Beta version of Python configuration tool. Generates .ini files from

Python script description.

arch/alpha/alpha_memory.cc:
dev/io_device.cc:
    Add DEFINE_SIM_OBJECT_CLASS_NAME for intermediate SimObjects.
test/paramtest.cc:
    Fix stupid spelling.

--HG--
extra : convert_revision : dc020208cb6507c1afb1ed771a7218daba678e09

1 files changed, 743 insertions, 0 deletions

diff --git a/util/config/m5config.py b/util/config/m5config.py
new file mode 100644
index 000000000..ea5d68504
--- /dev/null
+++ b/util/config/m5config.py
@@ -0,0 +1,743 @@
+from __future__ import generators
+
+import os
+import re
+import sys
+
+#####################################################################
+#
+# M5 Python Configuration Utility
+#
+# The basic idea is to write simple Python programs that build Python
+# objects corresponding to M5 SimObjects for the deisred simulation
+# configuration.  For now, the Python emits a .ini file that can be
+# parsed by M5.  In the future, some tighter integration between M5
+# and the Python interpreter may allow bypassing the .ini file.
+#
+# Each SimObject class in M5 is represented by a Python class with the
+# same name.  The Python inheritance tree mirrors the M5 C++ tree
+# (e.g., SimpleCPU derives from BaseCPU in both cases, and all
+# SimObjects inherit from a single SimObject base class).  To specify
+# an instance of an M5 SimObject in a configuration, the user simply
+# instantiates the corresponding Python object.  The parameters for
+# that SimObject are given by assigning to attributes of the Python
+# object, either using keyword assignment in the constructor or in
+# separate assignment statements.  For example:
+#
+# cache = BaseCache('my_cache', root, size=64*K)
+# cache.hit_latency = 3
+# cache.assoc = 8
+#
+# (The first two constructor arguments specify the name of the created
+# cache and its parent node in the hierarchy.)
+#
+# The magic lies in the mapping of the Python attributes for SimObject
+# classes to the actual SimObject parameter specifications.  This
+# allows parameter validity checking in the Python code.  Continuing
+# the example above, the statements "cache.blurfl=3" or
+# "cache.assoc='hello'" would both result in runtime errors in Python,
+# since the BaseCache object has no 'blurfl' parameter and the 'assoc'
+# parameter requires an integer, respectively.  This magic is done
+# primarily by overriding the special __setattr__ method that controls
+# assignment to object attributes.
+#
+# The Python module provides another class, ConfigNode, which is a
+# superclass of SimObject.  ConfigNode implements the parent/child
+# relationship for building the configuration hierarchy tree.
+# Concrete instances of ConfigNode can be used to group objects in the
+# hierarchy, but do not correspond to SimObjects themselves (like a
+# .ini section with "children=" but no "type=".
+#
+# Once a set of Python objects have been instantiated in a hierarchy,
+# calling 'instantiate(obj)' (where obj is the root of the hierarchy)
+# will generate a .ini file.  See simple-4cpu.py for an example
+# (corresponding to m5-test/simple-4cpu.ini).
+#
+#####################################################################
+
+#####################################################################
+#
+# ConfigNode/SimObject classes
+#
+# The Python class hierarchy rooted by ConfigNode (which is the base
+# class of SimObject, which in turn is the base class of all other M5
+# SimObject classes) has special attribute behavior.  In general, an
+# object in this hierarchy has three categories of attribute-like
+# things:
+#
+# 1. Regular Python methods and variables.  These must start with an
+# underscore to be treated normally.
+#
+# 2. SimObject parameters.  These values are stored as normal Python
+# attributes, but all assignments to these attributes are checked
+# against the pre-defined set of parameters stored in the class's
+# _param_dict dictionary.  Assignments to attributes that do not
+# correspond to predefined parameters, or that are not of the correct
+# type, incur runtime errors.
+#
+# 3. Hierarchy children.  The child nodes of a ConfigNode are stored
+# in the node's _children dictionary, but can be accessed using the
+# Python attribute dot-notation (just as they are printed out by the
+# simulator).  Children cannot be created using attribute assigment;
+# they must be added by specifying the parent node in the child's
+# constructor or using the '+=' operator.
+
+# The SimObject parameters are the most complex, for a few reasons.
+# First, both parameter descriptions and parameter values are
+# inherited.  Thus parameter description lookup must go up the
+# inheritance chain like normal attribute lookup, but this behavior
+# must be explicitly coded since the lookup occurs in each class's
+# _param_dict attribute.  Second, because parameter values can be set
+# on SimObject classes (to implement default values), the parameter
+# checking behavior must be enforced on class attribute assignments as
+# well as instance attribute assignments.  Finally, because we allow
+# class specialization via inheritance (e.g., see the L1Cache class in
+# the simple-4cpu.py example), we must do parameter checking even on
+# class instantiation.  To provide all these features, we use a
+# metaclass to define most of the SimObject parameter behavior for
+# this class hierarchy.
+#
+#####################################################################
+
+# The metaclass for ConfigNode (and thus for everything that dervies
+# from ConfigNode, including SimObject).  This class controls how new
+# classes that derive from ConfigNode are instantiated, and provides
+# inherited class behavior (just like a class controls how instances
+# of that class are instantiated, and provides inherited instance
+# behavior).
+class MetaConfigNode(type):
+
+    # __new__ is called before __init__, and is where the statements
+    # in the body of the class definition get loaded into the class's
+    # __dict__.  We intercept this to filter out parameter assignments
+    # and only allow "private" attributes to be passed to the base
+    # __new__ (starting with underscore).
+    def __new__(cls, name, bases, dict):
+        priv_keys = [k for k in dict.iterkeys() if k.startswith('_')]
+        priv_dict = {}
+        for k in priv_keys: priv_dict[k] = dict[k]; del dict[k]
+        # entries left in dict will get passed to __init__, where we'll
+        # deal with them as params.
+        return super(MetaConfigNode, cls).__new__(cls, name, bases, priv_dict)
+
+    # initialization: start out with an empty param dict (makes life
+    # simpler if we can assume _param_dict is always valid).  Also
+    # build inheritance list to simplify searching for inherited
+    # params.  Finally set parameters specified in class definition
+    # (if any).
+    def __init__(cls, name, bases, dict):
+        super(MetaConfigNode, cls).__init__(cls, name, bases, {})
+        # initialize _param_dict to empty
+        cls._param_dict = {}
+        # __mro__ is the ordered list of classes Python uses for
+        # method resolution.  We want to pick out the ones that have a
+        # _param_dict attribute for doing parameter lookups.
+        cls._param_bases = \
+                         [c for c in cls.__mro__ if hasattr(c, '_param_dict')]
+        # initialize attributes with values from class definition
+        for (pname, value) in dict.items():
+            try:
+                setattr(cls, pname, value)
+            except Exception, exc:
+                print "Error setting '%s' to '%s' on class '%s'\n" \
+                      % (pname, value, cls.__name__), exc
+
+    # set the class's parameter dictionary (called when loading
+    # class descriptions)
+    def set_param_dict(cls, param_dict):
+        # should only be called once (current one should be empty one
+        # from __init__)
+        assert not cls._param_dict
+        cls._param_dict = param_dict
+        # initialize attributes with default values
+        for (pname, param) in param_dict.items():
+            try:
+                setattr(cls, pname, param.default)
+            except Exception, exc:
+                print "Error setting '%s' default on class '%s'\n" \
+                      % (pname, cls.__name__), exc
+
+    # Lookup a parameter description by name in the given class.  Use
+    # the _param_bases list defined in __init__ to go up the
+    # inheritance hierarchy if necessary.
+    def lookup_param(cls, param_name):
+        for c in cls._param_bases:
+            param = c._param_dict.get(param_name)
+            if param: return param
+        return None
+
+    # Set attribute (called on foo.attr_name = value when foo is an
+    # instance of class cls).
+    def __setattr__(cls, attr_name, value):
+        # normal processing for private attributes
+        if attr_name.startswith('_'):
+            object.__setattr__(cls, attr_name, value)
+            return
+        # no '_': must be SimObject param
+        param = cls.lookup_param(attr_name)
+        if not param:
+            raise AttributeError, \
+                  "Class %s has no parameter %s" % (cls.__name__, attr_name)
+        # It's ok: set attribute by delegating to 'object' class.
+        # Note the use of param.make_value() to verify/canonicalize
+        # the assigned value
+        object.__setattr__(cls, attr_name, param.make_value(value))
+
+    # generator that iterates across all parameters for this class and
+    # all classes it inherits from
+    def all_param_names(cls):
+        for c in cls._param_bases:
+            for p in c._param_dict.iterkeys():
+                yield p
+
+# The ConfigNode class is the root of the special hierarchy.  Most of
+# the code in this class deals with the configuration hierarchy itself
+# (parent/child node relationships).
+class ConfigNode(object):
+    # Specify metaclass.  Any class inheriting from ConfigNode will
+    # get this metaclass.
+    __metaclass__ = MetaConfigNode
+
+    # Constructor.  Since bare ConfigNodes don't have parameters, just
+    # worry about the name and the parent/child stuff.
+    def __init__(self, _name, _parent=None):
+        # Type-check _name
+        if type(_name) != str:
+            if isinstance(_name, ConfigNode):
+                # special case message for common error of trying to
+                # coerce a SimObject to the wrong type
+                raise TypeError, \
+                      "Attempt to coerce %s to %s" \
+                      % (_name.__class__.__name__, self.__class__.__name__)
+            else:
+                raise TypeError, \
+                      "%s name must be string (was %s, %s)" \
+                      % (self.__class__.__name__, _name, type(_name))
+        # if specified, parent must be a subclass of ConfigNode
+        if _parent != None and not isinstance(_parent, ConfigNode):
+            raise TypeError, \
+                  "%s parent must be ConfigNode subclass (was %s, %s)" \
+                  % (self.__class__.__name__, _name, type(_name))
+        self._name = _name
+        self._parent = _parent
+        self._children = {}
+        if (_parent):
+            _parent.__addChild(self)
+        # Set up absolute path from root.
+        if (_parent and _parent._path != 'Universe'):
+            self._path = _parent._path + '.' + self._name
+        else:
+            self._path = self._name
+
+    # When printing (e.g. to .ini file), just give the name.
+    def __str__(self):
+        return self._name
+
+    # Catch attribute accesses that could be requesting children, and
+    # satisfy them.  Note that __getattr__ is called only if the
+    # regular attribute lookup fails, so private and parameter lookups
+    # will already be satisfied before we ever get here.
+    def __getattr__(self, name):
+        try:
+            return self._children[name]
+        except KeyError:
+            raise AttributeError, \
+                  "Node '%s' has no attribute or child '%s'" \
+                  % (self._name, name)
+
+    # Set attribute.  All attribute assignments go through here.  Must
+    # be private attribute (starts with '_') or valid parameter entry.
+    # Basically identical to MetaConfigClass.__setattr__(), except
+    # this handles instances rather than class attributes.
+    def __setattr__(self, attr_name, value):
+        if attr_name.startswith('_'):
+            object.__setattr__(self, attr_name, value)
+            return
+        # not private; look up as param
+        param = self.__class__.lookup_param(attr_name)
+        if not param:
+            raise AttributeError, \
+                  "Class %s has no parameter %s" \
+                  % (self.__class__.__name__, attr_name)
+        # It's ok: set attribute by delegating to 'object' class.
+        # Note the use of param.make_value() to verify/canonicalize
+        # the assigned value
+        object.__setattr__(self, attr_name, param.make_value(value))
+
+    # Add a child to this node.
+    def __addChild(self, new_child):
+        # set child's parent before calling this function
+        assert new_child._parent == self
+        if not isinstance(new_child, ConfigNode):
+            raise TypeError, \
+                  "ConfigNode child must also be of class ConfigNode"
+        if new_child._name in self._children:
+            raise AttributeError, \
+                  "Node '%s' already has a child '%s'" \
+                  % (self._name, new_child._name)
+        self._children[new_child._name] = new_child
+
+    # operator overload for '+='.  You can say "node += child" to add
+    # # a child that was created with parent=None.  An early attempt
+    # at # playing with syntax; turns out not to be that useful.
+    def __iadd__(self, new_child):
+        if new_child._parent != None:
+            raise AttributeError, \
+                  "Node '%s' already has a parent" % new_child._name
+        new_child._parent = self
+        self.__addChild(new_child)
+        return self
+
+    # Print instance info to .ini file.
+    def _instantiate(self):
+        print '[' + self._path + ']'	# .ini section header
+        if self._children:
+            # instantiate children in sorted order for backward
+            # compatibility (else we can end up with cpu1 before cpu0).
+            child_names = self._children.keys()
+            child_names.sort()
+            print 'children =',
+            for child_name in child_names:
+                print child_name,
+            print
+        self._instantiateParams()
+        print
+        # recursively dump out children
+        if self._children:
+            for child_name in child_names:
+                self._children[child_name]._instantiate()
+
+    # ConfigNodes have no parameters.  Overridden by SimObject.
+    def _instantiateParams(self):
+        pass
+
+# SimObject is a minimal extension of ConfigNode, implementing a
+# hierarchy node that corresponds to an M5 SimObject.  It prints out a
+# "type=" line to indicate its SimObject class, prints out the
+# assigned parameters corresponding to its class, and allows
+# parameters to be set by keyword in the constructor.  Note that most
+# of the heavy lifting for the SimObject param handling is done in the
+# MetaConfigNode metaclass.
+
+class SimObject(ConfigNode):
+    # initialization: like ConfigNode, but handle keyword-based
+    # parameter initializers.
+    def __init__(self, _name, _parent=None, **params):
+        ConfigNode.__init__(self, _name, _parent)
+        for param, value in params.items():
+            setattr(self, param, value)
+
+    # print type and parameter values to .ini file
+    def _instantiateParams(self):
+        print "type =", self.__class__._name
+        for pname in self.__class__.all_param_names():
+            value = getattr(self, pname)
+            if value != None:
+                print pname, '=', value
+
+#####################################################################
+#
+# Parameter description classes
+#
+# The _param_dict dictionary in each class maps parameter names to
+# either a Param or a VectorParam object.  These objects contain the
+# parameter description string, the parameter type, and the default
+# value (loaded from the PARAM section of the .odesc files).  The
+# make_value() method on these objects is used to force whatever value
+# is assigned to the parameter to the appropriate type.
+#
+# Note that the default values are loaded into the class's attribute
+# space when the parameter dictionary is initialized (in
+# MetaConfigNode.set_param_dict()); after that point they aren't
+# used.
+#
+#####################################################################
+
+# Force parameter value (rhs of '=') to ptype (or None, which means
+# not set).
+def make_param_value(ptype, value):
+    # nothing to do if None or already correct type
+    if value == None or isinstance(value, ptype):
+        return value
+    # this type conversion will raise an exception if it's illegal
+    return ptype(value)
+
+# Regular parameter.
+class Param(object):
+    # Constructor.  E.g., Param(Int, "number of widgets", 5)
+    def __init__(self, ptype, desc, default=None):
+        self.ptype = ptype
+        self.desc = desc
+        self.default = default
+
+    # Convert assigned value to appropriate type.
+    def make_value(self, value):
+        return make_param_value(self.ptype, value)
+
+# The _VectorParamValue class is a wrapper for vector-valued
+# parameters.  The leading underscore indicates that users shouldn't
+# see this class; it's magically generated by VectorParam.  The
+# parameter values are stored in the 'value' field as a Python list of
+# whatever type the parameter is supposed to be.  The only purpose of
+# storing these instead of a raw Python list is that we can override
+# the __str__() method to not print out '[' and ']' in the .ini file.
+class _VectorParamValue(object):
+    def __init__(self, list):
+        self.value = list
+
+    def __str__(self):
+        return ' '.join(map(str, self.value))
+
+# Vector-valued parameter description.  Just like Param, except that
+# the value is a vector (list) of the specified type instead of a
+# single value.
+class VectorParam(object):
+    # Constructor.  The resulting parameter will be a list of ptype.
+    def __init__(self, ptype, desc, default=None):
+        self.ptype = ptype
+        self.desc = desc
+        self.default = default
+
+    # Convert assigned value to appropriate type.  If the RHS is not a
+    # list or tuple, it generates a single-element list.
+    def make_value(self, value):
+        if value == None: return value
+        if isinstance(value, list) or isinstance(value, tuple):
+            # list: coerce each element into new list
+            val_list = [make_param_value(self.ptype, v) for v in
+                        iter(value)]
+        else:
+            # singleton: coerce & wrap in a list
+            val_list = [ make_param_value(self.ptype, value) ]
+        # wrap list in _VectorParamValue (see above)
+        return _VectorParamValue(val_list)
+
+#####################################################################
+#
+# Parameter Types
+#
+# Though native Python types could be used to specify parameter types
+# (the 'ptype' field of the Param and VectorParam classes), it's more
+# flexible to define our own set of types.  This gives us more control
+# over how Python expressions are converted to values (via the
+# __init__() constructor) and how these values are printed out (via
+# the __str__() conversion method).  Eventually we'll need these types
+# to correspond to distinct C++ types as well.
+#
+#####################################################################
+
+# Integer parameter type.
+class Int(object):
+    # Constructor.  Value must be Python int or long (long integer).
+    def __init__(self, value):
+        t = type(value)
+        if t == int or t == long:
+            self.value = value
+        else:
+            raise TypeError, "Int param got value %s %s" % (repr(value), t)
+
+    # Use Python string conversion.  Note that this puts an 'L' on the
+    # end of long integers; we can strip that off here if it gives us
+    # trouble.
+    def __str__(self):
+        return str(self.value)
+
+# Counter, Addr, and Tick are just aliases for Int for now.
+class Counter(Int):
+    pass
+
+class Addr(Int):
+    pass
+
+class Tick(Int):
+    pass
+
+# Boolean parameter type.
+class Bool(object):
+
+    # Constructor.  Typically the value will be one of the Python bool
+    # constants True or False (or the aliases true and false below).
+    # Also need to take integer 0 or 1 values since bool was not a
+    # distinct type in Python 2.2.  Parse a bunch of boolean-sounding
+    # strings too just for kicks.
+    def __init__(self, value):
+        t = type(value)
+        if t == bool:
+            self.value = value
+        elif t == int or t == long:
+            if value == 1:
+                self.value = True
+            elif value == 0:
+                self.value = False
+        elif t == str:
+            v = value.lower()
+            if v == "true" or v == "t" or v == "yes" or v == "y":
+                self.value = True
+            elif v == "false" or v == "f" or v == "no" or v == "n":
+                self.value = False
+        # if we didn't set it yet, it must not be something we understand
+        if not hasattr(self, 'value'):
+            raise TypeError, "Bool param got value %s %s" % (repr(value), t)
+
+    # Generate printable string version.
+    def __str__(self):
+        if self.value: return "true"
+        else: return "false"
+
+# String-valued parameter.
+class String(object):
+    # Constructor.  Value must be Python string.
+    def __init__(self, value):
+        t = type(value)
+        if t == str:
+            self.value = value
+        else:
+            raise TypeError, "String param got value %s %s" % (repr(value), t)
+
+    # Generate printable string version.  Not too tricky.
+    def __str__(self):
+        return self.value
+
+
+# Enumerated types are a little more complex.  The user specifies the
+# type as Enum(foo) where foo is either a list or dictionary of
+# alternatives (typically strings, but not necessarily so).  (In the
+# long run, the integer value of the parameter will be the list index
+# or the corresponding dictionary value.  For now, since we only check
+# that the alternative is valid and then spit it into a .ini file,
+# there's not much point in using the dictionary.)
+
+# What Enum() must do is generate a new type encapsulating the
+# provided list/dictionary so that specific values of the parameter
+# can be instances of that type.  We define two hidden internal
+# classes (_ListEnum and _DictEnum) to serve as base classes, then
+# derive the new type from the appropriate base class on the fly.
+
+
+# Base class for list-based Enum types.
+class _ListEnum(object):
+    # Constructor.  Value must be a member of the type's map list.
+    def __init__(self, value):
+        if value in self.map:
+            self.value = value
+            self.index = self.map.index(value)
+        else:
+            raise TypeError, "Enum param got bad value '%s' (not in %s)" \
+                  % (value, self.map)
+
+    # Generate printable string version of value.
+    def __str__(self):
+        return str(self.value)
+
+class _DictEnum(object):
+    # Constructor.  Value must be a key in the type's map dictionary.
+    def __init__(self, value):
+        if value in self.map:
+            self.value = value
+            self.index = self.map[value]
+        else:
+            raise TypeError, "Enum param got bad value '%s' (not in %s)" \
+                  % (value, self.map.keys())
+
+    # Generate printable string version of value.
+    def __str__(self):
+        return str(self.value)
+
+# Enum metaclass... calling Enum(foo) generates a new type (class)
+# that derives from _ListEnum or _DictEnum as appropriate.
+class Enum(type):
+    # counter to generate unique names for generated classes
+    counter = 1
+
+    def __new__(cls, map):
+        if isinstance(map, dict):
+            base = _DictEnum
+            keys = map.keys()
+        elif isinstance(map, list):
+            base = _ListEnum
+            keys = map
+        else:
+            raise TypeError, "Enum map must be list or dict (got %s)" % map
+        classname = "Enum%04d" % Enum.counter
+        Enum.counter += 1
+        # New class derives from selected base, and gets a 'map'
+        # attribute containing the specified list or dict.
+        return type.__new__(cls, classname, (base,), { 'map': map })
+
+
+#
+# "Constants"... handy aliases for various values.
+#
+
+# For compatibility with C++ bool constants.
+false = False
+true = True
+
+# Some memory range specifications use this as a default upper bound.
+MAX_ADDR = 2 ** 63
+
+# For power-of-two sizing, e.g. 64*K gives an integer value 65536.
+K = 1024
+M = K*K
+G = K*M
+
+#####################################################################
+#
+# Object description loading.
+#
+# The final step is to define the classes corresponding to M5 objects
+# and their parameters.  These classes are described in .odesc files
+# in the source tree.  This code walks the tree to find those files
+# and loads up the descriptions (by evaluating them in pieces as
+# Python code).
+#
+#
+# Because SimObject classes inherit from other SimObject classes, and
+# can use arbitrary other SimObject classes as parameter types, we
+# have to do this in three steps:
+#
+# 1. Walk the tree to find all the .odesc files.  Note that the base
+# of the filename *must* match the class name.  This step builds a
+# mapping from class names to file paths.
+#
+# 2. Start generating empty class definitions (via def_class()) using
+# the OBJECT field of the .odesc files to determine inheritance.
+# def_class() recurses on demand to define needed base classes before
+# derived classes.
+#
+# 3. Now that all of the classes are defined, go through the .odesc
+# files one more time loading the parameter descriptions.
+#
+#####################################################################
+
+# dictionary: maps object names to file paths
+odesc_file = {}
+
+# dictionary: maps object names to boolean flag indicating whether
+# class definition was loaded yet.  Since SimObject is defined in
+# m5.config.py, count it as loaded.
+odesc_loaded = { 'SimObject': True }
+
+# Find odesc files in namelist and initialize odesc_file and
+# odesc_loaded dictionaries.  Called via os.path.walk() (see below).
+def find_odescs(process, dirpath, namelist):
+    # Prune out SCCS directories so we don't process s.*.odesc files.
+    i = 0
+    while i < len(namelist):
+        if namelist[i] == "SCCS":
+            del namelist[i]
+        else:
+            i = i + 1
+    # Find .odesc files and record them.
+    for name in namelist:
+        if name.endswith('.odesc'):
+            objname = name[:name.rindex('.odesc')]
+            path = os.path.join(dirpath, name)
+            if odesc_file.has_key(objname):
+                print "Warning: duplicate object names:", \
+                      odesc_file[objname], path
+            odesc_file[objname] = path
+            odesc_loaded[objname] = False
+
+
+# Regular expression string for parsing .odesc files.
+file_re_string = r'''
+^OBJECT: \s* (\w+) \s* \( \s* (\w+) \s* \)
+\s*
+^PARAMS: \s*\n ( (\s+.*\n)* )
+'''
+
+# Compiled regular expression object.
+file_re = re.compile(file_re_string, re.MULTILINE | re.VERBOSE)
+
+# .odesc file parsing function.  Takes a filename and returns tuple of
+# object name, object base, and parameter description section.
+def parse_file(path):
+    f = open(path, 'r').read()
+    m = file_re.search(f)
+    if not m:
+        print "Can't parse", path
+        sys.exit(1)
+    return (m.group(1), m.group(2), m.group(3))
+
+# Define SimObject class based on description in specified filename.
+# Class itself is empty except for _name attribute; parameter
+# descriptions will be loaded later.  Will recurse to define base
+# classes as needed before defining specified class.
+def def_class(path):
+    # load & parse file
+    (obj, parent, params) = parse_file(path)
+    # check to see if base class is defined yet; define it if not
+    if not odesc_loaded.has_key(parent):
+        print "No .odesc file found for", parent
+        sys.exit(1)
+    if not odesc_loaded[parent]:
+        def_class(odesc_file[parent])
+    # define the class.
+    s = "class %s(%s): _name = '%s'" % (obj, parent, obj)
+    try:
+        # execute in global namespace, so new class will be globally
+        # visible
+        exec s in globals()
+    except Exception, exc:
+        print "Object error in %s:" % path, exc
+    # mark this file as loaded
+    odesc_loaded[obj] = True
+
+# Munge an arbitrary Python code string to get it to execute (mostly
+# dealing with indentation).  Stolen from isa_parser.py... see
+# comments there for a more detailed description.
+def fixPythonIndentation(s):
+    # get rid of blank lines first
+    s = re.sub(r'(?m)^\s*\n', '', s);
+    if (s != '' and re.match(r'[ \t]', s[0])):
+        s = 'if 1:\n' + s
+    return s
+
+# Load parameter descriptions from .odesc file.  Object class must
+# already be defined.
+def def_params(path):
+    # load & parse file
+    (obj_name, parent_name, param_code) = parse_file(path)
+    # initialize param dict
+    param_dict = {}
+    # execute parameter descriptions.
+    try:
+        # "in globals(), param_dict" makes exec use the current
+        # globals as the global namespace (so all of the Param
+        # etc. objects are visible) and param_dict as the local
+        # namespace (so the newly defined parameter variables will be
+        # entered into param_dict).
+        exec fixPythonIndentation(param_code) in globals(), param_dict
+    except Exception, exc:
+        print "Param error in %s:" % path, exc
+        return
+    # Convert object name string to Python class object
+    obj = eval(obj_name)
+    # Set the object's parameter description dictionary (see MetaConfigNode).
+    obj.set_param_dict(param_dict)
+
+
+# Walk directory tree to find .odesc files.
+# Someday we'll have to make the root path an argument instead of
+# hard-coding it.  For now the assumption is you're running this in
+# util/config.
+root = '../..'
+os.path.walk(root, find_odescs, None)
+
+# Iterate through file dictionary and define classes.
+for objname, path in odesc_file.iteritems():
+    if not odesc_loaded[objname]:
+        def_class(path)
+
+# Iterate through files again and load parameters.
+for path in odesc_file.itervalues():
+    def_params(path)
+
+#####################################################################
+
+# The final hook to generate .ini files.  Called from configuration
+# script once config is built.
+def instantiate(*objs):
+    for obj in objs:
+        obj._instantiate()