Android device tree for basic x86_64 PC

#
# SPDX-FileCopyrightText: The LineageOS Project
# SPDX-License-Identifier: Apache-2.0
#

Steps to boot

(The example environment used in below is a x86_64 PC running Debian with GRUB boot manager, and the hard drive is connected to SATA bus)

1. Build this target, and then enter the output directory, using the following commands:

source build/envsetup.sh
breakfast basic_x86_64_pc
m kernel ramdisk recoveryimage systemimage vendorimage
cout

2. Put the kernel and ramdisk images to anywhere that the boot manager can access.

mkdir /android
cp kernel ramdisk.img ramdisk-recovery.img /android/

3. Create empty partitions

Ensure to have the following partitions:

Purpose	Minimum size	Example path
system	2.5 GB	/dev/sda5
vendor	256 MB	/dev/sda6
userdata	2 GB	/dev/sda7

4. Write system and vendor image

dd if=system.img of=/dev/sda5
dd if=vendor.img of=/dev/sda6

5. Add GRUB boot entries

Get the kernel parameters using the following command:

get_build_var BOARD_KERNEL_CMDLINE

Add the following to /boot/grub/custom.cfg:

menuentry "Android" {
    set gfxpayload=keep # For VESA framebuffer when booted from BIOS
    linux /android/kernel <kernel parameters>
    initrd /android/ramdisk.img
}

menuentry "Android Recovery" {
    set gfxpayload=keep # For VESA framebuffer when booted from BIOS
    linux /android/kernel <kernel parameters>
    initrd /android/ramdisk-recovery.img
}

Update the parameter androidboot.partition_map:

• Make it reflect the actual partition setup. For this example: sda5,system;sda6,vendor;sda7,userdata
• Escape ';' characters, by prepending '\' before these. For this example: sda5,system\;sda6,vendor\;sda7,userdata

Details about creating bootable GRUB disk

A FAT32 partition containing GRUB and Android boot files

The partition should be EFI System Partition on GPT disk, or a partition with type W95 FAT32 otherwise.

Directory structure:

Path	Source	Description
/android/kernel	out/target/product/basic_x86_64_pc/kernel
/android/ramdisk.img	out/target/product/basic_x86_64_pc/ramdisk.img
/android/ramdisk-recovery.img	out/target/product/basic_x86_64_pc/ramdisk-recovery.img
/boot/grub/grub.cfg	Manually written	Content is provided below
/boot/grub/i386-pc/	prebuilts/bootmgr/grub/linux-x86/i386-pc/lib/grub/i386-pc/	For BIOS boot
/boot/grub/x86_64-efi/	prebuilts/bootmgr/grub/linux-x86/x86_64-efi/lib/grub/x86_64-efi/	For UEFI boot
/EFI/BOOT/BOOTX64.EFI	Generated using command	For UEFI boot

Content of /boot/grub/grub.cfg:

insmod normal
insmod linux
insmod test

if [ "$grub_platform" = "efi" ]; then
    insmod efi_gop
elif [ "$grub_platform" = "pc" ]; then
    insmod vbe
fi

<Same as the content from `/boot/grub/custom.cfg` in above of the page>

Content of grub-standalone.cfg:

search --file --no-floppy --set=root /android/kernel
set prefix=($root)'/boot/grub'
configfile $prefix/grub.cfg

Command to create /EFI/BOOT/BOOTX64.EFI:

PATH=prebuilts/bootmgr/tools/linux-x86/bin/:$PATH prebuilts/bootmgr/grub/linux-x86/x86_64-efi/bin/grub-mkstandalone \
    -d prebuilts/bootmgr/grub/linux-x86/x86_64-efi/lib/grub/x86_64-efi \
    --fonts="" \
    --format=x86_64-efi \
    --locales="" \
    --modules="configfile disk fat part_gpt search" \
    --output=BOOTX64.EFI \
    "boot/grub/grub.cfg=grub-standalone.cfg"

BIOS boot support

Import GRUB boot.img:

dd if=prebuilts/bootmgr/grub/linux-x86/i386-pc/lib/grub/i386-pc/boot.img of=boot.img bs=446 count=1

Create GRUB core.img:

PATH=prebuilts/bootmgr/tools/linux-x86/bin/:$PATH prebuilts/bootmgr/grub/linux-x86/i386-pc/bin/grub-mkimage \
    --compression=auto \
    --config=grub-standalone.cfg \
    --directory=prebuilts/bootmgr/grub/linux-x86/i386-pc/lib/grub/i386-pc \
    --format=i386-pc \
    --output=core.img \
    --prefix=/boot/grub \
    fat msdospart part_msdos part_gpt biosdisk search configfile

Confirm the start sector of GRUB core.img on disk. If the disk uses GPT partition scheme, create a 1MB partition with type BIOS boot partition, and use its start sector. Otherwise, use sector 1.

Patch and write GRUB boot.img and core.img:

gcc device/virt/virt-common/utilities/grub_i386-pc_img_patch/grub_i386-pc_img_patch.c -o grub_i386-pc_img_patch
./grub_i386-pc_img_patch <start sector of core.img> boot.img core.img
dd if=boot.img of=/dev/sdX bs=446 count=1
dd if=core.img of=/dev/sdX bs=512 count=2048 seek=<start sector of core.img>