尝试写一个strlen

 1#include <stdio.h>
 2
 3extern int strlen2(char *str);
 4
 5int main() {
 6        char a[] = "hello,world";
 7        int len = strlen2(a);
 8
 9        printf("%s len:%d  \n", a, len);
10
11        return 0;
12}

 1SECTION .data
 2
 3SECTION .text
 4	global strlen2
 5
 6strlen2:
 7	mov rax, rdi
 8next:
 9	cmp byte [rax], 0
10	je down
11	inc rax
12	jmp next
13down:
14	sub rax, rdi
15	ret