The nightlier feature enables 8 and 16-bit atomics, but requires patching LLVM. Building the compiler is computationally expensive, so it may take quite a bit of time. See the system requirements for building the rust compiler for more specifics.

1. Clone the rust source and checkout this specific commit:

   git clone https://github.com/rust-lang/rust.git
   cd rust
   git checkout 3a8e71385940c2f02ec4b23876c0a36fd09bdefe
   

2. Configure the build script to use rust-lld and optionally remove unnecessary targets to speed up the LLVM build:

   cp config.toml.example config.toml
   # Set lld to true
   sed -i 's/#lld = false/lld = true/' config.toml
   # Only build the MIPS and X86 targets
   sed -i 's/#targets.*$/targets = "Mips;X86"/' config.toml
   # Don't build any experimental targets
   sed -i 's/#experimental-targets.*$/experimental-targets = ""/' config.toml
   

3. Patch LLVM.

   git submodule update --init --progress src/llvm-project
   cd src/llvm-project
   git apply /path/to/patches/llvm_atomic_fence.patch
   

4. Build the rust compiler:

   # For the initial build
   ./x.py build -i library/std
   # To rebuild
   ./x.py build -i library/std --keep-stage 1
   

5. Create a new toolchain with the patched compiler:

   rustup toolchain link psx build/x86_64-unknown-linux-gnu/stage1
   

   where psx is the name for the new toolchain.

6. When using cargo-psx, make sure to set the toolchain argument to psx.

   cargo psx run --toolchain psx