Update the arm-* and aarch64-* platform docs. #146419

thejpster · 2025-09-10T18:31:19Z

This PR updates some of the arm*-unknown-none target docs, and adds some missing target pages.

aarch64-none-elf and aarch64-none-elf-softfloat

The Rust Embedded Devices Working Group's Arm Team is added as a maintainer, and a target page is added. Links are added to the EDWG's support crates for this target.

armv7a-none-eabi and armv7a-none-eabihf

The Rust Embedded Devices Working Group's Arm Team is added as a maintainer, and a target page is added. Links are added to the EDWG's support crates for this target.

armv7r-none-eabi and armv7r-none-eabihf

The Rust Embedded Devices Working Group's Arm Team is added as a maintainer, and the target page is split from the Big Endian versions. Links are added to the EDWG's support crates for this target.

armebv7r-none-eabi and armveb7r-none-eabihf

The target page is split from the Little Endian versions. No change in maintainers.

I have agreement to add EDWG/T-Arm as maintainers, which was voted upon in their repo.

rustbot · 2025-09-10T18:31:23Z

Some changes occurred in src/doc/rustc/src/platform-support

cc @Noratrieb

rustbot · 2025-09-10T18:31:25Z

r? @lcnr

rustbot has assigned @lcnr.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

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The Rust Embedded Devices Working Group (wg-embedded) Arm Team (t-arm) agreed to listed as maintainers of: * aarch64-unknown-none * aarch64-unknown-none-softfloat * armv7a-none-eabi * armv7r-none-eabi * armv7r-none-eabihf The aarch64-unknown-none* target didn't have a page so I added it. wg-embedded t-arm did not want to take over: * armebv7r-none-eabi * armebv7r-none-eabihf So I gave them their own target page. The current maintainer remains.

thejpster · 2025-09-10T18:52:36Z

Force-pushed with fixed markdown formatting.

src/doc/rustc/src/platform-support/armv7a-none-eabi.md

From #1.

src/doc/rustc/src/platform-support/aarch64-unknown-none.md

lcnr · 2025-09-11T10:11:43Z

r? @workingjubilee maybe?

rustbot · 2025-09-11T10:11:47Z

workingjubilee is currently at their maximum review capacity.
They may take a while to respond.

workingjubilee

I may find more nits but the maintainer assent one is blocking, I think.

View changes since this review

src/doc/rustc/src/platform-support/aarch64-unknown-none.md

workingjubilee · 2025-09-11T20:44:38Z

src/doc/rustc/src/platform-support/armebv7r-none-eabi.md

+
+## Target maintainers
+
+* [@chrisnc](https://github.com/chrisnc)


Uhm. Hrm.

@chrisnc Do you assent?

@thejpster I am not sure I have seen an assent by Chris to maintain this specific target variant.

The armebv7r and armv7r targets were on the same page, and so I concluded Chris was the maintainer for both. Pretty sure he wrote the page back in 90893e4.

https://doc.rust-lang.org/beta/rustc/platform-support/armv7r-none-eabi.html

The format for these was updated a while ago to drop the bullet points for ease of copy-pasting the usernames in GitHub issues and PRs. Please drop those, no matter who's being listed here (and in all the other files) :)

Oh, you're right, I got confused.

I think it would still be helpful to have assent here on this new split and shared responsibility and such.

I have been provided with more information on the context it was assented to, that @chrisnc both is fine with the EDWG helping out and does not want to impede them but neither is he interested in definitely becoming part of that team. I am deciding it is trustworthy enough for this to go ahead, as we can always roll back changes if more information comes to light, I just wanted enough information to be able to presume the situation was correct.

Gelbpunkt

I only looked at the aarch64 document since that's what I'm most familiar with, most of my comments should also apply to the other documents from what I can tell. I'm very happy about more extensive documentation, this is a fairly good first step.

View changes since this review

src/doc/rustc/src/platform-support/aarch64-unknown-none.md

Gelbpunkt · 2025-09-12T08:31:04Z

src/doc/rustc/src/platform-support/aarch64-unknown-none.md

+## Start-up and Low-Level Code
+
+The [Rust Embedded Devices Working Group Arm Team] maintain the
+[`aarch64-cpu`] crate, which may be useful for writing bare-metal code using
+this target.
+
+The *TrustedFirmware* group also maintain [Rust crates for this
+target](https://github.com/ArmFirmwareCrates).
+
+[`aarch64-cpu`]: https://docs.rs/aarch64-cpu


I'm not really sure how the maintainers feel about endorsing third-party crates like this. I think this section could just be dropped and, if you really want to have some start-up code, replaced with a tiny linker script + assembly + Rust entrypoint example when e.g. booting with the Linux boot protocol.

For many targets the code required is more than can fit into a target doc, and often involves multiple files that would be tedious and error prone to copy-paste into a new project. ArmFirmwareCrates is from Arm themselves, so it seemed legit to refer to it. But I can take it out.

I personally find it pretty hard to get started with many of these targets so I think giving people links to code that works and runs is very useful. I’m happy to not have it here, but I don’t know where else it would go.

For a target, if the maintainers think it worthwhile to recommend a crate that deals with the special needs of that target, then we generally do not impede such. Often, external software is required anyways for a target, e.g. specialty linkers or compilers or headers or... whatever. If quite a lot of such supplemental material is needed, it may come as an advisory against maintaining the target at all, but this doesn't seem to rise to such a threshold.

Gelbpunkt · 2025-09-12T08:32:19Z

src/doc/rustc/src/platform-support/armebv7r-none-eabi.md

+
+## Target maintainers
+
+* [@chrisnc](https://github.com/chrisnc)


The format for these was updated a while ago to drop the bullet points for ease of copy-pasting the usernames in GitHub issues and PRs. Please drop those, no matter who's being listed here (and in all the other files) :)

…-metal targets

thejpster · 2025-09-12T19:28:06Z

The format for these was updated a while ago to drop the bullet points for ease of copy-pasting the usernames in GitHub issues and PRs

It seems the existing target docs were not updated when this rule came in. I'm removed the bullets for all the targets maintained by the Rust Embedded Devices Working Group's Arm Team as requested.

Removes a bunch of information that isn't, strictly speaking, target specific.

workingjubilee

@thejpster This looks good to go. I believe you are making some final small edits per our conversation, please ping me again when they're in and I'll take a quick glance at them.

View changes since this review

This is important to note, as it affects how easy it is to build a binary, and that `#![no_std]` is mandatory. A different PR should probably add this to all the other platform pages.

thejpster · 2025-09-13T18:27:32Z

Notes added to all the arm-none-, thumb-none-* and aarch64-unknown-none-* pages noting that they are no_std only, as discussed.

workingjubilee · 2025-09-13T18:29:09Z

looks good to me!

@bors r+ rollup

bors · 2025-09-13T18:29:12Z

📌 Commit afd324a has been approved by workingjubilee

It is now in the queue for this repository.

Rollup of 8 pull requests Successful merges: - #113095 (Document `become` keyword) - #146159 (Some hygiene doc improvements) - #146171 (tidy: check that error messages don't start with a capitalized letter) - #146419 (Update the arm-* and aarch64-* platform docs.) - #146473 (Revert "Constify SystemTime methods") - #146506 (Fix small typo in check-cfg.md) - #146517 (fix Condvar::wait_timeout docs) - #146521 (document `core::ffi::VaArgSafe`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #146419 - thejpster:update-arm-target-docs, r=workingjubilee Update the arm-* and aarch64-* platform docs. This PR updates some of the arm*-unknown-none target docs, and adds some missing target pages. ## aarch64-none-elf and aarch64-none-elf-softfloat The Rust Embedded Devices Working Group's Arm Team is added as a maintainer, and a target page is added. Links are added to the EDWG's support crates for this target. ## armv7a-none-eabi and armv7a-none-eabihf The Rust Embedded Devices Working Group's Arm Team is added as a maintainer, and a target page is added. Links are added to the EDWG's support crates for this target. ## armv7r-none-eabi and armv7r-none-eabihf The Rust Embedded Devices Working Group's Arm Team is added as a maintainer, and the target page is split from the Big Endian versions. Links are added to the EDWG's support crates for this target. ## armebv7r-none-eabi and armveb7r-none-eabihf The target page is split from the Little Endian versions. No change in maintainers. I have agreement to add EDWG/T-Arm as maintainers, which was voted upon in [their repo](rust-embedded/wg#851).

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 10, 2025

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thejpster force-pushed the update-arm-target-docs branch from 8a54175 to faf0e14 Compare September 10, 2025 18:51

fbstj reviewed Sep 10, 2025

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Pick up changes from robamu that I missed.

f1abb70

From #1.

thejpster force-pushed the update-arm-target-docs branch from 827e2cd to f1abb70 Compare September 10, 2025 19:31

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workingjubilee requested changes Sep 10, 2025

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thejpster added 3 commits September 10, 2025 23:36

Add missing links in platform-support.md

3d3769a

Add aarch64-unknown-none to SUMMARY.md

5a74222

Update aarch64-unknown-none.md to include -softfloat too

409a1fb

rustbot assigned workingjubilee and unassigned lcnr Sep 11, 2025

workingjubilee requested changes Sep 11, 2025

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 11, 2025

thejpster added 2 commits September 11, 2025 22:04

Cleanups from review comments.

1621ce6

Insert missing word.

a0d1f5a

Gelbpunkt suggested changes Sep 12, 2025

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Remove bullet points from the target maintainer list for the arm bare…

4383a4f

…-metal targets

Re-order and re-work the aarch64-unknown-none platform support page.

ea661e9

Removes a bunch of information that isn't, strictly speaking, target specific.

workingjubilee approved these changes Sep 13, 2025

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Note that these targets are bare-metal.

afd324a

This is important to note, as it affects how easy it is to build a binary, and that `#![no_std]` is mandatory. A different PR should probably add this to all the other platform pages.

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 13, 2025

This was referenced Sep 13, 2025

Promote armv8r-none-eabihf target to Tier 2 #146520

Open

Promote armv7a-none-eabihf to Tier 2 #146522

Open

Demote both armebv7r-none-* targets. #146523

Open

jhpratt mentioned this pull request Sep 13, 2025

Rollup of 8 pull requests #146526

Merged

bors merged commit 04f17d8 into rust-lang:master Sep 14, 2025
10 checks passed

rustbot added this to the 1.91.0 milestone Sep 14, 2025

thejpster deleted the update-arm-target-docs branch September 14, 2025 08:44


		## Target maintainers

		* [@chrisnc](https://github.com/chrisnc)

Update the arm-* and aarch64-* platform docs. #146419

Update the arm-* and aarch64-* platform docs. #146419

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thejpster commented Sep 10, 2025

aarch64-none-elf and aarch64-none-elf-softfloat

armv7a-none-eabi and armv7a-none-eabihf

armv7r-none-eabi and armv7r-none-eabihf

armebv7r-none-eabi and armveb7r-none-eabihf

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