inlining a simple assembly function

Question

I (tried to) follow an old answer, but I must be doing something wrong: the function is not inlined (it is still called in the disassembly). Here is what I did:

get_regs.h:
inline unsigned long __get_esp(void) {
__asm__("movl %esp,%eax");
}

program.c:
...
#include "get_regs.h "
...
extern unsigned long __get_esp(void);
...
tmp = __get_esp();

Compiled as (other options for various reasons):
gcc -g -fno-stack-protector -mpreferred-stack-boundary=2 program.c

This follows the second recommendation to include the definition in the header file.

I realize I could use extended assembly and copy the result from %eax to tmp, but would like to understand to do the inlining. I found some hits on SO, but none seemed to cover my case.

System:
- Ubuntu 12.04
- gcc 4.6.3.
- x86 32 bit

Answer 1

You'll need to enable compiler optimization (even the most basic level) for inlining to possibly take place.

By the way, unless you have any special need for a non inlined copy of the function, you can drop the extern re-declaration, and just use the inlined declaration included in the header file.