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) 26 27if 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:] 41else: 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 47fout.write(data) 48 49checksum = 0 50for b in data: 51 # catch Python 2 vs. 3 differences 52 if isinstance(b, int): 53 checksum += b 54 else: 55 checksum += ord(b) 56checksum = (256 - checksum) % 256 57 58# Python 3 no longer allows chr(checksum) 59fout.write(struct.pack('B', checksum)) 60 61fin.close() 62fout.close() 63