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Castlevania: Symphony of the Night disassembly

Creates a full decompilation in C, that compiles the same binaries as the commercial video game Castlevania: Symphony of the Night for PS1.

The game is divided in three modules: SLUS_000.67 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.

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

Bins decomp progress

SHA-1 checksum File name Progress
54828d4e44ea9575f2a0917ff63def42a304abff SLUS_000.67 N/A
2eac5f7162e77416166c2511c787995488f01c37 DRA.BIN progress DRA.BIN
d076912661e67a38afae0a1b5044ab5f10bcfb39 RIC.BIN progress RIC.BIN
e42976f45b47d1c4912a198ae486b77ee6d77c9c ST/DRE.BIN progress DRE.BIN
adb3303e1ea707c63dfa978511a88cab4f61970a ST/MAD.BIN progress MAD.BIN
5d06216b895ab5ff892c88b0d9eff67ff16e2bd1 ST/NO3.BIN progress NO3.BIN
7c78a2bec6a26acfb62456e7f517915fe0c0e3f5 ST/NP3.BIN progress NP3.BIN
bc2fabbe5ef0d1288490b6f1ddbf11092a2c0c57 ST/ST0.BIN progress ST0.BIN
2ae313f4e394422e4c5f37a2d8e976e92f9e3cda ST/WRP.BIN progress WRP.BIN
3bbdd3b73f8f86cf5f6c88652e9e6452a7fb5992 ST/RWRP.BIN progress RWRP.BIN

How to setup the project (assuming linux ubuntu/debian or windows with WSL)

  • sudo apt-get install gcc-mipsel-linux-gnu binutils-mips-linux-gnu
  • pip install spimdisasm tqdm intervaltree
  • Inside the folder of your choice git clone https://github.com/Xeeynamo/sotn-decomp.git
  • git submodule update --init
  • Inside the newly created repo, create a new iso/ folder, and extract the content of the game disc

How to build

  • Run make extract to generate the assembly files in the asm/ directory
  • Run make all to compile the binaries in the build/ directory you don’t need to use it now but note that make clean deletes the build directory Some non-matching functions are present in the source preprocessed 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.

How to decompile

  • After setup and build, choose an overlay (eg. ST/WRP)
  • Look for one of those function which hasn't successfully decompiled yet (eg. INCLUDE_ASM("asm/st/wrp/nonmatchings/6FD0", func_801873A0);)
  • Look for its assembly file (eg. asm/st/wrp/nonmatchings/6FD0/func_801873A0.s)
  • Run SOURCE=src/st/wrp/6FD0.c make ctx.c then ASSEMBLY=asm/st/wrp/nonmatchings/6FD0/func_801873A0.s make decompile to dump the decompiled code into ctx.c.m2c
  • Replace the INCLUDE_ASM(...); you targeted with the content of ctx.c.m2c
  • run make expected and invoke python3 ./tools/asm-differ/diff.py -mwo --overlay st/wrp func_801873A0 You will probably have some differences from your compiled code to the original; keep refactoring the code and move variables around until you have a 100% match.

There are a few tricks to make the process more streamlined:

  • Use decomp.me with GCC 2.7.2 for PS1. Be aware that the repo is using GCC 2.6.x, so decomp.me will sometimes give a slightly different output.
  • The “context” section of decomp.me, is provided by the cmd SOURCE=src/st/wrp/6FD0.c make ctx.c as mentionned in the how to decompile.
  • Use decomp-permuter to solve some mismatches
  • Use this and this guide to understand how some compiler patterns work
  • Use the #ifndef NON_MATCHING if your code is logically equivalent but you cannot yet fully match it

Resources:

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
  • Integrate ASPSX instead of GNU AS
  • Split binary data (eg. map layout, graphics, other assets) into individual files

Notes

  • 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.
  • 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 have been created with a different compiler and with -O1 rather than -O2