How to compile Rust and LLVM for ESP32 on a Raspberry Pi (aarch64)
ESP32 is a series of microcontrollers that has the particularity to have both integrated Bluetooth and Wi-Fi. It makes it the perfect microcontroller when you need low-power, networked, and smart hardware that doesn't require an OS.
I had to run compile and run Rust code on an ESP32. Unfortunately, they don't run a traditional architecture but the Xtensa instruction set that is currently not officially supported by the Rust compiler.
The esp-rs GitHub organization contains the fork of the Rust compiler to support the Xtensa architecture.
Unfortunately, it seems that the
src/llvm-project submodule is out of date and does not support the
arm64) architecture, as when trying to follow the instructions I encountered the following error:
cargo:warning=cc: error: esp32/rust/src/llvm-project/compiler-rt/lib/builtins/aarch64/lse.S: No such file or directory cargo:warning=cc: fatal error: no input files cargo:warning=compilation terminated. exit status: 1
Which, according to this issue, is due to an outdated LLVM version.
Here is how I fixed the build and successfully built Rust and LLVM to compile Rust binaries for ESP32:
You will need at least 20GB of free space and a Rust toolchain: https://rustup.rs.
# starting from $HOME $ mkdir esp32 $ cd esp32 $ git clone https://github.com/esp-rs/rust.git $ cd rust
Here is the trick: you need to update the
$ git submodule update --init --recursive --remote src/llvm-project
Then, you can finally build Rust (warning: it will take a lot of time, so I recommend to run it for the night):
$ ./configure --experimental-targets=Xtensa $ python3 x.py dist --stage 2
# still in esp32/rust $ rustup toolchain link esp `pwd`/build/aarch64-unknown-linux-gnu/stage2
Still in your recently cloned
rust folder (warning: it will take a lot of time, so I recommend to run it for the night):
$ cd src/llvm-project $ mkdir build $ cd build $ cmake -G Ninja -DLLVM_ENABLE_PROJECTS='clang' -DCMAKE_BUILD_TYPE=Release ../llvm $ cmake --build . $ export PATH="$HOME/esp32/rust/src/llvm-project/build/bin:$PATH"
Your Rust toolcahin for ESP32 is now set up!
You can check it by running:
$ rustc --print target-list | grep xtensa
$ which clang
Which should return your newly built
See you tomorrow for a post on how to build and flash a Rust program to an ESP32.