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Message-ID: <YhZ16cMMcHQIvS9d@google.com> Date: Wed, 23 Feb 2022 17:59:05 +0000 From: Sean Christopherson <seanjc@...gle.com> To: Nathan Chancellor <nathan@...nel.org> Cc: Paolo Bonzini <pbonzini@...hat.com>, Nick Desaulniers <ndesaulniers@...gle.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org, llvm@...ts.linux.dev, linux-kernel@...r.kernel.org, Like Xu <like.xu.linux@...il.com> Subject: Re: [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls On Wed, Feb 23, 2022, Nathan Chancellor wrote: > Hi Sean, > > On Wed, Feb 23, 2022 at 04:23:55PM +0000, Sean Christopherson wrote: > > Cast kvm_x86_ops.func to 'void *' when updating KVM static calls that are > > conditionally patched to __static_call_return0(). clang complains about > > using mismatching pointers in the ternary operator, which breaks the > > build when compiling with CONFIG_KVM_WERROR=y. > > > > >> arch/x86/include/asm/kvm-x86-ops.h:82:1: warning: pointer type mismatch > > ('bool (*)(struct kvm_vcpu *)' and 'void *') [-Wpointer-type-mismatch] > > > > Fixes: 5be2226f417d ("KVM: x86: allow defining return-0 static calls") > > Reported-by: Like Xu <like.xu.linux@...il.com> > > Reported-by: kernel test robot <lkp@...el.com> > > Signed-off-by: Sean Christopherson <seanjc@...gle.com> > > Thank you for the patch! Is this a bug in clang? IMO, no. I think it's completely reasonable for the compiler to complain that KVM is generating two different pointer types out of a ternary operator. clang is somewhat inconsistent, though it may be deliberate. clang doesn't complain about implicitly casting a 'void *' to another data type, e.g. this complies clean, where "data" is a 'void *' struct kvm_vcpu *x = vcpu ? : data; But changing it to a function on the lhs triggers the warn: typeof(kvm_x86_ops.vcpu_run) x = kvm_x86_ops.vcpu_run ? : data; Again, complaining in the function pointer case seems reasonable.
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