handle DW_AT_type on an enumeration

DWARF allows an enumeration type to have a DW_AT_type.  GDB doesn't
recognize this, but there is a patch to change GCC to emit it, and a
DWARF proposal to further allow an enum type with a DW_AT_type to omit
the DW_AT_byte_size.  This patch changes gdb to implement this.

Built and regtested on x86-64 Fedora 20.

2014-04-14  Tom Tromey  <tromey@redhat.com>

	* dwarf2read.c (read_enumeration_type): Handle DW_AT_type.

2014-04-14  Tom Tromey  <tromey@redhat.com>

	* gdb.dwarf2/enum-type.exp: New file.

gdb/ChangeLog

@@ -1,3 +1,7 @@
+2014-04-14  Tom Tromey  <tromey@redhat.com>
+
+	* dwarf2read.c (read_enumeration_type): Handle DW_AT_type.
+
 2014-04-14  Sanimir Agovic  <sanimir.agovic@intel.com>
 
 	* eval.c (evaluate_subexp_for_sizeof): Add enum noside argument.

gdb/dwarf2read.c

@@ -13225,6 +13225,14 @@ read_enumeration_type (struct die_info *die, struct dwarf2_cu *cu)
   if (name != NULL)
     TYPE_TAG_NAME (type) = name;
 
+  attr = dwarf2_attr (die, DW_AT_type, cu);
+  if (attr != NULL)
+    {
+      struct type *underlying_type = die_type (die, cu);
+
+      TYPE_TARGET_TYPE (type) = underlying_type;
+    }
+
   attr = dwarf2_attr (die, DW_AT_byte_size, cu);
   if (attr)
     {
@@ -13243,9 +13251,25 @@ read_enumeration_type (struct die_info *die, struct dwarf2_cu *cu)
   if (die_is_declaration (die, cu))
     TYPE_STUB (type) = 1;
 
-  /* Finish the creation of this type by using the enum's children.  */
+  /* Finish the creation of this type by using the enum's children.
+     We must call this even when the underlying type has been provided
+     so that we can determine if we're looking at a "flag" enum.  */
   update_enumeration_type_from_children (die, type, cu);
 
+  /* If this type has an underlying type that is not a stub, then we
+     may use its attributes.  We always use the "unsigned" attribute
+     in this situation, because ordinarily we guess whether the type
+     is unsigned -- but the guess can be wrong and the underlying type
+     can tell us the reality.  However, we defer to a local size
+     attribute if one exists, because this lets the compiler override
+     the underlying type if needed.  */
+  if (TYPE_TARGET_TYPE (type) != NULL && !TYPE_STUB (TYPE_TARGET_TYPE (type)))
+    {
+      TYPE_UNSIGNED (type) = TYPE_UNSIGNED (TYPE_TARGET_TYPE (type));
+      if (TYPE_LENGTH (type) == 0)
+	TYPE_LENGTH (type) = TYPE_LENGTH (TYPE_TARGET_TYPE (type));
+    }
+
   return set_die_type (die, type, cu);
 }
 

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2014-04-14  Tom Tromey  <tromey@redhat.com>
+
+	* gdb.dwarf2/enum-type.exp: New file.
+
 2014-04-14  Sanimir Agovic  <sanimir.agovic@intel.com>
 
 	* gdb.mi/mi-vla-c99.exp: New file.

gdb/testsuite/gdb.dwarf2/enum-type.exp

@@ -0,0 +1,60 @@
+# 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 main.c enum-type-dw.S
+
+# Make some DWARF for the test.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    cu {} {
+	DW_TAG_compile_unit {
+                {DW_AT_language @DW_LANG_C}
+                {DW_AT_name     enum-type-dw.c}
+                {DW_AT_comp_dir /tmp}
+        } {
+	    declare_labels integer_label array_elt_label array_label \
+                big_array_label
+
+            integer_label: DW_TAG_base_type {
+                {DW_AT_byte_size 4 DW_FORM_sdata}
+                {DW_AT_encoding  @DW_ATE_signed}
+                {DW_AT_name      integer}
+            }
+
+	    DW_TAG_enumeration_type {
+		{DW_AT_name E}
+		{DW_AT_type :$integer_label}
+	    } {
+		DW_TAG_enumerator {
+		    {DW_AT_name ONE}
+		    {DW_AT_const_value 1}
+		}
+	    }
+	}
+    }
+}
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+gdb_test "print sizeof(enum E)" " = 4"