"KVM: x86: generalize guest_cpuid_has_ helpers" breaks clang

[Dmitry Vyukov]

Hi Radim,

I've just noticed that your commit "KVM: x86: generalize
guest_cpuid_has_ helpers" breaks clang build on this assert:

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));


In clang __builtin_constant_p is never true for function arguments,
it's true only for compile-time constants (what you can use as stack
array size, or C++ template argument). What would work is an
additional macro along the lines of:

#define x86_feature_cpuid(x) (BUILD_BUG_ON(!__builtin_constant_p(x),
__x86_feature_cpuid(x))

But again assuming that caller pass the constant directly.

Could you please fix it?

Thanks