Add a new function uses_seh() to the _ctypes extension module. This

will return True if Windows Structured Exception handling (SEH) is
used when calling functions, False otherwise.

Currently, only MSVC supports SEH.

Fix the test so that it doesn't crash when run with MingW compiled
_ctypes.  Note that two tests are still failing when mingw is used, I
suspect structure layout differences and function calling conventions
between MSVC and MingW.

Lib/ctypes/test/test_win32.py

@@ -30,15 +30,11 @@ if sys.platform == "win32":
             # or wrong calling convention
             self.assertRaises(ValueError, IsWindow, None)
 
-        def test_SEH(self):
-            # Call functions with invalid arguments, and make sure that access violations
-            # are trapped and raise an exception.
-            #
-            # Normally, in a debug build of the _ctypes extension
-            # module, exceptions are not trapped, so we can only run
-            # this test in a release build.
-            import sys
-            if not hasattr(sys, "getobjects"):
+        import _ctypes
+        if _ctypes.uses_seh():
+            def test_SEH(self):
+                # Call functions with invalid arguments, and make sure that access violations
+                # are trapped and raise an exception.
                 self.assertRaises(WindowsError, windll.kernel32.GetModuleHandleA, 32)
 
 class Structures(unittest.TestCase):

Modules/_ctypes/callproc.c

@@ -1526,7 +1526,21 @@ resize(PyObject *self, PyObject *args)
 	return Py_None;
 }
 
+static PyObject *
+uses_seh(PyObject *self, PyObject *args)
+{
+#if defined(DONT_USE_SEH) || !defined(MS_WIN32)
+	Py_INCREF(Py_False);
+	return Py_False;
+#else
+	Py_INCREF(Py_True);
+	return Py_True;
+#endif
+}
+
 PyMethodDef module_methods[] = {
+	{"uses_seh", uses_seh, METH_NOARGS,
+	 "Return whether ctypes uses Windows structured exception handling"},
 	{"resize", resize, METH_VARARGS, "Resize the memory buffer of a ctypes instance"},
 #ifdef CTYPES_UNICODE
 	{"set_conversion_mode", set_conversion_mode, METH_VARARGS, set_conversion_mode_doc},