[Ada] avoid error message pollution with uninitialized tagged variable

Consider the following function...

  3 procedure Foo is
  4    I : Integer := Ident (10);
  5    Obj : Base;
  6 begin
  7    Obj.X := I;
  8    Do_Nothing (Obj.X'Address);
  9 end Foo;

... where type "Base" is defined as a plain tagged record. If the user
stops execution before "Obj" gets initialized (for example, by inserting
a breakpoint "on" the function - or in other words, by inserting a
breakpoint using the function name as the location), one might get
the following of output if you try printing the value of obj:

    (gdb) p obj
    object size is larger than varsize-limit
    object size is larger than varsize-limit
    object size is larger than varsize-limit
    $1 = object size is larger than varsize-limit
    (x => 4204154)

Same thing with "info locals":

   (gdb) info locals
    i = 0
    obj = object size is larger than varsize-limit
    (x => 4204154)

We have also seen different error messages such as "Cannot read
memory at 0x...".

The error happens because we are trying to read the dispatch table
of a tagged type variable before it gets initialized.  So the errors
might legitimately occur, and are supposed to be be contained.
However, the way things are written in ada-lang.c:ada_tag_name,
although the exception is in fact contained, the error message still
gets to be printed out.

This patch prevents this from happening by eliminating the use of
catch_errors, and using a TRY_CATCH block instead.  Doing this removed
the need to use functions specifically fitted for catch_errors, and
thus some other simplifications could me made.  In the end, the code
got reorganized a bit to better show the logic behind it, as well as
the common patterns.

gdb/ChangeLog:

        * ada-lang.c (struct tag_args): Delete.
        (ada_get_tsd_type): Function body moved up in source file.
        (ada_tag_name_1, ada_tag_name_2): Delete.
        (ada_get_tsd_from_tag): New function.
        (ada_tag_name_from_tsd): New function.
        (ada_tag_name): Use a TRY_CATCH block instead of catch_errors
        to determine the tag name.

gdb/testsuite/ChangeLog:

        * gdb.ada/tagged_not_init: New testcase.

gdb/ChangeLog

@@ -1,3 +1,13 @@
+2012-02-29  Joel Brobecker  <brobecker@adacore.com>
+
+	* ada-lang.c (struct tag_args): Delete.
+	(ada_get_tsd_type): Function body moved up in source file.
+	(ada_tag_name_1, ada_tag_name_2): Delete.
+	(ada_get_tsd_from_tag): New function.
+	(ada_tag_name_from_tsd): New function.
+	(ada_tag_name): Use a TRY_CATCH block instead of catch_errors
+	to determine the tag name.
+
 2012-02-29  Joel Brobecker  <brobecker@adacore.com>
 
 	* ada-lang.h (ada_get_decoded_value, ada_get_decoded_type): Add

gdb/ada-lang.c

@@ -6029,44 +6029,6 @@ type_from_tag (struct value *tag)
   return NULL;
 }
 
-struct tag_args
-{
-  struct value *tag;
-  char *name;
-};
-
-
-static int ada_tag_name_1 (void *);
-static int ada_tag_name_2 (struct tag_args *);
-
-/* Wrapper function used by ada_tag_name.  Given a struct tag_args*
-   value ARGS, sets ARGS->name to the tag name of ARGS->tag.
-   The value stored in ARGS->name is valid until the next call to 
-   ada_tag_name_1.  */
-
-static int
-ada_tag_name_1 (void *args0)
-{
-  struct tag_args *args = (struct tag_args *) args0;
-  static char name[1024];
-  char *p;
-  struct value *val;
-
-  args->name = NULL;
-  val = ada_value_struct_elt (args->tag, "tsd", 1);
-  if (val == NULL)
-    return ada_tag_name_2 (args);
-  val = ada_value_struct_elt (val, "expanded_name", 1);
-  if (val == NULL)
-    return 0;
-  read_memory_string (value_as_address (val), name, sizeof (name) - 1);
-  for (p = name; *p != '\0'; p += 1)
-    if (isalpha (*p))
-      *p = tolower (*p);
-  args->name = name;
-  return 0;
-}
-
 /* Return the "ada__tags__type_specific_data" type.  */
 
 static struct type *
@@ -6079,55 +6041,98 @@ ada_get_tsd_type (struct inferior *inf)
   return data->tsd_type;
 }
 
-/* Utility function for ada_tag_name_1 that tries the second
-   representation for the dispatch table (in which there is no
-   explicit 'tsd' field in the referent of the tag pointer, and instead
-   the tsd pointer is stored just before the dispatch table.  */
-   
-static int
-ada_tag_name_2 (struct tag_args *args)
+/* Return the TSD (type-specific data) associated to the given TAG.
+   TAG is assumed to be the tag of a tagged-type entity.
+
+   May return NULL if we are unable to get the TSD.  */
+
+static struct value *
+ada_get_tsd_from_tag (struct value *tag)
+{
+  struct value *val;
+  struct type *type;
+
+  /* First option: The TSD is simply stored as a field of our TAG.
+     Only older versions of GNAT would use this format, but we have
+     to test it first, because there are no visible markers for
+     the current approach except the absence of that field.  */
+
+  val = ada_value_struct_elt (tag, "tsd", 1);
+  if (val)
+    return val;
+
+  /* Try the second representation for the dispatch table (in which
+     there is no explicit 'tsd' field in the referent of the tag pointer,
+     and instead the tsd pointer is stored just before the dispatch
+     table.  */
+
+  type = ada_get_tsd_type (current_inferior());
+  if (type == NULL)
+    return NULL;
+  type = lookup_pointer_type (lookup_pointer_type (type));
+  val = value_cast (type, tag);
+  if (val == NULL)
+    return NULL;
+  return value_ind (value_ptradd (val, -1));
+}
+
+/* Given the TSD of a tag (type-specific data), return a string
+   containing the name of the associated type.
+
+   The returned value is good until the next call.  May return NULL
+   if we are unable to determine the tag name.  */
+
+static char *
+ada_tag_name_from_tsd (struct value *tsd)
 {
-  struct type *info_type;
   static char name[1024];
   char *p;
-  struct value *val, *valp;
+  struct value *val;
 
-  args->name = NULL;
-  info_type = ada_get_tsd_type (current_inferior());
-  if (info_type == NULL)
-    return 0;
-  info_type = lookup_pointer_type (lookup_pointer_type (info_type));
-  valp = value_cast (info_type, args->tag);
-  if (valp == NULL)
-    return 0;
-  val = value_ind (value_ptradd (valp, -1));
+  val = ada_value_struct_elt (tsd, "expanded_name", 1);
   if (val == NULL)
-    return 0;
-  val = ada_value_struct_elt (val, "expanded_name", 1);
-  if (val == NULL)
-    return 0;
+    return NULL;
   read_memory_string (value_as_address (val), name, sizeof (name) - 1);
   for (p = name; *p != '\0'; p += 1)
     if (isalpha (*p))
       *p = tolower (*p);
-  args->name = name;
-  return 0;
+  return name;
 }
 
 /* The type name of the dynamic type denoted by the 'tag value TAG, as
-   a C string.  */
+   a C string.
+
+   Return NULL if the TAG is not an Ada tag, or if we were unable to
+   determine the name of that tag.  The result is good until the next
+   call.  */
 
 const char *
 ada_tag_name (struct value *tag)
 {
-  struct tag_args args;
+  volatile struct gdb_exception e;
+  char *name = NULL;
 
   if (!ada_is_tag_type (value_type (tag)))
     return NULL;
-  args.tag = tag;
-  args.name = NULL;
-  catch_errors (ada_tag_name_1, &args, NULL, RETURN_MASK_ALL);
-  return args.name;
+
+  /* It is perfectly possible that an exception be raised while trying
+     to determine the TAG's name, even under normal circumstances:
+     The associated variable may be uninitialized or corrupted, for
+     instance. We do not let any exception propagate past this point.
+     instead we return NULL.
+
+     We also do not print the error message either (which often is very
+     low-level (Eg: "Cannot read memory at 0x[...]"), but instead let
+     the caller print a more meaningful message if necessary.  */
+  TRY_CATCH (e, RETURN_MASK_ERROR)
+    {
+      struct value *tsd = ada_get_tsd_from_tag (tag);
+
+      if (tsd != NULL)
+	name = ada_tag_name_from_tsd (tsd);
+    }
+
+  return name;
 }
 
 /* The parent type of TYPE, or NULL if none.  */

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2012-02-29  Joel Brobecker  <brobecker@adacore.com>
+
+	* gdb.ada/tagged_not_init: New testcase.
+
 2012-02-29  Joel Brobecker  <brobecker@adacore.com>
 
 	* gdb.ada/arrayidx.exp: Adjust expected output for p_one_two_three.

gdb/testsuite/gdb.ada/tagged_not_init.exp

@@ -0,0 +1,36 @@
+# Copyright 2012 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/>.
+
+load_lib "ada.exp"
+
+if { [skip_ada_tests] } { return -1 }
+
+set testdir "tagged_not_init"
+set testfile "${testdir}/foo"
+set srcfile ${srcdir}/${subdir}/${testfile}.adb
+set binfile ${objdir}/${subdir}/${testfile}
+
+file mkdir ${objdir}/${subdir}/${testdir}
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable {debug}] != ""} {
+    return -1
+}
+
+clean_restart ${testfile}
+
+set bp_location [gdb_get_line_number "STOP" ${testdir}/foo.adb]
+runto "foo.adb:$bp_location"
+
+gdb_test "print obj" " = \\(x => -?$decimal\\)"
+

gdb/testsuite/gdb.ada/tagged_not_init/foo.adb

@@ -0,0 +1,24 @@
+--  Copyright 2012 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/>.
+
+with Pck; use Pck;
+
+procedure Foo is
+   I : Integer := Ident (10);  -- STOP
+   Obj : Base;
+begin
+   Obj.X := I;
+   Do_Nothing (Obj.X'Address);
+end Foo;

gdb/testsuite/gdb.ada/tagged_not_init/pck.adb

@@ -0,0 +1,26 @@
+--  Copyright 2012 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/>.
+
+package body Pck is
+   function Ident (I : Integer) return Integer is
+   begin
+      return I;
+   end Ident;
+
+   procedure Do_Nothing (A : System.Address) is
+   begin
+      null;
+   end Do_Nothing;
+end Pck;

gdb/testsuite/gdb.ada/tagged_not_init/pck.ads

@@ -0,0 +1,31 @@
+--  Copyright 2012 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/>.
+
+with System;
+
+package Pck is
+   type Base is tagged record
+      X : Integer := 42;
+   end record;
+
+   type Extension is new Base with
+      record
+         Y : Float := 42.0;
+      end record;
+
+   function Ident (I : Integer) return Integer;
+
+   procedure Do_Nothing (A : System.Address);
+end Pck;