3.8 KiB
Modding
Modding Minecraft: Pi Edition is possible by patching the binary at runtime. To make this easier minecraft-pi-docker includes a libary called libcore.so which provides several functions to help you patch the game.
Hex Addresses
Minecraft: Pi Edition has no symbols so you must patch the hex address of an instruction instead of using a function name. Hex addresses can be found using tools like Ghidra or RetDec. To find out what a function does, you can find its equivalent in Minecraft: Pocket Edition 0.6.1 and use its name for reference because Minecraft: Pocket Edition 0.6.1 includes symbols.
Loading Directories
minecraft-pi-docker loads mods from two locations, /app/minecraft-pi/mods, and ~/.minecraft/mods. The first location only exists in the Docker container and is immutable, so you should place your mods in ~/.minecraft/mods which is mounted on the host as ~/.minecraft-pi/mods.
C++ Strings
Minecraft: Pi Edition was compiled with an old version of GCC, so when interacting with C++ strings, make sure you set -D_GLIBCXX_USE_CXX11_ABI=0.
libcore.so API
Header files and the shared library can be download from Jenkins.
void overwrite(void *start, void *target)
This method replaces a function with another function.
Parameters
- start: The function you are replacing.
- target: The function you are replacing it with.
Return Value
None
Warning
This should never be used on functions that are only 1 byte long because it overwrites 2 bytes.
Example
static int func_injection(int a, int b) {
return a + 4;
}
__attribute__((constructor)) static void init() {
overwrite((void *) 0xabcde, func_injection);
}
void overwrite_call(void *start, void *original)
This allows you to overwrite a specific call of a function rather than the function itself. This allows you to call the original function. However, this does not effect VTables.
Parameters
- start: The address of the function call to overwrite.
- target: The function call you are replacing it with.
Return Value
None
Warning
This method can only be safely used 512 times in total.
Example
typedef int (*func_t)(int a, int b);
static func_t func = (func_t) 0xabcde;
static void *func_original = NULL;
static int func_injection(int a, int b) {
(*func)(a, b);
return a + 4;
}
__attribute__((constructor)) static void init() {
overwrite_call((void *) 0xabcd, func_injection);
}
void overwrite_calls(void *start, void *original)
This allows you to overwrite all calls of a function rather than the function itself. This allows you to call the original function. However, this does not effect VTables.
Parameters
- start: The function call to overwrite;
- target: The function call you are replacing it with.
Return Value
None
Warning
This method can only be safely used 512 times in total.
Example
typedef int (*func_t)(int a, int b);
static func_t func = (func_t) 0xabcde;
static void *func_original = NULL;
static int func_injection(int a, int b) {
(*func)(a, b);
return a + 4;
}
__attribute__((constructor)) static void init() {
overwrite_calls((void *) func, func_injection);
}
void patch(void *start, unsigned char patch[])
This allows you to replace a specific instruction.
Parameters
- start: The target instruction.
- patch: The new instruction (array length must be 4).
Return Value
None
Example
__attribute__((constructor)) static void init() {
unsigned char patch_data[4] = {0x00, 0x00, 0x00, 0x00};
patch((void *) 0xabcde, patch_data);
}