From tutorial at http://arjunsreedharan.org/post/82710718100/kernel-101-lets-write-a-kernel

Build with:

nasm -f elf32 kernel.asm -o kasm.o

gcc -m32 -c kernel.c -o kc.o

ld -m elf_i386 -T link.ld -o kernel kasm.o kc.o

For grub2, copy kernel to /boot/ and just run 'update-grub'

• reboot
• press 'c' from advanced grub menu to open limited shell
• grub> multiboot /boot/kernel-1
• (nothing happens)
• hit escape
• Select kernel to boot; displays same error
• press any key
• kernel loads

http://download-mirror.savannah.gnu.org/releases/grub/phcoder/multiboot.pdf
http://forum.osdev.org/viewtopic.php?f=1&t=16757
http://wiki.osdev.org/Creating_a_64-bit_kernel