[Ada/commit] varsize-limit error printing element of packed array...

[Joel Brobecker <brobecker at adacore dot com>]

... when that packed array is part of a discriminated record and
one of the bounds is a discriminant.

Hello!

Consider the following code:

   type FUNNY_CHAR_T is (NUL, ' ', '"', '#', [etc]);
   type FUNNY_STR_T is array (POSITIVE range <>) of FUNNY_CHAR_T;
   pragma PACK (FUNNY_STR_T);
   type FUNNY_STRING_T (SIZE : NATURAL := 1) is
      record
         STR    : FUNNY_STR_T (1 .. SIZE) := (others => '0');
         LENGTH : NATURAL := 4;
      end record;
   TEST: FUNNY_STRING_T(100);

GDB is able to print the value of variable "test" and "test.str".
But not "test.str(1)":

    (gdb) p test
    $1 = (size => 100, str => (33 'A', nul <repeats 99 times>), length => 1)
    (gdb) p test.str
    $2 = (33 'A', nul <repeats 99 times>)
    (gdb) p test.str(1)
    object size is larger than varsize-limit

The problem occurs during the phase where we are trying to resolve
the expression subscript operation. On the one hand of the subscript
operator, we have the result of the evaluation of "test.str", which
is our packed array. We have the following code to handle packed
arrays in particular:

      if (ada_is_constrained_packed_array_type
          (desc_base_type (value_type (argvec[0]))))
        argvec[0] = ada_coerce_to_simple_array (argvec[0]);

This eventually leads to a call to constrained_packed_array_type
to return the "simple array".  This function relies on a parallel
___XA type, when available, to determine the bounds.  In our case,
we find type...

    failure__funny_string_t__T4b___XA"

... which has one field describing the bounds of our array as:

    failure__funny_string_t__T3b___XDLU_1__size

The part that interests us is after the ___XD suffix or,
in other words: "LU_1__size". What this means in GNAT encoding
parlance is that the lower bound is 1, and that the upper bound
is the value of "size". "size" is our discriminant in this case.

Normally, we would access the record's discriminant in order to
get the upper bound's value, but we do not have that information,
here. We are in a mode where we are just trying to "fix" the type
without an actual value. This is what the call to to_fixed_range_type
is doing, and because the fix'ing fails, it ends up returning
the ___XDLU type unmodified as our index type.

This shouldn't be a problem, except that the later part of
constrained_packed_array_type then uses that index_type to
determine the array size, via a call to get_discrete_bounds.
The problem is that the upper bound of the ___XDLU type is
dynamic (in the DWARF sense) while get_discrete_bounds implicitly
assumes that the bounds are static, and therefore accesses
them using macros that assume the bounds values are constants:

    case TYPE_CODE_RANGE:
      *lowp = TYPE_LOW_BOUND (type);
      *highp = TYPE_HIGH_BOUND (type);

This therefore returns a bogus value for the upper bound,
leading to an unexpectedly large size for our array, which
later triggers the varsize-limit guard we've seen above.

This patch avoids the problem by adding special handling
of dynamic range types. It also extends the documentation
of the constrained_packed_array_type function to document
what happens in this situation.

gdb/ChangeLog:

        * ada-lang.c (constrained_packed_array_type): Set the length
        of the return array as if both bounds where zero if that
        returned array's index type is dynamic.

gdb/testsuite/ChangeLog:

        * gdb.ada/pkd_arr_elem: New Testcase.

Tested on x86_64-linux. I will push this patch is a few days...

Thank you,
-- 
Joel
---
 gdb/ada-lang.c                                 | 14 ++++++--
 gdb/testsuite/gdb.ada/pkd_arr_elem.exp         | 38 ++++++++++++++++++++++
 gdb/testsuite/gdb.ada/pkd_arr_elem/failure.adb | 45 ++++++++++++++++++++++++++
 gdb/testsuite/gdb.ada/pkd_arr_elem/pck.adb     | 21 ++++++++++++
 gdb/testsuite/gdb.ada/pkd_arr_elem/pck.ads     | 19 +++++++++++
 5 files changed, 135 insertions(+), 2 deletions(-)
 create mode 100644 gdb/testsuite/gdb.ada/pkd_arr_elem.exp
 create mode 100644 gdb/testsuite/gdb.ada/pkd_arr_elem/failure.adb
 create mode 100644 gdb/testsuite/gdb.ada/pkd_arr_elem/pck.adb
 create mode 100644 gdb/testsuite/gdb.ada/pkd_arr_elem/pck.ads

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 4320eec..5b5c22f 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -2146,7 +2146,15 @@ decode_packed_array_bitsize (struct type *type)
    but with the bit sizes of its elements (and those of any
    constituent arrays) recorded in the BITSIZE components of its
    TYPE_FIELD_BITSIZE values, and with *ELT_BITS set to its total size
-   in bits.  */
+   in bits.
+
+   Note that, for arrays whose index type has an XA encoding where
+   a bound references a record discriminant, getting that discriminant,
+   and therefore the actual value of that bound, is not possible
+   because none of the given parameters gives us access to the record.
+   This function assumes that it is OK in the context where it is being
+   used to return an array whose bounds are still dynamic and where
+   the length is arbitrary.  */
 
 static struct type *
 constrained_packed_array_type (struct type *type, long *elt_bits)
@@ -2176,7 +2184,9 @@ constrained_packed_array_type (struct type *type, long *elt_bits)
   TYPE_FIELD_BITSIZE (new_type, 0) = *elt_bits;
   TYPE_NAME (new_type) = ada_type_name (type);
 
-  if (get_discrete_bounds (index_type, &low_bound, &high_bound) < 0)
+  if ((TYPE_CODE (check_typedef (index_type)) == TYPE_CODE_RANGE
+       && is_dynamic_type (check_typedef (index_type)))
+      || get_discrete_bounds (index_type, &low_bound, &high_bound) < 0)
     low_bound = high_bound = 0;
   if (high_bound < low_bound)
     *elt_bits = TYPE_LENGTH (new_type) = 0;
diff --git a/gdb/testsuite/gdb.ada/pkd_arr_elem.exp b/gdb/testsuite/gdb.ada/pkd_arr_elem.exp
new file mode 100644
index 0000000..5154050
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/pkd_arr_elem.exp
@@ -0,0 +1,38 @@
+# Copyright 2014 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 }
+
+standard_ada_testfile failure
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable {debug}] != ""} {
+    return -1
+}
+
+clean_restart ${testfile}
+
+set bp_location [gdb_get_line_number "START" ${testdir}/failure.adb]
+runto "failure.adb:$bp_location"
+
+gdb_test "print test" \
+         "= \\(size => 100, str => \\(33 'A', nul <repeats 99 times>\\), length => 1\\)"
+
+gdb_test "print test.str" \
+         "= \\(33 'A', nul <repeats 99 times>\\)"
+
+gdb_test "print test.str(1)" \
+         "= 33 'A'"
diff --git a/gdb/testsuite/gdb.ada/pkd_arr_elem/failure.adb b/gdb/testsuite/gdb.ada/pkd_arr_elem/failure.adb
new file mode 100644
index 0000000..13ddaf4
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/pkd_arr_elem/failure.adb
@@ -0,0 +1,45 @@
+--  Copyright 2014 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 Failure is
+
+   type Funny_Char is
+        (NUL, ' ', '"', '#', '$', TMI, '&', ''',
+         '(', ')', SOT, ND,  ',', '-', '.', '/',
+         '0', '1', '2', '3', '4', '5', '6', '7',
+         '8', '9', ':', ';', UNS, INF, XMT, '?',
+         '!', 'A', 'B', 'C', 'D', 'E', 'F', 'G',
+         'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
+         'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
+         'X', 'Y', 'Z', BEL, SND, CR,  LF,  DLT);
+
+   type Funny_String is array (Positive range <>) of Funny_Char;
+   pragma Pack (Funny_String);
+
+   type Bounded_Funny_String (Size : Natural := 1) is
+      record
+         Str    : Funny_String (1 .. Size) := (others => '0');
+         Length : Natural := 4;
+      end record;
+
+   Test : Bounded_Funny_String (100);
+begin
+   Test.Str := (1 => 'A', others => NUL);
+   Test.Length := 1;
+   Do_Nothing (Test'Address); -- START
+end;
+
diff --git a/gdb/testsuite/gdb.ada/pkd_arr_elem/pck.adb b/gdb/testsuite/gdb.ada/pkd_arr_elem/pck.adb
new file mode 100644
index 0000000..2b31332
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/pkd_arr_elem/pck.adb
@@ -0,0 +1,21 @@
+--  Copyright 2014 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
+   procedure Do_Nothing (A : System.Address) is
+   begin
+      null;
+   end Do_Nothing;
+end Pck;
diff --git a/gdb/testsuite/gdb.ada/pkd_arr_elem/pck.ads b/gdb/testsuite/gdb.ada/pkd_arr_elem/pck.ads
new file mode 100644
index 0000000..100d7d5
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/pkd_arr_elem/pck.ads
@@ -0,0 +1,19 @@
+--  Copyright 2014 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
+   procedure Do_Nothing (A : System.Address);
+end Pck;
-- 
1.9.1