Add safty check for record_external_fns

src/staticdata.c

@@ -1032,6 +1032,24 @@ static void record_gvars(jl_serializer_state *s, arraylist_t *globals) JL_NOTSAF
     }
 }
 
+static void record_external_fns(jl_serializer_state *s, arraylist_t *external_fns) JL_NOTSAFEPOINT
+{
+    if (!s->incremental) {
+        assert(external_fns->len == 0);
+        (void) external_fns;
+        return;
+    }
+
+    // We could call jl_queue_for_serialization here, but that should
+    // always be a no-op.
+#if defined(JL_NDEBUG)
+    for (size_t i = 0; i < external_fns->len; i++) {
+        jl_code_instance_t *ci = (jl_code_instance_t*)external_fns->data[i];
+        assert(jl_object_in_image((jl_value_t*)ci));
+    }
+#endif
+}
+
 jl_value_t *jl_find_ptr = NULL;
 // The main function for serializing all the items queued in `visited`
 static void jl_write_values(jl_serializer_state *s) JL_GC_DISABLED
@@ -2309,7 +2327,7 @@ static void jl_save_system_image_to_stream(ios_t *f,
         jl_serialize_reachable(&s);
         // step 1.2: now that we have marked all bindings (badly), ensure all gvars are part of the sysimage
         record_gvars(&s, &gvars);
-        // TODO record external_fns?
+        record_external_fns(&s, &external_fns);
         jl_serialize_reachable(&s);
         // step 1.3: prune (garbage collect) some special weak references from
         // built-in type caches