Experiment: DMAC Same-Pointer and Overlap Cases
Experiment ID: EXP-DMAC-OVERLAP-20260806-A · State: ACCEPTANCE ELIGIBLE · Classification: bounded real-hardware measurement
Question
What does sceDmacMemcpy do for same-pointer and overlapping transfers under controlled source-owned patterns?
Fixture and environment
Source-owned RAM-only probe using distinctive per-byte patterns and guard checks. Hardware: PSP-3001, 6.61-ARK, PSPLink-qualified session. The public record contains aggregate results only; no title data, private path, or raw capture is published.
Controls and procedure
- Validate source/destination spans and record raw return values.
- Run same-pointer self-copy, forward overlap, and backward overlap.
- Include public-prior-art invalid-pointer and zero-length controls, keeping unmeasured parameter combinations separate.
- Repeat the accepted bounded cases across two probe revisions / two runs as documented by the current runtime source.
Public-safe observation
| Case | Measured result | Boundary |
|---|---|---|
| same pointer, 16 KiB-style checked range | return 0; no observed corruption | measured case only |
forward overlap, dst=src+16 |
checked bytes matched memmove-like result | measured offset/size only |
backward overlap, dst=src-16 |
checked bytes matched memmove-like result | measured offset/size only |
| size 0 / NULL pointer controls | public PSP-shaped error classes | prior-art-supported controls |
Interpretation
Forward and backward overlap behaved correctly for the measured PSP-3001 cases. This supports FIND-DMAC-OVERLAP-001 and a memmove-like implementation for the bounded domain.
Claims not supported
- No universal “memmove guarantee” across sizes, alignments, regions, cache states, models, or firmware.
- No exact large-transfer ceiling. The preliminary high-size tail-loss question is deliberately withheld pending the corrected boundary probe.
- No busy/asynchronous claim from this single-threaded campaign.
Implementation comparison
The current public HLE keeps the measured overlap behavior and leaves the unverified ceiling visible in src/rt/hle.c. See the public DMAC synthesis.
Replication
Use owned RAM and deterministic nonlinear byte patterns. Report exact size, overlap offset, alignment, cache preparation, return code, first mismatch, and repeat count. Do not submit arbitrary addresses, retail content, or private captures.
Related: FIND-DMAC-OVERLAP-001 · CONFLICT-DMAC-SAMEPTR-001 · EXP-DMAC-BOUNDARY-001 (planned).
Publication safety: public-safe aggregate only. Last reviewed: 2026-08-11.