Use correct default for target functions that return pointer

* target.c (return_null): Define.
	(update_current_target): Use it instead of return_zero for
	functions that return a pointer.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2014-01-07  Andreas Schwab  <schwab@linux-m68k.org>
+
+	* target.c (return_null): Define.
+	(update_current_target): Use it instead of return_zero for
+	functions that return a pointer.
+
 2014-01-07  Edjunior Barbosa Machado  <emachado@linux.vnet.ibm.com>
 
 	* source.c (add_path): Fix check for duplicated paths in the previously

gdb/target.c

@@ -64,6 +64,8 @@ static int return_one (void);
 
 static int return_minus_one (void);
 
+static void *return_null (void);
+
 void target_ignore (void);
 
 static void target_command (char *, int);
@@ -806,10 +808,10 @@ update_current_target (void)
 	    return_zero);
   de_fault (to_extra_thread_info,
 	    (char *(*) (struct thread_info *))
-	    return_zero);
+	    return_null);
   de_fault (to_thread_name,
 	    (char *(*) (struct thread_info *))
-	    return_zero);
+	    return_null);
   de_fault (to_stop,
 	    (void (*) (ptid_t))
 	    target_ignore);
@@ -819,7 +821,7 @@ update_current_target (void)
 	    tcomplain);
   de_fault (to_pid_to_exec_file,
 	    (char *(*) (int))
-	    return_zero);
+	    return_null);
   de_fault (to_async,
 	    (void (*) (void (*) (enum inferior_event_type, void*), void*))
 	    tcomplain);
@@ -918,7 +920,7 @@ update_current_target (void)
 	    tcomplain);
   de_fault (to_traceframe_info,
 	    (struct traceframe_info * (*) (void))
-	    return_zero);
+	    return_null);
   de_fault (to_supports_evaluation_of_breakpoint_conditions,
 	    (int (*) (void))
 	    return_zero);
@@ -3634,6 +3636,12 @@ return_minus_one (void)
   return -1;
 }
 
+static void *
+return_null (void)
+{
+  return 0;
+}
+
 /*
  * Find the next target down the stack from the specified target.
  */