我们可以在 GDB 会话中定义新的数据类型吗

问题描述

有没有办法在 gdb 中定义新的数据类型(C 结构或联合).这个想法是定义一个结构，然后让 gdb 从解释为新定义的结构的地址打印数据.

Is there a way to define a new data type (C structure or union) in gdb. The idea is to define a structure and then make gdb print data from an address interpreted as the newly defined structure.

例如，假设我们有一个示例结构.

For example, lets say we have a sample structure.

struct sample {
  int i;
  struct sample *less;
  struct sample *more;
}

如果 0x804b320 是 struct sample 数组的地址.该二进制文件没有调试信息，因此 gdb 可以理解 struct sample.有什么方法可以在 gdb 会话中定义 struct sample 吗?这样我们就可以打印 p *(struct sample *)0x804b320

And if 0x804b320 is the address of an array of struct sample. The binary doesn't have debugging information so that gdb understands struct sample. Is there any way to define struct sample in a gdb session? So that we can print p *(struct sample *)0x804b320

推荐答案

是的，这里是如何做到这一点的:

Yes, here is how to make this work:

// sample.h
struct sample {
  int i;
  struct sample *less;
  struct sample *more;
};

// main.c
#include <stdio.h>
#include <assert.h>
#include "sample.h"
int main()
{
  struct sample sm;
  sm.i = 42;
  sm.less = sm.more = &sm;

  printf("&sm = %p
", &sm);
  assert(sm.i == 0);  // will fail
}

gcc main.c   # Note: no '-g' flag

gdb -q ./a.out
(gdb) run
&sm = 0x7fffffffd6b0
a.out: main.c:11: main: Assertion `sm.i == 0' failed.

Program received signal SIGABRT, Aborted.
0x00007ffff7a8da75 in raise ()
(gdb) fr 3
#3  0x00000000004005cc in main ()

没有局部变量，没有类型struct sample:

No local variables, no type struct sample:

(gdb) p sm
No symbol "sm" in current context.
(gdb) p (struct sample *)0x7fffffffd6b0
No struct type named sample.

所以我们开始工作了:

// sample.c
#include "sample.h"
struct sample foo;

gcc -g -c sample.c

(gdb) add-symbol-file sample.o 0
add symbol table from file "sample.o" at
    .text_addr = 0x0

(gdb) p (struct sample *)0x7fffffffd6b0
$1 = (struct sample *) 0x7fffffffd6b0
(gdb) p *$1
$2 = {i = 42, less = 0x7fffffffd6b0, more = 0x7fffffffd6b0}

瞧！

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