linux-kernel - Re: [PATCH] KVM: arm64: Avoid shadowing a previous local

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Message-ID: <da6be00d39c37ad26bfad9e75e814cb1@kernel.org>
Date:   Wed, 27 Oct 2021 08:34:31 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Avoid shadowing a previous local

On 2021-10-27 03:42, Qian Cai wrote:
> It is less-prone to have a different variable name from the one in a 
> wider
> scope. This is also flagged by GCC (W=2):
> 
> In file included from ./include/linux/kvm_host.h:39,
>                  from arch/arm64/kvm/arm.c:12:
> arch/arm64/kvm/arm.c: In function 'kvm_arch_vcpu_ioctl_run':
> ./arch/arm64/include/asm/kvm_host.h:638:26: warning: declaration of
> 'ret' shadows a previous local [-Wshadow]
>   638 |   typeof(f(__VA_ARGS__)) ret;    \
>       |                          ^~~
> arch/arm64/kvm/arm.c:852:9: note: in expansion of macro 
> 'kvm_call_hyp_ret'
>   852 |   ret = kvm_call_hyp_ret(__kvm_vcpu_run, vcpu);
>       |         ^~~~~~~~~~~~~~~~
> arch/arm64/kvm/arm.c:773:6: note: shadowed declaration is here
>   773 |  int ret;
>       |      ^~~
> 
> Signed-off-by: Qian Cai <quic_qiancai@...cinc.com>
> ---
>  arch/arm64/include/asm/kvm_host.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h
> b/arch/arm64/include/asm/kvm_host.h
> index 4be8486042a7..4693d84ccd95 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -635,16 +635,16 @@ void kvm_arm_resume_guest(struct kvm *kvm);
> 
>  #define kvm_call_hyp_ret(f, ...)					\
>  	({								\
> -		typeof(f(__VA_ARGS__)) ret;				\
> +		typeof(f(__VA_ARGS__)) __ret;				\
>  									\
>  		if (has_vhe()) {					\
> -			ret = f(__VA_ARGS__);				\
> +			__ret = f(__VA_ARGS__);				\
>  			isb();						\
>  		} else {						\
> -			ret = kvm_call_hyp_nvhe(f, ##__VA_ARGS__);	\
> +			__ret = kvm_call_hyp_nvhe(f, ##__VA_ARGS__);	\
>  		}							\
>  									\
> -		ret;							\
> +		__ret;							\
>  	})
>  #else /* __KVM_NVHE_HYPERVISOR__ */
>  #define kvm_call_hyp(f, ...) f(__VA_ARGS__)

I don't think this makes much sense. This is bound to eventually clash
with another variable, and you're back to square one.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...