From: Eric Biggers <ebiggers@kernel.org>
To: Emanuele Rocca <emanuele.rocca@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>,
linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] lib/crc: arm64: use .arch_extension to enable CRC and crypto
Date: Thu, 5 Nov 2026 19:42:20 +0000 [thread overview]
Message-ID: <20261105194220.GC3266627@google.com> (raw)
In-Reply-To: <20261105154145.557042-1-emanuele.rocca@arm.com>
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
prev parent reply other threads:[~2026-11-05 19:42 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-05 15:41 [PATCH] lib/crc: arm64: use .arch_extension to enable CRC and crypto Emanuele Rocca
2026-11-05 19:42 ` Eric Biggers [this message]
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