Claude (auto-RE)
3ef2c438ae
With word A = 2 the screen lists Stage01 SELECTABLE, carrying a High Score and a
Best Time, and Stage02-Stage08 GREYED OUT. One cleared stage, one selectable
entry, at the bit index that names it -- the mask's meaning is now visible on
screen rather than inferred from disassembly.
Two runs, identical navigation, fresh boot each:
control word A 0x00000002 -> MISSION SELECT opens normally
poked word A 0xFFFFFFFF -> MmAllocatePhysicalMemoryEx fails on 128 MB,
guest throws, Xenia shows "Disc Read Error"
So last commit's heap failure was caused by the poke, and by a careless one:
0xFFFFFFFF claims stages that do not exist (0, 17, 24-31 in word A). Poking only
real story ids (0x0001FFFE = stages 1-16) does not blow the heap. That the list
screen changes behaviour with the mask is itself evidence word A feeds it.
Getting a trustworthy control took three tries, and every failure produced a
plausible wrong answer rather than an error:
1. the title-glyph oracle fired during the ATTRACT MOVIE, so A was pressed at
nothing and the run "reported 0 failures" for a screen it never reached;
2. Xvfb keeps the previous instance's framebuffer until the new one draws, so
a screenshot seconds after launch showed the OLD run -- "MAIN MENU reached
after 1s", against a process that no longer existed;
3. a single-pixel "is NEW GAME white?" test matched a white LOADING FLASH.
Fixes, all in challenge_probe.sh: blank the root and refuse screen oracles for
the first 40 s; identify a screen by a PATTERN of sampled points (white text AND
the dark panel behind it), not one pixel; require two consecutive samples. The
new oracle was validated offline against all six saved screenshots and accepts
exactly the one real main menu.
General lesson worth the words: a navigation oracle that can only fail by
returning the wrong screen will happily produce a whole run of confident,
meaningless results.
Reverse-engineering knowledge base
This directory is the spec-side of the clean-room: it records what the original Project Sylpheed binary does (behaviour) and how its data is laid out, so that the Rust port can be implemented from these specs without re-deriving anything and without ever copying original code.
It exists to answer one question fast: "do we already know how X works, and how sure are we?"
The one rule that matters
Never document a claim more confidently than the evidence supports, and never paste original code here.
A wrong-but-confident note is worse than no note: someone builds on it and the bug hides for weeks. Every entry therefore carries an explicit confidence and its evidence. This mirrors the project method — measure the oracle, never infer; refute before believing.
Clean-room firewall
- ✅ Allowed: behaviour descriptions, field offsets/types, formulas, state machines,
observed input→output pairs, and references to the original by address
(
sub_821B68C0) or toxenia-rs/sylpheed.db. - ❌ Forbidden here and in
crates/: pasted decompiled C/C++ or verbatim disassembled function bodies presented as the thing to reimplement. Cite the address; describe the behaviour in your own words. Disassembly is a tool for understanding, not a source to copy.
Confidence levels
| Level | Meaning | Bar to reach it |
|---|---|---|
CONFIRMED |
Behaviour verified against ground truth. | ≥2 independent observations or one observation cross-checked against an oracle (canary framebuffer, a known-correct value, a second code path). |
PROBABLE |
Strong single-source inference. | One clean observation, or an unambiguous static read of the disassembly. |
HYPOTHESIS |
Educated guess, not yet tested. | Anything else. Must say what would confirm/refute it. |
Promotion requires new evidence, not re-reading the old evidence. A HYPOTHESIS that
"looks right again" is still a HYPOTHESIS. Only an independent check promotes it.
If evidence later contradicts an entry, demote it and record the contradiction — do
not silently edit the conclusion.
When to document
- Right after a function/structure crosses from
HYPOTHESISto at leastPROBABLE— before moving to the next code path, so the knowledge isn't lost or re-derived. - Whenever confidence changes (up or down) — append to the Evidence log, don't overwrite.
- Not while it's still a pure guess with no evidence — a one-liner in the relevant backlog/plan is enough until there's something to stand on.
What to document
- Functions/code paths →
docs/re/functions/<name>.md(one file per function or tight cluster). - Data structures / formats →
docs/re/structures/<name>.md. - Keep the index in
INDEX.md(one line each: name · confidence · one-line summary).
Use the templates: _TEMPLATE.function.md,
_TEMPLATE.structure.md.
How we find and confirm code paths (the toolchain)
Everything joins on the guest virtual address (PC) — code addresses are fixed by the XEX load, identical across our emulator and canary.
- Static (cheap, try first):
xenia-rs/sylpheed.db(DuckDB: 25 481 functions, xrefs, strings, vtables, imports). Query withxenia-rs/zq.py—zq.py grep <str>,zq.py xref <addr>,zq.py dis <lo> <hi>,zq.py fn <pc>. Entry points are usually a string (zq.py grep MSG_DEMO) or an import (movie/XMA API) xref'd back to the loader. - Dynamic (when static is ambiguous): run
xenia-rswith its probe suite —--pc-probe/--audit-pc-probe-hex(fires at block entry),--mem-watch(mid-block reads/writes of a VA),--lr-trace(call/return chains),--trace-instructions,--dump-addr(read guest memory). These already exist; prefer them over hacking canary. - Oracle (correctness ground truth): canary — the Wine cross-build
xenia-canary/build-cross/bin/Windows/Debug/xenia_canary.exe(the native Linux ELF crashes / does not run — do not use it). This is the only emulator that reaches the in-game menu; ourxenia-rsnever got past the intro video. Use canary to observe output (capture its framebuffer for texture colours), not usually to instrument code — though itsbuild-crosstoolchain does compile, so small C++ probes + rebuild are possible when needed. Run muted, one emulator process at a time, point it at the real ISO (not the symlink).
⚠️ VA-equality caveat: join code by PC (fixed), but never assume a data VA holds the same bytes across emulators — allocators differ. Compare data by content/layout.