Enable xray support for Mac

[quininer]

#102921

Upstream has supported Mac for a while, let's enable it.

I've tested it on M4 and it generates nop sled correctly.

• https://maskray.me/blog/2023-06-18-port-llvm-xray-to-apple-systems
• https://github.com/llvm/llvm-project/blob/llvmorg-20.1.4/clang/lib/Driver/XRayArgs.cpp#L31

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[rustbot]

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

[jieyouxu]

Since this affects the Tier 1 {x86_64,aarch64}-apple-darwin targets (albeit -Z instrument-xray is still unstable), asking Apple experts for second opinion as I neither have access to apple envs nor am I aware of how well LLVM xray currently works on those targets.

@rustbot ping apple

[rustbot]

Hey Apple notification group! This issue or PR could use some Apple-specific
guidance. Could one of you weigh in? Thanks <3

(In case it's useful, here are some instructions for tackling these sorts of
issues).

cc @BlackHoleFox @hkratz @inflation @madsmtm @nvzqz @shepmaster @thomcc

[jieyouxu]

@rustbot author (test nits)

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[jieyouxu]

Responded to your questions in #140790 (comment).
@rustbot author

[quininer]

I added tests for assembly output, which should be seen as supplementing the previous missing tests for xray.

I also added flag stable test, but I still don't think it's necessary. I don't see any other flags have this test, I can only get this from https://github.com/rust-lang/rust/blob/1.87.0/tests/ui/bootstrap/rustc_bootstrap.rs#L36 .
and this test has nothing to do with xray, but is a test of the order of -Z flag and target checks.

@rustbot ready

[jieyouxu]

Thanks, just a nit on the platform support test

[jieyouxu]

Suggestion: What I meant was you can gate this test behind nightly-channel only (//@ only-nightly), so the unstable flag is accepted by an unstable compiler (i.e. -Z instrument-xray is accepted) but rejected because it's not supported for the given platform. You can then check for the target-platform-gate message:

//~? ERROR XRay instrumentation is not supported for this target

You can also introduce a differential revision to check that this is accepted, however, on x86_64-apple-darwin and aarch64-apple-darwin: e.g.

//@ only-nightly (flag is still unstable)

//@ revisions: unsupported
//@[unsupported] compile-flags: -Z instrument-xray --target=x86_64-pc-windows-msvc

//@ revisions: x86_64_darwin
//@[x86_64_darwin] compile-flags: -Z instrument-xray --target=x86_64-apple-darwin
//@[x86_64_darwin] check-pass

//@ revisions: aarch64_darwin
//@[aarch64_darwin] compile-flags: -Z instrument-xray --target=aarch64-apple-darwin
//@[aarch64_darwin] check-pass

So i.e. this test would be platform-support.rs.

[jieyouxu]

Question: can this just be fn main() {}?

[quininer]

Ok, I just copy this from tests/ui/instrument-xray/target-not-supported.rs.

[quininer]

This does not seem to work, which would cause the test to fail on linux. (because darwin std cannot be built).

If we are just test flag, using no_main seems reasonable to me.

[jieyouxu]

Ah right, yeah that's fine.

[jieyouxu]

I also added flag stable test, but I still don't think it's necessary. I don't see any other flags have this test, I can only get this from https://github.com/rust-lang/rust/blob/1.87.0/tests/ui/bootstrap/rustc_bootstrap.rs#L36 .
and this test has nothing to do with xray, but is a test of the order of -Z flag and target checks.

Sorry I shouldn't have said "platform stability", I should've said "platform support".

@rustbot author

[madsmtm]

As someone with very little experience with XRay, I tried to test this end-to-end:

$ ./x build --set=build.sanitizers=true
$ echo "fn main() {}" > main.rs
$ rustc +stage1 -Zinstrument-xray=always main.rs
$ objdump -h -j xray_instr_map main # Works
$ XRAY_OPTIONS="patch_premain=true xray_mode=xray-basic verbosity=1" ./main # No-op?

But it doesn't seem to do anything? Probably because I'm not linking the runtime, but it's not clear to me how I'd go about doing that? Does bootstrap need to build it?

[quininer]

@madsmtm As with linux, you need to link to compiler-rt/xray. like https://crates.io/crates/clang-rt-xray

Anyway I don't really care about that, because I'll be using my own rt, like uftrace. So just rustc generate the correct nop sled and xray_instr_map section will good.

[jieyouxu]

As with linux, you need to link to compiler-rt/xray. like crates.io/crates/clang-rt-xray

Anyway I don't really care about that, because I'll be using my own rt, like uftrace. So just rustc generate the correct nop sled and xray_instr_map section will good.

Could you add that as a remark on the unstable docs for this flag? I imagine Mads won't be the only person asking that question.

[quininer]

Could you add that as a remark on the unstable docs for this flag?

@jieyouxu I think it is already mentioned in unstable book. https://github.com/rust-lang/rust/blob/1.87.0/src/doc/unstable-book/src/compiler-flags/instrument-xray.md?plain=1#L35

[quininer]

@rustbot ready