GH-139193: Fix dump_stack when PYTHON_LLTRACE=4 (GH-139384)

Author: sergey-miryanov

Include/internal/pycore_stackref.h

@@ -296,6 +296,12 @@ PyStackRef_IsError(_PyStackRef ref)
     return ref.bits == Py_TAG_INVALID;
 }
 
+static inline bool
+PyStackRef_IsMalformed(_PyStackRef ref)
+{
+    return (ref.bits & Py_TAG_BITS) == Py_TAG_INVALID;
+}
+
 static inline bool
 PyStackRef_IsValid(_PyStackRef ref)
 {

Python/ceval.c

@@ -160,6 +160,10 @@ dump_item(_PyStackRef item)
         printf("<NULL>");
         return;
     }
+    if (PyStackRef_IsMalformed(item)) {
+        printf("<INVALID>");
+        return;
+    }
     if (PyStackRef_IsTaggedInt(item)) {
         printf("%" PRId64, (int64_t)PyStackRef_UntagInt(item));
         return;