[bug#72457] After further research

[amano.kenji]

After further research, I concluded that it is better to have different 
bootloaders for creating hashes or gpg signatures instead of exposing service 
hooks.

Heads firmware just parses grub.cfg for a list of kernel images with initrd and 
shows kernel images on boot.

Thus, gnu guix can have `heads` bootloader which produces grub.cfg and copies 
kernel images and initrd to /boot.

`heads-signed` bootloader can sign all files in /boot with a gpg private key.

Heads is an alternative to BIOS and UEFI. It is an open-source firwmare for 
(coreboot) motherboards.