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

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Message-ID: <CAOesGMhv+0_SZb2eSiwCGaD77hd=a6EhMp6tVvcrZoBnrHKQjA@mail.gmail.com>
Date:	Thu, 4 Dec 2014 13:15:12 -0800
From:	Olof Johansson <olof@...om.net>
To:	Alexander Graf <agraf@...e.de>
Cc:	"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>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size

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.


-Olof
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