The debugging stub for your architecture supplies these three subroutines:
This routine arranges for
handle_exception to run when your
program stops. You must call this subroutine explicitly in your
program’s startup code.
This is the central workhorse, but your program never calls it
explicitly—the setup code arranges for
run when a trap is triggered.
handle_exception takes control when your program stops during
execution (for example, on a breakpoint), and mediates communications
with GDB on the host machine. This is where the communications
protocol is implemented;
handle_exception acts as the GDB
representative on the target machine. It begins by sending summary
information on the state of your program, then continues to execute,
retrieving and transmitting any information GDB needs, until you
execute a GDB command that makes your program resume; at that point,
handle_exception returns control to your own code on the target
Use this auxiliary subroutine to make your program contain a
breakpoint. Depending on the particular situation, this may be the only
way for GDB to get control. For instance, if your target
machine has some sort of interrupt button, you won’t need to call this;
pressing the interrupt button transfers control to
handle_exception—in effect, to GDB. On some machines,
simply receiving characters on the serial port may also trigger a trap;
again, in that situation, you don’t need to call
your own program—simply running ‘target remote’ from the host
GDB session gets control.
breakpoint if none of these is true, or if you simply want
to make certain your program stops at a predetermined point for the
start of your debugging session.