I tried to compile simple hello world program using such flags as -finline-functions, -finline-functions-called-once, but they don't seem to inline __i686.get_pc_thunk.bx. How can i force gcc do this?

Hey 10110111 ;-),

you can't force gcc to inline this "function", because it is added by the program linker (ld). The purpose of this thunk is to determine the IP (instruction pointer) value of the following instruction and it is usually used for position-independent code.

Though, if you have the following assembly snipped:

0x00 call <i686.get_pc_thunk.bx>
0x04 add $0x1191,%ebx

Then, after calling the thunk, the register ebx will contain the IP value 0x04. For the sake of completeness, this is how this thunk is implemented:

080483ca <__i686.get_pc_thunk.bx>:
80483ca: 8b 1c 24 mov (%esp),%ebx
80483cd: c3 ret


For the case you are interested in this position-independent code issue, please check this very good explanation: http://www.airs.com/blog/archives/41

- Andi -

Yes, i know how it is implemented. I came across this function while looking at disassembly. And just because i know this, i thought that it would be more efficient to replace function call with "mov (%esp),%ebx". It's just strange why linker can't optimize it this way...

That wouldn't work, the call instruction is needed to put the program counter on the stack.

Heh.. haven't thought about this

Still, a bit more efficient to inline:
;intel syntax
call next
next:
pop ebx


Though, as all this is being done by linker, i guess, linker can't change already existing code, so the result is a function...