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check-parity

Testing & Quality
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Check that aarch64 JIT interpreter functions match generic CPU behavior

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How to use this skill

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  1. Open your project in Codex.
  2. Copy the prompt below and paste it into your agent.
  3. Review the proposed files and risks before you approve installation.
Prompt to paste
I want to install this Agent Skill for this project in Codex.

Source SKILL.md: https://github.com/sebastianbiallas/pearpc/blob/HEAD/.claude/skills/check-parity/SKILL.md

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First, summarize what it does, its dependencies, license status if identifiable, and any risks. Show the exact files you propose to add under .agents/skills/check-parity/. Do not write files or run scripts until I approve.

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Check Interpreter Parity

Run the interpreter parity check and analyze results. If an opcode name is given, show a side-by-side diff for that specific opcode.

Steps

  1. Always run the stub audit first — this catches no-op stubs (the #1 bug source):

    python3 scripts/debug/stub_audit.py $ARGUMENTS

    If an opcode name was given, this shows a side-by-side generic vs JIT diff. If no arguments, it scans all functions and reports no-op stubs.

  2. Run ./scripts/debug/check_interpreter_parity.sh

  3. For any issues found:

    • Commented-out ppc_exception(): These are bugs. The exception is silently dropped. Enable the call.
    • GEN_INTERPRET with ppc_exception(): The exception will be silently dropped because GEN_INTERPRET doesn't check exception_pending. Need native gen_ function or change to GEN_INTERPRET_BRANCH/ENDBLOCK (but ENDBLOCK also doesn't work for synchronous exceptions — see doc/AGENT_DEBUGGING.md).
    • Missing MSR_POW handling: Must strip POW bit in ppc_set_msr().

  4. For each GEN_INTERPRET warning, check the x86 JIT (src/cpu/cpu_jitc_x86/ppc_opc.cc) to see how it handles the same opcode. The x86 JIT is the reference for how gen_ functions should work.

Critical rule

GEN_INTERPRET CANNOT dispatch synchronous exceptions. The only correct approaches are:

  • Native gen_ that jumps directly to ppc_program_exception_asm (like x86 JIT does)
  • GEN_INTERPRET_BRANCH which dispatches to npc (works but forces a dispatch on every call)