See http://hg.openjdk.java.net/jdk/jdk/file/fab77e2d8146/src/hotspot/share/classfile/stringTable.cpp#l784

StringTable::create_archived_string() has intimate knowledge of the internal layout of String objects, and archive each reference field manually. This is cumbersome and will need to be updated if we ever change the String layout.

We should use a variant of HeapShared::archive_reachable_objects_from() which already archiving objects with arbitrary layout.