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

On 3/17/23 17:12, Luis Machado wrote:
> On 3/17/23 17:07, Peter Maydell wrote:
>> On Fri, 17 Mar 2023 at 16:55, Luis Machado <[email protected]> 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 distr=
os 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.
>
> Just to clarify, there won't be any point releases for gdb's 9/10/11/12. =
 We might have a bug fix
> release for gdb 13 though (which isn't affected).
>

Just to complement, my plan is to make the backports available (via stable =
branch commits) so distro package
maintainers can pick those up easily. No new releases will be made for olde=
r gdb's, so the package maintainers
can pick the backport up as soon as they are pushed. There won't be waiting=
 for a new release of gdb.

>>
>>> If we decide qemu should now emit a different xml for pauth, it will fi=
x the crashes, but it also
>>> means older gdb's (9/10/11/12) will not be able to backtrace properly t=
hrough 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.
>>
>
> Fair enough.
>
>>> If someone decides to implement a debugging stub that reports pauth (fa=
st 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.
>
> I can negotiate that as well, though it borders being a new feature.
>
>>
>> thanks
>> -- PMM
>

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