systemc: If sc_main returns, don't do any more systemc stuff.

When sc_main returns, clear out any pending work in the scheduler and
also block the systemc kernel from doing actions which correspond with
the start of simulation.

It's most likely that work like oustanding timeouts might survive past
the end of sc_main, especially if it never officially called sc_stop.
It's also possible for sc_main to return and never actually call
sc_start. In that case, the kernel should not call callbacks of the
various objects (which may no longer even exist), or go through the
initialization phase.

If sc_main is never called at all, then the kernel's actions aren't
gated.

Change-Id: I49bf094be3283a92d846d2f3da224950bd893a5c
Reviewed-on: https://gem5-review.googlesource.com/12249
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

src/systemc/core/kernel.cc

@@ -40,6 +40,7 @@ namespace sc_gem5
 namespace
 {
 
+bool scMainDone = false;
 bool stopAfterCallbacks = false;
 bool startComplete = false;
 bool endComplete = false;
@@ -51,6 +52,9 @@ sc_core::sc_status _status = sc_core::SC_ELABORATION;
 bool Kernel::startOfSimulationComplete() { return startComplete; }
 bool Kernel::endOfSimulationComplete() { return endComplete; }
 
+bool Kernel::scMainFinished() { return scMainDone; }
+void Kernel::scMainFinished(bool finished) { scMainDone = finished; }
+
 sc_core::sc_status Kernel::status() { return _status; }
 void Kernel::status(sc_core::sc_status s) { _status = s; }
 
@@ -64,6 +68,9 @@ Kernel::Kernel(Params *params) :
 void
 Kernel::init()
 {
+    if (scMainDone)
+        return;
+
     status(::sc_core::SC_BEFORE_END_OF_ELABORATION);
     for (auto m: sc_gem5::allModules) {
         callbackModule(m);
@@ -84,6 +91,9 @@ Kernel::init()
 void
 Kernel::regStats()
 {
+    if (scMainDone)
+        return;
+
     for (auto m: sc_gem5::allModules)
         for (auto p: m->ports)
             p->_gem5Finalize();
@@ -106,6 +116,9 @@ Kernel::regStats()
 void
 Kernel::startup()
 {
+    if (scMainDone)
+        return;
+
     status(::sc_core::SC_START_OF_SIMULATION);
     for (auto m: sc_gem5::allModules) {
         m->sc_mod()->start_of_simulation();