Rollup merge of #123200 - maurer:kcfi-abort, r=compiler-errors

KCFI: Require -C panic=abort

While the KCFI scheme is not incompatible with unwinding, LLVM's `invoke` instruction does not currently support KCFI bundles. While it likely will in the near future, we won't be able to assume that in Rust for a while.

We encountered this problem while [turning on closure support](https://github.com/rust-lang/rust/pull/123106#issuecomment-2027436640).

r? ``@workingjubilee``

compiler/rustc_session/src/errors.rs

@@ -145,6 +145,10 @@ pub(crate) struct SanitizerCfiGeneralizePointersRequiresCfi;
 #[diag(session_sanitizer_cfi_normalize_integers_requires_cfi)]
 pub(crate) struct SanitizerCfiNormalizeIntegersRequiresCfi;
 
+#[derive(Diagnostic)]
+#[diag(session_sanitizer_kcfi_requires_panic_abort)]
+pub(crate) struct SanitizerKcfiRequiresPanicAbort;
+
 #[derive(Diagnostic)]
 #[diag(session_split_lto_unit_requires_lto)]
 pub(crate) struct SplitLtoUnitRequiresLto;

compiler/rustc_session/src/session.rs

@@ -1211,6 +1211,11 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         sess.dcx().emit_err(errors::SanitizerCfiRequiresLto);
     }
 
+    // KCFI requires panic=abort
+    if sess.is_sanitizer_kcfi_enabled() && sess.panic_strategy() != PanicStrategy::Abort {
+        sess.dcx().emit_err(errors::SanitizerKcfiRequiresPanicAbort);
+    }
+
     // LLVM CFI using rustc LTO requires a single codegen unit.
     if sess.is_sanitizer_cfi_enabled()
         && sess.lto() == config::Lto::Fat