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"""PEP 656 support.
This module implements logic to detect if the currently running Python is
linked against musl, and what musl version is used.
"""
import contextlib
import functools
import operator
import os
import re
import struct
import subprocess
import sys
from typing import IO, Iterator, NamedTuple, Optional, Tuple
def _read_unpacked(f: IO[bytes], fmt: str) -> Tuple[int, ...]:
return struct.unpack(fmt, f.read(struct.calcsize(fmt)))
def _parse_ld_musl_from_elf(f: IO[bytes]) -> Optional[str]:
"""Detect musl libc location by parsing the Python executable.
Based on: https://gist.github.com/lyssdod/f51579ae8d93c8657a5564aefc2ffbca
ELF header: https://refspecs.linuxfoundation.org/elf/gabi4+/ch4.eheader.html
"""
f.seek(0)
try:
ident = _read_unpacked(f, "16B")
except struct.error:
return None
if ident[:4] != tuple(b"\x7fELF"): # Invalid magic, not ELF.
return None
f.seek(struct.calcsize("HHI"), 1) # Skip file type, machine, and version.
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, p_fmt, p_idx = {
1: ("IIIIHHH", "IIIIIIII", (0, 1, 4)), # 32-bit.
2: ("QQQIHHH", "IIQQQQQQ", (0, 2, 5)), # 64-bit.
}[ident[4]]
except KeyError:
return None
else:
p_get = operator.itemgetter(*p_idx)
# Find the interpreter section and return its content.
try:
_, e_phoff, _, _, _, e_phentsize, e_phnum = _read_unpacked(f, e_fmt)
except struct.error:
return None
for i in range(e_phnum + 1):
f.seek(e_phoff + e_phentsize * i)
try:
p_type, p_offset, p_filesz = p_get(_read_unpacked(f, p_fmt))
except struct.error:
return None
if p_type != 3: # Not PT_INTERP.
continue
f.seek(p_offset)
interpreter = os.fsdecode(f.read(p_filesz)).strip("\0")
if "musl" not in interpreter:
return None
return interpreter
return None
class _MuslVersion(NamedTuple):
major: int
minor: int
def _parse_musl_version(output: str) -> Optional[_MuslVersion]:
lines = [n for n in (n.strip() for n in output.splitlines()) if n]
if len(lines) < 2 or lines[0][:4] != "musl":
return None
m = re.match(r"Version (\d+)\.(\d+)", lines[1])
if not m:
return None
return _MuslVersion(major=int(m.group(1)), minor=int(m.group(2)))
@functools.lru_cache()
def _get_musl_version(executable: str) -> Optional[_MuslVersion]:
"""Detect currently-running musl runtime version.
This is done by checking the specified executable's dynamic linking
information, and invoking the loader to parse its output for a version
string. If the loader is musl, the output would be something like::
musl libc (x86_64)
Version 1.2.2
Dynamic Program Loader
"""
with contextlib.ExitStack() as stack:
try:
f = stack.enter_context(open(executable, "rb"))
except IOError:
return None
ld = _parse_ld_musl_from_elf(f)
if not ld:
return None
proc = subprocess.run([ld], stderr=subprocess.PIPE, universal_newlines=True)
return _parse_musl_version(proc.stderr)
def platform_tags(arch: str) -> Iterator[str]:
"""Generate musllinux tags compatible to the current platform.
:param arch: Should be the part of platform tag after the ``linux_``
prefix, e.g. ``x86_64``. The ``linux_`` prefix is assumed as a
prerequisite for the current platform to be musllinux-compatible.
:returns: An iterator of compatible musllinux tags.
"""
sys_musl = _get_musl_version(sys.executable)
if sys_musl is None: # Python not dynamically linked against musl.
return
for minor in range(sys_musl.minor, -1, -1):
yield f"musllinux_{sys_musl.major}_{minor}_{arch}"
if __name__ == "__main__": # pragma: no cover
import sysconfig
plat = sysconfig.get_platform()
assert plat.startswith("linux-"), "not linux"
print("plat:", plat)
print("musl:", _get_musl_version(sys.executable))
print("tags:", end=" ")
for t in platform_tags(re.sub(r"[.-]", "_", plat.split("-", 1)[-1])):
print(t, end="\n ")
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