Print non-Ada unions without crashing

ada-lang.c is a bit too eager trying to decode unions in the Ada style
-- looking for discriminants and such.  This causes crashes when
printing a non-Ada union in Ada mode, something that can easily happen
when printing a value from history or certain registers on AArch64.

This patch fixes the bug by changing ada-lang.c to only apply special
Ada treatment to types coming from an Ada CU.  This in turn required a
couple of surprising changes.

First, some of the Ada code was already using HAVE_GNAT_AUX_INFO to
decide whether a type had already been fixed -- such types had
INIT_CPLUS_SPECIFIC called on them.  This patch changes these spots to
use the "none" identifier instead.

This then required changing value_rtti_type to avoid changing the
language-specific object attached to an Ada type, which seems like a
good change regardless.

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-04-19  Tom Tromey  <tromey@adacore.com>

	* ada-lang.c (ada_is_variant_part, ada_to_fixed_type_1):
	Check ADA_TYPE_P.
	(empty_record, ada_template_to_fixed_record_type_1)
	(template_to_static_fixed_type)
	(to_record_with_fixed_variant_part): Use INIT_NONE_SPECIFIC.
	* cp-abi.c (value_rtti_type): Check HAVE_CPLUS_STRUCT.
	* gdbtypes.h (INIT_NONE_SPECIFIC, ADA_TYPE_P): New
	macros.

gdb/testsuite/ChangeLog
2019-04-19  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/ptype_union.c: New file.
	* gdb.ada/ptype_union.exp: New file.

1 files changed, 13 insertions, 4 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index ccf8ed8039e..250ce438b1a 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -6961,6 +6961,10 @@ ada_is_wrapper_field (struct type *type, int field_num)
 int
 ada_is_variant_part (struct type *type, int field_num)
 {
+  /* Only Ada types are eligible.  */
+  if (!ADA_TYPE_P (type))
+    return 0;
+
   struct type *field_type = TYPE_FIELD_TYPE (type, field_num);
 
   return (TYPE_CODE (field_type) == TYPE_CODE_UNION
@@ -8258,7 +8262,7 @@ empty_record (struct type *templ)
   TYPE_CODE (type) = TYPE_CODE_STRUCT;
   TYPE_NFIELDS (type) = 0;
   TYPE_FIELDS (type) = NULL;
-  INIT_CPLUS_SPECIFIC (type);
+  INIT_NONE_SPECIFIC (type);
   TYPE_NAME (type) = "<empty>";
   TYPE_LENGTH (type) = 0;
   return type;
@@ -8312,7 +8316,7 @@ ada_template_to_fixed_record_type_1 (struct type *type,
 
   rtype = alloc_type_copy (type);
   TYPE_CODE (rtype) = TYPE_CODE_STRUCT;
-  INIT_CPLUS_SPECIFIC (rtype);
+  INIT_NONE_SPECIFIC (rtype);
   TYPE_NFIELDS (rtype) = nfields;
   TYPE_FIELDS (rtype) = (struct field *)
     TYPE_ALLOC (rtype, nfields * sizeof (struct field));
@@ -8587,7 +8591,7 @@ template_to_static_fixed_type (struct type *type0)
 	    {
 	      TYPE_TARGET_TYPE (type0) = type = alloc_type_copy (type0);
 	      TYPE_CODE (type) = TYPE_CODE (type0);
-	      INIT_CPLUS_SPECIFIC (type);
+	      INIT_NONE_SPECIFIC (type);
 	      TYPE_NFIELDS (type) = nfields;
 	      TYPE_FIELDS (type) = (struct field *)
 		TYPE_ALLOC (type, nfields * sizeof (struct field));
@@ -8636,7 +8640,7 @@ to_record_with_fixed_variant_part (struct type *type, const gdb_byte *valaddr,
 
   rtype = alloc_type_copy (type);
   TYPE_CODE (rtype) = TYPE_CODE_STRUCT;
-  INIT_CPLUS_SPECIFIC (rtype);
+  INIT_NONE_SPECIFIC (rtype);
   TYPE_NFIELDS (rtype) = nfields;
   TYPE_FIELDS (rtype) =
     (struct field *) TYPE_ALLOC (rtype, nfields * sizeof (struct field));
@@ -9005,6 +9009,11 @@ ada_to_fixed_type_1 (struct type *type, const gdb_byte *valaddr,
                    CORE_ADDR address, struct value *dval, int check_tag)
 {
   type = ada_check_typedef (type);
+
+  /* Only un-fixed types need to be handled here.  */
+  if (!HAVE_GNAT_AUX_INFO (type))
+    return type;
+
   switch (TYPE_CODE (type))
     {
     default: