Re: [PATCH] arm64: lse: Fix LSE atomics with LLVM

[Vincenzo Frascino <vincenzo.frascino@arm.com>]

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Hi Will,

On 18/02/2020 16:54, Will Deacon wrote:
> [+Sami]
> 

Thanks for this, I forgot to add Sami in Cc.

> On Tue, Feb 18, 2020 at 04:49:06PM +0000, Vincenzo Frascino wrote:
>> The introduction of the commit e0d5896bd356cd broke the compilation of
>> the kernel when the selected compiler is clang and it is used in
>> combination with "-no-integrated-as".
> 
> Curious, but have you tested this change with the integrated assembler as
> well?
> 

The integrated assembler as far as I am aware cannot assemble the kernel for
reasons independent from lse (AS=clang generates a lot of errors). Not sure how
Sami is testing it. I would be happy to learn it myself.

The default option for clang in the kernel Makefile is "-no-integrated-as"
though hence e0d5896bd356cd introduces a regression.

>> This happens because __LSE_PREAMBLE is defined as ".arch armv8-a+lse"
>> and this overrides the version of the architecture passed via -march
>> command line to the gas compiler.
>>
>> The issue was noticed during the development of pauth on arm64 and an
>> error example is reported below:
>>
>> $ aarch64-none-linux-gnu-as -EL -I ./arch/arm64/include
>>                                 -I ./arch/arm64/include/generated
>>                                 -I ./include -I ./include
>>                                 -I ./arch/arm64/include/uapi
>>                                 -I ./arch/arm64/include/generated/uapi
>>                                 -I ./include/uapi -I ./include/generated/uapi
>>                                 -I ./init -I ./init
>>                                 -march=armv8.3-a -o init/do_mounts.o
>>                                 /tmp/do_mounts-d7992a.s
>> /tmp/do_mounts-d7992a.s: Assembler messages:
>> /tmp/do_mounts-d7992a.s:1959: Error: selected processor does not support `autiasp'
>> /tmp/do_mounts-d7992a.s:2021: Error: selected processor does not support `paciasp'
>> /tmp/do_mounts-d7992a.s:2157: Error: selected processor does not support `autiasp'
>> /tmp/do_mounts-d7992a.s:2175: Error: selected processor does not support `paciasp'
>> /tmp/do_mounts-d7992a.s:2494: Error: selected processor does not support `autiasp'
>>
>> Fix the issue replacing ".arch armv8-a+lse" with ".arch_extension lse" that does
>> not override the command line parameter.
>>
>> Fixes: e0d5896bd356cd ("arm64: lse: fix LSE atomics with LLVM's integrated assembler")
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Reported-by: Amit Kachhap <Amit.Kachhap@arm.com>
>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>> ---
>>  arch/arm64/include/asm/lse.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/lse.h b/arch/arm64/include/asm/lse.h
>> index d429f7701c36..5d10051c3e62 100644
>> --- a/arch/arm64/include/asm/lse.h
>> +++ b/arch/arm64/include/asm/lse.h
>> @@ -6,7 +6,7 @@
>>  
>>  #ifdef CONFIG_ARM64_LSE_ATOMICS
>>  
>> -#define __LSE_PREAMBLE	".arch armv8-a+lse\n"
>> +#define __LSE_PREAMBLE	".arch_extension lse\n"
> 
> I'm ok with this, but Sami assumedly changed this for a reason in
> e0d5896bd356cd ("arm64: lse: fix LSE atomics with LLVM's integrated
> assembler").
> 
> Sami?
> 
> Will
> 

-- 
Regards,
Vincenzo

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