linux-kernel - Re: [PATCH] KVM: x86: avoid warning with -Wbitwise-instead-of-logical

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Date:   Fri, 15 Oct 2021 09:37:16 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        seanjc@...gle.com, torvic9@...lbox.org,
        Jim Mattson <jmattson@...gle.com>, llvm@...ts.linux.dev
Subject: Re: [PATCH] KVM: x86: avoid warning with -Wbitwise-instead-of-logical

On Fri, Oct 15, 2021 at 04:51:48AM -0400, Paolo Bonzini wrote:
> This is a new warning in clang top-of-tree (will be clang 14):
> 
> In file included from arch/x86/kvm/mmu/mmu.c:27:
> arch/x86/kvm/mmu/spte.h:318:9: error: use of bitwise '|' with boolean operands [-Werror,-Wbitwise-instead-of-logical]
>         return __is_bad_mt_xwr(rsvd_check, spte) |
>                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>                                                  ||
> arch/x86/kvm/mmu/spte.h:318:9: note: cast one or both operands to int to silence this warning
> 
> Reported-by: torvic9@...lbox.org
> Suggested-by: Jim Mattson <jmattson@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
>  arch/x86/kvm/mmu/spte.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> index eb7b227fc6cf..32bc7268c9ea 100644
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/arch/x86/kvm/mmu/spte.h
> @@ -314,9 +314,12 @@ static __always_inline bool is_rsvd_spte(struct rsvd_bits_validate *rsvd_check,
>  	 * Use a bitwise-OR instead of a logical-OR to aggregate the reserved
>  	 * bits and EPT's invalid memtype/XWR checks to avoid an extra Jcc
>  	 * (this is extremely unlikely to be short-circuited as true).
> +	 *
> +	 * (int) avoids clang's "use of bitwise '|' with boolean operands"
> +	 * warning.
>  	 */
> -	return __is_bad_mt_xwr(rsvd_check, spte) |
> -	       __is_rsvd_bits_set(rsvd_check, spte, level);
> +	return (int)__is_bad_mt_xwr(rsvd_check, spte) |
> +	       (int)__is_rsvd_bits_set(rsvd_check, spte, level);
>  }
>  
>  static inline bool spte_can_locklessly_be_made_writable(u64 spte)
> -- 
> 2.27.0
> 
>