A good way to test it (not as root!) is:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix system reconfigure gnu/system/examples/bare-bones.tmpl
/gnu/store/fm8lbh7r3j05bkd6kbnc9xwph6rmy0rz-system
/gnu/store/9l0dfdxj7ybck63r9zrgnxbyryn6f0kh-grub.cfg
/gnu/store/myrc5cinlhpj2yilhzv5y0szz2ax2i6z-grub-2.00
guix system: error: symlink: Mankas permeso: "/var/guix/profiles/system-192-link"
--8<---------------cut here---------------end--------------->8---

The generated grub.cfg whose name appears above has this entry:

--8<---------------cut here---------------start------------->8---
menuentry "GNU with Linux-Libre 4.5.2 (beta)" {
  insmod luks
  cryptomount -u cb67fc72-0d54-4c88-9d4b-b225f30b0f44
  search --file --set /gnu/store/dd2qbz6a5pszwnzay3s8mm9yim531nz0-linux-libre-4.5.2/bzImage
  linux /gnu/store/dd2qbz6a5pszwnzay3s8mm9yim531nz0-linux-libre-4.5.2/bzImage --root=/dev/mapper/foo --system=/gnu/store/fm8lbh7r3j05bkd6kbnc9xwph6rmy0rz-system --load=/gnu/store/fm8lbh7r3j05bkd6kbnc9xwph6rmy0rz-system/boot
  initrd /gnu/store/fm8lbh7r3j05bkd6kbnc9xwph6rmy0rz-system/initrd
}
--8<---------------cut here---------------end--------------->8---

Now, I haven’t tested this in reality and would appreciate help here.

We may have to add the patch to ‘guix-devel’ in (gnu packages
package-management) to test it.

Ludo’.