[3.7] bpo-9263: _PyObject_Dump() detects freed memory (GH-10061) (GH-10662)
* bpo-9263: _PyObject_Dump() detects freed memory (GH-10061)
_PyObject_Dump() now uses an heuristic to check if the object memory
has been freed: log "<freed object>" in that case.
The heuristic rely on the debug hooks on Python memory allocators
which fills the memory with DEADBYTE (0xDB) when memory is
deallocated. Use PYTHONMALLOC=debug to always enable these debug
hooks.
(cherry picked from commit 82af0b63b07aa8d92b50098e382b458143cfc677)
* bpo-9263: Fix _PyObject_Dump() for freed object (#10661)
If _PyObject_Dump() detects that the object is freed, don't try to
dump it (exit immediately).
Enhance also _PyObject_IsFreed(): it now detects if the pointer
itself looks like freed memory.
(cherry picked from commit 2cf5d32fd9e61488e8b0be55a2e92a752ba8b06b)
diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index 1b8b5ee..3b0c35b 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -2091,6 +2091,22 @@
}
+/* 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.