Add `codeview_annotation` intrinsic by gurry · Pull Request #160285 · rust-lang/rust

gurry · 2026-07-31T14:24:01Z

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This PR adds:

A new intrinsic called codeview_annotation, which lowers to llvm.codeview.annotation and allows users to emit arbitrary S_ANNOTATION records into PDB files
A std lib API to call this intrinsic

For the underlying motivation and design details see:

Intrinsic MCP: Add codeview_annotation intrinsic compiler-team#1026
API ACP: Add API to call codeview_annotation intrinsic libs-team#868

Tracking issues:

Intrinsic tracking issue: Tracking issue for MCP 1026: Add codeview_annotation intrinsic #162252
API tracking issue: Tracking Issue for codeview_annotation API #163964

Implementation details

Codgen happens only on LLVM backend and only if the target uses PDBs. It is a no-op in all other cases. A compile error will still be emitted in all cases (even on non-LLVM, non-PDB ones) if CodeViewAnnotationArgs::ARGS fails to const eval.
Had to change the feature gate on core::os module to a neutral core_os in order to add the new module core::os::windows. It was earlier gated on darwin_objc, which was not general enough.

rustbot · 2026-10-10T03:29:05Z

⚠️ #[miri::intrinsic_fallback_is_spec] must only be used if the function actively checks for all UB cases,
and explores the possible non-determinism of the intrinsic.

cc @rust-lang/miri

Any special-casing of Miri in the standard library requires review.

cc @rust-lang/miri

rustc_codegen_gcc is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_gcc instead.

cc @antoyo, @GuillaumeGomez

miri is developed in its own repository. If the Miri part of this change can be broken out, consider making this change to rust-lang/miri instead. However, if Miri needs adjusting for rustc changes, just ignore this message.

cc @rust-lang/miri

rustc_codegen_cranelift is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_cranelift instead.

cc @bjorn3

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

rustbot · 2026-10-10T03:29:08Z

r? @folkertdev

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gurry · 2026-10-10T06:06:20Z

⚠️ #[miri::intrinsic_fallback_is_spec] must only be used if the function actively checks for all UB cases, and explores the possible non-determinism of the intrinsic.

The function does not caues any UB or non-determinism (it returns () and has no run-time side effects) so the fallback should be fine.

rustc_codegen_gcc is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_gcc instead.

cc @antoyo, @GuillaumeGomez

...
rustc_codegen_cranelift is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_cranelift instead.

I have now removed the changes in rustc_codegen_gcc and rustc_codegen_cranelift. I had earlier added explicit no-op handling for the intrinic in these backends, but I think the fallback function is enough.

RalfJung · 2026-10-10T07:14:46Z

Please move this into the intrinsics folder.

View changes since the review

RalfJung · 2026-10-10T07:15:02Z

@@ -0,0 +1,17 @@
+// Verifies that `codeview_annotation` is a no-op under Miri
+// and that Miri does not try to const eval `CodeViewAnnotationArgs::ARGS`


Why should Miri not const-eval the args? That seems strange.

View changes since the review

My thinking was that Miri should not do anything at all upon encountering this intrinsic including const evaluating the args. That's what I meant by "no-op under Miri" in the comment.

Now I realize that perhaps Miri should actively try to const eval and raise an error if ARGS fails to eval because that's exactly what we're doing for LLVM+PDB targets. So that this particular behaviour will be consistent in all cases.

What are your thoughts?

So that this particular behaviour will be consistent in all cases.

Yeah that's what I thought -- and not just Miri but also other codegen backends.

I think you can just put a const { let _ignore = T::ARGS; } into the fallback body to achieve this.

Fixed. Added const block in the fallback body to force const eval, added miri test for when const eval fails (‎src/tools/miri/tests/fail/intrinsics/codeview-annotation.rs) and removed //@ only-msvc from ‎tests/ui/intrinsics/codeview-annotation-bad-args.rs which will now test const eval failure on all environments.

RalfJung · 2026-10-10T07:15:49Z

@@ -1,12 +1,11 @@
 //! OS-specific functionality.
-
-#![unstable(feature = "darwin_objc", issue = "145496")]
+#![stable(feature = "core_os", since = "CURRENT_RUSTC_VERSION")]


This PR should not stabilize anything. (It would have to go through the full team approval process otherwise as it would represent a permanent commitment we can never take back. And anyway a stabilization PR should never also add new features.) Why can't this be a new unstable feature instead?

View changes since the review

Got it.

If I change the feature gate on core::os to something like core_os, then anyone using items in, say, core::os::windows will require both the features codeview_annotation and core_os. That's acceptable, right?

It's suboptimal but better than a drive-by stabilization.

folkertdev

Some small things, @RalfJung does the const eval stuff look OK to you otherwise?

View changes since this review

folkertdev · 2026-10-13T08:51:53Z

+        .filter_map(|trait_clause| {
+            let trait_ref = trait_clause.skip_binder().trait_ref;
+            tcx.associated_items(trait_ref.def_id)
+                .in_definition_order()
+                .find(|item| {
+                    item.tag() == ty::AssocTag::Const
+                        && tcx.item_name(item.def_id).as_str() == "ARGS"
+                })
+                .map(|item| (item.def_id, trait_ref.args))
+        })
+        .next()


this can be find_map I think?

folkertdev · 2026-10-13T09:02:44Z

+        mir::ConstValue::Slice { alloc_id, meta } => Some((alloc_id, Size::ZERO, meta)),
+        mir::ConstValue::Indirect { alloc_id, offset } => read_slice_pointer(tcx, alloc_id, offset)


Why are both branches needed?

Looks like we'll only ever get ConstValue::Indirect in this case so I removed ConstValue::Slice. Thanks.

RalfJung · 2026-10-13T16:46:20Z

On the const-eval / Miri side there's just the fallback body and that seems reasonable to me.

rustbot · 2026-10-14T09:04:15Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

folkertdev

Looks good, thanks!

@bors r+

View changes since this review

folkertdev · 2026-10-16T22:22:29Z

+#[cfg_attr(windows, doc = "```")]
+#[cfg_attr(not(windows), doc = "```ignore (needs windows)")]


hmm, we have

```ignore-windows

but sadly not currently

```only-windows

it would be nice if rustdoc could do that

rust-bors · 2026-10-16T22:23:05Z

📌 Commit 9d8da0d has been approved by folkertdev

It is now in the queue for this repository.

rust-bors · 2026-10-17T01:47:45Z

☀️ Test successful - CI
Approved by: folkertdev
Duration: 2h 58m 8s
Pushing f4d7ecf to main...

github-actions · 2026-10-17T01:51:09Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 5d8fec0 (parent) -> f4d7ecf (this PR)

Test differences

Show 116 test diffs

Stage 1

[codegen] tests/codegen-llvm/intrinsics/codeview-annotation-non-pdb-targets.rs: [missing] -> pass (J2)
[codegen] tests/codegen-llvm/intrinsics/codeview-annotation.rs#OPT0: [missing] -> ignore (only executed when the target environment is msvc) (J2)
[codegen] tests/codegen-llvm/intrinsics/codeview-annotation.rs#OPT3: [missing] -> ignore (only executed when the target environment is msvc) (J2)
[ui] tests/ui/feature-gates/feature-gate-codeview_annotation.rs: [missing] -> ignore (only executed when the operating system is windows) (J4)
[ui] tests/ui/intrinsics/codeview-annotation-bad-args.rs: [missing] -> pass (J4)
[ui] tests/ui/intrinsics/codeview-annotation.rs: [missing] -> ignore (only executed when the operating system is windows) (J4)
[ui (polonius)] tests/ui/feature-gates/feature-gate-codeview_annotation.rs: [missing] -> ignore (only executed when the operating system is windows) (J7)
[ui (polonius)] tests/ui/intrinsics/codeview-annotation-bad-args.rs: [missing] -> pass (J7)
[ui (polonius)] tests/ui/intrinsics/codeview-annotation.rs: [missing] -> ignore (only executed when the operating system is windows) (J7)

Stage 2

[codegen] tests/codegen-llvm/intrinsics/codeview-annotation-non-pdb-targets.rs: [missing] -> pass (J0)
[codegen] tests/codegen-llvm/intrinsics/codeview-annotation.rs#OPT0: [missing] -> ignore (only executed when the target environment is msvc) (J0)
[codegen] tests/codegen-llvm/intrinsics/codeview-annotation.rs#OPT3: [missing] -> ignore (only executed when the target environment is msvc) (J0)
[ui] tests/ui/feature-gates/feature-gate-codeview_annotation.rs: [missing] -> ignore (only executed when the operating system is windows) (J1)
[ui] tests/ui/intrinsics/codeview-annotation.rs: [missing] -> ignore (only executed when the operating system is windows) (J1)
[ui] tests/ui/feature-gates/feature-gate-codeview_annotation.rs: [missing] -> pass (J3)
[ui] tests/ui/intrinsics/codeview-annotation.rs: [missing] -> pass (J3)
[codegen] tests/codegen-llvm/intrinsics/codeview-annotation-non-pdb-targets.rs: [missing] -> ignore (ignored when the target environment is msvc) (J5)
[codegen] tests/codegen-llvm/intrinsics/codeview-annotation.rs#OPT0: [missing] -> pass (J5)
[codegen] tests/codegen-llvm/intrinsics/codeview-annotation.rs#OPT3: [missing] -> pass (J5)
[ui] tests/ui/intrinsics/codeview-annotation-bad-args.rs: [missing] -> pass (J6)

Additionally, 96 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard f4d7ecfb0efc8330cef8f8020f192920d8721911 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

dist-loongarch64-linux: 5h 44m -> 1h 19m (-77.0%)
dist-loongarch64-musl: 5h 40m -> 1h 31m (-73.0%)
test-i686-gnu-nopt-1: 1h 31m -> 2h 24m (+58.5%)
test-x86_64-msvc-ext2: 1h 9m -> 1h 50m (+58.3%)
dist-arm-linux-gnueabi: 1h 4m -> 1h 41m (+57.9%)
test-x86_64-gnu: 1h 42m -> 2h 36m (+53.2%)
dist-s390x-linux: 1h 3m -> 1h 33m (+47.8%)
dist-x86_64-solaris: 1h 10m -> 1h 43m (+47.6%)
dist-powerpc64le-linux-musl: 1h 8m -> 1h 38m (+44.5%)
dist-i686-linux: 1h 20m -> 1h 53m (+42.2%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2026-10-17T03:13:18Z

Finished benchmarking commit (f4d7ecf): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This perf run didn't have relevant results for this metric.

Max RSS (memory usage)

Results (secondary 4.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.2%	[4.2%, 4.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary 2.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 490.438s -> 497.38s (1.42%)
Artifact size: 406.97 MiB -> 407.06 MiB (0.02%)

gurry changed the title ~~Add codeview_annotation intrinsic~~ Add codeview_annotation intrinsic Jul 31, 2026

gurry mentioned this pull request Jul 31, 2026

Add codeview_annotation intrinsic rust-lang/compiler-team#1026

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Add codeview_annotation intrinsic gurry/rust#1

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Add API to call codeview_annotation intrinsic rust-lang/libs-team#868

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gurry marked this pull request as ready for review October 10, 2026 03:29

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Tracking Issue for codeview_annotation API #163964

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Add codeview_annotation intrinsic

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rust-bors Bot merged commit f4d7ecf into rust-lang:main Oct 17, 2026
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Tracking issue for MCP 1026: Add codeview_annotation intrinsic #162252

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		@@ -0,0 +1,17 @@
		// Verifies that `codeview_annotation` is a no-op under Miri
		// and that Miri does not try to const eval `CodeViewAnnotationArgs::ARGS`

		mir::ConstValue::Slice { alloc_id, meta } => Some((alloc_id, Size::ZERO, meta)),
		mir::ConstValue::Indirect { alloc_id, offset } => read_slice_pointer(tcx, alloc_id, offset)

		#[cfg_attr(windows, doc = "```")]
		#[cfg_attr(not(windows), doc = "```ignore (needs windows)")]

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