Resident Evil 4 (GameCube) – complete byte-identical decompilation to C/C++

A complete, byte-identical decompilation of Resident Evil 4 for the Nintendo GameCube: the G4BE08 debug build (the "Nov 25 2004" prototype, both discs), whose Bio4.sym files name every function. Building the repository reproduces main.dol and all 114 REL overlays exactly (config/G4BE08/build.sha1, checked on every build).

The repository contains no game assets and no code or data copied from the discs. You need your own images of the debug discs to build (disc 1 for main.dol and most RELs, disc 2 for the four island-stage RELs); the original files are read from them at configure time.

Building

Linux, Python 3, ninja. Compilers and tools (decomp-toolkit, objdiff, wibo, the CodeWarrior builds) are downloaded by the first configure run, except the native SN GCC:

# 1. the native cc1/cc1plus (once): needs SN's GPL source drop, see tools/sn-gcc/build.sh
SN_GCC_SRC=/path/to/NGC_GNU_SRC/NGC tools/sn-gcc/build.sh

# 2. your disc images (disc 1: main.dol + 110 RELs; disc 2: the four island-stage RELs st3_0..st3_3)
cp re4_debug_disc1.iso re4_debug_disc2.gcm orig/G4BE08/

# 3. build and verify
python3 configure.py && ninja

ninja ends with the progress report (100% matched and linked for the DOL and the REL modules); build/tools/dtk shasum -c config/G4BE08/build.sha1 prints 115 OK lines. To work on a unit, python3 tools/bytecmp.py game/foo compares its object with the original word by word and python3 tools/fdiff.py game/foo <symbol> shows one function.

Layout

• src/game/ — the game (C++; a few newlib C units). src/em*/ enemies, src/wep*/ weapons, src/pl*/ player characters, src/st*/ rooms (one REL per room), src/t_*/, src/Tools/, src/tools/ the in-game debug editors, src/Sscrn/ the sub-screens, src/lib/ SDK, CRI and runtime.
• include/ — headers, including the reconstructed struct layouts.
• config/G4BE08/ — unit lists (objects.py, modules.py), symbols.txt, splits.txt, linker scripts, per-module REL data (modules/<mod>/), build.sha1.
• tools/ — build generator (project.py), the ProDG driver (ngccc.py), REL rebuild (make_rel.py, link_rel.py), the compare tools, sn-gcc/ (native compiler build), research/ (compiler-analysis kit), motion_export.py + motion/ (animation export to glTF/BVH, evaluated with the game's own code and verified against the game running in Dolphin).
• docs/overview.md — how the engine is put together: a reading guide to src/ by subsystem.
• docs/matching.md — how the matching was done: compiler provenance, the catalogue of compiler mechanisms and the source shapes that reproduce them, rules of thumb for both compilers. docs/unit-notes.md — per-unit notes. docs/research/ — the pass-by-pass research log.

What "matching" means here

Every unit compiles to the original bytes with the original compilers. Where the compiler needed a particular source shape to reproduce a register choice or a schedule and no natural spelling was found, the construct is marked with a // COMPILER-DIFF: comment (644 of them: dead tests, empty asm("") launders and anchors, register T x asm("rN") pins, padding statements). None of them emits an instruction: python3 tools/asmcheck.py --all compiles every GCC unit with its asm templates marked and lists the instructions that came from a template — the only hits are the hardware kernels below (TOTAL 231; the eight asm-bodied units are reported on their own line and kept out of that number). An earlier state of this tree had ~100 hand-placed instructions (asm("li %0,0"), asm("lis/addi"), asm("mr")) in the game code and ~100 register-pinning asm { } blocks in the CRI libraries; they were replaced by C on 2026-09-17 (docs/research/compiler.md, section "Asm-removal pass", records the recipe and the compiler mechanism per site). Each tag's mechanism is documented in docs/matching.md and docs/research/.

Assembly that remains, all of it code the original authors also wrote in assembly because their compilers had no other way to express it:

• GCC 2.95 game code: paired-single kernels (SINF/COSF/RSQRT/LIMIT_ANGLE in math_sub, the matrix kernels in trans, shape, dbmodule, quantised psq_l in Espgen42/espgen45), the GQR setup in main/scheduler, and the libsn sndvd exception handler.
• MWCC CRI libraries: the paired-single / cache / SPR kernels (mpv_umc, mpv_mc, dct_fsri, cftyp422_ppc, mpv_lib), the SDK's mtx/vec/quat/GX intrinsics, and one register-steering block in dct_ac (dctac_Init: the vendor's compiler build pooled .bss but not the function's 8-byte literals; ours pools both). Codeless asm { mr r11, x; mr x, r11 } pins (both moves are deleted by the allocator; they narrow the colour set by one register) and asm { mr v, v } self copies (an opaque second definition) remain in 27 places.
• Eight asm-bodied units: crt0 (__start), eabi, SN's tealeaf/fileserver/ppcdown/proview (src/lib/<name>.c), and Capcom's memset_2 and yz2asm (src/game/<name>.cpp). The originals were assembly (SN's libsn/crt0 objects and Capcom's own asm; no compiler idiom in the bytes), so each is a C file whose functions are whole-function top-level asm() bodies in GAS syntax (.globl/.type/label/.size, local .L_ labels, .4byte/.float/.skip data), compiled by the same ProDG driver as the rest (include/asm_regs.h supplies the r3/f1/GQR0 names as .set constants; NgcAs takes bare numbers). tools/asmcheck.py lists them as asm-bodied.

Naming

Function names are Capcom's, from the debug build's Bio4.sym files; they are C++-mangled, which is why the game code is C++ and the SDK, CRI and newlib units are C. File names and unit boundaries come from the D:/Bio4/Prog/<file>.cpp strings the asserts left in the binaries. Struct and field names are of three kinds: the vendor's, from the PS2 debug build's type information (matched to the GameCube layouts by tools/ps2sym.py); ours, named from usage and marked as such; and placeholders xNN (offset in hex, meaning unknown). Vendor names keep the vendor's spelling, so the tree mixes conventions on purpose. #line directives reproduce the vendor's line numbers in the assert strings. docs/naming.md has the full account and the counts.

Contributing

CONTRIBUTING.md: build, the three verification checks, the rules (bytes never change, no instruction-emitting asm, naming), and how to propose a rename with evidence.

Legal

The reconstructed game and SDK source is the intellectual property of its respective owners (Capcom, Nintendo, CRI Middleware) and is published for research and preservation only. The build scripts, tools and documentation written for this project are released under CC0 (LICENSE).