Source files for my latest blog post on working with assembly routines and C on Mac OS X - http://x3ro.de/2013/09/12/link-assembly-routine-with-c-on-osx.html

asm.s

global _my_pow
section .text

_my_pow:
    push    rbp             ; create stack frame
    mov     rbp, rsp

    cmp     edi, 0          ; Check if base is negative
    mov     eax, 0          ; and return 0 if so
    jl      end

    mov     eax, edi        ; grab the "base" argument
    mov     edx, esi        ; grab the "exponent" argument

multiply:
    imul    eax, edi        ; eax * base
    sub     esi, 1          ; exponent - 1

    cmp     esi, 1          ; Loop if exponent > 1
    jg      multiply

end:
    pop     rbp             ; restore the base pointer
    ret

Makefile

all: run

run: clean test
    ./test

test: asm.o test.o
	clang -o test asm.o test.o

asm64.o:
	nasm -f macho64 asm.s

test.o:
	clang -o test.o -c test.c

clean:
	rm *.o test

test.c

#include <stdio.h>

extern int my_pow(int base, int exp);

int main(int argc, char const *argv[]) {
    int base, exp, result;
    base = 2;
    exp = 8;
    result = my_pow(base,exp);
    printf("Result: %d\n", result);
    return 0;
}