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

[Luis Machado <luis.machado@arm.com>]

On 3/17/23 17:07, Peter Maydell wrote:
> 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.

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).

>
>> 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.
>

Fair enough.

>> 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.

I can negotiate that as well, though it borders being a new feature.

>
> thanks
> -- PMM

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