GRUB Multiboot header not found

Question

After reading this this question and it's primary answer, I ran readelf on my kernel, and noticed my .text section was at 0x00101000 and not 0x00100000. I also noticed a section above that read .not.gnu.build-i that was in the place the .text section is supposed to be. Is there a way I could make my .text section be in the correct place? I have already used align 4 to set it to 1M.

Answer 1

Your linker script (given that it is the same as in the other question) is the problem: By telling it to 4k-align the sections and putting multiboot in a separate section, you allocate 4k for it, so .text starts at an offset of 1M + 4k, which causes your problem. Change it to the following:

SECTIONS
{
    . = 1M;

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

[snip]

Answer 2

The issue is that LD (or LD via GCC) is automatically placing a notes section (if one was generated) in the first 4k. If linking the final kernel with GCC pass it the -Wl,--build-id=none option. If you are using LD directly to link the final binary then you can pass it --build-id=none .

If writing a multiboot ELF object the existence of this extra section can force the mulitboot header beyond the 8k position in the file. This is accounting for the fact that ELF headers usually take a minimum of the first 4k of the file. Add in the 4k for .note.gnu.build-id and .multiboot section is now beyond 8k mark of the physical file. This will cause a multiboot loader like GRUB to think your ELF executable doesn't have a multiboot header since it only looks through the first 8k of the file.