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Victor, if you run the test suite, one of the test cases should trigger the overflow. I used to compile with Undefined Behaviour Sanitizer to print messages when these errors occur; see <https://bugs.python.org/issue1621#msg271118> for my setup at the time. I presume Antoine did something similar.
I do not remember, but suspect the test case might be the following lines of "BaseLockTests.test_timeout" in Lib/test/lock_tests.py, testing a fraction of a second less than PY_TIMEOUT_MAX:
# TIMEOUT_MAX is ok
lock.acquire(timeout=TIMEOUT_MAX)
Perhaps reducing PY_TIMEOUT_MAX by a few centuries would be one way to avoid the problem. In my patch I avoided the problem by rearranging the arithmetic, so that the timeout value is only compared and reduced, never added.