Add ACT4 user-mode architectural test coverage for RV32IMAF(C)

[cyrilmhansen]

Summary

I have an experimental ACT4 bring-up for rv32emu user-mode RV32IMAF(C), currently staged in my fork:

cyrilmhansen#2

The branch adds ACT4 runner integration and fixes conformance issues exposed by the generated tests.

What This Covers

The default passing ACT batch is:

I,M,F,Zicsr,Zicntr,Zifencei,Zca,Zcf,Misalign,MisalignZca,Zaamo

Current local result:

ACT runner: 182/182 passed

The branch intentionally excludes Zalrsc for now because Zalrsc-sc.w still needs separate investigation.

Bugs Found By ACT4

ACT4 exposed several issues:

1. x0 can be clobbered through interpreter execution and constant propagation.
2. RV32F CSR handling is incomplete:
   • frm is not handled as a CSR.
   • fflags accesses do not preserve/mask the packed fcsr fields correctly.
   • dynamic rounding reads use an incorrect mask.
3. The ACT runner previously executed stale ELFs from earlier extension batches, so targeted runs like ACT_EXTENSIONS=F could fail because of unrelated generated tests.

Performance Note

The x0 fix currently uses a conservative interpreter repair after each instruction plus constant propagation pinning. This is correct and makes ACT pass, but it is on a hot path. It may be worth reviewing whether upstream prefers:

• keeping the conservative repair,
• replacing it with a lower-overhead per-opcode/rd audit,
• or gating optimizer-sensitive behavior in the architecture-test config.

The FP CSR fix should not be gated; it is architectural correctness rather than an optimization tradeoff.

Licensing

The ACT4 checkout is kept as a submodule rather than vendoring the test suite into rv32emu.

The local ACT tree documents:

• code under BSD-3-Clause or Apache-2.0
• documentation under CC-BY-4.0

So vendoring appears possible with the usual notice/attribution obligations, but a submodule is cleaner and avoids importing a large mixed-license test framework directly.

Validation

Validated locally:

PKG_CONFIG=/usr/bin/pkg-config make -j4

tools/run-act-elfs.sh build/rv32emu-user build/act/rv32emu-rv32imafc/elfs I,M,F,Zicsr,Zicntr,Zifencei,Zca,Zcf,Misalign,MisalignZca,Zaamo

Result:

ACT runner: 182/182 passed

Also validated targeted FP run:

tools/run-act-elfs.sh build/rv32emu-user build/act/rv32emu-rv32imafc/elfs F

Result:

ACT runner: 78/78 passed

Follow-Up Work

• Investigate Zalrsc-sc.w.
• Decide whether the x0 repair should be optimized before merging.
• Decide whether upstream wants ACT4 wired into CI or kept as a documented local/manual target first.