汇编语言学习系列 for循环实现

假如汇编语言要实现如下C语言的功能，编译环境Ubuntu14.04（32位）。

#include<stdio.h>
int fact_for(int n)
{
    int i;
    int result = 1;
    for(i = 2; i <= n; i++)
        result *= i;
    return result;
}

int main(){
    printf("%d\n", fact_for(3));
    return 0;
}

• 代码for.s

.section .data
        n: .int 3
        format: .asciz "%d\n"
.section .text
.global _start
_start:
        pushl %ebp
        movl %esp, %ebp
        subl $8, %esp
        
        movl n, %ecx        
        movl %ecx, (%esp)
        call fact_for

        pushl %eax
        pushl $format
        call printf
        
        movl $0, (%esp)
        call exit
        
fact_for:
        pushl %ebp
        movl %esp, %ebp
        pushl %ebx
        
        movl 8(%ebp), %edx    #get n
        movl $1, %eax        #init result
        movl $2, %ecx        #init i
        
        cmp %ecx, %edx
        jl .done
        
.loop:
        imul %ecx, %eax
        inc %ecx
        cmp %ecx, %edx
        jge .loop

.done:
        popl %ebx
        popl %ebp
        
        ret        

• 编译

as for.s -o for.o

• 链接

ld -lc -I /lib/ld-linux.so.2 for.o -ofor

• 执行

./for