FreeBSD/Linux Kernel Cross Reference
sys/scripts/extract-ikconfig

     #!/bin/sh
     # ----------------------------------------------------------------------
     # extract-ikconfig - Extract the .config file from a kernel image
     #
     # This will only work when the kernel was compiled with CONFIG_IKCONFIG.
     #
     # 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.
     #
    # (c) 2009,2010 Dick Streefland <dick@streefland.net>
    # Licensed under the terms of the GNU General Public License.
    # ----------------------------------------------------------------------
    
    cf1='IKCFG_ST\037\213\010'
    cf2='0123456789'
    
    dump_config()
    {
            if      pos=`tr "$cf1\n$cf2" "\n$cf2=" < "$1" | grep -abo "^$cf2"`
            then
                    pos=${pos%%:*}
                    tail -c+$(($pos+8)) "$1" | zcat > $tmp1 2> /dev/null
                    if      [ $? != 1 ]
                    then    # exit status must be 0 or 2 (trailing garbage warning)
                            cat $tmp1
                            exit 0
                    fi
            fi
    }
    
    try_decompress()
    {
            for     pos in `tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"`
            do
                    pos=${pos%%:*}
                    tail -c+$pos "$img" | $3 > $tmp2 2> /dev/null
                    dump_config $tmp2
            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:
    tmp1=/tmp/ikconfig$$.1
    tmp2=/tmp/ikconfig$$.2
    trap "rm -f $tmp1 $tmp2" 0
    
    # Initial attempt for uncompressed images or objects:
    dump_config "$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 kernel config." >&2
    exit 1

Cache object: 2db57e1de0bee3566b6c16f41dffad7a