On 31/08/17 11:23, Lothar Waßmann wrote: > 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.masah...@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.zyng...@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?
2^4 = 16 2^2 = 4 The ARM behaviour of the .align directive is a bit funky... Robin. > > > Lothar Waßmann > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-ker...@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >
