b712972d09
An audit of BACKLOG.md turned up a class of error with a single root cause: the README defines only the CONFIRMED/PROBABLE/HYPOTHESIS confidence scale, while the pages actually use a second vocabulary -- and 🔴 appears 98 times without ever being defined. It gets used for two different things, "refuted" and "blocked", and three entries slid from one into the other. README now defines ✅/🟡/❔/🔴/❌/🚧 and states the rule the corpus was missing: 🔴 never means "we have not run it yet". That is ❔ or 🚧. Its blocked sense is only for a real limit of the box -- no push credentials, no hardware Vulkan, a decision only the user can make -- and since the box can run the emulator, script input, screenshot and read guest memory, "needs a run" is never blocked. I made exactly this mistake on the world-unit item earlier today, which is what prompted looking for others. Fixed in BACKLOG.md: * the elimination test, marked 🔴 UNRUN and in fact run and refuted nine lines further down; * the frozen capture, marked 🔴 STILL UNRUN and in fact taken eleven lines down -- 🔴 wrong twice, since "the freeze did not happen this run" is a scheduling outcome and not a refutation; * a 🚧 STILL UNRUN item whose stated blocker (the boot-nav bug) is fixed; * the objective-counter heading, which asserts 0xbdb59668 as the answer while its own first body line refutes that address -- retitled to say what is actually solved, the method; * the paint-order "third measured permutation" question, answered inside its own entry by a third, fourth and fifth screen; * the UTF-16 endianness question -- resolved, and it is not a stale comment: localization.rs both documents LE and decodes with u16::from_le_bytes, so it is a code bug worth filing. Also fixes the corpus's only dangling link (INDEX.md pointed at structures/idxd-unnamed-keys.md, never written).
111 lines
5.8 KiB
Markdown
111 lines
5.8 KiB
Markdown
# Reverse-engineering knowledge base
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This directory is the **spec-side** of the clean-room: it records what the original
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*Project Sylpheed* binary **does** (behaviour) and how its **data is laid out**, so that
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the Rust port can be implemented **from these specs** without re-deriving anything and
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without ever copying original code.
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It exists to answer one question fast: *"do we already know how X works, and how sure are we?"*
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---
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## The one rule that matters
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> **Never document a claim more confidently than the evidence supports, and never
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> paste original code here.**
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A wrong-but-confident note is worse than no note: someone builds on it and the bug hides
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for weeks. Every entry therefore carries an explicit **confidence** and its **evidence**.
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This mirrors the project method — *measure the oracle, never infer; refute before believing.*
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### Clean-room firewall
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- ✅ Allowed: behaviour descriptions, field offsets/types, formulas, state machines,
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observed input→output pairs, and **references** to the original by address
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(`sub_821B68C0`) or to `xenia-rs/sylpheed.db`.
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- ❌ Forbidden here and in `crates/`: pasted decompiled C/C++ or verbatim disassembled
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function bodies presented as the thing to reimplement. Cite the address; describe the
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behaviour in your own words. Disassembly is a tool for *understanding*, not a source to copy.
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---
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## Confidence levels
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| Level | Meaning | Bar to reach it |
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|-------|---------|-----------------|
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| `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). |
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| `PROBABLE` | Strong single-source inference. | One clean observation, or an unambiguous static read of the disassembly. |
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| `HYPOTHESIS` | Educated guess, not yet tested. | Anything else. Must say what would confirm/refute it. |
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### The status markers
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The table above is the *confidence* scale. The markers that appear in
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`BACKLOG.md` and the `structures/` pages are a separate, and until now undefined,
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vocabulary. They mean:
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| Marker | Meaning |
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|---|---|
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| ✅ | Confirmed — verified against ground truth. |
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| 🟡 | Partial: true as far as it goes, or true under a stated assumption. |
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| ❔ | Open question. Nobody has answered it yet. |
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| 🔴 | **Refuted** — shown false — **or blocked by something the container cannot do.** |
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| ❌ | A specific claim that was tried and failed. Prefer 🔴. |
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| 🚧 | Work started and not finished. |
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**🔴 never means "we have not run it yet."** That is ❔ or 🚧. Reserve 🔴's
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"blocked" sense for a real limit of the box — no push credentials, no hardware
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Vulkan (lavapipe only), or a decision only the user can make. The box *can* run
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the emulator, script input, screenshot, read guest memory, and build and test
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Rust, so "needs a run" is never a blocker. This paragraph exists because the
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marker was undefined for 98 uses and three of them were mislabelled that way.
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**Promotion requires new evidence, not re-reading the old evidence.** A `HYPOTHESIS` that
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"looks right again" is still a `HYPOTHESIS`. Only an *independent* check promotes it.
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If evidence later contradicts an entry, **demote it and record the contradiction** — do
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not silently edit the conclusion.
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---
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## When to document
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- **Right after** a function/structure crosses from `HYPOTHESIS` to at least `PROBABLE` —
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before moving to the next code path, so the knowledge isn't lost or re-derived.
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- **Whenever confidence changes** (up or down) — append to the Evidence log, don't overwrite.
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- **Not** while it's still a pure guess with no evidence — a one-liner in the relevant
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backlog/plan is enough until there's something to stand on.
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## What to document
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- **Functions/code paths** → `docs/re/functions/<name>.md` (one file per function or tight cluster).
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- **Data structures / formats** → `docs/re/structures/<name>.md`.
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- Keep the index in [`INDEX.md`](INDEX.md) (one line each: name · confidence · one-line summary).
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Use the templates: [`_TEMPLATE.function.md`](_TEMPLATE.function.md),
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[`_TEMPLATE.structure.md`](_TEMPLATE.structure.md).
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---
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## How we find and confirm code paths (the toolchain)
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Everything joins on the **guest virtual address (PC)** — code addresses are fixed by the
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XEX load, identical across our emulator and canary.
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- **Static (cheap, try first):** `xenia-rs/sylpheed.db` (DuckDB: 25 481 functions, xrefs,
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strings, vtables, imports). Query with `xenia-rs/zq.py` — `zq.py grep <str>`,
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`zq.py xref <addr>`, `zq.py dis <lo> <hi>`, `zq.py fn <pc>`. Entry points are usually a
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**string** (`zq.py grep MSG_DEMO`) or an **import** (movie/XMA API) xref'd back to the loader.
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- **Dynamic (when static is ambiguous):** run `xenia-rs` with its probe suite —
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`--pc-probe` / `--audit-pc-probe-hex` (fires at block entry), `--mem-watch` (mid-block
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reads/writes of a VA), `--lr-trace` (call/return chains), `--trace-instructions`,
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`--dump-addr` (read guest memory). These already exist; prefer them over hacking canary.
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- **Oracle (correctness ground truth):** canary — the **Wine cross-build**
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`xenia-canary/build-cross/bin/Windows/Debug/xenia_canary.exe` (the native Linux ELF
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**crashes / does not run** — do not use it). This is the only emulator that reaches the
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in-game menu; our `xenia-rs` never got past the intro video. Use canary to *observe output*
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(capture its framebuffer for texture colours), not usually to instrument code — though its
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`build-cross` toolchain does compile, so small C++ probes + rebuild are possible when needed.
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Run **muted, one emulator process at a time**, point it at the real ISO (not the symlink).
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> ⚠️ **VA-equality caveat:** join **code** by PC (fixed), but **never** assume a data VA
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> holds the same bytes across emulators — allocators differ. Compare data by content/layout.
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