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This is Info file ./gdb.info, produced by Makeinfo version 1.68 from
the input file gdb.texinfo.
START-INFO-DIR-ENTRY
* Gdb: (gdb). The GNU debugger.
END-INFO-DIR-ENTRY
This file documents the GNU debugger GDB.
This is the Seventh Edition, February 1999, of `Debugging with GDB:
the GNU Source-Level Debugger' for GDB Version 4.18.
Copyright (C) 1988-1999 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the entire resulting derived work is distributed under the terms
of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions.

File: gdb.info, Node: Top, Next: Summary, Prev: (dir), Up: (dir)
Debugging with GDB
******************
This file describes GDB, the GNU symbolic debugger.
This is the Seventh Edition, February 1999, for GDB Version 4.18.
Copyright (C) 1988-1999 Free Software Foundation, Inc.
* Menu:
* Summary:: Summary of GDB
* Sample Session:: A sample GDB session
* Invocation:: Getting in and out of GDB
* Commands:: GDB commands
* Running:: Running programs under GDB
* Stopping:: Stopping and continuing
* Stack:: Examining the stack
* Source:: Examining source files
* Data:: Examining data
* Languages:: Using GDB with different languages
* Symbols:: Examining the symbol table
* Altering:: Altering execution
* GDB Files:: GDB files
* Targets:: Specifying a debugging target
* Controlling GDB:: Controlling GDB
* Sequences:: Canned sequences of commands
* Emacs:: Using GDB under GNU Emacs
* GDB Bugs:: Reporting bugs in GDB
* Formatting Documentation:: How to format and print GDB documentation
* Command Line Editing:: Command Line Editing
* Using History Interactively:: Using History Interactively
* Installing GDB:: Installing GDB
* Index:: Index
-- The Detailed Node Listing --
Summary of GDB
* Free Software:: Freely redistributable software
* Contributors:: Contributors to GDB
Getting In and Out of GDB
* Invoking GDB:: How to start GDB
* Quitting GDB:: How to quit GDB
* Shell Commands:: How to use shell commands inside GDB
Invoking GDB
* File Options:: Choosing files
* Mode Options:: Choosing modes
GDB Commands
* Command Syntax:: How to give commands to GDB
* Completion:: Command completion
* Help:: How to ask GDB for help
Running Programs Under GDB
* Compilation:: Compiling for debugging
* Starting:: Starting your program
* Arguments:: Your program's arguments
* Environment:: Your program's environment
* Working Directory:: Your program's working directory
* Input/Output:: Your program's input and output
* Attach:: Debugging an already-running process
* Kill Process:: Killing the child process
* Process Information:: Additional process information
* Threads:: Debugging programs with multiple threads
* Processes:: Debugging programs with multiple processes
Stopping and Continuing
* Breakpoints:: Breakpoints, watchpoints, and catchpoints
* Continuing and Stepping:: Resuming execution
* Signals:: Signals
* Thread Stops:: Stopping and starting multi-thread programs
Breakpoints and watchpoints
* Set Breaks:: Setting breakpoints
* Set Watchpoints:: Setting watchpoints
* Set Catchpoints:: Setting catchpoints
* Delete Breaks:: Deleting breakpoints
* Disabling:: Disabling breakpoints
* Conditions:: Break conditions
* Break Commands:: Breakpoint command lists
* Breakpoint Menus:: Breakpoint menus
Examining the Stack
* Frames:: Stack frames
* Backtrace:: Backtraces
* Selection:: Selecting a frame
* Frame Info:: Information on a frame
* Alpha/MIPS Stack:: Alpha and MIPS machines and the function stack
Examining Source Files
* List:: Printing source lines
* Search:: Searching source files
* Source Path:: Specifying source directories
* Machine Code:: Source and machine code
Examining Data
* Expressions:: Expressions
* Variables:: Program variables
* Arrays:: Artificial arrays
* Output Formats:: Output formats
* Memory:: Examining memory
* Auto Display:: Automatic display
* Print Settings:: Print settings
* Value History:: Value history
* Convenience Vars:: Convenience variables
* Registers:: Registers
* Floating Point Hardware:: Floating point hardware
Using GDB with Different Languages
* Setting:: Switching between source languages
* Show:: Displaying the language
* Checks:: Type and range checks
* Support:: Supported languages
Switching between source languages
* Filenames:: Filename extensions and languages.
* Manually:: Setting the working language manually
* Automatically:: Having GDB infer the source language
Type and range checking
* Type Checking:: An overview of type checking
* Range Checking:: An overview of range checking
Supported languages
* C:: C and C++
C Language Support
* C Operators:: C operators
C Language Support
* C Operators:: C and C++ operators
* C Constants:: C and C++ constants
* Cplus expressions:: C++ expressions
* C Defaults:: Default settings for C and C++
* C Checks:: C and C++ type and range checks
* Debugging C:: GDB and C
* Debugging C plus plus:: GDB features for C++
Modula-2
* M2 Operators:: Built-in operators
* Built-In Func/Proc:: Built-in functions and procedures
* M2 Constants:: Modula-2 constants
* M2 Defaults:: Default settings for Modula-2
* Deviations:: Deviations from standard Modula-2
* M2 Checks:: Modula-2 type and range checks
* M2 Scope:: The scope operators `::' and `.'
* GDB/M2:: GDB and Modula-2
Altering Execution
* Assignment:: Assignment to variables
* Jumping:: Continuing at a different address
* Signaling:: Giving your program a signal
* Returning:: Returning from a function
* Calling:: Calling your program's functions
* Patching:: Patching your program
GDB Files
* Files:: Commands to specify files
* Symbol Errors:: Errors reading symbol files
Specifying a Debugging Target
* Active Targets:: Active targets
* Target Commands:: Commands for managing targets
* Byte Order:: Choosing target byte order
* Remote:: Remote debugging
Remote debugging
* Remote Serial:: GDB remote serial protocol
* i960-Nindy Remote:: GDB with a remote i960 (Nindy)
* UDI29K Remote:: The UDI protocol for AMD29K
* EB29K Remote:: The EBMON protocol for AMD29K
* VxWorks Remote:: GDB and VxWorks
* ST2000 Remote:: GDB with a Tandem ST2000
* Hitachi Remote:: GDB and Hitachi Microprocessors
* MIPS Remote:: GDB and MIPS boards
* Simulator:: Simulated CPU target
Controlling GDB
* Prompt:: Prompt
* Editing:: Command editing
* History:: Command history
* Screen Size:: Screen size
* Numbers:: Numbers
* Messages/Warnings:: Optional warnings and messages
Canned Sequences of Commands
* Define:: User-defined commands
* Hooks:: User-defined command hooks
* Command Files:: Command files
* Output:: Commands for controlled output
Reporting Bugs in GDB
* Bug Criteria:: Have you found a bug?
* Bug Reporting:: How to report bugs
Installing GDB
* Separate Objdir:: Compiling GDB in another directory
* Config Names:: Specifying names for hosts and targets
* Configure Options:: Summary of options for configure

File: gdb.info, Node: Summary, Next: Sample Session, Prev: Top, Up: Top
Summary of GDB
**************
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:
* Start your program, specifying anything that might affect its
behavior.
* Make your program stop on specified conditions.
* Examine what has happened, when your program has stopped.
* Change things in your program, so you can experiment with
correcting the effects of one bug and go on to learn about another.
You can use GDB to debug programs written in C or C++. For more
information, see *Note C and C++: C.
Support for Modula-2 and Chill is partial. For information on
Modula-2, see *Note Modula-2: Modula-2. There is no further
documentation on Chill yet.
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
does not yet support entering expressions, printing values, or similar
features using Fortran syntax. It may be necessary to refer to some
variables with a trailing underscore.
* Menu:
* Free Software:: Freely redistributable software
* Contributors:: Contributors to GDB

File: gdb.info, Node: Free Software, Next: Contributors, Prev: Summary, Up: Summary
Free software
=============
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.

File: gdb.info, Node: Contributors, Prev: Free Software, Up: Summary
Contributors to GDB
===================
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: 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. 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 4 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.
Andreas Schwab contributed M68K 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, 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 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 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.
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, 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.

File: gdb.info, Node: Sample Session, Next: Invocation, Prev: Summary, Up: Top
A Sample GDB Session
********************
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
C-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 4.18, 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:
C-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

File: gdb.info, Node: Invocation, Next: Commands, Prev: Sample Session, Up: Top
Getting In and Out of GDB
*************************
This chapter discusses how to start GDB, and how to get out of it.
The essentials are:
* type `gdb' to start GDB.
* type `quit' or `C-d' to exit.
* Menu:
* Invoking GDB:: How to start GDB
* Quitting GDB:: How to quit GDB
* Shell Commands:: How to use shell commands inside GDB

File: gdb.info, Node: Invoking GDB, Next: Quitting GDB, Prev: Invocation, Up: Invocation
Invoking GDB
============
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, if you
want to debug a running process:
gdb PROGRAM 1234
would attach GDB to process `1234' (unless you also have a file named
`1234'; GDB does check for a core file first).
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.
You can run `gdb' without printing the front material, which
describes GDB's non-warranty, by specifying `-silent':
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.
* Menu:
* File Options:: Choosing files
* Mode Options:: Choosing modes

File: gdb.info, Node: File Options, Next: Mode Options, Up: Invoking GDB
Choosing files
--------------
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'
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' option followed by that
argument.)
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'
Read symbol table from file FILE.
`-exec FILE'
`-e FILE'
Use file FILE as the executable file to execute when appropriate,
and for examining pure data in conjunction with a core dump.
`-se FILE'
Read symbol table from file FILE and use it as the executable file.
`-core FILE'
`-c FILE'
Use file FILE as a core dump to examine.
`-c NUMBER'
Connect to process ID NUMBER, as with the `attach' command (unless
there is a file in core-dump format named NUMBER, in which case
`-c' specifies that file as a core dump to read).
`-command FILE'
`-x FILE'
Execute GDB commands from file FILE. *Note Command files: Command
Files.
`-directory DIRECTORY'
`-d DIRECTORY'
Add DIRECTORY to the path to search for source files.
`-m'
`-mapped'
*Warning: this option depends on operating system facilities that
are not supported on all systems.*
If memory-mapped files are available on your system through the
`mmap' system call, you can use this option to have GDB write the
symbols from your program into a reusable file in the current
directory. If the program you are debugging is called
`/tmp/fred', the mapped symbol file is `./fred.syms'. Future GDB
debugging sessions notice the presence of this file, and can
quickly map in symbol information from it, rather than reading the
symbol table from the executable program.
The `.syms' file is specific to the host machine where GDB is run.
It holds an exact image of the internal GDB symbol table. It
cannot be shared across multiple host platforms.
`-r'
`-readnow'
Read each symbol file's entire symbol table immediately, rather
than the default, which is to read it incrementally as it is
needed. This makes startup slower, but makes future operations
faster.
The `-mapped' and `-readnow' options are typically combined in order
to build a `.syms' file that contains complete symbol information.
(*Note Commands to specify files: Files, for information on `.syms'
files.) A simple GDB invocation to do nothing but build a `.syms' file
for future use is:
gdb -batch -nx -mapped -readnow programname

File: gdb.info, Node: Mode Options, Prev: File Options, Up: Invoking GDB
Choosing modes
--------------
You can run GDB in various alternative modes--for example, in batch
mode or quiet mode.
`-nx'
`-n'
Do not execute commands from any initialization files (normally
called `.gdbinit', or `gdb.ini' on PCs). Normally, the commands in
these files are executed after all the command options and
arguments have been processed. *Note Command files: Command Files.
`-quiet'
`-q'
"Quiet". Do not print the introductory and copyright messages.
These messages are also suppressed in batch mode.
`-batch'
Run in batch mode. Exit with status `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 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.
`-cd DIRECTORY'
Run GDB using DIRECTORY as its working directory, instead of the
current directory.
`-fullname'
`-f'
GNU Emacs sets this option when it runs GDB as a subprocess. It
tells GDB to output the full file name and line number in a
standard, recognizable fashion each time a stack frame is
displayed (which includes each time your program stops). This
recognizable format looks like two `\032' characters, followed by
the file name, line number and character position separated by
colons, and a newline. The Emacs-to-GDB interface program uses
the two `\032' characters as a signal to display the source code
for the frame.
`-b BPS'
Set the line speed (baud rate or bits per second) of any serial
interface used by GDB for remote debugging.
`-tty DEVICE'
Run using DEVICE for your program's standard input and output.

File: gdb.info, Node: Quitting GDB, Next: Shell Commands, Prev: Invoking GDB, Up: Invocation
Quitting GDB
============
`quit'
To exit GDB, use the `quit' command (abbreviated `q'), or type an
end-of-file character (usually `C-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 `C-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 (*note Debugging an
already-running process: Attach.).

File: gdb.info, Node: Shell Commands, Prev: Quitting GDB, Up: Invocation
Shell commands
==============
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'
Invoke a standard shell to execute COMMAND STRING. If it exists,
the environment variable `SHELL' determines which shell to run.
Otherwise GDB uses `/bin/sh'.
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-ARGS'
Execute the `make' program with the specified arguments. This is
equivalent to `shell make MAKE-ARGS'.

File: gdb.info, Node: Commands, Next: Running, Prev: Invocation, Up: Top
GDB Commands
************
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).
* Menu:
* Command Syntax:: How to give commands to GDB
* Completion:: Command completion
* Help:: How to ask GDB for help

File: gdb.info, Node: Command Syntax, Next: Completion, Prev: Commands, Up: Commands
Command syntax
==============
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 command names 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.
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' (*note Screen size:
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 (*note Command files:
Command Files.).

File: gdb.info, Node: Completion, Next: Help, Prev: Command Syntax, Up: Commands
Command completion
==================
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, 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 `?'.
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.
The most likely situation where you might need this is in typing the
name of a C++ function. This is because C++ allows function overloading
(multiple definitions of the same function, distinguished by argument
type). For example, when you want to set a breakpoint you may 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)'. 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) b 'bubble( <M-?>
bubble(double,double) bubble(int,int)
(gdb) b 'bubble(
In some cases, GDB can tell that completing a name requires using
quotes. When this happens, GDB inserts the quote for you (while
completing as much as it can) if you do not type the quote in the first
place:
(gdb) b bub <TAB>
GDB alters your input line to the following, and rings a bell:
(gdb) b 'bubble(
In general, GDB can tell that a quote is needed (and inserts it) if you
have not yet started typing the argument list when you ask for
completion on an overloaded symbol.
For more information about overloaded functions, *note C++
expressions: Cplus expressions.. You can use the command `set
overload-resolution off' to disable overload resolution; *note GDB
features for C++: Debugging C plus plus..

File: gdb.info, Node: Help, Prev: Completion, Up: Commands
Getting help
============
You can always ask GDB itself for information on its commands, using
the command `help'.
`help'
`h'
You can use `help' (abbreviated `h') with no arguments to display
a short list of named classes of commands:
(gdb) help
List of classes of commands:
running -- Running the program
stack -- Examining the stack
data -- Examining data
breakpoints -- Making program stop at certain points
files -- Specifying and examining files
status -- Status inquiries
support -- Support facilities
user-defined -- User-defined commands
aliases -- Aliases of other commands
obscure -- Obscure features
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 CLASS'
Using one of the general help classes as an argument, you can get a
list of the individual commands in that class. For example, here
is the help display for the class `status':
(gdb) help status
Status inquiries.
List of commands:
show -- Generic command for showing things set
with "set"
info -- Generic command for printing status
Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)
`help COMMAND'
With a command name as `help' argument, GDB displays a short
paragraph on how to use that command.
`complete ARGS'
The `complete 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:
info
inspect
ignore
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 Index point to all the sub-commands.
*Note Index::.
`info'
This command (abbreviated `i') is for describing the state of your
program. For example, you can list the arguments given to your
program 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'
You can assign the result of an expression to an environment
variable with `set'. For example, you can set the GDB prompt to a
$-sign with `set prompt $'.
`show'
In contrast to `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 three miscellaneous `show' subcommands, all of which are
exceptional in lacking corresponding `set' commands:
`show version'
Show what version of GDB is running. You should include this
information in GDB bug-reports. If multiple versions of GDB are in
use at your site, you may occasionally want to determine which
version of GDB you are running; as GDB evolves, new commands are
introduced, and old ones may wither away. The version number is
also announced when you start GDB.
`show copying'
Display information about permission for copying GDB.
`show warranty'
Display the GNU "NO WARRANTY" statement.

File: gdb.info, Node: Running, Next: Stopping, Prev: Commands, Up: Top
Running Programs Under GDB
**************************
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. You may redirect your
program's input and output, debug an already running process, or kill a
child process.
* Menu:
* Compilation:: Compiling for debugging
* Starting:: Starting your program
* Arguments:: Your program's arguments
* Environment:: Your program's environment
* Working Directory:: Your program's working directory
* Input/Output:: Your program's input and output
* Attach:: Debugging an already-running process
* Kill Process:: Killing the child process
* Process Information:: Additional process information
* Threads:: Debugging programs with multiple threads
* Processes:: Debugging programs with multiple processes

File: gdb.info, Node: Compilation, Next: Starting, Prev: Running, Up: Running
Compiling for debugging
=======================
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.
Many C 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 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.
When you debug a program compiled with `-g -O', remember that the
optimizer is rearranging 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!).
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.
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