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

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Date:   Thu, 31 Aug 2017 18:56:23 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Marc Zyngier <marc.zyngier@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] arm64: relax assembly code alignment from 16 byte to 4 byte

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.


 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