Auto merge of #86155 - alexcrichton:abort-on-unwind, r=nikomatsakis

rustc: Fill out remaining parts of C-unwind ABI

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.

4 files changed, 0 insertions, 63 deletions

diff --git a/src/test/ui/malformed/malformed-unwind-1.rs b/src/test/ui/malformed/malformed-unwind-1.rs
deleted file mode 100644
index 009695b177f..00000000000
--- a/src/test/ui/malformed/malformed-unwind-1.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-#![feature(unwind_attributes)]
-
-#[unwind] //~ ERROR malformed `unwind` attribute
-extern "C" fn f1() {}
-
-#[unwind = ""] //~ ERROR malformed `unwind` attribute
-extern "C" fn f2() {}
-
-fn main() {}
diff --git a/src/test/ui/malformed/malformed-unwind-1.stderr b/src/test/ui/malformed/malformed-unwind-1.stderr
deleted file mode 100644
index 0a553e8a245..00000000000
--- a/src/test/ui/malformed/malformed-unwind-1.stderr
+++ /dev/null
@@ -1,14 +0,0 @@
-error: malformed `unwind` attribute input
-  --> $DIR/malformed-unwind-1.rs:3:1
-   |
-LL | #[unwind]
-   | ^^^^^^^^^ help: must be of the form: `#[unwind(allowed|aborts)]`
-
-error: malformed `unwind` attribute input
-  --> $DIR/malformed-unwind-1.rs:6:1
-   |
-LL | #[unwind = ""]
-   | ^^^^^^^^^^^^^^ help: must be of the form: `#[unwind(allowed|aborts)]`
-
-error: aborting due to 2 previous errors
-
diff --git a/src/test/ui/malformed/malformed-unwind-2.rs b/src/test/ui/malformed/malformed-unwind-2.rs
deleted file mode 100644
index 9aafc7ca9b8..00000000000
--- a/src/test/ui/malformed/malformed-unwind-2.rs
+++ /dev/null
@@ -1,11 +0,0 @@
-#![feature(unwind_attributes)]
-
-#[unwind(allowed, aborts)]
-//~^ ERROR malformed `unwind` attribute
-extern "C" fn f1() {}
-
-#[unwind(unsupported)]
-//~^ ERROR malformed `unwind` attribute
-extern "C" fn f2() {}
-
-fn main() {}
diff --git a/src/test/ui/malformed/malformed-unwind-2.stderr b/src/test/ui/malformed/malformed-unwind-2.stderr
deleted file mode 100644
index 28512bf9ef1..00000000000
--- a/src/test/ui/malformed/malformed-unwind-2.stderr
+++ /dev/null
@@ -1,29 +0,0 @@
-error[E0633]: malformed `unwind` attribute input
-  --> $DIR/malformed-unwind-2.rs:3:1
-   |
-LL | #[unwind(allowed, aborts)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid argument
-   |
-help: the allowed arguments are `allowed` and `aborts`
-   |
-LL | #[unwind(allowed)]
-   |
-LL | #[unwind(aborts)]
-   |
-
-error[E0633]: malformed `unwind` attribute input
-  --> $DIR/malformed-unwind-2.rs:7:1
-   |
-LL | #[unwind(unsupported)]
-   | ^^^^^^^^^^^^^^^^^^^^^^ invalid argument
-   |
-help: the allowed arguments are `allowed` and `aborts`
-   |
-LL | #[unwind(allowed)]
-   |
-LL | #[unwind(aborts)]
-   |
-
-error: aborting due to 2 previous errors
-
-For more information about this error, try `rustc --explain E0633`.