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Disable unwinding for catch_unwind error payloads. #99032

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Closed

Disable unwinding for catch_unwind error payloads. #99032

wants to merge 3 commits into from

Commits on Sep 26, 2022

  1. Disable unwinding for catch_unwind error payloads. 

    This does something similar to what was suggested over
rust-lang#86027 (comment)
that is, to cheat a little bit and tweak/amend the `Box<dyn Any…>` obtained
from `catch_unwind`:
  - keep the `.type_id()` the same to avoid breakage with downcasting;
  - but make it so the virtual `.drop_in_place()` is somehow overridden with
    a shim around the real drop glue that prevents unwinding (_e.g._, by
    aborting when that happens).

This is achieved through the `DropNoUnwindSameAnyTypeId<T>`, wrapper:
  - with the very same layout as the `T` it wraps;
  - with an overridden/fake `.type_id()` so as to impersonate its inner `T`;
  - with a manual `impl Drop` which uses an abort bomb to ensure no
    unwinding can happen.

That way, the `Box<DropNoUnwindSameAnyTypeId<T>>`, when box-erased to a
`Box<dyn Any…>`, becomes, both layout-wise, and `type_id`-wise,
undistinguishable from a `Box<T>`, thence avoiding any breakage.

And yet, when that `Box<dyn Any…>` is implicitly dropped with
`catch_unwind`s, no further unwinding can happen.

Handle `resume_unwind` payloads too

Clean up logic: centralize drop-override in catch_unwind & virtual method
    @danielhenrymantilla
    danielhenrymantilla committed Sep 26, 2022
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  2. Make the abort display a nicer message 

    Mark `panic_abort` as `no-unwind`.

Co-Authored-By: Christopher Durham <cad97@cad97.com>
Co-Authored-By: Gary Guo <gary@garyguo.net>
    @danielhenrymantilla @CAD97 @nbdd0121
    3 people committed Sep 26, 2022
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  3. Fix & add panic payload tests. 

     1. Fix runtime UI test that expected drop of panic payload to unwind

 2. Add panic payload tests: ensure proper drop, and add one with catch_unwind

 3. Add test asserting proper abort of unwind in panic payload
    @danielhenrymantilla
    danielhenrymantilla committed Sep 26, 2022
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