bpo-36389: _PyObject_IsFreed() now also detects uninitialized memory (GH-12770)

Replace _PyMem_IsFreed() function with _PyMem_IsPtrFreed() inline
function. The function is now way more efficient, it became a simple
comparison on integers, rather than a short loop. It detects also
uninitialized bytes and "forbidden bytes" filled by debug hooks
on memory allocators.

Add unit tests on _PyObject_IsFreed().

1 files changed, 1 insertions, 17 deletions

diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index 1c2a32050f9..e919fad595b 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -1914,7 +1914,7 @@ _Py_GetAllocatedBlocks(void)
 
 /* Special bytes broadcast into debug memory blocks at appropriate times.
  * Strings of these are unlikely to be valid addresses, floats, ints or
- * 7-bit ASCII.
+ * 7-bit ASCII. If modified, _PyMem_IsPtrFreed() should be updated as well.
  */
 #undef CLEANBYTE
 #undef DEADBYTE
@@ -2059,22 +2059,6 @@ _PyMem_DebugRawCalloc(void *ctx, size_t nelem, size_t elsize)
 }
 
 
-/* Heuristic checking if the memory has been freed. Rely on the debug hooks on
-   Python memory allocators which fills the memory with DEADBYTE (0xDB) when
-   memory is deallocated. */
-int
-_PyMem_IsFreed(void *ptr, size_t size)
-{
-    unsigned char *bytes = ptr;
-    for (size_t i=0; i < size; i++) {
-        if (bytes[i] != DEADBYTE) {
-            return 0;
-        }
-    }
-    return 1;
-}
-
-
 /* The debug free first checks the 2*SST bytes on each end for sanity (in
    particular, that the FORBIDDENBYTEs with the api ID are still intact).
    Then fills the original bytes with DEADBYTE.