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Editorial Team
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Asked: 2026-05-22T22:35:30+00:00

So I have this executable, compiled with the -g options, that triggers loads of

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So I have this executable, compiled with the -g options, that triggers loads of unaligned userspace access warnings.

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

The error message provides some information: the program counter and the instruction, but I don’t know how to translate the PC into a file and line in my code.

I can sniff this as being in a loop performing some memory copying or something, since the address is very often the same.

So question: how can I find out what’s the file and line of my code causing this unaligned access, using Linux tools?

Any input on that?

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1 Answer

  1. Editorial Team

    Have a look at the addr2line utility

    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.

    A Simple c-example:

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

    compile it using

    gcc -Wall -ggdb3 g.c

    gdb gives this output:

    $ 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);

    Using that address with addr2line:

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