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gdb(1)				   GNU Tools				gdb(1)

NAME
       gdb - The GNU Debugger

SYNOPSIS
       gdb    [-help] [-nx] [-q] [-batch] [-cd=dir] [-f] [-k] [-wcore]
	      [-b bps] [-tty=dev] [-s symfile] [-e prog] [-se prog] [-c	core]
	      [-x cmds]	[-d dir] [prog[core|procID]]

DESCRIPTION
       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:

	  o   Start your program, specifying anything that  might  affect  its
	      behavior.

	  o   Make your	program	stop on	specified conditions.

	  o   Examine what has happened, when your program has stopped.

	  o   Change  things  in your program, so you can experiment with cor-
	      recting the effects of one bug and go on to learn	about another.

       You  can	 use  GDB  to  debug programs written in C, C++, and Modula-2.
       Fortran support will be added when a GNU	Fortran	compiler is ready.

       GDB is invoked with the shell command gdb.  Once	started, it reads com-
       mands  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,  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).

       Here are	some of	the most frequently needed GDB commands:

       break [file:]function
	       Set a breakpoint	at function (in	file).

       run [arglist]
	      Start your program (with arglist,	if specified).

       bt     Backtrace: display the program stack.

       print expr
	       Display the value of an expression.

       c      Continue running your program (after stopping, e.g. at a	break-
	      point).

       next   Execute  next program line (after	stopping); step	over any func-
	      tion calls in the	line.

       step   Execute next program line	(after stopping); step into any	 func-
	      tion calls in the	line.

       help [name]
	      Show  information	about GDB command name,	or general information
	      about using GDB.

       quit   Exit from	GDB.

       For full	details	on GDB,	see Using GDB: A Guide to the GNU Source-Level
       Debugger, by Richard M. Stallman	and Roland H. Pesch.  The same text is
       available online	as the gdb entry in the	info program.

OPTIONS
       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.

       -help

       -h     List all options,	with brief explanations.

       -symbols=file

       -s file
	       Read symbol table from file file.

       -exec=file

       -e file
	       Use file	file as	the executable file to execute when  appropri-
	      ate,  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.

       -command=file

       -x file
	       Execute GDB commands from file file.

       -directory=directory

       -d directory
	       Add directory to	the path to search for source files.

       -nx

       -n     Do  not  execute	commands  from	any  `.gdbinit'	initialization
	      files.  Normally,	the commands in	these files are	executed after
	      all the command options and arguments have been processed.

       -quiet

       -q     ``Quiet''.   Do  not  print  the introductory and	copyright mes-
	      sages.  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 `.gdbinit', if not	inhib-
	      ited).  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 exam-
	      ple 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     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 dis-
	      played (which includes each time the program stops).  This  rec-
	      ognizable	 format	 looks	like two ` 32' 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 `	32' characters as a signal to display the source  code
	      for the frame.

       -kernel

       -k     Use  gdb	in  kernel  debugging  mode.  The  prompt  is  set  to
	      ``(kgdb)''.

       -wcore This option may only be used  in	kernel	debugging  mode	 while
	      debugging	 a  ``live''  kernel and makes the corefile (/dev/mem)
	      writable.

       -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.

SEE ALSO
       `gdb' entry in info; Using GDB: A Guide to the GNU Source-Level	Debug-
       ger, Richard M. Stallman	and Roland H. Pesch, July 1991.

COPYING
       Copyright (c) 1991 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  that  the
       entire  resulting derived work is distributed under the terms of	a per-
       mission notice identical	to this	one.

       Permission is granted to	copy and distribute translations of this  man-
       ual into	another	language, under	the above conditions for modified ver-
       sions, except that this permission notice may be	included  in  transla-
       tions approved by the Free Software Foundation instead of in the	origi-
       nal English.

GNU Tools			   4nov1991				gdb(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SEE ALSO | COPYING

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