linux-kernel - Re: [PATCH 1/2] KVM: selftests: Make rseq compatible with glibc-2.35

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Message-ID: <616d4de6-81f6-9d14-4e57-4a79fec45690@redhat.com>
Date:   Tue, 9 Aug 2022 19:27:44 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, maz@...nel.org, oliver.upton@...ux.dev,
        andrew.jones@...ux.dev, seanjc@...gle.com,
        mathieu.desnoyers@...icios.com, yihyu@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH 1/2] KVM: selftests: Make rseq compatible with glibc-2.35

Hi Florian,

On 8/9/22 5:16 PM, Florian Weimer wrote:
>>> __builtin_thread_pointer doesn't work on all architectures/GCC
>>> versions.
>>> Is this a problem for selftests?
>>>
>>
>> It's a problem as the test case is running on all architectures. I think I
>> need introduce our own __builtin_thread_pointer() for where it's not
>> supported: (1) PowerPC  (2) x86 without GCC 11
>>
>> Please let me know if I still have missed cases where
>> __buitin_thread_pointer() isn't supported?
> 
> As far as I know, these are the two outliers that also have rseq
> support.  The list is a bit longer if we also consider non-rseq
> architectures (csky, hppa, ia64, m68k, microblaze, sparc, don't know
> about the Linux architectures without glibc support).
> 

For kvm/selftests, there are 3 architectures involved actually. So we
just need consider 4 cases: aarch64, x86, s390 and other. For other
case, we just use __builtin_thread_pointer() to maintain code's
integrity, but it's not called at all.

I think kvm/selftest is always relying on glibc if I'm correct.

Thanks,
Gavin