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Tracking issue for #[ffi_returns_twice] #58314

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gnzlbg opened this issue Feb 8, 2019 · 7 comments
Closed

Tracking issue for #[ffi_returns_twice] #58314

gnzlbg opened this issue Feb 8, 2019 · 7 comments
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A-FFI Area: Foreign function interface (FFI) B-unstable Blocker: Implemented in the nightly compiler and unstable. C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. T-lang Relevant to the language team, which will review and decide on the PR/issue.

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@gnzlbg
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gnzlbg commented Feb 8, 2019 •
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I'll update with the PR and RFC links when those are ready.

PR: #58315
RFC: rust-lang/rfcs#2633
@jonas-schievink jonas-schievink added B-unstable Blocker: Implemented in the nightly compiler and unstable. C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. labels Feb 9, 2019
@jonas-schievink
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Implemented in #58315

@gnzlbg gnzlbg changed the title Tracking issue for #[returns_twice] Tracking issue for #[ffi_returns_twice] Feb 9, 2019
@Centril Centril added the T-lang Relevant to the language team, which will review and decide on the PR/issue. label Feb 11, 2019
@Amanieu Amanieu mentioned this issue Oct 29, 2019
Merged
bors added a commit to rust-lang/libc that referenced this issue Nov 18, 2019
@bors
Auto merge of #1574 - Amanieu:deprecate-vfork, r=gnzlbg
a13ad69 
Deprecate vfork

The compiler may generate incorrect code for `vfork` and `setjmp` because they are missing the `#[returns_twice]` attribute which is currently unstable ([tracking issue](rust-lang/rust#58314)). Since `vfork` is impossible to use safely, I propose deprecating it until `#[returns_twice]` is stable.
@JohnTitor
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Could we stabilize this feature now? I'm not sure if this is unstable because it's newly added or there's a blocker but it'd be great if we could de-deprecate vfork on the libc :) cc @Amanieu

@Amanieu
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Amanieu commented Oct 15, 2020

I am very hesitant to do so since it would stabilize a horrible hack that C uses for two functions: vfork and setjmp. In particular:

  • This basically works by disabling a bunch of optimizations in LLVM, but it would likely require additional work in rustc for MIR optimizations.
  • Functions that return twice are a hack, you can't even implement such functions in C: they must be written in assembly.
  • If you really want to use vfork then you should use a C or asm wrapper that hides the "returns twice" hack and provides a safe callback interface that allows you to run a function in the child process.

@JohnTitor
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Ah, fair enough! I just thought this was missed from stabilizing eyes since rust-lang/libc#1574's OP says "I propose deprecating it until #[returns_twice] is stable". With the above comment, I'm fine to leave this feature as-is, thanks for clarifying!

@jonas-schievink jonas-schievink added the A-FFI Area: Foreign function interface (FFI) label Feb 25, 2021
@matejcik matejcik mentioned this issue May 11, 2021
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@joshtriplett
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Closing because rust-lang/rfcs#2633 was closed. (The ffi-unwind project is looking at this.)

@clubby789 clubby789 mentioned this issue Jan 30, 2024
Merged
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 6, 2024
@matthiaskrgr
Rollup merge of rust-lang#120502 - clubby789:remove-ffi-returns-twice…
6293990 
…, r=compiler-errors

Remove `ffi_returns_twice` feature

The [tracking issue](rust-lang#58314) and [RFC](rust-lang/rfcs#2633) have been closed for a couple of years.

There is also an attribute gate in R-A which should be removed if this lands.
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 6, 2024
@matthiaskrgr
Rollup merge of rust-lang#120502 - clubby789:remove-ffi-returns-twice…
2a488c4 
…, r=compiler-errors

Remove `ffi_returns_twice` feature

The [tracking issue](rust-lang#58314) and [RFC](rust-lang/rfcs#2633) have been closed for a couple of years.

There is also an attribute gate in R-A which should be removed if this lands.
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 6, 2024
@matthiaskrgr
Rollup merge of rust-lang#120502 - clubby789:remove-ffi-returns-twice…
59ba802 
…, r=compiler-errors

Remove `ffi_returns_twice` feature

The [tracking issue](rust-lang#58314) and [RFC](rust-lang/rfcs#2633) have been closed for a couple of years.

There is also an attribute gate in R-A which should be removed if this lands.
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Feb 7, 2024
@rust-timer
Unrolled build for rust-lang#120502
a87878b 
Rollup merge of rust-lang#120502 - clubby789:remove-ffi-returns-twice, r=compiler-errors

Remove `ffi_returns_twice` feature

The [tracking issue](rust-lang#58314) and [RFC](rust-lang/rfcs#2633) have been closed for a couple of years.

There is also an attribute gate in R-A which should be removed if this lands.
GuillaumeGomez pushed a commit to GuillaumeGomez/rustc_codegen_gcc that referenced this issue Feb 15, 2024
@matthiaskrgr
Rollup merge of #120502 - clubby789:remove-ffi-returns-twice, r=compi…
1f5316a 
…ler-errors

Remove `ffi_returns_twice` feature

The [tracking issue](rust-lang/rust#58314) and [RFC](rust-lang/rfcs#2633) have been closed for a couple of years.

There is also an attribute gate in R-A which should be removed if this lands.
@VorpalBlade
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Whatever became of this? Since FFI-unwind was mentioned, C-unwind now exists and is stable, so is it time to revisit this?

@Amanieu
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Amanieu commented Oct 23, 2024

This is completely unrelated to unwinding. It's about the weird ABI used by functions like vfork and setjmp which do not want to support in Rust.

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A-FFI Area: Foreign function interface (FFI) B-unstable Blocker: Implemented in the nightly compiler and unstable. C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. T-lang Relevant to the language team, which will review and decide on the PR/issue.
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@joshtriplett @Amanieu @Centril @gnzlbg @jonas-schievink @VorpalBlade @JohnTitor