sim: Include object header files in SWIG interfaces

When casting objects in the generated SWIG interfaces, SWIG uses
classical C-style casts ( (Foo *)bar; ). In some cases, this can
degenerate into the equivalent of a reinterpret_cast (mainly if only a
forward declaration of the type is available). This usually works for
most compilers, but it is known to break if multiple inheritance is
used anywhere in the object hierarchy.

This patch introduces the cxx_header attribute to Python SimObject
definitions, which should be used to specify a header to include in
the SWIG interface. The header should include the declaration of the
wrapped object. We currently don't enforce header the use of the
header attribute, but a warning will be generated for objects that do
not use it.

src/SConscript

@@ -451,6 +451,12 @@ sys.meta_path.remove(importer)
 sim_objects = m5.SimObject.allClasses
 all_enums = m5.params.allEnums
 
+if m5.SimObject.noCxxHeader:
+    print >> sys.stderr, \
+        "warning: At least one SimObject lacks a header specification. " \
+        "This can cause unexpected results in the generated SWIG " \
+        "wrappers."
+
 # Find param types that need to be explicitly wrapped with swig.
 # These will be recognized because the ParamDesc will have a
 # swig_decl() method.  Most param types are based on types that don't