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 10import sys 11import struct 12 13if len(sys.argv) < 3: 14 print('usage: signrom.py input output') 15 sys.exit(1) 16 17fin = open(sys.argv[1], 'rb') 18fout = open(sys.argv[2], 'wb') 19 20magic = fin.read(2) 21if magic != '\x55\xaa': 22 sys.exit("%s: option ROM does not begin with magic 55 aa" % sys.argv[1]) 23 24size_byte = ord(fin.read(1)) 25fin.seek(0) 26data = fin.read() 27 28size = size_byte * 512 29if len(data) > size: 30 sys.stderr.write('error: ROM is too large (%d > %d)\n' % (len(data), size)) 31 sys.exit(1) 32elif len(data) < size: 33 # Add padding if necessary, rounding the whole input to a multiple of 34 # 512 bytes according to the third byte of the input. 35 # size-1 because a final byte is added below to store the checksum. 36 data = data.ljust(size-1, '\0') 37else: 38 if ord(data[-1:]) != 0: 39 sys.stderr.write('WARNING: ROM includes nonzero checksum\n') 40 data = data[:size-1] 41 42fout.write(data) 43 44checksum = 0 45for b in data: 46 # catch Python 2 vs. 3 differences 47 if isinstance(b, int): 48 checksum += b 49 else: 50 checksum += ord(b) 51checksum = (256 - checksum) % 256 52 53# Python 3 no longer allows chr(checksum) 54fout.write(struct.pack('B', checksum)) 55 56fin.close() 57fout.close() 58