Tier 3 target proposal: bare-metal loongarch64

[heiher]

Proposal

This compiler MCP proposes new targets, loongarch64-unknown-none{-softfloat}, for bare-metal or "freestanding" loongarch64 binaries with no operating system, using ELF as the object format. This target is intended for firmware, kernels, modules, and other software running without an operating system.

Target Tier Policy Acknowledgements

A tier 3 target must have a designated developer or developers (the "target maintainers") on record to be CCed when issues arise regarding the target. (The mechanism to track and CC such developers may evolve over time.)

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

Targets must use naming consistent with any existing targets; for instance, a target for the same CPU or OS as an existing Rust target should use the same name for that CPU or OS. Targets should normally use the same names and naming conventions as used elsewhere in the broader ecosystem beyond Rust (such as in other toolchains), unless they have a very good reason to diverge. Changing the name of a target can be highly disruptive, especially once the target reaches a higher tier, so getting the name right is important even for a tier 3 target.

Target	Descriptions
loongarch64-unknown-none	LoongArch 64-bit, LP64D ABI (freestanding, hardfloat)
loongarch64-unknown-none-softfloat	LoongArch 64-bit, LP64S ABI (freestanding, softfloat)

ISA Docs

• LoongArch ELF psABI
• LoongArch Toolchain conventions

Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility. For example, if the name of the target makes people extremely likely to form incorrect beliefs about what it targets, the name should be changed or augmented to disambiguate it.

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Tier 3 targets may have unusual requirements to build or use, but must not create legal issues or impose onerous legal terms for the Rust project or for Rust developers or users.

There are no known legal issues or license incompatibilities.

Neither this policy nor any decisions made regarding targets shall create any binding agreement or estoppel by any party. If any member of an approving Rust team serves as one of the maintainers of a target, or has any legal or employment requirement (explicit or implicit) that might affect their decisions regarding a target, they must recuse themselves from any approval decisions regarding the target's tier status, though they may otherwise participate in discussion

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Tier 3 targets should attempt to implement as much of the standard libraries as possible and appropriate (core for most targets, alloc for targets that can support dynamic memory allocation, std for targets with an operating system or equivalent layer of system-provided functionality), but may leave some code unimplemented (either unavailable or stubbed out as appropriate), whether because the target makes it impossible to implement or challenging to implement. The authors of pull requests are not obligated to avoid calling any portions of the standard library on the basis of a tier 3 target not implementing those portions.

The loongarch64-unknown-none* target will implement core, and will support users using alloc with their own memory allocator. The loongarch64-unknown-none* target will not support std, and will not provide a default memory allocator.

The target must provide documentation for the Rust community explaining how to build for the target, using cross-compilation if possible. If the target supports running binaries, or running tests (even if they do not pass), the documentation must explain how to run such binaries or tests for the target, using emulation if possible or dedicated hardware if necessary.

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Tier 3 targets must not impose burden on the authors of pull requests, or other developers in the community, to maintain the target. In particular, do not post comments (automated or manual) on a PR that derail or suggest a block on the PR based on a tier 3 target. Do not send automated messages or notifications (via any medium, including via @) to a PR author or others involved with a PR regarding a tier 3 target, unless they have opted into such messages.

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Patches adding or updating tier 3 targets must not break any existing tier 2 or tier 1 target, and must not knowingly break another tier 3 target without approval of either the compiler team or the maintainers of the other tier 3 target.

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Mentors or Reviewers

r? @wesleywiser

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

cc @rust-lang/compiler @rust-lang/compiler-contributors

[rustbot]

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[heiher]

Most Rust freestanding/bare-metal targets use just -unknown-none here. Are the names loongarch64-unknown-none and loongarch64-unknown-none-softfloat suggested? or Any ideas are welcome. :)

Target	Descriptions
loongarch64-unknown-none	LoongArch 64-bit, LP64D ABI (freestanding, hardfloat)
loongarch64-unknown-none-softfloat	LoongArch 64-bit, LP64S ABI (freestanding, softfloat)

[wesleywiser]

@rustbot second

loongarch64-unknown-none and loongarch64-unkown-none-softfloat seem reasonable to me.

[apiraino]

@rustbot label -final-comment-period +major-change-accepted