""" ELF file parser. This provides a class ``ELFFile`` that parses an ELF executable in a similar interface to ``ZipFile``. Only the read interface is implemented. Based on: https://gist.github.com/lyssdod/f51579ae8d93c8657a5564aefc2ffbca ELF header: https://refspecs.linuxfoundation.org/elf/gabi4+/ch4.eheader.html """ import enum import os import struct from typing import IO, Optional, Tuple class ELFInvalid(ValueError): pass class EIClass(enum.IntEnum): C32 = 1 C64 = 2 class EIData(enum.IntEnum): Lsb = 1 Msb = 2 class EMachine(enum.IntEnum): I386 = 3 S390 = 22 Arm = 40 X8664 = 62 AArc64 = 183 class ELFFile: """ Representation of an ELF executable. """ def __init__(self, f: IO[bytes]) -> None: self._f = f try: ident = self._read("16B") except struct.error: raise ELFInvalid("unable to parse identification") magic = bytes(ident[:4]) if magic != b"\x7fELF": raise ELFInvalid(f"invalid magic: {magic!r}") self.capacity = ident[4] # Format for program header (bitness). self.encoding = ident[5] # Data structure encoding (endianness). try: # e_fmt: Format for program header. # p_fmt: Format for section header. # p_idx: Indexes to find p_type, p_offset, and p_filesz. e_fmt, self._p_fmt, self._p_idx = { (1, 1): ("HHIIIIIHHH", ">IIIIIIII", (0, 1, 4)), # 32-bit MSB. (2, 1): ("HHIQQQIHHH", ">IIQQQQQQ", (0, 2, 5)), # 64-bit MSB. }[(self.capacity, self.encoding)] except KeyError: raise ELFInvalid( f"unrecognized capacity ({self.capacity}) or " f"encoding ({self.encoding})" ) try: ( _, self.machine, # Architecture type. _, _, self._e_phoff, # Offset of program header. _, self.flags, # Processor-specific flags. _, self._e_phentsize, # Size of section. self._e_phnum, # Number of sections. ) = self._read(e_fmt) except struct.error as e: raise ELFInvalid("unable to parse machine and section information") from e def _read(self, fmt: str) -> Tuple[int, ...]: return struct.unpack(fmt, self._f.read(struct.calcsize(fmt))) @property def interpreter(self) -> Optional[str]: """ The path recorded in the ``PT_INTERP`` section header. """ for index in range(self._e_phnum): self._f.seek(self._e_phoff + self._e_phentsize * index) try: data = self._read(self._p_fmt) except struct.error: continue if data[self._p_idx[0]] != 3: # Not PT_INTERP. continue self._f.seek(data[self._p_idx[1]]) return os.fsdecode(self._f.read(data[self._p_idx[2]])).strip("\0") return None