python: Add DeprecatedParam type

There are times when we need to change the name of parameter, but this
breaks the external-facing python API used in configuration files. Using
this "type" for a parameter will warn users that they are using the old
name, but allow for backwards compatibility.

Declaring a SimObject parameter of type `DeprecatedParam` allows the
python configuration files to use the old name transparently. This
leverages some of the SimObject magic to remember the names of
deprecated parameters and the DeprecatedParam object stores the
"translation" from old name to new name.

This has been tested with Ports, "normal" parameters, and SimObject
parameters. It has not been tested with checkpointing as there are no
checkpointing tests in gem5 right now. The testing was manually adding
some deprecated params and checking that config scripts still run
correctly that use the old, deprecated, variables.

Change-Id: I0465a748c08a24278d6b1a9d9ee1bcd67baa5b13
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31954
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/m5/SimObject.py

@@ -467,6 +467,12 @@ class MetaSimObject(type):
         cls._params = multidict() # param descriptions
         cls._ports = multidict()  # port descriptions
 
+        # Parameter names that are deprecated. Dict[str, DeprecatedParam]
+        # The key is the "old_name" so that when the old_name is used in
+        # python config files, we will use the DeprecatedParam object to
+        # translate to the new type.
+        cls._deprecated_params = multidict()
+
         # class or instance attributes
         cls._values = multidict()   # param values
         cls._hr_values = multidict() # human readable param values
@@ -495,6 +501,7 @@ class MetaSimObject(type):
             cls._base = base
             cls._params.parent = base._params
             cls._ports.parent = base._ports
+            cls._deprecated_params.parent = base._deprecated_params
             cls._values.parent = base._values
             cls._hr_values.parent = base._hr_values
             cls._children.parent = base._children
@@ -532,6 +539,15 @@ class MetaSimObject(type):
             elif isinstance(val, Port):
                 cls._new_port(key, val)
 
+            # Deprecated variable names
+            elif isinstance(val, DeprecatedParam):
+                new_name, new_val = cls._get_param_by_value(val.newParam)
+                # Note: We don't know the (string) name of this variable until
+                # here, so now we can finish setting up the dep_param.
+                val.oldName = key
+                val.newName = new_name
+                cls._deprecated_params[key] = val
+
             # init-time-only keywords
             elif key in cls.init_keywords:
                 cls._set_keyword(key, val, cls.init_keywords[key])
@@ -604,6 +620,18 @@ class MetaSimObject(type):
             cls._port_refs[attr] = ref
         return ref
 
+    def _get_param_by_value(cls, value):
+        """Given an object, value, return the name and the value from the
+        internal list of parameter values. If this value can't be found, raise
+        a runtime error. This will search both the current object and its
+        parents.
+        """
+        for k,v in cls._value_dict.items():
+            if v == value:
+                return k,v
+        raise RuntimeError("Cannot find parameter {} in parameter list"
+                           .format(value))
+
     # Set attribute (called on foo.attr = value when foo is an
     # instance of class cls).
     def __setattr__(cls, attr, value):
@@ -1255,6 +1283,11 @@ class SimObject(object):
         return ref
 
     def __getattr__(self, attr):
+        if attr in self._deprecated_params:
+            dep_param = self._deprecated_params[attr]
+            dep_param.printWarning(self._name, self.__class__.__name__)
+            return getattr(self, self._deprecated_params[attr].newName)
+
         if attr in self._ports:
             return self._get_port_ref(attr)
 
@@ -1287,6 +1320,11 @@ class SimObject(object):
             object.__setattr__(self, attr, value)
             return
 
+        if attr in self._deprecated_params:
+            dep_param = self._deprecated_params[attr]
+            dep_param.printWarning(self._name, self.__class__.__name__)
+            return setattr(self, self._deprecated_params[attr].newName, value)
+
         if attr in self._ports:
             # set up port connection
             self._get_port_ref(attr).connect(value)