Issue with linker.ld in "User /Bare Bones" Tutorial – Incorrect Section Order for Multiboot and .text in ELF Kernel

[jjzhai]

Content:
In the "User
/Bare Bones" tutorial within the Kernel Basics section, there is an issue with the linker.ld file that causes the kernel to not load correctly when following the provided instructions. Specifically, the section placement in the linker.ld file needs to be adjusted for proper execution.

Currently, the tutorial suggests the following structure in the linker.ld file:

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.rodata BLOCK(4K) : ALIGN(4K)
{
    *(.multiboot)
}

.text BLOCK(4K) : ALIGN(4K)
{
    *(.text)
}

However, this configuration does not ensure that the Multiboot header will be located at the start of the executable, which is required for the bootloader (e.g., GRUB) to recognize the kernel as a valid multiboot-compliant kernel.

Solution:
To resolve this issue, the linker.ld file should be modified so that the Multiboot header is placed within the .text section to ensure it appears at the start of the kernel binary. The corrected linker.ld configuration is as follows:

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.text BLOCK(4K) : ALIGN(4K)
{
    *(.multiboot)
    *(.text)
}

Reason:
The Multiboot header must appear within the first 8 KB of the binary and should be placed at the beginning of the .text section to be properly recognized by the bootloader. By combining the .multiboot section with the .text section, we ensure that the Multiboot header is loaded correctly, and the kernel can boot as expected.

This change fixes the kernel loading issue and allows the tutorial to work as intended.

[Octocontrabass]

In the "User
/Bare Bones" tutorial

You mean this one?

To resolve this issue, the linker.ld file should be modified so that the Multiboot header is placed within the .text section to ensure it appears at the start of the kernel binary.

I prefer making the .multiboot section allocatable. Instead of changing linker.ld, change this line of start.s:

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.section .multiboot

To this:

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.section .multiboot, "a"

The linker can't rearrange allocatable sections, so you can ensure the .multiboot section comes first without combining it into the .text section.