Emulating Raspberry Pi 4 with Qemu

RasbperryPi4-qemu.md

Emulating Raspberry Pi 4 with Qemu

To be specific here, we're simply emulating Raspberry Pi OS (64-bit) in qemu. So it is as good for any other Raspberry Pis as it is for Raspberry Pi 4. :D

Hope it helps.

Shortcomings: No GUI yet, only console.

Steps

1. Download Raspberry Pi OS (64-bit) from Raspberry Pi operating system images.
   Here we downloaded Raspberry Pi OS (64-bit) with desktop, Kernel version: 6.1, Debian version: 11 (bullseye), Release date: May 3rd 2023, named 2023-05-03-raspios-bullseye-arm64.img. We put it in /home/mydir.
2. Install the required packages:

   $ # Cross compilers for arm64
   $ sudo apt install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu
   
   $ # Qemu itself
   $ sudo apt install qemu qemubuilder qemu-system-gui qemu-system-arm qemu-utils \
       qemu-system-data qemu-system

3. Build the Linux kernel for qemu arm64 (You can download the kernel from Kernel.org):

   $ wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.1.34.tar.xz
   $ tar xvJf linux-6.1.34.tar.xz
   $ cd linux-6.1.34
   
   $ # create a .config file
   $ ARCH=arm64 CROSS_COMPILE=/bin/aarch64-linux-gnu- make defconfig
   $ # Use the kvm_guest config as the base defconfig, which is suitable for qemu
   $ ARCH=arm64 CROSS_COMPILE=/bin/aarch64-linux-gnu- make kvm_guest.config
   $ # Build the kernel
   $ ARCH=arm64 CROSS_COMPILE=/bin/aarch64-linux-gnu- make -j8
   
   $ cp arch/arm64/boot/Image /home/mydir

4. Mount the image for enabling ssh and configuring username and password:
   1. Get the correct offset value with the help of fdisk utility:

      $ fdisk -l 2023-05-03-raspios-bullseye-arm64.img
      Disk 2023-05-03-raspios-bullseye-arm64.img: 4.11 GiB, 4412407808 bytes, 8617984 sectors
      Units: sectors of 1 * 512 = 512 bytes
      Sector size (logical/physical): 512 bytes / 512 bytes
      I/O size (minimum/optimal): 512 bytes / 512 bytes
      Disklabel type: dos
      Disk identifier: 0x3e247b30
      Device                                 Boot  Start     End Sectors  Size Id Type
      2023-05-03-raspios-bullseye-arm64.img1        8192  532479  524288  256M  c W95 FAT32 (LBA)
      2023-05-03-raspios-bullseye-arm64.img2      532480 8617983 8085504  3.9G 83 Linux

      As we can see, we have two partitions inside the downloaded image. The first device (partition) is the bootable partition, and the second one is the root filesystem. The first partition is what will be mounted as /boot in Raspberry Pi, and this is where we'll need to create some files.
      Obtain the correct offset of the first device by multiplying the start of the first partition (here 8192) by the sector size (here 512). Here it will be calculated as 8192 * 512 = 4194304
   2. Mount the image in /mnt/rpi directory:

      $ sudo mkdir /mnt/rpi
      $ sudo mount -o loop,offset=4194304 2023-05-03-raspios-bullseye-arm64.img /mnt/rpi

   3. Create a file named ssh to enable ssh:

      $ cd /mnt/rpi
      $ sudo touch ssh

   4. Additionally, create a file named userconf.txt in the same directory and put your desired username and password there, like <username>:<hashed-password> (might be better to leave the username as pi). This will be your default credentials:

      $ openssl passwd -6                                     # Generate the <hashed-password>
      $ echo 'pi:<hashed-password>' | sudo tee userconf.txt   # Put them inside `userconf.txt`

   5. Finally, unmount the image:

      $ sudo umount /mnt/rpi

5. Run qemu emulator:

   $ cd /home/mydir
   $ qemu-system-aarch64 -machine virt -cpu cortex-a72 -smp 6 -m 4G \
       -kernel Image -append "root=/dev/vda2 rootfstype=ext4 rw panic=0 console=ttyAMA0" \
       -drive format=raw,file=2023-05-03-raspios-bullseye-arm64.img,if=none,id=hd0,cache=writeback \
       -device virtio-blk,drive=hd0,bootindex=0 \
       -netdev user,id=mynet,hostfwd=tcp::2222-:22 \
       -device virtio-net-pci,netdev=mynet \
       -monitor telnet:127.0.0.1:5555,server,nowait

   This machine will be able to access the internet.
6. After the machine is completely booted up, you can login to it from your computer by using ssh and the username and password you specified:

   $ ssh -l pi localhost -p 2222

7. Done!

Troubleshooting

• If you had any problem with connecting to internet, it might be because of bad DNS configurations, and you should consider adding nameserver 8.8.8.8 to top of the file /etc/resolv.conf in the machine.
• You can access the qemu monitor console with:

  $ telnet localhost 5555