[not sure] weakrefs for old-style classes

src/runtime/classobj.cpp

@@ -272,8 +272,9 @@ Box* instanceSetitem(Box* _inst, Box* key, Box* value) {
 void setupClassobj() {
     classobj_cls = BoxedHeapClass::create(type_cls, object_cls, &BoxedClassobj::gcHandler,
                                           offsetof(BoxedClassobj, attrs), 0, sizeof(BoxedClassobj), false, "classobj");
-    instance_cls = BoxedHeapClass::create(type_cls, object_cls, &BoxedInstance::gcHandler,
-                                          offsetof(BoxedInstance, attrs), 0, sizeof(BoxedInstance), false, "instance");
+    instance_cls
+        = BoxedHeapClass::create(type_cls, object_cls, &BoxedInstance::gcHandler, offsetof(BoxedInstance, attrs),
+                                 offsetof(BoxedInstance, weakreflist), sizeof(BoxedInstance), false, "instance");
 
     classobj_cls->giveAttr("__new__",
                            new BoxedFunction(boxRTFunction((void*)classobjNew, UNKNOWN, 4, 0, false, false)));

src/runtime/classobj.h

@@ -54,6 +54,8 @@ public:
 
     BoxedClassobj* inst_cls;
 
+    Box** weakreflist;
+
     BoxedInstance(BoxedClassobj* inst_cls) : inst_cls(inst_cls) {}
 
     DEFAULT_CLASS(instance_cls);