binutils sim breakpoint support

[William Tambe]

What must be implemented within binutils sim such that when GDB use it
as a target, it can recognize a breakpoint.

In fact, within the simulator function sim_engine_run(), when the
breakpoint instruction is decoded, I am using the following to report
SIM_SIGTRAP

sim_engine_halt (sd, scpu, NULL, pc, sim_stopped, SIM_SIGTRAP);

However GDB fail printing the following in its console:
Program received signal SIGTRAP, Trace/breakpoint trap.
0x00000000 in ?? ()

Is the above use of sim_engine_halt() the proper way to report a
breakpoint so that GDB can handle breakpoints ?