仅使用Program计数器和可执行文件调查未对齐的用户空间访问

Question

因此，我有这个使用-g选项编译的可执行文件，它会触发加载未对齐的用户空间访问警告。

Unaligned userspace access in "softtest" pid=1407 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1406 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1406 pc=0x004148c2 ins=0x012e
Unaligned userspace access in "softtest" pid=1407 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1406 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1407 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1406 pc=0x004148c2 ins=0x012e
Unaligned userspace access in "softtest" pid=1407 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1406 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1406 pc=0x004148c2 ins=0x012e
Unaligned userspace access in "softtest" pid=1407 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1406 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1407 pc=0x0041515c ins=0x011e
Unaligned userspace access in "softtest" pid=1406 pc=0x004148c2 ins=0x012e

错误消息提供了一些信息:程序计数器和指令，但我不知道如何将PC转换为代码中的文件和行。

我可以察觉到这是在一个循环中执行一些内存复制之类的操作，因为地址经常是相同的。

那么问题是:如何使用Linux工具找出导致这种未对齐访问的代码文件和代码行？

对此有什么意见吗？

Answer 1

看一看addr2line实用程序

DESCRIPTION
       addr2line translates addresses into file names and line numbers.
       Given an address in an executable or an offset in a section of a
       relocatable object, it uses the debugging information
       to figure out which file name and line number are associated with it.

一个简单的c-示例：

1 #include <stdio.h>
2 
3 int main() {
4     int* a = 0;
5 
6     printf("%d", *a);
7     return 0;
8 }

使用以下命令编译它

gcc -Wall -ggdb3 g.c

gdb给出以下输出：

$ gdb -q  a.out 
Reading symbols from /tmp/tmp.M0766CSHGm/a.out...done.
(gdb) r
Starting program: /tmp/tmp.M0766CSHGm/a.out 

Program received signal SIGSEGV, Segmentation fault.
0x0000000000400538 in main () at g.c:6
6       printf("%d", *a);

将该地址与addr2line一起使用：

$ addr2line 0x0000000000400538
/tmp/tmp.M0766CSHGm/g.c:6