scripts/extract-ikconfig

   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
  14 cf1='IKCFG_ST\037\213\010'
  15 cf2='0123456789'
  16
  17 dump_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
  31 try_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 $tmp2
  38         done
  39 }
  40
  41 # Check invocation:
  42 me=${0##*/}
  43 img=$1
  44 if      [ $# -ne 1 -o ! -s "$img" ]
  45 then
  46         echo "Usage: $me <kernel-image>" >&2
  47         exit 2
  48 fi
  49
  50 # Prepare temp files:
  51 tmp1=/tmp/ikconfig$$.1
  52 tmp2=/tmp/ikconfig$$.2
  53 trap "rm -f $tmp1 $tmp2" 0
  54
  55 # Initial attempt for uncompressed images or objects:
  56 dump_config "$img"
  57
  58 # That didn't work, so retry after decompression.
  59 try_decompress '\037\213\010' xy  gunzip
  60 try_decompress 'BZh'          xy  bunzip2
  61 try_decompress '\135\0\0\0'   xxx unlzma
  62 try_decompress '\211\114\132' xy  'lzop -d'
  63
  64 # Bail out:
  65 echo "$me: Cannot find kernel config." >&2
  66 exit 1