75f0664bfe
Verified rather than adopted: a subagent proposed that every even operand slot is a type tag. Measured, the strong form is false and a precise form is true. TRUE: a SYMBOL operand is two words, a tag holding the constant 1 followed by the index. Slot 0 is the integer 1 in 19899/19899 calls whose slot 4 is a unit; slot 8 is tag-shaped in 100% of calls for every built-in taking a second unit; slot 16 is 1 in 152/152 for built-in 128, the only one taking a third. The 24 built-ins whose slot 0 is NOT the constant are exactly those taking no symbol there. This explains the unit slots 4/12/20 rather than replacing them. FALSE as stated: slot 8 is a bare double for built-ins 4, 20, 24, 26, 28, 29, 90, 106 and 127, and built-in 75 carries five bare indices at 0/4/8/12/16 with no tags at all. Each built-in has a fixed signature and is 100% self-consistent; none of the 34 with >=20 sites mixes the two. Symbol table 1 has three types -- 1 routes (1362), 6 messages (2247), 7 effects (81) -- and its operand slots are type-pure, measured the same way. Resolving them makes listings say what the script means: `request_script_message(MSG_VOICE_D_257, ...)`, a fourth independent confirmation of that name. Slots 24@4, 46@12 and 114@4 resolve 100% but MIX types 6 and 1, so they are left unresolved rather than guessed. Two more names withdrawn, neither replaced: * 88 `camera_at` -- ZERO call sites in all 28 stages; never testable. * 90 `camera_at_route` -- 8 sites, all Stage 02 phase 3, first operand is symtab-1 type 7 `eff_n0071`, an EFFECT name, in 8/8, with a per-missile Route_ADT301..308_p3M at slot 20. Not aimed at a camera. Left unnamed on purpose: replacing a guessed name with another guess is how the three names corrected earlier today went wrong. Also flagged: 115 `named_event`'s only symbol operand is an eff_* name in 84/84 sites, so that name is suspect too. Not renamed pending a handler read. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01PMRJjbxLqZtsb5Vb7KunPE
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.