Swap example.

asm_swap.s

.globl _swap
_swap:
	movl	(%rdi), %ebx
	movl	(%rsi), %eax
	movl	%eax, (%rdi)
	movl	%ebx, (%rsi)
	retq

asm_swap_ia32.s

.globl _swap
_swap:
	pushl %ebp
	movl  %esp, %ebp
	pushl %ebx
	movl  12(%ebp), %ecx
	movl  8(%ebp), %edx
	movl  (%ecx), %eax
	movl  (%edx), %ebx
	movl  %eax, (%edx)
	movl  %ebx, (%ecx)
	movl  -4(%ebp),%ebx
	movl  %ebp,%esp
	popl  %ebp
	ret

Makefile

OBJECTS=asm_swap.o swap.o

all: $(OBJECTS)
	$(CC) -o swap $(OBJECTS)

clean:
	rm -f swap *.o

swap.c

#include <stdio.h>

extern void swap(int *p, int *q);

int
main(void)
{
	int p, q;
	p = 10;
	q = 20;
	swap(&p, &q);
	printf("p=%d\nq=%d\n", p, q);
	return 0;
}