为什么为x86汇编函数将GDB断点设置在错误的地址? [英] Why is GDB breakpoint set at the wrong address for an x86 assembly function?

问题描述

我遇到一个问题，其中gdb在添加断点时将行号映射到错误的内存地址.

I am experiencing an issue where gdb is mapping a line number to the wrong memory address when adding a breakpoint.

以下x86 Linux汇编程序打印"hello".

The following x86 Linux assembly program prints "hello".

/* hello.s */

  .section .data
str:
  .ascii "hello\n"
  strlen = . - str

  .section .text

print:
  pushl %ebp
  movl  %esp, %ebp
  pushl %ebx
  movl  $4, %eax
  movl  $1, %ebx
  movl  $str, %ecx
  movl  $strlen, %edx
  int   $0x80
  popl  %ebx
  movl  %ebp, %esp
  popl  %ebp
  ret

  .globl _start
_start:
  call  print
  movl  $1, %eax
  movl  $0, %ebx
  int   $0x80

我用调试信息编译它，然后链接.

I compile it with debugging information, and then link.

$ as -g --32 -o hello.o hello.s
$ ld -m elf_i386 -o hello hello.o

接下来，在gdb中，我尝试在打印功能的第一行( pushl％ebp )的第11行上设置断点.

Next, in gdb, I try to set a breakpoint on line 11, the first line of the print function (pushl %ebp).

$ gdb ./hello
(gdb) break hello.s:11

断点3位于0x8048078:文件hello.s，第11行.

Breakpoint 3 at 0x8048078: file hello.s, line 11.

如输出所示，断点设置在地址0x8048078上.但是，这是错误的地址.当我在gdb中运行程序时，它在第14行中断.第11行的地址是0x8048074，已使用gdb的info命令进行了确认.

As shown in the output, the breakpoint is set at address 0x8048078. However, that is the wrong address. When I run my program in gdb, it breaks at line 14. The address of line 11 is 0x8048074, confirmed using gdb's info command.

(gdb) info line hello.s:11

"hello.s"的第11行开始于地址0x8048074，结束于0x8048075.

Line 11 of "hello.s" starts at address 0x8048074 and ends at 0x8048075 .

直接在打印指令上设置断点即可(将断点设置为第11行的地址，0x8048074).

Setting a breakpoint on the print instruction directly works (the break point is set for the address of line 11, 0x8048074).

当我为第11行添加一个断点时，gdb不会使用与使用上述info命令输出的地址相同的地址?这是我要中断的内存地址.

How come when I add a breakpoint for line 11, gdb does not use the same address as output by using the info command above? This is the memory address I am trying to break on.

我在gdb 7.11.1和8.0.1上都遇到相同的行为.我尝试添加 .type print，@ function 批注，但这并不能解决我的问题.

I am experiencing the same behavior on both gdb 7.11.1 and 8.0.1. I have tried adding a .type print,@function annotation, but that did not solve my issue.

推荐答案

怎么来

默认情况下，当您在函数或函数启动的行上设置断点时，GDB会尝试跳过函数序言.

By default, GDB tries to skip past function prolog, when you set a breakpoint on a function, or a line on which the function starts.

这往往是 C 开发人员想要的，因为他们通常对参数设置不感兴趣.

This tends to be what C developers want, since they usually aren't interested in parameter setup.

如果您需要其他功能，请使用 b *地址或 b& print 阻止GDB正常运行.

If you want something else, use b *address or b &print to prevent GDB from doing its usual thing.

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