Messages in this thread | | | Date | Wed, 23 Feb 2022 11:13:23 -0700 | From | Nathan Chancellor <> | Subject | Re: [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls |
| |
On Wed, Feb 23, 2022 at 05:59:05PM +0000, Sean Christopherson wrote: > 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@gmail.com> > > > Reported-by: kernel test robot <lkp@intel.com> > > > Signed-off-by: Sean Christopherson <seanjc@google.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;
Right, I would assume this is deliberate. I think warning in this case might be quite noisy, as the kernel implicitly converts 'void *' to typed pointers for certain function pointer callbacks (although this particular case is probably pretty rare).
> 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.
Ack, thank you for the clarification and explanation!
Cheers, Nathan
| |