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MRuby Decompiler

This is a decompiler for MRuby byte code. It's made for the MRuby version from 2015 (Rite binary version 0030). It can decompile about 70% of opcodes. The outputs currently are not 100% optimal and can still be optimized, but good enough for now. The main reason I made this is to decompile MRuby scripts for the game NieR:Automata. So it's mostly focused on the game's script files.

If you need auto recompiling for NieR Modding, check out NierAutoRebuild.

Usage

__init__.py can both compile and decompile Ruby/MRB files. This repository comes with precompiled mruby binaries.

1. Without command line

Drag any RB/MRB/BIN files or folder you want onto the __init__.py file. This will automatically (de-)compile them.
If it's a folder, it will decompile all files in the folder.

2. With command line

python __init__.py <file1> <file2> <folderX> ...

3. Compile tool to frozen executable (binary)

You can compile the main script to an executable, if you want to be python independent.

Currently supports Windows and Linux "python" is your Python 3 interpreter

In order to use, first install required dependencies... (feel free to make a "virtual environment")

python -m pip install -r requirements.txt

Next, run the build script.

python build_release.py

Once this is done, you can find your executable (or binary) in the dist folder. If you are on Linux, feel free to use chmod to give it the permissions it deserves :)

Issues and things to watch out for

  • For most function calls inside classes, modules, etc. the decompiler prefixes them with self. which can usually be omitted.
  • Simple where (aka switch) statements work mostly fine, but more complicated ones are a bit buggy.
  • Anything in general involving JMP opcodes (if, else, while, where statements) might not be 100% accurate, but good enough for most cases.
  • Since JMP opcodes don't have a representation in Ruby, when an unhandled JMP opcode is encountered, a warning is printed and instead an exception is thrown in the output code.
  • Some patterns (like exp1 && exp2 and if exp1 then exp2) are indistinguishable in the byte code. These kinds of patterns are currently not optimized for.
  • Since in Ruby everything has a return value and return values in general are a bit funny, you might see some random useless symbols in the output.