Implement a Multiboot-Compliant Bootloader Header

Multiboot header

Multiboot lets compliant bootloaders pass metadata to kernels like GRUB does for hobby OS projects. A valid header starts with magic 0x1BADB002, sets flags, and ends with a checksum making the sum of all three dwords zero. For example, flags 0x00000003 requests memory info and page-aligned modules.

Header layout

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• Place the header in the first 8 KB of the OS image (often first 32 KB for GRUB2)
• Kernel entry must be 32-bit protected mode for Multiboot v1
• GRUB fills the multiboot info structure with memory map and cmdline pointers

Loader expectations

QEMU can boot a Multiboot kernel with -kernel when the header is valid. GRUB's multiboot command passes a magic value in EAX and a pointer to the info structure in EBX at entry. The header must be dword-aligned and located within the first 8 KB of the file. If QEMU reports invalid magic, double-check endianness and that the checksum sum wraps to zero in 32-bit arithmetic.

Why for this exercise

You will embed a Multiboot-compliant header in your kernel image and boot it with QEMU/GRUB. This exercise requires the correct magic, flags, and checksum so a Multiboot loader recognizes your binary.