Fix JSPI suspend through call from side module to main module (emscripten-core#23581)

This fixes a basic use case where a side module calls a suspending main
module symbol. Without this change, we call through a promising JS
wrapper produced by `instrumentWasmExports()` and fail to suspend.

We have to dlsym() the side module symbol since if we call it directly
it will fail because of another JS trampoline on the main -> side module
edge.

Author: hoodmane

src/lib/libdylink.js

@@ -716,7 +716,14 @@ var LibraryDylink = {
           }
           if (prop in wasmImports && !wasmImports[prop].stub) {
             // No stub needed, symbol already exists in symbol table
-            return wasmImports[prop];
+            var res = wasmImports[prop];
+#if ASYNCIFY
+            // Asyncify wraps exports, and we need to look through those wrappers.
+            if (res.orig) {
+              res = res.orig;
+            }
+#endif
+            return res;
           }
           // Return a stub function that will resolve the symbol
           // when first called.
@@ -1248,7 +1255,7 @@ var LibraryDylink = {
 
 #if ASYNCIFY
       // Asyncify wraps exports, and we need to look through those wrappers.
-      if ('orig' in result) {
+      if (result.orig) {
         result = result.orig;
       }
 #endif

test/common.py

@@ -321,6 +321,17 @@ def decorated(self, *args, **kwargs):
   return decorated
 
 
+def requires_jspi(func):
+  assert callable(func)
+
+  @wraps(func)
+  def decorated(self, *args, **kwargs):
+    self.require_jspi()
+    return func(self, *args, **kwargs)
+
+  return decorated
+
+
 def node_pthreads(f):
   assert callable(f)
 

test/core/test_dlfcn_jspi.c

@@ -0,0 +1,29 @@
+// Copyright 2025 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <emscripten.h>
+#include <stdio.h>
+#include <dlfcn.h>
+
+EM_ASYNC_JS(int, test, (), {
+  console.log("sleeping");
+  await new Promise(res => setTimeout(res, 0));
+  console.log("slept");
+  return 77;
+});
+
+int test_wrapper() {
+  return test();
+}
+
+typedef int (*F)();
+
+int main() {
+  void* handle = dlopen("side.so", RTLD_NOW|RTLD_GLOBAL);
+  F side_module_trampoline = dlsym(handle, "side_module_trampoline");
+  int res = side_module_trampoline();
+  printf("done %d\n", res);
+  return 0;
+}

test/core/test_dlfcn_jspi.out

@@ -0,0 +1,4 @@
+side_module_trampoline
+sleeping
+slept
+done 77

test/core/test_dlfcn_jspi_side.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+int test_wrapper(void);
+
+int side_module_trampoline() {
+  printf("side_module_trampoline\n");
+  return test_wrapper();
+}

test/test_core.py

@@ -28,7 +28,7 @@
 from common import read_file, read_binary, requires_v8, requires_node, requires_wasm2js, requires_node_canary
 from common import compiler_for, crossplatform, no_4gb, no_2gb, also_with_minimal_runtime, also_with_modularize
 from common import with_all_fs, also_with_nodefs, also_with_nodefs_both, also_with_noderawfs, also_with_wasmfs
-from common import with_all_eh_sjlj, with_all_sjlj, also_with_standalone_wasm, can_do_standalone, no_wasm64, requires_wasm_eh
+from common import with_all_eh_sjlj, with_all_sjlj, also_with_standalone_wasm, can_do_standalone, no_wasm64, requires_wasm_eh, requires_jspi
 from common import NON_ZERO, WEBIDL_BINDER, EMBUILDER, PYTHON
 import clang_native
 
@@ -3762,6 +3762,21 @@ def test_dlfcn_asyncify(self):
       '''
     self.do_run(src, 'before sleep\nafter sleep\n42\n')
 
+  @requires_jspi
+  @needs_dylink
+  def test_dlfcn_jspi(self):
+    self.run_process(
+      [
+        EMCC,
+        "-o",
+        "side.so",
+        test_file("core/test_dlfcn_jspi_side.c"),
+        "-sSIDE_MODULE",
+      ]
+      + self.get_emcc_args()
+    )
+    self.do_run_in_out_file_test("core/test_dlfcn_jspi.c", emcc_args=["side.so", "-sMAIN_MODULE=2"])
+
   @needs_dylink
   def test_dlfcn_rtld_local(self):
     # Create two shared libraries that both depend on a third.

test/test_other.py

@@ -35,7 +35,7 @@
 from common import env_modify, no_mac, no_windows, only_windows, requires_native_clang, with_env_modify
 from common import create_file, parameterized, NON_ZERO, node_pthreads, TEST_ROOT, test_file
 from common import compiler_for, EMBUILDER, requires_v8, requires_node, requires_wasm64, requires_node_canary
-from common import requires_wasm_eh, crossplatform, with_all_eh_sjlj, with_all_sjlj
+from common import requires_wasm_eh, crossplatform, with_all_eh_sjlj, with_all_sjlj, requires_jspi
 from common import also_with_standalone_wasm, also_with_wasm2js, also_with_noderawfs
 from common import also_with_modularize, also_with_wasmfs, with_all_fs
 from common import also_with_minimal_runtime, also_with_wasm_bigint, also_with_wasm64, also_with_asan, flaky
@@ -195,17 +195,6 @@ def decorated(self, *args, **kwargs):
   return decorated
 
 
-def requires_jspi(func):
-  assert callable(func)
-
-  @wraps(func)
-  def decorated(self, *args, **kwargs):
-    self.require_jspi()
-    return func(self, *args, **kwargs)
-
-  return decorated
-
-
 def llvm_nm(file):
   output = shared.run_process([LLVM_NM, file], stdout=PIPE).stdout