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

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Date:   Wed, 10 Aug 2022 14:35:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Gavin Shan <gshan@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>, shuah <shuah@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        kvmarm <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>,
        maz <maz@...nel.org>, oliver upton <oliver.upton@...ux.dev>,
        andrew jones <andrew.jones@...ux.dev>,
        yihyu <yihyu@...hat.com>, shan gavin <shan.gavin@...il.com>
Subject: Re: [PATCH 1/2] KVM: selftests: Make rseq compatible with glibc-2.35

On 8/10/22 14:29, Mathieu Desnoyers wrote:
>> - By design, selftests/rseq and selftests/kvm are parallel. It's going to
>> introduce
>>    unnecessary dependency for selftests/kvm to use selftests/rseq/librseq.so. To
>>    me,
>>    it makes the maintainability even harder.
> In terms of build system, yes, selftests/rseq and selftests/kvm are side-by-side,
> and I agree it is odd to have a cross-dependency.
> 
> That's where moving rseq.c to tools/lib/ makes sense.
> 
>> - What selftests/kvm needs is rseq-thread-pointer.h, which accounts for ~5% of
>>    functionalities, provided by selftests/rseq/librseq.so.
> I've never seen this type of argument used to prevent using a library before, except
> on extremely memory-constrained devices, which is not our target here.

I agree.

To me, the main argument against moving librseq to tools/lib is a 
variant of the build-system argument, namely that recursive Make 
sucks[1] and selftests/kvm right now does not use tools/lib.  So, for a 
single-file library, it may be simply not worth the hassle.

On the other hand, if "somebody else" does the work, I would have no 
problem with having selftests/kvm depend on tools/lib, not at all.

Thanks,

Paolo

[1] Kbuild is a marvel that makes it work, but it works because there 
are no such cross-subdirectory dependencies and anyway 
tools/testing/selftests does not use Kbuild.