base,sim: Adding monitor function to GDB

The remote protocol provides a monitor query. This query allows to
provide a implementation defined behavior in the stub.

I proposed to use this command as a way to quit simulation with a
message provided by the GDB client.

Thus calling "monitor my_message" in the client will exit the
simulation with the exit message "GDB_MONITOR:my_message".

This is implemented through a derived class based on
GlobalSimLoopExitEvent and a small addition to the based class that adds
a clean method that will be called when returning siumation after the
Event.

Change-Id: Ib5fda569edcf6733cbcc6240ef6d2ec4dc6502ec
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63538
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
5 files changed