gh-106213: Make Emscripten trampolines work with JSPI

Include/internal/pycore_emscripten_trampoline.h

@@ -0,0 +1,54 @@
+#ifndef Py_EMSCRIPTEN_TRAMPOLINE_H
+#define Py_EMSCRIPTEN_TRAMPOLINE_H
+
+
+/**
+ * C function call trampolines to mitigate bad function pointer casts.
+ *
+ * Section 6.3.2.3, paragraph 8 reads:
+ *
+ *      A pointer to a function of one type may be converted to a pointer to a
+ *      function of another type and back again; the result shall compare equal to
+ *      the original pointer. If a converted pointer is used to call a function
+ *      whose type is not compatible with the pointed-to type, the behavior is
+ *      undefined.
+ *
+ * Typical native ABIs ignore additional arguments or fill in missing values
+ * with 0/NULL in function pointer cast. Compilers do not show warnings when a
+ * function pointer is explicitly casted to an incompatible type.
+ *
+ * Bad fpcasts are an issue in WebAssembly. WASM's indirect_call has strict
+ * function signature checks. Argument count, types, and return type must match.
+ *
+ * Third party code unintentionally rely on problematic fpcasts. The call
+ * trampoline mitigates common occurrences of bad fpcasts on Emscripten.
+ */
+
+#if defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
+
+void _Py_EmscriptenTrampoline_Init(void);
+
+PyObject*
+_PyEM_TrampolineCall(PyCFunctionWithKeywords func,
+                     PyObject* self,
+                     PyObject* args,
+                     PyObject* kw);
+
+#define _PyCFunction_TrampolineCall(meth, self, args) \
+    _PyEM_TrampolineCall( \
+        (*(PyCFunctionWithKeywords)(void(*)(void))(meth)), (self), (args), NULL)
+
+#define _PyCFunctionWithKeywords_TrampolineCall(meth, self, args, kw) \
+    _PyEM_TrampolineCall((meth), (self), (args), (kw))
+
+#else // defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
+
+#define _Py_EmscriptenTrampoline_Init()
+
+#define _PyCFunction_TrampolineCall(meth, self, args) \
+    (meth)((self), (args))
+#define _PyCFunctionWithKeywords_TrampolineCall(meth, self, args, kw) \
+    (meth)((self), (args), (kw))
+
+#endif // defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
+#endif // ndef Py_EMSCRIPTEN_SIGNAL_H

Include/internal/pycore_object.h

@@ -10,10 +10,13 @@ extern "C" {
 
 #include <stdbool.h>
 #include "pycore_gc.h"            // _PyObject_GC_IS_TRACKED()
+#include "pycore_emscripten_trampoline.h" // _PyCFunction_TrampolineCall()
 #include "pycore_interp.h"        // PyInterpreterState.gc
 #include "pycore_pystate.h"       // _PyInterpreterState_GET()
 #include "pycore_runtime.h"       // _PyRuntime
 
+
+
 /* We need to maintain an internal copy of Py{Var}Object_HEAD_INIT to avoid
    designated initializer conflicts in C++20. If we use the deinition in
    object.h, we will be mixing designated and non-designated initializers in
@@ -411,33 +414,6 @@ extern int _PyObject_IsInstanceDictEmpty(PyObject *);
 
 PyAPI_FUNC(PyObject *) _PyObject_LookupSpecial(PyObject *, PyObject *);
 
-/* C function call trampolines to mitigate bad function pointer casts.
- *
- * Typical native ABIs ignore additional arguments or fill in missing
- * values with 0/NULL in function pointer cast. Compilers do not show
- * warnings when a function pointer is explicitly casted to an
- * incompatible type.
- *
- * Bad fpcasts are an issue in WebAssembly. WASM's indirect_call has strict
- * function signature checks. Argument count, types, and return type must
- * match.
- *
- * Third party code unintentionally rely on problematic fpcasts. The call
- * trampoline mitigates common occurrences of bad fpcasts on Emscripten.
- */
-#if defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
-#define _PyCFunction_TrampolineCall(meth, self, args) \
-    _PyCFunctionWithKeywords_TrampolineCall( \
-        (*(PyCFunctionWithKeywords)(void(*)(void))(meth)), (self), (args), NULL)
-extern PyObject* _PyCFunctionWithKeywords_TrampolineCall(
-    PyCFunctionWithKeywords meth, PyObject *, PyObject *, PyObject *);
-#else
-#define _PyCFunction_TrampolineCall(meth, self, args) \
-    (meth)((self), (args))
-#define _PyCFunctionWithKeywords_TrampolineCall(meth, self, args, kw) \
-    (meth)((self), (args), (kw))
-#endif // __EMSCRIPTEN__ && PY_CALL_TRAMPOLINE
-
 #ifdef __cplusplus
 }
 #endif

Misc/NEWS.d/next/Core and Builtins/2023-06-29-09-42-56.gh-issue-106213.TCUgzM.rst

@@ -0,0 +1,2 @@
+Changed the way that Emscripten call trampolines work for compatibility with
+Wasm/JS Promise integration.

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 +1,78 @@
+#if defined(PY_CALL_TRAMPOLINE)
+
+#include <emscripten.h>
+#include <Python.h>
+
+static int type_reflection_available;
+
+/**
+ * This is the GoogleChromeLabs approved way to feature detect type-reflection:
+ * https://github.com/GoogleChromeLabs/wasm-feature-detect/blob/main/src/detectors/type-reflection/index.js
+ */
+EM_JS(int, _PyEM_detect_type_reflection, (), {
+  return "function" in WebAssembly;
+});
+
+void
+_Py_EmscriptenTrampoline_Init(){
+  type_reflection_available = _PyEM_detect_type_reflection();
+}
+
+/**
+ * Backwards compatible trampoline works with all JS runtimes
+ */
+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);
+}
+);
+
+/**
+ * In runtimes with WebAssembly type reflection, count the number of parameters
+ * and cast to the appropriate signature
+ */
+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();
+)
+
+
+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 (!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

Python/pylifecycle.c

@@ -7,6 +7,7 @@
 #include "pycore_codecs.h"        // _PyCodec_Lookup()
 #include "pycore_context.h"       // _PyContext_Init()
 #include "pycore_dict.h"          // _PyDict_Fini()
+#include "pycore_emscripten_trampoline.h"  // _Py_EmscriptenTrampoline_Init()
 #include "pycore_exceptions.h"    // _PyExc_InitTypes()
 #include "pycore_fileutils.h"     // _Py_ResetForceASCII()
 #include "pycore_floatobject.h"   // _PyFloat_InitTypes()
@@ -542,6 +543,9 @@ pycore_init_runtime(_PyRuntimeState *runtime,
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
+
+    _Py_EmscriptenTrampoline_Init();
+
     return _PyStatus_OK();
 }
 

configure.ac

@@ -4770,8 +4770,8 @@ PLATFORM_OBJS=
 
 AS_CASE([$ac_sys_system],
   [Emscripten], [
-    AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_signal.o'])
-    AS_VAR_APPEND([PLATFORM_HEADERS], [' $(srcdir)/Include/internal/pycore_emscripten_signal.h'])
+    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 $(srcdir)/Include/internal/pycore_emscripten_trampoline.h'])
   ],
 )
 AC_SUBST([PLATFORM_HEADERS])