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gdb(1)				   GNU Tools				gdb(1)

       gdb - The GNU Debugger

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

       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

	  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

       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

       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-

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

       edit [file:]function
	      look at the program line where it	is presently stopped.

       list [file:]function
	      type  the	 text  of  the	program	in the vicinity	of where it is
	      presently	stopped.

       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.

       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


       -h     List all options,	with brief explanations.


       -s file
	      Read symbol table	from file file.

       -write Enable writing into executable and core files.


       -e file
	      Use file file as the executable file to execute  when  appropri-
	      ate,  and	 for  examining	 pure  data in conjunction with	a core

	      Read symbol table	from file file and use it  as  the  executable


       -c file
	      Use file file as a core dump to examine.


       -x file
	      Execute GDB commands from	file file.


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


       -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.


       -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.

	      Run GDB using directory as its working directory,	instead	of the
	      current directory.


       -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.

       -b bps Set  the line speed (baud	rate or	bits per second) of any	serial
	      interface	used by	GDB for	remote debugging.

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

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

       Copyright (c) 1991, 2010	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 en-
       tire resulting derived work is distributed under	the terms of a permis-
       sion 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			   22may2002				gdb(1)


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