[Python-checkins] GH-133261: Make sure trashcan pointers look mortal -- 32 bit (GH-133450)

[ambv]

https://github.com/python/cpython/commit/d48616e08cbf069847026a2ee35017ad5cbe12a8
commit: d48616e08cbf069847026a2ee35017ad5cbe12a8
branch: main
author: Mark Shannon <m...@hotpy.org>
committer: ambv <luk...@langa.pl>
date: 2025-05-05T21:51:32+02:00
summary:

GH-133261: Make sure trashcan pointers look mortal -- 32 bit (GH-133450)

Make sure trashcan pointer look mortal -- 32 bit

files:
M Objects/object.c

diff --git a/Objects/object.c b/Objects/object.c
index e9a93f87be4cf7..723b0427e69251 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -2940,20 +2940,29 @@ pointer_to_safe_refcount(void *ptr)
 {
     uintptr_t full = (uintptr_t)ptr;
     assert((full & 3) == 0);
+#if SIZEOF_VOID_P > 4
     uint32_t refcnt = (uint32_t)full;
     if (refcnt >= (uint32_t)_Py_IMMORTAL_MINIMUM_REFCNT) {
         full = full - ((uintptr_t)_Py_IMMORTAL_MINIMUM_REFCNT) + 1;
     }
     return full + 2;
+#else
+    // Make the top two bits 0, so it appears mortal.
+    return (full >> 2) + 1;
+#endif
 }
 
 static void *
 safe_refcount_to_pointer(uintptr_t refcnt)
 {
+#if SIZEOF_VOID_P > 4
     if (refcnt & 1) {
         refcnt += _Py_IMMORTAL_MINIMUM_REFCNT - 1;
     }
     return (void *)(refcnt - 2);
+#else
+    return (void *)((refcnt -1) << 2);
+#endif
 }
 #endif
 

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