gh-141926: Do not unset RUNSHARED when cross-compiling

[zanieb]

An alternative to #141927 just removing what appears to be legacy code instead of providing a way to opt-in to different behavior.

Closes #141926
Closes astral-sh/python-build-standalone#864

• Issue: Support PGO in cross-compiles when transparent emulation is available #141926

[FFY00]

I think RUNSHARED should only need to be cleared to run the built interpreter on edge cases. Since nowadays it's more likely we need to keep it, I think it makes sense to keep it by default, and add some logic to adjust it when needed.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @FFY00 for commit 9152608 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F141958%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[emmatyping]

I think RUNSHARED should only need to be cleared to run the built interpreter on edge cases.

Wouldn't cross-compiling from say x86_64 to aarch64 on Linux where you haven't configured binfmt-misc to handle ARM binaries break? I know that is not uncommon to build software for SBCs like a Raspberry Pi with this setup.

[zanieb]

Wouldn't cross-compiling from say x86_64 to aarch64 on Linux where you haven't configured binfmt-misc to handle ARM binaries break?

Break at what step though? It looks like, e.g., PGO still runs when cross-compiling, so clearing RUNSHARED won't save you and this shouldn't cause a regression.

[emmatyping]

Break at what step though? It looks like, e.g., PGO still runs when cross-compiling, so clearing RUNSHARED won't save you and this shouldn't cause a regression.

Yeah thinking this over a bit more, I think you're right that any use-case where this could regress is either completely or subtly broken anyway.

[zanieb]

I presume these test failures on the refleaks bots are flakes? e.g.:

======================================================================
ERROR: test_interrupt (test.test_multiprocessing_fork.test_processes.WithProcessesTestProcess.test_interrupt)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/buildbot/buildarea/pull_request.cstratak-fedora-stable-s390x.refleak/build/Lib/contextlib.py", line 85, in inner
    return func(*args, **kwds)
  File "/home/buildbot/buildarea/pull_request.cstratak-fedora-stable-s390x.refleak/build/Lib/test/_test_multiprocessing.py", line 597, in test_interrupt
    exitcode = self._kill_process(multiprocessing.Process.interrupt)
  File "/home/buildbot/buildarea/pull_request.cstratak-fedora-stable-s390x.refleak/build/Lib/contextlib.py", line 85, in inner
    return func(*args, **kwds)
  File "/home/buildbot/buildarea/pull_request.cstratak-fedora-stable-s390x.refleak/build/Lib/test/_test_multiprocessing.py", line 578, in _kill_process
    self.assertEqual(join(), None)
                     ~~~~^^
  File "/home/buildbot/buildarea/pull_request.cstratak-fedora-stable-s390x.refleak/build/Lib/test/_test_multiprocessing.py", line 251, in __call__
    return self.func(*args, **kwds)
           ~~~~~~~~~^^^^^^^^^^^^^^^
  File "/home/buildbot/buildarea/pull_request.cstratak-fedora-stable-s390x.refleak/build/Lib/multiprocessing/process.py", line 156, in join
    res = self._popen.wait(timeout)
  File "/home/buildbot/buildarea/pull_request.cstratak-fedora-stable-s390x.refleak/build/Lib/multiprocessing/popen_fork.py", line 44, in wait
    return self.poll(os.WNOHANG if timeout == 0.0 else 0)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/buildbot/buildarea/pull_request.cstratak-fedora-stable-s390x.refleak/build/Lib/multiprocessing/popen_fork.py", line 28, in poll
    pid, sts = os.waitpid(self.pid, flag)
               ~~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/home/buildbot/buildarea/pull_request.cstratak-fedora-stable-s390x.refleak/build/Lib/test/_test_multiprocessing.py", line 574, in handler
    raise RuntimeError('join took too long: %s' % p)
RuntimeError: join took too long: <Process name='Process-1708' pid=2226706 parent=2212089 started daemon>

----------------------------------------------------------------------
Ran 162 tests in 33.825s

FAILED (errors=1, skipped=7)
test test.test_multiprocessing_fork.test_processes failed

[FFY00]

Yeah, the buildbot failures are unrelated, we are okay.