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#
# Option ROM signing utility
#
# Authors:
# Jan Kiszka <jan.kiszka@siemens.com>
#
# 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 != '\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)
if size_byte == 0:
# If the caller left the size field blank then we will fill it in,
# also rounding the whole input to a multiple of 512 bytes.
data = fin.read()
# +1 because we need a byte to store the checksum.
size = len(data) + 1
# Round up to next multiple of 512.
size += 511
size -= size % 512
if size >= 65536:
sys.exit("%s: option ROM size too large" % sys.argv[1])
# size-1 because a final byte is added below to store the checksum.
data = data.ljust(size-1, '\0')
data = data[:2] + chr(size/512) + data[3:]
else:
# Otherwise the input file specifies the size so use it.
# -1 because we overwrite the last byte of the file with the checksum.
size = size_byte * 512 - 1
data = fin.read(size)
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()
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