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Tracking issue for #[ffi_returns_twice] #58314

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gnzlbg opened this issue Feb 8, 2019 · 5 comments
Closed

Tracking issue for #[ffi_returns_twice] #58314

gnzlbg opened this issue Feb 8, 2019 · 5 comments
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A-ffi Area: Foreign Function Interface (FFI) B-unstable Feature: 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 •
edited

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 Feature: 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.
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Labels
A-ffi Area: Foreign Function Interface (FFI) B-unstable Feature: 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 @JohnTitor