You may want to specify executable and core dump file names. The usual way to do this is at start-up time, using the arguments to GDB's start-up commands (see Getting In and Out of GDB).
Occasionally it is necessary to change to a different file during a GDB session. Or you may run GDB and forget to specify a file you want to use. In these situations the GDB commands to specify new files are useful.
file
filenamerun
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 ]PATH
if necessary to locate your program. Omitting filename means to
discard information on the executable file.
symbol-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 your
program's symbol table.
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 environment; you may use either a gnu compiler, or
other compilers that adhere to the local conventions.
Best results are usually obtained from gnu compilers; for example,
using gcc
you can generate debugging information for
optimized code.
For most kinds of object files, with the exception of old SVR3 systems
using COFF, the symbol-file
command does not normally read the
symbol table in full right away. Instead, it scans the symbol table
quickly to find which source files and which symbols are present. The
details are read later, one source file at a time, as they are needed.
The purpose of this two-stage reading strategy is to make GDB
start up faster. For the most part, it is invisible except for
occasional pauses while the symbol table details for a particular source
file are being read. (The set verbose
command can turn these
pauses into messages if desired. See Optional warnings and messages.)
We have not implemented the two-stage strategy for COFF yet. When the
symbol table is stored in COFF format, symbol-file
reads the
symbol table data in full right away. Note that “stabs-in-COFF”
still does the two-stage strategy, since the debug info is actually
in stabs format.
symbol-file
filename [ -readnow
] [ -mapped
]file
filename [ -readnow
] [ -mapped
]If memory-mapped files are available on your system through the
mmap
system call, you can use another option, -mapped, to
cause GDB to write the symbols for your program into a reusable
file. Future GDB debugging sessions map in symbol information
from this auxiliary symbol file (if the program has not changed), rather
than spending time reading the symbol table from the executable
program. Using the -mapped option has the same effect as
starting GDB with the -mapped command-line option.
You can use both options together, to make sure the auxiliary symbol file has all the symbol information for your program.
The auxiliary symbol file for a program called myprog is called myprog.syms. Once this file exists (so long as it is newer than the corresponding executable), GDB always attempts to use it when you debug myprog; no special options or commands are needed.
The .syms file is specific to the host machine where you run GDB. It holds an exact image of the internal GDB symbol table. It cannot be shared across multiple host platforms.
core-file
[ filename ]core-file
with no argument specifies that no core file is
to be used.
Note that the core file is ignored when your program is actually running
under GDB. So, if you have been running your program and you
wish to debug a core file instead, you must kill the subprocess in which
the program is running. To do this, use the kill
command
(see Killing the child process).
add-symbol-file
filename addressadd-symbol-file
filename address [ -readnow
] [ -mapped
]add-symbol-file
filename -ssection address ...
add-symbol-file
command reads additional symbol table
information from the file filename. You would use this command
when filename has been dynamically loaded (by some other means)
into the program that is running. address should be the memory
address at which the file has been loaded; GDB cannot figure
this out for itself. You can additionally specify an arbitrary number
of -ssection address pairs, to give an explicit
section name and base address for that section. You can specify any
address as an expression.
The symbol table of the file filename is added to the symbol table
originally read with the symbol-file
command. You can use the
add-symbol-file
command any number of times; the new symbol data
thus read keeps adding to the old. To discard all old symbol data
instead, use the symbol-file
command without any arguments.
Although filename is typically a shared library file, an executable file, or some other object file which has been fully relocated for loading into a process, you can also load symbolic information from relocatable .o files, as long as:
add-symbol-file
command.
Some embedded operating systems, like Sun Chorus and VxWorks, can load
relocatable files into an already running program; such systems
typically make the requirements above easy to meet. However, it's
important to recognize that many native systems use complex link
procedures (.linkonce
section factoring and C++ constructor table
assembly, for example) that make the requirements difficult to meet. In
general, one cannot assume that using add-symbol-file
to read a
relocatable object file's symbolic information will have the same effect
as linking the relocatable object file into the program in the normal
way.
add-symbol-file
does not repeat if you press <RET> after using it.
You can use the -mapped and -readnow options just as with
the symbol-file
command, to change how GDB manages the symbol
table information for filename.
add-shared-symbol-file
add-shared-symbol-file
command can be used only under Harris' CXUX
operating system for the Motorola 88k. GDB automatically looks for
shared libraries, however if GDB does not find yours, you can run
add-shared-symbol-file
. It takes no arguments.
section
section
command changes the base address of section SECTION of
the exec file to ADDR. This can be used if the exec file does not contain
section addresses, (such as in the a.out format), or when the addresses
specified in the file itself are wrong. Each section must be changed
separately. The info files
command, described below, lists all
the sections and their addresses.
info files
info target
info files
and info target
are synonymous; both print the
current target (see Specifying a Debugging Target),
including the names of the executable and core dump files currently in
use by GDB, and the files from which symbols were loaded. The
command help target
lists all possible targets rather than
current ones.
maint info sections
maint info sections
. In addition to the section information
displayed by info files
, this command displays the flags and file
offset of each section in the executable and core dump files. In addition,
maint info sections
provides the following command options (which
may be arbitrarily combined):
ALLOBJ
ALLOC
LOAD
.bss
sections.
RELOC
READONLY
CODE
DATA
ROM
CONSTRUCTOR
HAS_CONTENTS
NEVER_LOAD
COFF_SHARED_LIBRARY
IS_COMMON
set trust-readonly-sections on
The default is off.
set trust-readonly-sections off
All file-specifying commands allow both absolute and relative file names as arguments. GDB always converts the file name to an absolute file name and remembers it that way.
GDB supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared libraries.
GDB automatically loads symbol definitions from shared libraries
when you use the run
command, or when you examine a core file.
(Before you issue the run
command, GDB does not understand
references to a function in a shared library, however—unless you are
debugging a core file).
On HP-UX, if the program loads a library explicitly, GDB
automatically loads the symbols at the time of the shl_load
call.
There are times, however, when you may wish to not automatically load symbol definitions from shared libraries, such as when they are particularly large or there are many of them.
To control the automatic loading of shared library symbols, use the commands:
set auto-solib-add
modeon
, symbols from all shared object libraries
will be loaded automatically when the inferior begins execution, you
attach to an independently started inferior, or when the dynamic linker
informs GDB that a new library has been loaded. If mode
is off
, symbols must be loaded manually, using the
sharedlibrary
command. The default value is on
.
show auto-solib-add
To explicitly load shared library symbols, use the sharedlibrary
command:
info share
info sharedlibrary
sharedlibrary
regexshare
regexrun
. If
regex is omitted all shared libraries required by your program are
loaded.
On some systems, such as HP-UX systems, GDB supports autoloading shared library symbols until a limiting threshold size is reached. This provides the benefit of allowing autoloading to remain on by default, but avoids autoloading excessively large shared libraries, up to a threshold that is initially set, but which you can modify if you wish.
Beyond that threshold, symbols from shared libraries must be explicitly
loaded. To load these symbols, use the command sharedlibrary
filename. The base address of the shared library is determined
automatically by GDB and need not be specified.
To display or set the threshold, use the commands:
set auto-solib-limit
thresholdsharedlibrary
command. The default threshold is 100 (i.e. 100
Mb).
show auto-solib-limit