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

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Message-ID: <c4773ecc-053f-9bc6-03af-5039397a4531@redhat.com>
Date:   Mon, 4 Oct 2021 11:49:06 +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>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "nathan@...nel.org" <nathan@...nel.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 11:30, torvic9@...lbox.org wrote:
> 
>> Paolo Bonzini <pbonzini@...hat.com> hat am 04.10.2021 11:26 geschrieben:
>>
>>   
>> 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:
> 
> So it's an issue with clang-14 then?
> (I add Nick and Nathan)

My clang here doesn't have the option, so I'm going to ask---are you 
using W=1?  I can see why clang is warning for KVM's code, but in my 
opinion such a check should only be in -Wextra.

Paolo

>>
>>           /*
>>            * 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
>