Add armv5te-none-eabi and thumbv5te-none-eabi targets

[QuinnPainter]

Creates two new Tier 3 targets, armv5te-none-eabi and thumbv5te-none-eabi. They are for the same target architecture (armv5te), but one defaults to the A32 instruction set and the other defaults to T32. Based on the existing armv4t-none-eabi and thumbv4t-none-eabi targets.

My particular use case for these targets is Nintendo DS homebrew, but they should be usable for any armv5te system.

Going through the Tier 3 target policy:

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.)

That will be me.

Targets must use naming consistent with any existing targets.

Naming is consistent with previous targets.

Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility.

No ambiguity here.

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.

Doesn't create any legal issues.

The target must not introduce license incompatibilities.

This doesn't introduce any new licenses.

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

Yep.

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.

No new license requirements.

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.

Everything this uses is FOSS, no proprietary required.

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.

OK.

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.

OK.

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.

This is a bare-metal target with only support for core (and alloc, if the user provides an 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.

Documentation has been added.

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.

OK.

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.

OK.

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.

This doesn't break any other targets.

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.

No unnecessary unconditional features here.

[rust-highfive]

r? @fee1-dead

(rust-highfive has picked a reviewer for you, use r? to override)

[rust-highfive]

⚠️ Warning ⚠️

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

[fee1-dead]

I am not familiar with the targets themselves and not familiar with the process for adding a target. Re-rolling.

r? rust-lang/compiler

[nagisa]

Rust supports switching the “mode” via the (currently unstable) instruction_set attribute, so I would argue that describing this in terms of that attribute would make the intent here clearer:

Suggested change

	The `thumbv5te-none-eabi` target is the same as this one, but with THUMB code as the default.
	The `thumbv5te-none-eabi` target is the same as this one, but the instruction set defaults to `t32` instead of `a32`.

[nagisa]

This sentence is probably superfluous/excessive for the documentation of the very generic baremetal target that *-none-* tend to be. There are a wide variety of applications in which v5te has been used (phones, PDAs, etc. and more recently a Kindle which is also a common homebrew/custom firmware target.)

[QuinnPainter]

That's fair, the DS specific parts can be removed. I was mostly basing this off of armv4t-none-eabi, which makes particular note of the GBA.

[nagisa]

Similarly this DS-specific note is probably overly specific for the generic target that *v5te-none-eabi is.

[nagisa]

I would argue that the thumb_base::opts ought to be changed so that it is also applicable to the bare-metal a32 targets, since the baremetal a32 and t32 targets will be way more similar for the same architecture than the thumb* targets between different arm architecture revisions. That said, ultimately I’d be happy with any solution here that does not produce ~the same options for the two targets added here in very different ways. In particular the two different methods to obtain largely the same TargetOptions is both difficult to review and will be more difficult to maintain in the future.

[QuinnPainter]

Yeah, I was thinking the same. How about for now, I just modify armv5te-none-eabi to use thumb_base so the two new targets are consistent, and a new issue can be opened to make thumb_base more generic?

[nagisa]

@bors r+

[bors]

📌 Commit c227f0a has been approved by nagisa

It is now in the queue for this repository.

[nagisa]

Sorry for the delay reviewing this T_T

[bors]

⌛ Testing commit c227f0a with merge e76ec86bc6cc3849009e9fb49585f96483ec32e3...

[bors]

💥 Test timed out

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[QuinnPainter]

Hmm, seems like the test machine timed out trying to read crates.io? Maybe just give it a retry?

[bors]

⌛ Testing commit c227f0a with merge cba4a38...

[bors]

☀️ Test successful - checks-actions
Approved by: nagisa
Pushing cba4a38 to master...

[rust-timer]

Finished benchmarking commit (cba4a38): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean1	range	count2
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.7%	[1.5%, 1.9%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean1	range	count2
Regressions ❌ (primary)	2.1%	[2.1%, 2.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-2.9%	[-2.9%, -2.9%]	1
All ❌✅ (primary)	-0.4%	[-2.9%, 2.1%]	2

Footnotes

1. the arithmetic mean of the percent change ↩ ↩²

2. number of relevant changes ↩ ↩²