DOS MZ executable: Python parsing library

DOS MZ file format is a traditional format for executables in MS-DOS environment. Many modern formats (i.e. Windows PE) still maintain compatibility stub with this format.

As opposed to .com file format (which basically sports one 64K code segment of raw CPU instructions), DOS MZ .exe file format allowed more flexible memory management, loading of larger programs and added support for relocations.

File extension

["exe", "ovl"]

KS implementation details

License: CC0-1.0

References

This page hosts a formal specification of DOS MZ executable using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Runtime library

All parsing code for Python generated by Kaitai Struct depends on the Python runtime library. You have to install it before you can parse data.

The Python runtime library can be installed from PyPI:

python3 -m pip install kaitaistruct

Code

Parse a local file and get structure in memory:

data = DosMz.from_file("path/to/local/file.["exe", "ovl"]")

Or parse structure from a bytes:

from kaitaistruct import KaitaiStream, BytesIO

raw = b"\x00\x01\x02..."
data = DosMz(KaitaiStream(BytesIO(raw)))

After that, one can get various attributes from the structure by invoking getter methods like:

data.hdr # => get hdr

Python source code to parse DOS MZ executable

dos_mz.py

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

from pkg_resources import parse_version
import kaitaistruct
from kaitaistruct import KaitaiStruct, KaitaiStream, BytesIO


if parse_version(kaitaistruct.__version__) < parse_version('0.9'):
    raise Exception("Incompatible Kaitai Struct Python API: 0.9 or later is required, but you have %s" % (kaitaistruct.__version__))

class DosMz(KaitaiStruct):
    """DOS MZ file format is a traditional format for executables in MS-DOS
    environment. Many modern formats (i.e. Windows PE) still maintain
    compatibility stub with this format.
    
    As opposed to .com file format (which basically sports one 64K code
    segment of raw CPU instructions), DOS MZ .exe file format allowed
    more flexible memory management, loading of larger programs and
    added support for relocations.
    """
    def __init__(self, _io, _parent=None, _root=None):
        self._io = _io
        self._parent = _parent
        self._root = _root if _root else self
        self._read()

    def _read(self):
        self.hdr = DosMz.MzHeader(self._io, self, self._root)
        self.mz_header2 = self._io.read_bytes((self.hdr.ofs_relocations - 28))
        self.relocations = [None] * (self.hdr.num_relocations)
        for i in range(self.hdr.num_relocations):
            self.relocations[i] = DosMz.Relocation(self._io, self, self._root)

        self.body = self._io.read_bytes_full()

    class MzHeader(KaitaiStruct):
        def __init__(self, _io, _parent=None, _root=None):
            self._io = _io
            self._parent = _parent
            self._root = _root if _root else self
            self._read()

        def _read(self):
            self.magic = self._io.read_bytes(2)
            self.last_page_extra_bytes = self._io.read_u2le()
            self.num_pages = self._io.read_u2le()
            self.num_relocations = self._io.read_u2le()
            self.header_size = self._io.read_u2le()
            self.min_allocation = self._io.read_u2le()
            self.max_allocation = self._io.read_u2le()
            self.initial_ss = self._io.read_u2le()
            self.initial_sp = self._io.read_u2le()
            self.checksum = self._io.read_u2le()
            self.initial_ip = self._io.read_u2le()
            self.initial_cs = self._io.read_u2le()
            self.ofs_relocations = self._io.read_u2le()
            self.overlay_id = self._io.read_u2le()


    class Relocation(KaitaiStruct):
        def __init__(self, _io, _parent=None, _root=None):
            self._io = _io
            self._parent = _parent
            self._root = _root if _root else self
            self._read()

        def _read(self):
            self.ofs = self._io.read_u2le()
            self.seg = self._io.read_u2le()