linux-kernel - Re: [PATCH 2/4] arm64: hide more compat

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Date:   Thu, 29 Oct 2020 14:35:53 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andrei Vagin <avagin@...il.com>,
        Michel Lespinasse <walken@...gle.com>,
        Mark Brown <broonie@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <dima@...sta.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] arm64: hide more compat_vdso code

On Mon, Oct 26, 2020 at 5:55 PM Mark Rutland <mark.rutland@....com> wrote:
> On Mon, Oct 26, 2020 at 05:03:29PM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > When CONFIG_COMPAT_VDSO is disabled, we get a warning
> > about a potential out-of-bounds access:
> >
> > arch/arm64/kernel/vdso.c: In function 'aarch32_vdso_mremap':
> > arch/arm64/kernel/vdso.c:86:37: warning: array subscript 1 is above array bounds of 'struct vdso_abi_info[1]' [-Warray-bounds]
> >    86 |  unsigned long vdso_size = vdso_info[abi].vdso_code_end -
> >       |                            ~~~~~~~~~^~~~~
> >
> > This is all in dead code however that the compiler is unable to
> > eliminate by itself.
> >
> > Change the array to individual local variables that can be
> > dropped in dead code elimination to let the compiler understand
> > this better.
> >
> > Fixes: 0cbc2659123e ("arm64: vdso32: Remove a bunch of #ifdef CONFIG_COMPAT_VDSO guards")
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
>
> This looks like a nice cleanup to me! I agree we don't need the array
> here.
>
> Reviewed-by: Mark Rutland <mark.rutland@....com>

Thanks!

I see the patch now conflicts with "mm: forbid splitting special mappings"
in -mm, by Dmitry Safonov. I have rebased my patch on top, should
I send it to Andrew for inclusion in -mm then?

      Arnd