diff -r 000000000000 -r 6474c204b198 js/src/jsapi-tests/testValueABI.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jsapi-tests/testValueABI.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,54 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "jsapi-tests/tests.h"
+
+/*
+ * Bug 689101 - jsval is technically a non-POD type because it has a private
+ * data member. On gcc, this doesn't seem to matter. On MSVC, this prevents
+ * returning a jsval from a function between C and C++ because it will use a
+ * retparam in C++ and a direct return value in C.
+ *
+ * Bug 712289 - jsval alignment was different on 32-bit platforms between C and
+ * C++ because the default alignments of js::Value and jsval_layout differ.
+ */
+
+extern "C" {
+
+extern bool
+C_ValueToObject(JSContext *cx, jsval v, JSObject **obj);
+
+extern jsval
+C_GetEmptyStringValue(JSContext *cx);
+
+extern size_t
+C_jsvalAlignmentTest();
+
+}
+
+BEGIN_TEST(testValueABI_retparam)
+{
+    JS::RootedObject obj(cx, JS::CurrentGlobalOrNull(cx));
+    jsval v = OBJECT_TO_JSVAL(obj);
+    obj = nullptr;
+    CHECK(C_ValueToObject(cx, v, obj.address()));
+    bool equal;
+    CHECK(JS_StrictlyEqual(cx, v, OBJECT_TO_JSVAL(obj), &equal));
+    CHECK(equal);
+
+    v = C_GetEmptyStringValue(cx);
+    CHECK(JSVAL_IS_STRING(v));
+
+    return true;
+}
+END_TEST(testValueABI_retparam)
+
+BEGIN_TEST(testValueABI_alignment)
+{
+    typedef struct { char c; jsval v; } AlignTest;
+    CHECK(C_jsvalAlignmentTest() == sizeof(AlignTest));
+
+    return true;
+}
+END_TEST(testValueABI_alignment)