RV32 with RVC GCC/G++ testing and observations

[Michael Clark]

Hi All,

I’ve performed some RV32 with RVC testing this weekend and thought I would share results.

The riscv-meta simple ABI/AEE emulator now supports RV32IMAFDC in addition to RV64IMAFDC and both have been cross-checked with spike for all FPU instructions on RV32 and RV64 and combinations of RVC (privileged ISA is not there, however the emulator can run simple riscv-pk programs)

If you have an RV64 toolchain installed you can run the riscv-meta RV64 tests:

# run RV64 and RV64C tests with spike

make test-run-rv64

make test-run-rvc64

# run RV64 and RV64C tests with the riscv-meta emulator

make test-emulate-rv64

make test-emulate-rvc64

If you have an RV32 toolchain installed you can run the riscv-meta RV32 tests:

# run RV32 and RV32C tests with spike

make test-run-rv32

make test-run-rvc32

# run RV32 and RV32C tests with the riscv-meta emulator

make test-emulate-rv32

make test-emulate-rvc32

Note: I synced to the latest toolchain and modified the build-rv32im.sh script in the riscv-tools priv-1.9 branch to build the RV32 toolchain using --with-arch=RV32IMAFD

Tested compilers

riscv-tools priv-1.9 branch

commit id: 65da94f84a2ba5a61a8bcf3ebdd8ca57f6d899ca

riscv32-unknown-elf-gcc (GCC) 6.1.0

riscv32-unknown-elf-g++ (GCC) 6.1.0

riscv64-unknown-elf-gcc (GCC) 6.1.0

riscv64-unknown-elf-g++ (GCC) 6.1.0

Observations

Some of these may be known issues.

RVC in riscv-meta

- The RVC encoding/decoding and emulation in the riscv-meta repo is working equivalently to spike/pk for complex test cases.

- The RVC decompress emulation was a critical path to isolate encoding issues vs relocation issues in the riscv-compress-elf tool I am working on.

- The tests revealed one bug in the riscv-meta RVC metadata for c.jal which is now fixed

- https://github.com/michaeljclark/riscv-meta/commit/11c7fe03853e1e2de6c59c2496ade0c3970b569a

64-bit integers in RV32 GCC (libgcc?)

- Some 64-bit integer arithmetic appears not to work with the RV32 gcc/g++ --with-arch=RV32IMAFD

- The test-sieve program is consistently wrong on spike and riscv-meta emulator so I suspect the compiler

- I have not had time to trace it but the test-sieve program should work the same on both RV64 and RV32

RVC in GCC

- Both 32-bit and 64-bit gcc compilers are not using RVC instructions for the whole executable

- This may be because the CRT is pre-compiled without RVC and the linker does not compress during link

- Work in progress riscv-meta compress-elf gets much higher compression ratios (although it still has relocation issues)

RVC in G++

- Both 32-bit and 64-bit g++ compilers are not outputing RVC instructions with the -mrvc flag (but the compiler accepts the flag). A known issue?

RVC in Spike

- There is a tiny RVC disassembly bug in the spike disassembler which I noticed is not fixed in the priv-1.9 branch. It’s a +2 -2 lines (see attached patch)

Cheers,

Michael.