Add support for nested panics to miri

src/tools/miri/src/concurrency/thread.rs

@@ -132,10 +132,15 @@ pub struct Thread<'mir, 'tcx> {
     /// The join status.
     join_status: ThreadJoinStatus,
 
-    /// The temporary used for storing the argument of
-    /// the call to `miri_start_panic` (the panic payload) when unwinding.
+    /// Stack of active panic payloads for the current thread. Used for storing
+    /// the argument of the call to `miri_start_panic` (the panic payload) when unwinding.
     /// This is pointer-sized, and matches the `Payload` type in `src/libpanic_unwind/miri.rs`.
-    pub(crate) panic_payload: Option<Scalar<Provenance>>,
+    ///
+    /// In real unwinding, the payload gets passed as an argument to the landing pad,
+    /// which then forwards it to 'Resume'. However this argument is implicit in MIR,
+    /// so we have to store it out-of-band. When there are multiple active unwinds,
+    /// the innermost one is always caught first, so we can store them as a stack.
+    pub(crate) panic_payloads: Vec<Scalar<Provenance>>,
 
     /// Last OS error location in memory. It is a 32-bit integer.
     pub(crate) last_error: Option<MPlaceTy<'tcx, Provenance>>,
@@ -205,7 +210,7 @@ impl<'mir, 'tcx> Thread<'mir, 'tcx> {
             stack: Vec::new(),
             top_user_relevant_frame: None,
             join_status: ThreadJoinStatus::Joinable,
-            panic_payload: None,
+            panic_payloads: Vec::new(),
             last_error: None,
             on_stack_empty,
         }
@@ -215,7 +220,7 @@ impl<'mir, 'tcx> Thread<'mir, 'tcx> {
 impl VisitTags for Thread<'_, '_> {
     fn visit_tags(&self, visit: &mut dyn FnMut(BorTag)) {
         let Thread {
-            panic_payload,
+            panic_payloads: panic_payload,
             last_error,
             stack,
             top_user_relevant_frame: _,
@@ -225,7 +230,9 @@ impl VisitTags for Thread<'_, '_> {
             on_stack_empty: _, // we assume the closure captures no GC-relevant state
         } = self;
 
-        panic_payload.visit_tags(visit);
+        for payload in panic_payload {
+            payload.visit_tags(visit);
+        }
         last_error.visit_tags(visit);
         for frame in stack {
             frame.visit_tags(visit)

src/tools/miri/src/shims/panic.rs

@@ -63,8 +63,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         let [payload] = this.check_shim(abi, Abi::Rust, link_name, args)?;
         let payload = this.read_scalar(payload)?;
         let thread = this.active_thread_mut();
-        assert!(thread.panic_payload.is_none(), "the panic runtime should avoid double-panics");
-        thread.panic_payload = Some(payload);
+        thread.panic_payloads.push(payload);
 
         // Jump to the unwind block to begin unwinding.
         this.unwind_to_block(unwind)?;
@@ -146,7 +145,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
             // The Thread's `panic_payload` holds what was passed to `miri_start_panic`.
             // This is exactly the second argument we need to pass to `catch_fn`.
-            let payload = this.active_thread_mut().panic_payload.take().unwrap();
+            let payload = this.active_thread_mut().panic_payloads.pop().unwrap();
 
             // Push the `catch_fn` stackframe.
             let f_instance = this.get_ptr_fn(catch_unwind.catch_fn)?.as_instance()?;

src/tools/miri/tests/fail/panic/double_panic.rs

@@ -1,6 +1,4 @@
-//@error-in-other-file: the program aborted
 //@normalize-stderr-test: "\| +\^+" -> "| ^"
-//@normalize-stderr-test: "unsafe \{ libc::abort\(\) \}|crate::intrinsics::abort\(\);" -> "ABORT();"
 //@normalize-stderr-test: "\n  +[0-9]+:[^\n]+" -> "$1"
 //@normalize-stderr-test: "\n at [^\n]+" -> "$1"
 
@@ -11,6 +9,7 @@ impl Drop for Foo {
     }
 }
 fn main() {
+    //~^ERROR: panic in a function that cannot unwind
     let _foo = Foo;
     panic!("first");
 }

src/tools/miri/tests/fail/panic/double_panic.stderr

@@ -2,30 +2,17 @@ thread 'main' panicked at 'first', $DIR/double_panic.rs:LL:CC
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 thread 'main' panicked at 'second', $DIR/double_panic.rs:LL:CC
 stack backtrace:
-thread panicked while panicking. aborting.
-error: abnormal termination: the program aborted execution
-  --> RUSTLIB/std/src/sys/PLATFORM/mod.rs:LL:CC
-   |
-LL |     ABORT();
-   | ^ the program aborted execution
-   |
-   = note: inside `std::sys::PLATFORM::abort_internal` at RUSTLIB/std/src/sys/PLATFORM/mod.rs:LL:CC
-   = note: inside `std::panicking::rust_panic_with_hook` at RUSTLIB/std/src/panicking.rs:LL:CC
-   = note: inside closure at RUSTLIB/std/src/panicking.rs:LL:CC
-   = note: inside `std::sys_common::backtrace::__rust_end_short_backtrace::<[closure@std::panicking::begin_panic_handler::{closure#0}], !>` at RUSTLIB/std/src/sys_common/backtrace.rs:LL:CC
-   = note: inside `std::panicking::begin_panic_handler` at RUSTLIB/std/src/panicking.rs:LL:CC
-note: inside `<Foo as std::ops::Drop>::drop`
+error: abnormal termination: panic in a function that cannot unwind
   --> $DIR/double_panic.rs:LL:CC
    |
-LL |         panic!("second");
-   | ^
-   = note: inside `std::ptr::drop_in_place::<Foo> - shim(Some(Foo))` at RUSTLIB/core/src/ptr/mod.rs:LL:CC
-note: inside `main`
-  --> $DIR/double_panic.rs:LL:CC
+LL | / fn main() {
+LL | |
+LL | |     let _foo = Foo;
+LL | |     panic!("first");
+LL | | }
+   | |_^ panic in a function that cannot unwind
    |
-LL | }
-   | ^
-   = note: this error originates in the macro `$crate::panic::panic_2021` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: inside `main` at $DIR/double_panic.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
 

src/tools/miri/tests/pass/panic/nested_panic_caught.rs

@@ -0,0 +1,25 @@
+//@normalize-stderr-test: "\| +\^+" -> "| ^"
+//@normalize-stderr-test: "\n  +[0-9]+:[^\n]+" -> "$1"
+//@normalize-stderr-test: "\n at [^\n]+" -> "$1"
+
+// Checks that nested panics work correctly.
+
+use std::panic::catch_unwind;
+
+fn double() {
+    struct Double;
+
+    impl Drop for Double {
+        fn drop(&mut self) {
+            let _ = catch_unwind(|| panic!("twice"));
+        }
+    }
+
+    let _d = Double;
+
+    panic!("once");
+}
+
+fn main() {
+    assert!(catch_unwind(|| double()).is_err());
+}

src/tools/miri/tests/pass/panic/nested_panic_caught.stderr

@@ -0,0 +1,4 @@
+thread 'main' panicked at 'once', $DIR/nested_panic_caught.rs:LL:CC
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+thread 'main' panicked at 'twice', $DIR/nested_panic_caught.rs:LL:CC
+stack backtrace: