Handle multiple action records in EH personality function

library/std/src/sys/personality/dwarf/eh.rs

@@ -48,9 +48,20 @@ pub struct EHContext<'a> {
 type LPad = *const u8;
 pub enum EHAction {
     None,
+    /// Destructors should be executed when stack unwinds.
     Cleanup(LPad),
+    /// Stack unwind should be stopped as the exception is going to be caught by `catch_unwind`.
     Catch(LPad),
+    /// Stack unwind should be stopped for termination (`UnwindAction::Terminate`).
+    ///
+    /// Note that due to inlining the landing pad can execute destructors before terminating. So
+    /// this is different from `Terminate`.
+    ///
+    /// Handling of this is mostly identical to `Catch`; except that Rust frames that have no
+    /// destructors but only `UnwindAction::Terminate` is considered as plain-old-frame (POF) and
+    /// forced unwind is allowed to unwind past it; so this is treated as `None` during forced unwind.
     Filter(LPad),
+    /// Process should be terminated as the call site does not permit unwinding.
     Terminate,
 }
 
@@ -160,7 +171,19 @@ unsafe fn interpret_cs_action(
         let action_record = unsafe { action_table.offset(cs_action_entry as isize - 1) };
         let mut action_reader = DwarfReader::new(action_record);
         let ttype_index = unsafe { action_reader.read_sleb128() };
-        if ttype_index == 0 {
+        let next_action = unsafe { action_reader.read_sleb128() };
+        if next_action != 0 {
+            // We observed multiple actions. Action records contain no duplicates (at least that is
+            // true for both LLVM/GCC), and as Rust does not have exception specification, this
+            // indicates that we have at least 2 of "cleanup", "catch" and "filter", so we should
+            // catch all exceptions.
+            //
+            // Note that even for the case of "cleanup" + "filter", decoding them as "catch" is
+            // fine: "filter" behaves identically to "catch" except for forced unwind; in case of
+            // forced unwind, hitting a "cleanup" landing pad is UB as it indicates that we're
+            // unwinding past a non-POF Rust frame.
+            EHAction::Catch(lpad)
+        } else if ttype_index == 0 {
             EHAction::Cleanup(lpad)
         } else if ttype_index > 0 {
             // Stop unwinding Rust panics at catch_unwind.

tests/ui/panics/lsda-multiple-action.rs

@@ -0,0 +1,29 @@
+//@ run-pass
+//@ needs-unwind
+//@ ignore-backends: gcc
+//@ compile-flags: -Copt-level=3
+
+struct Guard;
+
+impl Drop for Guard {
+    fn drop(&mut self) {
+        core::hint::black_box(());
+    }
+}
+
+#[inline(never)]
+fn unwind() {
+    if core::hint::black_box(true) {
+        std::panic::resume_unwind(Box::new(()));
+    }
+}
+
+fn main() {
+    // The `catch_unwind` will generate `landingpad catch` and the destructor will generate
+    // `landingpad cleanup`; after LLVM inlining it will become `landingpad cleanup catch`, and this
+    // is translated to action record chains in LSDA.
+    let _ = std::panic::catch_unwind(|| {
+        let _guard = Guard;
+        unwind();
+    });
+}