gh-129040: Use wasm-gc to handle pointer casts in wasi

Include/internal/pycore_object.h

@@ -8,7 +8,7 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
-#include "pycore_emscripten_trampoline.h" // _PyCFunction_TrampolineCall()
+#include "pycore_wasm_trampoline.h" // _PyCFunction_TrampolineCall()
 #include "pycore_gc.h"            // _PyObject_GC_TRACK()
 #include "pycore_pyatomic_ft_wrappers.h" // FT_ATOMIC_LOAD_PTR_ACQUIRE()
 #include "pycore_pystate.h"       // _PyInterpreterState_GET()
@@ -977,27 +977,6 @@ extern PyObject* _PyObject_NextNotImplemented(PyObject *);
 // Export for '_datetime' shared extension
 PyAPI_FUNC(PyObject*) _PyObject_GetState(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) \
-    (meth)((self), (args))
-#define _PyCFunctionWithKeywords_TrampolineCall(meth, self, args, kw) \
-    (meth)((self), (args), (kw))
-#endif // __EMSCRIPTEN__ && PY_CALL_TRAMPOLINE
-
 // Export these 2 symbols for '_pickle' shared extension
 PyAPI_DATA(PyTypeObject) _PyNone_Type;
 PyAPI_DATA(PyTypeObject) _PyNotImplemented_Type;

Include/internal/pycore_runtime_structs.h

@@ -271,16 +271,6 @@ struct pyruntimestate {
     struct _types_runtime_state types;
     struct _Py_time_runtime_state time;
 
-#if defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
-    // Used in "Python/emscripten_trampoline.c" to choose between wasm-gc
-    // trampoline and JavaScript trampoline.
-    PyObject* (*emscripten_trampoline)(int* success,
-                                       PyCFunctionWithKeywords func,
-                                       PyObject* self,
-                                       PyObject* args,
-                                       PyObject* kw);
-#endif
-
     /* All the objects that are shared by the runtime's interpreters. */
     struct _Py_cached_objects cached_objects;
     struct _Py_static_objects static_objects;

Include/internal/pycore_emscripten_trampoline.h → Include/internal/pycore_wasm_trampoline.h

@@ -1,7 +1,7 @@
-#ifndef Py_EMSCRIPTEN_TRAMPOLINE_H
-#define Py_EMSCRIPTEN_TRAMPOLINE_H
+#ifndef Py_WASM_TRAMPOLINE_H
+#define Py_WASM_TRAMPOLINE_H
 
-#include "pycore_typedefs.h"      // _PyRuntimeState
+#include "Python.h"
 
 /**
  * C function call trampolines to mitigate bad function pointer casts.
@@ -18,37 +18,44 @@
  * 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
+ * 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.
+ * trampoline mitigates common occurrences of bad fpcasts on Wasm targets.
  */
 
-#if defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
+#if defined(__wasm__) && defined(PY_CALL_TRAMPOLINE)
 
 PyObject*
-_PyEM_TrampolineCall(PyCFunctionWithKeywords func,
-                     PyObject* self,
-                     PyObject* args,
-                     PyObject* kw);
+_PyWasm_TrampolineCall(PyCFunctionWithKeywords func,
+                       PyObject* self,
+                       PyObject* args,
+                       PyObject* kw);
+
+int
+_PyWasm_TrampolineCallSetter(setter func,
+                             PyObject* self,
+                             PyObject* val,
+                             void* closure);
 
 #define _PyCFunction_TrampolineCall(meth, self, args) \
-    _PyEM_TrampolineCall(*_PyCFunctionWithKeywords_CAST(meth), (self), (args), NULL)
+    _PyWasm_TrampolineCall(*_PyCFunctionWithKeywords_CAST(meth), (self), (args), NULL)
 
 #define _PyCFunctionWithKeywords_TrampolineCall(meth, self, args, kw) \
-    _PyEM_TrampolineCall((meth), (self), (args), (kw))
+    _PyWasm_TrampolineCall((meth), (self), (args), (kw))
 
 #define descr_set_trampoline_call(set, obj, value, closure)                 \
-    ((int)_PyEM_TrampolineCall(_PyCFunctionWithKeywords_CAST(set), (obj),   \
-                               (value), (PyObject*)(closure)))
+    _PyWasm_TrampolineCallSetter((set), (obj), (value), (closure))
 
 #define descr_get_trampoline_call(get, obj, closure)                \
-    _PyEM_TrampolineCall(_PyCFunctionWithKeywords_CAST(get), (obj), \
-                         (PyObject*)(closure), NULL)
+    _PyWasm_TrampolineCall(_PyCFunctionWithKeywords_CAST(get), (obj), \
+                           (PyObject*)(closure), NULL)
+
 
+#else // defined(__wasm__) && defined(PY_CALL_TRAMPOLINE)
 
-#else // defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
+// Disable trampolines by directly calling the method.
 
 #define _PyCFunction_TrampolineCall(meth, self, args) \
     (meth)((self), (args))
@@ -62,6 +69,6 @@ _PyEM_TrampolineCall(PyCFunctionWithKeywords func,
 #define descr_get_trampoline_call(get, obj, closure) \
     (get)((obj), (closure))
 
-#endif // defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
+#endif // defined(__wasm__) && defined(PY_CALL_TRAMPOLINE)
 
-#endif // ndef Py_EMSCRIPTEN_SIGNAL_H
+#endif // ndef Py_WASM_TRAMPOLINE_H

Lib/test/test_capi/test_fpcast.py

@@ -0,0 +1,77 @@
+"""Tests for calling C functions through mis-cast function pointers.
+
+Extension modules frequently cast C functions with the wrong number of
+arguments to PyCFunction, getter, setter or ternaryfunc. Native ABIs tolerate
+this; on WebAssembly, call_indirect checks the signature, so CPython routes
+these calls through a trampoline (Python/wasm_trampoline.c) that detects the
+real signature. Calling each variant must work everywhere.
+"""
+import unittest
+from test.support import check_sanitizer, import_helper, is_wasm32
+
+_testcapi = import_helper.import_module('_testcapi')
+
+
+# Native ABIs tolerate these calls but they are implementation-defined behavior.
+# -fsanitize=undefined correctly trips on them.
+@unittest.skipIf(check_sanitizer(ub=True),
+                 "calls through mis-cast function pointers are UB natively")
+class FpcastTest(unittest.TestCase):
+    def check_calls(self, obj, prefix):
+        for arity in range(4):
+            with self.subTest(kind="noargs", arity=arity):
+                self.assertIsNone(getattr(obj, f"{prefix}noargs{arity}")())
+            with self.subTest(kind="o", arity=arity):
+                self.assertIsNone(getattr(obj, f"{prefix}o{arity}")(1))
+            with self.subTest(kind="varargs", arity=arity):
+                self.assertIsNone(getattr(obj, f"{prefix}varargs{arity}")())
+                self.assertIsNone(getattr(obj, f"{prefix}varargs{arity}")(1, 2))
+            with self.subTest(kind="kwargs", arity=arity):
+                self.assertIsNone(getattr(obj, f"{prefix}kwargs{arity}")())
+                self.assertIsNone(getattr(obj, f"{prefix}kwargs{arity}")(1, x=2))
+
+    def test_module_functions(self):
+        self.check_calls(_testcapi, "fpcast_")
+
+    def test_methods(self):
+        self.check_calls(_testcapi.FpcastTestType(), "")
+
+    def test_tp_call(self):
+        for arity in range(4):
+            with self.subTest(arity=arity):
+                cls = getattr(_testcapi, f"FpcastCallable{arity}")
+                self.assertIsNone(cls()())
+                self.assertIsNone(cls()(1, x=2))
+
+    def test_getset(self):
+        t = _testcapi.FpcastTestType()
+        self.assertIsNone(t.getset0)
+        self.assertIsNone(t.getset1)
+        self.assertIsNone(t.getset2)
+        t.getset1 = 5
+        sentinel = object()
+        t.getset2 = sentinel
+        self.assertIs(_testcapi.fpcast_last_set_value(), sentinel)
+        with self.assertRaises(AttributeError):
+            t.getset0 = 1
+
+    @unittest.skipUnless(is_wasm32, "requires the wasm call trampoline")
+    def test_unsupported_signature(self):
+        # A function with four pointer arguments matches none of the
+        # signatures the trampoline knows about: it must raise SystemError
+        # rather than trap.
+        t = _testcapi.FpcastTestType()
+        with self.assertRaises(SystemError):
+            _testcapi.fpcast_noargs4()
+        with self.assertRaises(SystemError):
+            t.noargs4()
+        with self.assertRaises(SystemError):
+            _testcapi.FpcastCallable4()()
+        with self.assertRaises(SystemError):
+            t.getset4
+        with self.assertRaises(SystemError):
+            t.getset4 = 1
+
+
+if __name__ == "__main__":
+    unittest.main()

Makefile.pre.in

@@ -1439,6 +1439,7 @@ PYTHON_HEADERS= \
 		$(srcdir)/Include/internal/pycore_uop.h \
 		$(srcdir)/Include/internal/pycore_uop_ids.h \
 		$(srcdir)/Include/internal/pycore_uop_metadata.h \
+		$(srcdir)/Include/internal/pycore_wasm_trampoline.h \
 		$(srcdir)/Include/internal/pycore_warnings.h \
 		$(srcdir)/Include/internal/pycore_weakref.h \
 		$(DTRACE_HEADERS) \
@@ -3153,13 +3154,6 @@ Python/asm_trampoline_universal2.o: $(srcdir)/Python/asm_trampoline_aarch64.S $(
 	rm -f Python/asm_trampoline_arm64-apple-darwin.o \
 	  Python/asm_trampoline_x86_64-apple-darwin.o
 
-Python/emscripten_trampoline_inner.wasm: $(srcdir)/Python/emscripten_trampoline_inner.c
-	# emcc has a path that ends with emsdk/upstream/emscripten/emcc, we're looking for emsdk/upstream/bin/clang.
-	$$(em-config LLVM_ROOT)/clang -o $@ $< -mgc -O2 -Wl,--no-entry -Wl,--import-table -Wl,--import-memory -target wasm32-unknown-unknown -nostdlib
-
-Python/emscripten_trampoline_wasm.c: Python/emscripten_trampoline_inner.wasm
-	$(PYTHON_FOR_REGEN) $(srcdir)/Platforms/emscripten/prepare_external_wasm.py $< $@ getWasmTrampolineModule
-
 JIT_SHIM_BUILD_OBJS=	@JIT_SHIM_BUILD_O@
 JIT_UNWIND_INFO_H=	$(if $(JIT_OBJS),jit_unwind_info.h $(patsubst jit_stencils-%.h,jit_unwind_info-%.h,@JIT_STENCILS_H@))
 JIT_BUILD_TARGETS=	jit_stencils.h @JIT_STENCILS_H@ $(JIT_UNWIND_INFO_H) $(JIT_SHIM_BUILD_OBJS)

Misc/NEWS.d/next/Build/2026-10-02-12-18-20.gh-issue-129040.6wJPY6.rst

@@ -0,0 +1,3 @@
+Added support for function call adaptor trampolines for wasi to prevent
+traps when C handlers take the wrong number of arguments. Dropped Emscripten
+function call adaptors support for JS runtimes that don't support wasm-gc.

Modules/Setup.stdlib.in

@@ -173,7 +173,7 @@
 @MODULE__XXTESTFUZZ_TRUE@_xxtestfuzz _xxtestfuzz/_xxtestfuzz.c _xxtestfuzz/fuzzer.c
 @MODULE__TESTBUFFER_TRUE@_testbuffer _testbuffer.c
 @MODULE__TESTINTERNALCAPI_TRUE@_testinternalcapi _testinternalcapi.c _testinternalcapi/test_lock.c _testinternalcapi/pytime.c _testinternalcapi/set.c _testinternalcapi/test_critical_sections.c _testinternalcapi/complex.c _testinternalcapi/interpreter.c _testinternalcapi/tokenizer.c _testinternalcapi/tuple.c _testinternalcapi/typecache.c
-@MODULE__TESTCAPI_TRUE@_testcapi _testcapimodule.c _testcapi/vectorcall.c _testcapi/heaptype.c _testcapi/abstract.c _testcapi/unicode.c _testcapi/dict.c _testcapi/set.c _testcapi/list.c _testcapi/tuple.c _testcapi/getargs.c _testcapi/datetime.c _testcapi/docstring.c _testcapi/mem.c _testcapi/watchers.c _testcapi/long.c _testcapi/float.c _testcapi/complex.c _testcapi/numbers.c _testcapi/structmember.c _testcapi/exceptions.c _testcapi/code.c _testcapi/buffer.c _testcapi/pyatomic.c _testcapi/run.c _testcapi/file.c _testcapi/codec.c _testcapi/immortal.c _testcapi/gc.c _testcapi/hash.c _testcapi/time.c _testcapi/bytes.c _testcapi/object.c _testcapi/modsupport.c _testcapi/monitoring.c _testcapi/config.c _testcapi/import.c _testcapi/frame.c _testcapi/type.c _testcapi/function.c _testcapi/module.c _testcapi/weakref.c _testcapi/marshal.c
+@MODULE__TESTCAPI_TRUE@_testcapi _testcapimodule.c _testcapi/vectorcall.c _testcapi/heaptype.c _testcapi/abstract.c _testcapi/unicode.c _testcapi/dict.c _testcapi/set.c _testcapi/list.c _testcapi/tuple.c _testcapi/getargs.c _testcapi/datetime.c _testcapi/docstring.c _testcapi/mem.c _testcapi/watchers.c _testcapi/long.c _testcapi/float.c _testcapi/complex.c _testcapi/numbers.c _testcapi/structmember.c _testcapi/exceptions.c _testcapi/code.c _testcapi/buffer.c _testcapi/pyatomic.c _testcapi/run.c _testcapi/file.c _testcapi/codec.c _testcapi/immortal.c _testcapi/gc.c _testcapi/hash.c _testcapi/time.c _testcapi/bytes.c _testcapi/object.c _testcapi/modsupport.c _testcapi/monitoring.c _testcapi/config.c _testcapi/import.c _testcapi/frame.c _testcapi/type.c _testcapi/function.c _testcapi/module.c _testcapi/weakref.c _testcapi/marshal.c _testcapi/fpcast.c
 @MODULE__TESTLIMITEDCAPI_TRUE@_testlimitedcapi _testlimitedcapi.c _testlimitedcapi/abstract.c _testlimitedcapi/bytearray.c _testlimitedcapi/bytes.c _testlimitedcapi/capsule.c _testlimitedcapi/codec.c _testlimitedcapi/complex.c _testlimitedcapi/dict.c _testlimitedcapi/eval.c _testlimitedcapi/float.c _testlimitedcapi/heaptype_relative.c _testlimitedcapi/import.c _testlimitedcapi/list.c _testlimitedcapi/long.c _testlimitedcapi/object.c _testlimitedcapi/pyos.c _testlimitedcapi/set.c _testlimitedcapi/slice.c _testlimitedcapi/slots.c _testlimitedcapi/sys.c _testlimitedcapi/threadstate.c _testlimitedcapi/tuple.c _testlimitedcapi/unicode.c _testlimitedcapi/vectorcall_limited.c _testlimitedcapi/version.c _testlimitedcapi/file.c _testlimitedcapi/weakref.c _testlimitedcapi/run.c _testlimitedcapi/type.c _testlimitedcapi/hash.c _testlimitedcapi/build.c
 @MODULE__TESTCLINIC_TRUE@_testclinic _testclinic.c
 @MODULE__TESTCLINIC_LIMITED_TRUE@_testclinic_limited _testclinic_limited.c