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rustc: Fill out remaining parts of C-unwind ABI

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This commit intends to fill out some of the remaining pieces of the
C-unwind ABI. This has a number of other changes with it though to move
this design space forward a bit. Notably contained within here is:

* On `panic=unwind`, the `extern "C"` ABI is now considered as "may
  unwind". This fixes a longstanding soundness issue where if you
  `panic!()` in an `extern "C"` function defined in Rust that's actually
  UB because the LLVM representation for the function has the `nounwind`
  attribute, but then you unwind.

* Whether or not a function unwinds now mainly considers the ABI of the
  function instead of first checking the panic strategy. This fixes a
  miscompile of `extern "C-unwind"` with `panic=abort` because that ABI
  can still unwind.

* The aborting stub for non-unwinding ABIs with `panic=unwind` has been
  reimplemented. Previously this was done as a small tweak during MIR
  generation, but this has been moved to a separate and dedicated MIR
  pass. This new pass will, for appropriate functions and function
  calls, insert a `cleanup` landing pad for any function call that may
  unwind within a function that is itself not allowed to unwind. Note
  that this subtly changes some behavior from before where previously on
  an unwind which was caught-to-abort it would run active destructors in
  the function, and now it simply immediately aborts the process.

* The `#[unwind]` attribute has been removed and all users in tests and
  such are now using `C-unwind` and `#![feature(c_unwind)]`.

I think this is largely the last piece of the RFC to implement.
Unfortunately I believe this is still not stabilizable as-is because
activating the feature gate changes the behavior of the existing `extern
"C"` ABI in a way that has no replacement. My thinking for how to enable
this is that we add support for the `C-unwind` ABI on stable Rust first,
and then after it hits stable we change the behavior of the `C` ABI.
That way anyone straddling stable/beta/nightly can switch to `C-unwind`
safely.
This commit is contained in:
Alex Crichton 2021-06-08 11:23:58 -07:00
parent 2939249f29
commit 1c07096a45
46 changed files with 431 additions and 478 deletions
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44
compiler/rustc_attr/src/builtin.rs
View file

@ -87,50 +87,6 @@ pub enum OptimizeAttr {
Size,
}
#[derive(Copy, Clone, PartialEq)]
pub enum UnwindAttr {
Allowed,
Aborts,
}
/// Determine what `#[unwind]` attribute is present in `attrs`, if any.
pub fn find_unwind_attr(sess: &Session, attrs: &[Attribute]) -> Option<UnwindAttr> {
attrs.iter().fold(None, |ia, attr| {
if sess.check_name(attr, sym::unwind) {
if let Some(meta) = attr.meta() {
if let MetaItemKind::List(items) = meta.kind {
if items.len() == 1 {
if items[0].has_name(sym::allowed) {
return Some(UnwindAttr::Allowed);
} else if items[0].has_name(sym::aborts) {
return Some(UnwindAttr::Aborts);
}
}
struct_span_err!(
sess.diagnostic(),
attr.span,
E0633,
"malformed `unwind` attribute input"
)
.span_label(attr.span, "invalid argument")
.span_suggestions(
attr.span,
"the allowed arguments are `allowed` and `aborts`",
(vec!["allowed", "aborts"])
.into_iter()
.map(|s| format!("#[unwind({})]", s)),
Applicability::MachineApplicable,
)
.emit();
}
}
}
ia
})
}
/// Represents the following attributes:
///
/// - `#[stable]`