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Auto merge of #76570 - cratelyn:implement-rfc-2945-c-unwind-abi, r=Amanieu

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Implement RFC 2945: "C-unwind" ABI

## Implement RFC 2945: "C-unwind" ABI

This branch implements [RFC 2945]. The tracking issue for this RFC is #74990.

The feature gate for the issue is `#![feature(c_unwind)]`.

This RFC was created as part of the ffi-unwind project group tracked at rust-lang/lang-team#19.

### Changes

Further details will be provided in commit messages, but a high-level overview
of the changes follows:

* A boolean `unwind` payload is added to the `C`, `System`, `Stdcall`,
and `Thiscall` variants, marking whether unwinding across FFI boundaries is
acceptable. The cases where each of these variants' `unwind` member is true
correspond with the `C-unwind`, `system-unwind`, `stdcall-unwind`, and
`thiscall-unwind` ABI strings introduced in RFC 2945 [3].

* This commit adds a `c_unwind` feature gate for the new ABI strings.
Tests for this feature gate are included in `src/test/ui/c-unwind/`, which
ensure that this feature gate works correctly for each of the new ABIs.
A new language features entry in the unstable book is added as well.

* We adjust the `rustc_middle::ty::layout::fn_can_unwind` function,
used to compute whether or not a `FnAbi` object represents a function that
should be able to unwind when `panic=unwind` is in use.

* Changes are also made to
`rustc_mir_build::build::should_abort_on_panic` so that the function ABI is
used to determind whether it should abort, assuming that the `panic=unwind`
strategy is being used, and no explicit unwind attribute was provided.

[RFC 2945]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md
This commit is contained in:
bors 2021-03-10 16:44:04 +00:00
commit 17a07d71bf
43 changed files with 661 additions and 70 deletions
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38
compiler/rustc_mir_build/src/build/mod.rs
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@ -548,7 +548,7 @@ macro_rules! unpack {
}};
}
fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, _abi: Abi) -> bool {
fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, abi: Abi) -> bool {
// Validate `#[unwind]` syntax regardless of platform-specific panic strategy.
let attrs = &tcx.get_attrs(fn_def_id.to_def_id());
let unwind_attr = attr::find_unwind_attr(&tcx.sess, attrs);
@ -558,12 +558,42 @@ fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, _abi: Abi) -> b
return false;
}
// This is a special case: some functions have a C abi but are meant to
// unwind anyway. Don't stop them.
match unwind_attr {
None => false, // FIXME(#58794); should be `!(abi == Abi::Rust || abi == Abi::RustCall)`
// If an `#[unwind]` attribute was found, we should adhere to it.
Some(UnwindAttr::Allowed) => false,
Some(UnwindAttr::Aborts) => true,
// If no attribute was found and the panic strategy is `unwind`, then we should examine
// the function's ABI string to determine whether it should abort upon panic.
None => {
use Abi::*;
match abi {
// In the case of ABI's that have an `-unwind` equivalent, check whether the ABI
// permits unwinding. If so, we should not abort. Otherwise, we should.
C { unwind } | Stdcall { unwind } | System { unwind } | Thiscall { unwind } => {
!unwind
}
// Rust and `rust-call` functions are allowed to unwind, and should not abort.
Rust | RustCall => false,
// Other ABI's should abort.
Cdecl
| Fastcall
| Vectorcall
| Aapcs
| Win64
| SysV64
| PtxKernel
| Msp430Interrupt
| X86Interrupt
| AmdGpuKernel
| EfiApi
| AvrInterrupt
| AvrNonBlockingInterrupt
| CCmseNonSecureCall
| RustIntrinsic
| PlatformIntrinsic
| Unadjusted => true,
}
}
}
}