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

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Message-ID: <CALMp9eRzadC50n=d=NFm7osVgKr+=UG7r2cWV2nOCfoPN41vvQ@mail.gmail.com>
Date:   Mon, 4 Oct 2021 10:12:33 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, torvic9@...lbox.org,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "nathan@...nel.org" <nathan@...nel.org>,
        "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 Mon, Oct 4, 2021 at 9:13 AM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> On Mon, Oct 4, 2021 at 2:49 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
> >
> > 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:

Casting the bool to an int doesn't seem that onerous.

> > > 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.
>
> This is a newly added warning in top of tree clang.
>
> >
> > 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
> > >
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers