GH-119866: Don't clear frame->stackpointer on release builds (GH-131750)

brandtbucher · web-flow · commit 4b3d5b604210 · 2025-03-26T19:00:16.000Z
diff --git a/Include/internal/pycore_interpframe.h b/Include/internal/pycore_interpframe.h
@@ -163,15 +163,17 @@ _PyFrame_GetLocalsArray(_PyInterpreterFrame *frame)
     return frame->localsplus;
 }
 
-/* Fetches the stack pointer, and sets stackpointer to NULL.
-   Having stackpointer == NULL ensures that invalid
-   values are not visible to the cycle GC. */
+// Fetches the stack pointer, and (on debug builds) sets stackpointer to NULL.
+// Having stackpointer == NULL makes it easier to catch missing stack pointer
+// spills/restores (which could expose invalid values to the GC) using asserts.
 static inline _PyStackRef*
 _PyFrame_GetStackPointer(_PyInterpreterFrame *frame)
 {
     assert(frame->stackpointer != NULL);
     _PyStackRef *sp = frame->stackpointer;
+#ifndef NDEBUG
     frame->stackpointer = NULL;
+#endif
     return sp;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -163,15 +163,17 @@ _PyFrame_GetLocalsArray(_PyInterpreterFrame *frame)`
`163`	`163`	`return frame->localsplus;`
`164`	`164`	`}`
`165`	`165`
`166`		`-/* Fetches the stack pointer, and sets stackpointer to NULL.`
`167`		`- Having stackpointer == NULL ensures that invalid`
`168`		`- values are not visible to the cycle GC. */`
	`166`	`+// Fetches the stack pointer, and (on debug builds) sets stackpointer to NULL.`
	`167`	`+// Having stackpointer == NULL makes it easier to catch missing stack pointer`
	`168`	`+// spills/restores (which could expose invalid values to the GC) using asserts.`
`169`	`169`	`static inline _PyStackRef*`
`170`	`170`	`_PyFrame_GetStackPointer(_PyInterpreterFrame *frame)`
`171`	`171`	`{`
`172`	`172`	`assert(frame->stackpointer != NULL);`
`173`	`173`	`_PyStackRef *sp = frame->stackpointer;`
	`174`	`+#ifndef NDEBUG`
`174`	`175`	`frame->stackpointer = NULL;`
	`176`	`+#endif`
`175`	`177`	`return sp;`
`176`	`178`	`}`
`177`	`179`