scripts: add extract-vmlinux

This script can be used to extract vmlinux from a compressed
kernel image (bzImage, etc..). It's inspired from (a subset of)
extract-ikconfig.

It's something a lot of people have been looking for (mainly
people with xen < 4 that doesn't support bzImages at all).

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Michal Marek <mmarek@suse.cz>

diff --git a/scripts/extract-vmlinux b/scripts/extract-vmlinux
new file mode 100755 (executable)
index 0000000..5061abc
--- /dev/null
+++ b/scripts/extract-vmlinux
@@ -0,0 +1,62 @@
+#!/bin/sh
+# ----------------------------------------------------------------------
+# extract-vmlinux - Extract uncompressed vmlinux from a kernel image
+#
+# Inspired from extract-ikconfig
+# (c) 2009,2010 Dick Streefland <dick@streefland.net>
+#
+# (c) 2011      Corentin Chary <corentin.chary@gmail.com>
+#
+# Licensed under the GNU General Public License, version 2 (GPLv2).
+# ----------------------------------------------------------------------
+
+check_vmlinux()
+{
+       # Use readelf to check if it's a valid ELF
+       # TODO: find a better to way to check that it's really vmlinux
+       #       and not just an elf
+       readelf -h $1 > /dev/null 2>&1 || return 1
+
+       cat $1
+       exit 0
+}
+
+try_decompress()
+{
+       # The obscure use of the "tr" filter is to work around older versions of
+       # "grep" that report the byte offset of the line instead of the pattern.
+
+       # Try to find the header ($1) and decompress from here
+       for     pos in `tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"`
+       do
+               pos=${pos%%:*}
+               tail -c+$pos "$img" | $3 > $tmp 2> /dev/null
+               check_vmlinux $tmp
+       done
+}
+
+# Check invocation:
+me=${0##*/}
+img=$1
+if     [ $# -ne 1 -o ! -s "$img" ]
+then
+       echo "Usage: $me <kernel-image>" >&2
+       exit 2
+fi
+
+# Prepare temp files:
+tmp=$(mktemp /tmp/vmlinux-XXX)
+trap "rm -f $tmp" 0
+
+# Initial attempt for uncompressed images or objects:
+check_vmlinux $img
+
+# That didn't work, so retry after decompression.
+try_decompress '\037\213\010' xy    gunzip
+try_decompress '\3757zXZ\000' abcde unxz
+try_decompress 'BZh'          xy    bunzip2
+try_decompress '\135\0\0\0'   xxx   unlzma
+try_decompress '\211\114\132' xy    'lzop -d'
+
+# Bail out:
+echo "$me: Cannot find vmlinux." >&2