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MaybeDangling: ensure references fit inside the address space - #160749

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RalfJung:maybe-dangling-address-space
Aug 10, 2026
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MaybeDangling: ensure references fit inside the address space#160749
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RalfJung:maybe-dangling-address-space

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@RalfJung

@RalfJungRalfJung commented Aug 8, 2026

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In the RFC we left open the question of the exact validity invariant for references inside MaybeDangling. This PR implements the strictest invariant I can think of: we already require references to be aligned, now we also require "addr + size" to be computable without overflow. This ensures that whatever niches we add to references in the future, MaybeDangling preserves those niches.

Cc @rust-lang/opsem @WaffleLapkin

Tracking issue: #118166
r? @oli-obk

  • I did not use an LLM to create a change in this PR.
  • I used an LLM to create a change in this PR, and I have explained below how it was used.

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Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

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

Some changes occurred to the CTFE machinery

cc @oli-obk, @lcnr

@rustbotrustbot 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 Aug 8, 2026
@RalfJungRalfJung mentioned this pull request Aug 8, 2026
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CAD97
CAD97 approved these changes Aug 8, 2026
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This is the obvious validity requirement, making the relaxation for MaybeDangling simply what's required for the nominal effect. LGTM

r+ (but I don't have r+ perms)

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WaffleLapkin
WaffleLapkin approved these changes Aug 10, 2026
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@bors r+

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📌 Commit 0226819 has been approved by WaffleLapkin

It is now in the queue for this repository.

@rust-borsrust-borsBot 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 Aug 10, 2026
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Aug 10, 2026
@JonathanBrouwer
Rollup merge ofrust-lang#160749- RalfJung:maybe-dangling-address-sp…
e888c61
…ace, r=WaffleLapkin
MaybeDangling: ensure references fit inside the address space
In the RFC we left open the question of the exact validity invariant for references inside `MaybeDangling`. This PR implements the strictest invariant I can think of: we already require references to be aligned, now we also require "addr + size" to be computable without overflow. This ensures that whatever niches we add to references in the future, `MaybeDangling` preserves those niches.
Cc @rust-lang/opsem @WaffleLapkin
Tracking issue: rust-lang#118166
r? @oli-obk
This was referenced Aug 10, 2026
Closed
Merged
rust-borsBot pushed a commit that referenced this pull request Aug 10, 2026
@bors
Auto merge of#160867- JonathanBrouwer:rollup-bas1App, r=JonathanBro…
12c36e2
…uwer
Rollup of 9 pull requests
Successful merges:
- #158404 (trait_solver: normalize next-gen region constraints)
- #160631 (Do not eagerly download rustfmt in bootstrap)
- #160642 (mir: prohibit projection into scalable vec)
- #160749 (MaybeDangling: ensure references fit inside the address space)
- #160791 (Use recognizer functions for enums and tuple structs)
- #160500 (Fix inaccurate description for crate and pathroot)
- #160590 (Docs & bors: Replace mentions of libs-api with libs)
- #160825 (Fix references to unsupported on sys::paths::unix)
- #160852 (Use `remove_dir_all` for `./x clean`)
Failed merges:
- #160829 (bootstrap: Make `main.rs` a stub that calls into the library crate)
@rust-bors
rust-borsBot merged commit cbc9fdd into rust-lang:mainAug 10, 2026
13 checks passed
@rustbotrustbot added this to the 1.99.0 milestone Aug 10, 2026
rust-timer added a commit that referenced this pull request Aug 10, 2026
@rust-timer
Unrolled build for#160749
e5c1f30
Rollup merge of #160749 - RalfJung:maybe-dangling-address-space, r=WaffleLapkin
MaybeDangling: ensure references fit inside the address space
In the RFC we left open the question of the exact validity invariant for references inside `MaybeDangling`. This PR implements the strictest invariant I can think of: we already require references to be aligned, now we also require "addr + size" to be computable without overflow. This ensures that whatever niches we add to references in the future, `MaybeDangling` preserves those niches.
Cc @rust-lang/opsem@WaffleLapkin
Tracking issue: #118166
r? @oli-obk
github-actionsBot pushed a commit to rust-lang/rustc-dev-guide that referenced this pull request Aug 11, 2026
@bors
Auto merge of #160867 - JonathanBrouwer:rollup-bas1App, r=JonathanBro…
f15f066
…uwer
Rollup of 9 pull requests
Successful merges:
- rust-lang/rust#158404 (trait_solver: normalize next-gen region constraints)
- rust-lang/rust#160631 (Do not eagerly download rustfmt in bootstrap)
- rust-lang/rust#160642 (mir: prohibit projection into scalable vec)
- rust-lang/rust#160749 (MaybeDangling: ensure references fit inside the address space)
- rust-lang/rust#160791 (Use recognizer functions for enums and tuple structs)
- rust-lang/rust#160500 (Fix inaccurate description for crate and pathroot)
- rust-lang/rust#160590 (Docs & bors: Replace mentions of libs-api with libs)
- rust-lang/rust#160825 (Fix references to unsupported on sys::paths::unix)
- rust-lang/rust#160852 (Use `remove_dir_all` for `./x clean`)
Failed merges:
- rust-lang/rust#160829 (bootstrap: Make `main.rs` a stub that calls into the library crate)
bjorn3 pushed a commit to bjorn3/stdarch that referenced this pull request Aug 13, 2026
@bors
Auto merge of #160867 - JonathanBrouwer:rollup-bas1App, r=JonathanBro…
4500f41
…uwer
Rollup of 9 pull requests
Successful merges:
- rust-lang/rust#158404 (trait_solver: normalize next-gen region constraints)
- rust-lang/rust#160631 (Do not eagerly download rustfmt in bootstrap)
- rust-lang/rust#160642 (mir: prohibit projection into scalable vec)
- rust-lang/rust#160749 (MaybeDangling: ensure references fit inside the address space)
- rust-lang/rust#160791 (Use recognizer functions for enums and tuple structs)
- rust-lang/rust#160500 (Fix inaccurate description for crate and pathroot)
- rust-lang/rust#160590 (Docs & bors: Replace mentions of libs-api with libs)
- rust-lang/rust#160825 (Fix references to unsupported on sys::paths::unix)
- rust-lang/rust#160852 (Use `remove_dir_all` for `./x clean`)
Failed merges:
- rust-lang/rust#160829 (bootstrap: Make `main.rs` a stub that calls into the library crate)
@RalfJung
RalfJung deleted the maybe-dangling-address-space branch August 15, 2026 06:49
@RalfJungRalfJung mentioned this pull request Aug 15, 2026
Merged
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Aug 15, 2026
@JonathanBrouwer
Rollup merge ofrust-lang#161125- RalfJung:MaybeDangling-validity, r…
337eccf
…=saethlin
fix buggy MaybeDangling<&T> validation logic
Fixes a critical regression in rust-lang#160749.
This is what caused the trouble in rust-lang/miri#5252.
r? @oli-obk or @saethlin
rust-timer added a commit that referenced this pull request Aug 15, 2026
@rust-timer
Unrolled build for#161125
62dfa33
Rollup merge of #161125 - RalfJung:MaybeDangling-validity, r=saethlin
fix buggy MaybeDangling<&T> validation logic
Fixes a critical regression in #160749.
This is what caused the trouble in rust-lang/miri#5252.
r? @oli-obk or @saethlin
rust-borsBot pushed a commit that referenced this pull request Aug 15, 2026
@bors
Unrolled build for#161125
b2712e3
Rollup merge of #161125 - RalfJung:MaybeDangling-validity, r=saethlin
fix buggy MaybeDangling<&T> validation logic
Fixes a critical regression in #160749.
This is what caused the trouble in rust-lang/miri#5252.
r? @oli-obk or @saethlin
RalfJung pushed a commit to saethlin/miri that referenced this pull request Aug 16, 2026
@JonathanBrouwer
Rollup merge of #161125 - RalfJung:MaybeDangling-validity, r=saethlin
7c98956
fix buggy MaybeDangling<&T> validation logic
Fixes a critical regression in rust-lang/rust#160749.
This is what caused the trouble in rust-lang#5252.
r? @oli-obk or @saethlin
pullBot pushed a commit to LeeeeeeM/miri that referenced this pull request Aug 16, 2026
@bors
Auto merge of #160867 - JonathanBrouwer:rollup-bas1App, r=JonathanBro…
74063f7
…uwer
Rollup of 9 pull requests
Successful merges:
- rust-lang/rust#158404 (trait_solver: normalize next-gen region constraints)
- rust-lang/rust#160631 (Do not eagerly download rustfmt in bootstrap)
- rust-lang/rust#160642 (mir: prohibit projection into scalable vec)
- rust-lang/rust#160749 (MaybeDangling: ensure references fit inside the address space)
- rust-lang/rust#160791 (Use recognizer functions for enums and tuple structs)
- rust-lang/rust#160500 (Fix inaccurate description for crate and pathroot)
- rust-lang/rust#160590 (Docs & bors: Replace mentions of libs-api with libs)
- rust-lang/rust#160825 (Fix references to unsupported on sys::paths::unix)
- rust-lang/rust#160852 (Use `remove_dir_all` for `./x clean`)
Failed merges:
- rust-lang/rust#160829 (bootstrap: Make `main.rs` a stub that calls into the library crate)
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