anchor.diff:  -define(BP_QUEUE,    5).
   -define(BP_STEPPED,  6).
   -define(BP_STEPPER,  7).
  +-define(EXC_SUBS,    8).
   
   %% userdevguide-begin gen_component:behaviour
   -ifdef(have_callback_support).
  
positive.code:                "** Source linetrace (enable in scalaris.hrl):~n ~.0p~n"
                 "** State:~n ~.0p~n"
                 "** Stacktrace:~n ~.0p~n",
      DbgVal = [Level, Reason,
                Msg,
                gc_mod(GCState),
                gc_hand(GCState),
                self(), catch pid_groups:group_and_name_of(self()),
                erlang:get(test_server_loc),
                {UState, GCState},
                Stacktrace],
      log_or_fail(DbgMsg, DbgVal, exception_throw).
  
  -spec log_or_fail(DbgMsg::string(), DbgVal::[term()],
                    Reason::unknown_message | exception_throw) -> ok.
  
negative.code: %     Options, _Slowest = 0.0,
       _BPs = [], _BPActive = false,
       _BPHoldbackQueue = [], _BPStepped = false,
       _BPStepperPid = unknown,
       _ExcSubs = []
      }.
  gc_mod(State) ->                element(?MOD, State).
  gc_hand(State) ->               element(?HAND, State).
  gc_set_hand(State, Handler) ->  setelement(?HAND, State, Handler).
  gc_exc_subs(State) ->           element(?EXC_SUBS, State).
  gc_set_exc_subs(State, Subs) -> setelement(?EXC_SUBS, State, Subs).
  %% opts
  %% slowest
  -spec gc_bps(gc_state()) -> [bp()].
  