Update Android system definitions and add riscv-linux-android as tier 3 target

[chriswailes]

This PR includes the following:

• Corrected Android system definitions for some types
• Support for the riscv64-linux-android target

The authoritative types for the system definitions can be found here: https://cs.android.com/android/platform/superproject/+/master:bionic/libc/include/sys/stat.h

Fixes rust-lang/compiler-team#640

[rustbot]

r? @Mark-Simulacrum

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[rustbot]

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

[chriswailes]

update?????

Yes. This modifies the existing definitions and adds support to the riscv64-linux-android target, bringing it up to date with internal Android platform definitions.

[Mark-Simulacrum]

I'm going to go ahead and nominate for T-libs-api since this seems like it's changing stable surface area, so probably merits discussion and FCP.

[Amanieu]

Could the library changes be split into a separate PR which can be reviewed independently? We discussed this in the libs-api meeting and we are mostly happy with these breaking changes given that they fix incorrect definitions and these types are deprecated since Rust 1.8.0 anyways.

[chriswailes]

Sure thing. BRB with another PR.

[Amanieu]

The libs part has been split off into a separate PR, which is now merged. Handing this back to T-compiler for the new target.

[Amanieu]

Would it be clearer if this target was called riscv64gc-linux-android? This makes it clear that this target is for the baseline RV64GC instruction set.

[wesleywiser]

I don't have a strong opinion on the target name but we do need a confirmation that the target satisfies the target tier policy. @chriswailes could you please quote the corresponding requirements verbatim from the tier 3 target tier policy to explain how the target meets those requirements? (Leaving a new comment here is fine.) You can find an example of this in the PR description for #86191. Thank you!

[chriswailes]

could you please quote the corresponding requirements verbatim from the tier 3 target tier policy to explain how the target meets those requirements?

Sure thing.

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.)

This is the Android support team which can be found here.

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 is complicated a bit by the different CPU features that are available for RISC-V and their naming conventions. The target name is consistent with existing Android targets but elides the gc suffix from riscv64. This is consistent with the triple being used in other compilers in Android for this target.

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.

No known issues here. Rust already has existing Android and RISC-V targets.

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.

Acknowledged.

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.

We are actively in the process of bringing up this target with the goal of bringing it to parity with existing Android targets.

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.

The existing documentation for Android is also applicable to this target.

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.

Acknowledged.

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.

Acknowledged.

Please let me know if you'd like me to expand on any of this information and I'd be happy to do so.

[chriswailes]

@wesleywiser Is the above acknowledgement sufficient or would you like some additional details?

[wesleywiser]

This looks good to me if you're willing to fill the template out 🙂

[Mark-Simulacrum]

@bors r+ rollup

Thanks! I think this looks good to me in terms of added documentation. It might be nice to update the docs here: https://doc.rust-lang.org/nightly/rustc/platform-support/android.html to reference riscv in the last list or explicitly note it's not supported as of X date in the LTS release (if true).

[bors]

📌 Commit 0081d64 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[EwoutH]

Thanks for this effort. Seems it's going to be useful rather sooner than later!

Qualcomm to Bring RISC-V Based Wearable Platform to Wear OS by Google
Important first milestone to bring RISC-V compatible CPUs to the Android Ecosystem