Disable retagging for variadic arguments in const-eval by icmccorm · Pull Request #157622 · rust-lang/rust

icmccorm · 2026-06-08T17:24:36Z

Fixes #5058 in Miri.

Retags occur on typed copies, which happen when we pass variadic arguments to a function. At the moment, variadic arguments receive RetagMode::FnEntry retags, which protects their permissions for the duration of the call. However, protection needs to be based on callee-side information, and the callee has now way of knowing what's contained within its VaList.

This PR disables retagging entirely when copying variable arguments. It also adds a new, passing test case that would originally fail before this change.

cc: @RalfJung, @folkertdev

rustbot · 2026-06-08T17:24:39Z

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

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

cc @rust-lang/miri

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

rustbot · 2026-06-08T17:24:41Z

r? @davidtwco

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folkertdev · 2026-06-08T18:50:16Z

r? me

Though I definitely want Ralf to have a look at this too

RalfJung

Thanks. :) I have one question, the rest are nits.

@rustbot author

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RalfJung · 2026-06-09T12:35:54Z

Why is this just a TB test? It also applies to SB, doesn't it?

Yup - I adjusted the test and moved it over to both_borrows.

rustbot · 2026-06-09T12:36:31Z

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

rustbot · 2026-06-10T13:59:51Z

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.

icmccorm · 2026-06-10T14:47:59Z

@rustbot ready

folkertdev

LGTM

r? RalfJung

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rustbot · 2026-06-10T18:29:10Z

RalfJung is not on the review rotation at the moment.
They may take a while to respond.

RalfJung · 2026-06-11T07:26:20Z

+    unsafe {
+        write_with_first_arg(&raw mut val, &val);
+    }
+}


Please add a trailing newline

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RalfJung · 2026-06-11T07:26:30Z

This looks great, thanks! With the last nit resolved, please squash the commits, then we can land this. Please use the --keep-base flag when squashing so that the force-push diff is easier to review; do not rebase on the latest master branch. Then write @rustbot ready after you force-pushed the squashed PR.

@rustbot author

Co-authored-by: Ralf Jung <post@ralfj.de>

icmccorm · 2026-06-11T20:54:12Z

@rustbot ready

RalfJung · 2026-06-12T08:38:32Z

@bors r=RalfJung,folkertdev rollup

rust-bors · 2026-06-12T08:38:34Z

📌 Commit cc89e06 has been approved by RalfJung,folkertdev

It is now in the queue for this repository.

@RalfJung

…adics, r=RalfJung,folkertdev Disable retagging for variadic arguments in const-eval Fixes [rust-lang#5058](rust-lang/miri#5058) in Miri. Retags occur on typed copies, which happen when we pass variadic arguments to a function. At the moment, variadic arguments receive `RetagMode::FnEntry` retags, which protects their permissions for the duration of the call. However, protection needs to be based on callee-side information, and the callee has now way of knowing what's contained within its `VaList`. This PR disables retagging entirely when copying variable arguments. It also adds a new, passing test case that would originally fail before this change. cc: @RalfJung, @folkertdev

@RalfJung

…adics, r=RalfJung,folkertdev Disable retagging for variadic arguments in const-eval Fixes [rust-lang#5058](rust-lang/miri#5058) in Miri. Retags occur on typed copies, which happen when we pass variadic arguments to a function. At the moment, variadic arguments receive `RetagMode::FnEntry` retags, which protects their permissions for the duration of the call. However, protection needs to be based on callee-side information, and the callee has now way of knowing what's contained within its `VaList`. This PR disables retagging entirely when copying variable arguments. It also adds a new, passing test case that would originally fail before this change. cc: @RalfJung, @folkertdev

@RalfJung

…adics, r=RalfJung,folkertdev Disable retagging for variadic arguments in const-eval Fixes [rust-lang#5058](rust-lang/miri#5058) in Miri. Retags occur on typed copies, which happen when we pass variadic arguments to a function. At the moment, variadic arguments receive `RetagMode::FnEntry` retags, which protects their permissions for the duration of the call. However, protection needs to be based on callee-side information, and the callee has now way of knowing what's contained within its `VaList`. This PR disables retagging entirely when copying variable arguments. It also adds a new, passing test case that would originally fail before this change. cc: @RalfJung, @folkertdev

…uwer Rollup of 17 pull requests Successful merges: - #156950 (Staticlib rename internal symbols) - #157322 (test pre-stabilization items on CI) - #157490 (Add field-wise CoerceShared reborrow tests) - #157655 (Make Share::share final and improve docs) - #157688 (Create experimental test job `aarch64-apple-macos-26` for evaluating `macos-26` runner images) - #157796 (rustdoc: Some more lazy formatting) - #157069 (Test that you can't implement Unpin for a compiler-generated future using TAIT) - #157202 (add #[rustc_no_writable] to slice::get_unchecked_mut) - #157622 (Disable retagging for variadic arguments in const-eval) - #157684 (-Zassumptions-on-binders: insert empty assumptions when entering binders in the solver) - #157695 (Extend capabilities of `TypeFoldable_Generic`) - #157752 (Rename `errors.rs` file to `diagnostics.rs` (6/N)) - #157766 (interpret: avoid computing layout of sized raw pointee) - #157785 (fuchsia: Support AddressSanitizer on riscv64gc-unknown-fuchsia) - #157795 (revert 157013) - #157798 (Prevent approving PRs that wait for Crater or formal decisions) - #157803 (Rename `errors.rs` file to `diagnostics.rs` (7/N))

@RalfJung

…adics, r=RalfJung,folkertdev Disable retagging for variadic arguments in const-eval Fixes [rust-lang#5058](rust-lang/miri#5058) in Miri. Retags occur on typed copies, which happen when we pass variadic arguments to a function. At the moment, variadic arguments receive `RetagMode::FnEntry` retags, which protects their permissions for the duration of the call. However, protection needs to be based on callee-side information, and the callee has now way of knowing what's contained within its `VaList`. This PR disables retagging entirely when copying variable arguments. It also adds a new, passing test case that would originally fail before this change. cc: @RalfJung, @folkertdev

…uwer Rollup of 23 pull requests Successful merges: - #144220 (Add powerpc64-unknown-linux-gnuelfv2 target) - #153238 (debuginfo: slices are DW_TAG_array_type's) - #157112 (Update aarch64-unknown-freebsd target description) - #157322 (test pre-stabilization items on CI) - #157348 (Don't track cwd for `-Zremap-cwd-prefix` in incremental compilation) - #157490 (Add field-wise CoerceShared reborrow tests) - #157655 (Make Share::share final and improve docs) - #157672 (Region inference: Simplify initialisation of region values) - #157680 (Require `#[pin_v2]` for explicit pin-projection patterns) - #157688 (Create experimental test job `aarch64-apple-macos-26` for evaluating `macos-26` runner images) - #157796 (rustdoc: Some more lazy formatting) - #157818 (miri subtree update) - #157069 (Test that you can't implement Unpin for a compiler-generated future using TAIT) - #157079 (Don't recover `&raw EXPR` as a missing comma) - #157202 (add #[rustc_no_writable] to slice::get_unchecked_mut) - #157622 (Disable retagging for variadic arguments in const-eval) - #157684 (-Zassumptions-on-binders: insert empty assumptions when entering binders in the solver) - #157695 (Extend capabilities of `TypeFoldable_Generic`) - #157766 (interpret: avoid computing layout of sized raw pointee) - #157785 (fuchsia: Support AddressSanitizer on riscv64gc-unknown-fuchsia) - #157795 (revert 157013) - #157798 (Prevent approving PRs that wait for Crater or formal decisions) - #157803 (Rename `errors.rs` file to `diagnostics.rs` (7/N)) Failed merges: - #157752 (Rename `errors.rs` file to `diagnostics.rs` (6/N))

@RalfJung

Rollup merge of #157622 - BorrowSanitizer:ignore-retags-variadics, r=RalfJung,folkertdev Disable retagging for variadic arguments in const-eval Fixes [#5058](rust-lang/miri#5058) in Miri. Retags occur on typed copies, which happen when we pass variadic arguments to a function. At the moment, variadic arguments receive `RetagMode::FnEntry` retags, which protects their permissions for the duration of the call. However, protection needs to be based on callee-side information, and the callee has now way of knowing what's contained within its `VaList`. This PR disables retagging entirely when copying variable arguments. It also adds a new, passing test case that would originally fail before this change. cc: @RalfJung, @folkertdev

…uwer Rollup of 23 pull requests Successful merges: - rust-lang/rust#144220 (Add powerpc64-unknown-linux-gnuelfv2 target) - rust-lang/rust#153238 (debuginfo: slices are DW_TAG_array_type's) - rust-lang/rust#157112 (Update aarch64-unknown-freebsd target description) - rust-lang/rust#157322 (test pre-stabilization items on CI) - rust-lang/rust#157348 (Don't track cwd for `-Zremap-cwd-prefix` in incremental compilation) - rust-lang/rust#157490 (Add field-wise CoerceShared reborrow tests) - rust-lang/rust#157655 (Make Share::share final and improve docs) - rust-lang/rust#157672 (Region inference: Simplify initialisation of region values) - rust-lang/rust#157680 (Require `#[pin_v2]` for explicit pin-projection patterns) - rust-lang/rust#157688 (Create experimental test job `aarch64-apple-macos-26` for evaluating `macos-26` runner images) - rust-lang/rust#157796 (rustdoc: Some more lazy formatting) - rust-lang/rust#157818 (miri subtree update) - rust-lang/rust#157069 (Test that you can't implement Unpin for a compiler-generated future using TAIT) - rust-lang/rust#157079 (Don't recover `&raw EXPR` as a missing comma) - rust-lang/rust#157202 (add #[rustc_no_writable] to slice::get_unchecked_mut) - rust-lang/rust#157622 (Disable retagging for variadic arguments in const-eval) - rust-lang/rust#157684 (-Zassumptions-on-binders: insert empty assumptions when entering binders in the solver) - rust-lang/rust#157695 (Extend capabilities of `TypeFoldable_Generic`) - rust-lang/rust#157766 (interpret: avoid computing layout of sized raw pointee) - rust-lang/rust#157785 (fuchsia: Support AddressSanitizer on riscv64gc-unknown-fuchsia) - rust-lang/rust#157795 (revert 157013) - rust-lang/rust#157798 (Prevent approving PRs that wait for Crater or formal decisions) - rust-lang/rust#157803 (Rename `errors.rs` file to `diagnostics.rs` (7/N)) Failed merges: - rust-lang/rust#157752 (Rename `errors.rs` file to `diagnostics.rs` (6/N))

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 Jun 8, 2026

rustbot assigned davidtwco Jun 8, 2026

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icmccorm force-pushed the ignore-retags-variadics branch from 885bef0 to 0c6954f Compare June 10, 2026 13:59

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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 Jun 11, 2026

Disable retagging for variadic arguments.

cc89e06

Co-authored-by: Ralf Jung <post@ralfj.de>

icmccorm force-pushed the ignore-retags-variadics branch from 0c6954f to cc89e06 Compare June 11, 2026 20:53

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 Jun 11, 2026

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GuillaumeGomez mentioned this pull request Jun 12, 2026

Rollup of 9 pull requests #157804

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Rollup of 14 pull requests #157809

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Rollup of 17 pull requests #157815

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Rollup of 23 pull requests #157827

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Rollup of 23 pull requests #157828

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rust-bors Bot merged commit 4203236 into rust-lang:main Jun 12, 2026
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RalfJung mentioned this pull request Jun 13, 2026

Unexpected UB: retagging of variadic arguments rust-lang/miri#5058

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