Change how Python architecture and language are handled

Currently, gdb's Python layer captures the current architecture and
language when "entering" Python code.  This has some undesirable
effects, and so this series changes how this is handled.

First, there is code like this:

  gdbpy_enter enter_py (python_gdbarch, python_language);

This is incorrect, because both of these are NULL when not otherwise
assigned.  This can cause crashes in some cases -- I've added one to
the test suite.  (Note that this crasher is just an example, other
ones along the same lines are possible.)

Second, when the language is captured in this way, it means that
Python code cannot affect the current language for its own purposes.
It's reasonable to want to write code like this:

    gdb.execute('set language mumble')
    ... stuff using the current language
    gdb.execute('set language previous-value')

However, this won't actually work, because the language is captured on
entry.  I've added a test to show this as well.

This patch changes gdb to try to avoid capturing the current values.
The Python concept of the current gdbarch is only set in those few
cases where a non-default value is computed or needed; and the
language is not captured at all -- instead, in the cases where it's
required, the current language is temporarily changed.

gdb/python/py-breakpoint.c

@@ -858,7 +858,7 @@ bppy_init (PyObject *self, PyObject *args, PyObject *kwargs)
 	    const struct breakpoint_ops *ops =
 	      breakpoint_ops_for_event_location (location.get (), false);
 
-	    create_breakpoint (python_gdbarch,
+	    create_breakpoint (gdbpy_enter::get_gdbarch (),
 			       location.get (), NULL, -1, NULL, false,
 			       0,
 			       temporary_bp, type,
@@ -954,15 +954,13 @@ gdbpy_breakpoint_cond_says_stop (const struct extension_language_defn *extlang,
   int stop;
   struct gdbpy_breakpoint_object *bp_obj = b->py_bp_object;
   PyObject *py_bp = (PyObject *) bp_obj;
-  struct gdbarch *garch;
 
   if (bp_obj == NULL)
     return EXT_LANG_BP_STOP_UNSET;
 
   stop = -1;
-  garch = b->gdbarch ? b->gdbarch : get_current_arch ();
 
-  gdbpy_enter enter_py (garch, current_language);
+  gdbpy_enter enter_py (b->gdbarch);
 
   if (bp_obj->is_finish_bp)
     bpfinishpy_pre_stop_hook (bp_obj);
@@ -1005,15 +1003,13 @@ gdbpy_breakpoint_has_cond (const struct extension_language_defn *extlang,
 			   struct breakpoint *b)
 {
   PyObject *py_bp;
-  struct gdbarch *garch;
 
   if (b->py_bp_object == NULL)
     return 0;
 
   py_bp = (PyObject *) b->py_bp_object;
-  garch = b->gdbarch ? b->gdbarch : get_current_arch ();
 
-  gdbpy_enter enter_py (garch, current_language);
+  gdbpy_enter enter_py (b->gdbarch);
   return PyObject_HasAttrString (py_bp, stop_func);
 }
 
@@ -1048,8 +1044,7 @@ gdbpy_breakpoint_created (struct breakpoint *bp)
       return;
     }
 
-  struct gdbarch *garch = bp->gdbarch ? bp->gdbarch : get_current_arch ();
-  gdbpy_enter enter_py (garch, current_language);
+  gdbpy_enter enter_py (bp->gdbarch);
 
   if (bppy_pending_object)
     {
@@ -1099,8 +1094,7 @@ gdbpy_breakpoint_deleted (struct breakpoint *b)
   bp = get_breakpoint (num);
   if (bp)
     {
-      struct gdbarch *garch = bp->gdbarch ? bp->gdbarch : get_current_arch ();
-      gdbpy_enter enter_py (garch, current_language);
+      gdbpy_enter enter_py (b->gdbarch);
 
       gdbpy_ref<gdbpy_breakpoint_object> bp_obj (bp->py_bp_object);
       if (bp_obj != NULL)
@@ -1131,8 +1125,7 @@ gdbpy_breakpoint_modified (struct breakpoint *b)
   bp = get_breakpoint (num);
   if (bp)
     {
-      struct gdbarch *garch = bp->gdbarch ? bp->gdbarch : get_current_arch ();
-      gdbpy_enter enter_py (garch, current_language);
+      gdbpy_enter enter_py (b->gdbarch);
 
       PyObject *bp_obj = (PyObject *) bp->py_bp_object;
       if (bp_obj)

gdb/python/py-cmd.c

@@ -90,7 +90,7 @@ cmdpy_dont_repeat (PyObject *self, PyObject *args)
 static void
 cmdpy_destroyer (struct cmd_list_element *self, void *context)
 {
-  gdbpy_enter enter_py (get_current_arch (), current_language);
+  gdbpy_enter enter_py;
 
   /* Release our hold on the command object.  */
   gdbpy_ref<cmdpy_object> cmd ((cmdpy_object *) context);
@@ -104,7 +104,7 @@ cmdpy_function (const char *args, int from_tty, cmd_list_element *command)
 {
   cmdpy_object *obj = (cmdpy_object *) command->context ();
 
-  gdbpy_enter enter_py (get_current_arch (), current_language);
+  gdbpy_enter enter_py;
 
   if (! obj)
     error (_("Invalid invocation of Python command object."));
@@ -223,7 +223,7 @@ cmdpy_completer_handle_brkchars (struct cmd_list_element *command,
 				 completion_tracker &tracker,
 				 const char *text, const char *word)
 {
-  gdbpy_enter enter_py (get_current_arch (), current_language);
+  gdbpy_enter enter_py;
 
   /* Calling our helper to obtain a reference to the PyObject of the Python
      function.  */
@@ -266,7 +266,7 @@ cmdpy_completer (struct cmd_list_element *command,
 		 completion_tracker &tracker,
 		 const char *text, const char *word)
 {
-  gdbpy_enter enter_py (get_current_arch (), current_language);
+  gdbpy_enter enter_py;
 
   /* Calling our helper to obtain a reference to the PyObject of the Python
      function.  */

gdb/python/py-connection.c

@@ -161,7 +161,7 @@ connpy_connection_removed (process_stratum_target *target)
   if (!gdb_python_initialized)
     return;
 
-  gdbpy_enter enter_py (get_current_arch (), current_language);
+  gdbpy_enter enter_py;
 
   if (!evregpy_no_listeners_p (gdb_py_events.connection_removed))
     if (emit_connection_event (target, gdb_py_events.connection_removed) < 0)

gdb/python/py-finishbreakpoint.c

@@ -293,7 +293,7 @@ bpfinishpy_init (PyObject *self, PyObject *args, PyObject *kwargs)
       /* Set a breakpoint on the return address.  */
       event_location_up location
 	= new_address_location (get_frame_pc (prev_frame), NULL, 0);
-      create_breakpoint (python_gdbarch,
+      create_breakpoint (gdbpy_enter::get_gdbarch (),
 			 location.get (), NULL, thread, NULL, false,
 			 0,
 			 1 /*temp_flag*/,
@@ -380,7 +380,7 @@ bpfinishpy_detect_out_scope_cb (struct breakpoint *b,
 static void
 bpfinishpy_handle_stop (struct bpstat *bs, int print_frame)
 {
-  gdbpy_enter enter_py (get_current_arch (), current_language);
+  gdbpy_enter enter_py;
 
   for (breakpoint *bp : all_breakpoints_safe ())
     bpfinishpy_detect_out_scope_cb (bp, bs == NULL ? NULL : bs->breakpoint_at);
@@ -392,7 +392,7 @@ bpfinishpy_handle_stop (struct bpstat *bs, int print_frame)
 static void
 bpfinishpy_handle_exit (struct inferior *inf)
 {
-  gdbpy_enter enter_py (target_gdbarch (), current_language);
+  gdbpy_enter enter_py (target_gdbarch ());
 
   for (breakpoint *bp : all_breakpoints_safe ())
     bpfinishpy_detect_out_scope_cb (bp, nullptr);

gdb/python/py-framefilter.c

@@ -74,11 +74,11 @@ extract_sym (PyObject *obj, gdb::unique_xmalloc_ptr<char> *name,
       if (*name == NULL)
 	return EXT_LANG_BT_ERROR;
       /* If the API returns a string (and not a symbol), then there is
-	no symbol derived language available and the frame filter has
-	either overridden the symbol with a string, or supplied a
-	entirely synthetic symbol/value pairing.  In that case, use
-	python_language.  */
-      *language = python_language;
+	 no symbol derived language available and the frame filter has
+	 either overridden the symbol with a string, or supplied a
+	 entirely synthetic symbol/value pairing.  In that case, use
+	 the current language.  */
+      *language = current_language;
       *sym = NULL;
       *sym_block = NULL;
     }
@@ -1157,7 +1157,7 @@ gdbpy_apply_frame_filter (const struct extension_language_defn *extlang,
       return EXT_LANG_BT_NO_FILTERS;
     }
 
-  gdbpy_enter enter_py (gdbarch, current_language);
+  gdbpy_enter enter_py (gdbarch);
 
   /* When we're limiting the number of frames, be careful to request
      one extra frame, so that we can print a message if there are more

gdb/python/py-inferior.c

@@ -86,7 +86,7 @@ python_on_normal_stop (struct bpstat *bs, int print_frame)
 
   stop_signal = inferior_thread ()->stop_signal ();
 
-  gdbpy_enter enter_py (get_current_arch (), current_language);
+  gdbpy_enter enter_py;
 
   if (emit_stop_event (bs, stop_signal) < 0)
     gdbpy_print_stack ();
@@ -98,7 +98,7 @@ python_on_resume (ptid_t ptid)
   if (!gdb_python_initialized)
     return;
 
-  gdbpy_enter enter_py (target_gdbarch (), current_language);
+  gdbpy_enter enter_py (target_gdbarch ());
 
   if (emit_continue_event (ptid) < 0)
     gdbpy_print_stack ();
@@ -110,7 +110,7 @@ python_on_resume (ptid_t ptid)
 static void
 python_on_inferior_call_pre (ptid_t thread, CORE_ADDR address)
 {
-  gdbpy_enter enter_py (target_gdbarch (), current_language);
+  gdbpy_enter enter_py (target_gdbarch ());
 
   if (emit_inferior_call_event (INFERIOR_CALL_PRE, thread, address) < 0)
     gdbpy_print_stack ();
@@ -122,7 +122,7 @@ python_on_inferior_call_pre (ptid_t thread, CORE_ADDR address)
 static void
 python_on_inferior_call_post (ptid_t thread, CORE_ADDR address)
 {
-  gdbpy_enter enter_py (target_gdbarch (), current_language);
+  gdbpy_enter enter_py (target_gdbarch ());
 
   if (emit_inferior_call_event (INFERIOR_CALL_POST, thread, address) < 0)
     gdbpy_print_stack ();
@@ -135,7 +135,7 @@ python_on_inferior_call_post (ptid_t thread, CORE_ADDR address)
 static void
 python_on_memory_change (struct inferior *inferior, CORE_ADDR addr, ssize_t len, const bfd_byte *data)
 {
-  gdbpy_enter enter_py (target_gdbarch (), current_language);
+  gdbpy_enter enter_py (target_gdbarch ());
 
   if (emit_memory_changed_event (addr, len) < 0)
     gdbpy_print_stack ();
@@ -148,7 +148,7 @@ python_on_memory_change (struct inferior *inferior, CORE_ADDR addr, ssize_t len,
 static void
 python_on_register_change (struct frame_info *frame, int regnum)
 {
-  gdbpy_enter enter_py (target_gdbarch (), current_language);
+  gdbpy_enter enter_py (target_gdbarch ());
 
   if (emit_register_changed_event (frame, regnum) < 0)
     gdbpy_print_stack ();
@@ -162,7 +162,7 @@ python_inferior_exit (struct inferior *inf)
   if (!gdb_python_initialized)
     return;
 
-  gdbpy_enter enter_py (target_gdbarch (), current_language);
+  gdbpy_enter enter_py (target_gdbarch ());
 
   if (inf->has_exit_code)
     exit_code = &inf->exit_code;
@@ -183,8 +183,7 @@ python_new_objfile (struct objfile *objfile)
 
   gdbpy_enter enter_py (objfile != NULL
 			? objfile->arch ()
-			: target_gdbarch (),
-			current_language);
+			: target_gdbarch ());
 
   if (objfile == NULL)
     {
@@ -237,7 +236,7 @@ python_new_inferior (struct inferior *inf)
   if (!gdb_python_initialized)
     return;
 
-  gdbpy_enter enter_py (python_gdbarch, python_language);
+  gdbpy_enter enter_py;
 
   if (evregpy_no_listeners_p (gdb_py_events.new_inferior))
     return;
@@ -265,7 +264,7 @@ python_inferior_deleted (struct inferior *inf)
   if (!gdb_python_initialized)
     return;
 
-  gdbpy_enter enter_py (python_gdbarch, python_language);
+  gdbpy_enter enter_py;
 
   if (evregpy_no_listeners_p (gdb_py_events.inferior_deleted))
     return;
@@ -312,7 +311,7 @@ add_thread_object (struct thread_info *tp)
   if (!gdb_python_initialized)
     return;
 
-  gdbpy_enter enter_py (python_gdbarch, python_language);
+  gdbpy_enter enter_py;
 
   gdbpy_ref<thread_object> thread_obj = create_thread_object (tp);
   if (thread_obj == NULL)
@@ -348,7 +347,7 @@ delete_thread_object (struct thread_info *tp, int ignore)
   if (!gdb_python_initialized)
     return;
 
-  gdbpy_enter enter_py (python_gdbarch, python_language);
+  gdbpy_enter enter_py;
 
   gdbpy_ref<inferior_object> inf_obj = inferior_to_inferior_object (tp->inf);
   if (inf_obj == NULL)
@@ -792,7 +791,7 @@ py_free_inferior (struct inferior *inf, void *datum)
   if (!gdb_python_initialized)
     return;
 
-  gdbpy_enter enter_py (python_gdbarch, python_language);
+  gdbpy_enter enter_py;
   gdbpy_ref<inferior_object> inf_obj ((inferior_object *) datum);
 
   inf_obj->inferior = NULL;

gdb/python/py-membuf.c

@@ -83,7 +83,8 @@ mbpy_str (PyObject *self)
 
   return PyString_FromFormat (_("Memory buffer for address %s, \
 which is %s bytes long."),
-			      paddress (python_gdbarch, membuf_obj->addr),
+			      paddress (gdbpy_enter::get_gdbarch (),
+					membuf_obj->addr),
 			      pulongest (membuf_obj->length));
 }
 

gdb/python/py-objfile.c

@@ -661,7 +661,7 @@ gdbpy_lookup_objfile (PyObject *self, PyObject *args, PyObject *kw)
 static void
 py_free_objfile (struct objfile *objfile, void *datum)
 {
-  gdbpy_enter enter_py (objfile->arch (), current_language);
+  gdbpy_enter enter_py (objfile->arch ());
   gdbpy_ref<objfile_object> object ((objfile_object *) datum);
   object->objfile = NULL;
 }

gdb/python/py-param.c

@@ -396,7 +396,7 @@ get_set_value (const char *args, int from_tty,
   PyObject *obj = (PyObject *) c->context ();
   gdb::unique_xmalloc_ptr<char> set_doc_string;
 
-  gdbpy_enter enter_py (get_current_arch (), current_language);
+  gdbpy_enter enter_py;
   gdbpy_ref<> set_doc_func (PyString_FromString ("get_set_string"));
 
   if (set_doc_func == NULL)
@@ -431,7 +431,7 @@ get_show_value (struct ui_file *file, int from_tty,
   PyObject *obj = (PyObject *) c->context ();
   gdb::unique_xmalloc_ptr<char> show_doc_string;
 
-  gdbpy_enter enter_py (get_current_arch (), current_language);
+  gdbpy_enter enter_py;
   gdbpy_ref<> show_doc_func (PyString_FromString ("get_show_string"));
 
   if (show_doc_func == NULL)

gdb/python/py-progspace.c

@@ -472,7 +472,7 @@ py_free_pspace (struct program_space *pspace, void *datum)
      being deleted.  */
   struct gdbarch *arch = target_gdbarch ();
 
-  gdbpy_enter enter_py (arch, current_language);
+  gdbpy_enter enter_py (arch);
   gdbpy_ref<pspace_object> object ((pspace_object *) datum);
   object->pspace = NULL;
 }