Re: Unknown ORC entry type 5 on RHEL 9 kernel

Philipp Rudo <[email protected]> writes:
> Hi Stephen,
>
> thanks for letting me know. And yes that is something we need to fix in
> the kernel rather than drgn.
>
> I took a quick look and found that the change was included when
> backporting fb799447ae29 ("x86,objtool: Split UNWIND_HINT_EMPTY in two")
> for 9.6. Thing is that I'll be heading to LPC tomorrow and won't have
> time to work on it properly before that...

Thanks for taking a deeper look! No worries on timing, it's not urgent.
If you think the most likely fix will be to backport commit
b9f174c811e3a ("x86/unwind/orc: Add ELF section with ORC version
identifier"), then I believe the drgn workaround I proposed in the
Github issue [1] should work fine: once the .orc_header section is
found, drgn will detect it and use the correct hash. The only difference
being that the "true" first broken version was 5.14.0-517.el9, which
might be worth encoding in the code in case somebody ever runs drgn
against a weird unreleased version from that development period.

[1]: https://github.com/osandov/drgn/issues/578#issuecomment-3614826789

> One more hint. When you want to get the history of RHEL, it's better to
> check the centos-stream repo then the changelog. There you have the
> full git history (modulo some embargoed CVE fixes).
>
> https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9

Thanks, that helps a lot!
Stephen

> Thanks
> Philipp
>
>
> On Thu, 04 Dec 2025 12:06:54 -0800
> Stephen Brennan <[email protected]> wrote:
>
>> Hi Philipp,
>> 
>> I wanted to let you know about an issue with drgn's stack unwinding on
>> the RHEL 9 kernel. It looks like that kernel backports some ORC changes,
>> without including a change Omar made (including an .orc_header section)
>> to help identify the ORC format version. I've included more details on
>> this drgn issue:
>> 
>> https://github.com/osandov/drgn/issues/578
>> 
>> The result is that drgn can't unwind stacks on the RHEL 9 kernel. I
>> think the best path forward would be to include the .orc_header patch:
>> b9f174c811e3a ("x86/unwind/orc: Add ELF section with ORC version identifier")
>> 
>> As it is, the RHEL 9 drgn can't unwind stacks on the RHEL 9 kernel,
>> which seems less than ideal.
>> 
>> Thanks,
>> Stephen
>>