Bootelf

Want to make your kernel elf file bootable?

Just append your elf to this boot sector and you will boot straight into it.

Details

• Interrupts are disabled
• Bottom 2G is identity mapped at virtaddr 0, top half base and -2G
• Your elf file is loaded at 0x7E00.
• Any memory below 0x7E00 should not be touched unless you've stopped using the bootloaders page tables, structures (including memory map!) and GDT
• You will get a Bootelf_data * passed in rdi (first argument in any sensible calling convention):

  struct Bootelf_data {
    u64 magic; // == 0xb00731f, read as bootelf
    u64 numEntries;
    struct Bootelf_memmap_entry *entries;
    struct Bootelf_framebuffer framebuffer;
  };
  
  // 32 bpp framebuffer
  struct Bootelf_framebuffer {
    u64 base;
    u32 pitch;
    u32 width;
    u32 height;
  };
  
  struct Bootelf_memmap_entry {
    u64 base;
    u64 size;
    u32 type;
    u32 acpi3type;
  };
  

  Bootelf_memmap_entry directly corresponds to the values aquired from a E820 memory map, and should be interpreted as such. Note that the framebuffer might be unmapped. If the base field in the framebuffer struct is 0, bootelf was unable to get you a framebuffer, and the standard VESA text mode will be active.