linux-kernel - Re: [PATCH] KVM: x86: fix clang build

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Date:   Wed, 13 Sep 2017 15:15:19 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] KVM: x86: fix clang build

On 13.09.2017 15:13, Radim Krčmář wrote:
> Clang resolves __builtin_constant_p() to false even if the expression is
> constant in the end.  The only purpose of that expression was to
> differentiate a case where the following expression couldn't be checked
> at compile-time, so we can just remove the check.
> 
> Clang handles the following two correctly.  Turn it into BUG_ON if there
> are any more problems with this.
> 
> Fixes: d6321d493319 ("KVM: x86: generalize guest_cpuid_has_ helpers")
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  arch/x86/kvm/cpuid.h | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index 1ea3c0e1e3a9..0bc5c1315708 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -59,7 +59,6 @@ static __always_inline struct cpuid_reg x86_feature_cpuid(unsigned x86_feature)
>  {
>  	unsigned x86_leaf = x86_feature / 32;
>  
> -	BUILD_BUG_ON(!__builtin_constant_p(x86_leaf));
>  	BUILD_BUG_ON(x86_leaf >= ARRAY_SIZE(reverse_cpuid));
>  	BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);
>  
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 

Thanks,

David