Index of Section 1 Manual Pages
|Interix / SUA||gdb.1||Interix / SUA
gdb - The GNU debugger
gdb [-help] [-nx] [-q] [-batch] [-cd=dir]
[-f] [-b bps] [-tty=dev] [-s symfile]
[-e prog] [-se prog] [-c core] [-d dir]
[-x file] [-epoch] [-mapped] [-nw | -w]
[ prog [ core | procID]]
You can use gdb(1) to view what is going on inside another program while
it executes, or to view what another program was doing at the moment it
The gdb utility can do the following four main things (plus other things
in support of these) to help you catch bugs while a program is executing:
* Start your program, specifying anything that might affect its
* 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 also 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.
* On Interix systems, gdb is most useful with C and C++ programs
compiled with gcc(1). It might also be useful with programs compiled
with cc(1) or c89(1).
The gdb debugger is invoked with the shell command gdb(1). Once started,
it reads commands 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 usual way to start
gdb is with one argument or two, specifying an executable program as the
You can also start with both an executable program and a core file
gdb program core
You can specify a process identifier (ID) as a second argument if you want
to debug a running process. The following code attaches gdb to process
1234 (unless you also have a file named 1234; gdb checks for a core file
gdb program 1234
The following is a list of commonly used gdb commands:
Set a breakpoint at function (in file).
Start your program (with arglist, if specified).
Backtrace: display the program stack.
Display the value of an expression.
Continue running your program (after stopping, for example, at a
Execute next program line (after stopping); step over any function
calls in the line.
Execute next program line (after stopping); step into any function
calls in the line.
Show information about gdb command name or general information about
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 PDF file, gdb_info.pdf.
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 is 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
All of the options and command-line arguments you give are processed in
sequential order. The order makes a difference when the -x option is used.
Run gdb using directory, instead of the current directory, as its
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 form each time a stack frame is displayed (which includes
each time the 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.
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.
Use mapped symbol files. This feature is not available on Interix.
Output information in the format used by the Epoch emacs-gdb
Fully read symbol files on first access.
Display version information, and then exit.
Run gdb as a command-line utility (default).
Run gdb as an X Windows application.
Under some circumstances, when a function is disassembled, the disassembly
may continue until the beginning of the next function. If the next
function is aligned to some boundary, a few instructions of "noise" may
appear at the end of the dissassembly; these can be ignored.
When disassembling or otherwise dealing with the range of instruction
locations that includes the end of a function, gdb treats the end as the
last byte before the beginning of the next function. On Intel processors,
there may be a .align that causes a few bytes of empty space (containing
random data) to be included in the range that nominally includes the end.
This can be safely ignored.
When debugging an execution thread, if you attempt to single-step over the
last statement of the thread-start routine, the debugger may warn about
not being able to set a breakpoint at address 0, even though you have not
set any breakpoints yourself. This is a warning only and does not
interfere with normal debugging.
Appendix B in the Professional SDK User's Guide contains an introduction
Using GDB: A Guide to the GNU Source-Level Debugger, Richard M. Stallman
and Roland H. Pesch, July 1991.
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 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,
except that this permission notice may be included in translations
approved by the Free Software Foundation instead of in the original