linux-kernel - Re: [PATCH 09/18] arm64: introduce binfmt

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Date:   Wed, 14 Dec 2016 15:09:22 +0530
From:   Yury Norov <ynorov@...iumnetworks.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     <arnd@...db.de>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-arch@...r.kernel.org>, <szabolcs.nagy@....com>,
        <heiko.carstens@...ibm.com>, <cmetcalf@...hip.com>,
        <philipp.tomsich@...obroma-systems.com>, <joseph@...esourcery.com>,
        <zhouchengming1@...wei.com>, <Prasun.Kapoor@...iumnetworks.com>,
        <agraf@...e.de>, <geert@...ux-m68k.org>, <kilobyte@...band.pl>,
        <manuel.montezelo@...il.com>, <pinskia@...il.com>,
        <linyongting@...wei.com>, <klimov.linux@...il.com>,
        <broonie@...nel.org>, <bamvor.zhangjian@...wei.com>,
        <maxim.kuvyrkov@...aro.org>, <Nathan_Lynch@...tor.com>,
        <schwidefsky@...ibm.com>, <davem@...emloft.net>,
        <christoph.muellner@...obroma-systems.com>
Subject: Re: [PATCH 09/18] arm64: introduce binfmt_elf32.c

On Mon, Dec 05, 2016 at 03:10:19PM +0000, Catalin Marinas wrote:
> On Fri, Oct 21, 2016 at 11:33:08PM +0300, Yury Norov wrote:
> > As we support more than one compat formats, it looks more reasonable
> > to not use fs/compat_binfmt.c. Custom binfmt_elf32.c allows to move aarch32
> > specific definitions there and make code more maintainable and readable.
> 
> Can you remind me why we need this patch (rather than using the default
> fs/compat_binfmt_elf.c which you include here anyway)?

https://patchwork.kernel.org/patch/8756121/

This is mostly to avoid runtime checks and hide some re-definitions
for aarch32 from ilp32, to avoid re-re-definition.

> 
> > --- /dev/null
> > +++ b/arch/arm64/kernel/binfmt_elf32.c
> > @@ -0,0 +1,31 @@
> > +/*
> > + * Support for AArch32 Linux ELF binaries.
> > + */
> > +
> > +/* AArch32 EABI. */
> > +#define EF_ARM_EABI_MASK		0xff000000
> > +
> > +#define compat_start_thread		compat_start_thread
> > +#define COMPAT_SET_PERSONALITY(ex)		\
> > +do {						\
> > +	clear_thread_flag(TIF_32BIT_AARCH64);	\
> > +	set_thread_flag(TIF_32BIT);		\
> > +} while (0)
> 
> You introduce this here but it seems to still be present in asm/elf.h.

Hmm... Maybe chunk that delete it from asm/elf.h was dropped at some
rebase. Thank you for the catch. I'll check it again.

Yury