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 <[email protected]>
---
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 <[email protected]>
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
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 <[email protected]>
> ---
>
> 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 <[email protected]>
> 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
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 <[email protected]>
>> ---
>>
>> 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 <[email protected]>
>> 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
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
On Thu, Aug 31, 2017 at 06:56:23PM +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 <[email protected]>
> ---
>
> 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 <[email protected]>
> 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.
Not sure why we ended up with 4. Possibly because we forgot the power of
2 difference for arm/arm64.
Queued for 4.14. Thanks.
--
Catalin
Hi Catalin,
2017-09-08 1:46 GMT+09:00 Catalin Marinas <[email protected]>:
> On Thu, Aug 31, 2017 at 06:56:23PM +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 <[email protected]>
>> ---
>>
>> 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 <[email protected]>
>> 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.
>
> Not sure why we ended up with 4. Possibly because we forgot the power of
> 2 difference for arm/arm64.
>
> Queued for 4.14. Thanks.
I still do not see this patch in linux-next.
Where was it queued?
--
Best Regards
Masahiro Yamada
On Wed, Sep 20, 2017 at 07:58:34PM +0900, Masahiro Yamada wrote:
> 2017-09-08 1:46 GMT+09:00 Catalin Marinas <[email protected]>:
> > On Thu, Aug 31, 2017 at 06:56:23PM +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 <[email protected]>
> >> ---
> >>
> >> 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 <[email protected]>
> >> 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.
> >
> > Not sure why we ended up with 4. Possibly because we forgot the power of
> > 2 difference for arm/arm64.
> >
> > Queued for 4.14. Thanks.
>
> I still do not see this patch in linux-next.
It won't make it into linux-next now, I'll push it as a fix for -rc2
(sorry, I've been away at Plumbers and didn't get the chance to send any
pull request). I'll push the patch out on fixes/core once I investigate
some unrelated failures.
--
Catalin