DWARF-5: DW_FORM_data16

DWARF-5 has new form DW_FORM_data16.  The problem is that GDB cannot pass
16-byte constant as a constant value as that would require GDB to use GCC
extension __int128.

Formerly such data was coded as DW_FORM_block* so GDB still decodes
DW_FORM_data16 like DW_FORM_block*.

gdb/ChangeLog
2017-02-20  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* dwarf2read.c (skip_one_die, read_attribute_value)
	(dwarf2_const_value_attr, dump_die_shallow)
	(dwarf2_get_attr_constant_value, dwarf2_fetch_constant_bytes)
	(skip_form_bytes, attr_form_is_constant): Handle DW_FORM_data16.

gdb/testsuite/ChangeLog
2017-02-20  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.dwarf2/formdata16.c: New file.
	* gdb.dwarf2/formdata16.exp: New file.
	* lib/dwarf.exp (Dwarf): Add DW_FORM_data16.

1 files changed, 77 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/formdata16.exp b/gdb/testsuite/gdb.dwarf2/formdata16.exp
new file mode 100644
index 0000000..bba2015
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/formdata16.exp
@@ -0,0 +1,77 @@
+# Copyright 2017 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 .c formdata16-dw.S
+
+# We need to know the endianess in order
+# to write some of the debugging info we'd like to generate.
+if [prepare_for_testing "failed to prepare for endianness test" ${testfile} ${srcfile}] {
+    return -1
+}
+
+set endianness "little"
+set test "show endian"
+gdb_test_multiple $test $test {
+    -re "(.* )(big|little)( endian.*)\r\n$gdb_prompt $" {
+	set endianness $expect_out(2,string)
+	pass "endianness"
+    }
+}
+
+set high "0x123456789abcdef0"
+set low "0x0fedcba987654321"
+if { $endianness == "big" } {
+    set pair $high,$low
+} else {
+    set pair $low,$high
+}
+
+# Make some DWARF for the test.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    global pair
+
+    cu { addr_size 4 } {
+ 	compile_unit {} {
+	    declare_labels int_label
+
+	    int_label: DW_TAG_base_type {
+		{DW_AT_byte_size 16 DW_FORM_udata}
+		{DW_AT_encoding @DW_ATE_unsigned}
+		{DW_AT_name "__uint128"}
+	    }
+
+	    DW_TAG_variable {
+		{name xxx}
+		{type :$int_label}
+		{const_value $pair DW_FORM_data16}
+	    }
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+			  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+gdb_test "p/x xxx" " = 0x123456789abcdef00fedcba987654321"