Continuation trapping semantics

crates/wasmtime/src/runtime/vm/stack_switching.rs

@@ -410,7 +410,7 @@ pub fn cont_new(
 /// executing themselves, but are an ancestor of the currently executing
 /// stack), we have the following: All the fields in the stack's
 /// `VMStackLimits` are valid, describing the stack's stack limit, and
-/// pointers where executing for that stack entered and exited WASM.
+/// pointers where executing for that stack entered and exited Wasm.
 ///
 /// Suspended continuations: For suspended continuations (including their
 /// ancestors), we have the following. Note that the initial stack can never

crates/wasmtime/src/runtime/vm/traphandlers.rs

@@ -19,6 +19,7 @@ pub use self::signals::*;
 use crate::ThrownException;
 use crate::runtime::module::lookup_code;
 use crate::runtime::store::{ExecutorRef, StoreOpaque};
+use crate::runtime::vm::stack_switching::VMStackChain;
 use crate::runtime::vm::sys::traphandlers;
 use crate::runtime::vm::{InterpreterRef, VMContext, VMStore, VMStoreContext, f32x4, f64x2, i8x16};
 use crate::{EntryStoreContext, prelude::*};
@@ -866,8 +867,28 @@ impl CallThreadState {
 
     pub(crate) fn entry_trap_handler(&self) -> Handler {
         unsafe {
+            fn running_on_continuation(stack_chain: *const VMStackChain) -> bool {
+                unsafe {
+                    match *stack_chain {
+                        VMStackChain::Continuation(_) => true,
+                        _ => false,
+                    }
+                }
+            }
             let vm_store_context = self.vm_store_context.as_ref();
-            let fp = *vm_store_context.last_wasm_entry_fp.get();
+            let vm_stack_chain = vm_store_context.stack_chain.get();
+            // The effects of trapping should not be delimited by the
+            // continuation stack segment we are running on, but
+            // rather the initial continuation stack segment, i.e. the
+            // toplevel part of the program. Therefore we must
+            // retrieve the entry fp of the initial stack.
+            let fp = if running_on_continuation(vm_stack_chain) {
+                let initial_stack_limits =
+                    (*vm_stack_chain).clone().into_stack_limits_iter().last();
+                (*initial_stack_limits.unwrap_or_else(|| panic!("Attempting to find the stack limits of the initial stacks from within a suspended continuation."))).last_wasm_entry_fp
+            } else {
+                *vm_store_context.last_wasm_entry_fp.get()
+            };
             let sp = *vm_store_context.last_wasm_entry_sp.get();
             let pc = *vm_store_context.last_wasm_entry_trap_handler.get();
             Handler { pc, sp, fp }

tests/misc_testsuite/stack-switching/trap.wast

@@ -0,0 +1,16 @@
+;;! stack_switching = true
+;;! reference_types = true
+
+(module
+  (type $ft (func))
+  (type $ct (cont $ft))
+
+  (func $fn
+    (unreachable))
+
+  (func $run_fn (export "run_fn")
+    (resume $ct (cont.new $ct (ref.func $fn))))
+
+  (elem declare func $fn)
+)
+(assert_trap (invoke "run_fn") "unreachable")