Add support for link-flavor rust-lld for iOS, tvOS and watchOS

[marysaka]

This adds support for rust-lld for Apple *OS targets.

This was tested against targets aarch64-apple-ios and aarch64-apple-ios-sim with a simple test program.

It currently doesn't work with targets armv7-apple-ios and armv7s-apple-ios because of symbols.o not being generated with the correct CPU subtype. This will require changes in the object crate to expose an API.

As ld64.lld requires -platform_version with the minimal version supported and an sdk version, I made rustc_target::apple_base public to get access to *os_deployment_target helper functions and also added tvos_deployment_target as it was missing.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @compiler-errors (or someone else) soon.

Please see the contribution instructions for more information.

[rust-highfive]

⚠️ Warning ⚠️

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

[compiler-errors]

r? @petrochenkov

[petrochenkov]

Sorry for the delay, I should be able to review this some time this week.

[petrochenkov]

@Thog
Any logic that cannot fail is supposed to go to target definitions in rustc_target.
That's why the *_deployment_target are currently private - they are used from rustc_target and that's enough.

Only get_apple_sdk_root really needs to be delayed until link time.
(Even the pre-existing cmd.args(&["-target", llvm_target]) and cmd.args(&["-arch", arch_name]) are misplaced and can be moved to rustc_target, I think.)

@rustbot author

[marysaka]

@Thog Any logic that cannot fail is supposed to go to target definitions in rustc_target. That's why the *_deployment_target are currently private - they are used from rustc_target and that's enough.

Only get_apple_sdk_root really needs to be delayed until link time. (Even the pre-existing cmd.args(&["-target", llvm_target]) and cmd.args(&["-arch", arch_name]) are misplaced and can be moved to rustc_target, I think.)

@rustbot author

I was not sure where to put that part initially, I will address this hopefully this week 👍

[marysaka]

@petrochenkov

After a quick look it seems that ios_llvm_target, ios_sim_llvm_target and watchos_sim_llvm_target are used for iOS and watchOS simulator target definitions.

However, at the time of writing arm64_32-apple-watchos and arm64-apple-tvos doesn't select the llvm target with the deployment target.

Should I change those definitions in this PR to make them conform to watchos_deployment_target and tvos_deployment_target respectively?

[petrochenkov]

@Thog
I'm not sure, I'm more familiar with the compiler infrastructure around rustc_target than with details of Apple targets specifically.
You can ping people who added those targets, or maybe PRs adding those targets have some answers.

[marysaka]

@petrochenkov I did a refactoring of the linker arguments as suggested and rebased. However, the unit tests that you introduced with #98212 are failing here.

As I understand it, the test checks that the flavor of every LinkArg match the linker_flavor of the target. That's unwanted here as I'm targeting ld.64 specifically and result on a failure.

Shouldn't this actually check that at least one flavor match the linker_flavor?

@Thog I'm not sure, I'm more familiar with the compiler infrastructure around rustc_target than with details of Apple targets specifically. You can ping people who added those targets, or maybe PRs adding those targets have some answers.

I think I will try to handle those changes in a separated PR later

[petrochenkov]

The unit test needs to be updated, to something like

--- a/compiler/rustc_target/src/spec/tests/tests_impl.rs
+++ b/compiler/rustc_target/src/spec/tests/tests_impl.rs
@@ -46,7 +46,10 @@ fn check_consistency(&self) {
                         )
                     }
                     (LinkerFlavor::Gcc, LldFlavor::Ld64) => {
-                        assert_matches!(flavor, LinkerFlavor::Gcc)
+                        assert_matches!(
+                            flavor,
+                            LinkerFlavor::Lld(LldFlavor::Ld64) | LinkerFlavor::Gcc
+                        )
                     }
                     (LinkerFlavor::Msvc | LinkerFlavor::Lld(LldFlavor::Link), LldFlavor::Link) => {
                         assert_matches!(

This case just didn't occur previously.

[marysaka]

@rustbot label -S-waiting-on-author +S-waiting-on-review

[petrochenkov]

Could you also squash commits into one after addressing the comments?
@rustbot author

[marysaka]

@rustbot label -S-waiting-on-author +S-waiting-on-review

[petrochenkov]

Thanks!
@bors r+

[bors]

📌 Commit 78bbe57 has been approved by petrochenkov

It is now in the queue for this repository.