LuaPytecode/luac.py

import struct
import array
from enum import IntEnum, Enum, auto


class InstructionType(Enum):
    ABC = auto(),
    ABx = auto(),
    AsBx = auto()

class ConstType(IntEnum):
    NIL     = 0,
    BOOL    = 1,
    NUMBER  = 3,
    STRING  = 4,

class Instruction:
    def __init__(self, type: InstructionType, name: str) -> None:
        self.type = type
        self.name = name
        self.opcode: int = None
        self.A: int = None
        self.B: int = None
        self.C: int = None

    def toString(self):
        instr = "%10s" % self.name
        regs = ""

        if self.type == InstructionType.ABC:
            regs = "%d %d %d" % (self.A, self.B, self.C) 
        elif self.type == InstructionType.ABx or self.type == InstructionType.AsBx:
            regs = "%d %d" % (self.A, self.B)

        return "%s : %s" % (instr, regs)

class Constant:
    def __init__(self, type: ConstType, data) -> None:
        self.type = type
        self.data = data

class Local:
    def __init(self, name: str, start: int, end: int):
        self.name = name
        self.start = start
        self.end = end

class Chunk:
    def __init__(self) -> None:
        self.constants: list[Constant] = []
        self.instructions: list[Instruction] = []
        self.protos: list[Chunk] = []

        self.name: str = "Unnamed proto"
        self.frst_line: int = 0
        self.last_line: int = 0
        self.numUpvals: int = 0
        self.numParams: int = 0
        self.isVarg: bool = False
        self.maxStack: int = 0

        self.upvalues: list[str] = []
        self.locals: list[Local] = []

    def appendInstruction(self, instr: Instruction):
        self.instructions.append(instr)

    def appendConstant(self, const: Constant):
        self.constants.append(const)

    def appendProto(self, proto):
        self.protos.append(proto)

instr_lookup_tbl = [
    Instruction(InstructionType.ABC, "MOVE"),  Instruction(InstructionType.ABx, "LOADK"), Instruction(InstructionType.ABC, "LOADBOOL"),
    Instruction(InstructionType.ABC, "LOADNIL"), Instruction(InstructionType.ABC, "GETUPVAL"), Instruction(InstructionType.ABx, "GETGLOBAL"),
    Instruction(InstructionType.ABC, "GETTABLE"), Instruction(InstructionType.ABx, "SETGLOBAL"), Instruction(InstructionType.ABC, "SETUPVAL"),
    Instruction(InstructionType.ABC, "SETTABLE"), Instruction(InstructionType.ABC, "NEWTABLE"), Instruction(InstructionType.ABC, "SELF"),
    Instruction(InstructionType.ABC, "ADD"), Instruction(InstructionType.ABC, "SUB"), Instruction(InstructionType.ABC, "MUL"),
    Instruction(InstructionType.ABC, "DIV"), Instruction(InstructionType.ABC, "MOD"), Instruction(InstructionType.ABC, "POW"),
    Instruction(InstructionType.ABC, "UNM"), Instruction(InstructionType.ABC, "NOT"), Instruction(InstructionType.ABC, "LEN"),
    Instruction(InstructionType.ABC, "CONCAT"), Instruction(InstructionType.AsBx, "JMP"), Instruction(InstructionType.ABC, "EQ"),
    Instruction(InstructionType.ABC, "LT"), Instruction(InstructionType.ABC, "LE"), Instruction(InstructionType.ABC, "TEST"),
    Instruction(InstructionType.ABC, "TESTSET"), Instruction(InstructionType.ABC, "CALL"), Instruction(InstructionType.ABC, "TAILCALL"),
    Instruction(InstructionType.ABC, "RETURN"), Instruction(InstructionType.AsBx, "FORLOOP"), Instruction(InstructionType.AsBx, "FORPREP"),
    Instruction(InstructionType.ABC, "TFORLOOP"), Instruction(InstructionType.ABC, "SETLIST"), Instruction(InstructionType.ABC, "CLOSE"),
    Instruction(InstructionType.ABx, "CLOSURE"), Instruction(InstructionType.ABC, "VARARG")
]

# at [p]osition, with [s]ize of bits
def _get_bits(num, p, s):
    # convert number into binary first 
    binary = bin(num) 

    # remove first two characters 
    binary = binary[2:] 

    # fill in missing bits
    for i in range(32 - len(binary)):
        binary = '0' + binary

    start = len(binary) - (p+s)
    end = len(binary) - p

    # extract k  bit sub-string 
    kBitSubStr = binary[start : end]

    # convert extracted sub-string into decimal again 
    return (int(kBitSubStr,2))

class LuaUndump:
    def __init__(self):
        self.rootChunk: Chunk = None
        self.index = 0

    @staticmethod
    def dis_chunk(chunk: Chunk):
        print("\n==== [[" + str(chunk.name) + "'s constants]] ====\n")
        for z in range(len(chunk.constants)):
            i = chunk.constants[z]
            print(str(z) + ": [" + i.type.name + "] " + str(i.data))

        print("\n==== [[" + str(chunk.name) + "'s dissassembly]] ====\n")
        for i in range(len(chunk.instructions)):
            print("[%3d] %s" % (i, chunk.instructions[i].toString()))

        print("\n==== [[" + str(chunk.name) + "'s protos]] ====\n")
        for z in chunk.protos:
            print("** decoding proto\n")
            LuaUndump.dis_chunk(z)
    
    def loadBlock(self, sz) -> bytearray:
        temp = bytearray(self.bytecode[self.index:self.index+sz])
        self.index = self.index + sz
        return temp

    def get_byte(self) -> int:
        return self.loadBlock(1)[0]

    def get_int32(self) -> int:
        if (self.big_endian):
            return int.from_bytes(self.loadBlock(4), byteorder='big', signed=False)
        else:
            return int.from_bytes(self.loadBlock(4), byteorder='little', signed=False)

    def get_int(self) -> int:
        if (self.big_endian):
            return int.from_bytes(self.loadBlock(self.int_size), byteorder='big', signed=False)
        else:
            return int.from_bytes(self.loadBlock(self.int_size), byteorder='little', signed=False)

    def get_size_t(self) -> int:
        if (self.big_endian):
            return int.from_bytes(self.loadBlock(self.size_t), byteorder='big', signed=False)
        else:
            return int.from_bytes(self.loadBlock(self.size_t), byteorder='little', signed=False)

    def get_double(self) -> int:
        if self.big_endian:
            return struct.unpack('>d', self.loadBlock(8))[0]
        else:
            return struct.unpack('<d', self.loadBlock(8))[0]

    def get_string(self, size) -> str:
        if (size == None):
            size = self.get_size_t()
            if (size == 0):
                return ""

        return "".join(chr(x) for x in self.loadBlock(size))

    def decode_chunk(self):
        chunk = Chunk()

        chunk.name = self.get_string(None)
        chunk.frst_line = self.get_int()
        chunk.last_line = self.get_int()

        chunk.numUpvals = self.get_byte()
        chunk.numParams = self.get_byte()
        chunk.isVarg = (self.get_byte() != 0)
        chunk.maxStack = self.get_byte()

        if (not chunk.name == ""):
            chunk.name = chunk.name[1:-1]

        # parse instructions
        num = self.get_int()
        for i in range(num):
            data   = self.get_int32()
            opcode = _get_bits(data, 0, 6)
            template = instr_lookup_tbl[opcode]
            instruction = Instruction(template.type, template.name)

            instruction.opcode = opcode
            instruction.A = _get_bits(data, 6, 8)

            if instruction.type == InstructionType.ABC:
                instruction.B = _get_bits(data, 23, 9)
                instruction.C = _get_bits(data, 14, 9)
            elif instruction.type == InstructionType.ABx:
                instruction.B = _get_bits(data, 14, 18)
            elif instruction.type == InstructionType.AsBx:
                instruction.B = _get_bits(data, 14, 18) - 131071

            chunk.appendInstruction(instruction)

        # get constants
        num = self.get_int()
        for i in range(num):
            constant: Constant = None
            type = self.get_byte()

            if type == 0: #nil
                constant = Constant(ConstType.NIL, None)
            elif type == 1: # bool
                constant = Constant(ConstType.BOOL, (self.get_byte() != 0))
            elif type == 3: # number
                constant = Constant(ConstType.NUMBER, self.get_double())
            elif type == 4: # string
                constant = Constant(ConstType.STRING, self.get_string(None)[:-1])
            else:
                raise Exception("Unknown Datatype! [%d]" % type)

            chunk.appendConstant(constant)

        # parse protos
        num = self.get_int()
        for i in range(num):
            chunk.appendProto(self.decode_chunk())

        # debug stuff

        # line numbers
        num = self.get_int()
        for i in range(num):
            self.get_int32()

        # locals
        num = self.get_int()
        for i in range(num):
            #print(self.get_string(None)[:-1]) # local name
            self.get_int32() # local start PC
            self.get_int32() # local end   PC

        # upvalues
        num = self.get_int()
        for i in range(num):
            self.get_string(None) # upvalue name

        return chunk
        
    def decode_rawbytecode(self, rawbytecode):
        # bytecode sanity checks
        if not rawbytecode[0:4] == b'\x1bLua':
            raise Exception("Lua Bytecode expected!")

        bytecode = array.array('b', rawbytecode)
        return self.decode_bytecode(bytecode)

    def decode_bytecode(self, bytecode):
        self.bytecode   = bytecode

        # aligns index, skips header
        self.index = 4
        
        self.vm_version = self.get_byte()
        self.bytecode_format = self.get_byte()
        self.big_endian = (self.get_byte() == 0)
        self.int_size   = self.get_byte()
        self.size_t     = self.get_byte()
        self.instr_size = self.get_byte() # gets size of instructions
        self.l_number_size = self.get_byte() # size of lua_Number
        self.integral_flag = self.get_byte()

        self.rootChunk = self.decode_chunk()
        return self.rootChunk
        
    def loadFile(self, luaCFile):
        with open(luaCFile, 'rb') as luac_file:
            bytecode = luac_file.read()
            return self.decode_rawbytecode(bytecode)

    def print_dissassembly(self):
        LuaUndump.dis_chunk(self.rootChunk)