July 14, 2019

Build a 64bit bootable image for a Raspberry Pi 4

Given the traction our previous post got, we thought we should jot down the steps to build a 64-bit bootable image for a RPi4. The distro we’re most familiar with is Debian, so we’ll go with a debian-like distro like Ubuntu. If you don’t feel like playing with kernel compilation and FS images, just grab the binary and dd it to an SD card!

First step, download the 64-bit ubuntu server distro for the RPi3:

http://cdimage.ubuntu.com/ubuntu/releases/bionic/release/ubuntu-18.04.2-preinstalled-server-arm64+raspi3.img.xz

Then make sure you follow the instructions from these posts which help us build the kernel and update the boot firmware. The steps from these posts are summarized below:

Build the toolchain

mkdir -p toolchains/aarch64
cd toolchains/aarch64
export TOOLCHAIN=`pwd` # Used later to reference the toolchain location

cd "$TOOLCHAIN"
wget https://ftp.gnu.org/gnu/binutils/binutils-2.32.tar.bz2
tar -xf binutils-2.32.tar.bz2
mkdir binutils-2.32-build
cd binutils-2.32-build
../binutils-2.32/configure --prefix="$TOOLCHAIN" --target=aarch64-linux-gnu --disable-nls
make -j4
make install
cd "$TOOLCHAIN"
wget https://ftp.gnu.org/gnu/gcc/gcc-9.1.0/gcc-9.1.0.tar.gz
tar -xf gcc-9.1.0.tar.gz
mkdir gcc-9.1.0-build
cd gcc-9.1.0-build
../gcc-9.1.0/configure --prefix="$TOOLCHAIN" --target=aarch64-linux-gnu --with-newlib --without-headers --disable-nls --disable-shared --disable-threads --disable-libssp --disable-decimal-float --disable-libquadmath --disable-libvtv --disable-libgomp --disable-libatomic --enable-languages=c
make all-gcc -j4
make install-gcc

Build the Raspberry Pi kernel

apt-get install bison flex
git clone https://github.com/raspberrypi/linux.git rpi-linux
cd rpi-linux
git checkout origin/rpi-4.19.y # change the branch name for newer versions
mkdir kernel-build
PATH=$PATH:$TOOLCHAIN/bin make O=./kernel-build/ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-  bcm2711_defconfig
PATH=$PATH:$TOOLCHAIN/bin make -j4 O=./kernel-build/ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
export KERNEL_VERSION=`cat ./kernel-build/include/generated/utsrelease.h | sed -e 's/.*"\(.*\)".*/\1/'` 
make -j4 O=./kernel-build/ DEPMOD=echo MODLIB=./kernel-install/lib/modules/${KERNEL_VERSION} INSTALL_FW_PATH=./kernel-install/lib/firmware modules_install
git clone https://github.com/raspberrypi/tools.git rpi-tools
cd rpi-tools/armstubs
git checkout 7f4a937e1bacbc111a22552169bc890b4bb26a94
PATH=$PATH:$TOOLCHAIN/bin make armstub8-gic.bin
echo "armstub=armstub8-gic.bin" >> config-extra.txt 
echo "enable_gic=1" >> config-extra.txt 
echo "arm_64bit=1" >> config-extra.txt
echo "total_mem=1024" >> config-extra.txt

We now have all the necessary files to create the boot partition and boot into the ubuntu-preinstalled image. Specifically:

Kernel: rpi-linux/kernel-build/arch/arm64/boot/Image

Bootstub: rpi-tools/armstubs/armstub8-gic.bin

Modules: rpi-linux/kernel-build/kernel-install/lib/modules/${KERNEL_VERSION}

Firmware: https://github.com/RPi-Distro/firmware-nonfree

So, first thing to do after we have finished building the above is to de-compress and loop mount the ubuntu-preinstalled image we downloaded:

xzcat ubuntu-18.04.2-preinstalled-server-arm64+raspi3.img.xz > ubuntu-18.04.2-preinstalled-server-arm64+raspi4.img
kpartx -av ubuntu-18.04.2-preinstalled-server-arm64+raspi4.img

You should end up with 2 device files:

/dev/mapper/loop0p1
/dev/mapper/loop0p2

Mount them under /mnt like this:

mount /dev/mapper/loop0p2 /mnt
mount /dev/mapper/loop0p1 /mnt/boot/firmware

Then copy in the kernel/stub, modules and firmware:

cp rpi-linux/kernel-build/arch/arm64/boot/Image /mnt/boot/firmware/kernel8.img
cp rpi-tools/armstubs/armstub8-gic.bin /mnt/boot/firmware/armstub8-gic.bin
cp -avf rpi-linux/kernel-build/kernel-install/lib/modules/${KERNEL_VERSION} /mnt/lib/modules/
git clone https://github.com/RPi-Distro/firmware-nonfree firmware-nonfree
cp -avf firmware-nonfree/* /mnt/lib/firmware

Append config-extra.txt to config.txt:

cat config-extra.txt >> /mnt/boot/firmware/config.txt

and we’re done! Unmount / detach the loop device, dd it to an sdcard, plug it into a RPi4 and party!

umount /mnt/boot/firmware
umount /mnt
kpartx -dv ubuntu-18.04.2-preinstalled-server-arm64+raspi4.img
losetup -d /dev/loop0
dd if=ubuntu-18.04.2-preinstalled-server-arm64+raspi4.img of=/dev/sdXX

If you’re too lazy to do the above, feel free to grab our image built using the above steps:

https://cloudkernels.net/ubuntu-18.04.2-preinstalled-server-arm64+raspi4+kvm.img.xz

(sha1sum: 0b1d8b72ea5410fb7928925fd76dd0218b4f7a94)