Document that safe functions are not 100% reliable

Author: vstinner

Include/internal/pycore_code.h

@@ -276,8 +276,9 @@ PyAPI_FUNC(int) _PyLineTable_NextAddressRange(PyCodeAddressRange *range);
 extern int _PyLineTable_PreviousAddressRange(PyCodeAddressRange *range);
 
 // Similar to PyCode_Addr2Line(), but return -1 if the code object is invalid
-// and can be called without an attached tstate.
-// Used by dump_frame() in Python/traceback.c.
+// and can be called without an attached tstate. Used by dump_frame() in
+// Python/traceback.c. The function uses heuristics to detect freed memory,
+// it's not 100% reliable.
 extern int _PyCode_SafeAddr2Line(PyCodeObject *co, int addr);
 
 

Include/internal/pycore_interpframe.h

@@ -25,7 +25,8 @@ static inline PyCodeObject *_PyFrame_GetCode(_PyInterpreterFrame *f) {
 }
 
 // Similar to _PyFrame_GetCode(), but return NULL if the frame is invalid or
-// freed. Used by dump_frame() in Python/traceback.c.
+// freed. Used by dump_frame() in Python/traceback.c. The function uses
+// heuristics to detect freed memory, it's not 100% reliable.
 static inline PyCodeObject*
 _PyFrame_SafeGetCode(_PyInterpreterFrame *f)
 {
@@ -66,9 +67,9 @@ _PyFrame_GetBytecode(_PyInterpreterFrame *f)
 #endif
 }
 
-// Similar to PyUnstable_InterpreterFrame_GetLasti(), but return NULL
-// if the frame is invalid or freed.
-// Used by dump_frame() in Python/traceback.c.
+// Similar to PyUnstable_InterpreterFrame_GetLasti(), but return NULL if the
+// frame is invalid or freed. Used by dump_frame() in Python/traceback.c. The
+// function uses heuristics to detect freed memory, it's not 100% reliable.
 static inline int
 _PyFrame_SafeGetLasti(struct _PyInterpreterFrame *f)
 {