linux之如何使用汇编语言从键盘读取输入字符串_编程设计

我正在尝试编写一个简单的程序，从键盘获取字符串，然后将其打印到屏幕上。到目前为止，我无法让它发挥作用。

代码如下:

    .section .rodata 
output: .string "you entered %s\n" 
input:  .string "%s" 
 
    .text 
.globl  main 
    .type   main, @function 
 
main: 
    pushl   %ebp 
    movl    %esp, %ebp 
 
    subl    $100, %esp 
    pushl   $input 
    call    scanf 
 
    movl    %ebp, %esp 
    subl    $100, %esp 
    pushl   $output 
    call    printf 
 
    xorl    %eax, %eax 
    movl    %ebp, %esp 
    popl    %ebp 
    ret

当我执行它时，对于任何给定的输入，输出都是 you entered (null)。当我将 subl $100, %esp 命令(call print 之前的命令)的偏移量设置为 subl $104, %esp 我得到 you entered %s，当偏移量设置为 108 时，我得到 you entered *gibberish*。

我觉得这是一个我需要猜测 scanf 将字符串保存在堆栈中的位置的游戏(为什么它不在它应该在的位置？)。

我正在使用 IA32 指令集。

如有任何帮助，我们将不胜感激。

请您参考如下方法:

基本上你的程序有3个问题:

subl    $100, %esp 
pushl   $input 
# Error 1: 
# As Frank Kotler already wrote at this point 
# only $input is stored on the stack; however 
# the address of the buffer must also be on 
# the stack (see Frank Kotler's comment) 
call    scanf 
 
movl    %ebp, %esp 
# Error 2: 
# Now the buffer is below ESP. 
# Because interrupts use the kernel stack they 
# will not overwrite the memory below ESP. 
# However signals will destroy the memory below 
# ESP!! 
# 
# Instead of the lines: 
#   movl    %ebp, %esp 
#   subl    $100, %esp 
# 
# You should use something like this: 
#   add $8, %esp 
# or: 
#   lea -100(%ebp), %esp 
# 
 
subl    $100, %esp 
# Error 3: 
# As for "scanf" the second argument 
# is missing on the stack 
pushl   $output 
call    printf