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>

src/sim/eventq.hh

@@ -46,6 +46,7 @@
 
 #include "base/debug.hh"
 #include "base/flags.hh"
+#include "base/trace.hh"
 #include "base/types.hh"
 #include "base/uncontended_mutex.hh"
 #include "debug/Event.hh"

src/sim/sim_events.hh

@@ -68,8 +68,11 @@ class GlobalSimLoopExitEvent : public GlobalEvent
     const std::string getCause() const { return cause; }
     int getCode() const { return code; }
 
-    void process();     // process event
-
+    virtual void process();// process event
+    virtual void clean(){};//cleaning event
+    ~GlobalSimLoopExitEvent (){
+      DPRINTF(Event,"GlobalSimLoopExitEvent destructed\n");
+    };
     virtual const char *description() const;
 };
 

src/sim/simulate.cc

@@ -184,9 +184,12 @@ struct DescheduleDeleter
  * terminate the loop.  Exported to Python.
  * @return The SimLoopExitEvent that caused the loop to exit.
  */
+GlobalSimLoopExitEvent *global_exit_event= nullptr;
 GlobalSimLoopExitEvent *
 simulate(Tick num_cycles)
 {
+    if (global_exit_event)//cleaning last global exit event
+        global_exit_event->clean();
     std::unique_ptr<GlobalSyncEvent, DescheduleDeleter> quantum_event;
     const Tick exit_tick = num_cycles < MaxTick - curTick() ?
                                         curTick() + num_cycles : MaxTick;
@@ -224,7 +227,7 @@ simulate(Tick num_cycles)
     BaseGlobalEvent *global_event = local_event->globalEvent();
     assert(global_event);
 
-    GlobalSimLoopExitEvent *global_exit_event =
+    global_exit_event =
         dynamic_cast<GlobalSimLoopExitEvent *>(global_event);
     assert(global_exit_event);