从 Valgrind 源代码访问用户变量

Question

我正在尝试用 valgrind 源代码做一些实验。我使用下面的代码作为我的测试代码：

#include <stdio.h>
int g_int = 12;
int main()
{
  int y = 10;
  int x;
  printf("%d\n",x);
  return x;
}

我构建了一个名为 "test.out" 的可执行文件。然后我执行了以下命令：

$./valgrind --tool=memcheck ./test.out

在我的测试代码中，我有一个未初始化的错误，valgrind 通过给我一些消息来报告来自“mc_errors.c”的错误：

../build/bin$ ./valgrind --tool=memcheck --track-origins=yes --read-var-info=yes ./test >> outpur.txt
==24255== Memcheck, a memory error detector
==24255== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==24255== Using Valgrind-3.14.0.GIT and LibVEX; rerun with -h for copyright info
==24255== Command: ./test
==24255== 
==24255== Conditional jump or move depends on uninitialised value(s)
==24255== I want to print my local variable here!
==24255==    at 0x4E87B83: vfprintf (vfprintf.c:1631)
==24255==    by 0x4E8F898: printf (printf.c:33)
==24255==    by 0x400548: main (test.c:10)
==24255==  Uninitialised value was created by a stack allocation
==24255==    at 0x400526: main (test.c:6)
==24255== 
==24255== Use of uninitialised value of size 8
==24255== I want to print my local variable here!
==24255==    at 0x4E8476B: _itoa_word (_itoa.c:179)
==24255==    by 0x4E8812C: vfprintf (vfprintf.c:1631)
==24255==    by 0x4E8F898: printf (printf.c:33)
==24255==    by 0x400548: main (test.c:10)
==24255==  Uninitialised value was created by a stack allocation
==24255==    at 0x400526: main (test.c:6)
==24255== 
==24255== Conditional jump or move depends on uninitialised value(s)
==24255== I want to print my local variable here!
==24255==    at 0x4E84775: _itoa_word (_itoa.c:179)
==24255==    by 0x4E8812C: vfprintf (vfprintf.c:1631)
==24255==    by 0x4E8F898: printf (printf.c:33)
==24255==    by 0x400548: main (test.c:10)
==24255==  Uninitialised value was created by a stack allocation
==24255==    at 0x400526: main (test.c:6)
==24255== 
==24255== Conditional jump or move depends on uninitialised value(s)
==24255== I want to print my local variable here!
==24255==    at 0x4E881AF: vfprintf (vfprintf.c:1631)
==24255==    by 0x4E8F898: printf (printf.c:33)
==24255==    by 0x400548: main (test.c:10)
==24255==  Uninitialised value was created by a stack allocation
==24255==    at 0x400526: main (test.c:6)
==24255== 
==24255== Conditional jump or move depends on uninitialised value(s)
==24255== I want to print my local variable here!
==24255==    at 0x4E87C59: vfprintf (vfprintf.c:1631)
==24255==    by 0x4E8F898: printf (printf.c:33)
==24255==    by 0x400548: main (test.c:10)
==24255==  Uninitialised value was created by a stack allocation
==24255==    at 0x400526: main (test.c:6)
==24255== 
==24255== Conditional jump or move depends on uninitialised value(s)
==24255== I want to print my local variable here!
==24255==    at 0x4E8841A: vfprintf (vfprintf.c:1631)
==24255==    by 0x4E8F898: printf (printf.c:33)
==24255==    by 0x400548: main (test.c:10)
==24255==  Uninitialised value was created by a stack allocation
==24255==    at 0x400526: main (test.c:6)
==24255== 
==24255== Conditional jump or move depends on uninitialised value(s)
==24255== I want to print my local variable here!
==24255==    at 0x4E87CAB: vfprintf (vfprintf.c:1631)
==24255==    by 0x4E8F898: printf (printf.c:33)
==24255==    by 0x400548: main (test.c:10)
==24255==  Uninitialised value was created by a stack allocation
==24255==    at 0x400526: main (test.c:6)
==24255== 
==24255== Conditional jump or move depends on uninitialised value(s)
==24255== I want to print my local variable here!
==24255==    at 0x4E87CE2: vfprintf (vfprintf.c:1631)
==24255==    by 0x4E8F898: printf (printf.c:33)
==24255==    by 0x400548: main (test.c:10)
==24255==  Uninitialised value was created by a stack allocation
==24255==    at 0x400526: main (test.c:6)
==24255== 
==24255== 
==24255== HEAP SUMMARY:
==24255==     in use at exit: 0 bytes in 0 blocks
==24255==   total heap usage: 1 allocs, 1 frees, 4,096 bytes allocated
==24255== 
==24255== All heap blocks were freed -- no leaks are possible
==24255== 
==24255== For counts of detected and suppressed errors, rerun with: -v
==24255== ERROR SUMMARY: 8 errors from 8 contexts (suppressed: 0 from 0)

现在我想用消息（错误报告) 来自 valgrind。我已经在 valgrind 源打印中添加了一个打印输出："I want to print my local variable here!" 是否有任何可能的方法使用任何内部 api 从 valgrind 源代码中读取用户源代码中的变量值？如果我能从用户代码中获取所有变量名，那将是一个加号。

Answer 1

尝试使用选项

--track-origins=yes

这将提供有关动态内存的更多信息。

此外，尝试

--read-var-info=yes

这应该与调试版本一起使用（请参阅关于使用 -g 进行编译的注释）。这将提供有关自动变量的更多信息。

Answer 2

使用 valgrind 选项 --vgdb-error=1

有了这个，当valgrind报错的时候，会等待一个gdb 附上。使用 gdb，您可以查看所有局部或全局变量。

有关详细信息，请参阅 http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.gdbserver。

Answer 3

您可以为此使用 VALGRIND_COUNT_ERRORS、VALGRIND_PRINTF Valgrind Client Requests。

在示例代码中如何使用它们：

#include <stdio.h>
#include <valgrind/valgrind.h>

int g_int = 12;
int main()
{
  int y = 10;
  int x;
  printf("%d\n",x);
  if (VALGRIND_COUNT_ERRORS > 0)
  {
    VALGRIND_PRINTF("y=%d, g_int=%d\n", y, g_int);
  }
  return x;
}

Valgrind 输出：

==4030== Memcheck, a memory error detector
==4030== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==4030== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==4030== Command: ./a.out
==4030== 
==4030== Conditional jump or move depends on uninitialised value(s)
==4030==    at 0x4E90DDA: vfprintf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E99285: printf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x400719: main (in /home/ks/a.out)
==4030== 
==4030== Use of uninitialised value of size 8
==4030==    at 0x4E8CDAB: _itoa_word (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E9046D: vfprintf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E99285: printf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x400719: main (in /home/ks/a.out)
==4030== 
==4030== Conditional jump or move depends on uninitialised value(s)
==4030==    at 0x4E8CDB5: _itoa_word (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E9046D: vfprintf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E99285: printf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x400719: main (in /home/ks/a.out)
==4030== 
==4030== Conditional jump or move depends on uninitialised value(s)
==4030==    at 0x4E90572: vfprintf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E99285: printf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x400719: main (in /home/ks/a.out)
==4030== 
==4030== Conditional jump or move depends on uninitialised value(s)
==4030==    at 0x4E9104C: vfprintf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E99285: printf (in /usr/lib64/libc-2.26.so)
==4030==    by 0x400719: main (in /home/ks/a.out)
==4030== 
0
**4030** y=10, g_int=12
==4030== Syscall param exit_group(status) contains uninitialised byte(s)
==4030==    at 0x4F1A478: _Exit (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E77B3A: __run_exit_handlers (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E77BD9: exit (in /usr/lib64/libc-2.26.so)
==4030==    by 0x4E5D040: (below main) (in /usr/lib64/libc-2.26.so)
==4030== 
==4030== 
==4030== HEAP SUMMARY:
==4030==     in use at exit: 0 bytes in 0 blocks
==4030==   total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==4030== 
==4030== All heap blocks were freed -- no leaks are possible
==4030== 
==4030== For counts of detected and suppressed errors, rerun with: -v
==4030== Use --track-origins=yes to see where uninitialised values come from
==4030== ERROR SUMMARY: 6 errors from 6 contexts (suppressed: 0 from 0)

变量 g_int 和 y 打印在这一行中：

**4030** y=10, g_int=12

从 Valgrind 源代码访问用户变量

Access User variables from Valgrind source code

c

profiling

valgrind

memory-profiling

memcheck