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s390x-unknown-none-softfloat

Tier: 2

IBM z/Architecture (s390x) code in ELF format for kernels, etc.

Target maintainers

@uweigand @cuviper

Requirements

This target is intended for kernel development on s390x only. 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 target does not assume existence of a FPU 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 Z System starting at Z10. Enabling additional target features or changing the -Ctarget-cpu may raise the ISA required from the z10 baseline.

extern "C" does not use a stable ABI and is subject to change between compiler or codegen backend versions.

The target only generates object files 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 target by adding it to the target list in bootstrap.toml:

[build]
target = ["s390x-unknown-none-softfloat"]

Building Rust programs

This target is not intended to build stand-alone binaries. You should only use it in conjunction with the kernel build toolchain.

Testing

As code generated by this target is intended to always be part of the kernel, there are no additional requirements for testing.

If you want to do native testing but do not have your own s390x machine, there are several options how to get access to one:

  • The IBM LinuxONE Community Cloud provides a self-service portal where you can create s390x virtual machine instances. These are intended for temporary use (limited to 120 days).

  • The IBM LinuxONE Open Source Cloud provides permanent access to s390x machines. This requires approval by IBM, which will normally be granted if you’re planning to use the machine to work on an open-source project that is relevant to the IBM Z ecosystem - the Rust compiler would certainly qualify.