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Grub has similar concept of modules like the Linux kernel.
They are a bunch of precompiled files which usually live at boot/grub/x86_64-efi/<module_name>.mod on the rootfs.
The module needs to be loaded before it can be used. "used" means that you can you can run a particular new command in grub.cfg. A way you install a module is having a insmod <module_name>.
Is it possible to embed a grub module withing the grub binary instead of having the modules living on the rootfs?
When you install grub, you can indicate grub-install --modules=… and get some modules preloaded.
You can also use grub-probe … which gives you the modules needed to access a given directory.
.mod files to the EFI partition?
Oct 8, 2021 at 15:16
grubx64.efi file is created.
Oct 8, 2021 at 15:25
grubx64.efi. I'm trying to understand if modules can also live within the bootloader binary or they always exist as a separate .mod file.
Oct 8, 2021 at 15:34
grubx64.efi is typically made by a low level command : grub-mkimage -p /boot/grub -O x86_64-efi -c grub-pre.cfg -o /tmp/grubx64.efi luks2 part_gpt cryptodisk gcry_rijndael pbkdf2 gcry_sha256 ext2 Then it embeds the partition table handling, filesystem and other things needed to load your favorite kernel.
Oct 8, 2021 at 16:13
grubx64.efi binary file. In case of Secure Boot, this is essential, as anything that loads program code without performing Secure Boot signature checks would be classifiable as a "Secure Boot circumvention device". The modules are ELF binaries, but when included, a single signature on the resulting .efi binary covers them all.