SHA: Assembly Branch for ARM SIMD "neon"

[SamGinrich]

Trying to build Crypto++ e.g. on a Raspberry PI 2B with make on current cursor of the source repository:

Normal CXXFLAGS would be -DNDEBUG -O2 -march=armv7-a -mtune=cortex-a7 -mfpu=neon-vfpv4 -mfloat-abi=hard

The link step for cryptest.exe fails with unresolved "*_neon" functions in sha.cpp .

Analysis:
It appears that the macro __ARM_ARCH__ in source files sha(1|256|512)_armv4.S is initially undefined,
as the flag -march=armv7-a controls __ARM_ARCH, instead.

Workaround
Macro mapping in the header of the sha*_armv4.S files

#if !defined(__ARM_ARCH__)
    #define __ARM_ARCH__ __ARM_ARCH
#endif

solves the linker problem, and cryptest.exe for SHA passes.

Is there a different defensive approach for the make-procedure?

EDIT 2026-06-15: workaround fragment corrected

[noloader]

Thanks @SamGinrich.

Do you have a patch or a diff?

[absolutegar]

It looks like your workaround for the unresolved *_neon functions in sha.cpp works, but you might also consider explicitly defining __ARM_ARCH__ when invoking make to eliminate any dependency on the macro's state in the assembly files. Adding -D__ARM_ARCH__=7 to your CXXFLAGS could provide a more direct approach to ensuring compatibility with ARMv7-A without modifying the source files.