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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
       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			   22may2002				gdb(1)


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