Add armv8r-none-eabihf target for the Cortex-R52.

[chrisnc]

No description provided.

[rustbot]

r? @WaffleLapkin

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[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

[WaffleLapkin]

What is the context there? Does the new target agree with the target policy? what is the reason for removing -unknown parts?

[moridinga]

What is the context there? Does the new target agree with the target policy? what is the reason for removing -unknown parts?

I think it is based on this text from the clang/llvm docs: The vendor needs to be specified only if there’s a relevant change, for instance between PC and Apple. Most of the time it can be omitted (and Unknown) will be assumed, which sets the defaults for the specified architecture.

[chrisnc]

Yes, as @moridinga says, unknown is unnecessary here, and the other {arm,thumb}*-none-eabi* targets don't include it, so I removed it from the v7r targets for consistency.

As for the armv8r addition, I think the operative clause of the target policy is this bullet:

• If introducing a new tier 2 or higher target that is identical to an existing Rust target except for the baseline expectations for the features or versions of CPUs, operating systems, libraries, runtime environments, and similar, then the proposed target must document to the satisfaction of the approving teams why the specific difference in baseline expectations provides sufficient value to justify a separate target.

This is a minor variation of the existing {arm,thumb}*-none-eabi* targets, just setting the version and minimum features for this specific sub-family, using the same convention as, e.g., thumbv7em-none-eabihf, of picking the least capable CPU that implements this version of the architecture and setting the default features to match. The R52 has been around several years now, and supported by LLVM going back to ~2016, but currently there's not a convenient way to target it with rust. armv7r-none-eabihf will work, but care must be taken because the set of floating-point features available differs substantially, and the defaults don't match any available R52 (and by default you won't get any v8 instructions of course).

Let me know which changes I should undo or any additional changes needed to align this PR with the target policy.

[WaffleLapkin]

r? @nagisa
(re-rolling assignment to someone who knows more about target policies, etc)

[chrisnc]

r? rust-lang/compiler

[chrisnc]

Bump?

[nagisa]

As for the armv8r addition, I think the operative clause of the target policy is this bullet:

Usually what we request target addition PRs to do is to copy over the ckecklist for the relevant tiers and confirm all the points are true, similar to what’s seen in this comment most recently.

[nagisa]

(also, really really sorry for the insane delay!)

[chrisnc]

Moved the minor changes to other targets to a separate PR which should be easier to merge: #113992.

[chrisnc]

I believe my earlier build error was due to a combination of having arm-none-eabi-gcc installed, but cc-rs not using it because it doesn't recognize this target. Made rust-lang/cc-rs#836 to add it. Building the toolchain using a patched version of cc-rs then correctly uses arm-none-eabi-gcc for compiler-rt, but there are still some errors. I'm a little fuzzy on why it worked when I don't have arm-none-eabi-gcc at all though.

[chrisnc]

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.)

I've designated myself in the platform support document.

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.

This target follows the naming pattern of other arm-none targets and matches how other toolchains refer to it.

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.

Not applicable here. armv8r unambiguously refers to the 32-bit Arm architecture, version 8, R-profile.

If possible, use only letters, numbers, dashes and underscores for the name. Periods (.) are known to cause issues in Cargo.

Check.

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.

Check.

The target must not introduce license incompatibilities.

Check.

Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).

Check.

The target must not cause the Rust tools or libraries built for any other host (even when supporting cross-compilation to the target) to depend on any new dependency less permissive than the Rust licensing policy. This applies whether the dependency is a Rust crate that would require adding new license exceptions (as specified by the tidy tool in the rust-lang/rust repository), or whether the dependency is a native library or binary. In other words, the introduction of the target must not cause a user installing or running a version of Rust or the Rust tools to be subject to any new license requirements.

Check.

Compiling, linking, and emitting functional binaries, libraries, or other code for the target (whether hosted on the target itself or cross-compiling from another target) must not depend on proprietary (non-FOSS) libraries. Host tools built for the target itself may depend on the ordinary runtime libraries supplied by the platform and commonly used by other applications built for the target, but those libraries must not be required for code generation for the target; cross-compilation to the target must not require such libraries at all. For instance, rustc built for the target may depend on a common proprietary C runtime library or console output library, but must not depend on a proprietary code generation library or code optimization library. Rust's license permits such combinations, but the Rust project has no interest in maintaining such combinations within the scope of Rust itself, even at tier 3.
"onerous" here is an intentionally subjective term. At a minimum, "onerous" legal/licensing terms include but are not limited to: non-disclosure requirements, non-compete requirements, contributor license agreements (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms, requirements conditional on the employer or employment of any particular Rust developers, revocable terms, any requirements that create liability for the Rust project or its developers or users, or any requirements that adversely affect the livelihood or prospects of the Rust project or its developers or users.

Check.

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 discussions.
This requirement does not prevent part or all of this policy from being cited in an explicit contract or work agreement (e.g. to implement or maintain support for a target). This requirement exists to ensure that a developer or team responsible for reviewing and approving a target does not face any legal threats or obligations that would prevent them from freely exercising their judgment in such approval, even if such judgment involves subjective matters or goes beyond the letter of these requirements.

Check.

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.

Par with other arm-none targets in this respect; core-only.

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.

Captured by arm-none platform support documentation and the additional platform support documentation in this PR.

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.
Backlinks such as those generated by the issue/PR tracker when linking to an issue or PR are not considered a violation of this policy, within reason. However, such messages (even on a separate repository) must not generate notifications to anyone involved with a PR who has not requested such notifications.

Check.

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.
In particular, this may come up when working on closely related targets, such as variations of the same architecture with different features. Avoid introducing unconditional uses of features that another variation of the target may not have; use conditional compilation or runtime detection, as appropriate, to let each target run code supported by that target.
Tier 3 targets must be able to produce assembly using at least one of rustc's supported backends from any host target.

This target is closely related to other arm-none targets, but does not interfere with them; the changes are strictly additive.

[chrisnc]

@rustbot ready

[wesleywiser]

Thanks @chrisnc!

@bors r+ rollup

[bors]

📌 Commit 9aff42e has been approved by wesleywiser

It is now in the queue for this repository.

[wllenyj]

Why can't the armv8r-none-eabihf target be installed by rustup?
It will note

$ rustup target add armv8r-none-eabihf
error: component 'rust-std' for target 'armv8r-none-eabihf' is unavailable for download for channel 'stable'

$ rustc -vV
rustc 1.79.0 (129f3b996 2024-06-10)
binary: rustc
commit-hash: 129f3b9964af4d4a709d1383930ade12dfe7c081
commit-date: 2024-06-10
host: aarch64-apple-darwin
release: 1.79.0
LLVM version: 18.1.7

[chrisnc]

@wllenyj this is because it's currently a Tier 3 target, so pre-built core is not available.
https://doc.rust-lang.org/nightly/rustc/target-tier-policy.html

You can build it yourself using:
https://doc.rust-lang.org/cargo/reference/unstable.html#build-std

[wllenyj]

@wllenyj this is because it's currently a Tier 3 target, so pre-built core is not available. https://doc.rust-lang.org/nightly/rustc/target-tier-policy.html

You can build it yourself using: https://doc.rust-lang.org/cargo/reference/unstable.html#build-std

oh, I got, thank you very much.