2018-02-26 22:43:35

by Matthias Kaehlcke

Subject: [PATCH] KVM: x86: Make enum conversion explicit in kvm_pdptr_read()

The type 'enum kvm_reg_ex' is an extension of 'enum kvm_reg', however
the extension is only semantical and the compiler doesn't know about the
relationship between the two types. In kvm_pdptr_read() a value of the
extended type is passed to kvm_x86_ops->cache_reg(), which expects a
value of the base type. Clang raises the following warning about the
type mismatch:

arch/x86/kvm/kvm_cache_regs.h:44:32: warning: implicit conversion from
enumeration type 'enum kvm_reg_ex' to different enumeration type
'enum kvm_reg' [-Wenum-conversion]
kvm_x86_ops->cache_reg(vcpu, VCPU_EXREG_PDPTR);

Cast VCPU_EXREG_PDPTR to 'enum kvm_reg' to make the compiler happy.

Signed-off-by: Matthias Kaehlcke <[email protected]>
---
arch/x86/kvm/kvm_cache_regs.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
index f500293dad8d..58ba12071014 100644
--- a/arch/x86/kvm/kvm_cache_regs.h
+++ b/arch/x86/kvm/kvm_cache_regs.h
@@ -41,7 +41,7 @@ static inline u64 kvm_pdptr_read(struct kvm_vcpu *vcpu, int index)

if (!test_bit(VCPU_EXREG_PDPTR,
(unsigned long *)&vcpu->arch.regs_avail))
- kvm_x86_ops->cache_reg(vcpu, VCPU_EXREG_PDPTR);
+ kvm_x86_ops->cache_reg(vcpu, (enum kvm_reg)VCPU_EXREG_PDPTR);

return vcpu->arch.walk_mmu->pdptrs[index];
}
--
2.16.1.291.g4437f3f132-goog

2018-02-26 22:47:37

by Guenter Roeck

Subject: Re: [PATCH] KVM: x86: Make enum conversion explicit in kvm_pdptr_read()

On Mon, Feb 26, 2018 at 2:42 PM, Matthias Kaehlcke <[email protected]> wrote:
> The type 'enum kvm_reg_ex' is an extension of 'enum kvm_reg', however
> the extension is only semantical and the compiler doesn't know about the
> relationship between the two types. In kvm_pdptr_read() a value of the
> extended type is passed to kvm_x86_ops->cache_reg(), which expects a
> value of the base type. Clang raises the following warning about the
> type mismatch:
>
> arch/x86/kvm/kvm_cache_regs.h:44:32: warning: implicit conversion from
> enumeration type 'enum kvm_reg_ex' to different enumeration type
> 'enum kvm_reg' [-Wenum-conversion]
> kvm_x86_ops->cache_reg(vcpu, VCPU_EXREG_PDPTR);
>
> Cast VCPU_EXREG_PDPTR to 'enum kvm_reg' to make the compiler happy.
>
> Signed-off-by: Matthias Kaehlcke <[email protected]>

Reviewed-by: Guenter Roeck <[email protected]>

> ---
> arch/x86/kvm/kvm_cache_regs.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
> index f500293dad8d..58ba12071014 100644
> --- a/arch/x86/kvm/kvm_cache_regs.h
> +++ b/arch/x86/kvm/kvm_cache_regs.h
> @@ -41,7 +41,7 @@ static inline u64 kvm_pdptr_read(struct kvm_vcpu *vcpu, int index)
>
> if (!test_bit(VCPU_EXREG_PDPTR,
> (unsigned long *)&vcpu->arch.regs_avail))
> - kvm_x86_ops->cache_reg(vcpu, VCPU_EXREG_PDPTR);
> + kvm_x86_ops->cache_reg(vcpu, (enum kvm_reg)VCPU_EXREG_PDPTR);
>
> return vcpu->arch.walk_mmu->pdptrs[index];
> }
> --
> 2.16.1.291.g4437f3f132-goog
>

2018-03-07 18:25:28

by Radim Krčmář

Subject: Re: [PATCH] KVM: x86: Make enum conversion explicit in kvm_pdptr_read()

2018-02-26 14:42-0800, Matthias Kaehlcke:
> The type 'enum kvm_reg_ex' is an extension of 'enum kvm_reg', however
> the extension is only semantical and the compiler doesn't know about the
> relationship between the two types. In kvm_pdptr_read() a value of the
> extended type is passed to kvm_x86_ops->cache_reg(), which expects a
> value of the base type. Clang raises the following warning about the
> type mismatch:

Yeah, expressing this in C type system seems impossible.

> arch/x86/kvm/kvm_cache_regs.h:44:32: warning: implicit conversion from
> enumeration type 'enum kvm_reg_ex' to different enumeration type
> 'enum kvm_reg' [-Wenum-conversion]
> kvm_x86_ops->cache_reg(vcpu, VCPU_EXREG_PDPTR);
>
> Cast VCPU_EXREG_PDPTR to 'enum kvm_reg' to make the compiler happy.
>
> Signed-off-by: Matthias Kaehlcke <[email protected]>
> ---

Applied, thanks.