+364      def _assert_values(self, values):  +365          for obj in values:  +366              with self.subTest(obj):  +367                  interpreters.channel_send(self.cid, obj)  +368                  got = interpreters.channel_recv(self.cid)  +369  +370                  self.assertEqual(got, obj)  +371                  self.assertIs(type(got), type(obj))  +372                  # XXX Check the following in the channel tests?  +373                  #self.assertIsNot(got, obj)  +374  +395      def test_int(self):  +396          self._assert_values(range(-1, 258))  +397The assert fails on -1 with:======================================================================FAIL: test_int (test.test__xxsubinterpreters.ShareableTypeTests) [-1]----------------------------------------------------------------------Traceback (most recent call last):  File "/data/prj/python/python3-3.8.0/Lib/test/test__xxsubinterpreters.py", line 371, in _assert_values    self.assertEqual(got, obj)AssertionError:4294967295 != -1Note that this value is the unsigned value for 32-bit int as -1root@x066:[/data/prj/python/python3-3.8.0]grep4294967295 /usr/include/sys/*.h/usr/include/sys/limits.h:#define ULONG_MAX     (4294967295UL)/usr/include/sys/limits.h:#define UINT_MAX      (4294967295U)/usr/include/sys/stdint.h:#define UINT32_MAX    (4294967295U)After quite a lot of "learning", I narrow the issue to: +1432  static int +1433  _long_shared(PyObject *obj, _PyCrossInterpreterData *data) +1434  { +1435      int64_t value = PyLong_AsLongLong(obj); +1436      if (value == -1 && PyErr_Occurred()) { +1437          if (PyErr_ExceptionMatches(PyExc_OverflowError)) { +1438              PyErr_SetString(PyExc_OverflowError, "try sending as bytes"); +1439          } +1440          return -1; +1441      } +1442      data->data = (void *)value; +1443      data->obj = NULL; +1444      data->new_object = _new_long_object; +1445      data->free = NULL; +1446      return 0; +1447  } +1448 +1426  static PyObject * +1427  _new_long_object(_PyCrossInterpreterData *data) +1428  { +1429      return PyLong_FromLongLong((int64_t)(data->data)); +1430  }The "value" is stored as a void data type, and the high-order 64-bits are zero. When it gets returned as a PyLong... it goes positive.I do not dare touch anything here without some "mentoring".Or, we change the test so that it knows it is in 32-bit mode, and compares with something else.In short, "mentoring" requested.p.s. not had time to test in 64-bit mode. Will post on that later.

64-bit mode, no error.root@x066:[/data/prj/python/python3-3.8.0]./python -m test -v test__xxsubinterpreters== CPython 3.8.0a0 (heads/master-dirty:d500e5307a, Sep 3 2018, 13:55:44) [C]== AIX-1-00C291F54C00-powerpc-64bit-COFF big-endian== cwd: /data/prj/python/python3-3.8.0/build/test_python_16908532== CPU count: 8== encodings: locale=ISO8859-1, FS=iso8859-1Run tests sequentially0:00:00 [1/1] test__xxsubinterpreterstest_bad_id (test.test__xxsubinterpreters.ChannelIDTests) ... ok...test_int (test.test__xxsubinterpreters.ShareableTypeTests) ... oktest_singletons (test.test__xxsubinterpreters.ShareableTypeTests) ... oktest_types (test.test__xxsubinterpreters.ShareableTypeTests) ... ok----------------------------------------------------------------------Ran 111 tests in 4.572sOK (skipped=5)== Tests result: SUCCESS ==

Thanks for bringing this up, Michael.  I'll give you a review on the PR sometime this week (while at the core sprint).

New changeseta909460a09cca79bd051c45b02e650862a57dbd9 by Eric Snow (Michael Felt) in branch 'master':bpo-34569: Fix subinterpreter 32-bit  ABI, pystate.c/_new_long_object() (gh-9127)https://github.com/python/cpython/commit/a909460a09cca79bd051c45b02e650862a57dbd9

Thanks, Michael.