为什么在移动堆栈指针时出现分段错误？

Question

Working with assembly code and wondering why I get a seg fault with the instruction subl $8, %esp?

        pushl %ebp
    movl %esp, %ebp

        movl 16(%ebp), %esi
        movl 12(%ebp), %edi
        movl 8(%ebp), %eax
        movl $0, %ebx
        subl $8, %esp
        jmp .LL1

.LL1:
        cmpl %ebx, %esi
        je .LL2
        movl %ebx, 4(%esp)
        movl %eax, (%esp)
        addl $1, %ebx
        jmp .LL1

.LL2:
    popl %ebp
    ret

segfault on subl $8, %esp

Answer 1

Are you sure that the code segfaults on subl $8, %esp ?

In your code, you subtract 8 from the stack pointer, but never restore the value. The address to return to is no longer the most recent thing on the stack when you execute ret .

The instruction

movl %esp, %ebp

copies the original value of %esp to %ebp . When you return, you restore the original of %ebp with popl , but never restore %esp , so you return to some garbage address.

Before the line

popl %ebp

add

movl %ebp, %esp

to correct the stack pointer before returning.