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Support Apple's TvOS Simulator on Apple Silicon #115692

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bcardarella opened this issue Sep 9, 2023 · 12 comments
Open

Support Apple's TvOS Simulator on Apple Silicon #115692

bcardarella opened this issue Sep 9, 2023 · 12 comments
Labels
C-feature-request Category: A feature request, i.e: not implemented / a PR. O-tvos Operating system: tvOS (including simulator) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@bcardarella
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Currently it appears that Rust can only compile for TvOS's Simulator running on x86. Apple Silicon need arm64. Specifically we need compile support for this target: https://github.com/apple/swift/blob/ffbc65c8c48cb38db190fa0618fe2b5937a334b8/utils/build-script-impl#L649-L658

Currently there is only:

➜  ~ rustc --print target-list | grep tvos
aarch64-apple-tvos
x86_64-apple-tvos
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Sep 9, 2023
@Urgau
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Urgau commented Sep 9, 2023

Isn't this aarch64-apple-tvos ? since in Rust we use aarch64 instead of arm64.

@bcardarella
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@Urgau according to this issue: #48862 (comment) Rust implemented support for the TvOS Simulator compile target of x86 but Swift itself is using arm64 as the compile target for the TvOS simulator. The original issue is from 2018 so perhaps Apple updated the Simulator when they released the M1/M2 macs?

@bcardarella
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A bit more on this, Apple added support for both x86 and arm64 tvos simulator in Swift 5.3: swiftlang/swift@795c363

@Nemo157
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Nemo157 commented Sep 10, 2023

There's some annoying lack of precision in the target names, for ios and tvos targets the simulator targets only get the -sim suffix when there's also a native target on the same architecture. If you look at the target definitions aarch64-apple-tvos is a tvos_llvm_target while x86_64-apple-tvos is a tvos_sim_llvm_target. What is needed is a new aarch64-apple-tvos-sim target to go next to the native target.

(EDIT: and as actually got mentioned just yesterday some standardization of the target names would make this less confusing, the newer watchos targets always use -sim on the simulator variants).

@bcardarella
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@Nemo157 agreed, the naming has been in part an issue. Would changing these names to follow a convention be considered a breaking change?

@Nemo157
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Nemo157 commented Sep 10, 2023

Yes, but they're tier 3 targets where breaking changes are allowed. There's an in-progress rename of another tier 3 target that provides a good example: #110596, the first step would probably be to start a discussion on zulip to gauge whether the target maintainers are on board with changing the name, and then submit an MCP like the wasi one.

@bcardarella
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@Nemo157 I've had difficulty with knowing where to post messages on Zulip before and get blasted pretty quickly. I've found that community to be pretty hostile to newcomers that are unaware of where the correct place is to ask questions

@thomcc
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thomcc commented Sep 10, 2023

So...

  1. I agree the name x86_64-apple-tvos are bad and need to change to x86_64-apple-tvos-sim, and some of our other -sim targets have the same issue too, which would be good to fix, and I have a plan written up below (that I can just take, probably). But...
  2. I don't think a rename of the x86_64-apple-tvos target needs to happen in order to add support for a aarch64-apple-tvos-sim target.

Moreover, even if we could just do the rename without any scrutiny beyond t-compiler r+ (one could make an argument for this in the case of x86_64-apple-tvos-sim), I would prefer if adding aarch64-apple-tvos-sim support to happened in a entirely separate PR from changing any existing target names.

So, if you wanna add aarch64-apple-tvos-sim, that should not be blocked by anything -- feel free to go for it if the inspiration strikes. CC me on the PR.

The rest of comment is about renaming all of the misnamed simulator targets, of which x86_64-apple-tvos is merely a single example. This is not relevant to the problem of adding aarch64-apple-tvos-sim support, so stop reading now if that's what you're here for.

--

So, renaming. I have Thoughts.

This issue applies to several simulator targets right now, a lot of them have names that fail to reflect that they're simulators (among other issues). They're mostly tier 3, with a single tier 2, we should just do all the renames in with a single batch MCP/FCP/whatever, to ensure everything that is a -sim ends in -sim.

Like, right now, to know if a target is a simulator, you either have to check it, memorize the set, or reason it out based on the history of Apple releases of hardware and software, and possibly also Rust's support for that target. For example, the reasoning you might have to apply for figuring out x86_64-apple-ios (which is not the hardest one to reason through) might be:

Well, iOS doesn't support x86_64 directly, but it does have simulator support, and catalyst support, and the simulator was added first, so the unsuffixed target name must implicitly be the simulator target.

Maybe this is an exaggeration, but it's pretty bad, got worse with the addition of catalyst. It also stands to continue to get worse in the future.

So, we can remove this by renaming simulator targets to end in -sim even if if there's no non-sim version of that triple, but what all would we need to change? These (including more discussion than they deserve):

  1. x86_64-apple-tvos should be renamed to x86_64-apple-tvos-sim.

    This should be uncontroversial and honestly, for a tier 3 target that exists mostly for development/debugging (shipping code for a simulator is probably impossible) and was no_std only prior to a few months ago... I'd almost say that we could probably just do it with only a compiler-team r+.

  2. i386-apple-ios should be i686-apple-ios-sim. This is a profoundly weird one but only really because the name is just a disaster. The fixed name is clear, this target is a simulator (so it should say so), and it has target features on-par with (or slightly better than) the other targets calling themselves i686-*.

    In practice, I don't think it gets much use, although if targetting 32-bit iOS you're probably using it as the simulator (e.g. it works on 64-bit macOS so that you can simulate against a 32-bit chip, as it took a while for iPhones to move to aarch64). The reason to rename it is that it causes a lot of confusion, from:

    • Folks not realizing that it's a simulator, because it doesn't say so. This is occasionally relevant, but presumably something like this is why we seem to have failed to set cfg(target_abi = "sim"), unlike every other simulator target.
    • Folks thinking it's actually honest-to-god i386, because it's in the name. This is very misleading because Rust doesn't support x86 anywhere that old. It's not that rare to find things that use i386 for "unspecified 32bit x86" and Apple calling this target i386 is just a case of that for the most part.

    This target is barely-supported, but won't go away any time soon (I believe we won't drop the 32-bit apple targets until after the currently in-progress iOS/macOS version bump). This simulator only was removed in late 2022, so it's not that obscure either.

    Which is all to say: it's name is busted enough to cause confusion, but the target probably isn't obscure or busted enough to deserve removal. I think we just rename it, and because we're doing it in a batch, we could probably do a single MCP for all three.

    Also, for whatever reason, this target doesn't have cfg(target_abi = "sim") like all the others, despite definitely being a simulator (by default the LLVM target ends with -simulator, and in clang __is_target_environment(simulator)[^env] reports true). My wild unfounded guess would be that this somehow was caused by the fact that the name doesn't have -sim in it.

  3. x86_64-apple-ios should be renamed to x86_64-apple-ios-sim. It is the normal simulator for x86_64 macs, and is the only one of these that is a tier 2 target (the others are tier 3).

    People use this (mainly for development, but some for CI) so we should do so as gently as possible. For example, at a minimum do whatever we're doing for wasm32-wasi.

If we do that, and then never add an apple simulator target that doesn't end with -sim (perhaps verified by a rustc-target unit test that checks that targets with -simulator in the LLVM triple always have target_abi = "sim" and have a rust triple ending in -sim), it would be really nice.

This is a lot, but writing all this down has been on my TODO for a while.

I'll file an MCP for the 3 target renames later, it's off topic for this but I got pinged and even emailed to ask.

@thomcc
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thomcc commented Sep 10, 2023

Also we should not call it arm64. It doesn't matter if Apple uses arm64 to refer to that architecture, we call it aarch64 on Apple and non-Apple targets alike and there's no reason to diverge here.

I am firmly against naming the simulator target which runs on the Apple Silicon Macs anything other than aarch64-apple-tvos-sim -- After all, the target name we use for iOS running on the same machines is aarch64-apple-ios-sim, which IMO has no issues.

@bcardarella
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@thomcc I'm 👍 on the larger more-correct effort. If you need help I'm happy to pull in some resources

@bcardarella
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fwiw, I'm not suggesting renaming to arm64. If Rust has a predefined naming convention that makes sense to stick to. I was just using the naming in Apple's own reference code. aarch64 is 👍

@fmease fmease added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. C-feature-request Category: A feature request, i.e: not implemented / a PR. O-tvos Operating system: tvOS (including simulator) and removed needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. labels Sep 29, 2023
workingjubilee added a commit to workingjubilee/rustc that referenced this issue Oct 28, 2023
…ustc, r=thomcc

tvOS simulator support on Apple Silicon for rustc

Closes or is a subtask of rust-lang#115692.

# Tier 3 Target Policy

At this tier, the Rust project provides no official support for a target, so we place minimal requirements on the introduction of targets.

> * 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.)

See [`src/doc/rustc/src/platform-support/apple-tvos.md`](https://github.com/rust-lang/rust/blob/4ab4d48ee59968d8d519ccda5e12c9d200cc092f/src/doc/rustc/src/platform-support/apple-tvos.md)

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

This naming scheme matches `$ARCH-$VENDOR-$OS-$ABI` (I think `sim` is the ABI here) which is matches the iOS apple silicon simulator (`aarch64-apple-ios-sim`). [There is some discussion about renaming some apple simulator targets](rust-lang#115692 (comment)) to match the `-sim` suffix but that is outside the scope of this PR.

> * 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.
>
>    * The target must not introduce license incompatibilities.
>    * Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).
>    * 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.
>    * 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.

This contribution is fully available under the standard Rust license with no additional legal restrictions whatsoever. This PR does not introduce any new dependency less permissive than the Rust license policy.

The new targets do not depend on proprietary libraries.

> * 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 new target implements as much of the standard library as the other tvOS targets do.

> * 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.

I have added the target to the other tvOS targets in [`src/doc/rustc/src/platform-support/apple-tvos.md`](https://github.com/rust-lang/rust/blob/4ab4d48ee59968d8d519ccda5e12c9d200cc092f/src/doc/rustc/src/platform-support/apple-tvos.md)

> * 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.
> * 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.
> * 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.

I acknowledge these requirements and intend to ensure that they are met.

This target does not touch any existing tier 2 or tier 1 targets and should not break any other targets.
workingjubilee added a commit to workingjubilee/rustc that referenced this issue Oct 29, 2023
…ustc, r=thomcc

tvOS simulator support on Apple Silicon for rustc

Closes or is a subtask of rust-lang#115692.

# Tier 3 Target Policy

At this tier, the Rust project provides no official support for a target, so we place minimal requirements on the introduction of targets.

> * 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.)

See [`src/doc/rustc/src/platform-support/apple-tvos.md`](https://github.com/rust-lang/rust/blob/4ab4d48ee59968d8d519ccda5e12c9d200cc092f/src/doc/rustc/src/platform-support/apple-tvos.md)

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

This naming scheme matches `$ARCH-$VENDOR-$OS-$ABI` (I think `sim` is the ABI here) which is matches the iOS apple silicon simulator (`aarch64-apple-ios-sim`). [There is some discussion about renaming some apple simulator targets](rust-lang#115692 (comment)) to match the `-sim` suffix but that is outside the scope of this PR.

> * 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.
>
>    * The target must not introduce license incompatibilities.
>    * Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).
>    * 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.
>    * 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.

This contribution is fully available under the standard Rust license with no additional legal restrictions whatsoever. This PR does not introduce any new dependency less permissive than the Rust license policy.

The new targets do not depend on proprietary libraries.

> * 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 new target implements as much of the standard library as the other tvOS targets do.

> * 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.

I have added the target to the other tvOS targets in [`src/doc/rustc/src/platform-support/apple-tvos.md`](https://github.com/rust-lang/rust/blob/4ab4d48ee59968d8d519ccda5e12c9d200cc092f/src/doc/rustc/src/platform-support/apple-tvos.md)

> * 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.
> * 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.
> * 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.

I acknowledge these requirements and intend to ensure that they are met.

This target does not touch any existing tier 2 or tier 1 targets and should not break any other targets.
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Oct 29, 2023
Rollup merge of rust-lang#115773 - simlay:arch64-apple-tvos-sim-for-rustc, r=thomcc

tvOS simulator support on Apple Silicon for rustc

Closes or is a subtask of rust-lang#115692.

# Tier 3 Target Policy

At this tier, the Rust project provides no official support for a target, so we place minimal requirements on the introduction of targets.

> * 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.)

See [`src/doc/rustc/src/platform-support/apple-tvos.md`](https://github.com/rust-lang/rust/blob/4ab4d48ee59968d8d519ccda5e12c9d200cc092f/src/doc/rustc/src/platform-support/apple-tvos.md)

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

This naming scheme matches `$ARCH-$VENDOR-$OS-$ABI` (I think `sim` is the ABI here) which is matches the iOS apple silicon simulator (`aarch64-apple-ios-sim`). [There is some discussion about renaming some apple simulator targets](rust-lang#115692 (comment)) to match the `-sim` suffix but that is outside the scope of this PR.

> * 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.
>
>    * The target must not introduce license incompatibilities.
>    * Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).
>    * 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.
>    * 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.

This contribution is fully available under the standard Rust license with no additional legal restrictions whatsoever. This PR does not introduce any new dependency less permissive than the Rust license policy.

The new targets do not depend on proprietary libraries.

> * 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 new target implements as much of the standard library as the other tvOS targets do.

> * 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.

I have added the target to the other tvOS targets in [`src/doc/rustc/src/platform-support/apple-tvos.md`](https://github.com/rust-lang/rust/blob/4ab4d48ee59968d8d519ccda5e12c9d200cc092f/src/doc/rustc/src/platform-support/apple-tvos.md)

> * 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.
> * 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.
> * 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.

I acknowledge these requirements and intend to ensure that they are met.

This target does not touch any existing tier 2 or tier 1 targets and should not break any other targets.
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madsmtm commented Feb 17, 2024

Also, for whatever reason, this target doesn't have cfg(target_abi = "sim") like all the others, despite definitely being a simulator (by default the LLVM target ends with -simulator, and in clang __is_target_environment(simulator)[^env] reports true). My wild unfounded guess would be that this somehow was caused by the fact that the name doesn't have -sim in it.

Also hit this today, filed #121210 for that.

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C-feature-request Category: A feature request, i.e: not implemented / a PR. O-tvos Operating system: tvOS (including simulator) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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