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From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: linux-arm-kernel@lists.infradead.org,
	Will Deacon <will.deacon@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>
Cc: Olof Johansson <olof@lixom.net>, Arnd Bergmann <arnd@arndb.de>,
	Rob Herring <robh@kernel.org>,
	Russell King <linux@armlinux.org.uk>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH] arm64: relax assembly code alignment from 16 byte to 4 byte
Date: Thu, 31 Aug 2017 18:56:23 +0900	[thread overview]
Message-ID: <1504173383-8367-1-git-send-email-yamada.masahiro@socionext.com> (raw)

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
-- 
2.7.4

             reply	other threads:[~2017-08-31  9:58 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-31  9:56 Masahiro Yamada [this message]
2017-08-31 10:23 ` [PATCH] arm64: relax assembly code alignment from 16 byte to 4 byte Lothar Waßmann
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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