Auto merge of #103503 - thomcc:tvos-support, r=workingjubilee

Support Apple tvOS in libstd

This target has existed in the compiler for a while, was `no_std`-only previously (even requiring `#![feature(restricted_std)]`). Apple tvOS is essentially the same as iOS, down to using the same version numbering, so there's no reason for this to be a `no_std`-only target the way it is currently.

Not yet tested much (I have an Apple TV, but haven't tested that this can deploy and run programs on it, nor the simulator). Uses the implementation strategy as the watchOS support in https://github.com/rust-lang/rust/pull/98101 and etc. That is, no `std::os::` interfaces aside from those in `std::os::unix`.

Includes an update to libc in order to pull in https://github.com/rust-lang/libc/pull/2958.

3 files changed, 88 insertions, 2 deletions

diff --git a/src/doc/rustc/src/SUMMARY.md b/src/doc/rustc/src/SUMMARY.md
index 2b0431a159b..1e17a90a842 100644
--- a/src/doc/rustc/src/SUMMARY.md
+++ b/src/doc/rustc/src/SUMMARY.md
@@ -16,6 +16,7 @@
     - [Target Tier Policy](target-tier-policy.md)
     - [Template for Target-specific Documentation](platform-support/TEMPLATE.md)
     - [aarch64-apple-ios-sim](platform-support/aarch64-apple-ios-sim.md)
+    - [\*-apple-tvos](platform-support/apple-tvos.md)
     - [\*-apple-watchos\*](platform-support/apple-watchos.md)
     - [aarch64-nintendo-switch-freestanding](platform-support/aarch64-nintendo-switch-freestanding.md)
     - [armeb-unknown-linux-gnueabi](platform-support/armeb-unknown-linux-gnueabi.md)
diff --git a/src/doc/rustc/src/platform-support.md b/src/doc/rustc/src/platform-support.md
index f69dcd5983d..62f628f8229 100644
--- a/src/doc/rustc/src/platform-support.md
+++ b/src/doc/rustc/src/platform-support.md
@@ -214,7 +214,7 @@ host tools.
 target | std | host | notes
 -------|:---:|:----:|-------
 `aarch64-apple-ios-macabi` | ? |  | Apple Catalyst on ARM64
-`aarch64-apple-tvos` | * |  | ARM64 tvOS
+[`aarch64-apple-tvos`](platform-support/apple-tvos.md) | ? |  | ARM64 tvOS
 [`aarch64-apple-watchos-sim`](platform-support/apple-watchos.md) | ✓ |  | ARM64 Apple WatchOS Simulator
 [`aarch64-kmc-solid_asp3`](platform-support/kmc-solid.md) | ✓ |  | ARM64 SOLID with TOPPERS/ASP3
 [`aarch64-nintendo-switch-freestanding`](platform-support/aarch64-nintendo-switch-freestanding.md) | * |  | ARM64 Nintendo Switch, Horizon
@@ -316,7 +316,7 @@ target | std | host | notes
 `thumbv7neon-unknown-linux-musleabihf` | ? |  | Thumb2-mode ARMv7a Linux with NEON, MUSL
 [`wasm64-unknown-unknown`](platform-support/wasm64-unknown-unknown.md) | ? |  | WebAssembly
 `x86_64-apple-ios-macabi` | ✓ |  | Apple Catalyst on x86_64
-`x86_64-apple-tvos` | * | | x86 64-bit tvOS
+[`x86_64-apple-tvos`](platform-support/apple-tvos.md) | ? | | x86 64-bit tvOS
 [`x86_64-apple-watchos-sim`](platform-support/apple-watchos.md) | ✓ | | x86 64-bit Apple WatchOS simulator
 [`x86_64-pc-nto-qnx710`](platform-support/nto-qnx.md) | ✓ |  | x86 64-bit QNX Neutrino 7.1 RTOS |
 [`x86_64-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | ✓ |
diff --git a/src/doc/rustc/src/platform-support/apple-tvos.md b/src/doc/rustc/src/platform-support/apple-tvos.md
new file mode 100644
index 00000000000..d87fd1959b4
--- /dev/null
+++ b/src/doc/rustc/src/platform-support/apple-tvos.md
@@ -0,0 +1,85 @@
+# `*-apple-tvos`
+- aarch64-apple-tvos
+- x86_64-apple-tvos
+
+**Tier: 3**
+
+Apple tvOS targets:
+- Apple tvOS on aarch64
+- Apple tvOS Simulator on x86_64
+
+## Target maintainers
+
+* [@thomcc](https://github.com/thomcc)
+
+## Requirements
+
+These targets are cross-compiled. You will need appropriate versions of Xcode
+and the SDKs for tvOS (`AppleTVOS.sdk`) and/or the tvOS Simulator
+(`AppleTVSimulator.sdk`) to build a toolchain and target these platforms.
+
+The targets support most (see below) of the standard library including the
+allocator to the best of my knowledge, however they are very new, not yet
+well-tested, and it is possible that there are various bugs.
+
+In theory we support back to tvOS version 7.0, although the actual minimum
+version you can target may be newer than this, for example due to the versions
+of Xcode and your SDKs.
+
+As with the other Apple targets, `rustc` respects the common environment
+variables used by Xcode to configure this, in this case
+`TVOS_DEPLOYMENT_TARGET`.
+
+#### Incompletely supported library functionality
+
+As mentioned, "most" of the standard library is supported, which means that some portions
+are known to be unsupported. The following APIs are currently known to have
+missing or incomplete support:
+
+- `std::process::Command`'s API will return an error if it is configured in a
+  manner which cannot be performed using `posix_spawn` -- this is because the
+  more flexible `fork`/`exec`-based approach is prohibited on these platforms in
+  favor of `posix_spawn{,p}` (which still probably will get you rejected from
+  app stores, so is likely sideloading-only). A concrete set of cases where this
+  will occur is difficult to enumerate (and would quickly become stale), but in
+  some cases it may be worked around by tweaking the manner in which `Command`
+  is invoked.
+
+## Building the target
+
+The targets can be built by enabling them for a `rustc` build in `config.toml`, by adding, for example:
+
+```toml
+[build]
+build-stage = 1
+target = ["aarch64-apple-tvos", "x86_64-apple-tvos"]
+```
+
+It's possible that cargo under `-Zbuild-std` may also be used to target them.
+
+## Building Rust programs
+
+*Note: Building for this target requires the corresponding TVOS SDK, as provided by Xcode.*
+
+Rust programs can be built for these targets
+
+```text
+$ rustc --target aarch64-apple-tvos your-code.rs
+...
+$ rustc --target x86_64-apple-tvos your-code.rs
+```
+
+## Testing
+
+There is no support for running the Rust or standard library testsuite on tvOS
+or the simulators at the moment. Testing has mostly been done manually with
+builds of static libraries called from Xcode or a simulator.
+
+It hopefully will be possible to improve this in the future.
+
+## Cross-compilation toolchains and C code
+
+This target can be cross-compiled from x86_64 or aarch64 macOS hosts.
+
+Other hosts are not supported for cross-compilation, but might work when also
+providing the required Xcode SDK.