Problem when disassembling raw data

[shahril96]

pydis threw an exception error when disassembling raw data.

Example:
0x66, 0x8C, 0x31, 0xC0

Expected Output:

db 0x66
db 0x8c
xor eax, eax

Pydis Output:

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    for instruction in pydis.decode(instructions, instruction_pointer):
  File "/home/shahril/.local/lib/python3.7/site-packages/pydis/decoder.py", line 71, in decode
    raise Exception(f'Failed while decoding: {status.name}')
Exception: Failed while decoding: BadRegister

Looking at the code here, decoder.py#L62, pydis quickly break if decoder returns !success.

However, official ZydisDisasm tool treated the "invalid" instruction as raw data, as shown here: https://github.com/zyantific/zydis/blob/326d1fb586630adfcad9491b9c440425c31ed0e3/tools/ZydisDisasm.c#L139

---

A hackish way I found to handle this problem is by using try...except:

import pydis

instructions = b"\x66\x8C\x31\xC0"
instruction_pointer = 0x007FFFFFFF400000

offset = 0

while True:
    try:
        if offset >= len(instructions):
            break
        for instr in pydis.decode(instructions[offset:], instruction_pointer):
            offset += instr.length
            print(instr)
        if offset < len(instructions):
            raise Exception()
    except:
        print(f"db 0x{instructions[offset]:02x}")
        offset += 1