gdb: backport an upstream patch to support fission with split debug.

The upstream patch was
commit 6c4474237ab3356b100ebbdd6ff1a8839745023d
Author: Doug Evans <dje@google.com>
Date:   Tue May 3 16:30:58 2016 -0700

    PR symtab/19914 fix handling of dwp + split debug

        PR symtab/19914
        * dwarf2read.c (open_and_init_dwp_file): Look at backlink if
        objfile is separate debug file.

        testsuite/
        * gdb.dwarf2/dwp-sepdebug.c: New file.
        * gdb.dwarf2/dwp-sepdebug.exp: New file.

TEST=build chrome with debug fission and put the .dwp file in the debug
     dir. gdb can read debug information from there.

3 files changed, 79 insertions, 3 deletions

diff --git a/gdb-7.11/gdb/dwarf2read.c b/gdb-7.11/gdb/dwarf2read.c
index 1020c1269..9fc871b1c 100644
--- a/gdb-7.11/gdb/dwarf2read.c
+++ b/gdb-7.11/gdb/dwarf2read.c
@@ -10837,12 +10837,26 @@ open_and_init_dwp_file (void)
   struct dwp_file *dwp_file;
   char *dwp_name;
   bfd *dbfd;
-  struct cleanup *cleanups;
+  struct cleanup *cleanups = make_cleanup (null_cleanup, 0);
 
   /* Try to find first .dwp for the binary file before any symbolic links
      resolving.  */
-  dwp_name = xstrprintf ("%s.dwp", objfile->original_name);
-  cleanups = make_cleanup (xfree, dwp_name);
+
+  /* If the objfile is a debug file, find the name of the real binary
+     file and get the name of dwp file from there.  */
+  if (objfile->separate_debug_objfile_backlink != NULL)
+    {
+      struct objfile *backlink = objfile->separate_debug_objfile_backlink;
+      const char *backlink_basename = lbasename (backlink->original_name);
+      char *debug_dirname = ldirname (objfile->original_name);
+
+      make_cleanup (xfree, debug_dirname);
+      dwp_name = xstrprintf ("%s%s%s.dwp", debug_dirname,
+			     SLASH_STRING, backlink_basename);
+    }
+  else
+    dwp_name = xstrprintf ("%s.dwp", objfile->original_name);
+  make_cleanup (xfree, dwp_name);
 
   dbfd = open_dwp_file (dwp_name);
   if (dbfd == NULL
diff --git a/gdb-7.11/gdb/testsuite/gdb.dwarf2/dwp-sepdebug.c b/gdb-7.11/gdb/testsuite/gdb.dwarf2/dwp-sepdebug.c
new file mode 100644
index 000000000..bb11da2d3
--- /dev/null
+++ b/gdb-7.11/gdb/testsuite/gdb.dwarf2/dwp-sepdebug.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 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 (int argc, char **argv)
+{
+  return 0;
+}
diff --git a/gdb-7.11/gdb/testsuite/gdb.dwarf2/dwp-sepdebug.exp b/gdb-7.11/gdb/testsuite/gdb.dwarf2/dwp-sepdebug.exp
new file mode 100644
index 000000000..a4e706826
--- /dev/null
+++ b/gdb-7.11/gdb/testsuite/gdb.dwarf2/dwp-sepdebug.exp
@@ -0,0 +1,40 @@
+# Copyright 2016 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/>.
+
+standard_testfile
+
+if { [build_executable ${testfile}.exp ${testfile} ${srcfile}] == -1 } {
+    return -1
+}
+if ![remote_file host exists [standard_output_file ${testfile}.dwp]] {
+    unsupported "testsuite run does not produce dwp files"
+    return 0
+}
+
+# Note: the procedure gdb_gnu_strip_debug will produce an executable called
+# ${binfile}, which is just like the executable ($binfile) but without
+# the debuginfo. Instead $binfile has a .gnu_debuglink section which contains
+# the name of a debuginfo only file. This file will be stored in the
+# gdb.base/ subdirectory.
+
+if [gdb_gnu_strip_debug $binfile$EXEEXT] {
+    # check that you have a recent version of strip and objcopy installed
+    unsupported "cannot produce separate debug info files"
+    return -1
+}
+
+clean_restart "$testfile"
+
+gdb_test "ptype main" {type = int \(int, char \*\*\)}