codekingpro/portable-devtools

1"""2ELF file parser.3 4This provides a class ``ELFFile`` that parses an ELF executable in a similar5interface to ``ZipFile``. Only the read interface is implemented.6 7ELF header: https://refspecs.linuxfoundation.org/elf/gabi4+/ch4.eheader.html8"""9 10from __future__ import annotations11 12import enum13import os14import struct15from typing import IO16 17 18class ELFInvalid(ValueError):19    pass20 21 22class EIClass(enum.IntEnum):23    C32 = 124    C64 = 225 26 27class EIData(enum.IntEnum):28    Lsb = 129    Msb = 230 31 32class EMachine(enum.IntEnum):33    I386 = 334    S390 = 2235    Arm = 4036    X8664 = 6237    AArc64 = 18338 39 40class ELFFile:41    """42    Representation of an ELF executable.43    """44 45    def __init__(self, f: IO[bytes]) -> None:46        self._f = f47 48        try:49            ident = self._read("16B")50        except struct.error as e:51            raise ELFInvalid("unable to parse identification") from e52        magic = bytes(ident[:4])53        if magic != b"\x7fELF":54            raise ELFInvalid(f"invalid magic: {magic!r}")55 56        self.capacity = ident[4]  # Format for program header (bitness).57        self.encoding = ident[5]  # Data structure encoding (endianness).58 59        try:60            # e_fmt: Format for program header.61            # p_fmt: Format for section header.62            # p_idx: Indexes to find p_type, p_offset, and p_filesz.63            e_fmt, self._p_fmt, self._p_idx = {64                (1, 1): ("<HHIIIIIHHH", "<IIIIIIII", (0, 1, 4)),  # 32-bit LSB.65                (1, 2): (">HHIIIIIHHH", ">IIIIIIII", (0, 1, 4)),  # 32-bit MSB.66                (2, 1): ("<HHIQQQIHHH", "<IIQQQQQQ", (0, 2, 5)),  # 64-bit LSB.67                (2, 2): (">HHIQQQIHHH", ">IIQQQQQQ", (0, 2, 5)),  # 64-bit MSB.68            }[(self.capacity, self.encoding)]69        except KeyError as e:70            raise ELFInvalid(71                f"unrecognized capacity ({self.capacity}) or encoding ({self.encoding})"72            ) from e73 74        try:75            (76                _,77                self.machine,  # Architecture type.78                _,79                _,80                self._e_phoff,  # Offset of program header.81                _,82                self.flags,  # Processor-specific flags.83                _,84                self._e_phentsize,  # Size of section.85                self._e_phnum,  # Number of sections.86            ) = self._read(e_fmt)87        except struct.error as e:88            raise ELFInvalid("unable to parse machine and section information") from e89 90    def _read(self, fmt: str) -> tuple[int, ...]:91        return struct.unpack(fmt, self._f.read(struct.calcsize(fmt)))92 93    @property94    def interpreter(self) -> str | None:95        """96        The path recorded in the ``PT_INTERP`` section header.97        """98        for index in range(self._e_phnum):99            self._f.seek(self._e_phoff + self._e_phentsize * index)100            try:101                data = self._read(self._p_fmt)102            except struct.error:103                continue104            if data[self._p_idx[0]] != 3:  # Not PT_INTERP.105                continue106            self._f.seek(data[self._p_idx[1]])107            return os.fsdecode(self._f.read(data[self._p_idx[2]])).strip("\0")108        return None109