linux-kernel - Re: [PATCH] arm64: Enable CONFIG

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Message-ID: <20141205111455.GC28339@e104818-lin.cambridge.arm.com>
Date:	Fri, 5 Dec 2014 11:14:55 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Olof Johansson <olof@...om.net>
Cc:	"agraf@...e.de" <agraf@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Will Deacon <Will.Deacon@....com>
Subject: Re: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size

On Thu, Dec 04, 2014 at 09:15:12PM +0000, Olof Johansson wrote:
> On Thu, Dec 4, 2014 at 7:46 AM, Alexander Graf <agraf@...e.de> wrote:
> > With binutils 2.25 the default alignment for 32bit arm sections changed to
> > have everything 64k aligned. Armv7 binaries built with this binutils version
> > run successfully on an arm64 system.
> >
> > Since effectively there is now the chance to run armv7 code on arm64 even
> > with 64k page size, it doesn't make sense to block people from enabling
> > CONFIG_COMPAT on those configurations.
> >
> > Signed-off-by: Alexander Graf <agraf@...e.de>
> > ---
> >  arch/arm64/Kconfig | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 9532f8d..3cf4f238 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -409,7 +409,6 @@ source "fs/Kconfig.binfmt"
> >
> >  config COMPAT
> >         bool "Kernel support for 32-bit EL0"
> > -       depends on !ARM64_64K_PAGES
> >         select COMPAT_BINFMT_ELF
> >         select HAVE_UID16
> >         select OLD_SIGSUSPEND3
> 
> This is hardly "compat". Sure, it's great to have a new binutils that
> has larger alignment, but practically not a single existing binary
> will work today if someone tries to do this.
> 
> So, it seems very premature to take this off. At the very least
> document it like Will requested, and make it depend on !ARM_64K_PAGES
> || EXPERT.

That would work for me. We need to be clear that most existing 32-bit
binaries will fail.

-- 
Catalin
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