Call C/C++ function from assembly (OSX Mavericks x64)

Question

This is a weird issue that I can't seem to find an answer to. This:

#include <iostream>
using namespace std;

void show_number(int number) {
    cout << number << endl;   // Shows '10' as expected
}

int main() {
    cout << endl; // Remove this and it fails

    __asm {
        mov rdi, 10
        call show_number
    }
}

actually works fine, except when you remove the initial cout << endl (first line of main). When you remove it, the cout in show_number seems to cause a segfault for some reason.

What causes this?

(OSX Mavericks x64, but should work in linux as well I think)

Answer 1

The Mac OS X ABI requires a 16-bytes stack alignment, before calling a function.

If your code is working, you're simply lucky, and this explains why you're getting e segmentation fault when modifying previous sections of the code.

So you need to ensure the stack is aligned on a 16-byte boundary.
I already answered a similar question a few times ago:

How to print argv[0] in NASM?

The interesting part is:

; Align stack on a 16 bytes boundary
mov     ebp,                esp
and     esp,                0xFFFFFFF0

Be sure to read the full answer, though...