from __future__ import print_function # # Option ROM signing utility # # Authors: # Jan Kiszka # # This work is licensed under the terms of the GNU GPL, version 2 or later. # See the COPYING file in the top-level directory. import sys import struct if len(sys.argv) < 3: print('usage: signrom.py input output') sys.exit(1) fin = open(sys.argv[1], 'rb') fout = open(sys.argv[2], 'wb') magic = fin.read(2) if magic != b'\x55\xaa': sys.exit("%s: option ROM does not begin with magic 55 aa" % sys.argv[1]) size_byte = ord(fin.read(1)) fin.seek(0) data = fin.read() size = size_byte * 512 if len(data) > size: sys.stderr.write('error: ROM is too large (%d > %d)\n' % (len(data), size)) sys.exit(1) elif len(data) < size: # Add padding if necessary, rounding the whole input to a multiple of # 512 bytes according to the third byte of the input. # size-1 because a final byte is added below to store the checksum. data = data.ljust(size-1, b'\0') else: if ord(data[-1:]) != 0: sys.stderr.write('WARNING: ROM includes nonzero checksum\n') data = data[:size-1] fout.write(data) checksum = 0 for b in data: # catch Python 2 vs. 3 differences if isinstance(b, int): checksum += b else: checksum += ord(b) checksum = (256 - checksum) % 256 # Python 3 no longer allows chr(checksum) fout.write(struct.pack('B', checksum)) fin.close() fout.close()