util/riscv/sifive-gpt.py

   1 #!/usr/bin/env python3
   2 #
   3 # SPDX-License-Identifier: GPL-2.0-only
   4
   5 import sys, os, struct, uuid, zlib, io
   6
   7 # This script wraps the bootblock in a GPT partition, because that's what
   8 # SiFive's bootrom will load.
   9
  10
  11 # Size of a GPT disk block, in bytes
  12 BLOCK_SIZE = 512
  13 BLOCK_MASK = BLOCK_SIZE - 1
  14
  15 # Size of the bootcode part of the MBR
  16 MBR_BOOTCODE_SIZE = 0x1be
  17
  18 # MBR trampoline to bootblock
  19 MBR_BOOTCODE = bytes([
  20     # j pc + 0x0800
  21     0x6f, 0x00, 0x10, 0x00,
  22 ])
  23
  24 # A protecive MBR, without the bootcode part
  25 PROTECTIVE_MBR_FOOTER = bytes([
  26     0x00, 0x00, 0x02, 0x00, 0xee, 0xff, 0xff, 0xff,
  27     0x01, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff,
  28     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  29     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  30     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  31     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  32     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  33     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  34     0x55, 0xaa
  35 ])
  36
  37
  38 # A "protective MBR"[1], which may also contain some boot code.
  39 # [1]: https://en.wikipedia.org/wiki/GUID_Partition_Table#PROTECTIVE-MBR
  40 class ProtectiveMBR:
  41     def __init__(self):
  42         self.bootcode = MBR_BOOTCODE + bytes(MBR_BOOTCODE_SIZE - len(MBR_BOOTCODE))
  43
  44     def generate(self, stream):
  45         assert len(self.bootcode) == MBR_BOOTCODE_SIZE
  46         mbr = self.bootcode + PROTECTIVE_MBR_FOOTER
  47         assert len(mbr) == BLOCK_SIZE
  48         stream.write(mbr)
  49
  50
  51 # Generate a GUID from a string
  52 class GUID(uuid.UUID):
  53     def __init__(self, string):
  54         super().__init__(string)
  55
  56     def get_bytes(self):
  57         return self.bytes_le
  58
  59 DUMMY_GUID_DISK_UNIQUE = GUID('17145242-abaa-441d-916a-3f26c970aba2')
  60 DUMMY_GUID_PART_UNIQUE = GUID('7552133d-c8de-4a20-924c-0e85f5ea81f2')
  61 GUID_TYPE_FSBL = GUID('5B193300-FC78-40CD-8002-E86C45580B47')
  62
  63
  64 # A GPT disk header
  65 # https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_table_header_(LBA_1)
  66 class GPTHeader:
  67     def __init__(self):
  68         self.current_lba = 1
  69         self.backup_lba = 1
  70         self.first_usable_lba = 2
  71         self.last_usable_lba = 0xff     # dummy value
  72         self.uniq = DUMMY_GUID_DISK_UNIQUE
  73         self.part_entries_lba = 2
  74         self.part_entries_number = 0
  75         self.part_entries_crc32 = 0
  76         self.part_entry_size = 128
  77
  78     def pack_with_crc(self, crc):
  79         header_size = 92
  80         header = struct.pack('<8sIIIIQQQQ16sQIII',
  81                 b'EFI PART', 0x10000, header_size, crc, 0,
  82                 self.current_lba, self.backup_lba, self.first_usable_lba,
  83                 self.last_usable_lba, self.uniq.get_bytes(),
  84                 self.part_entries_lba, self.part_entries_number,
  85                 self.part_entry_size, self.part_entries_crc32)
  86         assert len(header) == header_size
  87         return header
  88
  89     def generate(self, stream):
  90         crc = zlib.crc32(self.pack_with_crc(0))
  91         header = self.pack_with_crc(crc)
  92         stream.write(header.ljust(BLOCK_SIZE, b'\0'))
  93
  94
  95 # A GPT partition entry.
  96 # https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_entries_(LBA_2-33)
  97 class GPTPartition:
  98     def __init__(self):
  99         self.type = GUID('00000000-0000-0000-0000-000000000000')
 100         self.uniq = GUID('00000000-0000-0000-0000-000000000000')
 101         self.first_lba = 0
 102         self.last_lba = 0
 103         self.attr = 0
 104         self.name = ''
 105
 106     def generate(self, stream):
 107         name_utf16 = self.name.encode('UTF-16LE')
 108         part = struct.pack('<16s16sQQQ72s',
 109                 self.type.get_bytes(), self.uniq.get_bytes(),
 110                 self.first_lba, self.last_lba, self.attr,
 111                 name_utf16.ljust(72, b'\0'))
 112         assert len(part) == 128
 113         stream.write(part)
 114
 115
 116 class GPTImage:
 117     # The final image consists of:
 118     # - A protective MBR
 119     # - A GPT header
 120     # - A few GPT partition entries
 121     # - The content of the bootblock
 122     def __init__(self):
 123         self.mbr = ProtectiveMBR()
 124         self.header = GPTHeader()
 125         self.partitions = [ GPTPartition() for i in range(8) ]
 126         self.bootblock = b''
 127
 128
 129     # Fix up a few numbers to ensure consistency between the different
 130     # components.
 131     def fixup(self):
 132         # Align the bootblock to a whole number to LBA blocks
 133         bootblock_size = (len(self.bootblock) + BLOCK_SIZE - 1) & ~BLOCK_MASK
 134         self.bootblock = self.bootblock.ljust(bootblock_size)
 135
 136         # Propagate the number of partition entries
 137         self.header.part_entries_number = len(self.partitions)
 138         self.header.first_usable_lba = 2 + self.header.part_entries_number // 4
 139
 140         # Create a partition entry for the bootblock
 141         self.partitions[0].type = GUID_TYPE_FSBL
 142         self.partitions[0].uniq = DUMMY_GUID_PART_UNIQUE
 143         self.partitions[0].first_lba = self.header.first_usable_lba
 144         self.partitions[0].last_lba = \
 145             self.header.first_usable_lba + bootblock_size // BLOCK_SIZE
 146
 147         # Calculate the CRC32 checksum of the partitions array
 148         partition_array = io.BytesIO()
 149         for part in self.partitions:
 150             part.generate(partition_array)
 151         self.header.part_entries_crc32 = zlib.crc32(partition_array.getvalue())
 152
 153
 154     def generate(self, stream):
 155         self.mbr.generate(stream)
 156         self.header.generate(stream)
 157         for part in self.partitions:
 158             part.generate(stream)
 159         stream.write(self.bootblock)
 160
 161
 162 if __name__ == '__main__':
 163     if len(sys.argv) != 3:
 164         print('Usage:', file=sys.stderr)
 165         print('    %s bootblock.raw.bin bootblock.bin' % sys.argv[0],
 166                 file=sys.stderr)
 167         sys.exit(1)
 168
 169     image = GPTImage()
 170
 171     with open(sys.argv[1], 'rb') as f:
 172         image.bootblock = f.read()
 173
 174     image.fixup()
 175
 176     # Verify if first partition is at expected lba, otherwise trampoline will
 177     # fail
 178     if image.partitions[0].first_lba != 4:
 179         print('Warning: First partition not at expected location (LBA 4)')
 180         sys.exit(1)
 181
 182     with open(sys.argv[2], 'wb') as f:
 183         image.generate(f)