Compiling slint for riscv64-musl (LicheeRV Nano) - which toolchain to use and what to expect?

[sandreas]

Hello,

I would like to compile a slint app for riscv64-musl (LicheeRV Nano) and ran into some issues, mainly not having several libraries / linker issues, e.g. with libinput, libgbm and libxkbcom. I partially succeeded with implementing manual framebuffer rendering, but I would love to use the linuxkms-noseat backend with renderer-software.

The sourcecode of the project I'm trying to compile is as simple as it gets:
https://github.com/sandreas/rust-slint-riscv64-musl-demo

The file .cargo/config.toml contains instructions on using the linker and the sysroot:

[target.riscv64gc-unknown-linux-musl]
linker = "riscv64-linux-musl-gcc"
rustflags = ["-C", "link-arg=--sysroot=/home/andreas/projects/scpcom/LicheeSG-Nano-Build/buildroot/output/cvitek_SG200X_musl_riscv64/host/riscv64-buildroot-linux-musl/sysroot"]

The build magic happens in the build-licherv.sh, where I setup the toolchain locations and enable the features (slint/backend-linuxkms-noseat,slint/renderer-software,slint/compat-1-2) to use the software renderer.

Here are the toolchains I tried and failed:

forked imagebuilder buildroot toolchain
To build a microSD card image for the LicheeRV Nano, there is an official github repository (which is pretty old and unstable) and a modernized and improved one from scpcom: https://github.com/scpcom/LicheeSG-Nano-Build/
After building the image, I pointed to the sysroot of the image builder and noticed that it is just too old and lacks important features like zifencei.

prebuilt toolchain
After this I downloaded the precompiled toolchain from https://musl.cc/#binaries, extracted it to $HOME/riscv64-linux-musl-cross/.

Unfortunately this toolchain seems to lack libinput, libgbm and libxkbcom - collecting the missing riscv64 ones together from from alpine packages :

• https://dl-cdn.alpinelinux.org/v3.22/community/riscv64/libinput-libs-1.28.1-r0.apk
• https://dl-cdn.alpinelinux.org/v3.22/main/riscv64/libxkbcommon-1.8.1-r2.apk
• https://dl-cdn.alpinelinux.org/v3.22/main/riscv64/mesa-gbm-25.1.9-r0.apk

unfortunately did not succeed - some weird errors with the linking process.

manually built toolchain

Currently, I'm manually building the toolchain from https://github.com/riscv-collab/riscv-gnu-toolchain via:

git clone https://github.com/riscv-collab/riscv-gnu-toolchain
cd riscv-gnu-toolchain
./configure --prefix=/opt/riscv --enable-multilib
make musl

I would love to have some official statement regarding riscv64-musl and in the best case some instructions or documentation on how to build a Slint app for this platform. I know that you are trying to make a living of the embedded stuff, but since my app will be open source, I think everyone would benefit :-)

[tronical]

I don't see any issues with riscv in general, except that I think the skia renderer won't compile.

Regarding musl: The lack of dlopen will be a problem in some places. I think glutin requires it, so than will rule out OpenGL rendering. The same goes for Wayland support via winit.

So just linuxkms backend with -noseat and the Slint software renderer might work with musl.

The libinput etc libraries are a hard requirement though.

[sandreas]

Thank you for your quick response.

So just linuxkms backend with -noseat and the Slint software renderer might work with musl.

Yeah that's what I'm using in my demo project from above. Unfortunately the available toolchains do not have the required libraries installed (libinput, libgbm and libxkbcom (libseat is optional disabled in the project).

I was hoping for instructions on how to do it right...

• How would I integrate the required libraries into the toolchain?
  • Is it maybe enough to just extract them from the apk files and put them in the right place or is there a version dependency?
• Is the Cargo.toml and .cargo/config.toml in the demo project correct or is there something that needs to be adjusted?
• Is there maybe an official toolchain or docker image, so that I don't need to setup my own custom toolchain?

Thank you.

sandreas

[tronical]

Unfortunately, I don't know off-hand how to integrate these into your toolchain. Eventually, those will have to be compiled or cross-compiled against musl, I suppose. Once integrated and peg-config works, no further changes on the Slint side should be necessary, i.e. no changes to Cargo.toml or the like.

That said, we do have a riscv docker image that should have everything needed to compile with linuxkms-noseat and cross. You can find the Cross.toml config to use for that at https://github.com/slint-ui/slint/blob/master/Cross.toml . Note that this is riscv64gc and it uses glibc, not musl.

[sandreas]

Cool thank you!

That said, we do have a riscv docker image that should have everything needed to compile with linuxkms-noseat and cross.

That would be awesome.

Note that this is riscv64gc and it uses glibc, not musl.

Yeah, that's a problem. The whole platform is built on musl, so glibc won't really help. I noticed that even cross-rs/cross does not supply modern Docker Images for riscv64-musl (the latest is Ubuntu-22.04 with ghcr.io/rust-cross/rust-musl-cross:riscv64gc-unknown-linux-musl). It seems that this image is too old and pre-build actions are not gonna work because the mirrors are already down or never existed:

# Cross.toml


# debug via
# docker run -it ghcr.io/rust-cross/rust-musl-cross:riscv64gc-unknown-linux-musl /bin/bash
[target.riscv64gc-unknown-linux-musl]
image = "ghcr.io/rust-cross/rust-musl-cross:riscv64gc-unknown-linux-musl"
linker = "riscv64-linux-gnu-gcc"
rustflags = ["-C", "link-args=-static"]

pre-build = [
    "dpkg --add-architecture riskv64",
    "apt-get update",
    "apt-get install --assume-yes python3 python3-pip libfontconfig1-dev clang ninja-build" # for later add slint requirements: libfontconfig1-dev:riscv64 libxcb1-dev:riscv64 libxcb-render0-dev:riscv64 libxcb-shape0-dev:riscv64 libxcb-xfixes0-dev:riscv64 libxkbcommon-dev:riscv64 libinput-dev:riscv64 libgbm-dev:riscv64 libstdc++-10-dev:riscv64
]

[build.env]
passthrough = [
    "PKG_CONFIG_ALLOW_CROSS=1",
    "PKG_CONFIG_PATH=/usr/lib/riscv64-linux-musl/pkgconfig",
    # In the absence of a sysroot, the header files we install earlier (such as libfontconfig1-dev:riscv64) are in /usr/include
    # so remember to teach bindgen to also look there, despite its --target.
    "BINDGEN_EXTRA_CLANG_ARGS_riscv64gc_unknown_linux_musl=-I/usr/include",
    "SLINT_BACKEND_LINUXFB=1",
    "SLINT_NO_QT",
    "SLINT_STYLE",
    "SLINT_TEST_FILTER",
    "SLINT_INTERPRETER_ERROR_WHITELIST"
]

So maybe an upgrade of the image to ubuntu-24.04 would be required for cross-rs/cross...

Would you consider adding riscv64-musl, if I convince the cross team to update the riscv64-musl image?

[sandreas]

Ok, so I solved the problem with Cross via customized Docker- however, I would love to see and official riscv64-musl Dockerfile for slint.

[tronical]

I have no objections against a musl setup if somebody would like to contribute and maintain it.

I‘m curious, what’s the main driver for using musl on an embedded Linux system that drives a UI?

[sandreas]

I‘m curious, what’s the main driver for using musl on an embedded Linux system that drives a UI?

I'm working on an Open Source portable audio player inspired by the iPod Nano 7g from Apple, but repairable and you can build it yourself with only basic soldering skills. It's in a very early state. The working title of the project is Resonance (Player)... but this might change.
Unfortunately the display driver only seems to support BA24 - which is not yet supported by slint (see #9862)

The planned Hardware Stack:

• Measurements: ~70mm x 40mm x 15mm
• LicheeRV Nano (riscv64-musl)
• Apple USB-C to AudioJack Adapter (good enough audio quality, small, cheap and supports all headphone vendors)
• TP4057 USB-C Battery charging module (extremely small)
• 1000mah - 2000mah Lipo Battery (depending on the expected drain and space in the case)
• JST 1.25 Battery connector (very small, should fit in the case)
• 3D printed case that fits all the components
• Optional: MAX17043 Battery fuel gauge (to accurately measure battery percentage)
• 2.28" Touch LCD
• 5 to 7 Buttons - 1 Home button, 1 Power Button and Control buttons (vol+, next, play/pause, prev, vol-)

The planned software stack:

• Scpcom LicheeRV Nano Fork (https://github.com/scpcom/LicheeSG-Nano-Build)
• Rust / Slint (for UI)
• Cross (for compiling)
• Awedio crate (for audio)

References:

• Wishlist for building a music player (DAP) on top of this work scpcom/LicheeSG-Nano-Build#10
• Restore support for LCDs as in official images (e.g. ST7701) scpcom/LicheeSG-Nano-Build#17
• Instructions on how to integrate a custom Rust / Slint project scpcom/LicheeSG-Nano-Build#19
• Support for FB Renderer Format DrmFourcc(BA24) #9862

Here are some pictures:

Size comparison inner components

Display size comparison

Working display

Slint showing on the display via custom framebuffer implementation

[sandreas]

Ok, here are the steps to build a Slint UI for riscv64-musl (e.g. LicheeRV Nano)

• Add Cross to you project
• Add a Cross.toml to your project using the custom docker image https://hub.docker.com/r/sandreas/cross-riscv64-linux-musl (see my cross fork for the docker image changes)
• Build the project via cross build --no-default-features --features "slint/backend-linuxkms-noseat,slint/renderer-software,slint/compat-1-2" --target riscv64gc-unknown-linux-musl --release

For a full demo project see https://github.com/sandreas/rust-slint-riscv64-musl-demo. Be aware that you need a supported renderer format for the slint app to work (see #9862)