Re: [PATCH] crypto: aegis128/simd - build 32-bit ARM for v8 architecture explicitly

[Catalin Marinas <catalin.marinas@arm.com>]

On Wed, Oct 02, 2019 at 09:47:41AM -0700, Nick Desaulniers wrote:
> On Wed, Oct 2, 2019 at 12:55 AM Ard Biesheuvel
> <ard.biesheuvel@linaro.org> wrote:
> >
> > Now that the Clang compiler has taken it upon itself to police the
> > compiler command line, and reject combinations for arguments it views
> > as incompatible, the AEGIS128 no longer builds correctly, and errors
> > out like this:
> >
> >   clang-10: warning: ignoring extension 'crypto' because the 'armv7-a'
> >   architecture does not support it [-Winvalid-command-line-argument]
> >
> > So let's switch to armv8-a instead, which matches the crypto-neon-fp-armv8
> > FPU profile we specify. Since neither were actually supported by GCC
> > versions before 4.8, let's tighten the Kconfig dependencies as well so
> > we won't run into errors when building with an ancient compiler.
> >
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> 
> Thank you Ard, this fixes the build error for us.  Do you know if the
> "crypto extensions" are mandatory ISA extensions? 

I think they are optional (or at least most of them).

> I'm running into some inconsistencies between how clang parses target
> arch between command line flag, function __attribute__, assembler
> directive, and disassembler.  I see arch's like: armv8-a+crc,
> armv8-a+sve, armv8-a+fp16, armv8-a+memtag, armv8-a+lse, but I'm not
> familiar with the `+...` part of the target arch.

This page shows the possible combinations:

https://sourceware.org/binutils/docs/as/AArch64-Extensions.html#AArch64-Extensions

Basically if it's an optional feature in ARMv8.0, you pass armv8-a+...
For optional features only in higher versions, it would be
armv8.5-a+memtag. The table above also states whether it's enabled by
default (i.e. mandatory) in an architecture version. SB for example is
supported from 8.0 but only required in 8.5.

-- 
Catalin