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.