This is a simple container format that encapsulates multiple Mach-O files, each generally for a different architecture. XNU can execute these files just like single-arch Mach-Os and will pick the appropriate entry.
This page hosts a formal specification of macOS Mach-O multiarch ("fat") binary using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing 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 kaitaistructParse a local file and get structure in memory:
data = MachOFat.from_file("path/to/local/file.bin")
Or parse structure from a bytes:
from kaitaistruct import KaitaiStream, BytesIO
raw = b"\x00\x01\x02..."
data = MachOFat(KaitaiStream(BytesIO(raw)))
After that, one can get various attributes from the structure by invoking getter methods like:
data.magic # => get magic
# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
import kaitaistruct
from kaitaistruct import KaitaiStruct, KaitaiStream, BytesIO
if getattr(kaitaistruct, 'API_VERSION', (0, 9)) < (0, 9):
raise Exception("Incompatible Kaitai Struct Python API: 0.9 or later is required, but you have %s" % (kaitaistruct.__version__))
import mach_o
class MachOFat(KaitaiStruct):
"""This is a simple container format that encapsulates multiple Mach-O files,
each generally for a different architecture. XNU can execute these files just
like single-arch Mach-Os and will pick the appropriate entry.
.. seealso::
Source - https://opensource.apple.com/source/xnu/xnu-7195.121.3/EXTERNAL_HEADERS/mach-o/fat.h.auto.html
"""
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(4)
if not self.magic == b"\xCA\xFE\xBA\xBE":
raise kaitaistruct.ValidationNotEqualError(b"\xCA\xFE\xBA\xBE", self.magic, self._io, u"/seq/0")
self.num_fat_arch = self._io.read_u4be()
self.fat_archs = []
for i in range(self.num_fat_arch):
self.fat_archs.append(MachOFat.FatArch(self._io, self, self._root))
class FatArch(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.cpu_type = KaitaiStream.resolve_enum(MachO.CpuType, self._io.read_u4be())
self.cpu_subtype = self._io.read_u4be()
self.ofs_object = self._io.read_u4be()
self.len_object = self._io.read_u4be()
self.align = self._io.read_u4be()
@property
def object(self):
if hasattr(self, '_m_object'):
return self._m_object
_pos = self._io.pos()
self._io.seek(self.ofs_object)
self._raw__m_object = self._io.read_bytes(self.len_object)
_io__raw__m_object = KaitaiStream(BytesIO(self._raw__m_object))
self._m_object = mach_o.MachO(_io__raw__m_object)
self._io.seek(_pos)
return getattr(self, '_m_object', None)