How to access stack base pointer (rbp) using inline assembly?

Question

My requirement is to access a function call parameters by offsetting rbp using inline assembly. But I couldn't find a suitable operand constraint to specify the base pointer in x86. I am using Intel compiler but it's documentation states that it supports GCC style inline assembly. So GCC based example would be sufficient.

Answer 1

You can try:

#include <stdio.h>
#include <inttypes.h>

int
main(int argc, char **argv)
{
 uint64_t n;

 __asm__ __volatile__(
   "movq %%rbp, %0\n\t"
   : "=r"(n)
 );

 printf("rbp = 0x%" PRIx64 "\n", n);
 return 0;
}

Answer 2

I know you asked for inlined assembly, but note that on gcc you could also use __builtin_frame_address, which both frees you from the need for inlined assembly (yikes), and could provide frame levels further than the immediate one.

See here - http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html