[wasm] Fix catching of stack overflow in asm.js instantiation

There was a very narrow corner case where we would return from the
runtime function that tries to instantiate a module created by an
asm.js-to-wasm translation in an inconsistent state: returning a
Smi failure sentinel even though there is a pending exception.

Bug: chromium:1061808
Change-Id: I22f5c6cdb8d7f7abfddb2bb81dc9261c8a35bdeb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2106194Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66741}

src/asmjs/asm-js.cc

@@ -408,9 +408,12 @@ MaybeHandle<Object> AsmJs::InstantiateAsmWasm(Isolate* isolate,
     return single_function;
   }
 
-  Handle<String> exports_name =
-      isolate->factory()->InternalizeUtf8String("exports");
-  return Object::GetProperty(isolate, instance, exports_name);
+  // Here we rely on the fact that the exports object is eagerly created.
+  // The following check is a weak indicator for that. If this ever changes,
+  // then we'll have to call the "exports" getter, and be careful about
+  // handling possible stack overflow exceptions.
+  DCHECK(instance->exports_object().IsJSObject());
+  return handle(instance->exports_object(), isolate);
 }
 
 }  // namespace internal

src/runtime/runtime-compiler.cc

@@ -142,6 +142,7 @@ RUNTIME_FUNCTION(Runtime_InstantiateAsmJs) {
   DCHECK(function->code() ==
          isolate->builtins()->builtin(Builtins::kInstantiateAsmJs));
   function->set_code(isolate->builtins()->builtin(Builtins::kCompileLazy));
+  DCHECK(!isolate->has_pending_exception());
   return Smi::zero();
 }