gh-106213: Make Emscripten trampolines work with JSPI

Include/internal/pycore_object.h

@@ -426,11 +426,19 @@ PyAPI_FUNC(PyObject *) _PyObject_LookupSpecial(PyObject *, PyObject *);
  * trampoline mitigates common occurrences of bad fpcasts on Emscripten.
  */
 #if defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
+extern PyObject*
+_PyEM_TrampolineCall(PyCFunctionWithKeywords func,
+                     PyObject* self,
+                     PyObject* args,
+                     PyObject* kw);
+
 #define _PyCFunction_TrampolineCall(meth, self, args) \
-    _PyCFunctionWithKeywords_TrampolineCall( \
+    _PyEM_TrampolineCall( \
         (*(PyCFunctionWithKeywords)(void(*)(void))(meth)), (self), (args), NULL)
-extern PyObject* _PyCFunctionWithKeywords_TrampolineCall(
-    PyCFunctionWithKeywords meth, PyObject *, PyObject *, PyObject *);
+
+#define _PyCFunctionWithKeywords_TrampolineCall(meth, self, args, kw) \
+    _PyEM_TrampolineCall((meth), (self), (args), (kw))
+
 #else
 #define _PyCFunction_TrampolineCall(meth, self, args) \
     (meth)((self), (args))

Objects/descrobject.c

@@ -18,15 +18,21 @@ class property "propertyobject *" "&PyProperty_Type"
 
 // see pycore_object.h
 #if defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
-#include <emscripten.h>
-EM_JS(int, descr_set_trampoline_call, (setter set, PyObject *obj, PyObject *value, void *closure), {
-    return wasmTable.get(set)(obj, value, closure);
-});
-
-EM_JS(PyObject*, descr_get_trampoline_call, (getter get, PyObject *obj, void *closure), {
-    return wasmTable.get(get)(obj, closure);
-});
+extern PyObject*
+_PyEM_TrampolineCall(PyCFunctionWithKeywords func,
+                     PyObject* self,
+                     PyObject* args,
+                     PyObject* kw);
+
+#define descr_set_trampoline_call(set, obj, value, closure) \
+    ((int)_PyEM_TrampolineCall((PyCFunctionWithKeywords)(set), (obj), (value), (PyObject*)(closure)))
+
+
+#define descr_get_trampoline_call(get, obj, closure) \
+    _PyEM_TrampolineCall((PyCFunctionWithKeywords)(get), (obj), (PyObject*)(closure), NULL)
+
 #else
+
 #define descr_set_trampoline_call(set, obj, value, closure) \
     (set)((obj), (value), (closure))
 

Objects/methodobject.c

@@ -551,10 +551,3 @@ cfunction_call(PyObject *func, PyObject *args, PyObject *kwargs)
     return _Py_CheckFunctionResult(tstate, func, result, NULL);
 }
 
-#if defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
-#include <emscripten.h>
-
-EM_JS(PyObject*, _PyCFunctionWithKeywords_TrampolineCall, (PyCFunctionWithKeywords func, PyObject *self, PyObject *args, PyObject *kw), {
-    return wasmTable.get(func)(self, args, kw);
-});
-#endif

Python/emscripten_trampoline.c

@@ -0,0 +1,67 @@
+#if defined(PY_CALL_TRAMPOLINE)
+
+#include <emscripten.h>
+#include <Python.h>
+
+EMSCRIPTEN_KEEPALIVE int _PyEM_type_reflection_available;
+
+EM_JS_DEPS(_PyEMJS_TrampolineCall, "$getWasmTableEntry")
+EM_JS(PyObject*, _PyEMJS_TrampolineCall, (PyCFunctionWithKeywords func, PyObject *arg1, PyObject *arg2, PyObject *arg3), {
+    return getWasmTableEntry(func)(arg1, arg2, arg3);
+}
+);
+
+EM_JS(int, _PyEM_CountFuncParams, (PyCFunctionWithKeywords func), {
+  let n = _PyEM_CountFuncParams.cache.get(func);
+  if (n !== undefined) {
+    return n;
+  }
+  n = WebAssembly.Function.type(getWasmTableEntry(func)).parameters.length;
+  _PyEM_CountFuncParams.cache.set(func, n);
+  return n;
+}
+_PyEM_CountFuncParams.cache = new Map();
+switch(typeof Module.preRun) {
+    case "undefined":
+        Module.preRun = [];
+        break;
+    case "function":
+        Module.preRun = [Module.preRun];
+        break;
+}
+Module.preRun.push(() => HEAP32[__PyEM_type_reflection_available/4] = "Function" in WebAssembly);
+)
+
+
+typedef PyObject* (*zero_arg)(void);
+typedef PyObject* (*one_arg)(PyObject*);
+typedef PyObject* (*two_arg)(PyObject*, PyObject*);
+typedef PyObject* (*three_arg)(PyObject*, PyObject*, PyObject*);
+
+PyObject*
+_PyEM_TrampolineCall(PyCFunctionWithKeywords func,
+              PyObject* self,
+              PyObject* args,
+              PyObject* kw)
+{
+  if (!_PyEM_type_reflection_available) {
+    return _PyEMJS_TrampolineCall(func, self, args, kw);
+  } else {
+    switch (_PyEM_CountFuncParams(func)) {
+      case 0:
+        return ((zero_arg)func)();
+      case 1:
+        return ((one_arg)func)(self);
+      case 2:
+        return ((two_arg)func)(self, args);
+      case 3:
+        return ((three_arg)func)(self, args, kw);
+      default:
+        PyErr_SetString(PyExc_SystemError, "Handler takes too many arguments");
+        return NULL;
+    }
+  }
+}
+
+
+#endif

configure.ac

@@ -4770,7 +4770,7 @@ PLATFORM_OBJS=
 
 AS_CASE([$ac_sys_system],
   [Emscripten], [
-    AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_signal.o'])
+    AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_signal.o Python/emscripten_trampoline.o'])
     AS_VAR_APPEND([PLATFORM_HEADERS], [' $(srcdir)/Include/internal/pycore_emscripten_signal.h'])
   ],
 )