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Permit unwinding through FFI by default by cuviper · Pull Request #62603 · rust-lang/rust

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Aug 23, 2019

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Aug 25, 2019

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Aug 26, 2019 
Permit unwinding through FFI by default

This repeats #62505 for master (Rust 1.38+), as #58794 is not yet resolved. This is a stopgap until a stable alternative is available, like [RFC 2699](rust-lang/rfcs#2699), as long as progress is being made to that end.

r? @joshtriplett

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Aug 26, 2019

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Aug 28, 2019 
fix nounwind attribute logic

With #62603 landed, we no longer add abort-on-panic shims to `extern "C"` functions. However, that means we should also not emit `nounwind` for `extern fn` because we are not actually catching those panics. The comment justifying that `nounwind` in the source is just factually wrong.

I also noticed that we annotate `extern` *declarations* (of any ABI) with `nounwind`, which seems wrong? I removed this. Code like mozjpeg (the code that prompted the removal of the abort-on-panic shim) throws a panic from Rust code that enters C code (meaning the `extern "C"` *definition* must not have `nounwind`, or else we got UB), but then the panic bubbles through the C code and re-enters Rust code (meaning the `extern "C"` *declaration* that gets called from the Rust side must not have `nounwind` either).

This should be beta-backported if #62603 gets backported.

bors added a commit that referenced this pull request

Sep 14, 2019 
[beta] Rollup backports

Cherry-picked:

- Permit unwinding through FFI by default #62603
- pprust: Do not print spaces before some tokens #63897
- Account for doc comments coming from proc macros without spans #63930
- Support "soft" feature-gating using a lint #64066
- Update xLTO compatibility table in rustc book. #64092
- Include compiler-rt in the source tarball #64240
- Update LLVM submodule #64317

r? @Mark-Simulacrum