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.

7 files changed, 116 insertions, 5 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 22f22b9..013d80b 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,14 @@
+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.
+
 2019-04-19  Ilya Yu. Malakhov  <malakhov@mcst.ru>
 
 	PR symtab/24423:
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index ccf8ed8..250ce43 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:
diff --git a/gdb/cp-abi.c b/gdb/cp-abi.c
index d95b140..bbb74d4 100644
--- a/gdb/cp-abi.c
+++ b/gdb/cp-abi.c
@@ -109,7 +109,8 @@ value_rtti_type (struct value *v, int *full,
 {
   struct type *ret = NULL;
 
-  if ((current_cp_abi.rtti_type) == NULL)
+  if ((current_cp_abi.rtti_type) == NULL
+      || !HAVE_CPLUS_STRUCT (check_typedef (value_type (v))))
     return NULL;
   try
     {
diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
index 2125ed9..a5f6afc 100644
--- a/gdb/gdbtypes.h
+++ b/gdb/gdbtypes.h
@@ -1255,6 +1255,10 @@ extern void allocate_cplus_struct_type (struct type *);
   (TYPE_SPECIFIC_FIELD (type) == TYPE_SPECIFIC_CPLUS_STUFF \
    && TYPE_RAW_CPLUS_SPECIFIC (type) !=  &cplus_struct_default)
 
+#define INIT_NONE_SPECIFIC(type) \
+  (TYPE_SPECIFIC_FIELD (type) = TYPE_SPECIFIC_NONE, \
+   TYPE_MAIN_TYPE (type)->type_specific = {})
+
 extern const struct gnat_aux_type gnat_aux_default;
 
 extern void allocate_gnat_aux_type (struct type *);
@@ -1268,6 +1272,12 @@ extern void allocate_gnat_aux_type (struct type *);
 #define HAVE_GNAT_AUX_INFO(type) \
   (TYPE_SPECIFIC_FIELD (type) == TYPE_SPECIFIC_GNAT_STUFF)
 
+/* * True if TYPE is known to be an Ada type of some kind.  */
+#define ADA_TYPE_P(type)					\
+  (TYPE_SPECIFIC_FIELD (type) == TYPE_SPECIFIC_GNAT_STUFF	\
+    || (TYPE_SPECIFIC_FIELD (type) == TYPE_SPECIFIC_NONE	\
+	&& TYPE_FIXED_INSTANCE (type)))
+
 #define INIT_FUNC_SPECIFIC(type)					       \
   (TYPE_SPECIFIC_FIELD (type) = TYPE_SPECIFIC_FUNC,			       \
    TYPE_MAIN_TYPE (type)->type_specific.func_stuff = (struct func_type *)      \
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 89058f4..aaa110c 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2019-04-19  Tom Tromey  <tromey@adacore.com>
 
+	* gdb.ada/ptype_union.c: New file.
+	* gdb.ada/ptype_union.exp: New file.
+
+2019-04-19  Tom Tromey  <tromey@adacore.com>
+
 	PR symtab/24423:
 	* gdb.base/list0.h (foo): Add a control-l character.
 
diff --git a/gdb/testsuite/gdb.ada/ptype_union.c b/gdb/testsuite/gdb.ada/ptype_union.c
new file mode 100644
index 0000000..eef9c5a
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/ptype_union.c
@@ -0,0 +1,41 @@
+/* This test program is part of GDB, the GNU debugger.
+
+   Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+union a
+{
+  int l;
+  double m;
+};
+
+union b
+{
+  char *n;
+  float o;
+};
+
+struct s
+{
+  union a af;
+  union b bf;
+};
+
+struct s global;
+
+int main ()
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.ada/ptype_union.exp b/gdb/testsuite/gdb.ada/ptype_union.exp
new file mode 100644
index 0000000..4f33721
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/ptype_union.exp
@@ -0,0 +1,34 @@
+# Copyright 2019 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+standard_testfile .c
+
+if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
+    return -1
+}
+
+# The test case is written in C, because it was easy to make the
+# required type there; but the bug itself only happens in Ada.
+gdb_test "set lang ada" ""
+
+gdb_test "ptype global" \
+    [multi_line \
+	 "type = record" \
+	 "\[ \t\]*af: a;" \
+	 "\[ \t\]*bf: b;" \
+	 "end record"]
+
+gdb_test "print global" \
+    " = \\(af => \\(l => 0, m => 0.0\\), bf => \\(n => 0x0, o => 0.0\\)\\)"