Trust PAD types instead of using PAD___XVS.

        * ada-lang.c (trust_pad_over_xvs): New static variable.
        (ada_is_aligner_type): If !trust_pad_over_xvs and there is a
        parallel XVS type, follow the XVS type instead of the PAD type.
        (unwrap_value): Make sure that there is no parallel XVE type
        before returning the value as is.
        (set_ada_list, show_ada_list): New static variables.
        (set_ada_command, show_ada_command): New functions.
        (_initialize_ada_language): Add new "set/show ada" prefix commands.
        Add new "set/show ada trust-PAD-over-XVS" setting.

1 files changed, 60 insertions, 6 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 2f16644..e63cf88 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -7727,6 +7727,16 @@ ada_is_string_type (struct type *type)
     return 0;
 }
 
+/* The compiler sometimes provides a parallel XVS type for a given
+   PAD type.  Normally, it is safe to follow the PAD type directly,
+   but older versions of the compiler have a bug that causes the offset
+   of its "F" field to be wrong.  Following that field in that case
+   would lead to incorrect results, but this can be worked around
+   by ignoring the PAD type and using the associated XVS type instead.
+
+   Set to True if the debugger should trust the contents of PAD types.
+   Otherwise, ignore the PAD type if there is a parallel XVS type.  */
+static int trust_pad_over_xvs = 1;
 
 /* True if TYPE is a struct type introduced by the compiler to force the
    alignment of a value.  Such types have a single field with a
@@ -7737,10 +7747,7 @@ ada_is_aligner_type (struct type *type)
 {
   type = ada_check_typedef (type);
 
-  /* If we can find a parallel XVS type, then the XVS type should
-     be used instead of this type.  And hence, this is not an aligner
-     type.  */
-  if (ada_find_parallel_type (type, "___XVS") != NULL)
+  if (!trust_pad_over_xvs && ada_find_parallel_type (type, "___XVS") != NULL)
     return 0;
 
   return (TYPE_CODE (type) == TYPE_CODE_STRUCT
@@ -7918,8 +7925,11 @@ unwrap_value (struct value *val)
       struct type *raw_real_type =
         ada_check_typedef (ada_get_base_type (type));
 
-      if (type == raw_real_type)
-        return val;
+      /* If there is no parallel XVS or XVE type, then the value is
+	 already unwrapped.  Return it without further modification.  */
+      if ((type == raw_real_type)
+	  && ada_find_parallel_type (type, "___XVE") == NULL)
+	return val;
 
       return
         coerce_unspec_val_to_type
@@ -11373,11 +11383,55 @@ const struct language_defn ada_language_defn = {
 /* Provide a prototype to silence -Wmissing-prototypes.  */
 extern initialize_file_ftype _initialize_ada_language;
 
+/* Command-list for the "set/show ada" prefix command.  */
+static struct cmd_list_element *set_ada_list;
+static struct cmd_list_element *show_ada_list;
+
+/* Implement the "set ada" prefix command.  */
+
+static void
+set_ada_command (char *arg, int from_tty)
+{
+  printf_unfiltered (_(\
+"\"set ada\" must be followed by the name of a setting.\n"));
+  help_list (set_ada_list, "set ada ", -1, gdb_stdout);
+}
+
+/* Implement the "show ada" prefix command.  */
+
+static void
+show_ada_command (char *args, int from_tty)
+{
+  cmd_show_list (show_ada_list, from_tty, "");
+}
+
 void
 _initialize_ada_language (void)
 {
   add_language (&ada_language_defn);
 
+  add_prefix_cmd ("ada", no_class, set_ada_command,
+                  _("Prefix command for changing Ada-specfic settings"),
+                  &set_ada_list, "set ada ", 0, &setlist);
+
+  add_prefix_cmd ("ada", no_class, show_ada_command,
+                  _("Generic command for showing Ada-specific settings."),
+                  &show_ada_list, "show ada ", 0, &showlist);
+
+  add_setshow_boolean_cmd ("trust-PAD-over-XVS", class_obscure,
+                           &trust_pad_over_xvs, _("\
+Enable or disable an optimization trusting PAD types over XVS types"), _("\
+Show whether an optimization trusting PAD types over XVS types is activated"),
+                           _("\
+This is related to the encoding used by the GNAT compiler.  The debugger\n\
+should normally trust the contents of PAD types, but certain older versions\n\
+of GNAT have a bug that sometimes causes the information in the PAD type\n\
+to be incorrect.  Turning this setting \"off\" allows the debugger to\n\
+work around this bug.  It is always safe to turn this option \"off\", but\n\
+this incurs a slight performance penalty, so it is recommended to NOT change\n\
+this option to \"off\" unless necessary."),
+                            NULL, NULL, &set_ada_list, &show_ada_list);
+
   varsize_limit = 65536;
 
   obstack_init (&symbol_list_obstack);