[PATCH] KVM: x86: fix clang build

[PATCH] KVM: x86: fix clang build

[Radim Krčmář]

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@google.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.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);
 
-- 
2.14.1

Re: [PATCH] KVM: x86: fix clang build

[David Hildenbrand]

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@google.com>
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.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@redhat.com>

-- 

Thanks,

David