miri/const eval: support `MaybeDangling` by WaffleLapkin · Pull Request #150446 · rust-lang/rust

WaffleLapkin · 2025-12-27T21:10:03Z

View all comments

r? RalfJung

rustbot · 2025-12-27T21:10:07Z

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

The Miri subtree was changed

cc @rust-lang/miri

compiler/rustc_const_eval/src/interpret/validity.rs

src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs

theemathas · 2025-12-28T08:47:06Z

Does this have insta-stable behavior change for ManuallyDrop in consteval?

RalfJung · 2025-12-28T16:24:14Z

It should only affect the behavior of code that still has UB until MaybeDangling is stabilized.

RalfJung · 2026-01-04T11:52:30Z

It is very import that we land #150447 before landing this, to avoid a situation where we generate LLVM IR with UB but Miri reports no UB.

src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs

src/tools/miri/tests/pass/move_manually_drop.rs

WaffleLapkin · 2026-02-26T16:29:50Z

@RalfJung I think I've addressed the review comments and this is ready for review too :)

(still blocked on the compiler change though)

RalfJung

Looks good overall, thanks! All nits are minor.

View changes since this review

compiler/rustc_const_eval/src/interpret/validity.rs

RalfJung · 2026-03-06T11:19:37Z

src/tools/miri/tests/fail/validity/maybe_dangling_null.rs

This isn't even a borrow checking thing. Please move the test to tests/fail/validity and have it disable Stacked Borrows to ensure we don't rely on the aliasing model for catching this.

RalfJung · 2026-03-06T11:19:52Z

compiler/rustc_const_eval/src/interpret/validity.rs

                }
            }
+            ty::Adt(adt, _) if adt.is_maybe_dangling() => {
+                let could_dangle = mem::replace(&mut self.may_dangle, true);


Suggested change

let could_dangle = mem::replace(&mut self.may_dangle, true);

let old_may_dangle = mem::replace(&mut self.may_dangle, true);

RalfJung · 2026-03-06T11:20:13Z

compiler/rustc_const_eval/src/interpret/validity.rs

+                Ub(DanglingIntPointer { addr: 0, .. }) => NullPtr { ptr_kind, maybe: false },
+                Ub(DanglingIntPointer { addr: i, .. }) => DanglingPtrNoProvenance {
+                    ptr_kind,
+                    // FIXME this says "null pointer" when null but we need translate


Suggested change

// FIXME this says "null pointer" when null but we need translate

While we're at it

RalfJung · 2026-03-06T11:20:56Z

compiler/rustc_const_eval/src/interpret/validity.rs

This comment doesn't make sense any more since we're skipping that part when may_dangle is true.

RalfJung · 2026-03-06T11:21:51Z

compiler/rustc_const_eval/src/interpret/validity.rs

        // Make sure this is non-null. We checked dereferenceability above, but if `size` is zero
        // that does not imply non-null.


Suggested change

// Make sure this is non-null. We checked dereferenceability above, but if `size` is zero

// that does not imply non-null.

// Make sure this is non-null. This is obviously needed when `may_dangle` is set,

// but even if we did check dereferenceability above that would still allow null

// pointers if `size` is zero.

src/tools/miri/tests/fail/unaligned_pointers/maybe_dangling_unalighed.rs

RalfJung · 2026-03-06T11:24:20Z

src/tools/miri/tests/pass/both_borrows/maybe_dangling.rs

Given that this case was contentious, please also add a test like

// Under the current models, we do not forbid writing through // `MaybeDangling<&i32>`. That's not yet finally decided, but meanwhile // ensure we document this and notice when it changes. fn write_through_shr(x: MaybeDangling<&i32>) { let y: *mut i32 = transmute(x); y.write(1); } let mutref = &mut 0i32; write_through_shr(transmute(mutref));

WaffleLapkin · 2026-03-06T16:41:40Z

@RalfJung I think I addressed your nits, unless I missed something ^^'

RalfJung · 2026-03-06T21:11:26Z

src/tools/miri/tests/pass/both_borrows/maybe_dangling_shared_write.rs

I meant for this to just be a new test in the other file -- no reason to split it up.

compiler/rustc_const_eval/src/interpret/validity.rs

rustbot · 2026-03-09T11:36:26Z

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.

WaffleLapkin · 2026-03-09T11:43:48Z

@rustbot review

RalfJung · 2026-03-09T15:25:30Z

Awesome, thanks a lot!
@bors r+

rust-bors · 2026-03-09T15:25:33Z

📌 Commit 76a750a has been approved by RalfJung

It is now in the queue for this repository.

…r=RalfJung miri/const eval: support `MaybeDangling` r? RalfJung

…uwer Rollup of 4 pull requests Successful merges: - #147834 (Always make tuple elements a coercion site) - #150446 (miri/const eval: support `MaybeDangling`) - #153053 (stop marking `deref_patterns` as an incomplete feature) - #153398 (fix ICE in `const_c_variadic` when passing ZSTs)

Rollup merge of #150446 - WaffleLapkin:miri-maybe-dangling, r=RalfJung miri/const eval: support `MaybeDangling` r? RalfJung

…uwer Rollup of 4 pull requests Successful merges: - rust-lang/rust#147834 (Always make tuple elements a coercion site) - rust-lang/rust#150446 (miri/const eval: support `MaybeDangling`) - rust-lang/rust#153053 (stop marking `deref_patterns` as an incomplete feature) - rust-lang/rust#153398 (fix ICE in `const_c_variadic` when passing ZSTs)

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Dec 27, 2025

rustbot assigned RalfJung Dec 27, 2025

This comment has been minimized.

Sign in to view

WaffleLapkin force-pushed the miri-maybe-dangling branch from 96d2a1d to 72213c3 Compare December 27, 2025 21:22

This comment has been minimized.

Sign in to view

WaffleLapkin force-pushed the miri-maybe-dangling branch from 72213c3 to 0d9e008 Compare December 27, 2025 21:28

This comment has been minimized.

Sign in to view

WaffleLapkin force-pushed the miri-maybe-dangling branch from 0d9e008 to ae69218 Compare December 27, 2025 21:36

This comment has been minimized.

Sign in to view

theemathas reviewed Dec 28, 2025

View reviewed changes

compiler/rustc_const_eval/src/interpret/validity.rs Outdated Show resolved Hide resolved

theemathas reviewed Dec 28, 2025

View reviewed changes

src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs Outdated Show resolved Hide resolved

WaffleLapkin marked this pull request as draft December 28, 2025 13:42

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 28, 2025

RalfJung added the S-blocked Status: Blocked on something else such as an RFC or other implementation work. label Jan 4, 2026

RalfJung reviewed Jan 4, 2026

View reviewed changes

src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs Show resolved Hide resolved

RalfJung reviewed Jan 4, 2026

View reviewed changes

src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs Show resolved Hide resolved

RalfJung reviewed Jan 4, 2026

View reviewed changes

src/tools/miri/tests/pass/move_manually_drop.rs Outdated Show resolved Hide resolved

WaffleLapkin force-pushed the miri-maybe-dangling branch 2 times, most recently from e5b7d00 to 959b31b Compare February 26, 2026 14:28

WaffleLapkin marked this pull request as ready for review February 26, 2026 16:28

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 26, 2026

RalfJung requested changes Mar 6, 2026

View reviewed changes

This comment has been minimized.

Sign in to view

WaffleLapkin force-pushed the miri-maybe-dangling branch 3 times, most recently from 7b01b7c to 4a26802 Compare March 6, 2026 16:38

RalfJung reviewed Mar 6, 2026

View reviewed changes

compiler/rustc_const_eval/src/interpret/validity.rs Show resolved Hide resolved

miri/const eval: support MaybeDangling

76a750a

WaffleLapkin force-pushed the miri-maybe-dangling branch from 4a26802 to 76a750a Compare March 9, 2026 11:36

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 9, 2026

rust-bors bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 9, 2026

JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Mar 9, 2026

Rollup merge of rust-lang#150446 - WaffleLapkin:miri-maybe-dangling, …

c1085a6

…r=RalfJung miri/const eval: support `MaybeDangling` r? RalfJung

JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Mar 9, 2026

Rollup merge of rust-lang#150446 - WaffleLapkin:miri-maybe-dangling, …

23ccc57

…r=RalfJung miri/const eval: support `MaybeDangling` r? RalfJung

JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Mar 9, 2026

Rollup merge of rust-lang#150446 - WaffleLapkin:miri-maybe-dangling, …

c5f755a

…r=RalfJung miri/const eval: support `MaybeDangling` r? RalfJung

JonathanBrouwer mentioned this pull request Mar 9, 2026

Rollup of 4 pull requests #153617

Merged

rust-bors bot merged commit 8fc4e47 into rust-lang:main Mar 9, 2026
11 checks passed

rustbot added this to the 1.96.0 milestone Mar 9, 2026

rust-timer added a commit that referenced this pull request Mar 9, 2026

Unrolled build for #150446

d44f7f2

Rollup merge of #150446 - WaffleLapkin:miri-maybe-dangling, r=RalfJung miri/const eval: support `MaybeDangling` r? RalfJung

RalfJung mentioned this pull request Mar 10, 2026

Tracking Issue for MaybeDangling #118166

Open

5 tasks

WaffleLapkin deleted the miri-maybe-dangling branch March 10, 2026 17:12

	let could_dangle = mem::replace(&mut self.may_dangle, true);
	let old_may_dangle = mem::replace(&mut self.may_dangle, true);

		// Make sure this is non-null. We checked dereferenceability above, but if `size` is zero
		// that does not imply non-null.

-        // Make sure this is non-null. We checked dereferenceability above, but if `size` is zero
-        // that does not imply non-null.
+// Make sure this is non-null. This is obviously needed when `may_dangle` is set,
+// but even if we did check dereferenceability above that would still allow null
+// pointers if `size` is zero.

Uh oh!

Conversation

WaffleLapkin commented Dec 27, 2025 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Dec 27, 2025

Uh oh!

This comment has been minimized.

This comment has been minimized.

This comment has been minimized.

This comment has been minimized.

This comment has been minimized.

Uh oh!

Uh oh!

theemathas commented Dec 28, 2025

Uh oh!

RalfJung commented Dec 28, 2025

Uh oh!

RalfJung commented Jan 4, 2026

Uh oh!

Uh oh!

Uh oh!

Uh oh!

WaffleLapkin commented Feb 26, 2026

Uh oh!

RalfJung left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

RalfJung Mar 6, 2026

Choose a reason for hiding this comment

Uh oh!

RalfJung Mar 6, 2026

Choose a reason for hiding this comment

Uh oh!

RalfJung Mar 6, 2026

Choose a reason for hiding this comment

Uh oh!

RalfJung Mar 6, 2026

Choose a reason for hiding this comment

Uh oh!

RalfJung Mar 6, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

RalfJung Mar 6, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

This comment has been minimized.

WaffleLapkin commented Mar 6, 2026

Uh oh!

RalfJung Mar 6, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

rustbot commented Mar 9, 2026

Uh oh!

WaffleLapkin commented Mar 9, 2026

Uh oh!

RalfJung commented Mar 9, 2026

Uh oh!

rust-bors bot commented Mar 9, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

7 participants

WaffleLapkin commented Dec 27, 2025 •

edited by rustbot

Loading

RalfJung left a comment •

edited by rustbot

Loading

RalfJung Mar 6, 2026 •

edited

Loading