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Refactor ELF parsing logic to standalone class
This makes it easier to reuse the same code for manylinux, musllinux, and test code.
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"""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 | ||
""" | ||
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import enum | ||
import os | ||
import struct | ||
from typing import IO, Any, ContextManager, Optional, Tuple | ||
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class ElfInvalid(ValueError): | ||
pass | ||
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class EIClass(enum.IntEnum): | ||
C32 = 1 | ||
C64 = 2 | ||
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class EIData(enum.IntEnum): | ||
Lsb = 1 | ||
Msb = 2 | ||
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class EMachine(enum.IntEnum): | ||
I386 = 3 | ||
S390 = 22 | ||
Arm = 40 | ||
X8664 = 62 | ||
AArc64 = 183 | ||
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class ElfFile(ContextManager["ElfFile"]): | ||
"""Representation of an ELF executable.""" | ||
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def __init__(self, f: IO[bytes]) -> None: | ||
self._f = f | ||
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try: | ||
ident = self._read("16B") | ||
except struct.error: | ||
raise ElfInvalid | ||
if bytes(ident[:4]) != b"\x7fELF": # Invalid magic, not ELF. | ||
raise ElfInvalid | ||
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self.capacity = ident[4] # Format for program header (bitness). | ||
self.encoding = ident[5] # Data structure encoding (endianess). | ||
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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 LSB. | ||
(1, 2): (">HHIIIIIHHH", ">IIIIIIII", (0, 1, 4)), # 32-bit MSB. | ||
(2, 1): ("<HHIQQQIHHH", "<IIQQQQQQ", (0, 2, 5)), # 64-bit LSB. | ||
(2, 2): (">HHIQQQIHHH", ">IIQQQQQQ", (0, 2, 5)), # 64-bit MSB. | ||
}[(self.capacity, self.encoding)] | ||
except KeyError: | ||
raise ElfInvalid | ||
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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: | ||
raise ElfInvalid | ||
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def __enter__(self) -> "ElfFile": | ||
return self | ||
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def __exit__(self, typ: Any, val: Any, tb: Any) -> None: | ||
self.close() | ||
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def _read(self, fmt: str) -> Tuple[int, ...]: | ||
return struct.unpack(fmt, self._f.read(struct.calcsize(fmt))) | ||
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def close(self) -> None: | ||
self._f.close() | ||
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@property | ||
def interpreter(self) -> Optional[str]: | ||
"""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 |
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