Fission support for multiple CUs per DWO file

In some cases a compiler may produce a single object file (& thus single
DWO file) representing multiple source files. The most common example of
this is in whole program optimization (such as LLVM's LTO). Fission may
still be a beneficial feature to use here - to avoid the need to
read/link the debug info with system libraries and the like.

This change adds basic support for multiple CUs in a single DWO file to
support LLVM's output in this situation.

There is still outstanding work to design and implement a solution for
cross-CU references (usually using DW_FORM_ref_addr) in this scenario.
For now LLVM works around this by duplicating DIEs rather than making
cross-CU references in DWO files. This degrades debugger
behavior/quality especially for file-local entities.

2017-07-06  David Blaikie  <dblaikie@gmail.com>

	* dwarf2read.c (struct dwo_file): Use a htab of dwo_unit* (rather than
	a singular dwo_unit*) to support multiple CUs in the same way that
	multiple TUs are supported.
	(create_cus_hash_table): Replace create_dwo_cu with a function for
	parsing multiple CUs from a DWO file.
	(open_and_init_dwo_file): Use create_cus_hash_table rather than
	create_dwo_cu.
	(lookup_dwo_cutu): Lookup CU in the hash table in the dwo_file with
	htab_find, rather than comparing the signature to a singleton CU in
	the dwo_file.

2017-07-06  David Blaikie  <dblaikie@gmail.com>

	* gdb.dwarf2/fission-multi-cu.S: Test containing multiple CUs in a DWO,
	built from fissiont-multi-cu{1,2}.c.
	* gdb.dwarf2/fission-multi-cu.exp: Test similar to fission-base.exp,
	except putting 'main' and 'func' in separate CUs in the same DWO file.
	* gdb.dwarf2/fission-multi-cu1.c: First CU for the multi-CU-single-DWO
	test.
	* gdb.dwarf2/fission-multi-cu2.c: Second CU in the multi-CU-single-DWO
	test.

1 files changed, 67 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/fission-multi-cu.exp b/gdb/testsuite/gdb.dwarf2/fission-multi-cu.exp
new file mode 100644
index 0000000..1f23c5b6
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/fission-multi-cu.exp
@@ -0,0 +1,67 @@
+# Copyright 2012-2017 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
+
+# We run objcopy locally to split out the .dwo file.
+if [is_remote host] {
+    return 0
+}
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if ![dwarf2_support] {
+    return 0
+}
+
+# This test can only be run on x86-64 targets.
+if {![istarget x86_64-*] || ![is_lp64_target]} {
+    return 0
+}
+
+standard_testfile .S
+
+if [build_executable_from_fission_assembler \
+	"$testfile.exp" "$binfile" "$srcfile" {nodebug}] {
+    return -1
+}
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+# Make sure we can find the .dwo file, regardless of whether we're
+# running in parallel mode.
+gdb_test_no_output "set debug-file-directory [file dirname $binfile]" \
+    "set debug-file-directory"
+gdb_load $binfile
+
+if ![runto_main] {
+    return -1
+}
+
+# Do a few basic things to verify we're finding the DWO debug info.
+
+gdb_test "ptype main" "type = int \\(\\)"
+gdb_test "ptype func" "type = int \\(int\\)"
+
+gdb_test "frame" "#0 *main \\(\\) at ${testfile}2\\.c:$decimal.*" \
+    "frame in main"
+
+gdb_test "break func" "Breakpoint.*at.* file .*${testfile}1\\.c, line .*"
+
+gdb_test "continue" "Breakpoint.* func \\(arg=-1\\).*" \
+    "continue to func"
+
+gdb_test "frame" "#0 *func \\(arg=-1\\) at ${testfile}1\\.c:$decimal.*" \
+    "frame in func"