Question

我正在解决涉及创建小编译器的任务。我的编译器为简单赋值语句生成以下汇编代码

// global declaration
int k;

float x,y,z;
// inside main func
k=10;
x = y = k;

汇编代码（我＆＃39; m 获取分段错误（核心转储）：

 #   19
                    # b_push_ext_addr (x)
        subl    $8, %esp
        movl    $x, (%esp)
                    # b_push_ext_addr (y)
        subl    $8, %esp
        movl    $y, (%esp)
                    # b_push_ext_addr (k)
        subl    $8, %esp
        movl    $k, (%esp)
                    # b_deref (signed int)
        movl    (%esp), %eax

# Proplm on next Line ... why?
         movl (%eax), %edx


        movl    %edx, (%esp)
                    # b_convert (signed int -> float)
        fildl   (%esp)
        fstps   (%esp)
                    # b_assign (float)
        movl    (%esp), %edx
        addl    $8, %esp
        movl    (%esp), %eax
        movl    %edx, (%eax)
        movl    %edx, (%esp)
                    # b_deref (float)
        movl    (%esp), %eax
        movl    (%eax), %edx
        movl    %edx, (%esp)
                    # b_convert (float -> double)
        flds    (%esp)
        fstpl   (%esp)
                    # b_convert (double -> float)
        fldl    (%esp)
        fstps   (%esp)
                    # b_assign (float)
        movl    (%esp), %edx
        addl    $8, %esp
        movl    (%esp), %eax
        movl    %edx, (%eax)
        movl    %edx, (%esp)
                    # b_pop ()
        addl    $8, %esp

当我使用gdb时：它指向这一行：

(gdb) x/i $eip
=> 0x80485bd <main+336>:        mov    (%eax),%edx

Answer 1

实际的错误是在类似的指令下进一步向下：

    fstps   (%esp)       # stack has some float
                # b_assign (float)
    movl    (%esp), %edx # edx has a float now
    addl    $8, %esp
    movl    (%esp), %eax
    movl    %edx, (%eax)
    movl    %edx, (%esp) # write the float onto stack
                # b_deref (float)
    movl    (%esp), %eax # load the float from stack
    movl    (%eax), %edx # try to use float as pointer => segfault

在进行补偿时出现分段错误（核心转储）

1 个答案: