Script for patching a Raspberry Pi bootloader to support a larger kernel

uboot_patch.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# MIT License
#
# Copyright (c) 2022 Michael Bikovitsky
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.


import argparse
import re
import sys


def _main():
    args = _parse_command_line()

    # https://source.denx.de/u-boot/u-boot/-/blob/157861e6afa5c26134639e8a8f34540141672a0a/include/configs/rpi.h#L116
    DEFAULT_ENV = (
        b"kernel_addr_r=0x00080000\0"
        + b"scriptaddr=0x02400000\0"
        + b"pxefile_addr_r=0x02500000\0"
        + b"fdt_addr_r=0x02600000\0"
        + b"ramdisk_addr_r=0x02700000\0"
    )

    kernel_addr_r = 0x00080000
    scriptaddr = kernel_addr_r + args.size
    pxefile_addr_r = scriptaddr + 0x100000
    fdt_addr_r = pxefile_addr_r + 0x100000
    ramdisk_addr_r = fdt_addr_r + 0x100000

    new_env = (
        f"kernel_addr_r={kernel_addr_r:#010x}\0"
        + f"scriptaddr={scriptaddr:#010x}\0"
        + f"pxefile_addr_r={pxefile_addr_r:#010x}\0"
        + f"fdt_addr_r={fdt_addr_r:#010x}\0"
        + f"ramdisk_addr_r={ramdisk_addr_r:#010x}\0"
    ).encode("ASCII")

    if len(new_env) != len(DEFAULT_ENV):
        raise ValueError("Specified size is too big")

    with open(args.input, mode="rb") as f:
        bootloader = f.read()

    if len(re.findall(DEFAULT_ENV, bootloader)) != 1:
        raise ValueError("Unsupported bootloader memory configuration")

    new_bootloader = re.sub(DEFAULT_ENV, new_env, bootloader)

    with open(args.output, mode="wb") as f:
        f.write(new_bootloader)


def _parse_command_line() -> argparse.Namespace:
    parser = argparse.ArgumentParser(
        formatter_class=argparse.ArgumentDefaultsHelpFormatter
    )

    def int_any_base(string: str):
        return int(string, base=0)

    parser.add_argument("-i", "--input", required=True, help="Input filename")
    parser.add_argument("-o", "--output", required=True, help="Output filename")
    parser.add_argument(
        "-s",
        "--size",
        type=int_any_base,
        default=66584576,
        help="Required memory for kernel decompression, in bytes",
    )

    return parser.parse_args()


if __name__ == "__main__":
    sys.exit(_main())