(汇编新手)无法从GDB访问x86-64中的32位寄存器 [英] (Assembly newbie) Unable to access 32-bit registers in x86-64 from GDB

问题描述

所以我只是想在这个简单的程序中使用gdb访问 eax .

So I am just trying to access eax with gdb in this easy program.

C代码:

int main(){
    int a = 1;
    int b = 3;
    int c = a + b;
    return 1;
 }

这是我的gdb尝试:

(gdb) disas 
Dump of assembler code for function main:
0x000000000040049c <+0>: push   %rbp
0x000000000040049d <+1>: mov    %rsp,%rbp
0x00000000004004a0 <+4>: movl   $0x1,-0x4(%rbp)
0x00000000004004a7 <+11>:    movl   $0x3,-0x8(%rbp)
0x00000000004004ae <+18>:    mov    -0x8(%rbp),%eax
0x00000000004004b1 <+21>:    mov    -0x4(%rbp),%edx
=>  0x00000000004004b4 <+24>:    add    %edx,%eax
0x00000000004004b6 <+26>:    mov    %eax,-0xc(%rbp)
0x00000000004004b9 <+29>:    pop    %rbp
0x00000000004004ba <+30>:    retq 
End of assembler dump.

(gdb) x $rbp
0x7fffffffe620: 0x00000000
(gdb) x $rbp-4
0x7fffffffe61c: 0x00000001
(gdb) x $rbp-8
0x7fffffffe618: 0x00000003
(gdb) x $eax
0x3:    Cannot access memory at address 0x3

所以您可以看到，使用 x $ rbp 访问 rbp 没问题，但是我无法访问 eax .

So you can see, I have no trouble using x $rbp to access rbp, but I'm unable to access eax.

是否需要打开某些设置才能在64位系统上从gdb访问32位寄存器?

Is there some setting I need to turn on to access 32-bit registers from gdb on a 64-bit system?

推荐答案

x 命令代表 print 命令或 p ，它会显示其参数值.

The x command stands for examine. It accepts a pointer as input and shows what's there. You're looking for the print command, or p, which prints its argument's value.

p $eax

通过执行 x $ rbp ，您实际上正在查看堆栈中的内容.在您的示例中，看来 rbp 包含地址 0x7fffffffe620 .

By doing x $rbp, you're actually looking at what's on the stack. It appears that rbp contains the address 0x7fffffffe620 in your example.

您得到的错误消息 x $ eax 指示 eax 的值为3，并且由于该指针不是有效的指针，因此它向您显示一条错误消息

The error message you get doing x $eax indicates that the value of eax is 3, and since that's not a valid pointer, it shows you an error message instead.

这篇关于(汇编新手)无法从GDB访问x86-64中的32位寄存器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！