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panic_handler can be an unsafe fn #162967

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panic_handler can be an unsafe fn#162967
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A-attributesArea: Attributes (`#[…]`, `#![…]`)A-panicArea: Panicking machineryC-bugCategory: This is a bug.I-unsoundIssue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/SoundnessP-highHigh priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.T-langRelevant to the language team

Description

@theemathas
theemathas
opened on Sep 18, 2026

This issue is a variant of #134225. I am filing this issue on behalf of @zesterer, who discovered this.

This code currently compiles:

#![no_std]

#[panic_handler]
unsafe fn handle(_: &core::panic::PanicInfo) -> ! {
    loop {}
}

Presumably, this causes this unsafe function to be called if a panic happens. This is unsound, as this calls an unsafe function without considering its safety requirements.

Cursory github search for code that relies on this compiling: https://github.com/search?q=language%3Arust+%2F%23%5C%5Bpanic_handler%5C%5D%5Cnunsafe%2F&type=code

Meta

Reproducible on the playground with version 1.100.0-nightly (2026-09-17 330d317121e16b5db8e5)

Activity

  1. theemathas
    added
    A-attributesArea: Attributes (`#[…]`, `#![…]`)
    T-langRelevant to the language team
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    I-unsoundIssue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/Soundness
    C-bugCategory: This is a bug.
    A-panicArea: Panicking machinery
    on Sep 18, 2026
  2. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    on Sep 18, 2026
  3. theemathas
    removed
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Sep 18, 2026

  4. bjorn3 commented on Sep 18, 2026

    @bjorn3
    bjorn3
    on Sep 18, 2026
    Member

    #159016 would deny this if it lands.

  5. rustbot
    removed
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    on Sep 21, 2026

  6. rustbot commented on Sep 21, 2026

    @rustbot
    rustbot
    on Sep 21, 2026
    Collaborator

    Assigning P-high (discussion on Zulip)

  7. rustbot
    added
    P-highHigh priority
    on Sep 21, 2026
  8. JonathanBrouwer
    added a commit that references this issue on Oct 4, 2026

    Rollup merge of rust-lang#162974 - theemathas:fcw-unsafe-panic-handle…

    dff61b8
  9. rust-bors
    added a commit that references this issue on Oct 4, 2026

    Unrolled build for #162974 in rollup 163754

    00e4dad
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    A-attributesArea: Attributes (`#[…]`, `#![…]`)A-panicArea: Panicking machineryC-bugCategory: This is a bug.I-unsoundIssue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/SoundnessP-highHigh priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.T-langRelevant to the language team

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