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INFO-DIR-SECTION Programming & development tools.

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* Gdb: (gdb).                     The GNU debugger.

END-INFO-DIR-ENTRY

   This file documents the GNU debugger GDB.

   This is the Ninth Edition, April 2001, of `Debugging with GDB: the

GNU Source-Level Debugger' for GDB Version 20010707.

   Copyright (C)

1988,1989,1990,1991,1992,1993,1994,1995,1996,1998,1999,2000,2001

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 1.1 or

any later version published by the Free Software Foundation; with the

Invariant Sections being "A Sample GDB Session" and "Free Software",

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 have freedom to copy and

modify this GNU Manual, like GNU software.  Copies published by the Free

Software Foundation raise funds for GNU development."

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 Ninth Edition, April 2001, for GDB Version 20010707.

   Copyright (C) 1988-2001 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

* Tracepoints::                 Debugging remote targets non-intrusively

* Languages::                   Using GDB with different languages

* Symbols::                     Examining the symbol table

* Altering::                    Altering execution

* GDB Files::                   GDB files

* Targets::                     Specifying a debugging target

* Configurations::              Configuration-specific information

* Controlling GDB::             Controlling GDB

* Sequences::                   Canned sequences of commands

* Emacs::                       Using GDB under GNU Emacs

* Annotations::                 GDB's annotation interface.

* GDB/MI::                      GDB's Machine Interface.

* 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

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 and C++.  For more

information, see *Note Supported languages: Support.  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.  For information on Chill, see

*Note Chill::.

   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.

* Menu:

* Free Software::               Freely redistributable software

* Contributors::                Contributors to GDB

File: gdb.info,  Node: Free Software,  Next: Contributors,  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:

Andrew Cagney (releases 5.0 and 5.1); 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 DWARF2 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.

   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.

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 `' and the close quote

string to `', 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(,)

     define(baz,defn(foo))

     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 20010707, 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(,)

     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 "", rq=0x34c88 "")

         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 "", rq=0x34c88 "")

         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 ""

     (gdb) p rquote

     $2 = 0x35d50 ""

`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(foo))

     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,  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.  GDB will warn you if it is

unable to attach or to read core dumps.

   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.)

   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'

     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 `/tmp/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.

   You typically combine the `-mapped' and `-readnow' options 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 found in any initialization files (normally

     called `.gdbinit', or `gdb.ini' on PCs).  Normally, GDB executes

     the commands in these files after all the command options and

     arguments have been processed.  *Note Command files: Command Files.

`-quiet'

`-silent'

`-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.

`-nowindows'

`-nw'

     "No windows".  If GDB comes with a graphical user interface (GUI)

     built in, then this option tells GDB to only use the command-line

     interface.  If no GUI is available, this option has no effect.

`-windows'

`-w'

     If GDB includes a GUI, then this option requires it to be used if

     possible.

`-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.

`-epoch'

     The Epoch Emacs-GDB interface sets this option when it runs GDB as

     a subprocess.  It tells GDB to modify its print routines so as to

     allow Epoch to display values of expressions in a separate window.

`-annotate LEVEL'

     This option sets the "annotation level" inside GDB.  Its effect is

     identical to using `set annotate LEVEL' (*note Annotations::).

     Annotation level controls how much information does GDB print

     together with its prompt, values of expressions, source lines, and

     other types of output.  Level 0 is the normal, level 1 is for use

     when GDB is run as a subprocess of GNU Emacs, level 2 is the

     maximum annotation suitable for programs that control GDB.

`-async'

     Use the asynchronous event loop for the command-line interface.

     GDB processes all events, such as user keyboard input, via a

     special event loop.  This allows GDB to accept and process user

     commands in parallel with the debugged process being run(1), so

     you don't need to wait for control to return to GDB before you

     type the next command.  (_Note:_ as of version 5.1, the target

     side of the asynchronous operation is not yet in place, so

     `-async' does not work fully yet.)

     When the standard input is connected to a terminal device, GDB

     uses the asynchronous event loop by default, unless disabled by the

     `-noasync' option.

`-noasync'

     Disable the asynchronous event loop for the command-line interface.

`-baud BPS'

`-b BPS'

     Set the line speed (baud rate or bits per second) of any serial

     interface used by GDB for remote debugging.

`-tty DEVICE'

`-t DEVICE'

     Run using DEVICE for your program's standard input and output.

`-interpreter INTERP'

     Use the interpreter INTERP for interface with the controlling

     program or device.  This option is meant to be set by programs

     which communicate with GDB using it as a back end.

     `--interpreter=mi' (or `--interpreter=mi1') causes GDB to use the

     "gdb/mi interface" (*note The GDB/MI Interface: GDB/MI.). The

     older GDB/MI interface, included in GDB version 5.0 can be

     selected with `--interpreter=mi0'.

`-write'

     Open the executable and core files for both reading and writing.

     This is equivalent to the `set write on' command inside GDB (*note

     Patching::).

`-statistics'

     This option causes GDB to print statistics about time and memory

     usage after it completes each command and returns to the prompt.

`-version'

     This option causes GDB to print its version number and no-warranty

     blurb, and exit.

   ---------- Footnotes ----------

   (1) GDB built with DJGPP tools for MS-DOS/MS-Windows supports this

mode of operation, but the event loop is suspended when the debuggee

runs.

File: gdb.info,  Node: Quitting GDB,  Next: Shell Commands,  Prev: Invoking GDB,  Up: Invocation

Quitting GDB

============

`quit [EXPRESSION]'

`q'

     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 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-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 .  You can also use the 

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,  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 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 ) 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 ,

construct new arguments rather than repeating exactly as typed.  This

permits easy scanning of source or memory.

   GDB can also use  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  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  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  to enter it).  For

example, if you type

     (gdb) info bre 

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  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

 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 , GDB sounds a bell.  You can either supply more characters

and try again, or just press  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_' GDB just sounds the bell.  Typing  again

displays all the function names in your program that begin with those

characters, for example:

     (gdb) b make_ 

GDB sounds bell; press  again, to see:

     make_a_section_from_file     make_environ

     make_abs_section             make_function_type

     make_blockvector             make_pointer_type