How to make the 446 bytes boot image

[Jarl Friis]

Hi.

I am investigating grub2 for learning and building a bootable image (file)
in userspace.

I am building a image file with GPT and a BIOS boot partition. As far as I
understand the BIOS boot partition shall contain the core.img directly on
the partiotion (without a file system), these approx 30KiB is generated
using grub-mkimage.

How do I use grub to build the 446 bytes (boot.img) that shall be dumped at
the very begining of the disk (at the MBR) that shall load and run the core
image at the BIOS boot partition?

Jarl