QEMU [FreeBSD WIKI]

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QEMU provides good support for system-level RISC-V emulation. A full %%FreeBSD%% system can be run using its ''%%virt%%'' platform.

To run %%FreeBSD%%/RISC-V, QEMU version 5.0 or later is required. This can be installed via [[https://www.freshports.org/emulators/qemu50/|emulators/qemu50]] or [[https://www.freshports.org/emulators/qemu-devel/|emulators/qemu-devel]].

Also required is the %%OpenSBI%% bootloader, which can be installed from the [[https://www.freshports.org/sysutils/opensbi/|sysutils/opensbi]] port or package.

===== Generate a root filesystem =====

If you have built %%FreeBSD%% by hand and would like to generate a root filesystem and bootable image, you can follow these steps. If you downloaded a bootable %%FreeBSD%% image, skip to [[#Boot FreeBSD]].

**Create root partition**

<code>
# Install the system to a staging directory
setenv ROOTFSDIR $HOME/rootfsstage
make TARGET=riscv DESTDIR=$ROOTFSDIR NO_ROOT=yes installworld
make TARGET=riscv DESTDIR=$ROOTFSDIR NO_ROOT=yes installkernel
make TARGET=riscv DESTDIR=$ROOTFSDIR NO_ROOT=yes distribution

# Make any desired tweaks to the system, e.g. /etc/fstab
echo "# Device                Mountpoint      FStype  Options         Dump    Pass#" > $ROOTFSDIR/etc/fstab
echo "/dev/gpt/rootfs         /               ufs     rw,noatime      1       1" >> $ROOTFSDIR/etc/fstab
echo "/dev/gpt/swapfs         none            swap    sw              0       0" >> $ROOTFSDIR/etc/fstab
echo "hostname=qemu" > $ROOTFSDIR/etc/rc.conf
# Add be sure to add them to METALOG
echo "./etc/fstab type=file uname=root gname=wheel mode=0644" >> $ROOTFSDIR/METALOG
echo "./etc/rc.conf type=file uname=root gname=wheel mode=0644" >> $ROOTFSDIR/METALOG

# Create a UFS root filesystem from that directory
cd $ROOTFSDIR
makefs -B little \
    -o label=rootfs -o version=2 -o softupdates=1 \
    -D -s 6g \
    rootfs.ufs METALOG
</code>

//Note: specify -s or -f to ensure the filesystem is created with free inodes//

**Create EFI partition**

<code>
# Copy the EFI bootloader
setenv EFIDIR $HOME/efistage
mkdir -p $EFIDIR/EFI/BOOT/
cp $ROOTFSDIR/boot/loader.efi $EFIDIR/EFI/BOOT/BOOTRISCV64.EFI

# Create an EFI partition (msdosfs)
makefs -t msdos \
    -o fat_type=32 -o sectors_per_cluster=1 -o volume_label=EFISYS \
    -s 50m \
    efi.part $EFIDIR
</code>

**Create Image File**

Now, to combine our root and EFI partitions into a final image file:

<code>
mkimg -s gpt -f raw \             # GPT partition scheme
    -p efi:=efi.part \
    -p freebsd-swap/swapfs::2G \  # Swap partition (optional)
    -p freebsd-ufs/rootfs:=rootfs.ufs \
    -o riscv.img
</code>

''%%riscv.img%%'' is the final output. You may clean up all other temporary objects as you choose.

===== Boot FreeBSD =====

To boot using u-boot, install [[https://www.freshports.org/sysutils/u-boot-qemu-riscv64|sysutils/u-boot-qemu-riscv64]].

<code>
qemu-system-riscv64 -machine virt -smp 2 -m 2048 -nographic \
    -bios /usr/local/share/opensbi/lp64/generic/firmware/fw_jump.elf \
    -kernel /usr/local/share/u-boot/u-boot-qemu-riscv64/u-boot.bin \
    -drive file=/path/to/riscv.img,format=raw,id=hd0 \
    -device virtio-blk-device,drive=hd0
</code>

The %%FreeBSD%% kernel can also be booted directly, skipping the u-boot and ''%%loader(8)%%'' stages. This can be useful for quicker turnaround during kernel development, but is in general less flexible compare to u-boot.

<code>
qemu-system-riscv64 -machine virt -smp 2 -m 2048 -nographic \
    -bios /path/to/opensbi/fw_jump.elf \
    -kernel /path/to/freebsd/kernel \
    -drive file=/path/to/riscv.img,format=raw,id=hd0 \
    -device virtio-blk-device,drive=hd0
</code>

===== Networking =====

There are two main networking backends offered by QEMU, user and tap. User-mode networking requires almost no configuration, but tap based networking offers better performance, and allows the guest to obtain its own IP address on the network.

==== Configure tap(4) (Optional) ====

If using tap(4) for networking (as opposed to user-mode networking), you will need to load the (tun)tap module(s) if not already loaded.

If %%FreeBSD%% >= 13:

<code>
sudo kldload if_tuntap
</code>

Else:

<code>
sudo kldload if_tun if_tap
</code>

Configure the network with tap(4):

<code>
ifconfig tap0 create up
ifconfig bridge0 create up
ifconfig bridge0 addm em0 addm tap0 # em0 might depend on your ethernet device
</code>

==== User Networking ====

Add the following arguments to the QEMU commandline:

<code>
-netdev user,id=net0,ipv6=off,hostfwd=tcp::8022-:22 -device virtio-net-device,netdev=net0
</code>

This will forward port 8022 on the host to port 22 in the guest, meaning you can connect via ssh(1):

<code>
$ ssh -p 8022 root@localhost
</code>

==== Tap Networking ====

Add the following arguments to the QEMU commandline.

<code>
# ifname points to your tap device of choice
-netdev tap,ifname=tap0,script=no,id=net0 -device virtio-net-device,netdev=net0
</code>

===== Tips & Tricks =====

==== Commandline arguments ====

You can specify kernel commandline arguments via QEMU's ''%%-append%%'' option. For example:

<code>
-append "-v vfs.root.mountfrom=/dev/vtbd1p3"
</code>

The ''%%-v%%'' argument enables verbose boot messages, while the variable assignment instructs the system to attempt to mount root from ''%%/dev/vtbd1p3%%''. These will be ignored if booting with loader(8).