Debuggin info for unused sections

nick clifton nickc@redhat.com
Fri Jan 6 10:27:00 GMT 2012


Hi Praveen,

   [I have added the GDB list as I now think that this issue affects them.]

> While using -gc-sections to remove unused sections, the section is removed but the debug info in not removed.
>
> In,
>
> a.c:
> int main()
> {
>    return 0;
> }
> int fun ()
> {
>    return 0;
> }

> gcc -g3 -ffunction-sections -Wl,-gc-sections a.c
> readelf -wl a.out
> gives
>
> Line Number Statements:
>    Extended opcode 2: set Address to 0x4003f6
>    Special opcode 6: advance Address by 0 to 0x4003f6 and Line by 1 to 2
>    Special opcode 62: advance Address by 4 to 0x4003fa and Line by 1 to 3
>    Special opcode 76: advance Address by 5 to 0x4003ff and Line by 1 to 4
>    Advance PC by 2 to 0x400401
>    Extended opcode 1: End of Sequence
>
>    Extended opcode 2: set Address to 0x0
>    Special opcode 11: advance Address by 0 to 0x0 and Line by 6 to 7
>    Special opcode 62: advance Address by 4 to 0x4 and Line by 1 to 8
>    Special opcode 76: advance Address by 5 to 0x9 and Line by 1 to 9
>    Advance PC by 2 to 0xb
>    Extended opcode 1: End of Sequence


Originally I had just thought that this was a missed opportunity for the 
linker to remove unneeded debug information.  But then it occurred to me 
that leaving the bogus line number information in could cause problems 
for GDB.  As in:

   % gdb -nw a.out
   GNU gdb (GDB) 7.4.50.20120106-cvs
   [...]
   (gdb) break a.c:6
   Bus error (core dumped)

So it seems that we really do need to remove it after all.  I will look 
into it when I have the time.

Cheers
   Nick



More information about the Gdb mailing list