for def_id in tcx.hir().body_owners() {
if tcx.has_ffi_unwind_calls(def_id) {
+ // Given that this crate is compiled in `-C panic=unwind`, the `AbortUnwindingCalls`
+ // MIR pass will not be run on FFI-unwind call sites, therefore a foreign exception
+ // can enter Rust through these sites.
+ //
+ // On the other hand, crates compiled with `-C panic=abort` expects that all Rust
+ // functions cannot unwind (whether it's caused by Rust panic or foreign exception),
+ // and this expectation mismatch can cause unsoundness (#96926).
+ //
+ // To address this issue, we enforce that if FFI-unwind calls are used in a crate
+ // compiled with `panic=unwind`, then the final panic strategy must be `panic=unwind`.
+ // This will ensure that no crates will have wrong unwindability assumption.
+ //
+ // It should be noted that it is okay to link `panic=unwind` into a `panic=abort`
+ // program if it contains no FFI-unwind calls. In such case foreign exception can only
+ // enter Rust in a `panic=abort` crate, which will lead to an abort. There will also
+ // be no exceptions generated from Rust, so the assumption which `panic=abort` crates
+ // make, that no Rust function can unwind, indeed holds for crates compiled with
+ // `panic=unwind` as well. In such case this function returns `None`, indicating that
+ // the crate does not require a particular final panic strategy, and can be freely
+ // linked to crates with either strategy (we need such ability for libstd and its
+ // dependencies).
return Some(PanicStrategy::Unwind);
}
}