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

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

[Emanuele Rocca]

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>
---
 lib/crc/arm64/crc32-core.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/crc/arm64/crc32-core.S b/lib/crc/arm64/crc32-core.S
index 49d02cc485b3..0877d07ed1bf 100644
--- a/lib/crc/arm64/crc32-core.S
+++ b/lib/crc/arm64/crc32-core.S
@@ -11,7 +11,8 @@
 #include <linux/linkage.h>
 #include <asm/assembler.h>
 
-	.cpu		generic+crc+crypto
+	.arch_extension	crc
+	.arch_extension	crypto
 
 	.macro		bitle, reg
 	.endm
-- 
2.55.0

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

[Eric Biggers]

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