[PATCH v2] crypto/arm: accelerated SHA-512 using ARM generic ASM and NEON

[Ard Biesheuvel]

On 11 April 2015 at 10:48, Arnd Bergmann <arnd at arndb.de> wrote:
> On Saturday 11 April 2015 09:35:15 Ard Biesheuvel wrote:
>> On 10 April 2015 at 22:23, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
>> >
>> >> On 10 apr. 2015, at 22:08, Arnd Bergmann <arnd at arndb.de> wrote:
>> >>
>> >>> On Friday 10 April 2015 16:29:08 Ard Biesheuvel wrote:
>> >>> +#if __ARM_MAX_ARCH__>=7
>> >>> +.arch  armv7-a
>> >>> +.fpu   neon
>> >>> +
>> >>
>> >> This will cause a build failure on an ARMv7-M build, which is incompatible
>> >> with .arch  armv7-a and .fpu   neon.
>> >>
>> >
>> > The neon part depends on CONFIG_KERNEL_MODE_NEON, which would never be set for that platform, I suppose
>>
>> On second thought, that is not entirely true, but I still don't think
>> there is problem here:
>> the .arch/.fpu declarations are understood perfectly fine by GAS when
>> targeting ARMv7-M. Only, it will emit code that is incompatible with
>> it. However, this code is invoked at runtime only if a NEON unit has
>> been detected, so it will just be ignored on ARMv7-M
>
> Sorry, I should have collected my findings better when replying to your
> patch. What I remembered was that I saw a problem in this area in linux-next
> with randconfig builds, but I did not notice that it was for a different
> file, and I had not double-checked that patch yet in order to send it
> out.
>
> See below for the patch I'm currently using for my randconfig builder.
> Before you apply this, please check again which files are affected, as
> it's possible that there are other modules that suffer from the same
> problem.
>
>         Arnd
>
> 8<-----------
> Subject: [PATCH] ARM: crypto: avoid sha256 code on ARMv7-M
>
> The sha256 assembly implementation can deal with all architecture levels
> from ARMv4 to ARMv7-A, but not with ARMv7-M. Enabling it in an
> ARMv7-M kernel results in this build failure:
>
> arm-linux-gnueabi-ld: error: arch/arm/crypto/sha256_glue.o: Conflicting architecture profiles M/A
> arm-linux-gnueabi-ld: failed to merge target specific data of file arch/arm/crypto/sha256_glue.o
>
> This adds a Kconfig dependency to prevent the code from being disabled

... enabled?

> for ARMv7-M.
>
> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
>
> diff --git a/arch/arm/crypto/Kconfig b/arch/arm/crypto/Kconfig
> index 458729d2ce22..76463da22f81 100644
> --- a/arch/arm/crypto/Kconfig
> +++ b/arch/arm/crypto/Kconfig
> @@ -49,6 +49,7 @@ config CRYPTO_SHA2_ARM_CE
>  config CRYPTO_SHA256_ARM
>         tristate "SHA-224/256 digest algorithm (ARM-asm and NEON)"
>         select CRYPTO_HASH
> +       depends on !CPU_V7M
>         help
>           SHA-256 secure hash standard (DFIPS 180-2) implemented
>           using optimized ARM assembler and NEON, when available.
>

@Herbert: could you please apply this onto cryptodev before sending
out your pull request for v4.1?
And please disregard $subject, I will post a v3 with a similar
'depends on' added (unless you're ok to add it yourself)

Thanks,
Ard.