Castlevania: Symphony of the Night disassembly

Recompilable code that creates 1:1 binaries for the commercial videogame Castlevania: Symphony of the Night for the PlayStation 1. This repository aims to create a full decompilation in C.

Game revision

All the files refers to the SLUS-00067 version of the game.

SHA-1 checksum	File name	Progress
54828d4e44ea9575f2a0917ff63def42a304abff	main.exe	N/A
2eac5f7162e77416166c2511c787995488f01c37	DRA.BIN
d076912661e67a38afae0a1b5044ab5f10bcfb39	RIC.BIN
e42976f45b47d1c4912a198ae486b77ee6d77c9c	ST/DRE.BIN
adb3303e1ea707c63dfa978511a88cab4f61970a	ST/MAD.BIN
5d06216b895ab5ff892c88b0d9eff67ff16e2bd1	ST/NO3.BIN
7c78a2bec6a26acfb62456e7f517915fe0c0e3f5	ST/NP3.BIN
bc2fabbe5ef0d1288490b6f1ddbf11092a2c0c57	ST/ST0.BIN
2ae313f4e394422e4c5f37a2d8e976e92f9e3cda	ST/WRP.BIN
3bbdd3b73f8f86cf5f6c88652e9e6452a7fb5992	ST/RWRP.BIN

Build

1. You need gcc-mipsel-linux-gnu that you can easily install on any Debian-based Linux distribution. On Windows it is highly recommended to just use Ubuntu with WSL
2. Place your main.exe from the file SLUS_000.67, DRA.BIN and the ST folder in the root directory of the repository
3. Run make extract to generate the assembly files
4. Run make all to compile the binaries into the build/ directory

Check for function matching

Thanks to asm-differ you can check if a funtion written in C matches its assembly counterpart.

1. Be sure to resolve the submodule with git submodule update --init
2. Ensure to create a matching binary with make clean && make extract && make all && mkdir expected && cp -r build expected/
3. Choose a function to match (eg. func_8018E964), an overlay (eg. st/mad) and then invoke python3 ./tools/asm-differ/diff.py -mwo --overlay st/mad func_8018E964

Non-matching build

Some non-matching functions are present in the source code by disabled by the macro NON_MATCHING. You can still compile the game binaries by running CPP_FLAGS=-DNON_MATCHING make. In theory they might be logically equivalent in-game, but I cannot promise that. Few of them could match by tuning or changing the compiler.

Restore MAD (debug room)

The debug room overlay ST/MAD.BIN was compiled earlier than the first retail release of the game. All the offsets that refers to DRA.BIN points to invalid portions of data or to the wrong API calls, effectively breaking the majority of its original functionalities. That is why the debug room does not contain any object. By compiling the debug room with make mad_fix you can restore it by redirecting the old pointers to the retail version of the game.

Be aware that not all the offsets have been yet redirected, so it will still be not entirely functional until further update.

Technical details

The game is divided in three modules:

• main is the game engine of the game. It contains all the necessary logic to interact with the gamepad, CD, memory card, the SPU and to render the sprites on-screen. It appears to not contain any game logic by itself.
• DRA is the game itself. It contains the gameloop and the necessary API to draw maps, entities, load levels, handle entities, animations and collisions. It also contains some common data such as Alucard's sprites, candle's sprites and the common rooms' (save, loading, teleport) layout.
• ST/ are the overlays for each area. An area (eg. Castle's entrance, Alchemy Laboratory, etc.) contains all the unique logic to handle map's specific events, cutscenes, enemies' AI, collisions and more. It also contains the rooms and entities layout.

Notes

• I suspect that GCC 2.6.x / PSY-Q 3.4 have been used to originally compile DRA.BIN
• main.exe uses PS-X libraries that might've been created with a different compiler and with -O1 rather than -O2

To do

The project is very barebone at the moment and there is a massive room of improvement, mostly in the infrastructure:

• Not all the zone overlays (ST/{ZONE}/{ZONE}.BIN) are disassembled
• There is no CI/CD pipeline to test the correctness of the compiled code
• GNU AS might produce incorrect result. ASPSX might need to be used instead as a workaround.