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

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Date:   Wed, 13 Sep 2017 15:13:46 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: [PATCH] KVM: x86: fix clang build

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);
 
-- 
2.14.1