Fix redefining of attributes on aliased arguments.

src/elements.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 687 matching lines @@
                               Object* receiver) {
     Object* probe = GetParameterMapArg(parameter_map, key);
     if (!probe->IsTheHole()) {
       Context* context = Context::cast(parameter_map->get(0));
       int context_index = Smi::cast(probe)->value();
       ASSERT(!context->get(context_index)->IsTheHole());
       return context->get(context_index);
     } else {
       // Object is not mapped, defer to the arguments.
       FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
-      return ElementsAccessor::ForArray(arguments)->Get(arguments,
-                                                        key,
-                                                        obj,
-                                                        receiver);
+      MaybeObject* maybe_result = ElementsAccessor::ForArray(arguments)->Get(
+          arguments, key, obj, receiver);
+      Object* result;
+      if (!maybe_result->ToObject(&result)) return maybe_result;
+      // Elements of the arguments object in slow mode might be slow aliases.
+      if (result->IsAliasedArgumentsEntry()) {
+        AliasedArgumentsEntry* entry = AliasedArgumentsEntry::cast(result);
+        Context* context = Context::cast(parameter_map->get(0));
+        int context_index = entry->aliased_context_slot();
+        ASSERT(!context->get(context_index)->IsTheHole());
+        return context->get(context_index);
+      } else {
+        return result;
+      }
     }
   }
 
   static MaybeObject* SetLengthImpl(FixedArray* parameter_map,
                                     JSObject* obj,
                                     Object* length) {
     // TODO(mstarzinger): This was never implemented but will be used once we
     // correctly implement [[DefineOwnProperty]] on arrays.
     UNIMPLEMENTED();
     return obj;
@@ skipping 190 matching lines @@
   if (!maybe_obj->To(&new_backing_store)) return maybe_obj;
   new_backing_store->set(0, length);
   { MaybeObject* result = array->SetContent(new_backing_store);
     if (result->IsFailure()) return result;
   }
   return array;
 }
 
 
 } }  // namespace v8::internal