How to use grub-mkimage prefix?

[J. Eppler]

Hello,

I use the following command to create a grub image:

~~~
./grub-mkimage --verbose --output=out/grubaa64.efi
--config=out/grub.configfile --format=arm64-efi $GRUB_MODULES
Prefix not specified (use the -p option).
Usage: ./grub-mkimage [OPTION...] [OPTION]
~~~

I get the message: "prefix not specified". My problem is that I do not
understand what the prefix directory should be. The man page
`grub-mkimage` for the -p option only says: "set prefix directory". It
does not explain what a prefix directory value could be nor does it
explain the function of the prefix directory.

---

Appendix

config file:

~~~
$ cat out/grub.configfile
search.fs_label rootfs root
set prefix=($root)'/boot/grub'
configfile $prefix/grub.cfg
~~~

grub modules:

~~~
GRUB_MODULES="boot chain configfile echo efinet eval ext2 fat font
gettext gfxterm gzio help linux loadenv lsefi normal part_gpt part_msdos
read regexp search search_fs_file search_fs_uuid search_label terminal
terminfo test tftp time xen_boot"
~~~

best regards
  J. Eppler