DWARF: Add array DW_AT_bit_stride and DW_AT_byte_stride support

Consider the following declarations in Ada...

   type Item is range -32 .. 31;
   for Item'Size use 6;

   type Table is array (Natural range 0 .. 4) of Item;
   pragma Pack (Table);

... which declare a packed array whose elements are 6 bits long.
The debugger currently does not notice that the array is packed,
and thus prints values of this type incorrectly. This can be seen
in the "ptype" output:

    (gdb) ptype table
    type = array (0 .. 4) of foo.item

Normally, the debugger should print:

    (gdb) ptype table
    type = array (0 .. 4) of foo.item <packed: 6-bit elements>

The debugging information for this array looks like this:

        .uleb128 0xf    # (DIE (0x15c) DW_TAG_array_type)
        .long   .LASF9  # DW_AT_name: "pck__table"
        .byte   0x6     # DW_AT_bit_stride
        .long   0x1a9   # DW_AT_type
        .uleb128 0x10   # (DIE (0x16a) DW_TAG_subrange_type)
        .long   0x3b    # DW_AT_type
        .byte   0       # DW_AT_lower_bound
        .byte   0x4     # DW_AT_upper_bound
        .byte   0       # end of children of DIE 0x15c

The interesting part is the DW_AT_bit_stride attribute, which tells
the size of the array elements is 6 bits, rather than the normal
element type's size.

This patch adds support for this attribute by first creating
gdbtypes.c::create_array_type_with_stride, which is an enhanced
version of create_array_type taking an extra parameter as the stride.
The old create_array_type can then be re-implemented very simply
by calling the new create_array_type_with_stride.

We can then use this new function from dwarf2read, to create
arrays with or without stride.

gdb/ChangeLog:

        * gdbtypes.h (create_array_type_with_stride): Add declaration.
        * gdbtypes.c (create_array_type_with_stride): New function,
        renaming create_array_type, but with an added parameter
        called "bit_stride".
        (create_array_type): Re-implement using
        create_array_type_with_stride.
        * dwarf2read.c (read_array_type): Add support for DW_AT_byte_stride
        and DW_AT_bit_stride attributes.

gdb/testsuite/ChangeLog:

        * gdb.dwarf2/arr-stride.c: New file.
        * gdb.dwarf2/arr-stride.exp: New file.

The test, relying purely on generating an assembly file, only
verifies the type description of our array. But I was also
able to verify manually that the debugger print values of these
types correctly as well (which was not the case prior to this
patch).

3 files changed, 133 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 09cc8a3..476e1a3 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2014-02-26  Joel Brobecker  <brobecker@adacore.com>
+
+	* gdb.dwarf2/arr-stride.c: New file.
+	* gdb.dwarf2/arr-stride.exp: New file.
+
 2014-02-26  Pedro Alves  <palves@redhat.com>
 
 	* gdb.ada/tasks.exp: Set a task-specific breakpoint at break_me
diff --git a/gdb/testsuite/gdb.dwarf2/arr-stride.c b/gdb/testsuite/gdb.dwarf2/arr-stride.c
new file mode 100644
index 0000000..978ef8d
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/arr-stride.c
@@ -0,0 +1,20 @@
+/* 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/>.  */
+
+int
+main (void)
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.dwarf2/arr-stride.exp b/gdb/testsuite/gdb.dwarf2/arr-stride.exp
new file mode 100644
index 0000000..f2a1f39
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/arr-stride.exp
@@ -0,0 +1,108 @@
+# 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 dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+}
+
+standard_testfile arr-stride.c arr-stride-dw.S
+
+# Make some DWARF for the test.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    cu {} {
+ 	DW_TAG_compile_unit {
+                {DW_AT_language @DW_LANG_Ada95}
+                {DW_AT_name     foo.adb}
+                {DW_AT_comp_dir /tmp}
+        } {
+	    declare_labels integer_label array_elt_label array_label \
+                big_array_label
+
+            integer_label: DW_TAG_base_type {
+                {DW_AT_byte_size 4 DW_FORM_sdata}
+                {DW_AT_encoding  @DW_ATE_signed}
+                {DW_AT_name      integer}
+            }
+
+            array_elt_label: DW_TAG_subrange_type {
+                {DW_AT_lower_bound 0xe0 DW_FORM_data1}
+                {DW_AT_upper_bound 0x1f DW_FORM_data1}
+                {DW_AT_name        pck__item}
+                {DW_AT_type        :$integer_label}
+            }
+
+            DW_TAG_typedef {
+                {DW_AT_name pck__table}
+                {DW_AT_type :$array_label}
+            }
+
+	    array_label: DW_TAG_array_type {
+		{DW_AT_name pck__table}
+                {DW_AT_bit_stride 6 DW_FORM_data1}
+		{DW_AT_type :$array_elt_label}
+	    } {
+		DW_TAG_subrange_type {
+		    {DW_AT_type        :$integer_label}
+		    {DW_AT_lower_bound 0 DW_FORM_data1}
+		    {DW_AT_upper_bound 4 DW_FORM_data1}
+		}
+	    }
+
+            DW_TAG_typedef {
+                {DW_AT_name pck__big_table}
+                {DW_AT_type :$big_array_label}
+            }
+
+	    big_array_label: DW_TAG_array_type {
+		{DW_AT_name pck__big_table}
+                {DW_AT_byte_stride 1 DW_FORM_data1}
+		{DW_AT_type :$array_elt_label}
+	    } {
+		DW_TAG_subrange_type {
+		    {DW_AT_type        :$integer_label}
+		    {DW_AT_lower_bound 0 DW_FORM_data1}
+		    {DW_AT_upper_bound 4 DW_FORM_data1}
+		}
+	    }
+	}
+    }
+}
+
+if  {[gdb_compile ${srcdir}/${subdir}/${srcfile} ${binfile}1.o \
+	  object {nodebug}] != ""} {
+    return -1
+}
+
+if  {[gdb_compile $asm_file ${binfile}2.o object {nodebug}] != ""} {
+    return -1
+}
+
+if  {[gdb_compile [list ${binfile}1.o ${binfile}2.o] \
+	  "${binfile}" executable {}] != ""} {
+    return -1
+}
+
+clean_restart ${testfile}
+
+gdb_test_no_output "set language ada"
+
+gdb_test "ptype pck.table" \
+         "type = array \\(0 \\.\\. 4\\) of pck\\.item <packed: 6-bit elements>"
+
+gdb_test "ptype pck.big_table" \
+         "type = array \\(0 \\.\\. 4\\) of pck\\.item <packed: 8-bit elements>"