Shin Megami Tensei: Digital Devil Saga 1 & 2

A work-in-progress matching decompilation of Shin Megami Tensei: Digital Devil Saga and Digital Devil Saga 2 for PlayStation 2. The goal is to understand and document how the games work by reconstructing readable source code from their retail binaries. Matching builds verify the reconstruction against the original executables.

[!IMPORTANT] This is a binary reconstruction and analysis project for understanding and documenting how the games work. You cannot use this repository to play the games; it is not a port.

Building requires your own lawfully obtained copy of the corresponding game. Required files are extracted locally from your copy. Disc images and retail executables are not included.

Status and versions

Unfinished functions use assembly extracted from the original executable, so a matching build does not mean the decompilation is complete. Names, types, and source organization are still being recovered.

Version	Game	Serial	ELF SHA-1
dds1	Digital Devil Saga (USA)	SLUS_209.74	6d18898e2724bf1d145392766e8ba1e678487419
dds2	Digital Devil Saga 2 (USA)	SLUS_211.52	9be91ee1b4a535a4cb6ec89237b5a6ba41be2add

The badges track production-exact, source-owned game/engine code bytes and function counts for each game. Assembly fallbacks receive zero source credit. SDK/runtime code, handwritten assembly segments and VU1 microcode are outside those totals. Reading progress explains the measurements and comparison limits.

Quickstart

Requirements:

• Linux x86-64 or WSL2, with support for running 32-bit i386 programs.
• Python 3.10+, ninja, cpp, and git.
• Your own disc image of either supported game.

git clone https://github.com/Megami-Decomps/dds-decomp.git
cd dds-decomp
python -m pip install -r requirements.txt
python tools/download_tools.py

# Copy your disc image(s) into the repository root or orig/, then:
python tools/extract.py
python configure.py
ninja

ninja builds every extracted version and checks each executable against its retail SHA-1. Use ninja dds1 or ninja dds2 to build one game. A checksum mismatch fails the build.

Script and data sources are retail content and are not in the repository; see Building for importing them from your own disc image, plus the optional script, data, and development targets, generated files, and checksum troubleshooting. The toolchain notes explain the original compiler, assembler, and pinned 32-bit runtime.

Documentation and contributing

Start with the contribution guide and confirmed source idioms to reconstruct a function. Pick an INCLUDE_ASM function, replace it with readable C, check the whole unit with tools/check_unit.py, and verify that ninja still produces a matching executable.

DDS2 reuses much of DDS1's engine. The contribution guide also covers sharing reconstructed functions between games and recovering names and types.

The documentation index groups the available references:

• Code reconstruction: matching workflow, compiler behavior, and unit names.
• Scripts: compiled VM scripts and editable source.
• Field resources: interaction and transition tables, field formats, automaps, lighting, archives, and textures.
• Battle data: encounter and battle content tables.
• Development builds: experimental relocatable executables.

Acknowledgements

• splat, spimdisasm, m2c and objdiff
• decomp.me for the ee-gcc 2.96 toolchain packaging
• the Persona 3/4 decompilation projects, for SDK layout and naming conventions
• romwright, for analysis and cross-game pairing