linux-kernel - Re: [PATCH] kvm: x86: mmu: Add cast to negated bitmasks in update_permission

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Message-ID: <951ccf2a257fb8f8827f88e1c17ce64d23173e94.camel@perches.com>
Date:   Tue, 19 Jun 2018 14:55:05 -0700
From:   Joe Perches <joe@...ches.com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>, rkrcmar@...hat.com,
        Thomas Gleixner <tglx@...utronix.de>, hpa@...or.com,
        x86@...nel.org, kvm@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH] kvm: x86: mmu: Add cast to negated bitmasks in
 update_permission_bitmask()

On Tue, 2018-06-19 at 14:10 -0700, Matthias Kaehlcke wrote:
> On Tue, Jun 19, 2018 at 12:11:27PM -0700, Joe Perches wrote:
> > -Wconstant-conversion is only issued when a *constant value* is assigned to
> an incompatible type.
> 
> > Trying to allow a "make W=3" to be compiler warning message free
> > is also silly.
> > 
> > I think it's better to make the warning emitted only at a W=3
> > level instead.
> 
> Another difference with -Wsign-conversion is that enabling it would
> probably result in thousands of warnings. Do you have evidence that
> there is a significant number of spurious -Wconstant-conversion
> warnings?

Not my issue really.  You're advocating for
making the code more complex/ugly for a condition
where the result is identical.

Do you have evidence this is the only location in
an allyesconfig compilation?