Re: [PATCH] lib/crc: arm64: use .arch_extension to enable CRC and crypto

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Nov 05, 2026 at 03:41:45PM +0000, Emanuele Rocca wrote:
> Instead of using ".cpu generic+crc+crypto", use ".arch_extension crc" and
> ".arch_extension crypto" to enable the required instructions.
> 
> The ".cpu generic+crc+crypto" directive replaces the assembler's current
> feature set with generic+crc+crypto, dropping any other features that were
> previously enabled, for example by -march or by a toolchain configured with
> --with-arch=armv9-a. In contrast, ".arch_extension" enables the requested
> extensions while preserving the current feature set.
> 
> This is not a functional change: crc32-core.S only uses base A64
> instructions plus CRC32 and PMULL, which remain available, and BTI landing
> pads are emitted as HINT instructions. However, using .arch_extension
> avoids the pitfall of silently disabling features. See commit 9142c2f8f84b
> ("octeontx2: use arch_extension to enable LSE").
> 
> Signed-off-by: Emanuele Rocca <emanuele.rocca@arm.com>

Thanks.  Just to confirm, all supported versions of binutils and clang
support this?  (As per Documentation/process/changes.rst, the kernel
currently supports binutils 2.30 and later, and clang 17.0.1 and later.)

A lot of the arm64 crypto code uses ".arch armv8-a+crypto".  Should
those be replaced with ".arch_extension	crypto" for the same reason?

- Eric