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