[Ada] Fix the evaluation of access to packed array subscript

This change is relevant only for standard DWARF (as opposed to the GNAT
encodings extensions): at the time of writing it only makes a difference
with GCC patches that are to be integrated: see in particular
<https://gcc.gnu.org/ml/gcc-patches/2015-07/msg01364.html>.

Given the following Ada declarations:

    type Small is mod 2 ** 6;
    type Array_Type is array (0 .. 9) of Small
       with Pack;
    type Array_Access is access all Array_Type;

    A  : aliased Array_Type := (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
    AA : constant Array_Type := A'Access;

Before this change, we would get the following GDB session:

    (gdb) print aa.all(2)
    $1 = 3
    (gdb) print aa(2)
    $2 = 16

This is wrong: both expression should yield the same value: 3.  The
problem is simply that the routine which handles accesses to arrays lack
general handling for packed arrays.  After this patch, we have the
expected output:

    (gdb) print aa.all(2)
    $1 = 3
    (gdb) print aa(2)
    $2 = 3

gdb/ChangeLog:

	* ada-lang.c (ada_value_ptr_subscript): Update the heading
	comment.  Handle packed arrays.

gdb/testsuite/ChangeLog:

	* gdb.ada/access_to_packed_array.exp: New testcase.
	* gdb.ada/access_to_packed_array/foo.adb: New file.
	* gdb.ada/access_to_packed_array/pack.adb: New file.
	* gdb.ada/access_to_packed_array/pack.ads: New file.

Tested on x86_64-linux, no regression.

7 files changed, 133 insertions, 2 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index dadb7a0..3ca1bf1 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2015-09-14  Pierre-Marie de Rodat  <derodat@adacore.com>
+
+	* ada-lang.c (ada_value_ptr_subscript): Update the heading
+	comment.  Handle packed arrays.
+
 2015-09-14  Pedro Alves  <palves@redhat.com>
 
 	* NEWS (Changes in GDB 7.10, New commands>: Remove duplicate
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index d166d1c..49f3d9a 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -2757,14 +2757,27 @@ ada_value_subscript (struct value *arr, int arity, struct value **ind)
 
 /* Assuming ARR is a pointer to a GDB array, the value of the element
    of *ARR at the ARITY indices given in IND.
-   Does not read the entire array into memory.  */
+   Does not read the entire array into memory.
+
+   Note: Unlike what one would expect, this function is used instead of
+   ada_value_subscript for basically all non-packed array types.  The reason
+   for this is that a side effect of doing our own pointer arithmetics instead
+   of relying on value_subscript is that there is no implicit typedef peeling.
+   This is important for arrays of array accesses, where it allows us to
+   preserve the fact that the array's element is an array access, where the
+   access part os encoded in a typedef layer.  */
 
 static struct value *
 ada_value_ptr_subscript (struct value *arr, int arity, struct value **ind)
 {
   int k;
+  struct value *array_ind = ada_value_ind (arr);
   struct type *type
-    = check_typedef (value_enclosing_type (ada_value_ind (arr)));
+    = check_typedef (value_enclosing_type (array_ind));
+
+  if (TYPE_CODE (type) == TYPE_CODE_ARRAY
+      && TYPE_FIELD_BITSIZE (type, 0) > 0)
+    return value_subscript_packed (array_ind, arity, ind);
 
   for (k = 0; k < arity; k += 1)
     {
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index e135b56..17b264d 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2015-09-14  Pierre-Marie de Rodat  <derodat@adacore.com>
+
+	* gdb.ada/access_to_packed_array.exp: New testcase.
+	* gdb.ada/access_to_packed_array/foo.adb: New file.
+	* gdb.ada/access_to_packed_array/pack.adb: New file.
+	* gdb.ada/access_to_packed_array/pack.ads: New file.
+
 2015-09-14  Markus Metzger  <markus.t.metzger@intel.com>
 
 	* gdb.btrace/buffer-size.exp: Remove recording with unlimited BTS
diff --git a/gdb/testsuite/gdb.ada/access_to_packed_array.exp b/gdb/testsuite/gdb.ada/access_to_packed_array.exp
new file mode 100644
index 0000000..0dca780
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/access_to_packed_array.exp
@@ -0,0 +1,33 @@
+# Copyright 2015 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"
+
+standard_ada_testfile foo
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable [list debug]] != "" } {
+  return -1
+}
+
+clean_restart ${testfile}
+
+set bp_location [gdb_get_line_number "BREAK" ${testdir}/foo.adb]
+runto "foo.adb:$bp_location"
+
+gdb_test "print pack.a" "\\(0 => 1, 2, 3, 4, 5, 6, 7, 8, 9, 10\\)")
+gdb_test "pack.aa"      "\\(access pack\\.array_type\\) 0x.* <pack\\.a>")
+
+gdb_test "pack.a(2)"   "3"
+gdb_test "pack.aa(2)"  "3"
diff --git a/gdb/testsuite/gdb.ada/access_to_packed_array/foo.adb b/gdb/testsuite/gdb.ada/access_to_packed_array/foo.adb
new file mode 100644
index 0000000..71ae5bf
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/access_to_packed_array/foo.adb
@@ -0,0 +1,21 @@
+--  Copyright 2015 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 Pack;
+
+procedure Foo is
+begin
+   Pack.Do_Nothing (Pack.AA); --  BREAK
+end Foo;
diff --git a/gdb/testsuite/gdb.ada/access_to_packed_array/pack.adb b/gdb/testsuite/gdb.ada/access_to_packed_array/pack.adb
new file mode 100644
index 0000000..60d752d
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/access_to_packed_array/pack.adb
@@ -0,0 +1,23 @@
+--  Copyright 2015 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 Pack is
+
+   procedure Do_Nothing (A : Array_Access) is
+   begin
+      null;
+   end Do_Nothing;
+
+end Pack;
diff --git a/gdb/testsuite/gdb.ada/access_to_packed_array/pack.ads b/gdb/testsuite/gdb.ada/access_to_packed_array/pack.ads
new file mode 100644
index 0000000..bb08742
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/access_to_packed_array/pack.ads
@@ -0,0 +1,29 @@
+--  Copyright 2015 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 Pack is
+
+   type Small is mod 2 ** 6;
+   type Array_Type is array (0 .. 9) of Small
+      with Pack;
+   type Array_Access is access all Array_Type;
+
+   A  : aliased Array_Type :=
+     (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+   AA : constant Array_Access := A'Access;
+
+   procedure Do_Nothing (A : Array_Access);
+
+end Pack;