3 files changed, 37 insertions, 4 deletions

diff --git a/src/python/m5/SimObject.py b/src/python/m5/SimObject.py
index 3b84d6000..8e14b63d2 100644
--- a/src/python/m5/SimObject.py
+++ b/src/python/m5/SimObject.py
@@ -623,7 +623,7 @@ class SimObject(object):
 
     def path(self):
         if not self._parent:
-            return 'root'
+            return '(orphan)'
         ppath = self._parent.path()
         if ppath == 'root':
             return self._name
diff --git a/src/python/m5/simulate.py b/src/python/m5/simulate.py
index e43f90173..2db5c6952 100644
--- a/src/python/m5/simulate.py
+++ b/src/python/m5/simulate.py
@@ -39,13 +39,19 @@ from main import options
 import SimObject
 import ticks
 import objects
+from util import fatal
 
 # define a MaxTick parameter
 MaxTick = 2**63 - 1
 
 # The final hook to generate .ini files.  Called from the user script
 # once the config is built.
-def instantiate(root):
+def instantiate():
+    root = objects.Root.getInstance()
+
+    if not root:
+        fatal("Need to instantiate Root() before calling instantiate()")
+
     # we need to fix the global frequency
     ticks.fixGlobalFrequency()
 
@@ -136,7 +142,8 @@ def drain(root):
 def resume(root):
     root.resume()
 
-def checkpoint(root, dir):
+def checkpoint(dir):
+    root = objects.Root.getInstance()
     if not isinstance(root, objects.Root):
         raise TypeError, "Checkpoint must be called on a root object."
     doDrain(root)
@@ -144,7 +151,8 @@ def checkpoint(root, dir):
     internal.core.serializeAll(dir)
     resume(root)
 
-def restoreCheckpoint(root, dir):
+def restoreCheckpoint(dir):
+    root = objects.Root.getInstance()
     print "Restoring from checkpoint"
     internal.core.unserializeAll(dir)
     need_resume.append(root)
diff --git a/src/sim/Root.py b/src/sim/Root.py
index fff998e0d..c7404a11f 100644
--- a/src/sim/Root.py
+++ b/src/sim/Root.py
@@ -28,7 +28,32 @@
 
 from m5.SimObject import SimObject
 from m5.params import *
+from m5.util import fatal
 
 class Root(SimObject):
+
+    _the_instance = None
+
+    def __new__(cls, **kwargs):
+        if Root._the_instance:
+            fatal("Attempt to allocate multiple instances of Root.")
+            return None
+
+        # first call: allocate the unique instance
+        #
+        # If SimObject ever implements __new__, we may want to pass
+        # kwargs here, but for now this goes straight to
+        # object.__new__ which prints an ugly warning if you pass it
+        # args.  Seems like a bad design but that's the way it is.
+        Root._the_instance = SimObject.__new__(cls)
+        return Root._the_instance
+        
+    @classmethod
+    def getInstance(cls):
+        return Root._the_instance
+
+    def path(self):
+        return 'root'
+
     type = 'Root'
     dummy = Param.Int(0, "We don't support objects without params")