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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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2
compiler/rustc_feature/src/accepted.rs
View file

@ -80,6 +80,8 @@ declare_features! (
(accepted, braced_empty_structs, "1.8.0", Some(29720)),
/// Allows `c"foo"` literals.
(accepted, c_str_literals, "1.77.0", Some(105723)),
/// Allows `extern "C-unwind" fn` to enable unwinding across ABI boundaries and treat `extern "C" fn` as nounwind.
(accepted, c_unwind, "CURRENT_RUSTC_VERSION", Some(74990)),
/// Allows `#[cfg_attr(predicate, multiple, attributes, here)]`.
(accepted, cfg_attr_multi, "1.33.0", Some(54881)),
/// Allows the use of `#[cfg(doctest)]`, set when rustdoc is collecting doctests.

2
compiler/rustc_feature/src/unstable.rs
View file

@ -363,8 +363,6 @@ declare_features! (
(unstable, async_for_loop, "1.77.0", Some(118898)),
/// Allows builtin # foo() syntax
(unstable, builtin_syntax, "1.71.0", Some(110680)),
/// Treat `extern "C"` function as nounwind.
(unstable, c_unwind, "1.52.0", Some(74990)),
/// Allows using C-variadics.
(unstable, c_variadic, "1.34.0", Some(44930)),
/// Allows the use of `#[cfg(overflow_checks)` to check if integer overflow behaviour.

36
compiler/rustc_middle/src/ty/layout.rs
View file

@ -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

34
compiler/rustc_mir_transform/src/ffi_unwind_calls.rs
View file

@ -11,38 +11,6 @@ use rustc_target::spec::PanicStrategy;
use crate::errors;
/// Some of the functions declared as "may unwind" by `fn_can_unwind` can't actually unwind. In
/// particular, `extern "C"` is still considered as can-unwind on stable, but we need to consider
/// it cannot-unwind here. So below we check `fn_can_unwind() && abi_can_unwind()` before concluding
/// that a function call can unwind.
fn abi_can_unwind(abi: Abi) -> bool {
use Abi::*;
match abi {
C { unwind }
| System { unwind }
| Cdecl { unwind }
| Stdcall { unwind }
| Fastcall { unwind }
| Vectorcall { unwind }
| Thiscall { unwind }
| Aapcs { unwind }
| Win64 { unwind }
| SysV64 { unwind } => unwind,
PtxKernel
| Msp430Interrupt
| X86Interrupt
| EfiApi
| AvrInterrupt
| AvrNonBlockingInterrupt
| RiscvInterruptM
| RiscvInterruptS
| CCmseNonSecureCall
| Wasm
| Unadjusted => false,
RustIntrinsic | Rust | RustCall | RustCold => unreachable!(), // these ABIs are already skipped earlier
}
}
// Check if the body of this def_id can possibly leak a foreign unwind into Rust code.
fn has_ffi_unwind_calls(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> bool {
debug!("has_ffi_unwind_calls({local_def_id:?})");
@ -103,7 +71,7 @@ fn has_ffi_unwind_calls(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> bool {
_ => bug!("invalid callee of type {:?}", ty),
};
if layout::fn_can_unwind(tcx, fn_def_id, sig.abi()) && abi_can_unwind(sig.abi()) {
if layout::fn_can_unwind(tcx, fn_def_id, sig.abi()) {
// We have detected a call that can possibly leak foreign unwind.
//
// Because the function body itself can unwind, we are not aborting this function call