* [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls
@ 2022-02-23 16:23 Sean Christopherson
2022-02-23 17:27 ` Nathan Chancellor
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Sean Christopherson @ 2022-02-23 16:23 UTC (permalink / raw)
To: Paolo Bonzini, Nathan Chancellor, Nick Desaulniers
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, llvm, linux-kernel, Like Xu
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>
---
arch/x86/include/asm/kvm_host.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 713e08f62385..f285ddb8b66b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1547,8 +1547,8 @@ static inline void kvm_ops_static_call_update(void)
WARN_ON(!kvm_x86_ops.func); __KVM_X86_OP(func)
#define KVM_X86_OP_OPTIONAL __KVM_X86_OP
#define KVM_X86_OP_OPTIONAL_RET0(func) \
- static_call_update(kvm_x86_##func, kvm_x86_ops.func ? : \
- (void *) __static_call_return0);
+ static_call_update(kvm_x86_##func, (void *)kvm_x86_ops.func ? : \
+ (void *)__static_call_return0);
#include <asm/kvm-x86-ops.h>
#undef __KVM_X86_OP
}
base-commit: f4bc051fc91ab9f1d5225d94e52d369ef58bec58
--
2.35.1.473.g83b2b277ed-goog
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls
2022-02-23 16:23 [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls Sean Christopherson
@ 2022-02-23 17:27 ` Nathan Chancellor
2022-02-23 17:59 ` Sean Christopherson
2022-02-23 22:23 ` David Dunn
2022-02-24 14:23 ` Paolo Bonzini
2 siblings, 1 reply; 7+ messages in thread
From: Nathan Chancellor @ 2022-02-23 17:27 UTC (permalink / raw)
To: Sean Christopherson
Cc: Paolo Bonzini, Nick Desaulniers, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel, kvm, llvm, linux-kernel, Like Xu
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? I ended up creating a
small reproducer in case we need to file a bug with clang upstream:
https://godbolt.org/z/P7nEdzejE
This does shut up the warning and I can still spawn guests on my AMD and
Intel systems so:
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
> ---
> arch/x86/include/asm/kvm_host.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 713e08f62385..f285ddb8b66b 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1547,8 +1547,8 @@ static inline void kvm_ops_static_call_update(void)
> WARN_ON(!kvm_x86_ops.func); __KVM_X86_OP(func)
> #define KVM_X86_OP_OPTIONAL __KVM_X86_OP
> #define KVM_X86_OP_OPTIONAL_RET0(func) \
> - static_call_update(kvm_x86_##func, kvm_x86_ops.func ? : \
> - (void *) __static_call_return0);
> + static_call_update(kvm_x86_##func, (void *)kvm_x86_ops.func ? : \
> + (void *)__static_call_return0);
> #include <asm/kvm-x86-ops.h>
> #undef __KVM_X86_OP
> }
>
> base-commit: f4bc051fc91ab9f1d5225d94e52d369ef58bec58
> --
> 2.35.1.473.g83b2b277ed-goog
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls
2022-02-23 17:27 ` Nathan Chancellor
@ 2022-02-23 17:59 ` Sean Christopherson
2022-02-23 18:13 ` Nathan Chancellor
0 siblings, 1 reply; 7+ messages in thread
From: Sean Christopherson @ 2022-02-23 17:59 UTC (permalink / raw)
To: Nathan Chancellor
Cc: Paolo Bonzini, Nick Desaulniers, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel, kvm, llvm, linux-kernel, Like Xu
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;
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.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls
2022-02-23 17:59 ` Sean Christopherson
@ 2022-02-23 18:13 ` Nathan Chancellor
2022-02-23 18:56 ` Sean Christopherson
0 siblings, 1 reply; 7+ messages in thread
From: Nathan Chancellor @ 2022-02-23 18:13 UTC (permalink / raw)
To: Sean Christopherson
Cc: Paolo Bonzini, Nick Desaulniers, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel, kvm, llvm, linux-kernel, Like Xu
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
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls
2022-02-23 18:13 ` Nathan Chancellor
@ 2022-02-23 18:56 ` Sean Christopherson
0 siblings, 0 replies; 7+ messages in thread
From: Sean Christopherson @ 2022-02-23 18:56 UTC (permalink / raw)
To: Nathan Chancellor
Cc: Paolo Bonzini, Nick Desaulniers, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel, kvm, llvm, linux-kernel, Like Xu
On Wed, Feb 23, 2022, Nathan Chancellor wrote:
> 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).
Aha! Looks like clang's behavior is correct, assuming a function is not considered
an "object". From C99 "6.5.15 Conditional operator":
One of the following shall hold for the second and third operands:
— both operands have arithmetic type;
— both operands have the same structure or union type;
— both operands have void type;
— both operands are pointers to qualified or unqualified versions of compatible types;
— one operand is a pointer and the other is a null pointer constant; or
— one operand is a pointer to an object or incomplete type and the other is a pointer to a
qualified or unqualified version of void.
That last case would explain why clang warns about a function pointer but not a
object pointer when the third operand is a 'void *'.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls
2022-02-23 16:23 [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls Sean Christopherson
2022-02-23 17:27 ` Nathan Chancellor
@ 2022-02-23 22:23 ` David Dunn
2022-02-24 14:23 ` Paolo Bonzini
2 siblings, 0 replies; 7+ messages in thread
From: David Dunn @ 2022-02-23 22:23 UTC (permalink / raw)
To: Sean Christopherson
Cc: Paolo Bonzini, Nathan Chancellor, Nick Desaulniers,
Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel, kvm,
llvm, linux-kernel, Like Xu
Reviewed-by: David Dunn <daviddunn@google.com>
On Wed, Feb 23, 2022 at 8:24 AM Sean Christopherson <seanjc@google.com> wrote:
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 713e08f62385..f285ddb8b66b 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1547,8 +1547,8 @@ static inline void kvm_ops_static_call_update(void)
> WARN_ON(!kvm_x86_ops.func); __KVM_X86_OP(func)
> #define KVM_X86_OP_OPTIONAL __KVM_X86_OP
> #define KVM_X86_OP_OPTIONAL_RET0(func) \
> - static_call_update(kvm_x86_##func, kvm_x86_ops.func ? : \
> - (void *) __static_call_return0);
> + static_call_update(kvm_x86_##func, (void *)kvm_x86_ops.func ? : \
> + (void *)__static_call_return0);
> #include <asm/kvm-x86-ops.h>
> #undef __KVM_X86_OP
> }
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls
2022-02-23 16:23 [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls Sean Christopherson
2022-02-23 17:27 ` Nathan Chancellor
2022-02-23 22:23 ` David Dunn
@ 2022-02-24 14:23 ` Paolo Bonzini
2 siblings, 0 replies; 7+ messages in thread
From: Paolo Bonzini @ 2022-02-24 14:23 UTC (permalink / raw)
To: Sean Christopherson, Nathan Chancellor, Nick Desaulniers
Cc: Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel, kvm,
llvm, linux-kernel, Like Xu
On 2/23/22 17:23, 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>
> ---
> arch/x86/include/asm/kvm_host.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 713e08f62385..f285ddb8b66b 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1547,8 +1547,8 @@ static inline void kvm_ops_static_call_update(void)
> WARN_ON(!kvm_x86_ops.func); __KVM_X86_OP(func)
> #define KVM_X86_OP_OPTIONAL __KVM_X86_OP
> #define KVM_X86_OP_OPTIONAL_RET0(func) \
> - static_call_update(kvm_x86_##func, kvm_x86_ops.func ? : \
> - (void *) __static_call_return0);
> + static_call_update(kvm_x86_##func, (void *)kvm_x86_ops.func ? : \
> + (void *)__static_call_return0);
> #include <asm/kvm-x86-ops.h>
> #undef __KVM_X86_OP
> }
>
> base-commit: f4bc051fc91ab9f1d5225d94e52d369ef58bec58
Queued, thanks.
Paolo
^ permalink raw reply [flat|nested] 7+ messages in thread
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2022-02-23 16:23 [PATCH] KVM: x86: Fix pointer mistmatch warning when patching RET0 static calls Sean Christopherson
2022-02-23 17:27 ` Nathan Chancellor
2022-02-23 17:59 ` Sean Christopherson
2022-02-23 18:13 ` Nathan Chancellor
2022-02-23 18:56 ` Sean Christopherson
2022-02-23 22:23 ` David Dunn
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