linux-kernel - Re: [PATCH v2] kvm: x86: mmu: Add cast to negated bitmasks in update_permission

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Date:   Mon, 25 Jun 2018 10:34:43 -0700
From:   Joe Perches <joe@...ches.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     pbonzini@...hat.com, Matthias Kaehlcke <mka@...omium.org>,
        rkrcmar@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
        hpa@...or.com, x86@...nel.org, kvm@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] kvm: x86: mmu: Add cast to negated bitmasks in
 update_permission_bitmask()

On Mon, 2018-06-25 at 13:12 -0400, Nick Desaulniers wrote:
> On Mon, Jun 25, 2018 at 1:05 PM Joe Perches <joe@...ches.com> wrote:
> > On Mon, 2018-06-25 at 12:47 -0400, Nick Desaulniers wrote:
[]
> > > Here's an actual bug this warning caught applied to drivers/input/:
> > > 
> > > dae1a432ab1f ("Input: mousedev - fix implicit conversion warning"):
> > > https://patchwork.kernel.org/patch/9753771/
> > 
> > What bug is that?
> > 
> > $ cat test.c
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <memory.h>
> > 
> > int main(int argc, char **argv)
> > {
> >         static const signed char a[3] = {0x60, 3, 200};
> >         static const unsigned char b[3] = {0x60, 3, 200};
> > 
> >         printf("a and b are %s\n",
> >                memcmp(a, b, 3) == 0 ? "identical" : "different");
> > }
> > $ gcc test.c
> > $ ./a.out
> > a and b are identical
> > 
> Good point, poor choice of example on my part.

Is there an actual example of this so-called "bug"
in the kernel code?