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chore(audit): mark P4 PPCBUGs applied; append P4 progress section

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P4 phase merged at d945aea. Update audit-findings.md status fields
(43 PPCBUGs marked applied) and append the P4 progress section to
audit-report-2026-04-29.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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MechaCat02
2026-05-02 12:09:26 +02:00
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audit-report-2026-04-29.md
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@@ -365,6 +365,41 @@ After applying Phase 1 alone, run `xenia-rs check sylpheed.iso -n 4B --parallel`
---
### P4 — 32-bit ABI writeback truncation sweep (merged 2026-05-02, HEAD d945aea)
**PPCBUGs fixed**: ~43 IDs across the 4a/4b/4c/4d sub-sections.
- 4a active poisoning: 006 (negx), 008 (subfex), 018 (subfzex), 019 (subfmex), 028 (orcx), 029 (norx), 030 (nandx), 031 (eqvx), 033 (andcx)
- 4a/4d coupled: 034+035+036+037 (extsbx/extshx writeback + CR0)
- 4b immediate ALU: 001 (addi), 002 (addic), 003 (addicx), 004 (mulli), 005 (subficx), 007 (subfcx CA)
- 4b mul/div + srawx coupled: 009 (mullwx), 010+011 (divwx + CR0), 041+042+043 (srawx/srawix + CR0)
- 4b loads: 095-098 (lha/lhax/lhau/lhaux), 105 (lwa/lwax/lwaux)
- 4c latent: 012-017 (addx/addcx/addex/addzex/addmex/subfx), 032 (andx/orx/xorx CR0)
- 4d CR0 catch-all: 020 (in mulhwx/mulhwux/divwux/andx/orx/xorx/cntlzwx etc.), 023 (andisx), 024 (rlwinmx), 025 (rlwimix), 026 (rlwnmx), 044 (slwx/srwx)
**Batches**:
- Batch 1 (e18a0a4): 4a active poisoning NOT/SUB family — 9 PPCBUGs
- Batch 2 (145a7a4): 4a/4d coupled extsbx+extshx+CR0 — 4 PPCBUGs (must land together)
- Batch 3 (bf8208e): 4b immediate ALU — 6 PPCBUGs
- Batch 4 (82a9bff): 4b mul/div + srawx coupled — 6 PPCBUGs (two coupling groups)
- Batch 5 (20a730d): 4b halfword + lwa loads — 5 PPCBUGs
- Batch 6 (16993bb): 4c latent + 4d CR0 catch-all — ~13 PPCBUGs
- Review-fix (49103bb): subfx/subfcx OE predicate + mulli test rigor
**Phase invariants restored**: every 32-bit ABI GPR write zero-extends from a u32 result, every CR0 update views the result as i32, every CA bit comes from a 32-bit unsigned compare. Downstream 64-bit unsigned compares (the addis-incident shape) can no longer be fed polluted upper bits from any of the 40+ touched ALU sites. The frozen-snapshot drift detected in PPCBUG-003 (addicx CR0) and PPCBUG-023 (andisx CR0) is also resolved.
**Review findings**:
- BLOCKING issue caught: subfx and subfcx OE handlers in batch 6 still used the legacy `sum_overflow_64` helper. The helper compares the 32-bit `true_diff` against a u64 view of the result; any legitimate i32::MIN result (bit 31 set) spuriously triggered OV=1. Fixed in 49103bb with two new discriminating regression tests.
- Minor caught: `mulli_overflow_wraps_to_32` rubber-stamped — both pre/post fix wrote 0 for the chosen inputs. Redesigned to use polluted-upper-bits inputs that genuinely discriminate.
**Gate results**:
- `cargo test --workspace --release`: **494 passed, 0 failed** (up from 470 at P3 merge; 24 new regression tests across the batches)
- 64-bit ABI ops verified untouched: rldicl/rldicr/rldic/rldimi/rldcl/rldcr, sldx/srdx/sradx/sradix, mulhdx/mulhdux/mulldx, divdx/divdux, cntlzdx, extswx
- **Acid test** `-n 4B --parallel --reservations-table`: deferred per user direction
**Conclusion**: P4 is the largest ABI-correctness sweep of the audit. The systemic invariant is restored. Next: P5 — FPU correctness (~30 IDs).
---
## Index — every PPCBUG referenced (in numerical order)
This list intentionally includes every ID found in `audit-findings.md` so nothing is dropped. For each entry's full description / file:line / fix snippet / test recommendation, see the corresponding `### PPCBUG-NNN` heading in `audit-findings.md`.