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.

6 files changed, 140 insertions, 1 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 83fcd10..2de892a 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,12 @@
 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.
+
+2017-02-20  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
 	* dwarf2read.c (read_file_scope): Rename DW_MACRO_GNU_*.
 	(dwarf_parse_macro_header): Accept DWARF version 5.
 	(dwarf_decode_macro_bytes, dwarf_decode_macros): Rename DW_MACRO_GNU_*.
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index c7a2e73..ae7d3f2 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -7414,6 +7414,9 @@ skip_one_die (const struct die_reader_specs *reader, const gdb_byte *info_ptr,
 	case DW_FORM_ref_sig8:
 	  info_ptr += 8;
 	  break;
+	case DW_FORM_data16:
+	  info_ptr += 16;
+	  break;
 	case DW_FORM_string:
 	  read_direct_string (abfd, info_ptr, &bytes_read);
 	  info_ptr += bytes_read;
@@ -16554,6 +16557,13 @@ read_attribute_value (const struct die_reader_specs *reader,
       DW_UNSND (attr) = read_8_bytes (abfd, info_ptr);
       info_ptr += 8;
       break;
+    case DW_FORM_data16:
+      blk = dwarf_alloc_block (cu);
+      blk->size = 16;
+      blk->data = read_n_bytes (abfd, info_ptr, 16);
+      info_ptr += 16;
+      DW_BLOCK (attr) = blk;
+      break;
     case DW_FORM_sec_offset:
       DW_UNSND (attr) = read_offset (abfd, info_ptr, &cu->header, &bytes_read);
       info_ptr += bytes_read;
@@ -19297,6 +19307,7 @@ dwarf2_const_value_attr (const struct attribute *attr, struct type *type,
     case DW_FORM_block4:
     case DW_FORM_block:
     case DW_FORM_exprloc:
+    case DW_FORM_data16:
       blk = DW_BLOCK (attr);
       if (TYPE_LENGTH (type) != blk->size)
 	dwarf2_const_value_length_mismatch_complaint (name, blk->size,
@@ -20251,6 +20262,9 @@ dump_die_shallow (struct ui_file *f, int indent, struct die_info *die)
 	  fprintf_unfiltered (f, "expression: size %s",
 			      pulongest (DW_BLOCK (&die->attrs[i])->size));
 	  break;
+	case DW_FORM_data16:
+	  fprintf_unfiltered (f, "constant of 16 bytes");
+	  break;
 	case DW_FORM_ref_addr:
 	  fprintf_unfiltered (f, "ref address: ");
 	  fputs_filtered (hex_string (DW_UNSND (&die->attrs[i])), f);
@@ -20412,6 +20426,7 @@ dwarf2_get_attr_constant_value (const struct attribute *attr, int default_value)
     return DW_UNSND (attr);
   else
     {
+      /* For DW_FORM_data16 see attr_form_is_constant.  */
       complaint (&symfile_complaints,
 		 _("Attribute value is not a constant (%s)"),
                  dwarf_form_name (attr->form));
@@ -20695,6 +20710,7 @@ dwarf2_fetch_constant_bytes (sect_offset offset,
     case DW_FORM_block4:
     case DW_FORM_block:
     case DW_FORM_exprloc:
+    case DW_FORM_data16:
       result = DW_BLOCK (attr)->data;
       *len = DW_BLOCK (attr)->size;
       break;
@@ -21603,6 +21619,10 @@ skip_form_bytes (bfd *abfd, const gdb_byte *bytes, const gdb_byte *buffer_end,
       bytes += 8;
       break;
 
+    case DW_FORM_data16:
+      bytes += 16;
+      break;
+
     case DW_FORM_string:
       read_direct_string (abfd, bytes, &bytes_read);
       bytes += bytes_read;
@@ -22266,7 +22286,10 @@ attr_form_is_section_offset (const struct attribute *attr)
    (lineptr, loclistptr, macptr or rangelistptr).  The DWARF spec says
    that, if an attribute's can be either a constant or one of the
    section offset classes, DW_FORM_data4 and DW_FORM_data8 should be
-   taken as section offsets, not constants.  */
+   taken as section offsets, not constants.
+
+   DW_FORM_data16 is not considered as dwarf2_get_attr_constant_value
+   cannot handle that.  */
 
 static int
 attr_form_is_constant (const struct attribute *attr)
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index e235c5f..c18f1e6 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,11 @@
 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.
+
+2017-02-20  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
 	* gdb.arch/amd64-entry-value-param-dwarf5.S: New file.
 	* gdb.arch/amd64-entry-value-param-dwarf5.c: New file.
 	* gdb.arch/amd64-entry-value-param-dwarf5.exp: New file.
diff --git a/gdb/testsuite/gdb.dwarf2/formdata16.c b/gdb/testsuite/gdb.dwarf2/formdata16.c
new file mode 100644
index 0000000..956545f
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/formdata16.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   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/>.  */
+
+int
+main ()
+{
+  return 0;
+}
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"
diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index 149038c..1ccdc5d 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -481,6 +481,10 @@ namespace eval Dwarf {
 		_op .8byte $value
 	    }
 
+	    DW_FORM_data16 {
+		_op .8byte $value
+	    }
+
 	    DW_FORM_strp {
 		variable _strings
 		variable _cu_offset_size