Debugging with GDB Manual The GNU Source-Level Debugger (769148-001, March 2014)

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GDB needs to know the file name of the program to be debugged, both in order to read its symbol
table and in order to start your program. To debug a core dump of a previous run, you must also
tell GDB the name of the core dump file.
Commands to specify files
You can specify executable and core dump file names as arguments to the GDB start-up command
(see“Getting In and Out of GDB” (page 19)).
Occasionally it is necessary to change to a different file during a GDB session. In these situations
the GDB commands to specify new files are useful.
file filename Use filename as the program to be debugged. It is read for
its symbols and for the contents of pure memory. It is also
the program executed when you use the run command. If
you do not specify a directory and the file is not found in
the GDB working directory, GDB uses the environment
variable PATH as a list of directories to search, just as the
shell does when looking for a program to run. You can
change the value of this variable, for both GDB and your
program, using the path command.
On systems with memory-mapped files, an auxiliary file
named filename.syms may hold symbol table information
for filename. If so, GDB maps in the symbol table from
`filename.syms', starting up more quickly. See the
descriptions of the file options -mapped and -readnow
(available on the command line, and with the commands
file, symbol-file, or add-symbol-file, described
below) for more information.
file file with no argument makes GDB discard any information
it has on both executable file and the symbol table.
exec-file [ filename ] Specify that the program to be run (but not the symbol table)
is found in file- name. GDB searches the environment
variable PATH if necessary to locate your program. Omitting
filename means to discard information on the executable
file.
symbol-file [ filename ] Read symbol table information from file filename. PATH is
searched when necessary. Use the file command to get both
symbol table and program to run from the same file.
symbol-file with no argument clears out GDB information on
the symbol table of your program.
The symbol-file command causes GDB to forget the contents
of its convenience variables, the value history, and all
breakpoints and auto-display expressions. This is because
they may contain pointers to the internal data recording
symbols and data types, which are part of the old symbol
table data being discarded inside GDB.
symbol-file does not repeat if you press RET again after
executing it once. When GDB is configured for a particular
environment, it understands debugging information in
whatever format is the standard generated for that
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