Issue #8651: PyArg_Parse*() functions raise an OverflowError if the file

doesn't have PY_SSIZE_T_CLEAN define and the size doesn't fit in an int
(length bigger than 2^31-1).

Lib/test/test_xml_etree_c.py

@@ -1,6 +1,8 @@
 # xml.etree test for cElementTree
 
 from test import support
+from test.support import precisionbigmemtest, _2G
+import unittest
 
 cET = support.import_module('xml.etree.cElementTree')
 
@@ -31,12 +33,28 @@ def sanity():
     """
 
 
+class MiscTests(unittest.TestCase):
+    # Issue #8651.
+    @support.precisionbigmemtest(size=support._2G + 100, memuse=1)
+    def test_length_overflow(self, size):
+        if size < support._2G + 100:
+            self.skipTest("not enough free memory, need at least 2 GB")
+        data = b'x' * size
+        parser = cET.XMLParser()
+        try:
+            self.assertRaises(OverflowError, parser.feed, data)
+        finally:
+            data = None
+
+
 def test_main():
     from test import test_xml_etree, test_xml_etree_c
 
     # Run the tests specific to the C implementation
     support.run_doctest(test_xml_etree_c, verbosity=True)
 
+    support.run_unittest(MiscTests)
+
     # Assign the C implementation before running the doctests
     # Patch the __name__, to prevent confusion with the pure Python test
     pyET = test_xml_etree.ET