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Update guarantees of unwinding past an extern "C" function #887

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Update guarantees of unwinding past an extern "C" function #887

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14 changes: 9 additions & 5 deletions src/items/functions.md
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Original file line number Diff line number Diff line change
Expand Up @@ -174,12 +174,15 @@ extern "C" fn new_i32() -> i32 { 0 }
let fptr: extern "C" fn() -> i32 = new_i32;
```

Functions with an ABI that differs from `"Rust"` do not support unwinding in the
exact same way that Rust does. Therefore, unwinding past the end of functions
with such ABIs causes the process to abort.
Functions with an ABI that differs from `"Rust"` do not support unwinding in
the exact same way that Rust does. Therefore, unwinding past the end of
functions with such ABIs results in undefined behavior, and will differ between
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Can you link undefined behavior to behavior-considered-undefined.md?

platforms and compiler editions. If you cannot guarantee this will not happen,
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I'm not sure what "compiler editions" means here. "Edition" has a specific meaning in Rust, and I don't think that is what is being referred to here. I think it would be fine to end the sentence at "undefined behavior", with the link leading the reader to understanding what that means.

you should use [`catch_unwind`] or similar to abort the program instead if
unwinding would pass through the function.

> **Note**: The LLVM backend of the `rustc` implementation
aborts the process by executing an illegal instruction.
> **Note**: Currently, in nightly `rustc` the LLVM backend aborts the process
> by executing an illegal instruction. However, this is not the behavior in stable.
Comment on lines +184 to +185
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We generally don't include notes about specific versions of the rustc compiler in the reference. I'm also not sure what this is referring to, since it no longer aborts on unwind.


## Const functions

Expand Down Expand Up @@ -372,3 +375,4 @@ fn foo_oof(#[some_inert_attribute] arg: u8) {
[`link_section`]: ../abi.md#the-link_section-attribute
[`no_mangle`]: ../abi.md#the-no_mangle-attribute
[built-in attributes]: ../attributes.html#built-in-attributes-index
[`catch_unwind`]: ../../std/panic/fn.catch_unwind.html