1#!/bin/sh
2# ----------------------------------------------------------------------
3# extract-ikconfig - Extract the .config file from a kernel image
4#
5# This will only work when the kernel was compiled with CONFIG_IKCONFIG.
6#
7# The obscure use of the "tr" filter is to work around older versions of
8# "grep" that report the byte offset of the line instead of the pattern.
9#
10# (c) 2009,2010 Dick Streefland <dick@streefland.net>
11# Licensed under the terms of the GNU General Public License.
12# ----------------------------------------------------------------------
13
14cf1='IKCFG_ST\037\213\010'
15cf2='0123456789'
16
17dump_config()
18{
19	if	pos=`tr "$cf1\n$cf2" "\n$cf2=" < "$1" | grep -abo "^$cf2"`
20	then
21		pos=${pos%%:*}
22		tail -c+$(($pos+8)) "$1" | zcat > $tmp1 2> /dev/null
23		if	[ $? != 1 ]
24		then	# exit status must be 0 or 2 (trailing garbage warning)
25			cat $tmp1
26			exit 0
27		fi
28	fi
29}
30
31try_decompress()
32{
33	for	pos in `tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"`
34	do
35		pos=${pos%%:*}
36		tail -c+$pos "$img" | $3 > $tmp2 2> /dev/null
37		dump_config $tmp2
38	done
39}
40
41# Check invocation:
42me=${0##*/}
43img=$1
44if	[ $# -ne 1 -o ! -s "$img" ]
45then
46	echo "Usage: $me <kernel-image>" >&2
47	exit 2
48fi
49
50# Prepare temp files:
51tmp1=/tmp/ikconfig$$.1
52tmp2=/tmp/ikconfig$$.2
53trap "rm -f $tmp1 $tmp2" 0
54
55# Initial attempt for uncompressed images or objects:
56dump_config "$img"
57
58# That didn't work, so retry after decompression.
59try_decompress '\037\213\010' xy    gunzip
60try_decompress '\3757zXZ\000' abcde unxz
61try_decompress 'BZh'          xy    bunzip2
62try_decompress '\135\0\0\0'   xxx   unlzma
63try_decompress '\211\114\132' xy    'lzop -d'
64try_decompress '\002\041\114\030' xyy 'lz4 -d -l'
65try_decompress '\050\265\057\375' xxx unzstd
66
67# Bail out:
68echo "$me: Cannot find kernel config." >&2
69exit 1
70