writeups/2020/gctf/sprint/disassemble.py

#!/usr/bin/env python3

import fileinput
import re

literalMove = re.compile(r"^%1\$(\d*)s%3\$hn%1\$(\d*)s%1\$(\d*)s%(\d*)\$hn$")
regMove = re.compile(r"^%1\$(\d*)s%3\$hn%1\$(\d*)s%1\$\*(\d*)\$s%(\d*)\$hn$")
regAdd = re.compile(r"^%1\$(\d*)s%3\$hn%1\$(\d*)s%1\$\*(\d*)\$s%1\$\*(\d*)\$s%(\d*)\$hn$")
regLiteralAdd = re.compile(r"^%1\$(\d*)s%3\$hn%1\$(\d*)s%1\$\*(\d*)\$s%1\$(\d*)s%(\d*)\$hn$")
literalRegAdd = re.compile(r"^%1\$(\d*)s%3\$hn%1\$(\d*)s%1\$(\d*)s%1\$\*(\d*)\$s%(\d*)\$hn$")
jump = re.compile(r"^%1\$(\d*)s%3\$hn$")
condJump = re.compile(r"^%(\d*)\$c%1\$(\d*)s%2\$c%4\$s%1\$(\d*)s%3\$hn$")

# The address of the instruction being read
addr = 0


def showRegisterDest(regRef):
    if regRef == 6:
        regStr = "(%r1)"
    elif regRef >= 7 and regRef <= 23 and regRef % 2 == 1:
        regStr = "%r{}".format(regRef // 2 - 2)
    else:
        print("bad destination: {}".format(regRef))
        exit()
    return regStr


def showRegisterSource(regRef):
    if regRef == 5:
        regStr = "(%r1)"
    elif regRef >= 6 and regRef <= 22 and regRef % 2 == 0:
        regStr = "%r{}".format(regRef // 2 - 2)
    else:
        print("bad source")
        exit()
    return regStr


for line in fileinput.input():
    oldAddr = addr
    addr += len(line)
    m = literalMove.match(line)
    if m:
        nextAddr = int(m.group(1))
        filler = int(m.group(2))
        literal = int(m.group(3))
        regRef = int(m.group(4))

        if addr != nextAddr:
            print("address is not the next instruction")
            exit()
        if nextAddr + filler != 0x10000:
            print("first two numbers do not add to 0x10000")
            exit()

        dest = showRegisterDest(regRef)
        print("{:04x}: mov 0x{:x}, {}".format(oldAddr, literal, dest))
        continue

    m = regMove.match(line)
    if m:
        nextAddr = int(m.group(1))
        filler = int(m.group(2))
        sourceRef = int(m.group(3))
        destRef = int(m.group(4))

        if addr != nextAddr:
            print("address is not the next instruction")
            exit()
        if nextAddr + filler != 0x10000:
            print("first two numbers do not add to 0x10000")
            exit()

        source = showRegisterSource(sourceRef)
        dest = showRegisterDest(destRef)
        print("{:04x}: mov {}, {}".format(oldAddr, source, dest))
        continue

    m = regAdd.match(line)
    if m:
        nextAddr = int(m.group(1))
        filler = int(m.group(2))
        source1Ref = int(m.group(3))
        source2Ref = int(m.group(4))
        destRef = int(m.group(5))

        if addr != nextAddr:
            print("address is not the next instruction")
            exit()
        if nextAddr + filler != 0x10000:
            print("first two numbers do not add to 0x10000")
            exit()

        source1 = showRegisterSource(source1Ref)
        source2 = showRegisterSource(source2Ref)
        dest = showRegisterDest(destRef)
        print("{:04x}: add {}, {}, {}".format(oldAddr, source1, source2, dest))
        continue

    m = regLiteralAdd.match(line)
    if m:
        nextAddr = int(m.group(1))
        filler = int(m.group(2))
        sourceRef = int(m.group(3))
        literal = int(m.group(4))
        destRef = int(m.group(5))

        if addr != nextAddr:
            print("address is not the next instruction")
            exit()
        if nextAddr + filler != 0x10000:
            print("first two numbers do not add to 0x10000")
            exit()

        source = showRegisterSource(sourceRef)
        dest = showRegisterDest(destRef)
        print("{:04x}: add {}, 0x{:x}, {}".format(oldAddr, source, literal, dest))
        continue

    m = literalRegAdd.match(line)
    if m:
        nextAddr = int(m.group(1))
        filler = int(m.group(2))
        sourceRef = int(m.group(4))
        literal = int(m.group(3))
        destRef = int(m.group(5))

        if addr != nextAddr:
            print("address is not the next instruction")
            exit()
        if nextAddr + filler != 0x10000:
            print("first two numbers do not add to 0x10000")
            exit()

        source = showRegisterSource(sourceRef)
        dest = showRegisterDest(destRef)
        print("{:04x}: add {}, 0x{:x}, {}".format(oldAddr, source, literal, dest))
        continue

    m = jump.match(line)
    if m:
        target = int(m.group(1))
        if target == 0xfffe:
            print("{:04x}: halt".format(oldAddr))
        else:
            print("{:04x}: jmp {:04x}".format(oldAddr, target))
        continue

    m = condJump.match(line)
    if m:
        sourceRef = int(m.group(1))
        fill1 = int(m.group(2))
        fill2 = int(m.group(3))

        source = showRegisterSource(sourceRef)

        zeroTarget = (fill1 + fill2 + 2) % 0x10000
        nonzeroTarget = (fill1 * 2 + fill2 + 3) % 0x10000

        if zeroTarget == addr:
            print("{:04x}: jnz {}, {:04x}".format(oldAddr, source, nonzeroTarget))
        elif nonzeroTarget == addr:
            print("{:04x}: jz {}, {:04x}".format(oldAddr, source, zeroTarget))
        else:
            print("neither jump target is the next instruction")
            exit()
        continue

    print(line[:-1])