Issue 40436: pythoninfo collect_gdb() blows up when gdb fails to run

We had this weird traceback when running pythoninfo in Fedora build with Python 3.9.0a6:

+ /builddir/build/BUILD/Python-3.9.0a6/build/optimized/python -m test.pythoninfo
ERROR: collect_gdb() failed
Traceback (most recent call last):
  File "/builddir/build/BUILD/Python-3.9.0a6/Lib/test/pythoninfo.py", line 761, in collect_info
    collect_func(info_add)
  File "/builddir/build/BUILD/Python-3.9.0a6/Lib/test/pythoninfo.py", line 383, in collect_gdb
    version = version.splitlines()[0]
IndexError: list index out of range


I have debugged the problem and it is:


>>> subprocess.run(["gdb", "-nx", "--version"])
CompletedProcess(args=['gdb', '-nx', '--version'], returncode=-11)

There is a segfault. Possibly because gdb was linked to libpython from 3.9.0a5 and we run it trough subprocess from 3.9.0a6.


The code in pythoninfo is:

    try:
        proc = subprocess.Popen(["gdb", "-nx", "--version"],
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE,
                                universal_newlines=True)
        version = proc.communicate()[0]
    except OSError:
        return

That means it is designed to ignore errors. But it only ignores some errors. Should it only attempt to parse the version when proc.returncode is 0?

I don't know yet if the tests will fail as well, maybe the problem will be bigger.

BTW The test gdb also crashes in the same way:

test test_gdb crashed -- Traceback (most recent call last):
  File "/builddir/build/BUILD/Python-3.9.0a6/Lib/test/libregrtest/runtest.py", line 270, in _runtest_inner
    refleak = _runtest_inner2(ns, test_name)
  File "/builddir/build/BUILD/Python-3.9.0a6/Lib/test/libregrtest/runtest.py", line 221, in _runtest_inner2
    the_module = importlib.import_module(abstest)
  File "/builddir/build/BUILD/Python-3.9.0a6/Lib/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 790, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "/builddir/build/BUILD/Python-3.9.0a6/Lib/test/test_gdb.py", line 41, in <module>
    gdb_version, gdb_major_version, gdb_minor_version = get_gdb_version()
  File "/builddir/build/BUILD/Python-3.9.0a6/Lib/test/test_gdb.py", line 38, in get_gdb_version
    raise Exception("unable to parse GDB version: %r" % version)
Exception: unable to parse GDB version: ''

1 test failed again:
    test_gdb

New changeset ec9bea4a3766bd815148a27f61eb24e7dd459ac7 by Victor Stinner in branch 'master':
bpo-40436: Fix code parsing gdb version (GH-19792)
https://github.com/python/cpython/commit/ec9bea4a3766bd815148a27f61eb24e7dd459ac7

I fixed test.pythoninfo to ignore gdb output if the command failed. I also enhanced test_gdb error message: display stdout, stderr and the exit code. Backport to 3.8 and 3.7 will be merged as soon as the CI pass.

New changeset d9e904919197a22b95946f11ba5f24b796088c06 by Miss Islington (bot) in branch '3.8':
bpo-40436: Fix code parsing gdb version (GH-19792)
https://github.com/python/cpython/commit/d9e904919197a22b95946f11ba5f24b796088c06

New changeset beba1a808000d5fc445cb28eab96bdb4cdb7c959 by Miss Islington (bot) in branch '3.7':
bpo-40436: Fix code parsing gdb version (GH-19792)
https://github.com/python/cpython/commit/beba1a808000d5fc445cb28eab96bdb4cdb7c959

Thanks Miro for the bug report, it's now fixed ;-)

In PR 19792, Miro proposed to skip test_gdb is gdb is available but exit with non-zero exit code. I chose to raise a hard exception instead, to notify CI owners that something is wrong. I prefer to not make gdb error "silent". Otherwise, we may miss that python-gdb.py is no longer tested on a CI.

I marked bpo-29685 "test_gdb failed" as duplicate of this issue. Extract:

(...)
  File "/home/studio/Python-3.6.0/Lib/test/test_gdb.py", line 46, in <module>
    gdb_version, gdb_major_version, gdb_minor_version = get_gdb_version()
  File "/home/studio/Python-3.6.0/Lib/test/test_gdb.py", line 43, in get_gdb_version
    raise Exception("unable to parse GDB version: %r" % version)
Exception: unable to parse GDB version: ''

stage: patch review -> resolved