Emulation

As part of another project, I need to be able to build software for the PinePhone, and that means I need an ARM64 environment with as much oomph as possible (trying to compile stuff on the PinePhone = bad idea).

The solution is to run a Debian VM that, in turn, runs a Qemu ARM64 emulator with a Debian image.

Nearly every step that follows is taken verbatim from this guide by Blahcat, so all credit goes there.  The only reason I made my own post is because I had to change a couple lines in order to get the network working. Hopefully this brings you joy.

Get that VM going

I’m a VirtualBox guy, but you do you. You’ll also want the latest Debian ISO, which at the time of writing is Buster. I gave mine 4 cores, 4GB of RAM, and 20GB of storage.

Install Qemu

Terminal. sudo apt install qemu. Nuff said.

Download the Debian Bits

You need the initrd and kernel of the Debian installer. Blahcat’s links are outdated, so here’s the latest:

wget http://ftp.debian.org/debian/dists/Debian10.4/main/installer-arm64/current/images/netboot/debian-installer/arm64/initrd.gz

wget http://ftp.debian.org/debian/dists/Debian10.4/main/installer-arm64/current/images/netboot/debian-installer/arm64/linux

Make a disk. To hold stuff.

Blahcat recommends 20G, but that’s the size of my Debian VM. I haven’t managed to fill up 12G yet — but, as said before, you do you.

qemu-img create -f qcow2 disk.qcow2 12G

Invoke the Installer

This is where I depart the most from Blahcat. Every time I followed their instructions, the resulting image was unable to connect to the internet, even though it ran a blasted net installer. The solution, in my case, was to force the emulation of an ethernet adapter (in addition to the one that Qemu automatically creates). Some of the command that follows is likely malformed, redundant, or both, but by golly it worked.

qemu-system-aarch64 -smp 2 -M virt -cpu cortex-a57 -m 1G \
    -initrd initrd.gz \
    -kernel linux -append "root=/dev/ram console=ttyAMA0" \
    -global virtio-blk-device.scsi=off \
    -device virtio-scsi-device,id=scsi \
    -drive file=disk.qcow2,id=rootimg,cache=unsafe,if=none \
    -device scsi-hd,drive=rootimg \
    -device e1000,netdev=net0 \
    -net nic \
    -netdev user,hostfwd=tcp:127.0.0.1:2222-:22,id=net0 \
    -nographic

During installation you’ll be asked to pick an Ethernet adapter; pick the Intel one and life is good.

Extract your fancy new kernel

Let it be known that I have no idea how half this stuff works, nor what nbd stands for. Essentially, you mount your new image, extract the kernel and initrd, and use them the next time you invoke the image.

sudo apt install nbd-client
sudo modprobe nbd max_part=8
sudo qemu-nbd --connect=/dev/nbd0 disk.qcow2
mkdir mnt
sudo mount /dev/nbd0p1 mnt
cp mnt/initrd.img-4.19.0-9-arm64 mnt/vmlinuz-4.19.0-9-arm64 .
sync
sudo umount /dev/nbd0p1
sudo nbd-client -d /dev/nbd0

Engage!

You should now be able to run your new, emulated system – and have internet access too!

qemu-system-aarch64 -smp 2 -M virt -cpu cortex-a57 -m 1G \
    -initrd initrd.img-4.19.0-9-arm64 \
    -kernel vmlinuz-4.19.0-9-arm64 \
    -append "root=/dev/sda2 console=ttyAMA0" \
    -global virtio-blk-device.scsi=off \
    -device virtio-scsi-device,id=scsi \
    -drive file=disk.qcow2,id=rootimg,cache=unsafe,if=none \
    -device scsi-hd,drive=rootimg \
    -device e1000,netdev=net0 \
    -net nic \
    -netdev user,hostfwd=tcp:127.0.0.1:2222-:22,id=net0 \
    -nographic