83 lines
2.9 KiB
Markdown
83 lines
2.9 KiB
Markdown
# Modding
|
|
Modding Minecraft: Pi Edition is possible by patching the binary at runtime. To make this easier ``minecraft-pi-dcoker`` 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](https://ghidra-sre.org) or [RetDec](https://retdec.com). 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``.
|
|
|
|
## ``libcore.so`` API
|
|
Header files and the shared library can be download from [Jenkins](https://jenkins.thebrokenrail.com/job/minecraft-pi-docker/job/master/lastSuccessfulBuild/artifact/out/lib).
|
|
|
|
### ``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
|
|
The original contents of the function.
|
|
|
|
#### Warning
|
|
This should never be used on functions that are only 1 byte long because it overwrites 2 bytes.
|
|
|
|
#### Example
|
|
```c
|
|
static int func_injection(int a, int b) {
|
|
return a + 4;
|
|
}
|
|
|
|
__attribute__((constructor)) static void init() {
|
|
overwrite((void *) 0xabcde, func_injection);
|
|
}
|
|
```
|
|
|
|
### ``void revert_overwrite(void *start, void *original)``
|
|
This allows you to revert ``overwrite()``. This can be used to call the original version of a function.
|
|
|
|
#### Parameters
|
|
- **start:** The function that was overwritten.
|
|
- **original:** The return value of ``overwrite()``.
|
|
|
|
#### Return Value
|
|
None
|
|
|
|
#### Example
|
|
```c
|
|
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) {
|
|
revert_overwrite((void *) func, func_original);
|
|
(*func)(a, b);
|
|
revert_overwrite((void *) func, func_original);
|
|
|
|
return a + 4;
|
|
}
|
|
|
|
__attribute__((constructor)) static void init() {
|
|
func_original = overwrite((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
|
|
```c
|
|
__attribute__((constructor)) static void init() {
|
|
unsigned char patch_data[4] = {0x00, 0x00, 0x00, 0x00};
|
|
patch((void *) 0xabcde, patch_data);
|
|
}
|
|
```
|