From: "Lothar Waßmann" <LW@KARO-electronics.de>
To: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: linux-arm-kernel@lists.infradead.org,
Will Deacon <will.deacon@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Rob Herring <robh@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Marc Zyngier <marc.zyngier@arm.com>,
Russell King <linux@armlinux.org.uk>,
linux-kernel@vger.kernel.org, Olof Johansson <olof@lixom.net>
Subject: Re: [PATCH] arm64: relax assembly code alignment from 16 byte to 4 byte
Date: Thu, 31 Aug 2017 12:23:28 +0200 [thread overview]
Message-ID: <20170831122328.2334a4de@karo-electronics.de> (raw)
In-Reply-To: <1504173383-8367-1-git-send-email-yamada.masahiro@socionext.com>
Hi,
On Thu, 31 Aug 2017 18:56:23 +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@socionext.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@arm.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.
>
>
> arch/arm64/include/asm/linkage.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
> index 636c1bc..1b26629 100644
> --- a/arch/arm64/include/asm/linkage.h
> +++ b/arch/arm64/include/asm/linkage.h
> @@ -1,7 +1,7 @@
> #ifndef __ASM_LINKAGE_H
> #define __ASM_LINKAGE_H
>
> -#define __ALIGN .align 4
> -#define __ALIGN_STR ".align 4"
> +#define __ALIGN .align 2
> +#define __ALIGN_STR ".align 2"
>
> #endif
>
My math tells me, that 2 is one half of 4 but 4 is one fourth of 16, so
this change doesn't line up with your commit message, or am I missing
something?
Lothar Waßmann
next prev parent reply other threads:[~2017-08-31 10:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-31 9:56 [PATCH] arm64: relax assembly code alignment from 16 byte to 4 byte Masahiro Yamada
2017-08-31 10:23 ` Lothar Waßmann [this message]
2017-08-31 10:38 ` Robin Murphy
2017-09-07 16:46 ` Catalin Marinas
2017-09-20 10:58 ` Masahiro Yamada
2017-09-20 12:19 ` Catalin Marinas
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