Re: s390x stack unwinding with perf?

[Heiko Carstens <hca@linux.ibm.com>]

On Wed, Dec 20, 2023 at 01:58:36PM +0100, Daan De Meyer wrote:
> > FWIW, this is now upstream and will land in 6.7, together with a similar
> > patch which adds user stacktrace support:
> 
> > 504b73d00a55 ("s390/perf: implement perf_callchain_user()")
> > aa44433ac4ee ("s390: add USER_STACKTRACE support")
> 
> > Please let us know if there are any problems.
> 
> I've been trying out the new userspace stacktrace support on Fedora
> Rawhide but I'm having some problems getting it to work. I rebuilt
> systemd and all of its dependencies (specifically, glibc) with
> -mbackchain using copr
> (https://copr.fedorainfracloud.org/coprs/daandemeyer/fno-omit-frame-pointer/builds/),
> built a Fedora Rawhide image with the rebuilt packages and perf using
> mkosi, started an s390x virtual machine and ran "perf record -g
> journalctl --verify" followed by "perf report -g 'graph,0.5,caller'".
> On x86, this gives me a sensible perf report. On s390x, it seems a lot
> of information is still missing.
...
> To reproduce (from a s390x host system):
...
> - bin/mkosi -f qemu"

This fails with "bootctl not found".

Looking at the binaries in the copr repo it looks like the generated
code does create backchains. So in theory walking backchains should
work.

Could you please give examples what does not work, and what you would
expect? Right now I don't know what to look at.