Rust out-of-tree module

This is a basic template for an out-of-tree Linux kernel module written in Rust.

Please note that:

• The Rust support is experimental.

• The kernel that the module is built against needs to be Rust-enabled (CONFIG_RUST=y).

• The kernel tree (KDIR) requires the Rust metadata to be available. These are generated during the kernel build, but may not be available for installed/distributed kernels (the scripts that install/distribute kernel headers etc. for the different package systems and Linux distributions are not updated to take into account Rust support yet).

• All Rust symbols are EXPORT_SYMBOL_GPL.

Example:

$ make KDIR=.../linux-with-rust-support LLVM=1
make -C .../linux-with-rust-support M=$PWD
make[1]: Entering directory '.../linux-with-rust-support'
  RUSTC [M] .../rust-out-of-tree-module/rust_out_of_tree.o
  MODPOST .../rust-out-of-tree-module/Module.symvers
  CC [M]  .../rust-out-of-tree-module/rust_out_of_tree.mod.o
  LD [M]  .../rust-out-of-tree-module/rust_out_of_tree.ko
make[1]: Leaving directory '.../linux-with-rust-support'

[    1.076945] rust_out_of_tree: Rust out-of-tree sample (init)
[    1.084944] rust_out_of_tree: My numbers are [72, 108, 200]
[    1.085944] rust_out_of_tree: Rust out-of-tree sample (exit)

For details about the Rust support, see https://rust-for-linux.com.

For details about out-of-tree modules, see https://docs.kernel.org/kbuild/modules.html.

rust-analyzer

Rust for Linux (with https://lore.kernel.org/rust-for-linux/[email protected]/ applied) supports building a rust-project.json configuration for rust-analyzer, including for out-of-tree modules:

make -C .../linux-with-rust-support M=$PWD rust-analyzer

RP1 Rust Driver

This repo uses the basic template from the Rust for Linux project: https://github.com/Rust-for-Linux/rust-out-of-tree-module

Getting Rust on the Raspberry Pi 5

In order to get Rust on the raspberry pi 5, we need to compile a custom kernel.

This guide from raspberry pi is very useful, I follow many of the same exact steps but with some tweaks for LLVM: https://www.raspberrypi.com/documentation/computers/linux_kernel.html

• I used kernel version 6.8 on the raspberry pi fork.
  • https://github.com/raspberrypi/linux/tree/rpi-6.8.y
• Apply patch from Rust for Linux branch rust-pci to the pi kernel.
  • https://github.com/Rust-for-Linux/linux/tree/rust-pci
  • https://github.com/torvalds/linux/compare/master...Rust-for-Linux:linux:rust-pci.patch
• Run the kernel defconfig from the pi kernel guide, but with some tweaks:
  • make ARCH=arm64 LLVM=1 bcm2712_defconfig
  • Note the change from CROSS_COMPILE to LLVM because Rust uses the LLVM toolchains.
• Enable Rust support for arm64
  • Use the quick start guide to get depedencies set up: https://docs.kernel.org/rust/quick-start.html
  • Add select HAVE_RUST to arch/arm64/Kconfig
  • Edit scripts/generate_rust_target.rs so that it supports ARM64. I think I looked at what Asahi used for these options.
  • Use menuconfig to enable Rust support.
    • General Setup -> Rust support
    • Press z to show hidden options, then viewing the help for Rust support will show you the depends which are inhibiting the option.
    • I had to turn off MODVERSIONS to satisfy the depends for Rust support.
• Add ioremap to the rust helpers.c.
  • I think the ioremap supplied by CONFIG_IOREMAP_GENERIC doesn't let bindgen generate ioremap automatically so the helper is needed.
• Compile the kernel
  • See the linux kernel guide from raspberry pi above. The kernel compile and install to the sd card is very similar, but with LLVM instead of CROSS_COMPILE. These are the commands that are different:
  • make ARCH=arm64 LLVM=1 Image modules dtbs -j20
  • sudo env PATH=$PATH make ARCH=arm64 LLVM=1 INSTALL_MOD_PATH=sdcard/ext4 modules_install