On 31/08/17 11:23, Lothar Wa?mann wrote:

Hi,

On Thu, 31 Aug 2017 18:56:23 +0900 Masahiro Yamada wrote:

quoted

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 <redacted>
---

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 [off-list ref]
  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?

2^4 = 16
2^2 = 4

The ARM behaviour of the .align directive is a bit funky...

Robin.

Lothar Wa?mann

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