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SubjectRe: [PATCH 1/2] ARM: drop unnecessary WASM
On 06.03.2019 00:39, Robin Murphy wrote:
> Hi Stefan,
>
> On 2019-03-05 10:18 pm, Stefan Agner wrote:
>> The W macro for generating wide instructions when targeting Thumb-2
>> is not required for the preload data instructions (pld, pldw) since
>> they are only available as wide instructions. The GNU assembler seems
>> to work with or without the .w appended when compiling an Thumb-2
>> kernel. However, Clang's integrated assembler does not consider the
>> .w variants as valid instructions:
>>
>> ./arch/arm/include/asm/processor.h:133:5: error: invalid instruction
>> "pldw.w\t%a0 \n"
>> ^
>> <inline asm>:2:1: note: instantiated into assembly here
>> pldw.w [r0]
>> ^
>> 1 error generated.
>
> Have you filed a bug against Clang for that? Something like "pldwal.w"
> may be super-redundant, but it's still perfectly valid syntax. The
> "Standard assembler syntax fields" section of the Arm ARM even calls
> out that "...the .W qualifier has no effect" on ARM/A32 instructions
> since they are inherently 32-bit; that should equally apply for 32-bit
> only Thumb/T32 instructions. There are certainly a few instructions
> which don't allow a condition code (even "AL"), but off-hand I don't
> remember any not having the optional {<q>} field in their syntax.

Good point, bug filed:
https://bugs.llvm.org/show_bug.cgi?id=40972

Will send a v2 and note that this is a work around for Clang and
reference the bug.

--
Stefan

>
> That said, obviously the patch itself is no problem since the syntax
> *is* redundant here, but it really is just a workaround for an
> assembler bug.
>
> Robin.
>
>> Drop the macro to make sure non-wide variants of pld and pldw are
>> emitted in all cases.
>>
>> Signed-off-by: Stefan Agner <stefan@agner.ch>
>> ---
>> arch/arm/include/asm/processor.h | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
>> index 120f4c9bbfde..042d77cf686d 100644
>> --- a/arch/arm/include/asm/processor.h
>> +++ b/arch/arm/include/asm/processor.h
>> @@ -131,8 +131,8 @@ static inline void prefetchw(const void *ptr)
>> __asm__ __volatile__(
>> ".arch_extension mp\n"
>> __ALT_SMP_ASM(
>> - WASM(pldw) "\t%a0",
>> - WASM(pld) "\t%a0"
>> + "pldw\t%a0",
>> + "pld\t%a0"
>> )
>> :: "p" (ptr));
>> }
>>

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