linux-kernel - Re: [PATCH 09/14] KVM: selftests: Explicitly disable builtins for mem*() overrides

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Date:   Sat, 24 Dec 2022 10:16:55 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Tom Rix <trix@...hat.com>, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        kvmarm@...ts.cs.columbia.edu, linux-riscv@...ts.infradead.org,
        llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Ricardo Koller <ricarkol@...gle.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Raghavendra Rao Ananta <rananta@...gle.com>
Subject: Re: [PATCH 09/14] KVM: selftests: Explicitly disable builtins for
 mem*() overrides

On 12/13/22 01:16, Sean Christopherson wrote:
> Explicitly disable the compiler's builtin memcmp(), memcpy(), and
> memset().  Because only lib/string_override.c is built with -ffreestanding,
> the compiler reserves the right to do what it wants and can try to link the
> non-freestanding code to its own crud.
> 
>    /usr/bin/x86_64-linux-gnu-ld: /lib/x86_64-linux-gnu/libc.a(memcmp.o): in function `memcmp_ifunc':
>    (.text+0x0): multiple definition of `memcmp'; tools/testing/selftests/kvm/lib/string_override.o:
>    tools/testing/selftests/kvm/lib/string_override.c:15: first defined here
>    clang: error: linker command failed with exit code 1 (use -v to see invocation)

Hmm, that's weird though.  I think it's an effect of ifunc and maybe 
even a linker bug.  The patch makes sense anyway.

Paolo