[wasm] Initial signal handler

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 38a26be1e29a70450d6d08460fbe0e7473b25244..bd5aadb72265384515bf732be9adf39791767476 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1201,6 +1201,10 @@ Object* Isolate::UnwindAndFindHandler() {
   for (StackFrameIterator iter(this); !iter.done(); iter.Advance()) {
     StackFrame* frame = iter.frame();
 
+    if (frame->is_wasm()) {
+      trap_handler::ClearThreadInWasm();
+    }
+
     // For JSEntryStub frames we always have a handler.
     if (frame->is_entry() || frame->is_entry_construct()) {
       StackHandler* handler = frame->top_handler();
@@ -1232,6 +1236,13 @@ Object* Isolate::UnwindAndFindHandler() {
 
           handler_sp = return_sp;
           handler_fp = frame->fp();
+
+          // This is going to be handled by Wasm, so we need to set the TLS flag
+          // again.
+          if (trap_handler::ShouldEnableTrapHandler()) {
+            trap_handler::SetThreadInWasm();
+          }
+
           break;
         }
       }