cpu: Query CPU for inst executed from Python

This patch adds the ability for the simulator to query the number of
instructions a CPU has executed so far per hw-thread. This can be used
to enable more flexible periodic events such as taking checkpoints
starting 1s into simulation and X instructions thereafter.

src/cpu/BaseCPU.py

@@ -101,6 +101,7 @@ class BaseCPU(MemObject):
     Counter totalInsts();
     void scheduleInstStop(ThreadID tid, Counter insts, const char *cause);
     void scheduleLoadStop(ThreadID tid, Counter loads, const char *cause);
+    uint64_t getCurrentInstCount(ThreadID tid);
 ''')
 
     @classmethod

src/cpu/base.cc

@@ -691,6 +691,12 @@ BaseCPU::scheduleInstStop(ThreadID tid, Counter insts, const char *cause)
     comInstEventQueue[tid]->schedule(event, now + insts);
 }
 
+uint64_t
+BaseCPU::getCurrentInstCount(ThreadID tid)
+{
+    return Tick(comInstEventQueue[tid]->getCurTick());
+}
+
 AddressMonitor::AddressMonitor() {
     armed = false;
     waiting = false;

src/cpu/base.hh

@@ -465,6 +465,15 @@ class BaseCPU : public MemObject
      */
     void scheduleLoadStop(ThreadID tid, Counter loads, const char *cause);
 
+    /**
+     * Get the number of instructions executed by the specified thread
+     * on this CPU. Used by Python to control simulation.
+     *
+     * @param tid Thread monitor
+     * @return Number of instructions executed
+     */
+    uint64_t getCurrentInstCount(ThreadID tid);
+
   public:
     /**
      * @{