Re: [PATCH 4/5] xor/arm64: Use shared NEON intrinsics implementation from 32-bit ARM

On Mon, 30 Mar 2026, at 07:32, Christoph Hellwig wrote:
> On Fri, Mar 27, 2026 at 03:45:56PM +0100, Ard Biesheuvel wrote:
>> On Fri, 27 Mar 2026, at 14:50, Christoph Hellwig wrote:
>> > On Fri, Mar 27, 2026 at 12:30:52PM +0100, Ard Biesheuvel wrote:
>> >> From: Ard Biesheuvel <[email protected]>
>> >> 
>> >> Tweak the arm64 code so that the pure NEON intrinsics implementation of
>> >> XOR is shared between arm64 and ARM.
>> >
>> > Instead of hiding the implementation in a header, just split xor-neon.c
>> > into two .c files, one of which could be built by arm32 as well.
>> 
>> That is what patch 3/5 does. This patch wires up that version into arm64, and drops the copy that has become redundant as a result.
>
> Yeah, sorry - I misread the series a little.
>
>> 
>> > probably
>> > in the arm/ instead of the arm64/ subdirectory, but we can also add a
>> > new arm-common one if that's what the arm maintainers prefer.
>> 
>> Having the shared pure NEON version in arm/ is perfectly fine.
>
> So here would be my preference:
>
>  - keep all the arm/arm64 code in lib/raid/xor/arm
>  - have the neon and EOR3 code in a single xor-neon.c file, with an
>    ifdef CONFIG_ARM64 around the EOE3 routines
>
> This avoid the including of .c files which is always a bit ugly.
> But if there is a strong argument to prefer including of the .c file I
> can live with that as well.
>

I've respun it without the include. Instead, I've added this to arm/xor-neon.c

+#ifdef CONFIG_ARM64
+extern typeof(__xor_neon_2) __xor_eor3_2 __alias(__xor_neon_2);
+#endif

so that __xor_eor3_2() exists in the arm64 build as an alias. That way, the arm64-only EOR3 implementation can just remain a separate compilation unit.

I could move the eor3 code under arm/ too, but that seems a bit odd given that it is arm64 only, and a arm64/ sub-directory exists.