While using a debug build with -fno-elide-constructors turned on, which turns off C++ Return Value Optimization, I get a crash because the JvmtiAgentList::Iterator destructor frees the same _stack object twice.  This happens because code like

Iterator it = xrun_agents();

creates a temprary object.  My understanding is that Return Value Optimization is not guaranteed with C++14, so we should not be relying on it for code correctness.