linux-kernel - Re: [PATCH] arm64: relax assembly code alignment from 16 byte to 4 byte

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Message-ID: <20170920121907.x4jxd74tuogkb52a@localhost>
Date:   Wed, 20 Sep 2017 13:19:07 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Rob Herring <robh@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Olof Johansson <olof@...om.net>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: relax assembly code alignment from 16 byte to 4
 byte

On Wed, Sep 20, 2017 at 07:58:34PM +0900, Masahiro Yamada wrote:
> 2017-09-08 1:46 GMT+09:00 Catalin Marinas <catalin.marinas@....com>:
> > On Thu, Aug 31, 2017 at 06:56:23PM +0900, Masahiro Yamada wrote:
> >> Aarch64 instructions must be word aligned.  The current 16 byte
> >> alignment is more than enough.  Relax it into 4 byte alignment.
> >>
> >> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> >> ---
> >>
> >> I do not know why arm64 Linux requires 16 byte alignment.
> >>
> >> I dug git-history of arch/arm64/include/asm/linkage.h
> >> and the only commit I see is:
> >>
> >>   commit aeed41a9371ee02257b608eb06a9058507a7d0f4
> >>   Author: Marc Zyngier <Marc.Zyngier@....com>
> >>   Date:   Fri Oct 19 17:33:27 2012 +0100
> >>
> >>       arm64: fix alignment padding in assembly code
> >>
> >> It just opt out of the asm-generic variant to remove 0x90.
> >> So, the amount of alignment might not be not optimized yet.
> >>
> >> Please correct me if I am missing something.
> >
> > Not sure why we ended up with 4. Possibly because we forgot the power of
> > 2 difference for arm/arm64.
> >
> > Queued for 4.14. Thanks.
> 
> I still do not see this patch in linux-next.

It won't make it into linux-next now, I'll push it as a fix for -rc2
(sorry, I've been away at Plumbers and didn't get the chance to send any
pull request). I'll push the patch out on fixes/core once I investigate
some unrelated failures.

-- 
Catalin