Re: [PATCH 09/11] tests/tcg: disable pauth for aarch64 gdb tests

[Peter Maydell]

On Fri, 17 Mar 2023 at 16:55, Luis Machado <luis.machado@arm.com> wrote:
> On 3/17/23 16:37, Peter Maydell wrote:
> > Having run into this problem in another couple of situations, one of
> > which involved gdb 10, I think I'm increasingly favouring option
> > 2 here. The affected gdbs seem to be quite widely deployed, and
> > the bug results in crashes even for users who didn't really
> > care about pauth. So I'd rather we didn't release a QEMU 8.0
> > which crashes these affected deployed gdbs.
> >
>
> Are the affected gdb's packaged by distros? If so, a backport the distros can 
> pick up
> will solve this in a quick package update.

Yes, it's exactly because these gdbs are distro-packaged
that I don't want QEMU to make them crash. I think it's
going to take a long time for the fix to go into gdb branches
and gdb to make a point release and distros to pick up that
point release, and in the meantime that's a lot of crashing
gdb bug reports that we're going to have to field.

> If we decide qemu should now emit a different xml for pauth, it will fix the 
> crashes, but it also
> means older gdb's (9/10/11/12) will not be able to backtrace properly through 
> pauth-signed frames.
>
> Maybe that's a reasonable drawback for qemu users?

"No backtrace through pauth frames" is the situation we've
been in ever since we implemented pauth in 2019, so I think
that's fine. It's not regressing something that used to work.

> If someone decides to implement a debugging stub that reports pauth (fast 
> models, for example), it will
> also crash gdb, so I still plan to do the backport anyway.

If you're backporting the fix, you could also backport the
(hopefully tiny) change that says "treat pauth_v2 the same
way we do pauth", and then users with an updated older
gdb will also get working backtraces.

thanks
-- PMM