| #!/usr/bin/env python3 |
| # |
| # SPDX-License-Identifier: GPL-2.0-only |
| |
| import sys, os, struct, uuid, zlib, io |
| |
| # This script wraps the bootblock in a GPT partition, because that's what |
| # SiFive's bootrom will load. |
| |
| |
| # Size of a GPT disk block, in bytes |
| BLOCK_SIZE = 512 |
| BLOCK_MASK = BLOCK_SIZE - 1 |
| |
| # Size of the bootcode part of the MBR |
| MBR_BOOTCODE_SIZE = 0x1be |
| |
| # MBR trampoline to bootblock |
| MBR_BOOTCODE = bytes([ |
| # j pc + 0x0800 |
| 0x6f, 0x00, 0x10, 0x00, |
| ]) |
| |
| # A protecive MBR, without the bootcode part |
| PROTECTIVE_MBR_FOOTER = bytes([ |
| 0x00, 0x00, 0x02, 0x00, 0xee, 0xff, 0xff, 0xff, |
| 0x01, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff, |
| 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, |
| 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, |
| 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, |
| 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, |
| 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, |
| 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, |
| 0x55, 0xaa |
| ]) |
| |
| |
| # A "protective MBR"[1], which may also contain some boot code. |
| # [1]: https://en.wikipedia.org/wiki/GUID_Partition_Table#PROTECTIVE-MBR |
| class ProtectiveMBR: |
| def __init__(self): |
| self.bootcode = MBR_BOOTCODE + bytes(MBR_BOOTCODE_SIZE - len(MBR_BOOTCODE)) |
| |
| def generate(self, stream): |
| assert len(self.bootcode) == MBR_BOOTCODE_SIZE |
| mbr = self.bootcode + PROTECTIVE_MBR_FOOTER |
| assert len(mbr) == BLOCK_SIZE |
| stream.write(mbr) |
| |
| |
| # Generate a GUID from a string |
| class GUID(uuid.UUID): |
| def __init__(self, string): |
| super().__init__(string) |
| |
| def get_bytes(self): |
| return self.bytes_le |
| |
| DUMMY_GUID_DISK_UNIQUE = GUID('17145242-abaa-441d-916a-3f26c970aba2') |
| DUMMY_GUID_PART_UNIQUE = GUID('7552133d-c8de-4a20-924c-0e85f5ea81f2') |
| GUID_TYPE_FSBL = GUID('5B193300-FC78-40CD-8002-E86C45580B47') |
| |
| |
| # A GPT disk header |
| # https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_table_header_(LBA_1) |
| class GPTHeader: |
| def __init__(self): |
| self.current_lba = 1 |
| self.backup_lba = 1 |
| self.first_usable_lba = 2 |
| self.last_usable_lba = 0xff # dummy value |
| self.uniq = DUMMY_GUID_DISK_UNIQUE |
| self.part_entries_lba = 2 |
| self.part_entries_number = 0 |
| self.part_entries_crc32 = 0 |
| self.part_entry_size = 128 |
| |
| def pack_with_crc(self, crc): |
| header_size = 92 |
| header = struct.pack('<8sIIIIQQQQ16sQIII', |
| b'EFI PART', 0x10000, header_size, crc, 0, |
| self.current_lba, self.backup_lba, self.first_usable_lba, |
| self.last_usable_lba, self.uniq.get_bytes(), |
| self.part_entries_lba, self.part_entries_number, |
| self.part_entry_size, self.part_entries_crc32) |
| assert len(header) == header_size |
| return header |
| |
| def generate(self, stream): |
| crc = zlib.crc32(self.pack_with_crc(0)) |
| header = self.pack_with_crc(crc) |
| stream.write(header.ljust(BLOCK_SIZE, b'\0')) |
| |
| |
| # A GPT partition entry. |
| # https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_entries_(LBA_2-33) |
| class GPTPartition: |
| def __init__(self): |
| self.type = GUID('00000000-0000-0000-0000-000000000000') |
| self.uniq = GUID('00000000-0000-0000-0000-000000000000') |
| self.first_lba = 0 |
| self.last_lba = 0 |
| self.attr = 0 |
| self.name = '' |
| |
| def generate(self, stream): |
| name_utf16 = self.name.encode('UTF-16LE') |
| part = struct.pack('<16s16sQQQ72s', |
| self.type.get_bytes(), self.uniq.get_bytes(), |
| self.first_lba, self.last_lba, self.attr, |
| name_utf16.ljust(72, b'\0')) |
| assert len(part) == 128 |
| stream.write(part) |
| |
| |
| class GPTImage: |
| # The final image consists of: |
| # - A protective MBR |
| # - A GPT header |
| # - A few GPT partition entries |
| # - The content of the bootblock |
| def __init__(self): |
| self.mbr = ProtectiveMBR() |
| self.header = GPTHeader() |
| self.partitions = [ GPTPartition() for i in range(8) ] |
| self.bootblock = b'' |
| |
| |
| # Fix up a few numbers to ensure consistency between the different |
| # components. |
| def fixup(self): |
| # Align the bootblock to a whole number to LBA blocks |
| bootblock_size = (len(self.bootblock) + BLOCK_SIZE - 1) & ~BLOCK_MASK |
| self.bootblock = self.bootblock.ljust(bootblock_size) |
| |
| # Propagate the number of partition entries |
| self.header.part_entries_number = len(self.partitions) |
| self.header.first_usable_lba = 2 + self.header.part_entries_number // 4 |
| |
| # Create a partition entry for the bootblock |
| self.partitions[0].type = GUID_TYPE_FSBL |
| self.partitions[0].uniq = DUMMY_GUID_PART_UNIQUE |
| self.partitions[0].first_lba = self.header.first_usable_lba |
| self.partitions[0].last_lba = \ |
| self.header.first_usable_lba + bootblock_size // BLOCK_SIZE |
| |
| # Calculate the CRC32 checksum of the partitions array |
| partition_array = io.BytesIO() |
| for part in self.partitions: |
| part.generate(partition_array) |
| self.header.part_entries_crc32 = zlib.crc32(partition_array.getvalue()) |
| |
| |
| def generate(self, stream): |
| self.mbr.generate(stream) |
| self.header.generate(stream) |
| for part in self.partitions: |
| part.generate(stream) |
| stream.write(self.bootblock) |
| |
| |
| if __name__ == '__main__': |
| if len(sys.argv) != 3: |
| print('Usage:', file=sys.stderr) |
| print(' %s bootblock.raw.bin bootblock.bin' % sys.argv[0], |
| file=sys.stderr) |
| sys.exit(1) |
| |
| image = GPTImage() |
| |
| with open(sys.argv[1], 'rb') as f: |
| image.bootblock = f.read() |
| |
| image.fixup() |
| |
| # Verify if first partition is at expected lba, otherwise trampoline will |
| # fail |
| if image.partitions[0].first_lba != 4: |
| print('Warning: First partition not at expected location (LBA 4)') |
| sys.exit(1) |
| |
| with open(sys.argv[2], 'wb') as f: |
| image.generate(f) |