Add gdb.free_objfile event registry

Currently, Python code can use event registries to detect when gdb
loads a new objfile, and when gdb clears the objfile list.  However,
there's no way to detect the removal of an objfile, say when the
inferior calls dlclose.

This patch adds a gdb.free_objfile event registry and arranges for an
event to be emitted in this case.

gdb/python/py-all-events.def

@@ -27,6 +27,7 @@ GDB_PY_DEFINE_EVENT(stop)
 GDB_PY_DEFINE_EVENT(cont)
 GDB_PY_DEFINE_EVENT(exited)
 GDB_PY_DEFINE_EVENT(new_objfile)
+GDB_PY_DEFINE_EVENT(free_objfile)
 GDB_PY_DEFINE_EVENT(clear_objfiles)
 GDB_PY_DEFINE_EVENT(new_inferior)
 GDB_PY_DEFINE_EVENT(inferior_deleted)

gdb/python/py-event-types.def

@@ -86,6 +86,11 @@ GDB_PY_DEFINE_EVENT_TYPE (new_objfile,
 			  "GDB new object file event object",
 			  event_object_type);
 
+GDB_PY_DEFINE_EVENT_TYPE (free_objfile,
+			  "FreeObjFileEvent",
+			  "GDB free object file event object",
+			  event_object_type);
+
 GDB_PY_DEFINE_EVENT_TYPE (clear_objfiles,
 			  "ClearObjFilesEvent",
 			  "GDB clear object files event object",

gdb/python/py-event.h

@@ -74,6 +74,7 @@ extern gdbpy_ref<> create_thread_event_object (PyTypeObject *py_type,
 					       PyObject *thread);
 
 extern int emit_new_objfile_event (struct objfile *objfile);
+extern int emit_free_objfile_event (struct objfile *objfile);
 extern int emit_clear_objfiles_event (void);
 
 extern void evpy_dealloc (PyObject *self);

gdb/python/py-inferior.c

@@ -197,6 +197,20 @@ python_new_objfile (struct objfile *objfile)
     }
 }
 
+/* Emit a Python event when an objfile is about to be removed.  */
+
+static void
+python_free_objfile (struct objfile *objfile)
+{
+  if (!gdb_python_initialized)
+    return;
+
+  gdbpy_enter enter_py (objfile->arch ());
+
+  if (emit_free_objfile_event (objfile) < 0)
+    gdbpy_print_stack ();
+}
+
 /* Return a reference to the Python object of type Inferior
    representing INFERIOR.  If the object has already been created,
    return it and increment the reference count,  otherwise, create it.
@@ -853,6 +867,7 @@ gdbpy_initialize_inferior (void)
   gdb::observers::new_objfile.attach
     (python_new_objfile, "py-inferior",
      { &auto_load_new_objfile_observer_token });
+  gdb::observers::free_objfile.attach (python_free_objfile, "py-inferior");
   gdb::observers::inferior_added.attach (python_new_inferior, "py-inferior");
   gdb::observers::inferior_removed.attach (python_inferior_deleted,
 					   "py-inferior");

gdb/python/py-newobjfileevent.c

@@ -53,6 +53,42 @@ emit_new_objfile_event (struct objfile *objfile)
   return -1;
 }
 
+/* Create an event object representing a to-be-freed objfile.  Return
+   nullptr, with the Python exception set, on error.  */
+
+static gdbpy_ref<>
+create_free_objfile_event_object (struct objfile *objfile)
+{
+  gdbpy_ref<> objfile_event
+    = create_event_object (&free_objfile_event_object_type);
+  if (objfile_event == nullptr)
+    return nullptr;
+
+  gdbpy_ref<> py_objfile = objfile_to_objfile_object (objfile);
+  if (py_objfile == nullptr
+      || evpy_add_attribute (objfile_event.get (), "objfile",
+			     py_objfile.get ()) < 0)
+    return nullptr;
+
+  return objfile_event;
+}
+
+/* Callback function which notifies observers when a free objfile
+   event occurs.  This function will create a new Python event object.
+   Return -1 if emit fails.  */
+
+int
+emit_free_objfile_event (struct objfile *objfile)
+{
+  if (evregpy_no_listeners_p (gdb_py_events.free_objfile))
+    return 0;
+
+  gdbpy_ref<> event = create_free_objfile_event_object (objfile);
+  if (event == nullptr)
+    return -1;
+  return evpy_emit_event (event.get (), gdb_py_events.free_objfile);
+}
+
 
 /* Subroutine of emit_clear_objfiles_event to simplify it.  */