In a DWARF file, what's the difference between .debug_str and .strtab?

Question

I'm working with DWARF parser that looks for string data in the .debug_str section. In the ELF files I'm parsing, the string data is in the .strtab section. What's the difference between these two sections? Both contain strings, right?

Answer 1

What's the difference between these two sections?

They have ~nothing to do with each other.

Both contain strings, right?

Well, yes. And every section contains bytes, so next you'll be asking "what's the difference between .text and .data?".

The .debug_str section contains debug strings, which are needed for debugging. The .strtab section contains symbol names which are needed for (static) linking.

Neither section (in fact no section) is needed at runtime.

why .strtab is present in final executable linked with -g (even though it won't be used for static linking anymore)?

1. The .strtab is usually present in final executable built with or without -g and
2. It's present to help with debugging. Consider:

int foo() { abort(); }
int bar() { return foo(); }
int main() { return bar(); }

gcc t.c
strip a.out -o a.stripped

gdb -q ./a.stripped
(gdb) run
Starting program: /tmp/a.stripped

Program received signal SIGABRT, Aborted.
0x00007ffff7a4bc37 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56  ../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  0x00007ffff7a4bc37 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007ffff7a4f028 in __GI_abort () at abort.c:89
#2  0x0000000000400536 in ?? ()
#3  0x0000000000400544 in ?? ()
#4  0x0000000000400554 in ?? ()
#5  0x00007ffff7a36f45 in __libc_start_main (main=0x400546, argc=1, argv=0x7fffffffde58, init=, fini=, rtld_fini=, stack_end=0x7fffffffde48) at libc-start.c:287
#6  0x0000000000400469 in ?? ()

Not very useful, is it? Compare to unstripped binary:

gdb -q ./a.out
(gdb) r
Starting program: /tmp/a.out

Program received signal SIGABRT, Aborted.
0x00007ffff7a4bc37 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56  ../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  0x00007ffff7a4bc37 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007ffff7a4f028 in __GI_abort () at abort.c:89
#2  0x0000000000400536 in foo ()
#3  0x0000000000400544 in bar ()
#4  0x0000000000400554 in main ()