On Fri, Apr 9, 2021 at 3:12 PM Nathan Chancellor <nathan@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx > Fixes: d8f1308a025f ("crypto: arm/curve25519 - wire up NEON implementation") > Link: https://github.com/ClangBuiltLinux/continuous-integration2/issues/118 > Reported-by: Arnd Bergmann <arnd@xxxxxxxx> > Suggested-by: Arnd Bergmann <arnd@xxxxxxxx> > Suggested-by: Jessica Clarke <jrtc27@xxxxxxxxxx> > Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> 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@xxxxxxxxxx> Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > --- > 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
