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Stabilise c_unwind

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This commit is contained in:
Gary Guo 2023-08-25 13:45:35 +01:00
parent 5978f35330
commit ebdfcd93a3
11 changed files with 10 additions and 102 deletions
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36
compiler/rustc_middle/src/ty/layout.rs
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@ -1182,37 +1182,6 @@ pub fn fn_can_unwind(tcx: TyCtxt<'_>, fn_def_id: Option<DefId>, abi: SpecAbi) ->
// ABIs have such an option. Otherwise the only other thing here is Rust
// itself, and those ABIs are determined by the panic strategy configured
// for this compilation.
//
// Unfortunately at this time there's also another caveat. Rust [RFC
// 2945][rfc] has been accepted and is in the process of being implemented
// and stabilized. In this interim state we need to deal with historical
// rustc behavior as well as plan for future rustc behavior.
//
// Historically functions declared with `extern "C"` were marked at the
// codegen layer as `nounwind`. This happened regardless of `panic=unwind`
// or not. This is UB for functions in `panic=unwind` mode that then
// actually panic and unwind. Note that this behavior is true for both
// externally declared functions as well as Rust-defined function.
//
// To fix this UB rustc would like to change in the future to catch unwinds
// from function calls that may unwind within a Rust-defined `extern "C"`
// function and forcibly abort the process, thereby respecting the
// `nounwind` attribute emitted for `extern "C"`. This behavior change isn't
// ready to roll out, so determining whether or not the `C` family of ABIs
// unwinds is conditional not only on their definition but also whether the
// `#![feature(c_unwind)]` feature gate is active.
//
// Note that this means that unlike historical compilers rustc now, by
// default, unconditionally thinks that the `C` ABI may unwind. This will
// prevent some optimization opportunities, however, so we try to scope this
// change and only assume that `C` unwinds with `panic=unwind` (as opposed
// to `panic=abort`).
//
// Eventually the check against `c_unwind` here will ideally get removed and
// this'll be a little cleaner as it'll be a straightforward check of the
// ABI.
//
// [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md
use SpecAbi::*;
match abi {
C { unwind }
@ -1224,10 +1193,7 @@ pub fn fn_can_unwind(tcx: TyCtxt<'_>, fn_def_id: Option<DefId>, abi: SpecAbi) ->
| Thiscall { unwind }
| Aapcs { unwind }
| Win64 { unwind }
| SysV64 { unwind } => {
unwind
|| (!tcx.features().c_unwind && tcx.sess.panic_strategy() == PanicStrategy::Unwind)
}
| SysV64 { unwind } => unwind,
PtxKernel
| Msp430Interrupt
| X86Interrupt