[PATCH] crypto: arm/curve25519 - Move '.fpu' after '.arch'

[PATCH] crypto: arm/curve25519 - Move '.fpu' after '.arch'

[Nathan Chancellor]

Debian's clang carries a patch that makes the default FPU mode
'vfp3-d16' instead of 'neon' for 'armv7-a' to avoid generating NEON
instructions on hardware that does not support them:

https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/raw/5a61ca6f21b4ad8c6ac4970e5ea5a7b5b4486d22/debian/patches/clang-arm-default-vfp3-on-armv7a.patch
https://bugs.debian.org/841474
https://bugs.debian.org/842142
https://bugs.debian.org/914268

This results in the following build error when clang's integrated
assembler is used because the '.arch' directive overrides the '.fpu'
directive:

arch/arm/crypto/curve25519-core.S:25:2: error: instruction requires: NEON
 vmov.i32 q0, #1
 ^
arch/arm/crypto/curve25519-core.S:26:2: error: instruction requires: NEON
 vshr.u64 q1, q0, #7
 ^
arch/arm/crypto/curve25519-core.S:27:2: error: instruction requires: NEON
 vshr.u64 q0, q0, #8
 ^
arch/arm/crypto/curve25519-core.S:28:2: error: instruction requires: NEON
 vmov.i32 d4, #19
 ^

Shuffle the order of the '.arch' and '.fpu' directives so that the code
builds regardless of the default FPU mode. This has been tested against
both clang with and without Debian's patch and GCC.

Cc: stable@vger.kernel.org
Fixes: d8f1308a025f ("crypto: arm/curve25519 - wire up NEON implementation")
Link: https://github.com/ClangBuiltLinux/continuous-integration2/issues/118
Reported-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Jessica Clarke <jrtc27@jrtc27.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/arm/crypto/curve25519-core.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/crypto/curve25519-core.S b/arch/arm/crypto/curve25519-core.S
index be18af52e7dc..b697fa5d059a 100644
--- a/arch/arm/crypto/curve25519-core.S
+++ b/arch/arm/crypto/curve25519-core.S
@@ -10,8 +10,8 @@
 #include <linux/linkage.h>
 
 .text
-.fpu neon
 .arch armv7-a
+.fpu neon
 .align 4
 
 ENTRY(curve25519_neon)

base-commit: e49d033bddf5b565044e2abe4241353959bc9120
-- 
2.31.1.189.g2e36527f23

Re: [PATCH] crypto: arm/curve25519 - Move '.fpu' after '.arch'

[Jason A. Donenfeld]

Seems reasonable to me.

Acked-by: Jason A. Donenfeld <Jason@zx2c4.com>

Re: [PATCH] crypto: arm/curve25519 - Move '.fpu' after '.arch'

[Nick Desaulniers]

On Fri, Apr 9, 2021 at 3:12 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Debian's clang carries a patch that makes the default FPU mode
> 'vfp3-d16' instead of 'neon' for 'armv7-a' to avoid generating NEON
> instructions on hardware that does not support them:
>
> https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/raw/5a61ca6f21b4ad8c6ac4970e5ea5a7b5b4486d22/debian/patches/clang-arm-default-vfp3-on-armv7a.patch
> https://bugs.debian.org/841474
> https://bugs.debian.org/842142
> https://bugs.debian.org/914268

Another good link would be the one from Jessica describing more
precisely what the ARM targets for Debian are:
https://wiki.debian.org/ArchitectureSpecificsMemo#armel

>
> This results in the following build error when clang's integrated
> assembler is used because the '.arch' directive overrides the '.fpu'
> directive:
>
> arch/arm/crypto/curve25519-core.S:25:2: error: instruction requires: NEON
>  vmov.i32 q0, #1
>  ^
> arch/arm/crypto/curve25519-core.S:26:2: error: instruction requires: NEON
>  vshr.u64 q1, q0, #7
>  ^
> arch/arm/crypto/curve25519-core.S:27:2: error: instruction requires: NEON
>  vshr.u64 q0, q0, #8
>  ^
> arch/arm/crypto/curve25519-core.S:28:2: error: instruction requires: NEON
>  vmov.i32 d4, #19
>  ^
>
> Shuffle the order of the '.arch' and '.fpu' directives so that the code
> builds regardless of the default FPU mode. This has been tested against
> both clang with and without Debian's patch and GCC.
>
> Cc: stable@vger.kernel.org
> Fixes: d8f1308a025f ("crypto: arm/curve25519 - wire up NEON implementation")
> Link: https://github.com/ClangBuiltLinux/continuous-integration2/issues/118
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Suggested-by: Arnd Bergmann <arnd@arndb.de>
> Suggested-by: Jessica Clarke <jrtc27@jrtc27.com>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Great work tracking down that Debian was carrying patches! Thank you!
I've run this through the same 3 assemblers.

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  arch/arm/crypto/curve25519-core.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/crypto/curve25519-core.S b/arch/arm/crypto/curve25519-core.S
> index be18af52e7dc..b697fa5d059a 100644
> --- a/arch/arm/crypto/curve25519-core.S
> +++ b/arch/arm/crypto/curve25519-core.S
> @@ -10,8 +10,8 @@
>  #include <linux/linkage.h>
>
>  .text
> -.fpu neon
>  .arch armv7-a
> +.fpu neon
>  .align 4
>
>  ENTRY(curve25519_neon)
>
> base-commit: e49d033bddf5b565044e2abe4241353959bc9120
> --
> 2.31.1.189.g2e36527f23
>


-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] crypto: arm/curve25519 - Move '.fpu' after '.arch'

[Herbert Xu]

On Fri, Apr 09, 2021 at 03:11:55PM -0700, Nathan Chancellor wrote:
> Debian's clang carries a patch that makes the default FPU mode
> 'vfp3-d16' instead of 'neon' for 'armv7-a' to avoid generating NEON
> instructions on hardware that does not support them:
> 
> https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/raw/5a61ca6f21b4ad8c6ac4970e5ea5a7b5b4486d22/debian/patches/clang-arm-default-vfp3-on-armv7a.patch
> https://bugs.debian.org/841474
> https://bugs.debian.org/842142
> https://bugs.debian.org/914268
> 
> This results in the following build error when clang's integrated
> assembler is used because the '.arch' directive overrides the '.fpu'
> directive:
> 
> arch/arm/crypto/curve25519-core.S:25:2: error: instruction requires: NEON
>  vmov.i32 q0, #1
>  ^
> arch/arm/crypto/curve25519-core.S:26:2: error: instruction requires: NEON
>  vshr.u64 q1, q0, #7
>  ^
> arch/arm/crypto/curve25519-core.S:27:2: error: instruction requires: NEON
>  vshr.u64 q0, q0, #8
>  ^
> arch/arm/crypto/curve25519-core.S:28:2: error: instruction requires: NEON
>  vmov.i32 d4, #19
>  ^
> 
> Shuffle the order of the '.arch' and '.fpu' directives so that the code
> builds regardless of the default FPU mode. This has been tested against
> both clang with and without Debian's patch and GCC.
> 
> Cc: stable@vger.kernel.org
> Fixes: d8f1308a025f ("crypto: arm/curve25519 - wire up NEON implementation")
> Link: https://github.com/ClangBuiltLinux/continuous-integration2/issues/118
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Suggested-by: Arnd Bergmann <arnd@arndb.de>
> Suggested-by: Jessica Clarke <jrtc27@jrtc27.com>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  arch/arm/crypto/curve25519-core.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt