Drew T
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BFM-decomp — the wiki
Brave Fencer Musashi (Square, PlayStation, 1998; USA release SLUS-00726), decompiled to C that rebuilds every shipped code binary byte for byte with the game's own 1990s toolchain. It is the first public decompilation of the game, and the whole of its game code is matched: the main executable, the always-resident engine, every location overlay and every code module streamed from the disc — 218 binaries, each verified by SHA1 against a redump image of the original disc on every build. The repository is github.com/Druthulu/BFM-decomp.
The claim is narrow and machine-checkable: matching means byte-identical output, nothing "functionally equivalent"
counts, and what the repository claims is exactly what make check-all proves. The live numbers are generated into the
README's progress block and docs/progress.json, never typed by hand; at the Phase-33 close
(September 2026) all three metrics — functions, instructions, distinct code — read 100%, with two things deliberately
not our C and stated as such: Sony's PsyQ library objects linked into the main executable (1,256 functions) and five
hand-written assembly routines kept verbatim.
The project was carried out end to end by an AI coding agent (Claude Code) under a written constitution and a two-gate phase system, in twelve weeks. How that was done — and what it cost — is the second half of this wiki.
Using the project
| Page | What it answers |
|---|---|
| Build from your own disc | The six-command recipe, what each step proves, the expected last lines, what to do when one fails |
| Toolchain setup | The pinned compiler/assembler triple and why it is pinned; every tool version; the optional Sony SDK; Ghidra and the emulator |
| Repository layout | What every top-level directory holds, and what is deliberately not in the repository |
| The matching workflow | Draft → gate → bank: the oracle ladder from a masked standalone compile to the whole-binary hash, and how a change is kept honest |
| The dedup engine | Why one matched function banks up to 138 copies: position-locked overlays, signatures, propagation, the registry that fail-closes |
| Overlays and modules | The disc, the 218 binaries, where each loads and how every load address was proven |
| Ghidra rebuild from text | The reverse-engineering database is not in git; here is how it regenerates from text + the disc, and the proof that it does |
| Verification and progress | The contract run, the three metrics and how they are computed, what CI proves without a disc, the published numbers |
| Contributing and the no-ROM policy | What may never enter the repository, what a useful contribution looks like now that the frontier is empty, the license split |
| Tools from this project | xsig, the permuter driver, the codegen map, the decomp.me replica, the drafter write-up — what stands on its own for other projects |
How to AI-decomp
How to AI-decomp — the transferable part: thirteen chapters on running a byte-exact decompilation with AI agents, written from this project's records for the next one (any console, any compiler). Governance, the byte gate, the bootstrap order, oracles and instruments, cards/lanes/waves, the knowledge base, reading the compiler's source, models and budgets, the economics as measured, integration and propagation, publishing, and a museum of the failures that looked right at the time.
The records behind the wiki
Everything here is a summary of files kept as it happened; when a page and a record disagree, the record wins.
docs/story.md— the narrative, first commit to public flip;docs/retrospective.md— what we believed, what failed, what it costdocs/matching-cookbook.md(some 500 compiler idioms, each byte-proven; grep it by section — it is 3.5 MB) and its symptom indexdocs/cookbook-index.md;docs/gcc-2.7.2-map/— the codegen map of the pinned compiler, by passdocs/decision-log.md— every strategic pivot with its measurement and its hindsight;docs/accelerators.md— what would have made earlier phases fasterphase-ends/— one PhaseEnd per phase, the digest of every phase and every rule (DIGEST.md), the per-phase logsdocs/SETUP.md— the environment reference, every tool's row;docs/verification.md— the contract and the last recorded rundocs/memory-map.mdanddocs/formats.md— addresses with provenance; the disc, container, archive and LZSS formats
Brave Fencer Musashi is © 1998 Square. This project is not affiliated with or endorsed by Square Enix. src/ asserts no
license (src/NOTICE.md); the project's own tools and documents are AGPL-3.0 (LICENSE).