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

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Message-ID: <1014177394.115022.1660052656961.JavaMail.zimbra@efficios.com>
Date:   Tue, 9 Aug 2022 09:44:16 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Gavin Shan <gshan@...hat.com>, shuah <shuah@...nel.org>
Cc:     Florian Weimer <fweimer@...hat.com>, kvmarm@...ts.cs.columbia.edu,
        KVM list <kvm@...r.kernel.org>,
        linux-kselftest <linux-kselftest@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>, maz <maz@...nel.org>,
        oliver upton <oliver.upton@...ux.dev>,
        andrew jones <andrew.jones@...ux.dev>,
        Sean Christopherson <seanjc@...gle.com>, yihyu@...hat.com,
        shan gavin <shan.gavin@...il.com>
Subject: Re: [PATCH 1/2] KVM: selftests: Make rseq compatible with
 glibc-2.35

----- On Aug 9, 2022, at 8:21 AM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:

> ----- Gavin Shan <gshan@...hat.com> wrote:
>> 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.
> 
> All those are handled in the rseq selftests and in librseq. Why duplicate all
> that logic again?

More to the point, considering that we have all the relevant rseq registration
code in tools/testing/selftests/rseq/rseq.c already, and the relevant thread
pointer getter code in tools/testing/selftests/rseq/rseq-*thread-pointer.h,
is there an easy way to get test applications in tools/testing/selftests/kvm
and in tools/testing/selftests/rseq to share that common code ?

Keeping duplicated compatibility code is bad for long-term maintainability.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com