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

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Date:   Tue, 9 Aug 2022 08:21:54 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Gavin Shan <gshan@...hat.com>
Cc:     Florian Weimer <fweimer@...hat.com>, 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 <oliver.upton@...ux.dev>,
        andrew jones <andrew.jones@...ux.dev>, 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


----- 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?

Thanks,

Mathieu 

> 
> Thanks,
> Gavin
> 

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