gh-132097: use a macro for semantically casting function pointers (#132406)

3 files changed, 29 insertions, 9 deletions

diff --git a/Include/internal/pycore_emscripten_trampoline.h b/Include/internal/pycore_emscripten_trampoline.h
index 7946eb5a74e..16916f1a8eb 100644
--- a/Include/internal/pycore_emscripten_trampoline.h
+++ b/Include/internal/pycore_emscripten_trampoline.h
@@ -37,17 +37,18 @@ _PyEM_TrampolineCall(PyCFunctionWithKeywords func,
                      PyObject* kw);
 
 #define _PyCFunction_TrampolineCall(meth, self, args) \
-    _PyEM_TrampolineCall( \
-        (*(PyCFunctionWithKeywords)(void(*)(void))(meth)), (self), (args), NULL)
+    _PyEM_TrampolineCall(*_PyCFunctionWithKeywords_CAST(meth), (self), (args), NULL)
 
 #define _PyCFunctionWithKeywords_TrampolineCall(meth, self, args, kw) \
     _PyEM_TrampolineCall((meth), (self), (args), (kw))
 
-#define descr_set_trampoline_call(set, obj, value, closure) \
-    ((int)_PyEM_TrampolineCall((PyCFunctionWithKeywords)(set), (obj), (value), (PyObject*)(closure)))
+#define descr_set_trampoline_call(set, obj, value, closure)                 \
+    ((int)_PyEM_TrampolineCall(_PyCFunctionWithKeywords_CAST(set), (obj),   \
+                               (value), (PyObject*)(closure)))
 
-#define descr_get_trampoline_call(get, obj, closure) \
-    _PyEM_TrampolineCall((PyCFunctionWithKeywords)(get), (obj), (PyObject*)(closure), NULL)
+#define descr_get_trampoline_call(get, obj, closure)                \
+    _PyEM_TrampolineCall(_PyCFunctionWithKeywords_CAST(get), (obj), \
+                         (PyObject*)(closure), NULL)
 
 
 #else // defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
diff --git a/Include/methodobject.h b/Include/methodobject.h
index cfff05f8033..e6ec6421d1e 100644
--- a/Include/methodobject.h
+++ b/Include/methodobject.h
@@ -33,7 +33,7 @@ typedef PyObject *(*PyCMethod)(PyObject *, PyTypeObject *, PyObject *const *,
 typedef PyCFunctionFast _PyCFunctionFast;
 typedef PyCFunctionFastWithKeywords _PyCFunctionFastWithKeywords;
 
-// Cast an function to the PyCFunction type to use it with PyMethodDef.
+// Cast a function to the PyCFunction type to use it with PyMethodDef.
 //
 // This macro can be used to prevent compiler warnings if the first parameter
 // uses a different pointer type than PyObject* (ex: METH_VARARGS and METH_O
@@ -49,8 +49,17 @@ typedef PyCFunctionFastWithKeywords _PyCFunctionFastWithKeywords;
 // used to prevent a compiler warning. If the function has a single parameter,
 // it triggers an undefined behavior when Python calls it with 2 parameters
 // (bpo-33012).
-#define _PyCFunction_CAST(func) \
-    _Py_CAST(PyCFunction, _Py_CAST(void(*)(void), (func)))
+#define _PyCFunction_CAST(func)                         \
+    _Py_FUNC_CAST(PyCFunction, func)
+// The macros below are given for semantic convenience, allowing users
+// to see whether a cast to suppress an undefined behavior is necessary.
+// Note: At runtime, the original function signature must be respected.
+#define _PyCFunctionFast_CAST(func)                     \
+    _Py_FUNC_CAST(PyCFunctionFast, func)
+#define _PyCFunctionWithKeywords_CAST(func)             \
+    _Py_FUNC_CAST(PyCFunctionWithKeywords, func)
+#define _PyCFunctionFastWithKeywords_CAST(func)         \
+    _Py_FUNC_CAST(PyCFunctionFastWithKeywords, func)
 
 PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
 PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);
diff --git a/Include/pyport.h b/Include/pyport.h
index 2a7192c2c55..ebce31f1d14 100644
--- a/Include/pyport.h
+++ b/Include/pyport.h
@@ -36,6 +36,16 @@
 // Macro to use the more powerful/dangerous C-style cast even in C++.
 #define _Py_CAST(type, expr) ((type)(expr))
 
+// Cast a function to another function type T.
+//
+// The macro first casts the function to the "void func(void)" type
+// to prevent compiler warnings.
+//
+// Note that using this cast only prevents the compiler from emitting
+// warnings, but does not prevent an undefined behavior at runtime if
+// the original function signature is not respected.
+#define _Py_FUNC_CAST(T, func) _Py_CAST(T, _Py_CAST(void(*)(void), (func)))
+
 // Static inline functions should use _Py_NULL rather than using directly NULL
 // to prevent C++ compiler warnings. On C23 and newer and on C++11 and newer,
 // _Py_NULL is defined as nullptr.