MicroCorruption/17-Lagos/disassemble.py

# Copied from MSProbe/msprobe.py

PC = 0 #Incremented by each disassembled instruction, incremented in words NOT bytes
asm = [0x7f7f, 0x4242, 0x4343] # fuck you *hardcodes your instructions
output = {}

register_names = ['pc', 'sp', 'sr', 'cg', 'r4', 'r5', 'r6', 'r7', 'r8', 'r9', 'r10', 'r11', 'r12', 'r13', 'r14', 'r15']

def dis_int(i: int, e: str = 'big'):
	dis_bytes(i.to_bytes(6,'big'), e)

def dis_bytes(b: bytes, e: str = 'big'):
	global PC, asm
	asm[0] = int.from_bytes(b[0:2], e)
	asm[1] = int.from_bytes(b[2:4], e)
	asm[2] = int.from_bytes(b[4:6], e)
	PC = 0
	return disassemble(asm[PC])



def bitrep(number, bits = 16):
	"""Converts to binary form, fixing leading zeroes."""
	mask = int('0b' + '1' * bits, 2)
	binstr = str(bin(number & mask))[2:]
	#negative = binstr[0] == '-'
	bitcount = len(binstr)
	leading0s = bits - bitcount
	return ('0' * leading0s) + binstr

def hexrep(number, zeroes = 4):
	"""Converts to hex form, fixing leading zeroes."""
	mask = int('0b' + '1' * (zeroes * 4), 2)
	hexstr = hex(number & mask)[2:]
	hexcount = len(hexstr)
	leading0s = zeroes - hexcount
	return ('0' * leading0s) + hexstr

def disassemble(instruction):
	"""Main disassembly, calls other disassembly functions given a 2-byte instruction."""
	#Let's start by getting the binary representation.
	#Need to invert bytes because little endian.
	ins = bitrep(instruction)
	#What kind of instruction are we dealing with?
	if ins[0:3] == '001':
		return disassemble_jump_instruction(ins)
	elif ins[0:6] == '000100':
		return disassemble_one_word_instruction(ins)
	else:
		return disassemble_two_word_instruction(ins)

one_word_opcodes = ['rrc', 'swpb', 'rra', 'sxt', 'push', 'call', 'reti']
def disassemble_one_word_instruction(ins):
	"""Given a one-operand (format I) instruction in a 16-bit string, output disassembly."""
	global PC #Get PC

	bytemode = '.b' if ins[9] == '1' else ''
	opcodeID = int(ins[6:9], 2)
	opcode = one_word_opcodes[opcodeID]
	reg = int(ins[12:], 2)

	adrmode = int(ins[10:12], 2)
	reg_output, extensionWord = disassemble_addressing_mode(reg, adrmode)

	PC += 1 + (1 if extensionWord else 0)

	return opcode + bytemode + ' ' + reg_output

jump_opcodes = ['jne', 'jeq', 'jlo', 'jhs', 'jn ', 'jge', 'jl ', 'jmp']
def disassemble_jump_instruction(ins):
	"""Given a jump instruction (format II) in a 16-bit string, output disassembly."""
	global PC #Get PC

	condition = int(ins[3:6], 2) #Get condition code from bits
	#Sign extend
	offset = ins[6] * 6 + ins[6:]
	sign_subtract = 65536 if offset[0] == '1' else 0 #Sign bit
	pcOffset = ((int(offset, 2) - sign_subtract) * 2) + 2

	#Add a plus if it's not negative for readability
	plus = '+' if sign_subtract == 0 else ''

	PC += 1

	return jump_opcodes[condition] + ' ' + plus + hex(pcOffset)

#Two-operand opcodes start at 4 (0b0100)
two_word_opcodes = ['!!!', '!!!', '!!!', '!!!', 'mov', 'add', 'addc', 'subc', 'sub', 'cmp', 'dadd', 'bit', 'bic', 'bis', 'xor', 'and']
def disassemble_two_word_instruction(ins):
	"""Given a two-operand instruction (format III) in a 16-bit string, output disassembly."""
	global PC #Get PC

	bytemode = '.b' if ins[9] == '1' else ''
	opcodeID = int(ins[0:4], 2)
	opcode = two_word_opcodes[opcodeID]

	srcReg = int(ins[4:8], 2)
	srcAdrMode = int(ins[10:12], 2)

	reg_output_src, extWordSrc = disassemble_addressing_mode(srcReg, srcAdrMode)
	PC += 1 if extWordSrc else 0

	dstReg = int(ins[12:], 2)
	dstAdrMode = int(ins[8], 2)

	reg_output_dst, ext_word_dst = disassemble_addressing_mode(dstReg, dstAdrMode)
	PC += 1 if ext_word_dst else 0

	PC += 1 #Instruction word

	finalins = opcode + bytemode + ' ' + reg_output_src + ', ' + reg_output_dst

	#Disassemble pseudo (emulated) instructions

	#These are the easy ones to catch
	finalins = 'ret' if finalins == 'mov @sp+, pc' else finalins

	#Status register twiddling
	finalins = 'clrc' if finalins == 'bic #1, sr' else finalins
	finalins = 'setc' if finalins == 'bis #1, sr' else finalins
	finalins = 'clrz' if finalins == 'bic #2, sr' else finalins
	finalins = 'setz' if finalins == 'bis #2, sr' else finalins
	finalins = 'clrn' if finalins == 'bic #4, sr' else finalins
	finalins = 'setn' if finalins == 'bis #4, sr' else finalins
	finalins = 'dint' if finalins == 'bic #8, sr' else finalins
	finalins = 'eint' if finalins == 'bic #8, sr' else finalins
	#nop = mov dst, dst
	finalins = 'nop' if opcode == 'mov' and reg_output_src == reg_output_dst else finalins

	#These ones require a small amount of effort because it uses any register.
	#All of these are one-operand instructions, so if we need to reassemble
	#the instruction, it'll simply follow the one-operand format.

	reassembleins = True
	uses_dest = True

	#Branch. Requires a little bit of extra sanity checking
	#because it could get mistaken for ret
	if opcode == 'mov' and reg_output_dst == 'pc' and finalins != 'ret': #br = mov src, pc
		opcode = 'br'
		uses_dest = False #We're actually using src here

	#Pop. Could also get mistaken for ret.
	elif opcode == 'mov' and reg_output_src == '@sp+' and finalins != 'ret': #pop = mov @sp+, dst
		opcode = 'pop'

	#Shift and rotate left

	elif opcode == 'add' and srcReg == dstReg: #rla = add dst, dst
		opcode = 'rla'
	elif opcode == 'addc' and srcReg == dstReg: #rlc = addc dst, dst
		opcode = 'rlc'

	#Common one-operand instructions

	elif opcode == 'xor' and reg_output_src == '#0xffff {-1}': #inv = xor 0xffff, dst
		opcode = 'inv'
	#Extra sanity checking to prevent being mistaken for nop
	elif opcode == 'mov' and reg_output_src == '#0' and reg_output_dst != '#0': #clr = mov #0, dst
		opcode = 'clr'
	elif opcode == 'cmp' and reg_output_src == '#0': #tst = cmp #0, dst
		opcode = 'tst'


	#Increment and decrement (by one or two)

	elif opcode == 'sub' and reg_output_src == '#1': #dec = sub #1, dst
		opcode = 'dec'
	elif opcode == 'sub' and reg_output_src == '#2': #decd = sub #2, dst
		opcode = 'decd'
	elif opcode == 'add' and reg_output_src == '#1': #inc = add #1, dst
		opcode = 'inc'
	elif opcode == 'add' and reg_output_src == '#2': #incd = add #1, dst
		opcode = 'incd'

	#Add and subtract only the carry bit:

	elif opcode == 'addc' and reg_output_src == '#0': #adc = addc #0, dst
		opcode = 'adc'
	elif opcode == 'dadd' and reg_output_src == '#0': #dadc = dadd #0, dst
		opcode = 'dadc'
	elif opcode == 'subc' and reg_output_src == '#0': #sbc = subc #0, dst
		opcode = 'sbc'

	#The instruction is not an emulated instruction
	else:
		reassembleins = False

	if reassembleins:
		finalins = opcode + bytemode + ' ' + (reg_output_dst if uses_dest else reg_output_src)

	return finalins


adr_modes = ['{register}', '{index}({register})', '@{register}', '@{register}+']

def disassemble_addressing_mode(reg, adrmode):
	"""Outputs disassembly of a register's addressing mode and whether an extension
	word was used (to update PC accordingly in the calling function),
	given the register number and addressing mode number."""

	#http://mspgcc.sourceforge.net/manual/x147.html

	extensionWord = False
	#print(f"{PC = :x}, {asm = }", end="");

	#r2 (status register) and r3 (CG) are encoded as constant registers
	if reg == 2:
		if adrmode == 0: #Normal access
			reg_output = adr_modes[adrmode].format(register=register_names[reg])
		elif adrmode == 1: #Absolute address using extension word
			reg_output = '&' + hex(asm[PC + 1]) #Get next word
			extensionWord = True
		elif adrmode == 2:
			reg_output = '#4'
		elif adrmode == 3:
			reg_output = '#8'

	elif reg == 3:
		if adrmode == 0:
			reg_output = '#0'
		elif adrmode == 1:
			reg_output = '#1'
		elif adrmode == 2:
			reg_output = '#2'
		elif adrmode == 3:
			#Just a little reminder that all bits set == -1
			reg_output = '#0xffff {-1}'

	elif adrmode == 0:
		reg_output = adr_modes[adrmode].format(register=register_names[reg])

	elif adrmode == 1:
		reg_output = adr_modes[adrmode].format(register=register_names[reg], index=hex(asm[PC + 1]))
		extensionWord = True

	elif adrmode == 2:
		reg_output = adr_modes[adrmode].format(register=register_names[reg])

	elif adrmode == 3 and reg == 0: #PC was incremented for a constant
		reg_output = '#' + hex(asm[PC + 1])
		extensionWord = True

	elif adrmode == 3:
		reg_output = adr_modes[adrmode].format(register=register_names[reg])

	return (reg_output, extensionWord)