Support for AArch64

Support for AArch64 with AES and SHA2 is now fully supported with most algos optimized for NEON, AES & SHA with exceptions noted below.

This is provided as source code only and may be built on native Linux by following the existing procedure subject to any modifications described below.

Bitcoin talk discussion thread: https://bitcointalk.org/index.php?topic=5226770.0

Requirements:

• An ARM CPU supporting AArch64.
• Linux OS.
• MacOS on ARM does not work natively but does work at full speed from a Linux VM using UTM & Qemu.

Status

cpuminer-opt-23.15 is released

Update v24.2 is released with more NEON optimizations, some requiring SHA3 extension.

ARM support is now feature complete, on par with x86_64 with SSE4.2, AES_NI & SHA extensions.

Development environment:

• Orange Pi 5 Plus 16 GB, Rockchip 8 core CPU with AES & SHA2
• Ubuntu Mate 22.04
• GCC-11.4

Secondary environment:

• Mac Mini M2
• MacOS 14.1 Sonoma
• UTM/Qemu VM emulator
• Ubuntu Mate 22.04 VM guest (update: Ubuntu Mate 24.04)

Compile with:

$ ./arm-build-sh

The only change from build.sh is the addition of "-flax-vector-conversions" to CFLAGS. The compiler will remind you if you forget. Specific achitectures and features can be compiled using examples in armbuild-all.sh.

The miner has been tested on Raspberry Pi 4B, Orange Pi 5 Plus, and Mac Mini from a Linux VM. It compiles for all minor versions of armv8.x with or without AES, or SHA2, or both. Update: compiles with armv9 and sha3.

Known problems:

• Verthash algo is not working. (update: problem found, will be fixed in v24.3)
• MacOS is not working natively, workaround with linux VM.
• CPU and feature detection and reporting is incomplete. (update, will be fixed in v24.3)
• Some algorithms too difficult to test with a CPU are not optimized for NEON.

Short term plan:

• Figure out what's going on with verthash. Update: problem was using ROR for 32 bit rotation.
• Detection of ARM CPU model and architecture minor version.
• Find NEON optimization opportunities that exploit it's architecture and instruction set.
• Apply lessons learned to x86_64.

Long term:

• SHA512, x86_64 & AArch64.
• ARM SVE
• x86_64 AVX10 (update: initial support in v24.2)
• RISC-V

Some notable observations about the problems observed:

The problem with verthash was using the scalar ROR instrution for bit rotation. Documentaion says it supports 64 & 32 bit registers but not how. It is assumed "registers" means hardware dependent and 32 bit works on A32 only and 64 bit on A64 only.

Multiplications are implemented differently, particularly widening multiplcatiom where the product is twice the bit width of the souces. X86_64 operates on lanes 0 & 2 while ARM operates on lanes 0 & 1 of the source data. In effect x86_64 assumes the data is pre-widened and discards lanes 1 & 3 leaving 2 zero extended 64 bit source integers. With ARM the source arguments are packed into a smaller vector and the product is widened to 64 bits upon multiplication:

uint64x2_t = uint32x2_t * uint32x2_t

Most widening multiplications use the x86_64 format requiring a workaround for ARM. The curent workaround seems to be functioning correctly where needed but with significant extra overhead. (update: overhead reduced in v24.3)

SHA512 support in cpuminer-opt is not assured. It is little used and may not be worth the effort. X64 looks like an enlarged clone of sha256 with 128 bit operations replaced with equivalent 256 bit ops. AArch64 implements sha512 using 128 bit registers and splitting the 256 bit operations over 2 128 bit instructions, complicating implementation and reducing performance gain.

SVE deosn't seem to be useable for hashing. It uses Vector Agnostic Programming which abstracts the logical vector size from the vector register size. This creates run time overhead for SVE to determine HW register size.

Biggest MAC problems seem to be with JSON, possibly a configure issue choosing whether to use system or local version of JSON. Other than missing GMP most problems occur at link or load time.