• CoreBoot

GRUB2 is a modular, multiboot-capable bootloader for many operating systems that can be used as a payload for coreboot.

How to build GRUB2 as a payload

It's recommended that you use the latest SVN version of GRUB, since coreboot support is being actively developed and evolves rapidly.

 $ svn co svn://svn.savannah.gnu.org/grub/trunk/grub2
 $ cd grub2
 $ ./autogen.sh
 $ ./configure --with-platform=coreboot
 $ make
 $ MODULES="normal ls cat help ext2 iso9660 reiserfs xfs fat part_msdos part_gpt ata serial memdisk multiboot linux minicmd configfile search tar at_keyboard"
 $ ./grub-mkelfimage -d . $MODULES -o ..../coreboot-v3/payload.elf --prefix='(ata0)/boot/grub'

See below about module selection.

GRUB2 modules

GRUB2 is a modular system, you can include whichever modules you need into the image. A few noteworthy ones are:

*normal, ls, cat, help: These make the user interface more complete/usable.
*ext2, iso9660, reiserfs, xfs, fat: Commonly used filesystems.
*part_msdos, part_gpt: Commonly used partition maps.
*ata: Driver for ATA / ATAPI disks.
*serial: Driver for serial terminal.
*memdisk: Allows you to embed a virtual disk into the GRUB image (see below)
*multiboot: Loader for Multiboot kernels (such as the kernel of [http://www.netbsd.org/ NetBSD] or [http://www.opensolaris.com/ OpenSolaris])
*linux: Loader for [http://www.kernel.org/ Linux] bzImages.
*boot: Needed by all loaders.

You might also want to check the CommandList.

Building a memdisk image

Build your memory disk using your preferred filesystem. For example, tar. Then load the memdisk module, and include the image in your build.

 $ mkdir -p boot/grub
 (put a grub.cfg file in boot/grub, see example below)
 $ tar -cf memdisk.tar boot
 $ MODULES="see above :-)"
 $ ./grub-mkelfimage -d . $MODULES -o ..../coreboot-v3/payload.elf -m memdisk.tar --prefix='(memdisk)/boot/grub'

GRUB will automatically use the the memdisk for finding modules and the grub.cfg file.

Hints and Tricks

Loading grub.cfg from disk

It is suggested that grub.cfg is contained in a memdisk/tar image. This grub.cfg can be used to load other configuration files from any mass storage media, or to load another Multiboot payload (e.g. GRUB itself).

echo -n "Press `ESC' to enter the menu... "

# If disks don't have time to spin, you might want to increase
# this number.
if sleep --verbose --interruptible 2 ; then
  set timeout=0
fi

set default=0
set fallback=1

menuentry "Search & load /boot/multiboot.img" {
        search -s -f /boot/multiboot.img
        if multiboot /boot/multiboot.img ; then
                boot
        fi
        unset timeout
}

# For separate /boot partition.
menuentry "Search & load /multiboot.img" {
        search -s -f /multiboot.img
        if multiboot /multiboot.img ; then
                boot
        fi
        unset timeout
}

menuentry "Search & source /boot/grub/grub.cfg" {
        search -s -f /boot/grub/grub.cfg
        source /boot/grub/grub.cfg
        unset timeout
}

# For separate /boot partition.
menuentry "Search & source /grub/grub.cfg" {
        search -s -f /grub/grub.cfg
        source /grub/grub.cfg
        unset timeout
}

menuentry "Reboot" {
        reboot
}

Building Coreboot with GRUB2 payload

Please consult the documentation that Coreboot for the build instructions once it becomes available. As of June 2009, building Coreboot is not well documented. Following script will build coreboot.rom and run it under qemu. The script should be run in the GRUB2 source directory after it has been compiled for the coreboot platform. coreboot-v2 is assumed to be checked out into a directory under the same directory and the GRUB2 sources. Instead of memdisk, a CD-ROM image is used, which allows all modules to be included.

#!/bin/sh

set -e

GRUB_SRC=`pwd`
COREBOOT_SRC=../coreboot-v2
QEMU_VGABIOS=/usr/share/qemu/vgabios-cirrus.bin

MODULES="at_keyboard iso9660 ata"
LISTS="moddep.lst command.lst fs.lst partmap.lst parttool.lst handler.lst"
./grub-mkelfimage -d . $MODULES -o payload.elf --prefix='(ata2)/'
genisoimage -r -J -o modules.iso *.mod $LISTS

cd $COREBOOT_SRC/targets
rm -rf emulation/qemu-x86/qemu-x86
cp $GRUB_SRC/payload.elf emulation/qemu-x86/
./buildtarget emulation/qemu-x86
cd emulation/qemu-x86/qemu-x86
make PAYLOAD=$GRUB_SRC/payload.elf
cp -f $QEMU_VGABIOS vgabios-cirrus.bin
qemu -L . -bios coreboot.rom -cdrom $GRUB_SRC/modules.iso

To Do

USBSupport (in progress).

Check some research papers for more information concerning this software.

How to help and report bugs, etc

Contact the GRUB upstream mailing list for more information.

CategoryDocumentation