x86 NASM程序集中的阶乘函数出错 [英] Factorial function in x86 NASM assembly goes wrong

问题描述

我正在使用x86 NASM学习汇编语言.我想编写一个简单的递归阶乘函数，使用EAX寄存器将一个参数传递给该函数.之后，我想在屏幕上打印结果，但是什么也没有发生.坐在电脑上凝视着我之后，我不知道我的代码有什么问题.你们可以帮助新手解决这个问题吗?

I'm learning assembly language using x86 NASM. I wanted to write a simple recursive factorial function to which I am passing one parameter using EAX register. After that, I want to print my result on the screen but nothing happens. After sitting and staring on my computer I don't have any clue what is wrong with my code. Can you guys help newbie with this problem?

我知道阶乘函数的序言和结尾不是必需的，因为我没有使用堆栈，但是对我来说代码更易读;)

I know that the prologue and epilogue of factorial funtion is not required due I'm not using stack but for me code is more readable ;)

这是我的代码:

global main
extern printf

section .data
    message db "%03X", 0x10, 0x0

section .text
main:
    mov eax, 5
    call factorial
    push eax
    push message
    call printf
    add esp, 0x8
    mov eax, 1
    mov ebx, 0
    int 0x80

factorial:
    push ebp
    push edx
    mov ebp, esp
    mov edx, eax
    cmp edx, 0
    jne not_equal_zero
    mov eax, 1
    jmp exit
not_equal_zero:
    mov eax, edx
    sub eax, 1
    call factorial
    imul eax, edx
exit:
    mov esp, ebp
    pop edx
    pop ebp
    ret

推荐答案

C库-我想您使用的是GCC的库-无法立即输出 printf 的结果.而是将其存储在称为缓冲区的单独内存中，并偶然输出.在这种情况下，程序将以 int 0x80/​​ eax = 1 结束的速度比刷新缓冲区的速度快.您可以插入手动刷新:

The C library - I guess you use the one from GCC - doesn't output the result of printf immediately. Rather, it is stored in a separate memory called buffer and outputted by chance. In this case the program will be ended by int 0x80/eax=1 faster than the buffer will be flushed. You can insert a manual flush:

...
extern fflush
...
push 0
call fflush
add esp, 4
...

最好的解决方案是使用C exit 函数.替换

The best solution is to use the C exit function. Replace

mov ebx,0
mov eax,1
int 0x80

作者

push 0
call exit

或简单地替换为

ret

在这种情况下，您不需要手动刷新缓冲区.这将退出或 ret 为您完成.

In this case you don't need to flush the buffer manually. This will exit or ret do for you.

BTW:LF(换行符)被编码为10个十进制和0x0A十六进制.

BTW: LF (line feed) is coded as 10 decimal and 0x0A hexadecimal.

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