Re: [Valgrind-users] Illegal instruction error in some versions of valgrind

[Paul F. <pj...@wa...>]

On 27/01/2026 01:06, Steve Edmonds wrote:
> Hi. I have just joined the group to see if I can resolve a long 
> standing issue with valgrind on Opensuse.
> I have been using some accounting software for many years, initially 
> it ran fine and then at some point it started causing a segmentation 
> fault.
>
> I then started using it with valgrind, successful with some versions 
> of valgrind and not with others, when it fails I get the following 
> before termination and core dump.
>
> ==199084==  Illegal opcode at address 0x453BC82
> ==199084==    at 0x453BC82: write_vec (xcb_conn.c:262)
>
> Using valgrind from the latest Leap 15.6 and 16.0 repositories fails 
> (valgrind-3.26.0-355.d_t.2.x86_64.rpm, 3.24.0-150600.3.3.1, 
> 3.22.0-150600.1.3, 3.24.0-160000.2.2 and 3.25.1-160000.1.1) I do have 
> the software running successfully with versions 3.25.1-350.d_t.1 (on 
> Leap 15.6) and 3.13.0-lp150.4.61-x86_64 (on Leap 15.0 in a VM). I am 
> trying to get to grips with what might determine a successful version 
> of valgrind, I can no longer locate the rpm for 3.25.1-350.d_t.1 to 
> try on Leap 16.0 and quite happy to build from source if there is some 
> configuration in the source that will resolve this issue.

Hi Steve

Trying older Valgrind versions is unlikely solve the problem.

What application are you trying to run under Valgrind? I just tried 
Valgrind 3.25.1 on openSUSE LEAP 16.0 running kwrite and there were no 
major issues.

In gdb (with kwrite again) that piece of code looks like

261     n = *count;
262     if (n > IOV_MAX)
263 n = IOV_MAX;

Nothing unusual in the assembler, like like it is using SSE instructions.

Can you also post the op-code bytes that Valgrind fails to handle?

Lastly, have you built your own copy of libxcb.so.1? If so, did you use 
any GCC options like -march? There are a few amd64 CPU features that 
like AVX512 that Valgrind does not support.

Regards

Paul