linux-kernel - Re: [BUG] [5.15] Compilation error in arch/x86/kvm/mmu/spte.h with clang-14

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Message-ID: <b6abc5a3-39ea-b463-9df5-f50bdcb16d08@redhat.com>
Date:   Mon, 4 Oct 2021 11:26:08 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     torvic9@...lbox.org, "seanjc@...gle.com" <seanjc@...gle.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "bp@...en8.de" <bp@...en8.de>
Subject: Re: [BUG] [5.15] Compilation error in arch/x86/kvm/mmu/spte.h with
 clang-14

On 04/10/21 11:08, torvic9@...lbox.org wrote:
> I encounter the following issue when compiling 5.15-rc4 with 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

The warning is wrong, as mentioned in the line right above:

         /*
          * 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).
          */

Paolo