Support different types in the parameter store

The test framework stores size_t and int32_t values in the parameter store
by converting them all to int. This is ok in practice, since we assume int
covers int32_t and we don't have test data larger than 2GB. But it's
confusing and error-prone. So make the parameter store a union, which allows
size_t values not to be potentially truncated and makes the code a little
clearer.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/scripts/test_generate_test_code.py b/tests/scripts/test_generate_test_code.py
index 9a78ca1..c198ad0 100755
--- a/tests/scripts/test_generate_test_code.py
+++ b/tests/scripts/test_generate_test_code.py
@@ -485,9 +485,10 @@
         args, local, arg_dispatch = parse_function_arguments(line)
         self.assertEqual(args, ['char*', 'int', 'int'])
         self.assertEqual(local, '')
-        self.assertEqual(arg_dispatch, ['(char *) params[0]',
-                                        '*( (int *) params[1] )',
-                                        '*( (int *) params[2] )'])
+        self.assertEqual(arg_dispatch,
+                         ['(char *) params[0]',
+                          '((mbedtls_test_argument_t*)params[1])->s32',
+                          '((mbedtls_test_argument_t*)params[2])->s32'])
 
     def test_hex_params(self):
         """
@@ -499,10 +500,10 @@
         self.assertEqual(args, ['char*', 'hex', 'int'])
         self.assertEqual(local,
                          '    data_t data1 = {(uint8_t *) params[1], '
-                         '*( (uint32_t *) params[2] )};\n')
+                         '((mbedtls_test_argument_t*)params[2])->len};\n')
         self.assertEqual(arg_dispatch, ['(char *) params[0]',
                                         '&data1',
-                                        '*( (int *) params[3] )'])
+                                        '((mbedtls_test_argument_t*)params[3])->s32'])
 
     def test_unsupported_arg(self):
         """