Stack overflow checking dysfunctional with USE_STACKCHECK

Include/ceval.h

Index: Include/ceval.h
===================================================================
--- Include/ceval.h	(revision 66050)
+++ Include/ceval.h	(working copy)
@@ -46,22 +46,34 @@
 PyAPI_FUNC(void) Py_SetRecursionLimit(int);
 PyAPI_FUNC(int) Py_GetRecursionLimit(void);
 
-#define Py_EnterRecursiveCall(where)                                    \
+#define Py_EnterRecursiveCall(where)  \
 	    (_Py_MakeRecCheck(PyThreadState_GET()->recursion_depth) &&  \
 	     _Py_CheckRecursiveCall(where))
 #define Py_LeaveRecursiveCall()				\
-    do{ if((--PyThreadState_GET()->recursion_depth) <   \
-	   _Py_CheckRecursionLimit - 50)                \
-	  PyThreadState_GET()->overflowed = 0;          \
-    } while(0)
+    do{ if(_Py_MakeEndRecCheck(PyThreadState_GET()->recursion_depth))  \
+	  PyThreadState_GET()->overflowed = 0;  \
+	} while(0)
 PyAPI_FUNC(int) _Py_CheckRecursiveCall(char *where);
 PyAPI_DATA(int) _Py_CheckRecursionLimit;
+
 #ifdef USE_STACKCHECK
-#  define _Py_MakeRecCheck(x)  (++(x) > --_Py_CheckRecursionLimit)
+/* With USE_STACKCHECK, we artificially decrement the recursion limit in order
+   to trigger regular stack checks in _Py_CheckRecursiveCall(), except if
+   the "overflowed" flag is set, in which case we need the true value
+   of _Py_CheckRecursionLimit for _Py_MakeEndRecCheck() to function properly.
+*/
+#  define _Py_MakeRecCheck(x)  \
+	(++(x) > (_Py_CheckRecursionLimit += PyThreadState_GET()->overflowed - 1))
 #else
 #  define _Py_MakeRecCheck(x)  (++(x) > _Py_CheckRecursionLimit)
 #endif
 
+#ifdef USE_STACKCHECK
+#  define _Py_MakeEndRecCheck(x)  (--(x) < _Py_CheckRecursionLimit - 50)
+#else
+#  define _Py_MakeEndRecCheck(x)  (--(x) < _Py_CheckRecursionLimit - 50)
+#endif
+
 #define Py_ALLOW_RECURSION \
   do { unsigned char _old = PyThreadState_GET()->recursion_critical;\
     PyThreadState_GET()->recursion_critical = 1;