[PATCH] [Ada] Enhance type printing for arrays with variable-sized elements

[Pierre-Marie de Rodat <derodat at adacore dot com>]

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 the patch series
submission at
<https://gcc.gnu.org/ml/gcc-patches/2015-07/msg01353.html>.

Given the following Ada declarations:

   subtype Small_Int is Natural range 0 .. 100;
   type R_Type (L : Small_Int := 0) is record
      S : String (1 .. L);
   end record;
   type A_Type is array (Natural range <>) of R_Type;

   A : A_Type := (1 => (L => 0, S => ""),
                  2 => (L => 2, S => "ab"));

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

    (gdb) ptype a
    type = array (1 .. 2) of foo.r_type <packed: 838-bit elements>

This is wrong: "a" is not a packed array.  This output comes from the
fact that, because R_Type has a dynamic size (with a maximum), the
compiler has to describe in the debugging information the size allocated
for each array element (i.e. the stride, in DWARF parlance: see
DW_AT_byte_stride).  Ada type printing currently assumes that arrays
with a stride are packed, hence the above output.

In practice, GNAT never performs bit-packing for arrays that contain
variable-sized elements.  Leveraging this fact, this patch enhances type
printing so that ptype does not pretend that arrays are packed when they
have a stride and they contain dynamic elements.  After this change, we
get the following expected output:

    (gdb) ptype a
    type = array (1 .. 2) of foo.r_type

gdb/ChangeLog:

	* ada-typeprint.c (print_array_type): Do not describe arrays as
	packed when they embed dynamic elements.

gdb/testsuite/ChangeLog:

	* gdb.ada/array_of_variable_length.exp: New testcase.
	* gdb.ada/array_of_variable_length/foo.adb: New file.
	* gdb.ada/array_of_variable_length/pck.adb: New file.
	* gdb.ada/array_of_variable_length/pck.ads: New file.

Tested on x86_64-linux, no regression.
---
 gdb/ada-typeprint.c                                | 11 ++++++--
 gdb/testsuite/gdb.ada/array_of_variable_length.exp | 33 ++++++++++++++++++++++
 .../gdb.ada/array_of_variable_length/foo.adb       | 21 ++++++++++++++
 .../gdb.ada/array_of_variable_length/pck.adb       | 23 +++++++++++++++
 .../gdb.ada/array_of_variable_length/pck.ads       | 32 +++++++++++++++++++++
 5 files changed, 117 insertions(+), 3 deletions(-)
 create mode 100644 gdb/testsuite/gdb.ada/array_of_variable_length.exp
 create mode 100644 gdb/testsuite/gdb.ada/array_of_variable_length/foo.adb
 create mode 100644 gdb/testsuite/gdb.ada/array_of_variable_length/pck.adb
 create mode 100644 gdb/testsuite/gdb.ada/array_of_variable_length/pck.ads

diff --git a/gdb/ada-typeprint.c b/gdb/ada-typeprint.c
index fd85138..1fb0f0e 100644
--- a/gdb/ada-typeprint.c
+++ b/gdb/ada-typeprint.c
@@ -386,6 +386,7 @@ print_array_type (struct type *type, struct ui_file *stream, int show,
 {
   int bitsize;
   int n_indices;
+  struct type *elt_type = NULL;
 
   if (ada_is_constrained_packed_array_type (type))
     type = ada_coerce_to_simple_array_type (type);
@@ -448,11 +449,15 @@ print_array_type (struct type *type, struct ui_file *stream, int show,
 	fprintf_filtered (stream, "%s<>", i == i0 ? "" : ", ");
     }
 
+  elt_type = ada_array_element_type (type, n_indices);
   fprintf_filtered (stream, ") of ");
   wrap_here ("");
-  ada_print_type (ada_array_element_type (type, n_indices), "", stream,
-		  show == 0 ? 0 : show - 1, level + 1, flags);
-  if (bitsize > 0)
+  ada_print_type (elt_type, "", stream, show == 0 ? 0 : show - 1, level + 1,
+		  flags);
+  /* Arrays with variable-length elements are never bit-packed in practice but
+     compilers have to describe their stride so that we can properly fetch
+     individual elements.  Do not say the array is packed in this case.  */
+  if (bitsize > 0 && !is_dynamic_type (elt_type))
     fprintf_filtered (stream, " <packed: %d-bit elements>", bitsize);
 }
 
diff --git a/gdb/testsuite/gdb.ada/array_of_variable_length.exp b/gdb/testsuite/gdb.ada/array_of_variable_length.exp
new file mode 100644
index 0000000..625d0a8
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/array_of_variable_length.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"
+
+# Pck.A is an array that embeds elements with variable size so compilers will
+# emit DWARF attributes such as DW_AT_byte_stride to tell GDB how to fetch
+# individual elements.  Array stride is also a way to describe packed arrays:
+# make sure we do not consider Pck.A as a packed array.
+gdb_test "ptype pck.a" "array \\(1 \\.\\. 2\\) of pck\\.r_type"
diff --git a/gdb/testsuite/gdb.ada/array_of_variable_length/foo.adb b/gdb/testsuite/gdb.ada/array_of_variable_length/foo.adb
new file mode 100644
index 0000000..b8846cf
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/array_of_variable_length/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 Pck; use Pck;
+
+procedure Foo is
+begin
+   Do_Nothing (A); --  BREAK
+end Foo;
diff --git a/gdb/testsuite/gdb.ada/array_of_variable_length/pck.adb b/gdb/testsuite/gdb.ada/array_of_variable_length/pck.adb
new file mode 100644
index 0000000..a6ffddc
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/array_of_variable_length/pck.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 Pck is
+
+   procedure Do_Nothing (A : A_Type) is
+   begin
+      null;
+   end Do_Nothing;
+
+end Pck;
diff --git a/gdb/testsuite/gdb.ada/array_of_variable_length/pck.ads b/gdb/testsuite/gdb.ada/array_of_variable_length/pck.ads
new file mode 100644
index 0000000..ce2a21e
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/array_of_variable_length/pck.ads
@@ -0,0 +1,32 @@
+--  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 Pck is
+
+   subtype Small_Int is Natural range 0 .. 100;
+
+   type R_Type (L : Small_Int := 0) is record
+      S : String (1 .. L);
+   end record;
+
+   type A_Type is array (Natural range <>) of R_Type;
+
+   A : A_Type :=
+     (1 => (L => 0, S => ""),
+      2 => (L => 2, S => "ab"));
+
+   procedure Do_Nothing (A : A_Type);
+
+end Pck;
-- 
2.5.1