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

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Date:   Mon, 4 Oct 2021 09:13:14 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     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 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:
> >
> > 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