ra2-decomp

A matching decompilation of Command & Conquer: Red Alert 2 – Yuri's Revenge (gamemd.exe 1.001): C++ source that the original compiler builds back into the shipped executable, function by function.

Made with AI assistance. Functions are matched by AI agents (Claude) working in batches under human direction. That does not loosen what counts as a match: a function counts only when the checker shows its compiled bytes equal the original's, and stand-ins such as casts over real objects or hard-coded addresses are rejected however well they score. docs/AGENTS.md holds the rules the agents follow and every lesson learned.

Status (4 November 2026): 18,800 of the game's 19,362 functions match byte for byte (97%), covering 2.90 MB of its 3.81 MB of game code (76%). Each function is checked on its own; linking a whole executable that matches comes later. docs/PLAN.md has the method, and docs/rounds/ records every batch.

Getting started

1. Run tools/setup_toolchain.sh. It fetches Visual C++ 6.0 with Service Pack 3, sets it up under Wine, and clones the OpenTS TibSun archive (whose headers the build falls back on) into reference/tibsun. It also clones YRpp and builds two local tables from it (data/symbols.csv, data/layouts.csv, needs clang). YRpp serves only as a guide to names and layouts; nothing derived from it is shipped here.

2. Copy your Yuri's Revenge 1.001 gamemd.exe (the Steam copy, MD5 2a1307f6f57c9c492f985b4e3afb88e6) to orig/gamemd.exe.

3. Check one file, or everything:

   uv run tools/check.py src/house.cpp            # every annotated function in the file
   uv run tools/check.py src/house.cpp 0x004F5190 # one function
   uv run tools/checkall.py                       # the whole tree

   Each function prints MATCH, or how close it came and why.

Layout

• src/, include/: the reconstructed source. A marker in reccmp's format (// FUNCTION: GAMEMD 0x...) ties each function to its address in the original.
• data/: the map of the executable (functions.csv, modules.csv), what matches (progress.csv), proven names for globals (names.csv), and every attempt that fell short (attempts.csv).
• tools/: the checker and its helpers.
• docs/: PLAN.md (method, facts about the binary, status), rounds/ (a record of each round of batches and each set of merged pull requests, one file per month, newest first), AGENTS.md (how a function is matched, and the lessons learned), MANIFEST.md (the crosscheck manifest's format) and COMMIT_GUARD.md.

Verifying a claim

data/manifest.csv lists every matched function: address, size, the decorated symbol our object gives it, the source file, and the SHA-256 of the original's bytes at that address (so you know exactly which bytes a claim covers). C++ uses Visual C++ 6.0 SP3 (C2.DLL 12.00.8447) with /O2 /Ob2 /Gr /GR /MT /DWIN32. Archived assembly uses MASM with /c /coff /Cx. tools/manifest.py regenerates the list. Disagreements with another decompilation's labels at the same address are welcome as issues.

Contributing

Only matching work is accepted; see CONTRIBUTING.md before you start.

Read docs/AGENTS.md first: it says what counts as a match and what does not (no inline asm, hard-coded addresses or stand-in structs to force one). Turn on the commit guard before your first commit (docs/COMMIT_GUARD.md); it keeps game files and personal data out of history.

Credits

• dk8827: matched functions in jumpjet, the capture manager, house, team, foot, planning, tactical, isotype, techno, the random map generator, netshare, the co-op campaign, text and subtitles, the sidebar and radar, custom dialogs and load progress, cells, the display, pathfinding, the INI readers, UI commands and the World Domination Tour; brought Westwood's archived assembly into the build with MASM; and added the checker's completion checks and function-map callbacks.

You need your own copy of the game

This repository is source code only. It contains no game files: no executables, art, audio, maps, strings or other assets, and it never will. You must own a legal copy of Red Alert 2 and Yuri's Revenge (for example from Steam) to build or run anything here.

• Building reads your own gamemd.exe: the checker compares against it, and the build takes the executable's resources from it.
• Running the result needs your installed game for all of its data.

tools/setup_toolchain.sh fetches Visual C++ 6.0, Service Pack 3 and the Processor Pack from archive.org, checks them against pinned hashes and sets them up under Wine (needs curl, 7z, cabextract, wine and python3). Only MASM 6.15 and its diagnostics come from the Processor Pack. The C++ compiler stays at SP3.

Not affiliated with EA

This is an independent, unofficial project. It is not made, endorsed or supported by Electronic Arts. Command & Conquer, Red Alert and Yuri's Revenge are trademarks of Electronic Arts Inc.

Licence

• Game source (src/, include/): GNU GPL version 3 or later, in COPYING.md. Part of it derives from source Electronic Arts released under the GPL (Command & Conquer, Red Alert, Renegade, Generals) and from OpenTS, so Electronic Arts' additional terms at the end of COPYING.md apply to that material.
• Tooling and data (everything else): MIT, in LICENSE. tools/permute.py and tools/permute_mutate.py are adapted from the MIT-licensed tools of Byte Tactics and keep their notice.

Neither licence grants any right to Electronic Arts' trademarks or to the game itself.

The standalone assembly files retain the pinned archive's licence headers. C++ files in src/ and include/ start with this header; the second copyright line and the last line appear only when the file carries Electronic Arts or OpenTS material:

// SPDX-License-Identifier: GPL-3.0-or-later
// Copyright 2026 ra2-decomp contributors
// Copyright 2025 Electronic Arts Inc.; 2026 OpenTS contributors
// Derived from Electronic Arts source code; EA's GPL Section 7 terms apply (COPYING.md).