Resurrect gdb-add-index as a contrib script

This includes changes made in Fedora's gdb packaging[1], Doug's
robustness patch[2] from before gdb-add-index was dropped, some
corrections, and some more changes Doug accumulated in the
meantime[3].

[1]: http://pkgs.fedoraproject.org/cgit/gdb.git/log/gdb-gdb-add-index-script.patch?id=fe74423b0812bae6d7bb027584e401a2ac37d24d
[2]: https://sourceware.org/ml/gdb-patches/2010-09/msg00130.html
[3]: https://sourceware.org/ml/gdb-patches/2013-11/msg00297.html

It would be a good idea to mention the existance of this script
in (info "(gdb) Index Files"), but I'm boycotting invariant
sections/cover texts because non-free docs are a PITA, so somebody
else would need to do that.

Summary of previous activity:

97924a9 Actual removal
c29c521 Attempted removal (accidentally left gdb-add-index.sh in place)
c2bbed2 Addition

gdb/ChangeLog

@@ -1,3 +1,12 @@
+2013-12-03  Tom Tromey  <tromey@redhat.com>
+	    Jan Kratochvil  <jan.kratochvil@redhat.com>
+	    Doug Evans  <dje@google.com>
+	    Samuel Bronson  <naesten@gmail.com>
+
+	Bring back gdb-add-index as a contrib script.
+	* contrib/gdb-add-index.sh: New file.
+	* NEWS: Note the addition.
+
 2013-12-03  Samuel Bronson  <naesten@gmail.com>
 
 	* MAINTAINERS (Write After Approval): Add myself to the list.

gdb/NEWS

@@ -32,6 +32,9 @@
   Before, the former would print "<optimized out>", and the latter
   "*value not available*".
 
+* New script contrib/gdb-add-index.sh for adding .gdb_index sections
+  to binaries.
+
 * Python scripting
 
   ** Frame filters and frame decorators have been added.

gdb/contrib/gdb-add-index.sh

@@ -0,0 +1,69 @@
+#! /bin/sh
+
+# Add a .gdb_index section to a file.
+
+# Copyright (C) 2010, 2012-2013 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/>.
+
+# This program assumes gdb and objcopy are in $PATH.
+# If not, or you want others, pass the following in the environment
+GDB=${GDB:=gdb}
+OBJCOPY=${OBJCOPY:=objcopy}
+
+myname="${0##*/}"
+
+if test $# != 1; then
+    echo "usage: $myname FILE" 1>&2
+    exit 1
+fi
+
+file="$1"
+
+if test ! -r "$file"; then
+    echo "$myname: unable to access: $file" 1>&2
+    exit 1
+fi
+
+dir="${file%/*}"
+test "$dir" = "$file" && dir="."
+index="${file}.gdb-index"
+
+rm -f $index
+# Ensure intermediate index file is removed when we exit.
+trap "rm -f $index" 0
+
+$GDB --batch -nx -iex 'set auto-load no' \
+    -ex "file $file" -ex "save gdb-index $dir" || {
+    # Just in case.
+    status=$?
+    echo "$myname: gdb error generating index for $file" 1>&2
+    exit $status
+}
+
+# In some situations gdb can exit without creating an index.  This is
+# not an error.
+# E.g., if $file is stripped.  This behaviour is akin to stripping an
+# already stripped binary, it's a no-op.
+status=0
+
+if test -f "$index"; then
+    $OBJCOPY --add-section .gdb_index="$index" \
+	--set-section-flags .gdb_index=readonly "$file" "$file"
+    status=$?
+else
+    echo "$myname: No index was created for $file" 1>&2
+    echo "$myname: [Was there no debuginfo? Was there already an index?]" 1>&2
+fi
+
+exit $status