PR python/18285

gdb/ChangeLog:

	PR python/18285
	* NEWS: Document new gdb.XMethodWorker.get_result_type method.
	* eval.c (evaluate_subexp_standard) <OP_FUNCALL>: Handle
	EVAL_AVOID_SIDE_EFFECTS for xmethods.
	* extension-priv.h (struct extension_language_ops)
	<get_xmethod_result_type>: New member.
	* extension.c (get_xmethod_result_type): New function.
	* extension.h (get_xmethod_result_type): Declare.
	* python/py-xmethods.c (get_result_type_method_name): New static
	global.
	(py_get_result_type_method_name): Ditto.
	(gdbpy_get_xmethod_result_type): New function.
	(gdbpy_initialize_xmethods): Initialize py_get_result_type_method_name.
	* python/python-internal.h (gdbpy_get_xmethod_result_type): Declare.
	* python/python.c (python_extension_ops): Add
	gdbpy_get_xmethod_result_type.
	* python/lib/gdb/xmethod.py (XMethodWorker): Add get_result_type.
	* valarith.c (value_x_binop): Handle EVAL_AVOID_SIDE_EFFECTS for
	xmethods.
	(value_x_unop): Ditto.
	* value.c (result_type_of_xmethod): New function.
	* value.h (result_type_of_xmethod): Declare.

gdb/testsuite/ChangeLog:

	* gdb.python/py-xmethods.exp: Add ptype tests.
	* gdb.python/py-xmethods.py (E_method_char_worker): Add
	get_result_type method.

gdb/doc/ChangeLog:

	* python.texi (Xmethod API) <gdb.XMethodWorker.get_result_type>:
	Document.
	(Writing an Xmethod): Add get_result_type to example.

gdb/ChangeLog

@@ -1,3 +1,28 @@
+2015-04-29  Doug Evans  <dje@google.com>
+
+	PR python/18285
+	* NEWS: Document new gdb.XMethodWorker.get_result_type method.
+	* eval.c (evaluate_subexp_standard) <OP_FUNCALL>: Handle
+	EVAL_AVOID_SIDE_EFFECTS for xmethods.
+	* extension-priv.h (struct extension_language_ops)
+	<get_xmethod_result_type>: New member.
+	* extension.c (get_xmethod_result_type): New function.
+	* extension.h (get_xmethod_result_type): Declare.
+	* python/py-xmethods.c (get_result_type_method_name): New static
+	global.
+	(py_get_result_type_method_name): Ditto.
+	(gdbpy_get_xmethod_result_type): New function.
+	(gdbpy_initialize_xmethods): Initialize py_get_result_type_method_name.
+	* python/python-internal.h (gdbpy_get_xmethod_result_type): Declare.
+	* python/python.c (python_extension_ops): Add
+	gdbpy_get_xmethod_result_type.
+	* python/lib/gdb/xmethod.py (XMethodWorker): Add get_result_type.
+	* valarith.c (value_x_binop): Handle EVAL_AVOID_SIDE_EFFECTS for
+	xmethods.
+	(value_x_unop): Ditto.
+	* value.c (result_type_of_xmethod): New function.
+	* value.h (result_type_of_xmethod): Declare.
+
 2015-04-29  Gary Benson <gbenson@redhat.com>
 
 	* solib.c (solib_find_1): Allow fd argument to be NULL.

gdb/NEWS

@@ -2,7 +2,6 @@
 	     (Organized release by release)
 
 *** Changes since GDB 7.9
-=======
 
 * GDB now honors the content of the file /proc/PID/coredump_filter
   (PID is the process ID) on GNU/Linux systems.  This file can be used
@@ -54,6 +53,7 @@
   ** You can now write frame unwinders in Python.
   ** gdb.Type objects have a new method "optimized_out",
      returning optimized out gdb.Value instance of this type.
+  ** Xmethods can now specify a result type.
 
 * New commands
 

gdb/doc/ChangeLog

@@ -1,3 +1,9 @@
+2015-04-29  Doug Evans  <dje@google.com>
+
+	* python.texi (Xmethod API) <gdb.XMethodWorker.get_result_type>:
+	Document.
+	(Writing an Xmethod): Add get_result_type to example.
+
 2015-04-28  Sasha Smundak  <asmundak@google.com>
 
 	* python.texi: New method documented.

gdb/doc/python.texi

@@ -2455,6 +2455,13 @@ If the xmethod takes a single argument, then a single
 @code{gdb.Type} object corresponding to it can be returned.
 @end defun
 
+@defun XMethodWorker.get_result_type (self, *args)
+This method returns a @code{gdb.Type} object representing the type
+of the result of invoking this xmethod.
+The @var{args} argument is the same tuple of arguments that would be
+passed to the @code{__call__} method of this worker.
+@end defun
+
 @defun XMethodWorker.__call__ (self, *args)
 This is the method which does the @emph{work} of the xmethod.  The
 @var{args} arguments is the tuple of arguments to the xmethod.  Each
@@ -2572,6 +2579,9 @@ class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
     def get_arg_types(self):
         return None
 
+    def get_result_type(self, obj):
+        return gdb.lookup_type('int')
+ 
     def __call__(self, obj):
         return obj['a_']
  
@@ -2580,6 +2590,9 @@ class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
     def get_arg_types(self):
         return gdb.lookup_type('MyClass')
 
+    def get_result_type(self, obj):
+        return gdb.lookup_type('int')
+ 
     def __call__(self, obj, other):
         return obj['a_'] + other['a_']
 @end smallexample
@@ -2646,6 +2659,9 @@ class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
     def get_arg_types(self):
         return None
 
+    def get_result_type(self):
+        return gdb.lookup_type('int')
+
     def __call__(self, obj):
         return (self.class_type.sizeof +
                 obj['dsize_'] *

gdb/eval.c

@@ -1742,6 +1742,15 @@ evaluate_subexp_standard (struct type *expect_type,
 	      return value_zero (builtin_type (exp->gdbarch)->builtin_int,
 				 not_lval);
 	    }
+	  else if (TYPE_CODE (ftype) == TYPE_CODE_XMETHOD)
+	    {
+	      struct type *return_type
+		= result_type_of_xmethod (argvec[0], nargs, argvec + 1);
+
+	      if (return_type == NULL)
+		error (_("Xmethod is missing return type."));
+	      return value_zero (return_type, not_lval);
+	    }
 	  else if (TYPE_GNU_IFUNC (ftype))
 	    return allocate_value (TYPE_TARGET_TYPE (TYPE_TARGET_TYPE (ftype)));
 	  else if (TYPE_TARGET_TYPE (ftype))

gdb/extension-priv.h

@@ -265,7 +265,7 @@ struct extension_language_ops
   /* xmethod support:
      clone_xmethod_worker_data, free_xmethod_worker_data,
      get_matching_xmethod_workers, get_xmethod_arg_types,
-     invoke_xmethod.
+     get_xmethod_return_type, invoke_xmethod.
      These methods are optional and may be NULL, but if one of them is
      implemented then they all must be.  */
 
@@ -298,6 +298,18 @@ struct extension_language_ops
      int *nargs,
      struct type ***arg_types);
 
+  /* Given a WORKER servicing a particular method, fetch the type of the
+     result of the method.  OBJECT, ARGS, NARGS are the same as for
+     invoke_xmethod.  The result type is stored in *RESULT_TYPE.
+     For backward compatibility with 7.9, which did not support getting the
+     result type, if the get_result_type operation is not provided by WORKER
+     then EXT_LANG_RC_OK is returned and NULL is returned in *RESULT_TYPE.  */
+  enum ext_lang_rc (*get_xmethod_result_type)
+    (const struct extension_language_defn *extlang,
+     struct xmethod_worker *worker,
+     struct value *object, struct value **args, int nargs,
+     struct type **result_type);
+
   /* Invoke the xmethod serviced by WORKER.  The xmethod is invoked
      on OBJECT with arguments in the array ARGS.  NARGS is the length of
      this array.  Returns the value returned by the xmethod.  */

gdb/extension.c

@@ -964,6 +964,31 @@ get_xmethod_arg_types (struct xmethod_worker *worker, int *nargs)
   return type_array;
 }
 
+/* Return the type of the result of the xmethod encapsulated in WORKER.
+   OBJECT, ARGS, NARGS are the same as for invoke_xmethod.  */
+
+struct type *
+get_xmethod_result_type (struct xmethod_worker *worker,
+			 struct value *object, struct value **args, int nargs)
+{
+  enum ext_lang_rc rc;
+  struct type *result_type;
+  const struct extension_language_defn *extlang = worker->extlang;
+
+  gdb_assert (extlang->ops->get_xmethod_arg_types != NULL);
+
+  rc = extlang->ops->get_xmethod_result_type (extlang, worker,
+					      object, args, nargs,
+					      &result_type);
+  if (rc == EXT_LANG_RC_ERROR)
+    {
+      error (_("Error while fetching result type of an xmethod worker "
+	       "defined in %s."), extlang->capitalized_name);
+    }
+
+  return result_type;
+}
+
 /* Invokes the xmethod encapsulated in WORKER and returns the result.
    The method is invoked on OBJ with arguments in the ARGS array.  NARGS is
    the length of the this array.  */

gdb/extension.h

@@ -260,4 +260,8 @@ extern xmethod_worker_vec *get_matching_xmethod_workers
 
 extern struct type **get_xmethod_arg_types (struct xmethod_worker *, int *);
 
+extern struct type *get_xmethod_result_type (struct xmethod_worker *,
+					     struct value *object,
+					     struct value **args, int nargs);
+
 #endif /* EXTENSION_H */

gdb/python/lib/gdb/xmethod.py

@@ -101,9 +101,11 @@ class XMethodWorker(object):
     invokes the method when GDB wants it to.  Internally, GDB first invokes the
     'get_arg_types' method to perform overload resolution.  If GDB selects to
     invoke this Python xmethod, then it invokes it via the overridden
-    '__call__' method.
+    '__call__' method.  The 'get_result_type' method is used to implement
+    'ptype' on the xmethod.
 
-    Derived classes should override the 'get_arg_types' and '__call__' methods.
+    Derived classes should override the 'get_arg_types', 'get_result_type'
+    and '__call__' methods.
     """
 
     def get_arg_types(self):
@@ -117,6 +119,20 @@ class XMethodWorker(object):
         """
         raise NotImplementedError("XMethodWorker get_arg_types")
 
+    def get_result_type(self, *args):
+        """Return the type of the result of the xmethod.
+
+        Args:
+            args: Arguments to the method.  Each element of the tuple is a
+                gdb.Value object.  The first element is the 'this' pointer
+                value.  These are the same arguments passed to '__call__'.
+
+        Returns:
+            A gdb.Type object representing the type of the result of the
+            xmethod.
+        """
+        raise NotImplementedError("XMethodWorker get_result_type")
+
     def __call__(self, *args):
         """Invoke the xmethod.
 

gdb/python/py-xmethods.c

@@ -30,11 +30,13 @@
 static const char enabled_field_name[] = "enabled";
 static const char match_method_name[] = "match";
 static const char get_arg_types_method_name[] = "get_arg_types";
+static const char get_result_type_method_name[] = "get_result_type";
 static const char invoke_method_name[] = "invoke";
 static const char matchers_attr_str[] = "xmethods";
 
 static PyObject *py_match_method_name = NULL;
 static PyObject *py_get_arg_types_method_name = NULL;
+static PyObject *py_get_result_type_method_name = NULL;
 static PyObject *py_invoke_method_name = NULL;
 
 struct gdbpy_worker_data
@@ -502,6 +504,106 @@ gdbpy_get_xmethod_arg_types (const struct extension_language_defn *extlang,
   return EXT_LANG_RC_OK;
 }
 
+/* Implementation of get_xmethod_result_type for Python.  */
+
+enum ext_lang_rc
+gdbpy_get_xmethod_result_type (const struct extension_language_defn *extlang,
+			       struct xmethod_worker *worker,
+			       struct value *obj,
+			       struct value **args, int nargs,
+			       struct type **result_type_ptr)
+{
+  struct gdbpy_worker_data *worker_data = worker->data;
+  PyObject *py_worker = worker_data->worker;
+  PyObject *py_value_obj, *py_arg_tuple, *py_result_type;
+  PyObject *get_result_type_method;
+  struct type *obj_type, *this_type;
+  struct cleanup *cleanups;
+  int i;
+
+  cleanups = ensure_python_env (get_current_arch (), current_language);
+
+  /* First see if there is a get_result_type method.
+     If not this could be an old xmethod (pre 7.9.1).  */
+  get_result_type_method
+    = PyObject_GetAttrString (py_worker, get_result_type_method_name);
+  if (get_result_type_method == NULL)
+    {
+      PyErr_Clear ();
+      do_cleanups (cleanups);
+      *result_type_ptr = NULL;
+      return EXT_LANG_RC_OK;
+    }
+  make_cleanup_py_decref (get_result_type_method);
+
+  obj_type = check_typedef (value_type (obj));
+  this_type = check_typedef (type_object_to_type (worker_data->this_type));
+  if (TYPE_CODE (obj_type) == TYPE_CODE_PTR)
+    {
+      struct type *this_ptr = lookup_pointer_type (this_type);
+
+      if (!types_equal (obj_type, this_ptr))
+	obj = value_cast (this_ptr, obj);
+    }
+  else if (TYPE_CODE (obj_type) == TYPE_CODE_REF)
+    {
+      struct type *this_ref = lookup_reference_type (this_type);
+
+      if (!types_equal (obj_type, this_ref))
+	obj = value_cast (this_ref, obj);
+    }
+  else
+    {
+      if (!types_equal (obj_type, this_type))
+	obj = value_cast (this_type, obj);
+    }
+  py_value_obj = value_to_value_object (obj);
+  if (py_value_obj == NULL)
+    goto Fail;
+  make_cleanup_py_decref (py_value_obj);
+
+  py_arg_tuple = PyTuple_New (nargs + 1);
+  if (py_arg_tuple == NULL)
+    goto Fail;
+  make_cleanup_py_decref (py_arg_tuple);
+
+  /* PyTuple_SET_ITEM steals the reference of the element.  Hence INCREF the
+     reference to the 'this' object as we have a cleanup to DECREF it.  */
+  Py_INCREF (py_value_obj);
+  PyTuple_SET_ITEM (py_arg_tuple, 0, py_value_obj);
+
+  for (i = 0; i < nargs; i++)
+    {
+      PyObject *py_value_arg = value_to_value_object (args[i]);
+
+      if (py_value_arg == NULL)
+	goto Fail;
+      PyTuple_SET_ITEM (py_arg_tuple, i + 1, py_value_arg);
+    }
+
+  py_result_type = PyObject_CallObject (get_result_type_method, py_arg_tuple);
+  if (py_result_type == NULL)
+    goto Fail;
+  make_cleanup_py_decref (py_result_type);
+
+  *result_type_ptr = type_object_to_type (py_result_type);
+  if (*result_type_ptr == NULL)
+    {
+      PyErr_SetString (PyExc_TypeError,
+		       _("Type returned by the get_result_type method of an"
+			 " xmethod worker object is not a gdb.Type object."));
+      goto Fail;
+    }
+
+  do_cleanups (cleanups);
+  return EXT_LANG_RC_OK;
+
+ Fail:
+  gdbpy_print_stack ();
+  do_cleanups (cleanups);
+  return EXT_LANG_RC_ERROR;
+}
+
 /* Implementation of invoke_xmethod for Python.  */
 
 struct value *
@@ -638,5 +740,10 @@ gdbpy_initialize_xmethods (void)
   if (py_get_arg_types_method_name == NULL)
     return -1;
 
+  py_get_result_type_method_name
+    = PyString_FromString (get_result_type_method_name);
+  if (py_get_result_type_method_name == NULL)
+    return -1;
+
   return 1;
 }

gdb/python/python-internal.h

@@ -348,6 +348,11 @@ extern enum ext_lang_rc gdbpy_get_xmethod_arg_types
    struct xmethod_worker *worker,
    int *nargs,
    struct type ***arg_types);
+extern enum ext_lang_rc gdbpy_get_xmethod_result_type
+  (const struct extension_language_defn *extlang,
+   struct xmethod_worker *worker,
+   struct value *object, struct value **args, int nargs,
+   struct type **result_type);
 extern struct value *gdbpy_invoke_xmethod
   (const struct extension_language_defn *extlang,
    struct xmethod_worker *worker,

gdb/python/python.c

@@ -192,6 +192,7 @@ const struct extension_language_ops python_extension_ops =
   gdbpy_free_xmethod_worker_data,
   gdbpy_get_matching_xmethod_workers,
   gdbpy_get_xmethod_arg_types,
+  gdbpy_get_xmethod_result_type,
   gdbpy_invoke_xmethod
 };
 

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2015-04-29  Doug Evans  <dje@google.com>
+
+	* gdb.python/py-xmethods.exp: Add ptype tests.
+	* gdb.python/py-xmethods.py (E_method_char_worker): Add
+	get_result_type method.
+
 2015-04-29  Luis Machado  <lgustavo@codesourcery.com>
 
 	* gdb.base/watch-bitfields.exp: Switch to software watchpoints if

gdb/testsuite/gdb.python/py-xmethods.exp

@@ -107,8 +107,9 @@ gdb_test "p a_ptr->geta()" "From Python <A_geta>.*30" "After: a_ptr->geta()"
 gdb_test "p e.geta()" "From Python <A_geta>.*100" "After: e.geta()"
 gdb_test "p e_ptr->geta()" "From Python <A_geta>.*100" "After: e_ptr->geta()"
 gdb_test "p e_ref.geta()" "From Python <A_geta>.*100" "After: e_ref.geta()"
-gdb_test "p e.method(10)" "From Python <E_method_int>.*" "After: e.method(10)"
+gdb_test "p e.method(10)" "From Python <E_method_int>.* = void" \
-gdb_test "p e.method('a')" "From Python <E_method_char>.*" \
+  "After: e.method(10)"
+gdb_test "p e.method('a')" "From Python <E_method_char>.* = void" \
   "After: e.method('a')"
 gdb_test "p g.size_diff<float>  ()" "From Python G<>::size_diff.*" \
   "After: g.size_diff<float>()"
@@ -149,3 +150,11 @@ gdb_test_no_output "disable xmethod progspace E_methods;method_int" \
   "disable xmethod progspace E_methods;method_int"
 gdb_test "info xmethod progspace E_methods;method_int" ".* \\\[disabled\\\]" \
   "info xmethod xmethods E_methods;method_int"
+
+# PR 18285
+# First make sure both are enabled.
+gdb_test_no_output "enable xmethod progspace E_methods;method_char"
+gdb_test_no_output "enable xmethod progspace E_methods;method_int"
+gdb_test "pt e.method('a')" "type = void"
+gdb_test "pt e.method(10)" \
+    "NotImplementedError.*Error while fetching result type of an xmethod worker defined in Python."

gdb/testsuite/gdb.python/py-xmethods.py

@@ -60,6 +60,9 @@ class E_method_char_worker(XMethodWorker):
     def get_arg_types(self):
         return gdb.lookup_type('char')
 
+    def get_result_type(self, obj, arg):
+        return gdb.lookup_type('void')
+
     def __call__(self, obj, arg):
         print('From Python <E_method_char>')
         return None
@@ -72,6 +75,8 @@ class E_method_int_worker(XMethodWorker):
     def get_arg_types(self):
         return gdb.lookup_type('int')
 
+    # Note: get_result_type method elided on purpose
+
     def __call__(self, obj, arg):
         print('From Python <E_method_int>')
         return None

gdb/valarith.c

@@ -482,6 +482,21 @@ value_x_binop (struct value *arg1, struct value *arg2, enum exp_opcode op,
 	  argvec[1] = argvec[0];
 	  argvec++;
 	}
+      if (TYPE_CODE (value_type (argvec[0])) == TYPE_CODE_XMETHOD)
+	{
+	  /* Static xmethods are not supported yet.  */
+	  gdb_assert (static_memfuncp == 0);
+	  if (noside == EVAL_AVOID_SIDE_EFFECTS)
+	    {
+	      struct type *return_type
+		= result_type_of_xmethod (argvec[0], 2, argvec + 1);
+
+	      if (return_type == NULL)
+		error (_("Xmethod is missing return type."));
+	      return value_zero (return_type, VALUE_LVAL (arg1));
+	    }
+	  return call_xmethod (argvec[0], 2, argvec + 1);
+	}
       if (noside == EVAL_AVOID_SIDE_EFFECTS)
 	{
 	  struct type *return_type;
@@ -490,14 +505,6 @@ value_x_binop (struct value *arg1, struct value *arg2, enum exp_opcode op,
 	    = TYPE_TARGET_TYPE (check_typedef (value_type (argvec[0])));
 	  return value_zero (return_type, VALUE_LVAL (arg1));
 	}
-
-      if (TYPE_CODE (value_type (argvec[0])) == TYPE_CODE_XMETHOD)
-	{
-	  /* Static xmethods are not supported yet.  */
-	  gdb_assert (static_memfuncp == 0);
-	  return call_xmethod (argvec[0], 2, argvec + 1);
-	}
-      else
       return call_function_by_hand (argvec[0], 2 - static_memfuncp,
 				    argvec + 1);
     }
@@ -594,6 +601,21 @@ value_x_unop (struct value *arg1, enum exp_opcode op, enum noside noside)
 	  nargs --;
 	  argvec++;
 	}
+      if (TYPE_CODE (value_type (argvec[0])) == TYPE_CODE_XMETHOD)
+	{
+	  /* Static xmethods are not supported yet.  */
+	  gdb_assert (static_memfuncp == 0);
+	  if (noside == EVAL_AVOID_SIDE_EFFECTS)
+	    {
+	      struct type *return_type
+		= result_type_of_xmethod (argvec[0], 1, argvec + 1);
+
+	      if (return_type == NULL)
+		error (_("Xmethod is missing return type."));
+	      return value_zero (return_type, VALUE_LVAL (arg1));
+	    }
+	  return call_xmethod (argvec[0], 1, argvec + 1);
+	}
       if (noside == EVAL_AVOID_SIDE_EFFECTS)
 	{
 	  struct type *return_type;
@@ -602,13 +624,6 @@ value_x_unop (struct value *arg1, enum exp_opcode op, enum noside noside)
 	    = TYPE_TARGET_TYPE (check_typedef (value_type (argvec[0])));
 	  return value_zero (return_type, VALUE_LVAL (arg1));
 	}
-      if (TYPE_CODE (value_type (argvec[0])) == TYPE_CODE_XMETHOD)
-	{
-	  /* Static xmethods are not supported yet.  */
-	  gdb_assert (static_memfuncp == 0);
-	  return call_xmethod (argvec[0], 1, argvec + 1);
-	}
-      else
       return call_function_by_hand (argvec[0], nargs, argvec + 1);
     }
   throw_error (NOT_FOUND_ERROR,

gdb/value.c

@@ -2600,6 +2600,18 @@ value_of_xmethod (struct xmethod_worker *worker)
   return worker->value;
 }
 
+/* Return the type of the result of TYPE_CODE_XMETHOD value METHOD.  */
+
+struct type *
+result_type_of_xmethod (struct value *method, int argc, struct value **argv)
+{
+  gdb_assert (TYPE_CODE (value_type (method)) == TYPE_CODE_XMETHOD
+	      && method->lval == lval_xcallable && argc > 0);
+
+  return get_xmethod_result_type (method->location.xm_worker,
+				  argv[0], argv + 1, argc - 1);
+}
+
 /* Call the xmethod corresponding to the TYPE_CODE_XMETHOD value METHOD.  */
 
 struct value *

gdb/value.h

@@ -1080,7 +1080,10 @@ char *value_internal_function_name (struct value *);
 
 extern struct value *value_of_xmethod (struct xmethod_worker *);
 
-struct value *call_xmethod (struct value *function,
+extern struct type *result_type_of_xmethod (struct value *method,
+					    int argc, struct value **argv);
+
+extern struct value *call_xmethod (struct value *method,
 				   int argc, struct value **argv);
 
 #endif /* !defined (VALUE_H) */