Question

This code assembles fine using GCC in terminal:

.globl _sub
_sub:
    push %rbp
    mov %rbp,%rsp
    mov $0xBEEF,%eax
    pop %rbp
    ret

.globl _main

_main:
    push %rbp
    mov %rbp,%rsp
    call _sub
    mov $0,%eax
    pop %rbp
    ret

But when I run the a.out file, I get this error:

Segmentation fault: 11

If I run it in GDB this is the error I get:

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000001
0x0000000000000001 in ?? ()

Any ideas as to why this might be happening?

Answer 1

mov %rbp, %rsp corrupts the stack pointer. You probably want mov %rsp, %rbp instead.

Due to historical reasons, some assemblers consider operands to be left-to-right while others take them right-to-left.