mirror of https://github.com/python/cpython
gh-120754: Add a strace helper and test set of syscalls for open().read(), Take 2 (#123413)
This commit is contained in:
Cody Maloney
GitHub
parent
7d7d56d8b1
commit
9ad57cf58b
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@ -0,0 +1,170 @@
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import re
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import sys
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import textwrap
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import unittest
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from dataclasses import dataclass
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from functools import cache
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from test import support
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from test.support.script_helper import run_python_until_end
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_strace_binary = "/usr/bin/strace"
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_syscall_regex = re.compile(
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r"(?P<syscall>[^(]*)\((?P<args>[^)]*)\)\s*[=]\s*(?P<returncode>.+)")
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_returncode_regex = re.compile(
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br"\+\+\+ exited with (?P<returncode>\d+) \+\+\+")
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@dataclass
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class StraceEvent:
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syscall: str
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args: list[str]
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returncode: str
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@dataclass
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class StraceResult:
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strace_returncode: int
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python_returncode: int
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"""The event messages generated by strace. This is very similar to the
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stderr strace produces with returncode marker section removed."""
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event_bytes: bytes
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stdout: bytes
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stderr: bytes
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def events(self):
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"""Parse event_bytes data into system calls for easier processing.
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This assumes the program under inspection doesn't print any non-utf8
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strings which would mix into the strace output."""
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decoded_events = self.event_bytes.decode('utf-8')
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matches = [
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_syscall_regex.match(event)
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for event in decoded_events.splitlines()
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]
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return [
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StraceEvent(match["syscall"],
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[arg.strip() for arg in (match["args"].split(","))],
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match["returncode"]) for match in matches if match
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]
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def sections(self):
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"""Find all "MARK <X>" writes and use them to make groups of events.
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This is useful to avoid variable / overhead events, like those at
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interpreter startup or when opening a file so a test can verify just
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the small case under study."""
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current_section = "__startup"
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sections = {current_section: []}
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for event in self.events():
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if event.syscall == 'write' and len(
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event.args) > 2 and event.args[1].startswith("\"MARK "):
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# Found a new section, don't include the write in the section
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# but all events until next mark should be in that section
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current_section = event.args[1].split(
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" ", 1)[1].removesuffix('\\n"')
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if current_section not in sections:
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sections[current_section] = list()
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else:
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sections[current_section].append(event)
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return sections
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@support.requires_subprocess()
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def strace_python(code, strace_flags, check=True):
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"""Run strace and return the trace.
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Sets strace_returncode and python_returncode to `-1` on error."""
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res = None
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def _make_error(reason, details):
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return StraceResult(
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strace_returncode=-1,
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python_returncode=-1,
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event_bytes=f"error({reason},details={details}) = -1".encode('utf-8'),
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stdout=res.out if res else b"",
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stderr=res.err if res else b"")
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# Run strace, and get out the raw text
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try:
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res, cmd_line = run_python_until_end(
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"-c",
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textwrap.dedent(code),
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__run_using_command=[_strace_binary] + strace_flags)
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except OSError as err:
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return _make_error("Caught OSError", err)
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if check and res.rc:
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res.fail(cmd_line)
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# Get out program returncode
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stripped = res.err.strip()
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output = stripped.rsplit(b"\n", 1)
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if len(output) != 2:
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return _make_error("Expected strace events and exit code line",
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stripped[-50:])
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returncode_match = _returncode_regex.match(output[1])
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if not returncode_match:
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return _make_error("Expected to find returncode in last line.",
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output[1][:50])
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python_returncode = int(returncode_match["returncode"])
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if check and python_returncode:
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res.fail(cmd_line)
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return StraceResult(strace_returncode=res.rc,
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python_returncode=python_returncode,
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event_bytes=output[0],
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stdout=res.out,
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stderr=res.err)
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def get_events(code, strace_flags, prelude, cleanup):
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# NOTE: The flush is currently required to prevent the prints from getting
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# buffered and done all at once at exit
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prelude = textwrap.dedent(prelude)
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code = textwrap.dedent(code)
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cleanup = textwrap.dedent(cleanup)
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to_run = f"""
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print("MARK prelude", flush=True)
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{prelude}
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print("MARK code", flush=True)
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{code}
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print("MARK cleanup", flush=True)
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{cleanup}
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print("MARK __shutdown", flush=True)
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"""
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trace = strace_python(to_run, strace_flags)
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all_sections = trace.sections()
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return all_sections['code']
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def get_syscalls(code, strace_flags, prelude="", cleanup=""):
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"""Get the syscalls which a given chunk of python code generates"""
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events = get_events(code, strace_flags, prelude=prelude, cleanup=cleanup)
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return [ev.syscall for ev in events]
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# Moderately expensive (spawns a subprocess), so share results when possible.
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@cache
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def _can_strace():
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res = strace_python("import sys; sys.exit(0)", [], check=False)
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assert res.events(), "Should have parsed multiple calls"
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return res.strace_returncode == 0 and res.python_returncode == 0
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def requires_strace():
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if sys.platform != "linux":
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return unittest.skip("Linux only, requires strace.")
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if support.check_sanitizer(address=True, memory=True):
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return unittest.skip("LeakSanitizer does not work under ptrace (strace, gdb, etc)")
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return unittest.skipUnless(_can_strace(), "Requires working strace")
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__all__ = ["get_events", "get_syscalls", "requires_strace", "strace_python",
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"StraceEvent", "StraceResult"]
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@ -11,7 +11,7 @@ from functools import wraps
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from test.support import (
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cpython_only, swap_attr, gc_collect, is_emscripten, is_wasi,
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infinite_recursion,
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infinite_recursion, strace_helper
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)
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from test.support.os_helper import (
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TESTFN, TESTFN_ASCII, TESTFN_UNICODE, make_bad_fd,
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@ -24,6 +24,9 @@ import _io # C implementation of io
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import _pyio # Python implementation of io
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_strace_flags=["--trace=%file,%desc"]
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class AutoFileTests:
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# file tests for which a test file is automatically set up
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@ -359,6 +362,139 @@ class AutoFileTests:
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a = array('b', b'x'*10)
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f.readinto(a)
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@strace_helper.requires_strace()
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def test_syscalls_read(self):
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"""Check that the set of system calls produced by the I/O stack is what
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is expected for various read cases.
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It's expected as bits of the I/O implementation change, this will need
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to change. The goal is to catch changes that unintentionally add
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additional systemcalls (ex. additional calls have been looked at in
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bpo-21679 and gh-120754).
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"""
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self.f.write(b"Hello, World!")
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self.f.close()
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def check_readall(name, code, prelude="", cleanup="",
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extra_checks=None):
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with self.subTest(name=name):
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syscalls = strace_helper.get_events(code, _strace_flags,
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prelude=prelude,
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cleanup=cleanup)
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# The first call should be an open that returns a
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# file descriptor (fd). Afer that calls may vary. Once the file
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# is opened, check calls refer to it by fd as the filename
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# could be removed from the filesystem, renamed, etc. See:
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# Time-of-check time-of-use (TOCTOU) software bug class.
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#
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# There are a number of related but distinct open system calls
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# so not checking precise name here.
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self.assertGreater(
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len(syscalls),
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1,
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f"Should have had at least an open call|calls={syscalls}")
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fd_str = syscalls[0].returncode
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# All other calls should contain the fd in their argument set.
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for ev in syscalls[1:]:
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self.assertIn(
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fd_str,
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ev.args,
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f"Looking for file descriptor in arguments|ev={ev}"
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)
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# There are a number of related syscalls used to implement
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# behaviors in a libc (ex. fstat, newfstatat, statx, open, openat).
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# Allow any that use the same substring.
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def count_similarname(name):
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return len([ev for ev in syscalls if name in ev.syscall])
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checks = [
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# Should open and close the file exactly once
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("open", 1),
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("close", 1),
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# There should no longer be an isatty call (All files being
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# tested are block devices / not character devices).
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('ioctl', 0),
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# Should only have one fstat (bpo-21679, gh-120754)
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# note: It's important this uses a fd rather than filename,
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# That is validated by the `fd` check above.
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# note: fstat, newfstatat, and statx have all been observed
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# here in the underlying C library implementations.
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("stat", 1)
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]
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if extra_checks:
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checks += extra_checks
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for call, count in checks:
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self.assertEqual(
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count_similarname(call),
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count,
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msg=f"call={call}|count={count}|syscalls={syscalls}"
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)
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# "open, read, close" file using different common patterns.
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check_readall(
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"open builtin with default options",
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f"""
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f = open('{TESTFN}')
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f.read()
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f.close()
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"""
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)
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check_readall(
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"open in binary mode",
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f"""
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f = open('{TESTFN}', 'rb')
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f.read()
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f.close()
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"""
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)
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check_readall(
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"open in text mode",
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f"""
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f = open('{TESTFN}', 'rt')
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f.read()
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f.close()
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""",
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# GH-122111: read_text uses BufferedIO which requires looking up
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# position in file. `read_bytes` disables that buffering and avoids
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# these calls which is tested the `pathlib read_bytes` case.
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extra_checks=[("seek", 1)]
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)
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check_readall(
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"pathlib read_bytes",
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"p.read_bytes()",
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prelude=f"""from pathlib import Path; p = Path("{TESTFN}")""",
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# GH-122111: Buffering is disabled so these calls are avoided.
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extra_checks=[("seek", 0)]
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)
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check_readall(
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"pathlib read_text",
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"p.read_text()",
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prelude=f"""from pathlib import Path; p = Path("{TESTFN}")"""
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)
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# Focus on just `read()`.
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calls = strace_helper.get_syscalls(
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prelude=f"f = open('{TESTFN}')",
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code="f.read()",
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cleanup="f.close()",
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strace_flags=_strace_flags
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)
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# One to read all the bytes
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# One to read the EOF and get a size 0 return.
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self.assertEqual(calls.count("read"), 2)
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class CAutoFileTests(AutoFileTests, unittest.TestCase):
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FileIO = _io.FileIO
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modulename = '_io'
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@ -4,6 +4,7 @@ from test import support
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from test.support import check_sanitizer
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from test.support import import_helper
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from test.support import os_helper
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from test.support import strace_helper
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from test.support import warnings_helper
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from test.support.script_helper import assert_python_ok
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import subprocess
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@ -3415,7 +3416,7 @@ class POSIXProcessTestCase(BaseTestCase):
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@unittest.skipIf(not sysconfig.get_config_var("HAVE_VFORK"),
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"vfork() not enabled by configure.")
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@unittest.skipIf(sys.platform != "linux", "Linux only, requires strace.")
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@strace_helper.requires_strace()
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@mock.patch("subprocess._USE_POSIX_SPAWN", new=False)
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def test_vfork_used_when_expected(self):
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# This is a performance regression test to ensure we default to using
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@ -3423,36 +3424,25 @@ class POSIXProcessTestCase(BaseTestCase):
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# Technically this test could pass when posix_spawn is used as well
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# because libc tends to implement that internally using vfork. But
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# that'd just be testing a libc+kernel implementation detail.
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strace_binary = "/usr/bin/strace"
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# The only system calls we are interested in.
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strace_filter = "--trace=clone,clone2,clone3,fork,vfork,exit,exit_group"
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true_binary = "/bin/true"
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strace_command = [strace_binary, strace_filter]
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try:
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does_strace_work_process = subprocess.run(
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strace_command + [true_binary],
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stderr=subprocess.PIPE,
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stdout=subprocess.DEVNULL,
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)
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rc = does_strace_work_process.returncode
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stderr = does_strace_work_process.stderr
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except OSError:
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rc = -1
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stderr = ""
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if rc or (b"+++ exited with 0 +++" not in stderr):
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self.skipTest("strace not found or not working as expected.")
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# Are intersted in the system calls:
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# clone,clone2,clone3,fork,vfork,exit,exit_group
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# Unfortunately using `--trace` with that list to strace fails because
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# not all are supported on all platforms (ex. clone2 is ia64 only...)
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# So instead use `%process` which is recommended by strace, and contains
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# the above.
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true_binary = "/bin/true"
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strace_args = ["--trace=%process"]
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with self.subTest(name="default_is_vfork"):
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vfork_result = assert_python_ok(
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"-c",
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textwrap.dedent(f"""\
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import subprocess
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subprocess.check_call([{true_binary!r}])"""),
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__run_using_command=strace_command,
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vfork_result = strace_helper.strace_python(
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f"""\
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import subprocess
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subprocess.check_call([{true_binary!r}])""",
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strace_args
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)
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# Match both vfork() and clone(..., flags=...|CLONE_VFORK|...)
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self.assertRegex(vfork_result.err, br"(?i)vfork")
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self.assertRegex(vfork_result.event_bytes, br"(?i)vfork")
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# Do NOT check that fork() or other clones did not happen.
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# If the OS denys the vfork it'll fallback to plain fork().
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@ -3465,9 +3455,8 @@ class POSIXProcessTestCase(BaseTestCase):
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("setgroups", "", "extra_groups=[]", True),
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):
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with self.subTest(name=sub_name):
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non_vfork_result = assert_python_ok(
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"-c",
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textwrap.dedent(f"""\
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non_vfork_result = strace_helper.strace_python(
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f"""\
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import subprocess
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{preamble}
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try:
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@ -3475,11 +3464,11 @@ class POSIXProcessTestCase(BaseTestCase):
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[{true_binary!r}], **dict({sp_kwarg}))
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except PermissionError:
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if not {expect_permission_error}:
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raise"""),
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__run_using_command=strace_command,
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raise""",
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strace_args
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)
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# Ensure neither vfork() or clone(..., flags=...|CLONE_VFORK|...).
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self.assertNotRegex(non_vfork_result.err, br"(?i)vfork")
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self.assertNotRegex(non_vfork_result.event_bytes, br"(?i)vfork")
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@unittest.skipUnless(mswindows, "Windows specific tests")
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