New python event "clear_objfiles".

If one is watching new_objfile events in python, it helps to know
when the list of objfiles is cleared.  This patch adds a new
clear_objfiles event to support this.

This patch is all just cut-n-paste-n-tweak derived from
the new_objfiles event.

gdb/ChangeLog:

	* NEWS: Mention new event gdb.clear_objfiles.
	* python/py-event.h (emit_clear_objfiles_event): Clear
	* python/py-events.h (events_object): New member clear_objfiles.
	* python/py-evts.c (gdbpy_initialize_py_events): Add clear_objfiles
	event.
	* python/py-inferior.c (python_new_objfile): If objfile is NULL,
	emit clear_objfiles event.
	* python/py-newobjfileevent.c (create_clear_objfiles_event_object): New
	function.
	(emit_clear_objfiles_event): New function.
	(clear_objfiles): New event.
	* python/python-internal.h (gdbpy_initialize_clear_objfiles_event):
	Declare.
	* python/python.c (_initialize_python): Call
	gdbpy_initialize_clear_objfiles_event.

gdb/doc/ChangeLog:

	* python.texi (Events In Python): Document clear_objfiles event.

gdb/testsuite/ChangeLog:

	* gdb.python/py-events.exp: Update expected output for clear_objfiles
	event.
	* gdb.python/py-events.py: Add clear_objfiles event.

1 files changed, 16 insertions, 7 deletions

diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c
index 181059a..1b38d55 100644
--- a/gdb/python/py-inferior.c
+++ b/gdb/python/py-inferior.c
@@ -137,23 +137,32 @@ python_inferior_exit (struct inferior *inf)
 }
 
 /* Callback used to notify Python listeners about new objfiles loaded in the
-   inferior.  */
+   inferior.  OBJFILE may be NULL which means that the objfile list has been
+   cleared (emptied).  */
 
 static void
 python_new_objfile (struct objfile *objfile)
 {
   struct cleanup *cleanup;
 
-  if (objfile == NULL)
-    return;
-
   if (!gdb_python_initialized)
     return;
 
-  cleanup = ensure_python_env (get_objfile_arch (objfile), current_language);
+  cleanup = ensure_python_env (objfile != NULL
+			       ? get_objfile_arch (objfile)
+			       : target_gdbarch (),
+			       current_language);
 
-  if (emit_new_objfile_event (objfile) < 0)
-    gdbpy_print_stack ();
+  if (objfile == NULL)
+    {
+      if (emit_clear_objfiles_event () < 0)
+	gdbpy_print_stack ();
+    }
+  else
+    {
+      if (emit_new_objfile_event (objfile) < 0)
+	gdbpy_print_stack ();
+    }
 
   do_cleanups (cleanup);
 }