fix boundary conditions

Author: picnixz

Objects/codeobject.c

@@ -445,10 +445,9 @@ _PyCode_Validate(struct _PyCodeConstructor *con)
      *
      * See https://github.com/python/cpython/issues/126119 for details.
      */
-    int max_stacksize = (int)(INT_MAX / sizeof(PyObject *))
-                        - FRAME_SPECIALS_SIZE
-                        - (int)PyTuple_GET_SIZE(con->localsplusnames);
-    if (con->stacksize >= max_stacksize) {
+    int ub = (int)(INT_MAX / sizeof(PyObject *)) - FRAME_SPECIALS_SIZE;
+    Py_ssize_t nlocalsplus = PyTuple_GET_SIZE(con->localsplusnames);
+    if (nlocalsplus >= (Py_ssize_t)ub || con->stacksize >= (int)ub - nlocalsplus) {
         PyErr_SetString(PyExc_OverflowError, "code: co_stacksize is too large");
         return -1;
     }

Objects/frameobject.c

@@ -1806,6 +1806,7 @@ frame_sizeof(PyFrameObject *f, PyObject *Py_UNUSED(ignored))
 {
     Py_ssize_t base = offsetof(PyFrameObject, _f_frame_data)
                       + offsetof(_PyInterpreterFrame, localsplus);
+    assert(base <= INT_MAX);
     PyCodeObject *code = _PyFrame_GetCode(f->f_frame);
     int nslots = _PyFrame_NumSlotsForCodeObject(code);
     assert(nslots >= 0);

Objects/genobject.c

@@ -819,6 +819,7 @@ gen_sizeof(PyGenObject *gen, PyObject *Py_UNUSED(ignored))
 {
     Py_ssize_t base = offsetof(PyGenObject, gi_iframe)
                       + offsetof(_PyInterpreterFrame, localsplus);
+    assert(base <= INT_MAX);
     PyCodeObject *code = _PyGen_GetCode(gen);
     int nslots = _PyFrame_NumSlotsForCodeObject(code);
     assert(nslots >= 0);