# 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 to `xenia-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 `HYPOTHESIS` to at least `PROBABLE` —
  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`](INDEX.md) (one line each: name · confidence · one-line summary).

Use the templates: [`_TEMPLATE.function.md`](_TEMPLATE.function.md),
[`_TEMPLATE.structure.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 with `xenia-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-rs` with 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; our `xenia-rs` never got past the intro video. Use canary to *observe output*
  (capture its framebuffer for texture colours), not usually to instrument code — though its
  `build-cross` toolchain 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.
