scripts/signrom.py

   1 #
   2 # Option ROM signing utility
   3 #
   4 # Authors:
   5 #  Jan Kiszka <jan.kiszka@siemens.com>
   6 #
   7 # This work is licensed under the terms of the GNU GPL, version 2 or later.
   8 # See the COPYING file in the top-level directory.
   9
  10 import sys
  11 import struct
  12
  13 if len(sys.argv) < 3:
  14     print('usage: signrom.py input output')
  15     sys.exit(1)
  16
  17 fin = open(sys.argv[1], 'rb')
  18 fout = open(sys.argv[2], 'wb')
  19
  20 magic = fin.read(2)
  21 if magic != '\x55\xaa':
  22     sys.exit("%s: option ROM does not begin with magic 55 aa" % sys.argv[1])
  23
  24 size_byte = ord(fin.read(1))
  25 fin.seek(0)
  26
  27 if size_byte == 0:
  28     # If the caller left the size field blank then we will fill it in,
  29     # also rounding the whole input to a multiple of 512 bytes.
  30     data = fin.read()
  31     # +1 because we need a byte to store the checksum.
  32     size = len(data) + 1
  33     # Round up to next multiple of 512.
  34     size += 511
  35     size -= size % 512
  36     if size >= 65536:
  37         sys.exit("%s: option ROM size too large" % sys.argv[1])
  38     # size-1 because a final byte is added below to store the checksum.
  39     data = data.ljust(size-1, '\0')
  40     data = data[:2] + chr(size/512) + data[3:]
  41 else:
  42     # Otherwise the input file specifies the size so use it.
  43     # -1 because we overwrite the last byte of the file with the checksum.
  44     size = size_byte * 512 - 1
  45     data = fin.read(size)
  46
  47 fout.write(data)
  48
  49 checksum = 0
  50 for b in data:
  51     # catch Python 2 vs. 3 differences
  52     if isinstance(b, int):
  53         checksum += b
  54     else:
  55         checksum += ord(b)
  56 checksum = (256 - checksum) % 256
  57
  58 # Python 3 no longer allows chr(checksum)
  59 fout.write(struct.pack('B', checksum))
  60
  61 fin.close()
  62 fout.close()