182 lines
6.0 KiB
Python
Executable File
182 lines
6.0 KiB
Python
Executable File
#!/usr/bin/python3
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# This file is part of the coreboot project.
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#
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# Copyright (C) 2018 Jonathan Neuschäfer
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; version 2 of the License.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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import sys, os, struct, uuid, zlib, io
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# This script wraps the bootblock in a GPT partition, because that's what
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# SiFive's bootrom will load.
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# Size of a GPT disk block, in bytes
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BLOCK_SIZE = 512
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BLOCK_MASK = BLOCK_SIZE - 1
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# Size of the bootcode part of the MBR
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MBR_BOOTCODE_SIZE = 0x1be
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# A protecive MBR, without the bootcode part
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PROTECTIVE_MBR_FOOTER = bytes([
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0x00, 0x00, 0x02, 0x00, 0xee, 0xff, 0xff, 0xff,
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0x01, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x55, 0xaa
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])
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# A "protective MBR"[1], which may also contain some boot code.
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# [1]: https://en.wikipedia.org/wiki/GUID_Partition_Table#PROTECTIVE-MBR
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class ProtectiveMBR:
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def __init__(self):
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self.bootcode = bytes(MBR_BOOTCODE_SIZE)
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def generate(self, stream):
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assert len(self.bootcode) == MBR_BOOTCODE_SIZE
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mbr = self.bootcode + PROTECTIVE_MBR_FOOTER
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assert len(mbr) == BLOCK_SIZE
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stream.write(mbr)
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# Generate a GUID from a string
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class GUID(uuid.UUID):
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def __init__(self, string):
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super().__init__(string)
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def get_bytes(self):
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return self.bytes_le
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DUMMY_GUID_DISK_UNIQUE = GUID('17145242-abaa-441d-916a-3f26c970aba2')
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DUMMY_GUID_PART_UNIQUE = GUID('7552133d-c8de-4a20-924c-0e85f5ea81f2')
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GUID_TYPE_FSBL = GUID('5B193300-FC78-40CD-8002-E86C45580B47')
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# A GPT disk header
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# https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_table_header_(LBA_1)
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class GPTHeader:
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def __init__(self):
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self.current_lba = 1
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self.backup_lba = 1
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self.first_usable_lba = 2
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self.last_usable_lba = 0xff # dummy value
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self.uniq = DUMMY_GUID_DISK_UNIQUE
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self.part_entries_lba = 2
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self.part_entries_number = 0
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self.part_entries_crc32 = 0
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self.part_entry_size = 128
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def pack_with_crc(self, crc):
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header_size = 92
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header = struct.pack('<8sIIIIQQQQ16sQIII',
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b'EFI PART', 0x100, header_size, crc, 0,
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self.current_lba, self.backup_lba, self.first_usable_lba,
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self.last_usable_lba, self.uniq.get_bytes(),
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self.part_entries_lba, self.part_entries_number,
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self.part_entry_size, self.part_entries_crc32)
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assert len(header) == header_size
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return header
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def generate(self, stream):
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crc = zlib.crc32(self.pack_with_crc(0))
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header = self.pack_with_crc(crc)
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stream.write(header.ljust(BLOCK_SIZE, b'\0'))
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# A GPT partition entry.
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# https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_entries_(LBA_2-33)
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class GPTPartition:
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def __init__(self):
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self.type = GUID('00000000-0000-0000-0000-000000000000')
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self.uniq = GUID('00000000-0000-0000-0000-000000000000')
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self.first_lba = 0
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self.last_lba = 0
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self.attr = 0
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self.name = ''
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def generate(self, stream):
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name_utf16 = self.name.encode('UTF-16LE')
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part = struct.pack('<16s16sQQQ72s',
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self.type.get_bytes(), self.uniq.get_bytes(),
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self.first_lba, self.last_lba, self.attr,
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name_utf16.ljust(72, b'\0'))
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assert len(part) == 128
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stream.write(part)
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class GPTImage:
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# The final image consists of:
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# - A protective MBR
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# - A GPT header
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# - A few GPT partition entries
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# - The content of the bootblock
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def __init__(self):
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self.mbr = ProtectiveMBR()
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self.header = GPTHeader()
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self.partitions = [ GPTPartition() for i in range(8) ]
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self.bootblock = b''
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# Fix up a few numbers to ensure consistency between the different
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# components.
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def fixup(self):
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# Align the bootblock to a whole number to LBA blocks
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bootblock_size = (len(self.bootblock) + BLOCK_SIZE - 1) & ~BLOCK_MASK
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self.bootblock = self.bootblock.ljust(bootblock_size)
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# Propagate the number of partition entries
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self.header.part_entries_number = len(self.partitions)
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self.header.first_usable_lba = 2 + self.header.part_entries_number // 4
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# Create a partition entry for the bootblock
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self.partitions[0].type = GUID_TYPE_FSBL
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self.partitions[0].uniq = DUMMY_GUID_PART_UNIQUE
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self.partitions[0].first_lba = self.header.first_usable_lba
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self.partitions[0].last_lba = \
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self.header.first_usable_lba + bootblock_size // BLOCK_SIZE
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# Calculate the CRC32 checksum of the partitions array
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partition_array = io.BytesIO()
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for part in self.partitions:
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part.generate(partition_array)
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self.header.part_entries_crc32 = zlib.crc32(partition_array.getvalue())
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def generate(self, stream):
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self.mbr.generate(stream)
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self.header.generate(stream)
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for part in self.partitions:
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part.generate(stream)
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stream.write(self.bootblock)
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if __name__ == '__main__':
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if len(sys.argv) != 3:
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print('Usage:', file=sys.stderr)
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print(' %s bootblock.raw.bin bootblock.bin' % sys.argv[0],
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file=sys.stderr)
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sys.exit(1)
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image = GPTImage()
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with open(sys.argv[1], 'rb') as f:
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image.bootblock = f.read()
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image.fixup()
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with open(sys.argv[2], 'wb') as f:
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image.generate(f)
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