python: Updates to improve debugging output

This changeset updates SimObject and Proxy so that certain errors are
easier to diagnose. In SimObject, the warn() statement could cause
another exception, so it's split into two statements. In Proxy, it is
helpful to know which attribute is referenced when there's a mistake.

Change-Id: I3704a247b8b40e18ffc5e4a6241a74829313c07e
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/51787
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/m5/SimObject.py

@@ -1534,9 +1534,9 @@ class SimObject(object, metaclass=MetaSimObject):
     def add_child(self, name, child):
         child = coerceSimObjectOrVector(child)
         if child.has_parent():
-            warn(f"{self}.{name} already has parent (Previously declared as "
-                 f"{child._parent}.{name}), not resetting parent.\n"
+            warn(f"{self}.{name} already has parent not resetting parent.\n"
                  f"\tNote: {name} is not a parameter of {type(self).__name__}")
+            warn(f"(Previously declared as {child._parent}.{name}")
             return
         if name in self._children:
             # This code path had an undiscovered bug that would make it fail

src/python/m5/proxy.py

@@ -172,7 +172,8 @@ class AttrProxy(BaseProxy):
         if attr.startswith('_'):
             return super(AttrProxy, self).__getattr__(self, attr)
         if hasattr(self, '_pdesc'):
-            raise AttributeError("Attribute reference on bound proxy")
+            raise AttributeError("Attribute reference on bound proxy "
+                                f"({self}.{attr})")
         # Return a copy of self rather than modifying self in place
         # since self could be an indirect reference via a variable or
         # parameter