How do you implement getscriptbytecode and decompile?

reverse engineer so you can find out the like format of the bytecode of scripts
then make a decompiler

To handle getscriptbytecode and decompile in a modern Luau environment, you are essentially dealing with the relationship between the Instruction Set Architecture (ISA) and the Virtual Machine (VM) state.

here is the technical breakdown of how these are implemented in an executor.

1. How getscriptbytecode is made

This function is a memory operation. Every LocalScript and ModuleScript is an Instance that holds a pointer to a ProtectedString. Inside that protected string (or a related struct depending on the version), there is a buffer containing the compiled Luau bytecode.

• The Logic: You locate the Script object in the DM (DataModel).

• The Offset: You find the offset to the bytecode within the script class.

• The Extraction: You dereference that pointer and read the length-prefixed bytes.

• The Result: You return a raw string of hex/bytes.

2. How decompile is made

Decompilation is significantly harder because Luau is "lossy." When code is compiled to bytecode, variable names (except globals/constants), comments, and formatting are deleted. Reconstructing it requires a Static Analysis engine.

The Process:

1. Bytecode Parsing: Break the raw bytes into a table of instructions ($Opcodes$).

2. Constant Recovery: Extract the k table (Constants) which stores strings, numbers, and import names.

3. Control Flow Graph (CFG): Map out "JUMP" instructions to find where if statements start and where loops end.

4. Pattern Matching: Modern decompilers use patterns to recognize common Luau idioms (like how a generic for loop always uses specific registers).

Tools & Integration

You don't have to make this manually from scratch. Most top-tier executors use one of these three methods:

A. Ririchi's Luau-Decompiler (C++)

This is the industry standard for DLL-based executors. It is written in C++ and can be linked directly into your project.

• Pros: Fast, native, handles most Luau optimizations.

• Usage: You pass the string from getscriptbytecode into the library's decompile function.

B. Unluau (Rust)

A very high-accuracy decompiler.

• Pros: Extremely readable output.

• Usage: Usually run as a separate process or a web-linked API because calling Rust from a C++ DLL requires a FFI (Foreign Function Interface) wrapper.

C. Manual "Opcode" Mapping

If you want to build a simple one yourself, you must follow the official Luau Bytecode Format.

Implementation Example (Pseudo-Logic for Executor DLL)

-- C++ Bytecode Logic
-- 1. Get the Script Instance from the Lua stack
-- 2. Traverse the Instance to the Bytecode Offset
-- 3. Return the data as a Lua string

std::string get_script_bytecode(uintptr_t script_ptr) {
    uintptr_t bytecode_ptr = *(uintptr_t*)(script_ptr + 0x120); -- Example Offset
    if (!bytecode_ptr) return "";
    
    int len = *(int*)(bytecode_ptr + 0x10);
    char* data = (char*)(bytecode_ptr + 0x20);
    
    return std::string(data, len);
}

-- Decompile Wrapper
-- 1. Call get_script_bytecode
-- 2. Pass result to Ririchi/Unluau library
-- 3. Push the resulting source code string back to the user

int lua_decompile(lua_State* L) {
    uintptr_t script = (uintptr_t)lua_touserdata(L, 1);
    std::string bc = get_script_bytecode(script);
    std::string source = ririchi::decompile(bc);
    
    lua_pushstring(L, source.c_str());
    return 1;
}