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GhidraBoy: Sharp SM83 / Game Boy extension for Ghidra

Very experimental! No compatibility guarantees!

Ghidra version: Ghidra 10.1_PUBLIC_20211210

Tetris disassembly

Features

  • Sharp SM83 (CPU core used in Game Boy) support for Sleigh
  • Game Boy ROM loader:
    • Can load unbanked ROMs (<= 32kB, e.g. Tetris)
    • Can load banked ROMs (> >32kB, e.g. Pokemon)
    • Can load greyscale boot ROMs (DMG/DMG0/MGB/SGB/SGB2)
    • Can load color boot ROMs (CGB/CGB0)
  • Memory blocks based on the hardware memory map
    • Banked regions use overlays (TODO: figure out if there's a better way to support them)
    • GB vs GBC differences are handled (e.g. banked WRAM)
  • Symbols for hardware registers (0xFFxx range)
    • GB vs GBC differences are handled (e.g. existence of KEY1 register)
  • Game Boy cartridge header data types
    • Enumerated types for some things

How to install

  1. Download a prebuilt GhidraBoy release, or build it yourself.
  2. Start Ghidra
  3. File -> Install Extensions
  4. Press the plus icon ("Add extension")
  5. Choose the built or downloaded GhidraBoy zip file
  6. Restart Ghidra when prompted to load the extension properly

How to build

As a prerequisite, you need to have a Ghidra installation somewhere (an actual installation, not a copy of Ghidra source code!).

export GHIDRA_INSTALL_DIR=/path/to/ghidra
./gradlew

or

./gradlew -Pghidra.dir=/path/to/ghidra

You can then find a built extension .zip in the build/distributions directory.

Open questions / problems

  • Decompiler output is difficult to read if certain instructions are used (e.g. rotates, JP HL for jumptables)
  • Default "ASM calling convention" assumes all registers can be inputs and/or outputs. Inputs/outputs are often guessed incorrectly, so manual tuning is required for almost every function
  • Are overlays the only / the best solution for handling banked memory areas? Right now in banked ROMs every function call to 0x4000-0x7fff needs to be manually resolved to the correct bank(s)

License

Licensed under the Apache License, Version 2.0.