loongarch*-unknown-none*

Tier: 2

Freestanding/bare-metal LoongArch64 binaries in ELF format: firmware, kernels, etc.

Target maintainers

• WANG Rui wangrui@loongson.cn
• WANG Xuerui git@xen0n.name

Requirements

This target is cross-compiled. There is no support for std. There is no default allocator, but it's possible to use alloc by supplying an allocator.

The *-softfloat target does not assume existence of FPU or any other LoongArch ISA extension, and does not make use of any non-GPR register. This allows the generated code to run in environments, such as kernels, which may need to avoid the use of such registers or which may have special considerations about the use of such registers (e.g. saving and restoring them to avoid breaking userspace code using the same registers). You can change code generation to use additional CPU features via the -C target-feature= codegen options to rustc, or via the #[target_feature] mechanism within Rust code.

By default, code generated with the soft-float target should run on any LoongArch64 hardware, with the hard-float target additionally requiring an FPU; enabling additional target features may raise this baseline.

Code generated with the targets will use the small code model by default. You can change this using the -C code-model= option to rustc.

On loongarch64-unknown-none*, extern "C" uses the architecture's standard calling convention.

The targets generate binaries in the ELF format. Any alternate formats or special considerations for binary layout will require linker options or linker scripts.

Building the target

You can build Rust with support for the targets by adding them to the target list in config.toml:

[build]
build-stage = 1
target = [
  "loongarch64-unknown-none",
  "loongarch64-unknown-none-softfloat",
]

Testing

As the targets support a variety of different environments and do not support std, they do not support running the Rust test suite.

Building Rust programs

Starting with Rust 1.74, precompiled artifacts are provided via rustup:

# install cross-compile toolchain
rustup target add loongarch64-unknown-none
# target flag may be used with any cargo or rustc command
cargo build --target loongarch64-unknown-none

Cross-compilation toolchains and C code

For cross builds, you will need an appropriate LoongArch C/C++ toolchain for linking, or if you want to compile C code along with Rust (such as for Rust crates with C dependencies).

Rust may be able to use an loongarch64-unknown-linux-gnu- toolchain with appropriate standalone flags to build for this toolchain (depending on the assumptions of that toolchain, see below), or you may wish to use a separate loongarch64-unknown-none toolchain.

On some LoongArch hosts that use ELF binaries, you may be able to use the host C toolchain, if it does not introduce assumptions about the host environment that don't match the expectations of a standalone environment. Otherwise, you may need a separate toolchain for standalone/freestanding development, just as when cross-compiling from a non-LoongArch platform.