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Recently I assembled a ClockworkPi DevTerm R-01[1], a cyberdeck-like terminal with a RISC-V[2] compute module. While the retro-future design of the DevTerm really appealed to me, and I've also been wanting to work with RISC-V for a while to learn a new architecture making the R-01 a perfect esoteric project platform.
After trying out a few things like DOSBox[3], Surf[4], and ScummVM[5], I found the Allwinner D1[6] RISC-V chip wasn't powerful enough to do much other than some basic window management, Interactive Fiction[7], and browsing `gopher://` with Bombadillo[8]. However I still wanted to use it as a terminal to access other systems, which lead me to attempting to install Tailscale[9] to leverage the mesh VPN and other features.
Installing `tailscale` was un-eventful, as it's had RISC-V support[10] for a while, and following the install guide did what was expected. The problem is `tailscaled` fails due to the required `tun` kernel module missing in the 5.4.61 kernel running on the DevTerm.
Jan 26 02:25:17 localhost systemd[1]: Started Tailscale node agent. Jan 26 02:25:17 localhost tailscaled[1074605]: wgengine.NewUserspaceEngine(tun "tailscale0") ... Jan 26 02:25:17 localhost tailscaled[1074605]: Linux kernel version: 5.4.61 Jan 26 02:25:17 localhost tailscaled[1074605]: is CONFIG_TUN enabled in your kernel? `modprobe tun` failed with: modprobe: FATAL: Module tun not found in directory /lib/modules/5.4.61 Jan 26 02:25:19 localhost tailscaled[1074605]: tun module not loaded nor found on disk Jan 26 02:25:19 localhost tailscaled[1074605]: wgengine.NewUserspaceEngine(tun "tailscale0") error: tstun.New("tailscale0"): CreateTUN("tailscale0") failed; /dev/net/tun does not exist Jan 26 02:25:19 localhost tailscaled[1074605]: flushing log. Jan 26 02:25:19 localhost tailscaled[1074605]: logger closing down
The first step was finding if the R-01 kernel source was available so re-build the exact kernel version and include the `tun` module by setting `CONFIG_TUN=m`. Looking around the ClockworkPi website, Discord, and Github I eventually found the How to Compile Kernel[11] documentation. This had links to the original source and the toolchain.
Since the R-01 isn't exactly fast, cross-building this on a x86 system was required. My personal Debian server is a bit of mess when it comes to package pinning, so I created a new 8 CPU, 8GiB memory virtual machine in qemu and install Ubuntu 22.04 "Jammy Jellyfish"[12] since that's what the R-01 is running and what ClockworkPi has in it's documentation.
After setting up the VM, install required packages for cross-building the kernel,
sudo apt-get install gcc-11-riscv64-linux-gnu binutils-riscv64-linux-gnu qemu-user-static build-essential git wget curl vim libncurses-dev flex automake autoconf bison libssl-dev
Clone the kernel source[13] into `~/git`,
mkdir ~/git git clone https://github.com/cuu/last_linux-5.4.git
Download the ClockworkPi toolchain from https://github.com/cuu/toolchain-thead-glibc[14], which is a README pointing to a Mega link. While it's a bit concerning coming from Mega, since it's a tarball and running in a VM it's not that risky. There's also a section on installing the official RISC-V toolchain which is another option, but requires additional building.
Untar in home directory,
cd ~ tar -xvzf riscv64-glibc-gcc-thead_20200702.tar.gz
Copy the running kernel config in `/proc/config.gz` on the DevTerm to the VM. The `config.gz` contains the configuration for how the running `5.4.61` kernel was configured and is loaded to set everything the exact same way when building the new kernel.
cd ~/git/last_linux-5.4 scp cpi@devterm:/proc/config.gz . gunzip config.gz mv config .config
There are two ways to enable the TUN/TAP module,
Edit `.config` and set `CONFIG_TUN=m`
or
Interactively run `menuconfig` and set it in `Device Drivers -> Network device support -> Universal TUN/TAP device driver support`
export PATH=~/riscv64-glibc-gcc-thead_20200702/bin/:$PATH make LOCALVERSION= CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv menuconfig
Build the kernel using the provided `m.sh` script, but first edit it to include the `PATH` for the toolchain and `LOCALVERSION=`. If `LOCALVERSION=` isn't set then the kernel version will include a `+` at the end and modules will not load due to a version mis-match,
export PATH=~/riscv64-glibc-gcc-thead_20200702/bin/:$PATH make LOCALVERSION= CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv make LOCALVERSION= CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv INSTALL_MOD_PATH=test/rootfs/ modules_install make LOCALVERSION= CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv INSTALL_PATH=test/boot/ zinstall mkdir -p test/boot/ cp arch/riscv/boot/dts/sunxi/board.dtb test/boot/
Run `./m.sh` and wait a few minutes while it builds.
When successful, the new kernel and modules are in `test/boot/`
Create a tarball of the new modules and copy them to the DevTerm,
cd ~/git/last_linux-5.4/test/rootfs/lib/modules tar -cvzf 5.4.61.modules.tar.gz 5.4.61/ scp 5.4.61.modules.tar.gz cpi@devterm:~
On the DevTerm, backup original modules directory,
cd /lib/modules sudo mv 5.4.61 5.4.61.orig
and untar the new modules directory,
cd /lib/modules sudo tar -xvzf ~/5.4.61.modules.tar.gz
Load the new TUN/TAP Module,
sudo modprobe tun
If successfull `dmesg` will show,
tun: Universal TUN/TAP device driver, 1.6
Now that the TUN/TAP module is loaded, start `tailscaled` and finish setting up Tailscale,
sudo service tailscaled start sudo tailscale up
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