This is the Tenth Edition, of Debugging with gdb: the gnu Source-Level Debugger for gdb Version 9.2 for GNAT Pro 22.0w.
Copyright © 1988-2020 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being “Free Software” and “Free Software Needs Free Documentation”, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below.
(a) The FSF's Back-Cover Text is: “You are free to copy and modify this GNU Manual. Buying copies from GNU Press supports the FSF in developing GNU and promoting software freedom.”
This file describes gdb, the gnu symbolic debugger.
This is the Tenth Edition, for gdb Version 9.2 for GNAT Pro 22.0w.
Copyright (C) 1988-2020 Free Software Foundation, Inc.
This edition of the GDB manual is dedicated to the memory of Fred Fish. Fred was a long-standing contributor to GDB and to Free software in general. We will miss him.
.gdb_index
section format
The purpose of a debugger such as gdb is to allow you to see what is going on “inside” another program while it executes—or what another program was doing at the moment it crashed.
gdb can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act:
You can use gdb to debug programs written in C and C++. For more information, see Supported Languages. For more information, see C and C++.
Support for D is partial. For information on D, see D.
Support for Modula-2 is partial. For information on Modula-2, see Modula-2.
Support for OpenCL C is partial. For information on OpenCL C, see OpenCL C.
Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. gdb does not support entering expressions, printing values, or similar features using Pascal syntax.
gdb can be used to debug programs written in Fortran, although it may be necessary to refer to some variables with a trailing underscore.
gdb can be used to debug programs written in Objective-C, using either the Apple/NeXT or the GNU Objective-C runtime.
gdb is free software, protected by the gnu General Public License (GPL). The GPL gives you the freedom to copy or adapt a licensed program—but every person getting a copy also gets with it the freedom to modify that copy (which means that they must get access to the source code), and the freedom to distribute further copies. Typical software companies use copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve these freedoms.
Fundamentally, the General Public License is a license which says that you have these freedoms and that you cannot take these freedoms away from anyone else.
The biggest deficiency in the free software community today is not in the software—it is the lack of good free documentation that we can include with the free software. Many of our most important programs do not come with free reference manuals and free introductory texts. Documentation is an essential part of any software package; when an important free software package does not come with a free manual and a free tutorial, that is a major gap. We have many such gaps today.
Consider Perl, for instance. The tutorial manuals that people normally use are non-free. How did this come about? Because the authors of those manuals published them with restrictive terms—no copying, no modification, source files not available—which exclude them from the free software world.
That wasn't the first time this sort of thing happened, and it was far from the last. Many times we have heard a GNU user eagerly describe a manual that he is writing, his intended contribution to the community, only to learn that he had ruined everything by signing a publication contract to make it non-free.
Free documentation, like free software, is a matter of freedom, not price. The problem with the non-free manual is not that publishers charge a price for printed copies—that in itself is fine. (The Free Software Foundation sells printed copies of manuals, too.) The problem is the restrictions on the use of the manual. Free manuals are available in source code form, and give you permission to copy and modify. Non-free manuals do not allow this.
The criteria of freedom for a free manual are roughly the same as for free software. Redistribution (including the normal kinds of commercial redistribution) must be permitted, so that the manual can accompany every copy of the program, both on-line and on paper.
Permission for modification of the technical content is crucial too. When people modify the software, adding or changing features, if they are conscientious they will change the manual too—so they can provide accurate and clear documentation for the modified program. A manual that leaves you no choice but to write a new manual to document a changed version of the program is not really available to our community.
Some kinds of limits on the way modification is handled are acceptable. For example, requirements to preserve the original author's copyright notice, the distribution terms, or the list of authors, are ok. It is also no problem to require modified versions to include notice that they were modified. Even entire sections that may not be deleted or changed are acceptable, as long as they deal with nontechnical topics (like this one). These kinds of restrictions are acceptable because they don't obstruct the community's normal use of the manual.
However, it must be possible to modify all the technical content of the manual, and then distribute the result in all the usual media, through all the usual channels. Otherwise, the restrictions obstruct the use of the manual, it is not free, and we need another manual to replace it.
Please spread the word about this issue. Our community continues to lose manuals to proprietary publishing. If we spread the word that free software needs free reference manuals and free tutorials, perhaps the next person who wants to contribute by writing documentation will realize, before it is too late, that only free manuals contribute to the free software community.
If you are writing documentation, please insist on publishing it under the GNU Free Documentation License or another free documentation license. Remember that this decision requires your approval—you don't have to let the publisher decide. Some commercial publishers will use a free license if you insist, but they will not propose the option; it is up to you to raise the issue and say firmly that this is what you want. If the publisher you are dealing with refuses, please try other publishers. If you're not sure whether a proposed license is free, write to licensing@gnu.org.
You can encourage commercial publishers to sell more free, copylefted manuals and tutorials by buying them, and particularly by buying copies from the publishers that paid for their writing or for major improvements. Meanwhile, try to avoid buying non-free documentation at all. Check the distribution terms of a manual before you buy it, and insist that whoever seeks your business must respect your freedom. Check the history of the book, and try to reward the publishers that have paid or pay the authors to work on it.
The Free Software Foundation maintains a list of free documentation published by other publishers, at http://www.fsf.org/doc/other-free-books.html.
Richard Stallman was the original author of gdb, and of many other gnu programs. Many others have contributed to its development. This section attempts to credit major contributors. One of the virtues of free software is that everyone is free to contribute to it; with regret, we cannot actually acknowledge everyone here. The file ChangeLog in the gdb distribution approximates a blow-by-blow account.
Changes much prior to version 2.0 are lost in the mists of time.
Plea: Additions to this section are particularly welcome. If you or your friends (or enemies, to be evenhanded) have been unfairly omitted from this list, we would like to add your names!
So that they may not regard their many labors as thankless, we particularly thank those who shepherded gdb through major releases: Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0); Jim Blandy (release 4.18); Jason Molenda (release 4.17); Stan Shebs (release 4.14); Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9); Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4); John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2, 3.1, and 3.0).
Richard Stallman, assisted at various times by Peter TerMaat, Chris Hanson, and Richard Mlynarik, handled releases through 2.8.
Michael Tiemann is the author of most of the gnu C++ support in gdb, with significant additional contributions from Per Bothner and Daniel Berlin. James Clark wrote the gnu C++ demangler. Early work on C++ was by Peter TerMaat (who also did much general update work leading to release 3.0).
gdb uses the BFD subroutine library to examine multiple object-file formats; BFD was a joint project of David V. Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
David Johnson wrote the original COFF support; Pace Willison did the original support for encapsulated COFF.
Brent Benson of Harris Computer Systems contributed DWARF 2 support.
Adam de Boor and Bradley Davis contributed the ISI Optimum V support. Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS support. Jean-Daniel Fekete contributed Sun 386i support. Chris Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. David Johnson contributed Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. Jeff Law contributed HP PA and SOM support. Keith Packard contributed NS32K support. Doug Rabson contributed Acorn Risc Machine support. Bob Rusk contributed Harris Nighthawk CX-UX support. Chris Smith contributed Convex support (and Fortran debugging). Jonathan Stone contributed Pyramid support. Michael Tiemann contributed SPARC support. Tim Tucker contributed support for the Gould NP1 and Gould Powernode. Pace Willison contributed Intel 386 support. Jay Vosburgh contributed Symmetry support. Marko Mlinar contributed OpenRISC 1000 support.
Andreas Schwab contributed M68K gnu/Linux support.
Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries.
Jay Fenlason and Roland McGrath ensured that gdb and GAS agree about several machine instruction sets.
Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM contributed remote debugging modules for the i960, VxWorks, A29K UDI, and RDI targets, respectively.
Brian Fox is the author of the readline libraries providing command-line editing and command history.
Andrew Beers of SUNY Buffalo wrote the language-switching code, the Modula-2 support, and contributed the Languages chapter of this manual.
Fred Fish wrote most of the support for Unix System Vr4. He also enhanced the command-completion support to cover C++ overloaded symbols.
Hitachi America (now Renesas America), Ltd. sponsored the support for H8/300, H8/500, and Super-H processors.
NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D processors.
Toshiba sponsored the support for the TX39 Mips processor.
Matsushita sponsored the support for the MN10200 and MN10300 processors.
Fujitsu sponsored the support for SPARClite and FR30 processors.
Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware watchpoints.
Michael Snyder added support for tracepoints.
Stu Grossman wrote gdbserver.
Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly innumerable bug fixes and cleanups throughout gdb.
The following people at the Hewlett-Packard Company contributed support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0 (narrow mode), HP's implementation of kernel threads, HP's aC++ compiler, and the Text User Interface (nee Terminal User Interface): Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific information in this manual.
DJ Delorie ported gdb to MS-DOS, for the DJGPP project. Robert Hoehne made significant contributions to the DJGPP port.
Cygnus Solutions has sponsored gdb maintenance and much of its development since 1991. Cygnus engineers who have worked on gdb fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler, Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner, Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David Zuhn have made contributions both large and small.
Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for Cygnus Solutions, implemented the original gdb/mi interface.
Jim Blandy added support for preprocessor macros, while working for Red Hat.
Andrew Cagney designed gdb's architecture vector. Many people including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped with the migration of old architectures to this new framework.
Andrew Cagney completely re-designed and re-implemented gdb's unwinder framework, this consisting of a fresh new design featuring frame IDs, independent frame sniffers, and the sentinel frame. Mark Kettenis implemented the dwarf 2 unwinder, Jeff Johnston the libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and trad unwinders. The architecture-specific changes, each involving a complete rewrite of the architecture's frame code, were carried out by Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich Weigand.
Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from Tensilica, Inc. contributed support for Xtensa processors. Others who have worked on the Xtensa port of gdb in the past include Steve Tjiang, John Newlin, and Scott Foehner.
Michael Eager and staff of Xilinx, Inc., contributed support for the Xilinx MicroBlaze architecture.
Initial support for the FreeBSD/mips target and native configuration was developed by SRI International and the University of Cambridge Computer Laboratory under DARPA/AFRL contract FA8750-10-C-0237 ("CTSRD"), as part of the DARPA CRASH research programme.
Initial support for the FreeBSD/riscv target and native configuration was developed by SRI International and the University of Cambridge Computer Laboratory (Department of Computer Science and Technology) under DARPA contract HR0011-18-C-0016 ("ECATS"), as part of the DARPA SSITH research programme.
The original port to the OpenRISC 1000 is believed to be due to Alessandro Forin and Per Bothner. More recent ports have been the work of Jeremy Bennett, Franck Jullien, Stefan Wallentowitz and Stafford Horne.
You can use this manual at your leisure to read all about gdb. However, a handful of commands are enough to get started using the debugger. This chapter illustrates those commands.
One of the preliminary versions of gnu m4
(a generic macro
processor) exhibits the following bug: sometimes, when we change its
quote strings from the default, the commands used to capture one macro
definition within another stop working. In the following short m4
session, we define a macro foo
which expands to 0000
; we
then use the m4
built-in defn
to define bar
as the
same thing. However, when we change the open quote string to
<QUOTE>
and the close quote string to <UNQUOTE>
, the same
procedure fails to define a new synonym baz
:
$ cd gnu/m4 $ ./m4 define(foo,0000) foo 0000 define(bar,defn(`foo')) bar 0000 changequote(<QUOTE>,<UNQUOTE>) define(baz,defn(<QUOTE>foo<UNQUOTE>)) baz Ctrl-d m4: End of input: 0: fatal error: EOF in string
Let us use gdb to try to see what is going on.
$ gdb m4 gdb is free software and you are welcome to distribute copies of it under certain conditions; type "show copying" to see the conditions. There is absolutely no warranty for gdb; type "show warranty" for details. gdb 9.2 for GNAT Pro 22.0w, Copyright 1999 Free Software Foundation, Inc... (gdb)
gdb reads only enough symbol data to know where to find the rest when needed; as a result, the first prompt comes up very quickly. We now tell gdb to use a narrower display width than usual, so that examples fit in this manual.
(gdb) set width 70
We need to see how the m4
built-in changequote
works.
Having looked at the source, we know the relevant subroutine is
m4_changequote
, so we set a breakpoint there with the gdb
break
command.
(gdb) break m4_changequote Breakpoint 1 at 0x62f4: file builtin.c, line 879.
Using the run
command, we start m4
running under gdb
control; as long as control does not reach the m4_changequote
subroutine, the program runs as usual:
(gdb) run Starting program: /work/Editorial/gdb/gnu/m4/m4 define(foo,0000) foo 0000
To trigger the breakpoint, we call changequote
. gdb
suspends execution of m4
, displaying information about the
context where it stops.
changequote(<QUOTE>,<UNQUOTE>) Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) at builtin.c:879 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
Now we use the command n
(next
) to advance execution to
the next line of the current function.
(gdb) n 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\ : nil,
set_quotes
looks like a promising subroutine. We can go into it
by using the command s
(step
) instead of next
.
step
goes to the next line to be executed in any
subroutine, so it steps into set_quotes
.
(gdb) s set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") at input.c:530 530 if (lquote != def_lquote)
The display that shows the subroutine where m4
is now
suspended (and its arguments) is called a stack frame display. It
shows a summary of the stack. We can use the backtrace
command (which can also be spelled bt
), to see where we are
in the stack as a whole: the backtrace
command displays a
stack frame for each active subroutine.
(gdb) bt #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") at input.c:530 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70) at builtin.c:882 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30) at macro.c:71 #4 0x79dc in expand_input () at macro.c:40 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
We step through a few more lines to see what happens. The first two
times, we can use ‘s’; the next two times we use n
to avoid
falling into the xstrdup
subroutine.
(gdb) s 0x3b5c 532 if (rquote != def_rquote) (gdb) s 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \ def_lquote : xstrdup(lq); (gdb) n 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup(rq); (gdb) n 538 len_lquote = strlen(rquote);
The last line displayed looks a little odd; we can examine the variables
lquote
and rquote
to see if they are in fact the new left
and right quotes we specified. We use the command p
(print
) to see their values.
(gdb) p lquote $1 = 0x35d40 "<QUOTE>" (gdb) p rquote $2 = 0x35d50 "<UNQUOTE>"
lquote
and rquote
are indeed the new left and right quotes.
To look at some context, we can display ten lines of source
surrounding the current line with the l
(list
) command.
(gdb) l 533 xfree(rquote); 534 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\ : xstrdup (lq); 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup (rq); 537 538 len_lquote = strlen(rquote); 539 len_rquote = strlen(lquote); 540 } 541 542 void
Let us step past the two lines that set len_lquote
and
len_rquote
, and then examine the values of those variables.
(gdb) n 539 len_rquote = strlen(lquote); (gdb) n 540 } (gdb) p len_lquote $3 = 9 (gdb) p len_rquote $4 = 7
That certainly looks wrong, assuming len_lquote
and
len_rquote
are meant to be the lengths of lquote
and
rquote
respectively. We can set them to better values using
the p
command, since it can print the value of
any expression—and that expression can include subroutine calls and
assignments.
(gdb) p len_lquote=strlen(lquote) $5 = 7 (gdb) p len_rquote=strlen(rquote) $6 = 9
Is that enough to fix the problem of using the new quotes with the
m4
built-in defn
? We can allow m4
to continue
executing with the c
(continue
) command, and then try the
example that caused trouble initially:
(gdb) c Continuing. define(baz,defn(<QUOTE>foo<UNQUOTE>)) baz 0000
Success! The new quotes now work just as well as the default ones. The
problem seems to have been just the two typos defining the wrong
lengths. We allow m4
exit by giving it an EOF as input:
Ctrl-d Program exited normally.
The message ‘Program exited normally.’ is from gdb; it
indicates m4
has finished executing. We can end our gdb
session with the gdb quit
command.
(gdb) quit
This chapter discusses how to start gdb, and how to get out of it. The essentials are:
Invoke gdb by running the program gdb
. Once started,
gdb reads commands from the terminal until you tell it to exit.
You can also run gdb
with a variety of arguments and options,
to specify more of your debugging environment at the outset.
The command-line options described here are designed to cover a variety of situations; in some environments, some of these options may effectively be unavailable.
The most usual way to start gdb is with one argument, specifying an executable program:
gdb program
You can also start with both an executable program and a core file specified:
gdb program core
You can, instead, specify a process ID as a second argument or use option
-p
, if you want to debug a running process:
gdb program 1234 gdb -p 1234
would attach gdb to process 1234
. With option -p you
can omit the program filename.
Taking advantage of the second command-line argument requires a fairly complete operating system; when you use gdb as a remote debugger attached to a bare board, there may not be any notion of “process”, and there is often no way to get a core dump. gdb will warn you if it is unable to attach or to read core dumps.
You can optionally have gdb
pass any arguments after the
executable file to the inferior using --args
. This option stops
option processing.
gdb --args gcc -O2 -c foo.c
This will cause gdb
to debug gcc
, and to set
gcc
's command-line arguments (see Arguments) to ‘-O2 -c foo.c’.
You can run gdb
without printing the front material, which describes
gdb's non-warranty, by specifying --silent
(or -q
/--quiet
):
gdb --silent
You can further control how gdb starts up by using command-line options. gdb itself can remind you of the options available.
Type
gdb -help
to display all available options and briefly describe their use (‘gdb -h’ is a shorter equivalent).
All options and command line arguments you give are processed in sequential order. The order makes a difference when the ‘-x’ option is used.
When gdb starts, it reads any arguments other than options as specifying an executable file and core file (or process ID). This is the same as if the arguments were specified by the ‘-se’ and ‘-c’ (or ‘-p’) options respectively. (gdb reads the first argument that does not have an associated option flag as equivalent to the ‘-se’ option followed by that argument; and the second argument that does not have an associated option flag, if any, as equivalent to the ‘-c’/‘-p’ option followed by that argument.) If the second argument begins with a decimal digit, gdb will first attempt to attach to it as a process, and if that fails, attempt to open it as a corefile. If you have a corefile whose name begins with a digit, you can prevent gdb from treating it as a pid by prefixing it with ./, e.g. ./12345.
If gdb has not been configured to included core file support, such as for most embedded targets, then it will complain about a second argument and ignore it.
Many options have both long and short forms; both are shown in the following list. gdb also recognizes the long forms if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with ‘--’ rather than ‘-’, though we illustrate the more usual convention.)
-symbols
file-s
file-exec
file-e
file-se
file-core
file-c
file-pid
number-p
numberattach
command.
-command
file-x
filesource
command would.
See Command files.
-eval-command
command-ex
commandThis option may be used multiple times to call multiple commands. It may also be interleaved with ‘-command’ as required.
gdb -ex 'target sim' -ex 'load' \ -x setbreakpoints -ex 'run' a.out
-init-command
file-ix
file-init-eval-command
command-iex
command-directory
directory-d
directory-r
-readnow
--readnever
You can run gdb in various alternative modes—for example, in batch mode or quiet mode.
-nx
-n
--with-system-gdbinit
configure option (see System-wide configuration).
It is loaded first when gdb starts, before command line options
have been processed.
--with-system-gdbinit-dir
configure option (see System-wide configuration).
Files in this directory are loaded in alphabetical order immediately after
system.gdbinit (if enabled) when gdb starts, before command line
options have been processed. Files need to have a recognized scripting
language extension (.py/.scm) or be named with a .gdb
extension to be interpreted as regular gdb commands. gdb
will not recurse into any subdirectories of this directory.
-x
and
-ex
have been processed. Command line options -x
and
-ex
are processed last, after ./.gdbinit has been loaded.
For further documentation on startup processing, See Startup. For documentation on how to write command files, See Command Files.
-nh
-quiet
-silent
-q
-batch
0
after processing all the
command files specified with ‘-x’ (and all commands from
initialization files, if not inhibited with ‘-n’). Exit with
nonzero status if an error occurs in executing the gdb commands
in the command files. Batch mode also disables pagination, sets unlimited
terminal width and height see Screen Size, and acts as if set confirm
off were in effect (see Messages/Warnings).
Batch mode may be useful for running gdb as a filter, for example to download and run a program on another computer; in order to make this more useful, the message
Program exited normally.
(which is ordinarily issued whenever a program running under
gdb control terminates) is not issued when running in batch
mode.
-batch-silent
stdout
is prevented (stderr
is
unaffected). This is much quieter than ‘-silent’ and would be useless
for an interactive session.
This is particularly useful when using targets that give ‘Loading section’ messages, for example.
Note that targets that give their output via gdb, as opposed to
writing directly to stdout
, will also be made silent.
-return-child-result
This option is useful in conjunction with ‘-batch’ or ‘-batch-silent’,
when gdb is being used as a remote program loader or simulator
interface.
-nowindows
-nw
-windows
-w
-cd
directory-data-directory
directory-D
directory-fullname
-f
-annotate
levelThe annotation mechanism has largely been superseded by gdb/mi
(see GDB/MI).
--args
-baud
bps-b
bps-l
timeout-tty
device-t
device-tui
-interpreter
interp‘--interpreter=mi’ (or ‘--interpreter=mi3’) causes
gdb to use the gdb/mi interface version 3 (see The gdb/mi Interface) included since gdb version 9.1. gdb/mi
version 2 (mi2
), included in gdb 6.0 and version 1 (mi1
),
included in gdb 5.3, are also available. Earlier gdb/mi
interfaces are no longer supported.
-write
-statistics
-version
-configuration
Here's the description of what gdb does during session startup:
If you wish to disable the auto-loading during startup, you must do something like the following:
$ gdb -iex "set auto-load python-scripts off" myprogram
Option ‘-ex’ does not work because the auto-loading is then turned off too late.
Init files use the same syntax as command files (see Command Files) and are processed by gdb in the same way. The init file in your home directory can set options (such as ‘set complaints’) that affect subsequent processing of command line options and operands. Init files are not executed if you use the ‘-nx’ option (see Choosing Modes).
To display the list of init files loaded by gdb at startup, you can use gdb --help.
The gdb init files are normally called .gdbinit. The DJGPP port of gdb uses the name gdb.ini, due to the limitations of file names imposed by DOS filesystems. The Windows port of gdb uses the standard name, but if it finds a gdb.ini file in your home directory, it warns you about that and suggests to rename the file to the standard name.
quit
[expression]q
quit
command (abbreviated
q
), or type an end-of-file character (usually Ctrl-d). If you
do not supply expression, gdb will terminate normally;
otherwise it will terminate using the result of expression as the
error code.
An interrupt (often Ctrl-c) does not exit from gdb, but rather terminates the action of any gdb command that is in progress and returns to gdb command level. It is safe to type the interrupt character at any time because gdb does not allow it to take effect until a time when it is safe.
If you have been using gdb to control an attached process or
device, you can release it with the detach
command
(see Debugging an Already-running Process).
If you need to execute occasional shell commands during your
debugging session, there is no need to leave or suspend gdb; you can
just use the shell
command.
shell
command-string!
command-string!
and command-string.
If it exists, the environment variable SHELL
determines which
shell to run. Otherwise gdb uses the default shell
(/bin/sh on Unix systems, COMMAND.COM on MS-DOS, etc.).
The utility make
is often needed in development environments.
You do not have to use the shell
command for this purpose in
gdb:
make
make-argsmake
program with the specified
arguments. This is equivalent to ‘shell make make-args’.
pipe [
command] |
shell_command| [
command] |
shell_commandpipe -d
delim command delim shell_command| -d
delim command delim shell_command|
.
If no command is provided, the last command executed is repeated.
In case the command contains a |
, the option -d
delim
can be used to specify an alternate delimiter string delim that separates
the command from the shell_command.
Example:
(gdb) p var $1 = { black = 144, red = 233, green = 377, blue = 610, white = 987 } (gdb) pipe p var|wc 7 19 80 (gdb) |p var|wc -l 7 (gdb) p /x var $4 = { black = 0x90, red = 0xe9, green = 0x179, blue = 0x262, white = 0x3db } (gdb) ||grep red red => 0xe9, (gdb) | -d ! echo this contains a | char\n ! sed -e 's/|/PIPE/' this contains a PIPE char (gdb) | -d xxx echo this contains a | char!\n xxx sed -e 's/|/PIPE/' this contains a PIPE char! (gdb)
The convenience variables $_shell_exitcode
and $_shell_exitsignal
can be used to examine the exit status of the last shell command launched
by shell
, make
, pipe
and |
.
See Convenience Variables.
You may want to save the output of gdb commands to a file. There are several commands to control gdb's logging.
set logging on
set logging off
set logging file
fileset logging overwrite [on|off]
overwrite
if
you want set logging on
to overwrite the logfile instead.
set logging redirect [on|off]
redirect
if you want output to go only to the log file.
set logging debugredirect [on|off]
debugredirect
if you want debug output to go only to the log file.
show logging
You can also redirect the output of a gdb command to a shell command. See pipe.
You can abbreviate a gdb command to the first few letters of the command name, if that abbreviation is unambiguous; and you can repeat certain gdb commands by typing just <RET>. You can also use the <TAB> key to get gdb to fill out the rest of a word in a command (or to show you the alternatives available, if there is more than one possibility).
A gdb command is a single line of input. There is no limit on
how long it can be. It starts with a command name, which is followed by
arguments whose meaning depends on the command name. For example, the
command step
accepts an argument which is the number of times to
step, as in ‘step 5’. You can also use the step
command
with no arguments. Some commands do not allow any arguments.
gdb command names may always be truncated if that abbreviation is
unambiguous. Other possible command abbreviations are listed in the
documentation for individual commands. In some cases, even ambiguous
abbreviations are allowed; for example, s
is specially defined as
equivalent to step
even though there are other commands whose
names start with s
. You can test abbreviations by using them as
arguments to the help
command.
A blank line as input to gdb (typing just <RET>) means to
repeat the previous command. Certain commands (for example, run
)
will not repeat this way; these are commands whose unintentional
repetition might cause trouble and which you are unlikely to want to
repeat. User-defined commands can disable this feature; see
dont-repeat.
The list
and x
commands, when you repeat them with
<RET>, construct new arguments rather than repeating
exactly as typed. This permits easy scanning of source or memory.
gdb can also use <RET> in another way: to partition lengthy
output, in a way similar to the common utility more
(see Screen Size). Since it is easy to press one
<RET> too many in this situation, gdb disables command
repetition after any command that generates this sort of display.
Any text from a # to the end of the line is a comment; it does nothing. This is useful mainly in command files (see Command Files).
The Ctrl-o binding is useful for repeating a complex sequence of commands. This command accepts the current line, like <RET>, and then fetches the next line relative to the current line from the history for editing.
Many commands change their behavior according to command-specific
variables or settings. These settings can be changed with the
set
subcommands. For example, the print
command
(see Examining Data) prints arrays differently depending on
settings changeable with the commands set print elements
NUMBER-OF-ELEMENTS
and set print array-indexes
, among others.
You can change these settings to your preference in the gdbinit files loaded at gdb startup. See Startup.
The settings can also be changed interactively during the debugging session. For example, to change the limit of array elements to print, you can do the following:
(gdb) set print elements 10 (gdb) print some_array $1 = {0, 10, 20, 30, 40, 50, 60, 70, 80, 90...}
The above set print elements 10
command changes the number of
elements to print from the default of 200 to 10. If you only intend
this limit of 10 to be used for printing some_array
, then you
must restore the limit back to 200, with set print elements
200
.
Some commands allow overriding settings with command options. For
example, the print
command supports a number of options that
allow overriding relevant global print settings as set by set
print
subcommands. See print options. The example above could be
rewritten as:
(gdb) print -elements 10 -- some_array
$1 = {0, 10, 20, 30, 40, 50, 60, 70, 80, 90...}
Alternatively, you can use the with
command to change a setting
temporarily, for the duration of a command invocation.
with
setting [
value] [--
command]
w
setting [
value] [--
command]
setting is any setting you can change with the set
subcommands. value is the value to assign to setting
while running command
.
If no command is provided, the last command executed is repeated.
If a command is provided, it must be preceded by a double dash
(--
) separator. This is required because some settings accept
free-form arguments, such as expressions or filenames.
For example, the command
(gdb) with print array on -- print some_array
is equivalent to the following 3 commands:
(gdb) set print array on (gdb) print some_array (gdb) set print array off
The with
command is particularly useful when you want to
override a setting while running user-defined commands, or commands
defined in Python or Guile. See Extending GDB.
(gdb) with print pretty on -- my_complex_command
To change several settings for the same command, you can nest
with
commands. For example, with language ada -- with
print elements 10
temporarily changes the language to Ada and sets a
limit of 10 elements to print for arrays and strings.
gdb can fill in the rest of a word in a command for you, if there is only one possibility; it can also show you what the valid possibilities are for the next word in a command, at any time. This works for gdb commands, gdb subcommands, command options, and the names of symbols in your program.
Press the <TAB> key whenever you want gdb to fill out the rest of a word. If there is only one possibility, gdb fills in the word, and waits for you to finish the command (or press <RET> to enter it). For example, if you type
(gdb) info bre <TAB>
gdb fills in the rest of the word ‘breakpoints’, since that is
the only info
subcommand beginning with ‘bre’:
(gdb) info breakpoints
You can either press <RET> at this point, to run the info
breakpoints
command, or backspace and enter something else, if
‘breakpoints’ does not look like the command you expected. (If you
were sure you wanted info breakpoints
in the first place, you
might as well just type <RET> immediately after ‘info bre’,
to exploit command abbreviations rather than command completion).
If there is more than one possibility for the next word when you press <TAB>, gdb sounds a bell. You can either supply more characters and try again, or just press <TAB> a second time; gdb displays all the possible completions for that word. For example, you might want to set a breakpoint on a subroutine whose name begins with ‘make_’, but when you type b make_<TAB> gdb just sounds the bell. Typing <TAB> again displays all the function names in your program that begin with those characters, for example:
(gdb) b make_ <TAB>
gdb sounds bell; press <TAB> again, to see:
make_a_section_from_file make_environ make_abs_section make_function_type make_blockvector make_pointer_type make_cleanup make_reference_type make_command make_symbol_completion_list (gdb) b make_
After displaying the available possibilities, gdb copies your partial input (‘b make_’ in the example) so you can finish the command.
If you just want to see the list of alternatives in the first place, you can press M-? rather than pressing <TAB> twice. M-? means <META> ?. You can type this either by holding down a key designated as the <META> shift on your keyboard (if there is one) while typing ?, or as <ESC> followed by ?.
If the number of possible completions is large, gdb will print as much of the list as it has collected, as well as a message indicating that the list may be truncated.
(gdb) b m<TAB><TAB> main <... the rest of the possible completions ...> *** List may be truncated, max-completions reached. *** (gdb) b m
This behavior can be controlled with the following commands:
set max-completions
limitset max-completions unlimited
show max-completions
Sometimes the string you need, while logically a “word”, may contain
parentheses or other characters that gdb normally excludes from
its notion of a word. To permit word completion to work in this
situation, you may enclose words in '
(single quote marks) in
gdb commands.
A likely situation where you might need this is in typing an expression that involves a C++ symbol name with template parameters. This is because when completing expressions, GDB treats the ‘<’ character as word delimiter, assuming that it's the less-than comparison operator (see C and C++ Operators).
For example, when you want to call a C++ template function
interactively using the print
or call
commands, you may
need to distinguish whether you mean the version of name
that
was specialized for int
, name<int>()
, or the version
that was specialized for float
, name<float>()
. To use
the word-completion facilities in this situation, type a single quote
'
at the beginning of the function name. This alerts
gdb that it may need to consider more information than usual
when you press <TAB> or M-? to request word completion:
(gdb) p 'func< M-? func<int>() func<float>() (gdb) p 'func<
When setting breakpoints however (see Specify Location), you don't usually need to type a quote before the function name, because gdb understands that you want to set a breakpoint on a function:
(gdb) b func< M-? func<int>() func<float>() (gdb) b func<
This is true even in the case of typing the name of C++ overloaded
functions (multiple definitions of the same function, distinguished by
argument type). For example, when you want to set a breakpoint you
don't need to distinguish whether you mean the version of name
that takes an int
parameter, name(int)
, or the version
that takes a float
parameter, name(float)
.
(gdb) b bubble( M-? bubble(int) bubble(double) (gdb) b bubble(dou M-? bubble(double)
See quoting names for a description of other scenarios that require quoting.
For more information about overloaded functions, see C++ Expressions. You can use the command set
overload-resolution off
to disable overload resolution;
see gdb Features for C++.
When completing in an expression which looks up a field in a structure, gdb also tries2 to limit completions to the field names available in the type of the left-hand-side:
(gdb) p gdb_stdout.M-? magic to_fputs to_rewind to_data to_isatty to_write to_delete to_put to_write_async_safe to_flush to_read
This is because the gdb_stdout
is a variable of the type
struct ui_file
that is defined in gdb sources as
follows:
struct ui_file { int *magic; ui_file_flush_ftype *to_flush; ui_file_write_ftype *to_write; ui_file_write_async_safe_ftype *to_write_async_safe; ui_file_fputs_ftype *to_fputs; ui_file_read_ftype *to_read; ui_file_delete_ftype *to_delete; ui_file_isatty_ftype *to_isatty; ui_file_rewind_ftype *to_rewind; ui_file_put_ftype *to_put; void *to_data; }
Some commands accept options starting with a leading dash. For
example, print -pretty
. Similarly to command names, you can
abbreviate a gdb option to the first few letters of the
option name, if that abbreviation is unambiguous, and you can also use
the <TAB> key to get gdb to fill out the rest of a word
in an option (or to show you the alternatives available, if there is
more than one possibility).
Some commands take raw input as argument. For example, the print
command processes arbitrary expressions in any of the languages
supported by gdb. With such commands, because raw input may
start with a leading dash that would be confused with an option or any
of its abbreviations, e.g. print -p
(short for print
-pretty
or printing negative p
?), if you specify any command
option, then you must use a double-dash (--
) delimiter to
indicate the end of options.
Some options are described as accepting an argument which can be
either on
or off
. These are known as boolean
options. Similarly to boolean settings commands—on
and
off
are the typical values, but any of 1
, yes
and
enable
can also be used as “true” value, and any of 0
,
no
and disable
can also be used as “false” value. You
can also omit a “true” value, as it is implied by default.
For example, these are equivalent:
(gdb) print -object on -pretty off -element unlimited -- *myptr (gdb) p -o -p 0 -e u -- *myptr
You can discover the set of options some command accepts by completing
on -
after the command name. For example:
(gdb) print -<TAB><TAB> -address -max-depth -raw-values -union -array -null-stop -repeats -vtbl -array-indexes -object -static-members -elements -pretty -symbol
Completion will in some cases guide you with a suggestion of what kind of argument an option expects. For example:
(gdb) print -elements <TAB><TAB> NUMBER unlimited
Here, the option expects a number (e.g., 100
), not literal
NUMBER
. Such metasyntactical arguments are always presented in
uppercase.
(For more on using the print
command, see Examining Data.)
You can always ask gdb itself for information on its commands,
using the command help
.
help
h
help
(abbreviated h
) with no arguments to
display a short list of named classes of commands:
(gdb) help List of classes of commands: aliases -- Aliases of other commands breakpoints -- Making program stop at certain points data -- Examining data files -- Specifying and examining files internals -- Maintenance commands obscure -- Obscure features running -- Running the program stack -- Examining the stack status -- Status inquiries support -- Support facilities tracepoints -- Tracing of program execution without stopping the program user-defined -- User-defined commands Type "help" followed by a class name for a list of commands in that class. Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (gdb)
help
classstatus
:
(gdb) help status Status inquiries. List of commands: info -- Generic command for showing things about the program being debugged show -- Generic command for showing things about the debugger Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (gdb)
help
commandhelp
argument, gdb displays a
short paragraph on how to use that command.
apropos [-v]
regexpapropos
command searches through all of the gdb
commands, and their documentation, for the regular expression specified in
args. It prints out all matches found. The optional flag ‘-v’,
which stands for ‘verbose’, indicates to output the full documentation
of the matching commands and highlight the parts of the documentation
matching regexp. For example:
apropos alias
results in:
alias -- Define a new command that is an alias of an existing command aliases -- Aliases of other commands d -- Delete some breakpoints or auto-display expressions del -- Delete some breakpoints or auto-display expressions delete -- Delete some breakpoints or auto-display expressions
while
apropos -v cut.*thread apply
results in the below output, where ‘cut for 'thread apply’ is highlighted if styling is enabled.
taas -- Apply a command to all threads (ignoring errors and empty output). Usage: taas COMMAND shortcut for 'thread apply all -s COMMAND' tfaas -- Apply a command to all frames of all threads (ignoring errors and empty output). Usage: tfaas COMMAND shortcut for 'thread apply all -s frame apply all -s COMMAND'
complete
argscomplete
args command lists all the possible completions
for the beginning of a command. Use args to specify the beginning of the
command you want completed. For example:
complete i
results in:
if ignore info inspect
This is intended for use by gnu Emacs.
In addition to help
, you can use the gdb commands info
and show
to inquire about the state of your program, or the state
of gdb itself. Each command supports many topics of inquiry; this
manual introduces each of them in the appropriate context. The listings
under info
and under show
in the Command, Variable, and
Function Index point to all the sub-commands. See Command and Variable Index.
info
i
) is for describing the state of your
program. For example, you can show the arguments passed to a function
with info args
, list the registers currently in use with info
registers
, or list the breakpoints you have set with info breakpoints
.
You can get a complete list of the info
sub-commands with
help info
.
set
set
. For example, you can set the gdb prompt to a $-sign with
set prompt $
.
show
info
, show
is for describing the state of
gdb itself.
You can change most of the things you can show
, by using the
related command set
; for example, you can control what number
system is used for displays with set radix
, or simply inquire
which is currently in use with show radix
.
To display all the settable parameters and their current
values, you can use show
with no arguments; you may also use
info set
. Both commands produce the same display.
Here are several miscellaneous show
subcommands, all of which are
exceptional in lacking corresponding set
commands:
show version
show copying
info copying
show warranty
info warranty
show configuration
When you run a program under gdb, you must first generate debugging information when you compile it.
You may start gdb with its arguments, if any, in an environment of your choice. If you are doing native debugging, you may redirect your program's input and output, debug an already running process, or kill a child process.
In order to debug a program effectively, you need to generate debugging information when you compile it. This debugging information is stored in the object file; it describes the data type of each variable or function and the correspondence between source line numbers and addresses in the executable code.
To request debugging information, specify the ‘-g’ option when you run the compiler.
Programs that are to be shipped to your customers are compiled with optimizations, using the ‘-O’ compiler option. However, some compilers are unable to handle the ‘-g’ and ‘-O’ options together. Using those compilers, you cannot generate optimized executables containing debugging information.
gcc, the gnu C/C++ compiler, supports ‘-g’ with or without ‘-O’, making it possible to debug optimized code. We recommend that you always use ‘-g’ whenever you compile a program. You may think your program is correct, but there is no sense in pushing your luck. For more information, see Optimized Code.
Older versions of the gnu C compiler permitted a variant option ‘-gg’ for debugging information. gdb no longer supports this format; if your gnu C compiler has this option, do not use it.
gdb knows about preprocessor macros and can show you their expansion (see Macros). Most compilers do not include information about preprocessor macros in the debugging information if you specify the -g flag alone. Version 3.1 and later of gcc, the gnu C compiler, provides macro information if you are using the DWARF debugging format, and specify the option -g3.
See Options for Debugging Your Program or GCC, for more information on gcc options affecting debug information.
You will have the best debugging experience if you use the latest version of the DWARF debugging format that your compiler supports. DWARF is currently the most expressive and best supported debugging format in gdb.
run
r
run
command to start your program under gdb.
You must first specify the program name with an argument to
gdb (see Getting In and Out of gdb), or by using the file
or exec-file
command (see Commands to Specify Files).
If you are running your program in an execution environment that
supports processes, run
creates an inferior process and makes
that process run your program. In some environments without processes,
run
jumps to the start of your program. Other targets,
like ‘remote’, are always running. If you get an error
message like this one:
The "remote" target does not support "run". Try "help target" or "continue".
then use continue
to run your program. You may need load
first (see load).
The execution of a program is affected by certain information it receives from its superior. gdb provides ways to specify this information, which you must do before starting your program. (You can change it after starting your program, but such changes only affect your program the next time you start it.) This information may be divided into four categories:
run
command. If a shell is available on your target, the shell
is used to pass the arguments, so that you may use normal conventions
(such as wildcard expansion or variable substitution) in describing
the arguments.
In Unix systems, you can control which shell is used with the
SHELL
environment variable. If you do not define SHELL
,
gdb uses the default shell (/bin/sh). You can disable
use of any shell with the set startup-with-shell
command (see
below for details).
set environment
and unset
environment
to change parts of the environment that affect
your program. See Your Program's Environment.
run
command line, or you can use the tty
command to
set a different device for your program.
See Your Program's Input and Output.
Warning: While input and output redirection work, you cannot use pipes to pass the output of the program you are debugging to another program; if you attempt this, gdb is likely to wind up debugging the wrong program.
When you issue the run
command, your program begins to execute
immediately. See Stopping and Continuing, for discussion
of how to arrange for your program to stop. Once your program has
stopped, you may call functions in your program, using the print
or call
commands. See Examining Data.
If the modification time of your symbol file has changed since the last time gdb read its symbols, gdb discards its symbol table, and reads it again. When it does this, gdb tries to retain your current breakpoints.
start
main
, but
other languages such as Ada do not require a specific name for their
main procedure. The debugger provides a convenient way to start the
execution of the program and to stop at the beginning of the main
procedure, depending on the language used.
The ‘start’ command does the equivalent of setting a temporary breakpoint at the beginning of the main procedure and then invoking the ‘run’ command.
Some programs contain an elaboration phase where some startup code is
executed before the main procedure is called. This depends on the
languages used to write your program. In C++, for instance,
constructors for static and global objects are executed before
main
is called. It is therefore possible that the debugger stops
before reaching the main procedure. However, the temporary breakpoint
will remain to halt execution.
Specify the arguments to give to your program as arguments to the ‘start’ command. These arguments will be given verbatim to the underlying ‘run’ command. Note that the same arguments will be reused if no argument is provided during subsequent calls to ‘start’ or ‘run’.
It is sometimes necessary to debug the program during elaboration. In
these cases, using the start
command would stop the execution
of your program too late, as the program would have already completed
the elaboration phase. Under these circumstances, either insert
breakpoints in your elaboration code before running your program or
use the starti
command.
starti
starti
command will stop execution at
the start of the elaboration phase.
set exec-wrapper
wrappershow exec-wrapper
unset exec-wrapper
You can use any program that eventually calls execve
with
its arguments as a wrapper. Several standard Unix utilities do
this, e.g. env
and nohup
. Any Unix shell script ending
with exec "$@"
will also work.
For example, you can use env
to pass an environment variable to
the debugged program, without setting the variable in your shell's
environment:
(gdb) set exec-wrapper env 'LD_PRELOAD=libtest.so' (gdb) run
This command is available when debugging locally on most targets, excluding djgpp, Cygwin, MS Windows, and QNX Neutrino.
set startup-with-shell
set startup-with-shell on
set startup-with-shell off
show startup-with-shell
run
command are passed to the shell, which does variable
substitution, expands wildcard characters and performs redirection of
I/O. In some circumstances, it may be useful to disable such use of a
shell, for example, when debugging the shell itself or diagnosing
startup failures such as:
(gdb) run Starting program: ./a.out During startup program terminated with signal SIGSEGV, Segmentation fault.
which indicates the shell or the wrapper specified with ‘exec-wrapper’ crashed, not your program. Most often, this is caused by something odd in your shell's non-interactive mode initialization file—such as .cshrc for C-shell, $.zshenv for the Z shell, or the file specified in the ‘BASH_ENV’ environment variable for BASH.
set auto-connect-native-target
set auto-connect-native-target on
set auto-connect-native-target off
show auto-connect-native-target
target remote
), the run
command starts your program as a
native process under gdb, on your local machine. If you're
sure you don't want to debug programs on your local machine, you can
tell gdb to not connect to the native target automatically
with the set auto-connect-native-target off
command.
If on
, which is the default, and if gdb is not
connected to a target already, the run
command automaticaly
connects to the native target, if one is available.
If off
, and if gdb is not connected to a target
already, the run
command fails with an error:
(gdb) run Don't know how to run. Try "help target".
If gdb is already connected to a target, gdb always
uses it with the run
command.
In any case, you can explicitly connect to the native target with the
target native
command. For example,
(gdb) set auto-connect-native-target off (gdb) run Don't know how to run. Try "help target". (gdb) target native (gdb) run Starting program: ./a.out [Inferior 1 (process 10421) exited normally]
In case you connected explicitly to the native
target,
gdb remains connected even if all inferiors exit, ready for
the next run
command. Use the disconnect
command to
disconnect.
Examples of other commands that likewise respect the
auto-connect-native-target
setting: attach
, info
proc
, info os
.
set disable-randomization
set disable-randomization on
This feature is implemented only on certain targets, including gnu/Linux. On gnu/Linux you can get the same behavior using
(gdb) set exec-wrapper setarch `uname -m` -R
set disable-randomization off
On targets where it is available, virtual address space randomization protects the programs against certain kinds of security attacks. In these cases the attacker needs to know the exact location of a concrete executable code. Randomizing its location makes it impossible to inject jumps misusing a code at its expected addresses.
Prelinking shared libraries provides a startup performance advantage but it makes addresses in these libraries predictable for privileged processes by having just unprivileged access at the target system. Reading the shared library binary gives enough information for assembling the malicious code misusing it. Still even a prelinked shared library can get loaded at a new random address just requiring the regular relocation process during the startup. Shared libraries not already prelinked are always loaded at a randomly chosen address.
Position independent executables (PIE) contain position independent code similar to the shared libraries and therefore such executables get loaded at a randomly chosen address upon startup. PIE executables always load even already prelinked shared libraries at a random address. You can build such executable using gcc -fPIE -pie.
Heap (malloc storage), stack and custom mmap areas are always placed randomly
(as long as the randomization is enabled).
show disable-randomization
The arguments to your program can be specified by the arguments of the
run
command.
They are passed to a shell, which expands wildcard characters and
performs redirection of I/O, and thence to your program. Your
SHELL
environment variable (if it exists) specifies what shell
gdb uses. If you do not define SHELL
, gdb uses
the default shell (/bin/sh on Unix).
On non-Unix systems, the program is usually invoked directly by gdb, which emulates I/O redirection via the appropriate system calls, and the wildcard characters are expanded by the startup code of the program, not by the shell.
run
with no arguments uses the same arguments used by the previous
run
, or those set by the set args
command.
set args
set args
has no arguments, run
executes your program
with no arguments. Once you have run your program with arguments,
using set args
before the next run
is the only way to run
it again without arguments.
show args
The environment consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running your program with a modified environment without having to start gdb over again.
path
directoryPATH
environment variable
(the search path for executables) that will be passed to your program.
The value of PATH
used by gdb does not change.
You may specify several directory names, separated by whitespace or by a
system-dependent separator character (‘:’ on Unix, ‘;’ on
MS-DOS and MS-Windows). If directory is already in the path, it
is moved to the front, so it is searched sooner.
You can use the string ‘$cwd’ to refer to whatever is the current
working directory at the time gdb searches the path. If you
use ‘.’ instead, it refers to the directory where you executed the
path
command. gdb replaces ‘.’ in the
directory argument (with the current path) before adding
directory to the search path.
show paths
PATH
environment variable).
show environment
[varname]environment
as env
.
set environment
varname [=
value]For example, this command:
set env USER = foo
tells the debugged program, when subsequently run, that its user is named ‘foo’. (The spaces around ‘=’ are used for clarity here; they are not actually required.)
Note that on Unix systems, gdb runs your program via a shell,
which also inherits the environment set with set environment
.
If necessary, you can avoid that by using the ‘env’ program as a
wrapper instead of using set environment
. See set exec-wrapper, for an example doing just that.
Environment variables that are set by the user are also transmitted to gdbserver to be used when starting the remote inferior. see QEnvironmentHexEncoded.
unset environment
varnameunset environment
removes the variable from the environment,
rather than assigning it an empty value.
Environment variables that are unset by the user are also unset on gdbserver when starting the remote inferior. see QEnvironmentUnset.
Warning: On Unix systems, gdb runs your program using
the shell indicated by your SHELL
environment variable if it
exists (or /bin/sh
if not). If your SHELL
variable
names a shell that runs an initialization file when started
non-interactively—such as .cshrc for C-shell, $.zshenv
for the Z shell, or the file specified in the ‘BASH_ENV’
environment variable for BASH—any variables you set in that file
affect your program. You may wish to move setting of environment
variables to files that are only run when you sign on, such as
.login or .profile.
Each time you start your program with run
, the inferior will be
initialized with the current working directory specified by the
set cwd command. If no directory has been specified by this
command, then the inferior will inherit gdb's current working
directory as its working directory if native debugging, or it will
inherit the remote server's current working directory if remote
debugging.
set cwd
[directory]glob
-expanded in order to resolve tildes (~). If no
argument has been specified, the command clears the setting and resets
it to an empty state. This setting has no effect on gdb's
working directory, and it only takes effect the next time you start
the inferior. The ~ in directory is a short for the
home directory, usually pointed to by the HOME environment
variable. On MS-Windows, if HOME is not defined, gdb
uses the concatenation of HOMEDRIVE and HOMEPATH as
fallback.
You can also change gdb's current working directory by using
the cd
command.
See cd command.
show cwd
cd
[directory]The gdb working directory serves as a default for the commands that specify files for gdb to operate on. See Commands to Specify Files. See set cwd command.
pwd
It is generally impossible to find the current working directory of
the process being debugged (since a program can change its directory
during its run). If you work on a system where gdb supports
the info proc
command (see Process Information), you can
use the info proc
command to find out the
current working directory of the debuggee.
By default, the program you run under gdb does input and output to the same terminal that gdb uses. gdb switches the terminal to its own terminal modes to interact with you, but it records the terminal modes your program was using and switches back to them when you continue running your program.
info terminal
You can redirect your program's input and/or output using shell
redirection with the run
command. For example,
run > outfile
starts your program, diverting its output to the file outfile.
Another way to specify where your program should do input and output is
with the tty
command. This command accepts a file name as
argument, and causes this file to be the default for future run
commands. It also resets the controlling terminal for the child
process, for future run
commands. For example,
tty /dev/ttyb
directs that processes started with subsequent run
commands
default to do input and output on the terminal /dev/ttyb and have
that as their controlling terminal.
An explicit redirection in run
overrides the tty
command's
effect on the input/output device, but not its effect on the controlling
terminal.
When you use the tty
command or redirect input in the run
command, only the input for your program is affected. The input
for gdb still comes from your terminal. tty
is an alias
for set inferior-tty
.
You can use the show inferior-tty
command to tell gdb to
display the name of the terminal that will be used for future runs of your
program.
set inferior-tty [
tty ]
show inferior-tty
attach
process-idinfo files
shows your active
targets.) The command takes as argument a process ID. The usual way to
find out the process-id of a Unix process is with the ps
utility,
or with the ‘jobs -l’ shell command.
attach
does not repeat if you press <RET> a second time after
executing the command.
To use attach
, your program must be running in an environment
which supports processes; for example, attach
does not work for
programs on bare-board targets that lack an operating system. You must
also have permission to send the process a signal.
When you use attach
, the debugger finds the program running in
the process first by looking in the current working directory, then (if
the program is not found) by using the source file search path
(see Specifying Source Directories). You can also use
the file
command to load the program. See Commands to Specify Files.
The first thing gdb does after arranging to debug the specified
process is to stop it. You can examine and modify an attached process
with all the gdb commands that are ordinarily available when
you start processes with run
. You can insert breakpoints; you
can step and continue; you can modify storage. If you would rather the
process continue running, you may use the continue
command after
attaching gdb to the process.
detach
detach
command to release it from gdb control. Detaching
the process continues its execution. After the detach
command,
that process and gdb become completely independent once more, and you
are ready to attach
another process or start one with run
.
detach
does not repeat if you press <RET> again after
executing the command.
If you exit gdb while you have an attached process, you detach
that process. If you use the run
command, you kill that process.
By default, gdb asks for confirmation if you try to do either of these
things; you can control whether or not you need to confirm by using the
set confirm
command (see Optional Warnings and Messages).
kill
This command is useful if you wish to debug a core dump instead of a running process. gdb ignores any core dump file while your program is running.
On some operating systems, a program cannot be executed outside gdb
while you have breakpoints set on it inside gdb. You can use the
kill
command in this situation to permit running your program
outside the debugger.
The kill
command is also useful if you wish to recompile and
relink your program, since on many systems it is impossible to modify an
executable file while it is running in a process. In this case, when you
next type run
, gdb notices that the file has changed, and
reads the symbol table again (while trying to preserve your current
breakpoint settings).
gdb lets you run and debug multiple programs in a single session. In addition, gdb on some systems may let you run several programs simultaneously (otherwise you have to exit from one before starting another). In the most general case, you can have multiple threads of execution in each of multiple processes, launched from multiple executables.
gdb represents the state of each program execution with an object called an inferior. An inferior typically corresponds to a process, but is more general and applies also to targets that do not have processes. Inferiors may be created before a process runs, and may be retained after a process exits. Inferiors have unique identifiers that are different from process ids. Usually each inferior will also have its own distinct address space, although some embedded targets may have several inferiors running in different parts of a single address space. Each inferior may in turn have multiple threads running in it.
To find out what inferiors exist at any moment, use info inferiors
:
info inferiors
gdb displays for each inferior (in this order):
An asterisk ‘*’ preceding the gdb inferior number indicates the current inferior.
For example,
(gdb) info inferiors Num Description Executable 2 process 2307 hello * 1 process 3401 goodbye
To switch focus between inferiors, use the inferior
command:
inferior
infnoThe debugger convenience variable ‘$_inferior’ contains the number of the current inferior. You may find this useful in writing breakpoint conditional expressions, command scripts, and so forth. See Convenience Variables, for general information on convenience variables.
You can get multiple executables into a debugging session via the
add-inferior
and clone-inferior
commands. On some
systems gdb can add inferiors to the debug session
automatically by following calls to fork
and exec
. To
remove inferiors from the debugging session use the
remove-inferiors
command.
add-inferior [ -copies
n ] [ -exec
executable ]
file
command with the executable name as its argument.
clone-inferior [ -copies
n ] [
infno ]
(gdb) info inferiors Num Description Executable * 1 process 29964 helloworld (gdb) clone-inferior Added inferior 2. 1 inferiors added. (gdb) info inferiors Num Description Executable 2 <null> helloworld * 1 process 29964 helloworld
You can now simply switch focus to inferior 2 and run it.
remove-inferiors
infno...
kill
or detach
command first.
To quit debugging one of the running inferiors that is not the current
inferior, you can either detach from it by using the detach inferior
command (allowing it to run independently), or kill it
using the kill inferiors
command:
detach inferior
infno...
info inferiors
,
but its Description will show ‘<null>’.
kill inferiors
infno...
info inferiors
, but its
Description will show ‘<null>’.
After the successful completion of a command such as detach
,
detach inferiors
, kill
or kill inferiors
, or after
a normal process exit, the inferior is still valid and listed with
info inferiors
, ready to be restarted.
To be notified when inferiors are started or exit under gdb's
control use set print inferior-events
:
set print inferior-events
set print inferior-events on
set print inferior-events off
set print inferior-events
command allows you to enable or
disable printing of messages when gdb notices that new
inferiors have started or that inferiors have exited or have been
detached. By default, these messages will not be printed.
show print inferior-events
Many commands will work the same with multiple programs as with a
single program: e.g., print myglobal
will simply display the
value of myglobal
in the current inferior.
Occasionally, when debugging gdb itself, it may be useful to
get more info about the relationship of inferiors, programs, address
spaces in a debug session. You can do that with the maint info program-spaces
command.
maint info program-spaces
gdb displays for each program space (in this order):
file
command.
An asterisk ‘*’ preceding the gdb program space number indicates the current program space.
In addition, below each program space line, gdb prints extra information that isn't suitable to display in tabular form. For example, the list of inferiors bound to the program space.
(gdb) maint info program-spaces Id Executable * 1 hello 2 goodbye Bound inferiors: ID 1 (process 21561)
Here we can see that no inferior is running the program hello
,
while process 21561
is running the program goodbye
. On
some targets, it is possible that multiple inferiors are bound to the
same program space. The most common example is that of debugging both
the parent and child processes of a vfork
call. For example,
(gdb) maint info program-spaces Id Executable * 1 vfork-test Bound inferiors: ID 2 (process 18050), ID 1 (process 18045)
Here, both inferior 2 and inferior 1 are running in the same program
space as a result of inferior 1 having executed a vfork
call.
In some operating systems, such as GNU/Linux and Solaris, a single program may have more than one thread of execution. The precise semantics of threads differ from one operating system to another, but in general the threads of a single program are akin to multiple processes—except that they share one address space (that is, they can all examine and modify the same variables). On the other hand, each thread has its own registers and execution stack, and perhaps private memory.
gdb provides these facilities for debugging multi-thread programs:
libthread_db
to use if the default choice
isn't compatible with the program.
The gdb thread debugging facility allows you to observe all threads while your program runs—but whenever gdb takes control, one thread in particular is always the focus of debugging. This thread is called the current thread. Debugging commands show program information from the perspective of the current thread.
Whenever gdb detects a new thread in your program, it displays the target system's identification for the thread with a message in the form ‘[New systag]’, where systag is a thread identifier whose form varies depending on the particular system. For example, on gnu/Linux, you might see
[New Thread 0x41e02940 (LWP 25582)]
when gdb notices a new thread. In contrast, on other systems, the systag is simply something like ‘process 368’, with no further qualifier.
For debugging purposes, gdb associates its own thread number —always a single integer—with each thread of an inferior. This number is unique between all threads of an inferior, but not unique between threads of different inferiors.
You can refer to a given thread in an inferior using the qualified
inferior-num.thread-num syntax, also known as
qualified thread ID, with inferior-num being the inferior
number and thread-num being the thread number of the given
inferior. For example, thread 2.3
refers to thread number 3 of
inferior 2. If you omit inferior-num (e.g., thread 3
),
then gdb infers you're referring to a thread of the current
inferior.
Until you create a second inferior, gdb does not show the inferior-num part of thread IDs, even though you can always use the full inferior-num.thread-num form to refer to threads of inferior 1, the initial inferior.
Some commands accept a space-separated thread ID list as argument. A list element can be:
*
(e.g.,
‘1.*’) or *
. The former refers to all threads of the
given inferior, and the latter form without an inferior qualifier
refers to all threads of the current inferior.
For example, if the current inferior is 1, and inferior 7 has one thread with ID 7.1, the thread list ‘1 2-3 4.5 6.7-9 7.*’ includes threads 1 to 3 of inferior 1, thread 5 of inferior 4, threads 7 to 9 of inferior 6 and all threads of inferior 7. That is, in expanded qualified form, the same as ‘1.1 1.2 1.3 4.5 6.7 6.8 6.9 7.1’.
In addition to a per-inferior number, each thread is also assigned a unique global number, also known as global thread ID, a single integer. Unlike the thread number component of the thread ID, no two threads have the same global ID, even when you're debugging multiple inferiors.
From gdb's perspective, a process always has at least one thread. In other words, gdb assigns a thread number to the program's “main thread” even if the program is not multi-threaded.
The debugger convenience variables ‘$_thread’ and ‘$_gthread’ contain, respectively, the per-inferior thread number and the global thread number of the current thread. You may find this useful in writing breakpoint conditional expressions, command scripts, and so forth. See Convenience Variables, for general information on convenience variables.
If gdb detects the program is multi-threaded, it augments the usual message about stopping at a breakpoint with the ID and name of the thread that hit the breakpoint.
Thread 2 "client" hit Breakpoint 1, send_message () at client.c:68
Likewise when the program receives a signal:
Thread 1 "main" received signal SIGINT, Interrupt.
info threads
[thread-id-list]gdb displays for each thread (in this order):
thread name
, below), or, in some cases, by the
program itself.
An asterisk ‘*’ to the left of the gdb thread number indicates the current thread.
For example,
(gdb) info threads Id Target Id Frame * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8) 2 process 35 thread 23 0x34e5 in sigpause () 3 process 35 thread 27 0x34e5 in sigpause () at threadtest.c:68
If you're debugging multiple inferiors, gdb displays thread IDs using the qualified inferior-num.thread-num format. Otherwise, only thread-num is shown.
If you specify the ‘-gid’ option, gdb displays a column indicating each thread's global thread ID:
(gdb) info threads Id GId Target Id Frame 1.1 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8) 1.2 3 process 35 thread 23 0x34e5 in sigpause () 1.3 4 process 35 thread 27 0x34e5 in sigpause () * 2.1 2 process 65 thread 1 main (argc=1, argv=0x7ffffff8)
On Solaris, you can display more information about user threads with a Solaris-specific command:
maint info sol-threads
thread
thread-idgdb responds by displaying the system identifier of the thread you selected, and its current stack frame summary:
(gdb) thread 2 [Switching to thread 2 (Thread 0xb7fdab70 (LWP 12747))] #0 some_function (ignore=0x0) at example.c:8 8 printf ("hello\n");
As with the ‘[New ...]’ message, the form of the text after ‘Switching to’ depends on your system's conventions for identifying threads.
thread apply [
thread-id-list | all [-ascending]] [
flag]...
commandthread apply
command allows you to apply the named
command to one or more threads. Specify the threads that you
want affected using the thread ID list syntax (see thread ID lists), or specify all
to apply to all threads. To apply a
command to all threads in descending order, type thread apply all
command. To apply a command to all threads in ascending order,
type thread apply all -ascending command.
The flag arguments control what output to produce and how to handle
errors raised when applying command to a thread. flag
must start with a -
directly followed by one letter in
qcs
. If several flags are provided, they must be given
individually, such as -c -q
.
By default, gdb displays some thread information before the
output produced by command, and an error raised during the
execution of a command will abort thread apply
. The
following flags can be used to fine-tune this behavior:
-c
-c
, which stands for ‘continue’, causes any
errors in command to be displayed, and the execution of
thread apply
then continues.
-s
-s
, which stands for ‘silent’, causes any errors
or empty output produced by a command to be silently ignored.
That is, the execution continues, but the thread information and errors
are not printed.
-q
-q
(‘quiet’) disables printing the thread
information.
Flags -c
and -s
cannot be used together.
taas [
option]...
commandthread apply all -s [
option]...
command.
Applies command on all threads, ignoring errors and empty output.
The taas
command accepts the same options as the thread
apply all
command. See thread apply all.
tfaas [
option]...
commandthread apply all -s -- frame apply all -s [
option]...
command.
Applies command on all frames of all threads, ignoring errors
and empty output. Note that the flag -s
is specified twice:
The first -s
ensures that thread apply
only shows the thread
information of the threads for which frame apply
produces
some output. The second -s
is needed to ensure that frame
apply
shows the frame information of a frame only if the
command successfully produced some output.
It can for example be used to print a local variable or a function argument without knowing the thread or frame where this variable or argument is, using:
(gdb) tfaas p some_local_var_i_do_not_remember_where_it_is
The tfaas
command accepts the same options as the frame
apply
command. See frame apply.
thread name [
name]
On some systems, such as gnu/Linux, gdb is able to determine the name of the thread as given by the OS. On these systems, a name specified with ‘thread name’ will override the system-give name, and removing the user-specified name will cause gdb to once again display the system-specified name.
thread find [
regexp]
As well as being the complement to the ‘thread name’ command, this command also allows you to identify a thread by its target systag. For instance, on gnu/Linux, the target systag is the LWP id.
(gdb) thread find 26688 Thread 4 has target id 'Thread 0x41e02940 (LWP 26688)' (gdb) info thread 4 Id Target Id Frame 4 Thread 0x41e02940 (LWP 26688) 0x00000031ca6cd372 in select ()
set print thread-events
set print thread-events on
set print thread-events off
set print thread-events
command allows you to enable or
disable printing of messages when gdb notices that new threads have
started or that threads have exited. By default, these messages will
be printed if detection of these events is supported by the target.
Note that these messages cannot be disabled on all targets.
show print thread-events
See Stopping and Starting Multi-thread Programs, for more information about how gdb behaves when you stop and start programs with multiple threads.
See Setting Watchpoints, for information about watchpoints in programs with multiple threads.
set libthread-db-search-path
[path]libthread_db
.
If you omit path, ‘libthread-db-search-path’ will be reset to
its default value ($sdir:$pdir
on gnu/Linux and Solaris systems).
Internally, the default value comes from the LIBTHREAD_DB_SEARCH_PATH
macro.
On gnu/Linux and Solaris systems, gdb uses a “helper”
libthread_db
library to obtain information about threads in the
inferior process. gdb will use ‘libthread-db-search-path’
to find libthread_db
. gdb also consults first if inferior
specific thread debugging library loading is enabled
by ‘set auto-load libthread-db’ (see libthread_db.so.1 file).
A special entry ‘$sdir’ for ‘libthread-db-search-path’ refers to the default system directories that are normally searched for loading shared libraries. The ‘$sdir’ entry is the only kind not needing to be enabled by ‘set auto-load libthread-db’ (see libthread_db.so.1 file).
A special entry ‘$pdir’ for ‘libthread-db-search-path’
refers to the directory from which libpthread
was loaded in the inferior process.
For any libthread_db
library gdb finds in above directories,
gdb attempts to initialize it with the current inferior process.
If this initialization fails (which could happen because of a version
mismatch between libthread_db
and libpthread
), gdb
will unload libthread_db
, and continue with the next directory.
If none of libthread_db
libraries initialize successfully,
gdb will issue a warning and thread debugging will be disabled.
Setting libthread-db-search-path
is currently implemented
only on some platforms.
show libthread-db-search-path
set debug libthread-db
show debug libthread-db
libthread_db
-related events.
Use 1
to enable, 0
to disable.
On most systems, gdb has no special support for debugging
programs which create additional processes using the fork
function. When a program forks, gdb will continue to debug the
parent process and the child process will run unimpeded. If you have
set a breakpoint in any code which the child then executes, the child
will get a SIGTRAP
signal which (unless it catches the signal)
will cause it to terminate.
However, if you want to debug the child process there is a workaround
which isn't too painful. Put a call to sleep
in the code which
the child process executes after the fork. It may be useful to sleep
only if a certain environment variable is set, or a certain file exists,
so that the delay need not occur when you don't want to run gdb
on the child. While the child is sleeping, use the ps
program to
get its process ID. Then tell gdb (a new invocation of
gdb if you are also debugging the parent process) to attach to
the child process (see Attach). From that point on you can debug
the child process just like any other process which you attached to.
On some systems, gdb provides support for debugging programs
that create additional processes using the fork
or vfork
functions. On gnu/Linux platforms, this feature is supported
with kernel version 2.5.46 and later.
The fork debugging commands are supported in native mode and when
connected to gdbserver
in either target remote
mode or
target extended-remote
mode.
By default, when a program forks, gdb will continue to debug the parent process and the child process will run unimpeded.
If you want to follow the child process instead of the parent process,
use the command set follow-fork-mode
.
set follow-fork-mode
modefork
or
vfork
. A call to fork
or vfork
creates a new
process. The mode argument can be:
parent
child
show follow-fork-mode
fork
or vfork
call.
On Linux, if you want to debug both the parent and child processes, use the
command set detach-on-fork
.
set detach-on-fork
modeon
follow-fork-mode
) will be detached and allowed to run
independently. This is the default.
off
follow-fork-mode
) is debugged as usual, while the other
is held suspended.
show detach-on-fork
If you choose to set ‘detach-on-fork’ mode off, then gdb
will retain control of all forked processes (including nested forks).
You can list the forked processes under the control of gdb by
using the info inferiors
command, and switch from one fork
to another by using the inferior
command (see Debugging Multiple Inferiors and Programs).
To quit debugging one of the forked processes, you can either detach
from it by using the detach inferiors
command (allowing it
to run independently), or kill it using the kill inferiors
command. See Debugging Multiple Inferiors and Programs.
If you ask to debug a child process and a vfork
is followed by an
exec
, gdb executes the new target up to the first
breakpoint in the new target. If you have a breakpoint set on
main
in your original program, the breakpoint will also be set on
the child process's main
.
On some systems, when a child process is spawned by vfork
, you
cannot debug the child or parent until an exec
call completes.
If you issue a run
command to gdb after an exec
call executes, the new target restarts. To restart the parent
process, use the file
command with the parent executable name
as its argument. By default, after an exec
call executes,
gdb discards the symbols of the previous executable image.
You can change this behaviour with the set follow-exec-mode
command.
set follow-exec-mode
modeexec
. An
exec
call replaces the program image of a process.
follow-exec-mode
can be:
new
exec
call can be restarted afterwards by restarting the
original inferior.
For example:
(gdb) info inferiors (gdb) info inferior Id Description Executable * 1 <null> prog1 (gdb) run process 12020 is executing new program: prog2 Program exited normally. (gdb) info inferiors Id Description Executable 1 <null> prog1 * 2 <null> prog2
same
exec
call, with
e.g., the run
command, restarts the executable the process was
running after the exec
call. This is the default mode.
For example:
(gdb) info inferiors Id Description Executable * 1 <null> prog1 (gdb) run process 12020 is executing new program: prog2 Program exited normally. (gdb) info inferiors Id Description Executable * 1 <null> prog2
follow-exec-mode
is supported in native mode and
target extended-remote
mode.
You can use the catch
command to make gdb stop whenever
a fork
, vfork
, or exec
call is made. See Setting Catchpoints.
On certain operating systems3, gdb is able to save a snapshot of a program's state, called a checkpoint, and come back to it later.
Returning to a checkpoint effectively undoes everything that has
happened in the program since the checkpoint
was saved. This
includes changes in memory, registers, and even (within some limits)
system state. Effectively, it is like going back in time to the
moment when the checkpoint was saved.
Thus, if you're stepping thru a program and you think you're getting close to the point where things go wrong, you can save a checkpoint. Then, if you accidentally go too far and miss the critical statement, instead of having to restart your program from the beginning, you can just go back to the checkpoint and start again from there.
This can be especially useful if it takes a lot of time or steps to reach the point where you think the bug occurs.
To use the checkpoint
/restart
method of debugging:
checkpoint
checkpoint
command takes no arguments, but each checkpoint
is assigned a small integer id, similar to a breakpoint id.
info checkpoints
Checkpoint ID
Process ID
Code Address
Source line, or label
restart
checkpoint-idNote that breakpoints, gdb variables, command history etc. are not affected by restoring a checkpoint. In general, a checkpoint only restores things that reside in the program being debugged, not in the debugger.
delete checkpoint
checkpoint-idReturning to a previously saved checkpoint will restore the user state of the program being debugged, plus a significant subset of the system (OS) state, including file pointers. It won't “un-write” data from a file, but it will rewind the file pointer to the previous location, so that the previously written data can be overwritten. For files opened in read mode, the pointer will also be restored so that the previously read data can be read again.
Of course, characters that have been sent to a printer (or other external device) cannot be “snatched back”, and characters received from eg. a serial device can be removed from internal program buffers, but they cannot be “pushed back” into the serial pipeline, ready to be received again. Similarly, the actual contents of files that have been changed cannot be restored (at this time).
However, within those constraints, you actually can “rewind” your program to a previously saved point in time, and begin debugging it again — and you can change the course of events so as to debug a different execution path this time.
Finally, there is one bit of internal program state that will be different when you return to a checkpoint — the program's process id. Each checkpoint will have a unique process id (or pid), and each will be different from the program's original pid. If your program has saved a local copy of its process id, this could potentially pose a problem.
On some systems such as gnu/Linux, address space randomization is performed on new processes for security reasons. This makes it difficult or impossible to set a breakpoint, or watchpoint, on an absolute address if you have to restart the program, since the absolute location of a symbol will change from one execution to the next.
A checkpoint, however, is an identical copy of a process. Therefore if you create a checkpoint at (eg.) the start of main, and simply return to that checkpoint instead of restarting the process, you can avoid the effects of address randomization and your symbols will all stay in the same place.
The principal purposes of using a debugger are so that you can stop your program before it terminates; or so that, if your program runs into trouble, you can investigate and find out why.
Inside gdb, your program may stop for any of several reasons,
such as a signal, a breakpoint, or reaching a new line after a
gdb command such as step
. You may then examine and
change variables, set new breakpoints or remove old ones, and then
continue execution. Usually, the messages shown by gdb provide
ample explanation of the status of your program—but you can also
explicitly request this information at any time.
info program
A breakpoint makes your program stop whenever a certain point in
the program is reached. For each breakpoint, you can add conditions to
control in finer detail whether your program stops. You can set
breakpoints with the break
command and its variants (see Setting Breakpoints), to specify the place where your program
should stop by line number, function name or exact address in the
program.
On some systems, you can set breakpoints in shared libraries before the executable is run.
A watchpoint is a special breakpoint that stops your program when the value of an expression changes. The expression may be a value of a variable, or it could involve values of one or more variables combined by operators, such as ‘a + b’. This is sometimes called data breakpoints. You must use a different command to set watchpoints (see Setting Watchpoints), but aside from that, you can manage a watchpoint like any other breakpoint: you enable, disable, and delete both breakpoints and watchpoints using the same commands.
You can arrange to have values from your program displayed automatically whenever gdb stops at a breakpoint. See Automatic Display.
A catchpoint is another special breakpoint that stops your program
when a certain kind of event occurs, such as the throwing of a C++
exception or the loading of a library. As with watchpoints, you use a
different command to set a catchpoint (see Setting Catchpoints), but aside from that, you can manage a catchpoint like any
other breakpoint. (To stop when your program receives a signal, use the
handle
command; see Signals.)
gdb assigns a number to each breakpoint, watchpoint, or catchpoint when you create it; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be enabled or disabled; if disabled, it has no effect on your program until you enable it again.
Some gdb commands accept a space-separated list of breakpoints on which to operate. A list element can be either a single breakpoint number, like ‘5’, or a range of such numbers, like ‘5-7’. When a breakpoint list is given to a command, all breakpoints in that list are operated on.
Breakpoints are set with the break
command (abbreviated
b
). The debugger convenience variable ‘$bpnum’ records the
number of the breakpoint you've set most recently; see Convenience Variables, for a discussion of what you can do with
convenience variables.
break
locationWhen using source languages that permit overloading of symbols, such as C++, a function name may refer to more than one possible place to break. See Ambiguous Expressions, for a discussion of that situation.
It is also possible to insert a breakpoint that will stop the program
only if a specific thread (see Thread-Specific Breakpoints)
or a specific task (see Ada Tasks) hits that breakpoint.
break
break
sets a breakpoint at
the next instruction to be executed in the selected stack frame
(see Examining the Stack). In any selected frame but the
innermost, this makes your program stop as soon as control
returns to that frame. This is similar to the effect of a
finish
command in the frame inside the selected frame—except
that finish
does not leave an active breakpoint. If you use
break
without an argument in the innermost frame, gdb stops
the next time it reaches the current location; this may be useful
inside loops.
gdb normally ignores breakpoints when it resumes execution, until at
least one instruction has been executed. If it did not do this, you
would be unable to proceed past a breakpoint without first disabling the
breakpoint. This rule applies whether or not the breakpoint already
existed when your program stopped.
break ... if
condtbreak
argsbreak
command, and the breakpoint is set in the same
way, but the breakpoint is automatically deleted after the first time your
program stops there. See Disabling Breakpoints.
hbreak
argsbreak
command and the breakpoint is set in the same way, but the
breakpoint requires hardware support and some target hardware may not
have this support. The main purpose of this is EPROM/ROM code
debugging, so you can set a breakpoint at an instruction without
changing the instruction. This can be used with the new trap-generation
provided by SPARClite DSU and most x86-based targets. These targets
will generate traps when a program accesses some data or instruction
address that is assigned to the debug registers. However the hardware
breakpoint registers can take a limited number of breakpoints. For
example, on the DSU, only two data breakpoints can be set at a time, and
gdb will reject this command if more than two are used. Delete
or disable unused hardware breakpoints before setting new ones
(see Disabling Breakpoints).
See Break Conditions.
For remote targets, you can restrict the number of hardware
breakpoints gdb will use, see set remote hardware-breakpoint-limit.
thbreak
argshbreak
command and the breakpoint is set in
the same way. However, like the tbreak
command,
the breakpoint is automatically deleted after the
first time your program stops there. Also, like the hbreak
command, the breakpoint requires hardware support and some target hardware
may not have this support. See Disabling Breakpoints.
See also Break Conditions.
rbreak
regexbreak
command. You can delete them, disable them, or make
them conditional the same way as any other breakpoint.
In programs using different languages, gdb chooses the syntax to print the list of all breakpoints it sets according to the ‘set language’ value: using ‘set language auto’ (see Set Language Automatically) means to use the language of the breakpoint's function, other values mean to use the manually specified language (see Set Language Manually).
The syntax of the regular expression is the standard one used with tools
like grep. Note that this is different from the syntax used by
shells, so for instance foo*
matches all functions that include
an fo
followed by zero or more o
s. There is an implicit
.*
leading and trailing the regular expression you supply, so to
match only functions that begin with foo
, use ^foo
.
When debugging C++ programs, rbreak
is useful for setting
breakpoints on overloaded functions that are not members of any special
classes.
The rbreak
command can be used to set breakpoints in
all the functions in a program, like this:
(gdb) rbreak .
rbreak
file:
regexrbreak
is called with a filename qualification, it limits
the search for functions matching the given regular expression to the
specified file. This can be used, for example, to set breakpoints on
every function in a given file:
(gdb) rbreak file.c:.
The colon separating the filename qualifier from the regex may optionally be surrounded by spaces.
info breakpoints
[list...
]info break
[list...
]If a breakpoint is conditional, there are two evaluation modes: “host” and
“target”. If mode is “host”, breakpoint condition evaluation is done by
gdb on the host's side. If it is “target”, then the condition
is evaluated by the target. The info break
command shows
the condition on the line following the affected breakpoint, together with
its condition evaluation mode in between parentheses.
Breakpoint commands, if any, are listed after that. A pending breakpoint is allowed to have a condition specified for it. The condition is not parsed for validity until a shared library is loaded that allows the pending breakpoint to resolve to a valid location.
info break
with a breakpoint
number n as argument lists only that breakpoint. The
convenience variable $_
and the default examining-address for
the x
command are set to the address of the last breakpoint
listed (see Examining Memory).
info break
displays a count of the number of times the breakpoint
has been hit. This is especially useful in conjunction with the
ignore
command. You can ignore a large number of breakpoint
hits, look at the breakpoint info to see how many times the breakpoint
was hit, and then run again, ignoring one less than that number. This
will get you quickly to the last hit of that breakpoint.
For a breakpoints with an enable count (xref) greater than 1,
info break
also displays that count.
gdb allows you to set any number of breakpoints at the same place in your program. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (see Break Conditions).
It is possible that a breakpoint corresponds to several locations in your program. Examples of this situation are:
In all those cases, gdb will insert a breakpoint at all the relevant locations.
A breakpoint with multiple locations is displayed in the breakpoint table using several rows—one header row, followed by one row for each breakpoint location. The header row has ‘<MULTIPLE>’ in the address column. The rows for individual locations contain the actual addresses for locations, and show the functions to which those locations belong. The number column for a location is of the form breakpoint-number.location-number.
For example:
Num Type Disp Enb Address What 1 breakpoint keep y <MULTIPLE> stop only if i==1 breakpoint already hit 1 time 1.1 y 0x080486a2 in void foo<int>() at t.cc:8 1.2 y 0x080486ca in void foo<double>() at t.cc:8
You cannot delete the individual locations from a breakpoint. However,
each location can be individually enabled or disabled by passing
breakpoint-number.location-number as argument to the
enable
and disable
commands. It's also possible to
enable
and disable
a range of location-number
locations using a breakpoint-number and two location-numbers,
in increasing order, separated by a hyphen, like
breakpoint-number.location-number1-location-number2,
in which case gdb acts on all the locations in the range (inclusive).
Disabling or enabling the parent breakpoint (see Disabling) affects
all of the locations that belong to that breakpoint.
It's quite common to have a breakpoint inside a shared library. Shared libraries can be loaded and unloaded explicitly, and possibly repeatedly, as the program is executed. To support this use case, gdb updates breakpoint locations whenever any shared library is loaded or unloaded. Typically, you would set a breakpoint in a shared library at the beginning of your debugging session, when the library is not loaded, and when the symbols from the library are not available. When you try to set breakpoint, gdb will ask you if you want to set a so called pending breakpoint—breakpoint whose address is not yet resolved.
After the program is run, whenever a new shared library is loaded, gdb reevaluates all the breakpoints. When a newly loaded shared library contains the symbol or line referred to by some pending breakpoint, that breakpoint is resolved and becomes an ordinary breakpoint. When a library is unloaded, all breakpoints that refer to its symbols or source lines become pending again.
This logic works for breakpoints with multiple locations, too. For example, if you have a breakpoint in a C++ template function, and a newly loaded shared library has an instantiation of that template, a new location is added to the list of locations for the breakpoint.
Except for having unresolved address, pending breakpoints do not differ from regular breakpoints. You can set conditions or commands, enable and disable them and perform other breakpoint operations.
gdb provides some additional commands for controlling what happens when the ‘break’ command cannot resolve breakpoint address specification to an address:
set breakpoint pending auto
set breakpoint pending on
set breakpoint pending off
show breakpoint pending
The settings above only affect the break
command and its
variants. Once breakpoint is set, it will be automatically updated
as shared libraries are loaded and unloaded.
For some targets, gdb can automatically decide if hardware or
software breakpoints should be used, depending on whether the
breakpoint address is read-only or read-write. This applies to
breakpoints set with the break
command as well as to internal
breakpoints set by commands like next
and finish
. For
breakpoints set with hbreak
, gdb will always use hardware
breakpoints.
You can control this automatic behaviour with the following commands:
set breakpoint auto-hw on
set breakpoint auto-hw off
gdb normally implements breakpoints by replacing the program code at the breakpoint address with a special instruction, which, when executed, given control to the debugger. By default, the program code is so modified only when the program is resumed. As soon as the program stops, gdb restores the original instructions. This behaviour guards against leaving breakpoints inserted in the target should gdb abrubptly disconnect. However, with slow remote targets, inserting and removing breakpoint can reduce the performance. This behavior can be controlled with the following commands::
set breakpoint always-inserted off
set breakpoint always-inserted on
gdb handles conditional breakpoints by evaluating these conditions when a breakpoint breaks. If the condition is true, then the process being debugged stops, otherwise the process is resumed.
If the target supports evaluating conditions on its end, gdb may download the breakpoint, together with its conditions, to it.
This feature can be controlled via the following commands:
set breakpoint condition-evaluation host
set breakpoint condition-evaluation target
set breakpoint condition-evaluation auto
gdb itself sometimes sets breakpoints in your program for
special purposes, such as proper handling of longjmp
(in C
programs). These internal breakpoints are assigned negative numbers,
starting with -1
; ‘info breakpoints’ does not display them.
You can see these breakpoints with the gdb maintenance command
‘maint info breakpoints’ (see maint info breakpoints).
You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place where this may happen. (This is sometimes called a data breakpoint.) The expression may be as simple as the value of a single variable, or as complex as many variables combined by operators. Examples include:
int
occupies 4 bytes).
You can set a watchpoint on an expression even if the expression can
not be evaluated yet. For instance, you can set a watchpoint on
‘*global_ptr’ before ‘global_ptr’ is initialized.
gdb will stop when your program sets ‘global_ptr’ and
the expression produces a valid value. If the expression becomes
valid in some other way than changing a variable (e.g. if the memory
pointed to by ‘*global_ptr’ becomes readable as the result of a
malloc
call), gdb may not stop until the next time
the expression changes.
Depending on your system, watchpoints may be implemented in software or hardware. gdb does software watchpointing by single-stepping your program and testing the variable's value each time, which is hundreds of times slower than normal execution. (But this may still be worth it, to catch errors where you have no clue what part of your program is the culprit.)
On some systems, such as most PowerPC or x86-based targets, gdb includes support for hardware watchpoints, which do not slow down the running of your program.
watch
[-l
|-location
] expr [thread
thread-id] [mask
maskvalue](gdb) watch foo
If the command includes a [thread
thread-id]
argument, gdb breaks only when the thread identified by
thread-id changes the value of expr. If any other threads
change the value of expr, gdb will not break. Note
that watchpoints restricted to a single thread in this way only work
with Hardware Watchpoints.
Ordinarily a watchpoint respects the scope of variables in expr
(see below). The -location
argument tells gdb to
instead watch the memory referred to by expr. In this case,
gdb will evaluate expr, take the address of the result,
and watch the memory at that address. The type of the result is used
to determine the size of the watched memory. If the expression's
result does not have an address, then gdb will print an
error.
The [mask
maskvalue] argument allows creation
of masked watchpoints, if the current architecture supports this
feature (e.g., PowerPC Embedded architecture, see PowerPC Embedded.) A masked watchpoint specifies a mask in addition
to an address to watch. The mask specifies that some bits of an address
(the bits which are reset in the mask) should be ignored when matching
the address accessed by the inferior against the watchpoint address.
Thus, a masked watchpoint watches many addresses simultaneously—those
addresses whose unmasked bits are identical to the unmasked bits in the
watchpoint address. The mask
argument implies -location
.
Examples:
(gdb) watch foo mask 0xffff00ff (gdb) watch *0xdeadbeef mask 0xffffff00
rwatch
[-l
|-location
] expr [thread
thread-id] [mask
maskvalue]awatch
[-l
|-location
] expr [thread
thread-id] [mask
maskvalue]info watchpoints
[list...
]info break
(see Set Breaks).
If you watch for a change in a numerically entered address you need to dereference it, as the address itself is just a constant number which will never change. gdb refuses to create a watchpoint that watches a never-changing value:
(gdb) watch 0x600850 Cannot watch constant value 0x600850. (gdb) watch *(int *) 0x600850 Watchpoint 1: *(int *) 6293584
gdb sets a hardware watchpoint if possible. Hardware watchpoints execute very quickly, and the debugger reports a change in value at the exact instruction where the change occurs. If gdb cannot set a hardware watchpoint, it sets a software watchpoint, which executes more slowly and reports the change in value at the next statement, not the instruction, after the change occurs.
You can force gdb to use only software watchpoints with the
set can-use-hw-watchpoints 0 command. With this variable set to
zero, gdb will never try to use hardware watchpoints, even if
the underlying system supports them. (Note that hardware-assisted
watchpoints that were set before setting
can-use-hw-watchpoints
to zero will still use the hardware
mechanism of watching expression values.)
set can-use-hw-watchpoints
show can-use-hw-watchpoints
For remote targets, you can restrict the number of hardware watchpoints gdb will use, see set remote hardware-breakpoint-limit.
When you issue the watch
command, gdb reports
Hardware watchpoint num: expr
if it was able to set a hardware watchpoint.
Currently, the awatch
and rwatch
commands can only set
hardware watchpoints, because accesses to data that don't change the
value of the watched expression cannot be detected without examining
every instruction as it is being executed, and gdb does not do
that currently. If gdb finds that it is unable to set a
hardware breakpoint with the awatch
or rwatch
command, it
will print a message like this:
Expression cannot be implemented with read/access watchpoint.
Sometimes, gdb cannot set a hardware watchpoint because the data type of the watched expression is wider than what a hardware watchpoint on the target machine can handle. For example, some systems can only watch regions that are up to 4 bytes wide; on such systems you cannot set hardware watchpoints for an expression that yields a double-precision floating-point number (which is typically 8 bytes wide). As a work-around, it might be possible to break the large region into a series of smaller ones and watch them with separate watchpoints.
If you set too many hardware watchpoints, gdb might be unable to insert all of them when you resume the execution of your program. Since the precise number of active watchpoints is unknown until such time as the program is about to be resumed, gdb might not be able to warn you about this when you set the watchpoints, and the warning will be printed only when the program is resumed:
Hardware watchpoint num: Could not insert watchpoint
If this happens, delete or disable some of the watchpoints.
Watching complex expressions that reference many variables can also exhaust the resources available for hardware-assisted watchpoints. That's because gdb needs to watch every variable in the expression with separately allocated resources.
If you call a function interactively using print
or call
,
any watchpoints you have set will be inactive until gdb reaches another
kind of breakpoint or the call completes.
gdb automatically deletes watchpoints that watch local
(automatic) variables, or expressions that involve such variables, when
they go out of scope, that is, when the execution leaves the block in
which these variables were defined. In particular, when the program
being debugged terminates, all local variables go out of scope,
and so only watchpoints that watch global variables remain set. If you
rerun the program, you will need to set all such watchpoints again. One
way of doing that would be to set a code breakpoint at the entry to the
main
function and when it breaks, set all the watchpoints.
In multi-threaded programs, watchpoints will detect changes to the watched expression from every thread.
Warning: In multi-threaded programs, software watchpoints have only limited usefulness. If gdb creates a software watchpoint, it can only watch the value of an expression in a single thread. If you are confident that the expression can only change due to the current thread's activity (and if you are also confident that no other thread can become current), then you can use software watchpoints as usual. However, gdb may not notice when a non-current thread's activity changes the expression. (Hardware watchpoints, in contrast, watch an expression in all threads.)
See set remote hardware-watchpoint-limit.
You can use catchpoints to cause the debugger to stop for certain
kinds of program events, such as C++ exceptions or the loading of a
shared library. Use the catch
command to set a catchpoint.
catch
eventthrow
[regexp]rethrow
[regexp]catch
[regexp]If regexp is given, then only exceptions whose type matches the regular expression will be caught.
The convenience variable $_exception
is available at an
exception-related catchpoint, on some systems. This holds the
exception being thrown.
There are currently some limitations to C++ exception handling in gdb:
$_exception
convenience
variable rely on the presence of some SDT probes in libstdc++
.
If these probes are not present, then these features cannot be used.
These probes were first available in the GCC 4.8 release, but whether
or not they are available in your GCC also depends on how it was
built.
$_exception
convenience variable is only valid at the
instruction at which an exception-related catchpoint is set.
libstdc++
. You can use up
(see Selection) to get to your code.
set unwind-on-terminating-exception
.
exception
[name]catch exception Program_Error
),
the debugger will stop only when this specific exception is raised.
Otherwise, the debugger stops execution when any Ada exception is raised.
When inserting an exception catchpoint on a user-defined exception whose
name is identical to one of the exceptions defined by the language, the
fully qualified name must be used as the exception name. Otherwise,
gdb will assume that it should stop on the pre-defined exception
rather than the user-defined one. For instance, assuming an exception
called Constraint_Error
is defined in package Pck
, then
the command to use to catch such exceptions is catch exception
Pck.Constraint_Error.
The convenience variable $_ada_exception
holds the address of
the exception being thrown. This can be useful when setting a
condition for such a catchpoint.
exception unhandled
$_ada_exception
is set as for catch
exception
.
The convenience variable $_ada_exception
holds the address of
the exception being thrown. This can be useful when setting a
condition for such a catchpoint.
handlers
[name]When inserting a handlers catchpoint on a user-defined
exception whose name is identical to one of the exceptions
defined by the language, the fully qualified name must be used
as the exception name. Otherwise, gdb will assume that it
should stop on the pre-defined exception rather than the
user-defined one. For instance, assuming an exception called
Constraint_Error
is defined in package Pck
, then the
command to use to catch such exceptions handling is
catch handlers Pck.Constraint_Error.
The convenience variable $_ada_exception
is set as for
catch exception
.
assert
$_ada_exception
is not set by this catchpoint.
exec
exec
.
syscall
syscall
[name | number | group:groupname | g:groupname] ...
name can be any system call name that is valid for the underlying OS. Just what syscalls are valid depends on the OS. On GNU and Unix systems, you can find the full list of valid syscall names on /usr/include/asm/unistd.h.
Normally, gdb knows in advance which syscalls are valid for each OS, so you can use the gdb command-line completion facilities (see command completion) to list the available choices.
You may also specify the system call numerically. A syscall's number is the value passed to the OS's syscall dispatcher to identify the requested service. When you specify the syscall by its name, gdb uses its database of syscalls to convert the name into the corresponding numeric code, but using the number directly may be useful if gdb's database does not have the complete list of syscalls on your system (e.g., because gdb lags behind the OS upgrades).
You may specify a group of related syscalls to be caught at once using
the group:
syntax (g:
is a shorter equivalent). For
instance, on some platforms gdb allows you to catch all
network related syscalls, by passing the argument group:network
to catch syscall
. Note that not all syscall groups are
available in every system. You can use the command completion
facilities (see command completion) to list the
syscall groups available on your environment.
The example below illustrates how this command works if you don't provide arguments to it:
(gdb) catch syscall Catchpoint 1 (syscall) (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'close'), \ 0xffffe424 in __kernel_vsyscall () (gdb) c Continuing. Catchpoint 1 (returned from syscall 'close'), \ 0xffffe424 in __kernel_vsyscall () (gdb)
Here is an example of catching a system call by name:
(gdb) catch syscall chroot Catchpoint 1 (syscall 'chroot' [61]) (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'chroot'), \ 0xffffe424 in __kernel_vsyscall () (gdb) c Continuing. Catchpoint 1 (returned from syscall 'chroot'), \ 0xffffe424 in __kernel_vsyscall () (gdb)
An example of specifying a system call numerically. In the case below, the syscall number has a corresponding entry in the XML file, so gdb finds its name and prints it:
(gdb) catch syscall 252 Catchpoint 1 (syscall(s) 'exit_group') (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'exit_group'), \ 0xffffe424 in __kernel_vsyscall () (gdb) c Continuing. Program exited normally. (gdb)
Here is an example of catching a syscall group:
(gdb) catch syscall group:process Catchpoint 1 (syscalls 'exit' [1] 'fork' [2] 'waitpid' [7] 'execve' [11] 'wait4' [114] 'clone' [120] 'vfork' [190] 'exit_group' [252] 'waitid' [284] 'unshare' [310]) (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall fork), 0x00007ffff7df4e27 in open64 () from /lib64/ld-linux-x86-64.so.2 (gdb) c Continuing.
However, there can be situations when there is no corresponding name in XML file for that syscall number. In this case, gdb prints a warning message saying that it was not able to find the syscall name, but the catchpoint will be set anyway. See the example below:
(gdb) catch syscall 764 warning: The number '764' does not represent a known syscall. Catchpoint 2 (syscall 764) (gdb)
If you configure gdb using the ‘--without-expat’ option, it will not be able to display syscall names. Also, if your architecture does not have an XML file describing its system calls, you will not be able to see the syscall names. It is important to notice that these two features are used for accessing the syscall name database. In either case, you will see a warning like this:
(gdb) catch syscall warning: Could not open "syscalls/i386-linux.xml" warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'. GDB will not be able to display syscall names. Catchpoint 1 (syscall) (gdb)
Of course, the file name will change depending on your architecture and system.
Still using the example above, you can also try to catch a syscall by its number. In this case, you would see something like:
(gdb) catch syscall 252 Catchpoint 1 (syscall(s) 252)
Again, in this case gdb would not be able to display syscall's names.
fork
fork
.
vfork
vfork
.
load
[regexp]unload
[regexp]signal
[signal...
| ‘
all’
]With no arguments, this catchpoint will catch any signal that is not used internally by gdb, specifically, all signals except ‘SIGTRAP’ and ‘SIGINT’.
With the argument ‘all’, all signals, including those used by gdb, will be caught. This argument cannot be used with other signal names.
Otherwise, the arguments are a list of signal names as given to
handle
(see Signals). Only signals specified in this list
will be caught.
One reason that catch signal
can be more useful than
handle
is that you can attach commands and conditions to the
catchpoint.
When a signal is caught by a catchpoint, the signal's stop
and
print
settings, as specified by handle
, are ignored.
However, whether the signal is still delivered to the inferior depends
on the pass
setting; this can be changed in the catchpoint's
commands.
tcatch
eventUse the info break
command to list the current catchpoints.
It is often necessary to eliminate a breakpoint, watchpoint, or catchpoint once it has done its job and you no longer want your program to stop there. This is called deleting the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten.
With the clear
command you can delete breakpoints according to
where they are in your program. With the delete
command you can
delete individual breakpoints, watchpoints, or catchpoints by specifying
their breakpoint numbers.
It is not necessary to delete a breakpoint to proceed past it. gdb automatically ignores breakpoints on the first instruction to be executed when you continue execution without changing the execution address.
clear
clear
locationclear
functionclear
filename:
functionclear
linenumclear
filename:
linenumdelete
[breakpoints
] [list...
]set
confirm off
). You can abbreviate this command as d
.
Rather than deleting a breakpoint, watchpoint, or catchpoint, you might prefer to disable it. This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can enable it again later.
You disable and enable breakpoints, watchpoints, and catchpoints with
the enable
and disable
commands, optionally specifying
one or more breakpoint numbers as arguments. Use info break
to
print a list of all breakpoints, watchpoints, and catchpoints if you
do not know which numbers to use.
Disabling and enabling a breakpoint that has multiple locations affects all of its locations.
A breakpoint, watchpoint, or catchpoint can have any of several different states of enablement:
break
command starts out in this state.
tbreak
command starts out in this state.
You can use the following commands to enable or disable breakpoints, watchpoints, and catchpoints:
disable
[breakpoints
] [list...
]disable
as dis
.
enable
[breakpoints
] [list...
]enable
[breakpoints
] once
list...
enable
[breakpoints
] count
count list...
enable
[breakpoints
] delete
list...
tbreak
command start out in this state.
Except for a breakpoint set with tbreak
(see Setting Breakpoints), breakpoints that you set are initially enabled;
subsequently, they become disabled or enabled only when you use one of
the commands above. (The command until
can set and delete a
breakpoint of its own, but it does not change the state of your other
breakpoints; see Continuing and Stepping.)
The simplest sort of breakpoint breaks every time your program reaches a specified place. You can also specify a condition for a breakpoint. A condition is just a Boolean expression in your programming language (see Expressions). A breakpoint with a condition evaluates the expression each time your program reaches it, and your program stops only if the condition is true.
This is the converse of using assertions for program validation; in that situation, you want to stop when the assertion is violated—that is, when the condition is false. In C, if you want to test an assertion expressed by the condition assert, you should set the condition ‘! assert’ on the appropriate breakpoint.
Conditions are also accepted for watchpoints; you may not need them, since a watchpoint is inspecting the value of an expression anyhow—but it might be simpler, say, to just set a watchpoint on a variable name, and specify a condition that tests whether the new value is an interesting one.
Break conditions can have side effects, and may even call functions in your program. This can be useful, for example, to activate functions that log program progress, or to use your own print functions to format special data structures. The effects are completely predictable unless there is another enabled breakpoint at the same address. (In that case, gdb might see the other breakpoint first and stop your program without checking the condition of this one.) Note that breakpoint commands are usually more convenient and flexible than break conditions for the purpose of performing side effects when a breakpoint is reached (see Breakpoint Command Lists).
Breakpoint conditions can also be evaluated on the target's side if the target supports it. Instead of evaluating the conditions locally, gdb encodes the expression into an agent expression (see Agent Expressions) suitable for execution on the target, independently of gdb. Global variables become raw memory locations, locals become stack accesses, and so forth.
In this case, gdb will only be notified of a breakpoint trigger when its condition evaluates to true. This mechanism may provide faster response times depending on the performance characteristics of the target since it does not need to keep gdb informed about every breakpoint trigger, even those with false conditions.
Break conditions can be specified when a breakpoint is set, by using
‘if’ in the arguments to the break
command. See Setting Breakpoints. They can also be changed at any time
with the condition
command.
You can also use the if
keyword with the watch
command.
The catch
command does not recognize the if
keyword;
condition
is the only way to impose a further condition on a
catchpoint.
condition
bnum expressioncondition
, gdb checks expression immediately for
syntactic correctness, and to determine whether symbols in it have
referents in the context of your breakpoint. If expression uses
symbols not referenced in the context of the breakpoint, gdb
prints an error message:
No symbol "foo" in current context.
gdb does
not actually evaluate expression at the time the condition
command (or a command that sets a breakpoint with a condition, like
break if ...
) is given, however. See Expressions.
condition
bnumA special case of a breakpoint condition is to stop only when the breakpoint has been reached a certain number of times. This is so useful that there is a special way to do it, using the ignore count of the breakpoint. Every breakpoint has an ignore count, which is an integer. Most of the time, the ignore count is zero, and therefore has no effect. But if your program reaches a breakpoint whose ignore count is positive, then instead of stopping, it just decrements the ignore count by one and continues. As a result, if the ignore count value is n, the breakpoint does not stop the next n times your program reaches it.
ignore
bnum countTo make the breakpoint stop the next time it is reached, specify a count of zero.
When you use continue
to resume execution of your program from a
breakpoint, you can specify an ignore count directly as an argument to
continue
, rather than using ignore
. See Continuing and Stepping.
If a breakpoint has a positive ignore count and a condition, the condition is not checked. Once the ignore count reaches zero, gdb resumes checking the condition.
You could achieve the effect of the ignore count with a condition such as ‘$foo-- <= 0’ using a debugger convenience variable that is decremented each time. See Convenience Variables.
Ignore counts apply to breakpoints, watchpoints, and catchpoints.
You can give any breakpoint (or watchpoint or catchpoint) a series of commands to execute when your program stops due to that breakpoint. For example, you might want to print the values of certain expressions, or enable other breakpoints.
commands
[list...
]...
command-list ...
end
end
to terminate the commands.
To remove all commands from a breakpoint, type commands
and
follow it immediately with end
; that is, give no commands.
With no argument, commands
refers to the last breakpoint,
watchpoint, or catchpoint set (not to the breakpoint most recently
encountered). If the most recent breakpoints were set with a single
command, then the commands
will apply to all the breakpoints
set by that command. This applies to breakpoints set by
rbreak
, and also applies when a single break
command
creates multiple breakpoints (see Ambiguous Expressions).
Pressing <RET> as a means of repeating the last gdb command is disabled within a command-list.
You can use breakpoint commands to start your program up again. Simply
use the continue
command, or step
, or any other command
that resumes execution.
Any other commands in the command list, after a command that resumes
execution, are ignored. This is because any time you resume execution
(even with a simple next
or step
), you may encounter
another breakpoint—which could have its own command list, leading to
ambiguities about which list to execute.
If the first command you specify in a command list is silent
, the
usual message about stopping at a breakpoint is not printed. This may
be desirable for breakpoints that are to print a specific message and
then continue. If none of the remaining commands print anything, you
see no sign that the breakpoint was reached. silent
is
meaningful only at the beginning of a breakpoint command list.
The commands echo
, output
, and printf
allow you to
print precisely controlled output, and are often useful in silent
breakpoints. See Commands for Controlled Output.
For example, here is how you could use breakpoint commands to print the
value of x
at entry to foo
whenever x
is positive.
break foo if x>0 commands silent printf "x is %d\n",x cont end
One application for breakpoint commands is to compensate for one bug so
you can test for another. Put a breakpoint just after the erroneous line
of code, give it a condition to detect the case in which something
erroneous has been done, and give it commands to assign correct values
to any variables that need them. End with the continue
command
so that your program does not stop, and start with the silent
command so that no output is produced. Here is an example:
break 403 commands silent set x = y + 4 cont end
The dynamic printf command dprintf
combines a breakpoint with
formatted printing of your program's data to give you the effect of
inserting printf
calls into your program on-the-fly, without
having to recompile it.
In its most basic form, the output goes to the GDB console. However,
you can set the variable dprintf-style
for alternate handling.
For instance, you can ask to format the output by calling your
program's printf
function. This has the advantage that the
characters go to the program's output device, so they can recorded in
redirects to files and so forth.
If you are doing remote debugging with a stub or agent, you can also ask to have the printf handled by the remote agent. In addition to ensuring that the output goes to the remote program's device along with any other output the program might produce, you can also ask that the dprintf remain active even after disconnecting from the remote target. Using the stub/agent is also more efficient, as it can do everything without needing to communicate with gdb.
dprintf
location,
template,
expression[,
expression...]
set dprintf-style
stylegdb
printf
command.
call
printf
).
agent
gdbserver
) handle
the output itself. This style is only available for agents that
support running commands on the target.
set dprintf-function
functioncall
. By
default its value is printf
. You may set it to any expression.
that gdb can evaluate to a function, as per the call
command.
set dprintf-channel
channeldprintf-function
, in the manner of
fprintf
and similar functions. Otherwise, the dprintf format
string will be the first argument, in the manner of printf
.
As an example, if you wanted dprintf
output to go to a logfile
that is a standard I/O stream assigned to the variable mylog
,
you could do the following:
(gdb) set dprintf-style call (gdb) set dprintf-function fprintf (gdb) set dprintf-channel mylog (gdb) dprintf 25,"at line 25, glob=%d\n",glob Dprintf 1 at 0x123456: file main.c, line 25. (gdb) info break 1 dprintf keep y 0x00123456 in main at main.c:25 call (void) fprintf (mylog,"at line 25, glob=%d\n",glob) continue (gdb)
Note that the info break
displays the dynamic printf commands
as normal breakpoint commands; you can thus easily see the effect of
the variable settings.
set disconnected-dprintf on
set disconnected-dprintf off
dprintf
commands should continue to run if
gdb has disconnected from the target. This only applies
if the dprintf-style
is agent
.
show disconnected-dprintf off
dprintf
.
gdb does not check the validity of function and channel, relying on you to supply values that are meaningful for the contexts in which they are being used. For instance, the function and channel may be the values of local variables, but if that is the case, then all enabled dynamic prints must be at locations within the scope of those locals. If evaluation fails, gdb will report an error.
To save breakpoint definitions to a file use the save breakpoints
command.
save breakpoints [
filename]
source
command (see Command Files). Note that watchpoints
with expressions involving local variables may fail to be recreated
because it may not be possible to access the context where the
watchpoint is valid anymore. Because the saved breakpoint definitions
are simply a sequence of gdb commands that recreate the
breakpoints, you can edit the file in your favorite editing program,
and remove the breakpoint definitions you're not interested in, or
that can no longer be recreated.
gdb supports SDT probes in the code. SDT stands for Statically Defined Tracing, and the probes are designed to have a tiny runtime code and data footprint, and no dynamic relocations.
Currently, the following types of probes are supported on ELF-compatible systems:
SystemTap
(http://sourceware.org/systemtap/)
SDT probes4. SystemTap
probes are usable
from assembly, C and C++ languages5.
DTrace
(http://oss.oracle.com/projects/DTrace)
USDT probes. DTrace
probes are usable from C and
C++ languages.
Some SystemTap
probes have an associated semaphore variable;
for instance, this happens automatically if you defined your probe
using a DTrace-style .d file. If your probe has a semaphore,
gdb will automatically enable it when you specify a
breakpoint using the ‘-probe-stap’ notation. But, if you put a
breakpoint at a probe's location by some other method (e.g.,
break file:line
), then gdb will not automatically set
the semaphore. DTrace
probes do not support semaphores.
You can examine the available static static probes using info
probes
, with optional arguments:
info probes
[type] [provider [name [objfile]]]stap
for listing
SystemTap
probes or dtrace
for listing DTrace
probes. If omitted all probes are listed regardless of their types.
If given, provider is a regular expression used to match against provider names when selecting which probes to list. If omitted, probes by all probes from all providers are listed.
If given, name is a regular expression to match against probe names when selecting which probes to list. If omitted, probe names are not considered when deciding whether to display them.
If given, objfile is a regular expression used to select which
object files (executable or shared libraries) to examine. If not
given, all object files are considered.
info probes all
Some probe points can be enabled and/or disabled. The effect of
enabling or disabling a probe depends on the type of probe being
handled. Some DTrace
probes can be enabled or
disabled, but SystemTap
probes cannot be disabled.
You can enable (or disable) one or more probes using the following commands, with optional arguments:
enable probes
[provider [name [objfile]]]If given, name is a regular expression to match against probe names when selecting which probes to enable. If omitted, probe names are not considered when deciding whether to enable them.
If given, objfile is a regular expression used to select which object files (executable or shared libraries) to examine. If not given, all object files are considered.
disable probes
[provider [name [objfile]]]enable probes
command above for a description of the
optional arguments accepted by this command.
A probe may specify up to twelve arguments. These are available at the
point at which the probe is defined—that is, when the current PC is
at the probe's location. The arguments are available using the
convenience variables (see Convenience Vars)
$_probe_arg0
...$_probe_arg11
. In SystemTap
probes each probe argument is an integer of the appropriate size;
types are not preserved. In DTrace
probes types are preserved
provided that they are recognized as such by gdb; otherwise
the value of the probe argument will be a long integer. The
convenience variable $_probe_argc
holds the number of arguments
at the current probe point.
These variables are always available, but attempts to access them at any location other than a probe point will cause gdb to give an error message.
If you request too many active hardware-assisted breakpoints and watchpoints, you will see this error message:
Stopped; cannot insert breakpoints. You may have requested too many hardware breakpoints and watchpoints.
This message is printed when you attempt to resume the program, since only then gdb knows exactly how many hardware breakpoints and watchpoints it needs to insert.
When this message is printed, you need to disable or remove some of the hardware-assisted breakpoints and watchpoints, and then continue.
Some processor architectures place constraints on the addresses at which breakpoints may be placed. For architectures thus constrained, gdb will attempt to adjust the breakpoint's address to comply with the constraints dictated by the architecture.
One example of such an architecture is the Fujitsu FR-V. The FR-V is a VLIW architecture in which a number of RISC-like instructions may be bundled together for parallel execution. The FR-V architecture constrains the location of a breakpoint instruction within such a bundle to the instruction with the lowest address. gdb honors this constraint by adjusting a breakpoint's address to the first in the bundle.
It is not uncommon for optimized code to have bundles which contain instructions from different source statements, thus it may happen that a breakpoint's address will be adjusted from one source statement to another. Since this adjustment may significantly alter gdb's breakpoint related behavior from what the user expects, a warning is printed when the breakpoint is first set and also when the breakpoint is hit.
A warning like the one below is printed when setting a breakpoint that's been subject to address adjustment:
warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
Such warnings are printed both for user settable and gdb's internal breakpoints. If you see one of these warnings, you should verify that a breakpoint set at the adjusted address will have the desired affect. If not, the breakpoint in question may be removed and other breakpoints may be set which will have the desired behavior. E.g., it may be sufficient to place the breakpoint at a later instruction. A conditional breakpoint may also be useful in some cases to prevent the breakpoint from triggering too often.
gdb will also issue a warning when stopping at one of these adjusted breakpoints:
warning: Breakpoint 1 address previously adjusted from 0x00010414 to 0x00010410.
When this warning is encountered, it may be too late to take remedial action except in cases where the breakpoint is hit earlier or more frequently than expected.
Continuing means resuming program execution until your program
completes normally. In contrast, stepping means executing just
one more “step” of your program, where “step” may mean either one
line of source code, or one machine instruction (depending on what
particular command you use). Either when continuing or when stepping,
your program may stop even sooner, due to a breakpoint or a signal. (If
it stops due to a signal, you may want to use handle
, or use
‘signal 0’ to resume execution (see Signals),
or you may step into the signal's handler (see stepping and signal handlers).)
continue
[ignore-count]c
[ignore-count]fg
[ignore-count]ignore
(see Break Conditions).
The argument ignore-count is meaningful only when your program
stopped due to a breakpoint. At other times, the argument to
continue
is ignored.
The synonyms c
and fg
(for foreground, as the
debugged program is deemed to be the foreground program) are provided
purely for convenience, and have exactly the same behavior as
continue
.
To resume execution at a different place, you can use return
(see Returning from a Function) to go back to the
calling function; or jump
(see Continuing at a Different Address) to go to an arbitrary location in your program.
A typical technique for using stepping is to set a breakpoint (see Breakpoints; Watchpoints; and Catchpoints) at the beginning of the function or the section of your program where a problem is believed to lie, run your program until it stops at that breakpoint, and then step through the suspect area, examining the variables that are interesting, until you see the problem happen.
step
s
.
Warning: If you use thestep
command while control is within a function that was compiled without debugging information, execution proceeds until control reaches a function that does have debugging information. Likewise, it will not step into a function which is compiled without debugging information. To step through functions without debugging information, use thestepi
command, described below.
The step
command only stops at the first instruction of a source
line. This prevents the multiple stops that could otherwise occur in
switch
statements, for
loops, etc. step
continues
to stop if a function that has debugging information is called within
the line. In other words, step
steps inside any functions
called within the line.
Also, the step
command only enters a function if there is line
number information for the function. Otherwise it acts like the
next
command. This avoids problems when using cc -gl
on MIPS machines. Previously, step
entered subroutines if there
was any debugging information about the routine.
step
countstep
, but do so count times. If a
breakpoint is reached, or a signal not related to stepping occurs before
count steps, stepping stops right away.
next
[count]step
, but function calls that appear within
the line of code are executed without stopping. Execution stops when
control reaches a different line of code at the original stack level
that was executing when you gave the next
command. This command
is abbreviated n
.
An argument count is a repeat count, as for step
.
The next
command only stops at the first instruction of a
source line. This prevents multiple stops that could otherwise occur in
switch
statements, for
loops, etc.
set step-mode
set step-mode on
set step-mode on
command causes the step
command to
stop at the first instruction of a function which contains no debug line
information rather than stepping over it.
This is useful in cases where you may be interested in inspecting the
machine instructions of a function which has no symbolic info and do not
want gdb to automatically skip over this function.
set step-mode off
step
command to step over any functions which contains no
debug information. This is the default.
show step-mode
finish
fin
.
Contrast this with the return
command (see Returning from a Function).
set print finish
[on|off
]show print finish
finish
command will show the value that is
returned by the function. This can be disabled using set print
finish off
. When disabled, the value is still entered into the value
history (see Value History), but not displayed.
until
u
next
command, except that when until
encounters a jump, it
automatically continues execution until the program counter is greater
than the address of the jump.
This means that when you reach the end of a loop after single stepping
though it, until
makes your program continue execution until it
exits the loop. In contrast, a next
command at the end of a loop
simply steps back to the beginning of the loop, which forces you to step
through the next iteration.
until
always stops your program if it attempts to exit the current
stack frame.
until
may produce somewhat counterintuitive results if the order
of machine code does not match the order of the source lines. For
example, in the following excerpt from a debugging session, the f
(frame
) command shows that execution is stopped at line
206
; yet when we use until
, we get to line 195
:
(gdb) f #0 main (argc=4, argv=0xf7fffae8) at m4.c:206 206 expand_input(); (gdb) until 195 for ( ; argc > 0; NEXTARG) {
This happened because, for execution efficiency, the compiler had
generated code for the loop closure test at the end, rather than the
start, of the loop—even though the test in a C for
-loop is
written before the body of the loop. The until
command appeared
to step back to the beginning of the loop when it advanced to this
expression; however, it has not really gone to an earlier
statement—not in terms of the actual machine code.
until
with no argument works by means of single
instruction stepping, and hence is slower than until
with an
argument.
until
locationu
locationuntil
without an argument. The specified
location is actually reached only if it is in the current frame. This
implies that until
can be used to skip over recursive function
invocations. For instance in the code below, if the current location is
line 96
, issuing until 99
will execute the program up to
line 99
in the same invocation of factorial, i.e., after the inner
invocations have returned.
94 int factorial (int value) 95 { 96 if (value > 1) { 97 value *= factorial (value - 1); 98 } 99 return (value); 100 }
advance
locationuntil
, but advance
will
not skip over recursive function calls, and the target location doesn't
have to be in the same frame as the current one.
stepi
stepi
argsi
It is often useful to do ‘display/i $pc’ when stepping by machine instructions. This makes gdb automatically display the next instruction to be executed, each time your program stops. See Automatic Display.
An argument is a repeat count, as in step
.
nexti
nexti
argni
An argument is a repeat count, as in next
.
By default, and if available, gdb makes use of
target-assisted range stepping. In other words, whenever you
use a stepping command (e.g., step
, next
), gdb
tells the target to step the corresponding range of instruction
addresses instead of issuing multiple single-steps. This speeds up
line stepping, particularly for remote targets. Ideally, there should
be no reason you would want to turn range stepping off. However, it's
possible that a bug in the debug info, a bug in the remote stub (for
remote targets), or even a bug in gdb could make line
stepping behave incorrectly when target-assisted range stepping is
enabled. You can use the following command to turn off range stepping
if necessary:
set range-stepping
show range-stepping
If on
, and the target supports it, gdb tells the
target to step a range of addresses itself, instead of issuing
multiple single-steps. If off
, gdb always issues
single-steps, even if range stepping is supported by the target. The
default is on
.
The program you are debugging may contain some functions which are
uninteresting to debug. The skip
command lets you tell gdb to
skip a function, all functions in a file or a particular function in
a particular file when stepping.
For example, consider the following C function:
101 int func() 102 { 103 foo(boring()); 104 bar(boring()); 105 }
Suppose you wish to step into the functions foo
and bar
, but you
are not interested in stepping through boring
. If you run step
at line 103, you'll enter boring()
, but if you run next
, you'll
step over both foo
and boring
!
One solution is to step
into boring
and use the finish
command to immediately exit it. But this can become tedious if boring
is called from many places.
A more flexible solution is to execute skip boring. This instructs
gdb never to step into boring
. Now when you execute
step
at line 103, you'll step over boring
and directly into
foo
.
Functions may be skipped by providing either a function name, linespec
(see Specify Location), regular expression that matches the function's
name, file name or a glob
-style pattern that matches the file name.
On Posix systems the form of the regular expression is
“Extended Regular Expressions”. See for example ‘man 7 regex’
on gnu/Linux systems. On non-Posix systems the form of the regular
expression is whatever is provided by the regcomp
function of
the underlying system.
See for example ‘man 7 glob’ on gnu/Linux systems for a
description of glob
-style patterns.
skip
[options]skip
command takes zero or more options
that specify what to skip.
The options argument is any useful combination of the following:
-file
file-fi
file-gfile
file-glob-pattern-gfi
file-glob-pattern(gdb) skip -gfi utils/*.c
-function
linespec-fu
linespec-rfunction
regexp-rfu
regexpThis form is useful for complex function names.
For example, there is generally no need to step into C++ std::string
constructors or destructors. Plus with C++ templates it can be hard to
write out the full name of the function, and often it doesn't matter what
the template arguments are. Specifying the function to be skipped as a
regular expression makes this easier.
(gdb) skip -rfu ^std::(allocator|basic_string)<.*>::~?\1 *\(
If you want to skip every templated C++ constructor and destructor
in the std
namespace you can do:
(gdb) skip -rfu ^std::([a-zA-z0-9_]+)<.*>::~?\1 *\(
If no options are specified, the function you're currently debugging will be skipped.
skip function
[linespec]If you do not specify linespec, the function you're currently debugging will be skipped.
(If you have a function called file
that you want to skip, use
skip function file.)
skip file
[filename](gdb) skip file boring.c File boring.c will be skipped when stepping.
If you do not specify filename, functions whose source lives in the file you're currently debugging will be skipped.
Skips can be listed, deleted, disabled, and enabled, much like breakpoints. These are the commands for managing your list of skips:
info skip
[range]info skip
prints the following information about each skip:
skip delete
[range]skip enable
[range]skip disable
[range]set debug skip
[on|off
]show debug skip
A signal is an asynchronous event that can happen in a program. The
operating system defines the possible kinds of signals, and gives each
kind a name and a number. For example, in Unix SIGINT
is the
signal a program gets when you type an interrupt character (often Ctrl-c);
SIGSEGV
is the signal a program gets from referencing a place in
memory far away from all the areas in use; SIGALRM
occurs when
the alarm clock timer goes off (which happens only if your program has
requested an alarm).
Some signals, including SIGALRM
, are a normal part of the
functioning of your program. Others, such as SIGSEGV
, indicate
errors; these signals are fatal (they kill your program immediately) if the
program has not specified in advance some other way to handle the signal.
SIGINT
does not indicate an error in your program, but it is normally
fatal so it can carry out the purpose of the interrupt: to kill the program.
gdb has the ability to detect any occurrence of a signal in your program. You can tell gdb in advance what to do for each kind of signal.
Normally, gdb is set up to let the non-erroneous signals like
SIGALRM
be silently passed to your program
(so as not to interfere with their role in the program's functioning)
but to stop your program immediately whenever an error signal happens.
You can change these settings with the handle
command.
info signals
info handle
info signals
siginfo handle
is an alias for info signals
.
catch signal
[signal...
| ‘
all’
]handle
signal [keywords...
]The keywords allowed by the handle
command can be abbreviated.
Their full names are:
nostop
stop
print
keyword as well.
print
noprint
nostop
keyword as well.
pass
noignore
pass
and noignore
are synonyms.
nopass
ignore
nopass
and ignore
are synonyms.
When a signal stops your program, the signal is not visible to the
program until you
continue. Your program sees the signal then, if pass
is in
effect for the signal in question at that time. In other words,
after gdb reports a signal, you can use the handle
command with pass
or nopass
to control whether your
program sees that signal when you continue.
The default is set to nostop
, noprint
, pass
for
non-erroneous signals such as SIGALRM
, SIGWINCH
and
SIGCHLD
, and to stop
, print
, pass
for the
erroneous signals.
You can also use the signal
command to prevent your program from
seeing a signal, or cause it to see a signal it normally would not see,
or to give it any signal at any time. For example, if your program stopped
due to some sort of memory reference error, you might store correct
values into the erroneous variables and continue, hoping to see more
execution; but your program would probably terminate immediately as
a result of the fatal signal once it saw the signal. To prevent this,
you can continue with ‘signal 0’. See Giving your Program a Signal.
gdb optimizes for stepping the mainline code. If a signal
that has handle nostop
and handle pass
set arrives while
a stepping command (e.g., stepi
, step
, next
) is
in progress, gdb lets the signal handler run and then resumes
stepping the mainline code once the signal handler returns. In other
words, gdb steps over the signal handler. This prevents
signals that you've specified as not interesting (with handle
nostop
) from changing the focus of debugging unexpectedly. Note that
the signal handler itself may still hit a breakpoint, stop for another
signal that has handle stop
in effect, or for any other event
that normally results in stopping the stepping command sooner. Also
note that gdb still informs you that the program received a
signal if handle print
is set.
If you set handle pass
for a signal, and your program sets up a
handler for it, then issuing a stepping command, such as step
or stepi
, when your program is stopped due to the signal will
step into the signal handler (if the target supports that).
Likewise, if you use the queue-signal
command to queue a signal
to be delivered to the current thread when execution of the thread
resumes (see Giving your Program a Signal), then a
stepping command will step into the signal handler.
Here's an example, using stepi
to step to the first instruction
of SIGUSR1
's handler:
(gdb) handle SIGUSR1 Signal Stop Print Pass to program Description SIGUSR1 Yes Yes Yes User defined signal 1 (gdb) c Continuing. Program received signal SIGUSR1, User defined signal 1. main () sigusr1.c:28 28 p = 0; (gdb) si sigusr1_handler () at sigusr1.c:9 9 {
The same, but using queue-signal
instead of waiting for the
program to receive the signal first:
(gdb) n 28 p = 0; (gdb) queue-signal SIGUSR1 (gdb) si sigusr1_handler () at sigusr1.c:9 9 { (gdb)
On some targets, gdb can inspect extra signal information
associated with the intercepted signal, before it is actually
delivered to the program being debugged. This information is exported
by the convenience variable $_siginfo
, and consists of data
that is passed by the kernel to the signal handler at the time of the
receipt of a signal. The data type of the information itself is
target dependent. You can see the data type using the ptype
$_siginfo
command. On Unix systems, it typically corresponds to the
standard siginfo_t
type, as defined in the signal.h
system header.
Here's an example, on a gnu/Linux system, printing the stray referenced address that raised a segmentation fault.
(gdb) continue Program received signal SIGSEGV, Segmentation fault. 0x0000000000400766 in main () 69 *(int *)p = 0; (gdb) ptype $_siginfo type = struct { int si_signo; int si_errno; int si_code; union { int _pad[28]; struct {...} _kill; struct {...} _timer; struct {...} _rt; struct {...} _sigchld; struct {...} _sigfault; struct {...} _sigpoll; } _sifields; } (gdb) ptype $_siginfo._sifields._sigfault type = struct { void *si_addr; } (gdb) p $_siginfo._sifields._sigfault.si_addr $1 = (void *) 0x7ffff7ff7000
Depending on target support, $_siginfo
may also be writable.
On some targets, a SIGSEGV
can be caused by a boundary
violation, i.e., accessing an address outside of the allowed range.
In those cases gdb may displays additional information,
depending on how gdb has been told to handle the signal.
With handle stop SIGSEGV
, gdb displays the violation
kind: "Upper" or "Lower", the memory address accessed and the
bounds, while with handle nostop SIGSEGV
no additional
information is displayed.
The usual output of a segfault is:
Program received signal SIGSEGV, Segmentation fault 0x0000000000400d7c in upper () at i386-mpx-sigsegv.c:68 68 value = *(p + len);
While a bound violation is presented as:
Program received signal SIGSEGV, Segmentation fault Upper bound violation while accessing address 0x7fffffffc3b3 Bounds: [lower = 0x7fffffffc390, upper = 0x7fffffffc3a3] 0x0000000000400d7c in upper () at i386-mpx-sigsegv.c:68 68 value = *(p + len);
gdb supports debugging programs with multiple threads (see Debugging Programs with Multiple Threads). There are two modes of controlling execution of your program within the debugger. In the default mode, referred to as all-stop mode, when any thread in your program stops (for example, at a breakpoint or while being stepped), all other threads in the program are also stopped by gdb. On some targets, gdb also supports non-stop mode, in which other threads can continue to run freely while you examine the stopped thread in the debugger.
In all-stop mode, whenever your program stops under gdb for any reason, all threads of execution stop, not just the current thread. This allows you to examine the overall state of the program, including switching between threads, without worrying that things may change underfoot.
Conversely, whenever you restart the program, all threads start
executing. This is true even when single-stepping with commands
like step
or next
.
In particular, gdb cannot single-step all threads in lockstep. Since thread scheduling is up to your debugging target's operating system (not controlled by gdb), other threads may execute more than one statement while the current thread completes a single step. Moreover, in general other threads stop in the middle of a statement, rather than at a clean statement boundary, when the program stops.
You might even find your program stopped in another thread after continuing or even single-stepping. This happens whenever some other thread runs into a breakpoint, a signal, or an exception before the first thread completes whatever you requested.
Whenever gdb stops your program, due to a breakpoint or a signal, it automatically selects the thread where that breakpoint or signal happened. gdb alerts you to the context switch with a message such as ‘[Switching to Thread n]’ to identify the thread.
On some OSes, you can modify gdb's default behavior by locking the OS scheduler to allow only a single thread to run.
set scheduler-locking
modeoff
, then there is no
locking and any thread may run at any time. If on
, then only
the current thread may run when the inferior is resumed. The
step
mode optimizes for single-stepping; it prevents other
threads from preempting the current thread while you are stepping, so
that the focus of debugging does not change unexpectedly. Other
threads never get a chance to run when you step, and they are
completely free to run when you use commands like ‘continue’,
‘until’, or ‘finish’. However, unless another thread hits a
breakpoint during its timeslice, gdb does not change the
current thread away from the thread that you are debugging. The
replay
mode behaves like off
in record mode and like
on
in replay mode.
show scheduler-locking
By default, when you issue one of the execution commands such as
continue
, next
or step
, gdb allows only
threads of the current inferior to run. For example, if gdb
is attached to two inferiors, each with two threads, the
continue
command resumes only the two threads of the current
inferior. This is useful, for example, when you debug a program that
forks and you want to hold the parent stopped (so that, for instance,
it doesn't run to exit), while you debug the child. In other
situations, you may not be interested in inspecting the current state
of any of the processes gdb is attached to, and you may want
to resume them all until some breakpoint is hit. In the latter case,
you can instruct gdb to allow all threads of all the
inferiors to run with the set schedule-multiple
command.
set schedule-multiple
on
, all threads of
all processes are allowed to run. When off
, only the threads
of the current process are resumed. The default is off
. The
scheduler-locking
mode takes precedence when set to on
,
or while you are stepping and set to step
.
show schedule-multiple
For some multi-threaded targets, gdb supports an optional mode of operation in which you can examine stopped program threads in the debugger while other threads continue to execute freely. This minimizes intrusion when debugging live systems, such as programs where some threads have real-time constraints or must continue to respond to external events. This is referred to as non-stop mode.
In non-stop mode, when a thread stops to report a debugging event,
only that thread is stopped; gdb does not stop other
threads as well, in contrast to the all-stop mode behavior. Additionally,
execution commands such as continue
and step
apply by default
only to the current thread in non-stop mode, rather than all threads as
in all-stop mode. This allows you to control threads explicitly in
ways that are not possible in all-stop mode — for example, stepping
one thread while allowing others to run freely, stepping
one thread while holding all others stopped, or stepping several threads
independently and simultaneously.
To enter non-stop mode, use this sequence of commands before you run or attach to your program:
# If using the CLI, pagination breaks non-stop. set pagination off # Finally, turn it on! set non-stop on
You can use these commands to manipulate the non-stop mode setting:
set non-stop on
set non-stop off
show non-stop
Note these commands only reflect whether non-stop mode is enabled,
not whether the currently-executing program is being run in non-stop mode.
In particular, the set non-stop
preference is only consulted when
gdb starts or connects to the target program, and it is generally
not possible to switch modes once debugging has started. Furthermore,
since not all targets support non-stop mode, even when you have enabled
non-stop mode, gdb may still fall back to all-stop operation by
default.
In non-stop mode, all execution commands apply only to the current thread
by default. That is, continue
only continues one thread.
To continue all threads, issue continue -a
or c -a
.
You can use gdb's background execution commands (see Background Execution) to run some threads in the background while you continue to examine or step others from gdb. The MI execution commands (see GDB/MI Program Execution) are always executed asynchronously in non-stop mode.
Suspending execution is done with the interrupt
command when
running in the background, or Ctrl-c during foreground execution.
In all-stop mode, this stops the whole process;
but in non-stop mode the interrupt applies only to the current thread.
To stop the whole program, use interrupt -a
.
Other execution commands do not currently support the -a
option.
In non-stop mode, when a thread stops, gdb doesn't automatically make that thread current, as it does in all-stop mode. This is because the thread stop notifications are asynchronous with respect to gdb's command interpreter, and it would be confusing if gdb unexpectedly changed to a different thread just as you entered a command to operate on the previously current thread.
gdb's execution commands have two variants: the normal foreground (synchronous) behavior, and a background (asynchronous) behavior. In foreground execution, gdb waits for the program to report that some thread has stopped before prompting for another command. In background execution, gdb immediately gives a command prompt so that you can issue other commands while your program runs.
If the target doesn't support async mode, gdb issues an error message if you attempt to use the background execution commands.
To specify background execution, add a &
to the command. For example,
the background form of the continue
command is continue&
, or
just c&
. The execution commands that accept background execution
are:
run
attach
step
stepi
next
nexti
continue
finish
until
Background execution is especially useful in conjunction with non-stop
mode for debugging programs with multiple threads; see Non-Stop Mode.
However, you can also use these commands in the normal all-stop mode with
the restriction that you cannot issue another execution command until the
previous one finishes. Examples of commands that are valid in all-stop
mode while the program is running include help
and info break
.
You can interrupt your program while it is running in the background by
using the interrupt
command.
interrupt
interrupt -a
interrupt
stops the whole process, but in non-stop mode, it stops
only the current thread. To stop the whole program in non-stop mode,
use interrupt -a
.
When your program has multiple threads (see Debugging Programs with Multiple Threads), you can choose whether to set breakpoints on all threads, or on a particular thread.
break
location thread
thread-idbreak
location thread
thread-id if ...
Use the qualifier ‘thread thread-id’ with a breakpoint command to specify that you only want gdb to stop the program when a particular thread reaches this breakpoint. The thread-id specifier is one of the thread identifiers assigned by gdb, shown in the first column of the ‘info threads’ display.
If you do not specify ‘thread thread-id’ when you set a breakpoint, the breakpoint applies to all threads of your program.
You can use the thread
qualifier on conditional breakpoints as
well; in this case, place ‘thread thread-id’ before or
after the breakpoint condition, like this:
(gdb) break frik.c:13 thread 28 if bartab > lim
Thread-specific breakpoints are automatically deleted when gdb detects the corresponding thread is no longer in the thread list. For example:
(gdb) c Thread-specific breakpoint 3 deleted - thread 28 no longer in the thread list.
There are several ways for a thread to disappear, such as a regular
thread exit, but also when you detach from the process with the
detach
command (see Debugging an Already-running Process), or if gdb loses the remote connection
(see Remote Debugging), etc. Note that with some targets,
gdb is only able to detect a thread has exited when the user
explictly asks for the thread list with the info threads
command.
There is an unfortunate side effect when using gdb to debug multi-threaded programs. If one thread stops for a breakpoint, or for some other reason, and another thread is blocked in a system call, then the system call may return prematurely. This is a consequence of the interaction between multiple threads and the signals that gdb uses to implement breakpoints and other events that stop execution.
To handle this problem, your program should check the return value of each system call and react appropriately. This is good programming style anyways.
For example, do not write code like this:
sleep (10);
The call to sleep
will return early if a different thread stops
at a breakpoint or for some other reason.
Instead, write this:
int unslept = 10; while (unslept > 0) unslept = sleep (unslept);
A system call is allowed to return early, so the system is still conforming to its specification. But gdb does cause your multi-threaded program to behave differently than it would without gdb.
Also, gdb uses internal breakpoints in the thread library to monitor certain events such as thread creation and thread destruction. When such an event happens, a system call in another thread may return prematurely, even though your program does not appear to stop.
If you want to build on non-stop mode and observe program behavior without any chance of disruption by gdb, you can set variables to disable all of the debugger's attempts to modify state, whether by writing memory, inserting breakpoints, etc. These operate at a low level, intercepting operations from all commands.
When all of these are set to off
, then gdb is said to
be observer mode. As a convenience, the variable
observer
can be set to disable these, plus enable non-stop
mode.
Note that gdb will not prevent you from making nonsensical
combinations of these settings. For instance, if you have enabled
may-insert-breakpoints
but disabled may-write-memory
,
then breakpoints that work by writing trap instructions into the code
stream will still not be able to be placed.
set observer on
set observer off
on
, this disables all the permission variables
below (except for insert-fast-tracepoints
), plus enables
non-stop debugging. Setting this to off
switches back to
normal debugging, though remaining in non-stop mode.
show observer
set may-write-registers on
set may-write-registers off
print
, or the
jump
command. It defaults to on
.
show may-write-registers
set may-write-memory on
set may-write-memory off
print
. It
defaults to on
.
show may-write-memory
set may-insert-breakpoints on
set may-insert-breakpoints off
on
.
show may-insert-breakpoints
set may-insert-tracepoints on
set may-insert-tracepoints off
may-insert-fast-tracepoints
. It defaults to on
.
show may-insert-tracepoints
set may-insert-fast-tracepoints on
set may-insert-fast-tracepoints off
may-insert-tracepoints
. It defaults to on
.
show may-insert-fast-tracepoints
set may-interrupt on
set may-interrupt off
off
, the
interrupt
command will have no effect, nor will
Ctrl-c. It defaults to on
.
show may-interrupt
When you are debugging a program, it is not unusual to realize that you have gone too far, and some event of interest has already happened. If the target environment supports it, gdb can allow you to “rewind” the program by running it backward.
A target environment that supports reverse execution should be able to “undo” the changes in machine state that have taken place as the program was executing normally. Variables, registers etc. should revert to their previous values. Obviously this requires a great deal of sophistication on the part of the target environment; not all target environments can support reverse execution.
When a program is executed in reverse, the instructions that have most recently been executed are “un-executed”, in reverse order. The program counter runs backward, following the previous thread of execution in reverse. As each instruction is “un-executed”, the values of memory and/or registers that were changed by that instruction are reverted to their previous states. After executing a piece of source code in reverse, all side effects of that code should be “undone”, and all variables should be returned to their prior values6.
On some platforms, gdb has built-in support for reverse
execution, activated with the record
or record btrace
commands. See Process Record and Replay. Some remote targets,
typically full system emulators, support reverse execution directly
without requiring any special command.
If you are debugging in a target environment that supports reverse execution, gdb provides the following commands.
reverse-continue
[ignore-count]rc
[ignore-count]reverse-step
[count]Like the step
command, reverse-step
will only stop
at the beginning of a source line. It “un-executes” the previously
executed source line. If the previous source line included calls to
debuggable functions, reverse-step
will step (backward) into
the called function, stopping at the beginning of the last
statement in the called function (typically a return statement).
Also, as with the step
command, if non-debuggable functions are
called, reverse-step
will run thru them backward without stopping.
reverse-stepi
[count]reverse-stepi
will take you
back from the destination of the jump to the jump instruction itself.
reverse-next
[count]reverse-next
will take you back
to the caller of that function, before the function was called,
just as the normal next
command would take you from the last
line of a function back to its return to its caller
7.
reverse-nexti
[count]nexti
, reverse-nexti
executes a single instruction
in reverse, except that called functions are “un-executed” atomically.
That is, if the previously executed instruction was a return from
another function, reverse-nexti
will continue to execute
in reverse until the call to that function (from the current stack
frame) is reached.
reverse-finish
finish
command takes you to the point where the
current function returns, reverse-finish
takes you to the point
where it was called. Instead of ending up at the end of the current
function invocation, you end up at the beginning.
set exec-direction
set exec-direction reverse
step, stepi, next, nexti, continue, and finish
. The return
command cannot be used in reverse mode.
set exec-direction forward
On some platforms, gdb provides a special process record and replay target that can record a log of the process execution, and replay it later with both forward and reverse execution commands.
When this target is in use, if the execution log includes the record for the next instruction, gdb will debug in replay mode. In the replay mode, the inferior does not really execute code instructions. Instead, all the events that normally happen during code execution are taken from the execution log. While code is not really executed in replay mode, the values of registers (including the program counter register) and the memory of the inferior are still changed as they normally would. Their contents are taken from the execution log.
If the record for the next instruction is not in the execution log, gdb will debug in record mode. In this mode, the inferior executes normally, and gdb records the execution log for future replay.
The process record and replay target supports reverse execution (see Reverse Execution), even if the platform on which the inferior runs does not. However, the reverse execution is limited in this case by the range of the instructions recorded in the execution log. In other words, reverse execution on platforms that don't support it directly can only be done in the replay mode.
When debugging in the reverse direction, gdb will work in replay mode as long as the execution log includes the record for the previous instruction; otherwise, it will work in record mode, if the platform supports reverse execution, or stop if not.
Currently, process record and replay is supported on ARM, Aarch64,
Moxie, PowerPC, PowerPC64, S/390, and x86 (i386/amd64) running
GNU/Linux. Process record and replay can be used both when native
debugging, and when remote debugging via gdbserver
.
For architecture environments that support process record and replay, gdb provides the following commands:
record
methodfull
recording method. The following
recording methods are available:
full
btrace
formatrecord stop
.
The recording format can be specified as parameter. Without a parameter the command chooses the recording format. The following recording formats are available:
bts
pt
The trace can be recorded with very low overhead. The compressed trace format also allows small trace buffers to already contain a big number of instructions compared to BTS.
Decoding the recorded execution trace, on the other hand, is more expensive than decoding BTS trace. This is mostly due to the increased number of instructions to process. You should increase the buffer-size with care.
Not all recording formats may be available on all processors.
The process record and replay target can only debug a process that is already running. Therefore, you need first to start the process with the run or start commands, and then start the recording with the record method command.
Displaced stepping (see displaced stepping) will be automatically disabled when process record and replay target is started. That's because the process record and replay target doesn't support displaced stepping.
If the inferior is in the non-stop mode (see Non-Stop Mode) or in
the asynchronous execution mode (see Background Execution), not
all recording methods are available. The full
recording method
does not support these two modes.
record stop
When you stop the process record and replay target in record mode (at the end of the execution log), the inferior will be stopped at the next instruction that would have been recorded. In other words, if you record for a while and then stop recording, the inferior process will be left in the same state as if the recording never happened.
On the other hand, if the process record and replay target is stopped while in replay mode (that is, not at the end of the execution log, but at some earlier point), the inferior process will become “live” at that earlier state, and it will then be possible to continue the usual “live” debugging of the process from that state.
When the inferior process exits, or gdb detaches from it, process record and replay target will automatically stop itself.
record goto
record goto begin
record goto start
record goto end
record goto
nrecord save
filenameThis command may not be available for all recording methods.
record restore
filenamerecord save
.
set record full insn-number-max
limitset record full insn-number-max unlimited
full
recording method. Default value is 200000.
If limit is a positive number, then gdb will start
deleting instructions from the log once the number of the record
instructions becomes greater than limit. For every new recorded
instruction, gdb will delete the earliest recorded
instruction to keep the number of recorded instructions at the limit.
(Since deleting recorded instructions loses information, gdb
lets you control what happens when the limit is reached, by means of
the stop-at-limit
option, described below.)
If limit is unlimited
or zero, gdb will never
delete recorded instructions from the execution log. The number of
recorded instructions is limited only by the available memory.
show record full insn-number-max
full
recording method.
set record full stop-at-limit
full
recording method when the
number of recorded instructions reaches the limit. If ON (the
default), gdb will stop when the limit is reached for the
first time and ask you whether you want to stop the inferior or
continue running it and recording the execution log. If you decide
to continue recording, each new recorded instruction will cause the
oldest one to be deleted.
If this option is OFF, gdb will automatically delete the
oldest record to make room for each new one, without asking.
show record full stop-at-limit
stop-at-limit
.
set record full memory-query
full
recording method.
If ON, gdb will query whether to stop the inferior in that
case.
If this option is OFF (the default), gdb will automatically
ignore the effect of such instructions on memory. Later, when
gdb replays this execution log, it will mark the log of this
instruction as not accessible, and it will not affect the replay
results.
show record full memory-query
memory-query
.
The btrace
record target does not trace data. As a
convenience, when replaying, gdb reads read-only memory off
the live program directly, assuming that the addresses of the
read-only areas don't change. This for example makes it possible to
disassemble code while replaying, but not to print variables.
In some cases, being able to inspect variables might be useful.
You can use the following command for that:
set record btrace replay-memory-access
btrace
recording method when
accessing memory during replay. If read-only
(the default),
gdb will only allow accesses to read-only memory.
If read-write
, gdb will allow accesses to read-only
and to read-write memory. Beware that the accessed memory corresponds
to the live target and not necessarily to the current replay
position.
set record btrace cpu
identifierProcessor errata are defects in processor operation, caused by its design or manufacture. They can cause a trace not to match the specification. This, in turn, may cause trace decode to fail. gdb can detect erroneous trace packets and correct them, thus avoiding the decoding failures. These corrections are known as errata workarounds, and are enabled based on the processor on which the trace was recorded.
By default, gdb attempts to detect the processor automatically, and apply the necessary workarounds for it. However, you may need to specify the processor if gdb does not yet support it. This command allows you to do that, and also allows to disable the workarounds.
The argument identifier identifies the cpu and is of the
form: vendor:
processor identifier. In addition,
there are two special identifiers, none
and auto
(default).
The following vendor identifiers and corresponding processor identifiers are currently supported:
intel
| family/model[/stepping]
|
On GNU/Linux systems, the processor family, model, and
stepping can be obtained from /proc/cpuinfo
.
If identifier is auto
, enable errata workarounds for the
processor on which the trace was recorded. If identifier is
none
, errata workarounds are disabled.
For example, when using an old gdb on a new system, decode may fail because gdb does not support the new processor. It often suffices to specify an older processor that gdb supports.
(gdb) info record Active record target: record-btrace Recording format: Intel Processor Trace. Buffer size: 16kB. Failed to configure the Intel Processor Trace decoder: unknown cpu. (gdb) set record btrace cpu intel:6/158 (gdb) info record Active record target: record-btrace Recording format: Intel Processor Trace. Buffer size: 16kB. Recorded 84872 instructions in 3189 functions (0 gaps) for thread 1 (...).
show record btrace replay-memory-access
replay-memory-access
.
show record btrace cpu
set record btrace bts buffer-size
sizeset record btrace bts buffer-size unlimited
If size is a positive number, then gdb will try to
allocate a buffer of at least size bytes for each new thread
that uses the btrace recording method and the BTS format.
The actually obtained buffer size may differ from the requested
size. Use the info record
command to see the actual
buffer size for each thread that uses the btrace recording method and
the BTS format.
If limit is unlimited
or zero, gdb will try to
allocate a buffer of 4MB.
Bigger buffers mean longer traces. On the other hand, gdb will
also need longer to process the branch trace data before it can be used.
show record btrace bts buffer-size
sizeset record btrace pt buffer-size
sizeset record btrace pt buffer-size unlimited
If size is a positive number, then gdb will try to
allocate a buffer of at least size bytes for each new thread
that uses the btrace recording method and the Intel Processor Trace
format. The actually obtained buffer size may differ from the
requested size. Use the info record
command to see the
actual buffer size for each thread.
If limit is unlimited
or zero, gdb will try to
allocate a buffer of 4MB.
Bigger buffers mean longer traces. On the other hand, gdb will
also need longer to process the branch trace data before it can be used.
show record btrace pt buffer-size
sizeinfo record
full
full
recording method, it shows the state of process
record and its in-memory execution log buffer, including:
btrace
btrace
recording method, it shows:
For the bts
recording format, it also shows:
For the pt
recording format, it also shows:
record delete
record instruction-history
set record instruction-history-size
command. Instructions
are printed in execution order.
It can also print mixed source+disassembly if you specify the the
/m
or /s
modifier, and print the raw instructions in hex
as well as in symbolic form by specifying the /r
modifier.
The current position marker is printed for the instruction at the
current program counter value. This instruction can appear multiple
times in the trace and the current position marker will be printed
every time. To omit the current position marker, specify the
/p
modifier.
To better align the printed instructions when the trace contains
instructions from more than one function, the function name may be
omitted by specifying the /f
modifier.
Speculatively executed instructions are prefixed with ‘?’. This feature is not available for all recording formats.
There are several ways to specify what part of the execution log to disassemble:
record instruction-history
insnrecord instruction-history
insn, +/-
n+
, disassembles
n instructions after instruction number insn. If
n is preceded with -
, disassembles n
instructions before instruction number insn.
record instruction-history
record instruction-history -
record instruction-history
begin,
endThis command may not be available for all recording methods.
set record instruction-history-size
sizeset record instruction-history-size unlimited
record
instruction-history
command. The default value is 10.
A size of unlimited
means unlimited instructions.
show record instruction-history-size
record
instruction-history
command.
record function-call-history
/l
modifier is
specified), and the instructions numbers that form the sequence (if
the /i
modifier is specified). The function names are indented
to reflect the call stack depth if the /c
modifier is
specified. The /l
, /i
, and /c
modifiers can be
given together.
(gdb) list 1, 10 1 void foo (void) 2 { 3 } 4 5 void bar (void) 6 { 7 ... 8 foo (); 9 ... 10 } (gdb) record function-call-history /ilc 1 bar inst 1,4 at foo.c:6,8 2 foo inst 5,10 at foo.c:2,3 3 bar inst 11,13 at foo.c:9,10
By default, ten lines are printed. This can be changed using the
set record function-call-history-size
command. Functions are
printed in execution order. There are several ways to specify what
to print:
record function-call-history
funcrecord function-call-history
func, +/-
n+
, prints n functions after
function number func. If n is preceded with -
,
prints n functions before function number func.
record function-call-history
record function-call-history -
record function-call-history
begin,
endThis command may not be available for all recording methods.
set record function-call-history-size
sizeset record function-call-history-size unlimited
record function-call-history
command. The default value is 10.
A size of unlimited
means unlimited lines.
show record function-call-history-size
record function-call-history
command.
When your program has stopped, the first thing you need to know is where it stopped and how it got there.
Each time your program performs a function call, information about the call is generated. That information includes the location of the call in your program, the arguments of the call, and the local variables of the function being called. The information is saved in a block of data called a stack frame. The stack frames are allocated in a region of memory called the call stack.
When your program stops, the gdb commands for examining the stack allow you to see all of this information.
One of the stack frames is selected by gdb and many gdb commands refer implicitly to the selected frame. In particular, whenever you ask gdb for the value of a variable in your program, the value is found in the selected frame. There are special gdb commands to select whichever frame you are interested in. See Selecting a Frame.
When your program stops, gdb automatically selects the
currently executing frame and describes it briefly, similar to the
frame
command (see Information about a Frame).
The call stack is divided up into contiguous pieces called stack frames, or frames for short; each frame is the data associated with one call to one function. The frame contains the arguments given to the function, the function's local variables, and the address at which the function is executing.
When your program is started, the stack has only one frame, that of the
function main
. This is called the initial frame or the
outermost frame. Each time a function is called, a new frame is
made. Each time a function returns, the frame for that function invocation
is eliminated. If a function is recursive, there can be many frames for
the same function. The frame for the function in which execution is
actually occurring is called the innermost frame. This is the most
recently created of all the stack frames that still exist.
Inside your program, stack frames are identified by their addresses. A stack frame consists of many bytes, each of which has its own address; each kind of computer has a convention for choosing one byte whose address serves as the address of the frame. Usually this address is kept in a register called the frame pointer register (see $fp) while execution is going on in that frame.
gdb labels each existing stack frame with a level, a number that is zero for the innermost frame, one for the frame that called it, and so on upward. These level numbers give you a way of designating stack frames in gdb commands. The terms frame number and frame level can be used interchangeably to describe this number.
Some compilers provide a way to compile functions so that they operate without stack frames. (For example, the gcc option
‘-fomit-frame-pointer’
generates functions without a frame.) This is occasionally done with heavily used library functions to save the frame setup time. gdb has limited facilities for dealing with these function invocations. If the innermost function invocation has no stack frame, gdb nevertheless regards it as though it had a separate frame, which is numbered zero as usual, allowing correct tracing of the function call chain. However, gdb has no provision for frameless functions elsewhere in the stack.
A backtrace is a summary of how your program got where it is. It shows one line per frame, for many frames, starting with the currently executing frame (frame zero), followed by its caller (frame one), and on up the stack.
To print a backtrace of the entire stack, use the backtrace
command, or its alias bt
. This command will print one line per
frame for frames in the stack. By default, all stack frames are
printed. You can stop the backtrace at any time by typing the system
interrupt character, normally Ctrl-c.
backtrace [
option]... [
qualifier]... [
count]
bt [
option]... [
qualifier]... [
count]
The optional count can be one of the following:
-
n-
nOptions:
-full
-no-filters
Python
support.
-hide
-hide
option causes elided frames to not be printed at all.
The backtrace
command also supports a number of options that
allow overriding relevant global print settings as set by set
backtrace
and set print
subcommands:
-past-main [on|off]
main
. Related setting:
set backtrace past-main.
-past-entry [on|off]
-entry-values no|only|preferred|if-needed|both|compact|default
-frame-arguments all|scalars|none
-raw-frame-arguments [on|off]
-frame-info auto|source-line|location|source-and-location|location-and-address|short-location
The optional qualifier is maintained for backward compatibility. It can be one of the following:
full
-full
option.
no-filters
-no-filters
option.
hide
-hide
option.
The names where
and info stack
(abbreviated info s
)
are additional aliases for backtrace
.
In a multi-threaded program, gdb by default shows the
backtrace only for the current thread. To display the backtrace for
several or all of the threads, use the command thread apply
(see thread apply). For example, if you type thread
apply all backtrace, gdb will display the backtrace for all
the threads; this is handy when you debug a core dump of a
multi-threaded program.
Each line in the backtrace shows the frame number and the function name.
The program counter value is also shown—unless you use set
print address off
. The backtrace also shows the source file name and
line number, as well as the arguments to the function. The program
counter value is omitted if it is at the beginning of the code for that
line number.
Here is an example of a backtrace. It was made with the command ‘bt 3’, so it shows the innermost three frames.
#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) at builtin.c:993 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08) at macro.c:71 (More stack frames follow...)
The display for frame zero does not begin with a program counter
value, indicating that your program has stopped at the beginning of the
code for line 993
of builtin.c
.
The value of parameter data
in frame 1 has been replaced by
...
. By default, gdb prints the value of a parameter
only if it is a scalar (integer, pointer, enumeration, etc). See command
set print frame-arguments in Print Settings for more details
on how to configure the way function parameter values are printed.
The command set print frame-info (see Print Settings) controls
what frame information is printed.
If your program was compiled with optimizations, some compilers will optimize away arguments passed to functions if those arguments are never used after the call. Such optimizations generate code that passes arguments through registers, but doesn't store those arguments in the stack frame. gdb has no way of displaying such arguments in stack frames other than the innermost one. Here's what such a backtrace might look like:
#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) at builtin.c:993 #1 0x6e38 in expand_macro (sym=<optimized out>) at macro.c:242 #2 0x6840 in expand_token (obs=0x0, t=<optimized out>, td=0xf7fffb08) at macro.c:71 (More stack frames follow...)
The values of arguments that were not saved in their stack frames are shown as ‘<optimized out>’.
If you need to display the values of such optimized-out arguments, either deduce that from other variables whose values depend on the one you are interested in, or recompile without optimizations.
Most programs have a standard user entry point—a place where system
libraries and startup code transition into user code. For C this is
main
8.
When gdb finds the entry function in a backtrace
it will terminate the backtrace, to avoid tracing into highly
system-specific (and generally uninteresting) code.
If you need to examine the startup code, or limit the number of levels in a backtrace, you can change this behavior:
set backtrace past-main
set backtrace past-main on
set backtrace past-main off
show backtrace past-main
set backtrace past-entry
set backtrace past-entry on
main
(or equivalent) is called.
set backtrace past-entry off
show backtrace past-entry
set backtrace limit
nset backtrace limit 0
set backtrace limit unlimited
unlimited
or zero means unlimited levels.
show backtrace limit
You can control how file names are displayed.
set filename-display
set filename-display relative
set filename-display basename
set filename-display absolute
show filename-display
Most commands for examining the stack and other data in your program work on whichever stack frame is selected at the moment. Here are the commands for selecting a stack frame; all of them finish by printing a brief description of the stack frame just selected.
frame
[ frame-selection-spec ]f
[ frame-selection-spec ]level
nummain
.
As this is the most common method of navigating the frame stack, the string level can be omitted. For example, the following two commands are equivalent:
(gdb) frame 3 (gdb) frame level 3
address
stack-address(gdb) info frame Stack level 1, frame at 0x7fffffffda30: rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5 tail call frame, caller of frame at 0x7fffffffda30 source language c++. Arglist at unknown address. Locals at unknown address, Previous frame's sp is 0x7fffffffda30
The stack-address for this frame is 0x7fffffffda30
as
indicated by the line:
Stack level 1, frame at 0x7fffffffda30:
function
function-nameview
stack-address [ pc-addr ]This is useful mainly if the chaining of stack frames has been damaged by a bug, making it impossible for gdb to assign numbers properly to all frames. In addition, this can be useful when your program has multiple stacks and switches between them.
When viewing a frame outside the current backtrace using frame view then you can always return to the original stack using one of the previous stack frame selection instructions, for example frame level 0.
up
ndown
ndown
as do
.
All of these commands end by printing two lines of output describing the frame. The first line shows the frame number, the function name, the arguments, and the source file and line number of execution in that frame. The second line shows the text of that source line.
For example:
(gdb) up #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc) at env.c:10 10 read_input_file (argv[i]);
After such a printout, the list
command with no arguments
prints ten lines centered on the point of execution in the frame.
You can also edit the program at the point of execution with your favorite
editing program by typing edit
.
See Printing Source Lines,
for details.
select-frame
[ frame-selection-spec ]select-frame
command is a variant of frame
that does
not display the new frame after selecting it. This command is
intended primarily for use in gdb command scripts, where the
output might be unnecessary and distracting. The
frame-selection-spec is as for the frame command
described in Selecting a Frame.
up-silently
ndown-silently
nup
and down
,
respectively; they differ in that they do their work silently, without
causing display of the new frame. They are intended primarily for use
in gdb command scripts, where the output might be unnecessary and
distracting.
There are several other commands to print information about the selected stack frame.
frame
f
f
. With an
argument, this command is used to select a stack frame.
See Selecting a Frame.
info frame
info f
The verbose description is useful when
something has gone wrong that has made the stack format fail to fit
the usual conventions.
info frame
[ frame-selection-spec ]info f
[ frame-selection-spec ]info args [-q]
The optional flag ‘-q’, which stands for ‘quiet’, disables
printing header information and messages explaining why no argument
have been printed.
info args [-q] [-t
type_regexp] [
regexp]
If regexp is provided, print only the arguments whose names match the regular expression regexp.
If type_regexp is provided, print only the arguments whose
types, as printed by the whatis
command, match
the regular expression type_regexp.
If type_regexp contains space(s), it should be enclosed in
quote characters. If needed, use backslash to escape the meaning
of special characters or quotes.
If both regexp and type_regexp are provided, an argument
is printed only if its name matches regexp and its type matches
type_regexp.
info locals [-q]
The optional flag ‘-q’, which stands for ‘quiet’, disables
printing header information and messages explaining why no local variables
have been printed.
info locals [-q] [-t
type_regexp] [
regexp]
If regexp is provided, print only the local variables whose names match the regular expression regexp.
If type_regexp is provided, print only the local variables whose
types, as printed by the whatis
command, match
the regular expression type_regexp.
If type_regexp contains space(s), it should be enclosed in
quote characters. If needed, use backslash to escape the meaning
of special characters or quotes.
If both regexp and type_regexp are provided, a local variable is printed only if its name matches regexp and its type matches type_regexp.
The command info locals -q -t type_regexp can usefully be
combined with the commands frame apply and thread apply.
For example, your program might use Resource Acquisition Is
Initialization types (RAII) such as lock_something_t
: each
local variable of type lock_something_t
automatically places a
lock that is destroyed when the variable goes out of scope. You can
then list all acquired locks in your program by doing
thread apply all -s frame apply all -s info locals -q -t lock_something_t
or the equivalent shorter form
tfaas i lo -q -t lock_something_t
frame apply [all |
count |
-count | level
level...] [
option]...
commandframe apply
command allows you to apply the named
command to one or more frames.
all
all
to apply command to all frames.
level
level
to apply command to the set of frames identified
by the level list. level is a frame level or a range of frame
levels as level1-level2. The frame level is the number shown
in the first field of the ‘backtrace’ command output.
E.g., ‘2-4 6-8 3’ indicates to apply command for the frames
at levels 2, 3, 4, 6, 7, 8, and then again on frame at level 3.
Note that the frames on which frame apply
applies a command are
also influenced by the set backtrace
settings such as set
backtrace past-main
and set backtrace limit N
.
See Backtraces.
The frame apply
command also supports a number of options that
allow overriding relevant set backtrace
settings:
-past-main [on|off]
main
.
Related setting: set backtrace past-main.
-past-entry [on|off]
By default, gdb displays some frame information before the
output produced by command, and an error raised during the
execution of a command will abort frame apply
. The
following options can be used to fine-tune these behaviors:
-c
-c
, which stands for ‘continue’, causes any
errors in command to be displayed, and the execution of
frame apply
then continues.
-s
-s
, which stands for ‘silent’, causes any errors
or empty output produced by a command to be silently ignored.
That is, the execution continues, but the frame information and errors
are not printed.
-q
-q
(‘quiet’) disables printing the frame
information.
The following example shows how the flags -c
and -s
are
working when applying the command p j
to all frames, where
variable j
can only be successfully printed in the outermost
#1 main
frame.
(gdb) frame apply all p j #0 some_function (i=5) at fun.c:4 No symbol "j" in current context. (gdb) frame apply all -c p j #0 some_function (i=5) at fun.c:4 No symbol "j" in current context. #1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11 $1 = 5 (gdb) frame apply all -s p j #1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11 $2 = 5 (gdb)
By default, ‘frame apply’, prints the frame location information before the command output:
(gdb) frame apply all p $sp #0 some_function (i=5) at fun.c:4 $4 = (void *) 0xffffd1e0 #1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11 $5 = (void *) 0xffffd1f0 (gdb)
If the flag -q
is given, no frame information is printed:
(gdb) frame apply all -q p $sp $12 = (void *) 0xffffd1e0 $13 = (void *) 0xffffd1f0 (gdb)
faas
commandframe apply all -s
command.
Applies command on all frames, ignoring errors and empty output.
It can for example be used to print a local variable or a function argument without knowing the frame where this variable or argument is, using:
(gdb) faas p some_local_var_i_do_not_remember_where_it_is
The faas
command accepts the same options as the frame
apply
command. See frame apply.
Note that the command tfaas
command applies command
on all frames of all threads. See See Threads.
Frame filters are Python based utilities to manage and decorate the output of frames. See Frame Filter API, for further information.
Managing frame filters is performed by several commands available within gdb, detailed here.
info frame-filter
disable frame-filter
filter-dictionary filter-nameall
, global
,
progspace
, or the name of the object file where the frame filter
dictionary resides. When all
is specified, all frame filters
across all dictionaries are disabled. The filter-name is the name
of the frame filter and is used when all
is not the option for
filter-dictionary. A disabled frame-filter is not deleted, it
may be enabled again later.
enable frame-filter
filter-dictionary filter-nameall
, global
,
progspace
or the name of the object file where the frame filter
dictionary resides. When all
is specified, all frame filters across
all dictionaries are enabled. The filter-name is the name of the frame
filter and is used when all
is not the option for
filter-dictionary.
Example:
(gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 No PrimaryFunctionFilter 100 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 Yes BuildProgramFilter (gdb) disable frame-filter /build/test BuildProgramFilter (gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 No PrimaryFunctionFilter 100 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 No BuildProgramFilter (gdb) enable frame-filter global PrimaryFunctionFilter (gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 Yes PrimaryFunctionFilter 100 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 No BuildProgramFilter
set frame-filter priority
filter-dictionary filter-name priorityglobal
,
progspace
or the name of the object file where the frame filter
dictionary resides. The priority is an integer.
show frame-filter priority
filter-dictionary filter-nameglobal
,
progspace
or the name of the object file where the frame filter
dictionary resides.
Example:
(gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 Yes PrimaryFunctionFilter 100 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 No BuildProgramFilter (gdb) set frame-filter priority global Reverse 50 (gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 Yes PrimaryFunctionFilter 50 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 No BuildProgramFilter
gdb can print parts of your program's source, since the debugging information recorded in the program tells gdb what source files were used to build it. When your program stops, gdb spontaneously prints the line where it stopped. Likewise, when you select a stack frame (see Selecting a Frame), gdb prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command.
If you use gdb through its gnu Emacs interface, you may prefer to use Emacs facilities to view source; see Using gdb under gnu Emacs.
To print lines from a source file, use the list
command
(abbreviated l
). By default, ten lines are printed.
There are several ways to specify what part of the file you want to
print; see Specify Location, for the full list.
Here are the forms of the list
command most commonly used:
list
linenumlist
functionlist
list
command, this prints lines following the last lines
printed; however, if the last line printed was a solitary line printed
as part of displaying a stack frame (see Examining the Stack), this prints lines centered around that line.
list -
By default, gdb prints ten source lines with any of these forms of
the list
command. You can change this using set listsize
:
set listsize
countset listsize unlimited
list
command display count source lines (unless
the list
argument explicitly specifies some other number).
Setting count to unlimited
or 0 means there's no limit.
show listsize
list
prints.
Repeating a list
command with <RET> discards the argument,
so it is equivalent to typing just list
. This is more useful
than listing the same lines again. An exception is made for an
argument of ‘-’; that argument is preserved in repetition so that
each repetition moves up in the source file.
In general, the list
command expects you to supply zero, one or two
locations. Locations specify source lines; there are several ways
of writing them (see Specify Location), but the effect is always
to specify some source line.
Here is a complete description of the possible arguments for list
:
list
locationlist
first,
lastlist
command has two locations, and the
source file of the second location is omitted, this refers to
the same source file as the first location.
list ,
lastlist
first,
list +
list -
list
Several gdb commands accept arguments that specify a location of your program's code. Since gdb is a source-level debugger, a location usually specifies some line in the source code. Locations may be specified using three different formats: linespec locations, explicit locations, or address locations.
A linespec is a colon-separated list of source location parameters such as file name, function name, etc. Here are all the different ways of specifying a linespec:
-
offset+
offsetlist
command, the current line is the last one
printed; for the breakpoint commands, this is the line at which
execution stopped in the currently selected stack frame
(see Frames, for a description of stack frames.) When
used as the second of the two linespecs in a list
command,
this specifies the line offset lines up or down from the first
linespec.
:
linenumBy default, in C++ and Ada, function is interpreted as specifying all functions named function in all scopes. For C++, this means in all namespaces and classes. For Ada, this means in all packages.
For example, assuming a program with C++ symbols named
A::B::func
and B::func
, both commands break func and break B::func set a breakpoint on both symbols.
Commands that accept a linespec let you override this with the
-qualified
option. For example, break -qualified func sets a breakpoint on a free-function named func
ignoring
any C++ class methods and namespace functions called func
.
See Explicit Locations.
:
label:
function-pstap|-probe-stap
[objfile:
[provider:
]]nameSystemTap
provides a way for
applications to embed static probes. See Static Probe Points, for more
information on finding and using static probes. This form of linespec
specifies the location of such a static probe.
If objfile is given, only probes coming from that shared library or executable matching objfile as a regular expression are considered. If provider is given, then only probes from that provider are considered. If several probes match the spec, gdb will insert a breakpoint at each one of those probes.
Explicit locations allow the user to directly specify the source location's parameters using option-value pairs.
Explicit locations are useful when several functions, labels, or file names have the same name (base name for files) in the program's sources. In these cases, explicit locations point to the source line you meant more accurately and unambiguously. Also, using explicit locations might be faster in large programs.
For example, the linespec ‘foo:bar’ may refer to a function bar
defined in the file named foo or the label bar
in a function
named foo
. gdb must search either the file system or
the symbol table to know.
The list of valid explicit location options is summarized in the following table:
-source
filename-function
or -line
.
-function
function-label
or -line
) refer to the line that begins the body of the function.
In C, for example, this is the line with the open brace.
By default, in C++ and Ada, function is interpreted as specifying all functions named function in all scopes. For C++, this means in all namespaces and classes. For Ada, this means in all packages.
For example, assuming a program with C++ symbols named
A::B::func
and B::func
, both commands break -function func and break -function B::func set a
breakpoint on both symbols.
You can use the -qualified flag to override this (see below).
-qualified
For example, assuming a C++ program with symbols named
A::B::func
and B::func
, the break -qualified -function B::func command sets a breakpoint on B::func
, only.
(Note: the -qualified option can precede a linespec as well
(see Linespec Locations), so the particular example above could be
simplified as break -qualified B::func.)
-label
label-line
number-line 3
) or relative (-line +3
), depending on
the command. When specified without any other options, the line offset is
relative to the current line.
Explicit location options may be abbreviated by omitting any non-unique trailing characters from the option name, e.g., break -s main.c -li 3.
Address locations indicate a specific program address. They have the generalized form *address.
For line-oriented commands, such as list
and edit
, this
specifies a source line that contains address. For break
and
other breakpoint-oriented commands, this can be used to set breakpoints in
parts of your program which do not have debugging information or
source files.
Here address may be any expression valid in the current working language (see working language) that specifies a code address. In addition, as a convenience, gdb extends the semantics of expressions used in locations to cover several situations that frequently occur during debugging. Here are the various forms of address:
&
function. In Ada, this is function'Address
(although the Pascal form also works).
This form specifies the address of the function's first instruction,
before the stack frame and arguments have been set up.
'
filename':
funcaddr
To edit the lines in a source file, use the edit
command.
The editing program of your choice
is invoked with the current line set to
the active line in the program.
Alternatively, there are several ways to specify what part of the file you
want to print if you want to see other parts of the program:
edit
locationlocation
. Editing starts at
that location, e.g., at the specified source line of the
specified file. See Specify Location, for all the possible forms
of the location argument; here are the forms of the edit
command most commonly used:
edit
numberedit
functionYou can customize gdb to use any editor you want
9.
By default, it is /bin/ex, but you can change this
by setting the environment variable EDITOR
before using
gdb. For example, to configure gdb to use the
vi
editor, you could use these commands with the sh
shell:
EDITOR=/usr/bin/vi export EDITOR gdb ...
or in the csh
shell,
setenv EDITOR /usr/bin/vi gdb ...
There are two commands for searching through the current source file for a regular expression.
forward-search
regexpsearch
regexpfo
.
reverse-search
regexprev
.
Executable programs sometimes do not record the directories of the source files from which they were compiled, just the names. Even when they do, the directories could be moved between the compilation and your debugging session. gdb has a list of directories to search for source files; this is called the source path. Each time gdb wants a source file, it tries all the directories in the list, in the order they are present in the list, until it finds a file with the desired name.
For example, suppose an executable references the file /usr/src/foo-1.0/lib/foo.c, does not record a compilation directory, and the source path is /mnt/cross. gdb would look for the source file in the following locations:
If the source file is not present at any of the above locations then an error is printed. gdb does not look up the parts of the source file name, such as /mnt/cross/src/foo-1.0/lib/foo.c. Likewise, the subdirectories of the source path are not searched: if the source path is /mnt/cross, and the binary refers to foo.c, gdb would not find it under /mnt/cross/usr/src/foo-1.0/lib.
Plain file names, relative file names with leading directories, file names containing dots, etc. are all treated as described above, except that non-absolute file names are not looked up literally. If the source path is /mnt/cross, the source file is recorded as ../lib/foo.c, and no compilation directory is recorded, then gdb will search in the following locations:
The source path will always include two special entries ‘$cdir’ and ‘$cwd’, these refer to the compilation directory (if one is recorded) and the current working directory respectively.
‘$cdir’ causes gdb to search within the compilation directory, if one is recorded in the debug information. If no compilation directory is recorded in the debug information then ‘$cdir’ is ignored.
‘$cwd’ is not the same as ‘.’—the former tracks the current working directory as it changes during your gdb session, while the latter is immediately expanded to the current directory at the time you add an entry to the source path.
If a compilation directory is recorded in the debug information, and gdb has not found the source file after the first search using source path, then gdb will combine the compilation directory and the filename, and then search for the source file again using the source path.
For example, if the executable records the source file as /usr/src/foo-1.0/lib/foo.c, the compilation directory is recorded as /project/build, and the source path is /mnt/cross:$cdir:$cwd while the current working directory of the gdb session is /home/user, then gdb will search for the source file in the following locations:
If the file name in the previous example had been recorded in the executable as a relative path rather than an absolute path, then the first look up would not have occurred, but all of the remaining steps would be similar.
When searching for source files on MS-DOS and MS-Windows, where absolute paths start with a drive letter (e.g. C:/project/foo.c), gdb will remove the drive letter from the file name before appending it to a search directory from source path; for instance if the executable references the source file C:/project/foo.c and source path is set to D:/mnt/cross, then gdb will search in the following locations for the source file:
Note that the executable search path is not used to locate the source files.
Whenever you reset or rearrange the source path, gdb clears out any information it has cached about where source files are found and where each line is in the file.
When you start gdb, its source path includes only ‘$cdir’
and ‘$cwd’, in that order.
To add other directories, use the directory
command.
The search path is used to find both program source files and gdb script files (read using the ‘-command’ option and ‘source’ command).
In addition to the source path, gdb provides a set of commands that manage a list of source path substitution rules. A substitution rule specifies how to rewrite source directories stored in the program's debug information in case the sources were moved to a different directory between compilation and debugging. A rule is made of two strings, the first specifying what needs to be rewritten in the path, and the second specifying how it should be rewritten. In set substitute-path, we name these two parts from and to respectively. gdb does a simple string replacement of from with to at the start of the directory part of the source file name, and uses that result instead of the original file name to look up the sources.
Using the previous example, suppose the foo-1.0 tree has been
moved from /usr/src to /mnt/cross, then you can tell
gdb to replace /usr/src in all source path names with
/mnt/cross. The first lookup will then be
/mnt/cross/foo-1.0/lib/foo.c in place of the original location
of /usr/src/foo-1.0/lib/foo.c. To define a source path
substitution rule, use the set substitute-path
command
(see set substitute-path).
To avoid unexpected substitution results, a rule is applied only if the from part of the directory name ends at a directory separator. For instance, a rule substituting /usr/source into /mnt/cross will be applied to /usr/source/foo-1.0 but not to /usr/sourceware/foo-2.0. And because the substitution is applied only at the beginning of the directory name, this rule will not be applied to /root/usr/source/baz.c either.
In many cases, you can achieve the same result using the directory
command. However, set substitute-path
can be more efficient in
the case where the sources are organized in a complex tree with multiple
subdirectories. With the directory
command, you need to add each
subdirectory of your project. If you moved the entire tree while
preserving its internal organization, then set substitute-path
allows you to direct the debugger to all the sources with one single
command.
set substitute-path
is also more than just a shortcut command.
The source path is only used if the file at the original location no
longer exists. On the other hand, set substitute-path
modifies
the debugger behavior to look at the rewritten location instead. So, if
for any reason a source file that is not relevant to your executable is
located at the original location, a substitution rule is the only
method available to point gdb at the new location.
You can configure a default source path substitution rule by configuring gdb with the ‘--with-relocated-sources=dir’ option. The dir should be the name of a directory under gdb's configured prefix (set with ‘--prefix’ or ‘--exec-prefix’), and directory names in debug information under dir will be adjusted automatically if the installed gdb is moved to a new location. This is useful if gdb, libraries or executables with debug information and corresponding source code are being moved together.
directory
dirname ...
dir
dirname ...
The special strings ‘$cdir’ (to refer to the compilation
directory, if one is recorded), and ‘$cwd’ (to refer to the
current working directory) can also be included in the list of
directories dirname. Though these will already be in the source
path they will be moved forward in the list so gdb searches
them sooner.
directory
set directories
path-listshow directories
set substitute-path
from toFor example, if the file /foo/bar/baz.c was moved to /mnt/cross/baz.c, then the command
(gdb) set substitute-path /foo/bar /mnt/cross
will tell gdb to replace ‘/foo/bar’ with ‘/mnt/cross’, which will allow gdb to find the file baz.c even though it was moved.
In the case when more than one substitution rule have been defined, the rules are evaluated one by one in the order where they have been defined. The first one matching, if any, is selected to perform the substitution.
For instance, if we had entered the following commands:
(gdb) set substitute-path /usr/src/include /mnt/include (gdb) set substitute-path /usr/src /mnt/src
gdb would then rewrite /usr/src/include/defs.h into
/mnt/include/defs.h by using the first rule. However, it would
use the second rule to rewrite /usr/src/lib/foo.c into
/mnt/src/lib/foo.c.
unset substitute-path [path]
If no path is specified, then all substitution rules are deleted.
show substitute-path [path]
If no path is specified, then print all existing source path substitution rules.
If your source path is cluttered with directories that are no longer of interest, gdb may sometimes cause confusion by finding the wrong versions of source. You can correct the situation as follows:
directory
with no argument to reset the source path to its default value.
directory
with suitable arguments to reinstall the
directories you want in the source path. You can add all the
directories in one command.
You can use the command info line
to map source lines to program
addresses (and vice versa), and the command disassemble
to display
a range of addresses as machine instructions. You can use the command
set disassemble-next-line
to set whether to disassemble next
source line when execution stops. When run under gnu Emacs
mode, the info line
command causes the arrow to point to the
line specified. Also, info line
prints addresses in symbolic form as
well as hex.
info line
info line
locationFor example, we can use info line
to discover the location of
the object code for the first line of function
m4_changequote
:
(gdb) info line m4_changequote Line 895 of "builtin.c" starts at pc 0x634c <m4_changequote> and \ ends at 0x6350 <m4_changequote+4>.
We can also inquire (using *
addr as the form for
location) what source line covers a particular address:
(gdb) info line *0x63ff Line 926 of "builtin.c" starts at pc 0x63e4 <m4_changequote+152> and \ ends at 0x6404 <m4_changequote+184>.
After info line
, the default address for the x
command
is changed to the starting address of the line, so that ‘x/i’ is
sufficient to begin examining the machine code (see Examining Memory). Also, this address is saved as the value of the
convenience variable $_
(see Convenience Variables).
After info line
, using info line
again without
specifying a location will display information about the next source
line.
disassemble
disassemble /m
disassemble /s
disassemble /r
/m
or /s
modifier and print the raw instructions in hex
as well as in symbolic form by specifying the /r
modifier.
The default memory range is the function surrounding the
program counter of the selected frame. A single argument to this
command is a program counter value; gdb dumps the function
surrounding this value. When two arguments are given, they should
be separated by a comma, possibly surrounded by whitespace. The
arguments specify a range of addresses to dump, in one of two forms:
,
end,+
length+
length (exclusive).
When 2 arguments are specified, the name of the function is also printed (since there could be several functions in the given range).
The argument(s) can be any expression yielding a numeric value, such as ‘0x32c4’, ‘&main+10’ or ‘$pc - 8’.
If the range of memory being disassembled contains current program counter,
the instruction at that location is shown with a =>
marker.
The following example shows the disassembly of a range of addresses of HP PA-RISC 2.0 code:
(gdb) disas 0x32c4, 0x32e4 Dump of assembler code from 0x32c4 to 0x32e4: 0x32c4 <main+204>: addil 0,dp 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26 0x32cc <main+212>: ldil 0x3000,r31 0x32d0 <main+216>: ble 0x3f8(sr4,r31) 0x32d4 <main+220>: ldo 0(r31),rp 0x32d8 <main+224>: addil -0x800,dp 0x32dc <main+228>: ldo 0x588(r1),r26 0x32e0 <main+232>: ldil 0x3000,r31 End of assembler dump.
Here is an example showing mixed source+assembly for Intel x86
with /m
or /s
, when the program is stopped just after
function prologue in a non-optimized function with no inline code.
(gdb) disas /m main Dump of assembler code for function main: 5 { 0x08048330 <+0>: push %ebp 0x08048331 <+1>: mov %esp,%ebp 0x08048333 <+3>: sub $0x8,%esp 0x08048336 <+6>: and $0xfffffff0,%esp 0x08048339 <+9>: sub $0x10,%esp 6 printf ("Hello.\n"); => 0x0804833c <+12>: movl $0x8048440,(%esp) 0x08048343 <+19>: call 0x8048284 <puts@plt> 7 return 0; 8 } 0x08048348 <+24>: mov $0x0,%eax 0x0804834d <+29>: leave 0x0804834e <+30>: ret End of assembler dump.
The /m
option is deprecated as its output is not useful when
there is either inlined code or re-ordered code.
The /s
option is the preferred choice.
Here is an example for AMD x86-64 showing the difference between
/m
output and /s
output.
This example has one inline function defined in a header file,
and the code is compiled with ‘-O2’ optimization.
Note how the /m
output is missing the disassembly of
several instructions that are present in the /s
output.
foo.h:
int foo (int a) { if (a < 0) return a * 2; if (a == 0) return 1; return a + 10; }
foo.c:
#include "foo.h" volatile int x, y; int main () { x = foo (y); return 0; }
(gdb) disas /m main Dump of assembler code for function main: 5 { 6 x = foo (y); 0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y> 0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x> 7 return 0; 8 } 0x000000000040041d <+29>: xor %eax,%eax 0x000000000040041f <+31>: retq 0x0000000000400420 <+32>: add %eax,%eax 0x0000000000400422 <+34>: jmp 0x400417 <main+23> End of assembler dump. (gdb) disas /s main Dump of assembler code for function main: foo.c: 5 { 6 x = foo (y); 0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y> foo.h: 4 if (a < 0) 0x0000000000400406 <+6>: test %eax,%eax 0x0000000000400408 <+8>: js 0x400420 <main+32> 6 if (a == 0) 7 return 1; 8 return a + 10; 0x000000000040040a <+10>: lea 0xa(%rax),%edx 0x000000000040040d <+13>: test %eax,%eax 0x000000000040040f <+15>: mov $0x1,%eax 0x0000000000400414 <+20>: cmovne %edx,%eax foo.c: 6 x = foo (y); 0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x> 7 return 0; 8 } 0x000000000040041d <+29>: xor %eax,%eax 0x000000000040041f <+31>: retq foo.h: 5 return a * 2; 0x0000000000400420 <+32>: add %eax,%eax 0x0000000000400422 <+34>: jmp 0x400417 <main+23> End of assembler dump.
Here is another example showing raw instructions in hex for AMD x86-64,
(gdb) disas /r 0x400281,+10 Dump of assembler code from 0x400281 to 0x40028b: 0x0000000000400281: 38 36 cmp %dh,(%rsi) 0x0000000000400283: 2d 36 34 2e 73 sub $0x732e3436,%eax 0x0000000000400288: 6f outsl %ds:(%rsi),(%dx) 0x0000000000400289: 2e 32 00 xor %cs:(%rax),%al End of assembler dump.
Addresses cannot be specified as a location (see Specify Location).
So, for example, if you want to disassemble function bar
in file foo.c, you must type ‘disassemble 'foo.c'::bar’
and not ‘disassemble foo.c:bar’.
Some architectures have more than one commonly-used set of instruction mnemonics or other syntax.
For programs that were dynamically linked and use shared libraries, instructions that call functions or branch to locations in the shared libraries might show a seemingly bogus location—it's actually a location of the relocation table. On some architectures, gdb might be able to resolve these to actual function names.
set disassembler-options
option1[,
option2...]
-M
/--disassembler-options
section of the ‘objdump’
manual and/or the output of objdump --help
(see objdump).
The default value is the empty string.
If it is necessary to specify more than one disassembler option, then multiple options can be placed together into a comma separated list. Currently this command is only supported on targets ARM, MIPS, PowerPC and S/390.
show disassembler-options
set disassembly-flavor
instruction-setdisassemble
or x/i
commands.
Currently this command is only defined for the Intel x86 family. You
can set instruction-set to either intel
or att
.
The default is att
, the AT&T flavor used by default by Unix
assemblers for x86-based targets.
show disassembly-flavor
set disassemble-next-line
show disassemble-next-line
The usual way to examine data in your program is with the print
command (abbreviated p
), or its synonym inspect
. It
evaluates and prints the value of an expression of the language your
program is written in (see Using gdb with Different Languages). It may also print the expression using a
Python-based pretty-printer (see Pretty Printing).
print [[
options] --]
exprprint [[
options] --] /
f exprThe print
command supports a number of options that allow
overriding relevant global print settings as set by set print
subcommands:
-address [on|off]
-array [on|off]
-array-indexes [on|off]
-elements
number-of-elements|unlimited
unlimited
causes there to be no limit. Related setting:
set print elements.
-max-depth
depth|unlimited
-null-stop [on|off]
-object [on|off]
-pretty [on|off]
-raw-values [on|off]
-repeats
number-of-repeats|unlimited
unlimited
causes
all elements to be individually printed. Related setting: set print repeats.
-static-members [on|off]
-symbol [on|off]
-union [on|off]
-vtbl [on|off]
Because the print
command accepts arbitrary expressions which
may look like options (including abbreviations), if you specify any
command option, then you must use a double dash (--
) to mark
the end of option processing.
For example, this prints the value of the -p
expression:
(gdb) print -p
While this repeats the last value in the value history (see below)
with the -pretty
option in effect:
(gdb) print -p --
Here is an example including both on option and an expression:
(gdb) print -pretty -- *myptr $1 = { next = 0x0, flags = { sweet = 1, sour = 1 }, meat = 0x54 "Pork" }
print [
options]
print [
options] /
fA more low-level way of examining data is with the x
command.
It examines data in memory at a specified address and prints it in a
specified format. See Examining Memory.
If you are interested in information about types, or about how the
fields of a struct or a class are declared, use the ptype
exp
command rather than print
. See Examining the Symbol Table.
Another way of examining values of expressions and type information is
through the Python extension command explore
(available only if
the gdb build is configured with --with-python
). It
offers an interactive way to start at the highest level (or, the most
abstract level) of the data type of an expression (or, the data type
itself) and explore all the way down to leaf scalar values/fields
embedded in the higher level data types.
explore
argThe working of the explore
command can be illustrated with an
example. If a data type struct ComplexStruct
is defined in your
C program as
struct SimpleStruct { int i; double d; }; struct ComplexStruct { struct SimpleStruct *ss_p; int arr[10]; };
followed by variable declarations as
struct SimpleStruct ss = { 10, 1.11 }; struct ComplexStruct cs = { &ss, { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 } };
then, the value of the variable cs
can be explored using the
explore
command as follows.
(gdb) explore cs The value of `cs' is a struct/class of type `struct ComplexStruct' with the following fields: ss_p = <Enter 0 to explore this field of type `struct SimpleStruct *'> arr = <Enter 1 to explore this field of type `int [10]'> Enter the field number of choice:
Since the fields of cs
are not scalar values, you are being
prompted to chose the field you want to explore. Let's say you choose
the field ss_p
by entering 0
. Then, since this field is a
pointer, you will be asked if it is pointing to a single value. From
the declaration of cs
above, it is indeed pointing to a single
value, hence you enter y
. If you enter n
, then you will
be asked if it were pointing to an array of values, in which case this
field will be explored as if it were an array.
`cs.ss_p' is a pointer to a value of type `struct SimpleStruct' Continue exploring it as a pointer to a single value [y/n]: y The value of `*(cs.ss_p)' is a struct/class of type `struct SimpleStruct' with the following fields: i = 10 .. (Value of type `int') d = 1.1100000000000001 .. (Value of type `double') Press enter to return to parent value:
If the field arr
of cs
was chosen for exploration by
entering 1
earlier, then since it is as array, you will be
prompted to enter the index of the element in the array that you want
to explore.
`cs.arr' is an array of `int'. Enter the index of the element you want to explore in `cs.arr': 5 `(cs.arr)[5]' is a scalar value of type `int'. (cs.arr)[5] = 4 Press enter to return to parent value:
In general, at any stage of exploration, you can go deeper towards the leaf values by responding to the prompts appropriately, or hit the return key to return to the enclosing data structure (the higher level data structure).
Similar to exploring values, you can use the explore
command to
explore types. Instead of specifying a value (which is typically a
variable name or an expression valid in the current context of the
program being debugged), you specify a type name. If you consider the
same example as above, your can explore the type
struct ComplexStruct
by passing the argument
struct ComplexStruct
to the explore
command.
(gdb) explore struct ComplexStruct
By responding to the prompts appropriately in the subsequent interactive
session, you can explore the type struct ComplexStruct
in a
manner similar to how the value cs
was explored in the above
example.
The explore
command also has two sub-commands,
explore value
and explore type
. The former sub-command is
a way to explicitly specify that value exploration of the argument is
being invoked, while the latter is a way to explicitly specify that type
exploration of the argument is being invoked.
explore value
exprexplore
explores the value of the
expression expr (if expr is an expression valid in the
current context of the program being debugged). The behavior of this
command is identical to that of the behavior of the explore
command being passed the argument expr.
explore type
argexplore
explores the type of arg (if
arg is a type visible in the current context of program being
debugged), or the type of the value/expression arg (if arg
is an expression valid in the current context of the program being
debugged). If arg is a type, then the behavior of this command is
identical to that of the explore
command being passed the
argument arg. If arg is an expression, then the behavior of
this command will be identical to that of the explore
command
being passed the type of arg as the argument.
print
and many other gdb commands accept an expression and
compute its value. Any kind of constant, variable or operator defined
by the programming language you are using is valid in an expression in
gdb. This includes conditional expressions, function calls,
casts, and string constants. It also includes preprocessor macros, if
you compiled your program to include this information; see
Compilation.
Beware that nested functions usually need a context to be set up before being called. Unfortunately, GDB currently has no knowledge of this setup, and hence generally cannot call nested functions correctly. Therefore, the result of such a call is likely to be erroneous, and may even crash the program being debugged.
gdb supports array constants in expressions input by
the user. The syntax is {element, element...}. For example,
you can use the command print {1, 2, 3}
to create an array
of three integers. If you pass an array to a function or assign it
to a program variable, gdb copies the array to memory that
is malloc
ed in the target program.
Because C is so widespread, most of the expressions shown in examples in this manual are in C. See Using gdb with Different Languages, for information on how to use expressions in other languages.
In this section, we discuss operators that you can use in gdb expressions regardless of your programming language.
Casts are supported in all languages, not just in C, because it is so useful to cast a number into a pointer in order to examine a structure at that address in memory.
gdb supports these operators, in addition to those common to programming languages:
@
::
{
type}
addrExpressions can sometimes contain some ambiguous elements. For instance, some programming languages (notably Ada, C++ and Objective-C) permit a single function name to be defined several times, for application in different contexts. This is called overloading. Another example involving Ada is generics. A generic package is similar to C++ templates and is typically instantiated several times, resulting in the same function name being defined in different contexts.
In some cases and depending on the language, it is possible to adjust the expression to remove the ambiguity. For instance in C++, you can specify the signature of the function you want to break on, as in break function(types). In Ada, using the fully qualified name of your function often makes the expression unambiguous as well.
When an ambiguity that needs to be resolved is detected, the debugger has the capability to display a menu of numbered choices for each possibility, and then waits for the selection with the prompt ‘>’. The first option is always ‘[0] cancel’, and typing 0 <RET> aborts the current command. If the command in which the expression was used allows more than one choice to be selected, the next option in the menu is ‘[1] all’, and typing 1 <RET> selects all possible choices.
For example, the following session excerpt shows an attempt to set a
breakpoint at the overloaded symbol String::after
.
We choose three particular definitions of that function name:
(gdb) b String::after [0] cancel [1] all [2] file:String.cc; line number:867 [3] file:String.cc; line number:860 [4] file:String.cc; line number:875 [5] file:String.cc; line number:853 [6] file:String.cc; line number:846 [7] file:String.cc; line number:735 > 2 4 6 Breakpoint 1 at 0xb26c: file String.cc, line 867. Breakpoint 2 at 0xb344: file String.cc, line 875. Breakpoint 3 at 0xafcc: file String.cc, line 846. Multiple breakpoints were set. Use the "delete" command to delete unwanted breakpoints. (gdb)
set multiple-symbols
modeBy default, mode is set to all
. If the command with which
the expression is used allows more than one choice, then gdb
automatically selects all possible choices. For instance, inserting
a breakpoint on a function using an ambiguous name results in a breakpoint
inserted on each possible match. However, if a unique choice must be made,
then gdb uses the menu to help you disambiguate the expression.
For instance, printing the address of an overloaded function will result
in the use of the menu.
When mode is set to ask
, the debugger always uses the menu
when an ambiguity is detected.
Finally, when mode is set to cancel
, the debugger reports
an error due to the ambiguity and the command is aborted.
show multiple-symbols
multiple-symbols
setting.
The most common kind of expression to use is the name of a variable in your program.
Variables in expressions are understood in the selected stack frame (see Selecting a Frame); they must be either:
or
This means that in the function
foo (a) int a; { bar (a); { int b = test (); bar (b); } }
you can examine and use the variable a
whenever your program is
executing within the function foo
, but you can only use or
examine the variable b
while your program is executing inside
the block where b
is declared.
There is an exception: you can refer to a variable or function whose
scope is a single source file even if the current execution point is not
in this file. But it is possible to have more than one such variable or
function with the same name (in different source files). If that
happens, referring to that name has unpredictable effects. If you wish,
you can specify a static variable in a particular function or file by
using the colon-colon (::
) notation:
file::variable function::variable
Here file or function is the name of the context for the
static variable. In the case of file names, you can use quotes to
make sure gdb parses the file name as a single word—for example,
to print a global value of x
defined in f2.c:
(gdb) p 'f2.c'::x
The ::
notation is normally used for referring to
static variables, since you typically disambiguate uses of local variables
in functions by selecting the appropriate frame and using the
simple name of the variable. However, you may also use this notation
to refer to local variables in frames enclosing the selected frame:
void foo (int a) { if (a < 10) bar (a); else process (a); /* Stop here */ } int bar (int a) { foo (a + 5); }
For example, if there is a breakpoint at the commented line,
here is what you might see
when the program stops after executing the call bar(0)
:
(gdb) p a $1 = 10 (gdb) p bar::a $2 = 5 (gdb) up 2 #2 0x080483d0 in foo (a=5) at foobar.c:12 (gdb) p a $3 = 5 (gdb) p bar::a $4 = 0
These uses of ‘::’ are very rarely in conflict with the very similar use of the same notation in C++. When they are in conflict, the C++ meaning takes precedence; however, this can be overridden by quoting the file or function name with single quotes.
For example, suppose the program is stopped in a method of a class
that has a field named includefile
, and there is also an
include file named includefile that defines a variable,
some_global
.
(gdb) p includefile $1 = 23 (gdb) p includefile::some_global A syntax error in expression, near `'. (gdb) p 'includefile'::some_global $2 = 27
Warning: Occasionally, a local variable may appear to have the wrong value at certain points in a function—just after entry to a new scope, and just before exit.You may see this problem when you are stepping by machine instructions. This is because, on most machines, it takes more than one instruction to set up a stack frame (including local variable definitions); if you are stepping by machine instructions, variables may appear to have the wrong values until the stack frame is completely built. On exit, it usually also takes more than one machine instruction to destroy a stack frame; after you begin stepping through that group of instructions, local variable definitions may be gone.
This may also happen when the compiler does significant optimizations. To be sure of always seeing accurate values, turn off all optimization when compiling.
Another possible effect of compiler optimizations is to optimize unused variables out of existence, or assign variables to registers (as opposed to memory addresses). Depending on the support for such cases offered by the debug info format used by the compiler, gdb might not be able to display values for such local variables. If that happens, gdb will print a message like this:
No symbol "foo" in current context.
To solve such problems, either recompile without optimizations, or use a different debug info format, if the compiler supports several such formats. See Compilation, for more information on choosing compiler options. See C and C++, for more information about debug info formats that are best suited to C++ programs.
If you ask to print an object whose contents are unknown to gdb, e.g., because its data type is not completely specified by the debug information, gdb will say ‘<incomplete type>’. See incomplete type, for more about this.
If you try to examine or use the value of a (global) variable for which gdb has no type information, e.g., because the program includes no debug information, gdb displays an error message. See unknown type, for more about unknown types. If you cast the variable to its declared type, gdb gets the variable's value using the cast-to type as the variable's type. For example, in a C program:
(gdb) p var 'var' has unknown type; cast it to its declared type (gdb) p (float) var $1 = 3.14
If you append @entry string to a function parameter name you get its value at the time the function got called. If the value is not available an error message is printed. Entry values are available only with some compilers. Entry values are normally also printed at the function parameter list according to set print entry-values.
Breakpoint 1, d (i=30) at gdb.base/entry-value.c:29 29 i++; (gdb) next 30 e (i); (gdb) print i $1 = 31 (gdb) print i@entry $2 = 30
Strings are identified as arrays of char
values without specified
signedness. Arrays of either signed char
or unsigned char
get
printed as arrays of 1 byte sized integers. -fsigned-char
or
-funsigned-char
gcc options have no effect as gdb
defines literal string type "char"
as char
without a sign.
For program code
char var0[] = "A"; signed char var1[] = "A";
You get during debugging
(gdb) print var0 $1 = "A" (gdb) print var1 $2 = {65 'A', 0 '\0'}
It is often useful to print out several successive objects of the same type in memory; a section of an array, or an array of dynamically determined size for which only a pointer exists in the program.
You can do this by referring to a contiguous span of memory as an artificial array, using the binary operator ‘@’. The left operand of ‘@’ should be the first element of the desired array and be an individual object. The right operand should be the desired length of the array. The result is an array value whose elements are all of the type of the left argument. The first element is actually the left argument; the second element comes from bytes of memory immediately following those that hold the first element, and so on. Here is an example. If a program says
int *array = (int *) malloc (len * sizeof (int));
you can print the contents of array
with
p *array@len
The left operand of ‘@’ must reside in memory. Array values made with ‘@’ in this way behave just like other arrays in terms of subscripting, and are coerced to pointers when used in expressions. Artificial arrays most often appear in expressions via the value history (see Value History), after printing one out.
Another way to create an artificial array is to use a cast. This re-interprets a value as if it were an array. The value need not be in memory:
(gdb) p/x (short[2])0x12345678 $1 = {0x1234, 0x5678}
As a convenience, if you leave the array length out (as in ‘(type[])value’) gdb calculates the size to fill the value (as ‘sizeof(value)/sizeof(type)’:
(gdb) p/x (short[])0x12345678 $2 = {0x1234, 0x5678}
Sometimes the artificial array mechanism is not quite enough; in
moderately complex data structures, the elements of interest may not
actually be adjacent—for example, if you are interested in the values
of pointers in an array. One useful work-around in this situation is
to use a convenience variable (see Convenience Variables) as a counter in an expression that prints the first
interesting value, and then repeat that expression via <RET>. For
instance, suppose you have an array dtab
of pointers to
structures, and you are interested in the values of a field fv
in each structure. Here is an example of what you might type:
set $i = 0 p dtab[$i++]->fv <RET> <RET> ...
By default, gdb prints a value according to its data type. Sometimes this is not what you want. For example, you might want to print a number in hex, or a pointer in decimal. Or you might want to view data in memory at a certain address as a character string or as an instruction. To do these things, specify an output format when you print a value.
The simplest use of output formats is to say how to print a value
already computed. This is done by starting the arguments of the
print
command with a slash and a format letter. The format
letters supported are:
x
d
u
o
t
a
(gdb) p/a 0x54320 $3 = 0x54320 <_initialize_vx+396>
The command info symbol 0x54320
yields similar results.
See info symbol.
c
Without this format, gdb displays char
,
unsigned char
, and signed char
data as character
constants. Single-byte members of vectors are displayed as integer
data.
f
s
Without this format, gdb displays pointers to and arrays of
char
, unsigned char
, and signed char
as
strings. Single-byte members of a vector are displayed as an integer
array.
z
r
For example, to print the program counter in hex (see Registers), type
p/x $pc
Note that no space is required before the slash; this is because command names in gdb cannot contain a slash.
To reprint the last value in the value history with a different format,
you can use the print
command with just a format and no
expression. For example, ‘p/x’ reprints the last value in hex.
You can use the command x
(for “examine”) to examine memory in
any of several formats, independently of your program's data types.
x/
nfu addrx
addrx
x
command to examine memory.
n, f, and u are all optional parameters that specify how much memory to display and how to format it; addr is an expression giving the address where you want to start displaying memory. If you use defaults for nfu, you need not type the slash ‘/’. Several commands set convenient defaults for addr.
print
(‘x’, ‘d’, ‘u’, ‘o’, ‘t’, ‘a’, ‘c’,
‘f’, ‘s’), and in addition ‘i’ (for machine instructions).
The default is ‘x’ (hexadecimal) initially. The default changes
each time you use either x
or print
.
b
h
w
g
Each time you specify a unit size with x
, that size becomes the
default unit the next time you use x
. For the ‘i’ format,
the unit size is ignored and is normally not written. For the ‘s’ format,
the unit size defaults to ‘b’, unless it is explicitly given.
Use x /hs to display 16-bit char strings and x /ws to display
32-bit strings. The next use of x /s will again display 8-bit strings.
Note that the results depend on the programming language of the
current compilation unit. If the language is C, the ‘s’
modifier will use the UTF-16 encoding while ‘w’ will use
UTF-32. The encoding is set by the programming language and cannot
be altered.
info breakpoints
(to
the address of the last breakpoint listed), info line
(to the
starting address of a line), and print
(if you use it to display
a value from memory).
For example, ‘x/3uh 0x54320’ is a request to display three halfwords
(h
) of memory, formatted as unsigned decimal integers (‘u’),
starting at address 0x54320
. ‘x/4xw $sp’ prints the four
words (‘w’) of memory above the stack pointer (here, ‘$sp’;
see Registers) in hexadecimal (‘x’).
You can also specify a negative repeat count to examine memory backward
from the given address. For example, ‘x/-3uh 0x54320’ prints three
halfwords (h
) at 0x54314
, 0x54328
, and 0x5431c
.
Since the letters indicating unit sizes are all distinct from the letters specifying output formats, you do not have to remember whether unit size or format comes first; either order works. The output specifications ‘4xw’ and ‘4wx’ mean exactly the same thing. (However, the count n must come first; ‘wx4’ does not work.)
Even though the unit size u is ignored for the formats ‘s’
and ‘i’, you might still want to use a count n; for example,
‘3i’ specifies that you want to see three machine instructions,
including any operands. For convenience, especially when used with
the display
command, the ‘i’ format also prints branch delay
slot instructions, if any, beyond the count specified, which immediately
follow the last instruction that is within the count. The command
disassemble
gives an alternative way of inspecting machine
instructions; see Source and Machine Code.
If a negative repeat count is specified for the formats ‘s’ or ‘i’, the command displays null-terminated strings or instructions before the given address as many as the absolute value of the given number. For the ‘i’ format, we use line number information in the debug info to accurately locate instruction boundaries while disassembling backward. If line info is not available, the command stops examining memory with an error message.
All the defaults for the arguments to x
are designed to make it
easy to continue scanning memory with minimal specifications each time
you use x
. For example, after you have inspected three machine
instructions with ‘x/3i addr’, you can inspect the next seven
with just ‘x/7’. If you use <RET> to repeat the x
command,
the repeat count n is used again; the other arguments default as
for successive uses of x
.
When examining machine instructions, the instruction at current program
counter is shown with a =>
marker. For example:
(gdb) x/5i $pc-6 0x804837f <main+11>: mov %esp,%ebp 0x8048381 <main+13>: push %ecx 0x8048382 <main+14>: sub $0x4,%esp => 0x8048385 <main+17>: movl $0x8048460,(%esp) 0x804838c <main+24>: call 0x80482d4 <puts@plt>
The addresses and contents printed by the x
command are not saved
in the value history because there is often too much of them and they
would get in the way. Instead, gdb makes these values available for
subsequent use in expressions as values of the convenience variables
$_
and $__
. After an x
command, the last address
examined is available for use in expressions in the convenience variable
$_
. The contents of that address, as examined, are available in
the convenience variable $__
.
If the x
command has a repeat count, the address and contents saved
are from the last memory unit printed; this is not the same as the last
address printed if several units were printed on the last line of output.
Most targets have an addressable memory unit size of 8 bits. This means that to each memory address are associated 8 bits of data. Some targets, however, have other addressable memory unit sizes. Within gdb and this document, the term addressable memory unit (or memory unit for short) is used when explicitly referring to a chunk of data of that size. The word byte is used to refer to a chunk of data of 8 bits, regardless of the addressable memory unit size of the target. For most systems, addressable memory unit is a synonym of byte.
When you are debugging a program running on a remote target machine
(see Remote Debugging), you may wish to verify the program's image
in the remote machine's memory against the executable file you
downloaded to the target. Or, on any target, you may want to check
whether the program has corrupted its own read-only sections. The
compare-sections
command is provided for such situations.
compare-sections
[section-name|-r
]-r
, compares all loadable read-only sections.
Note: for remote targets, this command can be accelerated if the target supports computing the CRC checksum of a block of memory (see qCRC packet).
If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the automatic display list so that gdb prints its value each time your program stops. Each expression added to the list is given a number to identify it; to remove an expression from the list, you specify that number. The automatic display looks like this:
2: foo = 38 3: bar[5] = (struct hack *) 0x3804
This display shows item numbers, expressions and their current values. As with
displays you request manually using x
or print
, you can
specify the output format you prefer; in fact, display
decides
whether to use print
or x
depending your format
specification—it uses x
if you specify either the ‘i’
or ‘s’ format, or a unit size; otherwise it uses print
.
display
exprdisplay
does not repeat if you press <RET> again after using it.
display/
fmt exprdisplay/
fmt addrFor example, ‘display/i $pc’ can be helpful, to see the machine instruction about to be executed each time execution stops (‘$pc’ is a common name for the program counter; see Registers).
undisplay
dnums...
delete display
dnums...
2-4
.
undisplay
does not repeat if you press <RET> after using it.
(Otherwise you would just get the error ‘No display number ...’.)
disable display
dnums...
2-4
.
enable display
dnums...
2-4
.
display
info display
If a display expression refers to local variables, then it does not make
sense outside the lexical context for which it was set up. Such an
expression is disabled when execution enters a context where one of its
variables is not defined. For example, if you give the command
display last_char
while inside a function with an argument
last_char
, gdb displays this argument while your program
continues to stop inside that function. When it stops elsewhere—where
there is no variable last_char
—the display is disabled
automatically. The next time your program stops where last_char
is meaningful, you can enable the display expression once again.
gdb provides the following ways to control how arrays, structures, and symbols are printed.
These settings are useful for debugging programs in any language:
set print address
set print address on
on
. For example, this is what a stack frame display looks like with
set print address on
:
(gdb) f #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>") at input.c:530 530 if (lquote != def_lquote)
set print address off
set print address off
:
(gdb) set print addr off (gdb) f #0 set_quotes (lq="<<", rq=">>") at input.c:530 530 if (lquote != def_lquote)
You can use ‘set print address off’ to eliminate all machine
dependent displays from the gdb interface. For example, with
print address off
, you should get the same text for backtraces on
all machines—whether or not they involve pointer arguments.
show print address
When gdb prints a symbolic address, it normally prints the
closest earlier symbol plus an offset. If that symbol does not uniquely
identify the address (for example, it is a name whose scope is a single
source file), you may need to clarify. One way to do this is with
info line
, for example ‘info line *0x4537’. Alternately,
you can set gdb to print the source file and line number when
it prints a symbolic address:
set print symbol-filename on
set print symbol-filename off
show print symbol-filename
Another situation where it is helpful to show symbol filenames and line numbers is when disassembling code; gdb shows you the line number and source file that corresponds to each instruction.
Also, you may wish to see the symbolic form only if the address being printed is reasonably close to the closest earlier symbol:
set print max-symbolic-offset
max-offsetset print max-symbolic-offset unlimited
unlimited
, which tells gdb
to always print the symbolic form of an address if any symbol precedes
it. Zero is equivalent to unlimited
.
show print max-symbolic-offset
If you have a pointer and you are not sure where it points, try
‘set print symbol-filename on’. Then you can determine the name
and source file location of the variable where it points, using
‘p/a pointer’. This interprets the address in symbolic form.
For example, here gdb shows that a variable ptt
points
at another variable t
, defined in hi2.c:
(gdb) set print symbol-filename on (gdb) p/a ptt $4 = 0xe008 <t in hi2.c>
Warning: For pointers that point to a local variable, ‘p/a’
does not show the symbol name and filename of the referent, even with
the appropriate set print
options turned on.
You can also enable ‘/a’-like formatting all the time using ‘set print symbol on’:
set print symbol on
set print symbol off
show print symbol
Other settings control how different kinds of objects are printed:
set print array
set print array on
set print array off
show print array
set print array-indexes
set print array-indexes on
set print array-indexes off
show print array-indexes
set print elements
number-of-elementsset print elements unlimited
set print elements
command.
This limit also applies to the display of strings.
When gdb starts, this limit is set to 200.
Setting number-of-elements to unlimited
or zero means
that the number of elements to print is unlimited.
show print elements
set print frame-arguments
valueall
scalars
...
. This is the default. Here is an example where
only scalar arguments are shown:
#1 0x08048361 in call_me (i=3, s=..., ss=0xbf8d508c, u=..., e=green) at frame-args.c:23
none
...
. In this case, the example above now becomes:
#1 0x08048361 in call_me (i=..., s=..., ss=..., u=..., e=...) at frame-args.c:23
presence
...
.
The ...
are not printed for function without any arguments.
None of the argument names and values are printed.
In this case, the example above now becomes:
#1 0x08048361 in call_me (...) at frame-args.c:23
By default, only scalar arguments are printed. This command can be used
to configure the debugger to print the value of all arguments, regardless
of their type. However, it is often advantageous to not print the value
of more complex parameters. For instance, it reduces the amount of
information printed in each frame, making the backtrace more readable.
Also, it improves performance when displaying Ada frames, because
the computation of large arguments can sometimes be CPU-intensive,
especially in large applications. Setting print frame-arguments
to scalars
(the default), none
or presence
avoids
this computation, thus speeding up the display of each Ada frame.
show print frame-arguments
set print raw-frame-arguments on
set print raw-frame-arguments off
show print raw-frame-arguments
set print entry-values
valueThe default value is default
(see below for its description). Older
gdb behaved as with the setting no
. Compilers not supporting
this feature will behave in the default
setting the same way as with the
no
setting.
This functionality is currently supported only by DWARF 2 debugging format and the compiler has to produce ‘DW_TAG_call_site’ tags. With gcc, you need to specify -O -g during compilation, to get this information.
The value parameter can be one of the following:
no
#0 equal (val=5) #0 different (val=6) #0 lost (val=<optimized out>) #0 born (val=10) #0 invalid (val=<optimized out>)
only
#0 equal (val@entry=5) #0 different (val@entry=5) #0 lost (val@entry=5) #0 born (val@entry=<optimized out>) #0 invalid (val@entry=<optimized out>)
preferred
#0 equal (val@entry=5) #0 different (val@entry=5) #0 lost (val@entry=5) #0 born (val=10) #0 invalid (val@entry=<optimized out>)
if-needed
#0 equal (val=5) #0 different (val=6) #0 lost (val@entry=5) #0 born (val=10) #0 invalid (val=<optimized out>)
both
#0 equal (val=5, val@entry=5) #0 different (val=6, val@entry=5) #0 lost (val=<optimized out>, val@entry=5) #0 born (val=10, val@entry=<optimized out>) #0 invalid (val=<optimized out>, val@entry=<optimized out>)
compact
<optimized out>
. If not in MI mode (see GDB/MI) and if both
values are known and identical, print the shortened
param=param@entry=VALUE
notation.
#0 equal (val=val@entry=5) #0 different (val=6, val@entry=5) #0 lost (val@entry=5) #0 born (val=10) #0 invalid (val=<optimized out>)
default
param=param@entry=VALUE
notation.
#0 equal (val=val@entry=5) #0 different (val=6, val@entry=5) #0 lost (val=<optimized out>, val@entry=5) #0 born (val=10) #0 invalid (val=<optimized out>)
For analysis messages on possible failures of frame argument values at function
entry resolution see set debug entry-values.
show print entry-values
set print frame-info
valueset print frame-arguments
and set print address
) are also influencing if and how some frame
information is displayed. In particular, the frame program counter is never
printed if set print address
is off.
The possible values for set print frame-info
are:
short-location
location
short-location
but also print the source file and source line
number.
location-and-address
location
but print the program counter even if located at the
beginning of the location source line.
source-line
source-and-location
location
and source-line
are printing.
auto
frame
prints the information printed by
source-and-location
while stepi
will switch between
source-line
and source-and-location
depending on the program
counter.
The default value is auto
.
set print repeats
number-of-repeatsset print repeats unlimited
"<repeats
n times>"
, where n is the number of
identical repetitions, instead of displaying the identical elements
themselves. Setting the threshold to unlimited
or zero will
cause all elements to be individually printed. The default threshold
is 10.
show print repeats
set print max-depth
depthset print max-depth unlimited
For example, given this C code
typedef struct s1 { int a; } s1; typedef struct s2 { s1 b; } s2; typedef struct s3 { s2 c; } s3; typedef struct s4 { s3 d; } s4; s4 var = { { { { 3 } } } };
The following table shows how different values of depth will
effect how var
is printed by gdb:
depth setting | Result of ‘p var’
|
---|---|
unlimited | $1 = {d = {c = {b = {a = 3}}}}
|
0
| $1 = {...}
|
1
| $1 = {d = {...}}
|
2
| $1 = {d = {c = {...}}}
|
3
| $1 = {d = {c = {b = {...}}}}
|
4
| $1 = {d = {c = {b = {a = 3}}}}
|
To see the contents of structures that have been hidden the user can either increase the print max-depth, or they can print the elements of the structure that are visible, for example
(gdb) set print max-depth 2 (gdb) p var $1 = {d = {c = {...}}} (gdb) p var.d $2 = {c = {b = {...}}} (gdb) p var.d.c $3 = {b = {a = 3}}
The pattern used to replace nested structures varies based on
language, for most languages {...}
is used, but Fortran uses
(...)
.
show print max-depth
set print null-stop
show print null-stop
set print pretty on
$1 = { next = 0x0, flags = { sweet = 1, sour = 1 }, meat = 0x54 "Pork" }
set print pretty off
$1 = {next = 0x0, flags = {sweet = 1, sour = 1}, \ meat = 0x54 "Pork"}
This is the default format.
show print pretty
set print raw-values on
set print raw-values off
The default setting is “off”.
show print raw-values
set print sevenbit-strings on
\
nnn. This setting is
best if you are working in English (ascii) and you use the
high-order bit of characters as a marker or “meta” bit.
set print sevenbit-strings off
show print sevenbit-strings
set print union on
set print union off
"{...}"
instead.
show print union
For example, given the declarations
typedef enum {Tree, Bug} Species; typedef enum {Big_tree, Acorn, Seedling} Tree_forms; typedef enum {Caterpillar, Cocoon, Butterfly} Bug_forms; struct thing { Species it; union { Tree_forms tree; Bug_forms bug; } form; }; struct thing foo = {Tree, {Acorn}};
with set print union on
in effect ‘p foo’ would print
$1 = {it = Tree, form = {tree = Acorn, bug = Cocoon}}
and with set print union off
in effect it would print
$1 = {it = Tree, form = {...}}
set print union
affects programs written in C-like languages
and in Pascal.
These settings are of interest when debugging C++ programs:
set print demangle
set print demangle on
show print demangle
set print asm-demangle
set print asm-demangle on
show print asm-demangle
set demangle-style
styleshow demangle-style
set print object
set print object on
set print object off
show print object
set print static-members
set print static-members on
set print static-members off
show print static-members
set print pascal_static-members
set print pascal_static-members on
set print pascal_static-members off
show print pascal_static-members
set print vtbl
set print vtbl on
vtbl
commands do not work on programs compiled with the HP
ANSI C++ compiler (aCC
).)
set print vtbl off
show print vtbl
gdb provides a mechanism to allow pretty-printing of values using Python code. It greatly simplifies the display of complex objects. This mechanism works for both MI and the CLI.
When gdb prints a value, it first sees if there is a pretty-printer registered for the value. If there is then gdb invokes the pretty-printer to print the value. Otherwise the value is printed normally.
Pretty-printers are normally named. This makes them easy to manage. The ‘info pretty-printer’ command will list all the installed pretty-printers with their names. If a pretty-printer can handle multiple data types, then its subprinters are the printers for the individual data types. Each such subprinter has its own name. The format of the name is printer-name;subprinter-name.
Pretty-printers are installed by registering them with gdb. Typically they are automatically loaded and registered when the corresponding debug information is loaded, thus making them available without having to do anything special.
There are three places where a pretty-printer can be registered.
See Selecting Pretty-Printers, for further information on how pretty-printers are selected,
See Writing a Pretty-Printer, for implementing pretty printers for new types.
Here is how a C++ std::string
looks without a pretty-printer:
(gdb) print s $1 = { static npos = 4294967295, _M_dataplus = { <std::allocator<char>> = { <__gnu_cxx::new_allocator<char>> = { <No data fields>}, <No data fields> }, members of std::basic_string<char, std::char_traits<char>, std::allocator<char> >::_Alloc_hider: _M_p = 0x804a014 "abcd" } }
With a pretty-printer for std::string
only the contents are printed:
(gdb) print s $2 = "abcd"
info pretty-printer [
object-regexp [
name-regexp]]
object-regexp is a regular expression matching the objects
whose pretty-printers to list.
Objects can be global
, the program space's file
(see Progspaces In Python),
and the object files within that program space (see Objfiles In Python).
See Selecting Pretty-Printers, for details on how gdb
looks up a printer from these three objects.
name-regexp is a regular expression matching the name of the printers to list.
disable pretty-printer [
object-regexp [
name-regexp]]
enable pretty-printer [
object-regexp [
name-regexp]]
Example:
Suppose we have three pretty-printers installed: one from library1.so
named foo
that prints objects of type foo
, and
another from library2.so named bar
that prints two types of objects,
bar1
and bar2
.
(gdb) info pretty-printer library1.so: foo library2.so: bar bar1 bar2 (gdb) info pretty-printer library2 library2.so: bar bar1 bar2 (gdb) disable pretty-printer library1 1 printer disabled 2 of 3 printers enabled (gdb) info pretty-printer library1.so: foo [disabled] library2.so: bar bar1 bar2 (gdb) disable pretty-printer library2 bar;bar1 1 printer disabled 1 of 3 printers enabled (gdb) info pretty-printer library2 library1.so: foo [disabled] library2.so: bar bar1 [disabled] bar2 (gdb) disable pretty-printer library2 bar 1 printer disabled 0 of 3 printers enabled (gdb) info pretty-printer library2 library1.so: foo [disabled] library2.so: bar [disabled] bar1 [disabled] bar2
Note that for bar
the entire printer can be disabled,
as can each individual subprinter.
Printing values and frame arguments is done by default using the enabled pretty printers.
The print option -raw-values
and gdb setting
set print raw-values
(see set print raw-values) can be
used to print values without applying the enabled pretty printers.
Similarly, the backtrace option -raw-frame-arguments
and
gdb setting set print raw-frame-arguments
(see set print raw-frame-arguments) can be used to ignore the
enabled pretty printers when printing frame argument values.
Values printed by the print
command are saved in the gdb
value history. This allows you to refer to them in other expressions.
Values are kept until the symbol table is re-read or discarded
(for example with the file
or symbol-file
commands).
When the symbol table changes, the value history is discarded,
since the values may contain pointers back to the types defined in the
symbol table.
The values printed are given history numbers by which you can
refer to them. These are successive integers starting with one.
print
shows you the history number assigned to a value by
printing ‘$num = ’ before the value; here num is the
history number.
To refer to any previous value, use ‘$’ followed by the value's
history number. The way print
labels its output is designed to
remind you of this. Just $
refers to the most recent value in
the history, and $$
refers to the value before that.
$$
n refers to the nth value from the end; $$2
is the value just prior to $$
, $$1
is equivalent to
$$
, and $$0
is equivalent to $
.
For example, suppose you have just printed a pointer to a structure and want to see the contents of the structure. It suffices to type
p *$
If you have a chain of structures where the component next
points
to the next one, you can print the contents of the next one with this:
p *$.next
You can print successive links in the chain by repeating this command—which you can do by just typing <RET>.
Note that the history records values, not expressions. If the value of
x
is 4 and you type these commands:
print x set x=5
then the value recorded in the value history by the print
command
remains 4 even though the value of x
has changed.
show values
show
values
does not change the history.
show values
nshow values +
show values +
produces no display.
Pressing <RET> to repeat show values
n has exactly the
same effect as ‘show values +’.
gdb provides convenience variables that you can use within gdb to hold on to a value and refer to it later. These variables exist entirely within gdb; they are not part of your program, and setting a convenience variable has no direct effect on further execution of your program. That is why you can use them freely.
Convenience variables are prefixed with ‘$’. Any name preceded by ‘$’ can be used for a convenience variable, unless it is one of the predefined machine-specific register names (see Registers). (Value history references, in contrast, are numbers preceded by ‘$’. See Value History.)
You can save a value in a convenience variable with an assignment expression, just as you would set a variable in your program. For example:
set $foo = *object_ptr
would save in $foo
the value contained in the object pointed to by
object_ptr
.
Using a convenience variable for the first time creates it, but its
value is void
until you assign a new value. You can alter the
value with another assignment at any time.
Convenience variables have no fixed types. You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience variable, when used as an expression, has the type of its current value.
show convenience
show conv
.
init-if-undefined $
variable =
expressionIf the variable is already defined then the expression is not evaluated so any side-effects do not occur.
One of the ways to use a convenience variable is as a counter to be incremented or a pointer to be advanced. For example, to print a field from successive elements of an array of structures:
set $i = 0 print bar[$i++]->contents
Repeat that command by typing <RET>.
Some convenience variables are created automatically by gdb and given values likely to be useful.
$_
$_
is automatically set by the x
command to
the last address examined (see Examining Memory). Other
commands which provide a default address for x
to examine also
set $_
to that address; these commands include info line
and info breakpoint
. The type of $_
is void *
except when set by the x
command, in which case it is a pointer
to the type of $__
.
$__
$__
is automatically set by the x
command
to the value found in the last address examined. Its type is chosen
to match the format in which the data was printed.
$_exitcode
$_exitsignal
to void
.
$_exitsignal
$_exitcode
to void
.
To distinguish between whether the program being debugged has exited
(i.e., $_exitcode
is not void
) or signalled (i.e.,
$_exitsignal
is not void
), the convenience function
$_isvoid
can be used (see Convenience Functions). For example, considering the following source code:
#include <signal.h> int main (int argc, char *argv[]) { raise (SIGALRM); return 0; }
A valid way of telling whether the program being debugged has exited or signalled would be:
(gdb) define has_exited_or_signalled Type commands for definition of ``has_exited_or_signalled''. End with a line saying just ``end''. >if $_isvoid ($_exitsignal) >echo The program has exited\n >else >echo The program has signalled\n >end >end (gdb) run Starting program: Program terminated with signal SIGALRM, Alarm clock. The program no longer exists. (gdb) has_exited_or_signalled The program has signalled
As can be seen, gdb correctly informs that the program being
debugged has signalled, since it calls raise
and raises a
SIGALRM
signal. If the program being debugged had not called
raise
, then gdb would report a normal exit:
(gdb) has_exited_or_signalled The program has exited
$_exception
$_exception
is set to the exception object being
thrown at an exception-related catchpoint. See Set Catchpoints.
$_ada_exception
$_ada_exception
is set to the address of the
exception being caught or thrown at an Ada exception-related
catchpoint. See Set Catchpoints.
$_probe_argc
$_probe_arg0...$_probe_arg11
$_sdata
$_sdata
contains extra collected static tracepoint
data. See Tracepoint Action Lists. Note that
$_sdata
could be empty, if not inspecting a trace buffer, or
if extra static tracepoint data has not been collected.
$_siginfo
$_siginfo
contains extra signal information
(see extra signal information). Note that $_siginfo
could be empty, if the application has not yet received any signals.
For example, it will be empty before you execute the run
command.
$_tlb
$_tlb
is automatically set when debugging
applications running on MS-Windows in native mode or connected to
gdbserver that supports the qGetTIBAddr
request.
See General Query Packets.
This variable contains the address of the thread information block.
$_inferior
$_thread
$_gthread
$_gdb_major
$_gdb_minor
$_gdb_minor
. These variables allow you to
write scripts that work with different versions of gdb
without errors caused by features unavailable in some of those
versions.
$_shell_exitcode
$_shell_exitsignal
shell
and |
are launching
shell commands. When a launched command terminates, gdb
automatically maintains the variables $_shell_exitcode
and $_shell_exitsignal
according to the exit status of the last
launched command. These variables are set and used similarly to
the variables $_exitcode
and $_exitsignal
.
gdb also supplies some convenience functions. These have a syntax similar to convenience variables. A convenience function can be used in an expression just like an ordinary function; however, a convenience function is implemented internally to gdb.
These functions do not require gdb to be configured with
Python
support, which means that they are always available.
$_isvoid (
expr)
void
. Otherwise it
returns zero.
A void
expression is an expression where the type of the result
is void
. For example, you can examine a convenience variable
(see Convenience Variables) to check whether
it is void
:
(gdb) print $_exitcode $1 = void (gdb) print $_isvoid ($_exitcode) $2 = 1 (gdb) run Starting program: ./a.out [Inferior 1 (process 29572) exited normally] (gdb) print $_exitcode $3 = 0 (gdb) print $_isvoid ($_exitcode) $4 = 0
In the example above, we used $_isvoid
to check whether
$_exitcode
is void
before and after the execution of the
program being debugged. Before the execution there is no exit code to
be examined, therefore $_exitcode
is void
. After the
execution the program being debugged returned zero, therefore
$_exitcode
is zero, which means that it is not void
anymore.
The void
expression can also be a call of a function from the
program being debugged. For example, given the following function:
void foo (void) { }
The result of calling it inside gdb is void
:
(gdb) print foo () $1 = void (gdb) print $_isvoid (foo ()) $2 = 1 (gdb) set $v = foo () (gdb) print $v $3 = void (gdb) print $_isvoid ($v) $4 = 1
$_gdb_setting_str (
setting)
set
or
show
command (see Controlling GDB).
(gdb) show print frame-arguments Printing of non-scalar frame arguments is "scalars". (gdb) p $_gdb_setting_str("print frame-arguments") $1 = "scalars" (gdb) p $_gdb_setting_str("height") $2 = "30" (gdb)
$_gdb_setting (
setting)
The value type for boolean and auto boolean settings is int
.
The boolean values off
and on
are converted to
the integer values 0
and 1
. The value auto
is
converted to the value -1
.
The value type for integer settings is either unsigned int
or int
, depending on the setting.
Some integer settings accept an unlimited
value.
Depending on the setting, the set
command also accepts
the value 0
or the value −1
as a synonym for
unlimited
.
For example, set height unlimited
is equivalent to
set height 0
.
Some other settings that accept the unlimited
value
use the value 0
to literally mean zero.
For example, set history size 0
indicates to not
record any gdb commands in the command history.
For such settings, −1
is the synonym
for unlimited
.
See the documentation of the corresponding set
command for
the numerical value equivalent to unlimited
.
The $_gdb_setting
function converts the unlimited value
to a 0
or a −1
value according to what the
set
command uses.
(gdb) p $_gdb_setting_str("height") $1 = "30" (gdb) p $_gdb_setting("height") $2 = 30 (gdb) set height unlimited (gdb) p $_gdb_setting_str("height") $3 = "unlimited" (gdb) p $_gdb_setting("height") $4 = 0 (gdb) p $_gdb_setting_str("history size") $5 = "unlimited" (gdb) p $_gdb_setting("history size") $6 = -1 (gdb) p $_gdb_setting_str("disassemble-next-line") $7 = "auto" (gdb) p $_gdb_setting("disassemble-next-line") $8 = -1 (gdb)
Other setting types (enum, filename, optional filename, string, string noescape)
are returned as string values.
$_gdb_maint_setting_str (
setting)
$_gdb_setting_str
function, but works with
maintenance set
variables.
$_gdb_maint_setting (
setting)
$_gdb_setting
function, but works with
maintenance set
variables.
The following functions require gdb to be configured with
Python
support.
$_memeq(
buf1,
buf2,
length)
$_regex(
str,
regex)
Python
's
regular expression support.
$_streq(
str1,
str2)
$_strlen(
str)
$_caller_is(
name[,
number_of_frames])
If the optional argument number_of_frames is provided, it is the number of frames up in the stack to look. The default is 1.
Example:
(gdb) backtrace #0 bottom_func () at testsuite/gdb.python/py-caller-is.c:21 #1 0x00000000004005a0 in middle_func () at testsuite/gdb.python/py-caller-is.c:27 #2 0x00000000004005ab in top_func () at testsuite/gdb.python/py-caller-is.c:33 #3 0x00000000004005b6 in main () at testsuite/gdb.python/py-caller-is.c:39 (gdb) print $_caller_is ("middle_func") $1 = 1 (gdb) print $_caller_is ("top_func", 2) $1 = 1
$_caller_matches(
regexp[,
number_of_frames])
If the optional argument number_of_frames is provided,
it is the number of frames up in the stack to look.
The default is 1.
$_any_caller_is(
name[,
number_of_frames])
If the optional argument number_of_frames is provided, it is the number of frames up in the stack to look. The default is 1.
This function differs from $_caller_is
in that this function
checks all stack frames from the immediate caller to the frame specified
by number_of_frames, whereas $_caller_is
only checks the
frame specified by number_of_frames.
$_any_caller_matches(
regexp[,
number_of_frames])
If the optional argument number_of_frames is provided, it is the number of frames up in the stack to look. The default is 1.
This function differs from $_caller_matches
in that this function
checks all stack frames from the immediate caller to the frame specified
by number_of_frames, whereas $_caller_matches
only checks the
frame specified by number_of_frames.
$_as_string(
value)
This function is useful to obtain the textual label (enumerator) of an enumeration value. For example, assuming the variable node is of an enumerated type:
(gdb) printf "Visiting node of type %s\n", $_as_string(node) Visiting node of type NODE_INTEGER
$_cimag(
value)
$_creal(
value)
$_cimag
) or real ($_creal
) part of
the complex number value.
The type of the imaginary or real part depends on the type of the
complex number, e.g., using $_cimag
on a float complex
will return an imaginary part of type float
.
gdb provides the ability to list and get help on convenience functions.
help function
You can refer to machine register contents, in expressions, as variables
with names starting with ‘$’. The names of registers are different
for each machine; use info registers
to see the names used on
your machine.
info registers
info all-registers
info registers
reggroup ...
maint print reggroups
(see Maintenance Commands).
info registers
regname ...
gdb has four “standard” register names that are available (in
expressions) on most machines—whenever they do not conflict with an
architecture's canonical mnemonics for registers. The register names
$pc
and $sp
are used for the program counter register and
the stack pointer. $fp
is used for a register that contains a
pointer to the current stack frame, and $ps
is used for a
register that contains the processor status. For example,
you could print the program counter in hex with
p/x $pc
or print the instruction to be executed next with
x/i $pc
or add four to the stack pointer11 with
set $sp += 4
Whenever possible, these four standard register names are available on
your machine even though the machine has different canonical mnemonics,
so long as there is no conflict. The info registers
command
shows the canonical names. For example, on the SPARC, info
registers
displays the processor status register as $psr
but you
can also refer to it as $ps
; and on x86-based machines $ps
is an alias for the eflags register.
gdb always considers the contents of an ordinary register as an integer when the register is examined in this way. Some machines have special registers which can hold nothing but floating point; these registers are considered to have floating point values. There is no way to refer to the contents of an ordinary register as floating point value (although you can print it as a floating point value with ‘print/f $regname’).
Some registers have distinct “raw” and “virtual” data formats. This
means that the data format in which the register contents are saved by
the operating system is not the same one that your program normally
sees. For example, the registers of the 68881 floating point
coprocessor are always saved in “extended” (raw) format, but all C
programs expect to work with “double” (virtual) format. In such
cases, gdb normally works with the virtual format only (the format
that makes sense for your program), but the info registers
command
prints the data in both formats.
Some machines have special registers whose contents can be interpreted
in several different ways. For example, modern x86-based machines
have SSE and MMX registers that can hold several values packed
together in several different formats. gdb refers to such
registers in struct
notation:
(gdb) print $xmm1 $1 = { v4_float = {0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044}, v2_double = {9.92129282474342e-303, 2.7585945287983262e-313}, v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000", v8_int16 = {0, 0, 14072, 315, 11, 0, 13, 0}, v4_int32 = {0, 20657912, 11, 13}, v2_int64 = {88725056443645952, 55834574859}, uint128 = 0x0000000d0000000b013b36f800000000 }
To set values of such registers, you need to tell gdb which
view of the register you wish to change, as if you were assigning
value to a struct
member:
(gdb) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
Normally, register values are relative to the selected stack frame (see Selecting a Frame). This means that you get the value that the register would contain if all stack frames farther in were exited and their saved registers restored. In order to see the true contents of hardware registers, you must select the innermost frame (with ‘frame 0’).
Usually ABIs reserve some registers as not needed to be saved by the callee (a.k.a.: “caller-saved”, “call-clobbered” or “volatile” registers). It may therefore not be possible for gdb to know the value a register had before the call (in other words, in the outer frame), if the register value has since been changed by the callee. gdb tries to deduce where the inner frame saved (“callee-saved”) registers, from the debug info, unwind info, or the machine code generated by your compiler. If some register is not saved, and gdb knows the register is “caller-saved” (via its own knowledge of the ABI, or because the debug/unwind info explicitly says the register's value is undefined), gdb displays ‘<not saved>’ as the register's value. With targets that gdb has no knowledge of the register saving convention, if a register was not saved by the callee, then its value and location in the outer frame are assumed to be the same of the inner frame. This is usually harmless, because if the register is call-clobbered, the caller either does not care what is in the register after the call, or has code to restore the value that it does care about. Note, however, that if you change such a register in the outer frame, you may also be affecting the inner frame. Also, the more “outer” the frame is you're looking at, the more likely a call-clobbered register's value is to be wrong, in the sense that it doesn't actually represent the value the register had just before the call.
Depending on the configuration, gdb may be able to give you more information about the status of the floating point hardware.
info float
Depending on the configuration, gdb may be able to give you more information about the status of the vector unit.
info vector
gdb provides interfaces to useful OS facilities that can help you debug your program.
Some operating systems supply an auxiliary vector to programs at startup. This is akin to the arguments and environment that you specify for a program, but contains a system-dependent variety of binary values that tell system libraries important details about the hardware, operating system, and process. Each value's purpose is identified by an integer tag; the meanings are well-known but system-specific. Depending on the configuration and operating system facilities, gdb may be able to show you this information. For remote targets, this functionality may further depend on the remote stub's support of the ‘qXfer:auxv:read’ packet, see qXfer auxiliary vector read.
info auxv
On some targets, gdb can access operating system-specific information and show it to you. The types of information available will differ depending on the type of operating system running on the target. The mechanism used to fetch the data is described in Operating System Information. For remote targets, this functionality depends on the remote stub's support of the ‘qXfer:osdata:read’ packet, see qXfer osdata read.
info os
infotypeOn gnu/Linux, the following values of infotype are valid:
cpus
files
modules
msg
processes
procgroups
semaphores
shm
sockets
threads
info os
Memory region attributes allow you to describe special handling required by regions of your target's memory. gdb uses attributes to determine whether to allow certain types of memory accesses; whether to use specific width accesses; and whether to cache target memory. By default the description of memory regions is fetched from the target (if the current target supports this), but the user can override the fetched regions.
Defined memory regions can be individually enabled and disabled. When a memory region is disabled, gdb uses the default attributes when accessing memory in that region. Similarly, if no memory regions have been defined, gdb uses the default attributes when accessing all memory.
When a memory region is defined, it is given a number to identify it; to enable, disable, or remove a memory region, you specify that number.
mem
lower upper attributes...
mem auto
delete mem
nums...
disable mem
nums...
enable mem
nums...
info mem
The access mode attributes set whether gdb may make read or write accesses to a memory region.
While these attributes prevent gdb from performing invalid memory accesses, they do nothing to prevent the target system, I/O DMA, etc. from accessing memory.
ro
wo
rw
The access size attribute tells gdb to use specific sized accesses in the memory region. Often memory mapped device registers require specific sized accesses. If no access size attribute is specified, gdb may use accesses of any size.
8
16
32
64
The data cache attributes set whether gdb will cache target memory. While this generally improves performance by reducing debug protocol overhead, it can lead to incorrect results because gdb does not know about volatile variables or memory mapped device registers.
cache
nocache
gdb can be instructed to refuse accesses to memory that is not explicitly described. This can be useful if accessing such regions has undesired effects for a specific target, or to provide better error checking. The following commands control this behaviour.
set mem inaccessible-by-default [on|off]
on
is specified, make gdb treat memory not
explicitly described by the memory ranges as non-existent and refuse accesses
to such memory. The checks are only performed if there's at least one
memory range defined. If off
is specified, make gdb
treat the memory not explicitly described by the memory ranges as RAM.
The default value is on
.
show mem inaccessible-by-default
You can use the commands dump
, append
, and
restore
to copy data between target memory and a file. The
dump
and append
commands write data to a file, and the
restore
command reads data from a file back into the inferior's
memory. Files may be in binary, Motorola S-record, Intel hex,
Tektronix Hex, or Verilog Hex format; however, gdb can only
append to binary files, and cannot read from Verilog Hex files.
dump
[format] memory
filename start_addr end_addrdump
[format] value
filename exprThe format parameter may be any one of:
binary
ihex
srec
tekhex
verilog
gdb uses the same definitions of these formats as the gnu binary utilities, like ‘objdump’ and ‘objcopy’. If format is omitted, gdb dumps the data in raw binary form.
append
[binary
] memory
filename start_addr end_addrappend
[binary
] value
filename exprrestore
filename [binary
] bias start endrestore
command can automatically recognize any known bfd
file format, except for raw binary. To restore a raw binary file you
must specify the optional keyword binary
after the filename.
If bias is non-zero, its value will be added to the addresses contained in the file. Binary files always start at address zero, so they will be restored at address bias. Other bfd files have a built-in location; they will be restored at offset bias from that location.
If start and/or end are non-zero, then only data between file offset start and file offset end will be restored. These offsets are relative to the addresses in the file, before the bias argument is applied.
A core file or core dump is a file that records the memory image of a running process and its process status (register values etc.). Its primary use is post-mortem debugging of a program that crashed while it ran outside a debugger. A program that crashes automatically produces a core file, unless this feature is disabled by the user. See Files, for information on invoking gdb in the post-mortem debugging mode.
Occasionally, you may wish to produce a core file of the program you are debugging in order to preserve a snapshot of its state. gdb has a special command for that.
generate-core-file [
file]
gcore [
file]
Note that this command is implemented only for some systems (as of this writing, gnu/Linux, FreeBSD, Solaris, and S390).
On gnu/Linux, this command can take into account the value of the
file /proc/pid/coredump_filter when generating the core
dump (see set use-coredump-filter), and by default honors the
VM_DONTDUMP
flag for mappings where it is present in the file
/proc/pid/smaps (see set dump-excluded-mappings).
set use-coredump-filter on
set use-coredump-filter off
To make use of this feature, you have to write in the
/proc/pid/coredump_filter file a value, in hexadecimal,
which is a bit mask representing the memory mapping types. If a bit
is set in the bit mask, then the memory mappings of the corresponding
types will be dumped; otherwise, they will be ignored. This
configuration is inherited by child processes. For more information
about the bits that can be set in the
/proc/pid/coredump_filter file, please refer to the
manpage of core(5)
.
By default, this option is on
. If this option is turned
off
, gdb does not read the coredump_filter file
and instead uses the same default value as the Linux kernel in order
to decide which pages will be dumped in the core dump file. This
value is currently 0x33
, which means that bits 0
(anonymous private mappings), 1
(anonymous shared mappings),
4
(ELF headers) and 5
(private huge pages) are active.
This will cause these memory mappings to be dumped automatically.
set dump-excluded-mappings on
set dump-excluded-mappings off
on
is specified, gdb will dump memory mappings
marked with the VM_DONTDUMP
flag. This flag is represented in
the file /proc/pid/smaps with the acronym dd
.
The default value is off
.
If the program you are debugging uses a different character set to represent characters and strings than the one gdb uses itself, gdb can automatically translate between the character sets for you. The character set gdb uses we call the host character set; the one the inferior program uses we call the target character set.
For example, if you are running gdb on a gnu/Linux system, which
uses the ISO Latin 1 character set, but you are using gdb's
remote protocol (see Remote Debugging) to debug a program
running on an IBM mainframe, which uses the ebcdic character set,
then the host character set is Latin-1, and the target character set is
ebcdic. If you give gdb the command set
target-charset EBCDIC-US
, then gdb translates between
ebcdic and Latin 1 as you print character or string values, or use
character and string literals in expressions.
gdb has no way to automatically recognize which character set
the inferior program uses; you must tell it, using the set
target-charset
command, described below.
Here are the commands for controlling gdb's character set support:
set target-charset
charsetset host-charset
charsetBy default, gdb uses a host character set appropriate to the
system it is running on; you can override that default using the
set host-charset
command. On some systems, gdb cannot
automatically determine the appropriate host character set. In this
case, gdb uses ‘UTF-8’.
gdb can only use certain character sets as its host character
set. If you type set host-charset <TAB><TAB>,
gdb will list the host character sets it supports.
set charset
charsetshow charset
show host-charset
show target-charset
set target-wide-charset
charsetwchar_t
type. To
display the list of supported wide character sets, type
set target-wide-charset <TAB><TAB>.
show target-wide-charset
Here is an example of gdb's character set support in action. Assume that the following source code has been placed in the file charset-test.c:
#include <stdio.h> char ascii_hello[] = {72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100, 33, 10, 0}; char ibm1047_hello[] = {200, 133, 147, 147, 150, 107, 64, 166, 150, 153, 147, 132, 90, 37, 0}; main () { printf ("Hello, world!\n"); }
In this program, ascii_hello
and ibm1047_hello
are arrays
containing the string ‘Hello, world!’ followed by a newline,
encoded in the ascii and ibm1047 character sets.
We compile the program, and invoke the debugger on it:
$ gcc -g charset-test.c -o charset-test $ gdb -nw charset-test GNU gdb 2001-12-19-cvs Copyright 2001 Free Software Foundation, Inc. ... (gdb)
We can use the show charset
command to see what character sets
gdb is currently using to interpret and display characters and
strings:
(gdb) show charset The current host and target character set is `ISO-8859-1'. (gdb)
For the sake of printing this manual, let's use ascii as our initial character set:
(gdb) set charset ASCII (gdb) show charset The current host and target character set is `ASCII'. (gdb)
Let's assume that ascii is indeed the correct character set for our
host system — in other words, let's assume that if gdb prints
characters using the ascii character set, our terminal will display
them properly. Since our current target character set is also
ascii, the contents of ascii_hello
print legibly:
(gdb) print ascii_hello $1 = 0x401698 "Hello, world!\n" (gdb) print ascii_hello[0] $2 = 72 'H' (gdb)
gdb uses the target character set for character and string literals you use in expressions:
(gdb) print '+' $3 = 43 '+' (gdb)
The ascii character set uses the number 43 to encode the ‘+’ character.
gdb relies on the user to tell it which character set the
target program uses. If we print ibm1047_hello
while our target
character set is still ascii, we get jibberish:
(gdb) print ibm1047_hello $4 = 0x4016a8 "\310\205\223\223\226k@\246\226\231\223\204Z%" (gdb) print ibm1047_hello[0] $5 = 200 '\310' (gdb)
If we invoke the set target-charset
followed by <TAB><TAB>,
gdb tells us the character sets it supports:
(gdb) set target-charset ASCII EBCDIC-US IBM1047 ISO-8859-1 (gdb) set target-charset
We can select ibm1047 as our target character set, and examine the
program's strings again. Now the ascii string is wrong, but
gdb translates the contents of ibm1047_hello
from the
target character set, ibm1047, to the host character set,
ascii, and they display correctly:
(gdb) set target-charset IBM1047 (gdb) show charset The current host character set is `ASCII'. The current target character set is `IBM1047'. (gdb) print ascii_hello $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012" (gdb) print ascii_hello[0] $7 = 72 '\110' (gdb) print ibm1047_hello $8 = 0x4016a8 "Hello, world!\n" (gdb) print ibm1047_hello[0] $9 = 200 'H' (gdb)
As above, gdb uses the target character set for character and string literals you use in expressions:
(gdb) print '+' $10 = 78 '+' (gdb)
The ibm1047 character set uses the number 78 to encode the ‘+’ character.
gdb caches data exchanged between the debugger and a target. Each cache is associated with the address space of the inferior. See Inferiors and Programs, about inferior and address space. Such caching generally improves performance in remote debugging (see Remote Debugging), because it reduces the overhead of the remote protocol by bundling memory reads and writes into large chunks. Unfortunately, simply caching everything would lead to incorrect results, since gdb does not necessarily know anything about volatile values, memory-mapped I/O addresses, etc. Furthermore, in non-stop mode (see Non-Stop Mode) memory can be changed while a gdb command is executing. Therefore, by default, gdb only caches data known to be on the stack12 or in the code segment. Other regions of memory can be explicitly marked as cacheable; see Memory Region Attributes.
set remotecache on
set remotecache off
show remotecache
set stack-cache on
set stack-cache off
on
, use
caching. By default, this option is on
.
show stack-cache
set code-cache on
set code-cache off
on
,
use caching. By default, this option is on
. This improves
performance of disassembly in remote debugging.
show code-cache
info dcache
[line
]If a line number is specified, the contents of that line will be
printed in hex.
set dcache size
sizeset dcache line-size
line-sizeshow dcache size
show dcache line-size
Memory can be searched for a particular sequence of bytes with the
find
command.
find
[/
sn] start_addr, +
len,
val1 [,
val2, ...
]find
[/
sn] start_addr,
end_addr,
val1 [,
val2, ...
]s and n are optional parameters. They may be specified in either order, apart or together.
b
h
w
g
All values are interpreted in the current language. This means, for example, that if the current source language is C/C++ then searching for the string “hello” includes the trailing '\0'. The null terminator can be removed from searching by using casts, e.g.: ‘{char[5]}"hello"’.
If the value size is not specified, it is taken from the
value's type in the current language.
This is useful when one wants to specify the search
pattern as a mixture of types.
Note that this means, for example, that in the case of C-like languages
a search for an untyped 0x42 will search for ‘(int) 0x42’
which is typically four bytes.
You can use strings as search values. Quote them with double-quotes
("
).
The string value is copied into the search pattern byte by byte,
regardless of the endianness of the target and the size specification.
The address of each match found is printed as well as a count of the number of matches found.
The address of the last value found is stored in convenience variable ‘$_’. A count of the number of matches is stored in ‘$numfound’.
For example, if stopped at the printf
in this function:
void hello () { static char hello[] = "hello-hello"; static struct { char c; short s; int i; } __attribute__ ((packed)) mixed = { 'c', 0x1234, 0x87654321 }; printf ("%s\n", hello); }
you get during debugging:
(gdb) find &hello[0], +sizeof(hello), "hello" 0x804956d <hello.1620+6> 1 pattern found (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o' 0x8049567 <hello.1620> 0x804956d <hello.1620+6> 2 patterns found. (gdb) find &hello[0], +sizeof(hello), {char[5]}"hello" 0x8049567 <hello.1620> 0x804956d <hello.1620+6> 2 patterns found. (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l' 0x8049567 <hello.1620> 1 pattern found (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321 0x8049560 <mixed.1625> 1 pattern found (gdb) print $numfound $1 = 1 (gdb) print $_ $2 = (void *) 0x8049560
Whenever gdb prints a value memory will be allocated within gdb to hold the contents of the value. It is possible in some languages with dynamic typing systems, that an invalid program may indicate a value that is incorrectly large, this in turn may cause gdb to try and allocate an overly large amount of memory.
set max-value-size
bytesset max-value-size unlimited
Setting this variable does not effect values that have already been allocated within gdb, only future allocations.
There's a minimum size that max-value-size
can be set to in
order that gdb can still operate correctly, this minimum is
currently 16 bytes.
The limit applies to the results of some subexpressions as well as to
complete expressions. For example, an expression denoting a simple
integer component, such as x.y.z
, may fail if the size of
x.y is dynamic and exceeds bytes. On the other hand,
gdb is sometimes clever; the expression A[i]
, where
A is an array variable with non-constant size, will generally
succeed regardless of the bounds on A, as long as the component
size is less than bytes.
The default value of max-value-size
is currently 64k.
show max-value-size
Almost all compilers support optimization. With optimization disabled, the compiler generates assembly code that corresponds directly to your source code, in a simplistic way. As the compiler applies more powerful optimizations, the generated assembly code diverges from your original source code. With help from debugging information generated by the compiler, gdb can map from the running program back to constructs from your original source.
gdb is more accurate with optimization disabled. If you can recompile without optimization, it is easier to follow the progress of your program during debugging. But, there are many cases where you may need to debug an optimized version.
When you debug a program compiled with ‘-g -O’, remember that the optimizer has rearranged your code; the debugger shows you what is really there. Do not be too surprised when the execution path does not exactly match your source file! An extreme example: if you define a variable, but never use it, gdb never sees that variable—because the compiler optimizes it out of existence.
Some things do not work as well with ‘-g -O’ as with just ‘-g’, particularly on machines with instruction scheduling. If in doubt, recompile with ‘-g’ alone, and if this fixes the problem, please report it to us as a bug (including a test case!). See Variables, for more information about debugging optimized code.
Inlining is an optimization that inserts a copy of the function
body directly at each call site, instead of jumping to a shared
routine. gdb displays inlined functions just like
non-inlined functions. They appear in backtraces. You can view their
arguments and local variables, step into them with step
, skip
them with next
, and escape from them with finish
.
You can check whether a function was inlined by using the
info frame
command.
For gdb to support inlined functions, the compiler must record information about inlining in the debug information — gcc using the dwarf 2 format does this, and several other compilers do also. gdb only supports inlined functions when using dwarf 2. Versions of gcc before 4.1 do not emit two required attributes (‘DW_AT_call_file’ and ‘DW_AT_call_line’); gdb does not display inlined function calls with earlier versions of gcc. It instead displays the arguments and local variables of inlined functions as local variables in the caller.
The body of an inlined function is directly included at its call site; unlike a non-inlined function, there are no instructions devoted to the call. gdb still pretends that the call site and the start of the inlined function are different instructions. Stepping to the call site shows the call site, and then stepping again shows the first line of the inlined function, even though no additional instructions are executed.
This makes source-level debugging much clearer; you can see both the
context of the call and then the effect of the call. Only stepping by
a single instruction using stepi
or nexti
does not do
this; single instruction steps always show the inlined body.
There are some ways that gdb does not pretend that inlined function calls are the same as normal calls:
finish
command. This is a limitation of compiler-generated
debugging information; after finish
, you can step to the next line
and print a variable where your program stored the return value.
Function B
can call function C
in its very last statement. In
unoptimized compilation the call of C
is immediately followed by return
instruction at the end of B
code. Optimizing compiler may replace the
call and return in function B
into one jump to function C
instead. Such use of a jump instruction is called tail call.
During execution of function C
, there will be no indication in the
function call stack frames that it was tail-called from B
. If function
A
regularly calls function B
which tail-calls function C
,
then gdb will see A
as the caller of C
. However, in
some cases gdb can determine that C
was tail-called from
B
, and it will then create fictitious call frame for that, with the
return address set up as if B
called C
normally.
This functionality is currently supported only by DWARF 2 debugging format and the compiler has to produce ‘DW_TAG_call_site’ tags. With gcc, you need to specify -O -g during compilation, to get this information.
info frame command (see Frame Info) will indicate the tail call frame
kind by text tail call frame
such as in this sample gdb output:
(gdb) x/i $pc - 2 0x40066b <b(int, double)+11>: jmp 0x400640 <c(int, double)> (gdb) info frame Stack level 1, frame at 0x7fffffffda30: rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5 tail call frame, caller of frame at 0x7fffffffda30 source language c++. Arglist at unknown address. Locals at unknown address, Previous frame's sp is 0x7fffffffda30
The detection of all the possible code path executions can find them ambiguous. There is no execution history stored (possible Reverse Execution is never used for this purpose) and the last known caller could have reached the known callee by multiple different jump sequences. In such case gdb still tries to show at least all the unambiguous top tail callers and all the unambiguous bottom tail calees, if any.
set debug entry-values
show debug entry-values
The analysis messages for tail calls can for example show why the virtual tail
call frame for function c
has not been recognized (due to the indirect
reference by variable x
):
static void __attribute__((noinline, noclone)) c (void); void (*x) (void) = c; static void __attribute__((noinline, noclone)) a (void) { x++; } static void __attribute__((noinline, noclone)) c (void) { a (); } int main (void) { x (); return 0; } Breakpoint 1, DW_OP_entry_value resolving cannot find DW_TAG_call_site 0x40039a in main a () at t.c:3 3 static void __attribute__((noinline, noclone)) a (void) { x++; } (gdb) bt #0 a () at t.c:3 #1 0x000000000040039a in main () at t.c:5
Another possibility is an ambiguous virtual tail call frames resolution:
int i; static void __attribute__((noinline, noclone)) f (void) { i++; } static void __attribute__((noinline, noclone)) e (void) { f (); } static void __attribute__((noinline, noclone)) d (void) { f (); } static void __attribute__((noinline, noclone)) c (void) { d (); } static void __attribute__((noinline, noclone)) b (void) { if (i) c (); else e (); } static void __attribute__((noinline, noclone)) a (void) { b (); } int main (void) { a (); return 0; } tailcall: initial: 0x4004d2(a) 0x4004ce(b) 0x4004b2(c) 0x4004a2(d) tailcall: compare: 0x4004d2(a) 0x4004cc(b) 0x400492(e) tailcall: reduced: 0x4004d2(a) | (gdb) bt #0 f () at t.c:2 #1 0x00000000004004d2 in a () at t.c:8 #2 0x0000000000400395 in main () at t.c:9
Frames #0 and #2 are real, #1 is a virtual tail call frame.
The code can have possible execution paths main->a->b->c->d->f
or
main->a->b->e->f
, gdb cannot find which one from the inferior state.
initial:
state shows some random possible calling sequence gdb
has found. It then finds another possible calling sequence - that one is
prefixed by compare:
. The non-ambiguous intersection of these two is
printed as the reduced:
calling sequence. That one could have many
further compare:
and reduced:
statements as long as there remain
any non-ambiguous sequence entries.
For the frame of function b
in both cases there are different possible
$pc
values (0x4004cc
or 0x4004ce
), therefore this frame is
also ambiguous. The only non-ambiguous frame is the one for function a
,
therefore this one is displayed to the user while the ambiguous frames are
omitted.
There can be also reasons why printing of frame argument values at function entry may fail:
int v; static void __attribute__((noinline, noclone)) c (int i) { v++; } static void __attribute__((noinline, noclone)) a (int i); static void __attribute__((noinline, noclone)) b (int i) { a (i); } static void __attribute__((noinline, noclone)) a (int i) { if (i) b (i - 1); else c (0); } int main (void) { a (5); return 0; } (gdb) bt #0 c (i=i@entry=0) at t.c:2 #1 0x0000000000400428 in a (DW_OP_entry_value resolving has found function "a" at 0x400420 can call itself via tail calls i=<optimized out>) at t.c:6 #2 0x000000000040036e in main () at t.c:7
gdb cannot find out from the inferior state if and how many times did
function a
call itself (via function b
) as these calls would be
tail calls. Such tail calls would modify the i
variable, therefore
gdb cannot be sure the value it knows would be right - gdb
prints <optimized out>
instead.
Some languages, such as C and C++, provide a way to define and invoke “preprocessor macros” which expand into strings of tokens. gdb can evaluate expressions containing macro invocations, show the result of macro expansion, and show a macro's definition, including where it was defined.
You may need to compile your program specially to provide gdb with information about preprocessor macros. Most compilers do not include macros in their debugging information, even when you compile with the -g flag. See Compilation.
A program may define a macro at one point, remove that definition later, and then provide a different definition after that. Thus, at different points in the program, a macro may have different definitions, or have no definition at all. If there is a current stack frame, gdb uses the macros in scope at that frame's source code line. Otherwise, gdb uses the macros in scope at the current listing location; see List.
Whenever gdb evaluates an expression, it always expands any macro invocations present in the expression. gdb also provides the following commands for working with macros explicitly.
macro expand
expressionmacro exp
expressionmacro expand-once
expressionmacro exp1
expressioninfo macro [-a|-all] [--]
macroinfo macros
locationmacro define
macro replacement-listmacro define
macro(
arglist)
replacement-listA definition introduced by this command is in scope in every
expression evaluated in gdb, until it is removed with the
macro undef
command, described below. The definition overrides
all definitions for macro present in the program being debugged,
as well as any previous user-supplied definition.
macro undef
macromacro
define
command, described above; it cannot remove definitions present
in the program being debugged.
macro list
macro define
command.
Here is a transcript showing the above commands in action. First, we show our source files:
$ cat sample.c #include <stdio.h> #include "sample.h" #define M 42 #define ADD(x) (M + x) main () { #define N 28 printf ("Hello, world!\n"); #undef N printf ("We're so creative.\n"); #define N 1729 printf ("Goodbye, world!\n"); } $ cat sample.h #define Q < $
Now, we compile the program using the gnu C compiler, gcc. We pass the -gdwarf-213 and -g3 flags to ensure the compiler includes information about preprocessor macros in the debugging information.
$ gcc -gdwarf-2 -g3 sample.c -o sample $
Now, we start gdb on our sample program:
$ gdb -nw sample GNU gdb 2002-05-06-cvs Copyright 2002 Free Software Foundation, Inc. GDB is free software, ... (gdb)
We can expand macros and examine their definitions, even when the program is not running. gdb uses the current listing position to decide which macro definitions are in scope:
(gdb) list main 3 4 #define M 42 5 #define ADD(x) (M + x) 6 7 main () 8 { 9 #define N 28 10 printf ("Hello, world!\n"); 11 #undef N 12 printf ("We're so creative.\n"); (gdb) info macro ADD Defined at /home/jimb/gdb/macros/play/sample.c:5 #define ADD(x) (M + x) (gdb) info macro Q Defined at /home/jimb/gdb/macros/play/sample.h:1 included at /home/jimb/gdb/macros/play/sample.c:2 #define Q < (gdb) macro expand ADD(1) expands to: (42 + 1) (gdb) macro expand-once ADD(1) expands to: once (M + 1) (gdb)
In the example above, note that macro expand-once
expands only
the macro invocation explicit in the original text — the invocation of
ADD
— but does not expand the invocation of the macro M
,
which was introduced by ADD
.
Once the program is running, gdb uses the macro definitions in force at the source line of the current stack frame:
(gdb) break main Breakpoint 1 at 0x8048370: file sample.c, line 10. (gdb) run Starting program: /home/jimb/gdb/macros/play/sample Breakpoint 1, main () at sample.c:10 10 printf ("Hello, world!\n"); (gdb)
At line 10, the definition of the macro N
at line 9 is in force:
(gdb) info macro N Defined at /home/jimb/gdb/macros/play/sample.c:9 #define N 28 (gdb) macro expand N Q M expands to: 28 < 42 (gdb) print N Q M $1 = 1 (gdb)
As we step over directives that remove N
's definition, and then
give it a new definition, gdb finds the definition (or lack
thereof) in force at each point:
(gdb) next Hello, world! 12 printf ("We're so creative.\n"); (gdb) info macro N The symbol `N' has no definition as a C/C++ preprocessor macro at /home/jimb/gdb/macros/play/sample.c:12 (gdb) next We're so creative. 14 printf ("Goodbye, world!\n"); (gdb) info macro N Defined at /home/jimb/gdb/macros/play/sample.c:13 #define N 1729 (gdb) macro expand N Q M expands to: 1729 < 42 (gdb) print N Q M $2 = 0 (gdb)
In addition to source files, macros can be defined on the compilation command line using the -Dname=value syntax. For macros defined in such a way, gdb displays the location of their definition as line zero of the source file submitted to the compiler.
(gdb) info macro __STDC__ Defined at /home/jimb/gdb/macros/play/sample.c:0 -D__STDC__=1 (gdb)
In some applications, it is not feasible for the debugger to interrupt the program's execution long enough for the developer to learn anything helpful about its behavior. If the program's correctness depends on its real-time behavior, delays introduced by a debugger might cause the program to change its behavior drastically, or perhaps fail, even when the code itself is correct. It is useful to be able to observe the program's behavior without interrupting it.
Using gdb's trace
and collect
commands, you can
specify locations in the program, called tracepoints, and
arbitrary expressions to evaluate when those tracepoints are reached.
Later, using the tfind
command, you can examine the values
those expressions had when the program hit the tracepoints. The
expressions may also denote objects in memory—structures or arrays,
for example—whose values gdb should record; while visiting
a particular tracepoint, you may inspect those objects as if they were
in memory at that moment. However, because gdb records these
values without interacting with you, it can do so quickly and
unobtrusively, hopefully not disturbing the program's behavior.
The tracepoint facility is currently available only for remote targets. See Targets. In addition, your remote target must know how to collect trace data. This functionality is implemented in the remote stub; however, none of the stubs distributed with gdb support tracepoints as of this writing. The format of the remote packets used to implement tracepoints are described in Tracepoint Packets.
It is also possible to get trace data from a file, in a manner reminiscent
of corefiles; you specify the filename, and use tfind
to search
through the file. See Trace Files, for more details.
This chapter describes the tracepoint commands and features.
Before running such a trace experiment, an arbitrary number of tracepoints can be set. A tracepoint is actually a special type of breakpoint (see Set Breaks), so you can manipulate it using standard breakpoint commands. For instance, as with breakpoints, tracepoint numbers are successive integers starting from one, and many of the commands associated with tracepoints take the tracepoint number as their argument, to identify which tracepoint to work on.
For each tracepoint, you can specify, in advance, some arbitrary set of data that you want the target to collect in the trace buffer when it hits that tracepoint. The collected data can include registers, local variables, or global data. Later, you can use gdb commands to examine the values these data had at the time the tracepoint was hit.
Tracepoints do not support every breakpoint feature. Ignore counts on tracepoints have no effect, and tracepoints cannot run gdb commands when they are hit. Tracepoints may not be thread-specific either.
Some targets may support fast tracepoints, which are inserted in a different way (such as with a jump instead of a trap), that is faster but possibly restricted in where they may be installed.
Regular and fast tracepoints are dynamic tracing facilities, meaning that they can be used to insert tracepoints at (almost) any location in the target. Some targets may also support controlling static tracepoints from gdb. With static tracing, a set of instrumentation points, also known as markers, are embedded in the target program, and can be activated or deactivated by name or address. These are usually placed at locations which facilitate investigating what the target is actually doing. gdb's support for static tracing includes being able to list instrumentation points, and attach them with gdb defined high level tracepoints that expose the whole range of convenience of gdb's tracepoints support. Namely, support for collecting registers values and values of global or local (to the instrumentation point) variables; tracepoint conditions and trace state variables. The act of installing a gdb static tracepoint on an instrumentation point, or marker, is referred to as probing a static tracepoint marker.
gdbserver
supports tracepoints on some target systems.
See Tracepoints support in gdbserver
.
This section describes commands to set tracepoints and associated conditions and actions.
trace
locationtrace
command is very similar to the break
command.
Its argument location can be any valid location.
See Specify Location. The trace
command defines a tracepoint,
which is a point in the target program where the debugger will briefly stop,
collect some data, and then allow the program to continue. Setting a tracepoint
or changing its actions takes effect immediately if the remote stub
supports the ‘InstallInTrace’ feature (see install tracepoint in tracing).
If remote stub doesn't support the ‘InstallInTrace’ feature, all
these changes don't take effect until the next tstart
command, and once a trace experiment is running, further changes will
not have any effect until the next trace experiment starts. In addition,
gdb supports pending tracepoints—tracepoints whose
address is not yet resolved. (This is similar to pending breakpoints.)
Pending tracepoints are not downloaded to the target and not installed
until they are resolved. The resolution of pending tracepoints requires
gdb support—when debugging with the remote target, and
gdb disconnects from the remote stub (see disconnected tracing), pending tracepoints can not be resolved (and downloaded to
the remote stub) while gdb is disconnected.
Here are some examples of using the trace
command:
(gdb) trace foo.c:121 // a source file and line number (gdb) trace +2 // 2 lines forward (gdb) trace my_function // first source line of function (gdb) trace *my_function // EXACT start address of function (gdb) trace *0x2117c4 // an address
You can abbreviate trace
as tr
.
trace
location if
condftrace
location [ if
cond ]
ftrace
command sets a fast tracepoint. For targets that
support them, fast tracepoints will use a more efficient but possibly
less general technique to trigger data collection, such as a jump
instruction instead of a trap, or some sort of hardware support. It
may not be possible to create a fast tracepoint at the desired
location, in which case the command will exit with an explanatory
message.
gdb handles arguments to ftrace
exactly as for
trace
.
On 32-bit x86-architecture systems, fast tracepoints normally need to
be placed at an instruction that is 5 bytes or longer, but can be
placed at 4-byte instructions if the low 64K of memory of the target
program is available to install trampolines. Some Unix-type systems,
such as gnu/Linux, exclude low addresses from the program's
address space; but for instance with the Linux kernel it is possible
to let gdb use this area by doing a sysctl command
to set the mmap_min_addr
kernel parameter, as in
sudo sysctl -w vm.mmap_min_addr=32768
which sets the low address to 32K, which leaves plenty of room for
trampolines. The minimum address should be set to a page boundary.
strace
location [ if
cond ]
strace
command sets a static tracepoint. For targets that
support it, setting a static tracepoint probes a static
instrumentation point, or marker, found at location. It may not
be possible to set a static tracepoint at the desired location, in
which case the command will exit with an explanatory message.
gdb handles arguments to strace
exactly as for
trace
, with the addition that the user can also specify
-m
marker as location. This probes the marker
identified by the marker string identifier. This identifier
depends on the static tracepoint backend library your program is
using. You can find all the marker identifiers in the ‘ID’ field
of the info static-tracepoint-markers
command output.
See Listing Static Tracepoint Markers. For example, in the following small program using the UST
tracing engine:
main () { trace_mark(ust, bar33, "str %s", "FOOBAZ"); }
the marker id is composed of joining the first two arguments to the
trace_mark
call with a slash, which translates to:
(gdb) info static-tracepoint-markers Cnt Enb ID Address What 1 n ust/bar33 0x0000000000400ddc in main at stexample.c:22 Data: "str %s" [etc...]
so you may probe the marker above with:
(gdb) strace -m ust/bar33
Static tracepoints accept an extra collect action — collect
$_sdata
. This collects arbitrary user data passed in the probe point
call to the tracing library. In the UST example above, you'll see
that the third argument to trace_mark
is a printf-like format
string. The user data is then the result of running that formatting
string against the following arguments. Note that info
static-tracepoint-markers
command output lists that format string in
the ‘Data:’ field.
You can inspect this data when analyzing the trace buffer, by printing the $_sdata variable like any other variable available to gdb. See Tracepoint Action Lists.
The convenience variable $tpnum
records the tracepoint number
of the most recently set tracepoint.
delete tracepoint
[num]delete
command can remove tracepoints also.
Examples:
(gdb) delete trace 1 2 3 // remove three tracepoints (gdb) delete trace // remove all tracepoints
You can abbreviate this command as del tr
.
These commands are deprecated; they are equivalent to plain disable
and enable
.
disable tracepoint
[num]enable tracepoint
command.
If the command is issued during a trace experiment and the debug target
has support for disabling tracepoints during a trace experiment, then the
change will be effective immediately. Otherwise, it will be applied to the
next trace experiment.
enable tracepoint
[num]passcount
[n [num]]passcount
command sets the
passcount of the most recently defined tracepoint. If no passcount is
given, the trace experiment will run until stopped explicitly by the
user.
Examples:
(gdb) passcount 5 2 // Stop on the 5th execution of
// tracepoint 2
(gdb) passcount 12 // Stop on the 12th execution of the
// most recently defined tracepoint.
(gdb) trace foo (gdb) pass 3 (gdb) trace bar (gdb) pass 2 (gdb) trace baz (gdb) pass 1 // Stop tracing when foo has been
// executed 3 times OR when bar has
// been executed 2 times
// OR when baz has been executed 1 time.
The simplest sort of tracepoint collects data every time your program reaches a specified place. You can also specify a condition for a tracepoint. A condition is just a Boolean expression in your programming language (see Expressions). A tracepoint with a condition evaluates the expression each time your program reaches it, and data collection happens only if the condition is true.
Tracepoint conditions can be specified when a tracepoint is set, by
using ‘if’ in the arguments to the trace
command.
See Setting Tracepoints. They can
also be set or changed at any time with the condition
command,
just as with breakpoints.
Unlike breakpoint conditions, gdb does not actually evaluate the conditional expression itself. Instead, gdb encodes the expression into an agent expression (see Agent Expressions) suitable for execution on the target, independently of gdb. Global variables become raw memory locations, locals become stack accesses, and so forth.
For instance, suppose you have a function that is usually called frequently, but should not be called after an error has occurred. You could use the following tracepoint command to collect data about calls of that function that happen while the error code is propagating through the program; an unconditional tracepoint could end up collecting thousands of useless trace frames that you would have to search through.
(gdb) trace normal_operation if errcode > 0
A trace state variable is a special type of variable that is
created and managed by target-side code. The syntax is the same as
that for GDB's convenience variables (a string prefixed with “$”),
but they are stored on the target. They must be created explicitly,
using a tvariable
command. They are always 64-bit signed
integers.
Trace state variables are remembered by gdb, and downloaded to the target along with tracepoint information when the trace experiment starts. There are no intrinsic limits on the number of trace state variables, beyond memory limitations of the target.
Although trace state variables are managed by the target, you can use
them in print commands and expressions as if they were convenience
variables; gdb will get the current value from the target
while the trace experiment is running. Trace state variables share
the same namespace as other “$” variables, which means that you
cannot have trace state variables with names like $23
or
$pc
, nor can you have a trace state variable and a convenience
variable with the same name.
tvariable $
name [ =
expression ]
tvariable
command creates a new trace state variable named
$
name, and optionally gives it an initial value of
expression. The expression is evaluated when this command is
entered; the result will be converted to an integer if possible,
otherwise gdb will report an error. A subsequent
tvariable
command specifying the same name does not create a
variable, but instead assigns the supplied initial value to the
existing variable of that name, overwriting any previous initial
value. The default initial value is 0.
info tvariables
delete tvariable
[ $
name ...
]actions
[num]actions
without bothering about its number). You specify the
actions themselves on the following lines, one action at a time, and
terminate the actions list with a line containing just end
. So
far, the only defined actions are collect
, teval
, and
while-stepping
.
actions
is actually equivalent to commands
(see Breakpoint Command Lists), except that only the defined
actions are allowed; any other gdb command is rejected.
To remove all actions from a tracepoint, type ‘actions num’ and follow it immediately with ‘end’.
(gdb) collect data // collect some data (gdb) while-stepping 5 // single-step 5 times, collect data (gdb) end // signals the end of actions.
In the following example, the action list begins with collect
commands indicating the things to be collected when the tracepoint is
hit. Then, in order to single-step and collect additional data
following the tracepoint, a while-stepping
command is used,
followed by the list of things to be collected after each step in a
sequence of single steps. The while-stepping
command is
terminated by its own separate end
command. Lastly, the action
list is terminated by an end
command.
(gdb) trace foo (gdb) actions Enter actions for tracepoint 1, one per line: > collect bar,baz > collect $regs > while-stepping 12 > collect $pc, arr[i] > end end
collect
[/
mods] expr1,
expr2, ...
$regs
$args
$locals
$_ret
Note: The return address location can not always be reliably
determined up front, and the wrong address / registers may end up
collected instead. On some architectures the reliability is higher
for tracepoints at function entry, while on others it's the opposite.
When this happens, backtracing will stop because the return address is
found unavailable (unless another collect rule happened to match it).
$_probe_argc
$_probe_arg
n$_sdata
printf
function call. The
tracing library is able to collect user specified data formatted to a
character string using the format provided by the programmer that
instrumented the program. Other backends have similar mechanisms.
Here's an example of a UST marker call:
const char master_name[] = "$your_name"; trace_mark(channel1, marker1, "hello %s", master_name)
In this case, collecting $_sdata
collects the string
‘hello $yourname’. When analyzing the trace buffer, you can
inspect ‘$_sdata’ like any other variable available to
gdb.
You can give several consecutive collect
commands, each one
with a single argument, or one collect
command with several
arguments separated by commas; the effect is the same.
The optional mods changes the usual handling of the arguments.
s
requests that pointers to chars be handled as strings, in
particular collecting the contents of the memory being pointed at, up
to the first zero. The upper bound is by default the value of the
print elements
variable; if s
is followed by a decimal
number, that is the upper bound instead. So for instance
‘collect/s25 mystr’ collects as many as 25 characters at
‘mystr’.
The command info scope
(see info scope) is
particularly useful for figuring out what data to collect.
teval
expr1,
expr2, ...
collect
action were used.
while-stepping
nwhile-stepping
command is followed by the list of what to collect while stepping
(followed by its own end
command):
> while-stepping 12 > collect $regs, myglobal > end >
Note that $pc
is not automatically collected by
while-stepping
; you need to explicitly collect that register if
you need it. You may abbreviate while-stepping
as ws
or
stepping
.
set default-collect
expr1,
expr2, ...
collect
action prepended
to every tracepoint action list. The expressions are parsed
individually for each tracepoint, so for instance a variable named
xyz
may be interpreted as a global for one tracepoint, and a
local for another, as appropriate to the tracepoint's location.
show default-collect
info tracepoints
[num...
]info breakpoints
; in fact, info tracepoints
is the same
command, simply restricting itself to tracepoints.
A tracepoint's listing may include additional information specific to tracing:
passcount
n command
(gdb) info trace Num Type Disp Enb Address What 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7 while-stepping 20 collect globfoo, $regs end collect globfoo2 end pass count 1200 2 tracepoint keep y <MULTIPLE> collect $eip 2.1 y 0x0804859c in func4 at change-loc.h:35 installed on target 2.2 y 0xb7ffc480 in func4 at change-loc.h:35 installed on target 2.3 y <PENDING> set_tracepoint 3 tracepoint keep y 0x080485b1 in foo at change-loc.c:29 not installed on target (gdb)
This command can be abbreviated info tp
.
info static-tracepoint-markers
For each marker, the following columns are printed:
In addition, the following information may be printed for each marker:
(gdb) info static-tracepoint-markers Cnt ID Enb Address What 1 ust/bar2 y 0x0000000000400e1a in main at stexample.c:25 Data: number1 %d number2 %d Probed by static tracepoints: #2 2 ust/bar33 n 0x0000000000400c87 in main at stexample.c:24 Data: str %s (gdb)
tstart
tstop
Note: a trace experiment and data collection may stop automatically if any tracepoint's passcount is reached (see Tracepoint Passcounts), or if the trace buffer becomes full.
tstatus
Here is an example of the commands we described so far:
(gdb) trace gdb_c_test (gdb) actions Enter actions for tracepoint #1, one per line. > collect $regs,$locals,$args > while-stepping 11 > collect $regs > end > end (gdb) tstart [time passes ...] (gdb) tstop
You can choose to continue running the trace experiment even if
gdb disconnects from the target, voluntarily or
involuntarily. For commands such as detach
, the debugger will
ask what you want to do with the trace. But for unexpected
terminations (gdb crash, network outage), it would be
unfortunate to lose hard-won trace data, so the variable
disconnected-tracing
lets you decide whether the trace should
continue running without gdb.
set disconnected-tracing on
set disconnected-tracing off
detach
or
quit
will ask you directly what to do about a running trace no
matter what this variable's setting, so the variable is mainly useful
for handling unexpected situations, such as loss of the network.
show disconnected-tracing
When you reconnect to the target, the trace experiment may or may not still be running; it might have filled the trace buffer in the meantime, or stopped for one of the other reasons. If it is running, it will continue after reconnection.
Upon reconnection, the target will upload information about the tracepoints in effect. gdb will then compare that information to the set of tracepoints currently defined, and attempt to match them up, allowing for the possibility that the numbers may have changed due to creation and deletion in the meantime. If one of the target's tracepoints does not match any in gdb, the debugger will create a new tracepoint, so that you have a number with which to specify that tracepoint. This matching-up process is necessarily heuristic, and it may result in useless tracepoints being created; you may simply delete them if they are of no use.
If your target agent supports a circular trace buffer, then you can run a trace experiment indefinitely without filling the trace buffer; when space runs out, the agent deletes already-collected trace frames, oldest first, until there is enough room to continue collecting. This is especially useful if your tracepoints are being hit too often, and your trace gets terminated prematurely because the buffer is full. To ask for a circular trace buffer, simply set ‘circular-trace-buffer’ to on. You can set this at any time, including during tracing; if the agent can do it, it will change buffer handling on the fly, otherwise it will not take effect until the next run.
set circular-trace-buffer on
set circular-trace-buffer off
show circular-trace-buffer
set trace-buffer-size
nset trace-buffer-size unlimited
unlimited
or -1
to let the target use whatever size it
likes. This is also the default.
show trace-buffer-size
tstatus
to get a report of the actual buffer size.
set trace-user
textshow trace-user
set trace-notes
textshow trace-notes
set trace-stop-notes
texttstop
arguments; the set command is convenient way to fix a
stop note that is mistaken or incomplete.
show trace-stop-notes
There are a number of restrictions on the use of tracepoints. As described above, tracepoint data gathering occurs on the target without interaction from gdb. Thus the full capabilities of the debugger are not available during data gathering, and then at data examination time, you will be limited by only having what was collected. The following items describe some common problems, but it is not exhaustive, and you may run into additional difficulties not mentioned here.
$locals
or $args
, during while-stepping
may
behave erratically. The stepping action may enter a new scope (for
instance by stepping into a function), or the location of the variable
may change (for instance it is loaded into a register). The
tracepoint data recorded uses the location information for the
variables that is correct for the tracepoint location. When the
tracepoint is created, it is not possible, in general, to determine
where the steps of a while-stepping
sequence will advance the
program—particularly if a conditional branch is stepped.
*ptr@50
can be used to collect the 50 element array pointed to
by ptr
.
*(unsigned char *)$esp@300
(adjust to use the name of the actual stack pointer register on your
target architecture, and the amount of stack you wish to capture).
Then the backtrace
command will show a partial backtrace when
using a trace frame. The number of stack frames that can be examined
depends on the sizes of the frames in the collected stack. Note that
if you ask for a block so large that it goes past the bottom of the
stack, the target agent may report an error trying to read from an
invalid address.
$pc
must be the same as the address of
the tracepoint and use that when you are looking at a trace frame
for that tracepoint. However, this cannot work if the tracepoint has
multiple locations (for instance if it was set in a function that was
inlined), or if it has a while-stepping
loop. In those cases
gdb will warn you that it can't infer $pc
, and default
it to zero.
After the tracepoint experiment ends, you use gdb commands
for examining the trace data. The basic idea is that each tracepoint
collects a trace snapshot every time it is hit and another
snapshot every time it single-steps. All these snapshots are
consecutively numbered from zero and go into a buffer, and you can
examine them later. The way you examine them is to focus on a
specific trace snapshot. When the remote stub is focused on a trace
snapshot, it will respond to all gdb requests for memory and
registers by reading from the buffer which belongs to that snapshot,
rather than from real memory or registers of the program being
debugged. This means that all gdb commands
(print
, info registers
, backtrace
, etc.) will
behave as if we were currently debugging the program state as it was
when the tracepoint occurred. Any requests for data that are not in
the buffer will fail.
tfind
nThe basic command for selecting a trace snapshot from the buffer is
tfind
n, which finds trace snapshot number n,
counting from zero. If no argument n is given, the next
snapshot is selected.
Here are the various forms of using the tfind
command.
tfind start
tfind 0
(since 0 is the number of the first snapshot).
tfind none
tfind end
tfind
tfind -
tfind tracepoint
numtfind pc
addrtfind outside
addr1,
addr2tfind range
addr1,
addr2tfind line
[file:
]ntfind line
repeatedly can appear to have the same effect as
stepping from line to line in a live debugging session.
The default arguments for the tfind
commands are specifically
designed to make it easy to scan through the trace buffer. For
instance, tfind
with no argument selects the next trace
snapshot, and tfind -
with no argument selects the previous
trace snapshot. So, by giving one tfind
command, and then
simply hitting <RET> repeatedly you can examine all the trace
snapshots in order. Or, by saying tfind -
and then hitting
<RET> repeatedly you can examine the snapshots in reverse order.
The tfind line
command with no argument selects the snapshot
for the next source line executed. The tfind pc
command with
no argument selects the next snapshot with the same program counter
(PC) as the current frame. The tfind tracepoint
command with
no argument selects the next trace snapshot collected by the same
tracepoint as the current one.
In addition to letting you scan through the trace buffer manually, these commands make it easy to construct gdb scripts that scan through the trace buffer and print out whatever collected data you are interested in. Thus, if we want to examine the PC, FP, and SP registers from each trace frame in the buffer, we can say this:
(gdb) tfind start (gdb) while ($trace_frame != -1) > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \ $trace_frame, $pc, $sp, $fp > tfind > end Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
Or, if we want to examine the variable X
at each source line in
the buffer:
(gdb) tfind start (gdb) while ($trace_frame != -1) > printf "Frame %d, X == %d\n", $trace_frame, X > tfind line > end Frame 0, X = 1 Frame 7, X = 2 Frame 13, X = 255
tdump
This command takes no arguments. It prints all the data collected at the current trace snapshot.
(gdb) trace 444 (gdb) actions Enter actions for tracepoint #2, one per line: > collect $regs, $locals, $args, gdb_long_test > end (gdb) tstart (gdb) tfind line 444 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66) at gdb_test.c:444 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", ) (gdb) tdump Data collected at tracepoint 2, trace frame 1: d0 0xc4aa0085 -995491707 d1 0x18 24 d2 0x80 128 d3 0x33 51 d4 0x71aea3d 119204413 d5 0x22 34 d6 0xe0 224 d7 0x380035 3670069 a0 0x19e24a 1696330 a1 0x3000668 50333288 a2 0x100 256 a3 0x322000 3284992 a4 0x3000698 50333336 a5 0x1ad3cc 1758156 fp 0x30bf3c 0x30bf3c sp 0x30bf34 0x30bf34 ps 0x0 0 pc 0x20b2c8 0x20b2c8 fpcontrol 0x0 0 fpstatus 0x0 0 fpiaddr 0x0 0 p = 0x20e5b4 "gdb-test" p1 = (void *) 0x11 p2 = (void *) 0x22 p3 = (void *) 0x33 p4 = (void *) 0x44 p5 = (void *) 0x55 p6 = (void *) 0x66 gdb_long_test = 17 '\021' (gdb)
tdump
works by scanning the tracepoint's current collection
actions and printing the value of each expression listed. So
tdump
can fail, if after a run, you change the tracepoint's
actions to mention variables that were not collected during the run.
Also, for tracepoints with while-stepping
loops, tdump
uses the collected value of $pc
to distinguish between trace
frames that were collected at the tracepoint hit, and frames that were
collected while stepping. This allows it to correctly choose whether
to display the basic list of collections, or the collections from the
body of the while-stepping loop. However, if $pc
was not collected,
then tdump
will always attempt to dump using the basic collection
list, and may fail if a while-stepping frame does not include all the
same data that is collected at the tracepoint hit.
save tracepoints
filename
This command saves all current tracepoint definitions together with
their actions and passcounts, into a file filename
suitable for use in a later debugging session. To read the saved
tracepoint definitions, use the source
command (see Command Files). The save-tracepoints
command is a deprecated
alias for save tracepoints
(int) $trace_frame
(int) $tracepoint
(int) $trace_line
(char []) $trace_file
(char []) $trace_func
$tracepoint
.
Note: $trace_file
is not suitable for use in printf
,
use output
instead.
Here's a simple example of using these convenience variables for stepping through all the trace snapshots and printing some of their data. Note that these are not the same as trace state variables, which are managed by the target.
(gdb) tfind start (gdb) while $trace_frame != -1 > output $trace_file > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint > tfind > end
In some situations, the target running a trace experiment may no
longer be available; perhaps it crashed, or the hardware was needed
for a different activity. To handle these cases, you can arrange to
dump the trace data into a file, and later use that file as a source
of trace data, via the target tfile
command.
tsave [ -r ]
filenametsave [-ctf]
dirname-r
(“remote”) to direct the target to save
the data directly into filename in its own filesystem, which may be
more efficient if the trace buffer is very large. (Note, however, that
target tfile
can only read from files accessible to the host.)
By default, this command will save trace frame in tfile format.
You can supply the optional argument -ctf
to save data in CTF
format. The Common Trace Format (CTF) is proposed as a trace format
that can be shared by multiple debugging and tracing tools. Please go to
<http://www.efficios.com/ctf
> to get more information.
target tfile
filenametarget ctf
dirnametstatus
will report the state of the trace run at the moment
the data was saved, as well as the current trace frame you are examining.
Both filename and dirname must be on a filesystem accessible to
the host.
(gdb) target ctf ctf.ctf (gdb) tfind Found trace frame 0, tracepoint 2 39 ++a; /* set tracepoint 1 here */ (gdb) tdump Data collected at tracepoint 2, trace frame 0: i = 0 a = 0 b = 1 '\001' c = {"123", "456", "789", "123", "456", "789"} d = {{{a = 1, b = 2}, {a = 3, b = 4}}, {{a = 5, b = 6}, {a = 7, b = 8}}} (gdb) p b $1 = 1
If your program is too large to fit completely in your target system's memory, you can sometimes use overlays to work around this problem. gdb provides some support for debugging programs that use overlays.
Suppose you have a computer whose instruction address space is only 64 kilobytes long, but which has much more memory which can be accessed by other means: special instructions, segment registers, or memory management hardware, for example. Suppose further that you want to adapt a program which is larger than 64 kilobytes to run on this system.
One solution is to identify modules of your program which are relatively independent, and need not call each other directly; call these modules overlays. Separate the overlays from the main program, and place their machine code in the larger memory. Place your main program in instruction memory, but leave at least enough space there to hold the largest overlay as well.
Now, to call a function located in an overlay, you must first copy that overlay's machine code from the large memory into the space set aside for it in the instruction memory, and then jump to its entry point there.
Data Instruction Larger Address Space Address Space Address Space +-----------+ +-----------+ +-----------+ | | | | | | +-----------+ +-----------+ +-----------+<-- overlay 1 | program | | main | .----| overlay 1 | load address | variables | | program | | +-----------+ | and heap | | | | | | +-----------+ | | | +-----------+<-- overlay 2 | | +-----------+ | | | load address +-----------+ | | | .-| overlay 2 | | | | | | | mapped --->+-----------+ | | +-----------+ address | | | | | | | overlay | <-' | | | | area | <---' +-----------+<-- overlay 3 | | <---. | | load address +-----------+ `--| overlay 3 | | | | | +-----------+ | | +-----------+ | | +-----------+ A code overlay
The diagram (see A code overlay) shows a system with separate data and instruction address spaces. To map an overlay, the program copies its code from the larger address space to the instruction address space. Since the overlays shown here all use the same mapped address, only one may be mapped at a time. For a system with a single address space for data and instructions, the diagram would be similar, except that the program variables and heap would share an address space with the main program and the overlay area.
An overlay loaded into instruction memory and ready for use is called a mapped overlay; its mapped address is its address in the instruction memory. An overlay not present (or only partially present) in instruction memory is called unmapped; its load address is its address in the larger memory. The mapped address is also called the virtual memory address, or VMA; the load address is also called the load memory address, or LMA.
Unfortunately, overlays are not a completely transparent way to adapt a program to limited instruction memory. They introduce a new set of global constraints you must keep in mind as you design your program:
The overlay system described above is rather simple, and could be improved in many ways:
To use gdb's overlay support, each overlay in your program must correspond to a separate section of the executable file. The section's virtual memory address and load memory address must be the overlay's mapped and load addresses. Identifying overlays with sections allows gdb to determine the appropriate address of a function or variable, depending on whether the overlay is mapped or not.
gdb's overlay commands all start with the word overlay
;
you can abbreviate this as ov
or ovly
. The commands are:
overlay off
overlay manual
overlay map-overlay
and overlay unmap-overlay
commands described below.
overlay map-overlay
overlayoverlay map
overlayoverlay unmap-overlay
overlayoverlay unmap
overlayoverlay auto
overlay load-target
overlay load
overlay list-overlays
overlay list
Normally, when gdb prints a code address, it includes the name of the function the address falls in:
(gdb) print main $3 = {int ()} 0x11a0 <main>
When overlay debugging is enabled, gdb recognizes code in
unmapped overlays, and prints the names of unmapped functions with
asterisks around them. For example, if foo
is a function in an
unmapped overlay, gdb prints it this way:
(gdb) overlay list No sections are mapped. (gdb) print foo $5 = {int (int)} 0x100000 <*foo*>
When foo
's overlay is mapped, gdb prints the function's
name normally:
(gdb) overlay list Section .ov.foo.text, loaded at 0x100000 - 0x100034, mapped at 0x1016 - 0x104a (gdb) print foo $6 = {int (int)} 0x1016 <foo>
When overlay debugging is enabled, gdb can find the correct
address for functions and variables in an overlay, whether or not the
overlay is mapped. This allows most gdb commands, like
break
and disassemble
, to work normally, even on unmapped
code. However, gdb's breakpoint support has some limitations:
gdb can automatically track which overlays are mapped and which
are not, given some simple co-operation from the overlay manager in the
inferior. If you enable automatic overlay debugging with the
overlay auto
command (see Overlay Commands), gdb
looks in the inferior's memory for certain variables describing the
current state of the overlays.
Here are the variables your overlay manager must define to support gdb's automatic overlay debugging:
_ovly_table
:struct { /* The overlay's mapped address. */ unsigned long vma; /* The size of the overlay, in bytes. */ unsigned long size; /* The overlay's load address. */ unsigned long lma; /* Non-zero if the overlay is currently mapped; zero otherwise. */ unsigned long mapped; }
_novlys
:_ovly_table
.
To decide whether a particular overlay is mapped or not, gdb
looks for an entry in _ovly_table
whose vma
and
lma
members equal the VMA and LMA of the overlay's section in the
executable file. When gdb finds a matching entry, it consults
the entry's mapped
member to determine whether the overlay is
currently mapped.
In addition, your overlay manager may define a function called
_ovly_debug_event
. If this function is defined, gdb
will silently set a breakpoint there. If the overlay manager then
calls this function whenever it has changed the overlay table, this
will enable gdb to accurately keep track of which overlays
are in program memory, and update any breakpoints that may be set
in overlays. This will allow breakpoints to work even if the
overlays are kept in ROM or other non-writable memory while they
are not being executed.
When linking a program which uses overlays, you must place the overlays at their load addresses, while relocating them to run at their mapped addresses. To do this, you must write a linker script (see Overlay Description). Unfortunately, since linker scripts are specific to a particular host system, target architecture, and target memory layout, this manual cannot provide portable sample code demonstrating gdb's overlay support.
However, the gdb source distribution does contain an overlaid program, with linker scripts for a few systems, as part of its test suite. The program consists of the following files from gdb/testsuite/gdb.base:
d10v-elf
and m32r-elf
targets.
You can build the test program using the d10v-elf
GCC
cross-compiler like this:
$ d10v-elf-gcc -g -c overlays.c $ d10v-elf-gcc -g -c ovlymgr.c $ d10v-elf-gcc -g -c foo.c $ d10v-elf-gcc -g -c bar.c $ d10v-elf-gcc -g -c baz.c $ d10v-elf-gcc -g -c grbx.c $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \ baz.o grbx.o -Wl,-Td10v.ld -o overlays
The build process is identical for any other architecture, except that
you must substitute the appropriate compiler and linker script for the
target system for d10v-elf-gcc
and d10v.ld
.
Although programming languages generally have common aspects, they are
rarely expressed in the same manner. For instance, in ANSI C,
dereferencing a pointer p
is accomplished by *p
, but in
Modula-2, it is accomplished by p^
. Values can also be
represented (and displayed) differently. Hex numbers in C appear as
‘0x1ae’, while in Modula-2 they appear as ‘1AEH’.
Language-specific information is built into gdb for some languages, allowing you to express operations like the above in your program's native language, and allowing gdb to output values in a manner consistent with the syntax of your program's native language. The language you use to build expressions is called the working language.
There are two ways to control the working language—either have gdb
set it automatically, or select it manually yourself. You can use the
set language
command for either purpose. On startup, gdb
defaults to setting the language automatically. The working language is
used to determine how expressions you type are interpreted, how values
are printed, etc.
In addition to the working language, every source file that
gdb knows about has its own working language. For some object
file formats, the compiler might indicate which language a particular
source file is in. However, most of the time gdb infers the
language from the name of the file. The language of a source file
controls whether C++ names are demangled—this way backtrace
can
show each frame appropriately for its own language. There is no way to
set the language of a source file from within gdb, but you can
set the language associated with a filename extension. See Displaying the Language.
This is most commonly a problem when you use a program, such
as cfront
or f2c
, that generates C but is written in
another language. In that case, make the
program use #line
directives in its C output; that way
gdb will know the correct language of the source code of the original
program, and will display that source code, not the generated C code.
If a source file name ends in one of the following extensions, then gdb infers that its language is the one indicated.
In addition, you may set the language associated with a filename extension. See Displaying the Language.
If you allow gdb to set the language automatically, expressions are interpreted the same way in your debugging session and your program.
If you wish, you may set the language manually. To do this, issue the
command ‘set language lang’, where lang is the name of
a language, such as
c
or modula-2
.
For a list of the supported languages, type ‘set language’.
Setting the language manually prevents gdb from updating the working language automatically. This can lead to confusion if you try to debug a program when the working language is not the same as the source language, when an expression is acceptable to both languages—but means different things. For instance, if the current source file were written in C, and gdb was parsing Modula-2, a command such as:
print a = b + c
might not have the effect you intended. In C, this means to add
b
and c
and place the result in a
. The result
printed would be the value of a
. In Modula-2, this means to compare
a
to the result of b+c
, yielding a BOOLEAN
value.
To have gdb set the working language automatically, use ‘set language local’ or ‘set language auto’. gdb then infers the working language. That is, when your program stops in a frame (usually by encountering a breakpoint), gdb sets the working language to the language recorded for the function in that frame. If the language for a frame is unknown (that is, if the function or block corresponding to the frame was defined in a source file that does not have a recognized extension), the current working language is not changed, and gdb issues a warning.
This may not seem necessary for most programs, which are written entirely in one source language. However, program modules and libraries written in one source language can be used by a main program written in a different source language. Using ‘set language auto’ in this case frees you from having to set the working language manually.
The following commands help you find out which language is the working language, and also what language source files were written in.
show language
print
to
build and compute expressions that may involve variables in your program.
info frame
info source
In unusual circumstances, you may have source files with extensions not in the standard list. You can then set the extension associated with a language explicitly:
set extension-language
ext languageinfo extensions
Some languages are designed to guard you against making seemingly common errors through a series of compile- and run-time checks. These include checking the type of arguments to functions and operators and making sure mathematical overflows are caught at run time. Checks such as these help to ensure a program's correctness once it has been compiled by eliminating type mismatches and providing active checks for range errors when your program is running.
By default gdb checks for these errors according to the
rules of the current source language. Although gdb does not check
the statements in your program, it can check expressions entered directly
into gdb for evaluation via the print
command, for example.
Some languages, such as C and C++, are strongly typed, meaning that the arguments to operators and functions have to be of the correct type, otherwise an error occurs. These checks prevent type mismatch errors from ever causing any run-time problems. For example,
int klass::my_method(char *b) { return b ? 1 : 2; } (gdb) print obj.my_method (0) $1 = 2
but
(gdb) print obj.my_method (0x1234) Cannot resolve method klass::my_method to any overloaded instance
The second example fails because in C++ the integer constant ‘0x1234’ is not type-compatible with the pointer parameter type.
For the expressions you use in gdb commands, you can tell gdb to not enforce strict type checking or to treat any mismatches as errors and abandon the expression; When type checking is disabled, gdb successfully evaluates expressions like the second example above.
Even if type checking is off, there may be other reasons
related to type that prevent gdb from evaluating an expression.
For instance, gdb does not know how to add an int
and
a struct foo
. These particular type errors have nothing to do
with the language in use and usually arise from expressions which make
little sense to evaluate anyway.
gdb provides some additional commands for controlling type checking:
set check type on
set check type off
show check type
In some languages (such as Modula-2), it is an error to exceed the bounds of a type; this is enforced with run-time checks. Such range checking is meant to ensure program correctness by making sure computations do not overflow, or indices on an array element access do not exceed the bounds of the array.
For expressions you use in gdb commands, you can tell gdb to treat range errors in one of three ways: ignore them, always treat them as errors and abandon the expression, or issue warnings but evaluate the expression anyway.
A range error can result from numerical overflow, from exceeding an array index bound, or when you type a constant that is not a member of any type. Some languages, however, do not treat overflows as an error. In many implementations of C, mathematical overflow causes the result to “wrap around” to lower values—for example, if m is the largest integer value, and s is the smallest, then
m + 1 ⇒ s
This, too, is specific to individual languages, and in some cases specific to individual compilers or machines. See Supported Languages, for further details on specific languages.
gdb provides some additional commands for controlling the range checker:
set check range auto
set check range on
set check range off
set check range warn
show range
gdb supports C, C++, D, Go, Objective-C, Fortran,
OpenCL C, Pascal, Rust, assembly, Modula-2, and Ada.
Some gdb features may be used in expressions regardless of the
language you use: the gdb @
and ::
operators,
and the ‘{type}addr’ construct (see Expressions) can be used with the constructs of any supported
language.
The following sections detail to what degree each source language is supported by gdb. These sections are not meant to be language tutorials or references, but serve only as a reference guide to what the gdb expression parser accepts, and what input and output formats should look like for different languages. There are many good books written on each of these languages; please look to these for a language reference or tutorial.
Since C and C++ are so closely related, many features of gdb apply to both languages. Whenever this is the case, we discuss those languages together.
The C++ debugging facilities are jointly implemented by the C++
compiler and gdb. Therefore, to debug your C++ code
effectively, you must compile your C++ programs with a supported
C++ compiler, such as gnu g++
, or the HP ANSI C++
compiler (aCC
).
Operators must be defined on values of specific types. For instance,
+
is defined on numbers, but not on structures. Operators are
often defined on groups of types.
For the purposes of C and C++, the following definitions hold:
int
with any of its storage-class
specifiers; char
; enum
; and, for C++, bool
.
float
, double
, and
long double
(if supported by the target platform).
(
type *)
.
The following operators are supported. They are listed here in order of increasing precedence:
,
=
=
op=
b,
and translated to a =
a op b.
op=
and =
have the same precedence. The operator
op is any one of the operators |
, ^
, &
,
<<
, >>
, +
, -
, *
, /
, %
.
?:
?
b :
c can be thought
of as: if a then b else c. The argument a
should be of an integral type.
||
&&
|
^
&
==
, !=
<
, >
, <=
, >=
<<
, >>
@
+
, -
*
, /
, %
++
, --
*
++
.
&
++
.
For debugging C++, gdb implements a use of ‘&’ beyond what is
allowed in the C++ language itself: you can use ‘&(&ref)’
to examine the address
where a C++ reference variable (declared with ‘&ref’) is
stored.
-
++
.
!
++
.
~
++
.
.
, ->
struct
and union
data.
.*
, ->*
[]
[
i]
is defined as
*(
a+
i)
. Same precedence as ->
.
()
->
.
::
struct
, union
,
and class
types.
::
::
,
above.
If an operator is redefined in the user code, gdb usually attempts to invoke the redefined version instead of using the operator's predefined meaning.
gdb allows you to express the constants of C and C++ in the following ways:
long
value.
float
(as opposed to the default double
) type; or with
a letter ‘l’ or ‘L’, which specifies a long double
constant.
'
), or a number—the ordinal value of the corresponding character
(usually its ascii value). Within quotes, the single character may
be represented by a letter or by escape sequences, which are of
the form ‘\nnn’, where nnn is the octal representation
of the character's ordinal value; or of the form ‘\x’, where
‘x’ is a predefined special character—for example,
‘\n’ for newline.
Wide character constants can be written by prefixing a character constant with ‘L’, as in C. For example, ‘L'x'’ is the wide form of ‘x’. The target wide character set is used when computing the value of this constant (see Character Sets).
"
). Any valid character constant (as described
above) may appear. Double quotes within the string must be preceded by
a backslash, so for instance ‘"a\"b'c"’ is a string of five
characters.
Wide string constants can be written by prefixing a string constant with ‘L’, as in C. The target wide character set is used when computing the value of this constant (see Character Sets).
gdb expression handling can interpret most C++ expressions.
Warning: gdb can only debug C++ code if you use the proper compiler and the proper debug format. Currently, gdb works best when debugging C++ code that is compiled with the most recent version of gcc possible. The DWARF debugging format is preferred; gcc defaults to this on most popular platforms. Other compilers and/or debug formats are likely to work badly or not at all when using gdb to debug C++ code. See Compilation.
count = aml->GetOriginal(x, y)
this
following the same rules as C++. using
declarations in the current scope are also respected by gdb.
It does perform integral conversions and promotions, floating-point promotions, arithmetic conversions, pointer conversions, conversions of class objects to base classes, and standard conversions such as those of functions or arrays to pointers; it requires an exact match on the number of function arguments.
Overload resolution is always performed, unless you have specified
set overload-resolution off
. See gdb Features for C++.
You must specify set overload-resolution off
in order to use an
explicit function signature to call an overloaded function, as in
p 'foo(char,int)'('x', 13)
The gdb command-completion facility can simplify this; see Command Completion.
In the parameter list shown when gdb displays a frame, the values of reference variables are not displayed (unlike other variables); this avoids clutter, since references are often used for large structures. The address of a reference variable is always shown, unless you have specified ‘set print address off’.
::
—your
expressions can use it just as expressions in your program do. Since
one scope may be defined in another, you can use ::
repeatedly if
necessary, for example in an expression like
‘scope1::scope2::name’. gdb also allows
resolving name scope by reference to source files, in both C and C++
debugging (see Program Variables).
If you allow gdb to set range checking automatically, it
defaults to off
whenever the working language changes to
C or C++. This happens regardless of whether you or gdb
selects the working language.
If you allow gdb to set the language automatically, it recognizes source files whose names end with .c, .C, or .cc, etc, and when gdb enters code compiled from one of these files, it sets the working language to C or C++. See Having gdb Infer the Source Language, for further details.
By default, when gdb parses C or C++ expressions, strict type checking is used. However, if you turn type checking off, gdb will allow certain non-standard conversions, such as promoting integer constants to pointers.
Range checking, if turned on, is done on mathematical operations. Array indices are not checked, since they are often used to index a pointer that is not itself an array.
The set print union
and show print union
commands apply to
the union
type. When set to ‘on’, any union
that is
inside a struct
or class
is also printed. Otherwise, it
appears as ‘{...}’.
The @
operator aids in the debugging of dynamic arrays, formed
with pointers and a memory allocation function. See Expressions.
Some gdb commands are particularly useful with C++, and some are designed specifically for use with C++. Here is a summary:
rbreak
regexcatch throw
catch rethrow
catch catch
ptype
typenameinfo vtbl
expression.
info vtbl
command can be used to display the virtual
method tables of the object computed by expression. This shows
one entry per virtual table; there may be multiple virtual tables when
multiple inheritance is in use.
demangle
namedemangle
command.
set print demangle
show print demangle
set print asm-demangle
show print asm-demangle
set print object
show print object
set print vtbl
show print vtbl
vtbl
commands do not work on programs compiled with the HP
ANSI C++ compiler (aCC
).)
set overload-resolution on
set overload-resolution off
show overload-resolution
(
types)
rather than just symbol. You can
also use the gdb command-line word completion facilities to list the
available choices, or to finish the type list for you.
See Command Completion, for details on how to do this.
The ABI tags are visible in C++ demangled names. For example, a function that returns a std::string:
std::string function(int);
when compiled for the C++11 ABI is marked with the cxx11
ABI
tag, and gdb displays the symbol like this:
function[abi:cxx11](int)
You can set a breakpoint on such functions simply as if they had no tag. For example:
(gdb) b function(int) Breakpoint 2 at 0x40060d: file main.cc, line 10. (gdb) info breakpoints Num Type Disp Enb Address What 1 breakpoint keep y 0x0040060d in function[abi:cxx11](int) at main.cc:10
On the rare occasion you need to disambiguate between different ABI tags, you can do so by simply including the ABI tag in the function name, like:
(gdb) b ambiguous[abi:other_tag](int)
gdb can examine, set and perform computations with numbers in
decimal floating point format, which in the C language correspond to the
_Decimal32
, _Decimal64
and _Decimal128
types as
specified by the extension to support decimal floating-point arithmetic.
There are two encodings in use, depending on the architecture: BID (Binary Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for PowerPC and S/390. gdb will use the appropriate encoding for the configured target.
Because of a limitation in libdecnumber, the library used by gdb to manipulate decimal floating point numbers, it is not possible to convert (using a cast, for example) integers wider than 32-bit to decimal float.
In addition, in order to imitate gdb's behaviour with binary floating point computations, error checking in decimal float operations ignores underflow, overflow and divide by zero exceptions.
In the PowerPC architecture, gdb provides a set of pseudo-registers
to inspect _Decimal128
values stored in floating point registers.
See PowerPC for more details.
gdb can be used to debug programs written in D and compiled with GDC, LDC or DMD compilers. Currently gdb supports only one D specific feature — dynamic arrays.
gdb can be used to debug programs written in Go and compiled with gccgo or 6g compilers.
Here is a summary of the Go-specific features and restrictions:
The current Go package
For example, given the program:
package main var myglob = "Shall we?" func main () { // ... }
When stopped inside main
either of these work:
(gdb) p myglob (gdb) p main.myglob
Builtin Go types
string
type is recognized by gdb and is printed
as a string.
Builtin Go functions
unsafe.Sizeof
function and handles it internally.
Restrictions on Go expressions
&^
.
The Go _
“blank identifier” is not supported.
Automatic dereferencing of pointers is not supported.
This section provides information about some commands and command options that are useful for debugging Objective-C code. See also info classes, and info selectors, for a few more commands specific to Objective-C support.
The following commands have been extended to accept Objective-C method names as line specifications:
clear
break
info line
jump
list
A fully qualified Objective-C method name is specified as
-[Class methodName]
where the minus sign is used to indicate an instance method and a
plus sign (not shown) is used to indicate a class method. The class
name Class and method name methodName are enclosed in
brackets, similar to the way messages are specified in Objective-C
source code. For example, to set a breakpoint at the create
instance method of class Fruit
in the program currently being
debugged, enter:
break -[Fruit create]
To list ten program lines around the initialize
class method,
enter:
list +[NSText initialize]
In the current version of gdb, the plus or minus sign is required. In future versions of gdb, the plus or minus sign will be optional, but you can use it to narrow the search. It is also possible to specify just a method name:
break create
You must specify the complete method name, including any colons. If
your program's source files contain more than one create
method,
you'll be presented with a numbered list of classes that implement that
method. Indicate your choice by number, or type ‘0’ to exit if
none apply.
As another example, to clear a breakpoint established at the
makeKeyAndOrderFront:
method of the NSWindow
class, enter:
clear -[NSWindow makeKeyAndOrderFront:]
The print command has also been extended to accept methods. For example:
print -[object hash]
will tell gdb to send the hash
message to object
and print the result. Also, an additional command has been added,
print-object
or po
for short, which is meant to print
the description of an object. However, this command may only work
with certain Objective-C libraries that have a particular hook
function, _NSPrintForDebugger
, defined.
This section provides information about gdbs OpenCL C support.
gdb supports the builtin scalar and vector datatypes specified
by OpenCL 1.1. In addition the half- and double-precision floating point
data types of the cl_khr_fp16
and cl_khr_fp64
OpenCL
extensions are also known to gdb.
gdb supports accesses to vector components including the access as lvalue where possible. Since OpenCL C is based on C99 most C expressions supported by gdb can be used as well.
gdb supports the operators specified by OpenCL 1.1 for scalar and vector data types.
gdb can be used to debug programs written in Fortran, but it currently supports only the features of Fortran 77 language.
Some Fortran compilers (gnu Fortran 77 and Fortran 95 compilers among them) append an underscore to the names of variables and functions. When you debug programs compiled by those compilers, you will need to refer to variables and functions with a trailing underscore.
Operators must be defined on values of specific types. For instance,
+
is defined on numbers, but not on characters or other non-
arithmetic types. Operators are often defined on groups of types.
**
:
%
::
Fortran symbols are usually case-insensitive, so gdb by default uses case-insensitive matches for Fortran symbols. You can change that with the ‘set case-insensitive’ command, see Symbols, for the details.
gdb has some commands to support Fortran-specific features, such as displaying common blocks.
info common
[common-name]COMMON
block whose name is common-name. With no argument, the names of
all COMMON
blocks visible at the current program location are
printed.
Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. gdb does not support entering expressions, printing values, or similar features using Pascal syntax.
The Pascal-specific command set print pascal_static-members
controls whether static members of Pascal objects are displayed.
See pascal_static-members.
gdb supports the Rust Programming Language. Type- and value-printing, and expression parsing, are reasonably complete. However, there are a few peculiarities and holes to be aware of.
extern crate
behaves.
That is, if gdb is stopped at a breakpoint in a function in
crate ‘A’, module ‘B’, then break B::f
will attempt
to set a breakpoint in a function named ‘f’ in a crate named
‘B’.
As a consequence of this approach, linespecs also cannot refer to items using ‘self::’ or ‘super::’.
print ::x::y
will try to find the symbol
‘K::x::y’.
However, since it is useful to be able to refer to other crates when
debugging, gdb provides the extern
extension to
circumvent this. To use the extension, just put extern
before
a path expression to refer to the otherwise unavailable “global”
scope.
In the above example, if you wanted to refer to the symbol ‘y’ in
the crate ‘x’, you would use print extern x::y
.
if
or match
, or lambda expressions.
Drop
trait. Objects that may be created by the evaluator will
never be destroyed.
crate::f<u32>
, where the parser would require
crate::f::<u32>
.
Self
is not available.
use
statements are not available, so some names may not be
available in the crate.
The extensions made to gdb to support Modula-2 only support output from the gnu Modula-2 compiler (which is currently being developed). Other Modula-2 compilers are not currently supported, and attempting to debug executables produced by them is most likely to give an error as gdb reads in the executable's symbol table.
Operators must be defined on values of specific types. For instance,
+
is defined on numbers, but not on structures. Operators are
often defined on groups of types. For the purposes of Modula-2, the
following definitions hold:
INTEGER
, CARDINAL
, and
their subranges.
CHAR
and its subranges.
REAL
.
POINTER TO
type.
SET
and BITSET
types.
BOOLEAN
.
The following operators are supported, and appear in order of increasing precedence:
,
:=
:=
value is
value.
<
, >
<=
, >=
<
.
=
, <>
, #
<
. In gdb scripts, only <>
is
available for inequality, since #
conflicts with the script
comment character.
IN
<
.
OR
AND
, &
@
+
, -
*
/
*
.
DIV
, MOD
*
.
-
INTEGER
and REAL
data.
^
NOT
^
.
.
RECORD
field selector. Defined on RECORD
data. Same
precedence as ^
.
[]
ARRAY
data. Same precedence as ^
.
()
PROCEDURE
objects. Same precedence
as ^
.
::
, .
Warning: Set expressions and their operations are not yet supported, so gdb treats the use of the operatorIN
, or the use of operators+
,-
,*
,/
,=
, ,<>
,#
,<=
, and>=
on sets as an error.
Modula-2 also makes available several built-in procedures and functions. In describing these, the following metavariables are used:
ARRAY
variable.
CHAR
constant or variable.
SET OF
mtype (where mtype is the type of m).
All Modula-2 built-in procedures also return a result, described below.
ABS(
n)
CAP(
c)
CHR(
i)
DEC(
v)
DEC(
v,
i)
EXCL(
m,
s)
FLOAT(
i)
HIGH(
a)
INC(
v)
INC(
v,
i)
INCL(
m,
s)
MAX(
t)
MIN(
t)
ODD(
i)
ORD(
x)
SIZE(
x)
TRUNC(
r)
TSIZE(
x)
VAL(
t,
i)
Warning: Sets and their operations are not yet supported, so gdb treats the use of proceduresINCL
andEXCL
as an error.
gdb allows you to express the constants of Modula-2 in the following ways:
'
) or double ("
). They may
also be expressed by their ordinal value (their ascii value, usually)
followed by a ‘C’.
'
) or double ("
).
Escape sequences in the style of C are also allowed. See C and C++ Constants, for a brief explanation of escape
sequences.
TRUE
and
FALSE
.
Currently gdb can print the following data types in Modula-2 syntax: array types, record types, set types, pointer types, procedure types, enumerated types, subrange types and base types. You can also print the contents of variables declared using these type. This section gives a number of simple source code examples together with sample gdb sessions.
The first example contains the following section of code:
VAR s: SET OF CHAR ; r: [20..40] ;
and you can request gdb to interrogate the type and value of
r
and s
.
(gdb) print s {'A'..'C', 'Z'} (gdb) ptype s SET OF CHAR (gdb) print r 21 (gdb) ptype r [20..40]
Likewise if your source code declares s
as:
VAR s: SET ['A'..'Z'] ;
then you may query the type of s
by:
(gdb) ptype s type = SET ['A'..'Z']
Note that at present you cannot interactively manipulate set expressions using the debugger.
The following example shows how you might declare an array in Modula-2 and how you can interact with gdb to print its type and contents:
VAR s: ARRAY [-10..10] OF CHAR ;
(gdb) ptype s ARRAY [-10..10] OF CHAR
Note that the array handling is not yet complete and although the type
is printed correctly, expression handling still assumes that all
arrays have a lower bound of zero and not -10
as in the example
above.
Here are some more type related Modula-2 examples:
TYPE colour = (blue, red, yellow, green) ; t = [blue..yellow] ; VAR s: t ; BEGIN s := blue ;
The gdb interaction shows how you can query the data type and value of a variable.
(gdb) print s $1 = blue (gdb) ptype t type = [blue..yellow]
In this example a Modula-2 array is declared and its contents
displayed. Observe that the contents are written in the same way as
their C
counterparts.
VAR s: ARRAY [1..5] OF CARDINAL ; BEGIN s[1] := 1 ;
(gdb) print s $1 = {1, 0, 0, 0, 0} (gdb) ptype s type = ARRAY [1..5] OF CARDINAL
The Modula-2 language interface to gdb also understands pointer types as shown in this example:
VAR s: POINTER TO ARRAY [1..5] OF CARDINAL ; BEGIN NEW(s) ; s^[1] := 1 ;
and you can request that gdb describes the type of s
.
(gdb) ptype s type = POINTER TO ARRAY [1..5] OF CARDINAL
gdb handles compound types as we can see in this example. Here we combine array types, record types, pointer types and subrange types:
TYPE foo = RECORD f1: CARDINAL ; f2: CHAR ; f3: myarray ; END ; myarray = ARRAY myrange OF CARDINAL ; myrange = [-2..2] ; VAR s: POINTER TO ARRAY myrange OF foo ;
and you can ask gdb to describe the type of s
as shown
below.
(gdb) ptype s type = POINTER TO ARRAY [-2..2] OF foo = RECORD f1 : CARDINAL; f2 : CHAR; f3 : ARRAY [-2..2] OF CARDINAL; END
If type and range checking are set automatically by gdb, they
both default to on
whenever the working language changes to
Modula-2. This happens regardless of whether you or gdb
selected the working language.
If you allow gdb to set the language automatically, then entering code compiled from a file whose name ends with .mod sets the working language to Modula-2. See Having gdb Infer the Source Language, for further details.
A few changes have been made to make Modula-2 programs easier to debug. This is done primarily via loosening its type strictness:
:=
) returns the value of its right-hand
argument.
Warning: in this release, gdb does not yet perform type or range checking.
gdb considers two Modula-2 variables type equivalent if:
TYPE
t1 =
t2 statement
As long as type checking is enabled, any attempt to combine variables whose types are not equivalent is an error.
Range checking is done on all mathematical operations, assignment, array index bounds, and all built-in functions and procedures.
::
and .
There are a few subtle differences between the Modula-2 scope operator
(.
) and the gdb scope operator (::
). The two have
similar syntax:
module . id scope :: id
where scope is the name of a module or a procedure, module the name of a module, and id is any declared identifier within your program, except another module.
Using the ::
operator makes gdb search the scope
specified by scope for the identifier id. If it is not
found in the specified scope, then gdb searches all scopes
enclosing the one specified by scope.
Using the .
operator makes gdb search the current scope for
the identifier specified by id that was imported from the
definition module specified by module. With this operator, it is
an error if the identifier id was not imported from definition
module module, or if id is not an identifier in
module.
Some gdb commands have little use when debugging Modula-2 programs.
Five subcommands of set print
and show print
apply
specifically to C and C++: ‘vtbl’, ‘demangle’,
‘asm-demangle’, ‘object’, and ‘union’. The first four
apply to C++, and the last to the C union
type, which has no direct
analogue in Modula-2.
The @
operator (see Expressions), while available
with any language, is not useful with Modula-2. Its
intent is to aid the debugging of dynamic arrays, which cannot be
created in Modula-2 as they can in C or C++. However, because an
address can be specified by an integral constant, the construct
‘{type}adrexp’ is still useful.
In gdb scripts, the Modula-2 inequality operator #
is
interpreted as the beginning of a comment. Use <>
instead.
The extensions made to gdb for Ada only support output from the gnu Ada (GNAT) compiler. Other Ada compilers are not currently supported, and attempting to debug executables produced by them is most likely to be difficult.
The Ada mode of gdb supports a fairly large subset of Ada expression syntax, with some extensions. The philosophy behind the design of this subset is
Thus, for brevity, the debugger acts as if all names declared in user-written packages are directly visible, even if they are not visible according to Ada rules, thus making it unnecessary to fully qualify most names with their packages, regardless of context. Where this causes ambiguity, gdb asks the user's intent.
The debugger will start in Ada mode if it detects an Ada main program. As for other languages, it will enter Ada mode when stopped in a program that was translated from an Ada source file.
While in Ada mode, you may use `–' for comments. This is useful mostly for documenting command files. The standard gdb comment (‘#’) still works at the beginning of a line in Ada mode, but not in the middle (to allow based literals).
Here are the notable omissions from the subset:
in
) operator.
Characters.Latin_1
are not available and
concatenation is not implemented. Thus, escape characters in strings are
not currently available.
and
, or
,
xor
, not
, and relational tests other than equality)
are not implemented.
(gdb) set An_Array := (1, 2, 3, 4, 5, 6) (gdb) set An_Array := (1, others => 0) (gdb) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6) (gdb) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9)) (gdb) set A_Record := (1, "Peter", True); (gdb) set A_Record := (Name => "Peter", Id => 1, Alive => True)
Changing a
discriminant's value by assigning an aggregate has an
undefined effect if that discriminant is used within the record.
However, you can first modify discriminants by directly assigning to
them (which normally would not be allowed in Ada), and then performing an
aggregate assignment. For example, given a variable A_Rec
declared to have a type such as:
type Rec (Len : Small_Integer := 0) is record Id : Integer; Vals : IntArray (1 .. Len); end record;
you can assign a value with a different size of Vals
with two
assignments:
(gdb) set A_Rec.Len := 4 (gdb) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))
As this example also illustrates, gdb is very loose about the usual
rules concerning aggregates. You may leave out some of the
components of an array or record aggregate (such as the Len
component in the assignment to A_Rec
above); they will retain their
original values upon assignment. You may freely use dynamic values as
indices in component associations. You may even use overlapping or
redundant component associations, although which component values are
assigned in such cases is not defined.
new
operator is not implemented.
True
and False
, when not part of a qualified name,
are interpreted as if implicitly prefixed by Standard
, regardless of
context.
Should your program
redefine these names in a package or procedure (at best a dubious practice),
you will have to use fully qualified names to access their new definitions.
As it does for other languages, gdb makes certain generic extensions to Ada (see Expressions):
@
N displays the values of E and the
N-1 adjacent variables following it in memory as an array. In
Ada, this operator is generally not necessary, since its prime use is
in displaying parts of an array, and slicing will usually do this in
Ada. However, there are occasional uses when debugging programs in
which certain debugging information has been optimized away.
::
var means “the variable named var that
appears in function or file B.” When B is a file name,
you must typically surround it in single quotes.
{
type}
addr means “the variable of type
type that appears at address addr.”
In addition, gdb provides a few other shortcuts and outright additions specific to Ada:
(gdb) set x := y + 3 (gdb) print A(tmp := y + 1)
(gdb) break f (gdb) condition 1 (report(i); k += 1; A(k) > 100)
"One line.["0a"]Next line.["0a"]"
contains an ASCII newline character (Ada.Characters.Latin_1.LF
)
after each period.
(gdb) print 'max(x, y)
(3 => 10, 17, 1)
That is, in contrast to valid Ada, only the first component has a =>
clause.
(gdb) print <JMPBUF_SAVE>[0]
The debugger supports limited overloading. Given a subprogram call in which
the function symbol has multiple definitions, it will use the number of
actual parameters and some information about their types to attempt to narrow
the set of definitions. It also makes very limited use of context, preferring
procedures to functions in the context of the call
command, and
functions to procedures elsewhere.
If, after narrowing, the set of matching definitions still contains more than one definition, gdb will display a menu to query which one it should use, for instance:
(gdb) print f(1) Multiple matches for f [0] cancel [1] foo.f (integer) return boolean at foo.adb:23 [2] foo.f (foo.new_integer) return boolean at foo.adb:28 >
In this case, just select one menu entry either to cancel expression evaluation (type 0 and press <RET>) or to continue evaluation with a specific instance (type the corresponding number and press <RET>).
Here are a couple of commands to customize gdb's behavior in this case:
set ada print-signatures
on
by default.
See Overloading support for Ada.
show ada print-signatures
It is sometimes necessary to debug the program during elaboration, and
before reaching the main procedure.
As defined in the Ada Reference
Manual, the elaboration code is invoked from a procedure called
adainit
. To run your program up to the beginning of
elaboration, simply use the following two commands:
tbreak adainit
and run
.
A command is provided to list all Ada exceptions:
info exceptions
info exceptions
regexpinfo exceptions
command allows you to list all Ada exceptions
defined within the program being debugged, as well as their addresses.
With a regular expression, regexp, as argument, only those exceptions
whose names match regexp are listed.
Below is a small example, showing how the command can be used, first without argument, and next with a regular expression passed as an argument.
(gdb) info exceptions All defined Ada exceptions: constraint_error: 0x613da0 program_error: 0x613d20 storage_error: 0x613ce0 tasking_error: 0x613ca0 const.aint_global_e: 0x613b00 (gdb) info exceptions const.aint All Ada exceptions matching regular expression "const.aint": constraint_error: 0x613da0 const.aint_global_e: 0x613b00
It is also possible to ask gdb to stop your program's execution when an exception is raised. For more details, see Set Catchpoints.
Support for Ada tasks is analogous to that for threads (see Threads). gdb provides the following task-related commands:
info tasks
(gdb) info tasks ID TID P-ID Pri State Name 1 8088000 0 15 Child Activation Wait main_task 2 80a4000 1 15 Accept Statement b 3 809a800 1 15 Child Activation Wait a * 4 80ae800 3 15 Runnable c
In this listing, the asterisk before the last task indicates it to be the task currently being inspected.
Unactivated
Runnable
Terminated
Child Activation Wait
Accept Statement
Waiting on entry call
Async Select Wait
Delay Sleep
Child Termination Wait
Wait Child in Term Alt
Accepting RV with
tasknoinfo task
taskno(gdb) info tasks ID TID P-ID Pri State Name 1 8077880 0 15 Child Activation Wait main_task * 2 807c468 1 15 Runnable task_1 (gdb) info task 2 Ada Task: 0x807c468 Name: "task_1" Thread: 0 LWP: 0x1fac Parent: 1 ("main_task") Base Priority: 15 State: Runnable
task
(gdb) info tasks ID TID P-ID Pri State Name 1 8077870 0 15 Child Activation Wait main_task * 2 807c458 1 15 Runnable some_task (gdb) task [Current task is 2 "some_task"]
task
tasknothread
thread-id
command (see Threads). It switches the context of debugging
from the current task to the given task.
(gdb) info tasks ID TID P-ID Pri State Name 1 8077870 0 15 Child Activation Wait main_task * 2 807c458 1 15 Runnable some_task (gdb) task 1 [Switching to task 1 "main_task"] #0 0x8067726 in pthread_cond_wait () (gdb) bt #0 0x8067726 in pthread_cond_wait () #1 0x8056714 in system.os_interface.pthread_cond_wait () #2 0x805cb63 in system.task_primitives.operations.sleep () #3 0x806153e in system.tasking.stages.activate_tasks () #4 0x804aacc in un () at un.adb:5
break
location task
tasknobreak
location task
taskno if ...
break ... thread ...
command (see Thread Stops). The
location argument specifies source lines, as described
in Specify Location.
Use the qualifier ‘task taskno’ with a breakpoint command to specify that you only want gdb to stop the program when a particular Ada task reaches this breakpoint. The taskno is one of the numeric task identifiers assigned by gdb, shown in the first column of the ‘info tasks’ display.
If you do not specify ‘task taskno’ when you set a breakpoint, the breakpoint applies to all tasks of your program.
You can use the task
qualifier on conditional breakpoints as
well; in this case, place ‘task taskno’ before the
breakpoint condition (before the if
).
For example,
(gdb) info tasks ID TID P-ID Pri State Name 1 140022020 0 15 Child Activation Wait main_task 2 140045060 1 15 Accept/Select Wait t2 3 140044840 1 15 Runnable t1 * 4 140056040 1 15 Runnable t3 (gdb) b 15 task 2 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15. (gdb) cont Continuing. task # 1 running task # 2 running Breakpoint 5, test_task_debug () at test_task_debug.adb:15 15 flush; (gdb) info tasks ID TID P-ID Pri State Name 1 140022020 0 15 Child Activation Wait main_task * 2 140045060 1 15 Runnable t2 3 140044840 1 15 Runnable t1 4 140056040 1 15 Delay Sleep t3
When inspecting a core file, as opposed to debugging a live program, tasking support may be limited or even unavailable, depending on the platform being used. For instance, on x86-linux, the list of tasks is available, but task switching is not supported.
On certain platforms, the debugger needs to perform some memory writes in order to provide Ada tasking support. When inspecting a core file, this means that the core file must be opened with read-write privileges, using the command ‘"set write on"’ (see Patching). Under these circumstances, you should make a backup copy of the core file before inspecting it with gdb.
The Ravenscar Profile is a subset of the Ada tasking features, specifically designed for systems with safety-critical real-time requirements.
set ravenscar task-switching on
set ravenscar task-switching off
show ravenscar task-switching
When Ravenscar task-switching is enabled, Ravenscar tasks are announced by gdb as if they were threads:
(gdb) continue [New Ravenscar Thread 0x2b8f0]
Both Ravenscar tasks and the underlying CPU threads will show up in
the output of info threads
:
(gdb) info threads Id Target Id Frame 1 Thread 1 (CPU#0 [running]) simple () at simple.adb:10 2 Thread 2 (CPU#1 [running]) 0x0000000000003d34 in __gnat_initialize_cpu_devices () 3 Thread 3 (CPU#2 [running]) 0x0000000000003d28 in __gnat_initialize_cpu_devices () 4 Thread 4 (CPU#3 [halted ]) 0x000000000000c6ec in system.task_primitives.operations.idle () * 5 Ravenscar Thread 0x2b8f0 simple () at simple.adb:10 6 Ravenscar Thread 0x2f150 0x000000000000c6ec in system.task_primitives.operations.idle ()
One known limitation of the Ravenscar support in gdb is that
it isn't currently possible to single-step through the runtime
initialization sequence. If you need to debug this code, you should
use set ravenscar task-switching off
.
GNAT always uses code expansion for generic instantiation. This means that each time an instantiation occurs, a complete copy of the original code is made with appropriate substitutions.
It is not possible to refer to the original generic entities themselves
in gdb (there is no code to refer to), but it
is certainly possible to debug a particular instance of a generic, simply by
using the appropriate expanded names. For example, suppose that
Gen
is a generic package:
-- In file gen.ads: generic package Gen is function F (v1 : Integer) return Integer; end Gen; -- In file gen.adb: package body Gen is function F (v1 : Integer) return Integer is begin return v1+1; -- Line 5 end F; end Gen;
and we have the following expansions
with Gen; procedure G is package Gen1 is new Gen; package Gen2 is new Gen; I : Integer := 0; begin I := Gen1.F (I); I := Gen2.F (I); I := Gen1.F (I); I := Gen2.F (I); end;
Then to break on a call to procedure F
in the Gen2
instance, simply
use the command:
(gdb) break G.Gen2.F
To break at a particular line in a particular generic instance, say the return
statement in G.Gen2
, append the line specification to the file and
function name:
(gdb) break gen.adb:G.Gen2.F:5
To break on this line line in all instances of Gen
, use ‘*’
as the function name:
(gdb) break gen.adb:*:5
This will set individual breakpoints at all instances; they are independent of each other and you may remove, conditionalize, or otherwise modify them individually.
When a breakpoint occurs, you can step through the code of the generic instance in the normal manner. You can also examine values of data in the normal manner, providing the appropriate generic package qualification to refer to non-local entities.
set varsize-limit
sizeunlimited
removes the size limitation. By default, the limit is about 65KB.
The purpose of having such a limit is to prevent gdb from
trying to grab enormous chunks of virtual memory when asked to evaluate
a quantity whose bounds have been corrupted or have not yet been fully
initialized. The limit applies to the results of some subexpressions
as well as to complete expressions. For example, an expression denoting
a simple integer component, such as x.y.z
, may fail if the size of
x.y
is variable and exceeds size
. On the other hand,
gdb is sometimes clever; the expression A(i)
, where
A
is an array variable with non-constant size, will generally
succeed regardless of the bounds on A
, as long as the component
size is less than size.
show varsize-limit
Besides the omissions listed previously (see Omissions from Ada), we know of several problems with and limitations of Ada mode in gdb, some of which will be fixed with planned future releases of the debugger and the GNU Ada compiler.
up
commands to get to
frame containing the variable you wish to see.
Access to non-local variables does not, at the moment, work in
the test expressions for conditional breakpoints
(see Break conditions) unless you happen to specify these
while stopped in the subprogram in which they are to be applied.
Standard
for any of
the standard symbols defined by the Ada language. gdb knows about
this: it will strip the prefix from names when you use it, and will never
look for a name you have so qualified among local symbols, nor match against
symbols in other packages or subprograms. If you have
defined entities anywhere in your program other than parameters and
local variables whose simple names match names in Standard
,
GNAT's lack of qualification here can cause confusion. When this happens,
you can usually resolve the confusion
by qualifying the problematic names with package
Standard
explicitly.
Older versions of the compiler sometimes generate erroneous debugging information, resulting in the debugger incorrectly printing the value of affected entities. In some cases, the debugger is able to work around an issue automatically. In other cases, the debugger is able to work around the issue, but the work-around has to be specifically enabled.
set ada trust-PAD-over-XVS on
PAD
and PAD___XVS
types are involved (see ada/exp_dbug.ads
in the GCC sources for
a complete description of the encoding used by the GNAT compiler).
This is the default.
set ada trust-PAD-over-XVS off
ada
trust-PAD-over-XVS
to off
activates a work-around which may fix
the issue. It is always safe to set ada trust-PAD-over-XVS
to
off
, but this incurs a slight performance penalty, so it is
recommended to leave this setting to on
unless necessary.
Internally, the debugger also relies on the compiler following a number of conventions known as the ‘GNAT Encoding’, all documented in gcc/ada/exp_dbug.ads in the GCC sources. This encoding describes how the debugging information should be generated for certain types. In particular, this convention makes use of descriptive types, which are artificial types generated purely to help the debugger.
These encodings were defined at a time when the debugging information format used was not powerful enough to describe some of the more complex types available in Ada. Since DWARF allows us to express nearly all Ada features, the long-term goal is to slowly replace these descriptive types by their pure DWARF equivalent. To facilitate that transition, a new maintenance option is available to force the debugger to ignore those descriptive types. It allows the user to quickly evaluate how well gdb works without them.
maintenance ada set ignore-descriptive-types [on|off]
off
).
maintenance ada show ignore-descriptive-types
In addition to the other fully-supported programming languages,
gdb also provides a pseudo-language, called minimal
.
It does not represent a real programming language, but provides a set
of capabilities close to what the C or assembly languages provide.
This should allow most simple operations to be performed while debugging
an application that uses a language currently not supported by gdb.
If the language is set to auto
, gdb will automatically
select this language if the current frame corresponds to an unsupported
language.
The commands described in this chapter allow you to inquire about the symbols (names of variables, functions and types) defined in your program. This information is inherent in the text of your program and does not change as your program executes. gdb finds it in your program's symbol table, in the file indicated when you started gdb (see Choosing Files), or by one of the file-management commands (see Commands to Specify Files).
Occasionally, you may need to refer to symbols that contain unusual characters, which gdb ordinarily treats as word delimiters. The most frequent case is in referring to static variables in other source files (see Program Variables). File names are recorded in object files as debugging symbols, but gdb would ordinarily parse a typical file name, like foo.c, as the three words ‘foo’ ‘.’ ‘c’. To allow gdb to recognize ‘foo.c’ as a single symbol, enclose it in single quotes; for example,
p 'foo.c'::x
looks up the value of x
in the scope of the file foo.c.
set case-sensitive on
set case-sensitive off
set case-sensitive auto
set
case-sensitive
lets you do that by specifying on
for
case-sensitive matches or off
for case-insensitive ones. If
you specify auto
, case sensitivity is reset to the default
suitable for the source language. The default is case-sensitive
matches for all languages except for Fortran, for which the default is
case-insensitive matches.
show case-sensitive
set print type methods
set print type methods on
set print type methods off
ptype
, or using set
print type methods. Specifying on
will cause gdb to
display the methods; this is the default. Specifying off
will
cause gdb to omit the methods.
show print type methods
set print type nested-type-limit
limitset print type nested-type-limit unlimited
unlimited
or -1
will show all
nested definitions. By default, the type printer will not show any nested
types defined in classes.
show print type nested-type-limit
set print type typedefs
set print type typedefs on
set print type typedefs off
ptype
, or using set
print type typedefs. Specifying on
will cause gdb to
display the typedef definitions; this is the default. Specifying
off
will cause gdb to omit the typedef definitions.
Note that this controls whether the typedef definition itself is
printed, not whether typedef names are substituted when printing other
types.
show print type typedefs
info address
symbolNote the contrast with ‘print &symbol’, which does not work at all for a register variable, and for a stack local variable prints the exact address of the current instantiation of the variable.
info symbol
addr(gdb) info symbol 0x54320 _initialize_vx + 396 in section .text
This is the opposite of the info address
command. You can use
it to find out the name of a variable or a function given its address.
For dynamically linked executables, the name of executable or shared library containing the symbol is also printed:
(gdb) info symbol 0x400225 _start + 5 in section .text of /tmp/a.out (gdb) info symbol 0x2aaaac2811cf __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6
demangle
[-l
language] [–] nameThe ‘--’ option specifies the end of options, and is useful when name begins with a dash.
The parameter demangle-style
specifies how to interpret the kind
of mangling used. See Print Settings.
whatis[/
flags] [
arg]
$
, the last value in the value history.
If arg is an expression (see Expressions), it is not actually evaluated, and any side-effecting operations (such as assignments or function calls) inside it do not take place.
If arg is a variable or an expression, whatis
prints its
literal type as it is used in the source code. If the type was
defined using a typedef
, whatis
will not print
the data type underlying the typedef
. If the type of the
variable or the expression is a compound data type, such as
struct
or class
, whatis
never prints their
fields or methods. It just prints the struct
/class
name (a.k.a. its tag). If you want to see the members of
such a compound data type, use ptype
.
If arg is a type name that was defined using typedef
,
whatis
unrolls only one level of that typedef
.
Unrolling means that whatis
will show the underlying type used
in the typedef
declaration of arg. However, if that
underlying type is also a typedef
, whatis
will not
unroll it.
For C code, the type names may also have the form ‘class class-name’, ‘struct struct-tag’, ‘union union-tag’ or ‘enum enum-tag’.
flags can be used to modify how the type is displayed. Available flags are:
r
/r
flag disables this.
m
M
t
T
o
/tm
flags.
For example, given the following declarations:
struct tuv { int a1; char *a2; int a3; }; struct xyz { int f1; char f2; void *f3; struct tuv f4; }; union qwe { struct tuv fff1; struct xyz fff2; }; struct tyu { int a1 : 1; int a2 : 3; int a3 : 23; char a4 : 2; int64_t a5; int a6 : 5; int64_t a7 : 3; };
Issuing a ptype /o struct tuv command would print:
(gdb) ptype /o struct tuv /* offset | size */ type = struct tuv { /* 0 | 4 */ int a1; /* XXX 4-byte hole */ /* 8 | 8 */ char *a2; /* 16 | 4 */ int a3; /* total size (bytes): 24 */ }
Notice the format of the first column of comments. There, you can find two parts separated by the ‘|’ character: the offset, which indicates where the field is located inside the struct, in bytes, and the size of the field. Another interesting line is the marker of a hole in the struct, indicating that it may be possible to pack the struct and make it use less space by reorganizing its fields.
It is also possible to print offsets inside an union:
(gdb) ptype /o union qwe /* offset | size */ type = union qwe { /* 24 */ struct tuv { /* 0 | 4 */ int a1; /* XXX 4-byte hole */ /* 8 | 8 */ char *a2; /* 16 | 4 */ int a3; /* total size (bytes): 24 */ } fff1; /* 40 */ struct xyz { /* 0 | 4 */ int f1; /* 4 | 1 */ char f2; /* XXX 3-byte hole */ /* 8 | 8 */ void *f3; /* 16 | 24 */ struct tuv { /* 16 | 4 */ int a1; /* XXX 4-byte hole */ /* 24 | 8 */ char *a2; /* 32 | 4 */ int a3; /* total size (bytes): 24 */ } f4; /* total size (bytes): 40 */ } fff2; /* total size (bytes): 40 */ }
In this case, since struct tuv
and struct xyz
occupy the
same space (because we are dealing with an union), the offset is not
printed for them. However, you can still examine the offset of each
of these structures' fields.
Another useful scenario is printing the offsets of a struct containing bitfields:
(gdb) ptype /o struct tyu /* offset | size */ type = struct tyu { /* 0:31 | 4 */ int a1 : 1; /* 0:28 | 4 */ int a2 : 3; /* 0: 5 | 4 */ int a3 : 23; /* 3: 3 | 1 */ signed char a4 : 2; /* XXX 3-bit hole */ /* XXX 4-byte hole */ /* 8 | 8 */ int64_t a5; /* 16: 0 | 4 */ int a6 : 5; /* 16: 5 | 8 */ int64_t a7 : 3; "/* XXX 7-byte padding */ /* total size (bytes): 24 */ }
Note how the offset information is now extended to also include the first bit of the bitfield.
ptype[/
flags] [
arg]
ptype
accepts the same arguments as whatis
, but prints a
detailed description of the type, instead of just the name of the type.
See Expressions.
Contrary to whatis
, ptype
always unrolls any
typedef
s in its argument declaration, whether the argument is
a variable, expression, or a data type. This means that ptype
of a variable or an expression will not print literally its type as
present in the source code—use whatis
for that. typedef
s at
the pointer or reference targets are also unrolled. Only typedef
s of
fields, methods and inner class typedef
s of struct
s,
class
es and union
s are not unrolled even with ptype
.
For example, for this variable declaration:
typedef double real_t; struct complex { real_t real; double imag; }; typedef struct complex complex_t; complex_t var; real_t *real_pointer_var;
the two commands give this output:
(gdb) whatis var type = complex_t (gdb) ptype var type = struct complex { real_t real; double imag; } (gdb) whatis complex_t type = struct complex (gdb) whatis struct complex type = struct complex (gdb) ptype struct complex type = struct complex { real_t real; double imag; } (gdb) whatis real_pointer_var type = real_t * (gdb) ptype real_pointer_var type = double *
As with whatis
, using ptype
without an argument refers to
the type of $
, the last value in the value history.
Sometimes, programs use opaque data types or incomplete specifications of complex data structure. If the debug information included in the program does not allow gdb to display a full declaration of the data type, it will say ‘<incomplete type>’. For example, given these declarations:
struct foo; struct foo *fooptr;
but no definition for struct foo
itself, gdb will say:
(gdb) ptype foo $1 = <incomplete type>
“Incomplete type” is C terminology for data types that are not completely specified.
Othertimes, information about a variable's type is completely absent from the debug information included in the program. This most often happens when the program or library where the variable is defined includes no debug information at all. gdb knows the variable exists from inspecting the linker/loader symbol table (e.g., the ELF dynamic symbol table), but such symbols do not contain type information. Inspecting the type of a (global) variable for which gdb has no type information shows:
(gdb) ptype var type = <data variable, no debug info>
See no debug info variables, for how to print the values of such variables.
info types [-q] [
regexp]
value
, but
‘i type ^value$’ gives information only on types whose complete
name is value
.
In programs using different languages, gdb chooses the syntax to print the type description according to the ‘set language’ value: using ‘set language auto’ (see Set Language Automatically) means to use the language of the type, other values mean to use the manually specified language (see Set Language Manually).
This command differs from ptype
in two ways: first, like
whatis
, it does not print a detailed description; second, it
lists all source files and line numbers where a type is defined.
The output from ‘into types’ is proceeded with a header line describing what types are being listed. The optional flag ‘-q’, which stands for ‘quiet’, disables printing this header information.
info type-printers
info type-printers
displays all the available type printers.
enable type-printer
name...
disable type-printer
name...
info scope
location(gdb) info scope command_line_handler Scope for command_line_handler: Symbol rl is an argument at stack/frame offset 8, length 4. Symbol linebuffer is in static storage at address 0x150a18, length 4. Symbol linelength is in static storage at address 0x150a1c, length 4. Symbol p is a local variable in register $esi, length 4. Symbol p1 is a local variable in register $ebx, length 4. Symbol nline is a local variable in register $edx, length 4. Symbol repeat is a local variable at frame offset -8, length 4.
This command is especially useful for determining what data to collect during a trace experiment, see collect.
info source
info sources
info sources [-dirname | -basename] [--] [
regexp]
-dirname
, only files having a dirname matching regexp are shown.
If -basename
, only files having a basename matching regexp
are shown.
The matching is case-sensitive, except on operating systems that
have case-insensitive filesystem (e.g., MS-Windows).
info functions [-q] [-n]
In programs using different languages, gdb chooses the syntax to print the function name and type according to the ‘set language’ value: using ‘set language auto’ (see Set Language Automatically) means to use the language of the function, other values mean to use the manually specified language (see Set Language Manually).
The ‘-n’ flag excludes non-debugging symbols from the results. A non-debugging symbol is a symbol that comes from the executable's symbol table, not from the debug information (for example, DWARF) associated with the executable.
The optional flag ‘-q’, which stands for ‘quiet’, disables
printing header information and messages explaining why no functions
have been printed.
info functions [-q] [-n] [-t
type_regexp] [
regexp]
If regexp is provided, print only the functions whose names
match the regular expression regexp.
Thus, ‘info fun step’ finds all functions whose
names include step
; ‘info fun ^step’ finds those whose names
start with step
. If a function name contains characters that
conflict with the regular expression language (e.g.
‘operator*()’), they may be quoted with a backslash.
If type_regexp is provided, print only the functions whose
types, as printed by the whatis
command, match
the regular expression type_regexp.
If type_regexp contains space(s), it should be enclosed in
quote characters. If needed, use backslash to escape the meaning
of special characters or quotes.
Thus, ‘info fun -t '^int ('’ finds the functions that return
an integer; ‘info fun -t '(.*int.*'’ finds the functions that
have an argument type containing int; ‘info fun -t '^int (' ^step’
finds the functions whose names start with step
and that return
int.
If both regexp and type_regexp are provided, a function is printed only if its name matches regexp and its type matches type_regexp.
info variables [-q] [-n]
In programs using different languages, gdb chooses the syntax to print the variable name and type according to the ‘set language’ value: using ‘set language auto’ (see Set Language Automatically) means to use the language of the variable, other values mean to use the manually specified language (see Set Language Manually).
The ‘-n’ flag excludes non-debugging symbols from the results.
The optional flag ‘-q’, which stands for ‘quiet’, disables
printing header information and messages explaining why no variables
have been printed.
info variables [-q] [-n] [-t
type_regexp] [
regexp]
If regexp is provided, print only the variables whose names match the regular expression regexp.
If type_regexp is provided, print only the variables whose
types, as printed by the whatis
command, match
the regular expression type_regexp.
If type_regexp contains space(s), it should be enclosed in
quote characters. If needed, use backslash to escape the meaning
of special characters or quotes.
If both regexp and type_regexp are provided, an argument is printed only if its name matches regexp and its type matches type_regexp.
info modules
[-q
] [regexp]The optional flag ‘-q’, which stands for ‘quiet’, disables printing header information and messages explaining why no modules have been printed.
info module functions
[-q
] [-m
module-regexp] [-t
type-regexp] [regexp]info module variables
[-q
] [-m
module-regexp] [-t
type-regexp] [regexp]The optional flag ‘-q’, which stands for ‘quiet’, disables printing header information and messages explaining why no functions or variables have been printed.
info classes
info classes
regexpinfo selectors
info selectors
regexpset opaque-type-resolution on
struct
, class
, or
union
—for example, struct MyType *
—that is used in one
source file although the full declaration of struct MyType
is in
another source file. The default is on.
A change in the setting of this subcommand will not take effect until
the next time symbols for a file are loaded.
set opaque-type-resolution off
{<no data fields>}
show opaque-type-resolution
set print symbol-loading
set print symbol-loading full
set print symbol-loading brief
set print symbol-loading off
set print symbol-loading
command allows you to control the
printing of messages when gdb loads symbol information.
By default a message is printed for the executable and one for each
shared library, and normally this is what you want. However, when
debugging apps with large numbers of shared libraries these messages
can be annoying.
When set to brief
a message is printed for each executable,
and when gdb loads a collection of shared libraries at once
it will only print one message regardless of the number of shared
libraries. When set to off
no messages are printed.
show print symbol-loading
maint print symbols
[-pc
address] [filename]maint print symbols
[-objfile
objfile] [-source
source] [--
] [filename]maint print psymbols
[-objfile
objfile] [-pc
address] [--
] [filename]maint print psymbols
[-objfile
objfile] [-source
source] [--
] [filename]maint print msymbols
[-objfile
objfile] [--
] [filename]-objfile
objfile is specified, only dump symbols for
that objfile.
If -pc
address is specified, only dump symbols for the file
with code at that address. Note that address may be a symbol like
main
.
If -source
source is specified, only dump symbols for that
source file.
These commands are used to debug the gdb symbol-reading code.
These commands do not modify internal gdb state, therefore
‘maint print symbols’ will only print symbols for already expanded symbol
tables.
You can use the command info sources
to find out which files these are.
If you use ‘maint print psymbols’ instead, the dump shows information
about symbols that gdb only knows partially—that is, symbols
defined in files that gdb has skimmed, but not yet read completely.
Finally, ‘maint print msymbols’ just dumps “minimal symbols”, e.g.,
“ELF symbols”.
See Commands to Specify Files, for a discussion of how
gdb reads symbols (in the description of symbol-file
).
maint info symtabs
[ regexp ]maint info psymtabs
[ regexp ]struct symtab
or struct partial_symtab
structures whose names match regexp. If regexp is not
given, list them all. The output includes expressions which you can
copy into a gdb debugging this one to examine a particular
structure in more detail. For example:
(gdb) maint info psymtabs dwarf2read { objfile /home/gnu/build/gdb/gdb ((struct objfile *) 0x82e69d0) { psymtab /home/gnu/src/gdb/dwarf2read.c ((struct partial_symtab *) 0x8474b10) readin no fullname (null) text addresses 0x814d3c8 -- 0x8158074 globals (* (struct partial_symbol **) 0x8507a08 @ 9) statics (* (struct partial_symbol **) 0x40e95b78 @ 2882) dependencies (none) } } (gdb) maint info symtabs (gdb)
We see that there is one partial symbol table whose filename contains the string ‘dwarf2read’, belonging to the ‘gdb’ executable; and we see that gdb has not read in any symtabs yet at all. If we set a breakpoint on a function, that will cause gdb to read the symtab for the compilation unit containing that function:
(gdb) break dwarf2_psymtab_to_symtab Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c, line 1574. (gdb) maint info symtabs { objfile /home/gnu/build/gdb/gdb ((struct objfile *) 0x82e69d0) { symtab /home/gnu/src/gdb/dwarf2read.c ((struct symtab *) 0x86c1f38) dirname (null) fullname (null) blockvector ((struct blockvector *) 0x86c1bd0) (primary) linetable ((struct linetable *) 0x8370fa0) debugformat DWARF 2 } } (gdb)
maint info line-table
[ regexp ]struct linetable
from all struct symtab
instances whose name matches regexp. If regexp is not
given, list the struct linetable
from all struct symtab
.
maint set symbol-cache-size
sizemaint show symbol-cache-size
maint print symbol-cache
maint print symbol-cache-statistics
maint flush-symbol-cache
Once you think you have found an error in your program, you might want to find out for certain whether correcting the apparent error would lead to correct results in the rest of the run. You can find the answer by experiment, using the gdb features for altering execution of the program.
For example, you can store new values into variables or memory locations, give your program a signal, restart it at a different address, or even return prematurely from a function.
To alter the value of a variable, evaluate an assignment expression. See Expressions. For example,
print x=4
stores the value 4 into the variable x
, and then prints the
value of the assignment expression (which is 4).
See Using gdb with Different Languages, for more
information on operators in supported languages.
If you are not interested in seeing the value of the assignment, use the
set
command instead of the print
command. set
is
really the same as print
except that the expression's value is
not printed and is not put in the value history (see Value History). The expression is evaluated only for its effects.
If the beginning of the argument string of the set
command
appears identical to a set
subcommand, use the set
variable
command instead of just set
. This command is identical
to set
except for its lack of subcommands. For example, if your
program has a variable width
, you get an error if you try to set
a new value with just ‘set width=13’, because gdb has the
command set width
:
(gdb) whatis width type = double (gdb) p width $4 = 13 (gdb) set width=47 Invalid syntax in expression.
The invalid expression, of course, is ‘=47’. In
order to actually set the program's variable width
, use
(gdb) set var width=47
Because the set
command has many subcommands that can conflict
with the names of program variables, it is a good idea to use the
set variable
command instead of just set
. For example, if
your program has a variable g
, you run into problems if you try
to set a new value with just ‘set g=4’, because gdb has
the command set gnutarget
, abbreviated set g
:
(gdb) whatis g type = double (gdb) p g $1 = 1 (gdb) set g=4 (gdb) p g $2 = 1 (gdb) r The program being debugged has been started already. Start it from the beginning? (y or n) y Starting program: /home/smith/cc_progs/a.out "/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target. (gdb) show g The current BFD target is "=4".
The program variable g
did not change, and you silently set the
gnutarget
to an invalid value. In order to set the variable
g
, use
(gdb) set var g=4
gdb allows more implicit conversions in assignments than C; you can freely store an integer value into a pointer variable or vice versa, and you can convert any structure to any other structure that is the same length or shorter.
To store values into arbitrary places in memory, use the ‘{...}’
construct to generate a value of specified type at a specified address
(see Expressions). For example, {int}0x83040
refers
to memory location 0x83040
as an integer (which implies a certain size
and representation in memory), and
set {int}0x83040 = 4
stores the value 4 into that memory location.
Ordinarily, when you continue your program, you do so at the place where
it stopped, with the continue
command. You can instead continue at
an address of your own choosing, with the following commands:
jump
locationj
locationtbreak
command in conjunction with
jump
. See Setting Breakpoints.
The jump
command does not change the current stack frame, or
the stack pointer, or the contents of any memory location or any
register other than the program counter. If location is in
a different function from the one currently executing, the results may
be bizarre if the two functions expect different patterns of arguments or
of local variables. For this reason, the jump
command requests
confirmation if the specified line is not in the function currently
executing. However, even bizarre results are predictable if you are
well acquainted with the machine-language code of your program.
On many systems, you can get much the same effect as the jump
command by storing a new value into the register $pc
. The
difference is that this does not start your program running; it only
changes the address of where it will run when you continue. For
example,
set $pc = 0x485
makes the next continue
command or stepping command execute at
address 0x485
, rather than at the address where your program stopped.
See Continuing and Stepping.
The most common occasion to use the jump
command is to back
up—perhaps with more breakpoints set—over a portion of a program
that has already executed, in order to examine its execution in more
detail.
signal
signalsignal 2
and signal
SIGINT
are both ways of sending an interrupt signal.
Alternatively, if signal is zero, continue execution without
giving a signal. This is useful when your program stopped on account of
a signal and would ordinarily see the signal when resumed with the
continue
command; ‘signal 0’ causes it to resume without a
signal.
Note: When resuming a multi-threaded program, signal is delivered to the currently selected thread, not the thread that last reported a stop. This includes the situation where a thread was stopped due to a signal. So if you want to continue execution suppressing the signal that stopped a thread, you should select that same thread before issuing the ‘signal 0’ command. If you issue the ‘signal 0’ command with another thread as the selected one, gdb detects that and asks for confirmation.
Invoking the signal
command is not the same as invoking the
kill
utility from the shell. Sending a signal with kill
causes gdb to decide what to do with the signal depending on
the signal handling tables (see Signals). The signal
command
passes the signal directly to your program.
signal
does not repeat when you press <RET> a second time
after executing the command.
queue-signal
signalsignal 2
and
signal SIGINT
are both ways of sending an interrupt signal.
The handling of the signal must be set to pass the signal to the program,
otherwise gdb will report an error.
You can control the handling of signals from gdb with the
handle
command (see Signals).
Alternatively, if signal is zero, any currently queued signal
for the current thread is discarded and when execution resumes no signal
will be delivered. This is useful when your program stopped on account
of a signal and would ordinarily see the signal when resumed with the
continue
command.
This command differs from the signal
command in that the signal
is just queued, execution is not resumed. And queue-signal
cannot
be used to pass a signal whose handling state has been set to nopass
(see Signals).
See stepping into signal handlers, for information on how stepping commands behave when the thread has a signal queued.
return
return
expressionreturn
command. If you give an
expression argument, its value is used as the function's return
value.
When you use return
, gdb discards the selected stack frame
(and all frames within it). You can think of this as making the
discarded frame return prematurely. If you wish to specify a value to
be returned, give that value as the argument to return
.
This pops the selected stack frame (see Selecting a Frame), and any other frames inside of it, leaving its caller as the innermost remaining frame. That frame becomes selected. The specified value is stored in the registers used for returning values of functions.
The return
command does not resume execution; it leaves the
program stopped in the state that would exist if the function had just
returned. In contrast, the finish
command (see Continuing and Stepping) resumes execution until the
selected stack frame returns naturally.
gdb needs to know how the expression argument should be set for
the inferior. The concrete registers assignment depends on the OS ABI and the
type being returned by the selected stack frame. For example it is common for
OS ABI to return floating point values in FPU registers while integer values in
CPU registers. Still some ABIs return even floating point values in CPU
registers. Larger integer widths (such as long long int
) also have
specific placement rules. gdb already knows the OS ABI from its
current target so it needs to find out also the type being returned to make the
assignment into the right register(s).
Normally, the selected stack frame has debug info. gdb will always
use the debug info instead of the implicit type of expression when the
debug info is available. For example, if you type return -1, and the
function in the current stack frame is declared to return a long long
int
, gdb transparently converts the implicit int
value of -1
into a long long int
:
Breakpoint 1, func () at gdb.base/return-nodebug.c:29 29 return 31; (gdb) return -1 Make func return now? (y or n) y #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43 43 printf ("result=%lld\n", func ()); (gdb)
However, if the selected stack frame does not have a debug info, e.g., if the
function was compiled without debug info, gdb has to find out the type
to return from user. Specifying a different type by mistake may set the value
in different inferior registers than the caller code expects. For example,
typing return -1 with its implicit type int
would set only a part
of a long long int
result for a debug info less function (on 32-bit
architectures). Therefore the user is required to specify the return type by
an appropriate cast explicitly:
Breakpoint 2, 0x0040050b in func () (gdb) return -1 Return value type not available for selected stack frame. Please use an explicit cast of the value to return. (gdb) return (long long int) -1 Make selected stack frame return now? (y or n) y #0 0x00400526 in main () (gdb)
print
exprcall
exprvoid
returned values.
You can use this variant of the print
command if you want to
execute a function from your program that does not return anything
(a.k.a. a void function), but without cluttering the output
with void
returned values that gdb will otherwise
print. If the result is not void, it is printed and saved in the
value history.
It is possible for the function you call via the print
or
call
command to generate a signal (e.g., if there's a bug in
the function, or if you passed it incorrect arguments). What happens
in that case is controlled by the set unwindonsignal
command.
Similarly, with a C++ program it is possible for the function you
call via the print
or call
command to generate an
exception that is not handled due to the constraints of the dummy
frame. In this case, any exception that is raised in the frame, but has
an out-of-frame exception handler will not be found. GDB builds a
dummy-frame for the inferior function call, and the unwinder cannot
seek for exception handlers outside of this dummy-frame. What happens
in that case is controlled by the
set unwind-on-terminating-exception
command.
set unwindonsignal
show unwindonsignal
set unwind-on-terminating-exception
show unwind-on-terminating-exception
set may-call-functions
print
command. It
defaults to on
.
To call a function in the program, gdb has to temporarily
modify the state of the inferior. This has potentially undesired side
effects. Also, having gdb call nested functions is likely to
be erroneous and may even crash the program being debugged. You can
avoid such hazards by forbidding gdb from calling functions
in the program being debugged. If calling functions in the program
is forbidden, GDB will throw an error when a command (such as printing
an expression) starts a function call in the program.
show may-call-functions
Sometimes, a function you wish to call is missing debug information. In such case, gdb does not know the type of the function, including the types of the function's parameters. To avoid calling the inferior function incorrectly, which could result in the called function functioning erroneously and even crash, gdb refuses to call the function unless you tell it the type of the function.
For prototyped (i.e. ANSI/ISO style) functions, there are two ways to do that. The simplest is to cast the call to the function's declared return type. For example:
(gdb) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type (gdb) p (char *) getenv ("PATH") $1 = 0x7fffffffe7ba "/usr/local/bin:/"...
Casting the return type of a no-debug function is equivalent to casting the function to a pointer to a prototyped function that has a prototype that matches the types of the passed-in arguments, and calling that. I.e., the call above is equivalent to:
(gdb) p ((char * (*) (const char *)) getenv) ("PATH")
and given this prototyped C or C++ function with float parameters:
float multiply (float v1, float v2) { return v1 * v2; }
these calls are equivalent:
(gdb) p (float) multiply (2.0f, 3.0f) (gdb) p ((float (*) (float, float)) multiply) (2.0f, 3.0f)
If the function you wish to call is declared as unprototyped (i.e. old K&R style), you must use the cast-to-function-pointer syntax, so that gdb knows that it needs to apply default argument promotions (promote float arguments to double). See float promotion. For example, given this unprototyped C function with float parameters, and no debug info:
float multiply_noproto (v1, v2) float v1, v2; { return v1 * v2; }
you call it like this:
(gdb) p ((float (*) ()) multiply_noproto) (2.0f, 3.0f)
By default, gdb opens the file containing your program's executable code (or the corefile) read-only. This prevents accidental alterations to machine code; but it also prevents you from intentionally patching your program's binary.
If you'd like to be able to patch the binary, you can specify that
explicitly with the set write
command. For example, you might
want to turn on internal debugging flags, or even to make emergency
repairs.
set write on
set write off
If you have already loaded a file, you must load it again (using the
exec-file
or core-file
command) after changing set
write
, for your new setting to take effect.
show write
gdb supports on-demand compilation and code injection into programs running under gdb. GCC 5.0 or higher built with libcc1.so must be installed for this functionality to be enabled. This functionality is implemented with the following commands.
compile code
source-codecompile code -raw
– source-codeThe command allows you to specify source-code in two ways. The simplest method is to provide a single line of code to the command. E.g.:
compile code printf ("hello world\n");
If you specify options on the command line as well as source code, they may conflict. The ‘--’ delimiter can be used to separate options from actual source code. E.g.:
compile code -r -- printf ("hello world\n");
Alternatively you can enter source code as multiple lines of text. To enter this mode, invoke the ‘compile code’ command without any text following the command. This will start the multiple-line editor and allow you to type as many lines of source code as required. When you have completed typing, enter ‘end’ on its own line to exit the editor.
compile code >printf ("hello\n"); >printf ("world\n"); >end
Specifying ‘-raw’, prohibits gdb from wrapping the
provided source-code in a callable scope. In this case, you must
specify the entry point of the code by defining a function named
_gdb_expr_
. The ‘-raw’ code cannot access variables of the
inferior. Using ‘-raw’ option may be needed for example when
source-code requires ‘#include’ lines which may conflict with
inferior symbols otherwise.
compile file
filenamecompile file -raw
filenamecompile code
, but take the source code from filename.
compile file /home/user/example.c
compile print [[
options] --]
exprcompile print [[
options] --] /
f exprcompile print
command accepts the same options
as the print
command; see print options.
compile print [[
options] --]
compile print [[
options] --] /
fThe process of compiling and injecting the code can be inspected using:
set debug compile
show debug compile
set debug compile-cplus-types
show debug compile-cplus-types
compile
commandgdb needs to specify the right compilation options for the code to be injected, in part to make its ABI compatible with the inferior and in part to make the injected code compatible with gdb's injecting process.
The options used, in increasing precedence:
gdbarch
)-m32
) or 64-bit
(-m64
) compilation option.
DW_AT_producer
part of DWARF debugging information according
to the gcc option -grecord-gcc-switches
. One has to
explicitly specify -g
during inferior compilation otherwise
gcc produces no DWARF. This feature is only relevant for
platforms where -g
produces DWARF by default, otherwise one may
try to enforce DWARF by using -gdwarf-4
.
set compile-args
You can override compilation options using the following command:
set compile-args
compile
commands. These options override any conflicting ones
from the target architecture and/or options stored during inferior
compilation.
show compile-args
compile
commandThere are a few caveats to keep in mind when using the compile
command. As the caveats are different per language, the table below
highlights specific issues on a per language basis.
compile
command will have much the same
access to variables and types as it normally would if it were part of
the program currently being debugged in gdb.
Below is a sample program that forms the basis of the examples that follow. This program has been compiled and loaded into gdb, much like any other normal debugging session.
void function1 (void) { int i = 42; printf ("function 1\n"); } void function2 (void) { int j = 12; function1 (); } int main(void) { int k = 6; int *p; function2 (); return 0; }
For the purposes of the examples in this section, the program above has
been compiled, loaded into gdb, stopped at the function
main
, and gdb is awaiting input from the user.
To access variables and types for any program in gdb, the
program must be compiled and packaged with debug information. The
compile
command is not an exception to this rule. Without debug
information, you can still use the compile
command, but you will
be very limited in what variables and types you can access.
So with that in mind, the example above has been compiled with debug
information enabled. The compile
command will have access to
all variables and types (except those that may have been optimized
out). Currently, as gdb has stopped the program in the
main
function, the compile
command would have access to
the variable k
. You could invoke the compile
command
and type some source code to set the value of k
. You can also
read it, or do anything with that variable you would normally do in
C
. Be aware that changes to inferior variables in the
compile
command are persistent. In the following example:
compile code k = 3;
the variable k
is now 3. It will retain that value until
something else in the example program changes it, or another
compile
command changes it.
Normal scope and access rules apply to source code compiled and
injected by the compile
command. In the example, the variables
j
and k
are not accessible yet, because the program is
currently stopped in the main
function, where these variables
are not in scope. Therefore, the following command
compile code j = 3;
will result in a compilation error message.
Once the program is continued, execution will bring these variables in
scope, and they will become accessible; then the code you specify via
the compile
command will be able to access them.
You can create variables and types with the compile
command as
part of your source code. Variables and types that are created as part
of the compile
command are not visible to the rest of the program for
the duration of its run. This example is valid:
compile code int ff = 5; printf ("ff is %d\n", ff);
However, if you were to type the following into gdb after that command has completed:
compile code printf ("ff is %d\n'', ff);
a compiler error would be raised as the variable ff
no longer
exists. Object code generated and injected by the compile
command is removed when its execution ends. Caution is advised
when assigning to program variables values of variables created by the
code submitted to the compile
command. This example is valid:
compile code int ff = 5; k = ff;
The value of the variable ff
is assigned to k
. The variable
k
does not require the existence of ff
to maintain the value
it has been assigned. However, pointers require particular care in
assignment. If the source code compiled with the compile
command
changed the address of a pointer in the example program, perhaps to a
variable created in the compile
command, that pointer would point
to an invalid location when the command exits. The following example
would likely cause issues with your debugged program:
compile code int ff = 5; p = &ff;
In this example, p
would point to ff
when the
compile
command is executing the source code provided to it.
However, as variables in the (example) program persist with their
assigned values, the variable p
would point to an invalid
location when the command exists. A general rule should be followed
in that you should either assign NULL
to any assigned pointers,
or restore a valid location to the pointer before the command exits.
Similar caution must be exercised with any structs, unions, and typedefs
defined in compile
command. Types defined in the compile
command will no longer be available in the next compile
command.
Therefore, if you cast a variable to a type defined in the
compile
command, care must be taken to ensure that any future
need to resolve the type can be achieved.
(gdb) compile code static struct a { int a; } v = { 42 }; argv = &v; (gdb) compile code printf ("%d\n", ((struct a *) argv)->a); gdb command line:1:36: error: dereferencing pointer to incomplete type āstruct aā Compilation failed. (gdb) compile code struct a { int a; }; printf ("%d\n", ((struct a *) argv)->a); 42
Variables that have been optimized away by the compiler are not
accessible to the code submitted to the compile
command.
Access to those variables will generate a compiler error which gdb
will print to the console.
compile
commandgdb needs to find gcc for the inferior being debugged
which may not be obvious for remote targets of different architecture
than where gdb is running. Environment variable PATH
on
gdb host is searched for gcc binary matching the
target architecture and operating system. This search can be overriden
by set compile-gcc
gdb command below. PATH
is
taken from shell that executed gdb, it is not the value set by
gdb command set environment
). See Environment.
Specifically PATH
is searched for binaries matching regular expression
arch(-[^-]*)?-
os-gcc
according to the inferior target being
debugged. arch is processor name — multiarch is supported, so for
example both i386
and x86_64
targets look for pattern
(x86_64|i.86)
and both s390
and s390x
targets look
for pattern s390x?
. os is currently supported only for
pattern linux(-gnu)?
.
On Posix hosts the compiler driver gdb needs to find also
shared library libcc1.so from the compiler. It is searched in
default shared library search path (overridable with usual environment
variable LD_LIBRARY_PATH
), unrelated to PATH
or set
compile-gcc
settings. Contrary to it libcc1plugin.so is found
according to the installation of the found compiler — as possibly
specified by the set compile-gcc
command.
set compile-gcc
compile
commands. If this option is not set (it is set to
an empty string), the search described above will occur — that is the
default.
show compile-gcc
gdb needs to know the file name of the program to be debugged, both in order to read its symbol table and in order to start your program. To debug a core dump of a previous run, you must also tell gdb the name of the core dump file.
You may want to specify executable and core dump file names. The usual way to do this is at start-up time, using the arguments to gdb's start-up commands (see Getting In and Out of gdb).
Occasionally it is necessary to change to a different file during a
gdb session. Or you may run gdb and forget to
specify a file you want to use. Or you are debugging a remote target
via gdbserver
(see file). In these situations the gdb commands to specify
new files are useful.
file
filenamerun
command. If you do not specify a
directory and the file is not found in the gdb working directory,
gdb uses the environment variable PATH
as a list of
directories to search, just as the shell does when looking for a program
to run. You can change the value of this variable, for both gdb
and your program, using the path
command.
You can load unlinked object .o files into gdb using
the file
command. You will not be able to “run” an object
file, but you can disassemble functions and inspect variables. Also,
if the underlying BFD functionality supports it, you could use
gdb -write to patch object files using this technique. Note
that gdb can neither interpret nor modify relocations in this
case, so branches and some initialized variables will appear to go to
the wrong place. But this feature is still handy from time to time.
file
file
with no argument makes gdb discard any information it
has on both executable file and the symbol table.
exec-file
[ filename ]PATH
if necessary to locate your program. Omitting filename means to
discard information on the executable file.
symbol-file
[ filename [ -o
offset ]]PATH
is
searched when necessary. Use the file
command to get both symbol
table and program to run from the same file.
If an optional offset is specified, it is added to the start address of each section in the symbol file. This is useful if the program is relocated at runtime, such as the Linux kernel with kASLR enabled.
symbol-file
with no argument clears out gdb information on your
program's symbol table.
The symbol-file
command causes gdb to forget the contents of
some breakpoints and auto-display expressions. This is because they may
contain pointers to the internal data recording symbols and data types,
which are part of the old symbol table data being discarded inside
gdb.
symbol-file
does not repeat if you press <RET> again after
executing it once.
When gdb is configured for a particular environment, it understands debugging information in whatever format is the standard generated for that environment; you may use either a gnu compiler, or other compilers that adhere to the local conventions. Best results are usually obtained from gnu compilers; for example, using gcc you can generate debugging information for optimized code.
For most kinds of object files, with the exception of old SVR3 systems
using COFF, the symbol-file
command does not normally read the
symbol table in full right away. Instead, it scans the symbol table
quickly to find which source files and which symbols are present. The
details are read later, one source file at a time, as they are needed.
The purpose of this two-stage reading strategy is to make gdb
start up faster. For the most part, it is invisible except for
occasional pauses while the symbol table details for a particular source
file are being read. (The set verbose
command can turn these
pauses into messages if desired. See Optional Warnings and Messages.)
We have not implemented the two-stage strategy for COFF yet. When the
symbol table is stored in COFF format, symbol-file
reads the
symbol table data in full right away. Note that “stabs-in-COFF”
still does the two-stage strategy, since the debug info is actually
in stabs format.
symbol-file
[ -readnow
] filenamefile
[ -readnow
] filenamesymbol-file
[ -readnever
] filenamefile
[ -readnever
] filenamecore-file
[filename]core
core-file
with no argument specifies that no core file is
to be used.
Note that the core file is ignored when your program is actually running
under gdb. So, if you have been running your program and you
wish to debug a core file instead, you must kill the subprocess in which
the program is running. To do this, use the kill
command
(see Killing the Child Process).
add-symbol-file
filename [ -readnow
| -readnever
] [ -o
offset ] [ textaddress ] [ -s
section address ...
]add-symbol-file
command reads additional symbol table
information from the file filename. You would use this command
when filename has been dynamically loaded (by some other means)
into the program that is running. The textaddress parameter gives
the memory address at which the file's text section has been loaded.
You can additionally specify the base address of other sections using
an arbitrary number of ‘-s section address’ pairs.
If a section is omitted, gdb will use its default addresses
as found in filename. Any address or textaddress
can be given as an expression.
If an optional offset is specified, it is added to the start address of each section, except those for which the address was specified explicitly.
The symbol table of the file filename is added to the symbol table
originally read with the symbol-file
command. You can use the
add-symbol-file
command any number of times; the new symbol data
thus read is kept in addition to the old.
Changes can be reverted using the command remove-symbol-file
.
Although filename is typically a shared library file, an executable file, or some other object file which has been fully relocated for loading into a process, you can also load symbolic information from relocatable .o files, as long as:
add-symbol-file
command.
Some embedded operating systems, like Sun Chorus and VxWorks, can load
relocatable files into an already running program; such systems
typically make the requirements above easy to meet. However, it's
important to recognize that many native systems use complex link
procedures (.linkonce
section factoring and C++ constructor table
assembly, for example) that make the requirements difficult to meet. In
general, one cannot assume that using add-symbol-file
to read a
relocatable object file's symbolic information will have the same effect
as linking the relocatable object file into the program in the normal
way.
add-symbol-file
does not repeat if you press <RET> after using it.
remove-symbol-file
filenameremove-symbol-file -a
addressadd-symbol-file
command. The
file to remove can be identified by its filename or by an address
that lies within the boundaries of this symbol file in memory. Example:
(gdb) add-symbol-file /home/user/gdb/mylib.so 0x7ffff7ff9480 add symbol table from file "/home/user/gdb/mylib.so" at .text_addr = 0x7ffff7ff9480 (y or n) y Reading symbols from /home/user/gdb/mylib.so...done. (gdb) remove-symbol-file -a 0x7ffff7ff9480 Remove symbol table from file "/home/user/gdb/mylib.so"? (y or n) y (gdb)
remove-symbol-file
does not repeat if you press <RET> after using it.
add-symbol-file-from-memory
addresssyscall DSO
into each
process's address space; this DSO provides kernel-specific code for
some system calls. The argument can be any expression whose
evaluation yields the address of the file's shared object file header.
For this command to work, you must have used symbol-file
or
exec-file
commands in advance.
section
section addrsection
command changes the base address of the named
section of the exec file to addr. This can be used if the
exec file does not contain section addresses, (such as in the
a.out
format), or when the addresses specified in the file
itself are wrong. Each section must be changed separately. The
info files
command, described below, lists all the sections and
their addresses.
info files
info target
info files
and info target
are synonymous; both print the
current target (see Specifying a Debugging Target),
including the names of the executable and core dump files currently in
use by gdb, and the files from which symbols were loaded. The
command help target
lists all possible targets rather than
current ones.
maint info sections
maint info sections
. In addition to the section information
displayed by info files
, this command displays the flags and file
offset of each section in the executable and core dump files. In addition,
maint info sections
provides the following command options (which
may be arbitrarily combined):
ALLOBJ
ALLOC
LOAD
.bss
sections.
RELOC
READONLY
CODE
DATA
ROM
CONSTRUCTOR
HAS_CONTENTS
NEVER_LOAD
COFF_SHARED_LIBRARY
IS_COMMON
set trust-readonly-sections on
The default is off.
set trust-readonly-sections off
show trust-readonly-sections
All file-specifying commands allow both absolute and relative file names as arguments. gdb always converts the file name to an absolute file name and remembers it that way.
gdb supports gnu/Linux, MS-Windows, SunOS, Darwin/Mach-O, SVr4, IBM RS/6000 AIX, QNX Neutrino, FDPIC (FR-V), and DSBT (TIC6X) shared libraries.
On MS-Windows gdb must be linked with the Expat library to support shared libraries. See Expat.
gdb automatically loads symbol definitions from shared libraries
when you use the run
command, or when you examine a core file.
(Before you issue the run
command, gdb does not understand
references to a function in a shared library, however—unless you are
debugging a core file).
There are times, however, when you may wish to not automatically load symbol definitions from shared libraries, such as when they are particularly large or there are many of them.
To control the automatic loading of shared library symbols, use the commands:
set auto-solib-add
modeon
, symbols from all shared object libraries
will be loaded automatically when the inferior begins execution, you
attach to an independently started inferior, or when the dynamic linker
informs gdb that a new library has been loaded. If mode
is off
, symbols must be loaded manually, using the
sharedlibrary
command. The default value is on
.
If your program uses lots of shared libraries with debug info that takes large amounts of memory, you can decrease the gdb memory footprint by preventing it from automatically loading the symbols from shared libraries. To that end, type set auto-solib-add off before running the inferior, then load each library whose debug symbols you do need with sharedlibrary regexp, where regexp is a regular expression that matches the libraries whose symbols you want to be loaded.
show auto-solib-add
To explicitly load shared library symbols, use the sharedlibrary
command:
info share
regexinfo sharedlibrary
regexinfo dll
regexinfo sharedlibrary
.
sharedlibrary
regexshare
regexrun
. If
regex is omitted all shared libraries required by your program are
loaded.
nosharedlibrary
Sometimes you may wish that gdb stops and gives you control
when any of shared library events happen. The best way to do this is
to use catch load
and catch unload
(see Set Catchpoints).
gdb also supports the the set stop-on-solib-events
command for this. This command exists for historical reasons. It is
less useful than setting a catchpoint, because it does not allow for
conditions or commands as a catchpoint does.
set stop-on-solib-events
show stop-on-solib-events
Shared libraries are also supported in many cross or remote debugging configurations. gdb needs to have access to the target's libraries; this can be accomplished either by providing copies of the libraries on the host system, or by asking gdb to automatically retrieve the libraries from the target. If copies of the target libraries are provided, they need to be the same as the target libraries, although the copies on the target can be stripped as long as the copies on the host are not.
For remote debugging, you need to tell gdb where the target libraries are, so that it can load the correct copies—otherwise, it may try to load the host's libraries. gdb has two variables to specify the search directories for target libraries.
set sysroot
pathset sysroot
to find executables and shared libraries, they need
to be laid out in the same way that they are on the target, with
e.g. a /bin, /lib and /usr/lib hierarchy under
path.
If path starts with the sequence target: and the target
system is remote then gdb will retrieve the target binaries
from the remote system. This is only supported when using a remote
target that supports the remote get
command (see Sending files to a remote system). The part of path
following the initial target: (if present) is used as system
root prefix on the remote file system. If path starts with the
sequence remote: this is converted to the sequence
target: by set sysroot
14. If you want
to specify a local system root using a directory that happens to be
named target: or remote:, you need to use some
equivalent variant of the name like ./target:.
For targets with an MS-DOS based filesystem, such as MS-Windows and SymbianOS, gdb tries prefixing a few variants of the target absolute file name with path. But first, on Unix hosts, gdb converts all backslash directory separators into forward slashes, because the backslash is not a directory separator on Unix:
c:\foo\bar.dll ⇒ c:/foo/bar.dll
Then, gdb attempts prefixing the target file name with path, and looks for the resulting file name in the host file system:
c:/foo/bar.dll ⇒ /path/to/sysroot/c:/foo/bar.dll
If that does not find the binary, gdb tries removing the ‘:’ character from the drive spec, both for convenience, and, for the case of the host file system not supporting file names with colons:
c:/foo/bar.dll ⇒ /path/to/sysroot/c/foo/bar.dll
This makes it possible to have a system root that mirrors a target with more than one drive. E.g., you may want to setup your local copies of the target system shared libraries like so (note ‘c’ vs ‘z’):
/path/to/sysroot/c/sys/bin/foo.dll /path/to/sysroot/c/sys/bin/bar.dll /path/to/sysroot/z/sys/bin/bar.dll
and point the system root at /path/to/sysroot, so that gdb can find the correct copies of both c:\sys\bin\foo.dll, and z:\sys\bin\bar.dll.
If that still does not find the binary, gdb tries removing the whole drive spec from the target file name:
c:/foo/bar.dll ⇒ /path/to/sysroot/foo/bar.dll
This last lookup makes it possible to not care about the drive name, if you don't want or need to.
The set solib-absolute-prefix
command is an alias for set
sysroot
.
You can set the default system root by using the configure-time ‘--with-sysroot’ option. If the system root is inside gdb's configured binary prefix (set with ‘--prefix’ or ‘--exec-prefix’), then the default system root will be updated automatically if the installed gdb is moved to a new location.
show sysroot
set solib-search-path
pathshow solib-search-path
set target-file-system-kind
kindShared library file names as reported by the target system may not
make sense as is on the system gdb is running on. For
example, when remote debugging a target that has MS-DOS based file
system semantics, from a Unix host, the target may be reporting to
gdb a list of loaded shared libraries with file names such as
c:\Windows\kernel32.dll. On Unix hosts, there's no concept of
drive letters, so the ‘c:\’ prefix is not normally understood as
indicating an absolute file name, and neither is the backslash
normally considered a directory separator character. In that case,
the native file system would interpret this whole absolute file name
as a relative file name with no directory components. This would make
it impossible to point gdb at a copy of the remote target's
shared libraries on the host using set sysroot
, and impractical
with set solib-search-path
. Setting
target-file-system-kind
to dos-based
tells gdb
to interpret such file names similarly to how the target would, and to
map them to file names valid on gdb's native file system
semantics. The value of kind can be "auto"
, in addition
to one of the supported file system kinds. In that case, gdb
tries to determine the appropriate file system variant based on the
current target's operating system (see Configuring the Current ABI). The supported file system settings are:
unix
dos-based
auto
When processing file names provided by the user, gdb
frequently needs to compare them to the file names recorded in the
program's debug info. Normally, gdb compares just the
base names of the files as strings, which is reasonably fast
even for very large programs. (The base name of a file is the last
portion of its name, after stripping all the leading directories.)
This shortcut in comparison is based upon the assumption that files
cannot have more than one base name. This is usually true, but
references to files that use symlinks or similar filesystem
facilities violate that assumption. If your program records files
using such facilities, or if you provide file names to gdb
using symlinks etc., you can set basenames-may-differ
to
true
to instruct gdb to completely canonicalize each
pair of file names it needs to compare. This will make file-name
comparisons accurate, but at a price of a significant slowdown.
set basenames-may-differ
show basenames-may-differ
To speed up file loading, and reduce memory usage, gdb will
reuse the bfd
objects used to track open files. See BFD. The following commands
allow visibility and control of the caching behavior.
maint info bfds
bfd
object that is known to
gdb.
maint set bfd-sharing
maint show bfd-sharing
bfd
objects can be shared. When sharing is
enabled gdb reuses already open bfd
objects rather
than reopening the same file. Turning sharing off does not cause
already shared bfd
objects to be unshared, but all future files
that are opened will create a new bfd
object. Similarly,
re-enabling sharing does not cause multiple existing bfd
objects to be collapsed into a single shared bfd
object.
set debug bfd-cache
levelshow debug bfd-cache
gdb allows you to put a program's debugging information in a file separate from the executable itself, in a way that allows gdb to find and load the debugging information automatically. Since debugging information can be very large—sometimes larger than the executable code itself—some systems distribute debugging information for their executables in separate files, which users can install only when they need to debug a problem.
gdb supports two ways of specifying the separate debug info file:
Depending on the way the debug info file is specified, gdb uses two different methods of looking for the debug file:
So, for example, suppose you ask gdb to debug
/usr/bin/ls, which has a debug link that specifies the
file ls.debug, and a build ID whose value in hex is
abcdef1234
. If the list of the global debug directories includes
/usr/lib/debug, then gdb will look for the following
debug information files, in the indicated order:
Global debugging info directories default to what is set by gdb configure option --with-separate-debug-dir. During gdb run you can also set the global debugging info directories, and view the list gdb is currently using.
set debug-file-directory
directoriesshow debug-file-directory
A debug link is a special section of the executable file named
.gnu_debuglink
. The section must contain:
Any executable file format can carry a debug link, as long as it can
contain a section named .gnu_debuglink
with the contents
described above.
The build ID is a special section in the executable file (and in other
ELF binary files that gdb may consider). This section is
often named .note.gnu.build-id
, but that name is not mandatory.
It contains unique identification for the built files—the ID remains
the same across multiple builds of the same build tree. The default
algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
content for the build ID string. The same section with an identical
value is present in the original built binary with symbols, in its
stripped variant, and in the separate debugging information file.
The debugging information file itself should be an ordinary
executable, containing a full set of linker symbols, sections, and
debugging information. The sections of the debugging information file
should have the same names, addresses, and sizes as the original file,
but they need not contain any data—much like a .bss
section
in an ordinary executable.
The gnu binary utilities (Binutils) package includes the ‘objcopy’ utility that can produce the separated executable / debugging information file pairs using the following commands:
objcopy --only-keep-debug foo foo.debug strip -g foo
These commands remove the debugging information from the executable file foo and place it in the file foo.debug. You can use the first, second or both methods to link the two files:
objcopy --add-gnu-debuglink=foo.debug foo
Ulrich Drepper's elfutils package, starting with version 0.53, contains
a version of the strip
command such that the command strip foo -f
foo.debug has the same functionality as the two objcopy
commands and
the ln -s
command above, together.
ld --build-id
or
the gcc counterpart gcc -Wl,--build-id
. Build ID support plus
compatibility fixes for debug files separation are present in gnu binary
utilities (Binutils) package since version 2.18.
The CRC used in .gnu_debuglink
is the CRC-32 defined in
IEEE 802.3 using the polynomial:
x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 + x2 + x + 1
The function is computed byte at a time, taking the least
significant bit of each byte first. The initial pattern
0xffffffff
is used, to ensure leading zeros affect the CRC and
the final result is inverted to ensure trailing zeros also affect the
CRC.
Note: This is the same CRC polynomial as used in handling the
Remote Serial Protocol qCRC
packet (see qCRC packet).
However in the case of the Remote Serial Protocol, the CRC is computed
most significant bit first, and the result is not inverted, so
trailing zeros have no effect on the CRC value.
To complete the description, we show below the code of the function
which produces the CRC used in .gnu_debuglink
. Inverting the
initially supplied crc
argument means that an initial call to
this function passing in zero will start computing the CRC using
0xffffffff
.
unsigned long gnu_debuglink_crc32 (unsigned long crc, unsigned char *buf, size_t len) { static const unsigned long crc32_table[256] = { 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f, 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9, 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d }; unsigned char *end; crc = ~crc & 0xffffffff; for (end = buf + len; buf < end; ++buf) crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8); return ~crc & 0xffffffff; }
This computation does not apply to the “build ID” method.
Some systems ship pre-built executables and libraries that have a special ‘.gnu_debugdata’ section. This feature is called MiniDebugInfo. This section holds an LZMA-compressed object and is used to supply extra symbols for backtraces.
The intent of this section is to provide extra minimal debugging information for use in simple backtraces. It is not intended to be a replacement for full separate debugging information (see Separate Debug Files). The example below shows the intended use; however, gdb does not currently put restrictions on what sort of debugging information might be included in the section.
gdb has support for this extension. If the section exists, then it is used provided that no other source of debugging information can be found, and that gdb was configured with LZMA support.
This section can be easily created using objcopy and other standard utilities:
# Extract the dynamic symbols from the main binary, there is no need # to also have these in the normal symbol table. nm -D binary --format=posix --defined-only \ | awk '{ print $1 }' | sort > dynsyms # Extract all the text (i.e. function) symbols from the debuginfo. # (Note that we actually also accept "D" symbols, for the benefit # of platforms like PowerPC64 that use function descriptors.) nm binary --format=posix --defined-only \ | awk '{ if ($2 == "T" || $2 == "t" || $2 == "D") print $1 }' \ | sort > funcsyms # Keep all the function symbols not already in the dynamic symbol # table. comm -13 dynsyms funcsyms > keep_symbols # Separate full debug info into debug binary. objcopy --only-keep-debug binary debug # Copy the full debuginfo, keeping only a minimal set of symbols and # removing some unnecessary sections. objcopy -S --remove-section .gdb_index --remove-section .comment \ --keep-symbols=keep_symbols debug mini_debuginfo # Drop the full debug info from the original binary. strip --strip-all -R .comment binary # Inject the compressed data into the .gnu_debugdata section of the # original binary. xz mini_debuginfo objcopy --add-section .gnu_debugdata=mini_debuginfo.xz binary
When gdb finds a symbol file, it scans the symbols in the file in order to construct an internal symbol table. This lets most gdb operations work quickly—at the cost of a delay early on. For large programs, this delay can be quite lengthy, so gdb provides a way to build an index, which speeds up startup.
For convenience, gdb comes with a program, gdb-add-index, which can be used to add the index to a symbol file. It takes the symbol file as its only argument:
$ gdb-add-index symfile
See gdb-add-index.
It is also possible to do the work manually. Here is what gdb-add-index does behind the curtains.
The index is stored as a section in the symbol file. gdb can write the index to a file, then you can put it into the symbol file using objcopy.
To create an index file, use the save gdb-index
command:
save gdb-index [-dwarf-5]
directoryOnce you have created an index file you can merge it into your symbol file, here named symfile, using objcopy:
$ objcopy --add-section .gdb_index=symfile.gdb-index \ --set-section-flags .gdb_index=readonly symfile symfile
Or for -dwarf-5
:
$ objcopy --dump-section .debug_str=symfile.debug_str.new symfile $ cat symfile.debug_str >>symfile.debug_str.new $ objcopy --add-section .debug_names=symfile.gdb-index \ --set-section-flags .debug_names=readonly \ --update-section .debug_str=symfile.debug_str.new symfile symfile
gdb will normally ignore older versions of .gdb_index
sections that have been deprecated. Usually they are deprecated because
they are missing a new feature or have performance issues.
To tell gdb to use a deprecated index section anyway
specify set use-deprecated-index-sections on
.
The default is off
.
This can speed up startup, but may result in some functionality being lost.
See Index Section Format.
Warning: Setting use-deprecated-index-sections
to on
must be done before gdb reads the file. The following will not work:
$ gdb -ex "set use-deprecated-index-sections on" <program>
Instead you must do, for example,
$ gdb -iex "set use-deprecated-index-sections on" <program>
There are currently some limitation on indices. They only work when
using DWARF debugging information, not stabs. And, only the
-dwarf-5
index works for programs using Ada.
It is possible for gdb to automatically save a copy of this index in a cache on disk and retrieve it from there when loading the same binary in the future. This feature can be turned on with set index-cache on. The following commands can be used to tweak the behavior of the index cache.
set index-cache on
set index-cache off
set index-cache directory
directoryshow index-cache directory
The default value for this directory depends on the host platform. On most systems, the index is cached in the gdb subdirectory of the directory pointed to by the XDG_CACHE_HOME environment variable, if it is defined, else in the .cache/gdb subdirectory of your home directory. However, on some systems, the default may differ according to local convention.
There is no limit on the disk space used by index cache. It is perfectly safe
to delete the content of that directory to free up disk space.
show index-cache stats
While reading a symbol file, gdb occasionally encounters problems,
such as symbol types it does not recognize, or known bugs in compiler
output. By default, gdb does not notify you of such problems, since
they are relatively common and primarily of interest to people
debugging compilers. If you are interested in seeing information
about ill-constructed symbol tables, you can either ask gdb to print
only one message about each such type of problem, no matter how many
times the problem occurs; or you can ask gdb to print more messages,
to see how many times the problems occur, with the set
complaints
command (see Optional Warnings and Messages).
The messages currently printed, and their meanings, include:
inner block not inside outer block in
symbolgdb circumvents the problem by treating the inner block as if it had
the same scope as the outer block. In the error message, symbol
may be shown as “(don't know)
” if the outer block is not a
function.
block at
address out of order
gdb does not circumvent this problem, and has trouble
locating symbols in the source file whose symbols it is reading. (You
can often determine what source file is affected by specifying
set verbose on
. See Optional Warnings and Messages.)
bad block start address patched
gdb circumvents the problem by treating the symbol scope block as
starting on the previous source line.
bad string table offset in symbol
ngdb circumvents the problem by considering the symbol to have the
name foo
, which may cause other problems if many symbols end up
with this name.
unknown symbol type 0x
nn0x
nn is the symbol type of the
uncomprehended information, in hexadecimal.
gdb circumvents the error by ignoring this symbol information.
This usually allows you to debug your program, though certain symbols
are not accessible. If you encounter such a problem and feel like
debugging it, you can debug gdb
with itself, breakpoint
on complain
, then go up to the function read_dbx_symtab
and examine *bufp
to see the symbol.
stub type has NULL name
const/volatile indicator missing (ok if using g++ v1.x), got...
info mismatch between compiler and debugger
gdb will sometimes read an auxiliary data file. These files are kept in a directory known as the data directory.
You can set the data directory's name, and view the name gdb is currently using.
set data-directory
directoryshow data-directory
You can set the default data directory by using the configure-time ‘--with-gdb-datadir’ option. If the data directory is inside gdb's configured binary prefix (set with ‘--prefix’ or ‘--exec-prefix’), then the default data directory will be updated automatically if the installed gdb is moved to a new location.
The data directory may also be specified with the
--data-directory
command line option.
See Mode Options.
A target is the execution environment occupied by your program.
Often, gdb runs in the same host environment as your program;
in that case, the debugging target is specified as a side effect when
you use the file
or core
commands. When you need more
flexibility—for example, running gdb on a physically separate
host, or controlling a standalone system over a serial port or a
realtime system over a TCP/IP connection—you can use the target
command to specify one of the target types configured for gdb
(see Commands for Managing Targets).
It is possible to build gdb for several different target architectures. When gdb is built like that, you can choose one of the available architectures with the set architecture command.
set architecture
arch"auto"
, in addition to one of the
supported architectures.
show architecture
set processor
processor
set architecture
and show architecture
.
There are multiple classes of targets such as: processes, executable files or
recording sessions. Core files belong to the process class, making core file
and process mutually exclusive. Otherwise, gdb can work concurrently
on multiple active targets, one in each class. This allows you to (for
example) start a process and inspect its activity, while still having access to
the executable file after the process finishes. Or if you start process
recording (see Reverse Execution) and reverse-step
there, you are
presented a virtual layer of the recording target, while the process target
remains stopped at the chronologically last point of the process execution.
Use the core-file
and exec-file
commands to select a new core
file or executable target (see Commands to Specify Files). To
specify as a target a process that is already running, use the attach
command (see Debugging an Already-running Process).
target
type parametersFurther parameters are interpreted by the target protocol, but typically include things like device names or host names to connect with, process numbers, and baud rates.
The target
command does not repeat if you press <RET> again
after executing the command.
help target
info target
or info files
(see Commands to Specify Files).
help target
nameset gnutarget
argsset gnutarget
command. Unlike most target
commands,
with gnutarget
the target
refers to a program, not a machine.
Warning: To specify a file format with set gnutarget
,
you must know the actual BFD name.
show gnutarget
show gnutarget
command to display what file format
gnutarget
is set to read. If you have not set gnutarget
,
gdb will determine the file format for each file automatically,
and show gnutarget
displays ‘The current BFD target is "auto"’.
Here are some common targets (available, or not, depending on the GDB configuration):
target exec
programtarget core
filenametarget remote
mediumFor example, if you have a board connected to /dev/ttya on the machine running gdb, you could say:
target remote /dev/ttya
target remote
supports the load
command. This is only
useful if you have some other way of getting the stub to the target
system, and you can put it somewhere in memory where it won't get
clobbered by the download.
target sim
[simargs] ...
target sim load run
works; however, you cannot assume that a specific memory map, device
drivers, or even basic I/O is available, although some simulators do
provide these. For info about any processor-specific simulator details,
see the appropriate section in Embedded Processors.
target native
run
command spawn native processes (likewise attach
,
etc.) even when set auto-connect-native-target
is off
(see set auto-connect-native-target).
Different targets are available on different configurations of gdb; your configuration may have more or fewer targets.
Many remote targets require you to download the executable's code once you've successfully established a connection. You may wish to control various aspects of this process.
set hash
show hash
set debug monitor
show debug monitor
load
filename offsetload
command may be available. Where it exists, it
is meant to make filename (an executable) available for debugging
on the remote system—by downloading, or dynamic linking, for example.
load
also records the filename symbol table in gdb, like
the add-symbol-file
command.
If your gdb does not have a load
command, attempting to
execute it gets the error message “You can't do that when your
target is ...
”
The file is loaded at whatever address is specified in the executable. For some object file formats, you can specify the load address when you link the program; for other formats, like a.out, the object file format specifies a fixed address.
It is also possible to tell gdb to load the executable file at a specific offset described by the optional argument offset. When offset is provided, filename must also be provided.
Depending on the remote side capabilities, gdb may be able to load programs into flash memory.
load
does not repeat if you press <RET> again after using it.
unload
filenameunload
command may be available. Where it exists,
it does the opposite of the load
command.
If your gdb does not have an unload
command, attempting
to execute it triggers the error message “You can't do that when
your target is ...
”
unload
does not repeat if you press <RET> again after using it.
flash-erase
Some types of processors, such as the MIPS, PowerPC, and Renesas SH, offer the ability to run either big-endian or little-endian byte orders. Usually the executable or symbol will include a bit to designate the endian-ness, and you will not need to worry about which to use. However, you may still find it useful to adjust gdb's idea of processor endian-ness manually.
set endian big
set endian little
set endian auto
show endian
If the set endian auto
mode is in effect and no executable has
been selected, then the endianness used is the last one chosen either
by one of the set endian big
and set endian little
commands or by inferring from the last executable used. If no
endianness has been previously chosen, then the default for this mode
is inferred from the target gdb has been built for, and is
little
if the name of the target CPU has an el
suffix
and big
otherwise.
Note that these commands merely adjust interpretation of symbolic data on the host, and that they have absolutely no effect on the target system.
If you are trying to debug a program running on a machine that cannot run gdb in the usual way, it is often useful to use remote debugging. For example, you might use remote debugging on an operating system kernel, or on a small system which does not have a general purpose operating system powerful enough to run a full-featured debugger.
Some configurations of gdb have special serial or TCP/IP interfaces to make this work with particular debugging targets. In addition, gdb comes with a generic serial protocol (specific to gdb, but not specific to any particular target system) which you can use if you write the remote stubs—the code that runs on the remote system to communicate with gdb.
Other remote targets may be available in your
configuration of gdb; use help target
to list them.
This section describes how to connect to a remote target, including the types of connections and their differences, how to set up executable and symbol files on the host and target, and the commands used for connecting to and disconnecting from the remote target.
gdb supports two types of remote connections, target remote
mode and target extended-remote
mode. Note that many remote targets
support only target remote
mode. There are several major
differences between the two types of connections, enumerated here:
gdbserver
, gdbserver
will exit.
With target extended-remote mode: When the debugged program exits or
you detach from it, gdb remains connected to the target, even
though no program is running. You can rerun the program, attach to a
running program, or use monitor
commands specific to the target.
When using gdbserver
in this case, it does not exit unless it was
invoked using the --once option. If the --once option
was not used, you can ask gdbserver
to exit using the
monitor exit
command (see Monitor Commands for gdbserver).
file
command to specify the
program on the host system. If you are using gdbserver
there are
some differences in how to specify the location of the program on the
target.
With target remote mode: You must either specify the program to debug
on the gdbserver
command line or use the --attach option
(see Attaching to a Running Program).
With target extended-remote mode: You may specify the program to debug
on the gdbserver
command line, or you can load the program or attach
to it using gdb commands after connecting to gdbserver
.
You can start gdbserver
without supplying an initial command to run
or process ID to attach. To do this, use the --multi command line
option. Then you can connect using target extended-remote
and start
the program you want to debug (see below for details on using the
run
command in this scenario). Note that the conditions under which
gdbserver
terminates depend on how gdb connects to it
(target remote
or target extended-remote
). The
--multi option to gdbserver
has no influence on that.
run
commandrun
command is not
supported. Once a connection has been established, you can use all
the usual gdb commands to examine and change data. The
remote program is already running, so you can use commands like
step and continue.
With target extended-remote mode: The run
command is
supported. The run
command uses the value set by
set remote exec-file
(see set remote exec-file) to select
the program to run. Command line arguments are supported, except for
wildcard expansion and I/O redirection (see Arguments).
If you specify the program to debug on the command line, then the
run
command is not required to start execution, and you can
resume using commands like step and continue as with
target remote
mode.
attach
is
not supported. To attach to a running program using gdbserver
, you
must use the --attach option (see Running gdbserver).
With target extended-remote mode: To attach to a running program,
you may use the attach
command after the connection has been
established. If you are using gdbserver
, you may also invoke
gdbserver
using the --attach option
(see Running gdbserver).
gdb, running on the host, needs access to symbol and debugging
information for your program running on the target. This requires
access to an unstripped copy of your program, and possibly any associated
symbol files. Note that this section applies equally to both target
remote
mode and target extended-remote
mode.
Some remote targets (see qXfer executable filename read, and
see Host I/O Packets) allow gdb to access program files over
the same connection used to communicate with gdb. With such a
target, if the remote program is unstripped, the only command you need is
target remote
(or target extended-remote
).
If the remote program is stripped, or the target does not support remote
program file access, start up gdb using the name of the local
unstripped copy of your program as the first argument, or use the
file
command. Use set sysroot
to specify the location (on
the host) of target libraries (unless your gdb was compiled with
the correct sysroot using --with-sysroot
). Alternatively, you
may use set solib-search-path
to specify how gdb locates
target libraries.
The symbol file and target libraries must exactly match the executable
and libraries on the target, with one exception: the files on the host
system should not be stripped, even if the files on the target system
are. Mismatched or missing files will lead to confusing results
during debugging. On gnu/Linux targets, mismatched or missing
files may also prevent gdbserver
from debugging multi-threaded
programs.
gdb can communicate with the target over a serial line, a
local Unix domain socket, or
over an IP network using TCP or UDP. In
each case, gdb uses the same protocol for debugging your
program; only the medium carrying the debugging packets varies. The
target remote
and target extended-remote
commands
establish a connection to the target. Both commands accept the same
arguments, which indicate the medium to use:
target remote
serial-devicetarget extended-remote
serial-devicetarget remote /dev/ttyb
If you're using a serial line, you may want to give gdb the
‘--baud’ option, or use the set serial baud
command
(see set serial baud) before the
target
command.
target remote
local-sockettarget extended-remote
local-sockettarget remote /tmp/gdb-socket0
Note that this command has the same form as the command to connect
to a serial line. gdb will automatically determine which
kind of file you have specified and will make the appropriate kind
of connection.
This feature is not available if the host system does not support
Unix domain sockets.
target remote
host:
porttarget remote
[host]:
porttarget remote tcp:
host:
porttarget remote tcp:
[host]:
porttarget remote tcp4:
host:
porttarget remote tcp6:
host:
porttarget remote tcp6:
[host]:
porttarget extended-remote
host:
porttarget extended-remote
[host]:
porttarget extended-remote tcp:
host:
porttarget extended-remote tcp:
[host]:
porttarget extended-remote tcp4:
host:
porttarget extended-remote tcp6:
host:
porttarget extended-remote tcp6:
[host]:
portFor example, to connect to port 2828 on a terminal server named
manyfarms
:
target remote manyfarms:2828
To connect to port 2828 on a terminal server whose address is
2001:0db8:85a3:0000:0000:8a2e:0370:7334
, you can either use the
square bracket syntax:
target remote [2001:0db8:85a3:0000:0000:8a2e:0370:7334]:2828
or explicitly specify the IPv6 protocol:
target remote tcp6:2001:0db8:85a3:0000:0000:8a2e:0370:7334:2828
This last example may be confusing to the reader, because there is no visible separation between the hostname and the port number. Therefore, we recommend the user to provide IPv6 addresses using square brackets for clarity. However, it is important to mention that for gdb there is no ambiguity: the number after the last colon is considered to be the port number.
If your remote target is actually running on the same machine as your debugger session (e.g. a simulator for your target running on the same host), you can omit the hostname. For example, to connect to port 1234 on your local machine:
target remote :1234
Note that the colon is still required here.
target remote udp:
host:
porttarget remote udp:
[host]:
porttarget remote udp4:
host:
porttarget remote udp6:
[host]:
porttarget extended-remote udp:
host:
porttarget extended-remote udp:
host:
porttarget extended-remote udp:
[host]:
porttarget extended-remote udp4:
host:
porttarget extended-remote udp6:
host:
porttarget extended-remote udp6:
[host]:
portmanyfarms
:
target remote udp:manyfarms:2828
When using a UDP connection for remote debugging, you should
keep in mind that the `U' stands for “Unreliable”. UDP
can silently drop packets on busy or unreliable networks, which will
cause havoc with your debugging session.
target remote |
commandtarget extended-remote |
command/bin/sh
; it should expect remote
protocol packets on its standard input, and send replies on its
standard output. You could use this to run a stand-alone simulator
that speaks the remote debugging protocol, to make net connections
using programs like ssh
, or for other similar tricks.
If command closes its standard output (perhaps by exiting),
gdb will try to send it a SIGTERM
signal. (If the
program has already exited, this will have no effect.)
Whenever gdb is waiting for the remote program, if you type the interrupt character (often Ctrl-c), gdb attempts to stop the program. This may or may not succeed, depending in part on the hardware and the serial drivers the remote system uses. If you type the interrupt character once again, gdb displays this prompt:
Interrupted while waiting for the program. Give up (and stop debugging it)? (y or n)
In target remote
mode, if you type y, gdb abandons
the remote debugging session. (If you decide you want to try again later,
you can use target remote again to connect once more.) If you type
n, gdb goes back to waiting.
In target extended-remote
mode, typing n will leave
gdb connected to the target.
detach
detach
command to release it from gdb control.
Detaching from the target normally resumes its execution, but the results
will depend on your particular remote stub. After the detach
command in target remote
mode, gdb is free to connect to
another target. In target extended-remote
mode, gdb is
still connected to the target.
disconnect
disconnect
command closes the connection to the target, and
the target is generally not resumed. It will wait for gdb
(this instance or another one) to connect and continue debugging. After
the disconnect
command, gdb is again free to connect to
another target.
monitor
cmd
Some remote targets offer the ability to transfer files over the same
connection used to communicate with gdb. This is convenient
for targets accessible through other means, e.g. gnu/Linux systems
running gdbserver
over a network interface. For other targets,
e.g. embedded devices with only a single serial port, this may be
the only way to upload or download files.
Not all remote targets support these commands.
remote put
hostfile targetfileremote get
targetfile hostfileremote delete
targetfilegdbserver
Programgdbserver
is a control program for Unix-like systems, which
allows you to connect your program with a remote gdb via
target remote
or target extended-remote
—but without
linking in the usual debugging stub.
gdbserver
is not a complete replacement for the debugging stubs,
because it requires essentially the same operating-system facilities
that gdb itself does. In fact, a system that can run
gdbserver
to connect to a remote gdb could also run
gdb locally! gdbserver
is sometimes useful nevertheless,
because it is a much smaller program than gdb itself. It is
also easier to port than all of gdb, so you may be able to get
started more quickly on a new system by using gdbserver
.
Finally, if you develop code for real-time systems, you may find that
the tradeoffs involved in real-time operation make it more convenient to
do as much development work as possible on another system, for example
by cross-compiling. You can use gdbserver
to make a similar
choice for debugging.
gdb and gdbserver
communicate via either a serial line
or a TCP connection, using the standard gdb remote serial
protocol.
Warning:gdbserver
does not have any built-in security. Do not rungdbserver
connected to any public network; a gdb connection togdbserver
provides access to the target system with the same privileges as the user runninggdbserver
.
gdbserver
Run gdbserver
on the target system. You need a copy of the
program you want to debug, including any libraries it requires.
gdbserver
does not need your program's symbol table, so you can
strip the program if necessary to save space. gdb on the host
system does all the symbol handling.
To use the server, you must tell it how to communicate with gdb; the name of your program; and the arguments for your program. The usual syntax is:
target> gdbserver comm program [ args ... ]
comm is either a device name (to use a serial line), or a TCP
hostname and portnumber, or -
or stdio
to use
stdin/stdout of gdbserver
.
For example, to debug Emacs with the argument
‘foo.txt’ and communicate with gdb over the serial port
/dev/com1:
target> gdbserver /dev/com1 emacs foo.txt
gdbserver
waits passively for the host gdb to communicate
with it.
To use a TCP connection instead of a serial line:
target> gdbserver host:2345 emacs foo.txt
The only difference from the previous example is the first argument,
specifying that you are communicating with the host gdb via
TCP. The ‘host:2345’ argument means that gdbserver
is to
expect a TCP connection from machine ‘host’ to local TCP port 2345.
(Currently, the ‘host’ part is ignored.) You can choose any number
you want for the port number as long as it does not conflict with any
TCP ports already in use on the target system (for example, 23
is
reserved for telnet
).15 You must use the same port number with the host gdb
target remote
command.
The stdio
connection is useful when starting gdbserver
with ssh:
(gdb) target remote | ssh -T hostname gdbserver - hello
The ‘-T’ option to ssh is provided because we don't need a remote pty, and we don't want escape-character handling. Ssh does this by default when a command is provided, the flag is provided to make it explicit. You could elide it if you want to.
Programs started with stdio-connected gdbserver have /dev/null for
stdin
, and stdout
,stderr
are sent back to gdb for
display through a pipe connected to gdbserver.
Both stdout
and stderr
use the same pipe.
On some targets, gdbserver
can also attach to running programs.
This is accomplished via the --attach
argument. The syntax is:
target> gdbserver --attach comm pid
pid is the process ID of a currently running process. It isn't
necessary to point gdbserver
at a binary for the running process.
In target extended-remote
mode, you can also attach using the
gdb attach command
(see Attaching in Types of Remote Connections).
You can debug processes by name instead of process ID if your target has the
pidof
utility:
target> gdbserver --attach comm `pidof program`
In case more than one copy of program is running, or program
has multiple threads, most versions of pidof
support the
-s
option to only return the first process ID.
gdbserver
This section applies only when gdbserver
is run to listen on a TCP
port.
gdbserver
normally terminates after all of its debugged processes have
terminated in target remote mode. On the other hand, for target
extended-remote, gdbserver
stays running even with no processes left.
gdb normally terminates the spawned debugged process on its exit,
which normally also terminates gdbserver
in the target remote
mode. Therefore, when the connection drops unexpectedly, and gdb
cannot ask gdbserver
to kill its debugged processes, gdbserver
stays running even in the target remote mode.
When gdbserver
stays running, gdb can connect to it again later.
Such reconnecting is useful for features like disconnected tracing. For
completeness, at most one gdb can be connected at a time.
By default, gdbserver
keeps the listening TCP port open, so that
subsequent connections are possible. However, if you start gdbserver
with the --once option, it will stop listening for any further
connection attempts after connecting to the first gdb session. This
means no further connections to gdbserver
will be possible after the
first one. It also means gdbserver
will terminate after the first
connection with remote gdb has closed, even for unexpectedly closed
connections and even in the target extended-remote mode. The
--once option allows reusing the same port number for connecting to
multiple instances of gdbserver
running on the same host, since each
instance closes its port after the first connection.
gdbserver
You can use the --multi option to start gdbserver
without
specifying a program to debug or a process to attach to. Then you can
attach in target extended-remote
mode and run or attach to a
program. For more information,
see –multi Option in Types of Remote Connnections.
The --debug option tells gdbserver
to display extra
status information about the debugging process.
The --remote-debug option tells gdbserver
to display
remote protocol debug output.
The --debug-file=filename option tells gdbserver
to
write any debug output to the given filename. These options are intended
for gdbserver
development and for bug reports to the developers.
The --debug-format=option1[,option2,...] option tells
gdbserver
to include additional information in each output.
Possible options are:
none
all
timestamps
Options are processed in order. Thus, for example, if none appears last then no additional information is added to debugging output.
The --wrapper option specifies a wrapper to launch programs for debugging. The option should be followed by the name of the wrapper, then any command-line arguments to pass to the wrapper, then -- indicating the end of the wrapper arguments.
gdbserver
runs the specified wrapper program with a combined
command line including the wrapper arguments, then the name of the
program to debug, then any arguments to the program. The wrapper
runs until it executes your program, and then gdb gains control.
You can use any program that eventually calls execve
with
its arguments as a wrapper. Several standard Unix utilities do
this, e.g. env
and nohup
. Any Unix shell script ending
with exec "$@"
will also work.
For example, you can use env
to pass an environment variable to
the debugged program, without setting the variable in gdbserver
's
environment:
$ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
The --selftest option runs the self tests in gdbserver
:
$ gdbserver --selftest Ran 2 unit tests, 0 failed
These tests are disabled in release.
gdbserver
The basic procedure for connecting to the remote target is:
file
command before you
connect. Use set sysroot
to locate target libraries (unless your
gdb was compiled with the correct sysroot using
--with-sysroot
).
gdbserver
prior to using
the target
command. Otherwise you may get an error whose
text depends on the host system, but which usually looks something like
‘Connection refused’. Don't use the load
command in gdb when using target remote
mode, since the
program is already on the target.
gdbserver
During a gdb session using gdbserver
, you can use the
monitor
command to send special requests to gdbserver
.
Here are the available commands.
monitor help
monitor set debug 0
monitor set debug 1
monitor set remote-debug 0
monitor set remote-debug 1
monitor set debug-file filename
monitor set debug-file
monitor set debug-format option1
[,option2,...
]none
all
timestamps
Options are processed in order. Thus, for example, if none
appears last then no additional information is added to debugging output.
monitor set libthread-db-search-path [PATH]
libthread_db
(see set libthread-db-search-path). If you omit path,
‘libthread-db-search-path’ will be reset to its default value.
The special entry ‘$pdir’ for ‘libthread-db-search-path’ is
not supported in gdbserver
.
monitor exit
disconnect
to close the debugging session. gdbserver
will
detach from any attached processes and kill any processes it created.
Use monitor exit
to terminate gdbserver
at the end
of a multi-process mode debug session.
gdbserver
On some targets, gdbserver
supports tracepoints, fast
tracepoints and static tracepoints.
For fast or static tracepoints to work, a special library called the
in-process agent (IPA), must be loaded in the inferior process.
This library is built and distributed as an integral part of
gdbserver
. In addition, support for static tracepoints
requires building the in-process agent library with static tracepoints
support. At present, the UST (LTTng Userspace Tracer,
http://lttng.org/ust) tracing engine is supported. This support
is automatically available if UST development headers are found in the
standard include path when gdbserver
is built, or if
gdbserver
was explicitly configured using --with-ust
to point at such headers. You can explicitly disable the support
using --with-ust=no.
There are several ways to load the in-process agent in your program:
Specifying it as dependency at link time
-linproctrace
to the link command.
Using the system's preloading mechanisms
LD_PRELOAD=libinproctrace.so
in the environment. See also the description of gdbserver
's
--wrapper command line option.
Using
gdb to force loading the agent at run time
dlopen
. You'll use the call
command for that. For example:
(gdb) call dlopen ("libinproctrace.so", ...)
Note that on most Unix systems, for the dlopen
function to be
available, the program needs to be linked with -ldl
.
On systems that have a userspace dynamic loader, like most Unix
systems, when you connect to gdbserver
using target
remote
, you'll find that the program is stopped at the dynamic
loader's entry point, and no shared library has been loaded in the
program's address space yet, including the in-process agent. In that
case, before being able to use any of the fast or static tracepoints
features, you need to let the loader run and load the shared
libraries. The simplest way to do that is to run the program to the
main procedure. E.g., if debugging a C or C++ program, start
gdbserver
like so:
$ gdbserver :9999 myprogram
Start GDB and connect to gdbserver
like so, and run to main:
$ gdb myprogram (gdb) target remote myhost:9999 0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2 (gdb) b main (gdb) continue
The in-process tracing agent library should now be loaded into the
process; you can confirm it with the info sharedlibrary
command, which will list libinproctrace.so as loaded in the
process. You are now ready to install fast tracepoints, list static
tracepoint markers, probe static tracepoints markers, and start
tracing.
This section documents the configuration options available when debugging remote programs. For the options related to the File I/O extensions of the remote protocol, see system-call-allowed.
set remoteaddresssize
bitsshow remoteaddresssize
set serial baud
nshow serial baud
set serial parity
parityeven
, none
, and odd
. The default is none
.
show serial parity
set remotebreak
BREAK
signal to the remote
when you type Ctrl-c to interrupt the program running
on the remote. If set to off, gdb sends the ‘Ctrl-C’
character instead. The default is off, since most remote systems
expect to see ‘Ctrl-C’ as the interrupt signal.
show remotebreak
BREAK
or ‘Ctrl-C’ to
interrupt the remote program.
set remoteflow on
set remoteflow off
RTS
/CTS
)
on the serial port used to communicate to the remote target.
show remoteflow
set remotelogbase
baseascii
, octal
, and hex
. The default is
ascii
.
show remotelogbase
set remotelogfile
fileshow remotelogfile
set remotetimeout
numshow remotetimeout
set remote hardware-watchpoint-limit
limitset remote hardware-breakpoint-limit
limitunlimited
for unlimited
watchpoints or breakpoints.
show remote hardware-watchpoint-limit
show remote hardware-breakpoint-limit
set remote hardware-watchpoint-length-limit
limitunlimited
allows watchpoints of any
length.
show remote hardware-watchpoint-length-limit
set remote exec-file
filenameshow remote exec-file
run
with target
extended-remote
. This should be set to a filename valid on the
target system. If it is not set, the target will use a default
filename (e.g. the last program run).
set remote interrupt-sequence
BREAK
or
‘BREAK-g’ as the
sequence to the remote target in order to interrupt the execution.
‘Ctrl-C’ is a default. Some system prefers BREAK
which
is high level of serial line for some certain time.
Linux kernel prefers ‘BREAK-g’, a.k.a Magic SysRq g.
It is BREAK
signal followed by character g
.
show interrupt-sequence
BREAK
or BREAK-g
is sent by gdb to interrupt the remote program.
BREAK-g
is BREAK signal followed by g
and
also known as Magic SysRq g.
set remote interrupt-on-connect
BREAK
followed by g
which is known as Magic SysRq g in order to connect gdb.
show interrupt-on-connect
set tcp auto-retry on
set tcp connect-timeout
.
set tcp auto-retry off
show tcp auto-retry
set tcp connect-timeout
secondsset tcp connect-timeout unlimited
set tcp auto-retry on
) and waiting for connections
that are merely slow to complete, and represents an approximate cumulative
value. If seconds is unlimited
, there is no timeout and
gdb will keep attempting to establish a connection forever,
unless interrupted with Ctrl-c. The default is 15 seconds.
show tcp connect-timeout
The gdb remote protocol autodetects the packets supported by your debugging stub. If you need to override the autodetection, you can use these commands to enable or disable individual packets. Each packet can be set to ‘on’ (the remote target supports this packet), ‘off’ (the remote target does not support this packet), or ‘auto’ (detect remote target support for this packet). They all default to ‘auto’. For more information about each packet, see Remote Protocol.
During normal use, you should not have to use any of these commands. If you do, that may be a bug in your remote debugging stub, or a bug in gdb. You may want to report the problem to the gdb developers.
For each packet name, the command to enable or disable the
packet is set remote
name-packet
. The available settings
are:
Command Name | Remote Packet | Related Features
|
fetch-register
| p
| info registers
|
set-register
| P
| set
|
binary-download
| X
| load , set
|
read-aux-vector
| qXfer:auxv:read
| info auxv
|
symbol-lookup
| qSymbol
| Detecting multiple threads
|
attach
| vAttach
| attach
|
verbose-resume
| vCont
| Stepping or resuming multiple threads
|
run
| vRun
| run
|
software-breakpoint
| Z0
| break
|
hardware-breakpoint
| Z1
| hbreak
|
write-watchpoint
| Z2
| watch
|
read-watchpoint
| Z3
| rwatch
|
access-watchpoint
| Z4
| awatch
|
pid-to-exec-file
| qXfer:exec-file:read
| attach , run
|
target-features
| qXfer:features:read
| set architecture
|
library-info
| qXfer:libraries:read
| info sharedlibrary
|
memory-map
| qXfer:memory-map:read
| info mem
|
read-sdata-object
| qXfer:sdata:read
| print $_sdata
|
read-siginfo-object
| qXfer:siginfo:read
| print $_siginfo
|
write-siginfo-object
| qXfer:siginfo:write
| set $_siginfo
|
threads
| qXfer:threads:read
| info threads
|
get-thread-local-
| qGetTLSAddr
| Displaying __thread variables
|
get-thread-information-block-address
| qGetTIBAddr
| Display MS-Windows Thread Information Block.
|
search-memory
| qSearch:memory
| find
|
supported-packets
| qSupported
| Remote communications parameters
|
catch-syscalls
| QCatchSyscalls
| catch syscall
|
pass-signals
| QPassSignals
| handle signal
|
program-signals
| QProgramSignals
| handle signal
|
hostio-close-packet
| vFile:close
| remote get , remote put
|
hostio-open-packet
| vFile:open
| remote get , remote put
|
hostio-pread-packet
| vFile:pread
| remote get , remote put
|
hostio-pwrite-packet
| vFile:pwrite
| remote get , remote put
|
hostio-unlink-packet
| vFile:unlink
| remote delete
|
hostio-readlink-packet
| vFile:readlink
| Host I/O
|
hostio-fstat-packet
| vFile:fstat
| Host I/O
|
hostio-setfs-packet
| vFile:setfs
| Host I/O
|
noack-packet
| QStartNoAckMode
| Packet acknowledgment
|
osdata
| qXfer:osdata:read
| info os
|
query-attached
| qAttached
| Querying remote process attach state.
|
trace-buffer-size
| QTBuffer:size
| set trace-buffer-size
|
trace-status
| qTStatus
| tstatus
|
traceframe-info
| qXfer:traceframe-info:read
| Traceframe info
|
install-in-trace
| InstallInTrace
| Install tracepoint in tracing
|
disable-randomization
| QDisableRandomization
| set disable-randomization
|
startup-with-shell
| QStartupWithShell
| set startup-with-shell
|
environment-hex-encoded
| QEnvironmentHexEncoded
| set environment
|
environment-unset
| QEnvironmentUnset
| unset environment
|
environment-reset
| QEnvironmentReset
| Reset the inferior environment (i.e., unset user-set variables)
|
set-working-dir
| QSetWorkingDir
| set cwd
|
conditional-breakpoints-packet
| Z0 and Z1
| Support for target-side breakpoint condition evaluation
|
multiprocess-extensions
| multiprocess extensions
| Debug multiple processes and remote process PID awareness
|
swbreak-feature
| swbreak stop reason
| break
|
hwbreak-feature
| hwbreak stop reason
| hbreak
|
fork-event-feature
| fork stop reason
| fork
|
vfork-event-feature
| vfork stop reason
| vfork
|
exec-event-feature
| exec stop reason
| exec
|
thread-events
| QThreadEvents
| Tracking thread lifetime.
|
no-resumed-stop-reply
| no resumed thread left stop reply
| Tracking thread lifetime.
|
The stub files provided with gdb implement the target side of the communication protocol, and the gdb side is implemented in the gdb source file remote.c. Normally, you can simply allow these subroutines to communicate, and ignore the details. (If you're implementing your own stub file, you can still ignore the details: start with one of the existing stub files. sparc-stub.c is the best organized, and therefore the easiest to read.)
To debug a program running on another machine (the debugging target machine), you must first arrange for all the usual prerequisites for the program to run by itself. For example, for a C program, you need:
The next step is to arrange for your program to use a serial port to communicate with the machine where gdb is running (the host machine). In general terms, the scheme looks like this:
On certain remote targets, you can use an auxiliary program
gdbserver
instead of linking a stub into your program.
See Using the gdbserver
Program, for details.
The debugging stub is specific to the architecture of the remote machine; for example, use sparc-stub.c to debug programs on sparc boards.
These working remote stubs are distributed with gdb:
i386-stub.c
m68k-stub.c
sh-stub.c
sparc-stub.c
sparcl-stub.c
The README file in the gdb distribution may list other recently added stubs.
The debugging stub for your architecture supplies these three subroutines:
set_debug_traps
handle_exception
to run when your
program stops. You must call this subroutine explicitly in your
program's startup code.
handle_exception
handle_exception
to
run when a trap is triggered.
handle_exception
takes control when your program stops during
execution (for example, on a breakpoint), and mediates communications
with gdb on the host machine. This is where the communications
protocol is implemented; handle_exception
acts as the gdb
representative on the target machine. It begins by sending summary
information on the state of your program, then continues to execute,
retrieving and transmitting any information gdb needs, until you
execute a gdb command that makes your program resume; at that point,
handle_exception
returns control to your own code on the target
machine.
breakpoint
handle_exception
—in effect, to gdb. On some machines,
simply receiving characters on the serial port may also trigger a trap;
again, in that situation, you don't need to call breakpoint
from
your own program—simply running ‘target remote’ from the host
gdb session gets control.
Call breakpoint
if none of these is true, or if you simply want
to make certain your program stops at a predetermined point for the
start of your debugging session.
The debugging stubs that come with gdb are set up for a particular chip architecture, but they have no information about the rest of your debugging target machine.
First of all you need to tell the stub how to communicate with the serial port.
int getDebugChar()
getchar
for your target system; a
different name is used to allow you to distinguish the two if you wish.
void putDebugChar(int)
putchar
for your target system; a
different name is used to allow you to distinguish the two if you wish.
If you want gdb to be able to stop your program while it is
running, you need to use an interrupt-driven serial driver, and arrange
for it to stop when it receives a ^C
(‘\003’, the control-C
character). That is the character which gdb uses to tell the
remote system to stop.
Getting the debugging target to return the proper status to gdb
probably requires changes to the standard stub; one quick and dirty way
is to just execute a breakpoint instruction (the “dirty” part is that
gdb reports a SIGTRAP
instead of a SIGINT
).
Other routines you need to supply are:
void exceptionHandler (int
exception_number, void *
exception_address)
For the 386, exception_address should be installed as an interrupt
gate so that interrupts are masked while the handler runs. The gate
should be at privilege level 0 (the most privileged level). The
sparc and 68k stubs are able to mask interrupts themselves without
help from exceptionHandler
.
void flush_i_cache()
On target machines that have instruction caches, gdb requires this function to make certain that the state of your program is stable.
You must also make sure this library routine is available:
void *memset(void *, int, int)
memset
that sets an area of
memory to a known value. If you have one of the free versions of
libc.a
, memset
can be found there; otherwise, you must
either obtain it from your hardware manufacturer, or write your own.
If you do not use the GNU C compiler, you may need other standard library subroutines as well; this varies from one stub to another, but in general the stubs are likely to use any of the common library subroutines which gcc generates as inline code.
In summary, when your program is ready to debug, you must follow these steps.
getDebugChar
,putDebugChar
,flush_i_cache
,memset
,exceptionHandler
.
set_debug_traps(); breakpoint();
On some machines, when a breakpoint trap is raised, the hardware
automatically makes the PC point to the instruction after the
breakpoint. If your machine doesn't do that, you may need to adjust
handle_exception
to arrange for it to return to the instruction
after the breakpoint on this first invocation, so that your program
doesn't keep hitting the initial breakpoint instead of making
progress.
exceptionHook
. Normally you just use:
void (*exceptionHook)() = 0;
but if before calling set_debug_traps
, you set it to point to a
function in your program, that function is called when
gdb continues after stopping on a trap (for example, bus
error). The function indicated by exceptionHook
is called with
one parameter: an int
which is the exception number.
While nearly all gdb commands are available for all native and cross versions of the debugger, there are some exceptions. This chapter describes things that are only available in certain configurations.
There are three major categories of configurations: native configurations, where the host and target are the same, embedded operating system configurations, which are usually the same for several different processor architectures, and bare embedded processors, which are quite different from each other.
This section describes details specific to particular native configurations.
BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
interface that provides a uniform interface for accessing kernel virtual
memory images, including live systems and crash dumps. gdb
uses this interface to allow you to debug live kernels and kernel crash
dumps on many native BSD configurations. This is implemented as a
special kvm
debugging target. For debugging a live system, load
the currently running kernel into gdb and connect to the
kvm
target:
(gdb) target kvm
For debugging crash dumps, provide the file name of the crash dump as an argument:
(gdb) target kvm /var/crash/bsd.0
Once connected to the kvm
target, the following commands are
available:
kvm pcb
kvm proc
Some operating systems provide interfaces to fetch additional
information about running processes beyond memory and per-thread
register state. If gdb is configured for an operating system
with a supported interface, the command info proc
is available
to report information about the process running your program, or about
any process running on your system.
One supported interface is a facility called ‘/proc’ that can be used to examine the image of a running process using file-system subroutines. This facility is supported on gnu/Linux and Solaris systems.
On FreeBSD systems, system control nodes are used to query process information.
In addition, some systems may provide additional process information in core files. Note that a core file may include a subset of the information available from a live process. Process information is currently available from cores created on gnu/Linux and FreeBSD systems.
info proc
info proc
process-idOn some systems, process-id can be of the form
‘[pid]/tid’ which specifies a certain thread ID
within a process. If the optional pid part is missing, it means
a thread from the process being debugged (the leading ‘/’ still
needs to be present, or else gdb will interpret the number as
a process ID rather than a thread ID).
info proc cmdline
info proc cwd
info proc exe
info proc files
This example shows the open file descriptors for a process using a tty for standard input and output as well as two network sockets:
(gdb) info proc files 22136 process 22136 Open files: FD Type Offset Flags Name text file - r-------- /usr/bin/ssh ctty chr - rw------- /dev/pts/20 cwd dir - r-------- /usr/home/john root dir - r-------- / 0 chr 0x32933a4 rw------- /dev/pts/20 1 chr 0x32933a4 rw------- /dev/pts/20 2 chr 0x32933a4 rw------- /dev/pts/20 3 socket 0x0 rw----n-- tcp4 10.0.1.2:53014 -> 10.0.1.10:22 4 socket 0x0 rw------- unix stream:/tmp/ssh-FIt89oAzOn5f/agent.2456
info proc mappings
info proc stat
info proc status
For gnu/Linux systems, see the ‘proc’ man page for more information (type man 5 proc from your shell prompt).
For FreeBSD systems, info proc stat
is an alias for info
proc status
.
info proc all
info proc
subcommands.
set procfs-trace
procfs
API calls.
show procfs-trace
procfs
API call tracing.
set procfs-file
fileprocfs
API trace to the named
file. gdb appends the trace info to the previous
contents of the file. The default is to display the trace on the
standard output.
show procfs-file
procfs
API trace is written.
proc-trace-entry
proc-trace-exit
proc-untrace-entry
proc-untrace-exit
syscall
interface.
info pidlist
info meminfo
djgpp is a port of the gnu development tools to MS-DOS and MS-Windows. djgpp programs are 32-bit protected-mode programs that use the DPMI (DOS Protected-Mode Interface) API to run on top of real-mode DOS systems and their emulations.
gdb supports native debugging of djgpp programs, and defines a few commands specific to the djgpp port. This subsection describes those commands.
info dos
info dos sysinfo
info dos gdt
info dos ldt
info dos idt
A typical djgpp program uses 3 segments: a code segment, a data segment (used for both data and the stack), and a DOS segment (which allows access to DOS/BIOS data structures and absolute addresses in conventional memory). However, the DPMI host will usually define additional segments in order to support the DPMI environment.
These commands allow to display entries from the descriptor tables. Without an argument, all entries from the specified table are displayed. An argument, which should be an integer expression, means display a single entry whose index is given by the argument. For example, here's a convenient way to display information about the debugged program's data segment:
(gdb) info dos ldt $ds
0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)
This comes in handy when you want to see whether a pointer is outside the data segment's limit (i.e. garbled).
info dos pde
info dos pte
Without an argument, info dos pde displays the entire Page Directory, and info dos pte displays all the entries in all of the Page Tables. An argument, an integer expression, given to the info dos pde command means display only that entry from the Page Directory table. An argument given to the info dos pte command means display entries from a single Page Table, the one pointed to by the specified entry in the Page Directory.
These commands are useful when your program uses DMA (Direct Memory Access), which needs physical addresses to program the DMA controller.
These commands are supported only with some DPMI servers.
info dos address-pte
addri
is stored:
(gdb) info dos address-pte __djgpp_base_address + (char *)&i
Page Table entry for address 0x11a00d30:
Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30
This says that i
is stored at offset 0xd30
from the page
whose physical base address is 0x02698000
, and shows all the
attributes of that page.
Note that you must cast the addresses of variables to a char *
,
since otherwise the value of __djgpp_base_address
, the base
address of all variables and functions in a djgpp program, will
be added using the rules of C pointer arithmetics: if i
is
declared an int
, gdb will add 4 times the value of
__djgpp_base_address
to the address of i
.
Here's another example, it displays the Page Table entry for the transfer buffer:
(gdb) info dos address-pte *((unsigned *)&_go32_info_block + 3)
Page Table entry for address 0x29110:
Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110
(The + 3
offset is because the transfer buffer's address is the
3rd member of the _go32_info_block
structure.) The output
clearly shows that this DPMI server maps the addresses in conventional
memory 1:1, i.e. the physical (0x00029000
+ 0x110
) and
linear (0x29110
) addresses are identical.
This command is supported only with some DPMI servers.
In addition to native debugging, the DJGPP port supports remote debugging via a serial data link. The following commands are specific to remote serial debugging in the DJGPP port of gdb.
set com1base
addrset com1irq
irqIRQ
) line to use
for the COM1 serial port.
There are similar commands ‘set com2base’, ‘set com3irq’,
etc. for setting the port address and the IRQ
lines for the
other 3 COM ports.
The related commands ‘show com1base’, ‘show com1irq’ etc.
display the current settings of the base address and the IRQ
lines used by the COM ports.
info serial
gdb supports native debugging of MS Windows programs, including DLLs with and without symbolic debugging information.
MS-Windows programs that call SetConsoleMode
to switch off the
special meaning of the ‘Ctrl-C’ keystroke cannot be interrupted
by typing C-c. For this reason, gdb on MS-Windows
supports C-<BREAK> as an alternative interrupt key
sequence, which can be used to interrupt the debuggee even if it
ignores C-c.
There are various additional Cygwin-specific commands, described in this section. Working with DLLs that have no debugging symbols is described in Non-debug DLL Symbols.
info w32
info w32 selector
GetThreadSelectorEntry
function.
It takes an optional argument that is evaluated to
a long value to give the information about this given selector.
Without argument, this command displays information
about the six segment registers.
info w32 thread-information-block
$fs
selector for 32-bit programs and $gs
for 64-bit programs).
signal-event
idTo use it, create or edit the following keys in
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AeDebug
and/or
HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\AeDebug
(for x86_64 versions):
Debugger
(REG_SZ) — a command to launch the debugger.
Suggested command is: fully-qualified-path-to-gdb.exe -ex
"attach %ld" -ex "signal-event %ld" -ex "continue"
.
The first %ld
will be replaced by the process ID of the
crashing process, the second %ld
will be replaced by the ID of
the event that blocks the crashing process, waiting for gdb
to attach.
Auto
(REG_SZ) — either 1
or 0
. 1
will
make the system run debugger specified by the Debugger key
automatically, 0
will cause a dialog box with “OK” and
“Cancel” buttons to appear, which allows the user to either
terminate the crashing process (OK) or debug it (Cancel).
set cygwin-exceptions
modeon
, gdb will break on exceptions that
happen inside the Cygwin DLL. If mode is off
,
gdb will delay recognition of exceptions, and may ignore some
exceptions which seem to be caused by internal Cygwin DLL
“bookkeeping”. This option is meant primarily for debugging the
Cygwin DLL itself; the default value is off
to avoid annoying
gdb users with false SIGSEGV
signals.
show cygwin-exceptions
set new-console
modeon
the debuggee will
be started in a new console on next start.
If mode is off
, the debuggee will
be started in the same console as the debugger.
show new-console
set new-group
modeshow new-group
set debugevents
OutputDebugString
API call.
set debugexec
set debugexceptions
set debugmemory
set shell
show shell
Very often on windows, some of the DLLs that your program relies on do not include symbolic debugging information (for example, kernel32.dll). When gdb doesn't recognize any debugging symbols in a DLL, it relies on the minimal amount of symbolic information contained in the DLL's export table. This section describes working with such symbols, known internally to gdb as “minimal symbols”.
Note that before the debugged program has started execution, no DLLs will have been loaded. The easiest way around this problem is simply to start the program — either by setting a breakpoint or letting the program run once to completion.
In keeping with the naming conventions used by the Microsoft debugging
tools, DLL export symbols are made available with a prefix based on the
DLL name, for instance KERNEL32!CreateFileA
. The plain name is
also entered into the symbol table, so CreateFileA
is often
sufficient. In some cases there will be name clashes within a program
(particularly if the executable itself includes full debugging symbols)
necessitating the use of the fully qualified name when referring to the
contents of the DLL. Use single-quotes around the name to avoid the
exclamation mark (“!”) being interpreted as a language operator.
Note that the internal name of the DLL may be all upper-case, even
though the file name of the DLL is lower-case, or vice-versa. Since
symbols within gdb are case-sensitive this may cause
some confusion. If in doubt, try the info functions
and
info variables
commands or even maint print msymbols
(see Symbols). Here's an example:
(gdb) info function CreateFileA All functions matching regular expression "CreateFileA": Non-debugging symbols: 0x77e885f4 CreateFileA 0x77e885f4 KERNEL32!CreateFileA
(gdb) info function ! All functions matching regular expression "!": Non-debugging symbols: 0x6100114c cygwin1!__assert 0x61004034 cygwin1!_dll_crt0@0 0x61004240 cygwin1!dll_crt0(per_process *) [etc...]
Symbols extracted from a DLL's export table do not contain very much type information. All that gdb can do is guess whether a symbol refers to a function or variable depending on the linker section that contains the symbol. Also note that the actual contents of the memory contained in a DLL are not available unless the program is running. This means that you cannot examine the contents of a variable or disassemble a function within a DLL without a running program.
Variables are generally treated as pointers and dereferenced automatically. For this reason, it is often necessary to prefix a variable name with the address-of operator (“&”) and provide explicit type information in the command. Here's an example of the type of problem:
(gdb) print 'cygwin1!__argv' 'cygwin1!__argv' has unknown type; cast it to its declared type
(gdb) x 'cygwin1!__argv' 'cygwin1!__argv' has unknown type; cast it to its declared type
And two possible solutions:
(gdb) print ((char **)'cygwin1!__argv')[0] $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
(gdb) x/2x &'cygwin1!__argv' 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000 (gdb) x/x 0x10021608 0x10021608: 0x0022fd98 (gdb) x/s 0x0022fd98 0x22fd98: "/cygdrive/c/mydirectory/myprogram"
Setting a break point within a DLL is possible even before the program starts execution. However, under these circumstances, gdb can't examine the initial instructions of the function in order to skip the function's frame set-up code. You can work around this by using “*&” to set the breakpoint at a raw memory address:
(gdb) break *&'python22!PyOS_Readline' Breakpoint 1 at 0x1e04eff0
The author of these extensions is not entirely convinced that setting a break point within a shared DLL like kernel32.dll is completely safe.
This subsection describes gdb commands specific to the gnu Hurd native debugging.
set signals
set sigs
sigs
is a shorthand alias for
signals
.
show signals
show sigs
set signal-thread
set sigthread
libc
signal
thread. That thread is run when a signal is delivered to a running
process. set sigthread
is the shorthand alias of set
signal-thread
.
show signal-thread
show sigthread
set stopped
SIGSTOP
signal. The stopped process can be
continued by delivering a signal to it.
show stopped
set exceptions
show exceptions
set task pause
set thread default pause on
or set
thread pause on
(see below) to pause individual threads.
show task pause
set task detach-suspend-count
show task detach-suspend-count
set task exception-port
set task excp
set task excp
is a shorthand alias.
set noninvasive
set task pause
, set exceptions
, and
set signals
to values opposite to the defaults.
info send-rights
info receive-rights
info port-rights
info port-sets
info dead-names
info ports
info psets
info ports
for info
port-rights
and info psets
for info port-sets
.
set thread pause
set
task pause off
(see above), this command comes in handy to suspend
only the current thread.
show thread pause
set thread run
show thread run
set thread detach-suspend-count
set thread
takeover-suspend-count
to force it to an absolute value.
show thread detach-suspend-count
set thread exception-port
set thread excp
set task exception-port
(see above).
set thread excp
is the shorthand alias.
set thread takeover-suspend-count
set thread default
show thread default
set thread
commands has a set thread
default
counterpart (e.g., set thread default pause
, set
thread default exception-port
, etc.). The thread default
variety of commands sets the default thread properties for all
threads; you can then change the properties of individual threads with
the non-default commands.
gdb provides the following commands specific to the Darwin target:
set debug darwin
numshow debug darwin
set debug mach-o
numshow debug mach-o
set mach-exceptions on
set mach-exceptions off
show mach-exceptions
When the ABI of a system call is changed in the FreeBSD kernel, this is implemented by leaving a compatibility system call using the old ABI at the existing number and allocating a new system call number for the version using the new ABI. As a convenience, when a system call is caught by name (see catch syscall), compatibility system calls are also caught.
For example, FreeBSD 12 introduced a new variant of the kevent
system call and catching the kevent
system call by name catches
both variants:
(gdb) catch syscall kevent Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560]) (gdb)
This section describes configurations involving the debugging of embedded operating systems that are available for several different architectures.
gdb includes the ability to debug programs running on various real-time operating systems.
Debugging on VxWorks is supported on VxWorks 5.5, all versions of Vworks 6 starting with version 6.4, and VxWorks 653. gdb does not connect directly to the target running VxWorks, but instead relies on the Target Server, which is a process running on the host. The debugger establishes a connection with that process, and sends all debugging comands (resume task execution, read memory, read register, ...) through the Target Server.
Debugging a program on VxWorks 5.5 is performed by connecting to
the Target Server first. To establish this connection, use the
target wtx
command (WTX is the name of the protocol
used to communicate with the Target Server):
target wtx
target-server-nameVxWorks does not have a concept of processes, or even programs, like most Operating Systems do. Instead of running a program, one spawns a task (a.k.a. a thread), usually using a symbol name as the entry point for that thread. Every task created can be regarded as a kernel thread, since it shares memory and code with the rest of the system.
To create a new task under debugger control, use the run
command, passing as the first parameter the name of the symbol
to use as the entry point (all other parameters are ignored):
(gdb) run simple_main [...]
Instead of creating a new task, it is also possible to attach the
debugger to an already existing task, using the attach
command.
The equivalent of the Unix process ID is the task ID on VxWorks, and
these IDs should be used to identify the task that needs to be
debugged.
(gdb) attach 0xf70b0f0 Attaching to task 0xf70b0f0. [...]
As a convenience, GDB allows the use of the task name as a parameter
to the attach
command, in place of the task ID. When a task
name is specified, the first task whose name matches is selected.
If there are more than one tasks with the same name, the selection
process is random.
A list of all tasks currently running on the target can be obtained
using the info wtx threads
command.
info wtx threads
(gdb) info wtx threads 0xf710190 tShell 0xf712430 tWdbTask 0xf715600 tTelnetd [...]
GDB offers several modes for debugging VxWorks tasks:
When debugging in this mode, all Ada tasks controlled by the Ada run-time library are under gdb control, and their execution is automatically stopped or resumed as needed. In particular, when attaching to a task, all associated tasks in the same Ada "program" are automatically stopped and put under debugger control. New tasks being spawned by the Ada "program" are also automatically taken under debugger control.
This mode is specific to Ada programs because it, because it relies on the Ada runtime in order to extract the list of tasks currently running as part of the Ada program.
attach system
command.
To leave System Mode, use detach
.
set multi-tasks-mode [on|off]
on
, activate multi-tasks mode. The default is off
.
This setting should be properly set before using the attach
or run
command. As long as GDB controls the execution of one
or more tasks, attempting to change this setting will result in an
error.
This setting is ignored when debugging in System Mode.
Debugging on VxWorks 653 is very similar to debugging on VxWorks 5, and the commands available for VxWorks 5 are also generally available for VxWorks 653.
The one important distinction is the fact that VxWorks 653 provides the concept of Partitions, as defined by the ARINC 653 specification. These partitions usually have their own address space, and allow the user to make sure that tasks running in one partition cannot affect tasks running on another partition (on VxWorks AE, which is an ancestor of VxWorks 653, these partitions were called Protection Domains, or PD in short). Please refer to your VxWorks 653 manual for more information about the various types of partitions and their use.
info partitions
(gdb) info partitions PD-ID Name * 0x356738 coreOS 0xd799f0 ssl 0xd7ae20 part1 0xd80750 part2
partition
id-or-name(gdb) partition part1 [Switching to Partition part1 (0xd7ae20)] (gdb) partition 0xd80750 [Switching to Partition part2 (0xd80750)]
maintenance info link-path
(gdb) maintenance info link-path Partition Name [Link Path] 0x356738 coreOS [.] 0xd799f0 ssl [.] 0xd7ae20 part1 [.:ssl:ssl] 0xd80750 part2 [.:ssl]
The following Settings are provided:
set wtx tool-name
namegdb
.
show wtx tool-name
set wtx load-timeout
timeoutshow wtx load-timeout
set wtx load-from-gdb
argon
, GDB reads the module, and transmits it to
the target server in order to get it loaded. When set to off
(the default), GDB just sends the module's filename to the target
server, letting the target server read and send the module to
the target. The latter option is significantly faster, but requires
that the target server have file access to the module and that the path
to that module be the same for GDB and the target server. Running
GDB and the target server on the same host ensures that this requirement
is met.
show wtx load-timeout
wtx load-from-gdb
setting.
set wtx stack-size
sizerun
command). This does not affect the stack size
of a task spawned by other tasks, even if those tasks are under debugger
control. The default is 0x10000 bytes.
show wtx stack-size
run
command).
set wtx task-options
valshow wtx task-options
set wtx task-priority
priorityshow wtx task-priority
Some commands are also available to query the Target Server about the system running on the target.
info wtx
info wtx version
(gdb) info wtx WTX protocol version 2
info wtx vxworks-version
(gdb) info wtx vxworks-version VxWorks version 5.5
info wtx target-server
(gdb) info wtx target-server Target agent: version: 2.0 max transfer size in bytes: 1372 available agent modes: 3 Runtime: name: VxWorks version: 5.5 target processor type: 94 has write protect: 0 page size: 4096 endianness: 1234 BSP: Motorola MVME5110-2153 - MPC 7410 boot file: myhost:/path/to/vxWorks target main memory base address: 0 target memory size: 268435456 number of memory regions: 0 target server memory pool base: 0x1ff558 target server memory pool size: 16646314
Some of the information (such as the list of tasks currently running on the system) can only be retrieved by using some of TCL procedures provided by VxWorks. A minimal TCL intepreter is therefore included in GDB.
tcl tcl-command
tcl-command
.
Finally, the following commands may be useful to gdb maintainers wishing to instrument the part of the code in gdb responsible for supporting the WTX protocol.
set wtx debug events
levelshow wtx debug events
set wtx debug objfiles
levelshow wtx debug objfiles
set wtx debug breakpoints
levelshow wtx debug breakpoints
set wtx debug watchpoints
levelshow wtx debug watchpoints
set wtx debug tcl
levelshow wtx debug tcl
Debugging on VxWorks 6 follows the same principles as those for debugging VxWorks 5. The main difference is that gdb needs to connect to a DFW server in addition to the Target Server. The DFW server is another server running on the host (see your VxWorks 6 Manuals for more information about this process).
To start a debugging session, use the target dfw
command.
It will get both DFW and WTX connections established (therefore, do
not use the target wtx
command with VxWorks 6).
The following settings are provided:
set dfw timeout
durationshow dfw timeout
set dfw server-name
namedfw
; if only one DFW server is
registered in the registry, GDB will connect to this server by
default.
show dfw server-name
The following commands may be useful to gdb maintainers wishing to instrument the part of the code in gdb responsible for supporting the DFW protocol.
dfw send
set dfw debug requests
set dfw debug requests on
set dfw debug requests off
show dfw debug requests
set dfw debug responses
set dfw debug responses on
set dfw debug responses off
show dfw debug responses
set dfw debug unknown-identifiers
set dfw debug unknown-identifiers on
set dfw debug unknown-identifiers off
show dfw debug unknown-identifiers
Unlike most Operating Systems, the loading of modules in memory has to be performed manually by the user. Modules can be a self-contained program, or just part of a program consisting of multiple modules (this is similar to programs depending on shared libraries).
To load a new module on the target, use the load
command.
In addition to loading the module on the target, the debugger will
also load its symbol table and debugging information.
Modules may also be unloaded at any time, using the unload
command.
wtx add-symbol-file
fileadd-symbol-file
command, except
that it does not require base addresses to be provided. Instead,
these addresses are automatically computed based on some information
provided by the Target Server.
This command is normally rarely needed, since GDB should automatically load the symbols from all modules either when connecting to the target, or when the module is loaded on the target. But this may become useful when the module fullpath provided by the target server does not correspond to the module's fullpath on the host where GDB is running.
This section goes into details specific to particular embedded configurations.
Whenever a specific embedded processor has a simulator, gdb allows to send an arbitrary command to the simulator.
sim
commandgdb provides the following ARC-specific commands:
set debug arc
show debug arc
maint print arc arc-instruction
addressgdb provides the following ARM-specific commands:
set arm disassembler
"std"
style is the standard style.
show arm disassembler
set arm apcs32
show arm apcs32
set arm fpu
fputypeauto
softfpa
fpa
softvfp
vfp
show arm fpu
set arm abi
show arm abi
set arm fallback-mode (arm|thumb|auto)
T
bit in the CPSR
register).
show arm fallback-mode
set arm force-mode (arm|thumb|auto)
show arm force-mode
set debug arm
show debug arm
target sim
[simargs] ...
--swi-support=
typeall
.
none
demon
angel
redboot
all
The Motorola m68k configuration includes ColdFire support.
The MicroBlaze is a soft-core processor supported on various Xilinx
FPGAs, such as Spartan or Virtex series. Boards with these processors
usually have JTAG ports which connect to a host system running the Xilinx
Embedded Development Kit (EDK) or Software Development Kit (SDK).
This host system is used to download the configuration bitstream to
the target FPGA. The Xilinx Microprocessor Debugger (XMD) program
communicates with the target board using the JTAG interface and
presents a gdbserver
interface to the board. By default
xmd
uses port 1234
. (While it is possible to change
this default port, it requires the use of undocumented xmd
commands. Contact Xilinx support if you need to do this.)
Use these GDB commands to connect to the MicroBlaze target processor.
target remote :1234
xmd
.
target remote
xmd-host:1234
xmd
running on a different system named xmd-host.
load
set debug microblaze
nshow debug microblaze
ngdb supports these special commands for MIPS targets:
set mipsfpu double
set mipsfpu single
set mipsfpu none
set mipsfpu auto
show mipsfpu
In previous versions the only choices were double precision or no floating point, so ‘set mipsfpu on’ will select double precision and ‘set mipsfpu off’ will select no floating point.
As usual, you can inquire about the mipsfpu
variable with
‘show mipsfpu’.
The OpenRISC 1000 provides a free RISC instruction set architecture. It is mainly provided as a soft-core which can run on Xilinx, Altera and other FPGA's.
gdb for OpenRISC supports the below commands when connecting to a target:
target sim
Example: target sim
set debug or1k
show debug or1k
gdb supports using the DVC (Data Value Compare) register to implement in hardware simple hardware watchpoint conditions of the form:
(gdb) watch ADDRESS|VARIABLE \ if ADDRESS|VARIABLE == CONSTANT EXPRESSION
The DVC register will be automatically used when gdb detects
such pattern in a condition expression, and the created watchpoint uses one
debug register (either the exact-watchpoints
option is on and the
variable is scalar, or the variable has a length of one byte). This feature
is available in native gdb running on a Linux kernel version 2.6.34
or newer.
When running on PowerPC embedded processors, gdb automatically uses
ranged hardware watchpoints, unless the exact-watchpoints
option is on,
in which case watchpoints using only one debug register are created when
watching variables of scalar types.
You can create an artificial array to watch an arbitrary memory region using one of the following commands (see Expressions):
(gdb) watch *((char *) address)@length (gdb) watch {char[length]} address
PowerPC embedded processors support masked watchpoints. See the discussion
about the mask
argument in Set Watchpoints.
PowerPC embedded processors support hardware accelerated
ranged breakpoints. A ranged breakpoint stops execution of
the inferior whenever it executes an instruction at any address within
the range it specifies. To set a ranged breakpoint in gdb,
use the break-range
command.
gdb provides the following PowerPC-specific commands:
break-range
start-location,
end-locationset powerpc soft-float
show powerpc soft-float
set powerpc vector-abi
show powerpc vector-abi
set powerpc exact-watchpoints
show powerpc exact-watchpoints
When configured for debugging the Atmel AVR, gdb supports the following AVR-specific commands:
info io_registers
When configured for debugging CRIS, gdb provides the following CRIS-specific commands:
set cris-version
vershow cris-version
set cris-dwarf2-cfi
gcc-cris
whose version is below
R59
.
show cris-dwarf2-cfi
set cris-mode
modeshow cris-mode
For the Renesas Super-H processor, gdb provides these commands:
set sh calling-convention
conventionshow sh calling-convention
This section describes characteristics of architectures that affect all uses of gdb with the architecture, both native and cross.
When gdb is debugging the AArch64 architecture, it provides the following special commands:
set debug aarch64
show debug aarch64
When gdb is debugging the AArch64 architecture, if the Scalable Vector
Extension (SVE) is present, then gdb will provide the vector registers
$z0
through $z31
, vector predicate registers $p0
through
$p15
, and the $ffr
register. In addition, the pseudo register
$vg
will be provided. This is the vector granule for the current thread
and represents the number of 64-bit chunks in an SVE z
register.
If the vector length changes, then the $vg
register will be updated,
but the lengths of the z
and p
registers will not change. This
is a known limitation of gdb and does not affect the execution of the
target process.
When gdb is debugging the AArch64 architecture, and the program is
using the v8.3-A feature Pointer Authentication (PAC), then whenever the link
register $lr
is pointing to an PAC function its value will be masked.
When GDB prints a backtrace, any addresses that required unmasking will be
postfixed with the marker [PAC]. When using the MI, this is printed as part
of the addr_flags
field.
set struct-convention
modestruct
s and
union
s from functions to mode. Possible values of
mode are "pcc"
, "reg"
, and "default"
(the
default). "default"
or "pcc"
means that struct
s
are returned on the stack, while "reg"
means that a
struct
or a union
whose size is 1, 2, 4, or 8 bytes will
be returned in a register.
show struct-convention
struct
s
from functions.
Memory Protection Extension (MPX) adds the bound registers ‘BND0’ 16 through ‘BND3’. Bound registers store a pair of 64-bit values which are the lower bound and upper bound. Bounds are effective addresses or memory locations. The upper bounds are architecturally represented in 1's complement form. A bound having lower bound = 0, and upper bound = 0 (1's complement of all bits set) will allow access to the entire address space.
‘BND0’ through ‘BND3’ are represented in gdb as ‘bnd0raw’
through ‘bnd3raw’. Pseudo registers ‘bnd0’ through ‘bnd3’
display the upper bound performing the complement of one operation on the
upper bound value, i.e. when upper bound in ‘bnd0raw’ is 0 in the
gdb ‘bnd0’ it will be 0xfff...
. In this sense it
can also be noted that the upper bounds are inclusive.
As an example, assume that the register BND0 holds bounds for a pointer having access allowed for the range between 0x32 and 0x71. The values present on bnd0raw and bnd registers are presented as follows:
bnd0raw = {0x32, 0xffffffff8e} bnd0 = {lbound = 0x32, ubound = 0x71} : size 64
This way the raw value can be accessed via bnd0raw...bnd3raw. Any change on bnd0...bnd3 or bnd0raw...bnd3raw is reflect on its counterpart. When the bnd0...bnd3 registers are displayed via Python, the display includes the memory size, in bits, accessible to the pointer.
Bounds can also be stored in bounds tables, which are stored in application memory. These tables store bounds for pointers by specifying the bounds pointer's value along with its bounds. Evaluating and changing bounds located in bound tables is therefore interesting while investigating bugs on MPX context. gdb provides commands for this purpose:
show mpx bound
pointerset mpx bound
pointer,
lbound,
uboundWhen you call an inferior function on an Intel MPX enabled program, GDB sets the inferior's bound registers to the init (disabled) state before calling the function. As a consequence, bounds checks for the pointer arguments passed to the function will always pass.
This is necessary because when you call an inferior function, the program is usually in the middle of the execution of other function. Since at that point bound registers are in an arbitrary state, not clearing them would lead to random bound violations in the called function.
You can still examine the influence of the bound registers on the execution of the called function by stopping the execution of the called function at its prologue, setting bound registers, and continuing the execution. For example:
$ break *upper Breakpoint 2 at 0x4009de: file i386-mpx-call.c, line 47. $ print upper (a, b, c, d, 1) Breakpoint 2, upper (a=0x0, b=0x6e0000005b, c=0x0, d=0x0, len=48).... $ print $bnd0 {lbound = 0x0, ubound = ffffffff} : size -1
At this last step the value of bnd0 can be changed for investigation of bound violations caused along the execution of the call. In order to know how to set the bound registers or bound table for the call consult the ABI.
See the following section.
Alpha- and MIPS-based computers use an unusual stack frame, which sometimes requires gdb to search backward in the object code to find the beginning of a function.
To improve response time (especially for embedded applications, where gdb may be restricted to a slow serial line for this search) you may want to limit the size of this search, using one of these commands:
set heuristic-fence-post
limitheuristic-fence-post
must search
and therefore the longer it takes to run. You should only need to use
this command when debugging a stripped executable.
show heuristic-fence-post
These commands are available only when gdb is configured for debugging programs on Alpha or MIPS processors.
Several MIPS-specific commands are available when debugging MIPS programs:
set mips abi
argshow mips abi
set mips compression
argPossible values of arg are ‘mips16’ and ‘micromips’. The default compressed ISA encoding is ‘mips16’, as executables containing MIPS16 code frequently are not identified as such.
This setting is “sticky”; that is, it retains its value across debugging sessions until reset either explicitly with this command or implicitly from an executable.
The compiler and/or assembler typically add symbol table annotations to
identify functions compiled for the MIPS16 or
microMIPS ISAs. If these function-scope annotations
are present, gdb uses them in preference to the global
compressed ISA encoding setting.
show mips compression
set mipsfpu
show mipsfpu
set mips mask-address
argshow mips mask-address
set remote-mips64-transfers-32bit-regs
show remote-mips64-transfers-32bit-regs
set debug mips
show debug mips
When gdb is debugging the HP PA architecture, it provides the following special commands:
set debug hppa
show debug hppa
maint print unwind
address
When gdb is debugging the PowerPC architecture, it provides a set of
pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point
numbers stored in the floating point registers. These values must be stored
in two consecutive registers, always starting at an even register like
f0
or f2
.
The pseudo-registers go from $dl0
through $dl15
, and are formed
by joining the even/odd register pairs f0
and f1
for $dl0
,
f2
and f3
for $dl1
and so on.
For POWER7 processors, gdb provides a set of pseudo-registers, the 64-bit wide Extended Floating Point Registers (‘f32’ through ‘f63’).
When gdb is debugging the Nios II architecture, it provides the following special commands:
set debug nios2
show debug nios2
The M7 processor supports an Application Data Integrity (ADI) feature that detects invalid data accesses. When software allocates memory and enables ADI on the allocated memory, it chooses a 4-bit version number, sets the version in the upper 4 bits of the 64-bit pointer to that data, and stores the 4-bit version in every cacheline of that data. Hardware saves the latter in spare bits in the cache and memory hierarchy. On each load and store, the processor compares the upper 4 VA (virtual address) bits to the cacheline's version. If there is a mismatch, the processor generates a version mismatch trap which can be either precise or disrupting. The trap is an error condition which the kernel delivers to the process as a SIGSEGV signal.
Note that only 64-bit applications can use ADI and need to be built with ADI-enabled.
Values of the ADI version tags, which are in granularity of a cacheline (64 bytes), can be viewed or modified.
adi (examine | x) [ /
n ]
addradi examine
command displays the value of one ADI version tag per
cacheline.
n is a decimal integer specifying the number in bytes; the default is 1. It specifies how much ADI version information, at the ratio of 1:ADI block size, to display.
addr is the address in user address space where you want gdb to begin displaying the ADI version tags.
Below is an example of displaying ADI versions of variable "shmaddr".
(gdb) adi x/100 shmaddr 0xfff800010002c000: 0 0
adi (assign | a) [ /
n ]
addr =
tagadi assign
command is used to assign new ADI version tag
to an address.
n is a decimal integer specifying the number in bytes; the default is 1. It specifies how much ADI version information, at the ratio of 1:ADI block size, to modify.
addr is the address in user address space where you want gdb to begin modifying the ADI version tags.
tag is the new ADI version tag.
For example, do the following to modify then verify ADI versions of variable "shmaddr":
(gdb) adi a/100 shmaddr = 7 (gdb) adi x/100 shmaddr 0xfff800010002c000: 7 7
When gdb is debugging the S12Z architecture, it provides the following special command:
maint info bdccsr
You can alter the way gdb interacts with you by using the
set
command. For commands controlling how gdb displays
data, see Print Settings. Other settings are
described here.
gdb indicates its readiness to read a command by printing a string
called the prompt. This string is normally ‘(gdb)’. You
can change the prompt string with the set prompt
command. For
instance, when debugging gdb with gdb, it is useful to change
the prompt in one of the gdb sessions so that you can always tell
which one you are talking to.
Note: set prompt
does not add a space for you after the
prompt you set. This allows you to set a prompt which ends in a space
or a prompt that does not.
set prompt
newpromptshow prompt
Versions of gdb that ship with Python scripting enabled have prompt extensions. The commands for interacting with these extensions are:
set extended-prompt
promptFor example:
set extended-prompt Current working directory: \w (gdb)
Note that when an extended-prompt is set, it takes control of the prompt_hook hook. See prompt_hook, for further information.
show extended-prompt
set extended-prompt
, are replaced with the
corresponding strings each time the prompt is displayed.
gdb reads its input commands via the Readline interface. This
gnu library provides consistent behavior for programs which provide a
command line interface to the user. Advantages are gnu Emacs-style
or vi-style inline editing of commands, csh
-like history
substitution, and a storage and recall of command history across
debugging sessions.
You may control the behavior of command line editing in gdb with the
command set
.
set editing
set editing on
set editing off
show editing
See Command Line Editing,
for more details about the Readline
interface. Users unfamiliar with gnu Emacs or vi
are
encouraged to read that chapter.
gdb sets the Readline application name to ‘gdb’. This is useful for conditions in .inputrc.
gdb defines a bindable Readline command,
operate-and-get-next
. This is bound to C-o by default.
This command accepts the current line for execution and fetches the
next line relative to the current line from the history for editing.
Any argument is ignored.
gdb can keep track of the commands you type during your debugging sessions, so that you can be certain of precisely what happened. Use these commands to manage the gdb command history facility.
gdb uses the gnu History library, a part of the Readline package, to provide the history facility. See Using History Interactively, for the detailed description of the History library.
To issue a command to gdb without affecting certain aspects of the state which is seen by users, prefix it with ‘server ’ (see Server Prefix). This means that this command will not affect the command history, nor will it affect gdb's notion of which command to repeat if <RET> is pressed on a line by itself.
The server prefix does not affect the recording of values into the value
history; to print a value without recording it into the value history,
use the output
command instead of the print
command.
Here is the description of gdb commands related to command history.
set history filename
fnameGDBHISTFILE
, or to
./.gdb_history (./_gdb_history on MS-DOS) if this variable
is not set.
set history save
set history save on
set history filename
command. By default, this option is disabled.
set history save off
set history size
sizeset history size unlimited
unlimited
or if GDBHISTSIZE is
either a negative number or the empty string, then the number of commands
gdb keeps in the history list is unlimited.
set history remove-duplicates
countset history remove-duplicates unlimited
unlimited
then this lookbehind is unbounded. If count is 0, then
removal of duplicate history entries is disabled.
Only history entries added during the current session are considered for removal. This option is set to 0 by default.
History expansion assigns special meaning to the character !. See Event Designators, for more details.
Since ! is also the logical not operator in C, history expansion
is off by default. If you decide to enable history expansion with the
set history expansion on
command, you may sometimes need to
follow ! (when it is used as logical not, in an expression) with
a space or a tab to prevent it from being expanded. The readline
history facilities do not attempt substitution on the strings
!= and !(, even when history expansion is enabled.
The commands to control history expansion are:
set history expansion on
set history expansion
set history expansion off
show history
show history filename
show history save
show history size
show history expansion
show history
by itself displays all four states.
show commands
show commands
nshow commands +
Certain commands to gdb may produce large amounts of information output to the screen. To help you read all of it, gdb pauses and asks you for input at the end of each page of output. Type <RET> when you want to see one more page of output, q to discard the remaining output, or c to continue without paging for the rest of the current command. Also, the screen width setting determines when to wrap lines of output. Depending on what is being printed, gdb tries to break the line at a readable place, rather than simply letting it overflow onto the following line.
Normally gdb knows the size of the screen from the terminal
driver software. For example, on Unix gdb uses the termcap data base
together with the value of the TERM
environment variable and the
stty rows
and stty cols
settings. If this is not correct,
you can override it with the set height
and set
width
commands:
set height
lppset height unlimited
show height
set width
cplset width unlimited
show width
set
commands specify a screen height of lpp lines and
a screen width of cpl characters. The associated show
commands display the current settings.
If you specify a height of either unlimited
or zero lines,
gdb does not pause during output no matter how long the
output is. This is useful if output is to a file or to an editor
buffer.
Likewise, you can specify ‘set width unlimited’ or ‘set
width 0’ to prevent gdb from wrapping its output.
set pagination on
set pagination off
set height unlimited
. Note that
running gdb with the --batch option (see -batch) also automatically disables pagination.
show pagination
gdb can style its output on a capable terminal. This is enabled by default on most systems, but disabled by default when in batch mode (see Mode Options). Various style settings are available; and styles can also be disabled entirely.
set style enabled ‘
on|off’
show style enabled
set style sources ‘
on|off’
list
command, is styled. Note
that source styling only works if styling in general is enabled, and
if gdb was linked with the GNU Source Highlight library. The
default is ‘on’.
show style sources
Subcommands of set style
control specific forms of styling.
These subcommands all follow the same pattern: each style-able object
can be styled with a foreground color, a background color, and an
intensity.
For example, the style of file names can be controlled using the
set style filename
group of commands:
set style filename background
colorset style filename foreground
colorset style filename intensity
valueThe show style
command and its subcommands are styling
a style name in their output using its own style.
So, use show style to see the complete list of styles,
their characteristics and the visual aspect of each style.
The style-able objects are:
filename
function
set style function
family of commands. By default, this
style's foreground color is yellow.
variable
set style variable
family of commands. By default, this style's
foreground color is cyan.
address
set style address
family of commands. By default, this style's
foreground color is blue.
title
set style title
family of commands. By default, this style's
intensity is bold. Commands are using the title style to improve
the readability of large output. For example, the commands
apropos and help are using the title style
for the command names.
highlight
set style highlight
family of commands. By default, this style's
foreground color is red. Commands are using the highlight style to draw
the user attention to some specific parts of their output. For example,
the command apropos -v REGEXP uses the highlight style to
mark the documentation parts matching regexp.
tui-border
set style
. This was done for compatibility reasons, as TUI
controls to set the border's intensity predated the addition of
general styling to gdb. See TUI Configuration.
tui-active-border
You can always enter numbers in octal, decimal, or hexadecimal in gdb by the usual conventions: octal numbers begin with ‘0’, decimal numbers end with ‘.’, and hexadecimal numbers begin with ‘0x’. Numbers that neither begin with ‘0’ or ‘0x’, nor end with a ‘.’ are, by default, entered in base 10; likewise, the default display for numbers—when no particular format is specified—is base 10. You can change the default base for both input and output with the commands described below.
set input-radix
baseset input-radix 012 set input-radix 10. set input-radix 0xa
sets the input base to decimal. On the other hand, ‘set input-radix 10’ leaves the input radix unchanged, no matter what it was, since ‘10’, being without any leading or trailing signs of its base, is interpreted in the current radix. Thus, if the current radix is 16, ‘10’ is interpreted in hex, i.e. as 16 decimal, which doesn't change the radix.
set output-radix
baseshow input-radix
show output-radix
set radix
[base]show radix
set radix
sets the radix of input and output to
the same base; without an argument, it resets the radix back to its
default value of 10.
gdb can determine the ABI (Application Binary Interface) of your application automatically. However, sometimes you need to override its conclusions. Use these commands to manage gdb's view of the current ABI.
One gdb configuration can debug binaries for multiple operating
system targets, either via remote debugging or native emulation.
gdb will autodetect the OS ABI (Operating System ABI) in use,
but you can override its conclusion using the set osabi
command.
One example where this is useful is in debugging of binaries which use
an alternate C library (e.g. uClibc for gnu/Linux) which does
not have the same identifying marks that the standard C library for your
platform provides.
When gdb is debugging the AArch64 architecture, it provides a
“Newlib” OS ABI. This is useful for handling setjmp
and
longjmp
when debugging binaries that use the newlib C library.
The “Newlib” OS ABI can be selected by set osabi Newlib
.
show osabi
set osabi
set osabi
abi
Generally, the way that an argument of type float
is passed to a
function depends on whether the function is prototyped. For a prototyped
(i.e. ANSI/ISO style) function, float
arguments are passed unchanged,
according to the architecture's convention for float
. For unprototyped
(i.e. K&R style) functions, float
arguments are first promoted to type
double
and then passed.
Unfortunately, some forms of debug information do not reliably indicate whether a function is prototyped. If gdb calls a function that is not marked as prototyped, it consults set coerce-float-to-double.
set coerce-float-to-double
set coerce-float-to-double on
float
will be promoted to double
when passed
to an unprototyped function. This is the default setting.
set coerce-float-to-double off
float
will be passed directly to unprototyped
functions.
show coerce-float-to-double
float
to double
.
gdb needs to know the ABI used for your program's C++
objects. The correct C++ ABI depends on which C++ compiler was
used to build your application. gdb only fully supports
programs with a single C++ ABI; if your program contains code using
multiple C++ ABI's or if gdb can not identify your
program's ABI correctly, you can tell gdb which ABI to use.
Currently supported ABI's include “gnu-v2”, for g++
versions
before 3.0, “gnu-v3”, for g++
versions 3.0 and later, and
“hpaCC” for the HP ANSI C++ compiler. Other C++ compilers may
use the “gnu-v2” or “gnu-v3” ABI's as well. The default setting is
“auto”.
show cp-abi
set cp-abi
set cp-abi
abiset cp-abi auto
gdb sometimes reads files with commands and settings automatically, without being explicitly told so by the user. We call this feature auto-loading. While auto-loading is useful for automatically adapting gdb to the needs of your project, it can sometimes produce unexpected results or introduce security risks (e.g., if the file comes from untrusted sources).
There are various kinds of files gdb can automatically load. In addition to these files, gdb supports auto-loading code written in various extension languages. See Auto-loading extensions.
Note that loading of these associated files (including the local .gdbinit
file) requires accordingly configured auto-load safe-path
(see Auto-loading safe path).
For these reasons, gdb includes commands and options to let you control when to auto-load files and which files should be auto-loaded.
set auto-load off
$ gdb -iex "set auto-load off" untrusted-executable corefile
Be aware that system init file (see System-wide configuration)
and init files from your home directory (see Home Directory Init File)
still get read (as they come from generally trusted directories).
To prevent gdb from auto-loading even those init files, use the
-nx option (see Mode Options), in addition to
set auto-load no
.
show auto-load
(gdb) show auto-load gdb-scripts: Auto-loading of canned sequences of commands scripts is on. libthread-db: Auto-loading of inferior specific libthread_db is on. local-gdbinit: Auto-loading of .gdbinit script from current directory is on. python-scripts: Auto-loading of Python scripts is on. safe-path: List of directories from which it is safe to auto-load files is $debugdir:$datadir/auto-load. scripts-directory: List of directories from which to load auto-loaded scripts is $debugdir:$datadir/auto-load.
info auto-load
(gdb) info auto-load gdb-scripts: Loaded Script Yes /home/user/gdb/gdb-gdb.gdb libthread-db: No auto-loaded libthread-db. local-gdbinit: Local .gdbinit file "/home/user/gdb/.gdbinit" has been loaded. python-scripts: Loaded Script Yes /home/user/gdb/gdb-gdb.py
These are gdb control commands for the auto-loading:
See set auto-load off. | Disable auto-loading globally.
|
See show auto-load. | Show setting of all kinds of files.
|
See info auto-load. | Show state of all kinds of files.
|
See set auto-load gdb-scripts. | Control for gdb command scripts.
|
See show auto-load gdb-scripts. | Show setting of gdb command scripts.
|
See info auto-load gdb-scripts. | Show state of gdb command scripts.
|
See set auto-load python-scripts. | Control for gdb Python scripts.
|
See show auto-load python-scripts. | Show setting of gdb Python scripts.
|
See info auto-load python-scripts. | Show state of gdb Python scripts.
|
See set auto-load guile-scripts. | Control for gdb Guile scripts.
|
See show auto-load guile-scripts. | Show setting of gdb Guile scripts.
|
See info auto-load guile-scripts. | Show state of gdb Guile scripts.
|
See set auto-load scripts-directory. | Control for gdb auto-loaded scripts location.
|
See show auto-load scripts-directory. | Show gdb auto-loaded scripts location.
|
See add-auto-load-scripts-directory. | Add directory for auto-loaded scripts location list.
|
See set auto-load local-gdbinit. | Control for init file in the current directory.
|
See show auto-load local-gdbinit. | Show setting of init file in the current directory.
|
See info auto-load local-gdbinit. | Show state of init file in the current directory.
|
See set auto-load libthread-db. | Control for thread debugging library.
|
See show auto-load libthread-db. | Show setting of thread debugging library.
|
See info auto-load libthread-db. | Show state of thread debugging library.
|
See set auto-load safe-path. | Control directories trusted for automatic loading.
|
See show auto-load safe-path. | Show directories trusted for automatic loading.
|
See add-auto-load-safe-path. | Add directory trusted for automatic loading.
|
By default, gdb reads and executes the canned sequences of commands from init file (if any) in the current working directory, see Init File in the Current Directory during Startup.
Note that loading of this local .gdbinit file also requires accordingly
configured auto-load safe-path
(see Auto-loading safe path).
set auto-load local-gdbinit [on|off]
show auto-load local-gdbinit
info auto-load local-gdbinit
This feature is currently present only on gnu/Linux native hosts.
gdb reads in some cases thread debugging library from places specific to the inferior (see set libthread-db-search-path).
The special ‘libthread-db-search-path’ entry ‘$sdir’ is processed without checking this ‘set auto-load libthread-db’ switch as system libraries have to be trusted in general. In all other cases of ‘libthread-db-search-path’ entries gdb checks first if ‘set auto-load libthread-db’ is enabled before trying to open such thread debugging library.
Note that loading of this debugging library also requires accordingly configured
auto-load safe-path
(see Auto-loading safe path).
set auto-load libthread-db [on|off]
show auto-load libthread-db
info auto-load libthread-db
As the files of inferior can come from untrusted source (such as submitted by an application user) gdb does not always load any files automatically. gdb provides the ‘set auto-load safe-path’ setting to list directories trusted for loading files not explicitly requested by user. Each directory can also be a shell wildcard pattern.
If the path is not set properly you will see a warning and the file will not get loaded:
$ ./gdb -q ./gdb Reading symbols from /home/user/gdb/gdb...done. warning: File "/home/user/gdb/gdb-gdb.gdb" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load". warning: File "/home/user/gdb/gdb-gdb.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
To instruct gdb to go ahead and use the init files anyway, invoke gdb like this:
$ gdb -q -iex "set auto-load safe-path /home/user/gdb" ./gdb
The list of trusted directories is controlled by the following commands:
set auto-load safe-path
[directories]FNM_PATHNAME
for system function fnmatch
(see fnmatch).
If you omit directories, ‘auto-load safe-path’ will be reset to
its default value as specified during gdb compilation.
The list of directories uses path separator (‘:’ on GNU and Unix systems, ‘;’ on MS-Windows and MS-DOS) to separate directories, similarly to the PATH environment variable.
show auto-load safe-path
add-auto-load-safe-path
This variable defaults to what --with-auto-load-dir
has been configured
to (see with-auto-load-dir). $debugdir and $datadir
substitution applies the same as for set auto-load scripts-directory.
The default set auto-load safe-path
value can be also overriden by
gdb configuration option --with-auto-load-safe-path.
Setting this variable to / disables this security protection, corresponding gdb configuration option is --without-auto-load-safe-path. This variable is supposed to be set to the system directories writable by the system superuser only. Users can add their source directories in init files in their home directories (see Home Directory Init File). See also deprecated init file in the current directory (see Init File in the Current Directory during Startup).
To force gdb to load the files it declined to load in the previous example, you could use one of the following ways:
On the other hand you can also explicitly forbid automatic files loading which also suppresses any such warning messages:
This setting applies to the file names as entered by user. If no entry matches gdb tries as a last resort to also resolve all the file names into their canonical form (typically resolving symbolic links) and compare the entries again. gdb already canonicalizes most of the filenames on its own before starting the comparison so a canonical form of directories is recommended to be entered.
For better visibility of all the file locations where you can place scripts to be auto-loaded with inferior — or to protect yourself against accidental execution of untrusted scripts — gdb provides a feature for printing all the files attempted to be loaded. Both existing and non-existing files may be printed.
For example the list of directories from which it is safe to auto-load files (see Auto-loading safe path) applies also to canonicalized filenames which may not be too obvious while setting it up.
(gdb) set debug auto-load on (gdb) file ~/src/t/true auto-load: Loading canned sequences of commands script "/tmp/true-gdb.gdb" for objfile "/tmp/true". auto-load: Updating directories of "/usr:/opt". auto-load: Using directory "/usr". auto-load: Using directory "/opt". warning: File "/tmp/true-gdb.gdb" auto-loading has been declined by your `auto-load safe-path' set to "/usr:/opt".
set debug auto-load [on|off]
show debug auto-load
By default, gdb is silent about its inner workings. If you are
running on a slow machine, you may want to use the set verbose
command. This makes gdb tell you when it does a lengthy
internal operation, so you will not think it has crashed.
Currently, the messages controlled by set verbose
are those
which announce that the symbol table for a source file is being read;
see symbol-file
in Commands to Specify Files.
set verbose on
set verbose off
show verbose
set verbose
is on or off.
By default, if gdb encounters bugs in the symbol table of an object file, it is silent; but if you are debugging a compiler, you may find this information useful (see Errors Reading Symbol Files).
set complaints
limitshow complaints
By default, gdb is cautious, and asks what sometimes seems to be a lot of stupid questions to confirm certain commands. For example, if you try to run a program which is already running:
(gdb) run The program being debugged has been started already. Start it from the beginning? (y or n)
If you are willing to unflinchingly face the consequences of your own commands, you can disable this “feature”:
set confirm off
set confirm on
show confirm
If you need to debug user-defined commands or sourced files you may find it useful to enable command tracing. In this mode each command will be printed as it is executed, prefixed with one or more ‘+’ symbols, the quantity denoting the call depth of each command.
set trace-commands on
set trace-commands off
show trace-commands
gdb has commands that enable optional debugging messages from various gdb subsystems; normally these commands are of interest to gdb maintainers, or when reporting a bug. This section documents those commands.
set exec-done-display
show exec-done-display
set debug aarch64
show debug aarch64
set debug arch
show debug arch
set debug aix-solib
show debug aix-thread
set debug aix-thread
show debug aix-thread
set debug check-physname
show debug check-physname
set debug coff-pe-read
show debug coff-pe-read
set debug dwarf-die
show debug dwarf-die
set debug dwarf-line
show debug dwarf-line
set debug dwarf-read
show debug dwarf-read
set debug displaced
show debug displaced
set debug event
show debug event
set debug expression
show debug expression
set debug fbsd-lwp
show debug fbsd-lwp
set debug fbsd-nat
show debug fbsd-nat
set debug frame
show debug frame
set debug gnu-nat
show debug gnu-nat
set debug infrun
show debug infrun
set debug jit
show debug jit
set debug lin-lwp
show debug lin-lwp
set debug linux-namespaces
show debug linux-namespaces
set debug mach-o
show debug mach-o
set debug notification
show debug notification
set debug observer
show debug observer
set debug overload
show debug overload
set debug parser
yydebug
variable in the expression
parser. See Tracing Your Parser, for
details. The default is off.
show debug parser
set debug remote
show debug remote
set debug remote-packet-max-chars
set debug remote
is on. This is useful to prevent gdb from
displaying lengthy remote packets and polluting the console.
The default value is 512
, which means gdb will truncate each
remote packet after 512 bytes.
Setting this option to unlimited
will disable truncation and will output
the full length of the remote packets.
show debug remote-packet-max-chars
set debug separate-debug-file
show debug separate-debug-file
set debug serial
show debug serial
set debug solib-frv
show debug solib-frv
set debug symbol-lookup
show debug symbol-lookup
set debug symfile
show debug symfile
set debug symtab-create
show debug symtab-create
set debug target
show debug target
set debug timestamp
show debug timestamp
set debug varobj
show debug varobj
set debug xml
show debug xml
set interactive-mode
on
, forces gdb to assume that GDB was started
in a terminal. In practice, this means that gdb should wait
for the user to answer queries generated by commands entered at
the command prompt. If off
, forces gdb to operate
in the opposite mode, and it uses the default answers to all queries.
If auto
(the default), gdb tries to determine whether
its standard input is a terminal, and works in interactive-mode if it
is, non-interactively otherwise.
In the vast majority of cases, the debugger should be able to guess correctly which mode should be used. But this setting can be useful in certain specific cases, such as running a MinGW gdb inside a cygwin window.
show interactive-mode
gdb provides several mechanisms for extension. gdb also provides the ability to automatically load extensions when it reads a file for debugging. This allows the user to automatically customize gdb for the program being debugged.
To facilitate the use of extension languages, gdb is capable of evaluating the contents of a file. When doing so, gdb can recognize which extension language is being used by looking at the filename extension. Files with an unrecognized filename extension are always treated as a gdb Command Files. See Command files.
You can control how gdb evaluates these files with the following setting:
set script-extension off
set script-extension soft
set script-extension strict
show script-extension
script-extension
option.
Aside from breakpoint commands (see Breakpoint Command Lists), gdb provides two ways to store sequences of commands for execution as a unit: user-defined commands and command files.
A user-defined command is a sequence of gdb commands to
which you assign a new name as a command. This is done with the
define
command. User commands may accept an unlimited number of arguments
separated by whitespace. Arguments are accessed within the user command
via $arg0...$argN
. A trivial example:
define adder print $arg0 + $arg1 + $arg2 end
To execute the command use:
adder 1 2 3
This defines the command adder
, which prints the sum of
its three arguments. Note the arguments are text substitutions, so they may
reference variables, use complex expressions, or even perform inferior
functions calls.
In addition, $argc
may be used to find out how many arguments have
been passed.
define adder if $argc == 2 print $arg0 + $arg1 end if $argc == 3 print $arg0 + $arg1 + $arg2 end end
Combining with the eval
command (see eval) makes it easier
to process a variable number of arguments:
define adder set $i = 0 set $sum = 0 while $i < $argc eval "set $sum = $sum + $arg%d", $i set $i = $i + 1 end print $sum end
define
commandnameThe definition of the command is made up of other gdb command lines,
which are given following the define
command. The end of these
commands is marked by a line containing end
.
document
commandnamehelp
. The command commandname must already be
defined. This command reads lines of documentation just as define
reads the lines of the command definition, ending with end
.
After the document
command is finished, help
on command
commandname displays the documentation you have written.
You may use the document
command again to change the
documentation of a command. Redefining the command with define
does not change the documentation.
define-prefix
commandnamedefine
command.
Note that define-prefix
can be used with a not yet defined
commandname. In such a case, commandname is defined as
an empty user-defined command.
In case you redefine a command that was marked as a user-defined
prefix command, the subcommands of the redefined command are kept
(and gdb indicates so to the user).
Example:
(gdb) define-prefix abc (gdb) define-prefix abc def (gdb) define abc def Type commands for definition of "abc def". End with a line saying just "end". >echo command initial def\n >end (gdb) define abc def ghi Type commands for definition of "abc def ghi". End with a line saying just "end". >echo command ghi\n >end (gdb) define abc def Keeping subcommands of prefix command "def". Redefine command "def"? (y or n) y Type commands for definition of "abc def". End with a line saying just "end". >echo command def\n >end (gdb) abc def ghi command ghi (gdb) abc def command def (gdb)
dont-repeat
help user-defined
show user
show user
commandnameshow max-user-call-depth
set max-user-call-depth
max-user-call-depth
controls how many recursion
levels are allowed in user-defined commands before gdb suspects an
infinite recursion and aborts the command.
This does not apply to user-defined python commands.
In addition to the above commands, user-defined commands frequently use control flow commands, described in Command Files.
When user-defined commands are executed, the commands of the definition are not printed. An error in any command stops execution of the user-defined command.
If used interactively, commands that would ask for confirmation proceed without asking when used inside a user-defined command. Many gdb commands that normally print messages to say what they are doing omit the messages when used in a user-defined command.
You may define hooks, which are a special kind of user-defined command. Whenever you run the command ‘foo’, if the user-defined command ‘hook-foo’ exists, it is executed (with no arguments) before that command.
A hook may also be defined which is run after the command you executed. Whenever you run the command ‘foo’, if the user-defined command ‘hookpost-foo’ exists, it is executed (with no arguments) after that command. Post-execution hooks may exist simultaneously with pre-execution hooks, for the same command.
It is valid for a hook to call the command which it hooks. If this occurs, the hook is not re-executed, thereby avoiding infinite recursion.
In addition, a pseudo-command, ‘stop’ exists. Defining (‘hook-stop’) makes the associated commands execute every time execution stops in your program: before breakpoint commands are run, displays are printed, or the stack frame is printed.
For example, to ignore SIGALRM
signals while
single-stepping, but treat them normally during normal execution,
you could define:
define hook-stop handle SIGALRM nopass end define hook-run handle SIGALRM pass end define hook-continue handle SIGALRM pass end
As a further example, to hook at the beginning and end of the echo
command, and to add extra text to the beginning and end of the message,
you could define:
define hook-echo echo <<<--- end define hookpost-echo echo --->>>\n end (gdb) echo Hello World <<<---Hello World--->>> (gdb)
You can define a hook for any single-word command in gdb, but
not for command aliases; you should define a hook for the basic command
name, e.g. backtrace
rather than bt
.
You can hook a multi-word command by adding hook-
or
hookpost-
to the last word of the command, e.g.
‘define target hook-remote’ to add a hook to ‘target remote’.
If an error occurs during the execution of your hook, execution of gdb commands stops and gdb issues a prompt (before the command that you actually typed had a chance to run).
If you try to define a hook which does not match any known command, you
get a warning from the define
command.
A command file for gdb is a text file made of lines that are gdb commands. Comments (lines starting with #) may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal.
You can request the execution of a command file with the source
command. Note that the source
command is also used to evaluate
scripts that are not Command Files. The exact behavior can be configured
using the script-extension
setting.
See Extending GDB.
source [-s] [-v]
filenameThe lines in a command file are generally executed sequentially, unless the order of execution is changed by one of the flow-control commands described below. The commands are not printed as they are executed. An error in any command terminates execution of the command file and control is returned to the console.
gdb first searches for filename in the current directory. If the file is not found there, and filename does not specify a directory, then gdb also looks for the file on the source search path (specified with the ‘directory’ command); except that $cdir is not searched because the compilation directory is not relevant to scripts.
If -s
is specified, then gdb searches for filename
on the search path even if filename specifies a directory.
The search is done by appending filename to each element of the
search path. So, for example, if filename is mylib/myscript
and the search path contains /home/user then gdb will
look for the script /home/user/mylib/myscript.
The search is also done if filename is an absolute path.
For example, if filename is /tmp/myscript and
the search path contains /home/user then gdb will
look for the script /home/user/tmp/myscript.
For DOS-like systems, if filename contains a drive specification,
it is stripped before concatenation. For example, if filename is
d:myscript and the search path contains c:/tmp then gdb
will look for the script c:/tmp/myscript.
If -v
, for verbose mode, is given then gdb displays
each command as it is executed. The option must be given before
filename, and is interpreted as part of the filename anywhere else.
Commands that would ask for confirmation if used interactively proceed without asking when used in a command file. Many gdb commands that normally print messages to say what they are doing omit the messages when called from command files.
gdb also accepts command input from standard input. In this mode, normal output goes to standard output and error output goes to standard error. Errors in a command file supplied on standard input do not terminate execution of the command file—execution continues with the next command.
gdb < cmds > log 2>&1
(The syntax above will vary depending on the shell used.) This example will execute commands from the file cmds. All output and errors would be directed to log.
Since commands stored on command files tend to be more general than commands typed interactively, they frequently need to deal with complicated situations, such as different or unexpected values of variables and symbols, changes in how the program being debugged is built, etc. gdb provides a set of flow-control commands to deal with these complexities. Using these commands, you can write complex scripts that loop over data structures, execute commands conditionally, etc.
if
else
if
command takes a single argument, which is an
expression to evaluate. It is followed by a series of commands that
are executed only if the expression is true (its value is nonzero).
There can then optionally be an else
line, followed by a series
of commands that are only executed if the expression was false. The
end of the list is marked by a line containing end
.
while
if
: the command takes a single argument, which is an expression
to evaluate, and must be followed by the commands to execute, one per
line, terminated by an end
. These commands are called the
body of the loop. The commands in the body of while
are
executed repeatedly as long as the expression evaluates to true.
loop_break
while
loop in whose body it is included.
Execution of the script continues after that while
s end
line.
loop_continue
while
loop in whose body it is included. Execution
branches to the beginning of the while
loop, where it evaluates
the controlling expression.
end
if
,
else
, or while
flow-control commands.
During the execution of a command file or a user-defined command, normal gdb output is suppressed; the only output that appears is what is explicitly printed by the commands in the definition. This section describes three commands useful for generating exactly the output you want.
echo
textA backslash at the end of text can be used, as in C, to continue the command onto subsequent lines. For example,
echo This is some text\n\ which is continued\n\ onto several lines.\n
produces the same output as
echo This is some text\n echo which is continued\n echo onto several lines.\n
output
expressionoutput/
fmt expressionprint
. See Output Formats, for more information.
printf
template,
expressions...
printf (template, expressions...);
As in C
printf
, ordinary characters in template
are printed verbatim, while conversion specification introduced
by the ‘%’ character cause subsequent expressions to be
evaluated, their values converted and formatted according to type and
style information encoded in the conversion specifications, and then
printed.
For example, you can print two values in hex like this:
printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
printf
supports all the standard C
conversion
specifications, including the flags and modifiers between the ‘%’
character and the conversion letter, with the following exceptions:
LC_NUMERIC'
) is not supported.
Note that the ‘ll’ type modifier is supported only if the
underlying C
implementation used to build gdb supports
the long long int
type, and the ‘L’ type modifier is
supported only if long double
type is available.
As in C
, printf
supports simple backslash-escape
sequences, such as \n
, ‘\t’, ‘\\’, ‘\"’,
‘\a’, and ‘\f’, that consist of backslash followed by a
single character. Octal and hexadecimal escape sequences are not
supported.
Additionally, printf
supports conversion specifications for DFP
(Decimal Floating Point) types using the following length modifiers
together with a floating point specifier.
letters:
Decimal32
types.
Decimal64
types.
Decimal128
types.
If the underlying C
implementation used to build gdb has
support for the three length modifiers for DFP types, other modifiers
such as width and precision will also be available for gdb to use.
In case there is no such C
support, no additional modifiers will be
available and the value will be printed in the standard way.
Here's an example of printing DFP types using the above conversion letters:
printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
eval
template,
expressions...
When a new object file is read (for example, due to the file
command, or because the inferior has loaded a shared library),
gdb will look for the command file objfile-gdb.gdb.
See Auto-loading extensions.
Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be printed.
set auto-load gdb-scripts [on|off]
show auto-load gdb-scripts
info auto-load gdb-scripts [
regexp]
If regexp is supplied only canned sequences of commands scripts with matching names are printed.
You can extend gdb using the Python programming language. This feature is available only if gdb was configured using --with-python. gdb can be built against either Python 2 or Python 3; which one you have depends on this configure-time option.
Python scripts used by gdb should be installed in data-directory/python, where data-directory is the data directory as determined at gdb startup (see Data Files). This directory, known as the python directory, is automatically added to the Python Search Path in order to allow the Python interpreter to locate all scripts installed at this location.
Additionally, gdb commands and convenience functions which are written in Python and are located in the data-directory/python/gdb/command or data-directory/python/gdb/function directories are automatically imported when gdb starts.
gdb provides two commands for accessing the Python interpreter, and one related setting:
python-interactive
[command]pi
[command]python-interactive
command can be used
to start an interactive Python prompt. To return to gdb,
type the EOF
character (e.g., Ctrl-D on an empty prompt).
Alternatively, a single-line Python command can be given as an argument and evaluated. If the command is an expression, the result will be printed; otherwise, nothing will be printed. For example:
(gdb) python-interactive 2 + 3 5
python
[command]py
[command]python
command can be used to evaluate Python code.
If given an argument, the python
command will evaluate the
argument as a Python command. For example:
(gdb) python print 23 23
If you do not provide an argument to python
, it will act as a
multi-line command, like define
. In this case, the Python
script is made up of subsequent command lines, given after the
python
command. This command list is terminated using a line
containing end
. For example:
(gdb) python >print 23 >end 23
set python print-stack
set python print-stack
: if full
, then
full Python stack printing is enabled; if none
, then Python stack
and message printing is disabled; if message
, the default, only
the message component of the error is printed.
It is also possible to execute a Python script from the gdb interpreter:
source
script-namescript-extension
setting. See Extending GDB.
You can get quick online help for gdb's Python API by issuing the command python help (gdb).
Functions and methods which have two or more optional arguments allow
them to be specified using keyword syntax. This allows passing some
optional arguments while skipping others. Example:
gdb.some_function ('foo', bar = 1, baz = 2)
.
At startup, gdb overrides Python's sys.stdout
and
sys.stderr
to print using gdb's output-paging streams.
A Python program which outputs to one of these streams may have its
output interrupted by the user (see Screen Size). In this
situation, a Python KeyboardInterrupt
exception is thrown.
Some care must be taken when writing Python code to run in gdb. Two things worth noting in particular:
SIGCHLD
and SIGINT
.
Python code must not override these, or even change the options using
sigaction
. If your program changes the handling of these
signals, gdb will most likely stop working correctly. Note
that it is unfortunately common for GUI toolkits to install a
SIGCHLD
handler.
gdb introduces a new Python module, named gdb
. All
methods and classes added by gdb are placed in this module.
gdb automatically import
s the gdb
module for
use in all scripts evaluated by the python
command.
Some types of the gdb
module come with a textual representation
(accessible through the repr
or str
functions). These are
offered for debugging purposes only, expect them to change over time.
Evaluate command, a string, as a gdb CLI command. If a GDB exception happens while command runs, it is translated as described in Exception Handling.
The from_tty flag specifies whether gdb ought to consider this command as having originated from the user invoking it interactively. It must be a boolean value. If omitted, it defaults to
False
.By default, any output produced by command is sent to gdb's standard output (and to the log output if logging is turned on). If the to_string parameter is
True
, then output will be collected bygdb.execute
and returned as a string. The default isFalse
, in which case the return value isNone
. If to_string isTrue
, the gdb virtual terminal will be temporarily set to unlimited width and height, and its pagination will be disabled; see Screen Size.
Return a sequence holding all of gdb's breakpoints. See Breakpoints In Python, for more information. In gdb version 7.11 and earlier, this function returned
None
if there were no breakpoints. This peculiarity was subsequently fixed, and nowgdb.breakpoints
returns an empty sequence in this case.
Return a Python list holding a collection of newly set
gdb.Breakpoint
objects matching function names defined by the regex pattern. If the minsyms keyword isTrue
, all system functions (those not explicitly defined in the inferior) will also be included in the match. The throttle keyword takes an integer that defines the maximum number of pattern matches for functions matched by the regex pattern. If the number of matches exceeds the integer value of throttle, aRuntimeError
will be raised and no breakpoints will be created. If throttle is not defined then there is no imposed limit on the maximum number of matches and breakpoints to be created. The symtabs keyword takes a Python iterable that yields a collection ofgdb.Symtab
objects and will restrict the search to those functions only contained within thegdb.Symtab
objects.
Return the value of a gdb parameter given by its name, a string; the parameter name string may contain spaces if the parameter has a multi-part name. For example, ‘print object’ is a valid parameter name.
If the named parameter does not exist, this function throws a
gdb.error
(see Exception Handling). Otherwise, the parameter's value is converted to a Python value of the appropriate type, and returned.
Return a value from gdb's value history (see Value History). The number argument indicates which history element to return. If number is negative, then gdb will take its absolute value and count backward from the last element (i.e., the most recent element) to find the value to return. If number is zero, then gdb will return the most recent element. If the element specified by number doesn't exist in the value history, a
gdb.error
exception will be raised.If no exception is raised, the return value is always an instance of
gdb.Value
(see Values From Inferior).
Return the value of the convenience variable (see Convenience Vars) named name. name must be a string. The name should not include the ‘$’ that is used to mark a convenience variable in an expression. If the convenience variable does not exist, then
None
is returned.
Set the value of the convenience variable (see Convenience Vars) named name. name must be a string. The name should not include the ‘$’ that is used to mark a convenience variable in an expression. If value is
None
, then the convenience variable is removed. Otherwise, if value is not agdb.Value
(see Values From Inferior), it is is converted using thegdb.Value
constructor.
Parse expression, which must be a string, as an expression in the current language, evaluate it, and return the result as a
gdb.Value
.This function can be useful when implementing a new command (see Commands In Python), as it provides a way to parse the command's argument as an expression. It is also useful simply to compute values.
Return the
gdb.Symtab_and_line
object corresponding to the pc value. See Symbol Tables In Python. If an invalid value of pc is passed as an argument, then thesymtab
andline
attributes of the returnedgdb.Symtab_and_line
object will beNone
and 0 respectively. This is identical togdb.current_progspace().find_pc_line(pc)
and is included for historical compatibility.
Put event, a callable object taking no arguments, into gdb's internal event queue. This callable will be invoked at some later point, during gdb's event processing. Events posted using
post_event
will be run in the order in which they were posted; however, there is no way to know when they will be processed relative to other events inside gdb.gdb is not thread-safe. If your Python program uses multiple threads, you must be careful to only call gdb-specific functions in the gdb thread.
post_event
ensures this. For example:(gdb) python >import threading > >class Writer(): > def __init__(self, message): > self.message = message; > def __call__(self): > gdb.write(self.message) > >class MyThread1 (threading.Thread): > def run (self): > gdb.post_event(Writer("Hello ")) > >class MyThread2 (threading.Thread): > def run (self): > gdb.post_event(Writer("World\n")) > >MyThread1().start() >MyThread2().start() >end (gdb) Hello World
Print a string to gdb's paginated output stream. The optional stream determines the stream to print to. The default stream is gdb's standard output stream. Possible stream values are:
gdb.STDOUT
- gdb's standard output stream.
gdb.STDERR
- gdb's standard error stream.
gdb.STDLOG
- gdb's log stream (see Logging Output).
Writing to
sys.stdout
orsys.stderr
will automatically call this function and will automatically direct the output to the relevant stream.
Flush the buffer of a gdb paginated stream so that the contents are displayed immediately. gdb will flush the contents of a stream automatically when it encounters a newline in the buffer. The optional stream determines the stream to flush. The default stream is gdb's standard output stream. Possible stream values are:
gdb.STDOUT
- gdb's standard output stream.
gdb.STDERR
- gdb's standard error stream.
gdb.STDLOG
- gdb's log stream (see Logging Output).
Flushing
sys.stdout
orsys.stderr
will automatically call this function for the relevant stream.
Return the name of the current target character set (see Character Sets). This differs from
gdb.parameter('target-charset')
in that ‘auto’ is never returned.
Return the name of the current target wide character set (see Character Sets). This differs from
gdb.parameter('target-wide-charset')
in that ‘auto’ is never returned.
Return the name of the shared library holding the given address as a string, or
None
. This is identical togdb.current_progspace().solib_name(address)
and is included for historical compatibility.
Return locations of the line specified by expression, or of the current line if no argument was given. This function returns a Python tuple containing two elements. The first element contains a string holding any unparsed section of expression (or
None
if the expression has been fully parsed). The second element contains eitherNone
or another tuple that contains all the locations that match the expression represented asgdb.Symtab_and_line
objects (see Symbol Tables In Python). If expression is provided, it is decoded the way that gdb's inbuiltbreak
oredit
commands do (see Specify Location).
If prompt_hook is callable, gdb will call the method assigned to this operation before a prompt is displayed by gdb.
The parameter
current_prompt
contains the current gdb prompt. This method must return a Python string, orNone
. If a string is returned, the gdb prompt will be set to that string. IfNone
is returned, gdb will continue to use the current prompt.Some prompts cannot be substituted in gdb. Secondary prompts such as those used by readline for command input, and annotation related prompts are prohibited from being changed.
When executing the python
command, Python exceptions
uncaught within the Python code are translated to calls to
gdb error-reporting mechanism. If the command that called
python
does not handle the error, gdb will
terminate it and print an error message containing the Python
exception name, the associated value, and the Python call stack
backtrace at the point where the exception was raised. Example:
(gdb) python print foo Traceback (most recent call last): File "<string>", line 1, in <module> NameError: name 'foo' is not defined
gdb errors that happen in gdb commands invoked by Python code are converted to Python exceptions. The type of the Python exception depends on the error.
gdb.error
RuntimeError
, for compatibility with earlier
versions of gdb.
If an error occurring in gdb does not fit into some more
specific category, then the generated exception will have this type.
gdb.MemoryError
gdb.error
which is thrown when an
operation tried to access invalid memory in the inferior.
KeyboardInterrupt
KeyboardInterrupt
exception.
In all cases, your exception handler will see the gdb error message as its value and the Python call stack backtrace at the Python statement closest to where the gdb error occured as the traceback.
When implementing gdb commands in Python via
gdb.Command
, or functions via gdb.Function
, it is useful
to be able to throw an exception that doesn't cause a traceback to be
printed. For example, the user may have invoked the command
incorrectly. gdb provides a special exception class that can
be used for this purpose.
gdb.GdbError
(gdb) python >class HelloWorld (gdb.Command): > """Greet the whole world.""" > def __init__ (self): > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER) > def invoke (self, args, from_tty): > argv = gdb.string_to_argv (args) > if len (argv) != 0: > raise gdb.GdbError ("hello-world takes no arguments") > print "Hello, World!" >HelloWorld () >end (gdb) hello-world 42 hello-world takes no arguments
gdb provides values it obtains from the inferior program in
an object of type gdb.Value
. gdb uses this object
for its internal bookkeeping of the inferior's values, and for
fetching values when necessary.
Inferior values that are simple scalars can be used directly in
Python expressions that are valid for the value's data type. Here's
an example for an integer or floating-point value some_val
:
bar = some_val + 2
As result of this, bar
will also be a gdb.Value
object
whose values are of the same type as those of some_val
. Valid
Python operations can also be performed on gdb.Value
objects
representing a struct
or class
object. For such cases,
the overloaded operator (if present), is used to perform the operation.
For example, if val1
and val2
are gdb.Value
objects
representing instances of a class
which overloads the +
operator, then one can use the +
operator in their Python script
as follows:
val3 = val1 + val2
The result of the operation val3
is also a gdb.Value
object corresponding to the value returned by the overloaded +
operator. In general, overloaded operators are invoked for the
following operations: +
(binary addition), -
(binary
subtraction), *
(multiplication), /
, %
, <<
,
>>
, |
, &
, ^
.
Inferior values that are structures or instances of some class can
be accessed using the Python dictionary syntax. For example, if
some_val
is a gdb.Value
instance holding a structure, you
can access its foo
element with:
bar = some_val['foo']
Again, bar
will also be a gdb.Value
object. Structure
elements can also be accessed by using gdb.Field
objects as
subscripts (see Types In Python, for more information on
gdb.Field
objects). For example, if foo_field
is a
gdb.Field
object corresponding to element foo
of the above
structure, then bar
can also be accessed as follows:
bar = some_val[foo_field]
A gdb.Value
that represents a function can be executed via
inferior function call. Any arguments provided to the call must match
the function's prototype, and must be provided in the order specified
by that prototype.
For example, some_val
is a gdb.Value
instance
representing a function that takes two integers as arguments. To
execute this function, call it like so:
result = some_val (10,20)
Any values returned from a function call will be stored as a
gdb.Value
.
The following attributes are provided:
If this object is addressable, this read-only attribute holds a
gdb.Value
object representing the address. Otherwise, this attribute holdsNone
.
This read-only boolean attribute is true if the compiler optimized out this value, thus it is not available for fetching from the inferior.
The type of this
gdb.Value
. The value of this attribute is agdb.Type
object (see Types In Python).
The dynamic type of this
gdb.Value
. This uses the object's virtual table and the C++ run-time type information (RTTI) to determine the dynamic type of the value. If this value is of class type, it will return the class in which the value is embedded, if any. If this value is of pointer or reference to a class type, it will compute the dynamic type of the referenced object, and return a pointer or reference to that type, respectively. In all other cases, it will return the value's static type.Note that this feature will only work when debugging a C++ program that includes RTTI for the object in question. Otherwise, it will just return the static type of the value as in ptype foo (see ptype).
The value of this read-only boolean attribute is
True
if thisgdb.Value
has not yet been fetched from the inferior. gdb does not fetch values until necessary, for efficiency. For example:myval = gdb.parse_and_eval ('somevar')The value of
somevar
is not fetched at this time. It will be fetched when the value is needed, or when thefetch_lazy
method is invoked.
The following methods are provided:
Many Python values can be converted directly to a
gdb.Value
via this object initializer. Specifically:
- Python boolean
- A Python boolean is converted to the boolean type from the current language.
- Python integer
- A Python integer is converted to the C
long
type for the current architecture.- Python long
- A Python long is converted to the C
long long
type for the current architecture.- Python float
- A Python float is converted to the C
double
type for the current architecture.- Python string
- A Python string is converted to a target string in the current target language using the current target encoding. If a character cannot be represented in the current target encoding, then an exception is thrown.
gdb.Value
- If
val
is agdb.Value
, then a copy of the value is made.gdb.LazyString
- If
val
is agdb.LazyString
(see Lazy Strings In Python), then the lazy string'svalue
method is called, and its result is used.
This second form of the
gdb.Value
constructor returns agdb.Value
of type type where the value contents are taken from the Python buffer object specified by val. The number of bytes in the Python buffer object must be greater than or equal to the size of type.
Return a new instance of
gdb.Value
that is the result of casting this instance to the type described by type, which must be agdb.Type
object. If the cast cannot be performed for some reason, this method throws an exception.
For pointer data types, this method returns a new
gdb.Value
object whose contents is the object pointed to by the pointer. For example, iffoo
is a C pointer to anint
, declared in your C program asint *foo;then you can use the corresponding
gdb.Value
to access whatfoo
points to like this:bar = foo.dereference ()The result
bar
will be agdb.Value
object holding the value pointed to byfoo
.A similar function
Value.referenced_value
exists which also returnsgdb.Value
objects corresponding to the values pointed to by pointer values (and additionally, values referenced by reference values). However, the behavior ofValue.dereference
differs fromValue.referenced_value
by the fact that the behavior ofValue.dereference
is identical to applying the C unary operator*
on a given value. For example, consider a reference to a pointerptrref
, declared in your C++ program astypedef int *intptr; ... int val = 10; intptr ptr = &val; intptr &ptrref = ptr;Though
ptrref
is a reference value, one can apply the methodValue.dereference
to thegdb.Value
object corresponding to it and obtain agdb.Value
which is identical to that corresponding toval
. However, if you apply the methodValue.referenced_value
, the result would be agdb.Value
object identical to that corresponding toptr
.py_ptrref = gdb.parse_and_eval ("ptrref") py_val = py_ptrref.dereference () py_ptr = py_ptrref.referenced_value ()The
gdb.Value
objectpy_val
is identical to that corresponding toval
, andpy_ptr
is identical to that corresponding toptr
. In general,Value.dereference
can be applied whenever the C unary operator*
can be applied to the corresponding C value. For those cases where applying bothValue.dereference
andValue.referenced_value
is allowed, the results obtained need not be identical (as we have seen in the above example). The results are however identical when applied ongdb.Value
objects corresponding to pointers (gdb.Value
objects with type codeTYPE_CODE_PTR
) in a C/C++ program.
For pointer or reference data types, this method returns a new
gdb.Value
object corresponding to the value referenced by the pointer/reference value. For pointer data types,Value.dereference
andValue.referenced_value
produce identical results. The difference between these methods is thatValue.dereference
cannot get the values referenced by reference values. For example, consider a reference to anint
, declared in your C++ program asint val = 10; int &ref = val;then applying
Value.dereference
to thegdb.Value
object corresponding toref
will result in an error, while applyingValue.referenced_value
will result in agdb.Value
object identical to that corresponding toval
.py_ref = gdb.parse_and_eval ("ref") er_ref = py_ref.dereference () # Results in error py_val = py_ref.referenced_value () # Returns the referenced valueThe
gdb.Value
objectpy_val
is identical to that corresponding toval
.
Return a
gdb.Value
object which is a reference to the value encapsulated by this instance.
Return a
gdb.Value
object which is aconst
version of the value encapsulated by this instance.
Like
Value.cast
, but works as if the C++dynamic_cast
operator were used. Consult a C++ reference for details.
Like
Value.cast
, but works as if the C++reinterpret_cast
operator were used. Consult a C++ reference for details.
Convert a
gdb.Value
to a string, similarly to what thestr
function on thegdb.Value
. The representation of the same value may change across different versions of gdb, so you shouldn't, for instance, parse the strings returned by this method.All the arguments are keyword only. If an argument is not specified, the current global default setting is used.
raw
True
if pretty-printers (see Pretty Printing) should not be used to format the value.False
if enabled pretty-printers matching the type represented by thegdb.Value
should be used to format it.pretty_arrays
True
if arrays should be pretty printed to be more convenient to read,False
if they shouldn't (seeset print array
in Print Settings).pretty_structs
True
if structs should be pretty printed to be more convenient to read,False
if they shouldn't (seeset print pretty
in Print Settings).array_indexes
True
if array indexes should be included in the string representation of arrays,False
if they shouldn't (seeset print array-indexes
in Print Settings).symbols
True
if the string representation of a pointer should include the corresponding symbol name (if one exists),False
if it shouldn't (seeset print symbol
in Print Settings).unions
True
if unions which are contained in other structures or unions should be expanded,False
if they shouldn't (seeset print union
in Print Settings).deref_refs
True
if C++ references should be resolved to the value they refer to,False
(the default) if they shouldn't. Note that, unlike for theformat_string
method or thestr
function. There is no globalactual_objects
True
if the representation of a pointer to an object should identify the actual (derived) type of the object rather than the declared type, using the virtual function table.False
if the declared type should be used. (Seeset print object
in Print Settings).static_fields
True
if static members should be included in the string representation of a C++ object,False
if they shouldn't (seeset print static-members
in Print Settings).max_elements
- Number of array elements to print, or
0
to print an unlimited number of elements (seeset print elements
in Print Settings).max_depth
- The maximum depth to print for nested structs and unions, or
-1
to print an unlimited number of elements (seeset print max-depth
in Print Settings).repeat_threshold
- Set the threshold for suppressing display of repeated array elements, or
0
to represent all elements, even if repeated. (Seeset print repeats
in Print Settings).format
- A string containing a single character representing the format to use for the returned string. For instance,
'x'
is equivalent to using the gdb command/x
option and formats the value as a hexadecimal number.
If this
gdb.Value
represents a string, then this method converts the contents to a Python string. Otherwise, this method will throw an exception.Values are interpreted as strings according to the rules of the current language. If the optional length argument is given, the string will be converted to that length, and will include any embedded zeroes that the string may contain. Otherwise, for languages where the string is zero-terminated, the entire string will be converted.
For example, in C-like languages, a value is a string if it is a pointer to or an array of characters or ints of type
wchar_t
,char16_t
, orchar32_t
.If the optional encoding argument is given, it must be a string naming the encoding of the string in the
gdb.Value
, such as"ascii"
,"iso-8859-6"
or"utf-8"
. It accepts the same encodings as the corresponding argument to Python'sstring.decode
method, and the Python codec machinery will be used to convert the string. If encoding is not given, or if encoding is the empty string, then either thetarget-charset
(see Character Sets) will be used, or a language-specific encoding will be used, if the current language is able to supply one.The optional errors argument is the same as the corresponding argument to Python's
string.decode
method.If the optional length argument is given, the string will be fetched and converted to the given length.
If this
gdb.Value
represents a string, then this method converts the contents to agdb.LazyString
(see Lazy Strings In Python). Otherwise, this method will throw an exception.If the optional encoding argument is given, it must be a string naming the encoding of the
gdb.LazyString
. Some examples are: ‘ascii’, ‘iso-8859-6’ or ‘utf-8’. If the encoding argument is an encoding that gdb does recognize, gdb will raise an error.When a lazy string is printed, the gdb encoding machinery is used to convert the string during printing. If the optional encoding argument is not provided, or is an empty string, gdb will automatically select the encoding most suitable for the string type. For further information on encoding in gdb please see Character Sets.
If the optional length argument is given, the string will be fetched and encoded to the length of characters specified. If the length argument is not provided, the string will be fetched and encoded until a null of appropriate width is found.
If the
gdb.Value
object is currently a lazy value (gdb.Value.is_lazy
isTrue
), then the value is fetched from the inferior. Any errors that occur in the process will produce a Python exception.If the
gdb.Value
object is not a lazy value, this method has no effect.This method does not return a value.
gdb represents types from the inferior using the class
gdb.Type
.
The following type-related functions are available in the gdb
module:
This function looks up a type by its name, which must be a string.
If block is given, then name is looked up in that scope. Otherwise, it is searched for globally.
Ordinarily, this function will return an instance of
gdb.Type
. If the named type cannot be found, it will throw an exception.
If the type is a structure or class type, or an enum type, the fields
of that type can be accessed using the Python dictionary syntax.
For example, if some_type
is a gdb.Type
instance holding
a structure type, you can access its foo
field with:
bar = some_type['foo']
bar
will be a gdb.Field
object; see below under the
description of the Type.fields
method for a description of the
gdb.Field
class.
An instance of Type
has the following attributes:
The alignment of this type, in bytes. Type alignment comes from the debugging information; if it was not specified, then gdb will use the relevant ABI to try to determine the alignment. In some cases, even this is not possible, and zero will be returned.
The type code for this type. The type code will be one of the
TYPE_CODE_
constants defined below.
A boolean indicating whether this type is dynamic. In some situations, such as Rust
enum
types or Ada variant records, the concrete type of a value may vary depending on its contents.
The size of this type, in target
char
units. Usually, a target'schar
type will be an 8-bit byte. However, on some unusual platforms, this type may have a different size. A dynamic type may not have a fixed size; in this case, this attribute's value will beNone
.
The tag name for this type. The tag name is the name after
struct
,union
, orenum
in C and C++; not all languages have this concept. If this type has no tag name, thenNone
is returned.
The
gdb.Objfile
that this type was defined in, orNone
if there is no associated objfile.
The following methods are provided:
For structure and union types, this method returns the fields. Range types have two fields, the minimum and maximum values. Enum types have one field per enum constant. Function and method types have one field per parameter. The base types of C++ classes are also represented as fields. If the type has no fields, or does not fit into one of these categories, an empty sequence will be returned.
Each field is a
gdb.Field
object, with some pre-defined attributes:
bitpos
- This attribute is not available for
enum
orstatic
(as in C++) fields. The value is the position, counting in bits, from the start of the containing type. Note that, in a dynamic type, the position of a field may not be constant. In this case, the value will beNone
.enumval
- This attribute is only available for
enum
fields, and its value is the enumeration member's integer representation.name
- The name of the field, or
None
for anonymous fields.artificial
- This is
True
if the field is artificial, usually meaning that it was provided by the compiler and not the user. This attribute is always provided, and isFalse
if the field is not artificial.is_base_class
- This is
True
if the field represents a base class of a C++ structure. This attribute is always provided, and isFalse
if the field is not a base class of the type that is the argument offields
, or if that type was not a C++ class.bitsize
- If the field is packed, or is a bitfield, then this will have a non-zero value, which is the size of the field in bits. Otherwise, this will be zero; in this case the field's size is given by its type.
type
- The type of the field. This is usually an instance of
Type
, but it can beNone
in some situations.parent_type
- The type which contains this field. This is an instance of
gdb.Type
.
Return a new
gdb.Type
object which represents an array of this type. If one argument is given, it is the inclusive upper bound of the array; in this case the lower bound is zero. If two arguments are given, the first argument is the lower bound of the array, and the second argument is the upper bound of the array. An array's length must not be negative, but the bounds can be.
Return a new
gdb.Type
object which represents a vector of this type. If one argument is given, it is the inclusive upper bound of the vector; in this case the lower bound is zero. If two arguments are given, the first argument is the lower bound of the vector, and the second argument is the upper bound of the vector. A vector's length must not be negative, but the bounds can be.The difference between an
array
and avector
is that arrays behave like in C: when used in expressions they decay to a pointer to the first element whereas vectors are treated as first class values.
Return a new
gdb.Type
object which represents aconst
-qualified variant of this type.
Return a new
gdb.Type
object which represents avolatile
-qualified variant of this type.
Return a new
gdb.Type
object which represents an unqualified variant of this type. That is, the result is neitherconst
norvolatile
.
Return a Python
Tuple
object that contains two elements: the low bound of the argument type and the high bound of that type. If the type does not have a range, gdb will raise agdb.error
exception (see Exception Handling).
Return a new
gdb.Type
object which represents a reference to this type.
Return a new
gdb.Type
that represents the real type, after removing all layers of typedefs.
Return a new
gdb.Type
object which represents the target type of this type.For a pointer type, the target type is the type of the pointed-to object. For an array type (meaning C-like arrays), the target type is the type of the elements of the array. For a function or method type, the target type is the type of the return value. For a complex type, the target type is the type of the elements. For a typedef, the target type is the aliased type.
If the type does not have a target, this method will throw an exception.
If this
gdb.Type
is an instantiation of a template, this will return a newgdb.Value
orgdb.Type
which represents the value of the nth template argument (indexed starting at 0).If this
gdb.Type
is not a template type, or if the type has fewer than n template arguments, this will throw an exception. Ordinarily, only C++ code will have template types.If block is given, then name is looked up in that scope. Otherwise, it is searched for globally.
Return
gdb.Value
instance of this type whose value is optimized out. This allows a frame decorator to indicate that the value of an argument or a local variable is not known.
Each type has a code, which indicates what category this type falls
into. The available type categories are represented by constants
defined in the gdb
module:
gdb.TYPE_CODE_PTR
gdb.TYPE_CODE_ARRAY
gdb.TYPE_CODE_STRUCT
gdb.TYPE_CODE_UNION
gdb.TYPE_CODE_ENUM
gdb.TYPE_CODE_FLAGS
gdb.TYPE_CODE_FUNC
gdb.TYPE_CODE_INT
gdb.TYPE_CODE_FLT
gdb.TYPE_CODE_VOID
void
.
gdb.TYPE_CODE_SET
gdb.TYPE_CODE_RANGE
gdb.TYPE_CODE_STRING
gdb.TYPE_CODE_BITSTRING
gdb.TYPE_CODE_ERROR
gdb.TYPE_CODE_METHOD
gdb.TYPE_CODE_METHODPTR
gdb.TYPE_CODE_MEMBERPTR
gdb.TYPE_CODE_REF
gdb.TYPE_CODE_RVALUE_REF
gdb.TYPE_CODE_CHAR
gdb.TYPE_CODE_BOOL
gdb.TYPE_CODE_COMPLEX
gdb.TYPE_CODE_TYPEDEF
gdb.TYPE_CODE_NAMESPACE
gdb.TYPE_CODE_DECFLOAT
gdb.TYPE_CODE_INTERNAL_FUNCTION
Further support for types is provided in the gdb.types
Python module (see gdb.types).
A pretty-printer is just an object that holds a value and implements a specific interface, defined here. An example output is provided (see Pretty Printing).
gdb will call this method on a pretty-printer to compute the children of the pretty-printer's value.
This method must return an object conforming to the Python iterator protocol. Each item returned by the iterator must be a tuple holding two elements. The first element is the “name” of the child; the second element is the child's value. The value can be any Python object which is convertible to a gdb value.
This method is optional. If it does not exist, gdb will act as though the value has no children.
For efficiency, the
children
method should lazily compute its results. This will let gdb read as few elements as necessary, for example when various print settings (see Print Settings) or-var-list-children
(see GDB/MI Variable Objects) limit the number of elements to be displayed.Children may be hidden from display based on the value of ‘set print max-depth’ (see Print Settings).
The CLI may call this method and use its result to change the formatting of a value. The result will also be supplied to an MI consumer as a ‘displayhint’ attribute of the variable being printed.
This method is optional. If it does exist, this method must return a string or the special value
None
.Some display hints are predefined by gdb:
- ‘array’
- Indicate that the object being printed is “array-like”. The CLI uses this to respect parameters such as
set print elements
andset print array
.- ‘map’
- Indicate that the object being printed is “map-like”, and that the children of this value can be assumed to alternate between keys and values.
- ‘string’
- Indicate that the object being printed is “string-like”. If the printer's
to_string
method returns a Python string of some kind, then gdb will call its internal language-specific string-printing function to format the string. For the CLI this means adding quotation marks, possibly escaping some characters, respectingset print elements
, and the like.The special value
None
causes gdb to apply the default display rules.
gdb will call this method to display the string representation of the value passed to the object's constructor.
When printing from the CLI, if the
to_string
method exists, then gdb will prepend its result to the values returned bychildren
. Exactly how this formatting is done is dependent on the display hint, and may change as more hints are added. Also, depending on the print settings (see Print Settings), the CLI may print just the result ofto_string
in a stack trace, omitting the result ofchildren
.If this method returns a string, it is printed verbatim.
Otherwise, if this method returns an instance of
gdb.Value
, then gdb prints this value. This may result in a call to another pretty-printer.If instead the method returns a Python value which is convertible to a
gdb.Value
, then gdb performs the conversion and prints the resulting value. Again, this may result in a call to another pretty-printer. Python scalars (integers, floats, and booleans) and strings are convertible togdb.Value
; other types are not.Finally, if this method returns
None
then no further operations are peformed in this method and nothing is printed.If the result is not one of these types, an exception is raised.
gdb provides a function which can be used to look up the
default pretty-printer for a gdb.Value
:
This function takes a
gdb.Value
object as an argument. If a pretty-printer for this value exists, then it is returned. If no such printer exists, then this returnsNone
.
gdb provides several ways to register a pretty-printer: globally, per program space, and per objfile. When choosing how to register your pretty-printer, a good rule is to register it with the smallest scope possible: that is prefer a specific objfile first, then a program space, and only register a printer globally as a last resort.
The Python list
gdb.pretty_printers
contains an array of functions or callable objects that have been registered via addition as a pretty-printer. Printers in this list are calledglobal
printers, they're available when debugging all inferiors.
Each gdb.Progspace
contains a pretty_printers
attribute.
Each gdb.Objfile
also contains a pretty_printers
attribute.
Each function on these lists is passed a single gdb.Value
argument and should return a pretty-printer object conforming to the
interface definition above (see Pretty Printing API). If a function
cannot create a pretty-printer for the value, it should return
None
.
gdb first checks the pretty_printers
attribute of each
gdb.Objfile
in the current program space and iteratively calls
each enabled lookup routine in the list for that gdb.Objfile
until it receives a pretty-printer object.
If no pretty-printer is found in the objfile lists, gdb then
searches the pretty-printer list of the current program space,
calling each enabled function until an object is returned.
After these lists have been exhausted, it tries the global
gdb.pretty_printers
list, again calling each enabled function until an
object is returned.
The order in which the objfiles are searched is not specified. For a given list, functions are always invoked from the head of the list, and iterated over sequentially until the end of the list, or a printer object is returned.
For various reasons a pretty-printer may not work. For example, the underlying data structure may have changed and the pretty-printer is out of date.
The consequences of a broken pretty-printer are severe enough that
gdb provides support for enabling and disabling individual
printers. For example, if print frame-arguments
is on,
a backtrace can become highly illegible if any argument is printed
with a broken printer.
Pretty-printers are enabled and disabled by attaching an enabled
attribute to the registered function or callable object. If this attribute
is present and its value is False
, the printer is disabled, otherwise
the printer is enabled.
A pretty-printer consists of two parts: a lookup function to detect if the type is supported, and the printer itself.
Here is an example showing how a std::string
printer might be
written. See Pretty Printing API, for details on the API this class
must provide.
class StdStringPrinter(object): "Print a std::string" def __init__(self, val): self.val = val def to_string(self): return self.val['_M_dataplus']['_M_p'] def display_hint(self): return 'string'
And here is an example showing how a lookup function for the printer example above might be written.
def str_lookup_function(val): lookup_tag = val.type.tag if lookup_tag == None: return None regex = re.compile("^std::basic_string<char,.*>$") if regex.match(lookup_tag): return StdStringPrinter(val) return None
The example lookup function extracts the value's type, and attempts to
match it to a type that it can pretty-print. If it is a type the
printer can pretty-print, it will return a printer object. If not, it
returns None
.
We recommend that you put your core pretty-printers into a Python package. If your pretty-printers are for use with a library, we further recommend embedding a version number into the package name. This practice will enable gdb to load multiple versions of your pretty-printers at the same time, because they will have different names.
You should write auto-loaded code (see Python Auto-loading) such that it
can be evaluated multiple times without changing its meaning. An
ideal auto-load file will consist solely of import
s of your
printer modules, followed by a call to a register pretty-printers with
the current objfile.
Taken as a whole, this approach will scale nicely to multiple inferiors, each potentially using a different library version. Embedding a version number in the Python package name will ensure that gdb is able to load both sets of printers simultaneously. Then, because the search for pretty-printers is done by objfile, and because your auto-loaded code took care to register your library's printers with a specific objfile, gdb will find the correct printers for the specific version of the library used by each inferior.
To continue the std::string
example (see Pretty Printing API),
this code might appear in gdb.libstdcxx.v6
:
def register_printers(objfile): objfile.pretty_printers.append(str_lookup_function)
And then the corresponding contents of the auto-load file would be:
import gdb.libstdcxx.v6 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
The previous example illustrates a basic pretty-printer. There are a few things that can be improved on. The printer doesn't have a name, making it hard to identify in a list of installed printers. The lookup function has a name, but lookup functions can have arbitrary, even identical, names.
Second, the printer only handles one type, whereas a library typically has several types. One could install a lookup function for each desired type in the library, but one could also have a single lookup function recognize several types. The latter is the conventional way this is handled. If a pretty-printer can handle multiple data types, then its subprinters are the printers for the individual data types.
The gdb.printing
module provides a formal way of solving these
problems (see gdb.printing).
Here is another example that handles multiple types.
These are the types we are going to pretty-print:
struct foo { int a, b; }; struct bar { struct foo x, y; };
Here are the printers:
class fooPrinter: """Print a foo object.""" def __init__(self, val): self.val = val def to_string(self): return ("a=<" + str(self.val["a"]) + "> b=<" + str(self.val["b"]) + ">") class barPrinter: """Print a bar object.""" def __init__(self, val): self.val = val def to_string(self): return ("x=<" + str(self.val["x"]) + "> y=<" + str(self.val["y"]) + ">")
This example doesn't need a lookup function, that is handled by the
gdb.printing
module. Instead a function is provided to build up
the object that handles the lookup.
import gdb.printing def build_pretty_printer(): pp = gdb.printing.RegexpCollectionPrettyPrinter( "my_library") pp.add_printer('foo', '^foo$', fooPrinter) pp.add_printer('bar', '^bar$', barPrinter) return pp
And here is the autoload support:
import gdb.printing import my_library gdb.printing.register_pretty_printer( gdb.current_objfile(), my_library.build_pretty_printer())
Finally, when this printer is loaded into gdb, here is the corresponding output of ‘info pretty-printer’:
(gdb) info pretty-printer my_library.so: my_library foo bar
gdb provides a way for Python code to customize type display. This is mainly useful for substituting canonical typedef names for types.
A type printer is just a Python object conforming to a certain protocol. A simple base class implementing the protocol is provided; see gdb.types. A type printer must supply at least:
A boolean which is True if the printer is enabled, and False otherwise. This is manipulated by the
enable type-printer
anddisable type-printer
commands.
The name of the type printer. This must be a string. This is used by the
enable type-printer
anddisable type-printer
commands.
This is called by gdb at the start of type-printing. It is only called if the type printer is enabled. This method must return a new object that supplies a
recognize
method, as described below.
When displaying a type, say via the ptype
command, gdb
will compute a list of type recognizers. This is done by iterating
first over the per-objfile type printers (see Objfiles In Python),
followed by the per-progspace type printers (see Progspaces In Python), and finally the global type printers.
gdb will call the instantiate
method of each enabled
type printer. If this method returns None
, then the result is
ignored; otherwise, it is appended to the list of recognizers.
Then, when gdb is going to display a type name, it iterates
over the list of recognizers. For each one, it calls the recognition
function, stopping if the function returns a non-None
value.
The recognition function is defined as:
If type is not recognized, return
None
. Otherwise, return a string which is to be printed as the name of type. The type argument will be an instance ofgdb.Type
(see Types In Python).
gdb uses this two-pass approach so that type printers can efficiently cache information without holding on to it too long. For example, it can be convenient to look up type information in a type printer and hold it for a recognizer's lifetime; if a single pass were done then type printers would have to make use of the event system in order to avoid holding information that could become stale as the inferior changed.
Frame filters are Python objects that manipulate the visibility of a frame or frames when a backtrace (see Backtrace) is printed by gdb.
Only commands that print a backtrace, or, in the case of gdb/mi commands (see GDB/MI), those that return a collection of frames are affected. The commands that work with frame filters are:
backtrace
(see The backtrace command),
-stack-list-frames
(see The -stack-list-frames command),
-stack-list-variables
(see The -stack-list-variables command), -stack-list-arguments
see The -stack-list-arguments command) and
-stack-list-locals
(see The -stack-list-locals command).
A frame filter works by taking an iterator as an argument, applying
actions to the contents of that iterator, and returning another
iterator (or, possibly, the same iterator it was provided in the case
where the filter does not perform any operations). Typically, frame
filters utilize tools such as the Python's itertools
module to
work with and create new iterators from the source iterator.
Regardless of how a filter chooses to apply actions, it must not alter
the underlying gdb frame or frames, or attempt to alter the
call-stack within gdb. This preserves data integrity within
gdb. Frame filters are executed on a priority basis and care
should be taken that some frame filters may have been executed before,
and that some frame filters will be executed after.
An important consideration when designing frame filters, and well worth reflecting upon, is that frame filters should avoid unwinding the call stack if possible. Some stacks can run very deep, into the tens of thousands in some cases. To search every frame when a frame filter executes may be too expensive at that step. The frame filter cannot know how many frames it has to iterate over, and it may have to iterate through them all. This ends up duplicating effort as gdb performs this iteration when it prints the frames. If the filter can defer unwinding frames until frame decorators are executed, after the last filter has executed, it should. See Frame Decorator API, for more information on decorators. Also, there are examples for both frame decorators and filters in later chapters. See Writing a Frame Filter, for more information.
The Python dictionary gdb.frame_filters
contains key/object
pairings that comprise a frame filter. Frame filters in this
dictionary are called global
frame filters, and they are
available when debugging all inferiors. These frame filters must
register with the dictionary directly. In addition to the
global
dictionary, there are other dictionaries that are loaded
with different inferiors via auto-loading (see Python Auto-loading). The two other areas where frame filter dictionaries
can be found are: gdb.Progspace
which contains a
frame_filters
dictionary attribute, and each gdb.Objfile
object which also contains a frame_filters
dictionary
attribute.
When a command is executed from gdb that is compatible with
frame filters, gdb combines the global
,
gdb.Progspace
and all gdb.Objfile
dictionaries currently
loaded. All of the gdb.Objfile
dictionaries are combined, as
several frames, and thus several object files, might be in use.
gdb then prunes any frame filter whose enabled
attribute is False
. This pruned list is then sorted according
to the priority
attribute in each filter.
Once the dictionaries are combined, pruned and sorted, gdb
creates an iterator which wraps each frame in the call stack in a
FrameDecorator
object, and calls each filter in order. The
output from the previous filter will always be the input to the next
filter, and so on.
Frame filters have a mandatory interface which each frame filter must implement, defined here:
gdb will call this method on a frame filter when it has reached the order in the priority list for that filter.
For example, if there are four frame filters:
Name Priority Filter1 5 Filter2 10 Filter3 100 Filter4 1The order that the frame filters will be called is:
Filter3 -> Filter2 -> Filter1 -> Filter4Note that the output from
Filter3
is passed to the input ofFilter2
, and so on.This
filter
method is passed a Python iterator. This iterator contains a sequence of frame decorators that wrap eachgdb.Frame
, or a frame decorator that wraps another frame decorator. The first filter that is executed in the sequence of frame filters will receive an iterator entirely comprised of defaultFrameDecorator
objects. However, after each frame filter is executed, the previous frame filter may have wrapped some or all of the frame decorators with their own frame decorator. As frame decorators must also conform to a mandatory interface, these decorators can be assumed to act in a uniform manner (see Frame Decorator API).This method must return an object conforming to the Python iterator protocol. Each item in the iterator must be an object conforming to the frame decorator interface. If a frame filter does not wish to perform any operations on this iterator, it should return that iterator untouched.
This method is not optional. If it does not exist, gdb will raise and print an error.
The
name
attribute must be Python string which contains the name of the filter displayed by gdb (see Frame Filter Management). This attribute may contain any combination of letters or numbers. Care should be taken to ensure that it is unique. This attribute is mandatory.
The
enabled
attribute must be Python boolean. This attribute indicates to gdb whether the frame filter is enabled, and should be considered when frame filters are executed. Ifenabled
isTrue
, then the frame filter will be executed when any of the backtrace commands detailed earlier in this chapter are executed. Ifenabled
isFalse
, then the frame filter will not be executed. This attribute is mandatory.
The
priority
attribute must be Python integer. This attribute controls the order of execution in relation to other frame filters. There are no imposed limits on the range ofpriority
other than it must be a valid integer. The higher thepriority
attribute, the sooner the frame filter will be executed in relation to other frame filters. Althoughpriority
can be negative, it is recommended practice to assume zero is the lowest priority that a frame filter can be assigned. Frame filters that have the same priority are executed in unsorted order in that priority slot. This attribute is mandatory. 100 is a good default priority.
Frame decorators are sister objects to frame filters (see Frame Filter API). Frame decorators are applied by a frame filter and can only be used in conjunction with frame filters.
The purpose of a frame decorator is to customize the printed content
of each gdb.Frame
in commands where frame filters are executed.
This concept is called decorating a frame. Frame decorators decorate
a gdb.Frame
with Python code contained within each API call.
This separates the actual data contained in a gdb.Frame
from
the decorated data produced by a frame decorator. This abstraction is
necessary to maintain integrity of the data contained in each
gdb.Frame
.
Frame decorators have a mandatory interface, defined below.
gdb already contains a frame decorator called
FrameDecorator
. This contains substantial amounts of
boilerplate code to decorate the content of a gdb.Frame
. It is
recommended that other frame decorators inherit and extend this
object, and only to override the methods needed.
FrameDecorator
is defined in the Python module
gdb.FrameDecorator
, so your code can import it like:
from gdb.FrameDecorator import FrameDecorator
The
elided
method groups frames together in a hierarchical system. An example would be an interpreter, where multiple low-level frames make up a single call in the interpreted language. In this example, the frame filter would elide the low-level frames and present a single high-level frame, representing the call in the interpreted language, to the user.The
elided
function must return an iterable and this iterable must contain the frames that are being elided wrapped in a suitable frame decorator. If no frames are being elided this function may return an empty iterable, orNone
. Elided frames are indented from normal frames in aCLI
backtrace, or in the case ofGDB/MI
, are placed in thechildren
field of the eliding frame.It is the frame filter's task to also filter out the elided frames from the source iterator. This will avoid printing the frame twice.
This method returns the name of the function in the frame that is to be printed.
This method must return a Python string describing the function, or
None
.If this function returns
None
, gdb will not print any data for this field.
This method returns the address of the frame that is to be printed.
This method must return a Python numeric integer type of sufficient size to describe the address of the frame, or
None
.If this function returns a
None
, gdb will not print any data for this field.
This method returns the filename and path associated with this frame.
This method must return a Python string containing the filename and the path to the object file backing the frame, or
None
.If this function returns a
None
, gdb will not print any data for this field.
This method returns the line number associated with the current position within the function addressed by this frame.
This method must return a Python integer type, or
None
.If this function returns a
None
, gdb will not print any data for this field.
This method must return an iterable, or
None
. Returning an empty iterable, orNone
means frame arguments will not be printed for this frame. This iterable must contain objects that implement two methods, described here.This object must implement a
argument
method which takes a singleself
parameter and must return agdb.Symbol
(see Symbols In Python), or a Python string. The object must also implement avalue
method which takes a singleself
parameter and must return agdb.Value
(see Values From Inferior), a Python value, orNone
. If thevalue
method returnsNone
, and theargument
method returns agdb.Symbol
, gdb will look-up and print the value of thegdb.Symbol
automatically.A brief example:
class SymValueWrapper(): def __init__(self, symbol, value): self.sym = symbol self.val = value def value(self): return self.val def symbol(self): return self.sym class SomeFrameDecorator() ... ... def frame_args(self): args = [] try: block = self.inferior_frame.block() except: return None # Iterate over all symbols in a block. Only add # symbols that are arguments. for sym in block: if not sym.is_argument: continue args.append(SymValueWrapper(sym,None)) # Add example synthetic argument. args.append(SymValueWrapper(``foo'', 42)) return args
This method must return an iterable or
None
. Returning an empty iterable, orNone
means frame local arguments will not be printed for this frame.The object interface, the description of the various strategies for reading frame locals, and the example are largely similar to those described in the
frame_args
function, (see The frame filter frame_args function). Below is a modified example:class SomeFrameDecorator() ... ... def frame_locals(self): vars = [] try: block = self.inferior_frame.block() except: return None # Iterate over all symbols in a block. Add all # symbols, except arguments. for sym in block: if sym.is_argument: continue vars.append(SymValueWrapper(sym,None)) # Add an example of a synthetic local variable. vars.append(SymValueWrapper(``bar'', 99)) return vars
This method must return the underlying
gdb.Frame
that this frame decorator is decorating. gdb requires the underlying frame for internal frame information to determine how to print certain values when printing a frame.
There are three basic elements that a frame filter must implement: it must correctly implement the documented interface (see Frame Filter API), it must register itself with gdb, and finally, it must decide if it is to work on the data provided by gdb. In all cases, whether it works on the iterator or not, each frame filter must return an iterator. A bare-bones frame filter follows the pattern in the following example.
import gdb class FrameFilter(): def __init__(self): # Frame filter attribute creation. # # 'name' is the name of the filter that GDB will display. # # 'priority' is the priority of the filter relative to other # filters. # # 'enabled' is a boolean that indicates whether this filter is # enabled and should be executed. self.name = "Foo" self.priority = 100 self.enabled = True # Register this frame filter with the global frame_filters # dictionary. gdb.frame_filters[self.name] = self def filter(self, frame_iter): # Just return the iterator. return frame_iter
The frame filter in the example above implements the three requirements for all frame filters. It implements the API, self registers, and makes a decision on the iterator (in this case, it just returns the iterator untouched).
The first step is attribute creation and assignment, and as shown in
the comments the filter assigns the following attributes: name
,
priority
and whether the filter should be enabled with the
enabled
attribute.
The second step is registering the frame filter with the dictionary or
dictionaries that the frame filter has interest in. As shown in the
comments, this filter just registers itself with the global dictionary
gdb.frame_filters
. As noted earlier, gdb.frame_filters
is a dictionary that is initialized in the gdb
module when
gdb starts. What dictionary a filter registers with is an
important consideration. Generally, if a filter is specific to a set
of code, it should be registered either in the objfile
or
progspace
dictionaries as they are specific to the program
currently loaded in gdb. The global dictionary is always
present in gdb and is never unloaded. Any filters registered
with the global dictionary will exist until gdb exits. To
avoid filters that may conflict, it is generally better to register
frame filters against the dictionaries that more closely align with
the usage of the filter currently in question. See Python Auto-loading, for further information on auto-loading Python scripts.
gdb takes a hands-off approach to frame filter registration,
therefore it is the frame filter's responsibility to ensure
registration has occurred, and that any exceptions are handled
appropriately. In particular, you may wish to handle exceptions
relating to Python dictionary key uniqueness. It is mandatory that
the dictionary key is the same as frame filter's name
attribute. When a user manages frame filters (see Frame Filter Management), the names gdb will display are those contained
in the name
attribute.
The final step of this example is the implementation of the
filter
method. As shown in the example comments, we define the
filter
method and note that the method must take an iterator,
and also must return an iterator. In this bare-bones example, the
frame filter is not very useful as it just returns the iterator
untouched. However this is a valid operation for frame filters that
have the enabled
attribute set, but decide not to operate on
any frames.
In the next example, the frame filter operates on all frames and utilizes a frame decorator to perform some work on the frames. See Frame Decorator API, for further information on the frame decorator interface.
This example works on inlined frames. It highlights frames which are
inlined by tagging them with an “[inlined]” tag. By applying a
frame decorator to all frames with the Python itertools imap
method, the example defers actions to the frame decorator. Frame
decorators are only processed when gdb prints the backtrace.
This introduces a new decision making topic: whether to perform decision making operations at the filtering step, or at the printing step. In this example's approach, it does not perform any filtering decisions at the filtering step beyond mapping a frame decorator to each frame. This allows the actual decision making to be performed when each frame is printed. This is an important consideration, and well worth reflecting upon when designing a frame filter. An issue that frame filters should avoid is unwinding the stack if possible. Some stacks can run very deep, into the tens of thousands in some cases. To search every frame to determine if it is inlined ahead of time may be too expensive at the filtering step. The frame filter cannot know how many frames it has to iterate over, and it would have to iterate through them all. This ends up duplicating effort as gdb performs this iteration when it prints the frames.
In this example decision making can be deferred to the printing step. As each frame is printed, the frame decorator can examine each frame in turn when gdb iterates. From a performance viewpoint, this is the most appropriate decision to make as it avoids duplicating the effort that the printing step would undertake anyway. Also, if there are many frame filters unwinding the stack during filtering, it can substantially delay the printing of the backtrace which will result in large memory usage, and a poor user experience.
class InlineFilter(): def __init__(self): self.name = "InlinedFrameFilter" self.priority = 100 self.enabled = True gdb.frame_filters[self.name] = self def filter(self, frame_iter): frame_iter = itertools.imap(InlinedFrameDecorator, frame_iter) return frame_iter
This frame filter is somewhat similar to the earlier example, except
that the filter
method applies a frame decorator object called
InlinedFrameDecorator
to each element in the iterator. The
imap
Python method is light-weight. It does not proactively
iterate over the iterator, but rather creates a new iterator which
wraps the existing one.
Below is the frame decorator for this example.
class InlinedFrameDecorator(FrameDecorator): def __init__(self, fobj): super(InlinedFrameDecorator, self).__init__(fobj) def function(self): frame = fobj.inferior_frame() name = str(frame.name()) if frame.type() == gdb.INLINE_FRAME: name = name + " [inlined]" return name
This frame decorator only defines and overrides the function
method. It lets the supplied FrameDecorator
, which is shipped
with gdb, perform the other work associated with printing
this frame.
The combination of these two objects create this output from a backtrace:
#0 0x004004e0 in bar () at inline.c:11 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21 #2 0x00400566 in main () at inline.c:31
So in the case of this example, a frame decorator is applied to all
frames, regardless of whether they may be inlined or not. As
gdb iterates over the iterator produced by the frame filters,
gdb executes each frame decorator which then makes a decision
on what to print in the function
callback. Using a strategy
like this is a way to defer decisions on the frame content to printing
time.
It might be that the above example is not desirable for representing
inlined frames, and a hierarchical approach may be preferred. If we
want to hierarchically represent frames, the elided
frame
decorator interface might be preferable.
This example approaches the issue with the elided
method. This
example is quite long, but very simplistic. It is out-of-scope for
this section to write a complete example that comprehensively covers
all approaches of finding and printing inlined frames. However, this
example illustrates the approach an author might use.
This example comprises of three sections.
class InlineFrameFilter(): def __init__(self): self.name = "InlinedFrameFilter" self.priority = 100 self.enabled = True gdb.frame_filters[self.name] = self def filter(self, frame_iter): return ElidingInlineIterator(frame_iter)
This frame filter is very similar to the other examples. The only
difference is this frame filter is wrapping the iterator provided to
it (frame_iter
) with a custom iterator called
ElidingInlineIterator
. This again defers actions to when
gdb prints the backtrace, as the iterator is not traversed
until printing.
The iterator for this example is as follows. It is in this section of the example where decisions are made on the content of the backtrace.
class ElidingInlineIterator: def __init__(self, ii): self.input_iterator = ii def __iter__(self): return self def next(self): frame = next(self.input_iterator) if frame.inferior_frame().type() != gdb.INLINE_FRAME: return frame try: eliding_frame = next(self.input_iterator) except StopIteration: return frame return ElidingFrameDecorator(eliding_frame, [frame])
This iterator implements the Python iterator protocol. When the
next
function is called (when gdb prints each frame),
the iterator checks if this frame decorator, frame
, is wrapping
an inlined frame. If it is not, it returns the existing frame decorator
untouched. If it is wrapping an inlined frame, it assumes that the
inlined frame was contained within the next oldest frame,
eliding_frame
, which it fetches. It then creates and returns a
frame decorator, ElidingFrameDecorator
, which contains both the
elided frame, and the eliding frame.
class ElidingInlineDecorator(FrameDecorator): def __init__(self, frame, elided_frames): super(ElidingInlineDecorator, self).__init__(frame) self.frame = frame self.elided_frames = elided_frames def elided(self): return iter(self.elided_frames)
This frame decorator overrides one function and returns the inlined
frame in the elided
method. As before it lets
FrameDecorator
do the rest of the work involved in printing
this frame. This produces the following output.
#0 0x004004e0 in bar () at inline.c:11 #2 0x00400529 in main () at inline.c:25 #1 0x00400529 in max (b=6, a=12) at inline.c:15
In that output, max
which has been inlined into main
is
printed hierarchically. Another approach would be to combine the
function
method, and the elided
method to both print a
marker in the inlined frame, and also show the hierarchical
relationship.
In gdb terminology “unwinding” is the process of finding the previous frame (that is, caller's) from the current one. An unwinder has three methods. The first one checks if it can handle given frame (“sniff” it). For the frames it can sniff an unwinder provides two additional methods: it can return frame's ID, and it can fetch registers from the previous frame. A running gdb mantains a list of the unwinders and calls each unwinder's sniffer in turn until it finds the one that recognizes the current frame. There is an API to register an unwinder.
The unwinders that come with gdb handle standard frames. However, mixed language applications (for example, an application running Java Virtual Machine) sometimes use frame layouts that cannot be handled by the gdb unwinders. You can write Python code that can handle such custom frames.
You implement a frame unwinder in Python as a class with which has two
attributes, name
and enabled
, with obvious meanings, and
a single method __call__
, which examines a given frame and
returns an object (an instance of gdb.UnwindInfo class)
describing it. If an unwinder does not recognize a frame, it should
return None
. The code in gdb that enables writing
unwinders in Python uses this object to return frame's ID and previous
frame registers when gdb core asks for them.
An unwinder should do as little work as possible. Some otherwise innocuous operations can cause problems (even crashes, as this code is not not well-hardened yet). For example, making an inferior call from an unwinder is unadvisable, as an inferior call will reset gdb's stack unwinding process, potentially causing re-entrant unwinding.
An object passed to an unwinder (a gdb.PendingFrame
instance)
provides a method to read frame's registers:
This method returns the contents of the register reg in the frame as a
gdb.Value
object. reg can be either a register number or a register name; the values are platform-specific. They are usually found in the corresponding platform-tdep.h file in the gdb source tree. If reg does not name a register for the current architecture, this method will throw an exception.Note that this method will always return a
gdb.Value
for a valid register name. This does not mean that the value will be valid. For example, you may request a register that an earlier unwinder could not unwind—the value will be unavailable. Instead, thegdb.Value
returned from this method will be lazy; that is, its underlying bits will not be fetched until it is first used. So, attempting to use such a value will cause an exception at the point of use.The type of the returned
gdb.Value
depends on the register and the architecture. It is common for registers to have a scalar type, likelong long
; but many other types are possible, such as pointer, pointer-to-function, floating point or vector types.
It also provides a factory method to create a gdb.UnwindInfo
instance to be returned to gdb:
Returns a new
gdb.UnwindInfo
instance identified by given frame_id. The argument is used to build gdb's frame ID using one of functions provided by gdb. frame_id's attributes determine which function will be used, as follows:
sp, pc
- The frame is identified by the given stack address and PC. The stack address must be chosen so that it is constant throughout the lifetime of the frame, so a typical choice is the value of the stack pointer at the start of the function—in the DWARF standard, this would be the “Call Frame Address”.
This is the most common case by far. The other cases are documented for completeness but are only useful in specialized situations.
sp, pc, special
- The frame is identified by the stack address, the PC, and a “special” address. The special address is used on architectures that can have frames that do not change the stack, but which are still distinct, for example the IA-64, which has a second stack for registers. Both sp and special must be constant throughout the lifetime of the frame.
sp
- The frame is identified by the stack address only. Any other stack frame with a matching sp will be considered to match this frame. Inside gdb, this is called a “wild frame”. You will never need this.
Each attribute value should be an instance of
gdb.Value
.
Use PendingFrame.create_unwind_info
method described above to
create a gdb.UnwindInfo
instance. Use the following method to
specify caller registers that have been saved in this frame:
reg identifies the register. It can be a number or a name, just as for the
PendingFrame.read_register
method above. value is a register value (agdb.Value
object).
gdb comes with the module containing the base Unwinder
class. Derive your unwinder class from it and structure the code as
follows:
from gdb.unwinders import Unwinder class FrameId(object): def __init__(self, sp, pc): self.sp = sp self.pc = pc class MyUnwinder(Unwinder): def __init__(....): super(MyUnwinder, self).__init___(<expects unwinder name argument>) def __call__(pending_frame): if not <we recognize frame>: return None # Create UnwindInfo. Usually the frame is identified by the stack # pointer and the program counter. sp = pending_frame.read_register(<SP number>) pc = pending_frame.read_register(<PC number>) unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc)) # Find the values of the registers in the caller's frame and # save them in the result: unwind_info.add_saved_register(<register>, <value>) .... # Return the result: return unwind_info
An object file, a program space, and the gdb proper can have unwinders registered with it.
The gdb.unwinders
module provides the function to register a
unwinder:
locus is specifies an object file or a program space to which unwinder is added. Passing
None
orgdb
adds unwinder to the gdb's global unwinder list. The newly added unwinder will be called before any other unwinder from the same locus. Two unwinders in the same locus cannot have the same name. An attempt to add a unwinder with already existing name raises an exception unless replace isTrue
, in which case the old unwinder is deleted.
gdb first calls the unwinders from all the object files in no particular order, then the unwinders from the current program space, and finally the unwinders from gdb.
Xmethods are additional methods or replacements for existing methods of a C++ class. This feature is useful for those cases where a method defined in C++ source code could be inlined or optimized out by the compiler, making it unavailable to gdb. For such cases, one can define an xmethod to serve as a replacement for the method defined in the C++ source code. gdb will then invoke the xmethod, instead of the C++ method, to evaluate expressions. One can also use xmethods when debugging with core files. Moreover, when debugging live programs, invoking an xmethod need not involve running the inferior (which can potentially perturb its state). Hence, even if the C++ method is available, it is better to use its replacement xmethod if one is defined.
The xmethods feature in Python is available via the concepts of an
xmethod matcher and an xmethod worker. To
implement an xmethod, one has to implement a matcher and a
corresponding worker for it (more than one worker can be
implemented, each catering to a different overloaded instance of the
method). Internally, gdb invokes the match
method of a
matcher to match the class type and method name. On a match, the
match
method returns a list of matching worker objects.
Each worker object typically corresponds to an overloaded instance of
the xmethod. They implement a get_arg_types
method which
returns a sequence of types corresponding to the arguments the xmethod
requires. gdb uses this sequence of types to perform
overload resolution and picks a winning xmethod worker. A winner
is also selected from among the methods gdb finds in the
C++ source code. Next, the winning xmethod worker and the
winning C++ method are compared to select an overall winner. In
case of a tie between a xmethod worker and a C++ method, the
xmethod worker is selected as the winner. That is, if a winning
xmethod worker is found to be equivalent to the winning C++
method, then the xmethod worker is treated as a replacement for
the C++ method. gdb uses the overall winner to invoke the
method. If the winning xmethod worker is the overall winner, then
the corresponding xmethod is invoked via the __call__
method
of the worker object.
If one wants to implement an xmethod as a replacement for an existing C++ method, then they have to implement an equivalent xmethod which has exactly the same name and takes arguments of exactly the same type as the C++ method. If the user wants to invoke the C++ method even though a replacement xmethod is available for that method, then they can disable the xmethod.
See Xmethod API, for API to implement xmethods in Python. See Writing an Xmethod, for implementing xmethods in Python.
The gdb Python API provides classes, interfaces and functions to implement, register and manipulate xmethods. See Xmethods In Python.
An xmethod matcher should be an instance of a class derived from
XMethodMatcher
defined in the module gdb.xmethod
, or an
object with similar interface and attributes. An instance of
XMethodMatcher
has the following attributes:
A list of named methods managed by the matcher. Each object in the list is an instance of the class
XMethod
defined in the modulegdb.xmethod
, or any object with the following attributes:
name
- Name of the xmethod which should be unique for each xmethod managed by the matcher.
enabled
- A boolean value indicating whether the xmethod is enabled or disabled.
The class
XMethod
is a convenience class with same attributes as above along with the following constructor:
The XMethodMatcher
class has the following methods:
Constructs an enabled xmethod matcher with name name. The
methods
attribute is initialized toNone
.
Derived classes should override this method. It should return a xmethod worker object (or a sequence of xmethod worker objects) matching the class_type and method_name. class_type is a
gdb.Type
object, and method_name is a string value. If the matcher manages named methods as listed in itsmethods
attribute, then only those worker objects whose corresponding entries in themethods
list are enabled should be returned.
An xmethod worker should be an instance of a class derived from
XMethodWorker
defined in the module gdb.xmethod
,
or support the following interface:
This method returns a sequence of
gdb.Type
objects corresponding to the arguments that the xmethod takes. It can return an empty sequence orNone
if the xmethod does not take any arguments. If the xmethod takes a single argument, then a singlegdb.Type
object corresponding to it can be returned.
This method returns a
gdb.Type
object representing the type of the result of invoking this xmethod. The args argument is the same tuple of arguments that would be passed to the__call__
method of this worker.
This is the method which does the work of the xmethod. The args arguments is the tuple of arguments to the xmethod. Each element in this tuple is a gdb.Value object. The first element is always the
this
pointer value.
For gdb to lookup xmethods, the xmethod matchers
should be registered using the following function defined in the module
gdb.xmethod
:
The
matcher
is registered withlocus
, replacing an existing matcher with the same name asmatcher
ifreplace
isTrue
.locus
can be agdb.Objfile
object (see Objfiles In Python), or agdb.Progspace
object (see Progspaces In Python), orNone
. If it isNone
, thenmatcher
is registered globally.
Implementing xmethods in Python will require implementing xmethod matchers and xmethod workers (see Xmethods In Python). Consider the following C++ class:
class MyClass { public: MyClass (int a) : a_(a) { } int geta (void) { return a_; } int operator+ (int b); private: int a_; }; int MyClass::operator+ (int b) { return a_ + b; }
Let us define two xmethods for the class MyClass
, one
replacing the method geta
, and another adding an overloaded
flavor of operator+
which takes a MyClass
argument (the
C++ code above already has an overloaded operator+
which takes an int
argument). The xmethod matcher can be
defined as follows:
class MyClass_geta(gdb.xmethod.XMethod): def __init__(self): gdb.xmethod.XMethod.__init__(self, 'geta') def get_worker(self, method_name): if method_name == 'geta': return MyClassWorker_geta() class MyClass_sum(gdb.xmethod.XMethod): def __init__(self): gdb.xmethod.XMethod.__init__(self, 'sum') def get_worker(self, method_name): if method_name == 'operator+': return MyClassWorker_plus() class MyClassMatcher(gdb.xmethod.XMethodMatcher): def __init__(self): gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher') # List of methods 'managed' by this matcher self.methods = [MyClass_geta(), MyClass_sum()] def match(self, class_type, method_name): if class_type.tag != 'MyClass': return None workers = [] for method in self.methods: if method.enabled: worker = method.get_worker(method_name) if worker: workers.append(worker) return workers
Notice that the match
method of MyClassMatcher
returns
a worker object of type MyClassWorker_geta
for the geta
method, and a worker object of type MyClassWorker_plus
for the
operator+
method. This is done indirectly via helper classes
derived from gdb.xmethod.XMethod
. One does not need to use the
methods
attribute in a matcher as it is optional. However, if a
matcher manages more than one xmethod, it is a good practice to list the
xmethods in the methods
attribute of the matcher. This will then
facilitate enabling and disabling individual xmethods via the
enable/disable
commands. Notice also that a worker object is
returned only if the corresponding entry in the methods
attribute
of the matcher is enabled.
The implementation of the worker classes returned by the matcher setup above is as follows:
class MyClassWorker_geta(gdb.xmethod.XMethodWorker): def get_arg_types(self): return None def get_result_type(self, obj): return gdb.lookup_type('int') def __call__(self, obj): return obj['a_'] class MyClassWorker_plus(gdb.xmethod.XMethodWorker): def get_arg_types(self): return gdb.lookup_type('MyClass') def get_result_type(self, obj): return gdb.lookup_type('int') def __call__(self, obj, other): return obj['a_'] + other['a_']
For gdb to actually lookup a xmethod, it has to be registered with it. The matcher defined above is registered with gdb globally as follows:
gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
If an object obj
of type MyClass
is initialized in C++
code as follows:
MyClass obj(5);
then, after loading the Python script defining the xmethod matchers
and workers into GDBN
, invoking the method geta
or using
the operator +
on obj
will invoke the xmethods
defined above:
(gdb) p obj.geta() $1 = 5 (gdb) p obj + obj $2 = 10
Consider another example with a C++ template class:
template <class T> class MyTemplate { public: MyTemplate () : dsize_(10), data_ (new T [10]) { } ~MyTemplate () { delete [] data_; } int footprint (void) { return sizeof (T) * dsize_ + sizeof (MyTemplate<T>); } private: int dsize_; T *data_; };
Let us implement an xmethod for the above class which serves as a
replacement for the footprint
method. The full code listing
of the xmethod workers and xmethod matchers is as follows:
class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker): def __init__(self, class_type): self.class_type = class_type def get_arg_types(self): return None def get_result_type(self): return gdb.lookup_type('int') def __call__(self, obj): return (self.class_type.sizeof + obj['dsize_'] * self.class_type.template_argument(0).sizeof) class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher): def __init__(self): gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher') def match(self, class_type, method_name): if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>', class_type.tag) and method_name == 'footprint'): return MyTemplateWorker_footprint(class_type)
Notice that, in this example, we have not used the methods
attribute of the matcher as the matcher manages only one xmethod. The
user can enable/disable this xmethod by enabling/disabling the matcher
itself.
Programs which are being run under gdb are called inferiors
(see Inferiors and Programs). Python scripts can access
information about and manipulate inferiors controlled by gdb
via objects of the gdb.Inferior
class.
The following inferior-related functions are available in the gdb
module:
A gdb.Inferior
object has the following attributes:
Process ID of the inferior, as assigned by the underlying operating system.
Boolean signaling whether the inferior was created using `attach', or started by gdb itself.
A gdb.Inferior
object has the following methods:
Returns
True
if thegdb.Inferior
object is valid,False
if not. Agdb.Inferior
object will become invalid if the inferior no longer exists within gdb. All othergdb.Inferior
methods will throw an exception if it is invalid at the time the method is called.
This method returns a tuple holding all the threads which are valid when it is called. If there are no valid threads, the method will return an empty tuple.
Return the
gdb.Architecture
(see Architectures In Python) for this inferior. This represents the architecture of the inferior as a whole. Some platforms can have multiple architectures in a single address space, so this may not match the architecture of a particular frame (see Frames In Python).
Read length addressable memory units from the inferior, starting at address. Returns a buffer object, which behaves much like an array or a string. It can be modified and given to the
Inferior.write_memory
function. In Python 3, the return value is amemoryview
object.
Write the contents of buffer to the inferior, starting at address. The buffer parameter must be a Python object which supports the buffer protocol, i.e., a string, an array or the object returned from
Inferior.read_memory
. If given, length determines the number of addressable memory units from buffer to be written.
Search a region of the inferior memory starting at address with the given length using the search pattern supplied in pattern. The pattern parameter must be a Python object which supports the buffer protocol, i.e., a string, an array or the object returned from
gdb.read_memory
. Returns a PythonLong
containing the address where the pattern was found, orNone
if the pattern could not be found.
Return the thread object corresponding to handle, a thread library specific data structure such as
pthread_t
for pthreads library implementations.The function
Inferior.thread_from_thread_handle
provides the same functionality, but use ofInferior.thread_from_thread_handle
is deprecated.
gdb provides a general event facility so that Python code can be notified of various state changes, particularly changes that occur in the inferior.
An event is just an object that describes some state change. The type of the object and its attributes will vary depending on the details of the change. All the existing events are described below.
In order to be notified of an event, you must register an event handler
with an event registry. An event registry is an object in the
gdb.events
module which dispatches particular events. A registry
provides methods to register and unregister event handlers:
Add the given callable object to the registry. This object will be called when an event corresponding to this registry occurs.
Remove the given object from the registry. Once removed, the object will no longer receive notifications of events.
Here is an example:
def exit_handler (event): print "event type: exit" print "exit code: %d" % (event.exit_code) gdb.events.exited.connect (exit_handler)
In the above example we connect our handler exit_handler
to the
registry events.exited
. Once connected, exit_handler
gets
called when the inferior exits. The argument event in this example is
of type gdb.ExitedEvent
. As you can see in the example the
ExitedEvent
object has an attribute which indicates the exit code of
the inferior.
The following is a listing of the event registries that are available and details of the events they emit:
events.cont
gdb.ThreadEvent
.
Some events can be thread specific when gdb is running in non-stop
mode. When represented in Python, these events all extend
gdb.ThreadEvent
. Note, this event is not emitted directly; instead,
events which are emitted by this or other modules might extend this event.
Examples of these events are gdb.BreakpointEvent
and
gdb.ContinueEvent
.
In non-stop mode this attribute will be set to the specific thread which was involved in the emitted event. Otherwise, it will be set to
None
.
Emits gdb.ContinueEvent
which extends gdb.ThreadEvent
.
This event indicates that the inferior has been continued after a stop. For
inherited attribute refer to gdb.ThreadEvent
above.
events.exited
events.ExitedEvent
which indicates that the inferior has exited.
events.ExitedEvent
has two attributes:
An integer representing the exit code, if available, which the inferior has returned. (The exit code could be unavailable if, for example, gdb detaches from the inferior.) If the exit code is unavailable, the attribute does not exist.
events.stop
gdb.StopEvent
which extends gdb.ThreadEvent
.
Indicates that the inferior has stopped. All events emitted by this registry
extend StopEvent. As a child of gdb.ThreadEvent
, gdb.StopEvent
will indicate the stopped thread when gdb is running in non-stop
mode. Refer to gdb.ThreadEvent
above for more details.
Emits gdb.SignalEvent
which extends gdb.StopEvent
.
This event indicates that the inferior or one of its threads has received as
signal. gdb.SignalEvent
has the following attributes:
A string representing the signal received by the inferior. A list of possible signal values can be obtained by running the command
info signals
in the gdb command prompt.
Also emits gdb.BreakpointEvent
which extends gdb.StopEvent
.
gdb.BreakpointEvent
event indicates that one or more breakpoints have
been hit, and has the following attributes:
A sequence containing references to all the breakpoints (type
gdb.Breakpoint
) that were hit. See Breakpoints In Python, for details of thegdb.Breakpoint
object.
A reference to the first breakpoint that was hit. This function is maintained for backward compatibility and is now deprecated in favor of the
gdb.BreakpointEvent.breakpoints
attribute.
events.new_objfile
gdb.NewObjFileEvent
which indicates that a new object file has
been loaded by gdb. gdb.NewObjFileEvent
has one attribute:
A reference to the object file (
gdb.Objfile
) which has been loaded. See Objfiles In Python, for details of thegdb.Objfile
object.
events.clear_objfiles
gdb.ClearObjFilesEvent
which indicates that the list of object
files for a program space has been reset.
gdb.ClearObjFilesEvent
has one attribute:
A reference to the program space (
gdb.Progspace
) whose objfile list has been cleared. See Progspaces In Python.
events.inferior_call
gdb.InferiorCallPreEvent
, and after an inferior call,
this emits an event of type gdb.InferiorCallPostEvent
.
gdb.InferiorCallPreEvent
gdb.InferiorCallPostEvent
events.memory_changed
gdb.MemoryChangedEvent
which indicates that the memory of the
inferior has been modified by the gdb user, for instance via a
command like set *addr = value
. The event has the following
attributes:
events.register_changed
gdb.RegisterChangedEvent
which indicates that a register in the
inferior has been modified by the gdb user.
A gdb.Frame object representing the frame in which the register was modified.
events.breakpoint_created
gdb.Breakpoint
object.
events.breakpoint_modified
gdb.Breakpoint
object.
events.breakpoint_deleted
gdb.Breakpoint
object. When this event is
emitted, the gdb.Breakpoint
object will already be in its
invalid state; that is, the is_valid
method will return
False
.
events.before_prompt
events.new_inferior
The event is of type gdb.NewInferiorEvent
. This has a single
attribute:
events.inferior_deleted
remove-inferiors
.
The event is of type gdb.InferiorDeletedEvent
. This has a single
attribute:
events.new_thread
gdb.NewThreadEvent
, which extends gdb.ThreadEvent
.
This has a single attribute:
Python scripts can access information about, and manipulate inferior threads
controlled by gdb, via objects of the gdb.InferiorThread
class.
The following thread-related functions are available in the gdb
module:
This function returns the thread object for the selected thread. If there is no selected thread, this will return
None
.
To get the list of threads for an inferior, use the Inferior.threads()
method. See Inferiors In Python
A gdb.InferiorThread
object has the following attributes:
The name of the thread. If the user specified a name using
thread name
, then this returns that name. Otherwise, if an OS-supplied name is available, then it is returned. Otherwise, this returnsNone
.This attribute can be assigned to. The new value must be a string object, which sets the new name, or
None
, which removes any user-specified thread name.
The global ID of the thread, as assigned by GDB. You can use this to make Python breakpoints thread-specific, for example (see The Breakpoint.thread attribute).
ID of the thread, as assigned by the operating system. This attribute is a tuple containing three integers. The first is the Process ID (PID); the second is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID). Either the LWPID or TID may be 0, which indicates that the operating system does not use that identifier.
The inferior this thread belongs to. This attribute is represented as a
gdb.Inferior
object. This attribute is not writable.
A gdb.InferiorThread
object has the following methods:
Returns
True
if thegdb.InferiorThread
object is valid,False
if not. Agdb.InferiorThread
object will become invalid if the thread exits, or the inferior that the thread belongs is deleted. All othergdb.InferiorThread
methods will throw an exception if it is invalid at the time the method is called.
This changes gdb's currently selected thread to the one represented by this object.
Return the thread object's handle, represented as a Python
bytes
object. Agdb.Value
representation of the handle may be constructed viagdb.Value(bufobj, type)
where bufobj is the Pythonbytes
representation of the handle and type is agdb.Type
for the handle type.
The following recordings-related functions
(see Process Record and Replay) are available in the gdb
module:
Start a recording using the given method and format. If no format is given, the default format for the recording method is used. If no method is given, the default method will be used. Returns a
gdb.Record
object on success. Throw an exception on failure.The following strings can be passed as method:
"full"
"btrace"
: Possible values for format:"pt"
,"bts"
or leave out for default format.
Access a currently running recording. Return a
gdb.Record
object on success. ReturnNone
if no recording is currently active.
Stop the current recording. Throw an exception if no recording is currently active. All record objects become invalid after this call.
A gdb.Record
object has the following attributes:
A method specific instruction object representing the first instruction in this recording.
A method specific instruction object representing the current instruction, that is not actually part of the recording.
The instruction representing the current replay position. If there is no replay active, this will be
None
.
A gdb.Record
object has the following methods:
The common gdb.Instruction
class that recording method specific
instruction objects inherit from, has the following attributes:
A buffer with the raw instruction data. In Python 3, the return value is a
memoryview
object.
Additionally gdb.RecordInstruction
has the following attributes:
An integer identifying this instruction.
number
corresponds to the numbers seen inrecord instruction-history
(see Process Record and Replay).
A
gdb.Symtab_and_line
object representing the associated symtab and line of this instruction. May beNone
if no debug information is available.
A boolean indicating whether the instruction was executed speculatively.
If an error occured during recording or decoding a recording, this error is
represented by a gdb.RecordGap
object in the instruction list. It has
the following attributes:
An integer identifying this gap.
number
corresponds to the numbers seen inrecord instruction-history
(see Process Record and Replay).
A numerical representation of the reason for the gap. The value is specific to the current recording method.
A gdb.RecordFunctionSegment
object has the following attributes:
An integer identifying this function segment.
number
corresponds to the numbers seen inrecord function-call-history
(see Process Record and Replay).
A
gdb.Symbol
object representing the associated symbol. May beNone
if no debug information is available.
An integer representing the function call's stack level. May be
None
if the function call is a gap.
A list of
gdb.RecordInstruction
orgdb.RecordGap
objects associated with this function call.
A
gdb.RecordFunctionSegment
object representing the caller's function segment. If the call has not been recorded, this will be the function segment to which control returns. If neither the call nor the return have been recorded, this will beNone
.
A
gdb.RecordFunctionSegment
object representing the previous segment of this function call. May beNone
.
A
gdb.RecordFunctionSegment
object representing the next segment of this function call. May beNone
.
The following example demonstrates the usage of these objects and functions to create a function that will rewind a record to the last time a function in a different file was executed. This would typically be used to track the execution of user provided callback functions in a library which typically are not visible in a back trace.
def bringback (): rec = gdb.current_recording () if not rec: return insn = rec.instruction_history if len (insn) == 0: return try: position = insn.index (rec.replay_position) except: position = -1 try: filename = insn[position].sal.symtab.fullname () except: filename = None for i in reversed (insn[:position]): try: current = i.sal.symtab.fullname () except: current = None if filename == current: continue rec.goto (i) return
Another possible application is to write a function that counts the number of code executions in a given line range. This line range can contain parts of functions or span across several functions and is not limited to be contiguous.
def countrange (filename, linerange): count = 0 def filter_only (file_name): for call in gdb.current_recording ().function_call_history: try: if file_name in call.symbol.symtab.fullname (): yield call except: pass for c in filter_only (filename): for i in c.instructions: try: if i.sal.line in linerange: count += 1 break; except: pass return count
You can implement new gdb CLI commands in Python. A CLI
command is implemented using an instance of the gdb.Command
class, most commonly using a subclass.
The object initializer for
Command
registers the new command with gdb. This initializer is normally invoked from the subclass' own__init__
method.name is the name of the command. If name consists of multiple words, then the initial words are looked for as prefix commands. In this case, if one of the prefix commands does not exist, an exception is raised.
There is no support for multi-line commands.
command_class should be one of the ‘COMMAND_’ constants defined below. This argument tells gdb how to categorize the new command in the help system.
completer_class is an optional argument. If given, it should be one of the ‘COMPLETE_’ constants defined below. This argument tells gdb how to perform completion for this command. If not given, gdb will attempt to complete using the object's
complete
method (see below); if no such method is found, an error will occur when completion is attempted.prefix is an optional argument. If
True
, then the new command is a prefix command; sub-commands of this command may be registered.The help text for the new command is taken from the Python documentation string for the command's class, if there is one. If no documentation string is provided, the default value “This command is not documented.” is used.
By default, a gdb command is repeated when the user enters a blank line at the command prompt. A command can suppress this behavior by invoking the
dont_repeat
method. This is similar to the user commanddont-repeat
, see dont-repeat.
This method is called by gdb when this command is invoked.
argument is a string. It is the argument to the command, after leading and trailing whitespace has been stripped.
from_tty is a boolean argument. When true, this means that the command was entered by the user at the terminal; when false it means that the command came from elsewhere.
If this method throws an exception, it is turned into a gdb
error
call. Otherwise, the return value is ignored.To break argument up into an argv-like string use
gdb.string_to_argv
. This function behaves identically to gdb's internal argument lexerbuildargv
. It is recommended to use this for consistency. Arguments are separated by spaces and may be quoted. Example:print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"") ['1', '2 "3', '4 "5', "6 '7"]
This method is called by gdb when the user attempts completion on this command. All forms of completion are handled by this method, that is, the <TAB> and <M-?> key bindings (see Completion), and the
complete
command (see complete).The arguments text and word are both strings; text holds the complete command line up to the cursor's location, while word holds the last word of the command line; this is computed using a word-breaking heuristic.
The
complete
method can return several values:
- If the return value is a sequence, the contents of the sequence are used as the completions. It is up to
complete
to ensure that the contents actually do complete the word. A zero-length sequence is allowed, it means that there were no completions available. Only string elements of the sequence are used; other elements in the sequence are ignored.- If the return value is one of the ‘COMPLETE_’ constants defined below, then the corresponding gdb-internal completion function is invoked, and its result is used.
- All other results are treated as though there were no available completions.
When a new command is registered, it must be declared as a member of
some general class of commands. This is used to classify top-level
commands in the on-line help system; note that prefix commands are not
listed under their own category but rather that of their top-level
command. The available classifications are represented by constants
defined in the gdb
module:
gdb.COMMAND_NONE
gdb.COMMAND_RUNNING
start
, step
, and continue
are in this category.
Type help running at the gdb prompt to see a list of
commands in this category.
gdb.COMMAND_DATA
call
, find
, and print
are in this category. Type
help data at the gdb prompt to see a list of commands
in this category.
gdb.COMMAND_STACK
backtrace
, frame
, and return
are in this
category. Type help stack at the gdb prompt to see a
list of commands in this category.
gdb.COMMAND_FILES
file
, list
and section
are in this category.
Type help files at the gdb prompt to see a list of
commands in this category.
gdb.COMMAND_SUPPORT
help
, make
, and shell
are in this category. Type
help support at the gdb prompt to see a list of
commands in this category.
gdb.COMMAND_STATUS
info
, macro
,
and show
are in this category. Type help status at the
gdb prompt to see a list of commands in this category.
gdb.COMMAND_BREAKPOINTS
break
,
clear
, and delete
are in this category. Type help
breakpoints at the gdb prompt to see a list of commands in
this category.
gdb.COMMAND_TRACEPOINTS
trace
,
actions
, and tfind
are in this category. Type
help tracepoints at the gdb prompt to see a list of
commands in this category.
gdb.COMMAND_USER
gdb.COMMAND_OBSCURE
checkpoint
,
fork
, and stop
are in this category. Type help
obscure at the gdb prompt to see a list of commands in this
category.
gdb.COMMAND_MAINTENANCE
maintenance
and flushregs
commands are in this category.
Type help internals at the gdb prompt to see a list of
commands in this category.
A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it
from the complete
method. These predefined completion
constants are all defined in the gdb
module:
gdb.COMPLETE_NONE
gdb.COMPLETE_FILENAME
gdb.COMPLETE_LOCATION
gdb.COMPLETE_COMMAND
gdb.COMPLETE_SYMBOL
gdb.COMPLETE_EXPRESSION
The following code snippet shows how a trivial CLI command can be implemented in Python:
class HelloWorld (gdb.Command): """Greet the whole world.""" def __init__ (self): super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER) def invoke (self, arg, from_tty): print "Hello, World!" HelloWorld ()
The last line instantiates the class, and is necessary to trigger the
registration of the command with gdb. Depending on how the
Python code is read into gdb, you may need to import the
gdb
module explicitly.
You can implement new gdb parameters using Python. A new
parameter is implemented as an instance of the gdb.Parameter
class.
Parameters are exposed to the user via the set
and
show
commands. See Help.
There are many parameters that already exist and can be set in
gdb. Two examples are: set follow fork
and
set charset
. Setting these parameters influences certain
behavior in gdb. Similarly, you can define parameters that
can be used to influence behavior in custom Python scripts and commands.
The object initializer for
Parameter
registers the new parameter with gdb. This initializer is normally invoked from the subclass' own__init__
method.name is the name of the new parameter. If name consists of multiple words, then the initial words are looked for as prefix parameters. An example of this can be illustrated with the
set print
set of parameters. If name isprint foo
, thenset print foo
.If name consists of multiple words, and no prefix parameter group can be found, an exception is raised.
command-class should be one of the ‘COMMAND_’ constants (see Commands In Python). This argument tells gdb how to categorize the new parameter in the help system.
parameter-class should be one of the ‘PARAM_’ constants defined below. This argument tells gdb the type of the new parameter; this information is used for input validation and completion.
If parameter-class is
PARAM_ENUM
, then enum-sequence must be a sequence of strings. These strings represent the possible values for the parameter.If parameter-class is not
PARAM_ENUM
, then the presence of a fourth argument will cause an exception to be thrown.The help text for the new parameter is taken from the Python documentation string for the parameter's class, if there is one. If there is no documentation string, a default value is used.
If this attribute exists, and is a string, then its value is used as the help text for this parameter's
set
command. The value is examined whenParameter.__init__
is invoked; subsequent changes have no effect.
If this attribute exists, and is a string, then its value is used as the help text for this parameter's
show
command. The value is examined whenParameter.__init__
is invoked; subsequent changes have no effect.
The
value
attribute holds the underlying value of the parameter. It can be read and assigned to just as any other attribute. gdb does validation when assignments are made.
There are two methods that may be implemented in any Parameter
class. These are:
If this method exists, gdb will call it when a parameter's value has been changed via the
set
API (for example, set foo off). Thevalue
attribute has already been populated with the new value and may be used in output. This method must return a string. If the returned string is not empty, gdb will present it to the user.If this method raises the
gdb.GdbError
exception (see Exception Handling), then gdb will print the exception's string and theset
command will fail. Note, however, that thevalue
attribute will not be reset in this case. So, if your parameter must validate values, it should store the old value internally and reset the exposed value, like so:class ExampleParam (gdb.Parameter): def __init__ (self, name): super (ExampleParam, self).__init__ (name, gdb.COMMAND_DATA, gdb.PARAM_BOOLEAN) self.value = True self.saved_value = True def validate(self): return False def get_set_string (self): if not self.validate(): self.value = self.saved_value raise gdb.GdbError('Failed to validate') self.saved_value = self.value
gdb will call this method when a parameter's
show
API has been invoked (for example, show foo). The argumentsvalue
receives the string representation of the current value. This method must return a string.
When a new parameter is defined, its type must be specified. The
available types are represented by constants defined in the gdb
module:
gdb.PARAM_BOOLEAN
True
and False
are the only valid values.
gdb.PARAM_AUTO_BOOLEAN
None
.
gdb.PARAM_UINTEGER
gdb.PARAM_INTEGER
gdb.PARAM_STRING
gdb.PARAM_STRING_NOESCAPE
gdb.PARAM_OPTIONAL_FILENAME
None
.
gdb.PARAM_FILENAME
PARAM_STRING_NOESCAPE
, but uses file names for completion.
gdb.PARAM_ZINTEGER
PARAM_INTEGER
, except 0
is interpreted as itself.
gdb.PARAM_ZUINTEGER
PARAM_INTEGER
,
except 0 is interpreted as itself, and the value cannot be negative.
gdb.PARAM_ZUINTEGER_UNLIMITED
PARAM_ZUINTEGER
,
except the special value -1 should be interpreted to mean
“unlimited”. Other negative values are not allowed.
gdb.PARAM_ENUM
You can implement new convenience functions (see Convenience Vars)
in Python. A convenience function is an instance of a subclass of the
class gdb.Function
.
The initializer for
Function
registers the new function with gdb. The argument name is the name of the function, a string. The function will be visible to the user as a convenience variable of typeinternal function
, whose name is the same as the given name.The documentation for the new function is taken from the documentation string for the new class.
When a convenience function is evaluated, its arguments are converted to instances of
gdb.Value
, and then the function'sinvoke
method is called. Note that gdb does not predetermine the arity of convenience functions. Instead, all available arguments are passed toinvoke
, following the standard Python calling convention. In particular, a convenience function can have default values for parameters without ill effect.The return value of this method is used as its value in the enclosing expression. If an ordinary Python value is returned, it is converted to a
gdb.Value
following the usual rules.
The following code snippet shows how a trivial convenience function can be implemented in Python:
class Greet (gdb.Function): """Return string to greet someone. Takes a name as argument.""" def __init__ (self): super (Greet, self).__init__ ("greet") def invoke (self, name): return "Hello, %s!" % name.string () Greet ()
The last line instantiates the class, and is necessary to trigger the
registration of the function with gdb. Depending on how the
Python code is read into gdb, you may need to import the
gdb
module explicitly.
Now you can use the function in an expression:
(gdb) print $greet("Bob") $1 = "Hello, Bob!"
A program space, or progspace, represents a symbolic view of an address space. It consists of all of the objfiles of the program. See Objfiles In Python. See program spaces, for more details about program spaces.
The following progspace-related functions are available in the
gdb
module:
This function returns the program space of the currently selected inferior. See Inferiors and Programs. This is identical to
gdb.selected_inferior().progspace
(see Inferiors In Python) and is included for historical compatibility.
Each progspace is represented by an instance of the gdb.Progspace
class.
The
pretty_printers
attribute is a list of functions. It is used to look up pretty-printers. AValue
is passed to each function in order; if the function returnsNone
, then the search continues. Otherwise, the return value should be an object which is used to format the value. See Pretty Printing API, for more information.
The
type_printers
attribute is a list of type printer objects. See Type Printing API, for more information.
The
frame_filters
attribute is a dictionary of frame filter objects. See Frame Filter API, for more information.
A program space has the following methods:
Return the innermost
gdb.Block
containing the given pc value. If the block cannot be found for the pc value specified, the function will returnNone
.
Return the
gdb.Symtab_and_line
object corresponding to the pc value. See Symbol Tables In Python. If an invalid value of pc is passed as an argument, then thesymtab
andline
attributes of the returnedgdb.Symtab_and_line
object will beNone
and 0 respectively.
Returns
True
if thegdb.Progspace
object is valid,False
if not. Agdb.Progspace
object can become invalid if the program space file it refers to is not referenced by any inferior. All othergdb.Progspace
methods will throw an exception if it is invalid at the time the method is called.
Return a sequence of all the objfiles referenced by this program space. See Objfiles In Python.
Return the name of the shared library holding the given address as a string, or
None
.
One may add arbitrary attributes to gdb.Progspace
objects
in the usual Python way.
This is useful if, for example, one needs to do some extra record keeping
associated with the program space.
In this contrived example, we want to perform some processing when an objfile with a certain symbol is loaded, but we only want to do this once because it is expensive. To achieve this we record the results with the program space because we can't predict when the desired objfile will be loaded.
(gdb) python def clear_objfiles_handler(event): event.progspace.expensive_computation = None def expensive(symbol): """A mock routine to perform an "expensive" computation on symbol.""" print "Computing the answer to the ultimate question ..." return 42 def new_objfile_handler(event): objfile = event.new_objfile progspace = objfile.progspace if not hasattr(progspace, 'expensive_computation') or \ progspace.expensive_computation is None: # We use 'main' for the symbol to keep the example simple. # Note: There's no current way to constrain the lookup # to one objfile. symbol = gdb.lookup_global_symbol('main') if symbol is not None: progspace.expensive_computation = expensive(symbol) gdb.events.clear_objfiles.connect(clear_objfiles_handler) gdb.events.new_objfile.connect(new_objfile_handler) end (gdb) file /tmp/hello Reading symbols from /tmp/hello...done. Computing the answer to the ultimate question ... (gdb) python print gdb.current_progspace().expensive_computation 42 (gdb) run Starting program: /tmp/hello Hello. [Inferior 1 (process 4242) exited normally]
gdb loads symbols for an inferior from various symbol-containing files (see Files). These include the primary executable file, any shared libraries used by the inferior, and any separate debug info files (see Separate Debug Files). gdb calls these symbol-containing files objfiles.
The following objfile-related functions are available in the
gdb
module:
When auto-loading a Python script (see Python Auto-loading), gdb sets the “current objfile” to the corresponding objfile. This function returns the current objfile. If there is no current objfile, this function returns
None
.
Return a sequence of objfiles referenced by the current program space. See Objfiles In Python, and Progspaces In Python. This is identical to
gdb.selected_inferior().progspace.objfiles()
and is included for historical compatibility.
Look up name, a file name or build ID, in the list of objfiles for the current program space (see Progspaces In Python). If the objfile is not found throw the Python
ValueError
exception.If name is a relative file name, then it will match any source file name with the same trailing components. For example, if name is ‘gcc/expr.c’, then it will match source file name of /build/trunk/gcc/expr.c, but not /build/trunk/libcpp/expr.c or /build/trunk/gcc/x-expr.c.
If by_build_id is provided and is
True
then name is the build ID of the objfile. Otherwise, name is a file name. This is supported only on some operating systems, notably those which use the ELF format for binary files and the gnu Binutils. For more details about this feature, see the description of the --build-id command-line option in Command Line Options.
Each objfile is represented by an instance of the gdb.Objfile
class.
The file name of the objfile as a string, with symbolic links resolved.
The value is
None
if the objfile is no longer valid. See thegdb.Objfile.is_valid
method, described below.
The file name of the objfile as specified by the user as a string.
The value is
None
if the objfile is no longer valid. See thegdb.Objfile.is_valid
method, described below.
For separate debug info objfiles this is the corresponding
gdb.Objfile
object that debug info is being provided for. Otherwise this isNone
. Separate debug info objfiles are added with thegdb.Objfile.add_separate_debug_file
method, described below.
The build ID of the objfile as a string. If the objfile does not have a build ID then the value is
None
.This is supported only on some operating systems, notably those which use the ELF format for binary files and the gnu Binutils. For more details about this feature, see the description of the --build-id command-line option in Command Line Options.
The containing program space of the objfile as a
gdb.Progspace
object. See Progspaces In Python.
The
pretty_printers
attribute is a list of functions. It is used to look up pretty-printers. AValue
is passed to each function in order; if the function returnsNone
, then the search continues. Otherwise, the return value should be an object which is used to format the value. See Pretty Printing API, for more information.
The
type_printers
attribute is a list of type printer objects. See Type Printing API, for more information.
The
frame_filters
attribute is a dictionary of frame filter objects. See Frame Filter API, for more information.
One may add arbitrary attributes to gdb.Objfile
objects
in the usual Python way.
This is useful if, for example, one needs to do some extra record keeping
associated with the objfile.
In this contrived example we record the time when gdb loaded the objfile.
(gdb) python import datetime def new_objfile_handler(event): # Set the time_loaded attribute of the new objfile. event.new_objfile.time_loaded = datetime.datetime.today() gdb.events.new_objfile.connect(new_objfile_handler) end (gdb) file ./hello Reading symbols from ./hello...done. (gdb) python print gdb.objfiles()[0].time_loaded 2014-10-09 11:41:36.770345
A gdb.Objfile
object has the following methods:
Returns
True
if thegdb.Objfile
object is valid,False
if not. Agdb.Objfile
object can become invalid if the object file it refers to is not loaded in gdb any longer. All othergdb.Objfile
methods will throw an exception if it is invalid at the time the method is called.
Add file to the list of files that gdb will search for debug information for the objfile. This is useful when the debug info has been removed from the program and stored in a separate file. gdb has built-in support for finding separate debug info files (see Separate Debug Files), but if the file doesn't live in one of the standard places that gdb searches then this function can be used to add a debug info file from a different place.
Search for a global symbol named name in this objfile. Optionally, the search scope can be restricted with the domain argument. The domain argument must be a domain constant defined in the
gdb
module and described in Symbols In Python. This function is similar togdb.lookup_global_symbol
, except that the search is limited to this objfile.The result is a
gdb.Symbol
object orNone
if the symbol is not found.
Like
Objfile.lookup_global_symbol
, but searches for a global symbol with static linkage named name in this objfile.
When the debugged program stops, gdb is able to analyze its call
stack (see Stack frames). The gdb.Frame
class
represents a frame in the stack. A gdb.Frame
object is only valid
while its corresponding frame exists in the inferior's stack. If you try
to use an invalid frame object, gdb will throw a gdb.error
exception (see Exception Handling).
Two gdb.Frame
objects can be compared for equality with the ==
operator, like:
(gdb) python print gdb.newest_frame() == gdb.selected_frame () True
The following frame-related functions are available in the gdb
module:
Return a string explaining the reason why gdb stopped unwinding frames, as expressed by the given reason code (an integer, see the
unwind_stop_reason
method further down in this section).
gdb internally keeps a cache of the frames that have been unwound. This function invalidates this cache.
This function should not generally be called by ordinary Python code. It is documented for the sake of completeness.
A gdb.Frame
object has the following methods:
Returns true if the
gdb.Frame
object is valid, false if not. A frame object can become invalid if the frame it refers to doesn't exist anymore in the inferior. Allgdb.Frame
methods will throw an exception if it is invalid at the time the method is called.
Returns the
gdb.Architecture
object corresponding to the frame's architecture. See Architectures In Python.
Returns the type of the frame. The value can be one of:
gdb.NORMAL_FRAME
- An ordinary stack frame.
gdb.DUMMY_FRAME
- A fake stack frame that was created by gdb when performing an inferior function call.
gdb.INLINE_FRAME
- A frame representing an inlined function. The function was inlined into a
gdb.NORMAL_FRAME
that is older than this one.gdb.TAILCALL_FRAME
- A frame representing a tail call. See Tail Call Frames.
gdb.SIGTRAMP_FRAME
- A signal trampoline frame. This is the frame created by the OS when it calls into a signal handler.
gdb.ARCH_FRAME
- A fake stack frame representing a cross-architecture call.
gdb.SENTINEL_FRAME
- This is like
gdb.NORMAL_FRAME
, but it is only used for the newest frame.
Return an integer representing the reason why it's not possible to find more frames toward the outermost frame. Use
gdb.frame_stop_reason_string
to convert the value returned by this function to a string. The value can be one of:
gdb.FRAME_UNWIND_NO_REASON
- No particular reason (older frames should be available).
gdb.FRAME_UNWIND_NULL_ID
- The previous frame's analyzer returns an invalid result. This is no longer used by gdb, and is kept only for backward compatibility.
gdb.FRAME_UNWIND_OUTERMOST
- This frame is the outermost.
gdb.FRAME_UNWIND_UNAVAILABLE
- Cannot unwind further, because that would require knowing the values of registers or memory that have not been collected.
gdb.FRAME_UNWIND_INNER_ID
- This frame ID looks like it ought to belong to a NEXT frame, but we got it for a PREV frame. Normally, this is a sign of unwinder failure. It could also indicate stack corruption.
gdb.FRAME_UNWIND_SAME_ID
- This frame has the same ID as the previous one. That means that unwinding further would almost certainly give us another frame with exactly the same ID, so break the chain. Normally, this is a sign of unwinder failure. It could also indicate stack corruption.
gdb.FRAME_UNWIND_NO_SAVED_PC
- The frame unwinder did not find any saved PC, but we needed one to unwind further.
gdb.FRAME_UNWIND_MEMORY_ERROR
- The frame unwinder caused an error while trying to access memory.
gdb.FRAME_UNWIND_FIRST_ERROR
- Any stop reason greater or equal to this value indicates some kind of error. This special value facilitates writing code that tests for errors in unwinding in a way that will work correctly even if the list of the other values is modified in future gdb versions. Using it, you could write:
reason = gdb.selected_frame().unwind_stop_reason () reason_str = gdb.frame_stop_reason_string (reason) if reason >= gdb.FRAME_UNWIND_FIRST_ERROR: print "An error occured: %s" % reason_str
Return the frame's code block. See Blocks In Python. If the frame does not have a block – for example, if there is no debugging information for the code in question – then this will throw an exception.
Return the symbol for the function corresponding to this frame. See Symbols In Python.
Return the frame's symtab and line object. See Symbol Tables In Python.
Return the value of register in this frame. The register argument must be a string (e.g.,
'sp'
or'rax'
). Returns aGdb.Value
object. Throws an exception if register does not exist.
Return the value of variable in this frame. If the optional argument block is provided, search for the variable from that block; otherwise start at the frame's current block (which is determined by the frame's current program counter). The variable argument must be a string or a
gdb.Symbol
object; block must be agdb.Block
object.
In gdb, symbols are stored in blocks. A block corresponds
roughly to a scope in the source code. Blocks are organized
hierarchically, and are represented individually in Python as a
gdb.Block
. Blocks rely on debugging information being
available.
A frame has a block. Please see Frames In Python, for a more in-depth discussion of frames.
The outermost block is known as the global block. The global block typically holds public global variables and functions.
The block nested just inside the global block is the static block. The static block typically holds file-scoped variables and functions.
gdb provides a method to get a block's superblock, but there is currently no way to examine the sub-blocks of a block, or to iterate over all the blocks in a symbol table (see Symbol Tables In Python).
Here is a short example that should help explain blocks:
/* This is in the global block. */ int global; /* This is in the static block. */ static int file_scope; /* 'function' is in the global block, and 'argument' is in a block nested inside of 'function'. */ int function (int argument) { /* 'local' is in a block inside 'function'. It may or may not be in the same block as 'argument'. */ int local; { /* 'inner' is in a block whose superblock is the one holding 'local'. */ int inner; /* If this call is expanded by the compiler, you may see a nested block here whose function is 'inline_function' and whose superblock is the one holding 'inner'. */ inline_function (); } }
A gdb.Block
is iterable. The iterator returns the symbols
(see Symbols In Python) local to the block. Python programs
should not assume that a specific block object will always contain a
given symbol, since changes in gdb features and
infrastructure may cause symbols move across blocks in a symbol
table. You can also use Python's dictionary syntax to access
variables in this block, e.g.:
symbol = some_block['variable'] # symbol is of type gdb.Symbol
The following block-related functions are available in the gdb
module:
Return the innermost
gdb.Block
containing the given pc value. If the block cannot be found for the pc value specified, the function will returnNone
. This is identical togdb.current_progspace().block_for_pc(pc)
and is included for historical compatibility.
A gdb.Block
object has the following methods:
Returns
True
if thegdb.Block
object is valid,False
if not. A block object can become invalid if the block it refers to doesn't exist anymore in the inferior. All othergdb.Block
methods will throw an exception if it is invalid at the time the method is called. The block's validity is also checked during iteration over symbols of the block.
A gdb.Block
object has the following attributes:
One past the last address that appears in the block. This attribute is not writable.
The name of the block represented as a
gdb.Symbol
. If the block is not named, then this attribute holdsNone
. This attribute is not writable.For ordinary function blocks, the superblock is the static block. However, you should note that it is possible for a function block to have a superblock that is not the static block – for instance this happens for an inlined function.
The block containing this block. If this parent block does not exist, this attribute holds
None
. This attribute is not writable.
The global block associated with this block. This attribute is not writable.
The static block associated with this block. This attribute is not writable.
True
if thegdb.Block
object is a global block,False
if not. This attribute is not writable.
True
if thegdb.Block
object is a static block,False
if not. This attribute is not writable.
gdb represents every variable, function and type as an
entry in a symbol table. See Examining the Symbol Table.
Similarly, Python represents these symbols in gdb with the
gdb.Symbol
object.
The following symbol-related functions are available in the gdb
module:
This function searches for a symbol by name. The search scope can be restricted to the parameters defined in the optional domain and block arguments.
name is the name of the symbol. It must be a string. The optional block argument restricts the search to symbols visible in that block. The block argument must be a
gdb.Block
object. If omitted, the block for the current frame is used. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in thegdb
module and described later in this chapter.The result is a tuple of two elements. The first element is a
gdb.Symbol
object orNone
if the symbol is not found. If the symbol is found, the second element isTrue
if the symbol is a field of a method's object (e.g.,this
in C++), otherwise it isFalse
. If the symbol is not found, the second element isFalse
.
This function searches for a global symbol by name. The search scope can be restricted to by the domain argument.
name is the name of the symbol. It must be a string. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in the
gdb
module and described later in this chapter.The result is a
gdb.Symbol
object orNone
if the symbol is not found.
This function searches for a global symbol with static linkage by name. The search scope can be restricted to by the domain argument.
name is the name of the symbol. It must be a string. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in the
gdb
module and described later in this chapter.The result is a
gdb.Symbol
object orNone
if the symbol is not found.Note that this function will not find function-scoped static variables. To look up such variables, iterate over the variables of the function's
gdb.Block
and check thatblock.addr_class
isgdb.SYMBOL_LOC_STATIC
.There can be multiple global symbols with static linkage with the same name. This function will only return the first matching symbol that it finds. Which symbol is found depends on where gdb is currently stopped, as gdb will first search for matching symbols in the current object file, and then search all other object files. If the application is not yet running then gdb will search all object files in the order they appear in the debug information.
Similar to
gdb.lookup_static_symbol
, this function searches for global symbols with static linkage by name, and optionally restricted by the domain argument. However, this function returns a list of all matching symbols found, not just the first one.name is the name of the symbol. It must be a string. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in the
gdb
module and described later in this chapter.The result is a list of
gdb.Symbol
objects which could be empty if no matching symbols were found.Note that this function will not find function-scoped static variables. To look up such variables, iterate over the variables of the function's
gdb.Block
and check thatblock.addr_class
isgdb.SYMBOL_LOC_STATIC
.
A gdb.Symbol
object has the following attributes:
The type of the symbol or
None
if no type is recorded. This attribute is represented as agdb.Type
object. See Types In Python. This attribute is not writable.
The symbol table in which the symbol appears. This attribute is represented as a
gdb.Symtab
object. See Symbol Tables In Python. This attribute is not writable.
The line number in the source code at which the symbol was defined. This is an integer.
The name of the symbol, as used by the linker (i.e., may be mangled). This attribute is not writable.
The name of the symbol in a form suitable for output. This is either
name
orlinkage_name
, depending on whether the user asked gdb to display demangled or mangled names.
The address class of the symbol. This classifies how to find the value of a symbol. Each address class is a constant defined in the
gdb
module and described later in this chapter.
This is
True
if evaluating this symbol's value requires a frame (see Frames In Python) andFalse
otherwise. Typically, local variables will require a frame, but other symbols will not.
A gdb.Symbol
object has the following methods:
Returns
True
if thegdb.Symbol
object is valid,False
if not. Agdb.Symbol
object can become invalid if the symbol it refers to does not exist in gdb any longer. All othergdb.Symbol
methods will throw an exception if it is invalid at the time the method is called.
Compute the value of the symbol, as a
gdb.Value
. For functions, this computes the address of the function, cast to the appropriate type. If the symbol requires a frame in order to compute its value, then frame must be given. If frame is not given, or if frame is invalid, then this method will throw an exception.
The available domain categories in gdb.Symbol
are represented
as constants in the gdb
module:
gdb.SYMBOL_UNDEF_DOMAIN
gdb.SYMBOL_VAR_DOMAIN
gdb.SYMBOL_STRUCT_DOMAIN
gdb.SYMBOL_LABEL_DOMAIN
gdb.SYMBOL_MODULE_DOMAIN
gdb.SYMBOL_COMMON_BLOCK_DOMAIN
The available address class categories in gdb.Symbol
are represented
as constants in the gdb
module:
gdb.SYMBOL_LOC_UNDEF
gdb.SYMBOL_LOC_CONST
gdb.SYMBOL_LOC_STATIC
gdb.SYMBOL_LOC_REGISTER
gdb.SYMBOL_LOC_ARG
gdb.SYMBOL_LOC_REF_ARG
LOC_ARG
except that the value's address is stored at the
offset, not the value itself.
gdb.SYMBOL_LOC_REGPARM_ADDR
LOC_REGISTER
except
the register holds the address of the argument instead of the argument
itself.
gdb.SYMBOL_LOC_LOCAL
gdb.SYMBOL_LOC_TYPEDEF
SYMBOL_STRUCT_DOMAIN
all
have this class.
gdb.SYMBOL_LOC_BLOCK
gdb.SYMBOL_LOC_CONST_BYTES
gdb.SYMBOL_LOC_UNRESOLVED
gdb.SYMBOL_LOC_OPTIMIZED_OUT
gdb.SYMBOL_LOC_COMPUTED
gdb.SYMBOL_LOC_COMPUTED
Access to symbol table data maintained by gdb on the inferior
is exposed to Python via two objects: gdb.Symtab_and_line
and
gdb.Symtab
. Symbol table and line data for a frame is returned
from the find_sal
method in gdb.Frame
object.
See Frames In Python.
For more information on gdb's symbol table management, see Examining the Symbol Table, for more information.
A gdb.Symtab_and_line
object has the following attributes:
The symbol table object (
gdb.Symtab
) for this frame. This attribute is not writable.
Indicates the start of the address range occupied by code for the current source line. This attribute is not writable.
Indicates the end of the address range occupied by code for the current source line. This attribute is not writable.
Indicates the current line number for this object. This attribute is not writable.
A gdb.Symtab_and_line
object has the following methods:
Returns
True
if thegdb.Symtab_and_line
object is valid,False
if not. Agdb.Symtab_and_line
object can become invalid if the Symbol table and line object it refers to does not exist in gdb any longer. All othergdb.Symtab_and_line
methods will throw an exception if it is invalid at the time the method is called.
A gdb.Symtab
object has the following attributes:
The symbol table's backing object file. See Objfiles In Python. This attribute is not writable.
The name and possibly version number of the program that compiled the code in the symbol table. The contents of this string is up to the compiler. If no producer information is available then
None
is returned. This attribute is not writable.
A gdb.Symtab
object has the following methods:
Returns
True
if thegdb.Symtab
object is valid,False
if not. Agdb.Symtab
object can become invalid if the symbol table it refers to does not exist in gdb any longer. All othergdb.Symtab
methods will throw an exception if it is invalid at the time the method is called.
Return the global block of the underlying symbol table. See Blocks In Python.
Return the static block of the underlying symbol table. See Blocks In Python.
Return the line table associated with the symbol table. See Line Tables In Python.
Python code can request and inspect line table information from a
symbol table that is loaded in gdb. A line table is a
mapping of source lines to their executable locations in memory. To
acquire the line table information for a particular symbol table, use
the linetable
function (see Symbol Tables In Python).
A gdb.LineTable
is iterable. The iterator returns
LineTableEntry
objects that correspond to the source line and
address for each line table entry. LineTableEntry
objects have
the following attributes:
The source line number for this line table entry. This number corresponds to the actual line of source. This attribute is not writable.
The address that is associated with the line table entry where the executable code for that source line resides in memory. This attribute is not writable.
As there can be multiple addresses for a single source line, you may
receive multiple LineTableEntry
objects with matching
line
attributes, but with different pc
attributes. The
iterator is sorted in ascending pc
order. Here is a small
example illustrating iterating over a line table.
symtab = gdb.selected_frame().find_sal().symtab linetable = symtab.linetable() for line in linetable: print "Line: "+str(line.line)+" Address: "+hex(line.pc)
This will have the following output:
Line: 33 Address: 0x4005c8L Line: 37 Address: 0x4005caL Line: 39 Address: 0x4005d2L Line: 40 Address: 0x4005f8L Line: 42 Address: 0x4005ffL Line: 44 Address: 0x400608L Line: 42 Address: 0x40060cL Line: 45 Address: 0x400615L
In addition to being able to iterate over a LineTable
, it also
has the following direct access methods:
Return a Python
Tuple
ofLineTableEntry
objects for any entries in the line table for the given line, which specifies the source code line. If there are no entries for that source code line, the PythonNone
is returned.
Return a Python
Boolean
indicating whether there is an entry in the line table for this source line. ReturnTrue
if an entry is found, orFalse
if not.
Return a Python
List
of the source line numbers in the symbol table. Only lines with executable code locations are returned. The contents of theList
will just be the source line entries represented as PythonLong
values.
Python code can manipulate breakpoints via the gdb.Breakpoint
class.
A breakpoint can be created using one of the two forms of the
gdb.Breakpoint
constructor. The first one accepts a string
like one would pass to the break
(see Setting Breakpoints) and watch
(see Setting Watchpoints) commands, and can be used to
create both breakpoints and watchpoints. The second accepts separate Python
arguments similar to Explicit Locations, and can only be used to create
breakpoints.
Create a new breakpoint according to spec, which is a string naming the location of a breakpoint, or an expression that defines a watchpoint. The string should describe a location in a format recognized by the
break
command (see Setting Breakpoints) or, in the case of a watchpoint, by thewatch
command (see Setting Watchpoints).The optional type argument specifies the type of the breakpoint to create, as defined below.
The optional wp_class argument defines the class of watchpoint to create, if type is
gdb.BP_WATCHPOINT
. If wp_class is omitted, it defaults togdb.WP_WRITE
.The optional internal argument allows the breakpoint to become invisible to the user. The breakpoint will neither be reported when created, nor will it be listed in the output from
info breakpoints
(but will be listed with themaint info breakpoints
command).The optional temporary argument makes the breakpoint a temporary breakpoint. Temporary breakpoints are deleted after they have been hit. Any further access to the Python breakpoint after it has been hit will result in a runtime error (as that breakpoint has now been automatically deleted).
The optional qualified argument is a boolean that allows interpreting the function passed in
spec
as a fully-qualified name. It is equivalent tobreak
's-qualified
flag (see Linespec Locations and Explicit Locations).
This second form of creating a new breakpoint specifies the explicit location (see Explicit Locations) using keywords. The new breakpoint will be created in the specified source file source, at the specified function, label and line.
internal, temporary and qualified have the same usage as explained previously.
The available types are represented by constants defined in the gdb
module:
gdb.BP_BREAKPOINT
gdb.BP_WATCHPOINT
gdb.BP_HARDWARE_WATCHPOINT
gdb.BP_READ_WATCHPOINT
gdb.BP_ACCESS_WATCHPOINT
The available watchpoint types represented by constants are defined in the
gdb
module:
gdb.WP_READ
gdb.WP_WRITE
gdb.WP_ACCESS
The
gdb.Breakpoint
class can be sub-classed and, in particular, you may choose to implement thestop
method. If this method is defined in a sub-class ofgdb.Breakpoint
, it will be called when the inferior reaches any location of a breakpoint which instantiates that sub-class. If the method returnsTrue
, the inferior will be stopped at the location of the breakpoint, otherwise the inferior will continue.If there are multiple breakpoints at the same location with a
stop
method, each one will be called regardless of the return status of the previous. This ensures that allstop
methods have a chance to execute at that location. In this scenario if one of the methods returnsTrue
but the others returnFalse
, the inferior will still be stopped.You should not alter the execution state of the inferior (i.e., step, next, etc.), alter the current frame context (i.e., change the current active frame), or alter, add or delete any breakpoint. As a general rule, you should not alter any data within gdb or the inferior at this time.
Example
stop
implementation:class MyBreakpoint (gdb.Breakpoint): def stop (self): inf_val = gdb.parse_and_eval("foo") if inf_val == 3: return True return False
Return
True
if thisBreakpoint
object is valid,False
otherwise. ABreakpoint
object can become invalid if the user deletes the breakpoint. In this case, the object still exists, but the underlying breakpoint does not. In the cases of watchpoint scope, the watchpoint remains valid even if execution of the inferior leaves the scope of that watchpoint.
Permanently deletes the gdb breakpoint. This also invalidates the Python
Breakpoint
object. Any further access to this object's attributes or methods will raise an error.
This attribute is
True
if the breakpoint is enabled, andFalse
otherwise. This attribute is writable. You can use it to enable or disable the breakpoint.
This attribute is
True
if the breakpoint is silent, andFalse
otherwise. This attribute is writable.Note that a breakpoint can also be silent if it has commands and the first command is
silent
. This is not reported by thesilent
attribute.
This attribute is
True
if the breakpoint is pending, andFalse
otherwise. See Set Breaks. This attribute is read-only.
If the breakpoint is thread-specific, this attribute holds the thread's global id. If the breakpoint is not thread-specific, this attribute is
None
. This attribute is writable.
If the breakpoint is Ada task-specific, this attribute holds the Ada task id. If the breakpoint is not task-specific (or the underlying language is not Ada), this attribute is
None
. This attribute is writable.
This attribute holds the ignore count for the breakpoint, an integer. This attribute is writable.
This attribute holds the breakpoint's number — the identifier used by the user to manipulate the breakpoint. This attribute is not writable.
This attribute holds the breakpoint's type — the identifier used to determine the actual breakpoint type or use-case. This attribute is not writable.
This attribute tells whether the breakpoint is visible to the user when set, or when the ‘info breakpoints’ command is run. This attribute is not writable.
This attribute indicates whether the breakpoint was created as a temporary breakpoint. Temporary breakpoints are automatically deleted after that breakpoint has been hit. Access to this attribute, and all other attributes and functions other than the
is_valid
function, will result in an error after the breakpoint has been hit (as it has been automatically deleted). This attribute is not writable.
This attribute holds the hit count for the breakpoint, an integer. This attribute is writable, but currently it can only be set to zero.
This attribute holds the location of the breakpoint, as specified by the user. It is a string. If the breakpoint does not have a location (that is, it is a watchpoint) the attribute's value is
None
. This attribute is not writable.
This attribute holds a breakpoint expression, as specified by the user. It is a string. If the breakpoint does not have an expression (the breakpoint is not a watchpoint) the attribute's value is
None
. This attribute is not writable.
This attribute holds the condition of the breakpoint, as specified by the user. It is a string. If there is no condition, this attribute's value is
None
. This attribute is writable.
This attribute holds the commands attached to the breakpoint. If there are commands, this attribute's value is a string holding all the commands, separated by newlines. If there are no commands, this attribute is
None
. This attribute is writable.
A finish breakpoint is a temporary breakpoint set at the return address of
a frame, based on the finish
command. gdb.FinishBreakpoint
extends gdb.Breakpoint
. The underlying breakpoint will be disabled
and deleted when the execution will run out of the breakpoint scope (i.e.
Breakpoint.stop
or FinishBreakpoint.out_of_scope
triggered).
Finish breakpoints are thread specific and must be create with the right
thread selected.
Create a finish breakpoint at the return address of the
gdb.Frame
object frame. If frame is not provided, this defaults to the newest frame. The optional internal argument allows the breakpoint to become invisible to the user. See Breakpoints In Python, for further details about this argument.
In some circumstances (e.g.
longjmp
, C++ exceptions, gdbreturn
command, ...), a function may not properly terminate, and thus never hit the finish breakpoint. When gdb notices such a situation, theout_of_scope
callback will be triggered.You may want to sub-class
gdb.FinishBreakpoint
and override this method:class MyFinishBreakpoint (gdb.FinishBreakpoint) def stop (self): print "normal finish" return True def out_of_scope (): print "abnormal finish"
When gdb is stopped at a finish breakpoint and the frame used to build the
gdb.FinishBreakpoint
object had debug symbols, this attribute will contain agdb.Value
object corresponding to the return value of the function. The value will beNone
if the function return type isvoid
or if the return value was not computable. This attribute is not writable.
A lazy string is a string whose contents is not retrieved or encoded until it is needed.
A gdb.LazyString
is represented in gdb as an
address
that points to a region of memory, an encoding
that will be used to encode that region of memory, and a length
to delimit the region of memory that represents the string. The
difference between a gdb.LazyString
and a string wrapped within
a gdb.Value
is that a gdb.LazyString
will be treated
differently by gdb when printing. A gdb.LazyString
is
retrieved and encoded during printing, while a gdb.Value
wrapping a string is immediately retrieved and encoded on creation.
A gdb.LazyString
object has the following functions:
Convert the
gdb.LazyString
to agdb.Value
. This value will point to the string in memory, but will lose all the delayed retrieval, encoding and handling that gdb applies to agdb.LazyString
.
This attribute holds the address of the string. This attribute is not writable.
This attribute holds the length of the string in characters. If the length is -1, then the string will be fetched and encoded up to the first null of appropriate width. This attribute is not writable.
This attribute holds the encoding that will be applied to the string when the string is printed by gdb. If the encoding is not set, or contains an empty string, then gdb will select the most appropriate encoding when the string is printed. This attribute is not writable.
This attribute holds the type that is represented by the lazy string's type. For a lazy string this is a pointer or array type. To resolve this to the lazy string's character type, use the type's
target
method. See Types In Python. This attribute is not writable.
gdb uses architecture specific parameters and artifacts in a
number of its various computations. An architecture is represented
by an instance of the gdb.Architecture
class.
A gdb.Architecture
class has the following methods:
Return a list of disassembled instructions starting from the memory address start_pc. The optional arguments end_pc and count determine the number of instructions in the returned list. If both the optional arguments end_pc and count are specified, then a list of at most count disassembled instructions whose start address falls in the closed memory address interval from start_pc to end_pc are returned. If end_pc is not specified, but count is specified, then count number of instructions starting from the address start_pc are returned. If count is not specified but end_pc is specified, then all instructions whose start address falls in the closed memory address interval from start_pc to end_pc are returned. If neither end_pc nor count are specified, then a single instruction at start_pc is returned. For all of these cases, each element of the returned list is a Python
dict
with the following string keys:
addr
- The value corresponding to this key is a Python long integer capturing the memory address of the instruction.
asm
- The value corresponding to this key is a string value which represents the instruction with assembly language mnemonics. The assembly language flavor used is the same as that specified by the current CLI variable
disassembly-flavor
. See Machine Code.length
- The value corresponding to this key is the length (integer value) of the instruction in bytes.
When a new object file is read (for example, due to the file
command, or because the inferior has loaded a shared library),
gdb will look for Python support scripts in several ways:
objfile-gdb.py and .debug_gdb_scripts
section.
See Auto-loading extensions.
The auto-loading feature is useful for supplying application-specific debugging commands and scripts.
Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be printed.
set auto-load python-scripts [on|off]
show auto-load python-scripts
info auto-load python-scripts [
regexp]
Also printed is the list of Python scripts that were mentioned in
the .debug_gdb_scripts
section and were either not found
(see dotdebug_gdb_scripts section) or were not auto-loaded due to
auto-load safe-path
rejection (see Auto-loading).
This is useful because their names are not printed when gdb
tries to load them and fails. There may be many of them, and printing
an error message for each one is problematic.
If regexp is supplied only Python scripts with matching names are printed.
Example:
(gdb) info auto-load python-scripts Loaded Script Yes py-section-script.py full name: /tmp/py-section-script.py No my-foo-pretty-printers.py
When reading an auto-loaded file or script, gdb sets the
current objfile. This is available via the gdb.current_objfile
function (see Objfiles In Python). This can be useful for
registering objfile-specific pretty-printers and frame-filters.
gdb comes with several modules to assist writing Python code.
This module provides a collection of utilities for working with pretty-printers.
PrettyPrinter (
name,
subprinters=None)
SubPrettyPrinter (
name)
RegexpCollectionPrettyPrinter (
name)
FlagEnumerationPrinter (
name)
enum
values. Unlike
gdb's built-in enum
printing, this printer attempts to
work properly when there is some overlap between the enumeration
constants. The argument name is the name of the printer and
also the name of the enum
type to look up.
register_pretty_printer (
obj,
printer,
replace=False)
True
then any existing copy of the printer
is replaced. Otherwise a RuntimeError
exception is raised
if a printer with the same name already exists.
This module provides a collection of utilities for working with
gdb.Type
objects.
get_basic_type (
type)
C++ example:
typedef const int const_int; const_int foo (3); const_int& foo_ref (foo); int main () { return 0; }
Then in gdb:
(gdb) start (gdb) python import gdb.types (gdb) python foo_ref = gdb.parse_and_eval("foo_ref") (gdb) python print gdb.types.get_basic_type(foo_ref.type) int
has_field (
type,
field)
True
if type, assumed to be a type with fields
(e.g., a structure or union), has field field.
make_enum_dict (
enum_type)
dictionary
type produced from enum_type.
deep_items (
type)
gdb.Type.iteritems
method, except that the iterator returned
by deep_items
will recursively traverse anonymous struct or
union fields. For example:
struct A { int a; union { int b0; int b1; }; };
Then in gdb:
(gdb) python import gdb.types (gdb) python struct_a = gdb.lookup_type("struct A") (gdb) python print struct_a.keys () {['a', '']} (gdb) python print [k for k,v in gdb.types.deep_items(struct_a)] {['a', 'b0', 'b1']}
get_type_recognizers ()
apply_type_recognizers (recognizers, type_obj)
None
. This is called by
gdb during the type-printing process (see Type Printing API).
register_type_printer (locus, printer)
gdb.Objfile
, in which case
the printer is registered with that objfile; a gdb.Progspace
,
in which case the printer is registered with that progspace; or
None
, in which case the printer is registered globally.
TypePrinter
This module provides a method for prompt value-substitution.
substitute_prompt (
string)
The escape sequences you can pass to this function are:
\\
\e
\f
\n
\p
\r
\t
\v
\w
\[
\]
For example:
substitute_prompt ("frame: \f, args: \p{print frame-arguments}")
will return the string:
"frame: main, args: scalars"
You can extend gdb using the Guile implementation of the Scheme programming language. This feature is available only if gdb was configured using --with-guile.
Guile is an implementation of the Scheme programming language and is the GNU project's official extension language.
Guile support in gdb follows the Python support in gdb reasonably closely, so concepts there should carry over. However, some things are done differently where it makes sense.
gdb requires Guile version 2.0 or greater. Older versions are not supported.
Guile scripts used by gdb should be installed in data-directory/guile, where data-directory is the data directory as determined at gdb startup (see Data Files). This directory, known as the guile directory, is automatically added to the Guile Search Path in order to allow the Guile interpreter to locate all scripts installed at this location.
gdb provides two commands for accessing the Guile interpreter:
guile-repl
gr
guile-repl
command can be used to start an interactive
Guile prompt or repl. To return to gdb,
type ,q or the EOF
character (e.g., Ctrl-D on
an empty prompt). These commands do not take any arguments.
guile
[scheme-expression]gu
[scheme-expression]guile
command can be used to evaluate a Scheme expression.
If given an argument, gdb will pass the argument to the Guile interpreter for evaluation.
(gdb) guile (display (+ 20 3)) (newline) 23
The result of the Scheme expression is displayed using normal Guile rules.
(gdb) guile (+ 20 3) 23
If you do not provide an argument to guile
, it will act as a
multi-line command, like define
. In this case, the Guile
script is made up of subsequent command lines, given after the
guile
command. This command list is terminated using a line
containing end
. For example:
(gdb) guile >(display 23) >(newline) >end 23
It is also possible to execute a Guile script from the gdb interpreter:
source
script-namescript-extension
setting. See Extending GDB.
guile (load "script-name")
load
Guile function.
It takes a string argument that is the name of the script to load.
See the Guile documentation for a description of this function.
(see Loading).
You can get quick online help for gdb's Guile API by issuing the command help guile, or by issuing the command ,help from an interactive Guile session. Furthermore, most Guile procedures provided by gdb have doc strings which can be obtained with ,describe procedure-name or ,d procedure-name from the Guile interactive prompt.
At startup, gdb overrides Guile's current-output-port
and
current-error-port
to print using gdb's output-paging streams.
A Guile program which outputs to one of these streams may have its
output interrupted by the user (see Screen Size). In this
situation, a Guile signal
exception is thrown with value SIGINT
.
Guile's history mechanism uses the same naming as gdb's,
namely the user of dollar-variables (e.g., $1, $2, etc.).
The results of evaluations in Guile and in GDB are counted separately,
$1
in Guile is not the same value as $1
in gdb.
gdb is not thread-safe. If your Guile program uses multiple threads, you must be careful to only call gdb-specific functions in the gdb thread.
Some care must be taken when writing Guile code to run in gdb. Two things are worth noting in particular:
SIGCHLD
and SIGINT
.
Guile code must not override these, or even change the options using
sigaction
. If your program changes the handling of these
signals, gdb will most likely stop working correctly. Note
that it is unfortunately common for GUI toolkits to install a
SIGCHLD
handler.
gdb introduces a new Guile module, named gdb
. All
methods and classes added by gdb are placed in this module.
gdb does not automatically import
the gdb
module,
scripts must do this themselves. There are various options for how to
import a module, so gdb leaves the choice of how the gdb
module is imported to the user.
To simplify interactive use, it is recommended to add one of the following
to your ~/.gdbinit.
guile (use-modules (gdb))
guile (use-modules ((gdb) #:renamer (symbol-prefix-proc 'gdb:)))
Which one to choose depends on your preference.
The second one adds gdb:
as a prefix to all module functions
and variables.
The rest of this manual assumes the gdb
module has been imported
without any prefix. See the Guile documentation for use-modules
for more information
(see Using Guile Modules).
Example:
(gdb) guile (value-type (make-value 1)) ERROR: Unbound variable: value-type Error while executing Scheme code. (gdb) guile (use-modules (gdb)) (gdb) guile (value-type (make-value 1)) int (gdb)
The (gdb)
module provides these basic Guile functions.
Evaluate command, a string, as a gdb CLI command. If a gdb exception happens while command runs, it is translated as described in Guile Exception Handling.
from-tty specifies whether gdb ought to consider this command as having originated from the user invoking it interactively. It must be a boolean value. If omitted, it defaults to
#f
.By default, any output produced by command is sent to gdb's standard output (and to the log output if logging is turned on). If the to-string parameter is
#t
, then output will be collected byexecute
and returned as a string. The default is#f
, in which case the return value is unspecified. If to-string is#t
, the gdb virtual terminal will be temporarily set to unlimited width and height, and its pagination will be disabled; see Screen Size.
Return a value from gdb's value history (see Value History). The number argument indicates which history element to return. If number is negative, then gdb will take its absolute value and count backward from the last element (i.e., the most recent element) to find the value to return. If number is zero, then gdb will return the most recent element. If the element specified by number doesn't exist in the value history, a
gdb:error
exception will be raised.If no exception is raised, the return value is always an instance of
<gdb:value>
(see Values From Inferior In Guile).Note: gdb's value history is independent of Guile's.
$1
in gdb's value history contains the result of evaluating an expression from gdb's command line and$1
from Guile's history contains the result of evaluating an expression from Guile's command line.
Append value, an instance of
<gdb:value>
, to gdb's value history. Return its index in the history.Putting into history values returned by Guile extensions will allow the user convenient access to those values via CLI history facilities.
Parse expression as an expression in the current language, evaluate it, and return the result as a
<gdb:value>
. The expression must be a string.This function can be useful when implementing a new command (see Commands In Guile), as it provides a way to parse the command's arguments as an expression. It is also is useful when computing values. For example, it is the only way to get the value of a convenience variable (see Convenience Vars) as a
<gdb:value>
.
gdb provides these Scheme functions to access various configuration parameters.
Return a string containing gdb's data directory. This directory contains gdb's ancillary files.
Return a string containing gdb's Guile data directory. This directory contains the Guile modules provided by gdb.
Return a string containing the host configuration. This is the string passed to
--host
when gdb was configured.
Return a string containing the target configuration. This is the string passed to
--target
when gdb was configured.
The values exposed by gdb to Guile are known as gdb objects. There are several kinds of gdb object, and each is disjoint from all other types known to Guile.
Return the kind of the gdb object, e.g.,
<gdb:breakpoint>
, as a symbol.
gdb defines the following object types:
<gdb:arch>
<gdb:block>
<gdb:block-symbols-iterator>
<gdb:breakpoint>
<gdb:command>
<gdb:exception>
<gdb:frame>
<gdb:iterator>
<gdb:lazy-string>
<gdb:objfile>
<gdb:parameter>
<gdb:pretty-printer>
<gdb:pretty-printer-worker>
<gdb:progspace>
<gdb:symbol>
<gdb:symtab>
<gdb:sal>
<gdb:type>
<gdb:field>
<gdb:value>
The following gdb objects are managed internally so that the
Scheme function eq?
may be applied to them.
<gdb:arch>
<gdb:block>
<gdb:breakpoint>
<gdb:frame>
<gdb:objfile>
<gdb:progspace>
<gdb:symbol>
<gdb:symtab>
<gdb:type>
When executing the guile
command, Guile exceptions
uncaught within the Guile code are translated to calls to the
gdb error-reporting mechanism. If the command that called
guile
does not handle the error, gdb will
terminate it and report the error according to the setting of
the guile print-stack
parameter.
The guile print-stack
parameter has three settings:
none
message
(gdb) guile (display foo) ERROR: In procedure memoize-variable-access!: ERROR: Unbound variable: foo Error while executing Scheme code.
full
(gdb) set guile print-stack full (gdb) guile (display foo) Guile Backtrace: In ice-9/boot-9.scm: 157: 10 [catch #t #<catch-closure 2c76e20> ...] In unknown file: ?: 9 [apply-smob/1 #<catch-closure 2c76e20>] In ice-9/boot-9.scm: 157: 8 [catch #t #<catch-closure 2c76d20> ...] In unknown file: ?: 7 [apply-smob/1 #<catch-closure 2c76d20>] ?: 6 [call-with-input-string "(display foo)" ...] In ice-9/boot-9.scm: 2320: 5 [save-module-excursion #<procedure 2c2dc30 ... ()>] In ice-9/eval-string.scm: 44: 4 [read-and-eval #<input: string 27cb410> #:lang ...] 37: 3 [lp (display foo)] In ice-9/eval.scm: 387: 2 [eval # ()] 393: 1 [eval #<memoized foo> ()] In unknown file: ?: 0 [memoize-variable-access! #<memoized foo> ...] ERROR: In procedure memoize-variable-access!: ERROR: Unbound variable: foo Error while executing Scheme code.
gdb errors that happen in gdb commands invoked by Guile code are converted to Guile exceptions. The type of the Guile exception depends on the error.
Guile procedures provided by gdb can throw the standard
Guile exceptions like wrong-type-arg
and out-of-range
.
User interrupt (via C-c or by typing q at a pagination
prompt) is translated to a Guile signal
exception with value
SIGINT
.
gdb Guile procedures can also throw these exceptions:
gdb:error
gdb:invalid-object
<gdb:breakpoint>
object becomes invalid if the user deletes it
from the command line. The object still exists in Guile, but the
object it represents is gone. Further operations on this breakpoint
will throw this exception.
gdb:memory-error
gdb:pp-type-error
The following exception-related procedures are provided by the
(gdb)
module.
Return a
<gdb:exception>
object given by its key and args, which are the standard Guile parameters of an exception. See the Guile documentation for more information (see Exceptions).
Return
#t
if object is a<gdb:exception>
object. Otherwise return#f
.
gdb provides values it obtains from the inferior program in
an object of type <gdb:value>
. gdb uses this object
for its internal bookkeeping of the inferior's values, and for
fetching values when necessary.
gdb does not memoize <gdb:value>
objects.
make-value
always returns a fresh object.
(gdb) guile (eq? (make-value 1) (make-value 1)) $1 = #f (gdb) guile (equal? (make-value 1) (make-value 1)) $1 = #t
A <gdb:value>
that represents a function can be executed via
inferior function call with value-call
.
Any arguments provided to the call must match the function's prototype,
and must be provided in the order specified by that prototype.
For example, some-val
is a <gdb:value>
instance
representing a function that takes two integers as arguments. To
execute this function, call it like so:
(define result (value-call some-val 10 20))
Any values returned from a function call are <gdb:value>
objects.
Note: Unlike Python scripting in gdb,
inferior values that are simple scalars cannot be used directly in
Scheme expressions that are valid for the value's data type.
For example, (+ (parse-and-eval "int_variable") 2)
does not work.
And inferior values that are structures or instances of some class cannot
be accessed using any special syntax, instead value-field
must be used.
The following value-related procedures are provided by the
(gdb)
module.
Many Scheme values can be converted directly to a
<gdb:value>
with this procedure. If type is specified, the result is a value of this type, and if value can't be represented with this type an exception is thrown. Otherwise the type of the result is determined from value as described below.See Architectures In Guile, for a list of the builtin types for an architecture.
Here's how Scheme values are converted when type argument to
make-value
is not specified:
- Scheme boolean
- A Scheme boolean is converted the boolean type for the current language.
- Scheme integer
- A Scheme integer is converted to the first of a C
int
,unsigned int
,long
,unsigned long
,long long
orunsigned long long
type for the current architecture that can represent the value.If the Scheme integer cannot be represented as a target integer an
out-of-range
exception is thrown.- Scheme real
- A Scheme real is converted to the C
double
type for the current architecture.- Scheme string
- A Scheme string is converted to a string in the current target language using the current target encoding. Characters that cannot be represented in the current target encoding are replaced with the corresponding escape sequence. This is Guile's
SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE
conversion strategy (see Strings).Passing type is not supported in this case, if it is provided a
wrong-type-arg
exception is thrown.<gdb:lazy-string>
- If value is a
<gdb:lazy-string>
object (see Lazy Strings In Guile), then thelazy-string->value
procedure is called, and its result is used.Passing type is not supported in this case, if it is provided a
wrong-type-arg
exception is thrown.- Scheme bytevector
- If value is a Scheme bytevector and type is provided, value must be the same size, in bytes, of values of type type, and the result is essentially created by using
memcpy
.If value is a Scheme bytevector and type is not provided, the result is an array of type
uint8
of the same length.
Return
#t
if the compiler optimized out value, thus it is not available for fetching from the inferior. Otherwise return#f
.
If value is addressable, returns a
<gdb:value>
object representing the address. Otherwise,#f
is returned.
Return the type of value as a
<gdb:type>
object (see Types In Guile).
Return the dynamic type of value. This uses C++ run-time type information (RTTI) to determine the dynamic type of the value. If the value is of class type, it will return the class in which the value is embedded, if any. If the value is of pointer or reference to a class type, it will compute the dynamic type of the referenced object, and return a pointer or reference to that type, respectively. In all other cases, it will return the value's static type.
Note that this feature will only work when debugging a C++ program that includes RTTI for the object in question. Otherwise, it will just return the static type of the value as in ptype foo. See ptype.
Return a new instance of
<gdb:value>
that is the result of casting value to the type described by type, which must be a<gdb:type>
object. If the cast cannot be performed for some reason, this method throws an exception.
Like
value-cast
, but works as if the C++dynamic_cast
operator were used. Consult a C++ reference for details.
Like
value-cast
, but works as if the C++reinterpret_cast
operator were used. Consult a C++ reference for details.
For pointer data types, this method returns a new
<gdb:value>
object whose contents is the object pointed to by value. For example, iffoo
is a C pointer to anint
, declared in your C program asint *foo;then you can use the corresponding
<gdb:value>
to access whatfoo
points to like this:(define bar (value-dereference foo))The result
bar
will be a<gdb:value>
object holding the value pointed to byfoo
.A similar function
value-referenced-value
exists which also returns<gdb:value>
objects corresponding to the values pointed to by pointer values (and additionally, values referenced by reference values). However, the behavior ofvalue-dereference
differs fromvalue-referenced-value
by the fact that the behavior ofvalue-dereference
is identical to applying the C unary operator*
on a given value. For example, consider a reference to a pointerptrref
, declared in your C++ program astypedef int *intptr; ... int val = 10; intptr ptr = &val; intptr &ptrref = ptr;Though
ptrref
is a reference value, one can apply the methodvalue-dereference
to the<gdb:value>
object corresponding to it and obtain a<gdb:value>
which is identical to that corresponding toval
. However, if you apply the methodvalue-referenced-value
, the result would be a<gdb:value>
object identical to that corresponding toptr
.(define scm-ptrref (parse-and-eval "ptrref")) (define scm-val (value-dereference scm-ptrref)) (define scm-ptr (value-referenced-value scm-ptrref))The
<gdb:value>
objectscm-val
is identical to that corresponding toval
, andscm-ptr
is identical to that corresponding toptr
. In general,value-dereference
can be applied whenever the C unary operator*
can be applied to the corresponding C value. For those cases where applying bothvalue-dereference
andvalue-referenced-value
is allowed, the results obtained need not be identical (as we have seen in the above example). The results are however identical when applied on<gdb:value>
objects corresponding to pointers (<gdb:value>
objects with type codeTYPE_CODE_PTR
) in a C/C++ program.
For pointer or reference data types, this method returns a new
<gdb:value>
object corresponding to the value referenced by the pointer/reference value. For pointer data types,value-dereference
andvalue-referenced-value
produce identical results. The difference between these methods is thatvalue-dereference
cannot get the values referenced by reference values. For example, consider a reference to anint
, declared in your C++ program asint val = 10; int &ref = val;then applying
value-dereference
to the<gdb:value>
object corresponding toref
will result in an error, while applyingvalue-referenced-value
will result in a<gdb:value>
object identical to that corresponding toval
.(define scm-ref (parse-and-eval "ref")) (define err-ref (value-dereference scm-ref)) ;; error (define scm-val (value-referenced-value scm-ref)) ;; okThe
<gdb:value>
objectscm-val
is identical to that corresponding toval
.
Return field field-name from
<gdb:value>
object value.
Return the value of array value at index index. The value argument must be a subscriptable
<gdb:value>
object.
Perform an inferior function call, taking value as a pointer to the function to call. Each element of list arg-list must be a <gdb:value> object or an object that can be converted to a value. The result is the value returned by the function.
Return the Scheme boolean representing
<gdb:value>
value. The value must be “integer like”. Pointers are ok.
Return the Scheme integer representing
<gdb:value>
value. The value must be “integer like”. Pointers are ok.
Return the Scheme real number representing
<gdb:value>
value. The value must be a number.
Return a Scheme bytevector with the raw contents of
<gdb:value>
value. No transformation, endian or otherwise, is performed.
If value> represents a string, then this method converts the contents to a Guile string. Otherwise, this method will throw an exception.
Values are interpreted as strings according to the rules of the current language. If the optional length argument is given, the string will be converted to that length, and will include any embedded zeroes that the string may contain. Otherwise, for languages where the string is zero-terminated, the entire string will be converted.
For example, in C-like languages, a value is a string if it is a pointer to or an array of characters or ints of type
wchar_t
,char16_t
, orchar32_t
.If the optional encoding argument is given, it must be a string naming the encoding of the string in the
<gdb:value>
, such as"ascii"
,"iso-8859-6"
or"utf-8"
. It accepts the same encodings as the corresponding argument to Guile'sscm_from_stringn
function, and the Guile codec machinery will be used to convert the string. If encoding is not given, or if encoding is the empty string, then either thetarget-charset
(see Character Sets) will be used, or a language-specific encoding will be used, if the current language is able to supply one.The optional errors argument is one of
#f
,error
orsubstitute
.error
andsubstitute
must be symbols. If errors is not specified, or if its value is#f
, then the default conversion strategy is used, which is set with the Scheme functionset-port-conversion-strategy!
. If the value is'error
then an exception is thrown if there is any conversion error. If the value is'substitute
then any conversion error is replaced with question marks. See Strings.If the optional length argument is given, the string will be fetched and converted to the given length. The length must be a Scheme integer and not a
<gdb:value>
integer.
If this
<gdb:value>
represents a string, then this method converts value to a<gdb:lazy-string
(see Lazy Strings In Guile). Otherwise, this method will throw an exception.If the optional encoding argument is given, it must be a string naming the encoding of the
<gdb:lazy-string
. Some examples are:"ascii"
,"iso-8859-6"
or"utf-8"
. If the encoding argument is an encoding that gdb does not recognize, gdb will raise an error.When a lazy string is printed, the gdb encoding machinery is used to convert the string during printing. If the optional encoding argument is not provided, or is an empty string, gdb will automatically select the encoding most suitable for the string type. For further information on encoding in gdb please see Character Sets.
If the optional length argument is given, the string will be fetched and encoded to the length of characters specified. If the length argument is not provided, the string will be fetched and encoded until a null of appropriate width is found. The length must be a Scheme integer and not a
<gdb:value>
integer.
Return
#t
if value has not yet been fetched from the inferior. Otherwise return#f
. gdb does not fetch values until necessary, for efficiency. For example:(define myval (parse-and-eval "somevar"))The value of
somevar
is not fetched at this time. It will be fetched when the value is needed, or when thefetch-lazy
procedure is invoked.
Return a
<gdb:value>
that will be lazily fetched from the target. The object of type<gdb:type>
whose value to fetch is specified by its type and its target memory address, which is a Scheme integer.
If value is a lazy value (
(value-lazy? value)
is#t
), then the value is fetched from the inferior. Any errors that occur in the process will produce a Guile exception.If value is not a lazy value, this method has no effect.
The result of this function is unspecified.
Return the string representation (print form) of
<gdb:value>
value.
The (gdb)
module provides several functions for performing
arithmetic on <gdb:value>
objects.
The arithmetic is performed as if it were done by the target,
and therefore has target semantics which are not necessarily
those of Scheme. For example operations work with a fixed precision,
not the arbitrary precision of Scheme.
Wherever a function takes an integer or pointer as an operand, gdb will convert appropriate Scheme values to perform the operation.
Scheme does not provide a not-equal
function,
and thus Guile support in gdb does not either.
gdb represents types from the inferior in objects of type
<gdb:type>
.
The following type-related procedures are provided by the
(gdb)
module.
Return
#t
if object is an object of type<gdb:type>
. Otherwise return#f
.
This function looks up a type by its name, which must be a string.
If block is given, it is an object of type
<gdb:block>
, and name is looked up in that scope. Otherwise, it is searched for globally.Ordinarily, this function will return an instance of
<gdb:type>
. If the named type cannot be found, it will throw an exception.
Return the type code of type. The type code will be one of the
TYPE_CODE_
constants defined below.
Return the tag name of type. The tag name is the name after
struct
,union
, orenum
in C and C++; not all languages have this concept. If this type has no tag name, then#f
is returned.
Return the name of type. If this type has no name, then
#f
is returned.
Return the print name of type. This returns something even for anonymous types. For example, for an anonymous C struct
"struct {...}"
is returned.
Return the size of this type, in target
char
units. Usually, a target'schar
type will be an 8-bit byte. However, on some unusual platforms, this type may have a different size.
Return a new
<gdb:type>
that represents the real type of type, after removing all layers of typedefs.
Return a new
<gdb:type>
object which represents an array of this type. If one argument is given, it is the inclusive upper bound of the array; in this case the lower bound is zero. If two arguments are given, the first argument is the lower bound of the array, and the second argument is the upper bound of the array. An array's length must not be negative, but the bounds can be.
Return a new
<gdb:type>
object which represents a vector of this type. If one argument is given, it is the inclusive upper bound of the vector; in this case the lower bound is zero. If two arguments are given, the first argument is the lower bound of the vector, and the second argument is the upper bound of the vector. A vector's length must not be negative, but the bounds can be.The difference between an
array
and avector
is that arrays behave like in C: when used in expressions they decay to a pointer to the first element whereas vectors are treated as first class values.
Return a new
<gdb:type>
object which represents a pointer to type.
Return a list of two elements: the low bound and high bound of type. If type does not have a range, an exception is thrown.
Return a new
<gdb:type>
object which represents a reference to type.
Return a new
<gdb:type>
object which represents the target type of type.For a pointer type, the target type is the type of the pointed-to object. For an array type (meaning C-like arrays), the target type is the type of the elements of the array. For a function or method type, the target type is the type of the return value. For a complex type, the target type is the type of the elements. For a typedef, the target type is the aliased type.
If the type does not have a target, this method will throw an exception.
Return a new
<gdb:type>
object which represents aconst
-qualified variant of type.
Return a new
<gdb:type>
object which represents avolatile
-qualified variant of type.
Return a new
<gdb:type>
object which represents an unqualified variant of type. That is, the result is neitherconst
norvolatile
.
Return the fields of type as a list. For structure and union types,
fields
has the usual meaning. Range types have two fields, the minimum and maximum values. Enum types have one field per enum constant. Function and method types have one field per parameter. The base types of C++ classes are also represented as fields. If the type has no fields, or does not fit into one of these categories, an empty list will be returned. See Fields of a type in Guile.
Return the fields of type as a <gdb:iterator> object. See Iterators In Guile.
Return field named field-name in type. The result is an object of type
<gdb:field>
. See Fields of a type in Guile. If the type does not have fields, or field-name is not a field of type, an exception is thrown.For example, if
some-type
is a<gdb:type>
instance holding a structure type, you can access itsfoo
field with:(define bar (type-field some-type "foo"))
bar
will be a<gdb:field>
object.
Return
#t
if<gdb:type>
type has field named name. Otherwise return#f
.
Each type has a code, which indicates what category this type falls
into. The available type categories are represented by constants
defined in the (gdb)
module:
TYPE_CODE_PTR
TYPE_CODE_ARRAY
TYPE_CODE_STRUCT
TYPE_CODE_UNION
TYPE_CODE_ENUM
TYPE_CODE_FLAGS
TYPE_CODE_FUNC
TYPE_CODE_INT
TYPE_CODE_FLT
TYPE_CODE_VOID
void
.
TYPE_CODE_SET
TYPE_CODE_RANGE
TYPE_CODE_STRING
TYPE_CODE_BITSTRING
TYPE_CODE_ERROR
TYPE_CODE_METHOD
TYPE_CODE_METHODPTR
TYPE_CODE_MEMBERPTR
TYPE_CODE_REF
TYPE_CODE_CHAR
TYPE_CODE_BOOL
TYPE_CODE_COMPLEX
TYPE_CODE_TYPEDEF
TYPE_CODE_NAMESPACE
TYPE_CODE_DECFLOAT
TYPE_CODE_INTERNAL_FUNCTION
Further support for types is provided in the (gdb types)
Guile module (see Guile Types Module).
Each field is represented as an object of type <gdb:field>
.
The following field-related procedures are provided by the
(gdb)
module:
Return
#t
if object is an object of type<gdb:field>
. Otherwise return#f
.
Return the type of the field. This is usually an instance of
<gdb:type>
, but it can be#f
in some situations.
Return the bit position of
<gdb:field>
field. This attribute is not available forstatic
fields (as in C++).
If the field is packed, or is a bitfield, return the size of
<gdb:field>
field in bits. Otherwise, zero is returned; in which case the field's size is given by its type.
Return
#t
if the field is artificial, usually meaning that it was provided by the compiler and not the user. Otherwise return#f
.
Return
#t
if the field represents a base class of a C++ structure. Otherwise return#f
.
An example output is provided (see Pretty Printing).
A pretty-printer is represented by an object of type <gdb:pretty-printer>.
Pretty-printer objects are created with make-pretty-printer
.
The following pretty-printer-related procedures are provided by the
(gdb)
module:
Return a
<gdb:pretty-printer>
object named name.lookup-function is a function of one parameter: the value to be printed. If the value is handled by this pretty-printer, then lookup-function returns an object of type <gdb:pretty-printer-worker> to perform the actual pretty-printing. Otherwise lookup-function returns
#f
.
Return
#t
if object is a<gdb:pretty-printer>
object. Otherwise return#f
.
Return
#t
if pretty-printer is enabled. Otherwise return#f
.
Set the enabled flag of pretty-printer to flag. The value returned is unspecified.
Set the list of global pretty-printers to pretty-printers. The value returned is unspecified.
Return an object of type
<gdb:pretty-printer-worker>
.This function takes three parameters:
- ‘display-hint’
- display-hint provides a hint to gdb or gdb front end via MI to change the formatting of the value being printed. The value must be a string or
#f
(meaning there is no hint). Several values for display-hint are predefined by gdb:
- ‘array’
- Indicate that the object being printed is “array-like”. The CLI uses this to respect parameters such as
set print elements
andset print array
.- ‘map’
- Indicate that the object being printed is “map-like”, and that the children of this value can be assumed to alternate between keys and values.
- ‘string’
- Indicate that the object being printed is “string-like”. If the printer's
to-string
function returns a Guile string of some kind, then gdb will call its internal language-specific string-printing function to format the string. For the CLI this means adding quotation marks, possibly escaping some characters, respectingset print elements
, and the like.- ‘to-string’
- to-string is either a function of one parameter, the
<gdb:pretty-printer-worker>
object, or#f
.When printing from the CLI, if the
to-string
method exists, then gdb will prepend its result to the values returned bychildren
. Exactly how this formatting is done is dependent on the display hint, and may change as more hints are added. Also, depending on the print settings (see Print Settings), the CLI may print just the result ofto-string
in a stack trace, omitting the result ofchildren
.If this method returns a string, it is printed verbatim.
Otherwise, if this method returns an instance of
<gdb:value>
, then gdb prints this value. This may result in a call to another pretty-printer.If instead the method returns a Guile value which is convertible to a
<gdb:value>
, then gdb performs the conversion and prints the resulting value. Again, this may result in a call to another pretty-printer. Guile scalars (integers, floats, and booleans) and strings are convertible to<gdb:value>
; other types are not.Finally, if this method returns
#f
then no further operations are peformed in this method and nothing is printed.If the result is not one of these types, an exception is raised.
to-string may also be
#f
in which case it is left to children to print the value.- ‘children’
- children is either a function of one parameter, the
<gdb:pretty-printer-worker>
object, or#f
.gdb will call this function on a pretty-printer to compute the children of the pretty-printer's value.
This function must return a <gdb:iterator> object. Each item returned by the iterator must be a tuple holding two elements. The first element is the “name” of the child; the second element is the child's value. The value can be any Guile object which is convertible to a gdb value.
If children is
#f
, gdb will act as though the value has no children.Children may be hidden from display based on the value of ‘set print max-depth’ (see Print Settings).
gdb provides a function which can be used to look up the
default pretty-printer for a <gdb:value>
:
This function takes a
<gdb:value>
object as an argument. If a pretty-printer for this value exists, then it is returned. If no such printer exists, then this returns#f
.
There are three sets of pretty-printers that gdb searches:
Pretty-printer lookup is done by passing the value to be printed to the
lookup function of each enabled object in turn.
Lookup stops when a lookup function returns a non-#f
value
or when the list is exhausted.
Lookup functions must return either a <gdb:pretty-printer-worker>
object or #f
. Otherwise an exception is thrown.
gdb first checks the result of objfile-pretty-printers
of each <gdb:objfile>
in the current program space and iteratively
calls each enabled lookup function in the list for that <gdb:objfile>
until a non-#f
object is returned.
If no pretty-printer is found in the objfile lists, gdb then
searches the result of progspace-pretty-printers
of the current
program space, calling each enabled function until a non-#f
object
is returned.
After these lists have been exhausted, it tries the global pretty-printers
list, obtained with pretty-printers
, again calling each enabled
function until a non-#f
object is returned.
The order in which the objfiles are searched is not specified. For a
given list, functions are always invoked from the head of the list,
and iterated over sequentially until the end of the list, or a
<gdb:pretty-printer-worker>
object is returned.
For various reasons a pretty-printer may not work. For example, the underlying data structure may have changed and the pretty-printer is out of date.
The consequences of a broken pretty-printer are severe enough that
gdb provides support for enabling and disabling individual
printers. For example, if print frame-arguments
is on,
a backtrace can become highly illegible if any argument is printed
with a broken printer.
Pretty-printers are enabled and disabled from Scheme by calling
set-pretty-printer-enabled!
.
See Guile Pretty Printing API.
A pretty-printer consists of two basic parts: a lookup function to determine if the type is supported, and the printer itself.
Here is an example showing how a std::string
printer might be
written. See Guile Pretty Printing API, for details.
(define (make-my-string-printer value) "Print a my::string string" (make-pretty-printer-worker "string" (lambda (printer) (value-field value "_data")) #f))
And here is an example showing how a lookup function for the printer example above might be written.
(define (str-lookup-function pretty-printer value) (let ((tag (type-tag (value-type value)))) (and tag (string-prefix? "std::string<" tag) (make-my-string-printer value))))
Then to register this printer in the global printer list:
(append-pretty-printer! (make-pretty-printer "my-string" str-lookup-function))
The example lookup function extracts the value's type, and attempts to
match it to a type that it can pretty-print. If it is a type the
printer can pretty-print, it will return a <gdb:pretty-printer-worker> object.
If not, it returns #f
.
We recommend that you put your core pretty-printers into a Guile package. If your pretty-printers are for use with a library, we further recommend embedding a version number into the package name. This practice will enable gdb to load multiple versions of your pretty-printers at the same time, because they will have different names.
You should write auto-loaded code (see Guile Auto-loading) such that it
can be evaluated multiple times without changing its meaning. An
ideal auto-load file will consist solely of import
s of your
printer modules, followed by a call to a register pretty-printers with
the current objfile.
Taken as a whole, this approach will scale nicely to multiple inferiors, each potentially using a different library version. Embedding a version number in the Guile package name will ensure that gdb is able to load both sets of printers simultaneously. Then, because the search for pretty-printers is done by objfile, and because your auto-loaded code took care to register your library's printers with a specific objfile, gdb will find the correct printers for the specific version of the library used by each inferior.
To continue the my::string
example,
this code might appear in (my-project my-library v1)
:
(use-modules (gdb)) (define (register-printers objfile) (append-objfile-pretty-printer! (make-pretty-printer "my-string" str-lookup-function)))
And then the corresponding contents of the auto-load file would be:
(use-modules (gdb) (my-project my-library v1)) (register-printers (current-objfile))
The previous example illustrates a basic pretty-printer. There are a few things that can be improved on. The printer only handles one type, whereas a library typically has several types. One could install a lookup function for each desired type in the library, but one could also have a single lookup function recognize several types. The latter is the conventional way this is handled. If a pretty-printer can handle multiple data types, then its subprinters are the printers for the individual data types.
The (gdb printing)
module provides a formal way of solving this
problem (see Guile Printing Module).
Here is another example that handles multiple types.
These are the types we are going to pretty-print:
struct foo { int a, b; }; struct bar { struct foo x, y; };
Here are the printers:
(define (make-foo-printer value) "Print a foo object" (make-pretty-printer-worker "foo" (lambda (printer) (format #f "a=<~a> b=<~a>" (value-field value "a") (value-field value "a"))) #f)) (define (make-bar-printer value) "Print a bar object" (make-pretty-printer-worker "foo" (lambda (printer) (format #f "x=<~a> y=<~a>" (value-field value "x") (value-field value "y"))) #f))
This example doesn't need a lookup function, that is handled by the
(gdb printing)
module. Instead a function is provided to build up
the object that handles the lookup.
(use-modules (gdb printing)) (define (build-pretty-printer) (let ((pp (make-pretty-printer-collection "my-library"))) (pp-collection-add-tag-printer "foo" make-foo-printer) (pp-collection-add-tag-printer "bar" make-bar-printer) pp))
And here is the autoload support:
(use-modules (gdb) (my-library)) (append-objfile-pretty-printer! (current-objfile) (build-pretty-printer))
Finally, when this printer is loaded into gdb, here is the corresponding output of ‘info pretty-printer’:
(gdb) info pretty-printer my_library.so: my-library foo bar
You can implement new gdb CLI commands in Guile. A CLI
command object is created with the make-command
Guile function,
and added to gdb with the register-command!
Guile function.
This two-step approach is taken to separate out the side-effect of adding
the command to gdb from make-command
.
There is no support for multi-line commands, that is commands that
consist of multiple lines and are terminated with end
.
The argument name is the name of the command. If name consists of multiple words, then the initial words are looked for as prefix commands. In this case, if one of the prefix commands does not exist, an exception is raised.
The result is the
<gdb:command>
object representing the command. The command is not usable until it has been registered with gdb withregister-command!
.The rest of the arguments are optional.
The argument invoke is a procedure of three arguments: self, args and from-tty. The argument self is the
<gdb:command>
object representing the command. The argument args is a string representing the arguments passed to the command, after leading and trailing whitespace has been stripped. The argument from-tty is a boolean flag and specifies whether the command should consider itself to have been originated from the user invoking it interactively. If this function throws an exception, it is turned into a gdberror
call. Otherwise, the return value is ignored.The argument command-class is one of the ‘COMMAND_’ constants defined below. This argument tells gdb how to categorize the new command in the help system. The default is
COMMAND_NONE
.The argument completer is either
#f
, one of the ‘COMPLETE_’ constants defined below, or a procedure, also defined below. This argument tells gdb how to perform completion for this command. If not provided or if the value is#f
, then no completion is performed on the command.The argument prefix is a boolean flag indicating whether the new command is a prefix command; sub-commands of this command may be registered.
The argument doc-string is help text for the new command. If no documentation string is provided, the default value “This command is not documented.” is used.
Add command, a
<gdb:command>
object, to gdb's list of commands. It is an error to register a command more than once. The result is unspecified.
Return
#t
if object is a<gdb:command>
object. Otherwise return#f
.
By default, a gdb command is repeated when the user enters a blank line at the command prompt. A command can suppress this behavior by invoking the
dont-repeat
function. This is similar to the user commanddont-repeat
, see dont-repeat.
Convert a string to a list of strings split up according to gdb's argv parsing rules. It is recommended to use this for consistency. Arguments are separated by spaces and may be quoted. Example:
scheme@(guile-user)> (string->argv "1 2\\ \\\"3 '4 \"5' \"6 '7\"") $1 = ("1" "2 \"3" "4 \"5" "6 '7")
Throw a
gdb:user-error
exception. The argument message is the error message as a format string, like the fmt argument to theformat
Scheme function. See Formatted Output. The argument args is a list of the optional arguments of message.This is used when the command detects a user error of some kind, say a bad command argument.
(gdb) guile (use-modules (gdb)) (gdb) guile (register-command! (make-command "test-user-error" #:command-class COMMAND_OBSCURE #:invoke (lambda (self arg from-tty) (throw-user-error "Bad argument ~a" arg)))) end (gdb) test-user-error ugh ERROR: Bad argument ugh
If the completer option to
make-command
is a procedure, it takes three arguments: self which is the<gdb:command>
object, and text and word which are both strings. The argument text holds the complete command line up to the cursor's location. The argument word holds the last word of the command line; this is computed using a word-breaking heuristic.All forms of completion are handled by this function, that is, the <TAB> and <M-?> key bindings (see Completion), and the
complete
command (see complete).This procedure can return several kinds of values:
- If the return value is a list, the contents of the list are used as the completions. It is up to completer to ensure that the contents actually do complete the word. An empty list is allowed, it means that there were no completions available. Only string elements of the list are used; other elements in the list are ignored.
- If the return value is a
<gdb:iterator>
object, it is iterated over to obtain the completions. It is up tocompleter-procedure
to ensure that the results actually do complete the word. Only string elements of the result are used; other elements in the sequence are ignored.- All other results are treated as though there were no available completions.
When a new command is registered, it will have been declared as a member of
some general class of commands. This is used to classify top-level
commands in the on-line help system; note that prefix commands are not
listed under their own category but rather that of their top-level
command. The available classifications are represented by constants
defined in the gdb
module:
COMMAND_NONE
COMMAND_RUNNING
start
, step
, and continue
are in this category.
Type help running at the gdb prompt to see a list of
commands in this category.
COMMAND_DATA
call
, find
, and print
are in this category. Type
help data at the gdb prompt to see a list of commands
in this category.
COMMAND_STACK
backtrace
, frame
, and return
are in this
category. Type help stack at the gdb prompt to see a
list of commands in this category.
COMMAND_FILES
file
, list
and section
are in this category.
Type help files at the gdb prompt to see a list of
commands in this category.
COMMAND_SUPPORT
help
, make
, and shell
are in this category. Type
help support at the gdb prompt to see a list of
commands in this category.
COMMAND_STATUS
info
, macro
,
and show
are in this category. Type help status at the
gdb prompt to see a list of commands in this category.
COMMAND_BREAKPOINTS
break
,
clear
, and delete
are in this category. Type help
breakpoints at the gdb prompt to see a list of commands in
this category.
COMMAND_TRACEPOINTS
trace
,
actions
, and tfind
are in this category. Type
help tracepoints at the gdb prompt to see a list of
commands in this category.
COMMAND_USER
COMMAND_OBSCURE
checkpoint
,
fork
, and stop
are in this category. Type help
obscure at the gdb prompt to see a list of commands in this
category.
COMMAND_MAINTENANCE
maintenance
and flushregs
commands are in this category.
Type help internals at the gdb prompt to see a list of
commands in this category.
A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it
from the completer
procedure. These predefined completion
constants are all defined in the gdb
module:
COMPLETE_NONE
COMPLETE_FILENAME
COMPLETE_LOCATION
COMPLETE_COMMAND
COMPLETE_SYMBOL
COMPLETE_EXPRESSION
The following code snippet shows how a trivial CLI command can be implemented in Guile:
(gdb) guile (register-command! (make-command "hello-world" #:command-class COMMAND_USER #:doc "Greet the whole world." #:invoke (lambda (self args from-tty) (display "Hello, World!\n")))) end (gdb) hello-world Hello, World!
You can implement new gdb parameters using Guile 17.
There are many parameters that already exist and can be set in
gdb. Two examples are: set follow-fork
and
set charset
. Setting these parameters influences certain
behavior in gdb. Similarly, you can define parameters that
can be used to influence behavior in custom Guile scripts and commands.
A new parameter is defined with the make-parameter
Guile function,
and added to gdb with the register-parameter!
Guile function.
This two-step approach is taken to separate out the side-effect of adding
the parameter to gdb from make-parameter
.
Parameters are exposed to the user via the set
and
show
commands. See Help.
The argument name is the name of the new parameter. If name consists of multiple words, then the initial words are looked for as prefix parameters. An example of this can be illustrated with the
set print
set of parameters. If name isprint foo
, thenset print foo
. If name consists of multiple words, and no prefix parameter group can be found, an exception is raised.The result is the
<gdb:parameter>
object representing the parameter. The parameter is not usable until it has been registered with gdb withregister-parameter!
.The rest of the arguments are optional.
The argument command-class should be one of the ‘COMMAND_’ constants (see Commands In Guile). This argument tells gdb how to categorize the new parameter in the help system. The default is
COMMAND_NONE
.The argument parameter-type should be one of the ‘PARAM_’ constants defined below. This argument tells gdb the type of the new parameter; this information is used for input validation and completion. The default is
PARAM_BOOLEAN
.If parameter-type is
PARAM_ENUM
, then enum-list must be a list of strings. These strings represent the possible values for the parameter.If parameter-type is not
PARAM_ENUM
, then the presence of enum-list will cause an exception to be thrown.The argument set-func is a function of one argument: self which is the
<gdb:parameter>
object representing the parameter. gdb will call this function when a parameter's value has been changed via theset
API (for example, set foo off). The value of the parameter has already been set to the new value. This function must return a string to be displayed to the user. gdb will add a trailing newline if the string is non-empty. gdb generally doesn't print anything when a parameter is set, thus typically this function should return ‘""’. A non-empty string result should typically be used for displaying warnings and errors.The argument show-func is a function of two arguments: self which is the
<gdb:parameter>
object representing the parameter, and svalue which is the string representation of the current value. gdb will call this function when a parameter'sshow
API has been invoked (for example, show foo). This function must return a string, and will be displayed to the user. gdb will add a trailing newline.The argument doc is the help text for the new parameter. If there is no documentation string, a default value is used.
The argument set-doc is the help text for this parameter's
set
command.The argument show-doc is the help text for this parameter's
show
command.The argument initial-value specifies the initial value of the parameter. If it is a function, it takes one parameter, the
<gdb:parameter>
object and its result is used as the initial value of the parameter. The initial value must be valid for the parameter type, otherwise an exception is thrown.
Add parameter, a
<gdb:parameter>
object, to gdb's list of parameters. It is an error to register a parameter more than once. The result is unspecified.
Return
#t
if object is a<gdb:parameter>
object. Otherwise return#f
.
Return the value of parameter which may either be a
<gdb:parameter>
object or a string naming the parameter.
Assign parameter the value of new-value. The argument parameter must be an object of type
<gdb:parameter>
. gdb does validation when assignments are made.
When a new parameter is defined, its type must be specified. The
available types are represented by constants defined in the gdb
module:
PARAM_BOOLEAN
#t
and #f
are the only valid values.
PARAM_AUTO_BOOLEAN
#:auto
.
PARAM_UINTEGER
PARAM_ZINTEGER
PARAM_ZUINTEGER
PARAM_ZUINTEGER_UNLIMITED
PARAM_STRING
PARAM_STRING_NOESCAPE
PARAM_OPTIONAL_FILENAME
#f
.
PARAM_FILENAME
PARAM_STRING_NOESCAPE
, but uses file names for completion.
PARAM_ENUM
A program space, or progspace, represents a symbolic view of an address space. It consists of all of the objfiles of the program. See Objfiles In Guile. See program spaces, for more details about program spaces.
Each progspace is represented by an instance of the <gdb:progspace>
smob. See GDB Scheme Data Types.
The following progspace-related functions are available in the
(gdb)
module:
Return
#t
if object is a<gdb:progspace>
object. Otherwise return#f
.
Return
#t
if progspace is valid,#f
if not. A<gdb:progspace>
object can become invalid if the program it refers to is not loaded in gdb any longer.
This function returns the program space of the currently selected inferior. There is always a current progspace, this never returns
#f
. See Inferiors and Programs.
Return the absolute file name of progspace as a string. This is the name of the file passed as the argument to the
file
orsymbol-file
commands. If the program space does not have an associated file name, then#f
is returned. This occurs, for example, when gdb is started without a program to debug.A
gdb:invalid-object-error
exception is thrown if progspace is invalid.
Return the list of objfiles of progspace. The order of objfiles in the result is arbitrary. Each element is an object of type
<gdb:objfile>
. See Objfiles In Guile.A
gdb:invalid-object-error
exception is thrown if progspace is invalid.
Return the list of pretty-printers of progspace. Each element is an object of type
<gdb:pretty-printer>
. See Guile Pretty Printing API, for more information.
Set the list of registered
<gdb:pretty-printer>
objects for progspace to printer-list. See Guile Pretty Printing API, for more information.
gdb loads symbols for an inferior from various symbol-containing files (see Files). These include the primary executable file, any shared libraries used by the inferior, and any separate debug info files (see Separate Debug Files). gdb calls these symbol-containing files objfiles.
Each objfile is represented as an object of type <gdb:objfile>
.
The following objfile-related procedures are provided by the
(gdb)
module:
Return
#t
if object is a<gdb:objfile>
object. Otherwise return#f
.
Return
#t
if objfile is valid,#f
if not. A<gdb:objfile>
object can become invalid if the object file it refers to is not loaded in gdb any longer. All other<gdb:objfile>
procedures will throw an exception if it is invalid at the time the procedure is called.
Return the file name of objfile as a string, with symbolic links resolved.
Return the
<gdb:progspace>
that this object file lives in. See Progspaces In Guile, for more on progspaces.
Return the list of registered
<gdb:pretty-printer>
objects for objfile. See Guile Pretty Printing API, for more information.
Set the list of registered
<gdb:pretty-printer>
objects for objfile to printer-list. The printer-list must be a list of<gdb:pretty-printer>
objects. See Guile Pretty Printing API, for more information.
When auto-loading a Guile script (see Guile Auto-loading), gdb sets the “current objfile” to the corresponding objfile. This function returns the current objfile. If there is no current objfile, this function returns
#f
.
When the debugged program stops, gdb is able to analyze its call
stack (see Stack frames). The <gdb:frame>
class
represents a frame in the stack. A <gdb:frame>
object is only valid
while its corresponding frame exists in the inferior's stack. If you try
to use an invalid frame object, gdb will throw a
gdb:invalid-object
exception (see Guile Exception Handling).
Two <gdb:frame>
objects can be compared for equality with the
equal?
function, like:
(gdb) guile (equal? (newest-frame) (selected-frame)) #t
The following frame-related procedures are provided by the
(gdb)
module:
Returns
#t
if frame is valid,#f
if not. A frame object can become invalid if the frame it refers to doesn't exist anymore in the inferior. All<gdb:frame>
procedures will throw an exception if the frame is invalid at the time the procedure is called.
Return the function name of frame, or
#f
if it can't be obtained.
Return the
<gdb:architecture>
object corresponding to frame's architecture. See Architectures In Guile.
Return the type of frame. The value can be one of:
NORMAL_FRAME
- An ordinary stack frame.
DUMMY_FRAME
- A fake stack frame that was created by gdb when performing an inferior function call.
INLINE_FRAME
- A frame representing an inlined function. The function was inlined into a
NORMAL_FRAME
that is older than this one.TAILCALL_FRAME
- A frame representing a tail call. See Tail Call Frames.
SIGTRAMP_FRAME
- A signal trampoline frame. This is the frame created by the OS when it calls into a signal handler.
ARCH_FRAME
- A fake stack frame representing a cross-architecture call.
SENTINEL_FRAME
- This is like
NORMAL_FRAME
, but it is only used for the newest frame.
Return an integer representing the reason why it's not possible to find more frames toward the outermost frame. Use
unwind-stop-reason-string
to convert the value returned by this function to a string. The value can be one of:
FRAME_UNWIND_NO_REASON
- No particular reason (older frames should be available).
FRAME_UNWIND_NULL_ID
- The previous frame's analyzer returns an invalid result.
FRAME_UNWIND_OUTERMOST
- This frame is the outermost.
FRAME_UNWIND_UNAVAILABLE
- Cannot unwind further, because that would require knowing the values of registers or memory that have not been collected.
FRAME_UNWIND_INNER_ID
- This frame ID looks like it ought to belong to a NEXT frame, but we got it for a PREV frame. Normally, this is a sign of unwinder failure. It could also indicate stack corruption.
FRAME_UNWIND_SAME_ID
- This frame has the same ID as the previous one. That means that unwinding further would almost certainly give us another frame with exactly the same ID, so break the chain. Normally, this is a sign of unwinder failure. It could also indicate stack corruption.
FRAME_UNWIND_NO_SAVED_PC
- The frame unwinder did not find any saved PC, but we needed one to unwind further.
FRAME_UNWIND_MEMORY_ERROR
- The frame unwinder caused an error while trying to access memory.
FRAME_UNWIND_FIRST_ERROR
- Any stop reason greater or equal to this value indicates some kind of error. This special value facilitates writing code that tests for errors in unwinding in a way that will work correctly even if the list of the other values is modified in future gdb versions. Using it, you could write:
(define reason (frame-unwind-stop-readon (selected-frame))) (define reason-str (unwind-stop-reason-string reason)) (if (>= reason FRAME_UNWIND_FIRST_ERROR) (format #t "An error occured: ~s\n" reason-str))
Return the frame's code block as a
<gdb:block>
object. See Blocks In Guile.
Return the symbol for the function corresponding to this frame as a
<gdb:symbol>
object, or#f
if there isn't one. See Symbols In Guile.
Return the frame's
<gdb:sal>
(symtab and line) object. See Symbol Tables In Guile.
Return the value of register in frame. register should be a string, like ‘pc’.
Return the value of variable in frame. If the optional argument block is provided, search for the variable from that block; otherwise start at the frame's current block (which is determined by the frame's current program counter). The variable must be given as a string or a
<gdb:symbol>
object, and block must be a<gdb:block>
object.
Return a string explaining the reason why gdb stopped unwinding frames, as expressed by the given reason code (an integer, see the
frame-unwind-stop-reason
procedure above in this section).
In gdb, symbols are stored in blocks. A block corresponds
roughly to a scope in the source code. Blocks are organized
hierarchically, and are represented individually in Guile as an object
of type <gdb:block>
. Blocks rely on debugging information being
available.
A frame has a block. Please see Frames In Guile, for a more in-depth discussion of frames.
The outermost block is known as the global block. The global block typically holds public global variables and functions.
The block nested just inside the global block is the static block. The static block typically holds file-scoped variables and functions.
gdb provides a method to get a block's superblock, but there is currently no way to examine the sub-blocks of a block, or to iterate over all the blocks in a symbol table (see Symbol Tables In Guile).
Here is a short example that should help explain blocks:
/* This is in the global block. */ int global; /* This is in the static block. */ static int file_scope; /* 'function' is in the global block, and 'argument' is in a block nested inside of 'function'. */ int function (int argument) { /* 'local' is in a block inside 'function'. It may or may not be in the same block as 'argument'. */ int local; { /* 'inner' is in a block whose superblock is the one holding 'local'. */ int inner; /* If this call is expanded by the compiler, you may see a nested block here whose function is 'inline_function' and whose superblock is the one holding 'inner'. */ inline_function (); } }
The following block-related procedures are provided by the
(gdb)
module:
Returns
#t
if<gdb:block>
block is valid,#f
if not. A block object can become invalid if the block it refers to doesn't exist anymore in the inferior. All other<gdb:block>
methods will throw an exception if it is invalid at the time the procedure is called. The block's validity is also checked during iteration over symbols of the block.
Return the name of
<gdb:block>
block represented as a<gdb:symbol>
object. If the block is not named, then#f
is returned.For ordinary function blocks, the superblock is the static block. However, you should note that it is possible for a function block to have a superblock that is not the static block – for instance this happens for an inlined function.
Return the block containing
<gdb:block>
block. If the parent block does not exist, then#f
is returned.
Return the global block associated with
<gdb:block>
block.
Return the static block associated with
<gdb:block>
block.
Return
#t
if<gdb:block>
block is a global block. Otherwise return#f
.
Return
#t
if<gdb:block>
block is a static block. Otherwise return#f
.
Return a list of all symbols (as <gdb:symbol> objects) in
<gdb:block>
block.
Return an object of type
<gdb:iterator>
that will iterate over all symbols of the block. Guile programs should not assume that a specific block object will always contain a given symbol, since changes in gdb features and infrastructure may cause symbols move across blocks in a symbol table. See Iterators In Guile.
Return #t if the object is a <gdb:block-symbols-progress> object. This object would be obtained from the
progress
element of the<gdb:iterator>
object returned bymake-block-symbols-iterator
.
Return the innermost
<gdb:block>
containing the given pc value. If the block cannot be found for the pc value specified, the function will return#f
.
gdb represents every variable, function and type as an
entry in a symbol table. See Examining the Symbol Table.
Guile represents these symbols in gdb with the
<gdb:symbol>
object.
The following symbol-related procedures are provided by the
(gdb)
module:
Return
#t
if object is an object of type<gdb:symbol>
. Otherwise return#f
.
Return
#t
if the<gdb:symbol>
object is valid,#f
if not. A<gdb:symbol>
object can become invalid if the symbol it refers to does not exist in gdb any longer. All other<gdb:symbol>
procedures will throw an exception if it is invalid at the time the procedure is called.
Return the type of symbol or
#f
if no type is recorded. The result is an object of type<gdb:type>
. See Types In Guile.
Return the symbol table in which symbol appears. The result is an object of type
<gdb:symtab>
. See Symbol Tables In Guile.
Return the line number in the source code at which symbol was defined. This is an integer.
Return the name of symbol, as used by the linker (i.e., may be mangled).
Return the name of symbol in a form suitable for output. This is either
name
orlinkage_name
, depending on whether the user asked gdb to display demangled or mangled names.
Return the address class of the symbol. This classifies how to find the value of a symbol. Each address class is a constant defined in the
(gdb)
module and described later in this chapter.
Return
#t
if evaluating symbol's value requires a frame (see Frames In Guile) and#f
otherwise. Typically, local variables will require a frame, but other symbols will not.
Return
#t
if symbol is an argument of a function. Otherwise return#f
.
Return
#t
if symbol is a function or a method. Otherwise return#f
.
Compute the value of symbol, as a
<gdb:value>
. For functions, this computes the address of the function, cast to the appropriate type. If the symbol requires a frame in order to compute its value, then frame must be given. If frame is not given, or if frame is invalid, then an exception is thrown.
This function searches for a symbol by name. The search scope can be restricted to the parameters defined in the optional domain and block arguments.
name is the name of the symbol. It must be a string. The optional block argument restricts the search to symbols visible in that block. The block argument must be a
<gdb:block>
object. If omitted, the block for the current frame is used. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in the(gdb)
module and described later in this chapter.The result is a list of two elements. The first element is a
<gdb:symbol>
object or#f
if the symbol is not found. If the symbol is found, the second element is#t
if the symbol is a field of a method's object (e.g.,this
in C++), otherwise it is#f
. If the symbol is not found, the second element is#f
.
This function searches for a global symbol by name. The search scope can be restricted by the domain argument.
name is the name of the symbol. It must be a string. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in the
(gdb)
module and described later in this chapter.The result is a
<gdb:symbol>
object or#f
if the symbol is not found.
The available domain categories in <gdb:symbol>
are represented
as constants in the (gdb)
module:
SYMBOL_UNDEF_DOMAIN
SYMBOL_VAR_DOMAIN
SYMBOL_STRUCT_DOMAIN
SYMBOL_LABEL_DOMAIN
SYMBOL_VARIABLES_DOMAIN
SYMBOLS_VAR_DOMAIN
; it
contains everything minus functions and types.
SYMBOL_FUNCTIONS_DOMAIN
SYMBOL_TYPES_DOMAIN
The available address class categories in <gdb:symbol>
are represented
as constants in the gdb
module:
SYMBOL_LOC_UNDEF
SYMBOL_LOC_CONST
SYMBOL_LOC_STATIC
SYMBOL_LOC_REGISTER
SYMBOL_LOC_ARG
SYMBOL_LOC_REF_ARG
LOC_ARG
except that the value's address is stored at the
offset, not the value itself.
SYMBOL_LOC_REGPARM_ADDR
LOC_REGISTER
except
the register holds the address of the argument instead of the argument
itself.
SYMBOL_LOC_LOCAL
SYMBOL_LOC_TYPEDEF
SYMBOL_STRUCT_DOMAIN
all
have this class.
SYMBOL_LOC_BLOCK
SYMBOL_LOC_CONST_BYTES
SYMBOL_LOC_UNRESOLVED
SYMBOL_LOC_OPTIMIZED_OUT
SYMBOL_LOC_COMPUTED
Access to symbol table data maintained by gdb on the inferior
is exposed to Guile via two objects: <gdb:sal>
(symtab-and-line) and
<gdb:symtab>
. Symbol table and line data for a frame is returned
from the frame-find-sal
<gdb:frame>
procedure.
See Frames In Guile.
For more information on gdb's symbol table management, see Examining the Symbol Table.
The following symtab-related procedures are provided by the
(gdb)
module:
Return
#t
if object is an object of type<gdb:symtab>
. Otherwise return#f
.
Return
#t
if the<gdb:symtab>
object is valid,#f
if not. A<gdb:symtab>
object becomes invalid when the symbol table it refers to no longer exists in gdb. All other<gdb:symtab>
procedures will throw an exception if it is invalid at the time the procedure is called.
Return the symbol table's backing object file. See Objfiles In Guile.
Return the global block of the underlying symbol table. See Blocks In Guile.
Return the static block of the underlying symbol table. See Blocks In Guile.
The following symtab-and-line-related procedures are provided by the
(gdb)
module:
Return
#t
if object is an object of type<gdb:sal>
. Otherwise return#f
.
Return
#t
if sal is valid,#f
if not. A<gdb:sal>
object becomes invalid when the Symbol table object it refers to no longer exists in gdb. All other<gdb:sal>
procedures will throw an exception if it is invalid at the time the procedure is called.
Return the
<gdb:sal>
object corresponding to the pc value. If an invalid value of pc is passed as an argument, then thesymtab
andline
attributes of the returned<gdb:sal>
object will be#f
and 0 respectively.
Breakpoints in Guile are represented by objects of type
<gdb:breakpoint>
. New breakpoints can be created with the
make-breakpoint
Guile function, and then added to gdb with the
register-breakpoint!
Guile function.
This two-step approach is taken to separate out the side-effect of adding
the breakpoint to gdb from make-breakpoint
.
Support is also provided to view and manipulate breakpoints created outside of Guile.
The following breakpoint-related procedures are provided by the
(gdb)
module:
Create a new breakpoint at location, a string naming the location of the breakpoint, or an expression that defines a watchpoint. The contents can be any location recognized by the
break
command, or in the case of a watchpoint, by thewatch
command.The breakpoint is initially marked as ‘invalid’. The breakpoint is not usable until it has been registered with gdb with
register-breakpoint!
, at which point it becomes ‘valid’. The result is the<gdb:breakpoint>
object representing the breakpoint.The optional type denotes the breakpoint to create. This argument can be either
BP_BREAKPOINT
orBP_WATCHPOINT
, and defaults toBP_BREAKPOINT
.The optional wp-class argument defines the class of watchpoint to create, if type is
BP_WATCHPOINT
. If a watchpoint class is not provided, it is assumed to be aWP_WRITE
class.The optional internal argument allows the breakpoint to become invisible to the user. The breakpoint will neither be reported when registered, nor will it be listed in the output from
info breakpoints
(but will be listed with themaint info breakpoints
command). If an internal flag is not provided, the breakpoint is visible (non-internal).When a watchpoint is created, gdb will try to create a hardware assisted watchpoint. If successful, the type of the watchpoint is changed from
BP_WATCHPOINT
toBP_HARDWARE_WATCHPOINT
forWP_WRITE
,BP_READ_WATCHPOINT
forWP_READ
, andBP_ACCESS_WATCHPOINT
forWP_ACCESS
. If not successful, the type of the watchpoint is left asWP_WATCHPOINT
.The available types are represented by constants defined in the
gdb
module:
BP_BREAKPOINT
- Normal code breakpoint.
BP_WATCHPOINT
- Watchpoint breakpoint.
BP_HARDWARE_WATCHPOINT
- Hardware assisted watchpoint. This value cannot be specified when creating the breakpoint.
BP_READ_WATCHPOINT
- Hardware assisted read watchpoint. This value cannot be specified when creating the breakpoint.
BP_ACCESS_WATCHPOINT
- Hardware assisted access watchpoint. This value cannot be specified when creating the breakpoint.
The available watchpoint types represented by constants are defined in the
(gdb)
module:
Add breakpoint, a
<gdb:breakpoint>
object, to gdb's list of breakpoints. The breakpoint must have been created withmake-breakpoint
. One cannot register breakpoints that have been created outside of Guile. Once a breakpoint is registered it becomes ‘valid’. It is an error to register an already registered breakpoint. The result is unspecified.
Remove breakpoint from gdb's list of breakpoints. This also invalidates the Guile breakpoint object. Any further attempt to access the object will throw an exception.
If breakpoint was created from Guile with
make-breakpoint
it may be re-registered with gdb, in which case the breakpoint becomes valid again.
Return a list of all breakpoints. Each element of the list is a
<gdb:breakpoint>
object.
Return
#t
if object is a<gdb:breakpoint>
object, and#f
otherwise.
Return
#t
if breakpoint is valid,#f
otherwise. Breakpoints created withmake-breakpoint
are marked as invalid until they are registered with gdb withregister-breakpoint!
. A<gdb:breakpoint>
object can become invalid if the user deletes the breakpoint. In this case, the object still exists, but the underlying breakpoint does not. In the cases of watchpoint scope, the watchpoint remains valid even if execution of the inferior leaves the scope of that watchpoint.
Return the breakpoint's number — the identifier used by the user to manipulate the breakpoint.
Return the breakpoint's type — the identifier used to determine the actual breakpoint type or use-case.
Return
#t
if the breakpoint is visible to the user when hit, or when the ‘info breakpoints’ command is run. Otherwise return#f
.
Return the location of the breakpoint, as specified by the user. It is a string. If the breakpoint does not have a location (that is, it is a watchpoint) return
#f
.
Return the breakpoint expression, as specified by the user. It is a string. If the breakpoint does not have an expression (the breakpoint is not a watchpoint) return
#f
.
Return
#t
if the breakpoint is enabled, and#f
otherwise.
Set the enabled state of breakpoint to flag. If flag is
#f
it is disabled, otherwise it is enabled.
Return
#t
if the breakpoint is silent, and#f
otherwise.Note that a breakpoint can also be silent if it has commands and the first command is
silent
. This is not reported by thesilent
attribute.
Set the silent state of breakpoint to flag. If flag is
#f
the breakpoint is made silent, otherwise it is made non-silent (or noisy).
Set the ignore count for breakpoint to count.
Set the hit count of breakpoint to count. At present, count must be zero.
Return the global-thread-id for thread-specific breakpoint breakpoint. Return #f if breakpoint is not thread-specific.
Set the thread-id for breakpoint to global-thread-id If set to
#f
, the breakpoint is no longer thread-specific.
If the breakpoint is Ada task-specific, return the Ada task id. If the breakpoint is not task-specific (or the underlying language is not Ada), return
#f
.
Set the Ada task of breakpoint to task. If set to
#f
, the breakpoint is no longer task-specific.
Return the condition of breakpoint, as specified by the user. It is a string. If there is no condition, return
#f
.
Set the condition of breakpoint to condition, which must be a string. If set to
#f
then the breakpoint becomes unconditional.
Return the stop predicate of breakpoint. See
set-breakpoint-stop!
below in this section.
Set the stop predicate of breakpoint. The predicate procedure takes one argument: the <gdb:breakpoint> object. If this predicate is set to a procedure then it is invoked whenever the inferior reaches this breakpoint. If it returns
#t
, or any non-#f
value, then the inferior is stopped, otherwise the inferior will continue.If there are multiple breakpoints at the same location with a
stop
predicate, each one will be called regardless of the return status of the previous. This ensures that allstop
predicates have a chance to execute at that location. In this scenario if one of the methods returns#t
but the others return#f
, the inferior will still be stopped.You should not alter the execution state of the inferior (i.e., step, next, etc.), alter the current frame context (i.e., change the current active frame), or alter, add or delete any breakpoint. As a general rule, you should not alter any data within gdb or the inferior at this time.
Example
stop
implementation:(define (my-stop? bkpt) (let ((int-val (parse-and-eval "foo"))) (value=? int-val 3))) (define bkpt (make-breakpoint "main.c:42")) (register-breakpoint! bkpt) (set-breakpoint-stop! bkpt my-stop?)
Return the commands attached to breakpoint as a string, or
#f
if there are none.
A lazy string is a string whose contents is not retrieved or encoded until it is needed.
A <gdb:lazy-string>
is represented in gdb as an
address
that points to a region of memory, an encoding
that will be used to encode that region of memory, and a length
to delimit the region of memory that represents the string. The
difference between a <gdb:lazy-string>
and a string wrapped within
a <gdb:value>
is that a <gdb:lazy-string>
will be treated
differently by gdb when printing. A <gdb:lazy-string>
is
retrieved and encoded during printing, while a <gdb:value>
wrapping a string is immediately retrieved and encoded on creation.
The following lazy-string-related procedures are provided by the
(gdb)
module:
Return
#t
if object is an object of type<gdb:lazy-string>
. Otherwise return#f
.
Return the length of lazy-string in characters. If the length is -1, then the string will be fetched and encoded up to the first null of appropriate width.
Return the encoding that will be applied to lazy-string when the string is printed by gdb. If the encoding is not set, or contains an empty string, then gdb will select the most appropriate encoding when the string is printed.
Return the type that is represented by lazy-string's type. For a lazy string this is a pointer or array type. To resolve this to the lazy string's character type, use
type-target-type
. See Types In Guile.
Convert the
<gdb:lazy-string>
to a<gdb:value>
. This value will point to the string in memory, but will lose all the delayed retrieval, encoding and handling that gdb applies to a<gdb:lazy-string>
.
gdb uses architecture specific parameters and artifacts in a
number of its various computations. An architecture is represented
by an instance of the <gdb:arch>
class.
The following architecture-related procedures are provided by the
(gdb)
module:
Return
#t
if object is an object of type<gdb:arch>
. Otherwise return#f
.
Each architecture provides a set of predefined types, obtained by the following functions.
Return the
<gdb:type>
object for avoid
type of architecture arch.
Return the
<gdb:type>
object for achar
type of architecture arch.
Return the
<gdb:type>
object for ashort
type of architecture arch.
Return the
<gdb:type>
object for anint
type of architecture arch.
Return the
<gdb:type>
object for along
type of architecture arch.
Return the
<gdb:type>
object for asigned char
type of architecture arch.
Return the
<gdb:type>
object for anunsigned char
type of architecture arch.
Return the
<gdb:type>
object for anunsigned short
type of architecture arch.
Return the
<gdb:type>
object for anunsigned int
type of architecture arch.
Return the
<gdb:type>
object for anunsigned long
type of architecture arch.
Return the
<gdb:type>
object for afloat
type of architecture arch.
Return the
<gdb:type>
object for adouble
type of architecture arch.
Return the
<gdb:type>
object for along double
type of architecture arch.
Return the
<gdb:type>
object for abool
type of architecture arch.
Return the
<gdb:type>
object for along long
type of architecture arch.
Return the
<gdb:type>
object for anunsigned long long
type of architecture arch.
Return the
<gdb:type>
object for anint8
type of architecture arch.
Return the
<gdb:type>
object for auint8
type of architecture arch.
Return the
<gdb:type>
object for anint16
type of architecture arch.
Return the
<gdb:type>
object for auint16
type of architecture arch.
Return the
<gdb:type>
object for anint32
type of architecture arch.
Return the
<gdb:type>
object for auint32
type of architecture arch.
Return the
<gdb:type>
object for anint64
type of architecture arch.
Return the
<gdb:type>
object for auint64
type of architecture arch.
Example:
(gdb) guile (type-name (arch-uchar-type (current-arch))) "unsigned char"
The disassembler can be invoked from Scheme code. Furthermore, the disassembler can take a Guile port as input, allowing one to disassemble from any source, and not just target memory.
Return a list of disassembled instructions starting from the memory address start-pc.
The optional argument port specifies the input port to read bytes from. If port is
#f
then bytes are read from target memory.The optional argument offset specifies the address offset of the first byte in port. This is useful, for example, when port specifies a ‘bytevector’ and you want the bytevector to be disassembled as if it came from that address. The start-pc passed to the reader for port is offset by the same amount.
Example:
(gdb) guile (use-modules (rnrs io ports)) (gdb) guile (define pc (value->integer (parse-and-eval "$pc"))) (gdb) guile (define mem (open-memory #:start pc)) (gdb) guile (define bv (get-bytevector-n mem 10)) (gdb) guile (define bv-port (open-bytevector-input-port bv)) (gdb) guile (define arch (current-arch)) (gdb) guile (arch-disassemble arch pc #:port bv-port #:offset pc) (((address . 4195516) (asm . "mov $0x4005c8,%edi") (length . 5)))The optional arguments size and count determine the number of instructions in the returned list. If either size or count is specified as zero, then no instructions are disassembled and an empty list is returned. If both the optional arguments size and count are specified, then a list of at most count disassembled instructions whose start address falls in the closed memory address interval from start-pc to (start-pc + size - 1) are returned. If size is not specified, but count is specified, then count number of instructions starting from the address start-pc are returned. If count is not specified but size is specified, then all instructions whose start address falls in the closed memory address interval from start-pc to (start-pc + size - 1) are returned. If neither size nor count are specified, then a single instruction at start-pc is returned.
Each element of the returned list is an alist (associative list) with the following keys:
address
- The value corresponding to this key is a Guile integer of the memory address of the instruction.
asm
- The value corresponding to this key is a string value which represents the instruction with assembly language mnemonics. The assembly language flavor used is the same as that specified by the current CLI variable
disassembly-flavor
. See Machine Code.length
- The value corresponding to this key is the length of the instruction in bytes.
Return
#t
if object is a gdb stdio port. Otherwise return#f
.
gdb provides a port
interface to target memory.
This allows Guile code to read/write target memory using Guile's port and
bytevector functionality. The main routine is open-memory
which
returns a port object. One can then read/write memory using that object.
Return a port object that can be used for reading and writing memory. The port will be open according to mode, which is the standard mode argument to Guile port open routines, except that the ‘"a"’ and ‘"l"’ modes are not supported. See File Ports. The ‘"b"’ (binary) character may be present, but is ignored: memory ports are binary only. If ‘"0"’ is appended then the port is marked as unbuffered. The default is ‘"r"’, read-only and buffered.
The chunk of memory that can be accessed can be bounded. If both start and size are unspecified, all of memory can be accessed. If only start is specified, all of memory from that point on can be accessed. If only size if specified, all memory in the range [0,size) can be accessed. If both are specified, all memory in the rane [start,start+size) can be accessed.
Return
#t
if object is an object of type<gdb:memory-port>
. Otherwise return#f
.
Return the range of
<gdb:memory-port>
memory-port as a list of two elements:(start end)
. The range is start to end inclusive.
Return the size of the read buffer of
<gdb:memory-port>
memory-port.
Set the size of the read buffer of
<gdb:memory-port>
memory-port to size. The result is unspecified.
Return the size of the write buffer of
<gdb:memory-port>
memory-port.
Set the size of the write buffer of
<gdb:memory-port>
memory-port to size. The result is unspecified.
A memory port is closed like any other port, with close-port
.
Combined with Guile's bytevectors
, memory ports provide a lot
of utility. For example, to fill a buffer of 10 integers in memory,
one can do something like the following.
;; In the program: int buffer[10]; (use-modules (rnrs bytevectors)) (use-modules (rnrs io ports)) (define addr (parse-and-eval "buffer")) (define n 10) (define byte-size (* n 4)) (define mem-port (open-memory #:mode "r+" #:start (value->integer addr) #:size byte-size)) (define byte-vec (make-bytevector byte-size)) (do ((i 0 (+ i 1))) ((>= i n)) (bytevector-s32-native-set! byte-vec (* i 4) (* i 42))) (put-bytevector mem-port byte-vec) (close-port mem-port)
A simple iterator facility is provided to allow, for example, iterating over the set of program symbols without having to first construct a list of all of them. A useful contribution would be to add support for SRFI 41 and SRFI 45.
A
<gdb:iterator>
object is constructed with themake-iterator
procedure. It takes three arguments: the object to be iterated over, an object to record the progress of the iteration, and a procedure to return the next element in the iteration, or an implementation chosen value to denote the end of iteration.By convention, end of iteration is marked with
(end-of-iteration)
, and may be tested with theend-of-iteration?
predicate. The result of(end-of-iteration)
is chosen so that it is not otherwise used by the(gdb)
module. If you are using<gdb:iterator>
in your own code it is your responsibility to maintain this invariant.A trivial example for illustration's sake:
(use-modules (gdb iterator)) (define my-list (list 1 2 3)) (define iter (make-iterator my-list my-list (lambda (iter) (let ((l (iterator-progress iter))) (if (eq? l '()) (end-of-iteration) (begin (set-iterator-progress! iter (cdr l)) (car l)))))))Here is a slightly more realistic example, which computes a list of all the functions in
my-global-block
.(use-modules (gdb iterator)) (define this-sal (find-pc-line (frame-pc (selected-frame)))) (define this-symtab (sal-symtab this-sal)) (define this-global-block (symtab-global-block this-symtab)) (define syms-iter (make-block-symbols-iterator this-global-block)) (define functions (iterator-filter symbol-function? syms-iter))
Return
#t
if object is a<gdb:iterator>
object. Otherwise return#f
.
Return the first argument that was passed to
make-iterator
. This is the object being iterated over.
Set the object tracking iteration progress.
Invoke the procedure that was the third argument to
make-iterator
, passing it one argument, the<gdb:iterator>
object. The result is either the next element in the iteration, or an end marker as implemented by thenext!
procedure. By convention the end marker is the result of(end-of-iteration)
.
Return
#t
if object is the end of iteration marker. Otherwise return#f
.
These functions are provided by the (gdb iterator)
module to
assist in using iterators.
Return a
<gdb:iterator>
object that will iterate over list.
Return the list of objects obtained by applying proc to the object pointed to by iterator and to each subsequent object.
Apply proc to each element pointed to by iterator. The result is unspecified.
Return the list of elements pointed to by iterator that satisfy pred.
Run iterator until the result of
(pred element)
is true and return that as the result. Otherwise return#f
.
When a new object file is read (for example, due to the file
command, or because the inferior has loaded a shared library),
gdb will look for Guile support scripts in two ways:
objfile-gdb.scm and the .debug_gdb_scripts
section.
See Auto-loading extensions.
The auto-loading feature is useful for supplying application-specific debugging commands and scripts.
Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be printed.
set auto-load guile-scripts [on|off]
show auto-load guile-scripts
info auto-load guile-scripts [
regexp]
Also printed is the list of Guile scripts that were mentioned in
the .debug_gdb_scripts
section and were not found.
This is useful because their names are not printed when gdb
tries to load them and fails. There may be many of them, and printing
an error message for each one is problematic.
If regexp is supplied only Guile scripts with matching names are printed.
Example:
(gdb) info auto-load guile-scripts Loaded Script Yes scm-section-script.scm full name: /tmp/scm-section-script.scm No my-foo-pretty-printers.scm
When reading an auto-loaded file, gdb sets the
current objfile. This is available via the current-objfile
procedure (see Objfiles In Guile). This can be useful for
registering objfile-specific pretty-printers.
gdb comes with several modules to assist writing Guile code.
This module provides a collection of utilities for working with pretty-printers.
Usage:
(use-modules (gdb printing))
Add printer to the front of the list of pretty-printers for object. The object must either be a
<gdb:objfile>
object, or#f
in which case printer is added to the global list of printers.
Add printer to the end of the list of pretty-printers for object. The object must either be a
<gdb:objfile>
object, or#f
in which case printer is added to the global list of printers.
This module provides a collection of utilities for working with
<gdb:type>
objects.
Usage:
(use-modules (gdb types))
Return type with const and volatile qualifiers stripped, and with typedefs and C++ references converted to the underlying type.
C++ example:
typedef const int const_int; const_int foo (3); const_int& foo_ref (foo); int main () { return 0; }Then in gdb:
(gdb) start (gdb) guile (use-modules (gdb) (gdb types)) (gdb) guile (define foo-ref (parse-and-eval "foo_ref")) (gdb) guile (get-basic-type (value-type foo-ref)) int
Return
#t
if type, assumed to be a type with fields (e.g., a structure or union), has field field. Otherwise return#f
. This searches baseclasses, whereastype-has-field?
does not.
Return a Guile hash table produced from enum-type. Elements in the hash table are referenced with
hashq-ref
.
gdb provides two mechanisms for automatically loading extensions
when a new object file is read (for example, due to the file
command, or because the inferior has loaded a shared library):
objfile-gdb.ext and the .debug_gdb_scripts
section of modern file formats like ELF.
The auto-loading feature is useful for supplying application-specific debugging commands and features.
Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be printed. See the ‘auto-loading’ section of each extension language for more information. For gdb command files see Auto-loading sequences. For Python files see Python Auto-loading.
Note that loading of this script file also requires accordingly configured
auto-load safe-path
(see Auto-loading safe path).
When a new object file is read, gdb looks for a file named objfile-gdb.ext (we call it script-name below), where objfile is the object file's name and where ext is the file extension for the extension language:
script-name is formed by ensuring that the file name of objfile
is absolute, following all symlinks, and resolving .
and ..
components, and appending the -gdb.ext suffix.
If this file exists and is readable, gdb will evaluate it as a
script in the specified extension language.
If this file does not exist, then gdb will look for script-name file in all of the directories as specified below.
Note that loading of these files requires an accordingly configured
auto-load safe-path
(see Auto-loading safe path).
For object files using .exe suffix gdb tries to load first the scripts normally according to its .exe filename. But if no scripts are found gdb also tries script filenames matching the object file without its .exe suffix. This .exe stripping is case insensitive and it is attempted on any platform. This makes the script filenames compatible between Unix and MS-Windows hosts.
set auto-load scripts-directory
[directories]Each entry here needs to be covered also by the security setting
set auto-load safe-path
(see set auto-load safe-path).
This variable defaults to $debugdir:$datadir/auto-load. The default
set auto-load safe-path
value can be also overriden by gdb
configuration option --with-auto-load-dir.
Any reference to $debugdir will get replaced by debug-file-directory value (see Separate Debug Files) and any reference to $datadir will get replaced by data-directory which is determined at gdb startup (see Data Files). $debugdir and $datadir must be placed as a directory component — either alone or delimited by / or \ directory separators, depending on the host platform.
The list of directories uses path separator (‘:’ on GNU and Unix systems, ‘;’ on MS-Windows and MS-DOS) to separate directories, similarly to the PATH environment variable.
show auto-load scripts-directory
add-auto-load-scripts-directory
[directories...
]gdb does not track which files it has already auto-loaded this way. gdb will load the associated script every time the corresponding objfile is opened. So your -gdb.ext file should be careful to avoid errors if it is evaluated more than once.
.debug_gdb_scripts
section
For systems using file formats like ELF and COFF,
when gdb loads a new object file
it will look for a special section named .debug_gdb_scripts
.
If this section exists, its contents is a list of null-terminated entries
specifying scripts to load. Each entry begins with a non-null prefix byte that
specifies the kind of entry, typically the extension language and whether the
script is in a file or inlined in .debug_gdb_scripts
.
The following entries are supported:
SECTION_SCRIPT_ID_PYTHON_FILE = 1
SECTION_SCRIPT_ID_SCHEME_FILE = 3
SECTION_SCRIPT_ID_PYTHON_TEXT = 4
SECTION_SCRIPT_ID_SCHEME_TEXT = 6
If the entry specifies a file, gdb will look for the file first in the current directory and then along the source search path (see Specifying Source Directories), except that $cdir is not searched, since the compilation directory is not relevant to scripts.
File entries can be placed in section .debug_gdb_scripts
with,
for example, this GCC macro for Python scripts.
/* Note: The "MS" section flags are to remove duplicates. */ #define DEFINE_GDB_PY_SCRIPT(script_name) \ asm("\ .pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n\ .byte 1 /* Python */\n\ .asciz \"" script_name "\"\n\ .popsection \n\ ");
For Guile scripts, replace .byte 1
with .byte 3
.
Then one can reference the macro in a header or source file like this:
DEFINE_GDB_PY_SCRIPT ("my-app-scripts.py")
The script name may include directories if desired.
Note that loading of this script file also requires accordingly configured
auto-load safe-path
(see Auto-loading safe path).
If the macro invocation is put in a header, any application or library
using this header will get a reference to the specified script,
and with the use of "MS"
attributes on the section, the linker
will remove duplicates.
Script text entries allow to put the executable script in the entry
itself instead of loading it from a file.
The first line of the entry, everything after the prefix byte and up to
the first newline (0xa
) character, is the script name, and must not
contain any kind of space character, e.g., spaces or tabs.
The rest of the entry, up to the trailing null byte, is the script to
execute in the specified language. The name needs to be unique among
all script names, as gdb executes each script only once based
on its name.
Here is an example from file py-section-script.c in the gdb testsuite.
#include "symcat.h" #include "gdb/section-scripts.h" asm( ".pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n" ".byte " XSTRING (SECTION_SCRIPT_ID_PYTHON_TEXT) "\n" ".ascii \"gdb.inlined-script\\n\"\n" ".ascii \"class test_cmd (gdb.Command):\\n\"\n" ".ascii \" def __init__ (self):\\n\"\n" ".ascii \" super (test_cmd, self).__init__ (" "\\\"test-cmd\\\", gdb.COMMAND_OBSCURE)\\n\"\n" ".ascii \" def invoke (self, arg, from_tty):\\n\"\n" ".ascii \" print (\\\"test-cmd output, arg = %s\\\" % arg)\\n\"\n" ".ascii \"test_cmd ()\\n\"\n" ".byte 0\n" ".popsection\n" );
Loading of inlined scripts requires a properly configured
auto-load safe-path
(see Auto-loading safe path).
The path to specify in auto-load safe-path
is the path of the file
containing the .debug_gdb_scripts
section.
Given the multiple ways of auto-loading extensions, it might not always be clear which one to choose. This section provides some guidance.
Benefits of the -gdb.ext way:
Scripts specified in the .debug_gdb_scripts
section are searched for
in the source search path.
For publicly installed libraries, e.g., libstdc++, there typically
isn't a source directory in which to find the script.
Benefits of the .debug_gdb_scripts
way:
Scripts for libraries done the -gdb.ext way require an objfile to trigger their loading. When an application is statically linked the only objfile available is the executable, and it is cumbersome to attach all the scripts from all the input libraries to the executable's -gdb.ext script.
Some classes can be entirely inlined, and thus there may not be an associated shared library to attach a -gdb.ext script to.
In some circumstances, apps can be built out of large collections of internal
libraries, and the build infrastructure necessary to install the
-gdb.ext scripts in a place where gdb can find them is
cumbersome. It may be easier to specify the scripts in the
.debug_gdb_scripts
section as relative paths, and add a path to the
top of the source tree to the source search path.
The Guile and Python extension languages do not share any state, and generally do not interfere with each other. There are some things to be aware of, however.
Python was gdb's first extension language, and to avoid breaking existing behaviour Python comes first. This is generally solved by the “first one wins” principle. gdb maintains a list of enabled extension languages, and when it makes a call to an extension language, (say to pretty-print a value), it tries each in turn until an extension language indicates it has performed the request (e.g., has returned the pretty-printed form of a value). This extends to errors while performing such requests: If an error happens while, for example, trying to pretty-print an object then the error is reported and any following extension languages are not tried.
It is often useful to define alternate spellings of existing commands. For example, if a new gdb command defined in Python has a long name to type, it is handy to have an abbreviated version of it that involves less typing.
gdb itself uses aliases. For example ‘s’ is an alias of the ‘step’ command even though it is otherwise an ambiguous abbreviation of other commands like ‘set’ and ‘show’.
Aliases are also used to provide shortened or more common versions of multi-word commands. For example, gdb provides the ‘tty’ alias of the ‘set inferior-tty’ command.
You can define a new alias with the ‘alias’ command.
alias [-a] [--]
ALIAS =
COMMANDALIAS specifies the name of the new alias. Each word of ALIAS must consist of letters, numbers, dashes and underscores.
COMMAND specifies the name of an existing command that is being aliased.
The ‘-a’ option specifies that the new alias is an abbreviation of the command. Abbreviations are not shown in command lists displayed by the ‘help’ command.
The ‘--’ option specifies the end of options, and is useful when ALIAS begins with a dash.
Here is a simple example showing how to make an abbreviation of a command so that there is less to type. Suppose you were tired of typing ‘disas’, the current shortest unambiguous abbreviation of the ‘disassemble’ command and you wanted an even shorter version named ‘di’. The following will accomplish this.
(gdb) alias -a di = disas
Note that aliases are different from user-defined commands. With a user-defined command, you also need to write documentation for it with the ‘document’ command. An alias automatically picks up the documentation of the existing command.
Here is an example where we make ‘elms’ an abbreviation of ‘elements’ in the ‘set print elements’ command. This is to show that you can make an abbreviation of any part of a command.
(gdb) alias -a set print elms = set print elements (gdb) alias -a show print elms = show print elements (gdb) set p elms 20 (gdb) show p elms Limit on string chars or array elements to print is 200.
Note that if you are defining an alias of a ‘set’ command, and you want to have an alias for the corresponding ‘show’ command, then you need to define the latter separately.
Unambiguously abbreviated commands are allowed in COMMAND and ALIAS, just as they are normally.
(gdb) alias -a set pr elms = set p ele
Finally, here is an example showing the creation of a one word alias for a more complex command. This creates alias ‘spe’ of the command ‘set print elements’.
(gdb) alias spe = set print elements (gdb) spe 20
gdb supports multiple command interpreters, and some command infrastructure to allow users or user interface writers to switch between interpreters or run commands in other interpreters.
gdb currently supports two command interpreters, the console interpreter (sometimes called the command-line interpreter or cli) and the machine interface interpreter (or gdb/mi). This manual describes both of these interfaces in great detail.
By default, gdb will start with the console interpreter. However, the user may choose to start gdb with another interpreter by specifying the -i or --interpreter startup options. Defined interpreters include:
console
mi
mi3
). Used primarily
by programs wishing to use gdb as a backend for a debugger GUI
or an IDE. For more information, see The gdb/mi Interface.
mi3
mi2
mi1
You may execute commands in any interpreter from the current
interpreter using the appropriate command. If you are running the
console interpreter, simply use the interpreter-exec
command:
interpreter-exec mi "-data-list-register-names"
gdb/mi has a similar command, although it is only available in versions of gdb which support gdb/mi version 2 (or greater).
Note that interpreter-exec
only changes the interpreter for the
duration of the specified command. It does not change the interpreter
permanently.
Although you may only choose a single interpreter at startup, it is possible to run an independent interpreter on a specified input/output device (usually a tty).
For example, consider a debugger GUI or IDE that wants to provide a gdb console view. It may do so by embedding a terminal emulator widget in its GUI, starting gdb in the traditional command-line mode with stdin/stdout/stderr redirected to that terminal, and then creating an MI interpreter running on a specified input/output device. The console interpreter created by gdb at startup handles commands the user types in the terminal widget, while the GUI controls and synchronizes state with gdb using the separate MI interpreter.
To start a new secondary user interface running MI, use the
new-ui
command:
new-ui interpreter tty
The interpreter parameter specifies the interpreter to run.
This accepts the same values as the interpreter-exec
command.
For example, ‘console’, ‘mi’, ‘mi2’, etc. The
tty parameter specifies the name of the bidirectional file the
interpreter uses for input/output, usually the name of a
pseudoterminal slave on Unix systems. For example:
(gdb) new-ui mi /dev/pts/9
runs an MI interpreter on /dev/pts/9.
The gdb Text User Interface (TUI) is a terminal
interface which uses the curses
library to show the source
file, the assembly output, the program registers and gdb
commands in separate text windows. The TUI mode is supported only
on platforms where a suitable version of the curses
library
is available.
The TUI mode is enabled by default when you invoke gdb as ‘gdb -tui’. You can also switch in and out of TUI mode while gdb runs by using various TUI commands and key bindings, such as tui enable or C-x C-a. See TUI Commands, and TUI Key Bindings.
In TUI mode, gdb can display several text windows:
The source and assembly windows show the current program position by highlighting the current line and marking it with a ‘>’ marker. Breakpoints are indicated with two markers. The first marker indicates the breakpoint type:
B
b
H
h
The second marker indicates whether the breakpoint is enabled or not:
+
-
The source, assembly and register windows are updated when the current thread changes, when the frame changes, or when the program counter changes.
These windows are not all visible at the same time. The command window is always visible. The others can be arranged in several layouts:
A status line above the command window shows the following information:
No process
.
??
is displayed.
??
is displayed.
The TUI installs several key bindings in the readline keymaps (see Command Line Editing). The following key bindings are installed for both TUI mode and the gdb standard mode.
This key binding uses the bindable Readline function
tui-switch-mode
.
Think of this key binding as the Emacs C-x 1 binding.
This key binding uses the bindable Readline function
tui-delete-other-windows
.
Think of it as the Emacs C-x 2 binding.
This key binding uses the bindable Readline function
tui-change-windows
.
Think of it as the Emacs C-x o binding.
This key binding uses the bindable Readline function
tui-other-window
.
This key binding uses the bindable Readline function
next-keymap
.
The following key bindings only work in the TUI mode:
Because the arrow keys scroll the active window in the TUI mode, they are not available for their normal use by readline unless the command window has the focus. When another window is active, you must use other readline key bindings such as C-p, C-n, C-b and C-f to control the command window.
The TUI also provides a SingleKey mode, which binds several frequently used gdb commands to single keys. Type C-x s to switch into this mode, where the following key bindings are used:
Other keys temporarily switch to the gdb command prompt. The key that was pressed is inserted in the editing buffer so that it is possible to type most gdb commands without interaction with the TUI SingleKey mode. Once the command is entered the TUI SingleKey mode is restored. The only way to permanently leave this mode is by typing q or C-x s.
If gdb was built with Readline 8.0 or later, the TUI SingleKey keymap will be named ‘SingleKey’. This can be used in .inputrc to add additional bindings to this keymap.
The TUI has specific commands to control the text windows. These commands are always available, even when gdb is not in the TUI mode. When gdb is in the standard mode, most of these commands will automatically switch to the TUI mode.
Note that if gdb's stdout
is not connected to a
terminal, or gdb has been started with the machine interface
interpreter (see The gdb/mi Interface), most of
these commands will fail with an error, because it would not be
possible or desirable to enable curses window management.
tui enable
tui disable
info win
layout
namenext
prev
src
asm
split
regs
src
layout display the register, source, and command
windows. When in asm
or split
layout display the
register, assembler, and command windows.
focus
namenext
prev
src
asm
regs
cmd
refresh
tui reg
groupnext
prev
general
float
system
vector
all
update
winheight
name +
countwinheight
name -
countsrc
(the
source window), cmd
(the command window), asm
(the
disassembly window), or regs
(the register display window).
Several configuration variables control the appearance of TUI windows.
set tui border-kind
kindspace
ascii
acs
set tui border-mode
modeset tui active-border-mode
modenormal
standout
reverse
half
half-standout
bold
bold-standout
set tui tab-width
ncharsset tui compact-source
[on
|off
]Note that the colors of the TUI borders can be controlled using the
appropriate set style
commands. See Output Styling.
A special interface allows you to use gnu Emacs to view (and edit) the source files for the program you are debugging with gdb.
To use this interface, use the command M-x gdb in Emacs. Give the executable file you want to debug as an argument. This command starts gdb as a subprocess of Emacs, with input and output through a newly created Emacs buffer.
Running gdb under Emacs can be just like running gdb normally except for two things:
This applies both to gdb commands and their output, and to the input and output done by the program you are debugging.
This is useful because it means that you can copy the text of previous commands and input them again; you can even use parts of the output in this way.
All the facilities of Emacs' Shell mode are available for interacting with your program. In particular, you can send signals the usual way—for example, C-c C-c for an interrupt, C-c C-z for a stop.
Each time gdb displays a stack frame, Emacs automatically finds the source file for that frame and puts an arrow (‘=>’) at the left margin of the current line. Emacs uses a separate buffer for source display, and splits the screen to show both your gdb session and the source.
Explicit gdb list
or search commands still produce output as
usual, but you probably have no reason to use them from Emacs.
We call this text command mode. Emacs 22.1, and later, also uses a graphical mode, enabled by default, which provides further buffers that can control the execution and describe the state of your program. See GDB Graphical Interface.
If you specify an absolute file name when prompted for the M-x
gdb argument, then Emacs sets your current working directory to where
your program resides. If you only specify the file name, then Emacs
sets your current working directory to the directory associated
with the previous buffer. In this case, gdb may find your
program by searching your environment's PATH
variable, but on
some operating systems it might not find the source. So, although the
gdb input and output session proceeds normally, the auxiliary
buffer does not display the current source and line of execution.
The initial working directory of gdb is printed on the top line of the GUD buffer and this serves as a default for the commands that specify files for gdb to operate on. See Commands to Specify Files.
By default, M-x gdb calls the program called gdb. If you
need to call gdb by a different name (for example, if you
keep several configurations around, with different names) you can
customize the Emacs variable gud-gdb-command-name
to run the
one you want.
In the GUD buffer, you can use these special Emacs commands in addition to the standard Shell mode commands:
step
command; also
update the display window to show the current file and location.
next
command. Then update the display window
to show the current file and location.
stepi
command; update
display window accordingly.
finish
command.
continue
command.
up
command.
down
command.
In any source file, the Emacs command C-x <SPC> (gud-break
)
tells gdb to set a breakpoint on the source line point is on.
In text command mode, if you type M-x speedbar, Emacs displays a separate frame which shows a backtrace when the GUD buffer is current. Move point to any frame in the stack and type <RET> to make it become the current frame and display the associated source in the source buffer. Alternatively, click Mouse-2 to make the selected frame become the current one. In graphical mode, the speedbar displays watch expressions.
If you accidentally delete the source-display buffer, an easy way to get
it back is to type the command f
in the gdb buffer, to
request a frame display; when you run under Emacs, this recreates
the source buffer if necessary to show you the context of the current
frame.
The source files displayed in Emacs are in ordinary Emacs buffers which are visiting the source files in the usual way. You can edit the files with these buffers if you wish; but keep in mind that gdb communicates with Emacs in terms of line numbers. If you add or delete lines from the text, the line numbers that gdb knows cease to correspond properly with the code.
A more detailed description of Emacs' interaction with gdb is given in the Emacs manual (see Debuggers).
gdb/mi is a line based machine oriented text interface to gdb and is activated by specifying using the --interpreter command line option (see Mode Options). It is specifically intended to support the development of systems which use the debugger as just one small component of a larger system.
This chapter is a specification of the gdb/mi interface. It is written in the form of a reference manual.
Note that gdb/mi is still under construction, so some of the features described below are incomplete and subject to change (see gdb/mi Development and Front Ends).
This chapter uses the following notation:
|
separates two alternatives.
[
something ]
indicates that something is optional:
it may or may not be given.
(
group )*
means that group inside the parentheses
may repeat zero or more times.
(
group )+
means that group inside the parentheses
may repeat one or more times.
"
string"
means a literal string.
Interaction of a GDB/MI frontend with gdb involves three parts—commands sent to gdb, responses to those commands and notifications. Each command results in exactly one response, indicating either successful completion of the command, or an error. For the commands that do not resume the target, the response contains the requested information. For the commands that resume the target, the response only indicates whether the target was successfully resumed. Notifications is the mechanism for reporting changes in the state of the target, or in gdb state, that cannot conveniently be associated with a command and reported as part of that command response.
The important examples of notifications are:
There's no guarantee that whenever an MI command reports an error, gdb or the target are in any specific state, and especially, the state is not reverted to the state before the MI command was processed. Therefore, whenever an MI command results in an error, we recommend that the frontend refreshes all the information shown in the user interface.
In most cases when gdb accesses the target, this access is done in context of a specific thread and frame (see Frames). Often, even when accessing global data, the target requires that a thread be specified. The CLI interface maintains the selected thread and frame, and supplies them to target on each command. This is convenient, because a command line user would not want to specify that information explicitly on each command, and because user interacts with gdb via a single terminal, so no confusion is possible as to what thread and frame are the current ones.
In the case of MI, the concept of selected thread and frame is less useful. First, a frontend can easily remember this information itself. Second, a graphical frontend can have more than one window, each one used for debugging a different thread, and the frontend might want to access additional threads for internal purposes. This increases the risk that by relying on implicitly selected thread, the frontend may be operating on a wrong one. Therefore, each MI command should explicitly specify which thread and frame to operate on. To make it possible, each MI command accepts the ‘--thread’ and ‘--frame’ options, the value to each is gdb global identifier for thread and frame to operate on.
Usually, each top-level window in a frontend allows the user to select a thread and a frame, and remembers the user selection for further operations. However, in some cases gdb may suggest that the current thread or frame be changed. For example, when stopping on a breakpoint it is reasonable to switch to the thread where breakpoint is hit. For another example, if the user issues the CLI ‘thread’ or ‘frame’ commands via the frontend, it is desirable to change the frontend's selection to the one specified by user. gdb communicates the suggestion to change current thread and frame using the ‘=thread-selected’ notification.
Note that historically, MI shares the selected thread with CLI, so
frontends used the -thread-select
to execute commands in the
right context. However, getting this to work right is cumbersome. The
simplest way is for frontend to emit -thread-select
command
before every command. This doubles the number of commands that need
to be sent. The alternative approach is to suppress -thread-select
if the selected thread in gdb is supposed to be identical to the
thread the frontend wants to operate on. However, getting this
optimization right can be tricky. In particular, if the frontend
sends several commands to gdb, and one of the commands changes the
selected thread, then the behaviour of subsequent commands will
change. So, a frontend should either wait for response from such
problematic commands, or explicitly add -thread-select
for
all subsequent commands. No frontend is known to do this exactly
right, so it is suggested to just always pass the ‘--thread’ and
‘--frame’ options.
The execution of several commands depends on which language is selected. By default, the current language (see show language) is used. But for commands known to be language-sensitive, it is recommended to use the ‘--language’ option. This option takes one argument, which is the name of the language to use while executing the command. For instance:
-data-evaluate-expression --language c "sizeof (void*)" ^done,value="4" (gdb)
The valid language names are the same names accepted by the ‘set language’ command (see Manually), excluding ‘auto’, ‘local’ or ‘unknown’.
On some targets, gdb is capable of processing MI commands
even while the target is running. This is called asynchronous
command execution (see Background Execution). The frontend may
specify a preference for asynchronous execution using the
-gdb-set mi-async 1
command, which should be emitted before
either running the executable or attaching to the target. After the
frontend has started the executable or attached to the target, it can
find if asynchronous execution is enabled using the
-list-target-features
command.
-gdb-set mi-async on
-gdb-set mi-async off
When off
, which is the default, MI execution commands (e.g.,
-exec-continue
) are foreground commands, and gdb waits
for the program to stop before processing further commands.
When on
, MI execution commands are background execution
commands (e.g., -exec-continue
becomes the equivalent of the
c&
CLI command), and so gdb is capable of processing
MI commands even while the target is running.
-gdb-show mi-async
Note: In gdb version 7.7 and earlier, this option was called
target-async
instead of mi-async
, and it had the effect
of both putting MI in asynchronous mode and making CLI background
commands possible. CLI background commands are now always possible
“out of the box” if the target supports them. The old spelling is
kept as a deprecated alias for backwards compatibility.
Even if gdb can accept a command while target is running, many commands that access the target do not work when the target is running. Therefore, asynchronous command execution is most useful when combined with non-stop mode (see Non-Stop Mode). Then, it is possible to examine the state of one thread, while other threads are running.
When a given thread is running, MI commands that try to access the
target in the context of that thread may not work, or may work only on
some targets. In particular, commands that try to operate on thread's
stack will not work, on any target. Commands that read memory, or
modify breakpoints, may work or not work, depending on the target. Note
that even commands that operate on global state, such as print
,
set
, and breakpoint commands, still access the target in the
context of a specific thread, so frontend should try to find a
stopped thread and perform the operation on that thread (using the
‘--thread’ option).
Which commands will work in the context of a running thread is
highly target dependent. However, the two commands
-exec-interrupt
, to stop a thread, and -thread-info
,
to find the state of a thread, will always work.
gdb may be used to debug several processes at the same time. On some platforms, gdb may support debugging of several hardware systems, each one having several cores with several different processes running on each core. This section describes the MI mechanism to support such debugging scenarios.
The key observation is that regardless of the structure of the target, MI can have a global list of threads, because most commands that accept the ‘--thread’ option do not need to know what process that thread belongs to. Therefore, it is not necessary to introduce neither additional ‘--process’ option, nor an notion of the current process in the MI interface. The only strictly new feature that is required is the ability to find how the threads are grouped into processes.
To allow the user to discover such grouping, and to support arbitrary
hierarchy of machines/cores/processes, MI introduces the concept of a
thread group. Thread group is a collection of threads and other
thread groups. A thread group always has a string identifier, a type,
and may have additional attributes specific to the type. A new
command, -list-thread-groups
, returns the list of top-level
thread groups, which correspond to processes that gdb is
debugging at the moment. By passing an identifier of a thread group
to the -list-thread-groups
command, it is possible to obtain
the members of specific thread group.
To allow the user to easily discover processes, and other objects, he
wishes to debug, a concept of available thread group is
introduced. Available thread group is an thread group that
gdb is not debugging, but that can be attached to, using the
-target-attach
command. The list of available top-level thread
groups can be obtained using ‘-list-thread-groups --available’.
In general, the content of a thread group may be only retrieved only
after attaching to that thread group.
Thread groups are related to inferiors (see Inferiors and Programs). Each inferior corresponds to a thread group of a special type ‘process’, and some additional operations are permitted on such thread groups.
==>
|
mi-command
==>
[
token ]
cli-command nl, where
cli-command is any existing gdb CLI command.
==>
[
token ] "-"
operation ( " "
option )*
[ " --" ] ( " "
parameter )*
nl
==>
==>
"-"
parameter [ " "
parameter ]
==>
|
c-string
==>
==>
==>
"""
seven-bit-iso-c-string-content """
==>
CR | CR-LF
Notes:
Pragmatics:
The output from gdb/mi consists of zero or more out-of-band records followed, optionally, by a single result record. This result record is for the most recent command. The sequence of output records is terminated by ‘(gdb)’.
If an input command was prefixed with a token then the corresponding output for that command will also be prefixed by that same token.
==>
(
out-of-band-record )* [
result-record ] "(gdb)"
nl
==>
[
token ] "^"
result-class ( ","
result )*
nl
==>
|
stream-record
==>
|
status-async-output |
notify-async-output
==>
[
token ] "*"
async-output nl
==>
[
token ] "+"
async-output nl
==>
[
token ] "="
async-output nl
==>
( ","
result )*
==>
"done" | "running" | "connected" | "error" | "exit"
==>
"stopped" |
others (where others will be added
depending on the needs—this is still in development).
==>
"="
value
==>
==>
|
tuple |
list
==>
==>
"{}" | "{"
result ( ","
result )* "}"
==>
"[]" | "["
value ( ","
value )* "]" | "["
result ( ","
result )* "]"
==>
|
target-stream-output |
log-stream-output
==>
"~"
c-string nl
==>
"@"
c-string nl
==>
"&"
c-string nl
==>
CR | CR-LF
==>
Notes:
See gdb/mi Stream Records, for more details about the various output records.
For the developers convenience CLI commands can be entered directly,
but there may be some unexpected behaviour. For example, commands
that query the user will behave as if the user replied yes, breakpoint
command lists are not executed and some CLI commands, such as
if
, when
and define
, prompt for further input with
‘>’, which is not valid MI output.
This feature may be removed at some stage in the future and it is
recommended that front ends use the -interpreter-exec
command
(see -interpreter-exec).
The application which takes the MI output and presents the state of the program being debugged to the user is called a front end.
Since gdb/mi is used by a variety of front ends to gdb, changes to the MI interface may break existing usage. This section describes how the protocol changes and how to request previous version of the protocol when it does.
Some changes in MI need not break a carefully designed front end, and for these the MI version will remain unchanged. The following is a list of changes that may occur within one level, so front ends should parse MI output in a way that can handle them:
in_scope
(see -var-update) may be extended.
If the changes are likely to break front ends, the MI version level will be increased by one. The new versions of the MI protocol are not compatible with the old versions. Old versions of MI remain available, allowing front ends to keep using them until they are modified to use the latest MI version.
Since --interpreter=mi
always points to the latest MI version, it is
recommended that front ends request a specific version of MI when launching
gdb (e.g. --interpreter=mi2
) to make sure they get an
interpreter with the MI version they expect.
The following table gives a summary of the the released versions of the MI interface: the version number, the version of GDB in which it first appeared and the breaking changes compared to the previous version.
MI version | GDB version | Breaking changes
|
---|---|---|
1
|
5.1
|
None
|
2
|
6.0
|
|
3
|
9.1
|
|
If your front end cannot yet migrate to a more recent version of the MI protocol, you can nevertheless selectively enable specific features available in those recent MI versions, using the following commands:
-fix-multi-location-breakpoint-output
The best way to avoid unexpected changes in MI that might break your front end is to make your project known to gdb developers and follow development on gdb@sourceware.org and gdb-patches@sourceware.org.
In addition to a number of out-of-band notifications, the response to a gdb/mi command includes one of the following result indications:
"^done" [ ","
results ]
"^running"
"^connected"
"^error" "," "msg="
c-string [ "," "code="
c-string ]
msg=
c-string variable contains
the corresponding error message.
If present, the code=
c-string variable provides an error
code on which consumers can rely on to detect the corresponding
error condition. At present, only one error code is defined:
"^exit"
gdb internally maintains a number of output streams: the console, the target, and the log. The output intended for each of these streams is funneled through the gdb/mi interface using stream records.
Each stream record begins with a unique prefix character which identifies its stream (see gdb/mi Output Syntax). In addition to the prefix, each stream record contains a string-output. This is either raw text (with an implicit new line) or a quoted C string (which does not contain an implicit newline).
"~"
string-output"@"
string-output"&"
string-outputAsync records are used to notify the gdb/mi client of additional changes that have occurred. Those changes can either be a consequence of gdb/mi commands (e.g., a breakpoint modified) or a result of target activity (e.g., target stopped).
The following is the list of possible async records:
*running,thread-id="
thread"
*stopped,reason="
reason",thread-id="
id",stopped-threads="
stopped",core="
core"
breakpoint-hit
watchpoint-trigger
read-watchpoint-trigger
access-watchpoint-trigger
function-finished
location-reached
watchpoint-scope
end-stepping-range
exited-signalled
exited
exited-normally
signal-received
solib-event
stop-on-solib-events
(see Files) is
set or when a catch load
or catch unload
catchpoint is
in use (see Set Catchpoints).
fork
catch fork
(see Set Catchpoints) has been used.
vfork
catch vfork
(see Set Catchpoints) has been used.
syscall-entry
catch
syscall
(see Set Catchpoints) has been used.
syscall-return
catch syscall
(see Set Catchpoints) has been used.
exec
exec
. This is reported when catch exec
(see Set Catchpoints) has been used.
The id field identifies the global thread ID of the thread
that directly caused the stop – for example by hitting a breakpoint.
Depending on whether all-stop
mode is in effect (see All-Stop Mode), gdb may either
stop all threads, or only the thread that directly triggered the stop.
If all threads are stopped, the stopped field will have the
value of "all"
. Otherwise, the value of the stopped
field will be a list of thread identifiers. Presently, this list will
always include a single thread, but frontend should be prepared to see
several threads in the list. The core field reports the
processor core on which the stop event has happened. This field may be absent
if such information is not available.
=thread-group-added,id="
id"
=thread-group-removed,id="
id"
=thread-group-started,id="
id",pid="
pid"
=thread-group-exited,id="
id"[,exit-code="
code"]
=thread-created,id="
id",group-id="
gid"
=thread-exited,id="
id",group-id="
gid"
=thread-selected,id="
id"[,frame="
frame"]
-thread-select
or
-stack-select-frame
commands, but is emitted whenever an MI command
that is not documented to change the selected thread and frame actually
changes them. In particular, invoking, directly or indirectly
(via user-defined command), the CLI thread
or frame
commands,
will generate this notification. Changing the thread or frame from another
user interface (see Interpreters) will also generate this notification.
The frame field is only present if the newly selected thread is stopped. See GDB/MI Frame Information for the format of its value.
We suggest that in response to this notification, front ends
highlight the selected thread and cause subsequent commands to apply to
that thread.
=library-loaded,...
=library-unloaded,...
=library-loaded
notification.
The thread-group field, if present, specifies the id of the
thread group in whose context the library was unloaded. If the field is
absent, it means the library was unloaded in the context of all present
thread groups.
=traceframe-changed,num=
tfnum,tracepoint=
tpnum=traceframe-changed,end
=tsv-created,name=
name,initial=
initial=tsv-deleted,name=
name=tsv-deleted
=tsv-modified,name=
name,initial=
initial[,current=
current]
=breakpoint-created,bkpt={...}
=breakpoint-modified,bkpt={...}
=breakpoint-deleted,id=
numberThe bkpt argument is of the same form as returned by the various breakpoint commands; See GDB/MI Breakpoint Commands. The number is the ordinal number of the breakpoint.
Note that if a breakpoint is emitted in the result record of a
command, then it will not also be emitted in an async record.
=record-started,thread-group="
id",method="
method"[,format="
format"]
=record-stopped,thread-group="
id"
The method field indicates the method used to record execution. If the
method in use supports multiple recording formats, format will be present
and contain the currently used format. See Process Record and Replay,
for existing method and format values.
=cmd-param-changed,param=
param,value=
valueset
param is
changed to value. In the multi-word set
command,
the param is the whole parameter list to set
command.
For example, In command set check type on
, param
is check type
and value is on
.
=memory-changed,thread-group=
id,addr=
addr,len=
len[,type="code"]
type="code"
part is reported if the memory written to holds
executable code.
When gdb reports information about a breakpoint, a tracepoint, a watchpoint, or a catchpoint, it uses a tuple with the following fields:
number
type
catch-type
disp
enabled
enable
.
addr
addr_flags
func
filename
fullname
line
at
pending
evaluated-by
thread
task
cond
ignore
enable
traceframe-usage
static-tracepoint-marker-string-id
mask
pass
original-location
times
installed
what
locations
The value is a list of locations. The format of a location is described below.
A location in a multi-location breakpoint is represented as a tuple with the following fields:
number
enabled
enable
.
addr
addr_flags
func
file
fullname
line
thread-groups
For example, here is what the output of -break-insert
(see GDB/MI Breakpoint Commands) might be:
-> -break-insert main <- ^done,bkpt={number="1",type="breakpoint",disp="keep", enabled="y",addr="0x08048564",func="main",file="myprog.c", fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"], times="0"} <- (gdb)
Response from many MI commands includes an information about stack frame. This information is a tuple that may have the following fields:
level
func
addr
addr_flags
file
line
from
Whenever gdb has to report an information about a thread, it uses a tuple with the following fields. The fields are always present unless stated otherwise.
id
target-id
details
name
thread name
command, then this name is given. Otherwise, if
gdb can extract the thread name from the target, then that
name is given. If gdb cannot find the thread name, then this
field is omitted.
state
frame
core
Whenever a *stopped
record is emitted because the program
stopped after hitting an exception catchpoint (see Set Catchpoints),
gdb provides the name of the exception that was raised via
the exception-name
field. Also, for exceptions that were raised
with an exception message, gdb provides that message via
the exception-message
field.
This subsection presents several simple examples of interaction using the gdb/mi interface. In these examples, ‘->’ means that the following line is passed to gdb/mi as input, while ‘<-’ means the output received from gdb/mi.
Note the line breaks shown in the examples are here only for readability, they don't appear in the real output.
Setting a breakpoint generates synchronous output which contains detailed information of the breakpoint.
-> -break-insert main <- ^done,bkpt={number="1",type="breakpoint",disp="keep", enabled="y",addr="0x08048564",func="main",file="myprog.c", fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"], times="0"} <- (gdb)
Program execution generates asynchronous records and MI gives the reason that execution stopped.
-> -exec-run <- ^running <- (gdb) <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0", frame={addr="0x08048564",func="main", args=[{name="argc",value="1"},{name="argv",value="0xbfc4d4d4"}], file="myprog.c",fullname="/home/nickrob/myprog.c",line="68", arch="i386:x86_64"} <- (gdb) -> -exec-continue <- ^running <- (gdb) <- *stopped,reason="exited-normally" <- (gdb)
Quitting gdb just prints the result class ‘^exit’.
-> (gdb) <- -gdb-exit <- ^exit
Please note that ‘^exit’ is printed immediately, but it might take some time for gdb to actually exit. During that time, gdb performs necessary cleanups, including killing programs being debugged or disconnecting from debug hardware, so the frontend should wait till gdb exits and should only forcibly kill gdb if it fails to exit in reasonable time.
Here's what happens if you pass a non-existent command:
-> -rubbish <- ^error,msg="Undefined MI command: rubbish" <- (gdb)
The remaining sections describe blocks of commands. Each block of commands is laid out in a fashion similar to this section.
The motivation for this collection of commands.
A brief introduction to this collection of commands as a whole.
For each command in the block, the following is described:
-command args...
The corresponding gdb CLI command(s), if any.
Example(s) formatted for readability. Some of the described commands have not been implemented yet and these are labeled N.A. (not available).
This section documents gdb/mi commands for manipulating breakpoints.
-break-after
Command-break-after number count
The breakpoint number number is not in effect until it has been hit count times. To see how this is reflected in the output of the ‘-break-list’ command, see the description of the ‘-break-list’ command below.
The corresponding gdb command is ‘ignore’.
(gdb) -break-insert main ^done,bkpt={number="1",type="breakpoint",disp="keep", enabled="y",addr="0x000100d0",func="main",file="hello.c", fullname="/home/foo/hello.c",line="5",thread-groups=["i1"], times="0"} (gdb) -break-after 1 3 ~ ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",thread-groups=["i1"],times="0",ignore="3"}]} (gdb)
-break-commands
Command-break-commands number [ command1 ... commandN ]
Specifies the CLI commands that should be executed when breakpoint number is hit. The parameters command1 to commandN are the commands. If no command is specified, any previously-set commands are cleared. See Break Commands. Typical use of this functionality is tracing a program, that is, printing of values of some variables whenever breakpoint is hit and then continuing.
The corresponding gdb command is ‘commands’.
(gdb) -break-insert main ^done,bkpt={number="1",type="breakpoint",disp="keep", enabled="y",addr="0x000100d0",func="main",file="hello.c", fullname="/home/foo/hello.c",line="5",thread-groups=["i1"], times="0"} (gdb) -break-commands 1 "print v" "continue" ^done (gdb)
-break-condition
Command-break-condition number expr
Breakpoint number will stop the program only if the condition in expr is true. The condition becomes part of the ‘-break-list’ output (see the description of the ‘-break-list’ command below).
The corresponding gdb command is ‘condition’.
(gdb) -break-condition 1 1 ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",cond="1",thread-groups=["i1"],times="0",ignore="3"}]} (gdb)
-break-delete
Command-break-delete ( breakpoint )+
Delete the breakpoint(s) whose number(s) are specified in the argument list. This is obviously reflected in the breakpoint list.
The corresponding gdb command is ‘delete’.
(gdb) -break-delete 1 ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="0",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[]} (gdb)
-break-disable
Command-break-disable ( breakpoint )+
Disable the named breakpoint(s). The field ‘enabled’ in the break list is now set to ‘n’ for the named breakpoint(s).
The corresponding gdb command is ‘disable’.
(gdb) -break-disable 2 ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="n", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",thread-groups=["i1"],times="0"}]} (gdb)
-break-enable
Command-break-enable ( breakpoint )+
Enable (previously disabled) breakpoint(s).
The corresponding gdb command is ‘enable’.
(gdb) -break-enable 2 ^done (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",thread-groups=["i1"],times="0"}]} (gdb)
-break-info
Command-break-info breakpoint
Get information about a single breakpoint.
The result is a table of breakpoints. See GDB/MI Breakpoint Information, for details on the format of each breakpoint in the table.
The corresponding gdb command is ‘info break breakpoint’.
N.A.
-break-insert
Command-break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ] [ -c condition ] [ -i ignore-count ] [ -p thread-id ] [ location ]
If specified, location, can be one of:
The possible optional parameters of this command are:
See GDB/MI Breakpoint Information, for details on the format of the resulting breakpoint.
Note: this format is open to change.
The corresponding gdb commands are ‘break’, ‘tbreak’, ‘hbreak’, and ‘thbreak’.
(gdb) -break-insert main ^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c", fullname="/home/foo/recursive2.c,line="4",thread-groups=["i1"], times="0"} (gdb) -break-insert -t foo ^done,bkpt={number="2",addr="0x00010774",file="recursive2.c", fullname="/home/foo/recursive2.c,line="11",thread-groups=["i1"], times="0"} (gdb) -break-list ^done,BreakpointTable={nr_rows="2",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x0001072c", func="main",file="recursive2.c", fullname="/home/foo/recursive2.c,"line="4",thread-groups=["i1"], times="0"}, bkpt={number="2",type="breakpoint",disp="del",enabled="y", addr="0x00010774",func="foo",file="recursive2.c", fullname="/home/foo/recursive2.c",line="11",thread-groups=["i1"], times="0"}]} (gdb)
-dprintf-insert
Command-dprintf-insert [ -t ] [ -f ] [ -d ] [ -c condition ] [ -i ignore-count ] [ -p thread-id ] [ location ] [ format ] [ argument ]
If supplied, location may be specified the same way as for
the -break-insert
command. See -break-insert.
The possible optional parameters of this command are:
See GDB/MI Breakpoint Information, for details on the format of the resulting breakpoint.
The corresponding gdb command is ‘dprintf’.
(gdb) 4-dprintf-insert foo "At foo entry\n" 4^done,bkpt={number="1",type="dprintf",disp="keep",enabled="y", addr="0x000000000040061b",func="foo",file="mi-dprintf.c", fullname="mi-dprintf.c",line="25",thread-groups=["i1"], times="0",script={"printf \"At foo entry\\n\"","continue"}, original-location="foo"} (gdb) 5-dprintf-insert 26 "arg=%d, g=%d\n" arg g 5^done,bkpt={number="2",type="dprintf",disp="keep",enabled="y", addr="0x000000000040062a",func="foo",file="mi-dprintf.c", fullname="mi-dprintf.c",line="26",thread-groups=["i1"], times="0",script={"printf \"arg=%d, g=%d\\n\", arg, g","continue"}, original-location="mi-dprintf.c:26"} (gdb)
-break-list
Command-break-list
Displays the list of inserted breakpoints, showing the following fields:
If there are no breakpoints or watchpoints, the BreakpointTable
body
field is an empty list.
The corresponding gdb command is ‘info break’.
(gdb) -break-list ^done,BreakpointTable={nr_rows="2",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",line="5",thread-groups=["i1"], times="0"}, bkpt={number="2",type="breakpoint",disp="keep",enabled="y", addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c", line="13",thread-groups=["i1"],times="0"}]} (gdb)
Here's an example of the result when there are no breakpoints:
(gdb) -break-list ^done,BreakpointTable={nr_rows="0",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[]} (gdb)
-break-passcount
Command-break-passcount tracepoint-number passcount
Set the passcount for tracepoint tracepoint-number to passcount. If the breakpoint referred to by tracepoint-number is not a tracepoint, error is emitted. This corresponds to CLI command ‘passcount’.
-break-watch
Command-break-watch [ -a | -r ]
Create a watchpoint. With the ‘-a’ option it will create an access watchpoint, i.e., a watchpoint that triggers either on a read from or on a write to the memory location. With the ‘-r’ option, the watchpoint created is a read watchpoint, i.e., it will trigger only when the memory location is accessed for reading. Without either of the options, the watchpoint created is a regular watchpoint, i.e., it will trigger when the memory location is accessed for writing. See Setting Watchpoints.
Note that ‘-break-list’ will report a single list of watchpoints and breakpoints inserted.
The corresponding gdb commands are ‘watch’, ‘awatch’, and ‘rwatch’.
Setting a watchpoint on a variable in the main
function:
(gdb) -break-watch x ^done,wpt={number="2",exp="x"} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-trigger",wpt={number="2",exp="x"}, value={old="-268439212",new="55"}, frame={func="main",args=[],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="5",arch="i386:x86_64"} (gdb)
Setting a watchpoint on a variable local to a function. gdb will stop the program execution twice: first for the variable changing value, then for the watchpoint going out of scope.
(gdb) -break-watch C ^done,wpt={number="5",exp="C"} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-trigger", wpt={number="5",exp="C"},value={old="-276895068",new="3"}, frame={func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13", arch="i386:x86_64"} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-scope",wpnum="5", frame={func="callee3",args=[{name="strarg", value="0x11940 \"A string argument.\""}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18", arch="i386:x86_64"} (gdb)
Listing breakpoints and watchpoints, at different points in the program execution. Note that once the watchpoint goes out of scope, it is deleted.
(gdb) -break-watch C ^done,wpt={number="2",exp="C"} (gdb) -break-list ^done,BreakpointTable={nr_rows="2",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",thread-groups=["i1"], times="1"}, bkpt={number="2",type="watchpoint",disp="keep", enabled="y",addr="",what="C",thread-groups=["i1"],times="0"}]} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-trigger",wpt={number="2",exp="C"}, value={old="-276895068",new="3"}, frame={func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13", arch="i386:x86_64"} (gdb) -break-list ^done,BreakpointTable={nr_rows="2",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",thread-groups=["i1"], times="1"}, bkpt={number="2",type="watchpoint",disp="keep", enabled="y",addr="",what="C",thread-groups=["i1"],times="-5"}]} (gdb) -exec-continue ^running ^done,reason="watchpoint-scope",wpnum="2", frame={func="callee3",args=[{name="strarg", value="0x11940 \"A string argument.\""}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18", arch="i386:x86_64"} (gdb) -break-list ^done,BreakpointTable={nr_rows="1",nr_cols="6", hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"}, {width="14",alignment="-1",col_name="type",colhdr="Type"}, {width="4",alignment="-1",col_name="disp",colhdr="Disp"}, {width="3",alignment="-1",col_name="enabled",colhdr="Enb"}, {width="10",alignment="-1",col_name="addr",colhdr="Address"}, {width="40",alignment="2",col_name="what",colhdr="What"}], body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8", thread-groups=["i1"],times="1"}]} (gdb)
This section documents gdb/mi commands for manipulating catchpoints.
-catch-load
Command-catch-load [ -t ] [ -d ] regexp
Add a catchpoint for library load events. If the ‘-t’ option is used, the catchpoint is a temporary one (see Setting Breakpoints). If the ‘-d’ option is used, the catchpoint is created in a disabled state. The ‘regexp’ argument is a regular expression used to match the name of the loaded library.
The corresponding gdb command is ‘catch load’.
-catch-load -t foo.so ^done,bkpt={number="1",type="catchpoint",disp="del",enabled="y", what="load of library matching foo.so",catch-type="load",times="0"} (gdb)
-catch-unload
Command-catch-unload [ -t ] [ -d ] regexp
Add a catchpoint for library unload events. If the ‘-t’ option is used, the catchpoint is a temporary one (see Setting Breakpoints). If the ‘-d’ option is used, the catchpoint is created in a disabled state. The ‘regexp’ argument is a regular expression used to match the name of the unloaded library.
The corresponding gdb command is ‘catch unload’.
-catch-unload -d bar.so ^done,bkpt={number="2",type="catchpoint",disp="keep",enabled="n", what="load of library matching bar.so",catch-type="unload",times="0"} (gdb)
The following gdb/mi commands can be used to create catchpoints that stop the execution when Ada exceptions are being raised.
-catch-assert
Command-catch-assert [ -c condition] [ -d ] [ -t ]
Add a catchpoint for failed Ada assertions.
The possible optional parameters for this command are:
The corresponding gdb command is ‘catch assert’.
-catch-assert ^done,bkptno="5",bkpt={number="5",type="breakpoint",disp="keep", enabled="y",addr="0x0000000000404888",what="failed Ada assertions", thread-groups=["i1"],times="0", original-location="__gnat_debug_raise_assert_failure"} (gdb)
-catch-exception
Command-catch-exception [ -c condition] [ -d ] [ -e exception-name ] [ -t ] [ -u ]
Add a catchpoint stopping when Ada exceptions are raised. By default, the command stops the program when any Ada exception gets raised. But it is also possible, by using some of the optional parameters described below, to create more selective catchpoints.
The possible optional parameters for this command are:
The corresponding gdb commands are ‘catch exception’ and ‘catch exception unhandled’.
-catch-exception -e Program_Error ^done,bkptno="4",bkpt={number="4",type="breakpoint",disp="keep", enabled="y",addr="0x0000000000404874", what="`Program_Error' Ada exception", thread-groups=["i1"], times="0",original-location="__gnat_debug_raise_exception"} (gdb)
-catch-handlers
Command-catch-handlers [ -c condition] [ -d ] [ -e exception-name ] [ -t ]
Add a catchpoint stopping when Ada exceptions are handled. By default, the command stops the program when any Ada exception gets handled. But it is also possible, by using some of the optional parameters described below, to create more selective catchpoints.
The possible optional parameters for this command are:
The corresponding gdb command is ‘catch handlers’.
-catch-handlers -e Constraint_Error ^done,bkptno="4",bkpt={number="4",type="breakpoint",disp="keep", enabled="y",addr="0x0000000000402f68", what="`Constraint_Error' Ada exception handlers",thread-groups=["i1"], times="0",original-location="__gnat_begin_handler"} (gdb)
The following gdb/mi commands can be used to create catchpoints that stop the execution when C++ exceptions are being throw, rethrown, or caught.
-catch-throw
Command-catch-throw [ -t ] [ -r regexp]
Stop when the debuggee throws a C++ exception. If regexp is given, then only exceptions whose type matches the regular expression will be caught.
If ‘-t’ is given, then the catchpoint is enabled only for one stop, the catchpoint is automatically deleted after stopping once for the event.
The corresponding gdb commands are ‘catch throw’ and ‘tcatch throw’ (see Set Catchpoints).
-catch-throw -r exception_type ^done,bkpt={number="1",type="catchpoint",disp="keep",enabled="y", what="exception throw",catch-type="throw", thread-groups=["i1"], regexp="exception_type",times="0"} (gdb) -exec-run ^running (gdb) ~"\n" ~"Catchpoint 1 (exception thrown), 0x00007ffff7ae00ed in __cxa_throw () from /lib64/libstdc++.so.6\n" *stopped,bkptno="1",reason="breakpoint-hit",disp="keep", frame={addr="0x00007ffff7ae00ed",func="__cxa_throw", args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"}, thread-id="1",stopped-threads="all",core="6" (gdb)
-catch-rethrow
Command-catch-rethrow [ -t ] [ -r regexp]
Stop when a C++ exception is re-thrown. If regexp is given, then only exceptions whose type matches the regular expression will be caught.
If ‘-t’ is given, then the catchpoint is enabled only for one stop, the catchpoint is automatically deleted after the first event is caught.
The corresponding gdb commands are ‘catch rethrow’ and ‘tcatch rethrow’ (see Set Catchpoints).
-catch-rethrow -r exception_type ^done,bkpt={number="1",type="catchpoint",disp="keep",enabled="y", what="exception rethrow",catch-type="rethrow", thread-groups=["i1"], regexp="exception_type",times="0"} (gdb) -exec-run ^running (gdb) ~"\n" ~"Catchpoint 1 (exception rethrown), 0x00007ffff7ae00ed in __cxa_rethrow () from /lib64/libstdc++.so.6\n" *stopped,bkptno="1",reason="breakpoint-hit",disp="keep", frame={addr="0x00007ffff7ae00ed",func="__cxa_rethrow", args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"}, thread-id="1",stopped-threads="all",core="6" (gdb)
-catch-catch
Command-catch-catch [ -t ] [ -r regexp]
Stop when the debuggee catches a C++ exception. If regexp is given, then only exceptions whose type matches the regular expression will be caught.
If ‘-t’ is given, then the catchpoint is enabled only for one stop, the catchpoint is automatically deleted after the first event is caught.
The corresponding gdb commands are ‘catch catch’ and ‘tcatch catch’ (see Set Catchpoints).
-catch-catch -r exception_type ^done,bkpt={number="1",type="catchpoint",disp="keep",enabled="y", what="exception catch",catch-type="catch", thread-groups=["i1"], regexp="exception_type",times="0"} (gdb) -exec-run ^running (gdb) ~"\n" ~"Catchpoint 1 (exception caught), 0x00007ffff7ae00ed in __cxa_begin_catch () from /lib64/libstdc++.so.6\n" *stopped,bkptno="1",reason="breakpoint-hit",disp="keep", frame={addr="0x00007ffff7ae00ed",func="__cxa_begin_catch", args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"}, thread-id="1",stopped-threads="all",core="6" (gdb)
-exec-arguments
Command-exec-arguments args
Set the inferior program arguments, to be used in the next ‘-exec-run’.
The corresponding gdb command is ‘set args’.
(gdb) -exec-arguments -v word ^done (gdb)
-environment-cd
Command-environment-cd pathdir
Set gdb's working directory.
The corresponding gdb command is ‘cd’.
(gdb) -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb ^done (gdb)
-environment-directory
Command-environment-directory [ -r ] [ pathdir ]+
Add directories pathdir to beginning of search path for source files. If the ‘-r’ option is used, the search path is reset to the default search path. If directories pathdir are supplied in addition to the ‘-r’ option, the search path is first reset and then addition occurs as normal. Multiple directories may be specified, separated by blanks. Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command. If blanks are needed as part of a directory name, double-quotes should be used around the name. In the command output, the path will show up separated by the system directory-separator character. The directory-separator character must not be used in any directory name. If no directories are specified, the current search path is displayed.
The corresponding gdb command is ‘dir’.
(gdb) -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd" (gdb) -environment-directory "" ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd" (gdb) -environment-directory -r /home/jjohnstn/src/gdb /usr/src ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd" (gdb) -environment-directory -r ^done,source-path="$cdir:$cwd" (gdb)
-environment-path
Command-environment-path [ -r ] [ pathdir ]+
Add directories pathdir to beginning of search path for object files. If the ‘-r’ option is used, the search path is reset to the original search path that existed at gdb start-up. If directories pathdir are supplied in addition to the ‘-r’ option, the search path is first reset and then addition occurs as normal. Multiple directories may be specified, separated by blanks. Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command. If blanks are needed as part of a directory name, double-quotes should be used around the name. In the command output, the path will show up separated by the system directory-separator character. The directory-separator character must not be used in any directory name. If no directories are specified, the current path is displayed.
The corresponding gdb command is ‘path’.
(gdb) -environment-path ^done,path="/usr/bin" (gdb) -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin" (gdb) -environment-path -r /usr/local/bin ^done,path="/usr/local/bin:/usr/bin" (gdb)
-environment-pwd
Command-environment-pwd
Show the current working directory.
The corresponding gdb command is ‘pwd’.
(gdb) -environment-pwd ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb" (gdb)
-thread-info
Command-thread-info [ thread-id ]
Reports information about either a specific thread, if the thread-id parameter is present, or about all threads. thread-id is the thread's global thread ID. When printing information about all threads, also reports the global ID of the current thread.
The ‘info thread’ command prints the same information about all threads.
The result contains the following attributes:
-thread-info ^done,threads=[ {id="2",target-id="Thread 0xb7e14b90 (LWP 21257)", frame={level="0",addr="0xffffe410",func="__kernel_vsyscall", args=[]},state="running"}, {id="1",target-id="Thread 0xb7e156b0 (LWP 21254)", frame={level="0",addr="0x0804891f",func="foo", args=[{name="i",value="10"}], file="/tmp/a.c",fullname="/tmp/a.c",line="158",arch="i386:x86_64"}, state="running"}], current-thread-id="1" (gdb)
-thread-list-ids
Command-thread-list-ids
Produces a list of the currently known global gdb thread ids. At the end of the list it also prints the total number of such threads.
This command is retained for historical reasons, the
-thread-info
command should be used instead.
Part of ‘info threads’ supplies the same information.
(gdb) -thread-list-ids ^done,thread-ids={thread-id="3",thread-id="2",thread-id="1"}, current-thread-id="1",number-of-threads="3" (gdb)
-thread-select
Command-thread-select thread-id
Make thread with global thread number thread-id the current thread. It prints the number of the new current thread, and the topmost frame for that thread.
This command is deprecated in favor of explicitly using the ‘--thread’ option to each command.
The corresponding gdb command is ‘thread’.
(gdb) -exec-next ^running (gdb) *stopped,reason="end-stepping-range",thread-id="2",line="187", file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c" (gdb) -thread-list-ids ^done, thread-ids={thread-id="3",thread-id="2",thread-id="1"}, number-of-threads="3" (gdb) -thread-select 3 ^done,new-thread-id="3", frame={level="0",func="vprintf", args=[{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""}, {name="arg",value="0x2"}],file="vprintf.c",line="31",arch="i386:x86_64"} (gdb)
-ada-task-info
Command-ada-task-info [ task-id ]
Reports information about either a specific Ada task, if the task-id parameter is present, or about all Ada tasks.
The ‘info tasks’ command prints the same information about all Ada tasks (see Ada Tasks).
The result is a table of Ada tasks. The following columns are defined for each Ada task:
This field should always exist, as Ada tasks are always implemented
on top of a thread. But if gdb cannot find this corresponding
thread for any reason, the field is omitted.
-ada-task-info ^done,tasks={nr_rows="3",nr_cols="8", hdr=[{width="1",alignment="-1",col_name="current",colhdr=""}, {width="3",alignment="1",col_name="id",colhdr="ID"}, {width="9",alignment="1",col_name="task-id",colhdr="TID"}, {width="4",alignment="1",col_name="thread-id",colhdr=""}, {width="4",alignment="1",col_name="parent-id",colhdr="P-ID"}, {width="3",alignment="1",col_name="priority",colhdr="Pri"}, {width="22",alignment="-1",col_name="state",colhdr="State"}, {width="1",alignment="2",col_name="name",colhdr="Name"}], body=[{current="*",id="1",task-id=" 644010",thread-id="1",priority="48", state="Child Termination Wait",name="main_task"}]} (gdb)
These are the asynchronous commands which generate the out-of-band record ‘*stopped’. Currently gdb only really executes asynchronously with remote targets and this interaction is mimicked in other cases.
-exec-continue
Command-exec-continue [--reverse] [--all|--thread-group N]
Resumes the execution of the inferior program, which will continue to execute until it reaches a debugger stop event. If the ‘--reverse’ option is specified, execution resumes in reverse until it reaches a stop event. Stop events may include
The corresponding gdb corresponding is ‘continue’.
-exec-continue ^running (gdb) @Hello world *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame={ func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c", line="13",arch="i386:x86_64"} (gdb)
-exec-finish
Command-exec-finish [--reverse]
Resumes the execution of the inferior program until the current function is exited. Displays the results returned by the function. If the ‘--reverse’ option is specified, resumes the reverse execution of the inferior program until the point where current function was called.
The corresponding gdb command is ‘finish’.
Function returning void
.
-exec-finish ^running (gdb) @hello from foo *stopped,reason="function-finished",frame={func="main",args=[], file="hello.c",fullname="/home/foo/bar/hello.c",line="7",arch="i386:x86_64"} (gdb)
Function returning other than void
. The name of the internal
gdb variable storing the result is printed, together with the
value itself.
-exec-finish ^running (gdb) *stopped,reason="function-finished",frame={addr="0x000107b0",func="foo", args=[{name="a",value="1"],{name="b",value="9"}}, file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, gdb-result-var="$1",return-value="0" (gdb)
-exec-interrupt
Command-exec-interrupt [--all|--thread-group N]
Interrupts the background execution of the target. Note how the token associated with the stop message is the one for the execution command that has been interrupted. The token for the interrupt itself only appears in the ‘^done’ output. If the user is trying to interrupt a non-running program, an error message will be printed.
Note that when asynchronous execution is enabled, this command is asynchronous just like other execution commands. That is, first the ‘^done’ response will be printed, and the target stop will be reported after that using the ‘*stopped’ notification.
In non-stop mode, only the context thread is interrupted by default. All threads (in all inferiors) will be interrupted if the ‘--all’ option is specified. If the ‘--thread-group’ option is specified, all threads in that group will be interrupted.
The corresponding gdb command is ‘interrupt’.
(gdb) 111-exec-continue 111^running (gdb) 222-exec-interrupt 222^done (gdb) 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt", frame={addr="0x00010140",func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="13",arch="i386:x86_64"} (gdb) (gdb) -exec-interrupt ^error,msg="mi_cmd_exec_interrupt: Inferior not executing." (gdb)
-exec-jump
Command-exec-jump location
Resumes execution of the inferior program at the location specified by parameter. See Specify Location, for a description of the different forms of location.
The corresponding gdb command is ‘jump’.
-exec-jump foo.c:10 *running,thread-id="all" ^running
-exec-next
Command-exec-next [--reverse]
Resumes execution of the inferior program, stopping when the beginning of the next source line is reached.
If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program, stopping at the beginning of the previous source line. If you issue this command on the first line of a function, it will take you back to the caller of that function, to the source line where the function was called.
The corresponding gdb command is ‘next’.
-exec-next ^running (gdb) *stopped,reason="end-stepping-range",line="8",file="hello.c" (gdb)
-exec-next-instruction
Command-exec-next-instruction [--reverse]
Executes one machine instruction. If the instruction is a function call, continues until the function returns. If the program stops at an instruction in the middle of a source line, the address will be printed as well.
If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program, stopping at the previous instruction. If the previously executed instruction was a return from another function, it will continue to execute in reverse until the call to that function (from the current stack frame) is reached.
The corresponding gdb command is ‘nexti’.
(gdb) -exec-next-instruction ^running (gdb) *stopped,reason="end-stepping-range", addr="0x000100d4",line="5",file="hello.c" (gdb)
-exec-return
Command-exec-return
Makes current function return immediately. Doesn't execute the inferior. Displays the new current frame.
The corresponding gdb command is ‘return’.
(gdb) 200-break-insert callee4 200^done,bkpt={number="1",addr="0x00010734", file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"} (gdb) 000-exec-run 000^running (gdb) 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1", frame={func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8", arch="i386:x86_64"} (gdb) 205-break-delete 205^done (gdb) 111-exec-return 111^done,frame={level="0",func="callee3", args=[{name="strarg", value="0x11940 \"A string argument.\""}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18", arch="i386:x86_64"} (gdb)
-exec-run
Command-exec-run [ --all | --thread-group N ] [ --start ]
Starts execution of the inferior from the beginning. The inferior executes until either a breakpoint is encountered or the program exits. In the latter case the output will include an exit code, if the program has exited exceptionally.
When neither the ‘--all’ nor the ‘--thread-group’ option is specified, the current inferior is started. If the ‘--thread-group’ option is specified, it should refer to a thread group of type ‘process’, and that thread group will be started. If the ‘--all’ option is specified, then all inferiors will be started.
Using the ‘--start’ option instructs the debugger to stop
the execution at the start of the inferior's main subprogram,
following the same behavior as the start
command
(see Starting).
The corresponding gdb command is ‘run’.
(gdb) -break-insert main ^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c",line="4"} (gdb) -exec-run ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1", frame={func="main",args=[],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="4",arch="i386:x86_64"} (gdb)
Program exited normally:
(gdb) -exec-run ^running (gdb) x = 55 *stopped,reason="exited-normally" (gdb)
Program exited exceptionally:
(gdb) -exec-run ^running (gdb) x = 55 *stopped,reason="exited",exit-code="01" (gdb)
Another way the program can terminate is if it receives a signal such as
SIGINT
. In this case, gdb/mi displays this:
(gdb) *stopped,reason="exited-signalled",signal-name="SIGINT", signal-meaning="Interrupt"
-exec-step
Command-exec-step [--reverse]
Resumes execution of the inferior program, stopping when the beginning of the next source line is reached, if the next source line is not a function call. If it is, stop at the first instruction of the called function. If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program, stopping at the beginning of the previously executed source line.
The corresponding gdb command is ‘step’.
Stepping into a function:
-exec-step ^running (gdb) *stopped,reason="end-stepping-range", frame={func="foo",args=[{name="a",value="10"}, {name="b",value="0"}],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="11",arch="i386:x86_64"} (gdb)
Regular stepping:
-exec-step ^running (gdb) *stopped,reason="end-stepping-range",line="14",file="recursive2.c" (gdb)
-exec-step-instruction
Command-exec-step-instruction [--reverse]
Resumes the inferior which executes one machine instruction. If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program, stopping at the previously executed instruction. The output, once gdb has stopped, will vary depending on whether we have stopped in the middle of a source line or not. In the former case, the address at which the program stopped will be printed as well.
The corresponding gdb command is ‘stepi’.
(gdb) -exec-step-instruction ^running (gdb) *stopped,reason="end-stepping-range", frame={func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="10",arch="i386:x86_64"} (gdb) -exec-step-instruction ^running (gdb) *stopped,reason="end-stepping-range", frame={addr="0x000100f4",func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="10",arch="i386:x86_64"} (gdb)
-exec-until
Command-exec-until [ location ]
Executes the inferior until the location specified in the argument is reached. If there is no argument, the inferior executes until a source line greater than the current one is reached. The reason for stopping in this case will be ‘location-reached’.
The corresponding gdb command is ‘until’.
(gdb) -exec-until recursive2.c:6 ^running (gdb) x = 55 *stopped,reason="location-reached",frame={func="main",args=[], file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6", arch="i386:x86_64"} (gdb)
-enable-frame-filters
Command-enable-frame-filters
gdb allows Python-based frame filters to affect the output of the MI commands relating to stack traces. As there is no way to implement this in a fully backward-compatible way, a front end must request that this functionality be enabled.
Once enabled, this feature cannot be disabled.
Note that if Python support has not been compiled into gdb, this command will still succeed (and do nothing).
-stack-info-frame
Command-stack-info-frame
Get info on the selected frame.
The corresponding gdb command is ‘info frame’ or ‘frame’ (without arguments).
(gdb) -stack-info-frame ^done,frame={level="1",addr="0x0001076c",func="callee3", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17", arch="i386:x86_64"} (gdb)
-stack-info-depth
Command-stack-info-depth [ max-depth ]
Return the depth of the stack. If the integer argument max-depth is specified, do not count beyond max-depth frames.
There's no equivalent gdb command.
For a stack with frame levels 0 through 11:
(gdb) -stack-info-depth ^done,depth="12" (gdb) -stack-info-depth 4 ^done,depth="4" (gdb) -stack-info-depth 12 ^done,depth="12" (gdb) -stack-info-depth 11 ^done,depth="11" (gdb) -stack-info-depth 13 ^done,depth="12" (gdb)
-stack-list-arguments
Command-stack-list-arguments [ --no-frame-filters ] [ --skip-unavailable ] print-values [ low-frame high-frame ]
Display a list of the arguments for the frames between low-frame and high-frame (inclusive). If low-frame and high-frame are not provided, list the arguments for the whole call stack. If the two arguments are equal, show the single frame at the corresponding level. It is an error if low-frame is larger than the actual number of frames. On the other hand, high-frame may be larger than the actual number of frames, in which case only existing frames will be returned.
If print-values is 0 or --no-values
, print only the names of
the variables; if it is 1 or --all-values
, print also their
values; and if it is 2 or --simple-values
, print the name,
type and value for simple data types, and the name and type for arrays,
structures and unions. If the option --no-frame-filters
is
supplied, then Python frame filters will not be executed.
If the --skip-unavailable
option is specified, arguments that
are not available are not listed. Partially available arguments
are still displayed, however.
Use of this command to obtain arguments in a single frame is deprecated in favor of the ‘-stack-list-variables’ command.
gdb does not have an equivalent command. gdbtk
has a
‘gdb_get_args’ command which partially overlaps with the
functionality of ‘-stack-list-arguments’.
(gdb) -stack-list-frames ^done, stack=[ frame={level="0",addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8", arch="i386:x86_64"}, frame={level="1",addr="0x0001076c",func="callee3", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17", arch="i386:x86_64"}, frame={level="2",addr="0x0001078c",func="callee2", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22", arch="i386:x86_64"}, frame={level="3",addr="0x000107b4",func="callee1", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27", arch="i386:x86_64"}, frame={level="4",addr="0x000107e0",func="main", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32", arch="i386:x86_64"}] (gdb) -stack-list-arguments 0 ^done, stack-args=[ frame={level="0",args=[]}, frame={level="1",args=[name="strarg"]}, frame={level="2",args=[name="intarg",name="strarg"]}, frame={level="3",args=[name="intarg",name="strarg",name="fltarg"]}, frame={level="4",args=[]}] (gdb) -stack-list-arguments 1 ^done, stack-args=[ frame={level="0",args=[]}, frame={level="1", args=[{name="strarg",value="0x11940 \"A string argument.\""}]}, frame={level="2",args=[ {name="intarg",value="2"}, {name="strarg",value="0x11940 \"A string argument.\""}]}, {frame={level="3",args=[ {name="intarg",value="2"}, {name="strarg",value="0x11940 \"A string argument.\""}, {name="fltarg",value="3.5"}]}, frame={level="4",args=[]}] (gdb) -stack-list-arguments 0 2 2 ^done,stack-args=[frame={level="2",args=[name="intarg",name="strarg"]}] (gdb) -stack-list-arguments 1 2 2 ^done,stack-args=[frame={level="2", args=[{name="intarg",value="2"}, {name="strarg",value="0x11940 \"A string argument.\""}]}] (gdb)
-stack-list-frames
Command-stack-list-frames [ --no-frame-filters low-frame high-frame ]
List the frames currently on the stack. For each frame it displays the following info:
$pc
value for that frame.
$pc
.
If invoked without arguments, this command prints a backtrace for the
whole stack. If given two integer arguments, it shows the frames whose
levels are between the two arguments (inclusive). If the two arguments
are equal, it shows the single frame at the corresponding level. It is
an error if low-frame is larger than the actual number of
frames. On the other hand, high-frame may be larger than the
actual number of frames, in which case only existing frames will be
returned. If the option --no-frame-filters
is supplied, then
Python frame filters will not be executed.
The corresponding gdb commands are ‘backtrace’ and ‘where’.
Full stack backtrace:
(gdb) -stack-list-frames ^done,stack= [frame={level="0",addr="0x0001076c",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11", arch="i386:x86_64"}, frame={level="1",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="2",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="4",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="5",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="6",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="7",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="8",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="9",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="10",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="11",addr="0x00010738",func="main", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4", arch="i386:x86_64"}] (gdb)
Show frames between low_frame and high_frame:
(gdb) -stack-list-frames 3 5 ^done,stack= [frame={level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="4",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}, frame={level="5",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}] (gdb)
Show a single frame:
(gdb) -stack-list-frames 3 3 ^done,stack= [frame={level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"}] (gdb)
-stack-list-locals
Command-stack-list-locals [ --no-frame-filters ] [ --skip-unavailable ] print-values
Display the local variable names for the selected frame. If
print-values is 0 or --no-values
, print only the names of
the variables; if it is 1 or --all-values
, print also their
values; and if it is 2 or --simple-values
, print the name,
type and value for simple data types, and the name and type for arrays,
structures and unions. In this last case, a frontend can immediately
display the value of simple data types and create variable objects for
other data types when the user wishes to explore their values in
more detail. If the option --no-frame-filters
is supplied, then
Python frame filters will not be executed.
If the --skip-unavailable
option is specified, local variables
that are not available are not listed. Partially available local
variables are still displayed, however.
This command is deprecated in favor of the ‘-stack-list-variables’ command.
‘info locals’ in gdb, ‘gdb_get_locals’ in gdbtk
.
(gdb) -stack-list-locals 0 ^done,locals=[name="A",name="B",name="C"] (gdb) -stack-list-locals --all-values ^done,locals=[{name="A",value="1"},{name="B",value="2"}, {name="C",value="{1, 2, 3}"}] -stack-list-locals --simple-values ^done,locals=[{name="A",type="int",value="1"}, {name="B",type="int",value="2"},{name="C",type="int [3]"}] (gdb)
-stack-list-variables
Command-stack-list-variables [ --no-frame-filters ] [ --skip-unavailable ] print-values
Display the names of local variables and function arguments for the selected frame. If
print-values is 0 or --no-values
, print only the names of
the variables; if it is 1 or --all-values
, print also their
values; and if it is 2 or --simple-values
, print the name,
type and value for simple data types, and the name and type for arrays,
structures and unions. If the option --no-frame-filters
is
supplied, then Python frame filters will not be executed.
If the --skip-unavailable
option is specified, local variables
and arguments that are not available are not listed. Partially
available arguments and local variables are still displayed, however.
(gdb) -stack-list-variables --thread 1 --frame 0 --all-values ^done,variables=[{name="x",value="11"},{name="s",value="{a = 1, b = 2}"}] (gdb)
-stack-select-frame
Command-stack-select-frame framenum
Change the selected frame. Select a different frame framenum on the stack.
This command in deprecated in favor of passing the ‘--frame’ option to every command.
The corresponding gdb commands are ‘frame’, ‘up’, ‘down’, ‘select-frame’, ‘up-silent’, and ‘down-silent’.
(gdb) -stack-select-frame 2 ^done (gdb)
Variable objects are "object-oriented" MI interface for examining and changing values of expressions. Unlike some other MI interfaces that work with expressions, variable objects are specifically designed for simple and efficient presentation in the frontend. A variable object is identified by string name. When a variable object is created, the frontend specifies the expression for that variable object. The expression can be a simple variable, or it can be an arbitrary complex expression, and can even involve CPU registers. After creating a variable object, the frontend can invoke other variable object operations—for example to obtain or change the value of a variable object, or to change display format.
Variable objects have hierarchical tree structure. Any variable object that corresponds to a composite type, such as structure in C, has a number of child variable objects, for example corresponding to each element of a structure. A child variable object can itself have children, recursively. Recursion ends when we reach leaf variable objects, which always have built-in types. Child variable objects are created only by explicit request, so if a frontend is not interested in the children of a particular variable object, no child will be created.
For a leaf variable object it is possible to obtain its value as a string, or set the value from a string. String value can be also obtained for a non-leaf variable object, but it's generally a string that only indicates the type of the object, and does not list its contents. Assignment to a non-leaf variable object is not allowed.
A frontend does not need to read the values of all variable objects each time the program stops. Instead, MI provides an update command that lists all variable objects whose values has changed since the last update operation. This considerably reduces the amount of data that must be transferred to the frontend. As noted above, children variable objects are created on demand, and only leaf variable objects have a real value. As result, gdb will read target memory only for leaf variables that frontend has created.
The automatic update is not always desirable. For example, a frontend might want to keep a value of some expression for future reference, and never update it. For another example, fetching memory is relatively slow for embedded targets, so a frontend might want to disable automatic update for the variables that are either not visible on the screen, or “closed”. This is possible using so called “frozen variable objects”. Such variable objects are never implicitly updated.
Variable objects can be either fixed or floating. For the fixed variable object, the expression is parsed when the variable object is created, including associating identifiers to specific variables. The meaning of expression never changes. For a floating variable object the values of variables whose names appear in the expressions are re-evaluated every time in the context of the current frame. Consider this example:
void do_work(...) { struct work_state state; if (...) do_work(...); }
If a fixed variable object for the state
variable is created in
this function, and we enter the recursive call, the variable
object will report the value of state
in the top-level
do_work
invocation. On the other hand, a floating variable
object will report the value of state
in the current frame.
If an expression specified when creating a fixed variable object refers to a local variable, the variable object becomes bound to the thread and frame in which the variable object is created. When such variable object is updated, gdb makes sure that the thread/frame combination the variable object is bound to still exists, and re-evaluates the variable object in context of that thread/frame.
The following is the complete set of gdb/mi operations defined to access this functionality:
Operation | Description
|
-enable-pretty-printing
| enable Python-based pretty-printing
|
-var-create
| create a variable object
|
-var-delete
| delete the variable object and/or its children
|
-var-set-format
| set the display format of this variable
|
-var-show-format
| show the display format of this variable
|
-var-info-num-children
| tells how many children this object has
|
-var-list-children
| return a list of the object's children
|
-var-info-type
| show the type of this variable object
|
-var-info-expression
| print parent-relative expression that this variable object represents
|
-var-info-path-expression
| print full expression that this variable object represents
|
-var-show-attributes
| is this variable editable? does it exist here?
|
-var-evaluate-expression
| get the value of this variable
|
-var-assign
| set the value of this variable
|
-var-update
| update the variable and its children
|
-var-set-frozen
| set frozenness attribute
|
-var-set-update-range
| set range of children to display on update
|
In the next subsection we describe each operation in detail and suggest how it can be used.
-enable-pretty-printing
Command-enable-pretty-printing
gdb allows Python-based visualizers to affect the output of the MI variable object commands. However, because there was no way to implement this in a fully backward-compatible way, a front end must request that this functionality be enabled.
Once enabled, this feature cannot be disabled.
Note that if Python support has not been compiled into gdb, this command will still succeed (and do nothing).
This feature is currently (as of gdb 7.0) experimental, and may work differently in future versions of gdb.
-var-create
Command-var-create {name | "-"} {frame-addr | "*" | "@"} expression
This operation creates a variable object, which allows the monitoring of a variable, the result of an expression, a memory cell or a CPU register.
The name parameter is the string by which the object can be referenced. It must be unique. If ‘-’ is specified, the varobj system will generate a string “varNNNNNN” automatically. It will be unique provided that one does not specify name of that format. The command fails if a duplicate name is found.
The frame under which the expression should be evaluated can be specified by frame-addr. A ‘*’ indicates that the current frame should be used. A ‘@’ indicates that a floating variable object must be created.
expression is any expression valid on the current language set (must not begin with a ‘*’), or one of the following:
A varobj's contents may be provided by a Python-based pretty-printer. In this
case the varobj is known as a dynamic varobj. Dynamic varobjs
have slightly different semantics in some cases. If the
-enable-pretty-printing
command is not sent, then gdb
will never create a dynamic varobj. This ensures backward
compatibility for existing clients.
This operation returns attributes of the newly-created varobj. These are:
struct
), or for a dynamic varobj, this value
will not be interesting.
on
, the
actual (derived) type of the object is shown rather than the
declared one.
display_hint
method. See Pretty Printing API.
Typical output will look like this:
name="name",numchild="N",type="type",thread-id="M", has_more="has_more"
-var-delete
Command-var-delete [ -c ] name
Deletes a previously created variable object and all of its children. With the ‘-c’ option, just deletes the children.
Returns an error if the object name is not found.
-var-set-format
Command-var-set-format name format-spec
Sets the output format for the value of the object name to be format-spec.
The syntax for the format-spec is as follows:
format-spec ==> {binary | decimal | hexadecimal | octal | natural | zero-hexadecimal}
The natural format is the default format choosen automatically
based on the variable type (like decimal for an int
, hex
for pointers, etc.).
The zero-hexadecimal format has a representation similar to hexadecimal but with padding zeroes to the left of the value. For example, a 32-bit hexadecimal value of 0x1234 would be represented as 0x00001234 in the zero-hexadecimal format.
For a variable with children, the format is set only on the variable itself, and the children are not affected.
-var-show-format
Command-var-show-format name
Returns the format used to display the value of the object name.
format ==> format-spec
-var-info-num-children
Command-var-info-num-children name
Returns the number of children of a variable object name:
numchild=n
Note that this number is not completely reliable for a dynamic varobj. It will return the current number of children, but more children may be available.
-var-list-children
Command-var-list-children [print-values] name [from to]
Return a list of the children of the specified variable object and
create variable objects for them, if they do not already exist. With
a single argument or if print-values has a value of 0 or
--no-values
, print only the names of the variables; if
print-values is 1 or --all-values
, also print their
values; and if it is 2 or --simple-values
print the name and
value for simple data types and just the name for arrays, structures
and unions.
from and to, if specified, indicate the range of children to report. If from or to is less than zero, the range is reset and all children will be reported. Otherwise, children starting at from (zero-based) and up to and excluding to will be reported.
If a child range is requested, it will only affect the current call to
-var-list-children
, but not future calls to -var-update
.
For this, you must instead use -var-set-update-range
. The
intent of this approach is to enable a front end to implement any
update approach it likes; for example, scrolling a view may cause the
front end to request more children with -var-list-children
, and
then the front end could call -var-set-update-range
with a
different range to ensure that future updates are restricted to just
the visible items.
For each child the following results are returned:
For a dynamic varobj, this value cannot be used to form an expression. There is no way to do this at all with a dynamic varobj.
For C/C++ structures there are several pseudo children returned to designate access qualifiers. For these pseudo children exp is ‘public’, ‘private’, or ‘protected’. In this case the type and value are not present.
A dynamic varobj will not report the access qualifying
pseudo-children, regardless of the language. This information is not
available at all with a dynamic varobj.
on
, the
actual (derived) type of the object is shown rather than the
declared one.
display_hint
method. See Pretty Printing API.
The result may have its own attributes:
display_hint
method. See Pretty Printing API.
(gdb) -var-list-children n ^done,numchild=n,children=[child={name=name,exp=exp, numchild=n,type=type},(repeats N times)] (gdb) -var-list-children --all-values n ^done,numchild=n,children=[child={name=name,exp=exp, numchild=n,value=value,type=type},(repeats N times)]
-var-info-type
Command-var-info-type name
Returns the type of the specified variable name. The type is returned as a string in the same format as it is output by the gdb CLI:
type=typename
-var-info-expression
Command-var-info-expression name
Returns a string that is suitable for presenting this variable object in user interface. The string is generally not valid expression in the current language, and cannot be evaluated.
For example, if a
is an array, and variable object
A
was created for a
, then we'll get this output:
(gdb) -var-info-expression A.1 ^done,lang="C",exp="1"
Here, the value of lang
is the language name, which can be
found in Supported Languages.
Note that the output of the -var-list-children
command also
includes those expressions, so the -var-info-expression
command
is of limited use.
-var-info-path-expression
Command-var-info-path-expression name
Returns an expression that can be evaluated in the current
context and will yield the same value that a variable object has.
Compare this with the -var-info-expression
command, which
result can be used only for UI presentation. Typical use of
the -var-info-path-expression
command is creating a
watchpoint from a variable object.
This command is currently not valid for children of a dynamic varobj, and will give an error when invoked on one.
For example, suppose C
is a C++ class, derived from class
Base
, and that the Base
class has a member called
m_size
. Assume a variable c
is has the type of
C
and a variable object C
was created for variable
c
. Then, we'll get this output:
(gdb) -var-info-path-expression C.Base.public.m_size ^done,path_expr=((Base)c).m_size)
-var-show-attributes
Command-var-show-attributes name
List attributes of the specified variable object name:
status=attr [ ( ,attr )* ]
where attr is { { editable | noneditable } | TBD }
.
-var-evaluate-expression
Command-var-evaluate-expression [-f format-spec] name
Evaluates the expression that is represented by the specified variable
object and returns its value as a string. The format of the string
can be specified with the ‘-f’ option. The possible values of
this option are the same as for -var-set-format
(see -var-set-format). If the ‘-f’ option is not specified,
the current display format will be used. The current display format
can be changed using the -var-set-format
command.
value=value
Note that one must invoke -var-list-children
for a variable
before the value of a child variable can be evaluated.
-var-assign
Command-var-assign name expression
Assigns the value of expression to the variable object specified
by name. The object must be ‘editable’. If the variable's
value is altered by the assign, the variable will show up in any
subsequent -var-update
list.
(gdb) -var-assign var1 3 ^done,value="3" (gdb) -var-update * ^done,changelist=[{name="var1",in_scope="true",type_changed="false"}] (gdb)
-var-update
Command-var-update [print-values] {name | "*"}
Reevaluate the expressions corresponding to the variable object
name and all its direct and indirect children, and return the
list of variable objects whose values have changed; name must
be a root variable object. Here, “changed” means that the result of
-var-evaluate-expression
before and after the
-var-update
is different. If ‘*’ is used as the variable
object names, all existing variable objects are updated, except
for frozen ones (see -var-set-frozen). The option
print-values determines whether both names and values, or just
names are printed. The possible values of this option are the same
as for -var-list-children
(see -var-list-children). It is
recommended to use the ‘--all-values’ option, to reduce the
number of MI commands needed on each program stop.
With the ‘*’ parameter, if a variable object is bound to a currently running thread, it will not be updated, without any diagnostic.
If -var-set-update-range
was previously used on a varobj, then
only the selected range of children will be reported.
-var-update
reports all the changed varobjs in a tuple named
‘changelist’.
Each item in the change list is itself a tuple holding:
"true"
"false"
"invalid"
file
command. The front end should normally choose to delete these variable
objects.
In the future new values may be added to this list so the front should
be prepared for this possibility. See GDB/MI Development and Front Ends.
When a varobj's type changes, its children are also likely to have
become incorrect. Therefore, the varobj's children are automatically
deleted when this attribute is ‘true’. Also, the varobj's update
range, when set using the -var-set-update-range
command, is
unset.
The ‘numchild’ field in other varobj responses is generally not valid for a dynamic varobj – it will show the number of children that gdb knows about, but because dynamic varobjs lazily instantiate their children, this will not reflect the number of children which may be available.
The ‘new_num_children’ attribute only reports changes to the
number of children known by gdb. This is the only way to
detect whether an update has removed children (which necessarily can
only happen at the end of the update range).
-var-set-update-range
), then they will
be listed in this attribute.
(gdb) -var-assign var1 3 ^done,value="3" (gdb) -var-update --all-values var1 ^done,changelist=[{name="var1",value="3",in_scope="true", type_changed="false"}] (gdb)
-var-set-frozen
Command-var-set-frozen name flag
Set the frozenness flag on the variable object name. The
flag parameter should be either ‘1’ to make the variable
frozen or ‘0’ to make it unfrozen. If a variable object is
frozen, then neither itself, nor any of its children, are
implicitly updated by -var-update
of
a parent variable or by -var-update *
. Only
-var-update
of the variable itself will update its value and
values of its children. After a variable object is unfrozen, it is
implicitly updated by all subsequent -var-update
operations.
Unfreezing a variable does not update it, only subsequent
-var-update
does.
(gdb) -var-set-frozen V 1 ^done (gdb)
-var-set-update-range
command-var-set-update-range name from to
Set the range of children to be returned by future invocations of
-var-update
.
from and to indicate the range of children to report. If from or to is less than zero, the range is reset and all children will be reported. Otherwise, children starting at from (zero-based) and up to and excluding to will be reported.
(gdb) -var-set-update-range V 1 2 ^done
-var-set-visualizer
command-var-set-visualizer name visualizer
Set a visualizer for the variable object name.
visualizer is the visualizer to use. The special value ‘None’ means to disable any visualizer in use.
If not ‘None’, visualizer must be a Python expression. This expression must evaluate to a callable object which accepts a single argument. gdb will call this object with the value of the varobj name as an argument (this is done so that the same Python pretty-printing code can be used for both the CLI and MI). When called, this object must return an object which conforms to the pretty-printing interface (see Pretty Printing API).
The pre-defined function gdb.default_visualizer
may be used to
select a visualizer by following the built-in process
(see Selecting Pretty-Printers). This is done automatically when
a varobj is created, and so ordinarily is not needed.
This feature is only available if Python support is enabled. The MI
command -list-features
(see GDB/MI Support Commands)
can be used to check this.
Resetting the visualizer:
(gdb) -var-set-visualizer V None ^done
Reselecting the default (type-based) visualizer:
(gdb) -var-set-visualizer V gdb.default_visualizer ^done
Suppose SomeClass
is a visualizer class. A lambda expression
can be used to instantiate this class for a varobj:
(gdb) -var-set-visualizer V "lambda val: SomeClass()" ^done
This section describes the gdb/mi commands that manipulate data: examine memory and registers, evaluate expressions, etc.
For details about what an addressable memory unit is, see addressable memory unit.
-data-disassemble
Command-data-disassemble [ -s start-addr -e end-addr ] | [ -a addr ] | [ -f filename -l linenum [ -n lines ] ] -- mode
Where:
$pc
)
Modes 1 and 3 are deprecated. The output is “source centric”
which hasn't proved useful in practice.
See Machine Code, for a discussion of the difference between
/m
and /s
output of the disassemble
command.
The result of the -data-disassemble
command will be a list named
‘asm_insns’, the contents of this list depend on the mode
used with the -data-disassemble
command.
For modes 0 and 2 the ‘asm_insns’ list contains tuples with the following fields:
address
func-name
offset
inst
opcodes
For modes 1, 3, 4 and 5 the ‘asm_insns’ list contains tuples named ‘src_and_asm_line’, each of which has the following fields:
line
file
fullname
If the source file is not found this field will contain the path as
present in the debug information.
line_asm_insn
-data-disassemble
in mode 0 and 2, so ‘address’,
‘func-name’, ‘offset’, ‘inst’, and optionally
‘opcodes’.
Note that whatever included in the ‘inst’ field, is not manipulated directly by gdb/mi, i.e., it is not possible to adjust its format.
The corresponding gdb command is ‘disassemble’.
Disassemble from the current value of $pc
to $pc + 20
:
(gdb) -data-disassemble -s $pc -e "$pc + 20" -- 0 ^done, asm_insns=[ {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}, {address="0x000107c8",func-name="main",offset="12", inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"}, {address="0x000107cc",func-name="main",offset="16", inst="sethi %hi(0x11800), %o2"}, {address="0x000107d0",func-name="main",offset="20", inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"}] (gdb)
Disassemble the whole main
function. Line 32 is part of
main
.
-data-disassemble -f basics.c -l 32 -- 0 ^done,asm_insns=[ {address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"}, {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}, [...] {address="0x0001081c",func-name="main",offset="96",inst="ret "}, {address="0x00010820",func-name="main",offset="100",inst="restore "}] (gdb)
Disassemble 3 instructions from the start of main
:
(gdb) -data-disassemble -f basics.c -l 32 -n 3 -- 0 ^done,asm_insns=[ {address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"}, {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}] (gdb)
Disassemble 3 instructions from the start of main
in mixed mode:
(gdb) -data-disassemble -f basics.c -l 32 -n 3 -- 1 ^done,asm_insns=[ src_and_asm_line={line="31", file="../../../src/gdb/testsuite/gdb.mi/basics.c", fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c", line_asm_insn=[{address="0x000107bc", func-name="main",offset="0",inst="save %sp, -112, %sp"}]}, src_and_asm_line={line="32", file="../../../src/gdb/testsuite/gdb.mi/basics.c", fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c", line_asm_insn=[{address="0x000107c0", func-name="main",offset="4",inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}]}] (gdb)
-data-evaluate-expression
Command-data-evaluate-expression expr
Evaluate expr as an expression. The expression could contain an inferior function call. The function call will execute synchronously. If the expression contains spaces, it must be enclosed in double quotes.
The corresponding gdb commands are ‘print’, ‘output’, and
‘call’. In gdbtk
only, there's a corresponding
‘gdb_eval’ command.
In the following example, the numbers that precede the commands are the tokens described in gdb/mi Command Syntax. Notice how gdb/mi returns the same tokens in its output.
211-data-evaluate-expression A 211^done,value="1" (gdb) 311-data-evaluate-expression &A 311^done,value="0xefffeb7c" (gdb) 411-data-evaluate-expression A+3 411^done,value="4" (gdb) 511-data-evaluate-expression "A + 3" 511^done,value="4" (gdb)
-data-list-changed-registers
Command-data-list-changed-registers
Display a list of the registers that have changed.
gdb doesn't have a direct analog for this command; gdbtk
has the corresponding command ‘gdb_changed_register_list’.
On a PPC MBX board:
(gdb) -exec-continue ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame={ func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c", line="5",arch="powerpc"} (gdb) -data-list-changed-registers ^done,changed-registers=["0","1","2","4","5","6","7","8","9", "10","11","13","14","15","16","17","18","19","20","21","22","23", "24","25","26","27","28","30","31","64","65","66","67","69"] (gdb)
-data-list-register-names
Command-data-list-register-names [ ( regno )+ ]
Show a list of register names for the current target. If no arguments are given, it shows a list of the names of all the registers. If integer numbers are given as arguments, it will print a list of the names of the registers corresponding to the arguments. To ensure consistency between a register name and its number, the output list may include empty register names.
gdb does not have a command which corresponds to
‘-data-list-register-names’. In gdbtk
there is a
corresponding command ‘gdb_regnames’.
For the PPC MBX board:
(gdb) -data-list-register-names ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7", "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18", "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29", "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9", "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20", "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31", "", "pc","ps","cr","lr","ctr","xer"] (gdb) -data-list-register-names 1 2 3 ^done,register-names=["r1","r2","r3"] (gdb)
-data-list-register-values
Command -data-list-register-values
[ --skip-unavailable
] fmt [ ( regno )*]
Display the registers' contents. The format according to which the
registers' contents are to be returned is given by fmt, followed
by an optional list of numbers specifying the registers to display. A
missing list of numbers indicates that the contents of all the
registers must be returned. The --skip-unavailable
option
indicates that only the available registers are to be returned.
Allowed formats for fmt are:
x
o
t
d
r
N
The corresponding gdb commands are ‘info reg’, ‘info
all-reg’, and (in gdbtk
) ‘gdb_fetch_registers’.
For a PPC MBX board (note: line breaks are for readability only, they don't appear in the actual output):
(gdb) -data-list-register-values r 64 65 ^done,register-values=[{number="64",value="0xfe00a300"}, {number="65",value="0x00029002"}] (gdb) -data-list-register-values x ^done,register-values=[{number="0",value="0xfe0043c8"}, {number="1",value="0x3fff88"},{number="2",value="0xfffffffe"}, {number="3",value="0x0"},{number="4",value="0xa"}, {number="5",value="0x3fff68"},{number="6",value="0x3fff58"}, {number="7",value="0xfe011e98"},{number="8",value="0x2"}, {number="9",value="0xfa202820"},{number="10",value="0xfa202808"}, {number="11",value="0x1"},{number="12",value="0x0"}, {number="13",value="0x4544"},{number="14",value="0xffdfffff"}, {number="15",value="0xffffffff"},{number="16",value="0xfffffeff"}, {number="17",value="0xefffffed"},{number="18",value="0xfffffffe"}, {number="19",value="0xffffffff"},{number="20",value="0xffffffff"}, {number="21",value="0xffffffff"},{number="22",value="0xfffffff7"}, {number="23",value="0xffffffff"},{number="24",value="0xffffffff"}, {number="25",value="0xffffffff"},{number="26",value="0xfffffffb"}, {number="27",value="0xffffffff"},{number="28",value="0xf7bfffff"}, {number="29",value="0x0"},{number="30",value="0xfe010000"}, {number="31",value="0x0"},{number="32",value="0x0"}, {number="33",value="0x0"},{number="34",value="0x0"}, {number="35",value="0x0"},{number="36",value="0x0"}, {number="37",value="0x0"},{number="38",value="0x0"}, {number="39",value="0x0"},{number="40",value="0x0"}, {number="41",value="0x0"},{number="42",value="0x0"}, {number="43",value="0x0"},{number="44",value="0x0"}, {number="45",value="0x0"},{number="46",value="0x0"}, {number="47",value="0x0"},{number="48",value="0x0"}, {number="49",value="0x0"},{number="50",value="0x0"}, {number="51",value="0x0"},{number="52",value="0x0"}, {number="53",value="0x0"},{number="54",value="0x0"}, {number="55",value="0x0"},{number="56",value="0x0"}, {number="57",value="0x0"},{number="58",value="0x0"}, {number="59",value="0x0"},{number="60",value="0x0"}, {number="61",value="0x0"},{number="62",value="0x0"}, {number="63",value="0x0"},{number="64",value="0xfe00a300"}, {number="65",value="0x29002"},{number="66",value="0x202f04b5"}, {number="67",value="0xfe0043b0"},{number="68",value="0xfe00b3e4"}, {number="69",value="0x20002b03"}] (gdb)
-data-read-memory
Command
This command is deprecated, use -data-read-memory-bytes
instead.
-data-read-memory [ -o byte-offset ] address word-format word-size nr-rows nr-cols [ aschar ]
where:
print
command (see Output Formats).
This command displays memory contents as a table of nr-rows by
nr-cols words, each word being word-size bytes. In total,
nr-rows *
nr-cols *
word-size bytes are read
(returned as ‘total-bytes’). Should less than the requested number
of bytes be returned by the target, the missing words are identified
using ‘N/A’. The number of bytes read from the target is returned
in ‘nr-bytes’ and the starting address used to read memory in
‘addr’.
The address of the next/previous row or page is available in ‘next-row’ and ‘prev-row’, ‘next-page’ and ‘prev-page’.
The corresponding gdb command is ‘x’. gdbtk
has
‘gdb_get_mem’ memory read command.
Read six bytes of memory starting at bytes+6
but then offset by
-6
bytes. Format as three rows of two columns. One byte per
word. Display each word in hex.
(gdb) 9-data-read-memory -o -6 -- bytes+6 x 1 3 2 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6", next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396", prev-page="0x0000138a",memory=[ {addr="0x00001390",data=["0x00","0x01"]}, {addr="0x00001392",data=["0x02","0x03"]}, {addr="0x00001394",data=["0x04","0x05"]}] (gdb)
Read two bytes of memory starting at address shorts + 64
and
display as a single word formatted in decimal.
(gdb) 5-data-read-memory shorts+64 d 2 1 1 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2", next-row="0x00001512",prev-row="0x0000150e", next-page="0x00001512",prev-page="0x0000150e",memory=[ {addr="0x00001510",data=["128"]}] (gdb)
Read thirty two bytes of memory starting at bytes+16
and format
as eight rows of four columns. Include a string encoding with ‘x’
used as the non-printable character.
(gdb) 4-data-read-memory bytes+16 x 1 8 4 x 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32", next-row="0x000013c0",prev-row="0x0000139c", next-page="0x000013c0",prev-page="0x00001380",memory=[ {addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"}, {addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"}, {addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"}, {addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"}, {addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"}, {addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"}, {addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"}, {addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"}] (gdb)
-data-read-memory-bytes
Command-data-read-memory-bytes [ -o offset ] address count
where:
This command attempts to read all accessible memory regions in the specified range. First, all regions marked as unreadable in the memory map (if one is defined) will be skipped. See Memory Region Attributes. Second, gdb will attempt to read the remaining regions. For each one, if reading full region results in an errors, gdb will try to read a subset of the region.
In general, every single memory unit in the region may be readable or not, and the only way to read every readable unit is to try a read at every address, which is not practical. Therefore, gdb will attempt to read all accessible memory units at either beginning or the end of the region, using a binary division scheme. This heuristic works well for reading across a memory map boundary. Note that if a region has a readable range that is neither at the beginning or the end, gdb will not read it.
The result record (see GDB/MI Result Records) that is output of the command includes a field named ‘memory’ whose content is a list of tuples. Each tuple represent a successfully read memory block and has the following fields:
begin
end
offset
-data-read-memory-bytes
.
contents
The corresponding gdb command is ‘x’.
(gdb) -data-read-memory-bytes &a 10 ^done,memory=[{begin="0xbffff154",offset="0x00000000", end="0xbffff15e", contents="01000000020000000300"}] (gdb)
-data-write-memory-bytes
Command-data-write-memory-bytes address contents -data-write-memory-bytes address contents [count]
where:
There's no corresponding gdb command.
(gdb) -data-write-memory-bytes &a "aabbccdd" ^done (gdb)
(gdb) -data-write-memory-bytes &a "aabbccdd" 16e ^done (gdb)
The commands defined in this section implement MI support for tracepoints. For detailed introduction, see Tracepoints.
-trace-find
Command-trace-find mode [parameters...]
Find a trace frame using criteria defined by mode and parameters. The following table lists permissible modes and their parameters. For details of operation, see tfind.
If ‘none’ was passed as mode, the response does not have fields. Otherwise, the response may have the following fields:
The corresponding gdb command is ‘tfind’.
-trace-define-variable name [ value ]
Create trace variable name if it does not exist. If value is specified, sets the initial value of the specified trace variable to that value. Note that the name should start with the ‘$’ character.
The corresponding gdb command is ‘tvariable’.
-trace-frame-collected
Command-trace-frame-collected [--var-print-values var_pval] [--comp-print-values comp_pval] [--registers-format regformat] [--memory-contents]
This command returns the set of collected objects, register names, trace state variable names, memory ranges and computed expressions that have been collected at a particular trace frame. The optional parameters to the command affect the output format in different ways. See the output description table below for more details.
The reported names can be used in the normal manner to create varobjs and inspect the objects themselves. The items returned by this command are categorized so that it is clear which is a variable, which is a register, which is a trace state variable, which is a memory range and which is a computed expression.
For instance, if the actions were
collect myVar, myArray[myIndex], myObj.field, myPtr->field, myCount + 2 collect *(int*)0xaf02bef0@40
the object collected in its entirety would be myVar
. The
object myArray
would be partially collected, because only the
element at index myIndex
would be collected. The remaining
objects would be computed expressions.
An example output would be:
(gdb) -trace-frame-collected ^done, explicit-variables=[{name="myVar",value="1"}], computed-expressions=[{name="myArray[myIndex]",value="0"}, {name="myObj.field",value="0"}, {name="myPtr->field",value="1"}, {name="myCount + 2",value="3"}, {name="$tvar1 + 1",value="43970027"}], registers=[{number="0",value="0x7fe2c6e79ec8"}, {number="1",value="0x0"}, {number="2",value="0x4"}, ... {number="125",value="0x0"}], tvars=[{name="$tvar1",current="43970026"}], memory=[{address="0x0000000000602264",length="4"}, {address="0x0000000000615bc0",length="4"}] (gdb)
Where:
explicit-variables
--var-print-values
option affects how or whether the value
field is output. If var_pval is 0, then print only the names;
if it is 1, print also their values; and if it is 2, print the name,
type and value for simple data types, and the name and type for
arrays, structures and unions.
computed-expressions
--comp-print-values
option affects
this set like the --var-print-values
option affects the
explicit-variables
set. See above.
registers
--registers-format
option. See the -data-list-register-values command for a
list of the allowed formats. The default is ‘x’.
tvars
memory
address
length
contents
--memory-contents
option is specified.
There is no corresponding gdb command.
-trace-list-variables
Return a table of all defined trace variables. Each element of the table has the following fields:
The corresponding gdb command is ‘tvariables’.
(gdb) -trace-list-variables ^done,trace-variables={nr_rows="1",nr_cols="3", hdr=[{width="15",alignment="-1",col_name="name",colhdr="Name"}, {width="11",alignment="-1",col_name="initial",colhdr="Initial"}, {width="11",alignment="-1",col_name="current",colhdr="Current"}], body=[variable={name="$trace_timestamp",initial="0"} variable={name="$foo",initial="10",current="15"}]} (gdb)
-trace-save [ -r ] [ -ctf ] filename
Saves the collected trace data to filename. Without the ‘-r’ option, the data is downloaded from the target and saved in a local file. With the ‘-r’ option the target is asked to perform the save.
By default, this command will save the trace in the tfile format. You can supply the optional ‘-ctf’ argument to save it the CTF format. See Trace Files for more information about CTF.
The corresponding gdb command is ‘tsave’.
-trace-start
Starts a tracing experiment. The result of this command does not have any fields.
The corresponding gdb command is ‘tstart’.
-trace-status
Obtains the status of a tracing experiment. The result may include the following fields:
-trace-stop
command. The value of ‘overflow’ means
the tracing buffer is full. The value of ‘disconnection’ means
tracing was automatically stopped when gdb has disconnected.
The value of ‘passcount’ means tracing was stopped when a
tracepoint was passed a maximal number of times for that tracepoint.
This field is present if ‘supported’ field is not ‘0’.
1
means that the
trace buffer is circular and old trace frames will be discarded if
necessary to make room, 0
means that the trace buffer is linear
and may fill up.
1
means that
tracing will continue after gdb disconnects, 0
means
that the trace run will stop.
The corresponding gdb command is ‘tstatus’.
-trace-stop
Stops a tracing experiment. The result of this command has the same
fields as -trace-status
, except that the ‘supported’ and
‘running’ fields are not output.
The corresponding gdb command is ‘tstop’.
-symbol-info-functions
Command-symbol-info-functions [--include-nondebug] [--type type_regexp] [--name name_regexp] [--max-results limit]
Return a list containing the names and types for all global functions taken from the debug information. The functions are grouped by source file, and shown with the line number on which each function is defined.
The --include-nondebug
option causes the output to include
code symbols from the symbol table.
The options --type
and --name
allow the symbols returned
to be filtered based on either the name of the function, or the type
signature of the function.
The option --max-results
restricts the command to return no
more than limit results. If exactly limit results are
returned then there might be additional results available if a higher
limit is used.
The corresponding gdb command is ‘info functions’.
(gdb) -symbol-info-functions ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{line="36", name="f4", type="void (int *)", description="void f4(int *);"}, {line="42", name="main", type="int ()", description="int main();"}, {line="30", name="f1", type="my_int_t (int, int)", description="static my_int_t f1(int, int);"}]}, {filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[{line="33", name="f2", type="float (another_float_t)", description="float f2(another_float_t);"}, {line="39", name="f3", type="int (another_int_t)", description="int f3(another_int_t);"}, {line="27", name="f1", type="another_float_t (int)", description="static another_float_t f1(int);"}]}]} (gdb) -symbol-info-functions --name f1 ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{line="30", name="f1", type="my_int_t (int, int)", description="static my_int_t f1(int, int);"}]}, {filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[{line="27", name="f1", type="another_float_t (int)", description="static another_float_t f1(int);"}]}]} (gdb) -symbol-info-functions --type void ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{line="36", name="f4", type="void (int *)", description="void f4(int *);"}]}]} (gdb) -symbol-info-functions --include-nondebug ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{line="36", name="f4", type="void (int *)", description="void f4(int *);"}, {line="42", name="main", type="int ()", description="int main();"}, {line="30", name="f1", type="my_int_t (int, int)", description="static my_int_t f1(int, int);"}]}, {filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[{line="33", name="f2", type="float (another_float_t)", description="float f2(another_float_t);"}, {line="39", name="f3", type="int (another_int_t)", description="int f3(another_int_t);"}, {line="27", name="f1", type="another_float_t (int)", description="static another_float_t f1(int);"}]}], nondebug= [{address="0x0000000000400398",name="_init"}, {address="0x00000000004003b0",name="_start"}, ... ]}
-symbol-info-module-functions
Command-symbol-info-module-functions [--module module_regexp] [--name name_regexp] [--type type_regexp]
Return a list containing the names of all known functions within all know Fortran modules. The functions are grouped by source file and containing module, and shown with the line number on which each function is defined.
The option --module
only returns results for modules matching
module_regexp. The option --name
only returns functions
whose name matches name_regexp, and --type
only returns
functions whose type matches type_regexp.
The corresponding gdb command is ‘info module functions’.
(gdb) -symbol-info-module-functions ^done,symbols= [{module="mod1", files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[{line="21",name="mod1::check_all",type="void (void)", description="void mod1::check_all(void);"}]}]}, {module="mod2", files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[{line="30",name="mod2::check_var_i",type="void (void)", description="void mod2::check_var_i(void);"}]}]}, {module="mod3", files=[{filename="/projec/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/projec/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[{line="21",name="mod3::check_all",type="void (void)", description="void mod3::check_all(void);"}, {line="27",name="mod3::check_mod2",type="void (void)", description="void mod3::check_mod2(void);"}]}]}, {module="modmany", files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[{line="35",name="modmany::check_some",type="void (void)", description="void modmany::check_some(void);"}]}]}, {module="moduse", files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[{line="44",name="moduse::check_all",type="void (void)", description="void moduse::check_all(void);"}, {line="49",name="moduse::check_var_x",type="void (void)", description="void moduse::check_var_x(void);"}]}]}]
-symbol-info-module-variables
Command-symbol-info-module-variables [--module module_regexp] [--name name_regexp] [--type type_regexp]
Return a list containing the names of all known variables within all know Fortran modules. The variables are grouped by source file and containing module, and shown with the line number on which each variable is defined.
The option --module
only returns results for modules matching
module_regexp. The option --name
only returns variables
whose name matches name_regexp, and --type
only returns
variables whose type matches type_regexp.
The corresponding gdb command is ‘info module variables’.
(gdb) -symbol-info-module-variables ^done,symbols= [{module="mod1", files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[{line="18",name="mod1::var_const",type="integer(kind=4)", description="integer(kind=4) mod1::var_const;"}, {line="17",name="mod1::var_i",type="integer(kind=4)", description="integer(kind=4) mod1::var_i;"}]}]}, {module="mod2", files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[{line="28",name="mod2::var_i",type="integer(kind=4)", description="integer(kind=4) mod2::var_i;"}]}]}, {module="mod3", files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[{line="18",name="mod3::mod1",type="integer(kind=4)", description="integer(kind=4) mod3::mod1;"}, {line="17",name="mod3::mod2",type="integer(kind=4)", description="integer(kind=4) mod3::mod2;"}, {line="19",name="mod3::var_i",type="integer(kind=4)", description="integer(kind=4) mod3::var_i;"}]}]}, {module="modmany", files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[{line="33",name="modmany::var_a",type="integer(kind=4)", description="integer(kind=4) modmany::var_a;"}, {line="33",name="modmany::var_b",type="integer(kind=4)", description="integer(kind=4) modmany::var_b;"}, {line="33",name="modmany::var_c",type="integer(kind=4)", description="integer(kind=4) modmany::var_c;"}, {line="33",name="modmany::var_i",type="integer(kind=4)", description="integer(kind=4) modmany::var_i;"}]}]}, {module="moduse", files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[{line="42",name="moduse::var_x",type="integer(kind=4)", description="integer(kind=4) moduse::var_x;"}, {line="42",name="moduse::var_y",type="integer(kind=4)", description="integer(kind=4) moduse::var_y;"}]}]}]
-symbol-info-modules
Command-symbol-info-modules [--name name_regexp] [--max-results limit]
Return a list containing the names of all known Fortran modules. The modules are grouped by source file, and shown with the line number on which each modules is defined.
The option --name
allows the modules returned to be filtered
based the name of the module.
The option --max-results
restricts the command to return no
more than limit results. If exactly limit results are
returned then there might be additional results available if a higher
limit is used.
The corresponding gdb command is ‘info modules’.
(gdb) -symbol-info-modules ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[{line="16",name="mod1"}, {line="22",name="mod2"}]}, {filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[{line="16",name="mod3"}, {line="22",name="modmany"}, {line="26",name="moduse"}]}]} (gdb) -symbol-info-modules --name mod[123] ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[{line="16",name="mod1"}, {line="22",name="mod2"}]}, {filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[{line="16",name="mod3"}]}]}
-symbol-info-types
Command-symbol-info-types [--name name_regexp] [--max-results limit]
Return a list of all defined types. The types are grouped by source
file, and shown with the line number on which each user defined type
is defined. Some base types are not defined in the source code but
are added to the debug information by the compiler, for example
int
, float
, etc.; these types do not have an associated
line number.
The option --name
allows the list of types returned to be
filtered by name.
The option --max-results
restricts the command to return no
more than limit results. If exactly limit results are
returned then there might be additional results available if a higher
limit is used.
The corresponding gdb command is ‘info types’.
(gdb) -symbol-info-types ^done,symbols= {debug= [{filename="gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{name="float"}, {name="int"}, {line="27",name="typedef int my_int_t;"}]}, {filename="gdb.mi/mi-sym-info-2.c", fullname="/project/gdb.mi/mi-sym-info-2.c", symbols=[{line="24",name="typedef float another_float_t;"}, {line="23",name="typedef int another_int_t;"}, {name="float"}, {name="int"}]}]} (gdb) -symbol-info-types --name _int_ ^done,symbols= {debug= [{filename="gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{line="27",name="typedef int my_int_t;"}]}, {filename="gdb.mi/mi-sym-info-2.c", fullname="/project/gdb.mi/mi-sym-info-2.c", symbols=[{line="23",name="typedef int another_int_t;"}]}]}
-symbol-info-variables
Command-symbol-info-variables [--include-nondebug] [--type type_regexp] [--name name_regexp] [--max-results limit]
Return a list containing the names and types for all global variables taken from the debug information. The variables are grouped by source file, and shown with the line number on which each variable is defined.
The --include-nondebug
option causes the output to include
data symbols from the symbol table.
The options --type
and --name
allow the symbols returned
to be filtered based on either the name of the variable, or the type
of the variable.
The option --max-results
restricts the command to return no
more than limit results. If exactly limit results are
returned then there might be additional results available if a higher
limit is used.
The corresponding gdb command is ‘info variables’.
(gdb) -symbol-info-variables ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{line="25",name="global_f1",type="float", description="static float global_f1;"}, {line="24",name="global_i1",type="int", description="static int global_i1;"}]}, {filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[{line="21",name="global_f2",type="int", description="int global_f2;"}, {line="20",name="global_i2",type="int", description="int global_i2;"}, {line="19",name="global_f1",type="float", description="static float global_f1;"}, {line="18",name="global_i1",type="int", description="static int global_i1;"}]}]} (gdb) -symbol-info-variables --name f1 ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{line="25",name="global_f1",type="float", description="static float global_f1;"}]}, {filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[{line="19",name="global_f1",type="float", description="static float global_f1;"}]}]} (gdb) -symbol-info-variables --type float ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{line="25",name="global_f1",type="float", description="static float global_f1;"}]}, {filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[{line="19",name="global_f1",type="float", description="static float global_f1;"}]}]} (gdb) -symbol-info-variables --include-nondebug ^done,symbols= {debug= [{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[{line="25",name="global_f1",type="float", description="static float global_f1;"}, {line="24",name="global_i1",type="int", description="static int global_i1;"}]}, {filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[{line="21",name="global_f2",type="int", description="int global_f2;"}, {line="20",name="global_i2",type="int", description="int global_i2;"}, {line="19",name="global_f1",type="float", description="static float global_f1;"}, {line="18",name="global_i1",type="int", description="static int global_i1;"}]}], nondebug= [{address="0x00000000004005d0",name="_IO_stdin_used"}, {address="0x00000000004005d8",name="__dso_handle"} ... ]}
-symbol-list-lines
Command-symbol-list-lines filename
Print the list of lines that contain code and their associated program addresses for the given source filename. The entries are sorted in ascending PC order.
There is no corresponding gdb command.
(gdb) -symbol-list-lines basics.c ^done,lines=[{pc="0x08048554",line="7"},{pc="0x0804855a",line="8"}] (gdb)
This section describes the GDB/MI commands to specify executable file names and to read in and obtain symbol table information.
-file-exec-and-symbols
Command-file-exec-and-symbols file
Specify the executable file to be debugged. This file is the one from which the symbol table is also read. If no file is specified, the command clears the executable and symbol information. If breakpoints are set when using this command with no arguments, gdb will produce error messages. Otherwise, no output is produced, except a completion notification.
The corresponding gdb command is ‘file’.
(gdb) -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb)
-file-exec-file
Command-file-exec-file file
Specify the executable file to be debugged. Unlike ‘-file-exec-and-symbols’, the symbol table is not read from this file. If used without argument, gdb clears the information about the executable file. No output is produced, except a completion notification.
The corresponding gdb command is ‘exec-file’.
(gdb) -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb)
-file-list-exec-source-file
Command-file-list-exec-source-file
List the line number, the current source file, and the absolute path to the current source file for the current executable. The macro information field has a value of ‘1’ or ‘0’ depending on whether or not the file includes preprocessor macro information.
The gdb equivalent is ‘info source’
(gdb) 123-file-list-exec-source-file 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1" (gdb)
-file-list-exec-source-files
Command-file-list-exec-source-files
List the source files for the current executable.
It will always output both the filename and fullname (absolute file name) of a source file.
The gdb equivalent is ‘info sources’.
gdbtk
has an analogous command ‘gdb_listfiles’.
(gdb) -file-list-exec-source-files ^done,files=[ {file=foo.c,fullname=/home/foo.c}, {file=/home/bar.c,fullname=/home/bar.c}, {file=gdb_could_not_find_fullpath.c}] (gdb)
-file-list-shared-libraries
Command-file-list-shared-libraries [ regexp ]
List the shared libraries in the program. With a regular expression regexp, only those libraries whose names match regexp are listed.
The corresponding gdb command is ‘info shared’. The fields
have a similar meaning to the =library-loaded
notification.
The ranges
field specifies the multiple segments belonging to this
library. Each range has the following fields:
(gdb) -file-list-exec-source-files ^done,shared-libraries=[ {id="/lib/libfoo.so",target-name="/lib/libfoo.so",host-name="/lib/libfoo.so",symbols-loaded="1",thread-group="i1",ranges=[{from="0x72815989",to="0x728162c0"}]}, {id="/lib/libbar.so",target-name="/lib/libbar.so",host-name="/lib/libbar.so",symbols-loaded="1",thread-group="i1",ranges=[{from="0x76ee48c0",to="0x76ee9160"}]}] (gdb)
-file-symbol-file
Command-file-symbol-file file
Read symbol table info from the specified file argument. When used without arguments, clears gdb's symbol table info. No output is produced, except for a completion notification.
The corresponding gdb command is ‘symbol-file’.
(gdb) -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb)
-target-attach
Command-target-attach pid | gid | file
Attach to a process pid or a file file outside of gdb, or a thread group gid. If attaching to a thread group, the id previously returned by ‘-list-thread-groups --available’ must be used.
The corresponding gdb command is ‘attach’.
(gdb) -target-attach 34 =thread-created,id="1" *stopped,thread-id="1",frame={addr="0xb7f7e410",func="bar",args=[]} ^done (gdb)
-target-detach
Command-target-detach [ pid | gid ]
Detach from the remote target which normally resumes its execution. If either pid or gid is specified, detaches from either the specified process, or specified thread group. There's no output.
The corresponding gdb command is ‘detach’.
(gdb) -target-detach ^done (gdb)
-target-disconnect
Command-target-disconnect
Disconnect from the remote target. There's no output and the target is generally not resumed.
The corresponding gdb command is ‘disconnect’.
(gdb) -target-disconnect ^done (gdb)
-target-download
Command-target-download
Loads the executable onto the remote target. It prints out an update message every half second, which includes the fields:
Each message is sent as status record (see gdb/mi Output Syntax).
In addition, it prints the name and size of the sections, as they are downloaded. These messages include the following fields:
At the end, a summary is printed.
The corresponding gdb command is ‘load’.
Note: each status message appears on a single line. Here the messages have been broken down so that they can fit onto a page.
(gdb) -target-download +download,{section=".text",section-size="6668",total-size="9880"} +download,{section=".text",section-sent="512",section-size="6668", total-sent="512",total-size="9880"} +download,{section=".text",section-sent="1024",section-size="6668", total-sent="1024",total-size="9880"} +download,{section=".text",section-sent="1536",section-size="6668", total-sent="1536",total-size="9880"} +download,{section=".text",section-sent="2048",section-size="6668", total-sent="2048",total-size="9880"} +download,{section=".text",section-sent="2560",section-size="6668", total-sent="2560",total-size="9880"} +download,{section=".text",section-sent="3072",section-size="6668", total-sent="3072",total-size="9880"} +download,{section=".text",section-sent="3584",section-size="6668", total-sent="3584",total-size="9880"} +download,{section=".text",section-sent="4096",section-size="6668", total-sent="4096",total-size="9880"} +download,{section=".text",section-sent="4608",section-size="6668", total-sent="4608",total-size="9880"} +download,{section=".text",section-sent="5120",section-size="6668", total-sent="5120",total-size="9880"} +download,{section=".text",section-sent="5632",section-size="6668", total-sent="5632",total-size="9880"} +download,{section=".text",section-sent="6144",section-size="6668", total-sent="6144",total-size="9880"} +download,{section=".text",section-sent="6656",section-size="6668", total-sent="6656",total-size="9880"} +download,{section=".init",section-size="28",total-size="9880"} +download,{section=".fini",section-size="28",total-size="9880"} +download,{section=".data",section-size="3156",total-size="9880"} +download,{section=".data",section-sent="512",section-size="3156", total-sent="7236",total-size="9880"} +download,{section=".data",section-sent="1024",section-size="3156", total-sent="7748",total-size="9880"} +download,{section=".data",section-sent="1536",section-size="3156", total-sent="8260",total-size="9880"} +download,{section=".data",section-sent="2048",section-size="3156", total-sent="8772",total-size="9880"} +download,{section=".data",section-sent="2560",section-size="3156", total-sent="9284",total-size="9880"} +download,{section=".data",section-sent="3072",section-size="3156", total-sent="9796",total-size="9880"} ^done,address="0x10004",load-size="9880",transfer-rate="6586", write-rate="429" (gdb)
No equivalent.
N.A.
-target-flash-erase
Command-target-flash-erase
Erases all known flash memory regions on the target.
The corresponding gdb command is ‘flash-erase’.
The output is a list of flash regions that have been erased, with starting addresses and memory region sizes.
(gdb) -target-flash-erase ^done,erased-regions={address="0x0",size="0x40000"} (gdb)
-target-select
Command-target-select type parameters ...
Connect gdb to the remote target. This command takes two args:
The output is a connection notification, followed by the address at which the target program is, in the following form:
^connected,addr="address",func="function name", args=[arg list]
The corresponding gdb command is ‘target’.
(gdb) -target-select remote /dev/ttya ^connected,addr="0xfe00a300",func="??",args=[] (gdb)
-target-file-put
Command-target-file-put hostfile targetfile
Copy file hostfile from the host system (the machine running gdb) to targetfile on the target system.
The corresponding gdb command is ‘remote put’.
(gdb) -target-file-put localfile remotefile ^done (gdb)
-target-file-get
Command-target-file-get targetfile hostfile
Copy file targetfile from the target system to hostfile on the host system.
The corresponding gdb command is ‘remote get’.
(gdb) -target-file-get remotefile localfile ^done (gdb)
-target-file-delete
Command-target-file-delete targetfile
Delete targetfile from the target system.
The corresponding gdb command is ‘remote delete’.
(gdb) -target-file-delete remotefile ^done (gdb)
-info-ada-exceptions
Command-info-ada-exceptions [ regexp]
List all Ada exceptions defined within the program being debugged. With a regular expression regexp, only those exceptions whose names match regexp are listed.
The corresponding gdb command is ‘info exceptions’.
The result is a table of Ada exceptions. The following columns are defined for each exception:
-info-ada-exceptions aint ^done,ada-exceptions={nr_rows="2",nr_cols="2", hdr=[{width="1",alignment="-1",col_name="name",colhdr="Name"}, {width="1",alignment="-1",col_name="address",colhdr="Address"}], body=[{name="constraint_error",address="0x0000000000613da0"}, {name="const.aint_global_e",address="0x0000000000613b00"}]}
The commands describing how to ask gdb to stop when a program raises an exception are described at Ada Exception GDB/MI Catchpoint Commands.
Since new commands and features get regularly added to gdb/mi, some commands are available to help front-ends query the debugger about support for these capabilities. Similarly, it is also possible to query gdb about target support of certain features.
-info-gdb-mi-command
Command-info-gdb-mi-command cmd_name
Query support for the gdb/mi command named cmd_name.
Note that the dash (-
) starting all gdb/mi commands
is technically not part of the command name (see GDB/MI Input Syntax), and thus should be omitted in cmd_name. However,
for ease of use, this command also accepts the form with the leading
dash.
There is no corresponding gdb command.
The result is a tuple. There is currently only one field:
"true"
if the gdb/mi command exists,
"false"
otherwise.
Here is an example where the gdb/mi command does not exist:
-info-gdb-mi-command unsupported-command ^done,command={exists="false"}
And here is an example where the gdb/mi command is known to the debugger:
-info-gdb-mi-command symbol-list-lines ^done,command={exists="true"}
-list-features
CommandReturns a list of particular features of the MI protocol that this version of gdb implements. A feature can be a command, or a new field in an output of some command, or even an important bugfix. While a frontend can sometimes detect presence of a feature at runtime, it is easier to perform detection at debugger startup.
The command returns a list of strings, with each string naming an available feature. Each returned string is just a name, it does not have any internal structure. The list of possible feature names is given below.
Example output:
(gdb) -list-features ^done,result=["feature1","feature2"]
The current list of features is:
-var-set-frozen
command, as well
as possible presence of the frozen
field in the output
of -varobj-create
.
-break-insert
command.
-var-list-children
-thread-info
command.
-data-read-memory-bytes
and the
-data-write-memory-bytes
commands.
-ada-task-info
command.
-info-gdb-mi-command
command.
-exec-run
command supports the --start
option (see GDB/MI Program Execution).
-data-disassemble
command supports the -a
option (see GDB/MI Data Manipulation).
-list-target-features
Command
Returns a list of particular features that are supported by the
target. Those features affect the permitted MI commands, but
unlike the features reported by the -list-features
command, the
features depend on which target GDB is using at the moment. Whenever
a target can change, due to commands such as -target-select
,
-target-attach
or -exec-run
, the list of target features
may change, and the frontend should obtain it again.
Example output:
(gdb) -list-target-features ^done,result=["async"]
The current list of features is:
-gdb-exit
Command-gdb-exit
Exit gdb immediately.
Approximately corresponds to ‘quit’.
(gdb) -gdb-exit ^exit
-gdb-set
Command-gdb-set
Set an internal gdb variable.
The corresponding gdb command is ‘set’.
(gdb) -gdb-set $foo=3 ^done (gdb)
-gdb-show
Command-gdb-show
Show the current value of a gdb variable.
The corresponding gdb command is ‘show’.
(gdb) -gdb-show annotate ^done,value="0" (gdb)
-gdb-version
Command-gdb-version
Show version information for gdb. Used mostly in testing.
The gdb equivalent is ‘show version’. gdb by default shows this information when you start an interactive session.
(gdb) -gdb-version ~GNU gdb 5.2.1 ~Copyright 2000 Free Software Foundation, Inc. ~GDB is free software, covered by the GNU General Public License, and ~you are welcome to change it and/or distribute copies of it under ~ certain conditions. ~Type "show copying" to see the conditions. ~There is absolutely no warranty for GDB. Type "show warranty" for ~ details. ~This GDB was configured as "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi". ^done (gdb)
-list-thread-groups
Command-list-thread-groups [ --available ] [ --recurse 1 ] [ group ... ]
Lists thread groups (see Thread groups). When a single thread group is passed as the argument, lists the children of that group. When several thread group are passed, lists information about those thread groups. Without any parameters, lists information about all top-level thread groups.
Normally, thread groups that are being debugged are reported. With the ‘--available’ option, gdb reports thread groups available on the target.
The output of this command may have either a ‘threads’ result or a ‘groups’ result. The ‘thread’ result has a list of tuples as value, with each tuple describing a thread (see GDB/MI Thread Information). The ‘groups’ result has a list of tuples as value, each tuple describing a thread group. If top-level groups are requested (that is, no parameter is passed), or when several groups are passed, the output always has a ‘groups’ result. The format of the ‘group’ result is described below.
To reduce the number of roundtrips it's possible to list thread groups together with their children, by passing the ‘--recurse’ option and the recursion depth. Presently, only recursion depth of 1 is permitted. If this option is present, then every reported thread group will also include its children, either as ‘group’ or ‘threads’ field.
In general, any combination of option and parameters is permitted, with the following caveats:
The ‘groups’ result is a list of tuples, where each tuple may have the following fields:
id
type
pid
exit-code
num_children
threads
cores
executable
gdb -list-thread-groups ^done,groups=[{id="17",type="process",pid="yyy",num_children="2"}] -list-thread-groups 17 ^done,threads=[{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)", frame={level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]},state="running"}, {id="1",target-id="Thread 0xb7e156b0 (LWP 21254)", frame={level="0",addr="0x0804891f",func="foo",args=[{name="i",value="10"}], file="/tmp/a.c",fullname="/tmp/a.c",line="158",arch="i386:x86_64"},state="running"}]] -list-thread-groups --available ^done,groups=[{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]}] -list-thread-groups --available --recurse 1 ^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2], threads=[{id="1",target-id="Thread 0xb7e14b90",cores=[1]}, {id="2",target-id="Thread 0xb7e14b90",cores=[2]}]},..] -list-thread-groups --available --recurse 1 17 18 ^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2], threads=[{id="1",target-id="Thread 0xb7e14b90",cores=[1]}, {id="2",target-id="Thread 0xb7e14b90",cores=[2]}]},...]
-info-os
Command-info-os [ type ]
If no argument is supplied, the command returns a table of available operating-system-specific information types. If one of these types is supplied as an argument type, then the command returns a table of data of that type.
The types of information available depend on the target operating system.
The corresponding gdb command is ‘info os’.
When run on a gnu/Linux system, the output will look something like this:
gdb -info-os ^done,OSDataTable={nr_rows="10",nr_cols="3", hdr=[{width="10",alignment="-1",col_name="col0",colhdr="Type"}, {width="10",alignment="-1",col_name="col1",colhdr="Description"}, {width="10",alignment="-1",col_name="col2",colhdr="Title"}], body=[item={col0="cpus",col1="Listing of all cpus/cores on the system", col2="CPUs"}, item={col0="files",col1="Listing of all file descriptors", col2="File descriptors"}, item={col0="modules",col1="Listing of all loaded kernel modules", col2="Kernel modules"}, item={col0="msg",col1="Listing of all message queues", col2="Message queues"}, item={col0="processes",col1="Listing of all processes", col2="Processes"}, item={col0="procgroups",col1="Listing of all process groups", col2="Process groups"}, item={col0="semaphores",col1="Listing of all semaphores", col2="Semaphores"}, item={col0="shm",col1="Listing of all shared-memory regions", col2="Shared-memory regions"}, item={col0="sockets",col1="Listing of all internet-domain sockets", col2="Sockets"}, item={col0="threads",col1="Listing of all threads", col2="Threads"}] gdb -info-os processes ^done,OSDataTable={nr_rows="190",nr_cols="4", hdr=[{width="10",alignment="-1",col_name="col0",colhdr="pid"}, {width="10",alignment="-1",col_name="col1",colhdr="user"}, {width="10",alignment="-1",col_name="col2",colhdr="command"}, {width="10",alignment="-1",col_name="col3",colhdr="cores"}], body=[item={col0="1",col1="root",col2="/sbin/init",col3="0"}, item={col0="2",col1="root",col2="[kthreadd]",col3="1"}, item={col0="3",col1="root",col2="[ksoftirqd/0]",col3="0"}, ... item={col0="26446",col1="stan",col2="bash",col3="0"}, item={col0="28152",col1="stan",col2="bash",col3="1"}]} (gdb)
(Note that the MI output here includes a "Title"
column that
does not appear in command-line info os
; this column is useful
for MI clients that want to enumerate the types of data, such as in a
popup menu, but is needless clutter on the command line, and
info os
omits it.)
-add-inferior
Command-add-inferior
Creates a new inferior (see Inferiors and Programs). The created inferior is not associated with any executable. Such association may be established with the ‘-file-exec-and-symbols’ command (see GDB/MI File Commands). The command response has a single field, ‘inferior’, whose value is the identifier of the thread group corresponding to the new inferior.
gdb -add-inferior ^done,inferior="i3"
-interpreter-exec
Command-interpreter-exec interpreter command
Execute the specified command in the given interpreter.
The corresponding gdb command is ‘interpreter-exec’.
(gdb) -interpreter-exec console "break main" &"During symbol reading, couldn't parse type; debugger out of date?.\n" &"During symbol reading, bad structure-type format.\n" ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n" ^done (gdb)
-inferior-tty-set
Command-inferior-tty-set /dev/pts/1
Set terminal for future runs of the program being debugged.
The corresponding gdb command is ‘set inferior-tty’ /dev/pts/1.
(gdb) -inferior-tty-set /dev/pts/1 ^done (gdb)
-inferior-tty-show
Command-inferior-tty-show
Show terminal for future runs of program being debugged.
The corresponding gdb command is ‘show inferior-tty’.
(gdb) -inferior-tty-set /dev/pts/1 ^done (gdb) -inferior-tty-show ^done,inferior_tty_terminal="/dev/pts/1" (gdb)
-enable-timings
Command-enable-timings [yes | no]
Toggle the printing of the wallclock, user and system times for an MI command as a field in its output. This command is to help frontend developers optimize the performance of their code. No argument is equivalent to ‘yes’.
No equivalent.
(gdb) -enable-timings ^done (gdb) -break-insert main ^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y", addr="0x080484ed",func="main",file="myprog.c", fullname="/home/nickrob/myprog.c",line="73",thread-groups=["i1"], times="0"}, time={wallclock="0.05185",user="0.00800",system="0.00000"} (gdb) -enable-timings no ^done (gdb) -exec-run ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0", frame={addr="0x080484ed",func="main",args=[{name="argc",value="1"}, {name="argv",value="0xbfb60364"}],file="myprog.c", fullname="/home/nickrob/myprog.c",line="73",arch="i386:x86_64"} (gdb)
-complete
Command-complete command
Show a list of completions for partially typed CLI command.
This command is intended for gdb/mi frontends that cannot use two separate CLI and MI channels — for example: because of lack of PTYs like on Windows or because gdb is used remotely via a SSH connection.
The result consists of two or three fields:
1
if number of known completions is above
max-completions
limit (see Completion), otherwise it contains
0
. It is always present.
The corresponding gdb command is ‘complete’.
(gdb) -complete br ^done,completion="break", matches=["break","break-range"], max_completions_reached="0" (gdb) -complete "b ma" ^done,completion="b ma", matches=["b madvise","b main"],max_completions_reached="0" (gdb) -complete "b push_b" ^done,completion="b push_back(", matches=[ "b A::push_back(void*)", "b std::string::push_back(char)", "b std::vector<int, std::allocator<int> >::push_back(int&&)"], max_completions_reached="0" (gdb) -complete "nonexist" ^done,matches=[],max_completions_reached="0" (gdb)
This chapter describes annotations in gdb. Annotations were designed to interface gdb to graphical user interfaces or other similar programs which want to interact with gdb at a relatively high level.
The annotation mechanism has largely been superseded by gdb/mi (see GDB/MI).
Annotations start with a newline character, two ‘control-z’ characters, and the name of the annotation. If there is no additional information associated with this annotation, the name of the annotation is followed immediately by a newline. If there is additional information, the name of the annotation is followed by a space, the additional information, and a newline. The additional information cannot contain newline characters.
Any output not beginning with a newline and two ‘control-z’ characters denotes literal output from gdb. Currently there is no need for gdb to output a newline followed by two ‘control-z’ characters, but if there was such a need, the annotations could be extended with an ‘escape’ annotation which means those three characters as output.
The annotation level, which is specified using the --annotate command line option (see Mode Options), controls how much information gdb prints together with its prompt, values of expressions, source lines, and other types of output. Level 0 is for no annotations, level 1 is for use when gdb is run as a subprocess of gnu Emacs, level 3 is the maximum annotation suitable for programs that control gdb, and level 2 annotations have been made obsolete (see Limitations of the Annotation Interface).
set annotate
levelset annotate
sets the level of
annotations to the specified level.
show annotate
This chapter describes level 3 annotations.
A simple example of starting up gdb with annotations is:
$ gdb --annotate=3 GNU gdb 6.0 Copyright 2003 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-pc-linux-gnu" ^Z^Zpre-prompt (gdb) ^Z^Zprompt quit ^Z^Zpost-prompt $
Here ‘quit’ is input to gdb; the rest is output from gdb. The three lines beginning ‘^Z^Z’ (where ‘^Z’ denotes a ‘control-z’ character) are annotations; the rest is output from gdb.
If you prefix a command with ‘server ’ then it will not affect the command history, nor will it affect gdb's notion of which command to repeat if <RET> is pressed on a line by itself. This means that commands can be run behind a user's back by a front-end in a transparent manner.
The server
prefix does not affect the recording of values into
the value history; to print a value without recording it into the
value history, use the output
command instead of the
print
command.
Using this prefix also disables confirmation requests (see confirmation requests).
When gdb prompts for input, it annotates this fact so it is possible to know when to send output, when the output from a given command is over, etc.
Different kinds of input each have a different input type. Each
input type has three annotations: a pre-
annotation, which
denotes the beginning of any prompt which is being output, a plain
annotation, which denotes the end of the prompt, and then a post-
annotation which denotes the end of any echo which may (or may not) be
associated with the input. For example, the prompt
input type
features the following annotations:
^Z^Zpre-prompt ^Z^Zprompt ^Z^Zpost-prompt
prompt
commands
commands
command. The annotations are repeated for each command which is input.
overload-choice
query
prompt-for-continue
set height 0
to disable
prompting. This is because the counting of lines is buggy in the
presence of annotations.
^Z^Zquit
This annotation occurs right before gdb responds to an interrupt.
^Z^Zerror
This annotation occurs right before gdb responds to an error.
Quit and error annotations indicate that any annotations which gdb was
in the middle of may end abruptly. For example, if a
value-history-begin
annotation is followed by a error
, one
cannot expect to receive the matching value-history-end
. One
cannot expect not to receive it either, however; an error annotation
does not necessarily mean that gdb is immediately returning all the way
to the top level.
A quit or error annotation may be preceded by
^Z^Zerror-begin
Any output between that and the quit or error annotation is the error message.
Warning messages are not yet annotated.
The following annotations say that certain pieces of state may have changed.
^Z^Zframes-invalid
backtrace
command) may
have changed.
^Z^Zbreakpoints-invalid
When the program starts executing due to a gdb command such as
step
or continue
,
^Z^Zstarting
is output. When the program stops,
^Z^Zstopped
is output. Before the stopped
annotation, a variety of
annotations describe how the program stopped.
^Z^Zexited
exit-status^Z^Zsignalled
^Z^Zsignalled
, the
annotation continues:
intro-text ^Z^Zsignal-name name ^Z^Zsignal-name-end middle-text ^Z^Zsignal-string string ^Z^Zsignal-string-end end-text
where name is the name of the signal, such as SIGILL
or
SIGSEGV
, and string is the explanation of the signal, such
as Illegal Instruction
or Segmentation fault
. The arguments
intro-text, middle-text, and end-text are for the
user's benefit and have no particular format.
^Z^Zsignal
signalled
, but gdb is
just saying that the program received the signal, not that it was
terminated with it.
^Z^Zbreakpoint
number^Z^Zwatchpoint
numberThe following annotation is used instead of displaying source code:
^Z^Zsource filename:line:character:middle:addr
where filename is an absolute file name indicating which source file, line is the line number within that file (where 1 is the first line in the file), character is the character position within the file (where 0 is the first character in the file) (for most debug formats this will necessarily point to the beginning of a line), middle is ‘middle’ if addr is in the middle of the line, or ‘beg’ if addr is at the beginning of the line, and addr is the address in the target program associated with the source which is being displayed. The addr is in the form ‘0x’ followed by one or more lowercase hex digits (note that this does not depend on the language).
This chapter documents gdb's just-in-time (JIT) compilation interface. A JIT compiler is a program or library that generates native executable code at runtime and executes it, usually in order to achieve good performance while maintaining platform independence.
Programs that use JIT compilation are normally difficult to debug because portions of their code are generated at runtime, instead of being loaded from object files, which is where gdb normally finds the program's symbols and debug information. In order to debug programs that use JIT compilation, gdb has an interface that allows the program to register in-memory symbol files with gdb at runtime.
If you are using gdb to debug a program that uses this interface, then it should work transparently so long as you have not stripped the binary. If you are developing a JIT compiler, then the interface is documented in the rest of this chapter. At this time, the only known client of this interface is the LLVM JIT.
Broadly speaking, the JIT interface mirrors the dynamic loader interface. The JIT compiler communicates with gdb by writing data into a global variable and calling a function at a well-known symbol. When gdb attaches, it reads a linked list of symbol files from the global variable to find existing code, and puts a breakpoint in the function so that it can find out about additional code.
These are the relevant struct declarations that a C program should include to implement the interface:
typedef enum { JIT_NOACTION = 0, JIT_REGISTER_FN, JIT_UNREGISTER_FN } jit_actions_t; struct jit_code_entry { struct jit_code_entry *next_entry; struct jit_code_entry *prev_entry; const char *symfile_addr; uint64_t symfile_size; }; struct jit_descriptor { uint32_t version; /* This type should be jit_actions_t, but we use uint32_t to be explicit about the bitwidth. */ uint32_t action_flag; struct jit_code_entry *relevant_entry; struct jit_code_entry *first_entry; }; /* GDB puts a breakpoint in this function. */ void __attribute__((noinline)) __jit_debug_register_code() { }; /* Make sure to specify the version statically, because the debugger may check the version before we can set it. */ struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };
If the JIT is multi-threaded, then it is important that the JIT synchronize any modifications to this global data properly, which can easily be done by putting a global mutex around modifications to these structures.
To register code with gdb, the JIT should follow this protocol:
action_flag
to JIT_REGISTER
and call
__jit_debug_register_code
.
When gdb is attached and the breakpoint fires, gdb uses the
relevant_entry
pointer so it doesn't have to walk the list looking for
new code. However, the linked list must still be maintained in order to allow
gdb to attach to a running process and still find the symbol files.
If code is freed, then the JIT should use the following protocol:
relevant_entry
field of the descriptor at the code entry.
action_flag
to JIT_UNREGISTER
and call
__jit_debug_register_code
.
If the JIT frees or recompiles code without unregistering it, then gdb and the JIT will leak the memory used for the associated symbol files.
Generating debug information in platform-native file formats (like ELF or COFF) may be an overkill for JIT compilers; especially if all the debug info is used for is displaying a meaningful backtrace. The issue can be resolved by having the JIT writers decide on a debug info format and also provide a reader that parses the debug info generated by the JIT compiler. This section gives a brief overview on writing such a parser. More specific details can be found in the source file gdb/jit-reader.in, which is also installed as a header at includedir/gdb/jit-reader.h for easy inclusion.
The reader is implemented as a shared object (so this functionality is
not available on platforms which don't allow loading shared objects at
runtime). Two gdb commands, jit-reader-load
and
jit-reader-unload
are provided, to be used to load and unload
the readers from a preconfigured directory. Once loaded, the shared
object is used the parse the debug information emitted by the JIT
compiler.
Readers can be loaded and unloaded using the jit-reader-load
and jit-reader-unload
commands.
jit-reader-load
readerOnly one reader can be active at a time; trying to load a second
reader when one is already loaded will result in gdb
reporting an error. A new JIT reader can be loaded by first unloading
the current one using jit-reader-unload
and then invoking
jit-reader-load
.
jit-reader-unload
As mentioned, a reader is essentially a shared object conforming to a certain ABI. This ABI is described in jit-reader.h.
jit-reader.h defines the structures, macros and functions required to write a reader. It is installed (along with gdb), in includedir/gdb where includedir is the system include directory.
Readers need to be released under a GPL compatible license. A reader
can be declared as released under such a license by placing the macro
GDB_DECLARE_GPL_COMPATIBLE_READER
in a source file.
The entry point for readers is the symbol gdb_init_reader
,
which is expected to be a function with the prototype
extern struct gdb_reader_funcs *gdb_init_reader (void);
struct gdb_reader_funcs
contains a set of pointers to callback
functions. These functions are executed to read the debug info
generated by the JIT compiler (read
), to unwind stack frames
(unwind
) and to create canonical frame IDs
(get_frame_id
). It also has a callback that is called when the
reader is being unloaded (destroy
). The struct looks like this
struct gdb_reader_funcs { /* Must be set to GDB_READER_INTERFACE_VERSION. */ int reader_version; /* For use by the reader. */ void *priv_data; gdb_read_debug_info *read; gdb_unwind_frame *unwind; gdb_get_frame_id *get_frame_id; gdb_destroy_reader *destroy; };
The callbacks are provided with another set of callbacks by
gdb to do their job. For read
, these callbacks are
passed in a struct gdb_symbol_callbacks
and for unwind
and get_frame_id
, in a struct gdb_unwind_callbacks
.
struct gdb_symbol_callbacks
has callbacks to create new object
files and new symbol tables inside those object files. struct
gdb_unwind_callbacks
has callbacks to read registers off the current
frame and to write out the values of the registers in the previous
frame. Both have a callback (target_read
) to read bytes off the
target's address space.
The traditional debugging model is conceptually low-speed, but works fine, because most bugs can be reproduced in debugging-mode execution. However, as multi-core or many-core processors are becoming mainstream, and multi-threaded programs become more and more popular, there should be more and more bugs that only manifest themselves at normal-mode execution, for example, thread races, because debugger's interference with the program's timing may conceal the bugs. On the other hand, in some applications, it is not feasible for the debugger to interrupt the program's execution long enough for the developer to learn anything helpful about its behavior. If the program's correctness depends on its real-time behavior, delays introduced by a debugger might cause the program to fail, even when the code itself is correct. It is useful to be able to observe the program's behavior without interrupting it.
Therefore, traditional debugging model is too intrusive to reproduce some bugs. In order to reduce the interference with the program, we can reduce the number of operations performed by debugger. The In-Process Agent, a shared library, is running within the same process with inferior, and is able to perform some debugging operations itself. As a result, debugger is only involved when necessary, and performance of debugging can be improved accordingly. Note that interference with program can be reduced but can't be removed completely, because the in-process agent will still stop or slow down the program.
The in-process agent can interpret and execute Agent Expressions (see Agent Expressions) during performing debugging operations. The agent expressions can be used for different purposes, such as collecting data in tracepoints, and condition evaluation in breakpoints.
You can control whether the in-process agent is used as an aid for debugging with the following commands:
set agent on
set agent off
show agent
The in-process agent is able to communicate with both gdb and GDBserver (see In-Process Agent). This section documents the protocol used for communications between gdb or GDBserver and the IPA. In general, gdb or GDBserver sends commands (see IPA Protocol Commands) and data to in-process agent, and then in-process agent replies back with the return result of the command, or some other information. The data sent to in-process agent is composed of primitive data types, such as 4-byte or 8-byte type, and composite types, which are called objects (see IPA Protocol Objects).
The commands sent to and results received from agent may contain some complex data types called objects.
The in-process agent is running on the same machine with gdb or GDBserver, so it doesn't have to handle as much differences between two ends as remote protocol (see Remote Protocol) tries to handle. However, there are still some differences of two ends in two processes:
Here are the IPA Protocol Objects:
The following table describes important attributes of each IPA protocol object:
Name | Size | Description
|
---|---|---|
agent expression object |
| |
length | 4 | length of bytes code
|
byte code | length | contents of byte code
|
tracepoint action for collecting memory |
| |
'M' | 1 | type of tracepoint action
|
addr | 8 | if basereg is ‘-1’, addr is the
address of the lowest byte to collect, otherwise addr is the offset
of basereg for memory collecting.
|
len | 8 | length of memory for collecting
|
basereg | 4 | the register number containing the starting
memory address for collecting.
|
tracepoint action for collecting registers |
| |
'R' | 1 | type of tracepoint action
|
tracepoint action for collecting static trace data |
| |
'L' | 1 | type of tracepoint action
|
tracepoint action for expression evaluation |
| |
'X' | 1 | type of tracepoint action
|
agent expression | length of | agent expression object
|
tracepoint object |
| |
number | 4 | number of tracepoint
|
address | 8 | address of tracepoint inserted on
|
type | 4 | type of tracepoint
|
enabled | 1 | enable or disable of tracepoint
|
step_count | 8 | step
|
pass_count | 8 | pass
|
numactions | 4 | number of tracepoint actions
|
hit count | 8 | hit count
|
trace frame usage | 8 | trace frame usage
|
compiled_cond | 8 | compiled condition
|
orig_size | 8 | orig size
|
condition | 4 if condition is NULL otherwise length of agent expression object | zero if condition is NULL, otherwise is
agent expression object
|
actions | variable | numactions number of tracepoint action object
|
The spaces in each command are delimiters to ease reading this commands specification. They don't exist in real commands.
Replies:
Replies:
Your bug reports play an essential role in making gdb reliable.
Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of gdb work better. Bug reports are your contribution to the maintenance of gdb.
In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug.
If you are not sure whether you have found a bug, here are some guidelines:
A number of companies and individuals offer support for gnu products. If you obtained gdb from a support organization, we recommend you contact that organization first.
You can find contact information for many support companies and individuals in the file etc/SERVICE in the gnu Emacs distribution.
In any event, we also recommend that you submit bug reports for gdb to mailto:report@adacore.com.
The fundamental principle of reporting bugs usefully is this: report all the facts. If you are not sure whether to state a fact or leave it out, state it!
Often people omit facts because they think they know what causes the problem and assume that some details do not matter. Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it does not, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the debugger into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix the bug. It may be that the bug has been reported previously, but neither you nor we can know that unless your bug report is complete and self-contained.
Sometimes people give a few sketchy facts and ask, “Does this ring a bell?” Those bug reports are useless, and we urge everyone to refuse to respond to them except to chide the sender to report bugs properly.
To enable us to fix the bug, you should include all these things:
show
version
.
Without this, we will not know whether there is any point in looking for the bug in the current version of gdb.
show configuration
at gdb's prompt.
If we were to try to guess the arguments, we would probably guess wrong and then we might not encounter the bug.
Of course, if the bug is that gdb gets a fatal signal, then we will certainly notice it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. You might as well not give us a chance to make a mistake.
Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of gdb is out of synch, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and ours would not. If you told us to expect a crash, then when ours fails to crash, we would know that the bug was not happening for us. If you had not told us to expect a crash, then we would not be able to draw any conclusion from our observations.
To collect all this information, you can use a session recording program such as script, which is available on many Unix systems. Just run your gdb session inside script and then include the typescript file with your bug report.
Another way to record a gdb session is to run gdb inside Emacs and then save the entire buffer to a file.
The line numbers in our development sources will not match those in your sources. Your line numbers would convey no useful information to us.
Here are some things that are not necessary:
Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it.
This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. We recommend that you save your time for something else.
Of course, if you can find a simpler example to report instead of the original one, that is a convenience for us. Errors in the output will be easier to spot, running under the debugger will take less time, and so on.
However, simplification is not vital; if you do not want to do this, report the bug anyway and send us the entire test case you used.
A patch for the bug does help us if it is a good one. But do not omit the necessary information, such as the test case, on the assumption that a patch is all we need. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all.
Sometimes with a program as complicated as gdb it is very hard to construct an example that will make the program follow a certain path through the code. If you do not send us the example, we will not be able to construct one, so we will not be able to verify that the bug is fixed.
And if we cannot understand what bug you are trying to fix, or why your patch should be an improvement, we will not install it. A test case will help us to understand.
Such guesses are usually wrong. Even we cannot guess right about such things without first using the debugger to find the facts.
This chapter describes the basic features of the gnu command line editing interface.
The following paragraphs describe the notation used to represent keystrokes.
The text C-k is read as `Control-K' and describes the character produced when the <k> key is pressed while the Control key is depressed.
The text M-k is read as `Meta-K' and describes the character produced when the Meta key (if you have one) is depressed, and the <k> key is pressed. The Meta key is labeled <ALT> on many keyboards. On keyboards with two keys labeled <ALT> (usually to either side of the space bar), the <ALT> on the left side is generally set to work as a Meta key. The <ALT> key on the right may also be configured to work as a Meta key or may be configured as some other modifier, such as a Compose key for typing accented characters.
If you do not have a Meta or <ALT> key, or another key working as a Meta key, the identical keystroke can be generated by typing <ESC> first, and then typing <k>. Either process is known as metafying the <k> key.
The text M-C-k is read as `Meta-Control-k' and describes the character produced by metafying C-k.
In addition, several keys have their own names. Specifically, <DEL>, <ESC>, <LFD>, <SPC>, <RET>, and <TAB> all stand for themselves when seen in this text, or in an init file (see Readline Init File). If your keyboard lacks a <LFD> key, typing <C-j> will produce the desired character. The <RET> key may be labeled <Return> or <Enter> on some keyboards.
Often during an interactive session you type in a long line of text, only to notice that the first word on the line is misspelled. The Readline library gives you a set of commands for manipulating the text as you type it in, allowing you to just fix your typo, and not forcing you to retype the majority of the line. Using these editing commands, you move the cursor to the place that needs correction, and delete or insert the text of the corrections. Then, when you are satisfied with the line, you simply press <RET>. You do not have to be at the end of the line to press <RET>; the entire line is accepted regardless of the location of the cursor within the line.
In order to enter characters into the line, simply type them. The typed character appears where the cursor was, and then the cursor moves one space to the right. If you mistype a character, you can use your erase character to back up and delete the mistyped character.
Sometimes you may mistype a character, and not notice the error until you have typed several other characters. In that case, you can type C-b to move the cursor to the left, and then correct your mistake. Afterwards, you can move the cursor to the right with C-f.
When you add text in the middle of a line, you will notice that characters to the right of the cursor are `pushed over' to make room for the text that you have inserted. Likewise, when you delete text behind the cursor, characters to the right of the cursor are `pulled back' to fill in the blank space created by the removal of the text. A list of the bare essentials for editing the text of an input line follows.
(Depending on your configuration, the <Backspace> key be set to delete the character to the left of the cursor and the <DEL> key set to delete the character underneath the cursor, like C-d, rather than the character to the left of the cursor.)
The above table describes the most basic keystrokes that you need in order to do editing of the input line. For your convenience, many other commands have been added in addition to C-b, C-f, C-d, and <DEL>. Here are some commands for moving more rapidly about the line.
Notice how C-f moves forward a character, while M-f moves forward a word. It is a loose convention that control keystrokes operate on characters while meta keystrokes operate on words.
Killing text means to delete the text from the line, but to save it away for later use, usually by yanking (re-inserting) it back into the line. (`Cut' and `paste' are more recent jargon for `kill' and `yank'.)
If the description for a command says that it `kills' text, then you can be sure that you can get the text back in a different (or the same) place later.
When you use a kill command, the text is saved in a kill-ring. Any number of consecutive kills save all of the killed text together, so that when you yank it back, you get it all. The kill ring is not line specific; the text that you killed on a previously typed line is available to be yanked back later, when you are typing another line. Here is the list of commands for killing text.
Here is how to yank the text back into the line. Yanking means to copy the most-recently-killed text from the kill buffer.
You can pass numeric arguments to Readline commands. Sometimes the argument acts as a repeat count, other times it is the sign of the argument that is significant. If you pass a negative argument to a command which normally acts in a forward direction, that command will act in a backward direction. For example, to kill text back to the start of the line, you might type ‘M-- C-k’.
The general way to pass numeric arguments to a command is to type meta digits before the command. If the first `digit' typed is a minus sign (‘-’), then the sign of the argument will be negative. Once you have typed one meta digit to get the argument started, you can type the remainder of the digits, and then the command. For example, to give the C-d command an argument of 10, you could type ‘M-1 0 C-d’, which will delete the next ten characters on the input line.
Readline provides commands for searching through the command history for lines containing a specified string. There are two search modes: incremental and non-incremental.
Incremental searches begin before the user has finished typing the
search string.
As each character of the search string is typed, Readline displays
the next entry from the history matching the string typed so far.
An incremental search requires only as many characters as needed to
find the desired history entry.
To search backward in the history for a particular string, type
C-r. Typing C-s searches forward through the history.
The characters present in the value of the isearch-terminators
variable
are used to terminate an incremental search.
If that variable has not been assigned a value, the <ESC> and
C-J characters will terminate an incremental search.
C-g will abort an incremental search and restore the original line.
When the search is terminated, the history entry containing the
search string becomes the current line.
To find other matching entries in the history list, type C-r or C-s as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a Readline command will terminate the search and execute that command. For instance, a <RET> will terminate the search and accept the line, thereby executing the command from the history list. A movement command will terminate the search, make the last line found the current line, and begin editing.
Readline remembers the last incremental search string. If two C-rs are typed without any intervening characters defining a new search string, any remembered search string is used.
Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line.
Although the Readline library comes with a set of Emacs-like keybindings installed by default, it is possible to use a different set of keybindings. Any user can customize programs that use Readline by putting commands in an inputrc file, conventionally in his home directory. The name of this file is taken from the value of the environment variable INPUTRC. If that variable is unset, the default is ~/.inputrc. If that file does not exist or cannot be read, the ultimate default is /etc/inputrc.
When a program which uses the Readline library starts up, the init file is read, and the key bindings are set.
In addition, the C-x C-r
command re-reads this init file, thus
incorporating any changes that you might have made to it.
There are only a few basic constructs allowed in the Readline init file. Blank lines are ignored. Lines beginning with a ‘#’ are comments. Lines beginning with a ‘$’ indicate conditional constructs (see Conditional Init Constructs). Other lines denote variable settings and key bindings.
set
command within the init file.
The syntax is simple:
set variable value
Here, for example, is how to
change from the default Emacs-like key binding to use
vi
line editing commands:
set editing-mode vi
Variable names and values, where appropriate, are recognized without regard to case. Unrecognized variable names are ignored.
Boolean variables (those that can be set to on or off) are set to on if the value is null or empty, on (case-insensitive), or 1. Any other value results in the variable being set to off.
A great deal of run-time behavior is changeable with the following variables.
bell-style
bind-tty-special-chars
blink-matching-paren
colored-completion-prefix
colored-stats
comment-begin
insert-comment
command is executed. The default value
is "#"
.
completion-display-width
completion-ignore-case
completion-map-case
completion-prefix-display-length
completion-query-items
100
.
convert-meta
disable-completion
self-insert
. The default is ‘off’.
echo-control-characters
editing-mode
editing-mode
variable controls which default set of
key bindings is used. By default, Readline starts up in Emacs editing
mode, where the keystrokes are most similar to Emacs. This variable can be
set to either ‘emacs’ or ‘vi’.
emacs-mode-string
enable-bracketed-paste
enable-keypad
enable-meta-key
expand-tilde
history-preserve-point
previous-history
or next-history
. The default is ‘off’.
history-size
horizontal-scroll-mode
input-meta
meta-flag
is a synonym for this variable.
isearch-terminators
keymap
keymap
names are
emacs
,
emacs-standard
,
emacs-meta
,
emacs-ctlx
,
vi
,
vi-move
,
vi-command
, and
vi-insert
.
vi
is equivalent to vi-command
(vi-move
is also a
synonym); emacs
is equivalent to emacs-standard
.
Applications may add additional names.
The default value is emacs
.
The value of the editing-mode
variable also affects the
default keymap.
keyseq-timeout
rl_instream
by default).
The value is specified in milliseconds, so a value of 1000 means that
Readline will wait one second for additional input.
If this variable is set to a value less than or equal to zero, or to a
non-numeric value, Readline will wait until another key is pressed to
decide which key sequence to complete.
The default value is 500
.
mark-directories
mark-modified-lines
mark-symlinked-directories
mark-directories
).
The default is ‘off’.
match-hidden-files
menu-complete-display-prefix
output-meta
page-completions
more
-like pager
to display a screenful of possible completions at a time.
This variable is ‘on’ by default.
print-completions-horizontally
revert-all-at-newline
accept-line
is executed. By default,
history lines may be modified and retain individual undo lists across
calls to readline
. The default is ‘off’.
show-all-if-ambiguous
show-all-if-unmodified
show-mode-in-prompt
skip-completed-text
vi-cmd-mode-string
vi-ins-mode-string
visible-stats
Once you know the name of the command, simply place on a line in the init file the name of the key you wish to bind the command to, a colon, and then the name of the command. There can be no space between the key name and the colon – that will be interpreted as part of the key name. The name of the key can be expressed in different ways, depending on what you find most comfortable.
In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro).
Control-u: universal-argument Meta-Rubout: backward-kill-word Control-o: "> output"
In the example above, C-u is bound to the function
universal-argument
,
M-DEL is bound to the function backward-kill-word
, and
C-o is bound to run the macro
expressed on the right hand side (that is, to insert the text
‘> output’ into the line).
A number of symbolic character names are recognized while
processing this key binding syntax:
DEL,
ESC,
ESCAPE,
LFD,
NEWLINE,
RET,
RETURN,
RUBOUT,
SPACE,
SPC,
and
TAB.
"\C-u": universal-argument "\C-x\C-r": re-read-init-file "\e[11~": "Function Key 1"
In the above example, C-u is again bound to the function
universal-argument
(just as it was in the first example),
‘C-x C-r’ is bound to the function re-read-init-file
,
and ‘<ESC> <[> <1> <1> <~>’ is bound to insert
the text ‘Function Key 1’.
The following gnu Emacs style escape sequences are available when specifying key sequences:
In addition to the gnu Emacs style escape sequences, a second set of backslash escapes is available:
\a
\b
\d
\f
\n
\r
\t
\v
\
nnn\x
HHWhen entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including ‘"’ and ‘'’. For example, the following binding will make ‘C-x \’ insert a single ‘\’ into the line:
"\C-x\\": "\\"
Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be performed as the result of tests. There are four parser directives used.
$if
$if
construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
Readline. The text of the test, after any comparison operator,
extends to the end of the line;
unless otherwise noted, no characters are required to isolate it.
mode
mode=
form of the $if
directive is used to test
whether Readline is in emacs
or vi
mode.
This may be used in conjunction
with the ‘set keymap’ command, for instance, to set bindings in
the emacs-standard
and emacs-ctlx
keymaps only if
Readline is starting out in emacs
mode.
term
term=
form may be used to include terminal-specific
key bindings, perhaps to bind the key sequences output by the
terminal's function keys. The word on the right side of the
‘=’ is tested against both the full name of the terminal and
the portion of the terminal name before the first ‘-’. This
allows sun
to match both sun
and sun-cmd
,
for instance.
version
version
test may be used to perform comparisons against
specific Readline versions.
The version
expands to the current Readline version.
The set of comparison operators includes
‘=’ (and ‘==’), ‘!=’, ‘<=’, ‘>=’, ‘<’,
and ‘>’.
The version number supplied on the right side of the operator consists
of a major version number, an optional decimal point, and an optional
minor version (e.g., ‘7.1’). If the minor version is omitted, it
is assumed to be ‘0’.
The operator may be separated from the string version
and
from the version number argument by whitespace.
The following example sets a variable if the Readline version being used
is 7.0 or newer:
$if version >= 7.0 set show-mode-in-prompt on $endif
application
$if Bash # Quote the current or previous word "\C-xq": "\eb\"\ef\"" $endif
variable
mode=emacs
test described
above:
$if editing-mode == emacs set show-mode-in-prompt on $endif
$endif
$if
command.
$else
$if
directive are executed if
the test fails.
$include
$include /etc/inputrc
Here is an example of an inputrc file. This illustrates key binding, variable assignment, and conditional syntax.
# This file controls the behaviour of line input editing for # programs that use the GNU Readline library. Existing # programs include FTP, Bash, and GDB. # # You can re-read the inputrc file with C-x C-r. # Lines beginning with '#' are comments. # # First, include any system-wide bindings and variable # assignments from /etc/Inputrc $include /etc/Inputrc # # Set various bindings for emacs mode. set editing-mode emacs $if mode=emacs Meta-Control-h: backward-kill-word Text after the function name is ignored # # Arrow keys in keypad mode # #"\M-OD": backward-char #"\M-OC": forward-char #"\M-OA": previous-history #"\M-OB": next-history # # Arrow keys in ANSI mode # "\M-[D": backward-char "\M-[C": forward-char "\M-[A": previous-history "\M-[B": next-history # # Arrow keys in 8 bit keypad mode # #"\M-\C-OD": backward-char #"\M-\C-OC": forward-char #"\M-\C-OA": previous-history #"\M-\C-OB": next-history # # Arrow keys in 8 bit ANSI mode # #"\M-\C-[D": backward-char #"\M-\C-[C": forward-char #"\M-\C-[A": previous-history #"\M-\C-[B": next-history C-q: quoted-insert $endif # An old-style binding. This happens to be the default. TAB: complete # Macros that are convenient for shell interaction $if Bash # edit the path "\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f" # prepare to type a quoted word -- # insert open and close double quotes # and move to just after the open quote "\C-x\"": "\"\"\C-b" # insert a backslash (testing backslash escapes # in sequences and macros) "\C-x\\": "\\" # Quote the current or previous word "\C-xq": "\eb\"\ef\"" # Add a binding to refresh the line, which is unbound "\C-xr": redraw-current-line # Edit variable on current line. "\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y=" $endif # use a visible bell if one is available set bell-style visible # don't strip characters to 7 bits when reading set input-meta on # allow iso-latin1 characters to be inserted rather # than converted to prefix-meta sequences set convert-meta off # display characters with the eighth bit set directly # rather than as meta-prefixed characters set output-meta on # if there are more than 150 possible completions for # a word, ask the user if he wants to see all of them set completion-query-items 150 # For FTP $if Ftp "\C-xg": "get \M-?" "\C-xt": "put \M-?" "\M-.": yank-last-arg $endif
This section describes Readline commands that may be bound to key sequences. Command names without an accompanying key sequence are unbound by default.
In the following descriptions, point refers to the current cursor
position, and mark refers to a cursor position saved by the
set-mark
command.
The text between the point and mark is referred to as the region.
beginning-of-line (C-a)
end-of-line (C-e)
forward-char (C-f)
backward-char (C-b)
forward-word (M-f)
backward-word (M-b)
previous-screen-line ()
next-screen-line ()
clear-screen (C-l)
redraw-current-line ()
accept-line (Newline or Return)
add_history()
.
If this line is a modified history line, the history line is restored
to its original state.
previous-history (C-p)
next-history (C-n)
beginning-of-history (M-<)
end-of-history (M->)
reverse-search-history (C-r)
forward-search-history (C-s)
non-incremental-reverse-search-history (M-p)
non-incremental-forward-search-history (M-n)
history-search-forward ()
history-search-backward ()
history-substring-search-forward ()
history-substring-search-backward ()
yank-nth-arg (M-C-y)
yank-last-arg (M-. or M-_)
yank-nth-arg
.
Successive calls to yank-last-arg
move back through the history
list, inserting the last word (or the word specified by the argument to
the first call) of each line in turn.
Any numeric argument supplied to these successive calls determines
the direction to move through the history. A negative argument switches
the direction through the history (back or forward).
The history expansion facilities are used to extract the last argument,
as if the ‘!$’ history expansion had been specified.
(usually C-d)
stty
. If this character is read when there are no characters
on the line, and point is at the beginning of the line, Readline
interprets it as the end of input and returns eof.
delete-char (C-d)
backward-delete-char (Rubout)
forward-backward-delete-char ()
quoted-insert (C-q or C-v)
tab-insert (M-<TAB>)
self-insert (a, b, A, 1, !, ...)
bracketed-paste-begin ()
self-insert
instead of
executing any editing commands.
transpose-chars (C-t)
transpose-words (M-t)
upcase-word (M-u)
downcase-word (M-l)
capitalize-word (M-c)
overwrite-mode ()
emacs
mode; vi
mode does overwrite differently.
Each call to readline()
starts in insert mode.
In overwrite mode, characters bound to self-insert
replace
the text at point rather than pushing the text to the right.
Characters bound to backward-delete-char
replace the character
before point with a space.
By default, this command is unbound.
kill-line (C-k)
backward-kill-line (C-x Rubout)
unix-line-discard (C-u)
kill-whole-line ()
kill-word (M-d)
forward-word
.
backward-kill-word (M-<DEL>)
backward-word
.
unix-word-rubout (C-w)
unix-filename-rubout ()
delete-horizontal-space ()
kill-region ()
copy-region-as-kill ()
copy-backward-word ()
backward-word
.
By default, this command is unbound.
copy-forward-word ()
forward-word
.
By default, this command is unbound.
yank (C-y)
yank-pop (M-y)
yank
or yank-pop
.
digit-argument (
M-0,
M-1, ...
M--)
universal-argument ()
universal-argument
again ends the numeric argument, but is otherwise ignored.
As a special case, if this command is immediately followed by a
character that is neither a digit nor minus sign, the argument count
for the next command is multiplied by four.
The argument count is initially one, so executing this function the
first time makes the argument count four, a second time makes the
argument count sixteen, and so on.
By default, this is not bound to a key.
complete (<TAB>)
possible-completions (M-?)
completion-display-width
, the value of
the environment variable COLUMNS, or the screen width, in that order.
insert-completions (M-*)
possible-completions
.
menu-complete ()
complete
, but replaces the word to be completed
with a single match from the list of possible completions.
Repeated execution of menu-complete
steps through the list
of possible completions, inserting each match in turn.
At the end of the list of completions, the bell is rung
(subject to the setting of bell-style
)
and the original text is restored.
An argument of n moves n positions forward in the list
of matches; a negative argument may be used to move backward
through the list.
This command is intended to be bound to <TAB>, but is unbound
by default.
menu-complete-backward ()
menu-complete
, but moves backward through the list
of possible completions, as if menu-complete
had been given a
negative argument.
delete-char-or-list ()
delete-char
).
If at the end of the line, behaves identically to
possible-completions
.
This command is unbound by default.
start-kbd-macro (C-x ()
end-kbd-macro (C-x ))
call-last-kbd-macro (C-x e)
print-last-kbd-macro ()
re-read-init-file (C-x C-r)
abort (C-g)
bell-style
).
do-lowercase-version (M-A, M-B, M-
x, ...)
prefix-meta (<ESC>)
undo (C-_ or C-x C-u)
revert-line (M-r)
undo
command enough times to get back to the beginning.
tilde-expand (M-~)
set-mark (C-@)
exchange-point-and-mark (C-x C-x)
character-search (C-])
character-search-backward (M-C-])
skip-csi-sequence ()
insert-comment (M-#)
comment-begin
variable is inserted at the beginning of the current line.
If a numeric argument is supplied, this command acts as a toggle: if
the characters at the beginning of the line do not match the value
of comment-begin
, the value is inserted, otherwise
the characters in comment-begin
are deleted from the beginning of
the line.
In either case, the line is accepted as if a newline had been typed.
dump-functions ()
dump-variables ()
dump-macros ()
emacs-editing-mode (C-e)
vi
command mode, this causes a switch to emacs
editing mode.
vi-editing-mode (M-C-j)
emacs
editing mode, this causes a switch to vi
editing mode.
While the Readline library does not have a full set of vi
editing functions, it does contain enough to allow simple editing
of the line. The Readline vi
mode behaves as specified in
the posix standard.
In order to switch interactively between emacs
and vi
editing modes, use the command M-C-j (bound to emacs-editing-mode
when in vi
mode and to vi-editing-mode in emacs
mode).
The Readline default is emacs
mode.
When you enter a line in vi
mode, you are already placed in
`insertion' mode, as if you had typed an ‘i’. Pressing <ESC>
switches you into `command' mode, where you can edit the text of the
line with the standard vi
movement keys, move to previous
history lines with ‘k’ and subsequent lines with ‘j’, and
so forth.
This chapter describes how to use the gnu History Library interactively, from a user's standpoint. It should be considered a user's guide. For information on using the gnu History Library in your own programs, see Programming with GNU History.
The History library provides a history expansion feature that is similar
to the history expansion provided by csh
. This section
describes the syntax used to manipulate the history information.
History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current input line, or fix errors in previous commands quickly.
History expansion takes place in two parts. The first is to determine which line from the history list should be used during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is called the event, and the portions of that line that are acted upon are called words. Various modifiers are available to manipulate the selected words. The line is broken into words in the same fashion that Bash does, so that several words surrounded by quotes are considered one word. History expansions are introduced by the appearance of the history expansion character, which is ‘!’ by default.
History expansion implements shell-like quoting conventions: a backslash can be used to remove the special handling for the next character; single quotes enclose verbatim sequences of characters, and can be used to inhibit history expansion; and characters enclosed within double quotes may be subject to history expansion, since backslash can escape the history expansion character, but single quotes may not, since they are not treated specially within double quotes.
An event designator is a reference to a command line entry in the history list. Unless the reference is absolute, events are relative to the current position in the history list.
!
!
n!-
n!!
!
string!?
string[?]
^
string1^
string2^
!!:s/
string1/
string2/
.
!#
Word designators are used to select desired words from the event. A ‘:’ separates the event specification from the word designator. It may be omitted if the word designator begins with a ‘^’, ‘$’, ‘*’, ‘-’, or ‘%’. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.
For example,
!!
!!:$
!$
.
!fi:2
fi
.
Here are the word designators:
0 (zero)
0
th word. For many applications, this is the command word.
^
$
%
-
y*
0
th. This is a synonym for ‘1-$’.
It is not an error to use ‘*’ if there is just one word in the event;
the empty string is returned in that case.
*
-
If a word designator is supplied without an event specification, the previous command is used as the event.
After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a ‘:’.
h
t
r
e
p
s/
old/
new/
&
g
a
gs/
old/
new/
,
or with ‘&’.
G
The gdb project mourns the loss of the following long-time contributors:
Fred Fish
Michael Snyder
Beyond their technical contributions to the project, they were also enjoyable members of the Free Software Community. We will miss them.
The gdb 4 release includes an already-formatted reference card, ready for printing with PostScript or Ghostscript, in the gdb subdirectory of the main source directory18. If you can use PostScript or Ghostscript with your printer, you can print the reference card immediately with refcard.ps.
The release also includes the source for the reference card. You can format it, using TeX, by typing:
make refcard.dvi
The gdb reference card is designed to print in landscape mode on US “letter” size paper; that is, on a sheet 11 inches wide by 8.5 inches high. You will need to specify this form of printing as an option to your dvi output program.
All the documentation for gdb comes as part of the machine-readable
distribution. The documentation is written in Texinfo format, which is
a documentation system that uses a single source file to produce both
on-line information and a printed manual. You can use one of the Info
formatting commands to create the on-line version of the documentation
and TeX (or texi2roff
) to typeset the printed version.
gdb includes an already formatted copy of the on-line Info
version of this manual in the gdb subdirectory. The main Info
file is gdb-9.2 for GNAT Pro 22.0w/gdb/gdb.info, and it refers to
subordinate files matching ‘gdb.info*’ in the same directory. If
necessary, you can print out these files, or read them with any editor;
but they are easier to read using the info
subsystem in gnu
Emacs or the standalone info
program, available as part of the
gnu Texinfo distribution.
If you want to format these Info files yourself, you need one of the
Info formatting programs, such as texinfo-format-buffer
or
makeinfo
.
If you have makeinfo
installed, and are in the top level
gdb source directory (gdb-9.2 for GNAT Pro 22.0w, in the case of
version 9.2 for GNAT Pro 22.0w), you can make the Info file by typing:
cd gdb make gdb.info
If you want to typeset and print copies of this manual, you need TeX, a program to print its dvi output files, and texinfo.tex, the Texinfo definitions file.
TeX is a typesetting program; it does not print files directly, but produces output files called dvi files. To print a typeset document, you need a program to print dvi files. If your system has TeX installed, chances are it has such a program. The precise command to use depends on your system; lpr -d is common; another (for PostScript devices) is dvips. The dvi print command may require a file name without any extension or a ‘.dvi’ extension.
TeX also requires a macro definitions file called texinfo.tex. This file tells TeX how to typeset a document written in Texinfo format. On its own, TeX cannot either read or typeset a Texinfo file. texinfo.tex is distributed with GDB and is located in the gdb-version-number/texinfo directory.
If you have TeX and a dvi printer program installed, you can typeset and print this manual. First switch to the gdb subdirectory of the main source directory (for example, to gdb-9.2 for GNAT Pro 22.0w/gdb) and type:
make gdb.dvi
Then give gdb.dvi to your dvi printing program.
Building gdb requires various tools and packages to be available. Other packages will be used only if they are found.
make
will not work.
Expat is used for:
--with-guile
option to request Guile, and pass either the Guile
version number or the file name of the relevant pkg-config
program to choose a particular version of Guile.
iconv
implementation. If you are
on a GNU system, then this is provided by the GNU C Library. Some
other systems also provide a working iconv
.
If gdb is using the iconv
program which is installed
in a non-standard place, you will need to tell gdb where to
find it. This is done with --with-iconv-bin which specifies
the directory that contains the iconv
program. This program is
run in order to make a list of the available character sets.
On systems without iconv
, you can install GNU Libiconv. If
Libiconv is installed in a standard place, gdb will
automatically use it if it is needed. If you have previously
installed Libiconv in a non-standard place, you can use the
--with-libiconv-prefix option to configure.
gdb's top-level configure and Makefile will
arrange to build Libiconv if a directory named libiconv appears
in the top-most source directory. If Libiconv is built this way, and
if the operating system does not provide a suitable iconv
implementation, then the just-built library will automatically be used
by gdb. One easy way to set this up is to download GNU
Libiconv, unpack it inside the top-level directory of the gdb
source tree, and then rename the directory holding the Libiconv source
code to ‘libiconv’.
GNU MPFR is used to emulate target floating-point arithmetic during
expression evaluation when the target uses different floating-point
formats than the host. If GNU MPFR it is not available, gdb
will fall back to using host floating-point arithmetic.
--with-python
option to request Python, and pass either the
file name of the relevant python
executable, or the name of the
directory in which Python is installed, to choose a particular
installation of Python.
The ‘zlib’ library is likely included with your operating system distribution; if it is not, you can get the latest version from http://zlib.net.
gdb comes with a configure script that automates the process
of preparing gdb for installation; you can then use make
to
build the gdb
program.
The gdb distribution includes all the source code you need for gdb in a single directory, whose name is usually composed by appending the version number to ‘gdb’.
For example, the gdb version 9.2 for GNAT Pro 22.0w distribution is in the gdb-9.2 for GNAT Pro 22.0w directory. That directory contains:
gdb-9.2 for GNAT Pro 22.0w/configure
(and supporting files)gdb-9.2 for GNAT Pro 22.0w/gdb
gdb-9.2 for GNAT Pro 22.0w/bfd
gdb-9.2 for GNAT Pro 22.0w/include
gdb-9.2 for GNAT Pro 22.0w/libiberty
gdb-9.2 for GNAT Pro 22.0w/opcodes
gdb-9.2 for GNAT Pro 22.0w/readline
There may be other subdirectories as well.
The simplest way to configure and build gdb is to run configure from the gdb-version-number source directory, which in this example is the gdb-9.2 for GNAT Pro 22.0w directory.
First switch to the gdb-version-number source directory if you are not already in it; then run configure. Pass the identifier for the platform on which gdb will run as an argument.
For example:
cd gdb-9.2 for GNAT Pro 22.0w ./configure make
Running ‘configure’ and then running make
builds the
included supporting libraries, then gdb
itself. The configured
source files, and the binaries, are left in the corresponding source
directories.
configure is a Bourne-shell (/bin/sh
) script; if your
system does not recognize this automatically when you run a different
shell, you may need to run sh
on it explicitly:
sh configure
You should run the configure script from the top directory in the source tree, the gdb-version-number directory. If you run configure from one of the subdirectories, you will configure only that subdirectory. That is usually not what you want. In particular, if you run the first configure from the gdb subdirectory of the gdb-version-number directory, you will omit the configuration of bfd, readline, and other sibling directories of the gdb subdirectory. This leads to build errors about missing include files such as bfd/bfd.h.
You can install gdb anywhere. The best way to do this
is to pass the --prefix
option to configure
, and then
install it with make install
.
If you want to run gdb versions for several host or target machines,
you need a different gdb
compiled for each combination of
host and target. configure is designed to make this easy by
allowing you to generate each configuration in a separate subdirectory,
rather than in the source directory. If your make
program
handles the ‘VPATH’ feature (gnu make
does), running
make
in each of these directories builds the gdb
program specified there.
To build gdb
in a separate directory, run configure
with the ‘--srcdir’ option to specify where to find the source.
(You also need to specify a path to find configure
itself from your working directory. If the path to configure
would be the same as the argument to ‘--srcdir’, you can leave out
the ‘--srcdir’ option; it is assumed.)
For example, with version 9.2 for GNAT Pro 22.0w, you can build gdb in a separate directory for a Sun 4 like this:
cd gdb-9.2 for GNAT Pro 22.0w mkdir ../gdb-sun4 cd ../gdb-sun4 ../gdb-9.2 for GNAT Pro 22.0w/configure make
When configure builds a configuration using a remote source directory, it creates a tree for the binaries with the same structure (and using the same names) as the tree under the source directory. In the example, you'd find the Sun 4 library libiberty.a in the directory gdb-sun4/libiberty, and gdb itself in gdb-sun4/gdb.
Make sure that your path to the configure script has just one instance of gdb in it. If your path to configure looks like ../gdb-9.2 for GNAT Pro 22.0w/gdb/configure, you are configuring only one subdirectory of gdb, not the whole package. This leads to build errors about missing include files such as bfd/bfd.h.
One popular reason to build several gdb configurations in separate directories is to configure gdb for cross-compiling (where gdb runs on one machine—the host—while debugging programs that run on another machine—the target). You specify a cross-debugging target by giving the ‘--target=target’ option to configure.
When you run make
to build a program or library, you must run
it in a configured directory—whatever directory you were in when you
called configure (or one of its subdirectories).
The Makefile
that configure generates in each source
directory also runs recursively. If you type make
in a source
directory such as gdb-9.2 for GNAT Pro 22.0w (or in a separate configured
directory configured with ‘--srcdir=dirname/gdb-9.2 for GNAT Pro 22.0w’), you
will build all the required libraries, and then build GDB.
When you have multiple hosts or targets configured in separate
directories, you can run make
on them in parallel (for example,
if they are NFS-mounted on each of the hosts); they will not interfere
with each other.
The specifications used for hosts and targets in the configure script are based on a three-part naming scheme, but some short predefined aliases are also supported. The full naming scheme encodes three pieces of information in the following pattern:
architecture-vendor-os
For example, you can use the alias sun4
as a host argument,
or as the value for target in a --target=
target
option. The equivalent full name is ‘sparc-sun-sunos4’.
The configure script accompanying gdb does not provide
any query facility to list all supported host and target names or
aliases. configure calls the Bourne shell script
config.sub
to map abbreviations to full names; you can read the
script, if you wish, or you can use it to test your guesses on
abbreviations—for example:
% sh config.sub i386-linux i386-pc-linux-gnu % sh config.sub alpha-linux alpha-unknown-linux-gnu % sh config.sub hp9k700 hppa1.1-hp-hpux % sh config.sub sun4 sparc-sun-sunos4.1.1 % sh config.sub sun3 m68k-sun-sunos4.1.1 % sh config.sub i986v Invalid configuration `i986v': machine `i986v' not recognized
config.sub
is also distributed in the gdb source
directory (gdb-9.2 for GNAT Pro 22.0w, for version 9.2 for GNAT Pro 22.0w).
Here is a summary of the configure options and arguments that are most often useful for building gdb. configure also has several other options not listed here. see Running configure scripts, for a full explanation of configure.
configure [--help] [--prefix=dir] [--exec-prefix=dir] [--srcdir=dirname] [--target=target]
You may introduce options with a single ‘-’ rather than ‘--’ if you prefer; but you may abbreviate option names if you use ‘--’.
--help
--prefix=
dir--exec-prefix=
dir--srcdir=
dirname--target=
targetThere is no convenient way to generate a list of all available
targets. Also see the --enable-targets
option, below.
There are many other options that are specific to gdb. This lists just the most common ones; there are some very specialized options not described here.
--enable-targets=
[target]...
--enable-targets=all
--with-gdb-datadir=
path--datadir
).
--with-relocated-sources=
dir--prefix
or --exec-prefix
options to configure. This
option is useful if GDB is supposed to be moved to a different place
after it is built.
--enable-64-bit-bfd
--disable-gdbmi
--enable-tui
--with-curses
--with-libunwind-ia64
--with-system-readline
--with-system-zlib
--with-expat
--with-libiconv-prefix
[=
dir]iconv
that is built in to the C library is sufficient. If
your host does not have a working iconv
, you can get the latest
version of GNU iconv from `https://www.gnu.org/software/libiconv/'.
gdb's build system also supports building GNU libiconv as
part of the overall build. See Requirements.
--with-lzma
--with-mpfr
--with-python
[=
python]--with-guile[=GUILE]'
configure
to try to
use that version of Guile; or the file name of a pkg-config
executable, which will be queried to find the information needed to
compile and link against Guile.
--without-included-regex
--with-sysroot=
dir--prefix
or --exec-prefix options
, the
default system root will be automatically adjusted if and when
gdb is moved to a different location.
--with-system-gdbinit=
file--with-system-gdbinit-dir=
directory--enable-build-warnings
--enable-werror
-Werror
flag
to the compiler, which will fail the compilation if the compiler
outputs any warning messages.
--enable-ubsan
--enable-ubsan=yes
or
--enable-ubsan=auto
to configure
will enable it. The
undefined behavior sanitizer checks for C++ undefined behavior.
It has a performance cost, so if you are looking at gdb's
performance, you should disable it. The undefined behavior sanitizer
was first introduced in GCC 4.9.
gdb can be configured to have a system-wide init file and a system-wide init file directory; this file and files in that directory (if they have a recognized file extension) will be read and executed at startup (see What gdb does during startup).
Here are the corresponding configure options:
--with-system-gdbinit=
file--with-system-gdbinit-dir=
directoryIf gdb has been configured with the option --prefix=$prefix, they may be subject to relocation. Two possible cases:
If the configured location of the system-wide init file (as given by the
--with-system-gdbinit option at configure time) is in the
data-directory (as specified by --with-gdb-datadir at configure
time) or in one of its subdirectories, then gdb will look for the
system-wide init file in the directory specified by the
--data-directory command-line option.
Note that the system-wide init file is only read once, during gdb
initialization. If the data-directory is changed after gdb has
started with the set data-directory
command, the file will not be
reread.
This applies similarly to the system-wide directory specified in --with-system-gdbinit-dir.
Any supported scripting language can be used for these init files, as long as the file extension matches the scripting language. To be interpreted as regular gdb commands, the files needs to have a .gdb extension.
The system-gdbinit directory, located inside the data-directory (as specified by --with-gdb-datadir at configure time) contains a number of scripts which can be used as system-wide init files. To automatically source those scripts at startup, gdb should be configured with --with-system-gdbinit. Otherwise, any user should be able to source them by hand as needed.
The following scripts are currently available:
In addition to commands intended for gdb users, gdb includes a number of commands intended for gdb developers, that are not documented elsewhere in this manual. These commands are provided here for reference. (For commands that turn on debugging messages, see Debugging Output.)
maint agent
[-at
location,] expressionmaint agent-eval
[-at
location,] expressiongloba +
globb
will include bytecodes to record four bytes of memory at each
of the addresses of globa
and globb
, while discarding
the result of the addition, while an evaluation expression will do the
addition and return the sum.
If -at
is given, generate remote agent bytecode for location.
If not, generate remote agent bytecode for current frame PC address.
maint agent-printf
format,
expr,...
maint info breakpoints
breakpoint
watchpoint
longjmp
longjmp
calls.
longjmp resume
longjmp
.
until
until
command.
finish
finish
command.
shlib events
maint info btrace
maint btrace packet-history
bts
pt
maint btrace clear-packet-history
maint btrace clear
This implicitly truncates the branch trace to a single branch trace buffer. When updating branch trace incrementally, the branch trace available to gdb may be bigger than a single branch trace buffer.
maint set btrace pt skip-pad
maint show btrace pt skip-pad
set displaced-stepping
show displaced-stepping
set displaced-stepping on
set displaced-stepping off
set displaced-stepping auto
maint check-psymtabs
maint check-symtabs
maint expand-symtabs [
regexp]
maint set catch-demangler-crashes [on|off]
maint show catch-demangler-crashes
maint cplus first_component
namemaint cplus namespace
maint deprecate
command [replacement]maint undeprecate
commandmaint dump-me
SIGQUIT
signal.
maint internal-error
[message-text]maint internal-warning
[message-text]maint demangler-warning
[message-text]internal_error
,
internal_warning
or demangler_warning
and hence behave
as though an internal problem has been detected. In addition to
reporting the internal problem, these functions give the user the
opportunity to either quit gdb or (for internal_error
and internal_warning
) create a core file of the current
gdb session.
These commands take an optional parameter message-text that is used as the text of the error or warning message.
Here's an example of using internal-error
:
(gdb) maint internal-error testing, 1, 2 .../maint.c:121: internal-error: testing, 1, 2 A problem internal to GDB has been detected. Further debugging may prove unreliable. Quit this debugging session? (y or n) n Create a core file? (y or n) n (gdb)
maint set internal-error
action [ask|yes|no]
maint show internal-error
actionmaint set internal-warning
action [ask|yes|no]
maint show internal-warning
actionmaint set demangler-warning
action [ask|yes|no]
maint show demangler-warning
actioncorefile
option for demangler-warning
:
demangler warnings always create a core file and this cannot be
disabled.
maint packet
textmaint print architecture
[file]maint print c-tdesc
maint check xml-descriptions
dirmaint check libthread-db
libthread_db
functionality used by
gdb on GNU/Linux systems, and by extension also exercises the
proc_service
functions provided by gdb that
libthread_db
uses. Note that parts of the test may be skipped
on some platforms when debugging core files.
maint print dummy-frames
(gdb) b add ... (gdb) print add(2,3) Breakpoint 2, add (a=2, b=3) at ... 58 return (a + b); The program being debugged stopped while in a function called from GDB. ... (gdb) maint print dummy-frames 0xa8206d8: id={stack=0xbfffe734,code=0xbfffe73f,!special}, ptid=process 9353 (gdb)
Takes an optional file parameter.
maint print registers
[file]maint print raw-registers
[file]maint print cooked-registers
[file]maint print register-groups
[file]maint print remote-registers
[file]The command maint print raw-registers
includes the contents of
the raw register cache; the command maint print
cooked-registers
includes the (cooked) value of all registers,
including registers which aren't available on the target nor visible
to user; the command maint print register-groups
includes the
groups that each register is a member of; and the command maint
print remote-registers
includes the remote target's register numbers
and offsets in the `G' packets.
These commands take an optional parameter, a file name to which to write the information.
maint print reggroups
[file]The register groups info looks like this:
(gdb) maint print reggroups Group Type general user float user all user vector user system user save internal restore internal
flushregs
maint print objfiles
[regexp]maint print user-registers
$fp
, $pc
,
$sp
, and $ps
. See standard registers. User
registers can be used in expressions in the same way as the canonical
register names, but only the latter are listed by the info
registers
and maint print registers
commands.
maint print section-scripts [
regexp]
.debug_gdb_section
section.
If regexp is specified, only print scripts loaded by object files
matching regexp.
For each script, this command prints its name as specified in the objfile,
and the full path if known.
See dotdebug_gdb_scripts section.
maint print statistics
maint print target-stack
This command prints a short description of each layer that was pushed on the target stack, starting from the top layer down to the bottom one.
maint print type
exprmaint selftest
[filter]maint info selftests
maint set dwarf always-disassemble
maint show dwarf always-disassemble
info address
when using DWARF debugging
information.
The default is off
, which means that gdb should try to
describe a variable's location in an easily readable format. When
on
, gdb will instead display the DWARF location
expression in an assembly-like format. Note that some locations are
too complex for gdb to describe simply; in this case you will
always see the disassembly form.
Here is an example of the resulting disassembly:
(gdb) info addr argc Symbol "argc" is a complex DWARF expression: 1: DW_OP_fbreg 0
For more information on these expressions, see the DWARF standard.
maint set dwarf max-cache-age
maint show dwarf max-cache-age
In object files with inter-compilation-unit references, such as those produced by the GCC option ‘-feliminate-dwarf2-dups’, the DWARF reader needs to frequently refer to previously read compilation units. This setting controls how long a compilation unit will remain in the cache if it is not referenced. A higher limit means that cached compilation units will be stored in memory longer, and more total memory will be used. Setting it to zero disables caching, which will slow down gdb startup, but reduce memory consumption.
maint set dwarf unwinders
maint show dwarf unwinders
Many targets that support DWARF debugging use gdb's DWARF frame unwinders to build the backtrace. Many of these targets will also have a second mechanism for building the backtrace for use in cases where DWARF information is not available, this second mechanism is often an analysis of a function's prologue.
In order to extend testing coverage of the second level stack unwinding mechanisms it is helpful to be able to disable the DWARF stack unwinders, this can be done with this switch.
In normal use of gdb disabling the DWARF unwinders is not advisable, there are cases that are better handled through DWARF than prologue analysis, and the debug experience is likely to be better with the DWARF frame unwinders enabled.
If DWARF frame unwinders are not supported for a particular target architecture, then enabling this flag does not cause them to be used.
maint set worker-threads
maint show worker-threads
0
(disabled). A value of unlimited
lets gdb choose a
reasonable number. Note that this only controls worker threads started by
gdb itself; libraries used by gdb may start threads of their
own.
maint set profile
maint show profile
Profiling will be disabled until you use the ‘maint set profile’ command to enable it. When you enable profiling, the system will begin collecting timing and execution count data; when you disable profiling or exit gdb, the results will be written to a log file. Remember that if you use profiling, gdb will overwrite the profiling log file (often called gmon.out). If you have a record of important profiling data in a gmon.out file, be sure to move it to a safe location.
Configuring with ‘--enable-profiling’ arranges for gdb to be compiled with the ‘-pg’ compiler option.
maint set show-debug-regs
maint show show-debug-regs
on
to enable, off
to disable. If
enabled, the debug registers values are shown when gdb inserts or
removes a hardware breakpoint or watchpoint, and when the inferior
triggers a hardware-assisted breakpoint or watchpoint.
maint set show-all-tib
maint show show-all-tib
maint set target-async
maint show target-async
maint set target-non-stop
maint show target-non-stop
set non-stop
is off
(see Non-Stop Mode). The default is auto
, meaning non-stop mode is enabled
if supported by the target.
maint set target-non-stop auto
maint set target-non-stop on
maint set target-non-stop off
maint set tui-resize-message
maint show tui-resize-message
off
, which means
that gdb is silent during resizes. When on
,
gdb will display a message after a resize is completed; the
message will include a number indicating how many times the terminal
has been resized. This setting is intended for use by the test suite,
where it would otherwise be difficult to determine when a resize and
refresh has been completed.
maint set per-command
maint show per-command
maint set per-command space [on|off]
maint show per-command space
maint set per-command time [on|off]
maint show per-command time
maint set per-command symtab [on|off]
maint show per-command symtab
maint set check-libthread-db [on|off]
maint show check-libthread-db
maint space
valuemaint set per-command space
.
A non-zero value enables it, zero disables it.
maint time
valuemaint set per-command time
.
A non-zero value enables it, zero disables it.
maint translate-address
[section] addrinfo address
command (see Symbols), except that this
command also allows to find symbols in other sections.
If section was not specified, the section in which the symbol was found is also printed. For dynamically linked executables, the name of executable or shared library containing the symbol is printed as well.
maint test-options require-delimiter
maint test-options unknown-is-error
maint test-options unknown-is-operand
require-delimiter
variant requires a
double-dash delimiter to indicate end of options. The
unknown-is-error
and unknown-is-operand
do not. The
unknown-is-error
variant throws an error on unknown option,
while unknown-is-operand
treats unknown options as the start of
the command's operands. When run, the commands output the result of
the processed options. When completed, the commands store the
internal result of completion in a variable exposed by the maint
show test-options-completion-result
command.
maint show test-options-completion-result
maint test-options
subcommands. This is used by the testsuite to validate completion
support in the command options framework.
maint set test-settings
kindmaint show test-settings
kindmaint with
setting [
value] [--
command]
with
command, but works with maintenance set
variables. This is used by the testsuite to exercise the with
command's infrastructure.
The following command is useful for non-interactive invocations of gdb, such as in the test suite.
set watchdog
nsecshow watchdog
There may be occasions when you need to know something about the protocol—for example, if there is only one serial port to your target machine, you might want your program to do something special if it recognizes a packet meant for gdb.
In the examples below, ‘->’ and ‘<-’ are used to indicate transmitted and received data, respectively.
All gdb commands and responses (other than acknowledgments and notifications, see Notification Packets) are sent as a packet. A packet is introduced with the character ‘$’, the actual packet-data, and the terminating character ‘#’ followed by a two-digit checksum:
$
packet-data#
checksum
The two-digit checksum is computed as the modulo 256 sum of all characters between the leading ‘$’ and the trailing ‘#’ (an eight bit unsigned checksum).
Implementors should note that prior to gdb 5.0 the protocol specification also included an optional two-digit sequence-id:
$
sequence-id:
packet-data#
checksum
That sequence-id was appended to the acknowledgment. gdb has never output sequence-ids. Stubs that handle packets added since gdb 5.0 must not accept sequence-id.
When either the host or the target machine receives a packet, the first response expected is an acknowledgment: either ‘+’ (to indicate the package was received correctly) or ‘-’ (to request retransmission):
->$
packet-data#
checksum <-+
The ‘+’/‘-’ acknowledgments can be disabled once a connection is established. See Packet Acknowledgment, for details.
The host (gdb) sends commands, and the target (the debugging stub incorporated in your program) sends a response. In the case of step and continue commands, the response is only sent when the operation has completed, and the target has again stopped all threads in all attached processes. This is the default all-stop mode behavior, but the remote protocol also supports gdb's non-stop execution mode; see Remote Non-Stop, for details.
packet-data consists of a sequence of characters with the exception of ‘#’ and ‘$’ (see ‘X’ packet for additional exceptions).
Fields within the packet should be separated using ‘,’ ‘;’ or ‘:’. Except where otherwise noted all numbers are represented in hex with leading zeros suppressed.
Implementors should note that prior to gdb 5.0, the character ‘:’ could not appear as the third character in a packet (as it would potentially conflict with the sequence-id).
Binary data in most packets is encoded either as two hexadecimal digits per byte of binary data. This allowed the traditional remote protocol to work over connections which were only seven-bit clean. Some packets designed more recently assume an eight-bit clean connection, and use a more efficient encoding to send and receive binary data.
The binary data representation uses 7d
(ascii ‘}’)
as an escape character. Any escaped byte is transmitted as the escape
character followed by the original character XORed with 0x20
.
For example, the byte 0x7d
would be transmitted as the two
bytes 0x7d 0x5d
. The bytes 0x23
(ascii ‘#’),
0x24
(ascii ‘$’), and 0x7d
(ascii
‘}’) must always be escaped. Responses sent by the stub
must also escape 0x2a
(ascii ‘*’), so that it
is not interpreted as the start of a run-length encoded sequence
(described next).
Response data can be run-length encoded to save space.
Run-length encoding replaces runs of identical characters with one
instance of the repeated character, followed by a ‘*’ and a
repeat count. The repeat count is itself sent encoded, to avoid
binary characters in data: a value of n is sent as
n+29
. For a repeat count greater or equal to 3, this
produces a printable ascii character, e.g. a space (ascii
code 32) for a repeat count of 3. (This is because run-length
encoding starts to win for counts 3 or more.) Thus, for example,
‘0* ’ is a run-length encoding of “0000”: the space character
after ‘*’ means repeat the leading 0
32 - 29 = 3
more times.
The printable characters ‘#’ and ‘$’ or with a numeric value greater than 126 must not be used. Runs of six repeats (‘#’) or seven repeats (‘$’) can be expanded using a repeat count of only five (‘"’). For example, ‘00000000’ can be encoded as ‘0*"00’.
The error response returned for some packets includes a two character error number. That number is not well defined.
For any command not supported by the stub, an empty response (‘$#00’) should be returned. That way it is possible to extend the protocol. A newer gdb can tell if a packet is supported based on that response.
At a minimum, a stub is required to support the ‘g’ and ‘G’ commands for register access, and the ‘m’ and ‘M’ commands for memory access. Stubs that only control single-threaded targets can implement run control with the ‘c’ (continue), and ‘s’ (step) commands. Stubs that support multi-threading targets should support the ‘vCont’ command. All other commands are optional.
The following table provides a complete list of all currently defined commands and their corresponding response data. See File-I/O Remote Protocol Extension, for details about the File I/O extension of the remote protocol.
Each packet's description has a template showing the packet's overall syntax, followed by an explanation of the packet's meaning. We include spaces in some of the templates for clarity; these are not part of the packet's syntax. No gdb packet uses spaces to separate its components. For example, a template like ‘foo bar baz’ describes a packet beginning with the three ASCII bytes ‘foo’, followed by a bar, followed directly by a baz. gdb does not transmit a space character between the ‘foo’ and the bar, or between the bar and the baz.
Several packets and replies include a thread-id field to identify a thread. Normally these are positive numbers with a target-specific interpretation, formatted as big-endian hex strings. A thread-id can also be a literal ‘-1’ to indicate all threads, or ‘0’ to pick any thread.
In addition, the remote protocol supports a multiprocess feature in which the thread-id syntax is extended to optionally include both process and thread ID fields, as ‘ppid.tid’. The pid (process) and tid (thread) components each have the format described above: a positive number with target-specific interpretation formatted as a big-endian hex string, literal ‘-1’ to indicate all processes or threads (respectively), or ‘0’ to indicate an arbitrary process or thread. Specifying just a process, as ‘ppid’, is equivalent to ‘ppid.-1’. It is an error to specify all processes but a specific thread, such as ‘p-1.tid’. Note that the ‘p’ prefix is not used for those packets and replies explicitly documented to include a process ID, rather than a thread-id.
The multiprocess thread-id syntax extensions are only used if both gdb and the stub report support for the ‘multiprocess’ feature using ‘qSupported’. See multiprocess extensions, for more information.
Note that all packet forms beginning with an upper- or lower-case letter, other than those described here, are reserved for future use.
Here are the packet descriptions.
Reply:
Reply:
See Stop Reply Packets, for the reply specifications.
argv[]
array passed into program. arglen
specifies the number of bytes in the hex encoded byte stream
arg. See gdbserver
for more details.
Reply:
JTC: When does the transport layer state change? When it's received, or after the ACK is transmitted. In either case, there are problems if the command or the acknowledgment packet is dropped.
Stan: If people really wanted to add something like this, and get
it working for the first time, they ought to modify ser-unix.c to send
some kind of out-of-band message to a specially-setup stub and have the
switch happen "in between" packets, so that from remote protocol's point
of view, nothing actually happened.
Don't use this packet. Use the ‘Z’ and ‘z’ packets instead (see insert breakpoint or watchpoint packet).
Reply: See Stop Reply Packets, for the reply specifications.
Reply:
See Stop Reply Packets, for the reply specifications.
This packet is deprecated for multi-threading support. See vCont packet.
Reply:
See Stop Reply Packets, for the reply specifications.
This packet is deprecated for multi-threading support. See vCont packet.
Reply:
See Stop Reply Packets, for the reply specifications.
Don't use this packet; instead, define a general set packet
(see General Query Packets).
detach
command.
The second form, including a process ID, is used when multiprocess protocol extensions are enabled (see multiprocess extensions), to detach only a specific process. The pid is specified as a big-endian hex string.
Reply:
Reply:
DEPRECATED_REGISTER_RAW_SIZE
and gdbarch_register_name
.
When reading registers from a trace frame (see Using the Collected Data), the stub may also return a string of literal ‘x’'s in place of the register data digits, to indicate that the corresponding register has not been collected, thus its value is unavailable. For example, for an architecture with 4 registers of 4 bytes each, the following reply indicates to gdb that registers 0 and 2 have not been collected, while registers 1 and 3 have been collected, and both have zero value:
->g
<-xxxxxxxx00000000xxxxxxxx00000000
Reply:
Reply:
The exact effect of this packet is not specified.
For a bare-metal target, it may power cycle or reset the target system. For that reason, the ‘k’ packet has no reply.
For a single-process target, it may kill that process if possible.
A multiple-process target may choose to kill just one process, or all that are under gdb's control. For more precise control, use the vKill packet (see vKill packet).
If the target system immediately closes the connection in response to ‘k’, gdb does not consider the lack of packet acknowledgment to be an error, and assumes the kill was successful.
If connected using target extended-remote, and the target does
not close the connection in response to a kill request, gdb
probes the target state as if a new connection was opened
(see ? packet).
The stub need not use any particular size or alignment when gathering data from memory for the response; even if addr is word-aligned and length is a multiple of the word size, the stub is free to use byte accesses, or not. For this reason, this packet may not be suitable for accessing memory-mapped I/O devices. Reply:
Reply:
Reply:
Reply:
Don't use this packet; use the ‘R’ packet instead.
The ‘R’ packet has no reply.
This packet is deprecated for multi-threading support. See vCont packet.
Reply:
See Stop Reply Packets, for the reply specifications.
This packet is deprecated for multi-threading support. See vCont packet.
Reply:
See Stop Reply Packets, for the reply specifications.
Reply:
This packet is only available in extended mode (see extended mode).
Reply:
For each inferior thread, the leftmost action with a matching thread-id is applied. Threads that don't match any action remain in their current state. Thread IDs are specified using the syntax described in thread-id syntax. If multiprocess extensions (see multiprocess extensions) are supported, actions can be specified to match all threads in a process by using the ‘ppid.-1’ form of the thread-id. An action with no thread-id matches all threads. Specifying no actions is an error.
Currently supported actions are:
If the range is empty (start == end), then the action becomes equivalent to the ‘s’ action. In other words, single-step once, and report the stop (even if the stepped instruction jumps to start).
(A stop reply may be sent at any point even if the PC is still within the stepping range; for example, it is valid to implement this packet in a degenerate way as a single instruction step operation.)
The optional argument addr normally associated with the ‘c’, ‘C’, ‘s’, and ‘S’ packets is not supported in ‘vCont’.
The ‘t’ action is only relevant in non-stop mode (see Remote Non-Stop) and may be ignored by the stub otherwise. A stop reply should be generated for any affected thread not already stopped. When a thread is stopped by means of a ‘t’ action, the corresponding stop reply should indicate that the thread has stopped with signal ‘0’, regardless of whether the target uses some other signal as an implementation detail.
The server must ignore ‘c’, ‘C’, ‘s’, ‘S’, and ‘r’ actions for threads that are already running. Conversely, the server must ignore ‘t’ actions for threads that are already stopped.
Note: In non-stop mode, a thread is considered running until gdb acknowledges an asynchronous stop notification for it with the ‘vStopped’ packet (see Remote Non-Stop).
The stub must support ‘vCont’ if it reports support for multiprocess extensions (see multiprocess extensions).
Reply:
See Stop Reply Packets, for the reply specifications.
Reply:
^C
(‘\003’, the control-C character) character in all-stop mode
while the target is running, except this works in non-stop mode.
See interrupting remote targets, for more info on the all-stop
variant.
Reply:
Reply:
Reply:
Reply:
The ‘vMustReplyEmpty’ is used as a feature test to check how
gdbserver handles unknown packets, it is important that this
packet be handled in the same way as other unknown ‘v’ packets.
If this packet is handled differently to other unknown ‘v’
packets then it is possible that gdb may run into problems in
other areas, specifically around use of ‘vFile:setfs:’.
This packet is only available in extended mode (see extended mode).
Reply:
Reply:
Each breakpoint and watchpoint packet type is documented separately.
Implementation notes: A remote target shall return an empty string
for an unrecognized breakpoint or watchpoint packet type. A
remote target shall support either both or neither of a given
‘Ztype...’ and ‘ztype...’ packet pair. To
avoid potential problems with duplicate packets, the operations should
be implemented in an idempotent way.
A software breakpoint is implemented by replacing the instruction at addr with a software breakpoint or trap instruction. The kind is target-specific and typically indicates the size of the breakpoint in bytes that should be inserted. E.g., the arm and mips can insert either a 2 or 4 byte breakpoint. Some architectures have additional meanings for kind (see Architecture-Specific Protocol Details); if no architecture-specific value is being used, it should be ‘0’. kind is hex-encoded. cond_list is an optional list of conditional expressions in bytecode form that should be evaluated on the target's side. These are the conditions that should be taken into consideration when deciding if the breakpoint trigger should be reported back to gdb.
See also the ‘swbreak’ stop reason (see swbreak stop reason) for how to best report a software breakpoint event to gdb.
The cond_list parameter is comprised of a series of expressions, concatenated without separators. Each expression has the following form:
The optional cmd_list parameter introduces commands that may be run on the target, rather than being reported back to gdb. The parameter starts with a numeric flag persist; if the flag is nonzero, then the breakpoint may remain active and the commands continue to be run even when gdb disconnects from the target. Following this flag is a series of expressions concatenated with no separators. Each expression has the following form:
Implementation note: It is possible for a target to copy or move code that contains software breakpoints (e.g., when implementing overlays). The behavior of this packet, in the presence of such a target, is not defined.
Reply:
A hardware breakpoint is implemented using a mechanism that is not dependent on being able to modify the target's memory. The kind, cond_list, and cmd_list arguments have the same meaning as in ‘Z0’ packets.
Implementation note: A hardware breakpoint is not affected by code movement.
Reply:
Reply:
Reply:
Reply:
The ‘C’, ‘c’, ‘S’, ‘s’, ‘vCont’, ‘vAttach’, ‘vRun’, ‘vStopped’, and ‘?’ packets can receive any of the below as a reply. Except for ‘?’ and ‘vStopped’, that reply is only returned when the target halts. In the below the exact meaning of signal number is defined by the header include/gdb/signals.h in the gdb source code.
In non-stop mode, the server will simply reply ‘OK’ to commands such as ‘vCont’; any stop will be the subject of a future notification. See Remote Non-Stop.
As in the description of request packets, we include spaces in the reply templates for clarity; these are not part of the reply packet's syntax. No gdb stop reply packet uses spaces to separate its components.
The currently defined stop reasons are:
On some architectures, such as x86, at the architecture level, when a breakpoint instruction executes the program counter points at the breakpoint address plus an offset. On such targets, the stub is responsible for adjusting the PC to point back at the breakpoint address.
This packet should not be sent by default; older gdb versions did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see qSupported). The remote stub must also supply the appropriate ‘qSupported’ feature indicating support.
This packet is required for correct non-stop mode operation.
The same remarks about ‘qSupported’ and non-stop mode above apply.
fork
was called, and r
is the thread ID of the new child process. Refer to
thread-id syntax for the format of the thread-id
field. This packet is only applicable to targets that support
fork events.
This packet should not be sent by default; older gdb versions did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see qSupported). The remote stub must also supply the appropriate ‘qSupported’ feature indicating support.
vfork
was called, and r
is the thread ID of the new child process. Refer to
thread-id syntax for the format of the thread-id
field. This packet is only applicable to targets that support
vfork events.
This packet should not be sent by default; older gdb versions did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see qSupported). The remote stub must also supply the appropriate ‘qSupported’ feature indicating support.
exec
or terminated, so that the
address spaces of the parent and child process are no longer
shared. The r part is ignored. This packet is only
applicable to targets that support vforkdone events.
This packet should not be sent by default; older gdb versions did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see qSupported). The remote stub must also supply the appropriate ‘qSupported’ feature indicating support.
execve
was called, and r
is the absolute pathname of the file that was executed, in hex.
This packet is only applicable to targets that support exec events.
This packet should not be sent by default; older gdb versions did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see qSupported). The remote stub must also supply the appropriate ‘qSupported’ feature indicating support.
The second form of the response, including the process ID of the
exited process, can be used only when gdb has reported
support for multiprocess protocol extensions; see multiprocess extensions. Both AA and pid are formatted as big-endian
hex strings.
The second form of the response, including the process ID of the terminated process, can be used only when gdb has reported support for multiprocess protocol extensions; see multiprocess extensions. Both AA and pid are formatted as big-endian hex strings.
‘parameter...’ is a list of parameters as defined for this very system call.
The target replies with this packet when it expects gdb to call a host system call on behalf of the target. gdb replies with an appropriate ‘F’ packet and keeps up waiting for the next reply packet from the target. The latest ‘C’, ‘c’, ‘S’ or ‘s’ action is expected to be continued. See File-I/O Remote Protocol Extension, for more details.
Packets starting with ‘q’ are general query packets; packets starting with ‘Q’ are general set packets. General query and set packets are a semi-unified form for retrieving and sending information to and from the stub.
The initial letter of a query or set packet is followed by a name indicating what sort of thing the packet applies to. For example, gdb may use a ‘qSymbol’ packet to exchange symbol definitions with the stub. These packet names follow some conventions:
The name of a query or set packet should be separated from any parameters by a ‘:’; the parameters themselves should be separated by ‘,’ or ‘;’. Stubs must be careful to match the full packet name, and check for a separator or the end of the packet, in case two packet names share a common prefix. New packets should not begin with ‘qC’, ‘qP’, or ‘qL’19.
Like the descriptions of the other packets, each description here has a template showing the packet's overall syntax, followed by an explanation of the packet's meaning. We include spaces in some of the templates for clarity; these are not part of the packet's syntax. No gdb packet uses spaces to separate its components.
Here are the currently defined query and set packets:
Reply:
0xffffffff
is used to ensure leading zeros affect the CRC.
Note: This is the same CRC used in validating separate debug files (see Debugging Information in Separate Files). However the algorithm is slightly different. When validating separate debug files, the CRC is computed taking the least significant bit of each byte first, and the final result is inverted to detect trailing zeros.
Reply:
This packet is only available in extended mode (see extended mode).
Reply:
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This should only be done on targets that actually support disabling
address space randomization.
If value is ‘0’, gdbserver will not use a shell to start the inferior. If value is ‘1’, gdbserver will use a shell to start the inferior. All other values are considered an error.
This packet is only available in extended mode (see extended mode).
Reply:
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported). This should only be done on targets that actually support starting the inferior using a shell.
Use of this packet is controlled by the set startup-with-shell
command; see set startup-with-shell.
The packet is composed by hex-value, an hex encoded
representation of the name=value format representing an
environment variable. The name of the environment variable is
represented by name, and the value to be assigned to the
environment variable is represented by value. If the variable
has no value (i.e., the value is null
), then value will
not be present.
This packet is only available in extended mode (see extended mode).
Reply:
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported). This should only be done on targets that actually support passing environment variables to the starting inferior.
This packet is related to the set environment
command;
see set environment.
The packet is composed by hex-value, an hex encoded representation of the name of the environment variable to be unset.
This packet is only available in extended mode (see extended mode).
Reply:
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported). This should only be done on targets that actually support passing environment variables to the starting inferior.
This packet is related to the unset environment
command;
see unset environment.
This packet is only available in extended mode (see extended mode).
Reply:
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response
(see qSupported). This should only be done on targets that
actually support passing environment variables to the starting
inferior.
The packet is composed by directory, an hex encoded representation of the directory that the remote inferior will use as its current working directory. If directory is an empty string, the remote server should reset the inferior's current working directory to its original, empty value.
This packet is only available in extended mode (see extended mode).
Reply:
NOTE: This packet replaces the ‘qL’ query (see below).
Reply:
In response to each query, the target will reply with a list of one or more thread IDs, separated by commas. gdb will respond to each reply with a request for more thread ids (using the ‘qs’ form of the query), until the target responds with ‘l’ (lower-case ell, for last). Refer to thread-id syntax, for the format of the thread-id fields.
Note: gdb will send the qfThreadInfo
query during the
initial connection with the remote target, and the very first thread ID
mentioned in the reply will be stopped by gdb in a subsequent
message. Therefore, the stub should ensure that the first thread ID in
the qfThreadInfo
reply is suitable for being stopped by gdb.
thread-id is the thread ID associated with the thread for which to fetch the TLS address. See thread-id syntax.
offset is the (big endian, hex encoded) offset associated with the thread local variable. (This offset is obtained from the debug information associated with the variable.)
lm is the (big endian, hex encoded) OS/ABI-specific encoding of the load module associated with the thread local storage. For example, a gnu/Linux system will pass the link map address of the shared object associated with the thread local storage under consideration. Other operating environments may choose to represent the load module differently, so the precise meaning of this parameter will vary.
Reply:
thread-id is the thread ID associated with the thread.
Reply:
Don't use this packet; use the ‘qfThreadInfo’ query instead (see above).
Reply:
remote.c:parse_threadlist_response()
.
Reply:
Text
section by xxx from its original address.
Relocate the Data
section by yyy from its original address.
If the object file format provides segment information (e.g. elf
‘PT_LOAD’ program headers), gdb will relocate entire
segments by the supplied offsets.
Note: while a Bss
offset may be included in the response,
gdb ignores this and instead applies the Data
offset
to the Bss
section.
Don't use this packet; use the ‘qThreadExtraInfo’ query instead (see below).
Reply: see remote.c:remote_unpack_thread_info_response()
.
Reply:
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
Use of this packet is controlled by the set non-stop
command;
see Non-Stop Mode.
For ‘QCatchSyscalls:1’, each listed syscall sysno (encoded in hex) should be reported to gdb. If no syscall sysno is listed, every system call should be reported.
Note that if a syscall not in the list is reported, gdb will
still filter the event according to its own list from all corresponding
catch syscall
commands. However, it is more efficient to only
report the requested syscalls.
Multiple ‘QCatchSyscalls:1’ packets do not combine; any earlier ‘QCatchSyscalls:1’ list is completely replaced by the new list.
If the inferior process execs, the state of ‘QCatchSyscalls’ is kept for the new process too. On targets where exec may affect syscall numbers, for example with exec between 32 and 64-bit processes, the client should send a new packet with the new syscall list.
Reply:
Use of this packet is controlled by the set remote catch-syscalls
command (see set remote catch-syscalls).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
Reply:
Use of this packet is controlled by the set remote pass-signals
command (see set remote pass-signals).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
In some cases, the remote stub may need to decide whether to deliver a signal to the program or not without gdb involvement. One example of that is while detaching — the program's threads may have stopped for signals that haven't yet had a chance of being reported to gdb, and so the remote stub can use the signal list specified by this packet to know whether to deliver or ignore those pending signals.
This does not influence whether to deliver a signal as requested by a resumption packet (see vCont packet).
Signals are numbered identically to continue packets and stop replies (see Stop Reply Packets). Each signal list item should be strictly greater than the previous item. Multiple ‘QProgramSignals’ packets do not combine; any earlier ‘QProgramSignals’ list is completely replaced by the new list.
Reply:
Use of this packet is controlled by the set remote program-signals
command (see set remote program-signals).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
Reply:
Use of this packet is controlled by the set remote thread-events
command (see set remote thread-events).
Reply:
(Note that the qRcmd
packet's name is separated from the
command by a ‘,’, not a ‘:’, contrary to the naming
conventions above. Please don't use this packet as a model for new
packets.)
Reply:
Reply:
Reply:
The allowed forms for each feature (either a gdbfeature in the ‘qSupported’ packet, or a stubfeature in the response) are:
Whenever the stub receives a ‘qSupported’ request, the supplied set of gdb features should override any previous request. This allows gdb to put the stub in a known state, even if the stub had previously been communicating with a different version of gdb.
The following values of gdbfeature (for the packet sent by gdb) are defined:
Stubs should ignore any unknown values for gdbfeature. Any gdb which sends a ‘qSupported’ packet supports receiving packets of unlimited length (earlier versions of gdb may reject overly long responses). Additional values for gdbfeature may be defined in the future to let the stub take advantage of new features in gdb, e.g. incompatible improvements in the remote protocol—the ‘multiprocess’ feature is an example of such a feature. The stub's reply should be independent of the gdbfeature entries sent by gdb; first gdb describes all the features it supports, and then the stub replies with all the features it supports.
Similarly, gdb will silently ignore unrecognized stub feature responses, as long as each response uses one of the standard forms.
Some features are flags. A stub which supports a flag feature should respond with a ‘+’ form response. Other features require values, and the stub should respond with an ‘=’ form response.
Each feature has a default value, which gdb will use if ‘qSupported’ is not available or if the feature is not mentioned in the ‘qSupported’ response. The default values are fixed; a stub is free to omit any feature responses that match the defaults.
Not all features can be probed, but for those which can, the probing mechanism is useful: in some cases, a stub's internal architecture may not allow the protocol layer to know some information about the underlying target in advance. This is especially common in stubs which may be configured for multiple targets.
These are the currently defined stub features and their properties:
Feature Name | Value Required | Default | Probe Allowed
|
‘PacketSize’ | Yes | ‘-’ | No
|
‘qXfer:auxv:read’ | No | ‘-’ | Yes
|
‘qXfer:btrace:read’ | No | ‘-’ | Yes
|
‘qXfer:btrace-conf:read’ | No | ‘-’ | Yes
|
‘qXfer:exec-file:read’ | No | ‘-’ | Yes
|
‘qXfer:features:read’ | No | ‘-’ | Yes
|
‘qXfer:libraries:read’ | No | ‘-’ | Yes
|
‘qXfer:libraries-svr4:read’ | No | ‘-’ | Yes
|
‘augmented-libraries-svr4-read’ | No | ‘-’ | No
|
‘qXfer:memory-map:read’ | No | ‘-’ | Yes
|
‘qXfer:sdata:read’ | No | ‘-’ | Yes
|
‘qXfer:siginfo:read’ | No | ‘-’ | Yes
|
‘qXfer:siginfo:write’ | No | ‘-’ | Yes
|
‘qXfer:threads:read’ | No | ‘-’ | Yes
|
‘qXfer:traceframe-info:read’ | No | ‘-’ | Yes
|
‘qXfer:uib:read’ | No | ‘-’ | Yes
|
‘qXfer:fdpic:read’ | No | ‘-’ | Yes
|
‘Qbtrace:off’ | Yes | ‘-’ | Yes
|
‘Qbtrace:bts’ | Yes | ‘-’ | Yes
|
‘Qbtrace:pt’ | Yes | ‘-’ | Yes
|
‘Qbtrace-conf:bts:size’ | Yes | ‘-’ | Yes
|
‘Qbtrace-conf:pt:size’ | Yes | ‘-’ | Yes
|
‘QNonStop’ | No | ‘-’ | Yes
|
‘QCatchSyscalls’ | No | ‘-’ | Yes
|
‘QPassSignals’ | No | ‘-’ | Yes
|
‘QStartNoAckMode’ | No | ‘-’ | Yes
|
‘multiprocess’ | No | ‘-’ | No
|
‘ConditionalBreakpoints’ | No | ‘-’ | No
|
‘ConditionalTracepoints’ | No | ‘-’ | No
|
‘ReverseContinue’ | No | ‘-’ | No
|
‘ReverseStep’ | No | ‘-’ | No
|
‘TracepointSource’ | No | ‘-’ | No
|
‘QAgent’ | No | ‘-’ | No
|
‘QAllow’ | No | ‘-’ | No
|
‘QDisableRandomization’ | No | ‘-’ | No
|
‘EnableDisableTracepoints’ | No | ‘-’ | No
|
‘QTBuffer:size’ | No | ‘-’ | No
|
‘tracenz’ | No | ‘-’ | No
|
‘BreakpointCommands’ | No | ‘-’ | No
|
‘swbreak’ | No | ‘-’ | No
|
‘hwbreak’ | No | ‘-’ | No
|
‘fork-events’ | No | ‘-’ | No
|
‘vfork-events’ | No | ‘-’ | No
|
‘exec-events’ | No | ‘-’ | No
|
‘QThreadEvents’ | No | ‘-’ | No
|
‘no-resumed’ | No | ‘-’ | No
|
These are the currently defined stub features, in more detail:
Reply:
sym_name (hex encoded) is the name of a symbol whose value the target has previously requested.
sym_value (hex) is the value for symbol sym_name. If gdb cannot supply a value for sym_name, then this field will be empty.
Reply:
info threads
display. Some
examples of possible thread extra info strings are ‘Runnable’, or
‘Blocked on Mutex’.
Reply:
(Note that the qThreadExtraInfo
packet's name is separated from
the command by a ‘,’, not a ‘:’, contrary to the naming
conventions above. Please don't use this packet as a model for new
packets.)
Reply:
errno
value.
Here are the specific requests of this form defined so far. All the ‘qXfer:object:read:...’ requests use the same reply formats, listed above.
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
all
new
delta
If the trace buffer overflowed, returns an error indicating the overflow.
This packet is not probed by default; the remote stub must request it
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default; the remote stub must request it
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
Targets which maintain a list of libraries in the program's memory do not need to implement this packet; it is designed for platforms where the operating system manages the list of loaded libraries.
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is optional for better performance on SVR4 targets. gdb uses memory read packets to read the SVR4 library list otherwise.
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).
If the remote stub indicates it supports the augmented form of this packet then the annex part of the generic ‘qXfer’ packet may contain a semicolon-separated list of ‘name=value’ arguments. The currently supported arguments are:
start=
addressprev=
addressArguments that are not understood by the remote stub will be silently
ignored.
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response
(see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response
(see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
This packet is not probed by default.
loadmap
s on the target system. The
annex, either ‘exec’ or ‘interp’, specifies which loadmap
,
executable loadmap
or interpreter loadmap
to read.
This packet is not probed by default; the remote stub must request it,
by supplying an appropriate ‘qSupported’ response (see qSupported).
Reply:
errno
value.
Here are the specific requests of this form defined so far. All the ‘qXfer:object:write:...’ requests use the same reply formats, listed above.
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).
This query is used, for example, to know whether the remote process
should be detached or killed when a gdb session is ended with
the quit
command.
Reply:
Reply:
Reply:
Reply:
Reply:
Reply:
This section describes how the remote protocol is applied to specific target architectures. Also see Standard Target Features, for details of XML target descriptions for each architecture.
These breakpoint kinds are defined for the ‘Z0’ and ‘Z1’ packets.
The following g
/G
packets have previously been defined.
In the below, some thirty-two bit registers are transferred as
sixty-four bits. Those registers should be zero/sign extended (which?)
to fill the space allocated. Register bytes are transferred in target
byte order. The two nibbles within a register byte are transferred
most-significant – least-significant.
sr
). The ordering is the same
as MIPS32
.
These breakpoint kinds are defined for the ‘Z0’ and ‘Z1’ packets.
Here we describe the packets gdb uses to implement tracepoints (see Tracepoints).
Replies:
In the series of action packets for a given tracepoint, at most one can have an ‘S’ before its first action. If such a packet is sent, it and the following packets define “while-stepping” actions. Any prior packets define ordinary actions — that is, those taken when the tracepoint is first hit. If no action packet has an ‘S’, then all the packets in the series specify ordinary tracepoint actions.
The ‘action...’ portion of the packet is a series of actions, concatenated without separators. Each action has one of the following forms:
Any number of actions may be packed together in a single ‘QTDP’ packet, as long as the packet does not exceed the maximum packet length (400 bytes, for many stubs). There may be only one ‘R’ action per tracepoint, and it must precede any ‘M’ or ‘X’ actions. Any registers referred to by ‘M’ and ‘X’ actions must be collected by a preceding ‘R’ action. (The “while-stepping” actions are treated as if they were attached to a separate tracepoint, as far as these restrictions are concerned.)
Replies:
start is the offset of the bytes within the overall source string, while slen is the total length of the source string. This is intended for handling source strings that are longer than will fit in a single packet.
The available string types are ‘at’ for the location, ‘cond’ for the conditional, and ‘cmd’ for an action command. gdb sends a separate packet for each command in the action list, in the same order in which the commands are stored in the list.
The target does not need to do anything with source strings except report them back as part of the replies to the ‘qTfP’/‘qTsP’ query packets.
Although this packet is optional, and gdb will only send it
if the target replies with ‘TracepointSource’ See General Query Packets, it makes both disconnected tracing and trace files
much easier to use. Otherwise the user must be careful that the
tracepoints in effect while looking at trace frames are identical to
the ones in effect during the trace run; even a small discrepancy
could cause ‘tdump’ not to work, or a particular trace frame not
be found.
A successful reply from the stub indicates that the stub has found the requested frame. The response is a series of parts, concatenated without separators, describing the frame we selected. Each part has one of the following forms:
Replies:
gdb uses this to mark read-only regions of memory, like those
containing program code. Since these areas never change, they should
still have the same contents they did when the tracepoint was hit, so
there's no reason for the stub to refuse to provide their contents.
The reply has the form:
1
if the trace is presently
running, or 0
if not. It is followed by semicolon-separated
optional fields that an agent may use to report additional status.
If the trace is not running, the agent may report any of several explanations as one of the optional fields:
Additional optional fields supply statistical and other information. Although not required, they are extremely useful for users monitoring the progress of a trace run. If a trace has stopped, and these numbers are reported, they must reflect the state of the just-stopped trace.
1
means that the
trace buffer is circular and old trace frames will be discarded if
necessary to make room, 0
means that the trace buffer is linear
and may fill up.
1
means that
tracing will continue after gdb disconnects, 0
means
that the trace run will stop.
Replies:
while-stepping
steps are not counted as separate hits, but the
steps' space consumption is added into the usage number.
Replies:
qTfP
to get the first piece
of data, and multiple qTsP
to get additional pieces. Replies
to these packets generally take the form of the QTDP
packets
that define tracepoints. (FIXME add detailed syntax)
qTfV
to get the first vari of data,
and multiple qTsV
to get additional variables. Replies to
these packets follow the syntax of the QTDV
packets that define
trace state variables.
qTfSTM
to get the
first piece of data, and multiple qTsSTM
to get additional
pieces. Replies to these packets take the following form:
Reply:
The address is encoded in hex; id and extra are strings encoded in hex.
In response to each query, the target will reply with a list of one or
more markers, separated by commas. gdb will respond to each
reply with a request for more markers (using the ‘qs’ form of the
query), until the target responds with ‘l’ (lower-case ell, for
last).
qTsSTM
packets that list static
tracepoint markers.
l
indicates that no bytes are
available.
-1
tells the target to
use whatever size it prefers.
user
, notes
, and tstop
, the
text fields are arbitrary strings, hex-encoded.
When installing fast tracepoints in memory, the target may need to relocate the instruction currently at the tracepoint address to a different address in memory. For most instructions, a simple copy is enough, but, for example, call instructions that implicitly push the return address on the stack, and relative branches or other PC-relative instructions require offset adjustment, so that the effect of executing the instruction at a different address is the same as if it had executed in the original location.
In response to several of the tracepoint packets, the target may also respond with a number of intermediate ‘qRelocInsn’ request packets before the final result packet, to have gdb handle this relocation operation. If a packet supports this mechanism, its documentation will explicitly say so. See for example the above descriptions for the ‘QTStart’ and ‘QTDP’ packets. The format of the request is:
Replies:
The Host I/O packets allow gdb to perform I/O operations on the far side of a remote link. For example, Host I/O is used to upload and download files to a remote target with its own filesystem. Host I/O uses the same constant values and data structure layout as the target-initiated File-I/O protocol. However, the Host I/O packets are structured differently. The target-initiated protocol relies on target memory to store parameters and buffers. Host I/O requests are initiated by gdb, and the target's memory is not involved. See File-I/O Remote Protocol Extension, for more details on the target-initiated protocol.
The Host I/O request packets all encode a single operation along with its arguments. They have this format:
The valid responses to Host I/O packets are:
These are the supported Host I/O operations:
The data read should be returned as a binary attachment on success.
If zero bytes were read, the response should include an empty binary
attachment (i.e. a trailing semicolon). The return value is the
number of target bytes read; the binary attachment may be longer if
some characters were escaped.
write
system calls, there is no
separate count argument; the length of data in the
packet is used. ‘vFile:pwrite’ returns the number of bytes written,
which may be shorter than the length of data, or -1 if an
error occurred.
The data read should be returned as a binary attachment on success.
If zero bytes were read, the response should include an empty binary
attachment (i.e. a trailing semicolon). The return value is the
number of target bytes read; the binary attachment may be longer if
some characters were escaped.
vFile
operations with
filename arguments will operate. This is required for
gdb to be able to access files on remote targets where
the remote stub does not share a common filesystem with the
inferior(s).
If pid is nonzero, select the filesystem as seen by process
pid. If pid is zero, select the filesystem as seen by
the remote stub. Return 0 on success, or -1 if an error occurs.
If vFile:setfs:
indicates success, the selected filesystem
remains selected until the next successful vFile:setfs:
operation.
In all-stop mode, when a program on the remote target is running,
gdb may attempt to interrupt it by sending a ‘Ctrl-C’,
BREAK
or a BREAK
followed by g
, control of which
is specified via gdb's ‘interrupt-sequence’.
The precise meaning of BREAK
is defined by the transport
mechanism and may, in fact, be undefined. gdb does not
currently define a BREAK
mechanism for any of the network
interfaces except for TCP, in which case gdb sends the
telnet
BREAK sequence.
‘Ctrl-C’, on the other hand, is defined and implemented for all
transport mechanisms. It is represented by sending the single byte
0x03
without any of the usual packet overhead described in
the Overview section (see Overview). When a 0x03
byte is
transmitted as part of a packet, it is considered to be packet data
and does not represent an interrupt. E.g., an ‘X’ packet
(see X packet), used for binary downloads, may include an unescaped
0x03
as part of its packet.
BREAK
followed by g
is also known as Magic SysRq g.
When Linux kernel receives this sequence from serial port,
it stops execution and connects to gdb.
In non-stop mode, because packet resumptions are asynchronous
(see vCont packet), gdb is always free to send a remote
command to the remote stub, even when the target is running. For that
reason, gdb instead sends a regular packet (see vCtrlC packet) with the usual packet framing instead of the single byte
0x03
.
Stubs are not required to recognize these interrupt mechanisms and the precise meaning associated with receipt of the interrupt is implementation defined. If the target supports debugging of multiple threads and/or processes, it should attempt to interrupt all currently-executing threads and processes. If the stub is successful at interrupting the running program, it should send one of the stop reply packets (see Stop Reply Packets) to gdb as a result of successfully stopping the program in all-stop mode, and a stop reply for each stopped thread in non-stop mode. Interrupts received while the program is stopped are queued and the program will be interrupted when it is resumed next time.
The gdb remote serial protocol includes notifications, packets that require no acknowledgment. Both the GDB and the stub may send notifications (although the only notifications defined at present are sent by the stub). Notifications carry information without incurring the round-trip latency of an acknowledgment, and so are useful for low-impact communications where occasional packet loss is not a problem.
A notification packet has the form ‘% data # checksum’, where data is the content of the notification, and checksum is a checksum of data, computed and formatted as for ordinary gdb packets. A notification's data never contains ‘$’, ‘%’ or ‘#’ characters. Upon receiving a notification, the recipient sends no ‘+’ or ‘-’ to acknowledge the notification's receipt or to report its corruption.
Every notification's data begins with a name, which contains no colon characters, followed by a colon character.
Recipients should silently ignore corrupted notifications and notifications they do not understand. Recipients should restart timeout periods on receipt of a well-formed notification, whether or not they understand it.
Senders should only send the notifications described here when this protocol description specifies that they are permitted. In the future, we may extend the protocol to permit existing notifications in new contexts; this rule helps older senders avoid confusing newer recipients.
(Older versions of gdb ignore bytes received until they see the ‘$’ byte that begins an ordinary packet, so new stubs may transmit notifications without fear of confusing older clients. There are no notifications defined for gdb to send at the moment, but we assume that most older stubs would ignore them, as well.)
Each notification is comprised of three parts:
The purpose of an asynchronous notification mechanism is to report to gdb that something interesting happened in the remote stub.
The remote stub may send notification name:event at any time, but gdb acknowledges the notification when appropriate. The notification event is pending before gdb acknowledges. Only one notification at a time may be pending; if additional events occur before gdb has acknowledged the previous notification, they must be queued by the stub for later synchronous transmission in response to ack packets from gdb. Because the notification mechanism is unreliable, the stub is permitted to resend a notification if it believes gdb may not have received it.
Specifically, notifications may appear when gdb is not otherwise reading input from the stub, or when gdb is expecting to read a normal synchronous response or a ‘+’/‘-’ acknowledgment to a packet it has sent. Notification packets are distinct from any other communication from the stub so there is no ambiguity.
After receiving a notification, gdb shall acknowledge it by sending a ack packet as a regular, synchronous request to the stub. Such acknowledgment is not required to happen immediately, as gdb is permitted to send other, unrelated packets to the stub first, which the stub should process normally.
Upon receiving a ack packet, if the stub has other queued events to report to gdb, it shall respond by sending a normal event. gdb shall then send another ack packet to solicit further responses; again, it is permitted to send other, unrelated packets as well which the stub should process normally.
If the stub receives a ack packet and there are no additional event to report, the stub shall return an ‘OK’ response. At this point, gdb has finished processing a notification and the stub has completed sending any queued events. gdb won't accept any new notifications until the final ‘OK’ is received . If further notification events occur, the stub shall send a new notification, gdb shall accept the notification, and the process shall be repeated.
The process of asynchronous notification can be illustrated by the following example:
<-%Stop:T0505:98e7ffbf;04:4ce6ffbf;08:b1b6e54c;thread:p7526.7526;core:0;
...
->vStopped
<-T0505:68f37db7;04:40f37db7;08:63850408;thread:p7526.7528;core:0;
->vStopped
<-T0505:68e3fdb6;04:40e3fdb6;08:63850408;thread:p7526.7529;core:0;
->vStopped
<-OK
The following notifications are defined:
Notification | Ack | Event | Description
|
Stop | vStopped | reply. The reply has the form of a stop reply, as described in Stop Reply Packets. Refer to Remote Non-Stop, for information on how these notifications are acknowledged by gdb. | Report an asynchronous stop event in non-stop mode.
|
gdb's remote protocol supports non-stop debugging of multi-threaded programs, as described in Non-Stop Mode. If the stub supports non-stop mode, it should report that to gdb by including ‘QNonStop+’ in its ‘qSupported’ response (see qSupported).
gdb typically sends a ‘QNonStop’ packet only when establishing a new connection with the stub. Entering non-stop mode does not alter the state of any currently-running threads, but targets must stop all threads in any already-attached processes when entering all-stop mode. gdb uses the ‘?’ packet as necessary to probe the target state after a mode change.
In non-stop mode, when an attached process encounters an event that would otherwise be reported with a stop reply, it uses the asynchronous notification mechanism (see Notification Packets) to inform gdb. In contrast to all-stop mode, where all threads in all processes are stopped when a stop reply is sent, in non-stop mode only the thread reporting the stop event is stopped. That is, when reporting a ‘S’ or ‘T’ response to indicate completion of a step operation, hitting a breakpoint, or a fault, only the affected thread is stopped; any other still-running threads continue to run. When reporting a ‘W’ or ‘X’ response, all running threads belonging to other attached processes continue to run.
In non-stop mode, the target shall respond to the ‘?’ packet as follows. First, any incomplete stop reply notification/‘vStopped’ sequence in progress is abandoned. The target must begin a new sequence reporting stop events for all stopped threads, whether or not it has previously reported those events to gdb. The first stop reply is sent as a synchronous reply to the ‘?’ packet, and subsequent stop replies are sent as responses to ‘vStopped’ packets using the mechanism described above. The target must not send asynchronous stop reply notifications until the sequence is complete. If all threads are running when the target receives the ‘?’ packet, or if the target is not attached to any process, it shall respond ‘OK’.
If the stub supports non-stop mode, it should also support the ‘swbreak’ stop reason if software breakpoints are supported, and the ‘hwbreak’ stop reason if hardware breakpoints are supported (see swbreak stop reason). This is because given the asynchronous nature of non-stop mode, between the time a thread hits a breakpoint and the time the event is finally processed by gdb, the breakpoint may have already been removed from the target. Due to this, gdb needs to be able to tell whether a trap stop was caused by a delayed breakpoint event, which should be ignored, as opposed to a random trap signal, which should be reported to the user. Note the ‘swbreak’ feature implies that the target is responsible for adjusting the PC when a software breakpoint triggers, if necessary, such as on the x86 architecture.
By default, when either the host or the target machine receives a packet, the first response expected is an acknowledgment: either ‘+’ (to indicate the package was received correctly) or ‘-’ (to request retransmission). This mechanism allows the gdb remote protocol to operate over unreliable transport mechanisms, such as a serial line.
In cases where the transport mechanism is itself reliable (such as a pipe or TCP connection), the ‘+’/‘-’ acknowledgments are redundant. It may be desirable to disable them in that case to reduce communication overhead, or for other reasons. This can be accomplished by means of the ‘QStartNoAckMode’ packet; see QStartNoAckMode.
When in no-acknowledgment mode, neither the stub nor gdb shall send or expect ‘+’/‘-’ protocol acknowledgments. The packet and response format still includes the normal checksum, as described in Overview, but the checksum may be ignored by the receiver.
If the stub supports ‘QStartNoAckMode’ and prefers to operate in
no-acknowledgment mode, it should report that to gdb
by including ‘QStartNoAckMode+’ in its response to ‘qSupported’;
see qSupported.
If gdb also supports ‘QStartNoAckMode’ and it has not been
disabled via the set remote noack-packet off
command
(see Remote Configuration),
gdb may then send a ‘QStartNoAckMode’ packet to the stub.
Only then may the stub actually turn off packet acknowledgments.
gdb sends a final ‘+’ acknowledgment of the stub's ‘OK’
response, which can be safely ignored by the stub.
Note that set remote noack-packet
command only affects negotiation
between gdb and the stub when subsequent connections are made;
it does not affect the protocol acknowledgment state for any current
connection.
Since ‘+’/‘-’ acknowledgments are enabled by default when a
new connection is established,
there is also no protocol request to re-enable the acknowledgments
for the current connection, once disabled.
Example sequence of a target being re-started. Notice how the restart does not get any direct output:
->R00
<-+
target restarts ->?
<-+
<-T001:1234123412341234
->+
Example sequence of a target being stepped by a single instruction:
->G1445...
<-+
->s
<-+
time passes <-T001:1234123412341234
->+
->g
<-+
<-1455...
->+
The File I/O remote protocol extension (short: File-I/O) allows the target to use the host's file system and console I/O to perform various system calls. System calls on the target system are translated into a remote protocol packet to the host system, which then performs the needed actions and returns a response packet to the target system. This simulates file system operations even on targets that lack file systems.
The protocol is defined to be independent of both the host and target systems. It uses its own internal representation of datatypes and values. Both gdb and the target's gdb stub are responsible for translating the system-dependent value representations into the internal protocol representations when data is transmitted.
The communication is synchronous. A system call is possible only when gdb is waiting for a response from the ‘C’, ‘c’, ‘S’ or ‘s’ packets. While gdb handles the request for a system call, the target is stopped to allow deterministic access to the target's memory. Therefore File-I/O is not interruptible by target signals. On the other hand, it is possible to interrupt File-I/O by a user interrupt (‘Ctrl-C’) within gdb.
The target's request to perform a host system call does not finish the latest ‘C’, ‘c’, ‘S’ or ‘s’ action. That means, after finishing the system call, the target returns to continuing the previous activity (continue, step). No additional continue or step request from gdb is required.
(gdb) continue <- target requests 'system call X' target is stopped, gdb executes system call -> gdb returns result ... target continues, gdb returns to wait for the target <- target hits breakpoint and sends a Txx packet
The protocol only supports I/O on the console and to regular files on the host file system. Character or block special devices, pipes, named pipes, sockets or any other communication method on the host system are not supported by this protocol.
File I/O is not supported in non-stop mode.
The File-I/O protocol uses the F
packet as the request as well
as reply packet. Since a File-I/O system call can only occur when
gdb is waiting for a response from the continuing or stepping target,
the File-I/O request is a reply that gdb has to expect as a result
of a previous ‘C’, ‘c’, ‘S’ or ‘s’ packet.
This F
packet contains all information needed to allow gdb
to call the appropriate host system call:
At this point, gdb has to perform the following actions.
m
packet request. This additional communication has to be
expected by the target implementation and is handled as any other m
packet.
M
or X
packet. This packet has to be expected
by the target implementation and is handled as any other M
or X
packet.
Eventually gdb replies with another F
packet which contains all
necessary information for the target to continue. This at least contains
errno
, if has been changed by the system call.
After having done the needed type and value coercion, the target continues the latest continue or step action.
F
Request Packet
The F
request packet has the following format:
parameter... are the parameters to the system call. Parameters are hexadecimal integer values, either the actual values in case of scalar datatypes, pointers to target buffer space in case of compound datatypes and unspecified memory areas, or pointer/length pairs in case of string parameters. These are appended to the call-id as a comma-delimited list. All values are transmitted in ASCII string representation, pointer/length pairs separated by a slash.
F
Reply Packet
The F
reply packet has the following format:
errno is the errno
set by the call, in protocol-specific
representation.
This parameter can be omitted if the call was successful.
Ctrl-C flag is only sent if the user requested a break. In this case, errno must be sent as well, even if the call was successful. The Ctrl-C flag itself consists of the character ‘C’:
F0,0,C
or, if the call was interrupted before the host call has been performed:
F-1,4,C
assuming 4 is the protocol-specific representation of EINTR
.
If the ‘Ctrl-C’ flag is set in the gdb
reply packet (see The F Reply Packet),
the target should behave as if it had
gotten a break message. The meaning for the target is “system call
interrupted by SIGINT
”. Consequentially, the target should actually stop
(as with a break message) and return to gdb with a T02
packet.
It's important for the target to know in which state the system call was interrupted. There are two possible cases:
These two states can be distinguished by the target by the value of the
returned errno
. If it's the protocol representation of EINTR
, the system
call hasn't been performed. This is equivalent to the EINTR
handling
on POSIX systems. In any other case, the target may presume that the
system call has been finished — successfully or not — and should behave
as if the break message arrived right after the system call.
gdb must behave reliably. If the system call has not been called
yet, gdb may send the F
reply immediately, setting EINTR
as
errno
in the packet. If the system call on the host has been finished
before the user requests a break, the full action must be finished by
gdb. This requires sending M
or X
packets as necessary.
The F
packet may only be sent when either nothing has happened
or the full action has been completed.
By default and if not explicitly closed by the target system, the file
descriptors 0, 1 and 2 are connected to the gdb console. Output
on the gdb console is handled as any other file output operation
(write(1, ...)
or write(2, ...)
). Console input is handled
by gdb so that after the target read request from file descriptor
0 all following typing is buffered until either one of the following
conditions is met:
read
system call is treated as finished.
If the user has typed more characters than fit in the buffer given to
the read
call, the trailing characters are buffered in gdb until
either another read(0, ...)
is requested by the target, or debugging
is stopped at the user's request.
int open(const char *pathname, int flags); int open(const char *pathname, int flags, mode_t mode);
flags is the bitwise OR
of the following values:
O_CREAT
O_EXCL
O_CREAT
, if the file already exists it is
an error and open() fails.
O_TRUNC
O_RDWR
or O_WRONLY
is given) it will be
truncated to zero length.
O_APPEND
O_RDONLY
O_WRONLY
O_RDWR
Other bits are silently ignored.
mode is the bitwise OR
of the following values:
S_IRUSR
S_IWUSR
S_IRGRP
S_IWGRP
S_IROTH
S_IWOTH
Other bits are silently ignored.
open
returns the new file descriptor or -1 if an error
occurred.
EEXIST
O_CREAT
and O_EXCL
were used.
EISDIR
EACCES
ENAMETOOLONG
ENOENT
ENODEV
EROFS
EFAULT
ENOSPC
EMFILE
ENFILE
EINTR
int close(int fd);
close
returns zero on success, or -1 if an error occurred.
EBADF
EINTR
int read(int fd, void *buf, unsigned int count);
EBADF
EFAULT
EINTR
int write(int fd, const void *buf, unsigned int count);
EBADF
EFAULT
EFBIG
ENOSPC
EINTR
long lseek (int fd, long offset, int flag);
flag is one of:
SEEK_SET
SEEK_CUR
SEEK_END
EBADF
ESPIPE
EINVAL
EINTR
int rename(const char *oldpath, const char *newpath);
EISDIR
EEXIST
EBUSY
EINVAL
ENOTDIR
EFAULT
EACCES
ENAMETOOLONG
ENOENT
EROFS
ENOSPC
EINTR
int unlink(const char *pathname);
EACCES
EPERM
EBUSY
EFAULT
ENAMETOOLONG
ENOENT
ENOTDIR
EROFS
EINTR
int stat(const char *pathname, struct stat *buf); int fstat(int fd, struct stat *buf);
EBADF
ENOENT
ENOTDIR
EFAULT
EACCES
ENAMETOOLONG
EINTR
int gettimeofday(struct timeval *tv, void *tz);
EINVAL
EFAULT
int isatty(int fd);
EINTR
Note that the isatty
call is treated as a special case: it returns
1 to the target if the file descriptor is attached
to the gdb console, 0 otherwise. Implementing through system calls
would require implementing ioctl
and would be more complex than
needed.
int system(const char *command);
system
return value by calling WEXITSTATUS(retval)
. In case
/bin/sh could not be executed, 127 is returned.
EINTR
gdb takes over the full task of calling the necessary host calls
to perform the system
call. The return value of system
on
the host is simplified before it's returned
to the target. Any termination signal information from the child process
is discarded, and the return value consists
entirely of the exit status of the called command.
Due to security concerns, the system
call is by default refused
by gdb. The user has to allow this call explicitly with the
set remote system-call-allowed 1
command.
set remote system-call-allowed
system
calls in the File I/O
protocol for the remote target. The default is zero (disabled).
show remote system-call-allowed
system
calls are allowed in the File I/O
protocol.
The integral datatypes used in the system calls are int
,
unsigned int
, long
, unsigned long
,
mode_t
, and time_t
.
int
, unsigned int
, mode_t
and time_t
are
implemented as 32 bit values in this protocol.
long
and unsigned long
are implemented as 64 bit types.
See Limits, for corresponding MIN and MAX values (similar to those in limits.h) to allow range checking on host and target.
time_t
datatypes are defined as seconds since the Epoch.
All integral datatypes transferred as part of a memory read or write of a
structured datatype e.g. a struct stat
have to be given in big endian
byte order.
Pointers to target data are transmitted as they are. An exception is made for pointers to buffers for which the length isn't transmitted as part of the function call, namely strings. Strings are transmitted as a pointer/length pair, both as hex values, e.g.
1aaf/12
which is a pointer to data of length 18 bytes at position 0x1aaf.
The length is defined as the full string length in bytes, including
the trailing null byte. For example, the string "hello world"
at address 0x123456 is transmitted as
123456/d
Structured data which is transferred using a memory read or write (for
example, a struct stat
) is expected to be in a protocol-specific format
with all scalar multibyte datatypes being big endian. Translation to
this representation needs to be done both by the target before the F
packet is sent, and by gdb before
it transfers memory to the target. Transferred pointers to structured
data should point to the already-coerced data at any time.
The buffer of type struct stat
used by the target and gdb
is defined as follows:
struct stat { unsigned int st_dev; /* device */ unsigned int st_ino; /* inode */ mode_t st_mode; /* protection */ unsigned int st_nlink; /* number of hard links */ unsigned int st_uid; /* user ID of owner */ unsigned int st_gid; /* group ID of owner */ unsigned int st_rdev; /* device type (if inode device) */ unsigned long st_size; /* total size, in bytes */ unsigned long st_blksize; /* blocksize for filesystem I/O */ unsigned long st_blocks; /* number of blocks allocated */ time_t st_atime; /* time of last access */ time_t st_mtime; /* time of last modification */ time_t st_ctime; /* time of last change */ };
The integral datatypes conform to the definitions given in the appropriate section (see Integral Datatypes, for details) so this structure is of size 64 bytes.
The values of several fields have a restricted meaning and/or range of values.
st_dev
st_ino
st_mode
st_uid
st_gid
st_rdev
st_atime
st_mtime
st_ctime
The target gets a struct stat
of the above representation and is
responsible for coercing it to the target representation before
continuing.
Note that due to size differences between the host, target, and protocol
representations of struct stat
members, these members could eventually
get truncated on the target.
The buffer of type struct timeval
used by the File-I/O protocol
is defined as follows:
struct timeval { time_t tv_sec; /* second */ long tv_usec; /* microsecond */ };
The integral datatypes conform to the definitions given in the appropriate section (see Integral Datatypes, for details) so this structure is of size 8 bytes.
The following values are used for the constants inside of the protocol. gdb and target are responsible for translating these values before and after the call as needed.
All values are given in hexadecimal representation.
O_RDONLY 0x0 O_WRONLY 0x1 O_RDWR 0x2 O_APPEND 0x8 O_CREAT 0x200 O_TRUNC 0x400 O_EXCL 0x800
All values are given in octal representation.
S_IFREG 0100000 S_IFDIR 040000 S_IRUSR 0400 S_IWUSR 0200 S_IXUSR 0100 S_IRGRP 040 S_IWGRP 020 S_IXGRP 010 S_IROTH 04 S_IWOTH 02 S_IXOTH 01
All values are given in decimal representation.
EPERM 1 ENOENT 2 EINTR 4 EBADF 9 EACCES 13 EFAULT 14 EBUSY 16 EEXIST 17 ENODEV 19 ENOTDIR 20 EISDIR 21 EINVAL 22 ENFILE 23 EMFILE 24 EFBIG 27 ENOSPC 28 ESPIPE 29 EROFS 30 ENAMETOOLONG 91 EUNKNOWN 9999
EUNKNOWN
is used as a fallback error value if a host system returns
any error value not in the list of supported error numbers.
SEEK_SET 0 SEEK_CUR 1 SEEK_END 2
All values are given in decimal representation.
INT_MIN -2147483648 INT_MAX 2147483647 UINT_MAX 4294967295 LONG_MIN -9223372036854775808 LONG_MAX 9223372036854775807 ULONG_MAX 18446744073709551615
Example sequence of a write call, file descriptor 3, buffer is at target address 0x1234, 6 bytes should be written:
<-Fwrite,3,1234,6
request memory read from target ->m1234,6
<- XXXXXX return "6 bytes written" ->F6
Example sequence of a read call, file descriptor 3, buffer is at target address 0x1234, 6 bytes should be read:
<-Fread,3,1234,6
request memory write to target ->X1234,6:XXXXXX
return "6 bytes read" ->F6
Example sequence of a read call, call fails on the host due to invalid
file descriptor (EBADF
):
<-Fread,3,1234,6
->F-1,9
Example sequence of a read call, user presses Ctrl-c before syscall on host is called:
<-Fread,3,1234,6
->F-1,4,C
<-T02
Example sequence of a read call, user presses Ctrl-c after syscall on host is called:
<-Fread,3,1234,6
->X1234,6:XXXXXX
<-T02
On some platforms, a dynamic loader (e.g. ld.so) runs in the same process as your application to manage libraries. In this case, gdb can use the loader's symbol table and normal memory operations to maintain a list of shared libraries. On other platforms, the operating system manages loaded libraries. gdb can not retrieve the list of currently loaded libraries through memory operations, so it uses the ‘qXfer:libraries:read’ packet (see qXfer library list read) instead. The remote stub queries the target's operating system and reports which libraries are loaded.
The ‘qXfer:libraries:read’ packet returns an XML document which lists loaded libraries and their offsets. Each library has an associated name and one or more segment or section base addresses, which report where the library was loaded in memory.
For the common case of libraries that are fully linked binaries, the library should have a list of segments. If the target supports dynamic linking of a relocatable object file, its library XML element should instead include a list of allocated sections. The segment or section bases are start addresses, not relocation offsets; they do not depend on the library's link-time base addresses.
gdb must be linked with the Expat library to support XML library lists. See Expat.
A simple memory map, with one loaded library relocated by a single offset, looks like this:
<library-list> <library name="/lib/libc.so.6"> <segment address="0x10000000"/> </library> </library-list>
Another simple memory map, with one loaded library with three allocated sections (.text, .data, .bss), looks like this:
<library-list> <library name="sharedlib.o"> <section address="0x10000000"/> <section address="0x20000000"/> <section address="0x30000000"/> </library> </library-list>
The format of a library list is described by this DTD:
<!-- library-list: Root element with versioning --> <!ELEMENT library-list (library)*> <!ATTLIST library-list version CDATA #FIXED "1.0"> <!ELEMENT library (segment*, section*)> <!ATTLIST library name CDATA #REQUIRED> <!ELEMENT segment EMPTY> <!ATTLIST segment address CDATA #REQUIRED> <!ELEMENT section EMPTY> <!ATTLIST section address CDATA #REQUIRED>
In addition, segments and section descriptors cannot be mixed within a single library element, and you must supply at least one segment or section for each library.
On SVR4 platforms gdb can use the symbol table of a dynamic loader (e.g. ld.so) and normal memory operations to maintain a list of shared libraries. Still a special library list provided by this packet is more efficient for the gdb remote protocol.
The ‘qXfer:libraries-svr4:read’ packet returns an XML document which lists loaded libraries and their SVR4 linker parameters. For each library on SVR4 target, the following parameters are reported:
name
, the absolute file name from the l_name
field of
struct link_map
.
lm
with address of struct link_map
used for TLS
(Thread Local Storage) access.
l_addr
, the displacement as read from the field l_addr
of
struct link_map
. For prelinked libraries this is not an absolute
memory address. It is a displacement of absolute memory address against
address the file was prelinked to during the library load.
l_ld
, which is memory address of the PT_DYNAMIC
segment
Additionally the single main-lm
attribute specifies address of
struct link_map
used for the main executable. This parameter is used
for TLS access and its presence is optional.
gdb must be linked with the Expat library to support XML SVR4 library lists. See Expat.
A simple memory map, with two loaded libraries (which do not use prelink), looks like this:
<library-list-svr4 version="1.0" main-lm="0xe4f8f8"> <library name="/lib/ld-linux.so.2" lm="0xe4f51c" l_addr="0xe2d000" l_ld="0xe4eefc"/> <library name="/lib/libc.so.6" lm="0xe4fbe8" l_addr="0x154000" l_ld="0x152350"/> </library-list-svr>
The format of an SVR4 library list is described by this DTD:
<!-- library-list-svr4: Root element with versioning --> <!ELEMENT library-list-svr4 (library)*> <!ATTLIST library-list-svr4 version CDATA #FIXED "1.0"> <!ATTLIST library-list-svr4 main-lm CDATA #IMPLIED> <!ELEMENT library EMPTY> <!ATTLIST library name CDATA #REQUIRED> <!ATTLIST library lm CDATA #REQUIRED> <!ATTLIST library l_addr CDATA #REQUIRED> <!ATTLIST library l_ld CDATA #REQUIRED>
To be able to write into flash memory, gdb needs to obtain a memory map from the target. This section describes the format of the memory map.
The memory map is obtained using the ‘qXfer:memory-map:read’ (see qXfer memory map read) packet and is an XML document that lists memory regions.
gdb must be linked with the Expat library to support XML memory maps. See Expat.
The top-level structure of the document is shown below:
<?xml version="1.0"?> <!DOCTYPE memory-map PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN" "http://sourceware.org/gdb/gdb-memory-map.dtd"> <memory-map> region... </memory-map>
Each region can be either:
<memory type="ram" start="addr" length="length"/>
<memory type="rom" start="addr" length="length"/>
<memory type="flash" start="addr" length="length"> <property name="blocksize">blocksize</property> </memory>
Regions must not overlap. gdb assumes that areas of memory not covered by the memory map are RAM, and uses the ordinary ‘M’ and ‘X’ packets to write to addresses in such ranges.
The formal DTD for memory map format is given below:
<!-- ................................................... --> <!-- Memory Map XML DTD ................................ --> <!-- File: memory-map.dtd .............................. --> <!-- .................................... .............. --> <!-- memory-map.dtd --> <!-- memory-map: Root element with versioning --> <!ELEMENT memory-map (memory)*> <!ATTLIST memory-map version CDATA #FIXED "1.0.0"> <!ELEMENT memory (property)*> <!-- memory: Specifies a memory region, and its type, or device. --> <!ATTLIST memory type (ram|rom|flash) #REQUIRED start CDATA #REQUIRED length CDATA #REQUIRED> <!-- property: Generic attribute tag --> <!ELEMENT property (#PCDATA | property)*> <!ATTLIST property name (blocksize) #REQUIRED>
To efficiently update the list of threads and their attributes, gdb issues the ‘qXfer:threads:read’ packet (see qXfer threads read) and obtains the XML document with the following structure:
<?xml version="1.0"?> <threads> <thread id="id" core="0" name="name"> ... description ... </thread> </threads>
Each ‘thread’ element must have the ‘id’ attribute that identifies the thread (see thread-id syntax). The ‘core’ attribute, if present, specifies which processor core the thread was last executing on. The ‘name’ attribute, if present, specifies the human-readable name of the thread. The content of the of ‘thread’ element is interpreted as human-readable auxiliary information. The ‘handle’ attribute, if present, is a hex encoded representation of the thread handle.
To be able to know which objects in the inferior can be examined when inspecting a tracepoint hit, gdb needs to obtain the list of memory ranges, registers and trace state variables that have been collected in a traceframe.
This list is obtained using the ‘qXfer:traceframe-info:read’ (see qXfer traceframe info read) packet and is an XML document.
gdb must be linked with the Expat library to support XML traceframe info discovery. See Expat.
The top-level structure of the document is shown below:
<?xml version="1.0"?> <!DOCTYPE traceframe-info PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN" "http://sourceware.org/gdb/gdb-traceframe-info.dtd"> <traceframe-info> block... </traceframe-info>
Each traceframe block can be either:
<memory start="addr" length="length"/>
<tvar id="number"/>
The formal DTD for the traceframe info format is given below:
<!ELEMENT traceframe-info (memory | tvar)* > <!ATTLIST traceframe-info version CDATA #FIXED "1.0"> <!ELEMENT memory EMPTY> <!ATTLIST memory start CDATA #REQUIRED length CDATA #REQUIRED> <!ELEMENT tvar> <!ATTLIST tvar id CDATA #REQUIRED>
In order to display the branch trace of an inferior thread, gdb needs to obtain the list of branches. This list is represented as list of sequential code blocks that are connected via branches. The code in each block has been executed sequentially.
This list is obtained using the ‘qXfer:btrace:read’ (see qXfer btrace read) packet and is an XML document.
gdb must be linked with the Expat library to support XML traceframe info discovery. See Expat.
The top-level structure of the document is shown below:
<?xml version="1.0"?> <!DOCTYPE btrace PUBLIC "+//IDN gnu.org//DTD GDB Branch Trace V1.0//EN" "http://sourceware.org/gdb/gdb-btrace.dtd"> <btrace> block... </btrace>
<block begin="begin" end="end"/>
The formal DTD for the branch trace format is given below:
<!ELEMENT btrace (block* | pt) > <!ATTLIST btrace version CDATA #FIXED "1.0"> <!ELEMENT block EMPTY> <!ATTLIST block begin CDATA #REQUIRED end CDATA #REQUIRED> <!ELEMENT pt (pt-config?, raw?)> <!ELEMENT pt-config (cpu?)> <!ELEMENT cpu EMPTY> <!ATTLIST cpu vendor CDATA #REQUIRED family CDATA #REQUIRED model CDATA #REQUIRED stepping CDATA #REQUIRED> <!ELEMENT raw (#PCDATA)>
For each inferior thread, gdb can obtain the branch trace configuration using the ‘qXfer:btrace-conf:read’ (see qXfer btrace-conf read) packet.
The configuration describes the branch trace format and configuration settings for that format. The following information is described:
bts
size
pt
size
gdb must be linked with the Expat library to support XML branch trace configuration discovery. See Expat.
The formal DTD for the branch trace configuration format is given below:
<!ELEMENT btrace-conf (bts?, pt?)> <!ATTLIST btrace-conf version CDATA #FIXED "1.0"> <!ELEMENT bts EMPTY> <!ATTLIST bts size CDATA #IMPLIED> <!ELEMENT pt EMPTY> <!ATTLIST pt size CDATA #IMPLIED>
In some applications, it is not feasible for the debugger to interrupt the program's execution long enough for the developer to learn anything helpful about its behavior. If the program's correctness depends on its real-time behavior, delays introduced by a debugger might cause the program to fail, even when the code itself is correct. It is useful to be able to observe the program's behavior without interrupting it.
Using GDB's trace
and collect
commands, the user can
specify locations in the program, and arbitrary expressions to evaluate
when those locations are reached. Later, using the tfind
command, she can examine the values those expressions had when the
program hit the trace points. The expressions may also denote objects
in memory — structures or arrays, for example — whose values GDB
should record; while visiting a particular tracepoint, the user may
inspect those objects as if they were in memory at that moment.
However, because GDB records these values without interacting with the
user, it can do so quickly and unobtrusively, hopefully not disturbing
the program's behavior.
When GDB is debugging a remote target, the GDB agent code running on the target computes the values of the expressions itself. To avoid having a full symbolic expression evaluator on the agent, GDB translates expressions in the source language into a simpler bytecode language, and then sends the bytecode to the agent; the agent then executes the bytecode, and records the values for GDB to retrieve later.
The bytecode language is simple; there are forty-odd opcodes, the bulk of which are the usual vocabulary of C operands (addition, subtraction, shifts, and so on) and various sizes of literals and memory reference operations. The bytecode interpreter operates strictly on machine-level values — various sizes of integers and floating point numbers — and requires no information about types or symbols; thus, the interpreter's internal data structures are simple, and each bytecode requires only a few native machine instructions to implement it. The interpreter is small, and strict limits on the memory and time required to evaluate an expression are easy to determine, making it suitable for use by the debugging agent in real-time applications.
The agent represents bytecode expressions as an array of bytes. Each
instruction is one byte long (thus the term bytecode). Some
instructions are followed by operand bytes; for example, the goto
instruction is followed by a destination for the jump.
The bytecode interpreter is a stack-based machine; most instructions pop their operands off the stack, perform some operation, and push the result back on the stack for the next instruction to consume. Each element of the stack may contain either a integer or a floating point value; these values are as many bits wide as the largest integer that can be directly manipulated in the source language. Stack elements carry no record of their type; bytecode could push a value as an integer, then pop it as a floating point value. However, GDB will not generate code which does this. In C, one might define the type of a stack element as follows:
union agent_val { LONGEST l; DOUBLEST d; };
where LONGEST
and DOUBLEST
are typedef
names for
the largest integer and floating point types on the machine.
By the time the bytecode interpreter reaches the end of the expression,
the value of the expression should be the only value left on the stack.
For tracing applications, trace
bytecodes in the expression will
have recorded the necessary data, and the value on the stack may be
discarded. For other applications, like conditional breakpoints, the
value may be useful.
Separate from the stack, the interpreter has two registers:
pc
start
goto
and if_goto
instructions.
There are no instructions to perform side effects on the running program, or call the program's functions; we assume that these expressions are only used for unobtrusive debugging, not for patching the running code.
Most bytecode instructions do not distinguish between the various sizes of values, and operate on full-width values; the upper bits of the values are simply ignored, since they do not usually make a difference to the value computed. The exceptions to this rule are:
ref
n)ext
instruction
exists for this purpose.
ext
n)If the interpreter is unable to evaluate an expression completely for some reason (a memory location is inaccessible, or a divisor is zero, for example), we say that interpretation “terminates with an error”. This means that the problem is reported back to the interpreter's caller in some helpful way. In general, code using agent expressions should assume that they may attempt to divide by zero, fetch arbitrary memory locations, and misbehave in other ways.
Even complicated C expressions compile to a few bytecode instructions;
for example, the expression x + y * z
would typically produce
code like the following, assuming that x
and y
live in
registers, and z
is a global variable holding a 32-bit
int
:
reg 1 reg 2 const32 address of z ref32 ext 32 mul add end
In detail, these mean:
reg 1
x
) onto the
stack.
reg 2
y
).
const32
address of zz
onto the stack.
ref32
z
with z
's value.
ext 32
z
is a signed integer.
mul
y * z
.
add
x + y * z
.
end
Each bytecode description has the following form:
add
(0x02): a b ⇒ a+bIn this example, add
is the name of the bytecode, and
(0x02)
is the one-byte value used to encode the bytecode, in
hexadecimal. The phrase “a b ⇒ a+b” shows
the stack before and after the bytecode executes. Beforehand, the stack
must contain at least two values, a and b; since the top of
the stack is to the right, b is on the top of the stack, and
a is underneath it. After execution, the bytecode will have
popped a and b from the stack, and replaced them with a
single value, a+b. There may be other values on the stack below
those shown, but the bytecode affects only those shown.
Here is another example:
const8
(0x22) n: ⇒ nIn this example, the bytecode const8
takes an operand n
directly from the bytecode stream; the operand follows the const8
bytecode itself. We write any such operands immediately after the name
of the bytecode, before the colon, and describe the exact encoding of
the operand in the bytecode stream in the body of the bytecode
description.
For the const8
bytecode, there are no stack items given before
the ⇒; this simply means that the bytecode consumes no values
from the stack. If a bytecode consumes no values, or produces no
values, the list on either side of the ⇒ may be empty.
If a value is written as a, b, or n, then the bytecode treats it as an integer. If a value is written is addr, then the bytecode treats it as an address.
We do not fully describe the floating point operations here; although this design can be extended in a clean way to handle floating point values, they are not of immediate interest to the customer, so we avoid describing them, to save time.
float
(0x01): ⇒add
(0x02): a b ⇒ a+bsub
(0x03): a b ⇒ a-bmul
(0x04): a b ⇒ a*bdiv_signed
(0x05): a b ⇒ a/bdiv_unsigned
(0x06): a b ⇒ a/brem_signed
(0x07): a b ⇒ a modulo brem_unsigned
(0x08): a b ⇒ a modulo blsh
(0x09): a b ⇒ a<<brsh_signed
(0x0a): a b ⇒ (signed)
a>>brsh_unsigned
(0x0b): a b ⇒ a>>blog_not
(0x0e): a ⇒ !abit_and
(0x0f): a b ⇒ a&band
.
bit_or
(0x10): a b ⇒ a|bor
.
bit_xor
(0x11): a b ⇒ a^bor
.
bit_not
(0x12): a ⇒ ~aequal
(0x13): a b ⇒ a=bless_signed
(0x14): a b ⇒ a<bless_unsigned
(0x15): a b ⇒ a<bext
(0x16) n: a ⇒ a, sign-extended from n bitsThe number of source bits to preserve, n, is encoded as a single
byte unsigned integer following the ext
bytecode.
zero_ext
(0x2a) n: a ⇒ a, zero-extended from n bitsThe number of source bits to preserve, n, is encoded as a single
byte unsigned integer following the zero_ext
bytecode.
ref8
(0x17): addr ⇒ aref16
(0x18): addr ⇒ aref32
(0x19): addr ⇒ aref64
(0x1a): addr ⇒ aref
n, fetch an n-bit value from addr, using the
natural target endianness. Push the fetched value as an unsigned
integer.
Note that addr may not be aligned in any particular way; the
ref
n bytecodes should operate correctly for any address.
If attempting to access memory at addr would cause a processor
exception of some sort, terminate with an error.
ref_float
(0x1b): addr ⇒ dref_double
(0x1c): addr ⇒ dref_long_double
(0x1d): addr ⇒ dl_to_d
(0x1e): a ⇒ dd_to_l
(0x1f): d ⇒ adup
(0x28): a => a aswap
(0x2b): a b => b apop
(0x29): a =>pick
(0x32) n: a ... b => a ... b adup
; if n is one, it copies
the item under the top item, etc. If n exceeds the number of
items on the stack, terminate with an error.
rot
(0x33): a b c => c a bif_goto
(0x20) offset: a ⇒pc
register to start
+ offset.
Thus, an offset of zero denotes the beginning of the expression.
The offset is stored as a sixteen-bit unsigned value, stored
immediately following the if_goto
bytecode. It is always stored
most significant byte first, regardless of the target's normal
endianness. The offset is not guaranteed to fall at any particular
alignment within the bytecode stream; thus, on machines where fetching a
16-bit on an unaligned address raises an exception, you should fetch the
offset one byte at a time.
goto
(0x21) offset: ⇒pc
register to start
+ offset.
The offset is stored in the same way as for the if_goto
bytecode.
const8
(0x22) n: ⇒ nconst16
(0x23) n: ⇒ nconst32
(0x24) n: ⇒ nconst64
(0x25) n: ⇒ next
bytecode.
The constant n is stored in the appropriate number of bytes
following the const
b bytecode. The constant n is
always stored most significant byte first, regardless of the target's
normal endianness. The constant is not guaranteed to fall at any
particular alignment within the bytecode stream; thus, on machines where
fetching a 16-bit on an unaligned address raises an exception, you
should fetch n one byte at a time.
reg
(0x26) n: ⇒ aThe register number n is encoded as a 16-bit unsigned integer
immediately following the reg
bytecode. It is always stored most
significant byte first, regardless of the target's normal endianness.
The register number is not guaranteed to fall at any particular
alignment within the bytecode stream; thus, on machines where fetching a
16-bit on an unaligned address raises an exception, you should fetch the
register number one byte at a time.
getv
(0x2c) n: ⇒ vThe variable number n is encoded as a 16-bit unsigned integer
immediately following the getv
bytecode. It is always stored most
significant byte first, regardless of the target's normal endianness.
The variable number is not guaranteed to fall at any particular
alignment within the bytecode stream; thus, on machines where fetching a
16-bit on an unaligned address raises an exception, you should fetch the
register number one byte at a time.
setv
(0x2d) n: v ⇒ vgetv
.
trace
(0x0c): addr size ⇒trace_quick
(0x0d) size: addr ⇒ addrtrace
opcode.
This bytecode is equivalent to the sequence dup const8
size
trace
, but we provide it anyway to save space in bytecode strings.
trace16
(0x30) size: addr ⇒ addrtrace_quick16
, for consistency.
tracev
(0x2e) n: ⇒ agetv
.
tracenz
(0x2f) addr size ⇒printf
(0x34) numargs string ⇒printf
).
The value of numargs is the number of arguments to expect on the
stack, while string is the format string, prefixed with a
two-byte length. The last byte of the string must be zero, and is
included in the length. The format string includes escaped sequences
just as it appears in C source, so for instance the format string
"\t%d\n"
is six characters long, and the output will consist of
a tab character, a decimal number, and a newline. At the top of the
stack, above the values to be printed, this bytecode will pop a
“function” and “channel”. If the function is nonzero, then the
target may treat it as a function and call it, passing the channel as
a first argument, as with the C function fprintf
. If the
function is zero, then the target may simply call a standard formatted
print function of its choice. In all, this bytecode pops 2 +
numargs stack elements, and pushes nothing.
end
(0x27): ⇒Agent expressions can be used in several different ways by gdb, and the debugger can generate different bytecode sequences as appropriate.
One possibility is to do expression evaluation on the target rather than the host, such as for the conditional of a conditional tracepoint. In such a case, gdb compiles the source expression into a bytecode sequence that simply gets values from registers or memory, does arithmetic, and returns a result.
Another way to use agent expressions is for tracepoint data
collection. gdb generates a different bytecode sequence for
collection; in addition to bytecodes that do the calculation,
gdb adds trace
bytecodes to save the pieces of
memory that were used.
Some targets don't support floating-point, and some would rather not
have to deal with long long
operations. Also, different targets
will have different stack sizes, and different bytecode buffer lengths.
Thus, GDB needs a way to ask the target about itself. We haven't worked out the details yet, but in general, GDB should be able to send the target a packet asking it to describe itself. The reply should be a packet whose length is explicit, so we can add new information to the packet in future revisions of the agent, without confusing old versions of GDB, and it should contain a version number. It should contain at least the following information:
long long
is supported
Some of the design decisions apparent above are arguable.
First, note that you don't need different bytecodes for different operand sizes. You can generate code without knowing how big the stack elements actually are on the target. If the target only supports 32-bit ints, and you don't send any 64-bit bytecodes, everything just works. The observation here is that the MIPS and the Alpha have only fixed-size registers, and you can still get C's semantics even though most instructions only operate on full-sized words. You just need to make sure everything is properly sign-extended at the right times. So there is no need for 32- and 64-bit variants of the bytecodes. Just implement everything using the largest size you support.
GDB should certainly check to see what sizes the target supports, so the
user can get an error earlier, rather than later. But this information
is not necessary for correctness.
>
or <=
operators?less_
opcodes with log_not
, and swap the order
of the operands, yielding all four asymmetrical comparison operators.
For example, (x <= y)
is ! (x > y)
, which is ! (y <
x)
.
log_not
?ext
?zero_ext
?log_not
is equivalent to const8 0 equal
; it's used in half
the relational operators.
ext
n is equivalent to const8
s-n lsh const8
s-n rsh_signed
, where s is the size of the stack elements;
it follows ref
m and reg bytecodes when the value
should be signed. See the next bulleted item.
zero_ext
n is equivalent to const
m mask
log_and
; it's used whenever we push the value of a register, because we
can't assume the upper bits of the register aren't garbage.
ref
operators?ref
operators, and we
need the ext
bytecode anyway for accessing bitfields.
ref
operators?ref
operators again, and
const32
address ref32
is only one byte longer.
ref
n operators have to support unaligned fetches?In particular, structure bitfields may be several bytes long, but follow no alignment rules; members of packed structures are not necessarily aligned either.
In general, there are many cases where unaligned references occur in
correct C code, either at the programmer's explicit request, or at the
compiler's discretion. Thus, it is simpler to make the GDB agent
bytecodes work correctly in all circumstances than to make GDB guess in
each case whether the compiler did the usual thing.
goto
ops PC-relative?goto
ops?Suppose we have multiple branch ops with different offset sizes. As I generate code left-to-right, all my jumps are forward jumps (there are no loops in expressions), so I never know the target when I emit the jump opcode. Thus, I have to either always assume the largest offset size, or do jump relaxation on the code after I generate it, which seems like a big waste of time.
I can imagine a reasonable expression being longer than 256 bytes. I can't imagine one being longer than 64k. Thus, we need 16-bit offsets. This kind of reasoning is so bogus, but relaxation is pathetic.
The other approach would be to generate code right-to-left. Then I'd
always know my offset size. That might be fun.
reg
bytecode take a 16-bit register number?trace
and trace_quick
?x->y->z
, the agent must record the values of x
and
x->y
as well as the value of x->y->z
.
trace
bytecodes make the interpreter less general?trace
bytecodes, they don't get in
its way.
trace_quick
consume its arguments the way everything else does?trace_quick
is a kludge to save space; it
only exists so we needn't write dup const8
SIZE trace
before every memory reference. Therefore, it's okay for it not to
consume its arguments; it's meant for a specific context in which we
know exactly what it should do with the stack. If we're going to have a
kludge, it should be an effective kludge.
trace16
exist?dup const16
size trace
in those cases.
Whatever we decide to do with trace16
, we should at least leave
opcode 0x30 reserved, to remain compatible with the customer who added
it.
One of the challenges of using gdb to debug embedded systems is that there are so many minor variants of each processor architecture in use. It is common practice for vendors to start with a standard processor core — ARM, PowerPC, or MIPS, for example — and then make changes to adapt it to a particular market niche. Some architectures have hundreds of variants, available from dozens of vendors. This leads to a number of problems:
To address these problems, the gdb remote protocol allows a target system to not only identify itself to gdb, but to actually describe its own features. This lets gdb support processor variants it has never seen before — to the extent that the descriptions are accurate, and that gdb understands them.
gdb must be linked with the Expat library to support XML target descriptions. See Expat.
Target descriptions can be read from the target automatically, or specified by the user manually. The default behavior is to read the description from the target. gdb retrieves it via the remote protocol using ‘qXfer’ requests (see qXfer). The annex in the ‘qXfer’ packet will be ‘target.xml’. The contents of the ‘target.xml’ annex are an XML document, of the form described in Target Description Format.
Alternatively, you can specify a file to read for the target description. If a file is set, the target will not be queried. The commands to specify a file are:
set tdesc filename
pathunset tdesc filename
show tdesc filename
A target description annex is an XML document which complies with the Document Type Definition provided in the gdb sources in gdb/features/gdb-target.dtd. This means you can use generally available tools like xmllint to check that your feature descriptions are well-formed and valid. However, to help people unfamiliar with XML write descriptions for their targets, we also describe the grammar here.
Target descriptions can identify the architecture of the remote target and (for some architectures) provide information about custom register sets. They can also identify the OS ABI of the remote target. gdb can use this information to autoconfigure for your target, or to warn you if you connect to an unsupported target.
Here is a simple target description:
<target version="1.0"> <architecture>i386:x86-64</architecture> </target>
This minimal description only says that the target uses the x86-64 architecture.
A target description has the following overall form, with [ ] marking optional elements and ... marking repeatable elements. The elements are explained further below.
<?xml version="1.0"?> <!DOCTYPE target SYSTEM "gdb-target.dtd"> <target version="1.0"> [architecture] [osabi] [compatible] [feature...] </target>
The description is generally insensitive to whitespace and line breaks, under the usual common-sense rules. The XML version declaration and document type declaration can generally be omitted (gdb does not require them), but specifying them may be useful for XML validation tools. The ‘version’ attribute for ‘<target>’ may also be omitted, but we recommend including it; if future versions of gdb use an incompatible revision of gdb-target.dtd, they will detect and report the version mismatch.
It can sometimes be valuable to split a target description up into several different annexes, either for organizational purposes, or to share files between different possible target descriptions. You can divide a description into multiple files by replacing any element of the target description with an inclusion directive of the form:
<xi:include href="document"/>
When gdb encounters an element of this form, it will retrieve the named XML document, and replace the inclusion directive with the contents of that document. If the current description was read using ‘qXfer’, then so will be the included document; document will be interpreted as the name of an annex. If the current description was read from a file, gdb will look for document as a file in the same directory where it found the original description.
An ‘<architecture>’ element has this form:
<architecture>arch</architecture>
arch is one of the architectures from the set accepted by
set architecture
(see Specifying a Debugging Target).
This optional field was introduced in gdb version 7.0. Previous versions of gdb ignore it.
An ‘<osabi>’ element has this form:
<osabi>abi-name</osabi>
abi-name is an OS ABI name from the same selection accepted by
set osabi
(see Configuring the Current ABI).
This optional field was introduced in gdb version 7.0. Previous versions of gdb ignore it.
A ‘<compatible>’ element has this form:
<compatible>arch</compatible>
arch is one of the architectures from the set accepted by
set architecture
(see Specifying a Debugging Target).
A ‘<compatible>’ element is used to specify that the target
is able to run binaries in some other than the main target architecture
given by the ‘<architecture>’ element. For example, on the
Cell Broadband Engine, the main architecture is powerpc:common
or powerpc:common64
, but the system is able to run binaries
in the spu
architecture as well. The way to describe this
capability with ‘<compatible>’ is as follows:
<architecture>powerpc:common</architecture> <compatible>spu</compatible>
Each ‘<feature>’ describes some logical portion of the target system. Features are currently used to describe available CPU registers and the types of their contents. A ‘<feature>’ element has this form:
<feature name="name"> [type...] reg... </feature>
Each feature's name should be unique within the description. The name of a feature does not matter unless gdb has some special knowledge of the contents of that feature; if it does, the feature should have its standard name. See Standard Target Features.
Any register's value is a collection of bits which gdb must interpret. The default interpretation is a two's complement integer, but other types can be requested by name in the register description. Some predefined types are provided by gdb (see Predefined Target Types), and the description can define additional composite and enum types.
Each type element must have an ‘id’ attribute, which gives a unique (within the containing ‘<feature>’) name to the type. Types must be defined before they are used.
Some targets offer vector registers, which can be treated as arrays of scalar elements. These types are written as ‘<vector>’ elements, specifying the array element type, type, and the number of elements, count:
<vector id="id" type="type" count="count"/>
If a register's value is usefully viewed in multiple ways, define it with a union type containing the useful representations. The ‘<union>’ element contains one or more ‘<field>’ elements, each of which has a name and a type:
<union id="id"> <field name="name" type="type"/> ... </union>
If a register's value is composed from several separate values, define it with either a structure type or a flags type. A flags type may only contain bitfields. A structure type may either contain only bitfields or contain no bitfields. If the value contains only bitfields, its total size in bytes must be specified.
Non-bitfield values have a name and type.
<struct id="id"> <field name="name" type="type"/> ... </struct>
Both name and type values are required. No implicit padding is added.
Bitfield values have a name, start, end and type.
<struct id="id" size="size"> <field name="name" start="start" end="end" type="type"/> ... </struct>
<flags id="id" size="size"> <field name="name" start="start" end="end" type="type"/> ... </flags>
The name value is required. Bitfield values may be named with the empty string, ‘""’, in which case the field is “filler” and its value is not printed. Not all bits need to be specified, so “filler” fields are optional.
The start and end values are required, and type is optional. The field's start must be less than or equal to its end, and zero represents the least significant bit.
The default value of type is bool
for single bit fields,
and an unsigned integer otherwise.
Which to choose? Structures or flags?
Registers defined with ‘flags’ have these advantages over defining them with ‘struct’:
Registers defined with ‘struct’ have one advantage over defining them with ‘flags’:
(gdb) print $my_struct_reg.field3 $1 = 42
Each register is represented as an element with this form:
<reg name="name" bitsize="size" [regnum="num"] [save-restore="save-restore"] [type="type"] [group="group"]/>
The components are as follows:
p
and P
packets, and registers appear in the g
and G
packets
in order of increasing register number.
yes
or no
. The default is
yes
, which is appropriate for most registers except for
some system control registers; this is not related to the target's
ABI.
int
and float
. int
is an integer type of the correct size
for bitsize, and float
is a floating point type (in the
architecture's normal floating point format) of the correct size for
bitsize. The default is int
.
general
, float
, vector
or an
arbitrary string. Group names should be limited to alphanumeric characters.
If a group name is made up of multiple words the words may be separated by
hyphens; e.g. special-group
or ultra-special-group
. If no
group is specified, gdb will not display the register in
info registers
.
Type definitions in the self-description can build up composite types from basic building blocks, but can not define fundamental types. Instead, standard identifiers are provided by gdb for the fundamental types. The currently supported types are:
bool
int8
int16
int24
int32
int64
int128
uint8
uint16
uint24
uint32
uint64
uint128
code_ptr
data_ptr
ieee_single
ieee_double
arm_fpa_ext
i387_ext
i386_eflags
i386_mxcsr
Enum target types are useful in ‘struct’ and ‘flags’ register descriptions. See Target Description Format.
Enum types have a name, size and a list of name/value pairs.
<enum id="id" size="size"> <evalue name="name" value="value"/> ... </enum>
Enums must be defined before they are used.
<enum id="levels_type" size="4"> <evalue name="low" value="0"/> <evalue name="high" value="1"/> </enum> <flags id="flags_type" size="4"> <field name="X" start="0"/> <field name="LEVEL" start="1" end="1" type="levels_type"/> </flags> <reg name="flags" bitsize="32" type="flags_type"/>
Given that description, a value of 3 for the ‘flags’ register would be printed as:
(gdb) info register flags flags 0x3 [ X LEVEL=high ]
A target description must contain either no registers or all the target's registers. If the description contains no registers, then gdb will assume a default register layout, selected based on the architecture. If the description contains any registers, the default layout will not be used; the standard registers must be described in the target description, in such a way that gdb can recognize them.
This is accomplished by giving specific names to feature elements which contain standard registers. gdb will look for features with those names and verify that they contain the expected registers; if any known feature is missing required registers, or if any required feature is missing, gdb will reject the target description. You can add additional registers to any of the standard features — gdb will display them just as if they were added to an unrecognized feature.
This section lists the known features and their expected contents. Sample XML documents for these features are included in the gdb source tree, in the directory gdb/features.
Names recognized by gdb should include the name of the company or organization which selected the name, and the overall architecture to which the feature applies; so e.g. the feature containing ARM core registers is named ‘org.gnu.gdb.arm.core’.
The names of registers are not case sensitive for the purpose of recognizing standard features, but gdb will only display registers using the capitalization used in the description.
The ‘org.gnu.gdb.aarch64.core’ feature is required for AArch64 targets. It should contain registers ‘x0’ through ‘x30’, ‘sp’, ‘pc’, and ‘cpsr’.
The ‘org.gnu.gdb.aarch64.fpu’ feature is optional. If present, it should contain registers ‘v0’ through ‘v31’, ‘fpsr’, and ‘fpcr’.
The ‘org.gnu.gdb.aarch64.sve’ feature is optional. If present, it should contain registers ‘z0’ through ‘z31’, ‘p0’ through ‘p15’, ‘ffr’ and ‘vg’.
The ‘org.gnu.gdb.aarch64.pauth’ feature is optional. If present, it should contain registers ‘pauth_dmask’ and ‘pauth_cmask’.
ARC processors are highly configurable, so even core registers and their number are not completely predetermined. In addition flags and PC registers which are important to gdb are not “core” registers in ARC. It is required that one of the core registers features is present. ‘org.gnu.gdb.arc.aux-minimal’ feature is mandatory.
The ‘org.gnu.gdb.arc.core.v2’ feature is required for ARC EM and ARC HS targets with a normal register file. It should contain registers ‘r0’ through ‘r25’, ‘gp’, ‘fp’, ‘sp’, ‘r30’, ‘blink’, ‘lp_count’ and ‘pcl’. This feature may contain register ‘ilink’ and any of extension core registers ‘r32’ through ‘r59/acch’. ‘ilink’ and extension core registers are not available to read/write, when debugging GNU/Linux applications, thus ‘ilink’ is made optional.
The ‘org.gnu.gdb.arc.core-reduced.v2’ feature is required for ARC EM and ARC HS targets with a reduced register file. It should contain registers ‘r0’ through ‘r3’, ‘r10’ through ‘r15’, ‘gp’, ‘fp’, ‘sp’, ‘r30’, ‘blink’, ‘lp_count’ and ‘pcl’. This feature may contain register ‘ilink’ and any of extension core registers ‘r32’ through ‘r59/acch’.
The ‘org.gnu.gdb.arc.core.arcompact’ feature is required for ARCompact targets with a normal register file. It should contain registers ‘r0’ through ‘r25’, ‘gp’, ‘fp’, ‘sp’, ‘r30’, ‘blink’, ‘lp_count’ and ‘pcl’. This feature may contain registers ‘ilink1’, ‘ilink2’ and any of extension core registers ‘r32’ through ‘r59/acch’. ‘ilink1’ and ‘ilink2’ and extension core registers are not available when debugging GNU/Linux applications. The only difference with ‘org.gnu.gdb.arc.core.v2’ feature is in the names of ‘ilink1’ and ‘ilink2’ registers and that ‘r30’ is mandatory in ARC v2, but ‘ilink2’ is optional on ARCompact.
The ‘org.gnu.gdb.arc.aux-minimal’ feature is required for all ARC targets. It should contain registers ‘pc’ and ‘status32’.
The ‘org.gnu.gdb.arm.core’ feature is required for non-M-profile ARM targets. It should contain registers ‘r0’ through ‘r13’, ‘sp’, ‘lr’, ‘pc’, and ‘cpsr’.
For M-profile targets (e.g. Cortex-M3), the ‘org.gnu.gdb.arm.core’ feature is replaced by ‘org.gnu.gdb.arm.m-profile’. It should contain registers ‘r0’ through ‘r13’, ‘sp’, ‘lr’, ‘pc’, and ‘xpsr’.
The ‘org.gnu.gdb.arm.fpa’ feature is optional. If present, it should contain registers ‘f0’ through ‘f7’ and ‘fps’.
The ‘org.gnu.gdb.xscale.iwmmxt’ feature is optional. If present, it should contain at least registers ‘wR0’ through ‘wR15’ and ‘wCGR0’ through ‘wCGR3’. The ‘wCID’, ‘wCon’, ‘wCSSF’, and ‘wCASF’ registers are optional.
The ‘org.gnu.gdb.arm.vfp’ feature is optional. If present, it should contain at least registers ‘d0’ through ‘d15’. If they are present, ‘d16’ through ‘d31’ should also be included. gdb will synthesize the single-precision registers from halves of the double-precision registers.
The ‘org.gnu.gdb.arm.neon’ feature is optional. It does not need to contain registers; it instructs gdb to display the VFP double-precision registers as vectors and to synthesize the quad-precision registers from pairs of double-precision registers. If this feature is present, ‘org.gnu.gdb.arm.vfp’ must also be present and include 32 double-precision registers.
The ‘org.gnu.gdb.i386.core’ feature is required for i386/amd64 targets. It should describe the following registers:
The register sets may be different, depending on the target.
The ‘org.gnu.gdb.i386.sse’ feature is optional. It should describe registers:
The ‘org.gnu.gdb.i386.avx’ feature is optional and requires the ‘org.gnu.gdb.i386.sse’ feature. It should describe the upper 128 bits of ymm registers:
The ‘org.gnu.gdb.i386.mpx’ is an optional feature representing Intel Memory Protection Extension (MPX). It should describe the following registers:
The ‘org.gnu.gdb.i386.linux’ feature is optional. It should describe a single register, ‘orig_eax’.
The ‘org.gnu.gdb.i386.segments’ feature is optional. It should describe two system registers: ‘fs_base’ and ‘gs_base’.
The ‘org.gnu.gdb.i386.avx512’ feature is optional and requires the ‘org.gnu.gdb.i386.avx’ feature. It should describe additional xmm registers:
It should describe the upper 128 bits of additional ymm registers:
It should describe the upper 256 bits of zmm registers:
It should describe the additional zmm registers:
The ‘org.gnu.gdb.i386.pkeys’ feature is optional. It should describe a single register, ‘pkru’. It is a 32-bit register valid for i386 and amd64.
The ‘org.gnu.gdb.microblaze.core’ feature is required for MicroBlaze targets. It should contain registers ‘r0’ through ‘r31’, ‘rpc’, ‘rmsr’, ‘rear’, ‘resr’, ‘rfsr’, ‘rbtr’, ‘rpvr’, ‘rpvr1’ through ‘rpvr11’, ‘redr’, ‘rpid’, ‘rzpr’, ‘rtlbx’, ‘rtlbsx’, ‘rtlblo’, and ‘rtlbhi’.
The ‘org.gnu.gdb.microblaze.stack-protect’ feature is optional. If present, it should contain registers ‘rshr’ and ‘rslr’
The ‘org.gnu.gdb.mips.cpu’ feature is required for MIPS targets. It should contain registers ‘r0’ through ‘r31’, ‘lo’, ‘hi’, and ‘pc’. They may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.mips.cp0’ feature is also required. It should contain at least the ‘status’, ‘badvaddr’, and ‘cause’ registers. They may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.mips.fpu’ feature is currently required, though it may be optional in a future version of gdb. It should contain registers ‘f0’ through ‘f31’, ‘fcsr’, and ‘fir’. They may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.mips.dsp’ feature is optional. It should contain registers ‘hi1’ through ‘hi3’, ‘lo1’ through ‘lo3’, and ‘dspctl’. The ‘dspctl’ register should be 32-bit and the rest may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.mips.linux’ feature is optional. It should contain a single register, ‘restart’, which is used by the Linux kernel to control restartable syscalls.
‘
org.gnu.gdb.m68k.core’
‘
org.gnu.gdb.coldfire.core’
‘
org.gnu.gdb.fido.core’
‘
org.gnu.gdb.coldfire.fp’
The ‘org.gnu.gdb.nds32.core’ feature is required for NDS32 targets. It should contain at least registers ‘r0’ through ‘r10’, ‘r15’, ‘fp’, ‘gp’, ‘lp’, ‘sp’, and ‘pc’.
The ‘org.gnu.gdb.nds32.fpu’ feature is optional. If present, it should contain 64-bit double-precision floating-point registers ‘fd0’ through fdN, which should be ‘fd3’, ‘fd7’, ‘fd15’, or ‘fd31’ based on the FPU configuration implemented.
Note: The first sixteen 64-bit double-precision floating-point registers are overlapped with the thirty-two 32-bit single-precision floating-point registers. The 32-bit single-precision registers, if not being listed explicitly, will be synthesized from halves of the overlapping 64-bit double-precision registers. Listing 32-bit single-precision registers explicitly is deprecated, and the support to it could be totally removed some day.
The ‘org.gnu.gdb.nios2.cpu’ feature is required for Nios II targets. It should contain the 32 core registers (‘zero’, ‘at’, ‘r2’ through ‘r23’, ‘et’ through ‘ra’), ‘pc’, and the 16 control registers (‘status’ through ‘mpuacc’).
The ‘org.gnu.gdb.or1k.group0’ feature is required for OpenRISC 1000 targets. It should contain the 32 general purpose registers (‘r0’ through ‘r31’), ‘ppc’, ‘npc’ and ‘sr’.
The ‘org.gnu.gdb.power.core’ feature is required for PowerPC targets. It should contain registers ‘r0’ through ‘r31’, ‘pc’, ‘msr’, ‘cr’, ‘lr’, ‘ctr’, and ‘xer’. They may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.power.fpu’ feature is optional. It should contain registers ‘f0’ through ‘f31’ and ‘fpscr’.
The ‘org.gnu.gdb.power.altivec’ feature is optional. It should contain registers ‘vr0’ through ‘vr31’, ‘vscr’, and ‘vrsave’. gdb will define pseudo-registers ‘v0’ through ‘v31’ as aliases for the corresponding ‘vrX’ registers.
The ‘org.gnu.gdb.power.vsx’ feature is optional. It should contain registers ‘vs0h’ through ‘vs31h’. gdb will combine these registers with the floating point registers (‘f0’ through ‘f31’) and the altivec registers (‘vr0’ through ‘vr31’) to present the 128-bit wide registers ‘vs0’ through ‘vs63’, the set of vector-scalar registers for POWER7. Therefore, this feature requires both ‘org.gnu.gdb.power.fpu’ and ‘org.gnu.gdb.power.altivec’.
The ‘org.gnu.gdb.power.spe’ feature is optional. It should contain registers ‘ev0h’ through ‘ev31h’, ‘acc’, and ‘spefscr’. SPE targets should provide 32-bit registers in ‘org.gnu.gdb.power.core’ and provide the upper halves in ‘ev0h’ through ‘ev31h’. gdb will combine these to present registers ‘ev0’ through ‘ev31’ to the user.
The ‘org.gnu.gdb.power.ppr’ feature is optional. It should contain the 64-bit register ‘ppr’.
The ‘org.gnu.gdb.power.dscr’ feature is optional. It should contain the 64-bit register ‘dscr’.
The ‘org.gnu.gdb.power.tar’ feature is optional. It should contain the 64-bit register ‘tar’.
The ‘org.gnu.gdb.power.ebb’ feature is optional. It should contain registers ‘bescr’, ‘ebbhr’ and ‘ebbrr’, all 64-bit wide.
The ‘org.gnu.gdb.power.linux.pmu’ feature is optional. It should contain registers ‘mmcr0’, ‘mmcr2’, ‘siar’, ‘sdar’ and ‘sier’, all 64-bit wide. This is the subset of the isa 2.07 server PMU registers provided by gnu/Linux.
The ‘org.gnu.gdb.power.htm.spr’ feature is optional. It should contain registers ‘tfhar’, ‘texasr’ and ‘tfiar’, all 64-bit wide.
The ‘org.gnu.gdb.power.htm.core’ feature is optional. It should contain the checkpointed general-purpose registers ‘cr0’ through ‘cr31’, as well as the checkpointed registers ‘clr’ and ‘cctr’. These registers may all be either 32-bit or 64-bit depending on the target. It should also contain the checkpointed registers ‘ccr’ and ‘cxer’, which should both be 32-bit wide.
The ‘org.gnu.gdb.power.htm.fpu’ feature is optional. It should contain the checkpointed 64-bit floating-point registers ‘cf0’ through ‘cf31’, as well as the checkpointed 64-bit register ‘cfpscr’.
The ‘org.gnu.gdb.power.htm.altivec’ feature is optional. It should contain the checkpointed altivec registers ‘cvr0’ through ‘cvr31’, all 128-bit wide. It should also contain the checkpointed registers ‘cvscr’ and ‘cvrsave’, both 32-bit wide.
The ‘org.gnu.gdb.power.htm.vsx’ feature is optional. It should contain registers ‘cvs0h’ through ‘cvs31h’. gdb will combine these registers with the checkpointed floating point registers (‘cf0’ through ‘cf31’) and the checkpointed altivec registers (‘cvr0’ through ‘cvr31’) to present the 128-bit wide checkpointed vector-scalar registers ‘cvs0’ through ‘cvs63’. Therefore, this feature requires both ‘org.gnu.gdb.power.htm.altivec’ and ‘org.gnu.gdb.power.htm.fpu’.
The ‘org.gnu.gdb.power.htm.ppr’ feature is optional. It should contain the 64-bit checkpointed register ‘cppr’.
The ‘org.gnu.gdb.power.htm.dscr’ feature is optional. It should contain the 64-bit checkpointed register ‘cdscr’.
The ‘org.gnu.gdb.power.htm.tar’ feature is optional. It should contain the 64-bit checkpointed register ‘ctar’.
The ‘org.gnu.gdb.riscv.cpu’ feature is required for RISC-V targets. It should contain the registers ‘x0’ through ‘x31’, and ‘pc’. Either the architectural names (‘x0’, ‘x1’, etc) can be used, or the ABI names (‘zero’, ‘ra’, etc).
The ‘org.gnu.gdb.riscv.fpu’ feature is optional. If present, it should contain registers ‘f0’ through ‘f31’, ‘fflags’, ‘frm’, and ‘fcsr’. As with the cpu feature, either the architectural register names, or the ABI names can be used.
The ‘org.gnu.gdb.riscv.virtual’ feature is optional. If present, it should contain registers that are not backed by real registers on the target, but are instead virtual, where the register value is derived from other target state. In many ways these are like gdbs pseudo-registers, except implemented by the target. Currently the only register expected in this set is the one byte ‘priv’ register that contains the target's privilege level in the least significant two bits.
The ‘org.gnu.gdb.riscv.csr’ feature is optional. If present, it should contain all of the target's standard CSRs. Standard CSRs are those defined in the RISC-V specification documents. There is some overlap between this feature and the fpu feature; the ‘fflags’, ‘frm’, and ‘fcsr’ registers could be in either feature. The expectation is that these registers will be in the fpu feature if the target has floating point hardware, but can be moved into the csr feature if the target has the floating point control registers, but no other floating point hardware.
The ‘org.gnu.gdb.rx.core’ feature is required for RX targets. It should contain the registers ‘r0’ through ‘r15’, ‘usp’, ‘isp’, ‘psw’, ‘pc’, ‘intb’, ‘bpsw’, ‘bpc’, ‘fintv’, ‘fpsw’, and ‘acc’.
The ‘org.gnu.gdb.s390.core’ feature is required for S/390 and System z targets. It should contain the PSW and the 16 general registers. In particular, System z targets should provide the 64-bit registers ‘pswm’, ‘pswa’, and ‘r0’ through ‘r15’. S/390 targets should provide the 32-bit versions of these registers. A System z target that runs in 31-bit addressing mode should provide 32-bit versions of ‘pswm’ and ‘pswa’, as well as the general register's upper halves ‘r0h’ through ‘r15h’, and their lower halves ‘r0l’ through ‘r15l’.
The ‘org.gnu.gdb.s390.fpr’ feature is required. It should contain the 64-bit registers ‘f0’ through ‘f15’, and ‘fpc’.
The ‘org.gnu.gdb.s390.acr’ feature is required. It should contain the 32-bit registers ‘acr0’ through ‘acr15’.
The ‘org.gnu.gdb.s390.linux’ feature is optional. It should contain the register ‘orig_r2’, which is 64-bit wide on System z targets and 32-bit otherwise. In addition, the feature may contain the ‘last_break’ register, whose width depends on the addressing mode, as well as the ‘system_call’ register, which is always 32-bit wide.
The ‘org.gnu.gdb.s390.tdb’ feature is optional. It should contain the 64-bit registers ‘tdb0’, ‘tac’, ‘tct’, ‘atia’, and ‘tr0’ through ‘tr15’.
The ‘org.gnu.gdb.s390.vx’ feature is optional. It should contain 64-bit wide registers ‘v0l’ through ‘v15l’, which will be combined by gdb with the floating point registers ‘f0’ through ‘f15’ to present the 128-bit wide vector registers ‘v0’ through ‘v15’. In addition, this feature should contain the 128-bit wide vector registers ‘v16’ through ‘v31’.
The ‘org.gnu.gdb.s390.gs’ feature is optional. It should contain the 64-bit wide guarded-storage-control registers ‘gsd’, ‘gssm’, and ‘gsepla’.
The ‘org.gnu.gdb.s390.gsbc’ feature is optional. It should contain the 64-bit wide guarded-storage broadcast control registers ‘bc_gsd’, ‘bc_gssm’, and ‘bc_gsepla’.
The ‘org.gnu.gdb.sparc.cpu’ feature is required for sparc32/sparc64 targets. It should describe the following registers:
They may be 32-bit or 64-bit depending on the target.
Also the ‘org.gnu.gdb.sparc.fpu’ feature is required for sparc32/sparc64 targets. It should describe the following registers:
The ‘org.gnu.gdb.sparc.cp0’ feature is required for sparc32/sparc64 targets. It should describe the following registers:
The ‘org.gnu.gdb.tic6x.core’ feature is required for TMS320C6x targets. It should contain registers ‘A0’ through ‘A15’, registers ‘B0’ through ‘B15’, ‘CSR’ and ‘PC’.
The ‘org.gnu.gdb.tic6x.gp’ feature is optional. It should contain registers ‘A16’ through ‘A31’ and ‘B16’ through ‘B31’.
The ‘org.gnu.gdb.tic6x.c6xp’ feature is optional. It should contain registers ‘TSR’, ‘ILC’ and ‘RILC’.
Users of gdb often wish to obtain information about the state of the operating system running on the target—for example the list of processes, or the list of open files. This section describes the mechanism that makes it possible. This mechanism is similar to the target features mechanism (see Target Descriptions), but focuses on a different aspect of target.
Operating system information is retrieved from the target via the remote protocol, using ‘qXfer’ requests (see qXfer osdata read). The object name in the request should be ‘osdata’, and the annex identifies the data to be fetched.
When requesting the process list, the annex field in the ‘qXfer’ request should be ‘processes’. The returned data is an XML document. The formal syntax of this document is defined in gdb/features/osdata.dtd.
An example document is:
<?xml version="1.0"?> <!DOCTYPE target SYSTEM "osdata.dtd"> <osdata type="processes"> <item> <column name="pid">1</column> <column name="user">root</column> <column name="command">/sbin/init</column> <column name="cores">1,2,3</column> </item> </osdata>
Each item should include a column whose name is ‘pid’. The value of that column should identify the process on the target. The ‘user’ and ‘command’ columns are optional, and will be displayed by gdb. The ‘cores’ column, if present, should contain a comma-separated list of cores that this process is running on. Target may provide additional columns, which gdb currently ignores.
The trace file comes in three parts: a header, a textual description section, and a trace frame section with binary data.
The header has the form \x7fTRACE0\n
. The first byte is
0x7f
so as to indicate that the file contains binary data,
while the 0
is a version number that may have different values
in the future.
The description section consists of multiple lines of ascii text
separated by newline characters (0xa
). The lines may include a
variety of optional descriptive or context-setting information, such
as tracepoint definitions or register set size. gdb will
ignore any line that it does not recognize. An empty line marks the end
of this section.
R
sizeg
packet payload in the remote protocol. size
is an ascii decimal number. There should be only one such line in
a single trace file.
status
statusqTStatus
remote packet reply. There should be only one such line in a single trace
file.
tp
payloadqTfP
/qTsP
remote packet reply payload. A single tracepoint
may take multiple lines of definition, corresponding to the multiple
reply packets.
tsv
payloadqTfV
/qTsV
remote packet reply payload. A single variable
may take multiple lines of definition, corresponding to the multiple
reply packets.
tdesc
payloadqXfer
features
payload, and corresponds to the main target.xml
file. Includes are not allowed.
The trace frame section consists of a number of consecutive frames. Each frame begins with a two-byte tracepoint number, followed by a four-byte size giving the amount of data in the frame. The data in the frame consists of a number of blocks, each introduced by a character indicating its type (at least register, memory, and trace state variable). The data in this section is raw binary, not a hexadecimal or other encoding; its endianness matches the target's endianness.
R
bytesg
packet in the remote protocol. Note that these are the
actual bytes, in target order, not a hexadecimal encoding.
M
address length bytes...
V
number valueFuture enhancements of the trace file format may include additional types of blocks.
.gdb_index
section format
This section documents the index section that is created by save
gdb-index
(see Index Files). The index section is
DWARF-specific; some knowledge of DWARF is assumed in this
description.
The mapped index file format is designed to be directly
mmap
able on any architecture. In most cases, a datum is
represented using a little-endian 32-bit integer value, called an
offset_type
. Big endian machines must byte-swap the values
before using them. Exceptions to this rule are noted. The data is
laid out such that alignment is always respected.
A mapped index consists of several areas, laid out in order.
offset_type
unless otherwise noted:
gdb will only read version 4, 5, or 6 indices
by specifying set use-deprecated-index-sections on
.
GDB has a workaround for potentially broken version 7 indices so it is
currently not flagged as deprecated.
.debug_info
section. The second
element in each pair is the length of that CU. References to a CU
elsewhere in the map are done using a CU index, which is just the
0-based index into this table. Note that if there are type CUs, then
conceptually CUs and type CUs form a single list for the purposes of
CU indices.
DW_AT_high_pc
, the value is one byte beyond the end.
offset_type
value.
Each slot in the hash table consists of a pair of offset_type
values. The first value is the offset of the symbol's name in the
constant pool. The second value is the offset of the CU vector in the
constant pool.
If both values are 0, then this slot in the hash table is empty. This is ok because while 0 is a valid constant pool index, it cannot be a valid index for both a string and a CU vector.
The hash value for a table entry is computed by applying an
iterative hash function to the symbol's name. Starting with an
initial value of r = 0
, each (unsigned) character ‘c’ in
the string is incorporated into the hash using the formula depending on the
index version:
r = r * 67 + c - 113
.
r = r * 67 + tolower (c) - 113
.
The terminating ‘\0’ is not incorporated into the hash.
The step size used in the hash table is computed via
((hash * 17) & (size - 1)) | 1
, where ‘hash’ is the hash
value, and ‘size’ is the size of the hash table. The step size
is used to find the next candidate slot when handling a hash
collision.
The names of C++ symbols in the hash table are canonicalized. We don't currently have a simple description of the canonicalization algorithm; if you intend to create new index sections, you must read the code.
A CU vector in the constant pool is a sequence of offset_type
values. The first value is the number of CU indices in the vector.
Each subsequent value is the index and symbol attributes of a CU in
the CU list. This element in the hash table is used to indicate which
CUs define the symbol and how the symbol is used.
See below for the format of each CU index+attributes entry.
A string in the constant pool is zero-terminated.
Attributes were added to CU index values in .gdb_index
version 7.
If a symbol has multiple uses within a CU then there is one
CU index+attributes value for each use.
The format of each CU index+attributes entry is as follows (bit 0 = LSB):
offset_type
value is backwards compatible
with previous versions of the index.
The determination of whether a symbol is global or static is complicated. The authorative reference is the file dwarf2read.c in gdb sources.
This pseudo-code describes the computation of a symbol's kind and global/static attributes in the index.
is_external = get_attribute (die, DW_AT_external); language = get_attribute (cu_die, DW_AT_language); switch (die->tag) { case DW_TAG_typedef: case DW_TAG_base_type: case DW_TAG_subrange_type: kind = TYPE; is_static = 1; break; case DW_TAG_enumerator: kind = VARIABLE; is_static = language != CPLUS; break; case DW_TAG_subprogram: kind = FUNCTION; is_static = ! (is_external || language == ADA); break; case DW_TAG_constant: kind = VARIABLE; is_static = ! is_external; break; case DW_TAG_variable: kind = VARIABLE; is_static = ! is_external; break; case DW_TAG_namespace: kind = TYPE; is_static = 0; break; case DW_TAG_class_type: case DW_TAG_interface_type: case DW_TAG_structure_type: case DW_TAG_union_type: case DW_TAG_enumeration_type: kind = TYPE; is_static = language != CPLUS; break; default: assert (0); }
gdb [-help] [-nh] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps] [-tty=dev] [-s symfile] [-e prog] [-se prog] [-c core] [-p procID] [-x cmds] [-d dir] [prog|prog procID|prog core]
The purpose of a debugger such as gdb is to allow you to see what is going on “inside” another program while it executes – or what another program was doing at the moment it crashed.
gdb can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act:
You can use gdb to debug programs written in C, C++, Fortran and Modula-2.
gdb is invoked with the shell command gdb
. Once started, it reads
commands from the terminal until you tell it to exit with the gdb
command quit
. You can get online help from gdb itself
by using the command help
.
You can run gdb
with no arguments or options; but the most
usual way to start gdb is with one argument or two, specifying an
executable program as the argument:
gdb program
You can also start with both an executable program and a core file specified:
gdb program core
You can, instead, specify a process ID as a second argument or use option
-p
, if you want to debug a running process:
gdb program 1234 gdb -p 1234
would attach gdb to process 1234
. With option -p you
can omit the program filename.
Here are some of the most frequently needed gdb commands:
Any arguments other than options specify an executable file and core file (or process ID); that is, the first argument encountered with no associated option flag is equivalent to a -se option, and the second, if any, is equivalent to a -c option if it's the name of a file. Many options have both long and short forms; both are shown here. The long forms are also recognized if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with + rather than -, though we illustrate the more usual convention.)
All the options and command line arguments you give are processed in sequential order. The order makes a difference when the -x option is used.
0
after processing all the command
files specified with -x (and .gdbinit, if not inhibited).
Exit with nonzero status if an error occurs in executing the gdb
commands in the command files.
Batch mode may be useful for running gdb as a filter, for example to download and run a program on another computer; in order to make this more useful, the message
Program exited normally.
(which is ordinarily issued whenever a program running under gdb control
terminates) is not issued when running in batch mode.
gdbserver comm prog [args...] gdbserver –attach comm pid gdbserver –multi comm
gdbserver is a program that allows you to run gdb on a different machine than the one which is running the program being debugged.
First, you need to have a copy of the program you want to debug put onto the target system. The program can be stripped to save space if needed, as gdbserver doesn't care about symbols. All symbol handling is taken care of by the gdb running on the host system.
To use the server, you log on to the target system, and run the gdbserver program. You must tell it (a) how to communicate with gdb, (b) the name of your program, and (c) its arguments. The general syntax is:
target> gdbserver comm program [args ...]
For example, using a serial port, you might say:
target> gdbserver /dev/com1 emacs foo.txt
This tells gdbserver to debug emacs with an argument of foo.txt, and to communicate with gdb via /dev/com1. gdbserver now waits patiently for the host gdb to communicate with it.
To use a TCP connection, you could say:
target> gdbserver host:2345 emacs foo.txt
This says pretty much the same thing as the last example, except that we are
going to communicate with the host
gdb via TCP. The host:2345
argument means
that we are expecting to see a TCP connection from host
to local TCP port
2345. (Currently, the host
part is ignored.) You can choose any number you
want for the port number as long as it does not conflict with any existing TCP
ports on the target system. This same port number must be used in the host
gdbs target remote
command, which will be described shortly. Note that if
you chose a port number that conflicts with another service, gdbserver will
print an error message and exit.
gdbserver can also attach to running programs. This is accomplished via the --attach argument. The syntax is:
target> gdbserver --attach comm pid
pid is the process ID of a currently running process. It isn't necessary to point gdbserver at a binary for the running process.
To start gdbserver
without supplying an initial command to run
or process ID to attach, use the --multi command line option.
In such case you should connect using target extended-remote to start
the program you want to debug.
target> gdbserver --multi comm
You need an unstripped copy of the target program on your host system, since
gdb needs to examine its symbol tables and such. Start up gdb as you normally
would, with the target program as the first argument. (You may need to use the
--baud option if the serial line is running at anything except 9600 baud.)
That is gdb TARGET-PROG
, or gdb --baud BAUD TARGET-PROG
. After that, the only
new command you need to know about is target remote
(or target extended-remote
). Its argument is either
a device name (usually a serial device, like /dev/ttyb), or a HOST:PORT
descriptor. For example:
(gdb) target remote /dev/ttyb
communicates with the server via serial line /dev/ttyb, and:
(gdb) target remote the-target:2345
communicates via a TCP connection to port 2345 on host `the-target', where you previously started up gdbserver with the same port number. Note that for TCP connections, you must start up gdbserver prior to using the `target remote' command, otherwise you may get an error that looks something like `Connection refused'.
gdbserver can also debug multiple inferiors at once,
described in
Inferiors and Programs.
In such case use the extended-remote
gdb command variant:
(gdb) target extended-remote the-target:2345
The gdbserver option --multi may or may not be used in such case.
There are three different modes for invoking gdbserver:
gdbserver comm prog [args...]
The comm parameter specifies how should the server communicate
with gdb; it is either a device name (to use a serial line),
a TCP port number (:1234
), or -
or stdio
to use
stdin/stdout of gdbserver
. Specify the name of the program to
debug in prog. Any remaining arguments will be passed to the
program verbatim. When the program exits, gdb will close the
connection, and gdbserver
will exit.
gdbserver --attach comm pid
The comm parameter is as described above. Supply the process ID
of a running program in pid; gdb will do everything
else. Like with the previous mode, when the process pid exits,
gdb will close the connection, and gdbserver
will exit.
gdbserver --multi comm
In this mode, gdb can instruct gdbserver which command(s) to run. Unlike the other 2 modes, gdb will not close the connection when a process being debugged exits, so you can debug several processes in the same session.
In each of the modes you may specify these options:
target> gdbserver --attach comm pid
pid is the process ID of a currently running process. It isn't
necessary to point gdbserver at a binary for the running process.
gdbserver
without supplying an initial command to run
or process ID to attach, use this command line option.
Then you can connect using target extended-remote and start
the program you want to debug. The syntax is:
target> gdbserver --multi comm
gdbserver
to display extra status information about the debugging
process.
This option is intended for gdbserver
development and for bug reports to
the developers.
gdbserver
to display remote protocol debug output.
This option is intended for gdbserver
development and for bug reports to
the developers.
gdbserver
to send any debug output to the given filename.
This option is intended for gdbserver
development and for bug reports to
the developers.
gdbserver
to include extra information in each line
of debugging output.
See Other Command-Line Arguments for gdbserver.
gdbserver
with the --once option, it will stop listening for any further
connection attempts after connecting to the first gdb session.
gcore [-a] [-o prefix] pid1 [pid2...pidN]
Generate core dumps of one or more running programs with process IDs pid1, pid2, etc. A core file produced by gcore is equivalent to one produced by the kernel when the process crashes (and when ulimit -c was used to set up an appropriate core dump limit). However, unlike after a crash, after gcore finishes its job the program remains running without any change.
use-coredump-filter
(see set use-coredump-filter) and
enable dump-excluded-mappings
(see set dump-excluded-mappings).
~/.gdbinit ./.gdbinit
These files contain gdb commands to automatically execute during gdb startup. The lines of contents are canned sequences of commands, described in Sequences.
Please read more in Startup.
--with-system-gdbinit
during compilation)-nx
or -n
.
See more in
--with-system-gdbinit-dir
during compilation)-nx
or
-n
, as long as they have a recognized file extension.
See more in
System-wide configuration.
-nx
, -n
or -nh
.
set auto-load local-gdbinit
.
See more in
Init File in the Current Directory.
gdb-add-index filename
When gdb finds a symbol file, it scans the symbols in the file in order to construct an internal symbol table. This lets most gdb operations work quickly–at the cost of a delay early on. For large programs, this delay can be quite lengthy, so gdb provides a way to build an index, which speeds up startup.
To determine whether a file contains such an index, use the command
readelf -S filename: the index is stored in a section named
.gdb_index
. The index file can only be produced on systems
which use ELF binaries and DWARF debug information (i.e., sections
named .debug_*
).
gdb-add-index uses gdb and objdump found in the PATH environment variable. If you want to use different versions of these programs, you can specify them through the GDB and OBJDUMP environment variables.
See more in Index Files.
Copyright © 2007 Free Software Foundation, Inc. http://fsf.org/ Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
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Corresponding Source conveyed, and Installation Information provided, in accord with this section must be in a format that is publicly documented (and with an implementation available to the public in source code form), and must require no special password or key for unpacking, reading or copying.
“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.
Notwithstanding any other provision of this License, for material you add to a covered work, you may (if authorized by the copyright holders of that material) supplement the terms of this License with terms:
All other non-permissive additional terms are considered “further restrictions” within the meaning of section 10. If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term. If a license document contains a further restriction but permits relicensing or conveying under this License, you may add to a covered work material governed by the terms of that license document, provided that the further restriction does not survive such relicensing or conveying.
If you add terms to a covered work in accord with this section, you must place, in the relevant source files, a statement of the additional terms that apply to those files, or a notice indicating where to find the applicable terms.
Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as exceptions; the above requirements apply either way.
You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11).
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.
An “entity transaction” is a transaction transferring control of an organization, or substantially all assets of one, or subdividing an organization, or merging organizations. If propagation of a covered work results from an entity transaction, each party to that transaction who receives a copy of the work also receives whatever licenses to the work the party's predecessor in interest had or could give under the previous paragraph, plus a right to possession of the Corresponding Source of the work from the predecessor in interest, if the predecessor has it or can get it with reasonable efforts.
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.
Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributor's essential patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its contributor version.
In the following three paragraphs, a “patent license” is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission to practice a patent or covenant not to sue for patent infringement). To “grant” such a patent license to a party means to make such an agreement or commitment not to enforce a patent against the party.
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 http://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 http://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 http://www.gnu.org/philosophy/why-not-lgpl.html.
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. http://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.
A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.
A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.
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.
The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.
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 http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.
“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.
“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.
“Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.
An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.
To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:
Copyright (C) year your name. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 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 Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
with the Invariant Sections being list their titles, with the Front-Cover Texts being list, and with the Back-Cover Texts being list.
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.
#
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, background execution of commands: Background Execution--annotate
: Mode Options--args
: Mode Optionsgdbserver
option: Server--batch
: Mode Options--batch-silent
: Mode Options--baud
: Mode Options--cd
: Mode Options--command
: File Options--configuration
: Mode Options--core
: File Options--data-directory
: Mode Optionsgdbserver
option: Servergdbserver
option: Servergdbserver
option: Server--directory
: File Options--eval-command
: File Options--exec
: File Options--fullname
: Mode Options--init-command
: File Options--init-eval-command
: File Options--interpreter
: Mode Optionsgdbserver
option: Connecting--nh
: Mode Options--nowindows
: Mode Options--nx
: Mode Optionsgdbserver
option: Server--pid
: File Options--quiet
: Mode Options--readnever
, command-line option: File Options--readnow
: File Optionsgdbserver
option: Server--return-child-result
: Mode Options--se
: File Options--silent
: Mode Options--statistics
: Mode Options--symbols
: File Options--tty
: Mode Options--tui
: Mode Options--version
: Mode Options--windows
: Mode Optionsgdbserver
option: Server--write
: Mode Options-b
: Mode Options-c
: File Options-D
: Mode Options-d
: File Options-e
: File Options-ex
: File Options-f
: Mode Options-iex
: File Options-info-gdb-mi-command
: GDB/MI Support Commands-ix
: File Options-l
: Mode Options-n
: Mode Options-nw
: Mode Options-p
: File Options-q
: Mode Options-r
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: File Options-t
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: File Options.
, Modula-2 scope operator: M2 Scope.debug_gdb_scripts
section: dotdebug_gdb_scripts section.gnu_debuglink
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sections: Separate Debug Files::
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: ThreadsF
reply packet: The F Reply PacketF
request packet: The F Request Packetg++
, gnu C++ compiler: Cgdb.Value
: Values From Inferiorgdbserver
, command-line arguments: Servergdbserver
, connecting: Connectinglibthread_db
: Servergdbserver
, send all debug output to a single file: Servergdbserver
, target extended-remote
mode: Connectinggdbserver
, target remote
mode: Connectinggdbserver
, types of connections: Connectingheuristic-fence-post
(Alpha, MIPS): MIPSlist
, how many lines to display: Listtarget remote
: Connectinggdbserver
: ServerNew
systag message: Threadstarget remote
to: Connectingprocfs
API calls: Process Informationlibthread_db
: Threadstarget remote
: Connectingserver
, command prefix: Command HistorySIGQUIT
signal, dump core of gdb: Maintenance Commandsstruct gdb_reader_funcs
: Writing JIT Debug Info Readersstruct gdb_symbol_callbacks
: Writing JIT Debug Info Readersstruct gdb_unwind_callbacks
: Writing JIT Debug Info Readerssyscall DSO
: Filestarget remote
: Connectinggdbserver
: Servertarget remote
: Connectingx
command, default address: Machine Code!
: Shell Commands#
(a comment): Command Syntax$_
, convenience variable: Convenience Vars$__
, convenience variable: Convenience Vars$_ada_exception
, convenience variable: Set Catchpoints$_any_caller_is
, convenience function: Convenience Funs$_any_caller_matches
, convenience function: Convenience Funs$_as_string
, convenience function: Convenience Funs$_caller_is
, convenience function: Convenience Funs$_caller_matches
, convenience function: Convenience Funs$_cimag
, convenience function: Convenience Funs$_creal
, convenience function: Convenience Funs$_exception
, convenience variable: Set Catchpoints$_exitcode
, convenience variable: Convenience Vars$_exitsignal
, convenience variable: Convenience Vars$_gdb_maint_setting
, convenience function: Convenience Funs$_gdb_maint_setting_str
, convenience function: Convenience Funs$_gdb_major
, convenience variable: Convenience Vars$_gdb_minor
, convenience variable: Convenience Vars$_gdb_setting
, convenience function: Convenience Funs$_gdb_setting_str
, convenience function: Convenience Funs$_gthread
, convenience variable: Threads$_inferior
, convenience variable: Inferiors and Programs$_isvoid
, convenience function: Convenience Funs$_memeq
, convenience function: Convenience Funs$_probe_arg
, convenience variable: Static Probe Points$_regex
, convenience function: Convenience Funs$_sdata
, collect: Tracepoint Actions$_sdata
, inspect, convenience variable: Convenience Vars$_shell_exitcode
, convenience variable: Convenience Vars$_shell_exitsignal
, convenience variable: Convenience Vars$_siginfo
, convenience variable: Convenience Vars$_streq
, convenience function: Convenience Funs$_strlen
, convenience function: Convenience Funs$_thread
, convenience variable: Threads$_tlb
, convenience variable: Convenience Vars$bpnum
, convenience variable: Set Breaks$cdir
, convenience variable: Source Path$cwd
, convenience variable: Source Path$tpnum
: Create and Delete Tracepoints$trace_file
: Tracepoint Variables$trace_frame
: Tracepoint Variables$trace_func
: Tracepoint Variables$trace_line
: Tracepoint Variables$tracepoint
: Tracepoint Variables(
: Parameters In Guile(
: Commands In Guile-ada-task-info
: GDB/MI Ada Tasking Commands-add-inferior
: GDB/MI Miscellaneous Commands-break-after
: GDB/MI Breakpoint Commands-break-commands
: GDB/MI Breakpoint Commands-break-condition
: GDB/MI Breakpoint Commands-break-delete
: GDB/MI Breakpoint Commands-break-disable
: GDB/MI Breakpoint Commands-break-enable
: GDB/MI Breakpoint Commands-break-info
: GDB/MI Breakpoint Commands-break-insert
: GDB/MI Breakpoint Commands-break-list
: GDB/MI Breakpoint Commands-break-passcount
: GDB/MI Breakpoint Commands-break-watch
: GDB/MI Breakpoint Commands-catch-assert
: Ada Exception GDB/MI Catchpoint Commands-catch-catch
: C++ Exception GDB/MI Catchpoint Commands-catch-exception
: Ada Exception GDB/MI Catchpoint Commands-catch-handlers
: Ada Exception GDB/MI Catchpoint Commands-catch-load
: Shared Library GDB/MI Catchpoint Commands-catch-rethrow
: C++ Exception GDB/MI Catchpoint Commands-catch-throw
: C++ Exception GDB/MI Catchpoint Commands-catch-unload
: Shared Library GDB/MI Catchpoint Commands-complete
: GDB/MI Miscellaneous Commands-data-disassemble
: GDB/MI Data Manipulation-data-evaluate-expression
: GDB/MI Data Manipulation-data-list-changed-registers
: GDB/MI Data Manipulation-data-list-register-names
: GDB/MI Data Manipulation-data-list-register-values
: GDB/MI Data Manipulation-data-read-memory
: GDB/MI Data Manipulation-data-read-memory-bytes
: GDB/MI Data Manipulation-data-write-memory-bytes
: GDB/MI Data Manipulation-dprintf-insert
: GDB/MI Breakpoint Commands-enable-frame-filters
: GDB/MI Stack Manipulation-enable-pretty-printing
: GDB/MI Variable Objects-enable-timings
: GDB/MI Miscellaneous Commands-environment-cd
: GDB/MI Program Context-environment-directory
: GDB/MI Program Context-environment-path
: GDB/MI Program Context-environment-pwd
: GDB/MI Program Context-exec-arguments
: GDB/MI Program Context-exec-continue
: GDB/MI Program Execution-exec-finish
: GDB/MI Program Execution-exec-interrupt
: GDB/MI Program Execution-exec-jump
: GDB/MI Program Execution-exec-next
: GDB/MI Program Execution-exec-next-instruction
: GDB/MI Program Execution-exec-return
: GDB/MI Program Execution-exec-run
: GDB/MI Program Execution-exec-step
: GDB/MI Program Execution-exec-step-instruction
: GDB/MI Program Execution-exec-until
: GDB/MI Program Execution-file-exec-and-symbols
: GDB/MI File Commands-file-exec-file
: GDB/MI File Commands-file-list-exec-source-file
: GDB/MI File Commands-file-list-exec-source-files
: GDB/MI File Commands-file-list-shared-libraries
: GDB/MI File Commands-file-symbol-file
: GDB/MI File Commands-gdb-exit
: GDB/MI Miscellaneous Commands-gdb-set
: GDB/MI Miscellaneous Commands-gdb-show
: GDB/MI Miscellaneous Commands-gdb-version
: GDB/MI Miscellaneous Commands-inferior-tty-set
: GDB/MI Miscellaneous Commands-inferior-tty-show
: GDB/MI Miscellaneous Commands-info-ada-exceptions
: GDB/MI Ada Exceptions Commands-info-gdb-mi-command
: GDB/MI Support Commands-info-os
: GDB/MI Miscellaneous Commands-interpreter-exec
: GDB/MI Miscellaneous Commands-list-features
: GDB/MI Support Commands-list-target-features
: GDB/MI Support Commands-list-thread-groups
: GDB/MI Miscellaneous Commands-stack-info-depth
: GDB/MI Stack Manipulation-stack-info-frame
: GDB/MI Stack Manipulation-stack-list-arguments
: GDB/MI Stack Manipulation-stack-list-frames
: GDB/MI Stack Manipulation-stack-list-locals
: GDB/MI Stack Manipulation-stack-list-variables
: GDB/MI Stack Manipulation-stack-select-frame
: GDB/MI Stack Manipulation-symbol-info-functions
: GDB/MI Symbol Query-symbol-info-module-functions
: GDB/MI Symbol Query-symbol-info-module-variables
: GDB/MI Symbol Query-symbol-info-modules
: GDB/MI Symbol Query-symbol-info-types
: GDB/MI Symbol Query-symbol-info-variables
: GDB/MI Symbol Query-symbol-list-lines
: GDB/MI Symbol Query-target-attach
: GDB/MI Target Manipulation-target-detach
: GDB/MI Target Manipulation-target-disconnect
: GDB/MI Target Manipulation-target-download
: GDB/MI Target Manipulation-target-file-delete
: GDB/MI File Transfer Commands-target-file-get
: GDB/MI File Transfer Commands-target-file-put
: GDB/MI File Transfer Commands-target-flash-erase
: GDB/MI Target Manipulation-target-select
: GDB/MI Target Manipulation-thread-info
: GDB/MI Thread Commands-thread-list-ids
: GDB/MI Thread Commands-thread-select
: GDB/MI Thread Commands-trace-define-variable
: GDB/MI Tracepoint Commands-trace-find
: GDB/MI Tracepoint Commands-trace-frame-collected
: GDB/MI Tracepoint Commands-trace-list-variables
: GDB/MI Tracepoint Commands-trace-save
: GDB/MI Tracepoint Commands-trace-start
: GDB/MI Tracepoint Commands-trace-status
: GDB/MI Tracepoint Commands-trace-stop
: GDB/MI Tracepoint Commands-var-assign
: GDB/MI Variable Objects-var-create
: GDB/MI Variable Objects-var-delete
: GDB/MI Variable Objects-var-evaluate-expression
: GDB/MI Variable Objects-var-info-expression
: GDB/MI Variable Objects-var-info-num-children
: GDB/MI Variable Objects-var-info-path-expression
: GDB/MI Variable Objects-var-info-type
: GDB/MI Variable Objects-var-list-children
: GDB/MI Variable Objects-var-set-format
: GDB/MI Variable Objects-var-set-frozen
: GDB/MI Variable Objects-var-set-update-range
: GDB/MI Variable Objects-var-set-visualizer
: GDB/MI Variable Objects-var-show-attributes
: GDB/MI Variable Objects-var-show-format
: GDB/MI Variable Objects-var-update
: GDB/MI Variable Objects::
, in Modula-2: M2 Scope<gdb:arch>
: Architectures In Guile<gdb:block>
: Blocks In Guile<gdb:breakpoint>
: Breakpoints In Guile<gdb:iterator>
: Iterators In Guile<gdb:lazy-string>
: Lazy Strings In Guile<gdb:objfile>
: Objfiles In Guile<gdb:progspace>
: Progspaces In Guile<gdb:sal>
: Symbol Tables In Guile<gdb:symbol>
: Symbols In Guile<gdb:symtab>
: Symbol Tables In Guile<gdb:type>
: Types In Guile<gdb:value>
: Values From Inferior In Guile@
, referencing memory as an array: Arrays^connected
: GDB/MI Result Records^done
: GDB/MI Result Records^error
: GDB/MI Result Records^exit
: GDB/MI Result Records^running
: GDB/MI Result Records__init__ on TypePrinter
: gdb.typesabort (C-g)
: Miscellaneous Commandsaccept-line (Newline or Return)
: Commands For Historyactions
: Tracepoint Actionsada-task-info
: GDB/MI Support Commandsadd-auto-load-safe-path
: Auto-loading safe pathadd-auto-load-scripts-directory
: objfile-gdbdotext fileadd-inferior
: Inferiors and Programsadd-symbol-file
: Filesadd-symbol-file-from-memory
: Filesadi assign
: Sparc64adi examine
: Sparc64advance
location: Continuing and Steppingalias
: Aliasesappend
: Dump/Restore Filesappend-pretty-printer!
: Guile Printing Moduleapropos
: Helparch-bool-type
: Architectures In Guilearch-char-type
: Architectures In Guilearch-charset
: Architectures In Guilearch-disassemble
: Disassembly In Guilearch-double-type
: Architectures In Guilearch-float-type
: Architectures In Guilearch-int-type
: Architectures In Guilearch-int16-type
: Architectures In Guilearch-int32-type
: Architectures In Guilearch-int64-type
: Architectures In Guilearch-int8-type
: Architectures In Guilearch-long-type
: Architectures In Guilearch-longdouble-type
: Architectures In Guilearch-longlong-type
: Architectures In Guilearch-name
: Architectures In Guilearch-schar-type
: Architectures In Guilearch-short-type
: Architectures In Guilearch-uchar-type
: Architectures In Guilearch-uint-type
: Architectures In Guilearch-uint16-type
: Architectures In Guilearch-uint32-type
: Architectures In Guilearch-uint64-type
: Architectures In Guilearch-uint8-type
: Architectures In Guilearch-ulong-type
: Architectures In Guilearch-ulonglong-type
: Architectures In Guilearch-ushort-type
: Architectures In Guilearch-void-type
: Architectures In Guilearch-wide-charset
: Architectures In Guilearch?
: Architectures In GuileArchitecture.disassemble
: Architectures In PythonArchitecture.name
: Architectures In Pythonattach
: Attachattach&
: Background Executionawatch
: Set Watchpointsb
(break
): Set Breaksbacktrace
: Backtracebackward-char (C-b)
: Commands For Movingbackward-delete-char (Rubout)
: Commands For Textbackward-kill-line (C-x Rubout)
: Commands For Killingbackward-kill-word (M-<DEL>)
: Commands For Killingbackward-word (M-b)
: Commands For Movingbeginning-of-history (M-<)
: Commands For Historybeginning-of-line (C-a)
: Commands For Movingbell-style
: Readline Init File Syntaxbfd caching
: File Cachingbind-tty-special-chars
: Readline Init File Syntaxblink-matching-paren
: Readline Init File Syntaxblock-end
: Blocks In Guileblock-function
: Blocks In Guileblock-global-block
: Blocks In Guileblock-global?
: Blocks In Guileblock-start
: Blocks In Guileblock-static-block
: Blocks In Guileblock-static?
: Blocks In Guileblock-superblock
: Blocks In Guileblock-symbols
: Blocks In Guileblock-symbols-progress?
: Blocks In Guileblock-valid?
: Blocks In GuileBlock.end
: Blocks In PythonBlock.function
: Blocks In PythonBlock.global_block
: Blocks In PythonBlock.is_global
: Blocks In PythonBlock.is_static
: Blocks In PythonBlock.is_valid
: Blocks In PythonBlock.start
: Blocks In PythonBlock.static_block
: Blocks In PythonBlock.superblock
: Blocks In Pythonblock?
: Blocks In GuileBP_ACCESS_WATCHPOINT
: Breakpoints In GuileBP_ACCESS_WATCHPOINT
: Breakpoints In PythonBP_BREAKPOINT
: Breakpoints In GuileBP_BREAKPOINT
: Breakpoints In PythonBP_HARDWARE_WATCHPOINT
: Breakpoints In GuileBP_HARDWARE_WATCHPOINT
: Breakpoints In PythonBP_READ_WATCHPOINT
: Breakpoints In GuileBP_READ_WATCHPOINT
: Breakpoints In PythonBP_WATCHPOINT
: Breakpoints In GuileBP_WATCHPOINT
: Breakpoints In Pythonbracketed-paste-begin ()
: Commands For Textbreak
: Set Breaksbreak ... task
taskno (Ada): Ada Tasksbreak ... thread
thread-id: Thread-Specific Breakpointsbreak
, and Objective-C: Method Names in Commandsbreak-range
: PowerPC Embeddedbreakpoint annotation
: Annotations for Runningbreakpoint-commands
: Breakpoints In Guilebreakpoint-condition
: Breakpoints In Guilebreakpoint-enabled?
: Breakpoints In Guilebreakpoint-expression
: Breakpoints In Guilebreakpoint-hit-count
: Breakpoints In Guilebreakpoint-ignore-count
: Breakpoints In Guilebreakpoint-location
: Breakpoints In Guilebreakpoint-notifications
: GDB/MI Support Commandsbreakpoint-number
: Breakpoints In Guilebreakpoint-silent?
: Breakpoints In Guilebreakpoint-stop
: Breakpoints In Guilebreakpoint-task
: Breakpoints In Guilebreakpoint-thread
: Breakpoints In Guilebreakpoint-type
: Breakpoints In Guilebreakpoint-valid?
: Breakpoints In Guilebreakpoint-visible?
: Breakpoints In GuileBreakpoint.__init__
: Breakpoints In PythonBreakpoint.commands
: Breakpoints In PythonBreakpoint.condition
: Breakpoints In PythonBreakpoint.delete
: Breakpoints In PythonBreakpoint.enabled
: Breakpoints In PythonBreakpoint.expression
: Breakpoints In PythonBreakpoint.hit_count
: Breakpoints In PythonBreakpoint.ignore_count
: Breakpoints In PythonBreakpoint.is_valid
: Breakpoints In PythonBreakpoint.location
: Breakpoints In PythonBreakpoint.number
: Breakpoints In PythonBreakpoint.pending
: Breakpoints In PythonBreakpoint.silent
: Breakpoints In PythonBreakpoint.stop
: Breakpoints In PythonBreakpoint.task
: Breakpoints In PythonBreakpoint.temporary
: Breakpoints In PythonBreakpoint.thread
: Breakpoints In PythonBreakpoint.type
: Breakpoints In PythonBreakpoint.visible
: Breakpoints In Pythonbreakpoint?
: Breakpoints In GuileBreakpointEvent.breakpoint
: Events In PythonBreakpointEvent.breakpoints
: Events In Pythonbreakpoints
: Breakpoints In Guilebreakpoints-invalid annotation
: Invalidationbt
(backtrace
): Backtracec
(continue
): Continuing and Steppingc
(SingleKey TUI key): TUI Single Key ModeC-L
: TUI KeysC-x 1
: TUI KeysC-x 2
: TUI KeysC-x A
: TUI KeysC-x a
: TUI KeysC-x C-a
: TUI KeysC-x o
: TUI KeysC-x s
: TUI Keyscall
: Callingcall-last-kbd-macro (C-x e)
: Keyboard Macroscapitalize-word (M-c)
: Commands For Textcatch
: Set Catchpointscatch assert
: Set Catchpointscatch catch
: Set Catchpointscatch exception
: Set Catchpointscatch exception unhandled
: Set Catchpointscatch exec
: Set Catchpointscatch fork
: Set Catchpointscatch handlers
: Set Catchpointscatch load
: Set Catchpointscatch rethrow
: Set Catchpointscatch signal
: Set Catchpointscatch syscall
: Set Catchpointscatch throw
: Set Catchpointscatch unload
: Set Catchpointscatch vfork
: Set Catchpointscd
: Working Directorycdir
: Source Pathcharacter-search (C-])
: Miscellaneous Commandscharacter-search-backward (M-C-])
: Miscellaneous Commandscheckpoint
: Checkpoint/Restartclear
: Delete Breaksclear
, and Objective-C: Method Names in Commandsclear-screen (C-l)
: Commands For MovingClearObjFilesEvent.progspace
: Events In Pythonclone-inferior
: Inferiors and Programscollect
(tracepoints): Tracepoint Actionscolored-completion-prefix
: Readline Init File Syntaxcolored-stats
: Readline Init File SyntaxCommand.__init__
: Commands In PythonCommand.complete
: Commands In PythonCommand.dont_repeat
: Commands In PythonCommand.invoke
: Commands In Pythoncommand?
: Commands In GuileCOMMAND_BREAKPOINTS
: Commands In GuileCOMMAND_BREAKPOINTS
: Commands In PythonCOMMAND_DATA
: Commands In GuileCOMMAND_DATA
: Commands In PythonCOMMAND_FILES
: Commands In GuileCOMMAND_FILES
: Commands In PythonCOMMAND_MAINTENANCE
: Commands In GuileCOMMAND_MAINTENANCE
: Commands In PythonCOMMAND_NONE
: Commands In GuileCOMMAND_NONE
: Commands In PythonCOMMAND_OBSCURE
: Commands In GuileCOMMAND_OBSCURE
: Commands In PythonCOMMAND_RUNNING
: Commands In GuileCOMMAND_RUNNING
: Commands In PythonCOMMAND_STACK
: Commands In GuileCOMMAND_STACK
: Commands In PythonCOMMAND_STATUS
: Commands In GuileCOMMAND_STATUS
: Commands In PythonCOMMAND_SUPPORT
: Commands In GuileCOMMAND_SUPPORT
: Commands In PythonCOMMAND_TRACEPOINTS
: Commands In GuileCOMMAND_TRACEPOINTS
: Commands In PythonCOMMAND_USER
: Commands In GuileCOMMAND_USER
: Commands In Pythoncommands
: Break Commandscommands annotation
: Promptingcomment-begin
: Readline Init File Syntaxcompare-sections
: Memorycompile code
: Compiling and Injecting Codecompile file
: Compiling and Injecting Codecomplete
: Helpcomplete (<TAB>)
: Commands For CompletionCOMPLETE_COMMAND
: Commands In GuileCOMPLETE_COMMAND
: Commands In PythonCOMPLETE_EXPRESSION
: Commands In GuileCOMPLETE_EXPRESSION
: Commands In PythonCOMPLETE_FILENAME
: Commands In GuileCOMPLETE_FILENAME
: Commands In PythonCOMPLETE_LOCATION
: Commands In GuileCOMPLETE_LOCATION
: Commands In PythonCOMPLETE_NONE
: Commands In GuileCOMPLETE_NONE
: Commands In PythonCOMPLETE_SYMBOL
: Commands In GuileCOMPLETE_SYMBOL
: Commands In Pythoncompletion-display-width
: Readline Init File Syntaxcompletion-ignore-case
: Readline Init File Syntaxcompletion-map-case
: Readline Init File Syntaxcompletion-prefix-display-length
: Readline Init File Syntaxcompletion-query-items
: Readline Init File Syntaxcondition
: Conditionscontinue
: Continuing and Steppingcontinue&
: Background Executionconvert-meta
: Readline Init File Syntaxcopy-backward-word ()
: Commands For Killingcopy-forward-word ()
: Commands For Killingcopy-region-as-kill ()
: Commands For Killingcore-file
: Filesctf
: Trace FilesCtrl-o
(operate-and-get-next): Command Syntaxcurrent-arch
: Architectures In Guilecurrent-objfile
: Objfiles In Guilecurrent-progspace
: Progspaces In Guilecwd
: Source Pathd
(delete
): Delete Breaksd
(SingleKey TUI key): TUI Single Key Modedata-directory
: Guile Configurationdata-disassemble-a-option
: GDB/MI Support Commandsdata-read-memory-bytes
: GDB/MI Support Commandsdefault-visualizer
: Guile Pretty Printing APIdefine
: Definedefine-prefix
: Definedelete
: Delete Breaksdelete checkpoint
checkpoint-id: Checkpoint/Restartdelete display
: Auto Displaydelete mem
: Memory Region Attributesdelete tracepoint
: Create and Delete Tracepointsdelete tvariable
: Trace State Variablesdelete-breakpoint!
: Breakpoints In Guiledelete-char (C-d)
: Commands For Textdelete-char-or-list ()
: Commands For Completiondelete-horizontal-space ()
: Commands For Killingdemangle
: Symbolsdetach
: Attachdetach (remote)
: Connectingdetach inferiors
infno...
: Inferiors and Programsdfw send
: VxWorksdigit-argument (
M-0,
M-1, ...
M--)
: Numeric Argumentsdir
: Source Pathdirectory
: Source Pathdis
(disable
): Disablingdisable
: Disablingdisable display
: Auto Displaydisable frame-filter
: Frame Filter Managementdisable mem
: Memory Region Attributesdisable pretty-printer
: Pretty-Printer Commandsdisable probes
: Static Probe Pointsdisable tracepoint
: Enable and Disable Tracepointsdisable type-printer
: Symbolsdisable-completion
: Readline Init File Syntaxdisassemble
: Machine Codedisconnect
: Connectingdisplay
: Auto Displaydo
(down
): Selectiondo-lowercase-version (M-A, M-B, M-
x, ...)
: Miscellaneous Commandsdocument
: Definedont-repeat
: Commands In Guiledont-repeat
: DefineDown
: TUI Keysdown
: Selectiondown-silently
: Selectiondowncase-word (M-l)
: Commands For Textdprintf
: Dynamic Printfdprintf-style agent
: Dynamic Printfdprintf-style call
: Dynamic Printfdprintf-style gdb
: Dynamic Printfdump
: Dump/Restore Filesdump-functions ()
: Miscellaneous Commandsdump-macros ()
: Miscellaneous Commandsdump-variables ()
: Miscellaneous Commandse
(edit
): Editecho
: Outputecho-control-characters
: Readline Init File Syntaxedit
: Editediting-mode
: Readline Init File Syntaxelse
: Command Filesemacs-mode-string
: Readline Init File Syntaxenable
: Disablingenable display
: Auto Displayenable frame-filter
: Frame Filter Managementenable mem
: Memory Region Attributesenable pretty-printer
: Pretty-Printer Commandsenable probes
: Static Probe Pointsenable tracepoint
: Enable and Disable Tracepointsenable type-printer
: Symbolsenable-bracketed-paste
: Readline Init File Syntaxenable-keypad
: Readline Init File Syntaxenabled
: Xmethod APIenabled
: Type Printing APIend
(breakpoint commands): Break Commandsend
(if/else/while commands): Command Filesend
(user-defined commands): Defineend-kbd-macro (C-x ))
: Keyboard Macros (usually C-d)
: Commands For Textend-of-history (M->)
: Commands For Historyend-of-iteration
: Iterators In Guileend-of-iteration?
: Iterators In Guileend-of-line (C-e)
: Commands For Movingerror annotation
: Errorserror-begin annotation
: Errorserror-port
: I/O Ports in Guileeval
: OutputEventRegistry.connect
: Events In PythonEventRegistry.disconnect
: Events In Pythonexception-args
: Guile Exception Handlingexception-key
: Guile Exception Handlingexception?
: Guile Exception HandlingexceptionHandler
: Bootstrappingexchange-point-and-mark (C-x C-x)
: Miscellaneous Commandsexec-file
: Filesexec-run-start-option
: GDB/MI Support Commandsexecute
: Basic Guileexited annotation
: Annotations for RunningExitedEvent.exit_code
: Events In PythonExitedEvent.inferior
: Events In Pythonexpand-tilde
: Readline Init File Syntaxexplore
: Dataf
(frame
): Selectionf
(SingleKey TUI key): TUI Single Key Modefaas
: Frame Applyfg
(resume foreground execution): Continuing and Steppingfield-artificial?
: Types In Guilefield-base-class?
: Types In Guilefield-bitpos
: Types In Guilefield-bitsize
: Types In Guilefield-enumval
: Types In Guilefield-name
: Types In Guilefield-type
: Types In Guilefield?
: Types In Guilefile
: Filesfin
(finish
): Continuing and Steppingfind
: Searching Memoryfind-pc-line
: Symbol Tables In Guilefinish
: Continuing and Steppingfinish&
: Background ExecutionFinishBreakpoint.__init__
: Finish Breakpoints in PythonFinishBreakpoint.out_of_scope
: Finish Breakpoints in PythonFinishBreakpoint.return_value
: Finish Breakpoints in Pythonflash-erase
: Target Commandsflush_i_cache
: Bootstrappingflushregs
: Maintenance Commandsfo
(forward-search
): Searchfocus
: TUI Commandsforward-backward-delete-char ()
: Commands For Textforward-char (C-f)
: Commands For Movingforward-search
: Searchforward-search-history (C-s)
: Commands For Historyforward-word (M-f)
: Commands For Movingframe address
: Selectionframe apply
: Frame Applyframe function
: Selectionframe level
: Selectionframe view
: Selectionframe
, selecting: Selectionframe-arch
: Frames In Guileframe-block
: Frames In Guileframe-function
: Frames In Guileframe-name
: Frames In Guileframe-newer
: Frames In Guileframe-older
: Frames In Guileframe-pc
: Frames In Guileframe-read-register
: Frames In Guileframe-read-var
: Frames In Guileframe-sal
: Frames In Guileframe-select
: Frames In Guileframe-type
: Frames In Guileframe-unwind-stop-reason
: Frames In Guileframe-valid?
: Frames In GuileFrame.architecture
: Frames In PythonFrame.block
: Frames In PythonFrame.find_sal
: Frames In PythonFrame.function
: Frames In PythonFrame.is_valid
: Frames In PythonFrame.name
: Frames In PythonFrame.newer
: Frames In PythonFrame.older
: Frames In PythonFrame.pc
: Frames In PythonFrame.read_register
: Frames In PythonFrame.read_var
: Frames In PythonFrame.select
: Frames In PythonFrame.type
: Frames In PythonFrame.unwind_stop_reason
: Frames In Pythonframe?
: Frames In GuileFrameDecorator.address
: Frame Decorator APIFrameDecorator.elided
: Frame Decorator APIFrameDecorator.filename
: Frame Decorator APIFrameDecorator.frame_args
: Frame Decorator APIFrameDecorator.frame_locals
: Frame Decorator APIFrameDecorator.function
: Frame Decorator APIFrameDecorator.inferior_frame
: Frame Decorator APIFrameDecorator.line
: Frame Decorator APIFrameFilter.enabled
: Frame Filter APIFrameFilter.filter
: Frame Filter APIFrameFilter.name
: Frame Filter APIFrameFilter.priority
: Frame Filter APIframes-invalid annotation
: Invalidationfrozen-varobjs
: GDB/MI Support Commandsftrace
: Create and Delete TracepointsFunction
: Functions In PythonFunction.__init__
: Functions In PythonFunction.invoke
: Functions In Pythongcore
: Core File Generationgdb-object-kind
: GDB Scheme Data Typesgdb-version
: Guile Configurationgdb.Block
: Blocks In Pythongdb.block_for_pc
: Blocks In Pythongdb.BP_ACCESS_WATCHPOINT
: Breakpoints In Pythongdb.BP_BREAKPOINT
: Breakpoints In Pythongdb.BP_HARDWARE_WATCHPOINT
: Breakpoints In Pythongdb.BP_READ_WATCHPOINT
: Breakpoints In Pythongdb.BP_WATCHPOINT
: Breakpoints In Pythongdb.Breakpoint
: Breakpoints In Pythongdb.breakpoints
: Basic Pythongdb.COMMAND_BREAKPOINTS
: Commands In Pythongdb.COMMAND_DATA
: Commands In Pythongdb.COMMAND_FILES
: Commands In Pythongdb.COMMAND_MAINTENANCE
: Commands In Pythongdb.COMMAND_NONE
: Commands In Pythongdb.COMMAND_OBSCURE
: Commands In Pythongdb.COMMAND_RUNNING
: Commands In Pythongdb.COMMAND_STACK
: Commands In Pythongdb.COMMAND_STATUS
: Commands In Pythongdb.COMMAND_SUPPORT
: Commands In Pythongdb.COMMAND_TRACEPOINTS
: Commands In Pythongdb.COMMAND_USER
: Commands In Pythongdb.COMPLETE_COMMAND
: Commands In Pythongdb.COMPLETE_EXPRESSION
: Commands In Pythongdb.COMPLETE_FILENAME
: Commands In Pythongdb.COMPLETE_LOCATION
: Commands In Pythongdb.COMPLETE_NONE
: Commands In Pythongdb.COMPLETE_SYMBOL
: Commands In Pythongdb.convenience_variable
: Basic Pythongdb.current_objfile
: Objfiles In Pythongdb.current_progspace
: Progspaces In Pythongdb.current_recording
: Recordings In Pythongdb.decode_line
: Basic Pythongdb.default_visualizer
: Pretty Printing APIgdb.error
: Exception Handlinggdb.execute
: Basic Pythongdb.find_pc_line
: Basic Pythongdb.FinishBreakpoint
: Finish Breakpoints in Pythongdb.flush
: Basic Pythongdb.frame_stop_reason_string
: Frames In Pythongdb.FrameDecorator
: Frame Decorator APIgdb.Function
: Functions In Pythongdb.GdbError
: Exception Handlinggdb.history
: Basic Pythongdb.Inferior
: Inferiors In Pythongdb.InferiorCallPostEvent
: Events In Pythongdb.InferiorCallPreEvent
: Events In Pythongdb.inferiors
: Inferiors In Pythongdb.InferiorThread
: Threads In Pythongdb.invalidate_cached_frames
: Frames In Pythongdb.LazyString
: Lazy Strings In Pythongdb.LineTable
: Line Tables In Pythongdb.lookup_global_symbol
: Symbols In Pythongdb.lookup_objfile
: Objfiles In Pythongdb.lookup_static_symbol
: Symbols In Pythongdb.lookup_static_symbols
: Symbols In Pythongdb.lookup_symbol
: Symbols In Pythongdb.lookup_type
: Types In Pythongdb.MemoryError
: Exception Handlinggdb.newest_frame
: Frames In Pythongdb.Objfile
: Objfiles In Pythongdb.objfiles
: Objfiles In Pythongdb.PARAM_AUTO_BOOLEAN
: Parameters In Pythongdb.PARAM_BOOLEAN
: Parameters In Pythongdb.PARAM_ENUM
: Parameters In Pythongdb.PARAM_FILENAME
: Parameters In Pythongdb.PARAM_INTEGER
: Parameters In Pythongdb.PARAM_OPTIONAL_FILENAME
: Parameters In Pythongdb.PARAM_STRING
: Parameters In Pythongdb.PARAM_STRING_NOESCAPE
: Parameters In Pythongdb.PARAM_UINTEGER
: Parameters In Pythongdb.PARAM_ZINTEGER
: Parameters In Pythongdb.PARAM_ZUINTEGER
: Parameters In Pythongdb.PARAM_ZUINTEGER_UNLIMITED
: Parameters In Pythongdb.Parameter
: Parameters In Pythongdb.parameter
: Basic Pythongdb.parse_and_eval
: Basic Pythongdb.post_event
: Basic Pythongdb.pretty_printers
: Selecting Pretty-Printersgdb.Progspace
: Progspaces In Pythongdb.progspaces
: Progspaces In Pythongdb.prompt_hook
: Basic Pythongdb.PYTHONDIR
: Basic Pythongdb.rbreak
: Basic Pythongdb.search_memory
: Inferiors In Pythongdb.selected_frame
: Frames In Pythongdb.selected_inferior
: Inferiors In Pythongdb.selected_thread
: Threads In Pythongdb.set_convenience_variable
: Basic Pythongdb.solib_name
: Basic Pythongdb.start_recording
: Recordings In Pythongdb.STDERR
: Basic Pythongdb.STDLOG
: Basic Pythongdb.STDOUT
: Basic Pythongdb.stop_recording
: Recordings In Pythongdb.string_to_argv
: Commands In Pythongdb.Symbol
: Symbols In Pythongdb.SYMBOL_COMMON_BLOCK_DOMAIN
: Symbols In Pythongdb.SYMBOL_LABEL_DOMAIN
: Symbols In Pythongdb.SYMBOL_LOC_ARG
: Symbols In Pythongdb.SYMBOL_LOC_BLOCK
: Symbols In Pythongdb.SYMBOL_LOC_COMPUTED
: Symbols In Pythongdb.SYMBOL_LOC_CONST
: Symbols In Pythongdb.SYMBOL_LOC_CONST_BYTES
: Symbols In Pythongdb.SYMBOL_LOC_LOCAL
: Symbols In Pythongdb.SYMBOL_LOC_OPTIMIZED_OUT
: Symbols In Pythongdb.SYMBOL_LOC_REF_ARG
: Symbols In Pythongdb.SYMBOL_LOC_REGISTER
: Symbols In Pythongdb.SYMBOL_LOC_REGPARM_ADDR
: Symbols In Pythongdb.SYMBOL_LOC_STATIC
: Symbols In Pythongdb.SYMBOL_LOC_TYPEDEF
: Symbols In Pythongdb.SYMBOL_LOC_UNDEF
: Symbols In Pythongdb.SYMBOL_LOC_UNRESOLVED
: Symbols In Pythongdb.SYMBOL_MODULE_DOMAIN
: Symbols In Pythongdb.SYMBOL_STRUCT_DOMAIN
: Symbols In Pythongdb.SYMBOL_UNDEF_DOMAIN
: Symbols In Pythongdb.SYMBOL_VAR_DOMAIN
: Symbols In Pythongdb.Symtab
: Symbol Tables In Pythongdb.Symtab_and_line
: Symbol Tables In Pythongdb.target_charset
: Basic Pythongdb.target_wide_charset
: Basic Pythongdb.Type
: Types In Pythongdb.TYPE_CODE_ARRAY
: Types In Pythongdb.TYPE_CODE_BITSTRING
: Types In Pythongdb.TYPE_CODE_BOOL
: Types In Pythongdb.TYPE_CODE_CHAR
: Types In Pythongdb.TYPE_CODE_COMPLEX
: Types In Pythongdb.TYPE_CODE_DECFLOAT
: Types In Pythongdb.TYPE_CODE_ENUM
: Types In Pythongdb.TYPE_CODE_ERROR
: Types In Pythongdb.TYPE_CODE_FLAGS
: Types In Pythongdb.TYPE_CODE_FLT
: Types In Pythongdb.TYPE_CODE_FUNC
: Types In Pythongdb.TYPE_CODE_INT
: Types In Pythongdb.TYPE_CODE_INTERNAL_FUNCTION
: Types In Pythongdb.TYPE_CODE_MEMBERPTR
: Types In Pythongdb.TYPE_CODE_METHOD
: Types In Pythongdb.TYPE_CODE_METHODPTR
: Types In Pythongdb.TYPE_CODE_NAMESPACE
: Types In Pythongdb.TYPE_CODE_PTR
: Types In Pythongdb.TYPE_CODE_RANGE
: Types In Pythongdb.TYPE_CODE_REF
: Types In Pythongdb.TYPE_CODE_RVALUE_REF
: Types In Pythongdb.TYPE_CODE_SET
: Types In Pythongdb.TYPE_CODE_STRING
: Types In Pythongdb.TYPE_CODE_STRUCT
: Types In Pythongdb.TYPE_CODE_TYPEDEF
: Types In Pythongdb.TYPE_CODE_UNION
: Types In Pythongdb.TYPE_CODE_VOID
: Types In Pythongdb.unwinder.register_unwinder
: Unwinding Frames in Pythongdb.UnwindInfo.add_saved_register
: Unwinding Frames in Pythongdb.WP_ACCESS
: Breakpoints In Pythongdb.WP_READ
: Breakpoints In Pythongdb.WP_WRITE
: Breakpoints In Pythongdb.write
: Basic Pythongdb:error
: Guile Exception Handlinggdb:invalid-object
: Guile Exception Handlinggdb:memory-error
: Guile Exception Handlinggdb:pp-type-error
: Guile Exception Handlinggdb_init_reader
: Writing JIT Debug Info Readersgdbserver
: Servergenerate-core-file
: Core File Generationget-basic-type
: Guile Types ModulegetDebugChar
: Bootstrappinggnu_debuglink_crc32
: Separate Debug Filesgr
: Guile Commandsgu
: Guile Commandsguile
: Guile Commandsguile-data-directory
: Guile Configurationguile-repl
: Guile Commandsh
(help
): Helphandle
: Signalshandle_exception
: Stub Contentshbreak
: Set Breakshelp
: Helphelp function
: Convenience Funshelp target
: Target Commandshelp user-defined
: Definehistory-append!
: Basic Guilehistory-preserve-point
: Readline Init File Syntaxhistory-ref
: Basic Guilehistory-search-backward ()
: Commands For Historyhistory-search-forward ()
: Commands For Historyhistory-size
: Readline Init File Syntaxhistory-substring-search-backward ()
: Commands For Historyhistory-substring-search-forward ()
: Commands For Historyhook
: Hookshookpost
: Hookshorizontal-scroll-mode
: Readline Init File Syntaxhost-config
: Guile Configurationi
(info
): Helpi
(SingleKey TUI key): TUI Single Key Modeif
: Command Filesignore
: Conditionsinferior
infno: Inferiors and ProgramsInferior.architecture
: Inferiors In PythonInferior.is_valid
: Inferiors In PythonInferior.num
: Inferiors In PythonInferior.pid
: Inferiors In PythonInferior.progspace
: Inferiors In PythonInferior.read_memory
: Inferiors In PythonInferior.search_memory
: Inferiors In PythonInferior.thread_from_handle
: Inferiors In PythonInferior.thread_from_thread_handle
: Inferiors In PythonInferior.threads
: Inferiors In PythonInferior.was_attached
: Inferiors In PythonInferior.write_memory
: Inferiors In PythonInferiorCallPostEvent.address
: Events In PythonInferiorCallPostEvent.ptid
: Events In PythonInferiorCallPreEvent.address
: Events In PythonInferiorCallPreEvent.ptid
: Events In PythonInferiorThread.global_num
: Threads In PythonInferiorThread.handle
: Threads In PythonInferiorThread.inferior
: Threads In PythonInferiorThread.is_exited
: Threads In PythonInferiorThread.is_running
: Threads In PythonInferiorThread.is_stopped
: Threads In PythonInferiorThread.is_valid
: Threads In PythonInferiorThread.name
: Threads In PythonInferiorThread.num
: Threads In PythonInferiorThread.ptid
: Threads In PythonInferiorThread.switch
: Threads In Pythoninfo
: Helpinfo address
: Symbolsinfo all-registers
: Registersinfo args
: Frame Infoinfo auto-load
: Auto-loadinginfo auto-load gdb-scripts
: Auto-loading sequencesinfo auto-load guile-scripts
: Guile Auto-loadinginfo auto-load libthread-db
: libthread_db.so.1 fileinfo auto-load local-gdbinit
: Init File in the Current Directoryinfo auto-load python-scripts
: Python Auto-loadinginfo auxv
: OS Informationinfo breakpoints
: Set Breaksinfo checkpoints
: Checkpoint/Restartinfo classes
: Symbolsinfo common
: Special Fortran Commandsinfo copying
: Helpinfo dcache
: Caching Target Datainfo display
: Auto Displayinfo dll
: Filesinfo dos
: DJGPP Nativeinfo exceptions
: Ada Exceptionsinfo extensions
: Showinfo f
(info frame
): Frame Infoinfo files
: Filesinfo float
: Floating Point Hardwareinfo frame
: Frame Infoinfo frame
, show the source language: Showinfo frame-filter
: Frame Filter Managementinfo functions
: Symbolsinfo handle
: Signalsinfo inferiors [
id... ]
: Inferiors and Programsinfo io_registers
, AVR: AVRinfo line
: Machine Codeinfo line
, and Objective-C: Method Names in Commandsinfo locals
: Frame Infoinfo macro
: Macrosinfo macros
: Macrosinfo mem
: Memory Region Attributesinfo meminfo
: Process Informationinfo module
: Symbolsinfo modules
: Symbolsinfo os
: OS Informationinfo os cpus
: OS Informationinfo os files
: OS Informationinfo os modules
: OS Informationinfo os msg
: OS Informationinfo os processes
: OS Informationinfo os procgroups
: OS Informationinfo os semaphores
: OS Informationinfo os shm
: OS Informationinfo os sockets
: OS Informationinfo os threads
: OS Informationinfo partitions
: VxWorksinfo pidlist
: Process Informationinfo pretty-printer
: Pretty-Printer Commandsinfo probes
: Static Probe Pointsinfo proc
: Process Informationinfo program
: Stoppinginfo record
: Process Record and Replayinfo registers
: Registersinfo scope
: Symbolsinfo selectors
: Symbolsinfo serial
: DJGPP Nativeinfo set
: Helpinfo share
: Filesinfo sharedlibrary
: Filesinfo signals
: Signalsinfo skip
: Skipping Over Functions and Filesinfo source
: Symbolsinfo source
, show the source language: Showinfo sources
: Symbolsinfo stack
: Backtraceinfo static-tracepoint-markers
: Listing Static Tracepoint Markersinfo symbol
: Symbolsinfo target
: Filesinfo task
taskno: Ada Tasksinfo tasks
: Ada Tasksinfo terminal
: Input/Outputinfo threads
: Threadsinfo tp
[n...
]: Listing Tracepointsinfo tracepoints
[n...
]: Listing Tracepointsinfo tvariables
: Trace State Variablesinfo type-printers
: Symbolsinfo types
: Symbolsinfo variables
: Symbolsinfo vector
: Vector Unitinfo w32
: Cygwin Nativeinfo warranty
: Helpinfo watchpoints
[list...
]: Set Watchpointsinfo win
: TUI Commandsinfo wtx
: VxWorksinfo wtx target-server
: VxWorksinfo wtx threads
: VxWorksinfo wtx vxworks-version
: VxWorksinfo-gdb-mi-command
: GDB/MI Support Commandsinit-if-undefined
: Convenience Varsinput-meta
: Readline Init File Syntaxinput-port
: I/O Ports in Guileinsert-comment (M-#)
: Miscellaneous Commandsinsert-completions (M-*)
: Commands For Completioninspect
: Datainstantiate on type_printer
: Type Printing APIInstruction.data
: Recordings In PythonInstruction.decoded
: Recordings In PythonInstruction.pc
: Recordings In PythonInstruction.size
: Recordings In Pythoninterpreter-exec
: Interpretersinterrupt
: Background Executionisearch-terminators
: Readline Init File Syntaxiterator->list
: Iterators In Guileiterator-filter
: Iterators In Guileiterator-for-each
: Iterators In Guileiterator-map
: Iterators In Guileiterator-next!
: Iterators In Guileiterator-object
: Iterators In Guileiterator-progress
: Iterators In Guileiterator-until
: Iterators In Guileiterator?
: Iterators In Guilej
(jump
): Jumpingjit-reader-load
: Using JIT Debug Info Readersjit-reader-unload
: Using JIT Debug Info Readersjump
: Jumpingjump
, and Objective-C: Method Names in CommandsKeyboardInterrupt
: Exception Handlingkeymap
: Readline Init File Syntaxkill
: Kill Processkill inferiors
infno...
: Inferiors and Programskill-line (C-k)
: Commands For Killingkill-region ()
: Commands For Killingkill-whole-line ()
: Commands For Killingkill-word (M-d)
: Commands For Killingkvm
: BSD libkvm Interfacel
(list
): Listlanguage-option
: GDB/MI Support Commandslayout
: TUI Commandslazy-string->value
: Lazy Strings In Guilelazy-string-address
: Lazy Strings In Guilelazy-string-encoding
: Lazy Strings In Guilelazy-string-length
: Lazy Strings In Guilelazy-string-type
: Lazy Strings In Guilelazy-string?
: Lazy Strings In GuileLazyString.address
: Lazy Strings In PythonLazyString.encoding
: Lazy Strings In PythonLazyString.length
: Lazy Strings In PythonLazyString.type
: Lazy Strings In PythonLazyString.value
: Lazy Strings In PythonLeft
: TUI KeysLineTable.has_line
: Line Tables In PythonLineTable.line
: Line Tables In PythonLineTable.source_lines
: Line Tables In PythonLineTableEntry.line
: Line Tables In PythonLineTableEntry.pc
: Line Tables In Pythonlist
: Listlist
, and Objective-C: Method Names in Commandsload
filename offset: Target Commandslookup-block
: Blocks In Guilelookup-global-symbol
: Symbols In Guilelookup-symbol
: Symbols In Guilelookup-type
: Types In Guileloop_break
: Command Filesloop_continue
: Command Filesmacro define
: Macrosmacro exp1
: Macrosmacro expand
: Macrosmacro list
: Macrosmacro undef
: Macrosmaint ada set ignore-descriptive-types
: Ada Glitchesmaint ada show ignore-descriptive-types
: Ada Glitchesmaint agent
: Maintenance Commandsmaint agent-eval
: Maintenance Commandsmaint agent-printf
: Maintenance Commandsmaint btrace clear
: Maintenance Commandsmaint btrace clear-packet-history
: Maintenance Commandsmaint btrace packet-history
: Maintenance Commandsmaint check libthread-db
: Maintenance Commandsmaint check xml-descriptions
: Maintenance Commandsmaint check-psymtabs
: Maintenance Commandsmaint check-symtabs
: Maintenance Commandsmaint cplus first_component
: Maintenance Commandsmaint cplus namespace
: Maintenance Commandsmaint demangler-warning
: Maintenance Commandsmaint deprecate
: Maintenance Commandsmaint dump-me
: Maintenance Commandsmaint expand-symtabs
: Maintenance Commandsmaint flush-symbol-cache
: Symbolsmaint info bdccsr
, S12Z: S12Zmaint info bfds
: File Cachingmaint info breakpoints
: Maintenance Commandsmaint info btrace
: Maintenance Commandsmaint info line-table
: Symbolsmaint info program-spaces
: Inferiors and Programsmaint info psymtabs
: Symbolsmaint info sections
: Filesmaint info selftests
: Maintenance Commandsmaint info sol-threads
: Threadsmaint info symtabs
: Symbolsmaint internal-error
: Maintenance Commandsmaint internal-warning
: Maintenance Commandsmaint packet
: Maintenance Commandsmaint print arc arc-instruction
: ARCmaint print architecture
: Maintenance Commandsmaint print c-tdesc
[file]: Maintenance Commandsmaint print cooked-registers
: Maintenance Commandsmaint print dummy-frames
: Maintenance Commandsmaint print msymbols
: Symbolsmaint print objfiles
: Maintenance Commandsmaint print psymbols
: Symbolsmaint print raw-registers
: Maintenance Commandsmaint print reggroups
: Maintenance Commandsmaint print register-groups
: Maintenance Commandsmaint print registers
: Maintenance Commandsmaint print remote-registers
: Maintenance Commandsmaint print section-scripts
: Maintenance Commandsmaint print statistics
: Maintenance Commandsmaint print symbol-cache
: Symbolsmaint print symbol-cache-statistics
: Symbolsmaint print symbols
: Symbolsmaint print target-stack
: Maintenance Commandsmaint print type
: Maintenance Commandsmaint print unwind
, HPPA: HPPAmaint print user-registers
: Maintenance Commandsmaint selftest
: Maintenance Commandsmaint set bfd-sharing
: File Cachingmaint set btrace pt skip-pad
: Maintenance Commandsmaint set catch-demangler-crashes
: Maintenance Commandsmaint set check-libthread-db
: Maintenance Commandsmaint set demangler-warning
: Maintenance Commandsmaint set dwarf always-disassemble
: Maintenance Commandsmaint set dwarf max-cache-age
: Maintenance Commandsmaint set dwarf unwinders
: Maintenance Commandsmaint set internal-error
: Maintenance Commandsmaint set internal-warning
: Maintenance Commandsmaint set per-command
: Maintenance Commandsmaint set profile
: Maintenance Commandsmaint set show-all-tib
: Maintenance Commandsmaint set show-debug-regs
: Maintenance Commandsmaint set symbol-cache-size
: Symbolsmaint set target-async
: Maintenance Commandsmaint set target-non-stop
mode [on|off|auto]
: Maintenance Commandsmaint set test-settings
: Maintenance Commandsmaint set tui-resize-message
: Maintenance Commandsmaint set worker-threads
: Maintenance Commandsmaint show bfd-sharing
: File Cachingmaint show btrace pt skip-pad
: Maintenance Commandsmaint show catch-demangler-crashes
: Maintenance Commandsmaint show check-libthread-db
: Maintenance Commandsmaint show demangler-warning
: Maintenance Commandsmaint show dwarf always-disassemble
: Maintenance Commandsmaint show dwarf max-cache-age
: Maintenance Commandsmaint show dwarf unwinders
: Maintenance Commandsmaint show internal-error
: Maintenance Commandsmaint show internal-warning
: Maintenance Commandsmaint show per-command
: Maintenance Commandsmaint show profile
: Maintenance Commandsmaint show show-all-tib
: Maintenance Commandsmaint show show-debug-regs
: Maintenance Commandsmaint show symbol-cache-size
: Symbolsmaint show target-async
: Maintenance Commandsmaint show target-non-stop
: Maintenance Commandsmaint show test-options-completion-result
: Maintenance Commandsmaint show test-settings
: Maintenance Commandsmaint show tui-resize-message
: Maintenance Commandsmaint show worker-threads
: Maintenance Commandsmaint space
: Maintenance Commandsmaint test-options
: Maintenance Commandsmaint time
: Maintenance Commandsmaint translate-address
: Maintenance Commandsmaint undeprecate
: Maintenance Commandsmaint with
: Maintenance Commandsmaintenance info link-path
: VxWorksmake
: Shell Commandsmake-block-symbols-iterator
: Blocks In Guilemake-breakpoint
: Breakpoints In Guilemake-enum-hashtable
: Guile Types Modulemake-exception
: Guile Exception Handlingmake-field-iterator
: Types In Guilemake-iterator
: Iterators In Guilemake-lazy-value
: Values From Inferior In Guilemake-list-iterator
: Iterators In Guilemake-pretty-printer
: Guile Pretty Printing APImake-pretty-printer-worker
: Guile Pretty Printing APImake-value
: Values From Inferior In Guilemark-modified-lines
: Readline Init File Syntaxmark-symlinked-directories
: Readline Init File Syntaxmatch-hidden-files
: Readline Init File Syntaxmay-insert-breakpoints
: Observer Modemay-insert-fast-tracepoints
: Observer Modemay-insert-tracepoints
: Observer Modemay-interrupt
: Observer Modemay-write-memory
: Observer Modemay-write-registers
: Observer Modemem
: Memory Region Attributesmemory-port-range
: Memory Ports in Guilememory-port-read-buffer-size
: Memory Ports in Guilememory-port-write-buffer-size
: Memory Ports in Guilememory-port?
: Memory Ports in GuileMemoryChangedEvent.address
: Events In PythonMemoryChangedEvent.length
: Events In Pythonmemset
: Bootstrappingmenu-complete ()
: Commands For Completionmenu-complete-backward ()
: Commands For Completionmenu-complete-display-prefix
: Readline Init File Syntaxmeta-flag
: Readline Init File Syntaxmethods
: Xmethod APImonitor
: Connectingn
(next
): Continuing and Steppingn
(SingleKey TUI key): TUI Single Key Modename
: Xmethod APIname
: Type Printing APInew-ui
: Interpretersnewest-frame
: Frames In GuileNewInferiorEvent.inferior
: Events In PythonNewObjFileEvent.new_objfile
: Events In PythonNewThreadEvent.inferior_thread
: Events In Pythonnext
: Continuing and Steppingnext&
: Background Executionnext-history (C-n)
: Commands For Historynext-screen-line ()
: Commands For Movingnexti
: Continuing and Steppingnexti&
: Background Executionni
(nexti
): Continuing and Steppingnon-incremental-forward-search-history (M-n)
: Commands For Historynon-incremental-reverse-search-history (M-p)
: Commands For Historynosharedlibrary
: Fileso
(SingleKey TUI key): TUI Single Key ModeObjfile
: Objfiles In Pythonobjfile-filename
: Objfiles In Guileobjfile-pretty-printers
: Objfiles In Guileobjfile-progspace
: Objfiles In Guileobjfile-valid?
: Objfiles In GuileObjfile.add_separate_debug_file
: Objfiles In PythonObjfile.build_id
: Objfiles In PythonObjfile.filename
: Objfiles In PythonObjfile.frame_filters
: Objfiles In PythonObjfile.is_valid
: Objfiles In PythonObjfile.lookup_global_symbol
: Objfiles In PythonObjfile.lookup_static_symbol
: Objfiles In PythonObjfile.owner
: Objfiles In PythonObjfile.pretty_printers
: Objfiles In PythonObjfile.progspace
: Objfiles In PythonObjfile.type_printers
: Objfiles In PythonObjfile.username
: Objfiles In Pythonobjfile?
: Objfiles In Guileobjfiles
: Objfiles In Guileobserver
: Observer Modeopen-memory
: Memory Ports in Guileoutput
: Outputoutput-meta
: Readline Init File Syntaxoutput-port
: I/O Ports in Guileoverlay
: Overlay Commandsoverload-choice annotation
: Promptingoverwrite-mode ()
: Commands For Textpage-completions
: Readline Init File SyntaxPARAM_AUTO_BOOLEAN
: Parameters In GuilePARAM_AUTO_BOOLEAN
: Parameters In PythonPARAM_BOOLEAN
: Parameters In GuilePARAM_BOOLEAN
: Parameters In PythonPARAM_ENUM
: Parameters In GuilePARAM_ENUM
: Parameters In PythonPARAM_FILENAME
: Parameters In GuilePARAM_FILENAME
: Parameters In PythonPARAM_INTEGER
: Parameters In PythonPARAM_OPTIONAL_FILENAME
: Parameters In GuilePARAM_OPTIONAL_FILENAME
: Parameters In PythonPARAM_STRING
: Parameters In GuilePARAM_STRING
: Parameters In PythonPARAM_STRING_NOESCAPE
: Parameters In GuilePARAM_STRING_NOESCAPE
: Parameters In PythonPARAM_UINTEGER
: Parameters In GuilePARAM_UINTEGER
: Parameters In PythonPARAM_ZINTEGER
: Parameters In GuilePARAM_ZINTEGER
: Parameters In PythonPARAM_ZUINTEGER
: Parameters In GuilePARAM_ZUINTEGER
: Parameters In PythonPARAM_ZUINTEGER_UNLIMITED
: Parameters In GuilePARAM_ZUINTEGER_UNLIMITED
: Parameters In PythonParameter
: Parameters In GuileParameter
: Parameters In Pythonparameter-value
: Parameters In GuileParameter.__init__
: Parameters In PythonParameter.get_set_string
: Parameters In PythonParameter.get_show_string
: Parameters In PythonParameter.set_doc
: Parameters In PythonParameter.show_doc
: Parameters In PythonParameter.value
: Parameters In Pythonparameter?
: Parameters In Guileparse-and-eval
: Basic Guilepartition
: VxWorkspasscount
: Tracepoint Passcountspath
: Environmentpending-breakpoints
: GDB/MI Support CommandsPendingFrame.create_unwind_info
: Unwinding Frames in PythonPendingFrame.read_register
: Unwinding Frames in PythonPgDn
: TUI KeysPgUp
: TUI Keyspi
: Python Commandspipe
: Shell Commandspo
(print-object
): The Print Command with Objective-Cpossible-completions (M-?)
: Commands For Completionpost-commands annotation
: Promptingpost-overload-choice annotation
: Promptingpost-prompt annotation
: Promptingpost-prompt-for-continue annotation
: Promptingpost-query annotation
: Promptingpre-commands annotation
: Promptingpre-overload-choice annotation
: Promptingpre-prompt annotation
: Promptingpre-prompt-for-continue annotation
: Promptingpre-query annotation
: Promptingprefix-meta (<ESC>)
: Miscellaneous Commandsprepend-pretty-printer!
: Guile Printing Modulepretty-printer-enabled?
: Guile Pretty Printing APIpretty-printer?
: Guile Pretty Printing APIpretty-printers
: Guile Pretty Printing APIpretty_printer.children
: Pretty Printing APIpretty_printer.display_hint
: Pretty Printing APIpretty_printer.to_string
: Pretty Printing APIprevious-history (C-p)
: Commands For Historyprevious-screen-line ()
: Commands For Movingprint
: Dataprint-last-kbd-macro ()
: Keyboard Macrosprint-object
: The Print Command with Objective-Cprintf
: Outputproc-trace-entry
: Process Informationproc-trace-exit
: Process Informationproc-untrace-entry
: Process Informationproc-untrace-exit
: Process InformationProgspace
: Progspaces In Pythonprogspace-filename
: Progspaces In Guileprogspace-objfiles
: Progspaces In Guileprogspace-pretty-printers
: Progspaces In Guileprogspace-valid?
: Progspaces In GuileProgspace.block_for_pc
: Progspaces In PythonProgspace.filename
: Progspaces In PythonProgspace.find_pc_line
: Progspaces In PythonProgspace.frame_filters
: Progspaces In PythonProgspace.is_valid
: Progspaces In PythonProgspace.objfiles
: Progspaces In PythonProgspace.pretty_printers
: Progspaces In PythonProgspace.solib_name
: Progspaces In PythonProgspace.type_printers
: Progspaces In Pythonprogspace?
: Progspaces In Guileprogspaces
: Progspaces In Guileprompt annotation
: Promptingprompt-for-continue annotation
: Promptingptype
: SymbolsputDebugChar
: Bootstrappingpwd
: Working Directorypy
: Python Commandspython
: GDB/MI Support Commandspython
: Python Commandspython-interactive
: Python Commandsq
(quit
): Quitting GDBq
(SingleKey TUI key): TUI Single Key Modequery annotation
: Promptingqueue-signal
: Signalingquit
[expression]: Quitting GDBquit annotation
: Errorsquoted-insert (C-q or C-v)
: Commands For Textr
(run
): Startingr
(SingleKey TUI key): TUI Single Key Moderbreak
: Set Breaksrc
(reverse-continue
): Reverse Executionre-read-init-file (C-x C-r)
: Miscellaneous Commandsreadnow
: Filesrec
: Process Record and Replayrec btrace
: Process Record and Replayrec btrace bts
: Process Record and Replayrec btrace pt
: Process Record and Replayrec bts
: Process Record and Replayrec del
: Process Record and Replayrec full
: Process Record and Replayrec function-call-history
: Process Record and Replayrec instruction-history
: Process Record and Replayrec pt
: Process Record and Replayrec s
: Process Record and Replayrecognize on type_recognizer
: Type Printing APIrecord
: Process Record and Replayrecord btrace
: Process Record and Replayrecord btrace bts
: Process Record and Replayrecord btrace pt
: Process Record and Replayrecord bts
: Process Record and Replayrecord delete
: Process Record and Replayrecord full
: Process Record and Replayrecord function-call-history
: Process Record and Replayrecord goto
: Process Record and Replayrecord instruction-history
: Process Record and Replayrecord pt
: Process Record and Replayrecord restore
: Process Record and Replayrecord save
: Process Record and Replayrecord stop
: Process Record and ReplayRecord.begin
: Recordings In PythonRecord.end
: Recordings In PythonRecord.format
: Recordings In PythonRecord.function_call_history
: Recordings In PythonRecord.goto
: Recordings In PythonRecord.instruction_history
: Recordings In PythonRecord.method
: Recordings In PythonRecord.replay_position
: Recordings In PythonRecordFunctionSegment.instructions
: Recordings In PythonRecordFunctionSegment.level
: Recordings In PythonRecordFunctionSegment.next
: Recordings In PythonRecordFunctionSegment.number
: Recordings In PythonRecordFunctionSegment.prev
: Recordings In PythonRecordFunctionSegment.symbol
: Recordings In PythonRecordFunctionSegment.up
: Recordings In PythonRecordGap.error_code
: Recordings In PythonRecordGap.error_string
: Recordings In PythonRecordGap.number
: Recordings In PythonRecordInstruction.is_speculative
: Recordings In PythonRecordInstruction.number
: Recordings In PythonRecordInstruction.sal
: Recordings In Pythonredraw-current-line ()
: Commands For Movingrefresh
: TUI Commandsregister-breakpoint!
: Breakpoints In Guileregister-command!
: Commands In Guileregister-parameter!
: Parameters In Guileregister_xmethod_matcher
: Xmethod APIRegisterChangedEvent.frame
: Events In PythonRegisterChangedEvent.regnum
: Events In Pythonremote delete
: File Transferremote get
: File Transferremote put
: File Transferremove-inferiors
: Inferiors and Programsremove-symbol-file
: Filesrestart
checkpoint-id: Checkpoint/Restartrestore
: Dump/Restore FilesRET
(repeat last command): Command Syntaxreturn
: Returningreverse-continue
: Reverse Executionreverse-finish
: Reverse Executionreverse-next
: Reverse Executionreverse-nexti
: Reverse Executionreverse-search
: Searchreverse-search-history (C-r)
: Commands For Historyreverse-step
: Reverse Executionreverse-stepi
: Reverse Executionrevert-all-at-newline
: Readline Init File Syntaxrevert-line (M-r)
: Miscellaneous CommandsRight
: TUI Keysrn
(reverse-next
): Reverse Executionrni
(reverse-nexti
): Reverse Executionrs
(step
): Reverse Executionrsi
(reverse-stepi
): Reverse Executionrun
: Startingrun&
: Background Executionrwatch
: Set Watchpointss
(SingleKey TUI key): TUI Single Key Modes
(step
): Continuing and Steppingsal-last
: Symbol Tables In Guilesal-line
: Symbol Tables In Guilesal-pc
: Symbol Tables In Guilesal-symtab
: Symbol Tables In Guilesal-valid?
: Symbol Tables In Guilesal?
: Symbol Tables In Guilesave breakpoints
: Save Breakpointssave gdb-index
: Index Filessave tracepoints
: save tracepointssave-tracepoints
: save tracepointssearch
: Searchsection
: Filesselect-frame
: Selectionselected-frame
: Frames In Guileself
: Commands In Guileself-insert (a, b, A, 1, !, ...)
: Commands For Textset
: Helpset ada print-signatures
: Overloading support for Adaset ada trust-PAD-over-XVS
: Ada Glitchesset agent off
: In-Process Agentset agent on
: In-Process Agentset annotate
: Annotations Overviewset architecture
: Targetsset args
: Argumentsset arm
: ARMset auto-connect-native-target
: Startingset auto-load gdb-scripts
: Auto-loading sequencesset auto-load guile-scripts
: Guile Auto-loadingset auto-load libthread-db
: libthread_db.so.1 fileset auto-load local-gdbinit
: Init File in the Current Directoryset auto-load off
: Auto-loadingset auto-load python-scripts
: Python Auto-loadingset auto-load safe-path
: Auto-loading safe pathset auto-load scripts-directory
: objfile-gdbdotext fileset auto-solib-add
: Filesset backtrace
: Backtraceset basenames-may-differ
: Filesset breakpoint always-inserted
: Set Breaksset breakpoint auto-hw
: Set Breaksset breakpoint condition-evaluation
: Set Breaksset breakpoint pending
: Set Breaksset can-use-hw-watchpoints
: Set Watchpointsset case-sensitive
: Symbolsset charset
: Character Setsset check range
: Range Checkingset check type
: Type Checkingset circular-trace-buffer
: Starting and Stopping Trace Experimentsset code-cache
: Caching Target Dataset coerce-float-to-double
: ABIset com1base
: DJGPP Nativeset com1irq
: DJGPP Nativeset com2base
: DJGPP Nativeset com2irq
: DJGPP Nativeset com3base
: DJGPP Nativeset com3irq
: DJGPP Nativeset com4base
: DJGPP Nativeset com4irq
: DJGPP Nativeset complaints
: Messages/Warningsset confirm
: Messages/Warningsset cp-abi
: ABIset cwd
: Working Directoryset cygwin-exceptions
: Cygwin Nativeset data-directory
: Data Filesset dcache line-size
: Caching Target Dataset dcache size
: Caching Target Dataset debug
: Debugging Outputset debug aarch64
: AArch64set debug arc
: ARCset debug auto-load
: Auto-loading verbose modeset debug bfd-cache
level: File Cachingset debug darwin
: Darwinset debug entry-values
: Tail Call Framesset debug hppa
: HPPAset debug libthread-db
: Threadsset debug mach-o
: Darwinset debug mips
: MIPSset debug monitor
: Target Commandsset debug nios2
: Nios IIset debug skip
: Skipping Over Functions and Filesset debug-file-directory
: Separate Debug Filesset debugevents
: Cygwin Nativeset debugexceptions
: Cygwin Nativeset debugexec
: Cygwin Nativeset debugmemory
: Cygwin Nativeset default-collect
: Tracepoint Actionsset demangle-style
: Print Settingsset detach-on-fork
: Forksset dfw debug requests
: VxWorksset dfw debug responses
: VxWorksset dfw debug unknown-identifiers
: VxWorksset dfw server-name
: VxWorksset dfw timeout
: VxWorksset directories
: Source Pathset disable-randomization
: Startingset disassemble-next-line
: Machine Codeset disassembler-options
: Machine Codeset disassembly-flavor
: Machine Codeset disconnected-dprintf
: Dynamic Printfset disconnected-tracing
: Starting and Stopping Trace Experimentsset displaced-stepping
: Maintenance Commandsset dump-excluded-mappings
: Core File Generationset editing
: Editingset endian
: Byte Orderset environment
: Environmentset exceptions
, Hurd command: Hurd Nativeset exec-direction
: Reverse Executionset exec-done-display
: Debugging Outputset exec-wrapper
: Startingset extended-prompt
: Promptset extension-language
: Showset follow-exec-mode
: Forksset follow-fork-mode
: Forksset frame-filter priority
: Frame Filter Managementset gnutarget
: Target Commandsset guile print-stack
: Guile Exception Handlingset hash
, for remote monitors: Target Commandsset height
: Screen Sizeset history expansion
: Command Historyset history filename
: Command Historyset history remove-duplicates
: Command Historyset history save
: Command Historyset history size
: Command Historyset host-charset
: Character Setsset index-cache
: Index Filesset inferior-tty
: Input/Outputset input-radix
: Numbersset interactive-mode
: Other Misc Settingsset language
: Manuallyset libthread-db-search-path
: Threadsset listsize
: Listset logging
: Logging Outputset mach-exceptions
: Darwinset max-completions
: Completionset max-user-call-depth
: Defineset max-value-size
: Value Sizesset may-call-functions
: Callingset mem inaccessible-by-default
: Memory Region Attributesset mips abi
: MIPSset mips compression
: MIPSset mips mask-address
: MIPSset mipsfpu
: MIPS Embeddedset mpx bound
: i386set multi-tasks-mode
: VxWorksset multiple-symbols
: Ambiguous Expressionsset new-console
: Cygwin Nativeset new-group
: Cygwin Nativeset non-stop
: Non-Stop Modeset opaque-type-resolution
: Symbolsset osabi
: ABIset output-radix
: Numbersset overload-resolution
: Debugging C Plus Plusset pagination
: Screen Sizeset powerpc
: PowerPC Embeddedset print
: Print Settingsset print entry-values
: Print Settingsset print finish
: Continuing and Steppingset print frame-arguments
: Print Settingsset print frame-info
: Print Settingsset print inferior-events
: Inferiors and Programsset print symbol-loading
: Symbolsset print thread-events
: Threadsset print type methods
: Symbolsset print type nested-type-limit
: Symbolsset print type typedefs
: Symbolsset processor
: Targetsset procfs-file
: Process Informationset procfs-trace
: Process Informationset prompt
: Promptset python print-stack
: Python Commandsset radix
: Numbersset range-stepping
: Continuing and Steppingset ravenscar task-switching off
: Ravenscar Profileset ravenscar task-switching on
: Ravenscar Profileset record
: Process Record and Replayset record btrace
: Process Record and Replayset record btrace bts
: Process Record and Replayset record btrace pt
: Process Record and Replayset record full
: Process Record and Replayset remote
: Remote Configurationset remote system-call-allowed
: systemset remote-mips64-transfers-32bit-regs
: MIPSset remotecache
: Caching Target Dataset remoteflow
: Remote Configurationset schedule-multiple
: All-Stop Modeset script-extension
: Extending GDBset sh calling-convention
: Super-Hset shell
: Cygwin Nativeset signal-thread
: Hurd Nativeset signals
, Hurd command: Hurd Nativeset sigs
, Hurd command: Hurd Nativeset sigthread
: Hurd Nativeset solib-absolute-prefix
: Filesset solib-search-path
: Filesset stack-cache
: Caching Target Dataset startup-with-shell
: Startingset step-mode
: Continuing and Steppingset stop-on-solib-events
: Filesset stopped
, Hurd command: Hurd Nativeset struct-convention
: i386set style
: Output Stylingset substitute-path
: Source Pathset sysroot
: Filesset target-charset
: Character Setsset target-file-system-kind (unix|dos-based|auto)
: Filesset target-wide-charset
: Character Setsset task
, Hurd commands: Hurd Nativeset tcp
: Remote Configurationset thread
, Hurd command: Hurd Nativeset trace-buffer-size
: Starting and Stopping Trace Experimentsset trace-commands
: Messages/Warningsset trace-notes
: Starting and Stopping Trace Experimentsset trace-stop-notes
: Starting and Stopping Trace Experimentsset trace-user
: Starting and Stopping Trace Experimentsset trust-readonly-sections
: Filesset tui active-border-mode
: TUI Configurationset tui border-kind
: TUI Configurationset tui border-mode
: TUI Configurationset tui compact-source
: TUI Configurationset tui tab-width
: TUI Configurationset unwind-on-terminating-exception
: Callingset unwindonsignal
: Callingset use-coredump-filter
: Core File Generationset variable
: Assignmentset varsize-limit
: Ada Settingsset verbose
: Messages/Warningsset watchdog
: Maintenance Commandsset width
: Screen Sizeset write
: Patchingset wtx debug breakpoints
: VxWorksset wtx debug events
: VxWorksset wtx debug objfiles
: VxWorksset wtx debug tcl
: VxWorksset wtx debug watchpoints
: VxWorksset wtx load-from-gdb
: VxWorksset wtx load-timeout
: VxWorksset wtx stack-size
: VxWorksset wtx task-options
: VxWorksset wtx task-priority
: VxWorksset wtx tool-name
: VxWorksset-breakpoint-condition!
: Breakpoints In Guileset-breakpoint-enabled!
: Breakpoints In Guileset-breakpoint-hit-count!
: Breakpoints In Guileset-breakpoint-ignore-count!
: Breakpoints In Guileset-breakpoint-silent!
: Breakpoints In Guileset-breakpoint-stop!
: Breakpoints In Guileset-breakpoint-task!
: Breakpoints In Guileset-breakpoint-thread!
: Breakpoints In Guileset-iterator-progress!
: Iterators In Guileset-mark (C-@)
: Miscellaneous Commandsset-memory-port-read-buffer-size!
: Memory Ports in Guileset-memory-port-write-buffer-size!
: Memory Ports in Guileset-objfile-pretty-printers!
: Objfiles In Guileset-parameter-value!
: Parameters In Guileset-pretty-printer-enabled!
: Guile Pretty Printing APIset-pretty-printers!
: Guile Pretty Printing APIset-progspace-pretty-printers!
: Progspaces In Guileset_debug_traps
: Stub Contentsshare
: Filessharedlibrary
: Filesshell
: Shell Commandsshow
: Helpshow ada print-signatures
: Overloading support for Adashow ada trust-PAD-over-XVS
: Ada Glitchesshow agent
: In-Process Agentshow annotate
: Annotations Overviewshow architecture
: Targetsshow args
: Argumentsshow arm
: ARMshow auto-load
: Auto-loadingshow auto-load gdb-scripts
: Auto-loading sequencesshow auto-load guile-scripts
: Guile Auto-loadingshow auto-load libthread-db
: libthread_db.so.1 fileshow auto-load local-gdbinit
: Init File in the Current Directoryshow auto-load python-scripts
: Python Auto-loadingshow auto-load safe-path
: Auto-loading safe pathshow auto-load scripts-directory
: objfile-gdbdotext fileshow auto-solib-add
: Filesshow backtrace
: Backtraceshow basenames-may-differ
: Filesshow breakpoint always-inserted
: Set Breaksshow breakpoint auto-hw
: Set Breaksshow breakpoint condition-evaluation
: Set Breaksshow breakpoint pending
: Set Breaksshow can-use-hw-watchpoints
: Set Watchpointsshow case-sensitive
: Symbolsshow charset
: Character Setsshow check range
: Range Checkingshow check type
: Type Checkingshow circular-trace-buffer
: Starting and Stopping Trace Experimentsshow code-cache
: Caching Target Datashow coerce-float-to-double
: ABIshow com1base
: DJGPP Nativeshow com1irq
: DJGPP Nativeshow com2base
: DJGPP Nativeshow com2irq
: DJGPP Nativeshow com3base
: DJGPP Nativeshow com3irq
: DJGPP Nativeshow com4base
: DJGPP Nativeshow com4irq
: DJGPP Nativeshow commands
: Command Historyshow complaints
: Messages/Warningsshow configuration
: Helpshow confirm
: Messages/Warningsshow convenience
: Convenience Varsshow copying
: Helpshow cp-abi
: ABIshow cwd
: Working Directoryshow cygwin-exceptions
: Cygwin Nativeshow data-directory
: Data Filesshow dcache line-size
: Caching Target Datashow dcache size
: Caching Target Datashow debug
: Debugging Outputshow debug arc
: ARCshow debug auto-load
: Auto-loading verbose modeshow debug bfd-cache
: File Cachingshow debug darwin
: Darwinshow debug entry-values
: Tail Call Framesshow debug libthread-db
: Threadsshow debug mach-o
: Darwinshow debug mips
: MIPSshow debug monitor
: Target Commandsshow debug nios2
: Nios IIshow debug skip
: Skipping Over Functions and Filesshow debug-file-directory
: Separate Debug Filesshow default-collect
: Tracepoint Actionsshow detach-on-fork
: Forksshow dfw debug requests
: VxWorksshow dfw debug responses
: VxWorksshow dfw debug unknown-identifiers
: VxWorksshow dfw server-name
: VxWorksshow dfw timeout
: VxWorksshow directories
: Source Pathshow disassemble-next-line
: Machine Codeshow disassembler-options
: Machine Codeshow disassembly-flavor
: Machine Codeshow disconnected-dprintf
: Dynamic Printfshow disconnected-tracing
: Starting and Stopping Trace Experimentsshow displaced-stepping
: Maintenance Commandsshow editing
: Editingshow environment
: Environmentshow exceptions
, Hurd command: Hurd Nativeshow exec-done-display
: Debugging Outputshow extended-prompt
: Promptshow follow-fork-mode
: Forksshow frame-filter priority
: Frame Filter Managementshow gnutarget
: Target Commandsshow hash
, for remote monitors: Target Commandsshow height
: Screen Sizeshow history
: Command Historyshow host-charset
: Character Setsshow index-cache
: Index Filesshow inferior-tty
: Input/Outputshow input-radix
: Numbersshow interactive-mode
: Other Misc Settingsshow language
: Showshow libthread-db-search-path
: Threadsshow listsize
: Listshow logging
: Logging Outputshow mach-exceptions
: Darwinshow max-completions
: Completionshow max-user-call-depth
: Defineshow max-value-size
: Value Sizesshow may-call-functions
: Callingshow mem inaccessible-by-default
: Memory Region Attributesshow mips abi
: MIPSshow mips compression
: MIPSshow mips mask-address
: MIPSshow mipsfpu
: MIPS Embeddedshow mpx bound
: i386show multiple-symbols
: Ambiguous Expressionsshow new-console
: Cygwin Nativeshow new-group
: Cygwin Nativeshow non-stop
: Non-Stop Modeshow opaque-type-resolution
: Symbolsshow osabi
: ABIshow output-radix
: Numbersshow overload-resolution
: Debugging C Plus Plusshow pagination
: Screen Sizeshow paths
: Environmentshow print
: Print Settingsshow print finish
: Continuing and Steppingshow print inferior-events
: Inferiors and Programsshow print symbol-loading
: Symbolsshow print thread-events
: Threadsshow print type methods
: Symbolsshow print type nested-type-limit
: Symbolsshow print type typedefs
: Symbolsshow processor
: Targetsshow procfs-file
: Process Informationshow procfs-trace
: Process Informationshow prompt
: Promptshow radix
: Numbersshow range-stepping
: Continuing and Steppingshow ravenscar task-switching
: Ravenscar Profileshow record
: Process Record and Replayshow record btrace
: Process Record and Replayshow record full
: Process Record and Replayshow remote
: Remote Configurationshow remote system-call-allowed
: systemshow remote-mips64-transfers-32bit-regs
: MIPSshow remotecache
: Caching Target Datashow remoteflow
: Remote Configurationshow script-extension
: Extending GDBshow sh calling-convention
: Super-Hshow shell
: Cygwin Nativeshow signal-thread
: Hurd Nativeshow signals
, Hurd command: Hurd Nativeshow sigs
, Hurd command: Hurd Nativeshow sigthread
: Hurd Nativeshow solib-search-path
: Filesshow stack-cache
: Caching Target Datashow stop-on-solib-events
: Filesshow stopped
, Hurd command: Hurd Nativeshow struct-convention
: i386show style
: Output Stylingshow substitute-path
: Source Pathshow sysroot
: Filesshow target-charset
: Character Setsshow target-file-system-kind
: Filesshow target-wide-charset
: Character Setsshow task
, Hurd commands: Hurd Nativeshow tcp
: Remote Configurationshow thread
, Hurd command: Hurd Nativeshow trace-buffer-size
: Starting and Stopping Trace Experimentsshow trace-notes
: Starting and Stopping Trace Experimentsshow trace-stop-notes
: Starting and Stopping Trace Experimentsshow trace-user
: Starting and Stopping Trace Experimentsshow unwind-on-terminating-exception
: Callingshow unwindonsignal
: Callingshow user
: Defineshow values
: Value Historyshow varsize-limit
: Ada Settingsshow verbose
: Messages/Warningsshow version
: Helpshow warranty
: Helpshow width
: Screen Sizeshow write
: Patchingshow wtx debug breakpoints
: VxWorksshow wtx debug events
: VxWorksshow wtx debug objfiles
: VxWorksshow wtx debug tcl
: VxWorksshow wtx debug watchpoints
: VxWorksshow wtx load-from-gdb
: VxWorksshow wtx load-timeout
: VxWorksshow wtx stack-size
: VxWorksshow wtx task-options
: VxWorksshow wtx task-priority
: VxWorksshow wtx tool-name
: VxWorksshow-all-if-ambiguous
: Readline Init File Syntaxshow-all-if-unmodified
: Readline Init File Syntaxshow-mode-in-prompt
: Readline Init File Syntaxsi
(stepi
): Continuing and Steppingsignal
: Signalingsignal annotation
: Annotations for Runningsignal-event
: Cygwin Nativesignal-name annotation
: Annotations for Runningsignal-name-end annotation
: Annotations for Runningsignal-string annotation
: Annotations for Runningsignal-string-end annotation
: Annotations for RunningSignalEvent.stop_signal
: Events In Pythonsignalled annotation
: Annotations for Runningsilent
: Break Commandssim
, a command: Embedded Processorsskip
: Skipping Over Functions and Filesskip delete
: Skipping Over Functions and Filesskip disable
: Skipping Over Functions and Filesskip enable
: Skipping Over Functions and Filesskip file
: Skipping Over Functions and Filesskip function
: Skipping Over Functions and Filesskip-completed-text
: Readline Init File Syntaxskip-csi-sequence ()
: Miscellaneous Commandssource
: Command Filessource annotation
: Source Annotationsstart
: Startingstart-kbd-macro (C-x ()
: Keyboard Macrosstarti
: Startingstarting annotation
: Annotations for RunningSTDERR
: Basic Pythonstdio-port?
: I/O Ports in GuileSTDLOG
: Basic PythonSTDOUT
: Basic Pythonstep
: Continuing and Steppingstep&
: Background Executionstepi
: Continuing and Steppingstepi&
: Background Executionstop
, a pseudo-command: Hooksstopping annotation
: Annotations for Runningstrace
: Create and Delete Tracepointsstring->argv
: Commands In Guilesymbol-addr-class
: Symbols In Guilesymbol-argument?
: Symbols In Guilesymbol-constant?
: Symbols In Guilesymbol-file
: Filessymbol-function?
: Symbols In Guilesymbol-line
: Symbols In Guilesymbol-linkage-name
: Symbols In Guilesymbol-name
: Symbols In Guilesymbol-needs-frame?
: Symbols In Guilesymbol-print-name
: Symbols In Guilesymbol-symtab
: Symbols In Guilesymbol-type
: Symbols In Guilesymbol-valid?
: Symbols In Guilesymbol-value
: Symbols In Guilesymbol-variable?
: Symbols In GuileSymbol.addr_class
: Symbols In PythonSymbol.is_argument
: Symbols In PythonSymbol.is_constant
: Symbols In PythonSymbol.is_function
: Symbols In PythonSymbol.is_valid
: Symbols In PythonSymbol.is_variable
: Symbols In PythonSymbol.line
: Symbols In PythonSymbol.linkage_name
: Symbols In PythonSymbol.name
: Symbols In PythonSymbol.needs_frame
: Symbols In PythonSymbol.print_name
: Symbols In PythonSymbol.symtab
: Symbols In PythonSymbol.type
: Symbols In PythonSymbol.value
: Symbols In Pythonsymbol?
: Symbols In GuileSYMBOL_COMMON_BLOCK_DOMAIN
: Symbols In PythonSYMBOL_FUNCTIONS_DOMAIN
: Symbols In GuileSYMBOL_LABEL_DOMAIN
: Symbols In GuileSYMBOL_LABEL_DOMAIN
: Symbols In PythonSYMBOL_LOC_ARG
: Symbols In GuileSYMBOL_LOC_ARG
: Symbols In PythonSYMBOL_LOC_BLOCK
: Symbols In GuileSYMBOL_LOC_BLOCK
: Symbols In PythonSYMBOL_LOC_COMPUTED
: Symbols In GuileSYMBOL_LOC_COMPUTED
: Symbols In PythonSYMBOL_LOC_CONST
: Symbols In GuileSYMBOL_LOC_CONST
: Symbols In PythonSYMBOL_LOC_CONST_BYTES
: Symbols In GuileSYMBOL_LOC_CONST_BYTES
: Symbols In PythonSYMBOL_LOC_LOCAL
: Symbols In GuileSYMBOL_LOC_LOCAL
: Symbols In PythonSYMBOL_LOC_OPTIMIZED_OUT
: Symbols In GuileSYMBOL_LOC_OPTIMIZED_OUT
: Symbols In PythonSYMBOL_LOC_REF_ARG
: Symbols In GuileSYMBOL_LOC_REF_ARG
: Symbols In PythonSYMBOL_LOC_REGISTER
: Symbols In GuileSYMBOL_LOC_REGISTER
: Symbols In PythonSYMBOL_LOC_REGPARM_ADDR
: Symbols In GuileSYMBOL_LOC_REGPARM_ADDR
: Symbols In PythonSYMBOL_LOC_STATIC
: Symbols In GuileSYMBOL_LOC_STATIC
: Symbols In PythonSYMBOL_LOC_TYPEDEF
: Symbols In GuileSYMBOL_LOC_TYPEDEF
: Symbols In PythonSYMBOL_LOC_UNDEF
: Symbols In GuileSYMBOL_LOC_UNDEF
: Symbols In PythonSYMBOL_LOC_UNRESOLVED
: Symbols In GuileSYMBOL_LOC_UNRESOLVED
: Symbols In PythonSYMBOL_MODULE_DOMAIN
: Symbols In PythonSYMBOL_STRUCT_DOMAIN
: Symbols In GuileSYMBOL_STRUCT_DOMAIN
: Symbols In PythonSYMBOL_TYPES_DOMAIN
: Symbols In GuileSYMBOL_UNDEF_DOMAIN
: Symbols In GuileSYMBOL_UNDEF_DOMAIN
: Symbols In PythonSYMBOL_VAR_DOMAIN
: Symbols In GuileSYMBOL_VAR_DOMAIN
: Symbols In PythonSYMBOL_VARIABLES_DOMAIN
: Symbols In Guilesymtab-filename
: Symbol Tables In Guilesymtab-fullname
: Symbol Tables In Guilesymtab-global-block
: Symbol Tables In Guilesymtab-objfile
: Symbol Tables In Guilesymtab-static-block
: Symbol Tables In Guilesymtab-valid?
: Symbol Tables In GuileSymtab.filename
: Symbol Tables In PythonSymtab.fullname
: Symbol Tables In PythonSymtab.global_block
: Symbol Tables In PythonSymtab.is_valid
: Symbol Tables In PythonSymtab.linetable
: Symbol Tables In PythonSymtab.objfile
: Symbol Tables In PythonSymtab.producer
: Symbol Tables In PythonSymtab.static_block
: Symbol Tables In Pythonsymtab?
: Symbol Tables In GuileSymtab_and_line.is_valid
: Symbol Tables In PythonSymtab_and_line.last
: Symbol Tables In PythonSymtab_and_line.line
: Symbol Tables In PythonSymtab_and_line.pc
: Symbol Tables In PythonSymtab_and_line.symtab
: Symbol Tables In Pythonsysinfo
: DJGPP Nativetaas
: Threadstabset
: TUI Configurationtarget
: Target Commandstarget ctf
: Trace Filestarget record
: Process Record and Replaytarget record-btrace
: Process Record and Replaytarget record-full
: Process Record and Replaytarget sim
: OpenRISC 1000target tfile
: Trace Filestarget wtx
: VxWorkstarget-config
: Guile Configurationtask
(Ada): Ada Taskstbreak
: Set Breakstcatch
: Set Catchpointstcl
: VxWorkstdump
: tdumpteval
(tracepoints): Tracepoint Actionstfaas
: Threadstfile
: Trace Filestfind
: tfindthbreak
: Set Breaksthis
, inside C++ member functions: C Plus Plus Expressionsthread apply
: Threadsthread find
: Threadsthread name
: Threadsthread
thread-id: Threadsthread-info
: GDB/MI Support CommandsThreadEvent.inferior_thread
: Events In Pythonthrow-user-error
: Commands In Guiletrace
: Create and Delete Tracepointstranspose-chars (C-t)
: Commands For Texttranspose-words (M-t)
: Commands For Texttsave
: Trace Fileststart [
notes ]
: Starting and Stopping Trace Experimentststatus
: Starting and Stopping Trace Experimentststop [
notes ]
: Starting and Stopping Trace Experimentstty
: Input/Outputtui disable
: TUI Commandstui enable
: TUI Commandstui reg
: TUI Commandstvariable
: Trace State Variablestype-array
: Types In Guiletype-code
: Types In Guiletype-const
: Types In Guiletype-field
: Types In Guiletype-fields
: Types In Guiletype-has-field-deep?
: Guile Types Moduletype-has-field?
: Types In Guiletype-name
: Types In Guiletype-num-fields
: Types In Guiletype-pointer
: Types In Guiletype-print-name
: Types In Guiletype-range
: Types In Guiletype-reference
: Types In Guiletype-sizeof
: Types In Guiletype-strip-typedefs
: Types In Guiletype-tag
: Types In Guiletype-target
: Types In Guiletype-unqualified
: Types In Guiletype-vector
: Types In Guiletype-volatile
: Types In GuileType.alignof
: Types In PythonType.array
: Types In PythonType.code
: Types In PythonType.const
: Types In PythonType.dynamic
: Types In PythonType.fields
: Types In PythonType.name
: Types In PythonType.objfile
: Types In PythonType.optimized_out
: Types In PythonType.pointer
: Types In PythonType.range
: Types In PythonType.reference
: Types In PythonType.sizeof
: Types In PythonType.strip_typedefs
: Types In PythonType.tag
: Types In PythonType.target
: Types In PythonType.template_argument
: Types In PythonType.unqualified
: Types In PythonType.vector
: Types In PythonType.volatile
: Types In Pythontype?
: Types In GuileTYPE_CODE_ARRAY
: Types In GuileTYPE_CODE_ARRAY
: Types In PythonTYPE_CODE_BITSTRING
: Types In GuileTYPE_CODE_BITSTRING
: Types In PythonTYPE_CODE_BOOL
: Types In GuileTYPE_CODE_BOOL
: Types In PythonTYPE_CODE_CHAR
: Types In GuileTYPE_CODE_CHAR
: Types In PythonTYPE_CODE_COMPLEX
: Types In GuileTYPE_CODE_COMPLEX
: Types In PythonTYPE_CODE_DECFLOAT
: Types In GuileTYPE_CODE_DECFLOAT
: Types In PythonTYPE_CODE_ENUM
: Types In GuileTYPE_CODE_ENUM
: Types In PythonTYPE_CODE_ERROR
: Types In GuileTYPE_CODE_ERROR
: Types In PythonTYPE_CODE_FLAGS
: Types In GuileTYPE_CODE_FLAGS
: Types In PythonTYPE_CODE_FLT
: Types In GuileTYPE_CODE_FLT
: Types In PythonTYPE_CODE_FUNC
: Types In GuileTYPE_CODE_FUNC
: Types In PythonTYPE_CODE_INT
: Types In GuileTYPE_CODE_INT
: Types In PythonTYPE_CODE_INTERNAL_FUNCTION
: Types In GuileTYPE_CODE_INTERNAL_FUNCTION
: Types In PythonTYPE_CODE_MEMBERPTR
: Types In GuileTYPE_CODE_MEMBERPTR
: Types In PythonTYPE_CODE_METHOD
: Types In GuileTYPE_CODE_METHOD
: Types In PythonTYPE_CODE_METHODPTR
: Types In GuileTYPE_CODE_METHODPTR
: Types In PythonTYPE_CODE_NAMESPACE
: Types In GuileTYPE_CODE_NAMESPACE
: Types In PythonTYPE_CODE_PTR
: Types In GuileTYPE_CODE_PTR
: Types In PythonTYPE_CODE_RANGE
: Types In GuileTYPE_CODE_RANGE
: Types In PythonTYPE_CODE_REF
: Types In GuileTYPE_CODE_REF
: Types In PythonTYPE_CODE_RVALUE_REF
: Types In PythonTYPE_CODE_SET
: Types In GuileTYPE_CODE_SET
: Types In PythonTYPE_CODE_STRING
: Types In GuileTYPE_CODE_STRING
: Types In PythonTYPE_CODE_STRUCT
: Types In GuileTYPE_CODE_STRUCT
: Types In PythonTYPE_CODE_TYPEDEF
: Types In GuileTYPE_CODE_TYPEDEF
: Types In PythonTYPE_CODE_UNION
: Types In GuileTYPE_CODE_UNION
: Types In PythonTYPE_CODE_VOID
: Types In GuileTYPE_CODE_VOID
: Types In Pythonu
(SingleKey TUI key): TUI Single Key Modeu
(until
): Continuing and Steppingundefined-command-error-code
: GDB/MI Support Commandsundisplay
: Auto Displayundo (C-_ or C-x C-u)
: Miscellaneous Commandsuniversal-argument ()
: Numeric Argumentsunix-filename-rubout ()
: Commands For Killingunix-line-discard (C-u)
: Commands For Killingunix-word-rubout (C-w)
: Commands For Killingunload
filename: Target Commandsunset environment
: Environmentunset substitute-path
: Source Pathuntil
: Continuing and Steppinguntil&
: Background Executionunwind-stop-reason-string
: Frames In GuileUp
: TUI Keysup
: Selectionup-silently
: Selectionupcase-word (M-u)
: Commands For Textupdate
: TUI Commandsv
(SingleKey TUI key): TUI Single Key Modevalue->bool
: Values From Inferior In Guilevalue->bytevector
: Values From Inferior In Guilevalue->integer
: Values From Inferior In Guilevalue->lazy-string
: Values From Inferior In Guilevalue->real
: Values From Inferior In Guilevalue->string
: Values From Inferior In Guilevalue-abs
: Arithmetic In Guilevalue-add
: Arithmetic In Guilevalue-address
: Values From Inferior In Guilevalue-call
: Values From Inferior In Guilevalue-cast
: Values From Inferior In Guilevalue-dereference
: Values From Inferior In Guilevalue-div
: Arithmetic In Guilevalue-dynamic-cast
: Values From Inferior In Guilevalue-dynamic-type
: Values From Inferior In Guilevalue-fetch-lazy!
: Values From Inferior In Guilevalue-field
: Values From Inferior In Guilevalue-lazy?
: Values From Inferior In Guilevalue-logand
: Arithmetic In Guilevalue-logior
: Arithmetic In Guilevalue-lognot
: Arithmetic In Guilevalue-logxor
: Arithmetic In Guilevalue-lsh
: Arithmetic In Guilevalue-max
: Arithmetic In Guilevalue-min
: Arithmetic In Guilevalue-mod
: Arithmetic In Guilevalue-mul
: Arithmetic In Guilevalue-neg
: Arithmetic In Guilevalue-not
: Arithmetic In Guilevalue-optimized-out?
: Values From Inferior In Guilevalue-pos
: Arithmetic In Guilevalue-pow
: Arithmetic In Guilevalue-print
: Values From Inferior In Guilevalue-referenced-value
: Values From Inferior In Guilevalue-reinterpret-cast
: Values From Inferior In Guilevalue-rem
: Arithmetic In Guilevalue-rsh
: Arithmetic In Guilevalue-sub
: Arithmetic In Guilevalue-subscript
: Values From Inferior In Guilevalue-type
: Values From Inferior In GuileValue.__init__
: Values From InferiorValue.address
: Values From InferiorValue.cast
: Values From InferiorValue.const_value
: Values From InferiorValue.dereference
: Values From InferiorValue.dynamic_cast
: Values From InferiorValue.dynamic_type
: Values From InferiorValue.fetch_lazy
: Values From InferiorValue.format_string
: Values From InferiorValue.is_lazy
: Values From InferiorValue.is_optimized_out
: Values From InferiorValue.lazy_string
: Values From InferiorValue.reference_value
: Values From InferiorValue.referenced_value
: Values From InferiorValue.reinterpret_cast
: Values From InferiorValue.string
: Values From InferiorValue.type
: Values From Inferiorvalue<=?
: Arithmetic In Guilevalue<?
: Arithmetic In Guilevalue=?
: Arithmetic In Guilevalue>=?
: Arithmetic In Guilevalue>?
: Arithmetic In Guilevalue?
: Values From Inferior In Guilevi-cmd-mode-string
: Readline Init File Syntaxvi-ins-mode-string
: Readline Init File Syntaxvisible-stats
: Readline Init File Syntaxw
(SingleKey TUI key): TUI Single Key Modew
(with
): Command Settingswatch
: Set Watchpointswatchpoint annotation
: Annotations for Runningwhatis
: Symbolswhere
: Backtracewhile
: Command Fileswhile-stepping
(tracepoints): Tracepoint Actionswinheight
: TUI Commandswith command
: Command SettingsWP_ACCESS
: Breakpoints In GuileWP_ACCESS
: Breakpoints In PythonWP_READ
: Breakpoints In GuileWP_READ
: Breakpoints In PythonWP_WRITE
: Breakpoints In GuileWP_WRITE
: Breakpoints In Pythonwtx add-symbol-file
: VxWorksx
(examine memory): Memoryx
(examine), and info line
: Machine CodeXMethod.__init__
: Xmethod APIXMethodMatcher.__init__
: Xmethod APIXMethodMatcher.match
: Xmethod APIXMethodWorker.__call__
: Xmethod APIXMethodWorker.get_arg_types
: Xmethod APIXMethodWorker.get_result_type
: Xmethod APIyank (C-y)
: Commands For Killingyank-last-arg (M-. or M-_)
: Commands For Historyyank-nth-arg (M-C-y)
: Commands For Historyyank-pop (M-y)
: Commands For Killing|
: Shell Commands[1] On
DOS/Windows systems, the home directory is the one pointed to by the
HOME
environment variable.
[2] The completer can be confused by certain kinds of invalid expressions. Also, it only examines the static type of the expression, not the dynamic type.
[3] Currently, only gnu/Linux.
[4] See
http://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps
for more information on how to add SystemTap
SDT
probes in your applications.
[5] See http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation for a good reference on how the SDT probes are implemented.
[6] Note that some side effects are easier to undo than others. For instance, memory and registers are relatively easy, but device I/O is hard. Some targets may be able undo things like device I/O, and some may not.
The contract between gdb and the reverse executing target requires only that the target do something reasonable when gdb tells it to execute backwards, and then report the results back to gdb. Whatever the target reports back to gdb, gdb will report back to the user. gdb assumes that the memory and registers that the target reports are in a consistent state, but gdb accepts whatever it is given.
[7] Unless the code is too heavily optimized.
[8]
Note that embedded programs (the so-called “free-standing”
environment) are not required to have a main
function as the
entry point. They could even have multiple entry points.
[9]
The only restriction is that your editor (say ex
), recognizes the
following command-line syntax:
ex +number file
The optional numeric value +number specifies the number of the line in the file where to start editing.
[10] ‘b’ cannot be used because these format letters are also
used with the x
command, where ‘b’ stands for “byte”;
see Examining Memory.
[11] This is a way of removing
one word from the stack, on machines where stacks grow downward in
memory (most machines, nowadays). This assumes that the innermost
stack frame is selected; setting $sp
is not allowed when other
stack frames are selected. To pop entire frames off the stack,
regardless of machine architecture, use return
;
see Returning from a Function.
[12] In non-stop mode, it is moderately rare for a running thread to modify the stack of a stopped thread in a way that would interfere with a backtrace, and caching of stack reads provides a significant speed up of remote backtraces.
[13] This is the minimum. Recent versions of gcc support -gdwarf-3 and -gdwarf-4; we recommend always choosing the most recent version of DWARF.
[14] Historically the functionality to retrieve binaries from the remote system was provided by prefixing path with remote:
[15] If you choose a port number that
conflicts with another service, gdbserver
prints an error message
and exits.
[16] The register named with capital letters represent the architecture registers.
[17] Note that gdb parameters must not be confused with Guileās parameter objects (see Parameters).
[18] In gdb-9.2 for GNAT Pro 22.0w/gdb/refcard.ps of the version 9.2 for GNAT Pro 22.0w release.
[19] The ‘qP’ and ‘qL’ packets predate these conventions, and have arguments without any terminator for the packet name; we suspect they are in widespread use in places that are difficult to upgrade. The ‘qC’ packet has no arguments, but some existing stubs (e.g. RedBoot) are known to not check for the end of the packet.