surrender the rights. Therefore, you have certain responsibilities if you distribute copies of the software, or if you modify it: responsibilities to respect the freedom of others.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must pass on to the recipients the same freedoms that you received. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
Developers that use the GNU GPL protect your rights with two steps: (1) assert copyright on the software, and (2) offer you this License giving you legal permission to copy, distribute and/or modify it.
For the developers' and authors' protection, the GPL clearly explains that there is no warranty for this free software. For both users' and authors' sake, the GPL requires that modified versions be marked as changed, so that their problems will not be attributed erroneously to authors of previous versions.
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The Corresponding Source for a work in source code form is that same work.
All rights granted under this License are granted for the term of copyright on the Program, and are irrevocable provided the stated conditions are met. This License explicitly affirms your unlimited permission to run the unmodified Program. The output from running a covered work is covered by this License only if the output, given its content, constitutes a covered work. This License acknowledges your rights of fair use or other equivalent, as provided by copyright law.
You may make, run and propagate covered works that you do not convey, without conditions so long as your license otherwise remains in force. You may convey covered works to others for the sole purpose of having them make modifications exclusively for you, or provide you with facilities for running those works, provided that you comply with the terms of this License in conveying all material for which you do not control copyright. Those thus making or running the covered works for you must do so exclusively on your behalf, under your direction and control, on terms that prohibit them from making any copies of your copyrighted material outside their relationship with you.
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When you convey a covered work, you waive any legal power to forbid circumvention of technological measures to the extent such circumvention is effected by exercising rights under this License with respect to the covered work, and you disclaim any intention to limit operation or modification of the work as a means of enforcing, against the work's users, your or third parties' legal rights to forbid circumvention of technological measures.
You may convey verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice; keep intact all notices stating that this License and any non-permissive terms added in accord with section 7 apply to the code; keep intact all notices of the absence of any warranty; and give all recipients a copy of this License along with the Program.
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You may convey a covered work in object code form under the terms of sections 4 and 5, provided that you also convey the machine-readable Corresponding Source under the terms of this License, in one of these ways:
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If you convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term (regardless of how the transaction is characterized), the Corresponding Source conveyed under this section must be accompanied by the Installation Information. But this requirement does not apply if neither you nor any third party retains the ability to install modified object code on the User Product (for example, the work has been installed in ROM).
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“Additional permissions” are terms that supplement the terms of this License by making exceptions from one or more of its conditions. Additional permissions that are applicable to the entire Program shall be treated as though they were included in this License, to the extent that they are valid under applicable law. If additional permissions apply only to part of the Program, that part may be used separately under those permissions, but the entire Program remains governed by this License without regard to the additional permissions.
When you convey a copy of a covered work, you may at your option remove any additional permissions from that copy, or from any part of it. (Additional permissions may be written to require their own removal in certain cases when you modify the work.) You may place additional permissions on material, added by you to a covered work, for which you have or can give appropriate copyright permission.
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However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10.
You are not required to accept this License in order to receive or run a copy of the Program. Ancillary propagation of a covered work occurring solely as a consequence of using peer-to-peer transmission to receive a copy likewise does not require acceptance. However, nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a covered work, you indicate your acceptance of this License to do so.
Each time you convey a covered work, the recipient automatically receives a license from the original licensors, to run, modify and propagate that work, subject to this License. You are not responsible for enforcing compliance by third parties with this License.
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You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it.
A “contributor” is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributor's “contributor version”.
A contributor's “essential patent claims” are all patent claims owned or controlled by the contributor, whether already acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or selling its contributor version, but do not include claims that would be infringed only as a consequence of further modification of the contributor version. For purposes of this definition, “control” includes the right to grant patent sublicenses in a manner consistent with the requirements of this License.
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If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. “Knowingly relying” means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid.
If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it.
A patent license is “discriminatory” if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.
Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law.
If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program.
Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such.
The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License “or any later version” applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation.
If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Program.
Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version.
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee.
If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.
one line to give the program's name and a brief idea of what it does.
Copyright (C) year name of author
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see https://www.gnu.org/licenses/.
Also add information on how to contact you by electronic and paper mail.
If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode:
program Copyright (C) year name of author
This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’.
This is free software, and you are welcome to redistribute it
under certain conditions; type ‘show c’ for details.
The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an “about box”.
You should also get your employer (if you work as a programmer) or school, if any, to sign a “copyright disclaimer” for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see https://www.gnu.org/licenses/.
The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read https://www.gnu.org/licenses/why-not-lgpl.html.
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
https://www.fsf.org
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.
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The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.
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A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.
Examples of suitable formats for Transparent copies include plain ascii without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.
The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.
The “publisher” means any person or entity that distributes copies of the Document to the public.
A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.
The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.
You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and you may publicly display copies.
If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.
You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.
You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.
You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/copyleft/.
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Permission is granted to copy, distribute and/or modify this document
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or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
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If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
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If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
The GCC project would like to thank its many contributors. Without them the project would not have been nearly as successful as it has been. Any omissions in this list are accidental. Feel free to contact jlaw@ventanamicro.com or gerald@pfeifer.com if you have been left out or some of your contributions are not listed. Please keep this list in alphabetical order.
valarray<>, complex<>, maintaining the numerics library
(including that pesky <limits> :-) and keeping up-to-date anything
to do with numbers.
complex<>, sanity checking and disbursement, configuration
architecture, libio maintenance, and early math work.
debug-mode and associative and unordered containers.
collect2's --help documentation.
restrict support, and serving as release manager from 2000
to 2011.
<regex>.
<random>, and various improvements to C++11 features.
INTEGER*1, INTEGER*2, and
LOGICAL*1.
<regex> effort.
The following people are recognized for their contributions to GNAT, the Ada front end of GCC:
The following people are recognized for their contributions of new features, bug reports, testing and integration of classpath/libgcj for GCC version 4.1:
JTree implementation and lots Free Swing
additions and bug fixes.
GapContent bug fixes.
JList, Free Swing 1.5 updates and mouse event
fixes, lots of Free Swing work including JTable editing.
HTTPURLConnection fixes.
MessageFormat fixes.
Serialization fixes.
StAX
and DOM xml:id support.
TreePath and TreeSelection fixes.
URLClassLoader updates.
SocketTimeoutException.
BitSet bug fixes, HttpURLConnection
rewrite and improvements.
ClassLoader and nio cleanups, serialization fixes,
better Proxy support, bug fixes and IKVM integration.
AccessControlContext fixes.
VMClassLoader and AccessController
improvements.
basic and metal icon and plaf support
and lots of documenting, Lots of Free Swing and metal theme
additions. MetalIconFactory implementation.
MIDI framework, ALSA and DSSI
providers.
Serialization and URLClassLoader fixes,
gcj build speedups.
JFileChooser implementation.
Locale and net fixes, URI RFC2986
updates, Serialization fixes, Properties XML support and
generic branch work, VMIntegration guide update.
TimeZone bug fixing.
NetworkInterface implementation and updates.
BoxLayout, GrayFilter and
SplitPane, plus bug fixes all over. Lots of Free Swing work
including styled text.
String cleanups and optimization suggestions.
Locale updates, bug and
build fixes.
Pointer updates. Logger bug fixes.
Graphics2D upgraded to Cairo 0.5 and new regex
features.
TextLayout
fixes. GtkImage rewrite, 2D, awt, free swing and date/time fixes and
implementing the Qt4 peers.
FileChannel lock,
SystemLogger and FileHandler rotate implementations, NIO
FileChannel.map support, security and policy updates.
File locking fixes.
Image, Logger and URLClassLoader
updates.
MenuSelectionManager implementation.
BasicTreeUI and JTree fixes.
TreeNode enumerations and ActionCommand and various
fixes, XML and URL, AWT and Free Swing bug fixes.
CACAO integration, fdlibm updates.
VMClassLoader boot packages support suggestions.
Qt4
support for Darwin/OS X, Graphics2D support, gtk+
updates.
DEBUG support, build cleanups and
Kaffe integration. Qt4 build infrastructure, SHA1PRNG
and GdkPixbugDecoder updates.
Clipboard implementation, system call interrupts and network
timeouts and GdkPixpufDecoder fixes.
In addition to the above, all of which also contributed time and energy in testing GCC, we would like to thank the following for their contributions to testing:
And finally we'd like to thank everyone who uses the compiler, provides feedback and generally reminds us why we're doing this work in the first place.
GCC's command line options are indexed here without any initial ‘-’ or ‘--’. Where an option has both positive and negative forms (such as -foption and -fno-option), relevant entries in the manual are indexed under the most appropriate form; it may sometimes be useful to look up both forms.
###: Overall Options-fstrub=disable: Instrumentation OptionsA: Preprocessor Optionsall_load: Darwin Optionsallowable_client: Darwin Optionsanalyzer: Static Analyzer Optionsansi: Non-bugsansi: Other Builtinsansi: C Dialect Optionsansi: Standardsarch_errors_fatal: Darwin Optionsaux-info: C Dialect OptionsB: Directory OptionsBdynamic: VxWorks Optionsbind_at_load: Darwin Optionsblock-ops-unaligned-vsx: RS/6000 and PowerPC OptionsBstatic: VxWorks Optionsbundle: Darwin Optionsbundle_loader: Darwin Optionsc: Link OptionsC: Preprocessor Optionsc: Overall OptionsCC: Preprocessor Optionsclient_name: Darwin Optionscompatibility_version: Darwin Optionscoverage: Instrumentation Optionscurrent_version: Darwin Optionsd: Developer Optionsd: Preprocessor OptionsD: Preprocessor OptionsdA: Developer Optionsda: Developer OptionsdD: Developer OptionsdD: Preprocessor Optionsdead_strip: Darwin Optionsdependency-file: Darwin OptionsdH: Developer OptionsdI: Preprocessor OptionsdM: Preprocessor OptionsdN: Preprocessor OptionsdP: Developer Optionsdp: Developer OptionsdU: Preprocessor Optionsdump-analyzer-exploded-nodes: Static Analyzer Optionsdump-analyzer-exploded-nodes-2: Static Analyzer Optionsdump-analyzer-exploded-nodes-3: Static Analyzer Optionsdump-analyzer-feasibility: Static Analyzer Optionsdumpbase: Overall Optionsdumpbase-ext: Overall Optionsdumpdir: Overall Optionsdumpfullversion: Developer Optionsdumpmachine: Developer Optionsdumpspecs: Developer Optionsdumpversion: Developer Optionsdx: Developer Optionsdylib_file: Darwin Optionsdylinker_install_name: Darwin Optionsdynamic: Darwin Optionsdynamiclib: Darwin Optionse: Link OptionsE: Link OptionsE: Overall OptionsEB: MIPS OptionsEB: C-SKY OptionsEB: ARC OptionsEL: MIPS OptionsEL: C-SKY OptionsEL: ARC Optionsentry: Link Optionsexported_symbols_list: Darwin OptionsF: Darwin Optionsfabi-compat-version: C++ Dialect Optionsfabi-version: C++ Dialect Optionsfaccess-control: C++ Dialect Optionsfada-spec-parent: Overall Optionsfaggressive-loop-optimizations: Optimize Optionsfalign-functions: Optimize Optionsfalign-jumps: Optimize Optionsfalign-labels: Optimize Optionsfalign-loops: Optimize Optionsfaligned-new: C++ Dialect Optionsfallow-store-data-races: Optimize Optionsfanalyzer: Static Analyzer Optionsfanalyzer-call-summaries: Static Analyzer Optionsfanalyzer-checker: Static Analyzer Optionsfanalyzer-feasibility: Static Analyzer Optionsfanalyzer-fine-grained: Static Analyzer Optionsfanalyzer-show-duplicate-count: Static Analyzer Optionsfanalyzer-state-merge: Static Analyzer Optionsfanalyzer-state-purge: Static Analyzer Optionsfanalyzer-suppress-followups: Static Analyzer Optionsfanalyzer-transitivity: Static Analyzer Optionsfanalyzer-undo-inlining: Static Analyzer Optionsfasan-shadow-offset: Instrumentation Optionsfasm: C Dialect Optionsfassociative-math: Optimize Optionsfasynchronous-unwind-tables: Code Gen Optionsfauto-inc-dec: Optimize Optionsfauto-profile: Optimize Optionsfbit-tests: Code Gen Optionsfbranch-count-reg: Optimize Optionsfbranch-probabilities: Optimize Optionsfbuiltin: C Dialect Optionsfcall-saved: Code Gen Optionsfcall-used: Code Gen Optionsfcaller-saves: Optimize Optionsfcallgraph-info: Developer Optionsfcanon-prefix-map: Overall Optionsfcf-protection: Instrumentation Optionsfchar8_t: C++ Dialect Optionsfcheck-new: C++ Dialect Optionsfchecking: Developer Optionsfcode-hoisting: Optimize Optionsfcombine-stack-adjustments: Optimize Optionsfcommon: Common Variable Attributesfcommon: Code Gen Optionsfcompare-debug: Developer Optionsfcompare-debug-second: Developer Optionsfcompare-elim: Optimize Optionsfconcepts: C++ Dialect Optionsfconcepts-ts: C++ Dialect Optionsfcond-mismatch: C Dialect Optionsfconserve-stack: Optimize Optionsfconstant-cfstrings: Darwin Optionsfconstant-string-class: Objective-C and Objective-C++ Dialect Optionsfconstexpr-cache-depth: C++ Dialect Optionsfconstexpr-depth: C++ Dialect Optionsfconstexpr-fp-except: C++ Dialect Optionsfconstexpr-loop-limit: C++ Dialect Optionsfconstexpr-ops-limit: C++ Dialect Optionsfcontract-assumption-mode: C++ Dialect Optionsfcontract-build-level: C++ Dialect Optionsfcontract-continuation-mode: C++ Dialect Optionsfcontract-mode: C++ Dialect Optionsfcontract-role: C++ Dialect Optionsfcontract-strict-declarations: C++ Dialect Optionsfcontracts: C++ Dialect Optionsfcoroutines: C++ Dialect Optionsfcprop-registers: Optimize Optionsfcrossjumping: Optimize Optionsfcse-follow-jumps: Optimize Optionsfcse-skip-blocks: Optimize Optionsfcx-fortran-rules: Optimize Optionsfcx-limited-range: Optimize Optionsfdata-sections: Optimize Optionsfdbg-cnt: Developer Optionsfdbg-cnt-list: Developer Optionsfdce: Optimize Optionsfdebug-cpp: Preprocessor Optionsfdebug-prefix-map: Debugging Optionsfdebug-types-section: Debugging Optionsfdeclone-ctor-dtor: Optimize Optionsfdefer-pop: Optimize Optionsfdelayed-branch: Optimize Optionsfdelete-dead-exceptions: Code Gen Optionsfdelete-null-pointer-checks: Optimize Optionsfdevirtualize: Optimize Optionsfdevirtualize-at-ltrans: Optimize Optionsfdevirtualize-speculatively: Optimize Optionsfdiagnostics-color: Diagnostic Message Formatting Optionsfdiagnostics-column-origin: Diagnostic Message Formatting Optionsfdiagnostics-column-unit: Diagnostic Message Formatting Optionsfdiagnostics-escape-format: Diagnostic Message Formatting Optionsfdiagnostics-format: Diagnostic Message Formatting Optionsfdiagnostics-generate-patch: Diagnostic Message Formatting Optionsfdiagnostics-minimum-margin-width: Diagnostic Message Formatting Optionsfdiagnostics-parseable-fixits: Diagnostic Message Formatting Optionsfdiagnostics-path-format: Diagnostic Message Formatting Optionsfdiagnostics-show-caret: Diagnostic Message Formatting Optionsfdiagnostics-show-cwe: Diagnostic Message Formatting Optionsfdiagnostics-show-labels: Diagnostic Message Formatting Optionsfdiagnostics-show-line-numbers: Diagnostic Message Formatting Optionsfdiagnostics-show-location: Diagnostic Message Formatting Optionsfdiagnostics-show-option: Diagnostic Message Formatting Optionsfdiagnostics-show-path-depths: Diagnostic Message Formatting Optionsfdiagnostics-show-rules: Diagnostic Message Formatting Optionsfdiagnostics-show-template-tree: Diagnostic Message Formatting Optionsfdiagnostics-urls: Diagnostic Message Formatting Optionsfdirectives-only: Preprocessor Optionsfdisable-: Developer Optionsfdollars-in-identifiers: Interoperationfdollars-in-identifiers: Preprocessor Optionsfdpic: SH Optionsfdse: Optimize Optionsfdump-ada-spec: Overall Optionsfdump-analyzer: Static Analyzer Optionsfdump-analyzer-callgraph: Static Analyzer Optionsfdump-analyzer-exploded-graph: Static Analyzer Optionsfdump-analyzer-exploded-paths: Static Analyzer Optionsfdump-analyzer-json: Static Analyzer Optionsfdump-analyzer-state-purge: Static Analyzer Optionsfdump-analyzer-stderr: Static Analyzer Optionsfdump-analyzer-supergraph: Static Analyzer Optionsfdump-analyzer-untracked: Static Analyzer Optionsfdump-debug: Developer Optionsfdump-earlydebug: Developer Optionsfdump-final-insns: Developer Optionsfdump-go-spec: Overall Optionsfdump-ipa: Developer Optionsfdump-lang: Developer Optionsfdump-lang-all: Developer Optionsfdump-noaddr: Developer Optionsfdump-passes: Developer Optionsfdump-rtl-alignments: Developer Optionsfdump-rtl-all: Developer Optionsfdump-rtl-asmcons: Developer Optionsfdump-rtl-auto_inc_dec: Developer Optionsfdump-rtl-barriers: Developer Optionsfdump-rtl-bbpart: Developer Optionsfdump-rtl-bbro: Developer Optionsfdump-rtl-btl2: Developer Optionsfdump-rtl-bypass: Developer Optionsfdump-rtl-ce1: Developer Optionsfdump-rtl-ce2: Developer Optionsfdump-rtl-ce3: Developer Optionsfdump-rtl-combine: Developer Optionsfdump-rtl-compgotos: Developer Optionsfdump-rtl-cprop_hardreg: Developer Optionsfdump-rtl-csa: Developer Optionsfdump-rtl-cse1: Developer Optionsfdump-rtl-cse2: Developer Optionsfdump-rtl-dbr: Developer Optionsfdump-rtl-dce: Developer Optionsfdump-rtl-dce1: Developer Optionsfdump-rtl-dce2: Developer Optionsfdump-rtl-dfinish: Developer Optionsfdump-rtl-dfinit: Developer Optionsfdump-rtl-eh: Developer Optionsfdump-rtl-eh_ranges: Developer Optionsfdump-rtl-expand: Developer Optionsfdump-rtl-fwprop1: Developer Optionsfdump-rtl-fwprop2: Developer Optionsfdump-rtl-gcse1: Developer Optionsfdump-rtl-gcse2: Developer Optionsfdump-rtl-init-regs: Developer Optionsfdump-rtl-initvals: Developer Optionsfdump-rtl-into_cfglayout: Developer Optionsfdump-rtl-ira: Developer Optionsfdump-rtl-jump: Developer Optionsfdump-rtl-loop2: Developer Optionsfdump-rtl-mach: Developer Optionsfdump-rtl-mode_sw: Developer Optionsfdump-rtl-outof_cfglayout: Developer Optionsfdump-rtl-pass: Developer Optionsfdump-rtl-peephole2: Developer Optionsfdump-rtl-postreload: Developer Optionsfdump-rtl-pro_and_epilogue: Developer Optionsfdump-rtl-ree: Developer Optionsfdump-rtl-regclass: Developer Optionsfdump-rtl-rnreg: Developer Optionsfdump-rtl-sched1: Developer Optionsfdump-rtl-sched2: Developer Optionsfdump-rtl-seqabstr: Developer Optionsfdump-rtl-shorten: Developer Optionsfdump-rtl-sibling: Developer Optionsfdump-rtl-sms: Developer Optionsfdump-rtl-split1: Developer Optionsfdump-rtl-split2: Developer Optionsfdump-rtl-split3: Developer Optionsfdump-rtl-split4: Developer Optionsfdump-rtl-split5: Developer Optionsfdump-rtl-stack: Developer Optionsfdump-rtl-subreg1: Developer Optionsfdump-rtl-subreg2: Developer Optionsfdump-rtl-subregs_of_mode_finish: Developer Optionsfdump-rtl-subregs_of_mode_init: Developer Optionsfdump-rtl-unshare: Developer Optionsfdump-rtl-vartrack: Developer Optionsfdump-rtl-vregs: Developer Optionsfdump-rtl-web: Developer Optionsfdump-scos: Overall Optionsfdump-statistics: Developer Optionsfdump-tree: Developer Optionsfdump-tree-all: Developer Optionsfdump-unnumbered: Developer Optionsfdump-unnumbered-links: Developer Optionsfdwarf2-cfi-asm: Debugging Optionsfearly-inlining: Optimize Optionsfelide-constructors: C++ Dialect Optionsfelide-type: Diagnostic Message Formatting Optionsfeliminate-unused-debug-symbols: Debugging Optionsfeliminate-unused-debug-types: Debugging Optionsfemit-class-debug-always: Debugging Optionsfemit-struct-debug-baseonly: Debugging Optionsfemit-struct-debug-detailed: Debugging Optionsfemit-struct-debug-reduced: Debugging Optionsfenable-: Developer Optionsfenforce-eh-specs: C++ Dialect Optionsfexceptions: Code Gen Optionsfexcess-precision: Optimize Optionsfexec-charset: Preprocessor Optionsfexpensive-optimizations: Optimize Optionsfext-numeric-literals: C++ Dialect Optionsfextended-identifiers: Preprocessor Optionsfextern-tls-init: C++ Dialect Optionsffast-math: Optimize Optionsffat-lto-objects: Optimize Optionsffile-prefix-map: Overall Optionsffinite-loops: Optimize Optionsffinite-math-only: Optimize Optionsffix-and-continue: Darwin Optionsffixed: Code Gen Optionsffloat-store: Disappointmentsffloat-store: Optimize Optionsffold-simple-inlines: C++ Dialect Optionsfforward-propagate: Optimize Optionsffp-contract: Optimize Optionsffp-int-builtin-inexact: Optimize Optionsffreestanding: Common Function Attributesffreestanding: Warning Optionsffreestanding: C Dialect Optionsffreestanding: Standardsffunction-cse: Optimize Optionsffunction-sections: Optimize Optionsfgcse: Optimize Optionsfgcse-after-reload: Optimize Optionsfgcse-las: Optimize Optionsfgcse-lm: Optimize Optionsfgcse-sm: Optimize Optionsfgimple: C Dialect Optionsfgnu-keywords: C++ Dialect Optionsfgnu-runtime: Objective-C and Objective-C++ Dialect Optionsfgnu-tm: C Dialect Optionsfgnu-unique: Code Gen Optionsfgnu89-inline: C Dialect Optionsfgraphite-identity: Optimize Optionsfguess-branch-probability: Optimize Optionsfhardcfr-check-exceptions: Instrumentation Optionsfhardcfr-check-noreturn-calls: Instrumentation Optionsfhardcfr-check-returning-calls: Instrumentation Optionsfhardcfr-skip-leaf: Instrumentation Optionsfharden-compares: Instrumentation Optionsfharden-conditional-branches: Instrumentation Optionsfharden-control-flow-redundancy: Instrumentation Optionsfhoist-adjacent-loads: Optimize Optionsfhosted: C Dialect Optionsfident: Code Gen Optionsfif-conversion: Optimize Optionsfif-conversion2: Optimize Optionsfilelist: Darwin Optionsfimplement-inlines: C++ Dialect Optionsfimplicit-constexpr: C++ Dialect Optionsfimplicit-inline-templates: C++ Dialect Optionsfimplicit-templates: C++ Dialect Optionsfindirect-data: Darwin Optionsfindirect-inlining: Optimize Optionsfinhibit-size-directive: Code Gen Optionsfinline: Optimize Optionsfinline-functions: Optimize Optionsfinline-functions-called-once: Optimize Optionsfinline-limit: Optimize Optionsfinline-small-functions: Optimize Optionsfinline-stringops: Optimize Optionsfinput-charset: Preprocessor Optionsfinstrument-functions: Common Function Attributesfinstrument-functions: Instrumentation Optionsfinstrument-functions-exclude-file-list: Instrumentation Optionsfinstrument-functions-exclude-function-list: Instrumentation Optionsfinstrument-functions-once: Instrumentation Optionsfipa-bit-cp: Optimize Optionsfipa-cp: Optimize Optionsfipa-cp-clone: Optimize Optionsfipa-icf: Optimize Optionsfipa-modref: Optimize Optionsfipa-profile: Optimize Optionsfipa-pta: Optimize Optionsfipa-pure-const: Optimize Optionsfipa-ra: Optimize Optionsfipa-reference: Optimize Optionsfipa-reference-addressable: Optimize Optionsfipa-sra: Optimize Optionsfipa-stack-alignment: Optimize Optionsfipa-strict-aliasing: Optimize Optionsfipa-vrp: Optimize Optionsfira-algorithm: Optimize Optionsfira-hoist-pressure: Optimize Optionsfira-loop-pressure: Optimize Optionsfira-region: Optimize Optionsfira-share-save-slots: Optimize Optionsfira-share-spill-slots: Optimize Optionsfira-verbose: Developer Optionsfisolate-erroneous-paths-attribute: Optimize Optionsfisolate-erroneous-paths-dereference: Optimize Optionsfivar-visibility: Objective-C and Objective-C++ Dialect Optionsfivopts: Optimize Optionsfjump-tables: Code Gen Optionsfkeep-inline-dllexport: Optimize Optionsfkeep-inline-functions: Inlinefkeep-inline-functions: Optimize Optionsfkeep-static-consts: Optimize Optionsfkeep-static-functions: Optimize Optionsflang-info-include-translate: C++ Dialect Optionsflang-info-include-translate-not: C++ Dialect Optionsflang-info-module-cmi: C++ Dialect Optionsflarge-source-files: Preprocessor Optionsflat_namespace: Darwin Optionsflax-vector-conversions: C Dialect Optionsfleading-underscore: Code Gen Optionsflifetime-dse: Optimize Optionsflinker-output: Link Optionsflive-patching: Optimize Optionsflive-range-shrinkage: Optimize Optionsflocal-ivars: Objective-C and Objective-C++ Dialect Optionsfloop-block: Optimize Optionsfloop-interchange: Optimize Optionsfloop-nest-optimize: Optimize Optionsfloop-parallelize-all: Optimize Optionsfloop-strip-mine: Optimize Optionsfloop-unroll-and-jam: Optimize Optionsflra-remat: Optimize Optionsflto: Optimize Optionsflto-compression-level: Optimize Optionsflto-partition: Optimize Optionsflto-report: Developer Optionsflto-report-wpa: Developer Optionsfmacro-prefix-map: Preprocessor Optionsfmath-errno: Optimize Optionsfmax-errors: Warning Optionsfmax-include-depth: Preprocessor Optionsfmem-report: Developer Optionsfmem-report-wpa: Developer Optionsfmerge-all-constants: Optimize Optionsfmerge-constants: Optimize Optionsfmerge-debug-strings: Debugging Optionsfmessage-length: Diagnostic Message Formatting Optionsfmodule-header: C++ Dialect Optionsfmodule-implicit-inline: C++ Dialect Optionsfmodule-lazy: C++ Dialect Optionsfmodule-mapper: C++ Dialect Optionsfmodule-only: C++ Dialect Optionsfmodules-ts: C++ Dialect Optionsfmodulo-sched: Optimize Optionsfmodulo-sched-allow-regmoves: Optimize Optionsfmove-loop-invariants: Optimize Optionsfmove-loop-stores: Optimize Optionsfms-extensions: Unnamed Fieldsfms-extensions: C++ Dialect Optionsfms-extensions: C Dialect Optionsfmultiflags: Developer Optionsfnew-inheriting-ctors: C++ Dialect Optionsfnew-ttp-matching: C++ Dialect Optionsfnext-runtime: Objective-C and Objective-C++ Dialect Optionsfnil-receivers: Objective-C and Objective-C++ Dialect Optionsfno-access-control: C++ Dialect Optionsfno-allocation-dce: Optimize Optionsfno-analyzer: Static Analyzer Optionsfno-analyzer-call-summaries: Static Analyzer Optionsfno-analyzer-feasibility: Static Analyzer Optionsfno-analyzer-fine-grained: Static Analyzer Optionsfno-analyzer-show-duplicate-count: Static Analyzer Optionsfno-analyzer-state-merge: Static Analyzer Optionsfno-analyzer-state-purge: Static Analyzer Optionsfno-analyzer-suppress-followups: Static Analyzer Optionsfno-analyzer-transitivity: Static Analyzer Optionsfno-analyzer-undo-inlining: Static Analyzer Optionsfno-asm: C Dialect Optionsfno-bit-tests: Code Gen Optionsfno-branch-count-reg: Optimize Optionsfno-builtin: Other Builtinsfno-builtin: Common Function Attributesfno-builtin: Warning Optionsfno-builtin: C Dialect Optionsfno-canonical-system-headers: Preprocessor Optionsfno-char8_t: C++ Dialect Optionsfno-checking: Developer Optionsfno-common: Common Variable Attributesfno-common: Code Gen Optionsfno-compare-debug: Developer Optionsfno-debug-types-section: Debugging Optionsfno-default-inline: Inlinefno-defer-pop: Optimize Optionsfno-diagnostics-show-caret: Diagnostic Message Formatting Optionsfno-diagnostics-show-cwe: Diagnostic Message Formatting Optionsfno-diagnostics-show-labels: Diagnostic Message Formatting Optionsfno-diagnostics-show-line-numbers: Diagnostic Message Formatting Optionsfno-diagnostics-show-option: Diagnostic Message Formatting Optionsfno-diagnostics-show-rules: Diagnostic Message Formatting Optionsfno-dwarf2-cfi-asm: Debugging Optionsfno-elide-constructors: C++ Dialect Optionsfno-elide-type: Diagnostic Message Formatting Optionsfno-eliminate-unused-debug-symbols: Debugging Optionsfno-eliminate-unused-debug-types: Debugging Optionsfno-enforce-eh-specs: C++ Dialect Optionsfno-ext-numeric-literals: C++ Dialect Optionsfno-extern-tls-init: C++ Dialect Optionsfno-finite-loops: Optimize Optionsfno-fold-simple-inlines: C++ Dialect Optionsfno-fp-int-builtin-inexact: Optimize Optionsfno-function-cse: Optimize Optionsfno-gnu-keywords: C++ Dialect Optionsfno-gnu-unique: Code Gen Optionsfno-guess-branch-probability: Optimize Optionsfno-hardcfr-check-exceptions: Instrumentation Optionsfno-hardcfr-check-returning-calls: Instrumentation Optionsfno-ident: Code Gen Optionsfno-implement-inlines: C++ Interfacefno-implement-inlines: C++ Dialect Optionsfno-implicit-inline-templates: C++ Dialect Optionsfno-implicit-templates: Template Instantiationfno-implicit-templates: C++ Dialect Optionsfno-inline: Optimize Optionsfno-ira-share-save-slots: Optimize Optionsfno-ira-share-spill-slots: Optimize Optionsfno-jump-tables: Code Gen Optionsfno-keep-inline-dllexport: Optimize Optionsfno-lifetime-dse: Optimize Optionsfno-local-ivars: Objective-C and Objective-C++ Dialect Optionsfno-math-errno: Optimize Optionsfno-merge-debug-strings: Debugging Optionsfno-module-lazy: C++ Dialect Optionsfno-modules-ts: C++ Dialect Optionsfno-nil-receivers: Objective-C and Objective-C++ Dialect Optionsfno-nonansi-builtins: C++ Dialect Optionsfno-operator-names: C++ Dialect Optionsfno-optional-diags: C++ Dialect Optionsfno-peephole: Optimize Optionsfno-peephole2: Optimize Optionsfno-plt: Code Gen Optionsfno-pretty-templates: C++ Dialect Optionsfno-printf-return-value: Optimize Optionsfno-rtti: C++ Dialect Optionsfno-sanitize-recover: Instrumentation Optionsfno-sanitize-trap: Instrumentation Optionsfno-sanitize=all: Instrumentation Optionsfno-sched-interblock: Optimize Optionsfno-sched-spec: Optimize Optionsfno-set-stack-executable: x86 Windows Optionsfno-show-column: Diagnostic Message Formatting Optionsfno-signed-bitfields: C Dialect Optionsfno-signed-zeros: Optimize Optionsfno-stack-limit: Instrumentation Optionsfno-strict-flex-arrays: C Dialect Optionsfno-threadsafe-statics: C++ Dialect Optionsfno-toplevel-reorder: Optimize Optionsfno-trapping-math: Optimize Optionsfno-unsigned-bitfields: C Dialect Optionsfno-use-cxa-get-exception-ptr: C++ Dialect Optionsfno-var-tracking-assignments: Debugging Optionsfno-var-tracking-assignments-toggle: Developer Optionsfno-weak: C++ Dialect Optionsfno-working-directory: Preprocessor Optionsfno-writable-relocated-rdata: x86 Windows Optionsfno-zero-initialized-in-bss: Optimize Optionsfnon-call-exceptions: Code Gen Optionsfnonansi-builtins: C++ Dialect Optionsfnothrow-opt: C++ Dialect Optionsfobjc-abi-version: Objective-C and Objective-C++ Dialect Optionsfobjc-call-cxx-cdtors: Objective-C and Objective-C++ Dialect Optionsfobjc-direct-dispatch: Objective-C and Objective-C++ Dialect Optionsfobjc-exceptions: Objective-C and Objective-C++ Dialect Optionsfobjc-gc: Objective-C and Objective-C++ Dialect Optionsfobjc-nilcheck: Objective-C and Objective-C++ Dialect Optionsfobjc-std: Objective-C and Objective-C++ Dialect Optionsfoffload: C Dialect Optionsfoffload-options: C Dialect Optionsfomit-frame-pointer: Optimize Optionsfopenacc: C Dialect Optionsfopenacc-dim: C Dialect Optionsfopenmp: C Dialect Optionsfopenmp-simd: C Dialect Optionsfopenmp-target-simd-clone: C Dialect Optionsfoperator-names: C++ Dialect Optionsfopt-info: Developer Optionsfoptimize-sibling-calls: Optimize Optionsfoptimize-strlen: Optimize Optionsfoptional-diags: C++ Dialect Optionsforce_cpusubtype_ALL: Darwin Optionsforce_flat_namespace: Darwin Optionsfpack-struct: Code Gen Optionsfpartial-inlining: Optimize Optionsfpatchable-function-entry: Instrumentation Optionsfpcc-struct-return: Incompatibilitiesfpcc-struct-return: Code Gen Optionsfpch-deps: Preprocessor Optionsfpch-preprocess: Preprocessor Optionsfpeel-loops: Optimize Optionsfpeephole: Optimize Optionsfpeephole2: Optimize Optionsfpermissive: C++ Dialect Optionsfpermitted-flt-eval-methods: C Dialect Optionsfpermitted-flt-eval-methods=c11: C Dialect Optionsfpermitted-flt-eval-methods=ts-18661-3: C Dialect OptionsfPIC: Code Gen Optionsfpic: Code Gen OptionsfPIE: Code Gen Optionsfpie: Code Gen Optionsfplan9-extensions: Unnamed Fieldsfplan9-extensions: C Dialect Optionsfplt: Code Gen Optionsfplugin: Overall Optionsfplugin-arg: Overall Optionsfpost-ipa-mem-report: Developer Optionsfpre-ipa-mem-report: Developer Optionsfpredictive-commoning: Optimize Optionsfprefetch-loop-arrays: Optimize Optionsfpreprocessed: Preprocessor Optionsfpreserve-control-flow: Optimize Optionsfpretty-templates: C++ Dialect Optionsfprintf-return-value: Optimize Optionsfprofile-abs-path: Instrumentation Optionsfprofile-arcs: Other Builtinsfprofile-arcs: Instrumentation Optionsfprofile-correction: Optimize Optionsfprofile-dir: Instrumentation Optionsfprofile-exclude-files: Instrumentation Optionsfprofile-filter-files: Instrumentation Optionsfprofile-generate: Instrumentation Optionsfprofile-info-section: Instrumentation Optionsfprofile-note: Instrumentation Optionsfprofile-partial-training: Optimize Optionsfprofile-prefix-map: Instrumentation Optionsfprofile-prefix-path: Instrumentation Optionsfprofile-reorder-functions: Optimize Optionsfprofile-report: Developer Optionsfprofile-reproducible: Instrumentation Optionsfprofile-update: Instrumentation Optionsfprofile-use: Optimize Optionsfprofile-values: Optimize Optionsfpu: RX Optionsfrandom-seed: Developer Optionsfreciprocal-math: Optimize Optionsfrecord-gcc-switches: Code Gen Optionsfree: Optimize Optionsfreg-struct-return: Code Gen Optionsfrename-registers: Optimize Optionsfreorder-blocks: Optimize Optionsfreorder-blocks-algorithm: Optimize Optionsfreorder-blocks-and-partition: Optimize Optionsfreorder-functions: Optimize Optionsfreplace-objc-classes: Objective-C and Objective-C++ Dialect Optionsfreport-bug: Developer Optionsfrerun-cse-after-loop: Optimize Optionsfreschedule-modulo-scheduled-loops: Optimize Optionsfrounding-math: Optimize Optionsfrtti: C++ Dialect Optionsfsanitize-address-use-after-scope: Instrumentation Optionsfsanitize-coverage=trace-cmp: Instrumentation Optionsfsanitize-coverage=trace-pc: Instrumentation Optionsfsanitize-recover: Instrumentation Optionsfsanitize-sections: Instrumentation Optionsfsanitize-trap: Instrumentation Optionsfsanitize-undefined-trap-on-error: Instrumentation Optionsfsanitize=address: Instrumentation Optionsfsanitize=alignment: Instrumentation Optionsfsanitize=bool: Instrumentation Optionsfsanitize=bounds: Instrumentation Optionsfsanitize=bounds-strict: Instrumentation Optionsfsanitize=builtin: Instrumentation Optionsfsanitize=enum: Instrumentation Optionsfsanitize=float-cast-overflow: Instrumentation Optionsfsanitize=float-divide-by-zero: Instrumentation Optionsfsanitize=hwaddress: Instrumentation Optionsfsanitize=integer-divide-by-zero: Instrumentation Optionsfsanitize=kernel-address: Instrumentation Optionsfsanitize=kernel-hwaddress: Instrumentation Optionsfsanitize=leak: Instrumentation Optionsfsanitize=nonnull-attribute: Instrumentation Optionsfsanitize=null: Instrumentation Optionsfsanitize=object-size: Instrumentation Optionsfsanitize=pointer-compare: Instrumentation Optionsfsanitize=pointer-overflow: Instrumentation Optionsfsanitize=pointer-subtract: Instrumentation Optionsfsanitize=return: Instrumentation Optionsfsanitize=returns-nonnull-attribute: Instrumentation Optionsfsanitize=shadow-call-stack: Instrumentation Optionsfsanitize=shift: Instrumentation Optionsfsanitize=shift-base: Instrumentation Optionsfsanitize=shift-exponent: Instrumentation Optionsfsanitize=signed-integer-overflow: Instrumentation Optionsfsanitize=thread: Instrumentation Optionsfsanitize=undefined: Instrumentation Optionsfsanitize=unreachable: Instrumentation Optionsfsanitize=vla-bound: Instrumentation Optionsfsanitize=vptr: Instrumentation Optionsfsave-optimization-record: Developer Optionsfsched-critical-path-heuristic: Optimize Optionsfsched-dep-count-heuristic: Optimize Optionsfsched-group-heuristic: Optimize Optionsfsched-interblock: Optimize Optionsfsched-last-insn-heuristic: Optimize Optionsfsched-pressure: Optimize Optionsfsched-rank-heuristic: Optimize Optionsfsched-spec: Optimize Optionsfsched-spec-insn-heuristic: Optimize Optionsfsched-spec-load: Optimize Optionsfsched-spec-load-dangerous: Optimize Optionsfsched-stalled-insns: Optimize Optionsfsched-stalled-insns-dep: Optimize Optionsfsched-verbose: Developer Optionsfsched2-use-superblocks: Optimize Optionsfschedule-fusion: Optimize Optionsfschedule-insns: Optimize Optionsfschedule-insns2: Optimize Optionsfsection-anchors: Optimize Optionsfsel-sched-pipelining: Optimize Optionsfsel-sched-pipelining-outer-loops: Optimize Optionsfselective-scheduling: Optimize Optionsfselective-scheduling2: Optimize Optionsfsemantic-interposition: Optimize Optionsfset-stack-executable: x86 Windows Optionsfshort-enums: Non-bugsfshort-enums: Common Type Attributesfshort-enums: Structures unions enumerations and bit-fields implementationfshort-enums: Code Gen Optionsfshort-wchar: Code Gen Optionsfshow-column: Diagnostic Message Formatting Optionsfshrink-wrap: Optimize Optionsfshrink-wrap-separate: Optimize Optionsfsignaling-nans: Optimize Optionsfsigned-bitfields: Non-bugsfsigned-bitfields: C Dialect Optionsfsigned-char: Characters implementationfsigned-char: C Dialect Optionsfsigned-zeros: Optimize Optionsfsimd-cost-model: Optimize Optionsfsingle-precision-constant: Optimize Optionsfsized-deallocation: C++ Dialect Optionsfsjlj: Code Gen Optionsfsplit-ivs-in-unroller: Optimize Optionsfsplit-loops: Optimize Optionsfsplit-paths: Optimize Optionsfsplit-stack: Common Function Attributesfsplit-stack: Instrumentation Optionsfsplit-wide-types: Optimize Optionsfsplit-wide-types-early: Optimize Optionsfssa-backprop: Optimize Optionsfssa-phiopt: Optimize Optionsfsso-struct: C Dialect Optionsfstack-check: Instrumentation Optionsfstack-clash-protection: Instrumentation Optionsfstack-limit-register: Instrumentation Optionsfstack-limit-symbol: Instrumentation Optionsfstack-protector: Instrumentation Optionsfstack-protector-all: Instrumentation Optionsfstack-protector-explicit: Instrumentation Optionsfstack-protector-strong: Instrumentation Optionsfstack-usage: Developer Optionsfstack_reuse: Code Gen Optionsfstats: Developer Optionsfstdarg-opt: Optimize Optionsfstore-merging: Optimize Optionsfstrict-aliasing: Optimize Optionsfstrict-enums: C++ Dialect Optionsfstrict-flex-arrays: C Dialect Optionsfstrict-flex-arrays=level: C Dialect Optionsfstrict-overflow: Code Gen Optionsfstrict-volatile-bitfields: Code Gen Optionsfstrong-eval-order: C++ Dialect Optionsfstrub=all: Instrumentation Optionsfstrub=at-calls: Instrumentation Optionsfstrub=internal: Instrumentation Optionsfstrub=relaxed: Instrumentation Optionsfstrub=strict: Instrumentation Optionsfsync-libcalls: Code Gen Optionsfsyntax-only: Warning Optionsftabstop: Preprocessor Optionsftemplate-backtrace-limit: C++ Dialect Optionsftemplate-depth: C++ Dialect Optionsftest-coverage: Instrumentation Optionsfthread-jumps: Optimize Optionsfthreadsafe-statics: C++ Dialect Optionsftime-report: Developer Optionsftime-report-details: Developer Optionsftls-model: Code Gen Optionsftoplevel-reorder: Optimize Optionsftracer: Optimize Optionsftrack-macro-expansion: Preprocessor Optionsftrampolines: Code Gen Optionsftrapping-math: Optimize Optionsftrapv: Code Gen Optionsftree-bit-ccp: Optimize Optionsftree-builtin-call-dce: Optimize Optionsftree-ccp: Optimize Optionsftree-ch: Optimize Optionsftree-coalesce-vars: Optimize Optionsftree-copy-prop: Optimize Optionsftree-dce: Optimize Optionsftree-dominator-opts: Optimize Optionsftree-dse: Optimize Optionsftree-forwprop: Optimize Optionsftree-fre: Optimize Optionsftree-loop-distribute-patterns: Optimize Optionsftree-loop-distribution: Optimize Optionsftree-loop-if-convert: Optimize Optionsftree-loop-im: Optimize Optionsftree-loop-ivcanon: Optimize Optionsftree-loop-linear: Optimize Optionsftree-loop-optimize: Optimize Optionsftree-loop-vectorize: Optimize Optionsftree-parallelize-loops: Optimize Optionsftree-partial-pre: Optimize Optionsftree-phiprop: Optimize Optionsftree-pre: Optimize Optionsftree-pta: Optimize Optionsftree-reassoc: Optimize Optionsftree-scev-cprop: Optimize Optionsftree-sink: Optimize Optionsftree-slp-vectorize: Optimize Optionsftree-slsr: Optimize Optionsftree-sra: Optimize Optionsftree-switch-conversion: Optimize Optionsftree-tail-merge: Optimize Optionsftree-ter: Optimize Optionsftree-vectorize: Optimize Optionsftree-vrp: Optimize Optionsftrivial-auto-var-init: Optimize Optionsfunconstrained-commons: Optimize Optionsfunit-at-a-time: Optimize Optionsfunreachable-traps: Optimize Optionsfunroll-all-loops: Optimize Optionsfunroll-loops: Optimize Optionsfunsafe-math-optimizations: Optimize Optionsfunsigned-bitfields: Non-bugsfunsigned-bitfields: Structures unions enumerations and bit-fields implementationfunsigned-bitfields: C Dialect Optionsfunsigned-char: Characters implementationfunsigned-char: C Dialect Optionsfunswitch-loops: Optimize Optionsfunwind-tables: Code Gen Optionsfuse-cxa-atexit: C++ Dialect Optionsfuse-cxa-get-exception-ptr: C++ Dialect Optionsfuse-ld=bfd: Link Optionsfuse-ld=gold: Link Optionsfuse-ld=lld: Link Optionsfuse-ld=mold: Link Optionsfuse-linker-plugin: Optimize Optionsfvar-tracking: Debugging Optionsfvar-tracking-assignments: Debugging Optionsfvar-tracking-assignments-toggle: Developer Optionsfvariable-expansion-in-unroller: Optimize Optionsfvect-cost-model: Optimize Optionsfverbose-asm: Code Gen Optionsfversion-loops-for-strides: Optimize Optionsfvisibility: Code Gen Optionsfvisibility-inlines-hidden: C++ Dialect Optionsfvisibility-ms-compat: C++ Dialect Optionsfvpt: Optimize Optionsfvtable-verify: Instrumentation Optionsfvtv-counts: Instrumentation Optionsfvtv-debug: Instrumentation Optionsfweak: C++ Dialect Optionsfweb: Optimize Optionsfwhole-program: Optimize Optionsfwide-exec-charset: Preprocessor Optionsfworking-directory: Preprocessor Optionsfwrapv: Code Gen Optionsfwrapv-pointer: Code Gen Optionsfwritable-relocated-rdata: x86 Windows Optionsfzero-call-used-regs: Optimize Optionsfzero-initialized-in-bss: Optimize Optionsfzero-link: Objective-C and Objective-C++ Dialect OptionsG: System V OptionsG: RS/6000 and PowerPC OptionsG: Nios II OptionsG: MIPS OptionsG: M32R/D OptionsG: ARC Optionsg: Debugging Optionsgas-loc-support: Debugging Optionsgas-locview-support: Debugging Optionsgbtf: Debugging Optionsgcolumn-info: Debugging Optionsgctf: Debugging Optionsgdescribe-dies: Debugging Optionsgdwarf: Debugging Optionsgdwarf32: Debugging Optionsgdwarf64: Debugging Optionsgen-decls: Objective-C and Objective-C++ Dialect Optionsgfull: Darwin Optionsggdb: Debugging Optionsggnu-pubnames: Debugging Optionsginline-points: Debugging Optionsginternal-reset-location-views: Debugging Optionsgno-as-loc-support: Debugging Optionsgno-column-info: Debugging Optionsgno-inline-points: Debugging Optionsgno-internal-reset-location-views: Debugging Optionsgno-record-gcc-switches: Debugging Optionsgno-statement-frontiers: Debugging Optionsgno-strict-dwarf: Debugging Optionsgno-variable-location-views: Debugging Optionsgpubnames: Debugging Optionsgrecord-gcc-switches: Debugging Optionsgsplit-dwarf: Debugging Optionsgstatement-frontiers: Debugging Optionsgstrict-dwarf: Debugging Optionsgtoggle: Developer Optionsgused: Darwin Optionsgvariable-location-views: Debugging Optionsgvariable-location-views=incompat5: Debugging Optionsgvms: Debugging Optionsgz: Debugging OptionsH: Preprocessor Optionsheaderpad_max_install_names: Darwin Optionshelp: Overall OptionsI: Directory OptionsI-: Directory Optionsidirafter: Directory Optionsiframework: Darwin Optionsimacros: Preprocessor Optionsimage_base: Darwin Optionsimultilib: Directory Optionsinclude: Preprocessor Optionsinit: Darwin Optionsinstall_name: Darwin Optionsiplugindir=: Directory Optionsiprefix: Directory Optionsiquote: Directory Optionsisysroot: Directory Optionsisystem: Directory Optionsiwithprefix: Directory Optionsiwithprefixbefore: Directory Optionskeep_private_externs: Darwin OptionsL: Directory Optionsl: Link Optionslobjc: Link OptionsM: Preprocessor Optionsm1: SH Optionsm10: PDP-11 Optionsm128bit-long-double: x86 Optionsm16: x86 Optionsm16-bit: NDS32 Optionsm16-bit: CRIS Optionsm1reg-: Adapteva Epiphany Optionsm2: SH Optionsm210: MCore Optionsm2a: SH Optionsm2a-nofpu: SH Optionsm2a-single: SH Optionsm2a-single-only: SH Optionsm3: SH Optionsm31: S/390 and zSeries Optionsm32: x86 Optionsm32: SPARC Optionsm32: RS/6000 and PowerPC Optionsm32-bit: CRIS Optionsm32bit-doubles: RX Optionsm32bit-doubles: RL78 Optionsm32r: M32R/D Optionsm32r2: M32R/D Optionsm32rx: M32R/D Optionsm340: MCore Optionsm3dnow: x86 Optionsm3dnowa: x86 Optionsm3e: SH Optionsm4: SH Optionsm4-100: SH Optionsm4-100-nofpu: SH Optionsm4-100-single: SH Optionsm4-100-single-only: SH Optionsm4-200: SH Optionsm4-200-nofpu: SH Optionsm4-200-single: SH Optionsm4-200-single-only: SH Optionsm4-300: SH Optionsm4-300-nofpu: SH Optionsm4-300-single: SH Optionsm4-300-single-only: SH Optionsm4-340: SH Optionsm4-500: SH Optionsm4-nofpu: SH Optionsm4-single: SH Optionsm4-single-only: SH Optionsm40: PDP-11 Optionsm45: PDP-11 Optionsm4a: SH Optionsm4a-nofpu: SH Optionsm4a-single: SH Optionsm4a-single-only: SH Optionsm4al: SH Optionsm4byte-functions: MCore Optionsm5200: M680x0 Optionsm5206e: M680x0 Optionsm528x: M680x0 Optionsm5307: M680x0 Optionsm5407: M680x0 Optionsm64: x86 Optionsm64: SPARC Optionsm64: S/390 and zSeries Optionsm64: RS/6000 and PowerPC Optionsm64: Nvidia PTX Optionsm64bit-doubles: RX Optionsm64bit-doubles: RL78 Optionsm68000: M680x0 Optionsm68010: M680x0 Optionsm68020: M680x0 Optionsm68020-40: M680x0 Optionsm68020-60: M680x0 Optionsm68030: M680x0 Optionsm68040: M680x0 Optionsm68060: M680x0 Optionsm68881: M680x0 Optionsm8-bit: CRIS Optionsm80387: x86 Optionsm8bit-idiv: x86 Optionsm8byte-align: V850 Optionsm96bit-long-double: x86 OptionsmA6: ARC OptionsmA7: ARC Optionsmabi: Xtensa Optionsmabi: x86 Optionsmabi: RS/6000 and PowerPC Optionsmabi: RISC-V Optionsmabi: PRU Optionsmabi: LoongArch Optionsmabi: ARM Optionsmabi: AArch64 Optionsmabi=32: MIPS Optionsmabi=64: MIPS Optionsmabi=call0: Xtensa Optionsmabi=eabi: MIPS Optionsmabi=elfv1: RS/6000 and PowerPC Optionsmabi=elfv2: RS/6000 and PowerPC Optionsmabi=gnu: MMIX Optionsmabi=ibmlongdouble: RS/6000 and PowerPC Optionsmabi=ieeelongdouble: RS/6000 and PowerPC Optionsmabi=mmixware: MMIX Optionsmabi=n32: MIPS Optionsmabi=o64: MIPS Optionsmabi=windowed: Xtensa Optionsmabicalls: MIPS Optionsmabm: x86 Optionsmabort-on-noreturn: ARM Optionsmabs=2008: MIPS Optionsmabs=legacy: MIPS Optionsmabsdata: AVR Optionsmac0: PDP-11 Optionsmacc-4: FRV Optionsmacc-8: FRV Optionsmaccumulate-args: AVR Optionsmaccumulate-outgoing-args: x86 Optionsmaccumulate-outgoing-args: SH Optionsmaddress-mode=long: x86 Optionsmaddress-mode=short: x86 Optionsmads: RS/6000 and PowerPC Optionsmadx: x86 Optionsmaes: x86 Optionsmaix-struct-return: RS/6000 and PowerPC Optionsmaix32: RS/6000 and PowerPC Optionsmaix64: RS/6000 and PowerPC Optionsmalign-300: H8/300 Optionsmalign-call: ARC Optionsmalign-data: x86 Optionsmalign-data: RISC-V Optionsmalign-double: x86 Optionsmalign-int: M680x0 Optionsmalign-labels: FRV Optionsmalign-loops: M32R/D Optionsmalign-natural: RS/6000 and PowerPC Optionsmalign-power: RS/6000 and PowerPC Optionsmalign-stringops: x86 Optionsmalloc-cc: FRV Optionsmallow-string-insns: RX Optionsmallregs: RL78 Optionsmaltivec: RS/6000 and PowerPC Optionsmalu32: eBPF Optionsmam33: MN10300 Optionsmam33-2: MN10300 Optionsmam34: MN10300 Optionsmamx-bf16: x86 Optionsmamx-complex: x86 Optionsmamx-fp16: x86 Optionsmamx-int8: x86 Optionsmamx-tile: x86 Optionsmanchor: C-SKY Optionsmandroid: GNU/Linux Optionsmannotate-align: ARC Optionsmapcs: ARM Optionsmapcs-frame: ARM Optionsmapp-regs: V850 Optionsmapp-regs: SPARC OptionsmARC600: ARC OptionsmARC601: ARC OptionsmARC700: ARC Optionsmarch: x86 Optionsmarch: S/390 and zSeries Optionsmarch: RISC-V Optionsmarch: Nvidia PTX Optionsmarch: Nios II Optionsmarch: NDS32 Optionsmarch: MIPS Optionsmarch: M680x0 Optionsmarch: LoongArch Optionsmarch: HPPA Optionsmarch: CRIS Optionsmarch: C6X Optionsmarch: ARM Optionsmarch: AMD GCN Optionsmarch: AArch64 Optionsmarch=: C-SKY Optionsmarclinux: ARC Optionsmarclinux_prof: ARC Optionsmargonaut: ARC Optionsmarm: ARM Optionsmas100-syntax: RX Optionsmasm-hex: MSP430 Optionsmasm-syntax-unified: ARM Optionsmasm=dialect: x86 Optionsmatomic: ARC Optionsmatomic-libcalls: HPPA Optionsmatomic-model=model: SH Optionsmauto-litpools: Xtensa Optionsmauto-modify-reg: ARC Optionsmauto-pic: IA-64 Optionsmavoid-indexed-addresses: RS/6000 and PowerPC Optionsmavx: x86 Optionsmavx2: x86 Optionsmavx256-split-unaligned-load: x86 Optionsmavx256-split-unaligned-store: x86 Optionsmavx5124fmaps: x86 Optionsmavx5124vnniw: x86 Optionsmavx512bf16: x86 Optionsmavx512bitalg: x86 Optionsmavx512bw: x86 Optionsmavx512cd: x86 Optionsmavx512dq: x86 Optionsmavx512er: x86 Optionsmavx512f: x86 Optionsmavx512fp16: x86 Optionsmavx512ifma: x86 Optionsmavx512pf: x86 Optionsmavx512vbmi: x86 Optionsmavx512vbmi2: x86 Optionsmavx512vl: x86 Optionsmavx512vnni: x86 Optionsmavx512vp2intersect: x86 Optionsmavx512vpopcntdq: x86 Optionsmavxifma: x86 Optionsmavxneconvert: x86 Optionsmavxvnni: x86 Optionsmavxvnniint8: x86 Optionsmax-vect-align: Adapteva Epiphany Optionsmb: SH Optionsmbackchain: S/390 and zSeries Optionsmbarrel-shift-enabled: LM32 Optionsmbarrel-shifter: ARC Optionsmbarrel_shifter: ARC Optionsmbase-addresses: MMIX Optionsmbbit-peephole: ARC Optionsmbe8: ARM Optionsmbig: RS/6000 and PowerPC Optionsmbig-endian: RS/6000 and PowerPC Optionsmbig-endian: RISC-V Optionsmbig-endian: NDS32 Optionsmbig-endian: MicroBlaze Optionsmbig-endian: MCore Optionsmbig-endian: IA-64 Optionsmbig-endian: eBPF Optionsmbig-endian: C-SKY Optionsmbig-endian: C6X Optionsmbig-endian: ARM Optionsmbig-endian: ARC Optionsmbig-endian: AArch64 Optionsmbig-endian-data: RX Optionsmbig-switch: V850 Optionsmbig-switch: HPPA Optionsmbigtable: SH Optionsmbionic: GNU/Linux Optionsmbit-align: RS/6000 and PowerPC Optionsmbitfield: M680x0 Optionsmbitops: SH Optionsmblock-compare-inline-limit: RS/6000 and PowerPC Optionsmblock-compare-inline-loop-limit: RS/6000 and PowerPC Optionsmblock-move-inline-limit: RS/6000 and PowerPC Optionsmbmi: x86 Optionsmbmi2: x86 Optionsmboard: OpenRISC Optionsmbranch-cost: RISC-V Optionsmbranch-cost: MIPS Optionsmbranch-cost: LoongArch Optionsmbranch-cost: AVR Optionsmbranch-cost: Adapteva Epiphany Optionsmbranch-cost=: C-SKY Optionsmbranch-cost=num: SH Optionsmbranch-cost=number: M32R/D Optionsmbranch-index: ARC Optionsmbranch-likely: MIPS Optionsmbranch-predict: MMIX Optionsmbranch-protection: ARM Optionsmbranch-protection: AArch64 Optionsmbss-plt: RS/6000 and PowerPC Optionsmbuild-constants: DEC Alpha Optionsmbwx: DEC Alpha Optionsmbypass-cache: Nios II Optionsmc68000: M680x0 Optionsmc68020: M680x0 Optionsmcache: C-SKY Optionsmcache-block-size: NDS32 Optionsmcache-volatile: Nios II Optionsmcall-aixdesc: RS/6000 and PowerPC Optionsmcall-eabi: RS/6000 and PowerPC Optionsmcall-freebsd: RS/6000 and PowerPC Optionsmcall-linux: RS/6000 and PowerPC Optionsmcall-ms2sysv-xlogues: x86 Optionsmcall-netbsd: RS/6000 and PowerPC Optionsmcall-openbsd: RS/6000 and PowerPC Optionsmcall-prologues: AVR Optionsmcall-sysv: RS/6000 and PowerPC Optionsmcall-sysv-eabi: RS/6000 and PowerPC Optionsmcall-sysv-noeabi: RS/6000 and PowerPC Optionsmcallee-super-interworking: ARM Optionsmcaller-copies: HPPA Optionsmcaller-super-interworking: ARM Optionsmcallgraph-data: MCore Optionsmcase-vector-pcrel: ARC Optionsmcbcond: SPARC Optionsmcbranch-force-delay-slot: SH Optionsmcc-init: CRIS Optionsmccrt: C-SKY Optionsmcet-switch: x86 Optionsmcfv4e: M680x0 Optionsmcheck-zero-division: MIPS Optionsmcheck-zero-division: LoongArch Optionsmcix: DEC Alpha Optionsmcld: x86 Optionsmcldemote: x86 Optionsmclear-hwcap: Solaris 2 Optionsmclflushopt: x86 Optionsmclwb: x86 Optionsmclzero: x86 Optionsmcmodel: SPARC Optionsmcmodel: NDS32 Optionsmcmodel=kernel: x86 Optionsmcmodel=large: x86 Optionsmcmodel=large: RS/6000 and PowerPC Optionsmcmodel=large: OpenRISC Optionsmcmodel=large: AArch64 Optionsmcmodel=medany: RISC-V Optionsmcmodel=medium: x86 Optionsmcmodel=medium: RS/6000 and PowerPC Optionsmcmodel=medlow: RISC-V Optionsmcmodel=small: x86 Optionsmcmodel=small: RS/6000 and PowerPC Optionsmcmodel=small: OpenRISC Optionsmcmodel=small: AArch64 Optionsmcmodel=tiny: AArch64 Optionsmcmov: OpenRISC Optionsmcmov: NDS32 Optionsmcmove: Adapteva Epiphany Optionsmcmpb: RS/6000 and PowerPC Optionsmcmpccxadd: x86 Optionsmcmse: ARM Optionsmco-re: eBPF Optionsmcode-density: ARC Optionsmcode-density-frame: ARC Optionsmcode-readable: MIPS Optionsmcode-region: MSP430 Optionsmcoherent-ldcw: HPPA Optionsmcompact-branches=always: MIPS Optionsmcompact-branches=never: MIPS Optionsmcompact-branches=optimal: MIPS Optionsmcompact-casesi: ARC Optionsmcompat-align-parm: RS/6000 and PowerPC Optionsmcompress: FT32 Optionsmcond-exec: FRV Optionsmcond-move: FRV Optionsmcond-move-float: LoongArch Optionsmcond-move-int: LoongArch Optionsmconsole: x86 Windows Optionsmconst-align: CRIS Optionsmconst16: Xtensa Optionsmconstant-cfstrings: Darwin Optionsmconstant-gp: IA-64 Optionsmconstpool: C-SKY Optionsmcorea: Blackfin Optionsmcoreb: Blackfin Optionsmcp: C-SKY Optionsmcpu: x86 Optionsmcpu: Visium Optionsmcpu: SPARC Optionsmcpu: RX Optionsmcpu: RS/6000 and PowerPC Optionsmcpu: RL78 Optionsmcpu: RISC-V Optionsmcpu: M680x0 Optionsmcpu: FRV Optionsmcpu: eBPF Optionsmcpu: DEC Alpha Optionsmcpu: CRIS Optionsmcpu: ARM Optionsmcpu: ARC Optionsmcpu: AArch64 Optionsmcpu32: M680x0 Optionsmcpu=: MSP430 Optionsmcpu=: MicroBlaze Optionsmcpu=: M32C Optionsmcpu=: C-SKY Optionsmcpu=: Blackfin Optionsmcrc: MIPS Optionsmcrc32: x86 Optionsmcrypto: RS/6000 and PowerPC Optionsmcsr-check: RISC-V Optionsmcsync-anomaly: Blackfin Optionsmctor-dtor: NDS32 Optionsmcustom-fpu-cfg: Nios II Optionsmcustom-insn: Nios II Optionsmcx16: x86 OptionsMD: Preprocessor Optionsmdalign: SH Optionsmdata-align: CRIS Optionsmdata-region: MSP430 Optionsmdaz-ftz: x86 Optionsmdebug: Visium Optionsmdebug: S/390 and zSeries Optionsmdebug: M32R/D Optionsmdebug-main=prefix: VMS Optionsmdec-asm: PDP-11 Optionsmdirect-extern-access: x86 Optionsmdirect-extern-access: LoongArch Optionsmdisable-callt: V850 Optionsmdisable-fpregs: HPPA Optionsmdisable-indexing: HPPA Optionsmdiv: RISC-V Optionsmdiv: MCore Optionsmdiv: M680x0 Optionsmdiv: C-SKY Optionsmdiv-rem: ARC Optionsmdiv=strategy: SH Optionsmdivide-breaks: MIPS Optionsmdivide-enabled: LM32 Optionsmdivide-traps: MIPS Optionsmdivsi3_libfunc=name: SH Optionsmdll: x86 Windows Optionsmdlmzb: RS/6000 and PowerPC Optionsmdmx: MIPS Optionsmdouble: FRV Optionsmdouble: AVR Optionsmdouble-float: OpenRISC Optionsmdouble-float: MIPS Optionsmdouble-float: LoongArch Optionsmdouble-float: C-SKY Optionsmdpfp: ARC Optionsmdpfp-compact: ARC Optionsmdpfp-fast: ARC Optionsmdpfp_compact: ARC Optionsmdpfp_fast: ARC Optionsmdsp: MIPS Optionsmdsp: C-SKY Optionsmdsp-packa: ARC Optionsmdsp_packa: ARC Optionsmdspr2: MIPS Optionsmdump-tune-features: x86 Optionsmdvbf: ARC Optionsmdwarf2-asm: IA-64 Optionsmdword: FRV Optionsmdynamic-no-pic: RS/6000 and PowerPC OptionsmEA: ARC Optionsmea: ARC Optionsmeabi: RS/6000 and PowerPC Optionsmearly-cbranchsi: ARC Optionsmearly-stop-bits: IA-64 Optionsmeb: Nios II Optionsmeb: Moxie Optionsmedsp: C-SKY Optionsmel: Nios II Optionsmel: Moxie Optionsmelf: MMIX Optionsmelf: CRIS Optionsmelrw: C-SKY Optionsmemb: RS/6000 and PowerPC Optionsmembedded-data: MIPS Optionsmemregs=: M32C Optionsmenqcmd: x86 Optionsmep: V850 Optionsmepsilon: MMIX Optionsmesa: S/390 and zSeries Optionsmetrax100: CRIS Optionsmetrax4: CRIS Optionsmeva: MIPS Optionsmexpand-adddi: ARC Optionsmexplicit-relocs: MIPS Optionsmexplicit-relocs: LoongArch Optionsmexplicit-relocs: DEC Alpha Optionsmexr: H8/300 Optionsmext-perf: NDS32 Optionsmext-perf2: NDS32 Optionsmext-string: NDS32 Optionsmextern-sdata: MIPS Optionsmextra-l32r-costs: Xtensa OptionsMF: Preprocessor Optionsmf16c: x86 Optionsmfancy-math-387: x86 Optionsmfast-fp: Blackfin Optionsmfast-indirect-calls: HPPA Optionsmfast-sw-div: Nios II Optionsmfaster-structs: SPARC Optionsmfdiv: RISC-V Optionsmfdivdu: C-SKY Optionsmfdpic: FRV Optionsmfdpic: ARM Optionsmfentry: x86 Optionsmfentry-name: x86 Optionsmfentry-section: x86 Optionsmfix: DEC Alpha Optionsmfix-24k: MIPS Optionsmfix-and-continue: Darwin Optionsmfix-at697f: SPARC Optionsmfix-cmse-cve-2021-35465: ARM Optionsmfix-cortex-a53-835769: AArch64 Optionsmfix-cortex-a53-843419: AArch64 Optionsmfix-cortex-m3-ldrd: ARM Optionsmfix-gr712rc: SPARC Optionsmfix-r10000: MIPS Optionsmfix-r4000: MIPS Optionsmfix-r4400: MIPS Optionsmfix-r5900: MIPS Optionsmfix-rm7000: MIPS Optionsmfix-sb1: MIPS Optionsmfix-ut699: SPARC Optionsmfix-ut700: SPARC Optionsmfix-vr4120: MIPS Optionsmfix-vr4130: MIPS Optionsmfixed-cc: FRV Optionsmfixed-range: SH Optionsmfixed-range: IA-64 Optionsmfixed-range: HPPA Optionsmflat: SPARC Optionsmflip-mips16: MIPS Optionsmflip-thumb: ARM Optionsmfloat-abi: C-SKY Optionsmfloat-abi: ARM Optionsmfloat-ieee: DEC Alpha Optionsmfloat-vax: DEC Alpha Optionsmfloat128: RS/6000 and PowerPC Optionsmfloat128-hardware: RS/6000 and PowerPC Optionsmflush-func: MIPS Optionsmflush-func=name: M32R/D Optionsmflush-trap=number: M32R/D Optionsmfma: x86 Optionsmfma4: x86 Optionsmfmaf: SPARC Optionsmfmovd: SH Optionsmforce-indirect-call: x86 Optionsmforce-no-pic: Xtensa Optionsmfp-exceptions: MIPS Optionsmfp-mode: Adapteva Epiphany Optionsmfp-reg: DEC Alpha Optionsmfp-ret-in-387: x86 Optionsmfp-rounding-mode: DEC Alpha Optionsmfp-trap-mode: DEC Alpha Optionsmfp16-format: ARM Optionsmfp32: MIPS Optionsmfp64: MIPS Optionsmfpmath: x86 Optionsmfpmath: Optimize Optionsmfpr-32: FRV Optionsmfpr-64: FRV Optionsmfprnd: RS/6000 and PowerPC Optionsmfpu: Visium Optionsmfpu: SPARC Optionsmfpu: PDP-11 Optionsmfpu: LoongArch Optionsmfpu: ARM Optionsmfpu: ARC Optionsmfpu=: C-SKY Optionsmfpxx: MIPS Optionsmfract-convert-truncate: AVR Optionsmframe-header-opt: MIPS Optionsmfriz: RS/6000 and PowerPC Optionsmfsca: SH Optionsmfsgsbase: x86 Optionsmfsmuld: SPARC Optionsmfsrra: SH Optionsmft32b: FT32 Optionsmfull-regs: NDS32 Optionsmfull-toc: RS/6000 and PowerPC Optionsmfunction-return: x86 Optionsmfused-madd: Xtensa Optionsmfused-madd: SH Optionsmfused-madd: S/390 and zSeries Optionsmfused-madd: RS/6000 and PowerPC Optionsmfused-madd: MIPS Optionsmfused-madd: IA-64 Optionsmfxsr: x86 Optionsmg: VAX OptionsMG: Preprocessor Optionsmg10: RL78 Optionsmg13: RL78 Optionsmg14: RL78 Optionsmgas: HPPA Optionsmgas-isr-prologues: AVR Optionsmgcc-abi: V850 Optionsmgeneral-regs-only: x86 Optionsmgeneral-regs-only: ARM Optionsmgeneral-regs-only: AArch64 Optionsmgfni: x86 Optionsmghs: V850 Optionsmginv: MIPS Optionsmglibc: GNU/Linux Optionsmgnu: VAX Optionsmgnu-as: IA-64 Optionsmgnu-asm: PDP-11 Optionsmgnu-attribute: RS/6000 and PowerPC Optionsmgnu-ld: IA-64 Optionsmgnu-ld: HPPA Optionsmgomp: Nvidia PTX Optionsmgp32: MIPS Optionsmgp64: MIPS Optionsmgpopt: Nios II Optionsmgpopt: MIPS Optionsmgpr-32: FRV Optionsmgpr-64: FRV Optionsmgprel-ro: FRV Optionsmgprel-sec: Nios II Optionsmh: H8/300 Optionsmhal: Nios II Optionsmhalf-reg-file: Adapteva Epiphany Optionsmhard-dfp: S/390 and zSeries Optionsmhard-dfp: RS/6000 and PowerPC Optionsmhard-div: OpenRISC Optionsmhard-float: x86 Optionsmhard-float: Visium Optionsmhard-float: V850 Optionsmhard-float: SPARC Optionsmhard-float: S/390 and zSeries Optionsmhard-float: RS/6000 and PowerPC Optionsmhard-float: OpenRISC Optionsmhard-float: MIPS Optionsmhard-float: MicroBlaze Optionsmhard-float: M680x0 Optionsmhard-float: FRV Optionsmhard-float: C-SKY Optionsmhard-mul: OpenRISC Optionsmhard-quad-float: SPARC Optionsmharden-sls: x86 Optionsmharden-sls: AArch64 Optionsmhardlit: MCore Optionsmhigh-registers: C-SKY Optionsmhle: x86 Optionsmhotpatch: S/390 and zSeries Optionsmhp-ld: HPPA Optionsmhreset: x86 Optionsmhtm: S/390 and zSeries Optionsmhtm: RS/6000 and PowerPC Optionsmhw-div: Nios II Optionsmhw-mul: Nios II Optionsmhw-mulx: Nios II Optionsmhwmult=: MSP430 Optionsmiamcu: x86 Optionsmicplb: Blackfin Optionsmid-shared-library: Blackfin Optionsmieee: SH Optionsmieee: DEC Alpha Optionsmieee-conformant: DEC Alpha Optionsmieee-fp: x86 Optionsmieee-with-inexact: DEC Alpha Optionsmilp32: IA-64 Optionsmimadd: MIPS Optionsmimpure-text: Solaris 2 Optionsmincoming-stack-boundary: x86 Optionsmindexed-loads: ARC Optionsmindirect-branch: x86 Optionsmindirect-branch-cs-prefix: x86 Optionsmindirect-branch-register: x86 Optionsminline-all-stringops: x86 Optionsminline-atomics: RISC-V Optionsminline-float-divide-max-throughput: IA-64 Optionsminline-float-divide-min-latency: IA-64 Optionsminline-ic_invalidate: SH Optionsminline-int-divide: IA-64 Optionsminline-int-divide-max-throughput: IA-64 Optionsminline-int-divide-min-latency: IA-64 Optionsminline-plt: FRV Optionsminline-plt: Blackfin Optionsminline-sqrt-max-throughput: IA-64 Optionsminline-sqrt-min-latency: IA-64 Optionsminline-stringops-dynamically: x86 Optionsminrt: PRU Optionsminrt: MSP430 Optionsminsert-sched-nops: RS/6000 and PowerPC Optionsminstrument-return: x86 Optionsmint-register: RX Optionsmint16: PDP-11 Optionsmint32: PDP-11 Optionsmint32: H8/300 Optionsmint8: AVR Optionsminterlink-compressed: MIPS Optionsminterlink-mips16: MIPS Optionsmips1: MIPS Optionsmips16: MIPS Optionsmips2: MIPS Optionsmips3: MIPS Optionsmips32: MIPS Optionsmips32r3: MIPS Optionsmips32r5: MIPS Optionsmips32r6: MIPS Optionsmips3d: MIPS Optionsmips4: MIPS Optionsmips64: MIPS Optionsmips64r2: MIPS Optionsmips64r3: MIPS Optionsmips64r5: MIPS Optionsmips64r6: MIPS Optionsmirq-ctrl-saved: ARC Optionsmisa: Nvidia PTX Optionsmisa-spec: RISC-V Optionsmisel: RS/6000 and PowerPC Optionsmisize: SH Optionsmisize: ARC Optionsmisr-vector-size: NDS32 Optionsmissue-rate=number: M32R/D Optionsmistack: C-SKY Optionsmjli-always: ARC Optionsmjmp32: eBPF Optionsmjmpext: eBPF Optionsmjsr: RX Optionsmjump-in-delay: HPPA Optionsmkernel: eBPF Optionsmkernel: Darwin Optionsmkl: x86 Optionsmknuthdiv: MMIX Optionsml: SH Optionsmlam: x86 Optionsmlarge: MSP430 Optionsmlarge-data: DEC Alpha Optionsmlarge-data-threshold: x86 Optionsmlarge-text: DEC Alpha Optionsmleaf-id-shared-library: Blackfin Optionsmlibfuncs: MMIX Optionsmlibrary-pic: FRV Optionsmlinked-fp: FRV Optionsmlinker-opt: HPPA Optionsmlittle: RS/6000 and PowerPC Optionsmlittle-endian: RS/6000 and PowerPC Optionsmlittle-endian: RISC-V Optionsmlittle-endian: NDS32 Optionsmlittle-endian: MicroBlaze Optionsmlittle-endian: MCore Optionsmlittle-endian: IA-64 Optionsmlittle-endian: eBPF Optionsmlittle-endian: C-SKY Optionsmlittle-endian: C6X Optionsmlittle-endian: ARM Optionsmlittle-endian: ARC Optionsmlittle-endian: AArch64 Optionsmlittle-endian-data: RX Optionsmliw: MN10300 Optionsmll64: ARC Optionsmllsc: MIPS Optionsmload-store-pairs: MIPS Optionsmlocal-sdata: MIPS Optionsmlock: ARC Optionsmlong-calls: V850 Optionsmlong-calls: MIPS Optionsmlong-calls: HPPA Optionsmlong-calls: FRV Optionsmlong-calls: Blackfin Optionsmlong-calls: ARM Optionsmlong-calls: ARC Optionsmlong-calls: Adapteva Epiphany Optionsmlong-double: AVR Optionsmlong-double-128: x86 Optionsmlong-double-128: S/390 and zSeries Optionsmlong-double-64: x86 Optionsmlong-double-64: S/390 and zSeries Optionsmlong-double-80: x86 Optionsmlong-jump-table-offsets: M680x0 Optionsmlong-jumps: V850 Optionsmlong-load-store: HPPA Optionsmlong32: MIPS Optionsmlong64: MIPS Optionsmlongcall: RS/6000 and PowerPC Optionsmlongcalls: Xtensa Optionsmloongson-ext: MIPS Optionsmloongson-ext2: MIPS Optionsmloongson-mmi: MIPS Optionsmloop: V850 Optionsmloop: PRU Optionsmlow-precision-div: AArch64 Optionsmlow-precision-recip-sqrt: AArch64 Optionsmlow-precision-sqrt: AArch64 Optionsmlow64k: Blackfin Optionsmlp64: IA-64 Optionsmlpc-width: ARC Optionsmlra: VAX Optionsmlra: SPARC Optionsmlra: PDP-11 Optionsmlra: FT32 Optionsmlra: ARC Optionsmlra-priority-compact: ARC Optionsmlra-priority-noncompact: ARC Optionsmlra-priority-none: ARC Optionsmlwp: x86 Optionsmlxc1-sxc1: MIPS Optionsmlzcnt: x86 OptionsMM: Preprocessor Optionsmmac-24: ARC Optionsmmac-d16: ARC Optionsmmac_24: ARC Optionsmmac_d16: ARC Optionsmmacosx-version-min: Darwin Optionsmmad: MIPS Optionsmmadd4: MIPS Optionsmmain-is-OS_task: AVR Optionsmmainkernel: Nvidia PTX Optionsmmalloc64: VMS Optionsmmanual-endbr: x86 Optionsmmax: DEC Alpha Optionsmmax-constant-size: RX Optionsmmax-inline-memcpy-size: LoongArch Optionsmmax-inline-shift=: MSP430 Optionsmmax-stack-frame: CRIS Optionsmmcount-ra-address: MIPS Optionsmmcu: PRU Optionsmmcu: MIPS Optionsmmcu: AVR Optionsmmcu=: MSP430 OptionsMMD: Preprocessor Optionsmmedia: FRV Optionsmmedium-calls: ARC Optionsmmemcpy: MIPS Optionsmmemcpy: MicroBlaze Optionsmmemcpy: LoongArch Optionsmmemcpy-strategy=strategy: x86 Optionsmmemory-latency: DEC Alpha Optionsmmemory-model: SPARC Optionsmmemset-strategy=strategy: x86 Optionsmmfcrf: RS/6000 and PowerPC Optionsmmicromips: MIPS Optionsmmillicode: ARC Optionsmminimal-toc: RS/6000 and PowerPC Optionsmmixed-code: ARC Optionsmmma: RS/6000 and PowerPC Optionsmmmx: x86 Optionsmmodel=large: M32R/D Optionsmmodel=medium: M32R/D Optionsmmodel=small: M32R/D Optionsmmovbe: x86 Optionsmmovdir64b: x86 Optionsmmovdiri: x86 Optionsmmove-max: x86 Optionsmmp: C-SKY Optionsmmpy: ARC Optionsmmpy-option: ARC Optionsmms-bitfields: x86 Optionsmmt: MIPS Optionsmmul: RL78 Optionsmmul-bug-workaround: CRIS Optionsmmul.x: Moxie Optionsmmul32x16: ARC Optionsmmul64: ARC Optionsmmuladd: FRV Optionsmmulhw: RS/6000 and PowerPC Optionsmmult-bug: MN10300 Optionsmmultcost: ARC Optionsmmulti-cond-exec: FRV Optionsmmulticore: Blackfin Optionsmmultiple: RS/6000 and PowerPC Optionsmmultiple-stld: C-SKY Optionsmmusl: GNU/Linux Optionsmmvcle: S/390 and zSeries Optionsmmvme: RS/6000 and PowerPC Optionsmmwait: x86 Optionsmmwaitx: x86 Optionsmn: H8/300 Optionsmn-flash: AVR Optionsmnan=2008: MIPS Optionsmnan=legacy: MIPS Optionsmneeded: x86 Optionsmneon-for-64bits: ARM Optionsmnested-cond-exec: FRV Optionsmnewlib: OpenRISC Optionsmno-16-bit: NDS32 Optionsmno-4byte-functions: MCore Optionsmno-8byte-align: V850 Optionsmno-abicalls: MIPS Optionsmno-ac0: PDP-11 Optionsmno-align-double: x86 Optionsmno-align-int: M680x0 Optionsmno-align-loops: M32R/D Optionsmno-align-stringops: x86 Optionsmno-allow-string-insns: RX Optionsmno-altivec: RS/6000 and PowerPC Optionsmno-am33: MN10300 Optionsmno-app-regs: V850 Optionsmno-app-regs: SPARC Optionsmno-as100-syntax: RX Optionsmno-atomic-libcalls: HPPA Optionsmno-auto-litpools: Xtensa Optionsmno-avoid-indexed-addresses: RS/6000 and PowerPC Optionsmno-backchain: S/390 and zSeries Optionsmno-base-addresses: MMIX Optionsmno-bit-align: RS/6000 and PowerPC Optionsmno-bitfield: M680x0 Optionsmno-branch-likely: MIPS Optionsmno-branch-predict: MMIX Optionsmno-brcc: ARC Optionsmno-bwx: DEC Alpha Optionsmno-bypass-cache: Nios II Optionsmno-cache-volatile: Nios II Optionsmno-call-ms2sysv-xlogues: x86 Optionsmno-callgraph-data: MCore Optionsmno-cbcond: SPARC Optionsmno-check-zero-division: MIPS Optionsmno-cix: DEC Alpha Optionsmno-clearbss: MicroBlaze Optionsmno-cmov: NDS32 Optionsmno-cmpb: RS/6000 and PowerPC Optionsmno-co-re: eBPF Optionsmno-cond-exec: FRV Optionsmno-cond-exec: ARC Optionsmno-cond-move: FRV Optionsmno-const-align: CRIS Optionsmno-const16: Xtensa Optionsmno-crc: MIPS Optionsmno-crt0: Moxie Optionsmno-crt0: MN10300 Optionsmno-crypto: RS/6000 and PowerPC Optionsmno-csync-anomaly: Blackfin Optionsmno-custom-insn: Nios II Optionsmno-data-align: CRIS Optionsmno-debug: S/390 and zSeries Optionsmno-default: x86 Optionsmno-direct-extern-access: x86 Function Attributesmno-direct-extern-access: x86 Optionsmno-disable-callt: V850 Optionsmno-div: MCore Optionsmno-div: M680x0 Optionsmno-dlmzb: RS/6000 and PowerPC Optionsmno-double: FRV Optionsmno-dpfp-lrsr: ARC Optionsmno-dsp: MIPS Optionsmno-dspr2: MIPS Optionsmno-dwarf2-asm: IA-64 Optionsmno-dword: FRV Optionsmno-eabi: RS/6000 and PowerPC Optionsmno-early-stop-bits: IA-64 Optionsmno-eflags: FRV Optionsmno-embedded-data: MIPS Optionsmno-ep: V850 Optionsmno-epsilon: MMIX Optionsmno-eva: MIPS Optionsmno-explicit-relocs: MIPS Optionsmno-explicit-relocs: LoongArch Optionsmno-explicit-relocs: DEC Alpha Optionsmno-exr: H8/300 Optionsmno-ext-perf: NDS32 Optionsmno-ext-perf2: NDS32 Optionsmno-ext-string: NDS32 Optionsmno-extern-sdata: MIPS Optionsmno-fancy-math-387: x86 Optionsmno-fast-sw-div: Nios II Optionsmno-faster-structs: SPARC Optionsmno-fdpic: ARM Optionsmno-fix: DEC Alpha Optionsmno-fix-24k: MIPS Optionsmno-fix-cortex-a53-835769: AArch64 Optionsmno-fix-cortex-a53-843419: AArch64 Optionsmno-fix-r10000: MIPS Optionsmno-fix-r4000: MIPS Optionsmno-fix-r4400: MIPS Optionsmno-flat: SPARC Optionsmno-float: MIPS Optionsmno-float128: RS/6000 and PowerPC Optionsmno-float128-hardware: RS/6000 and PowerPC Optionsmno-flush-func: M32R/D Optionsmno-flush-trap: M32R/D Optionsmno-fmaf: SPARC Optionsmno-fp-in-toc: RS/6000 and PowerPC Optionsmno-fp-regs: DEC Alpha Optionsmno-fp-ret-in-387: x86 Optionsmno-fprnd: RS/6000 and PowerPC Optionsmno-fpu: Visium Optionsmno-fpu: SPARC Optionsmno-fsca: SH Optionsmno-fsmuld: SPARC Optionsmno-fsrra: SH Optionsmno-fused-madd: Xtensa Optionsmno-fused-madd: SH Optionsmno-fused-madd: S/390 and zSeries Optionsmno-fused-madd: RS/6000 and PowerPC Optionsmno-fused-madd: MIPS Optionsmno-fused-madd: IA-64 Optionsmno-ginv: MIPS Optionsmno-gnu-as: IA-64 Optionsmno-gnu-attribute: RS/6000 and PowerPC Optionsmno-gnu-ld: IA-64 Optionsmno-gpopt: Nios II Optionsmno-gpopt: MIPS Optionsmno-hard-dfp: S/390 and zSeries Optionsmno-hard-dfp: RS/6000 and PowerPC Optionsmno-hardlit: MCore Optionsmno-htm: S/390 and zSeries Optionsmno-htm: RS/6000 and PowerPC Optionsmno-hw-div: Nios II Optionsmno-hw-mul: Nios II Optionsmno-hw-mulx: Nios II Optionsmno-id-shared-library: Blackfin Optionsmno-ieee: SH Optionsmno-ieee-fp: x86 Optionsmno-imadd: MIPS Optionsmno-inline-float-divide: IA-64 Optionsmno-inline-int-divide: IA-64 Optionsmno-inline-sqrt: IA-64 Optionsmno-int16: PDP-11 Optionsmno-int32: PDP-11 Optionsmno-interlink-compressed: MIPS Optionsmno-interlink-mips16: MIPS Optionsmno-interrupts: AVR Optionsmno-isel: RS/6000 and PowerPC Optionsmno-jsr: RX Optionsmno-knuthdiv: MMIX Optionsmno-leaf-id-shared-library: Blackfin Optionsmno-libfuncs: MMIX Optionsmno-liw: MN10300 Optionsmno-llsc: MIPS Optionsmno-load-store-pairs: MIPS Optionsmno-local-sdata: MIPS Optionsmno-long-calls: V850 Optionsmno-long-calls: MIPS Optionsmno-long-calls: HPPA Optionsmno-long-calls: Blackfin Optionsmno-long-calls: ARM Optionsmno-long-jumps: V850 Optionsmno-longcall: RS/6000 and PowerPC Optionsmno-longcalls: Xtensa Optionsmno-loongson-ext: MIPS Optionsmno-loongson-ext2: MIPS Optionsmno-loongson-mmi: MIPS Optionsmno-low-precision-div: AArch64 Optionsmno-low-precision-recip-sqrt: AArch64 Optionsmno-low-precision-sqrt: AArch64 Optionsmno-low64k: Blackfin Optionsmno-lra: VAX Optionsmno-lra: SPARC Optionsmno-lsim: MCore Optionsmno-lsim: FR30 Optionsmno-mad: MIPS Optionsmno-max: DEC Alpha Optionsmno-mcount-ra-address: MIPS Optionsmno-mcu: MIPS Optionsmno-mdmx: MIPS Optionsmno-media: FRV Optionsmno-memcpy: MIPS Optionsmno-mfcrf: RS/6000 and PowerPC Optionsmno-mips16: MIPS Optionsmno-mips3d: MIPS Optionsmno-mma: RS/6000 and PowerPC Optionsmno-mmicromips: MIPS OptionsMno-modules: Preprocessor Optionsmno-mpy: ARC Optionsmno-ms-bitfields: x86 Optionsmno-mt: MIPS Optionsmno-mul-bug-workaround: CRIS Optionsmno-muladd: FRV Optionsmno-mulhw: RS/6000 and PowerPC Optionsmno-mult-bug: MN10300 Optionsmno-multi-cond-exec: FRV Optionsmno-multiple: RS/6000 and PowerPC Optionsmno-mvcle: S/390 and zSeries Optionsmno-nested-cond-exec: FRV Optionsmno-odd-spreg: MIPS Optionsmno-omit-leaf-frame-pointer: AArch64 Optionsmno-optimize-membar: FRV Optionsmno-pack: FRV Optionsmno-packed-stack: S/390 and zSeries Optionsmno-paired-single: MIPS Optionsmno-pc-relative-literal-loads: AArch64 Optionsmno-pcrel: RS/6000 and PowerPC Optionsmno-pic: IA-64 Optionsmno-pid: RX Optionsmno-plt: MIPS Optionsmno-pltseq: RS/6000 and PowerPC Optionsmno-popc: SPARC Optionsmno-popcntb: RS/6000 and PowerPC Optionsmno-popcntd: RS/6000 and PowerPC Optionsmno-postinc: Adapteva Epiphany Optionsmno-postmodify: Adapteva Epiphany Optionsmno-power8-fusion: RS/6000 and PowerPC Optionsmno-power8-vector: RS/6000 and PowerPC Optionsmno-powerpc-gfxopt: RS/6000 and PowerPC Optionsmno-powerpc-gpopt: RS/6000 and PowerPC Optionsmno-powerpc64: RS/6000 and PowerPC Optionsmno-prefixed: RS/6000 and PowerPC Optionsmno-privileged: RS/6000 and PowerPC Optionsmno-prolog-function: V850 Optionsmno-prologue-epilogue: CRIS Optionsmno-prototype: RS/6000 and PowerPC Optionsmno-push-args: x86 Optionsmno-quad-memory: RS/6000 and PowerPC Optionsmno-quad-memory-atomic: RS/6000 and PowerPC Optionsmno-readonly-in-sdata: RS/6000 and PowerPC Optionsmno-red-zone: x86 Optionsmno-register-names: IA-64 Optionsmno-regnames: RS/6000 and PowerPC Optionsmno-relax: V850 Optionsmno-relax: PRU Optionsmno-relax-immediate: MCore Optionsmno-relocatable: RS/6000 and PowerPC Optionsmno-relocatable-lib: RS/6000 and PowerPC Optionsmno-renesas: SH Optionsmno-rop-protect: RS/6000 and PowerPC Optionsmno-round-nearest: Adapteva Epiphany Optionsmno-save-mduc-in-interrupts: RL78 Optionsmno-scc: FRV Optionsmno-sched-ar-data-spec: IA-64 Optionsmno-sched-ar-in-data-spec: IA-64 Optionsmno-sched-br-data-spec: IA-64 Optionsmno-sched-br-in-data-spec: IA-64 Optionsmno-sched-control-spec: IA-64 Optionsmno-sched-count-spec-in-critical-path: IA-64 Optionsmno-sched-in-control-spec: IA-64 Optionsmno-sched-prefer-non-control-spec-insns: IA-64 Optionsmno-sched-prefer-non-data-spec-insns: IA-64 Optionsmno-sched-prolog: ARM Optionsmno-sdata: RS/6000 and PowerPC Optionsmno-sdata: IA-64 Optionsmno-sdata: ARC Optionsmno-sep-data: Blackfin Optionsmno-serialize-volatile: Xtensa Optionsmno-setlb: MN10300 Optionsmno-short: M680x0 Optionsmno-side-effects: CRIS Optionsmno-sim: RX Optionsmno-single-exit: MMIX Optionsmno-slow-bytes: MCore Optionsmno-small-exec: S/390 and zSeries Optionsmno-smartmips: MIPS Optionsmno-soft-cmpsf: Adapteva Epiphany Optionsmno-soft-float: DEC Alpha Optionsmno-space-regs: HPPA Optionsmno-specld-anomaly: Blackfin Optionsmno-split-addresses: MIPS Optionsmno-split-lohi: Adapteva Epiphany Optionsmno-stack-align: CRIS Optionsmno-stack-bias: SPARC Optionsmno-std-struct-return: SPARC Optionsmno-strict-align: RS/6000 and PowerPC Optionsmno-strict-align: M680x0 Optionsmno-strict-align: AArch64 Optionsmno-subxc: SPARC Optionsmno-sum-in-toc: RS/6000 and PowerPC Optionsmno-sym32: MIPS Optionsmno-target-align: Xtensa Optionsmno-text-section-literals: Xtensa Optionsmno-tls-markers: RS/6000 and PowerPC Optionsmno-toc: RS/6000 and PowerPC Optionsmno-toplevel-symbols: MMIX Optionsmno-tpf-trace: S/390 and zSeries Optionsmno-tpf-trace-skip: S/390 and zSeries Optionsmno-unaligned-access: MIPS Optionsmno-unaligned-access: ARM Optionsmno-unaligned-doubles: SPARC Optionsmno-uninit-const-in-rodata: MIPS Optionsmno-unroll-only-small-loops: x86 Optionsmno-update: RS/6000 and PowerPC Optionsmno-user-mode: SPARC Optionsmno-usermode: SH Optionsmno-v3push: NDS32 Optionsmno-v8plus: SPARC Optionsmno-vect-double: Adapteva Epiphany Optionsmno-virt: MIPS Optionsmno-vis: SPARC Optionsmno-vis2: SPARC Optionsmno-vis3: SPARC Optionsmno-vis4: SPARC Optionsmno-vis4b: SPARC Optionsmno-vliw-branch: FRV Optionsmno-volatile-asm-stop: IA-64 Optionsmno-volatile-cache: ARC Optionsmno-vrsave: RS/6000 and PowerPC Optionsmno-vsx: RS/6000 and PowerPC Optionsmno-vx: S/390 and zSeries Optionsmno-warn-devices-csv: MSP430 Optionsmno-warn-mcu: MSP430 Optionsmno-warn-multiple-fast-interrupts: RX Optionsmno-wide-bitfields: MCore Optionsmno-xgot: MIPS Optionsmno-xgot: M680x0 Optionsmno-xl-compat: RS/6000 and PowerPC Optionsmno-xpa: MIPS Optionsmno-zdcbranch: SH Optionsmno-zero-extend: MMIX Optionsmno-zvector: S/390 and zSeries Optionsmnobitfield: M680x0 Optionsmnodiv: FT32 Optionsmnomacsave: SH Optionsmnop-fun-dllimport: x86 Windows Optionsmnop-mcount: x86 Optionsmnopm: FT32 Optionsmnops: Adapteva Epiphany Optionsmnorm: ARC Optionsmodd-spreg: MIPS Optionsmomit-leaf-frame-pointer: x86 Optionsmomit-leaf-frame-pointer: Blackfin Optionsmomit-leaf-frame-pointer: AArch64 Optionsmone-byte-bool: Darwin Optionsmoptimize: Nvidia PTX Optionsmoptimize-membar: FRV Optionsmordered: HPPA Optionsmoverride: AArch64 OptionsMP: Preprocessor Optionsmpa-risc-1-0: HPPA Optionsmpa-risc-1-1: HPPA Optionsmpa-risc-2-0: HPPA Optionsmpack: FRV Optionsmpacked-stack: S/390 and zSeries 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Optionsmsmall-data-limit: RISC-V Optionsmsmall-data-limit: LoongArch Optionsmsmall-divides: MicroBlaze Optionsmsmall-exec: S/390 and zSeries Optionsmsmall-model: FR30 Optionsmsmall-text: DEC Alpha Optionsmsmall16: Adapteva Epiphany Optionsmsmallc: Nios II Optionsmsmart: C-SKY Optionsmsmartmips: MIPS Optionsmsmp: VxWorks Optionsmsoft-cmpsf: Adapteva Epiphany Optionsmsoft-div: OpenRISC Optionsmsoft-float: x86 Optionsmsoft-float: Visium Optionsmsoft-float: V850 Optionsmsoft-float: SPARC Optionsmsoft-float: S/390 and zSeries Optionsmsoft-float: RS/6000 and PowerPC Optionsmsoft-float: PDP-11 Optionsmsoft-float: OpenRISC Optionsmsoft-float: MIPS Optionsmsoft-float: MicroBlaze Optionsmsoft-float: M680x0 Optionsmsoft-float: LoongArch Optionsmsoft-float: HPPA Optionsmsoft-float: FRV Optionsmsoft-float: DEC Alpha Optionsmsoft-float: C-SKY Optionsmsoft-float: ARC Optionsmsoft-mul: OpenRISC Optionsmsoft-mult: HPPA Optionsmsoft-quad-float: SPARC Optionsmsoft-stack: Nvidia PTX Optionsmsp8: AVR 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C++ Dialect OptionsWdate-time: Warning OptionsWdeclaration-after-statement: Warning OptionsWdelete-incomplete: C++ Dialect OptionsWdelete-non-virtual-dtor: C++ Dialect OptionsWdeprecated: Warning OptionsWdeprecated-copy: C++ Dialect OptionsWdeprecated-declarations: Warning OptionsWdeprecated-enum-enum-conversion: C++ Dialect OptionsWdeprecated-enum-float-conversion: C++ Dialect OptionsWdesignated-init: Warning OptionsWdisabled-optimization: Warning OptionsWdiscarded-array-qualifiers: Warning OptionsWdiscarded-qualifiers: Warning OptionsWdiv-by-zero: Warning OptionsWdouble-promotion: Warning OptionsWduplicate-decl-specifier: Warning OptionsWduplicated-branches: Warning OptionsWduplicated-cond: Warning Optionsweak_reference_mismatches: Darwin OptionsWeffc++: C++ Dialect OptionsWempty-body: Warning OptionsWendif-labels: Warning OptionsWenum-compare: Warning OptionsWenum-conversion: Warning OptionsWenum-int-mismatch: Warning OptionsWerror: Warning OptionsWerror=: Warning OptionsWexceptions: C++ Dialect OptionsWexpansion-to-defined: Warning OptionsWextra: Warning OptionsWextra-semi: C++ Dialect OptionsWfatal-errors: Warning OptionsWfloat-conversion: Warning OptionsWfloat-equal: Warning OptionsWformat: Common Function AttributesWformat: Warning OptionsWformat-contains-nul: Warning OptionsWformat-extra-args: Warning OptionsWformat-nonliteral: Common Function AttributesWformat-nonliteral: Warning OptionsWformat-overflow: Warning OptionsWformat-security: Warning OptionsWformat-signedness: Warning OptionsWformat-truncation: Warning OptionsWformat-y2k: Warning OptionsWformat-zero-length: Warning OptionsWformat=: Warning OptionsWformat=1: Warning OptionsWformat=2: Warning OptionsWframe-address: Warning OptionsWframe-larger-than=: Warning OptionsWfree-nonheap-object: Warning Optionswhatsloaded: Darwin Optionswhyload: Darwin OptionsWif-not-aligned: Warning OptionsWignored-attributes: Warning OptionsWignored-qualifiers: Warning OptionsWimplicit: Warning OptionsWimplicit-fallthrough: Warning OptionsWimplicit-fallthrough=: Warning OptionsWimplicit-function-declaration: Warning OptionsWimplicit-int: Warning OptionsWinaccessible-base: C++ Dialect OptionsWincompatible-pointer-types: Warning OptionsWinfinite-recursion: Warning OptionsWinherited-variadic-ctor: C++ Dialect OptionsWinit-list-lifetime: C++ Dialect OptionsWinit-self: Warning OptionsWinline: InlineWinline: Warning OptionsWint-conversion: Warning OptionsWint-in-bool-context: Warning OptionsWint-to-pointer-cast: Warning OptionsWinterference-size: Warning OptionsWinvalid-constexpr: C++ Dialect OptionsWinvalid-imported-macros: C++ Dialect OptionsWinvalid-memory-model: Warning OptionsWinvalid-offsetof: C++ Dialect OptionsWinvalid-pch: Warning OptionsWinvalid-utf8: Warning OptionsWjump-misses-init: Warning OptionsWl: Link OptionsWlarger-than-byte-size: Warning OptionsWlarger-than=: Warning OptionsWliteral-suffix: C++ Dialect OptionsWlogical-not-parentheses: Warning OptionsWlogical-op: Warning OptionsWlong-long: Warning OptionsWlto-type-mismatch: Warning OptionsWmain: Warning OptionsWmaybe-uninitialized: Warning OptionsWmemset-elt-size: Warning OptionsWmemset-transposed-args: Warning OptionsWmisleading-indentation: Warning OptionsWmismatched-dealloc: Warning OptionsWmismatched-new-delete: C++ Dialect OptionsWmismatched-tags: C++ Dialect OptionsWmissing-attributes: Warning OptionsWmissing-braces: Warning OptionsWmissing-declarations: Warning OptionsWmissing-field-initializers: Warning OptionsWmissing-format-attribute: Warning OptionsWmissing-include-dirs: Warning OptionsWmissing-noreturn: Warning OptionsWmissing-parameter-type: Warning OptionsWmissing-profile: Warning OptionsWmissing-prototypes: Warning OptionsWmissing-requires: Warning OptionsWmissing-template-keyword: Warning OptionsWmisspelled-isr: AVR OptionsWmultichar: Warning OptionsWmultiple-inheritance: C++ Dialect OptionsWmultistatement-macros: Warning OptionsWnamespaces: C++ Dialect OptionsWnarrowing: C++ Dialect OptionsWnested-externs: Warning OptionsWno-abi: Warning OptionsWno-absolute-value: Warning OptionsWno-addr-space-convert: AVR OptionsWno-address: Warning OptionsWno-address-of-packed-member: Warning OptionsWno-aggregate-return: Warning OptionsWno-aggressive-loop-optimizations: Warning OptionsWno-aligned-new: C++ Dialect OptionsWno-all: Warning OptionsWno-alloc-size-larger-than: Warning OptionsWno-alloc-zero: Warning OptionsWno-alloca: Warning OptionsWno-alloca-larger-than: Warning OptionsWno-analyzer-allocation-size: Static Analyzer OptionsWno-analyzer-deref-before-check: Static Analyzer OptionsWno-analyzer-double-fclose: Static Analyzer OptionsWno-analyzer-double-free: Static Analyzer OptionsWno-analyzer-exposure-through-output-file: Static Analyzer OptionsWno-analyzer-exposure-through-uninit-copy: Static Analyzer OptionsWno-analyzer-fd-access-mode-mismatch: Static Analyzer OptionsWno-analyzer-fd-double-close: Static Analyzer OptionsWno-analyzer-fd-leak: Static Analyzer OptionsWno-analyzer-fd-phase-mismatch: Static Analyzer OptionsWno-analyzer-fd-type-mismatch: Static Analyzer OptionsWno-analyzer-fd-use-after-close: Static Analyzer OptionsWno-analyzer-fd-use-without-check: Static Analyzer OptionsWno-analyzer-file-leak: Static Analyzer OptionsWno-analyzer-free-of-non-heap: Static Analyzer OptionsWno-analyzer-imprecise-fp-arithmetic: Static Analyzer OptionsWno-analyzer-infinite-recursion: Static Analyzer OptionsWno-analyzer-jump-through-null: Static Analyzer OptionsWno-analyzer-malloc-leak: Static Analyzer OptionsWno-analyzer-mismatching-deallocation: Static Analyzer OptionsWno-analyzer-null-argument: Static Analyzer OptionsWno-analyzer-null-dereference: Static Analyzer OptionsWno-analyzer-out-of-bounds: Static Analyzer OptionsWno-analyzer-possible-null-argument: Static Analyzer OptionsWno-analyzer-possible-null-dereference: Static Analyzer OptionsWno-analyzer-putenv-of-auto-var: Static Analyzer OptionsWno-analyzer-shift-count-negative: Static Analyzer OptionsWno-analyzer-shift-count-overflow: Static Analyzer OptionsWno-analyzer-stale-setjmp-buffer: Static Analyzer OptionsWno-analyzer-tainted-allocation-size: Static Analyzer OptionsWno-analyzer-tainted-array-index: Static Analyzer OptionsWno-analyzer-tainted-assertion: Static Analyzer OptionsWno-analyzer-tainted-divisor: Static Analyzer OptionsWno-analyzer-tainted-offset: Static Analyzer OptionsWno-analyzer-tainted-size: Static Analyzer OptionsWno-analyzer-too-complex: Static Analyzer OptionsWno-analyzer-unsafe-call-within-signal-handler: Static Analyzer OptionsWno-analyzer-use-after-free: Static Analyzer OptionsWno-analyzer-use-of-pointer-in-stale-stack-frame: Static Analyzer OptionsWno-analyzer-use-of-uninitialized-value: Static Analyzer OptionsWno-analyzer-va-arg-type-mismatch: Static Analyzer OptionsWno-analyzer-va-list-exhausted: Static Analyzer OptionsWno-analyzer-va-list-leak: Static Analyzer OptionsWno-analyzer-va-list-use-after-va-end: Static Analyzer OptionsWno-analyzer-write-to-const: Static Analyzer OptionsWno-analyzer-write-to-string-literal: Static Analyzer OptionsWno-arith-conversion: Warning OptionsWno-array-bounds: Warning OptionsWno-array-compare: Warning OptionsWno-array-parameter: Warning OptionsWno-assign-intercept: Objective-C and Objective-C++ Dialect OptionsWno-attribute-alias: Warning OptionsWno-attribute-warning: Warning OptionsWno-attributes: Warning OptionsWno-bad-function-cast: Warning OptionsWno-bidi-chars: Warning OptionsWno-bool-compare: Warning OptionsWno-bool-operation: Warning OptionsWno-builtin-declaration-mismatch: Warning OptionsWno-builtin-macro-redefined: Warning OptionsWno-c++-compat: Warning OptionsWno-c++11-compat: Warning OptionsWno-c++11-extensions: Warning OptionsWno-c++14-compat: Warning OptionsWno-c++14-extensions: Warning OptionsWno-c++17-compat: Warning OptionsWno-c++17-extensions: Warning OptionsWno-c++20-compat: Warning OptionsWno-c++20-extensions: Warning OptionsWno-c++23-extensions: Warning OptionsWno-c11-c2x-compat: Warning OptionsWno-c90-c99-compat: Warning OptionsWno-c99-c11-compat: Warning OptionsWno-cast-align: Warning OptionsWno-cast-function-type: Warning OptionsWno-cast-qual: Warning OptionsWno-catch-value: C++ Dialect OptionsWno-char-subscripts: Warning OptionsWno-class-conversion: C++ Dialect OptionsWno-class-memaccess: C++ Dialect OptionsWno-clobbered: Warning OptionsWno-comma-subscript: C++ Dialect OptionsWno-complain-wrong-lang: Warning OptionsWno-conditionally-supported: C++ Dialect OptionsWno-conversion: Warning OptionsWno-conversion-null: C++ Dialect OptionsWno-coverage-invalid-line-number: Warning OptionsWno-coverage-mismatch: Warning OptionsWno-cpp: Warning OptionsWno-ctad-maybe-unsupported: C++ Dialect OptionsWno-ctor-dtor-privacy: C++ Dialect OptionsWno-dangling-else: Warning OptionsWno-dangling-pointer: Warning OptionsWno-dangling-reference: C++ Dialect OptionsWno-date-time: Warning OptionsWno-declaration-after-statement: Warning OptionsWno-delete-incomplete: C++ Dialect OptionsWno-delete-non-virtual-dtor: C++ Dialect OptionsWno-deprecated: Warning OptionsWno-deprecated-copy: C++ Dialect OptionsWno-deprecated-declarations: Warning OptionsWno-deprecated-enum-enum-conversion: C++ Dialect OptionsWno-deprecated-enum-float-conversion: C++ Dialect OptionsWno-designated-init: Warning OptionsWno-disabled-optimization: Warning OptionsWno-discarded-array-qualifiers: Warning OptionsWno-discarded-qualifiers: Warning OptionsWno-div-by-zero: Warning OptionsWno-double-promotion: Warning OptionsWno-duplicate-decl-specifier: Warning OptionsWno-duplicated-branches: Warning OptionsWno-duplicated-cond: Warning OptionsWno-effc++: C++ Dialect OptionsWno-empty-body: Warning OptionsWno-endif-labels: Warning OptionsWno-enum-compare: Warning OptionsWno-enum-conversion: Warning OptionsWno-enum-int-mismatch: Warning OptionsWno-error: Warning OptionsWno-error=: Warning OptionsWno-exceptions: C++ Dialect OptionsWno-extra: Warning OptionsWno-extra-semi: C++ Dialect OptionsWno-fatal-errors: Warning OptionsWno-float-conversion: Warning OptionsWno-float-equal: Warning OptionsWno-format: Warning OptionsWno-format-contains-nul: Warning OptionsWno-format-extra-args: Warning OptionsWno-format-nonliteral: Warning OptionsWno-format-overflow: Warning OptionsWno-format-security: Warning OptionsWno-format-signedness: Warning OptionsWno-format-truncation: Warning OptionsWno-format-y2k: Warning OptionsWno-format-zero-length: Warning OptionsWno-frame-address: Warning OptionsWno-frame-larger-than: Warning OptionsWno-free-nonheap-object: Warning OptionsWno-if-not-aligned: Warning OptionsWno-ignored-attributes: Warning OptionsWno-ignored-qualifiers: Warning OptionsWno-implicit: Warning OptionsWno-implicit-fallthrough: Warning OptionsWno-implicit-function-declaration: Warning OptionsWno-implicit-int: Warning OptionsWno-inaccessible-base: C++ Dialect OptionsWno-incompatible-pointer-types: Warning OptionsWno-infinite-recursion: Warning OptionsWno-inherited-variadic-ctor: C++ Dialect OptionsWno-init-list-lifetime: C++ Dialect OptionsWno-init-self: Warning OptionsWno-inline: Warning OptionsWno-int-conversion: Warning OptionsWno-int-in-bool-context: Warning OptionsWno-int-to-pointer-cast: Warning OptionsWno-invalid-constexpr: C++ Dialect OptionsWno-invalid-imported-macros: C++ Dialect OptionsWno-invalid-memory-model: Warning OptionsWno-invalid-offsetof: C++ Dialect OptionsWno-invalid-pch: Warning OptionsWno-invalid-utf8: Warning OptionsWno-jump-misses-init: Warning OptionsWno-larger-than: Warning OptionsWno-literal-suffix: C++ Dialect OptionsWno-logical-not-parentheses: Warning OptionsWno-logical-op: Warning OptionsWno-long-long: Warning OptionsWno-lto-type-mismatch: Warning OptionsWno-main: Warning OptionsWno-maybe-uninitialized: Warning OptionsWno-memset-elt-size: Warning OptionsWno-memset-transposed-args: Warning OptionsWno-misleading-indentation: Warning OptionsWno-mismatched-dealloc: Warning OptionsWno-mismatched-new-delete: C++ Dialect OptionsWno-mismatched-tags: C++ Dialect OptionsWno-missing-attributes: Warning OptionsWno-missing-braces: Warning OptionsWno-missing-declarations: Warning OptionsWno-missing-field-initializers: Warning OptionsWno-missing-format-attribute: Warning OptionsWno-missing-include-dirs: Warning OptionsWno-missing-noreturn: Warning OptionsWno-missing-parameter-type: Warning OptionsWno-missing-profile: Warning OptionsWno-missing-prototypes: Warning OptionsWno-missing-requires: Warning OptionsWno-missing-template-keyword: Warning OptionsWno-misspelled-isr: AVR OptionsWno-multichar: Warning OptionsWno-multiple-inheritance: C++ Dialect OptionsWno-multistatement-macros: Warning OptionsWno-namespaces: C++ Dialect OptionsWno-narrowing: C++ Dialect OptionsWno-nested-externs: Warning OptionsWno-noexcept: C++ Dialect OptionsWno-noexcept-type: C++ Dialect OptionsWno-non-template-friend: C++ Dialect OptionsWno-non-virtual-dtor: C++ Dialect OptionsWno-nonnull: Warning OptionsWno-nonnull-compare: Warning OptionsWno-normalized: Warning OptionsWno-null-dereference: Warning OptionsWno-odr: Warning OptionsWno-old-style-cast: C++ Dialect OptionsWno-old-style-declaration: Warning OptionsWno-old-style-definition: Warning OptionsWno-openacc-parallelism: Warning OptionsWno-openmp-simd: Warning OptionsWno-overflow: Warning OptionsWno-overlength-strings: Warning OptionsWno-overloaded-virtual: C++ Dialect OptionsWno-override-init: Warning OptionsWno-override-init-side-effects: Warning OptionsWno-packed: Warning OptionsWno-packed-bitfield-compat: Warning OptionsWno-packed-not-aligned: Warning OptionsWno-padded: Warning OptionsWno-parentheses: Warning OptionsWno-pedantic: Warning OptionsWno-pedantic-ms-format: Warning OptionsWno-pessimizing-move: C++ Dialect OptionsWno-placement-new: C++ Dialect OptionsWno-pmf-conversions: Bound member functionsWno-pmf-conversions: C++ Dialect OptionsWno-pointer-arith: Warning OptionsWno-pointer-compare: Warning OptionsWno-pointer-sign: Warning OptionsWno-pointer-to-int-cast: Warning OptionsWno-pragmas: Warning OptionsWno-prio-ctor-dtor: Warning OptionsWno-property-assign-default: Objective-C and Objective-C++ Dialect OptionsWno-protocol: Objective-C and Objective-C++ Dialect OptionsWno-range-loop-construct: C++ Dialect OptionsWno-redundant-decls: Warning OptionsWno-redundant-move: C++ Dialect OptionsWno-redundant-tags: C++ Dialect OptionsWno-register: C++ Dialect OptionsWno-reorder: C++ Dialect OptionsWno-restrict: Warning OptionsWno-return-local-addr: Warning OptionsWno-return-type: Warning OptionsWno-scalar-storage-order: Warning OptionsWno-selector: Objective-C and Objective-C++ Dialect OptionsWno-self-move: Warning OptionsWno-sequence-point: Warning OptionsWno-shadow: Warning OptionsWno-shadow-ivar: Warning OptionsWno-shift-count-negative: Warning OptionsWno-shift-count-overflow: Warning OptionsWno-shift-negative-value: Warning OptionsWno-shift-overflow: Warning OptionsWno-sign-compare: Warning OptionsWno-sign-conversion: Warning OptionsWno-sign-promo: C++ Dialect OptionsWno-sized-deallocation: C++ Dialect OptionsWno-sizeof-array-argument: Warning OptionsWno-sizeof-array-div: Warning OptionsWno-sizeof-pointer-div: Warning OptionsWno-sizeof-pointer-memaccess: Warning OptionsWno-stack-protector: Warning OptionsWno-stack-usage: Warning OptionsWno-strict-aliasing: Warning OptionsWno-strict-flex-arrays: Warning OptionsWno-strict-null-sentinel: C++ Dialect OptionsWno-strict-overflow: Warning OptionsWno-strict-prototypes: Warning OptionsWno-strict-selector-match: Objective-C and Objective-C++ Dialect OptionsWno-string-compare: Warning OptionsWno-stringop-overflow: Warning OptionsWno-stringop-overread: Warning OptionsWno-stringop-truncation: Warning OptionsWno-subobject-linkage: C++ Dialect OptionsWno-suggest-attribute=: Warning OptionsWno-suggest-attribute=cold: Warning OptionsWno-suggest-attribute=const: Warning OptionsWno-suggest-attribute=format: Warning OptionsWno-suggest-attribute=malloc: Warning OptionsWno-suggest-attribute=noreturn: Warning OptionsWno-suggest-attribute=pure: Warning OptionsWno-suggest-final-methods: C++ Dialect OptionsWno-suggest-final-types: C++ Dialect OptionsWno-suggest-override: C++ Dialect OptionsWno-switch: Warning OptionsWno-switch-bool: Warning OptionsWno-switch-default: Warning OptionsWno-switch-enum: Warning OptionsWno-switch-outside-range: Warning OptionsWno-switch-unreachable: Warning OptionsWno-sync-nand: Warning OptionsWno-system-headers: Warning OptionsWno-tautological-compare: Warning OptionsWno-templates: C++ Dialect OptionsWno-terminate: C++ Dialect OptionsWno-traditional: Warning OptionsWno-traditional-conversion: Warning OptionsWno-trampolines: Warning OptionsWno-trivial-auto-var-init: Warning OptionsWno-tsan: Warning OptionsWno-type-limits: Warning OptionsWno-undeclared-selector: Objective-C and Objective-C++ Dialect OptionsWno-undef: Warning OptionsWno-unicode: Warning OptionsWno-uninitialized: Warning OptionsWno-unknown-pragmas: Warning OptionsWno-unsafe-loop-optimizations: Warning OptionsWno-unsuffixed-float-constants: Warning OptionsWno-unused: Warning OptionsWno-unused-but-set-parameter: Warning OptionsWno-unused-but-set-variable: Warning OptionsWno-unused-const-variable: Warning OptionsWno-unused-function: Warning OptionsWno-unused-label: Warning OptionsWno-unused-local-typedefs: Warning OptionsWno-unused-parameter: Warning OptionsWno-unused-result: Warning OptionsWno-unused-value: Warning OptionsWno-unused-variable: Warning OptionsWno-use-after-free: C++ Dialect OptionsWno-useless-cast: C++ Dialect OptionsWno-varargs: Warning OptionsWno-variadic-macros: Warning OptionsWno-vector-operation-performance: Warning OptionsWno-vexing-parse: C++ Dialect OptionsWno-virtual-inheritance: C++ Dialect OptionsWno-virtual-move-assign: C++ Dialect OptionsWno-vla: Warning OptionsWno-vla-larger-than: Warning OptionsWno-vla-parameter: Warning OptionsWno-volatile: C++ Dialect OptionsWno-volatile-register-var: Warning OptionsWno-write-strings: Warning OptionsWno-xor-used-as-pow: Warning OptionsWno-zero-as-null-pointer-constant: C++ Dialect OptionsWnoexcept: C++ Dialect OptionsWnoexcept-type: C++ Dialect OptionsWnon-template-friend: C++ Dialect OptionsWnon-virtual-dtor: C++ Dialect OptionsWnonnull: Warning OptionsWnonnull-compare: Warning OptionsWnormalized: Warning OptionsWnormalized=: Warning OptionsWnull-dereference: Warning OptionsWobjc-root-class: Objective-C and Objective-C++ Dialect OptionsWodr: Warning OptionsWold-style-cast: C++ Dialect OptionsWold-style-declaration: Warning OptionsWold-style-definition: Warning OptionsWopenacc-parallelism: Warning OptionsWopenmp-simd: Warning OptionsWoverflow: Warning OptionsWoverlength-strings: Warning OptionsWoverloaded-virtual: C++ Dialect OptionsWoverride-init: Warning OptionsWoverride-init-side-effects: Warning OptionsWp: Preprocessor OptionsWpacked: Warning OptionsWpacked-bitfield-compat: Warning OptionsWpacked-not-aligned: Warning OptionsWpadded: Warning OptionsWparentheses: Warning OptionsWpedantic: Warning OptionsWpedantic-ms-format: Warning OptionsWpessimizing-move: C++ Dialect OptionsWplacement-new: C++ Dialect OptionsWpmf-conversions: C++ Dialect OptionsWpointer-arith: Pointer ArithWpointer-arith: Warning OptionsWpointer-compare: Warning OptionsWpointer-sign: Warning OptionsWpointer-to-int-cast: Warning OptionsWpragmas: Warning OptionsWprio-ctor-dtor: Warning OptionsWproperty-assign-default: Objective-C and Objective-C++ Dialect OptionsWprotocol: Objective-C and Objective-C++ Dialect OptionsWrange-loop-construct: C++ Dialect Optionswrapper: Overall OptionsWredundant-decls: Warning OptionsWredundant-move: C++ Dialect OptionsWredundant-tags: C++ Dialect OptionsWregister: C++ Dialect OptionsWreorder: C++ Dialect OptionsWrestrict: Warning OptionsWreturn-local-addr: Warning OptionsWreturn-type: Warning OptionsWscalar-storage-order: Warning OptionsWselector: Objective-C and Objective-C++ Dialect OptionsWself-move: Warning OptionsWsequence-point: Warning OptionsWshadow: Warning OptionsWshadow-ivar: Warning OptionsWshadow=compatible-local: Warning OptionsWshadow=global: Warning OptionsWshadow=local: Warning OptionsWshift-count-negative: Warning OptionsWshift-count-overflow: Warning OptionsWshift-negative-value: Warning OptionsWshift-overflow: Warning OptionsWsign-compare: Warning OptionsWsign-conversion: Warning OptionsWsign-promo: C++ Dialect OptionsWsized-deallocation: C++ Dialect OptionsWsizeof-array-argument: Warning OptionsWsizeof-array-div: Warning OptionsWsizeof-pointer-div: Warning OptionsWsizeof-pointer-memaccess: Warning OptionsWstack-protector: Warning OptionsWstack-usage: Warning OptionsWstrict-aliasing: Warning OptionsWstrict-aliasing=n: Warning OptionsWstrict-flex-arrays: Warning OptionsWstrict-null-sentinel: C++ Dialect OptionsWstrict-overflow: Warning OptionsWstrict-prototypes: Warning OptionsWstrict-selector-match: Objective-C and Objective-C++ Dialect OptionsWstring-compare: Warning OptionsWstringop-overflow: Warning OptionsWstringop-overread: Warning OptionsWstringop-truncation: Warning OptionsWsubobject-linkage: C++ Dialect OptionsWsuggest-attribute=: Warning OptionsWsuggest-attribute=cold: Warning OptionsWsuggest-attribute=const: Warning OptionsWsuggest-attribute=format: Warning OptionsWsuggest-attribute=malloc: Warning OptionsWsuggest-attribute=noreturn: Warning OptionsWsuggest-attribute=pure: Warning OptionsWsuggest-final-methods: C++ Dialect OptionsWsuggest-final-types: C++ Dialect OptionsWsuggest-override: C++ Dialect OptionsWswitch: Warning OptionsWswitch-bool: Warning OptionsWswitch-default: Warning OptionsWswitch-enum: Warning OptionsWswitch-outside-range: Warning OptionsWswitch-unreachable: Warning OptionsWsync-nand: Warning OptionsWsystem-headers: Warning OptionsWtautological-compare: Warning OptionsWtemplates: C++ Dialect OptionsWterminate: C++ Dialect OptionsWtraditional: Warning OptionsWtraditional-conversion: Warning OptionsWtrampolines: Warning OptionsWtrigraphs: Warning OptionsWtrivial-auto-var-init: Warning OptionsWtsan: Warning OptionsWtype-limits: Warning OptionsWundeclared-selector: Objective-C and Objective-C++ Dialect OptionsWundef: Warning OptionsWunicode: Warning OptionsWuninitialized: Warning OptionsWunknown-pragmas: Warning OptionsWunsafe-loop-optimizations: Warning OptionsWunsuffixed-float-constants: Warning OptionsWunused: Warning OptionsWunused-but-set-parameter: Warning OptionsWunused-but-set-variable: Warning OptionsWunused-const-variable: Warning OptionsWunused-function: Warning OptionsWunused-label: Warning OptionsWunused-local-typedefs: Warning OptionsWunused-macros: Warning OptionsWunused-parameter: Warning OptionsWunused-result: Warning OptionsWunused-value: Warning OptionsWunused-variable: Warning OptionsWuse-after-free: C++ Dialect OptionsWuseless-cast: C++ Dialect OptionsWvarargs: Warning OptionsWvariadic-macros: Warning OptionsWvector-operation-performance: Warning OptionsWvexing-parse: C++ Dialect OptionsWvirtual-inheritance: C++ Dialect OptionsWvirtual-move-assign: C++ Dialect OptionsWvla: Warning OptionsWvla-larger-than=: Warning OptionsWvolatile: C++ Dialect OptionsWvolatile-register-var: Warning OptionsWwrite-strings: Warning OptionsWxor-used-as-pow: Warning OptionsWzero-as-null-pointer-constant: C++ Dialect OptionsWzero-length-bounds: Warning Optionsx: Overall OptionsXassembler: Assembler OptionsXbind-lazy: VxWorks OptionsXbind-now: VxWorks OptionsXlinker: Link OptionsXpreprocessor: Preprocessor OptionsYm: System V OptionsYP: System V Optionsz: Link Options#pragma: Pragmas#pragma implementation: C++ Interface#pragma implementation, implied: C++ Interface#pragma interface: C++ Interface%include: Spec Files%include_noerr: Spec Files%rename: Spec Files': Incompatibilities//: C++ Comments?: extensions: Conditionals?: side effect: Conditionals__atomic_add_fetch: __atomic Builtins__atomic_always_lock_free: __atomic Builtins__atomic_and_fetch: __atomic Builtins__atomic_clear: __atomic Builtins__atomic_compare_exchange: __atomic Builtins__atomic_compare_exchange_n: __atomic Builtins__atomic_exchange: __atomic Builtins__atomic_exchange_n: __atomic Builtins__atomic_fetch_add: __atomic Builtins__atomic_fetch_and: __atomic Builtins__atomic_fetch_nand: __atomic Builtins__atomic_fetch_or: __atomic Builtins__atomic_fetch_sub: __atomic Builtins__atomic_fetch_xor: __atomic Builtins__atomic_is_lock_free: __atomic Builtins__atomic_load: __atomic Builtins__atomic_load_n: __atomic Builtins__atomic_nand_fetch: __atomic Builtins__atomic_or_fetch: __atomic Builtins__atomic_signal_fence: __atomic Builtins__atomic_store: __atomic Builtins__atomic_store_n: __atomic Builtins__atomic_sub_fetch: __atomic Builtins__atomic_test_and_set: __atomic Builtins__atomic_thread_fence: __atomic Builtins__atomic_xor_fetch: __atomic Builtins__builtin___clear_cache: Other Builtins__builtin___memcpy_chk: Object Size Checking__builtin___memmove_chk: Object Size Checking__builtin___mempcpy_chk: Object Size Checking__builtin___memset_chk: Object Size Checking__builtin___snprintf_chk: Object Size Checking__builtin___sprintf_chk: Object Size Checking__builtin___stpcpy_chk: Object Size Checking__builtin___strcat_chk: Object Size Checking__builtin___strcpy_chk: Object Size Checking__builtin___strncat_chk: Object Size Checking__builtin___strncpy_chk: Object Size Checking__builtin___strub_enter: Stack Scrubbing__builtin___strub_leave: Stack Scrubbing__builtin___strub_update: Stack Scrubbing__builtin___vsnprintf_chk: Object Size Checking__builtin___vsprintf_chk: Object Size Checking__builtin_add_overflow: Integer Overflow Builtins__builtin_add_overflow_p: Integer Overflow Builtins__builtin_addf128_round_to_odd: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_alloca: Other Builtins__builtin_alloca_with_align: Other Builtins__builtin_alloca_with_align_and_max: Other Builtins__builtin_apply: Constructing Calls__builtin_apply_args: Constructing Calls__builtin_arc_aligned: ARC Built-in Functions__builtin_arc_brk: ARC Built-in Functions__builtin_arc_core_read: ARC Built-in Functions__builtin_arc_core_write: ARC Built-in Functions__builtin_arc_divaw: ARC Built-in Functions__builtin_arc_flag: ARC Built-in Functions__builtin_arc_lr: ARC Built-in Functions__builtin_arc_mul64: ARC Built-in Functions__builtin_arc_mulu64: ARC Built-in Functions__builtin_arc_nop: ARC Built-in Functions__builtin_arc_norm: ARC Built-in Functions__builtin_arc_normw: ARC Built-in Functions__builtin_arc_rtie: ARC Built-in Functions__builtin_arc_sleep: ARC Built-in Functions__builtin_arc_sr: ARC Built-in Functions__builtin_arc_swap: ARC Built-in Functions__builtin_arc_swi: ARC Built-in Functions__builtin_arc_sync: ARC Built-in Functions__builtin_arc_trap_s: ARC Built-in Functions__builtin_arc_unimp_s: ARC Built-in Functions__builtin_assoc_barrier: Other Builtins__builtin_assume_aligned: Other Builtins__builtin_bit_cast: Other Builtins__builtin_bpf_load_byte: BPF Built-in Functions__builtin_bpf_load_half: BPF Built-in Functions__builtin_bpf_load_word: BPF Built-in Functions__builtin_bswap128: Other Builtins__builtin_bswap16: Other Builtins__builtin_bswap32: Other Builtins__builtin_bswap64: Other Builtins__builtin_call_with_static_chain: Other Builtins__builtin_cfuged: Basic PowerPC Built-in Functions Available on ISA 3.1__builtin_choose_expr: Other Builtins__builtin_clear_padding: Other Builtins__builtin_clrsb: Other Builtins__builtin_clrsbl: Other Builtins__builtin_clrsbll: Other Builtins__builtin_clz: Other Builtins__builtin_clzl: Other Builtins__builtin_clzll: Other Builtins__builtin_cntlzdm: Basic PowerPC Built-in Functions Available on ISA 3.1__builtin_cnttzdm: Basic PowerPC Built-in Functions Available on ISA 3.1__builtin_complex: Complex__builtin_constant_p: Other Builtins__builtin_convertvector: Vector Extensions__builtin_copysignq: x86 Built-in Functions__builtin_cpu_init: x86 Built-in Functions__builtin_cpu_init: Basic PowerPC Built-in Functions Available on all Configurations__builtin_cpu_is: x86 Built-in Functions__builtin_cpu_is: Basic PowerPC Built-in Functions Available on all Configurations__builtin_cpu_supports: x86 Built-in Functions__builtin_cpu_supports: Basic PowerPC Built-in Functions Available on all Configurations__builtin_ctz: Other Builtins__builtin_ctzl: Other Builtins__builtin_ctzll: Other Builtins__builtin_darn: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_darn_32: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_darn_raw: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_divf128_round_to_odd: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_dynamic_object_size: Other Builtins__builtin_dynamic_object_size: Object Size Checking__builtin_expect: Other Builtins__builtin_expect_with_probability: Other Builtins__builtin_extend_pointer: Other Builtins__builtin_extract_return_addr: Return Address__builtin_fabsq: x86 Built-in Functions__builtin_ffs: Other Builtins__builtin_ffsl: Other Builtins__builtin_ffsll: Other Builtins__builtin_FILE: Other Builtins__builtin_fmaf128_round_to_odd: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_fpclassify: Other Builtins__builtin_frame_address: Return Address__builtin_frob_return_addr: Return Address__builtin_FUNCTION: Other Builtins__builtin_goacc_parlevel_id: Other Builtins__builtin_goacc_parlevel_size: Other Builtins__builtin_has_attribute: Other Builtins__builtin_huge_val: Other Builtins__builtin_huge_valf: Other Builtins__builtin_huge_vall: Other Builtins__builtin_huge_valq: x86 Built-in Functions__builtin_ia32_crc32di: x86 Built-in Functions__builtin_ia32_crc32hi: x86 Built-in Functions__builtin_ia32_crc32qi: x86 Built-in Functions__builtin_ia32_crc32si: x86 Built-in Functions__builtin_ia32_loadhps: x86 Built-in Functions__builtin_ia32_loadlps: x86 Built-in Functions__builtin_ia32_loadss: x86 Built-in Functions__builtin_ia32_loadups: x86 Built-in Functions__builtin_ia32_pause: x86 Built-in Functions__builtin_ia32_pclmulqdq128: x86 Built-in Functions__builtin_ia32_storehps: x86 Built-in Functions__builtin_ia32_storelps: x86 Built-in Functions__builtin_ia32_storeups: x86 Built-in Functions__builtin_ia32_vec_ext_v16qi: x86 Built-in Functions__builtin_ia32_vec_ext_v2di: x86 Built-in Functions__builtin_ia32_vec_ext_v4sf: x86 Built-in Functions__builtin_ia32_vec_ext_v4si: x86 Built-in Functions__builtin_ia32_vec_set_v16qi: x86 Built-in Functions__builtin_ia32_vec_set_v2di: x86 Built-in Functions__builtin_ia32_vec_set_v4sf: x86 Built-in Functions__builtin_ia32_vec_set_v4si: x86 Built-in Functions__builtin_inf: Other Builtins__builtin_infd128: Other Builtins__builtin_infd32: Other Builtins__builtin_infd64: Other Builtins__builtin_inff: Other Builtins__builtin_infl: Other Builtins__builtin_infq: x86 Built-in Functions__builtin_is_constant_evaluated: Other Builtins__builtin_isfinite: Other Builtins__builtin_isgreater: Other Builtins__builtin_isgreaterequal: Other Builtins__builtin_isinf_sign: Other Builtins__builtin_isnormal: Other Builtins__builtin_issignaling: Other Builtins__builtin_isunordered: Other Builtins__builtin_LINE: Other Builtins__builtin_longjmp: Nonlocal Gotos__builtin_mul_overflow: Integer Overflow Builtins__builtin_mul_overflow_p: Integer Overflow Builtins__builtin_mulf128_round_to_odd: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_nan: Other Builtins__builtin_nand128: Other Builtins__builtin_nand32: Other Builtins__builtin_nand64: Other Builtins__builtin_nanf: Other Builtins__builtin_nanl: Other Builtins__builtin_nanq: x86 Built-in Functions__builtin_nans: Other Builtins__builtin_nansd128: Other Builtins__builtin_nansd32: Other Builtins__builtin_nansd64: Other Builtins__builtin_nansf: Other Builtins__builtin_nansl: Other Builtins__builtin_nansq: x86 Built-in Functions__builtin_nds32_isb: NDS32 Built-in Functions__builtin_nds32_isync: NDS32 Built-in Functions__builtin_nds32_mfsr: NDS32 Built-in Functions__builtin_nds32_mfusr: NDS32 Built-in Functions__builtin_nds32_mtsr: NDS32 Built-in Functions__builtin_nds32_mtusr: NDS32 Built-in Functions__builtin_nds32_setgie_dis: NDS32 Built-in Functions__builtin_nds32_setgie_en: NDS32 Built-in Functions__builtin_non_tx_store: S/390 System z Built-in Functions__builtin_object_size: Other Builtins__builtin_object_size: Object Size Checking__builtin_offsetof: Offsetof__builtin_parity: Other Builtins__builtin_parityl: Other Builtins__builtin_parityll: Other Builtins__builtin_pdepd: Basic PowerPC Built-in Functions Available on ISA 3.1__builtin_pextd: Basic PowerPC Built-in Functions Available on ISA 3.1__builtin_popcount: x86 Built-in Functions__builtin_popcount: Other Builtins__builtin_popcountl: x86 Built-in Functions__builtin_popcountl: Other Builtins__builtin_popcountll: x86 Built-in Functions__builtin_popcountll: Other Builtins__builtin_powi: Other Builtins__builtin_powif: Other Builtins__builtin_powil: Other Builtins__builtin_prefetch: Other Builtins__builtin_preserve_access_index: BPF Built-in Functions__builtin_preserve_field_info: BPF Built-in Functions__builtin_return: Constructing Calls__builtin_return_address: Return Address__builtin_riscv_pause: RISC-V Built-in Functions__builtin_rx_brk: RX Built-in Functions__builtin_rx_clrpsw: RX Built-in Functions__builtin_rx_int: RX Built-in Functions__builtin_rx_machi: RX Built-in Functions__builtin_rx_maclo: RX Built-in Functions__builtin_rx_mulhi: RX Built-in Functions__builtin_rx_mullo: RX Built-in Functions__builtin_rx_mvfachi: RX Built-in Functions__builtin_rx_mvfacmi: RX Built-in Functions__builtin_rx_mvfc: RX Built-in Functions__builtin_rx_mvtachi: RX Built-in Functions__builtin_rx_mvtaclo: RX Built-in Functions__builtin_rx_mvtc: RX Built-in Functions__builtin_rx_mvtipl: RX Built-in Functions__builtin_rx_racw: RX Built-in Functions__builtin_rx_revw: RX Built-in Functions__builtin_rx_rmpa: RX Built-in Functions__builtin_rx_round: RX Built-in Functions__builtin_rx_sat: RX Built-in Functions__builtin_rx_setpsw: RX Built-in Functions__builtin_rx_wait: RX Built-in Functions__builtin_sadd_overflow: Integer Overflow Builtins__builtin_saddl_overflow: Integer Overflow Builtins__builtin_saddll_overflow: Integer Overflow Builtins__builtin_set_thread_pointer: SH Built-in Functions__builtin_setjmp: Nonlocal Gotos__builtin_sh_get_fpscr: SH Built-in Functions__builtin_sh_set_fpscr: SH Built-in Functions__builtin_shuffle: Vector Extensions__builtin_shufflevector: Vector Extensions__builtin_smul_overflow: Integer Overflow Builtins__builtin_smull_overflow: Integer Overflow Builtins__builtin_smulll_overflow: Integer Overflow Builtins__builtin_speculation_safe_value: Other Builtins__builtin_sqrtf128_round_to_odd: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_ssub_overflow: Integer Overflow Builtins__builtin_ssubl_overflow: Integer Overflow Builtins__builtin_ssubll_overflow: Integer Overflow Builtins__builtin_stack_address: Return Address__builtin_sub_overflow: Integer Overflow Builtins__builtin_sub_overflow_p: Integer Overflow Builtins__builtin_subf128_round_to_odd: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_tabort: S/390 System z Built-in Functions__builtin_tbegin: S/390 System z Built-in Functions__builtin_tbegin_nofloat: S/390 System z Built-in Functions__builtin_tbegin_retry: S/390 System z Built-in Functions__builtin_tbegin_retry_nofloat: S/390 System z Built-in Functions__builtin_tbeginc: S/390 System z Built-in Functions__builtin_tend: S/390 System z Built-in Functions__builtin_tgmath: Other Builtins__builtin_thread_pointer: SH Built-in Functions__builtin_thread_pointer: RISC-V Built-in Functions__builtin_trap: Other Builtins__builtin_truncf128_round_to_odd: Basic PowerPC Built-in Functions Available on ISA 3.0__builtin_tx_assist: S/390 System z Built-in Functions__builtin_tx_nesting_depth: S/390 System z Built-in Functions__builtin_types_compatible_p: Other Builtins__builtin_uadd_overflow: Integer Overflow Builtins__builtin_uaddl_overflow: Integer Overflow Builtins__builtin_uaddll_overflow: Integer Overflow Builtins__builtin_umul_overflow: Integer Overflow Builtins__builtin_umull_overflow: Integer Overflow Builtins__builtin_umulll_overflow: Integer Overflow Builtins__builtin_unreachable: Other Builtins__builtin_usub_overflow: Integer Overflow Builtins__builtin_usubl_overflow: Integer Overflow Builtins__builtin_usubll_overflow: Integer Overflow Builtins__builtin_va_arg_pack: Constructing Calls__builtin_va_arg_pack_len: Constructing Calls__complex__ keyword: Complex__declspec(dllexport): Microsoft Windows Function Attributes__declspec(dllimport): Microsoft Windows Function Attributes__delay_cycles: PRU Built-in Functions__extension__: Alternate Keywords__far M32C Named Address Spaces: Named Address Spaces__far RL78 Named Address Spaces: Named Address Spaces__flash AVR Named Address Spaces: Named Address Spaces__flash1 AVR Named Address Spaces: Named Address Spaces__flash2 AVR Named Address Spaces: Named Address Spaces__flash3 AVR Named Address Spaces: Named Address Spaces__flash4 AVR Named Address Spaces: Named Address Spaces__flash5 AVR Named Address Spaces: Named Address Spaces__float128 data type: Floating Types__Float16 data type: Half-Precision__float80 data type: Floating Types__fp16 data type: Half-Precision__func__ identifier: Function Names__FUNCTION__ identifier: Function Names__halt: PRU Built-in Functions__has_nothrow_assign: Type Traits__has_nothrow_constructor: Type Traits__has_nothrow_copy: Type Traits__has_trivial_assign: Type Traits__has_trivial_constructor: Type Traits__has_trivial_copy: Type Traits__has_trivial_destructor: Type Traits__has_virtual_destructor: Type Traits__ibm128 data type: Floating Types__imag__ keyword: Complex__int128 data types: __int128__integer_pack: Type Traits__is_abstract: Type Traits__is_aggregate: Type Traits__is_base_of: Type Traits__is_class: Type Traits__is_empty: Type Traits__is_enum: Type Traits__is_final: Type Traits__is_literal_type: Type Traits__is_pod: Type Traits__is_polymorphic: Type Traits__is_same: C++ Concepts__is_standard_layout: Type Traits__is_trivial: Type Traits__is_union: Type Traits__lmbd: PRU Built-in Functions__memx AVR Named Address Spaces: Named Address Spaces__PRETTY_FUNCTION__ identifier: Function Names__real__ keyword: Complex__regio_symbol PRU Named Address Spaces: Named Address Spaces__seg_fs x86 named address space: Named Address Spaces__seg_gs x86 named address space: Named Address Spaces__STDC_HOSTED__: Standards__sync_add_and_fetch: __sync Builtins__sync_and_and_fetch: __sync Builtins__sync_bool_compare_and_swap: __sync Builtins__sync_fetch_and_add: __sync Builtins__sync_fetch_and_and: __sync Builtins__sync_fetch_and_nand: __sync Builtins__sync_fetch_and_or: __sync Builtins__sync_fetch_and_sub: __sync Builtins__sync_fetch_and_xor: __sync Builtins__sync_lock_release: __sync Builtins__sync_lock_test_and_set: __sync Builtins__sync_nand_and_fetch: __sync Builtins__sync_or_and_fetch: __sync Builtins__sync_sub_and_fetch: __sync Builtins__sync_synchronize: __sync Builtins__sync_val_compare_and_swap: __sync Builtins__sync_xor_and_fetch: __sync Builtins__thread: Thread-Local__underlying_type: Type Traits_Accum data type: Fixed-Point_Complex keyword: Complex_Decimal128 data type: Decimal Float_Decimal32 data type: Decimal Float_Decimal64 data type: Decimal Float_exit: Other Builtins_Exit: Other Builtins_Floatn data types: Floating Types_Floatnx data types: Floating Types_Fract data type: Fixed-Point_get_ssp: x86 control-flow protection intrinsics_HTM_FIRST_USER_ABORT_CODE: S/390 System z Built-in Functions_HTM_TBEGIN_INDETERMINATE: S/390 System z Built-in Functions_HTM_TBEGIN_PERSISTENT: S/390 System z Built-in Functions_HTM_TBEGIN_STARTED: S/390 System z Built-in Functions_HTM_TBEGIN_TRANSIENT: S/390 System z Built-in Functions_inc_ssp: x86 control-flow protection intrinsics_Sat data type: Fixed-Point_xabort: x86 transactional memory intrinsics_XABORT_CAPACITY: x86 transactional memory intrinsics_XABORT_CONFLICT: x86 transactional memory intrinsics_XABORT_DEBUG: x86 transactional memory intrinsics_XABORT_EXPLICIT: x86 transactional memory intrinsics_XABORT_NESTED: x86 transactional memory intrinsics_XABORT_RETRY: x86 transactional memory intrinsics_xbegin: x86 transactional memory intrinsics_xend: x86 transactional memory intrinsics_xtest: x86 transactional memory intrinsicsabi_tag function attribute: C++ Attributesabi_tag type attribute: C++ Attributesabi_tag variable attribute: C++ Attributesabort: Other Builtinsabs: Other Builtinsabsdata variable attribute, AVR: AVR Variable Attributesacos: Other Builtinsacosf: Other Builtinsacosh: Other Builtinsacoshf: Other Builtinsacoshl: Other Builtinsacosl: Other Builtinsaddress variable attribute, AVR: AVR Variable Attributesaddress_operand: Simple Constraintsalias function attribute: Common Function Attributesalias variable attribute: Common Variable Attributesaligned function attribute: Common Function Attributesaligned type attribute: Common Type Attributesaligned variable attribute: Common Variable Attributesalloc_align function attribute: Common Function Attributesalloc_size function attribute: Common Function Attributesalloc_size type attribute: Common Type Attributesalloc_size variable attribute: Common Variable Attributesalloca: Other Builtinsalloca vs variable-length arrays: Variable Lengthaltivec type attribute, PowerPC: PowerPC Type Attributesaltivec variable attribute, PowerPC: PowerPC Variable Attributesalways_inline function attribute: Common Function Attributesamdgpu_hsa_kernel function attribute, AMD GCN: AMD GCN Function Attributesarch= function attribute, AArch64: AArch64 Function Attributesarch= function attribute, ARM: ARM Function Attributesartificial function attribute: Common Function Attributesasin: Other Builtinsasinf: Other Builtinsasinh: Other Builtinsasinhf: Other Builtinsasinhl: Other Builtinsasinl: Other Builtinsasm assembler template: Extended Asmasm clobbers: Extended Asmasm constraints: Constraintsasm expressions: Extended Asmasm flag output operands: Extended Asmasm goto labels: Extended Asmasm inline: Size of an asmasm input operands: Extended Asmasm keyword: Using Assembly Language with Casm output operands: Extended Asmasm scratch registers: Extended Asmasm volatile: Extended Asmassume statement attribute: Statement Attributesassume_aligned function attribute: Common Function Attributesassumes: C++ Conceptsatan: Other Builtinsatan2: Other Builtinsatan2f: Other Builtinsatan2l: Other Builtinsatanf: Other Builtinsatanh: Other Builtinsatanhf: Other Builtinsatanhl: Other Builtinsatanl: Other Builtinsinline for C++ member fns: Inlineaux variable attribute, ARC: ARC Variable Attributesaxiom: C++ Conceptsbank_switch function attribute, M32C: M32C Function Attributesasm: Basic Asmbcmp: Other Builtinsbelow100 variable attribute, Xstormy16: Xstormy16 Variable Attributesbranch-protection function attribute, AArch64: AArch64 Function Attributesbreak_handler function attribute, MicroBlaze: MicroBlaze Function Attributesbrk_interrupt function attribute, RL78: RL78 Function Attributesbzero: Other Builtinsc++: Invoking G++inline: InlineC_INCLUDE_PATH: Environment Variablescabs: Other Builtinscabsf: Other Builtinscabsl: Other Builtinscacos: Other Builtinscacosf: Other Builtinscacosh: Other Builtinscacoshf: Other Builtinscacoshl: Other Builtinscacosl: Other Builtinscallee_pop_aggregate_return function attribute, x86: x86 Function Attributescalloc: Other Builtinscarg: Other Builtinscargf: Other Builtinscargl: Other Builtinscasin: Other Builtinscasinf: Other Builtinscasinh: Other Builtinscasinhf: Other Builtinscasinhl: Other Builtinscasinl: Other Builtinscatan: Other Builtinscatanf: Other Builtinscatanh: Other Builtinscatanhf: Other Builtinscatanhl: Other Builtinscatanl: Other Builtinscbrt: Other Builtinscbrtf: Other Builtinscbrtl: Other Builtinsccos: Other Builtinsccosf: Other Builtinsccosh: Other Builtinsccoshf: Other Builtinsccoshl: Other Builtinsccosl: Other Builtinscdecl function attribute, x86-32: x86 Function Attributesceil: Other Builtinsceilf: Other Builtinsceill: Other Builtinscexp: Other Builtinscexpf: Other Builtinscexpl: Other Builtinscf_check function attribute, x86: x86 Function Attributescimag: Other Builtinscimagf: Other Builtinscimagl: Other Builtinscleanup variable attribute: Common Variable Attributesclog: Other Builtinsclog10: Other Builtinsclog10f: Other Builtinsclog10l: Other Builtinsclogf: Other Builtinsclogl: Other Builtinscmodel= function attribute, AArch64: AArch64 Function Attributescold function attribute: Common Function Attributescold label attribute: Label Attributescommon variable attribute: Common Variable AttributesCOMPILER_PATH: Environment Variablesconj: Other Builtinsconjf: Other Builtinsconjl: Other Builtinsconst applied to function: Function Attributesconst function attribute: Common Function Attributesasm: Constraintsconstructor function attribute: Common Function Attributescopy function attribute: Common Function Attributescopy type attribute: Common Type Attributescopy variable attribute: Common Variable Attributescopysign: Other Builtinscopysignf: Other Builtinscopysignl: Other Builtinscos: Other Builtinscosf: Other Builtinscosh: Other Builtinscoshf: Other Builtinscoshl: Other Builtinscosl: Other BuiltinsCPATH: Environment VariablesCPLUS_INCLUDE_PATH: Environment Variablescpow: Other Builtinscpowf: Other Builtinscpowl: Other Builtinscproj: Other Builtinscprojf: Other Builtinscprojl: Other Builtinscpu= function attribute, AArch64: AArch64 Function Attributescreal: Other Builtinscrealf: Other Builtinscreall: Other Builtinscritical function attribute, MSP430: MSP430 Function Attributescsin: Other Builtinscsinf: Other Builtinscsinh: Other Builtinscsinhf: Other Builtinscsinhl: Other Builtinscsinl: Other Builtinscsqrt: Other Builtinscsqrtf: Other Builtinscsqrtl: Other Builtinsctan: Other Builtinsctanf: Other Builtinsctanh: Other Builtinsctanhf: Other Builtinsctanhl: Other Builtinsctanl: Other BuiltinsCXX_MODULE_MAPPER environment variable: C++ Dialect Optionsdcgettext: Other BuiltinsDD integer suffix: Decimal Floatdd integer suffix: Decimal FloatDEPENDENCIES_OUTPUT: Environment Variablesdeprecated enumerator attribute: Enumerator Attributesdeprecated function attribute: Common Function Attributesdeprecated type attribute: Common Type Attributesdeprecated variable attribute: Common Variable Attributesdesignated_init type attribute: Common Type Attributesdestructor function attribute: Common Function AttributesDF integer suffix: Decimal Floatdf integer suffix: Decimal Floatdgettext: Other Builtinsdiff-delete GCC_COLORS capability: Diagnostic Message Formatting Optionsdiff-filename GCC_COLORS capability: Diagnostic Message Formatting Optionsdiff-hunk GCC_COLORS capability: Diagnostic Message Formatting Optionsdiff-insert GCC_COLORS capability: Diagnostic Message Formatting Optionsdisinterrupt function attribute, Epiphany: Epiphany Function AttributesDL integer suffix: Decimal Floatdl integer suffix: Decimal Floatdllexport function attribute: Microsoft Windows Function Attributesdllexport variable attribute: Microsoft Windows Variable Attributesdllimport function attribute: Microsoft Windows Function Attributesdllimport variable attribute: Microsoft Windows Variable Attributesdrem: Other Builtinsdremf: Other Builtinsdreml: Other Builtinseightbit_data variable attribute, H8/300: H8/300 Variable AttributesEIND: AVR Optionseither function attribute, MSP430: MSP430 Function Attributeseither variable attribute, MSP430: MSP430 Variable Attributeserf: Other Builtinserfc: Other Builtinserfcf: Other Builtinserfcl: Other Builtinserff: Other Builtinserfl: Other Builtinserror function attribute: Common Function Attributeserror GCC_COLORS capability: Diagnostic Message Formatting Optionsexception function attribute: NDS32 Function Attributesexception_handler function attribute: Blackfin Function Attributesexit: Other Builtinsexp: Other Builtinsexp10: Other Builtinsexp10f: Other Builtinsexp10l: Other Builtinsexp2: Other Builtinsexp2f: Other Builtinsexp2l: Other Builtinsexpected_throw function attribute: Common Function Attributesexpf: Other Builtinsexpl: Other Builtinsexpm1: Other Builtinsexpm1f: Other Builtinsexpm1l: Other Builtinsasm: Extended Asm?:: Conditionalsexternally_visible function attribute: Common Function Attributesfabs: Other Builtinsfabsf: Other Builtinsfabsl: Other Builtinsfallthrough statement attribute: Statement Attributesfar function attribute, MIPS: MIPS Function Attributesfast_interrupt function attribute, M32C: M32C Function Attributesfast_interrupt function attribute, MicroBlaze: MicroBlaze Function Attributesfast_interrupt function attribute, RX: RX Function Attributesfastcall function attribute, x86-32: x86 Function Attributesfd_arg function attribute: Common Function Attributesfd_arg_read function attribute: Common Function Attributesfd_arg_write function attribute: Common Function Attributesfdim: Other Builtinsfdimf: Other Builtinsfdiml: Other Builtinsfentry_name function attribute, x86: x86 Function Attributesfentry_section function attribute, x86: x86 Function Attributesffs: Other Builtinsfix-cortex-a53-835769 function attribute, AArch64: AArch64 Function Attributesfixit-delete GCC_COLORS capability: Diagnostic Message Formatting Optionsfixit-insert GCC_COLORS capability: Diagnostic Message Formatting Optionsflatten function attribute: Common Function Attributesfloat as function value type: Incompatibilitiesfloor: Other Builtinsfloorf: Other Builtinsfloorl: Other Builtinsfma: Other Builtinsfmaf: Other Builtinsfmal: Other Builtinsfmax: Other Builtinsfmaxf: Other Builtinsfmaxl: Other Builtinsfmin: Other Builtinsfminf: Other Builtinsfminl: Other Builtinsfmod: Other Builtinsfmodf: Other Builtinsfmodl: Other Builtinsfnname GCC_COLORS capability: Diagnostic Message Formatting Optionsforce_align_arg_pointer function attribute, x86: x86 Function Attributesformat function attribute: Common Function Attributesformat_arg function attribute: Common Function Attributesforwarder_section function attribute, Epiphany: Epiphany Function Attributesfprintf: Other Builtinsfprintf_unlocked: Other Builtinsfputs: Other Builtinsfputs_unlocked: Other Builtinsfree: Other Builtinsfrexp: Other Builtinsfrexpf: Other Builtinsfrexpl: Other Builtinsfscanf: Other Builtinsfscanf, and constant strings: Incompatibilitiesfunction_return function attribute, x86: x86 Function Attributesfunction_vector function attribute, H8/300: H8/300 Function Attributesfunction_vector function attribute, M16C/M32C: M32C Function Attributesfunction_vector function attribute, SH: SH Function Attributesprintf, scanf, strftime or strfmon style arguments: Common Function Attributesg++: Invoking G++gamma: Other Builtinsgamma_r: Other Builtinsgammaf: Other Builtinsgammaf_r: Other Builtinsgammal: Other Builtinsgammal_r: Other BuiltinsGCC_COLORS environment variable: Diagnostic Message Formatting OptionsGCC_COMPARE_DEBUG: Environment VariablesGCC_EXEC_PREFIX: Environment VariablesGCC_EXTRA_DIAGNOSTIC_OUTPUT: Environment Variablesgcc_struct type attribute, PowerPC: PowerPC Type Attributesgcc_struct type attribute, x86: x86 Type Attributesgcc_struct variable attribute, PowerPC: PowerPC Variable Attributesgcc_struct variable attribute, x86: x86 Variable AttributesGCC_URLS environment variable: Diagnostic Message Formatting Optionsgeneral-regs-only function attribute, AArch64: AArch64 Function Attributesgeneral-regs-only function attribute, ARM: ARM Function Attributesgettext: Other Builtinslongjmp: Global Register Variablesgnu_inline function attribute: Common Function Attributeshardbool type attribute: Common Type AttributesHK fixed-suffix: Fixed-Pointhk fixed-suffix: Fixed-Pointhot function attribute: Common Function Attributeshot label attribute: Label Attributeshotpatch function attribute, S/390: S/390 Function AttributesHR fixed-suffix: Fixed-Pointhr fixed-suffix: Fixed-Pointhypot: Other Builtinshypotf: Other Builtinshypotl: Other Builtinsifunc function attribute: Common Function Attributesilogb: Other Builtinsilogbf: Other Builtinsilogbl: Other Builtinsimaxabs: Other Builtins#pragma implementation: C++ Interfaceindex: Other Builtinsindirect_branch function attribute, x86: x86 Function Attributesindirect_return function attribute, x86: x86 Function Attributesinit_priority variable attribute: C++ Attributesinline automatic for C++ member fns: Inlineinterrupt function attribute, ARC: ARC Function Attributesinterrupt function attribute, ARM: ARM Function Attributesinterrupt function attribute, AVR: AVR Function Attributesinterrupt function attribute, C-SKY: C-SKY Function Attributesinterrupt function attribute, Epiphany: Epiphany Function Attributesinterrupt function attribute, M32C: M32C Function Attributesinterrupt function attribute, M32R/D: M32R/D Function Attributesinterrupt function attribute, m68k: m68k Function Attributesinterrupt function attribute, MIPS: MIPS Function Attributesinterrupt function attribute, MSP430: MSP430 Function Attributesinterrupt function attribute, NDS32: NDS32 Function Attributesinterrupt function attribute, RISC-V: RISC-V Function Attributesinterrupt function attribute, RL78: RL78 Function Attributesinterrupt function attribute, RX: RX Function Attributesinterrupt function attribute, V850: V850 Function Attributesinterrupt function attribute, Visium: Visium Function Attributesinterrupt function attribute, x86: x86 Function Attributesinterrupt function attribute, Xstormy16: Xstormy16 Function Attributesinterrupt_handler function attribute, Blackfin: Blackfin Function Attributesinterrupt_handler function attribute, H8/300: H8/300 Function Attributesinterrupt_handler function attribute, m68k: m68k Function Attributesinterrupt_handler function attribute, MicroBlaze: MicroBlaze Function Attributesinterrupt_handler function attribute, SH: SH Function Attributesinterrupt_handler function attribute, V850: V850 Function Attributesinterrupt_thread function attribute, fido: m68k Function Attributesio variable attribute, AVR: AVR Variable Attributesio_low variable attribute, AVR: AVR Variable Attributesisalnum: Other Builtinsisalpha: Other Builtinsisascii: Other Builtinsisblank: Other Builtinsiscntrl: Other Builtinsisdigit: Other Builtinsisgraph: Other Builtinsislower: Other Builtinsisprint: Other Builtinsispunct: Other Builtinsisr function attribute, ARM: ARM Function Attributesisr function attribute, C-SKY: C-SKY Function Attributesisspace: Other Builtinsisupper: Other Builtinsiswalnum: Other Builtinsiswalpha: Other Builtinsiswblank: Other Builtinsiswcntrl: Other Builtinsiswdigit: Other Builtinsiswgraph: Other Builtinsiswlower: Other Builtinsiswprint: Other Builtinsiswpunct: Other Builtinsiswspace: Other Builtinsiswupper: Other Builtinsiswxdigit: Other Builtinsisxdigit: Other Builtinsj0: Other Builtinsj0f: Other Builtinsj0l: Other Builtinsj1: Other Builtinsj1f: Other Builtinsj1l: Other Builtinsjli_always function attribute, ARC: ARC Function Attributesjli_fixed function attribute, ARC: ARC Function Attributesjn: Other Builtinsjnf: Other Builtinsjnl: Other BuiltinsK fixed-suffix: Fixed-Pointk fixed-suffix: Fixed-Pointkeep_interrupts_masked function attribute, MIPS: MIPS Function Attributeskernel attribute, Nvidia PTX: Nvidia PTX Function Attributeskernel helper, function attribute, BPF: BPF Function Attributeskspisusp function attribute, Blackfin: Blackfin Function Attributesl1_data variable attribute, Blackfin: Blackfin Variable Attributesl1_data_A variable attribute, Blackfin: Blackfin Variable Attributesl1_data_B variable attribute, Blackfin: Blackfin Variable Attributesl1_text function attribute, Blackfin: Blackfin Function Attributesl2 function attribute, Blackfin: Blackfin Function Attributesl2 variable attribute, Blackfin: Blackfin Variable Attributeslabs: Other BuiltinsLANG: Environment VariablesLC_ALL: Environment VariablesLC_CTYPE: Environment VariablesLC_MESSAGES: Environment Variablesldexp: Other Builtinsldexpf: Other Builtinsldexpl: Other Builtinsleaf function attribute: Common Function Attributeslgamma: Other Builtinslgamma_r: Other Builtinslgammaf: Other Builtinslgammaf_r: Other Builtinslgammal: Other Builtinslgammal_r: Other BuiltinsLIBRARY_PATH: Environment VariablesLK fixed-suffix: Fixed-Pointlk fixed-suffix: Fixed-PointLL integer suffix: Long Longllabs: Other BuiltinsLLK fixed-suffix: Fixed-Pointllk fixed-suffix: Fixed-PointLLR fixed-suffix: Fixed-Pointllr fixed-suffix: Fixed-Pointllrint: Other Builtinsllrintf: Other Builtinsllrintl: Other Builtinsllround: Other Builtinsllroundf: Other Builtinsllroundl: Other Builtinslocus GCC_COLORS capability: Diagnostic Message Formatting Optionslog: Other Builtinslog10: Other Builtinslog10f: Other Builtinslog10l: Other Builtinslog1p: Other Builtinslog1pf: Other Builtinslog1pl: Other Builtinslog2: Other Builtinslog2f: Other Builtinslog2l: Other Builtinslogb: Other Builtinslogbf: Other Builtinslogbl: Other Builtinslogf: Other Builtinslogl: Other Builtinslong long data types: Long Longlong_call function attribute, ARC: ARC Function Attributeslong_call function attribute, ARM: ARM Function Attributeslong_call function attribute, Epiphany: Epiphany Function Attributeslong_call function attribute, MIPS: MIPS Function Attributeslongcall function attribute, Blackfin: Blackfin Function Attributeslongcall function attribute, PowerPC: PowerPC Function Attributeslongjmp: Global Register Variableslongjmp incompatibilities: Incompatibilitieslongjmp warnings: Warning Optionslower function attribute, MSP430: MSP430 Function Attributeslower variable attribute, MSP430: MSP430 Variable AttributesLR fixed-suffix: Fixed-Pointlr fixed-suffix: Fixed-Pointlrint: Other Builtinslrintf: Other Builtinslrintl: Other Builtinslround: Other Builtinslroundf: Other Builtinslroundl: Other Builtinsmalloc: Other Builtinsmalloc function attribute: Common Function Attributesmay_alias type attribute: Common Type Attributesmedium_call function attribute, ARC: ARC Function Attributesinline: Inlinememchr: Other Builtinsmemcmp: Other Builtinsmemcpy: Other Builtinsmempcpy: Other Builtinsmemset: Other Builtinsmicromips function attribute: MIPS Function Attributesmips16 function attribute, MIPS: MIPS Function Attributesmktemp, and constant strings: Incompatibilitiesmode type attribute: Common Type Attributesmode variable attribute: Common Variable Attributesmodel function attribute, M32R/D: M32R/D Function Attributesmodel variable attribute, IA-64: IA-64 Variable Attributesmodel variable attribute, LoongArch: LoongArch Variable Attributesmodel-name variable attribute, M32R/D: M32R/D Variable Attributesmodf: Other Builtinsmodff: Other Builtinsmodfl: Other Builtinsms_abi function attribute, x86: x86 Function Attributesms_hook_prologue function attribute, x86: x86 Function Attributesms_struct type attribute, PowerPC: PowerPC Type Attributesms_struct type attribute, x86: x86 Type Attributesms_struct variable attribute, PowerPC: PowerPC Variable Attributesms_struct variable attribute, x86: x86 Variable Attributesnaked function attribute, ARC: ARC Function Attributesnaked function attribute, ARM: ARM Function Attributesnaked function attribute, AVR: AVR Function Attributesnaked function attribute, C-SKY: C-SKY Function Attributesnaked function attribute, MCORE: MCORE Function Attributesnaked function attribute, MSP430: MSP430 Function Attributesnaked function attribute, NDS32: NDS32 Function Attributesnaked function attribute, RISC-V: RISC-V Function Attributesnaked function attribute, RL78: RL78 Function Attributesnaked function attribute, RX: RX Function Attributesnaked function attribute, x86: x86 Function Attributesnear function attribute, MIPS: MIPS Function Attributesnearbyint: Other Builtinsnearbyintf: Other Builtinsnearbyintl: Other Builtinsnested function attribute, NDS32: NDS32 Function Attributesnested_ready function attribute, NDS32: NDS32 Function Attributesnesting function attribute, Blackfin: Blackfin Function Attributesnextafter: Other Builtinsnextafterf: Other Builtinsnextafterl: Other Builtinsnexttoward: Other Builtinsnexttowardf: Other Builtinsnexttowardl: Other Builtinsnmi function attribute, NDS32: NDS32 Function Attributesnmi_handler function attribute, Blackfin: Blackfin Function Attributesno_caller_saved_registers function attribute, x86: x86 Function Attributesno_gccisr function attribute, AVR: AVR Function Attributesno_icf function attribute: Common Function Attributesno_instrument_function function attribute: Common Function Attributesno_profile_instrument_function function attribute: Common Function Attributesno_reorder function attribute: Common Function Attributesno_sanitize function attribute: Common Function Attributesno_sanitize_address function attribute: Common Function Attributesno_sanitize_coverage function attribute: Common Function Attributesno_sanitize_thread function attribute: Common Function Attributesno_sanitize_undefined function attribute: Common Function Attributesno_split_stack function attribute: Common Function Attributesno_stack_limit function attribute: Common Function Attributesno_stack_protector function attribute: Common Function Attributesnocf_check function attribute: x86 Function Attributesnoclone function attribute: Common Function Attributesnocommon variable attribute: Common Variable Attributesnocompression function attribute, MIPS: MIPS Function Attributesnodirect_extern_access function attribute: x86 Function Attributesnoinit variable attribute: Common Variable Attributesnoinline function attribute: Common Function Attributesnoipa function attribute: Common Function Attributesnomicromips function attribute: MIPS Function Attributesnomips16 function attribute, MIPS: MIPS Function Attributesnonnull function attribute: Common Function Attributesnonstring variable attribute: Common Variable Attributesnoplt function attribute: Common Function Attributesnoreturn function attribute: Common Function Attributesnosave_low_regs function attribute, SH: SH Function Attributesnot_nested function attribute, NDS32: NDS32 Function Attributesnote GCC_COLORS capability: Diagnostic Message Formatting Optionsnothrow function attribute: Common Function Attributesnotshared type attribute, ARM: ARM Type AttributesOBJC_INCLUDE_PATH: Environment Variablesobjc_nullability variable attribute: Common Variable Attributesobjc_root_class type attribute: Common Type Attributesomit-leaf-frame-pointer function attribute, AArch64: AArch64 Function Attributesasm: Constraintsoptimize function attribute: Common Function AttributesOS_main function attribute, AVR: AVR Function AttributesOS_task function attribute, AVR: AVR Function Attributesoutline-atomics function attribute, AArch64: AArch64 Function Attributespacked type attribute: Common Type Attributespacked variable attribute: Common Variable Attributespartial_save function attribute, NDS32: NDS32 Function Attributespatchable_function_entry function attribute: Common Function Attributespath GCC_COLORS capability: Diagnostic Message Formatting Optionspcs function attribute, ARM: ARM Function Attributespersistent variable attribute: Common Variable Attributespow: Other Builtinspow10: Other Builtinspow10f: Other Builtinspow10l: Other Builtinspowf: Other Builtinspowl: Other Builtinsprefer-vector-width function attribute, x86: x86 Function Attributespreserve_access_index type attribute, BPF: BPF Type Attributesprintf: Other Builtinsprintf_unlocked: Other Builtinsprogmem variable attribute, AVR: AVR Variable Attributespure function attribute: Common Function Attributesputchar: Other Builtinsputs: Other BuiltinsQ floating point suffix: Floating Typesq floating point suffix: Floating Typesqsort, and global register variables: Global Register Variablesquote GCC_COLORS capability: Diagnostic Message Formatting OptionsR fixed-suffix: Fixed-Pointr fixed-suffix: Fixed-PointRAMPD: AVR OptionsRAMPX: AVR OptionsRAMPY: AVR OptionsRAMPZ: AVR Optionsrange1 GCC_COLORS capability: Diagnostic Message Formatting Optionsrange2 GCC_COLORS capability: Diagnostic Message Formatting Optionsrealloc: Other Builtinsreentrant function attribute, MSP430: MSP430 Function Attributeslongjmp: Global Register Variablesregparm function attribute, x86: x86 Function Attributesremainder: Other Builtinsremainderf: Other Builtinsremainderl: Other Builtinsremquo: Other Builtinsremquof: Other Builtinsremquol: Other Builtinsrenesas function attribute, SH: SH Function Attributesrequires: C++ Conceptsresbank function attribute, SH: SH Function Attributesreset function attribute, NDS32: NDS32 Function Attributesretain function attribute: Common Function Attributesretain variable attribute: Common Variable Attributesreturns_nonnull function attribute: Common Function Attributesreturns_twice function attribute: Common Function Attributesrindex: Other Builtinsrint: Other Builtinsrintf: Other Builtinsrintl: Other Builtinsround: Other Builtinsroundf: Other Builtinsroundl: Other Builtinssaddr variable attribute, RL78: RL78 Variable Attributessave_all function attribute, NDS32: NDS32 Function Attributessave_volatiles function attribute, MicroBlaze: MicroBlaze Function Attributessaveall function attribute, Blackfin: Blackfin Function Attributessaveall function attribute, H8/300: H8/300 Function Attributesscalar_storage_order type attribute: Common Type Attributesscalb: Other Builtinsscalbf: Other Builtinsscalbl: Other Builtinsscalbln: Other Builtinsscalblnf: Other Builtinsscalbn: Other Builtinsscalbnf: Other Builtinsscanf, and constant strings: Incompatibilitiesscanfnl: Other Builtinssda variable attribute, V850: V850 Variable Attributessection function attribute: Common Function Attributessection variable attribute: Common Variable Attributessecure_call function attribute, ARC: ARC Function Attributesselectany variable attribute: Microsoft Windows Variable Attributessentinel function attribute: Common Function Attributessetjmp: Global Register Variablessetjmp incompatibilities: Incompatibilitiesshared attribute, Nvidia PTX: Nvidia PTX Variable Attributesshared variable attribute: Microsoft Windows Variable Attributesshort_call function attribute, ARC: ARC Function Attributesshort_call function attribute, ARM: ARM Function Attributesshort_call function attribute, Epiphany: Epiphany Function Attributesshort_call function attribute, MIPS: MIPS Function Attributesshortcall function attribute, Blackfin: Blackfin Function Attributesshortcall function attribute, PowerPC: PowerPC Function Attributes?:: Conditionalssign-return-address function attribute, AArch64: AArch64 Function Attributessignal function attribute, AVR: AVR Function Attributessignbit: Other Builtinssignbitd128: Other Builtinssignbitd32: Other Builtinssignbitd64: Other Builtinssignbitf: Other Builtinssignbitl: Other Builtinssignificand: Other Builtinssignificandf: Other Builtinssignificandl: Other Builtinssimd function attribute: Common Function Attributessin: Other Builtinssincos: Other Builtinssincosf: Other Builtinssincosl: Other Builtinssinf: Other Builtinssinh: Other Builtinssinhf: Other Builtinssinhl: Other Builtinssinl: Other Builtinssizeof: Typeofsnprintf: Other BuiltinsSOURCE_DATE_EPOCH: Environment Variablessp_switch function attribute, SH: SH Function Attributessprintf: Other Builtinssqrt: Other Builtinssqrtf: Other Builtinssqrtl: Other Builtinssscanf: Other Builtinssscanf, and constant strings: Incompatibilitiessseregparm function attribute, x86: x86 Function Attributesstack_protect function attribute: Common Function Attributesstdcall function attribute, x86-32: x86 Function Attributesstpcpy: Other Builtinsstpncpy: Other Builtinsstrcasecmp: Other Builtinsstrcat: Other Builtinsstrchr: Other Builtinsstrcmp: Other Builtinsstrcpy: Other Builtinsstrcspn: Other Builtinsstrdup: Other Builtinsstrfmon: Other Builtinsstrftime: Other Builtinsstrict-align function attribute, AArch64: AArch64 Function Attributesstrict_flex_array variable attribute: Common Variable Attributesstrlen: Other Builtinsstrncasecmp: Other Builtinsstrncat: Other Builtinsstrncmp: Other Builtinsstrncpy: Other Builtinsstrndup: Other Builtinsstrnlen: Other Builtinsstrpbrk: Other Builtinsstrrchr: Other Builtinsstrspn: Other Builtinsstrstr: Other Builtinsstrub type attribute: Common Type Attributesstruct: Unnamed Fieldsstruct __htm_tdb: S/390 System z Built-in FunctionsSUNPRO_DEPENDENCIES: Environment Variablessymver function attribute: Common Function Attributessyscall_linkage function attribute, IA-64: IA-64 Function Attributessysv_abi function attribute, x86: x86 Function Attributestainted_args function attribute: Common Function Attributestan: Other Builtinstanf: Other Builtinstanh: Other Builtinstanhf: Other Builtinstanhl: Other Builtinstanl: Other Builtinstarget function attribute: x86 Function Attributestarget function attribute: S/390 Function Attributestarget function attribute: PowerPC Function Attributestarget function attribute: Nios II Function Attributestarget function attribute: ARM Function Attributestarget function attribute: Common Function Attributestarget("3dnow") function attribute, x86: x86 Function Attributestarget("3dnowa") function attribute, x86: x86 Function Attributestarget("abm") function attribute, x86: x86 Function Attributestarget("adx") function attribute, x86: x86 Function Attributestarget("aes") function attribute, x86: x86 Function Attributestarget("align-stringops") function attribute, x86: x86 Function Attributestarget("altivec") function attribute, PowerPC: PowerPC Function Attributestarget("amx-bf16") function attribute, x86: x86 Function Attributestarget("amx-complex") function attribute, x86: x86 Function Attributestarget("amx-fp16") function attribute, x86: x86 Function Attributestarget("amx-int8") function attribute, x86: x86 Function Attributestarget("amx-tile") function attribute, x86: x86 Function Attributestarget("arch=ARCH") function attribute, x86: x86 Function Attributestarget("arm") function attribute, ARM: ARM Function Attributestarget("avoid-indexed-addresses") function attribute, PowerPC: PowerPC Function Attributestarget("avx") function attribute, x86: x86 Function Attributestarget("avx2") function attribute, x86: x86 Function Attributestarget("avx5124fmaps") function attribute, x86: x86 Function Attributestarget("avx5124vnniw") function attribute, x86: x86 Function Attributestarget("avx512bitalg") function attribute, x86: x86 Function Attributestarget("avx512bw") function attribute, x86: x86 Function Attributestarget("avx512cd") function attribute, x86: x86 Function Attributestarget("avx512dq") function attribute, x86: x86 Function Attributestarget("avx512er") function attribute, x86: x86 Function Attributestarget("avx512f") function attribute, x86: x86 Function Attributestarget("avx512ifma") function attribute, x86: x86 Function Attributestarget("avx512pf") function attribute, x86: x86 Function Attributestarget("avx512vbmi") function attribute, x86: x86 Function Attributestarget("avx512vbmi2") function attribute, x86: x86 Function Attributestarget("avx512vl") function attribute, x86: x86 Function Attributestarget("avx512vnni") function attribute, x86: x86 Function Attributestarget("avx512vpopcntdq") function attribute, x86: x86 Function Attributestarget("avxifma") function attribute, x86: x86 Function Attributestarget("avxneconvert") function attribute, x86: x86 Function Attributestarget("avxvnni") function attribute, x86: x86 Function Attributestarget("avxvnniint8") function attribute, x86: x86 Function Attributestarget("bmi") function attribute, x86: x86 Function Attributestarget("bmi2") function attribute, x86: x86 Function Attributestarget("cld") function attribute, x86: x86 Function Attributestarget("cldemote") function attribute, x86: x86 Function Attributestarget("clflushopt") function attribute, x86: x86 Function Attributestarget("clwb") function attribute, x86: x86 Function Attributestarget("clzero") function attribute, x86: x86 Function Attributestarget("cmpb") function attribute, PowerPC: PowerPC Function Attributestarget("cmpccxadd") function attribute, x86: x86 Function Attributestarget("cpu=CPU") function attribute, PowerPC: PowerPC Function Attributestarget("crc32") function attribute, x86: x86 Function Attributestarget("custom-fpu-cfg=name") function attribute, Nios II: Nios II Function Attributestarget("custom-insn=N") function attribute, Nios II: Nios II Function Attributestarget("cx16") function attribute, x86: x86 Function Attributestarget("default") function attribute, x86: x86 Function Attributestarget("dlmzb") function attribute, PowerPC: PowerPC Function Attributestarget("f16c") function attribute, x86: x86 Function Attributestarget("fancy-math-387") function attribute, x86: x86 Function Attributestarget("fma") function attribute, x86: x86 Function Attributestarget("fma4") function attribute, x86: x86 Function Attributestarget("fpmath=FPMATH") function attribute, x86: x86 Function Attributestarget("fprnd") function attribute, PowerPC: PowerPC Function Attributestarget("fpu=") function attribute, ARM: ARM Function Attributestarget("friz") function attribute, PowerPC: PowerPC Function Attributestarget("fsgsbase") function attribute, x86: x86 Function Attributestarget("fxsr") function attribute, x86: x86 Function Attributestarget("general-regs-only") function attribute, x86: x86 Function Attributestarget("gfni") function attribute, x86: x86 Function Attributestarget("hard-dfp") function attribute, PowerPC: PowerPC Function Attributestarget("hle") function attribute, x86: x86 Function Attributestarget("hreset") function attribute, x86: x86 Function Attributestarget("ieee-fp") function attribute, x86: x86 Function Attributestarget("inline-all-stringops") function attribute, x86: x86 Function Attributestarget("inline-stringops-dynamically") function attribute, x86: x86 Function Attributestarget("isel") function attribute, PowerPC: PowerPC Function Attributestarget("kl") function attribute, x86: x86 Function Attributestarget("longcall") function attribute, PowerPC: PowerPC Function Attributestarget("lwp") function attribute, x86: x86 Function Attributestarget("lzcnt") function attribute, x86: x86 Function Attributestarget("mfcrf") function attribute, PowerPC: PowerPC Function Attributestarget("mmx") function attribute, x86: x86 Function Attributestarget("movbe") function attribute, x86: x86 Function Attributestarget("movdir64b") function attribute, x86: x86 Function Attributestarget("movdiri") function attribute, x86: x86 Function Attributestarget("mulhw") function attribute, PowerPC: PowerPC Function Attributestarget("multiple") function attribute, PowerPC: PowerPC Function Attributestarget("mwait") function attribute, x86: x86 Function Attributestarget("mwaitx") function attribute, x86: x86 Function Attributestarget("no-custom-insn") function attribute, Nios II: Nios II Function Attributestarget("paired") function attribute, PowerPC: PowerPC Function Attributestarget("pclmul") function attribute, x86: x86 Function Attributestarget("pconfig") function attribute, x86: x86 Function Attributestarget("pku") function attribute, x86: x86 Function Attributestarget("popcnt") function attribute, x86: x86 Function Attributestarget("popcntb") function attribute, PowerPC: PowerPC Function Attributestarget("popcntd") function attribute, PowerPC: PowerPC Function Attributestarget("powerpc-gfxopt") function attribute, PowerPC: PowerPC Function Attributestarget("powerpc-gpopt") function attribute, PowerPC: PowerPC Function Attributestarget("prefetchi") function attribute, x86: x86 Function Attributestarget("prefetchwt1") function attribute, x86: x86 Function Attributestarget("prfchw") function attribute, x86: x86 Function Attributestarget("ptwrite") function attribute, x86: x86 Function Attributestarget("raoint") function attribute, x86: x86 Function Attributestarget("rdpid") function attribute, x86: x86 Function Attributestarget("rdrnd") function attribute, x86: x86 Function Attributestarget("rdseed") function attribute, x86: x86 Function Attributestarget("recip") function attribute, x86: x86 Function Attributestarget("recip-precision") function attribute, PowerPC: PowerPC Function Attributestarget("rtm") function attribute, x86: x86 Function Attributestarget("sahf") function attribute, x86: x86 Function Attributestarget("sgx") function attribute, x86: x86 Function Attributestarget("sha") function attribute, x86: x86 Function Attributestarget("shstk") function attribute, x86: x86 Function Attributestarget("sse") function attribute, x86: x86 Function Attributestarget("sse2") function attribute, x86: x86 Function Attributestarget("sse3") function attribute, x86: x86 Function Attributestarget("sse4") function attribute, x86: x86 Function Attributestarget("sse4.1") function attribute, x86: x86 Function Attributestarget("sse4.2") function attribute, x86: x86 Function Attributestarget("sse4a") function attribute, x86: x86 Function Attributestarget("ssse3") function attribute, x86: x86 Function Attributestarget("string") function attribute, PowerPC: PowerPC Function Attributestarget("tbm") function attribute, x86: x86 Function Attributestarget("thumb") function attribute, ARM: ARM Function Attributestarget("tune=TUNE") function attribute, PowerPC: PowerPC Function Attributestarget("tune=TUNE") function attribute, x86: x86 Function Attributestarget("uintr") function attribute, x86: x86 Function Attributestarget("update") function attribute, PowerPC: PowerPC Function Attributestarget("vaes") function attribute, x86: x86 Function Attributestarget("vpclmulqdq") function attribute, x86: x86 Function Attributestarget("vsx") function attribute, PowerPC: PowerPC Function Attributestarget("waitpkg") function attribute, x86: x86 Function Attributestarget("wbnoinvd") function attribute, x86: x86 Function Attributestarget("widekl") function attribute, x86: x86 Function Attributestarget("xop") function attribute, x86: x86 Function Attributestarget("xsave") function attribute, x86: x86 Function Attributestarget("xsavec") function attribute, x86: x86 Function Attributestarget("xsaveopt") function attribute, x86: x86 Function Attributestarget("xsaves") function attribute, x86: x86 Function Attributestarget_clones function attribute: Common Function Attributestargs GCC_COLORS capability: Diagnostic Message Formatting Optionstda variable attribute, V850: V850 Variable AttributesTERM_URLS environment variable: Diagnostic Message Formatting Optionstgamma: Other Builtinstgammaf: Other Builtinstgammal: Other Builtinsthiscall function attribute, x86-32: x86 Function Attributestiny_data variable attribute, H8/300: H8/300 Variable Attributestls-dialect= function attribute, AArch64: AArch64 Function Attributestls_model variable attribute: Common Variable AttributesTMPDIR: Environment Variablestoascii: Other Builtinstolower: Other Builtinstoupper: Other Builtinstowlower: Other Builtinstowupper: Other Builtinstransparent_union type attribute: Common Type Attributestrap_exit function attribute, SH: SH Function Attributestrapa_handler function attribute, SH: SH Function Attributestrunc: Other Builtinstruncf: Other Builtinstruncl: Other Builtinstune= function attribute, AArch64: AArch64 Function Attributestype-diff GCC_COLORS capability: Diagnostic Message Formatting Optionstype_info: Vague Linkagetypeof: TypeofUHK fixed-suffix: Fixed-Pointuhk fixed-suffix: Fixed-PointUHR fixed-suffix: Fixed-Pointuhr fixed-suffix: Fixed-PointUK fixed-suffix: Fixed-Pointuk fixed-suffix: Fixed-PointULK fixed-suffix: Fixed-Pointulk fixed-suffix: Fixed-PointULL integer suffix: Long LongULLK fixed-suffix: Fixed-Pointullk fixed-suffix: Fixed-PointULLR fixed-suffix: Fixed-Pointullr fixed-suffix: Fixed-PointULR fixed-suffix: Fixed-Pointulr fixed-suffix: Fixed-Pointunavailable enumerator attribute: Enumerator Attributesunavailable function attribute: Common Function Attributesunavailable type attribute: Common Type Attributesunavailable variable attribute: Common Variable Attributesuncached type attribute, ARC: ARC Type Attributesuninitialized variable attribute: Common Variable Attributesunion: Unnamed Fieldsunused function attribute: Common Function Attributesunused label attribute: Label Attributesunused type attribute: Common Type Attributesunused variable attribute: Common Variable Attributesupper function attribute, MSP430: MSP430 Function Attributesupper variable attribute, MSP430: MSP430 Variable AttributesUR fixed-suffix: Fixed-Pointur fixed-suffix: Fixed-Pointuse_debug_exception_return function attribute, MIPS: MIPS Function Attributesuse_hazard_barrier_return function attribute, MIPS: MIPS Function Attributesuse_shadow_register_set function attribute, MIPS: MIPS Function Attributesused function attribute: Common Function Attributesused variable attribute: Common Variable Attributeslongjmp: Global Register Variablesvec_blendv: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_cfuge: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_clrl: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_clrr: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_cntlzm: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_cnttzm: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_extracth: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_extractl: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_genpcvm: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_gnb: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_inserth: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_insertl: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_pdep: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_permx: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_pext: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_replace_element: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_replace_unaligned: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_sldb: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_splati: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_splati_ins: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_splatid: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_srdb: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_stril: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_stril_p: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_strir: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_strir_p: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_ternarylogic: PowerPC AltiVec Built-in Functions Available on ISA 3.1vec_xst_trunc: Basic PowerPC Built-in Functions Available on ISA 3.1vector function attribute, RX: RX Function Attributesvector_size type attribute: Common Type Attributesvector_size variable attribute: Common Variable Attributesversion_id function attribute, IA-64: IA-64 Function Attributesvfprintf: Other Builtinsvfscanf: Other Builtinsvisibility function attribute: Common Function Attributesvisibility type attribute: Common Type Attributesvisibility variable attribute: Common Variable Attributesvolatile applied to function: Function Attributesasm: Extended Asmvprintf: Other Builtinsvscanf: Other Builtinsvsnprintf: Other Builtinsvsprintf: Other Builtinsvsscanf: Other Builtinsvsx_xl_sext: Basic PowerPC Built-in Functions Available on ISA 3.1vsx_xl_zext: Basic PowerPC Built-in Functions Available on ISA 3.1W floating point suffix: Floating Typesw floating point suffix: Floating Typeswakeup function attribute, MSP430: MSP430 Function Attributeswarm function attribute, NDS32: NDS32 Function Attributeswarn_if_not_aligned type attribute: Common Type Attributeswarn_if_not_aligned variable attribute: Common Variable Attributeswarn_unused type attribute: C++ Attributeswarn_unused_result function attribute: Common Function Attributeswarning function attribute: Common Function Attributeswarning GCC_COLORS capability: Diagnostic Message Formatting Optionsweak function attribute: Common Function Attributesweak variable attribute: Common Variable Attributesweakref function attribute: Common Function Attributesy0: Other Builtinsy0f: Other Builtinsy0l: Other Builtinsy1: Other Builtinsy1f: Other Builtinsy1l: Other Builtinsyn: Other Builtinsynf: Other Builtinsynl: Other Builtinszda variable attribute, V850: V850 Variable Attributeszero_call_used_regs function attribute: Common Function Attributes[1] On some systems, ‘gcc -shared’ needs to build supplementary stub code for constructors to work. On multi-libbed systems, ‘gcc -shared’ must select the correct support libraries to link against. Failing to supply the correct flags may lead to subtle defects. Supplying them in cases where they are not necessary is innocuous. -shared suppresses the addition of startup code to alter the floating-point environment as done with -ffast-math, -Ofast or -funsafe-math-optimizations on some targets.
[2] Some users like to
distinguish module interface files with a new suffix, such as naming
the source module.cppm, which involves
teaching all tools about the new suffix. A different scheme, such as
naming module-m.cpp would be less invasive.
[3] Where applicable the soft limit is incremented as needed towards the hard limit.
[4] The precise contents of this output may change.
[5] Future versions of GCC may zero-extend, or use
a target-defined ptr_extend pattern. Do not rely on sign extension.
[6] The analogous feature in Fortran is called an assigned goto, but that name seems inappropriate in C, where one can do more than simply store label addresses in label variables.
[7] A “call-used” register is a register whose contents can be changed by a function call; therefore, a caller cannot assume that the register has the same contents on return from the function as it had before calling the function. Such registers are also called “call-clobbered”, “caller-saved”, or “volatile”.
[8] A file's basename is the name stripped of all leading path information and of trailing suffixes, such as ‘.h’ or ‘.C’ or ‘.cc’.
[9] The C++ standard just uses the term “dependent” for names that depend on the type or value of template parameters. This shorter term will also be used in the rest of this section.