Debugging ndk libraries

Use this with gdb to load debugging symbols of android libraries into your session https://stackoverflow.com/a/33087762.

You get the load address with https://github.com/minecraft-linux/mcpelauncher-linker/blob/5127987ca49c4aeca6d180f26a9a4ac5aa4501c2/src/linker.cpp#L21. Minecraft's load address is printed to the log as a hex number.

codelldb

Works on linux, macOS and windows on both arm64 and intel

  1. Install vscode
  2. Install codelldb extension
  3. Compile the launcher with -DCMAKE_BUILD_TYPE=Debug
  4. Add the following property (only the python api seem to ignore that we load debug info of .so files into a macOS / windows process) 
    "preRunCommands": [
    "breakpoint set --name mcpelauncher_linker_notifylldb -C \"script lldb.debugger.GetSelectedTarget().SetModuleLoadAddress(lldb.debugger.GetSelectedTarget().AddModule(lldb.process.ReadCStringFromMemory(lldb.frame.FindVariable('filename').unsigned, 255, lldb.SBError()), '', ''), lldb.frame.FindVariable('offset').unsigned)\" --auto-continue true",
]
    mcpelauncher-linker exposes this function used as an automated breakpoint and calls it before calling the constructor of the game, the address is available in the cli output as well.
  5. Enjoy having step debugging in mods compiled with debug information and better stack traces of the minecraft game

Development Utilities

Use readelf to list symbols of libminecraftpe.so

readelf --wide -s libminecraftpe.so

Symbols with prefix java_ are callable java native interface functions.

Use dextojar on classes.dex of the android apk + https://java-decompiler.github.io/ on the jar file to get an idea how mojang implemented the java functions.

Glcore patch

The Glcore patch is a patch to modifiy the android game to render on opengl 3.3 surfaces instead of opengl es 2, which is unavailable on macOS.

Due to absense of debugging symbols, is this patch unavailable on 1.17+ and macOS builds use a fallback via an opengl es2 emulation layer called angle. The goal of this section is to document how such a binary pattern has been created for 1.16.0.

To create such binary pattern to be able to find the required function without the debugging symbols, you might be able to use this ida pro plugin https://github.com/ajkhoury/SigMaker-x64.

For example here two patterns and the actual required function name of the game https://github.com/minecraft-linux/mcpelauncher-client/blob/eb2465a1f59422b1cf11d14b9838eeb5d5c32237/src/gl_core_patch.cpp#L22. This symbol can be found via readelf on 1.16.201.