GNU LD max-page-size for Multiboot2 header on elf64

RedDocMD · **Joined:** Mon Aug 02, 2021 8:41 am **Posts:** 1

I am using the following bit of assembly to insert a Multiboot2 header to my kernel:

Code:

.set LENGTH, (header_end - header_start)
.set ARCH, 0
.set MAGIC, 0xE85250D6
.set CHECKSUM, -(MAGIC + ARCH + LENGTH)

.section .multiboot
header_start:
    .int MAGIC /* Magic number */
    .int ARCH /* x86 protected mode */
    .int LENGTH /* Header length */
    .int CHECKSUM /* Multiboot2 checksum */
    /* Set the end flag */
    .word 0 /* Type */
    .word 0 /* Flag */
    .int 8 /* Size */
header_end:

I am using binutils 2.37 to assemble and link the kernel (cross-compiled to the x86_64-elf target).
The kernel thus formed fails the multiboot2 test:

Code:

grub-file --is-x86-multiboot2 build/simple-os.bin || echo "Not multiboot 2"

The Wiki mentions an issue here: https://wiki.osdev.org/Multiboot#Multiboot_2.
The fix suggested is to set the max-page-size while linking.
What would be the correct size to set?

Octocontrabass · **Joined:** Mon Mar 25, 2013 7:01 pm **Posts:** 5143

Set it to the smallest page size: 0x1000.

OSDev.org

GNU LD max-page-size for Multiboot2 header on elf64

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