What is the difference between gcc -ggdb and gcc -g
GccGdbGcc Problem Overview
When I use gcc to compile C programs
I usually use -g
to get some debug information into the elf file
so that gdb can help me if needed.
However, I noticed that some programs use -ggdb
, since it's supposed to make the
debug info more gdb friendly.
How do they differ and which is recommended to use?
Note: A link to the options for Debugging Your Program or GCC, http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html#Debugging-Options
Gcc Solutions
Solution 1 - Gcc
-g
and -ggdb
are similar with some slight differences, I read this here:
> -g
produces debugging information in the OS¹s native format (stabs, COFF, XCOFF, or DWARF 2).
>
> -ggdb
produces debugging information specifically intended for gdb.
>
> -ggdb3
produces extra debugging information, for example: including macro definitions.
>
> -ggdb
by itself without specifying the level defaults to -ggdb2
(i.e., gdb for level 2).
Solution 2 - Gcc
It is possible that there is no difference - depends on the OS native format and how portable you want the debugging info to be. See GCC manual Debugging Options.
Solution 3 - Gcc
I have atleast one example where -ggdb worked better for me than another debug option which we were using :
amitkar@lohgad:~> cat > main.c
#include <stdio.h>
int main(int argc, char **argv)
{
printf("Args :%d\n", argc);
for ( ;argc > 0;)
printf("%s\n", argv[--argc]);
return 0;
}
amitkar@lohgad:~> gcc -gstabs+ main.c -o main
amitkar@lohgad:~> file main
main: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), for GNU/Linux 2.6.4, dynamically linked (uses shared libs), not stripped
amitkar@lohgad:~> /usr/bin/gdb ./main
GNU gdb 6.6.50.20070726-cvs
Copyright (C) 2007 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "x86_64-suse-linux"...
Using host libthread_db library "/lib64/libthread_db.so.1".
(gdb) break main
Breakpoint 1 at 0x400577: file main.c, line 5.
(gdb) run
Starting program: /home/amitkar/main
Breakpoint 1, main (argc=Cannot access memory at address 0x8000df37d57c
) at main.c:5
5 printf("Args :%d\n", argc);
(gdb) print argc
Cannot access memory at address 0x8000df37d57c
(gdb)
Note: This happens only on x86-64 boxes and goes away when compiled with -ggdb. But newer versions of the debugger do work even with -gstabs+
Solution 4 - Gcc
One thing is that "-g" is portable (e.g. in Makefiles destined to be executed on non-GNU platforms). I had a portability issue regarding -g vs. -ggdb on an AIX machine recently, that's why I bring it up.
No idea on what -ggdb adds in usability, though.
Solution 5 - Gcc
This is the official explanation: http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html#Debugging-Options
Only few hard facts, but interesting anyway.