Question

这是一个应该找到最少data_items的简单程序。 a 0用于终止内存块。％ebx正在跟踪当前最小值，因为je指令，0永远不会被复制到其中。然而，这个程序返回0到操作系统，而不是3。

.section .data

data_items:
 .long 3,67,34,222,45,75,54,34,44,222,11,66,0

.section .text

.globl _start

_start:
 movl $0, %edi          #move 0 into the index register
 movl data_items(,%edi,4), %eax  #load the first byte of data
 movl %eax, %ebx        #first item, so its smalles, ebx tracks smallest

 start_loop:
  cmpl $0, %eax         #check if we hit the end
  je loop_exit
  incl %edi
  movl data_items(,%edi,4), %eax
  cmpl %ebx, %eax
  jge start_loop

  movl %eax, %ebx
  jmp start_loop

 loop_exit:
  movl $1, %eax
  int $0x80

编辑：在此处更正代码：

.section .data

data_items:
 .long 3,67,34,222,45,75,54,34,44,222,11,66,0

.section .text

.globl _start

_start:
 movl $0, %edi          #move 0 into the index register
 movl data_items(,%edi,4), %eax  #load the first byte of data
 movl %eax, %ebx        #first item, so its biggest, ebx tracks biggest

 start_loop:
  incl %edi
  movl data_items(,%edi,4), %eax
  cmpl $0, %eax
  je loop_exit

  cmpl %ebx, %eax
  jge start_loop

  movl %eax, %ebx
  jmp start_loop

 loop_exit:
  movl $1, %eax
  int $0x80

Answer 1

逻辑不对。

在C代码中，您的程序看起来像

edi = 0;
eax = data_items[edi];
ebx = eax;
while(eax != 0) {
    eax = data_items[++edi];
    if(eax < ebx) ebx = eax;
}
exit(ebx);

问题是您加载eax然后立即将其存储为最小值。如果eax = 0，则将其存储为最小值（因为它是），然后才会中断。

简单的x86 linux汇编程序返回意外值

1 个答案: