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Auto merge of #96959 - nbdd0121:unwind, r=Amanieu

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Prevent unwinding when `-C panic=abort` is used regardless declared ABI

Ensures that Rust code will abort with `-C panic=abort` regardless ABI used.
```rust
extern "C-unwind" {
    fn may_unwind();
}

// Will be nounwind with `-C panic=abort`, despite `C-unwind` ABI.
pub unsafe extern "C-unwind" fn rust_item_that_can_unwind() {
    may_unwind();
}
```

Current behaviour is that unwind will propagate through. While the current behaviour won't cause unsoundness it is inconsistent with the text reading of [RFC2945](https://rust-lang.github.io/rfcs/2945-c-unwind-abi.html).

I tweaked `fn_can_unwind` instead of tweaking `AbortUnwindingCalls` because this approach would allow Rust (non-direct) callers to also see that this function is nounwind, so it can prevent excessive landing pads generation.

For more discussions: https://rust-lang.zulipchat.com/#narrow/stream/210922-project-ffi-unwind/topic/soundness.20in.20mixed.20panic.20mode.

cc `@alexcrichton,` `@BatmanAoD`
r? `@Amanieu`

`@rustbot` label: T-compiler T-lang F-c_unwind
This commit is contained in:
bors 2022-05-17 15:04:50 +00:00
commit 00755e4ca6
2 changed files with 21 additions and 8 deletions
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8
compiler/rustc_middle/src/ty/layout.rs
View File

@ -2888,6 +2888,14 @@ pub fn fn_can_unwind<'tcx>(tcx: TyCtxt<'tcx>, fn_def_id: Option<DefId>, abi: Spe
return false;
}
// With `-C panic=abort`, all non-FFI functions are required to not unwind.
//
// Note that this is true regardless ABI specified on the function -- a `extern "C-unwind"`
// function defined in Rust is also required to abort.
if tcx.sess.panic_strategy() == PanicStrategy::Abort && !tcx.is_foreign_item(did) {
return false;
}
// With -Z panic-in-drop=abort, drop_in_place never unwinds.
//
// This is not part of `codegen_fn_attrs` as it can differ between crates

21
src/test/codegen/unwind-abis/c-unwind-abi-panic-abort.rs
View File

@ -1,22 +1,27 @@
// compile-flags: -C panic=abort
// Test that `nounwind` atributes are not applied to `C-unwind` extern functions
// even when the code is compiled with `panic=abort`.
// Test that `nounwind` atributes are also applied to extern `C-unwind` Rust functions
// when the code is compiled with `panic=abort`.
#![crate_type = "lib"]
#![feature(c_unwind)]
extern "C-unwind" {
fn may_unwind();
}
// CHECK: @rust_item_that_can_unwind() unnamed_addr #0
// CHECK: @rust_item_that_can_unwind() unnamed_addr [[ATTR0:#[0-9]+]]
#[no_mangle]
pub unsafe extern "C-unwind" fn rust_item_that_can_unwind() {
// CHECK: call void @_ZN4core9panicking15panic_no_unwind
may_unwind();
}
extern "C-unwind" {
// CHECK: @may_unwind() unnamed_addr [[ATTR1:#[0-9]+]]
fn may_unwind();
}
// Now, make sure that the LLVM attributes for this functions are correct. First, make
// sure that the first item is correctly marked with the `nounwind` attribute:
//
// CHECK-NOT: attributes #0 = { {{.*}}nounwind{{.*}} }
// CHECK: attributes [[ATTR0]] = { {{.*}}nounwind{{.*}} }
//
// Now, check that foreign item is correctly marked without the `nounwind` attribute.
// CHECK-NOT: attributes [[ATTR1]] = { {{.*}}nounwind{{.*}} }