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Revert "Add script to merge boot sector and patch GRUB for floppy (AI)"

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This reverts commit 7068176d91.
This commit is contained in:
Sebastiaan de Schaetzen
2026-02-23 09:52:40 +01:00
parent 7068176d91
commit 6d91edc897
1 changed files with 0 additions and 81 deletions
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scripts/merge_boot.py
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import sys
import struct
import math
import os
def merge_boot_sector(fat_img_path, boot_img_path, core_img_path):
# READ FAT boot sector to get BPB
with open(fat_img_path, 'rb') as f:
fat_sector = f.read(512)
# Read boot.img
with open(boot_img_path, 'rb') as b:
boot_sector = bytearray(b.read(512))
# Copy BPB from FAT sector (bytes 3 to 62) into boot sector
for i in range(3, 62):
boot_sector[i] = fat_sector[i]
# Write patched boot sector to FAT image sector 0
with open(fat_img_path, 'r+b') as f:
f.seek(0)
# Patch boot sector with LBA of core.img (diskboot.img)
# GRUB boot.S usually expects the LBA of the next stage at offset 0x5C (92) on some versions?
# Or it uses a blocklist?
# Standard GRUB boot.S loads one sector.
# The sector number is stored at offset 0x5C is for kernel_sector?
# Actually in GRUB2, boot.S uses a 'kernel_sector' field.
# Let's check offset.
# According to some docs, it is at 0x5C.
# We want to load sector 1.
# struct.pack_into('<Q', boot_sector, 0x5C, 1) // This might be wrong location
# Another approach:
# Standard boot.img usually has:
# 0x5C: kernel_sector (8 bytes, LBA)
# 0x64: kernel_segment (2 bytes)
# But this depends on exact version.
# Let's revert patching boot.S just to be safe, maybe default (1) is correct.
# Or maybe it relies on diskboot blocklist being correct.
# If I look at grub documentation: boot.img loads the first sector of core.img.
# The sector number is hardcoded at installation time.
# It is usually at offset (boot_img_size - 16)? No.
# Let's try 0x5C again but verify. In hex editor, usually see 0x01 there?
# Actually, let's just make sure we write boot sector back.
f.write(boot_sector)
# Now patch core.img (diskboot.img part, usually first 512 bytes)
# The blocklist is at offset 500 (0x1F4) of the first sector of core.img.
# We need to tell it where the rest of core.img is located on disk.
core_size = os.path.getsize(core_img_path)
core_sectors = math.ceil(core_size / 512)
rest_sectors = core_sectors - 1
if rest_sectors > 0:
start_sector = 2 # Because boot sector is 0, diskboot is 1, so rest starts at 2
segment = 0x820 # Load at 0x8200
with open(core_img_path, 'r+b') as c:
c.seek(0)
diskboot = bytearray(c.read(512))
struct.pack_into('<QHH', diskboot, 500, start_sector, rest_sectors, segment)
c.seek(0)
c.write(diskboot)
if __name__ == "__main__":
if len(sys.argv) != 4:
print("Usage: merge_boot.py <fat_img> <boot_img> <core_img>")
sys.exit(1)
merge_boot_sector(sys.argv[1], sys.argv[2], sys.argv[3])