buildroot/boot/grub2

Notes on using Grub2 for BIOS-based platforms
=============================================

1. Create a disk image
dd if=/dev/zero of=disk.img bs=1M count=32
2. Partition it (either legacy or GPT style partitions work)
cfdisk disk.img
- Create one partition, type Linux, for the root
filesystem. The only constraint is to make sure there
is enough free space *before* the first partition to
store Grub2. Leaving 1 MB of free space is safe.
3. Setup loop device and loop partitions
loop_dev=$(sudo losetup -f --show disk.img)
sudo partx -a "$loop_dev"
4. Prepare the root partition
sudo mkfs.ext3 -L root "${loop_dev}p1"
sudo mount "${loop_dev}p1" /mnt
sudo tar -C /mnt -xf output/images/rootfs.tar
sudo umount /mnt
5. Install Grub2
sudo ./output/host/sbin/grub-bios-setup \
-b ./output/host/lib/grub/i386-pc/boot.img \
-c ./output/images/grub.img -d . "$loop_dev"
6. Cleanup loop device
sudo partx -d "$loop_dev"
sudo losetup -d "$loop_dev"
7. Your disk.img is ready!

Using genimage
--------------

If you use genimage to generate your complete image,
installing Grub can be tricky. Here is how to achieve Grub's
installation with genimage:

partition boot {
in-partition-table = "no"
image = "path_to_boot.img"
offset = 0
size = 512
}
partition grub {
in-partition-table = "no"
image = "path_to_grub.img"
offset = 512
}

The result is not byte to byte identical to what
grub-bios-setup does but it works anyway.

To test your BIOS image in Qemu
-------------------------------

qemu-system-{i386,x86_64} -hda disk.img

Notes on using Grub2 for x86/x86_64 EFI-based platforms
=======================================================

1. Create a disk image
dd if=/dev/zero of=disk.img bs=1M count=32
2. Partition it with GPT partitions
cgdisk disk.img
- Create a first partition, type EF00, for the
bootloader and kernel image
- Create a second partition, type 8300, for the root
filesystem.
3. Setup loop device and loop partitions
loop_dev=$(sudo losetup -f --show disk.img)
sudo partx -a "$loop_dev"
4. Prepare the boot partition
sudo mkfs.vfat -n boot "${loop_dev}p1"
sudo mount "${loop_dev}p1" /mnt
sudo cp -a output/images/efi-part/* /mnt/
sudo cp output/images/bzImage /mnt/
sudo umount /mnt
5. Prepare the root partition
sudo mkfs.ext3 -L root "${loop_dev}p2"
sudo mount "${loop_dev}p2" /mnt
sudo tar -C /mnt -xf output/images/rootfs.tar
sudo umount /mnt
6 Cleanup loop device
sudo partx -d "$loop_dev"
sudo losetup -d "$loop_dev"
7. Your disk.img is ready!

To test your i386/x86-64 EFI image in Qemu
------------------------------------------

1. Download/install the EFI BIOS for Qemu
You can get it using the edk2 package in Buildroot (installed
in BINARIES_DIR), grab prebuilt images from the unofficial nightly
builds [0], or use one provided by your distribution as OVMF.

[0] https://github.com/retrage/edk2-nightly

2. qemu-system-{i386,x86_64} -bios -hda disk.img

Notes on using Grub2 for ARM u-boot-based platforms
===================================================

The following steps show how to use the Grub2 arm-uboot platform
support in the simplest way possible and with a single
buildroot-generated filesystem.

1. Load qemu_arm_vexpress_defconfig

2. Enable u-boot with the vexpress_ca9x4 board name and with
u-boot.elf image format.

3. Enable grub2 for the arm-uboot platform.

4. Enable "Install kernel image to /boot in target" in the kernel
menu to populate a /boot directory with zImage in it.

5. The upstream u-boot vexpress_ca9x4 doesn't have CONFIG_API enabled
by default, which is required.

Before building, patch u-boot (for example, make u-boot-extract to
edit the source before building) file
include/configs/vexpress_common.h to define:

#define CONFIG_API
#define CONFIG_SYS_MMC_MAX_DEVICE 1

6. Create a custom grub2 config file with the following contents and
set its path in BR2_TARGET_GRUB2_CFG:

set default="0"
set timeout="5"

menuentry "Buildroot" {
set root='(hd0)'
linux /boot/zImage root=/dev/mmcblk0 console=ttyAMA0
devicetree /boot/vexpress-v2p-ca9.dtb
}

7. Create a custom builtin config file with the following contents
and set its path in BR2_TARGET_GRUB2_BUILTIN_CONFIG:

set root=(hd0)
set prefix=/boot/grub

8. Create a custom post-build script which copies files from
${BINARIES_DIR}/boot-part to $(TARGET_DIR)/boot (set its path in
BR2_ROOTFS_POST_BUILD_SCRIPT):

#!/bin/sh
cp -r ${BINARIES_DIR}/boot-part/* ${TARGET_DIR}/boot/

9. make

10. Run qemu with:

qemu-system-arm -M vexpress-a9 -kernel output/images/u-boot -m 1024 \
-nographic -sd output/images/rootfs.ext2

11. In u-boot, stop at the prompt and run grub2 with:

=> ext2load mmc 0:0 ${loadaddr} /boot/grub/grub.img
=> bootm

12. This should bring the grub2 menu, upon which selecting the "Buildroot"
entry should boot Linux.


Notes on using Grub2 for Aarch64 EFI-based platforms
====================================================

The following steps show how to use the Grub2 arm64-efi platform,
using qemu and EFI firmware built for qemu.

1. Load aarch64_efi_defconfig

2. make

3. Download the EFI firmware for qemu aarch64

You can get it using the edk2 package in Buildroot (installed
in BINARIES_DIR), grab prebuilt images from the unofficial nightly
builds [1], or use one provided by your distribution as OVMF-aarch64
or AAVMF.

[1] https://github.com/retrage/edk2-nightly

4. Run qemu with:

qemu-system-aarch64 -M virt -cpu cortex-a57 -m 512 -nographic \
-bios /QEMU_EFI.fd -hda output/images/disk.img \
-netdev user,id=eth0 -device virtio-net-device,netdev=eth0

5. This should bring the grub2 menu, upon which selecting the
"Buildroot" entry should boot Linux.