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bpo-36389: Change PyMem_SetupDebugHooks() constants (GH-12782) 

Modify CLEANBYTE, DEADDYTE and FORBIDDENBYTE constants: use 0xCD,
0xDD and 0xFD, rather than 0xCB, 0xBB and 0xFB, to use the same byte
patterns than Windows CRT debug malloc() and free().
This commit is contained in:
Victor Stinner 2019-04-11 13:01:15 +02:00 committed by GitHub
parent 536a35b3f1
commit 4c409beb4c
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GPG Key ID: 4AEE18F83AFDEB23
6 changed files with 37 additions and 24 deletions
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11
Doc/c-api/memory.rst
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@ -440,8 +440,9 @@ Customize Memory Allocators
Setup hooks to detect bugs in the Python memory allocator functions.
Newly allocated memory is filled with the byte ``0xCB``, freed memory is
filled with the byte ``0xDB``.
Newly allocated memory is filled with the byte ``0xCD`` (``CLEANBYTE``),
freed memory is filled with the byte ``0xDD`` (``DEADBYTE``). Memory blocks
are surrounded by "forbidden bytes" (``FORBIDDENBYTE``: byte ``0xFD``).
Runtime checks:
@ -471,6 +472,12 @@ Customize Memory Allocators
if the GIL is held when functions of :c:data:`PYMEM_DOMAIN_OBJ` and
:c:data:`PYMEM_DOMAIN_MEM` domains are called.
.. versionchanged:: 3.8.0
Byte patterns ``0xCB`` (``CLEANBYTE``), ``0xDB`` (``DEADBYTE``) and
``0xFB`` (``FORBIDDENBYTE``) have been replaced with ``0xCD``, ``0xDD``
and ``0xFD`` to use the same values than Windows CRT debug ``malloc()``
and ``free()``.
.. _pymalloc:

19
Include/internal/pycore_pymem.h
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@ -160,21 +160,20 @@ PyAPI_FUNC(int) _PyMem_SetDefaultAllocator(
pointer value is checked.
The heuristic relies on the debug hooks on Python memory allocators which
fills newly allocated memory with CLEANBYTE (0xCB) and newly freed memory
with DEADBYTE (0xDB). Detect also "untouchable bytes" marked
with FORBIDDENBYTE (0xFB). */
fills newly allocated memory with CLEANBYTE (0xCD) and newly freed memory
with DEADBYTE (0xDD). Detect also "untouchable bytes" marked
with FORBIDDENBYTE (0xFD). */
static inline int _PyMem_IsPtrFreed(void *ptr)
{
uintptr_t value = (uintptr_t)ptr;
#if SIZEOF_VOID_P == 8
return (value == (uintptr_t)0xCBCBCBCBCBCBCBCB
|| value == (uintptr_t)0xDBDBDBDBDBDBDBDB
|| value == (uintptr_t)0xFBFBFBFBFBFBFBFB
);
return (value == (uintptr_t)0xCDCDCDCDCDCDCDCD
|| value == (uintptr_t)0xDDDDDDDDDDDDDDDD
|| value == (uintptr_t)0xFDFDFDFDFDFDFDFD);
#elif SIZEOF_VOID_P == 4
return (value == (uintptr_t)0xCBCBCBCB
|| value == (uintptr_t)0xDBDBDBDB
|| value == (uintptr_t)0xFBFBFBFB);
return (value == (uintptr_t)0xCDCDCDCD
|| value == (uintptr_t)0xDDDDDDDD
|| value == (uintptr_t)0xFDFDFDFD);
#else
# error "unknown pointer size"
#endif

8
Lib/test/test_capi.py
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@ -480,11 +480,11 @@ class PyMemDebugTests(unittest.TestCase):
r" The [0-9] pad bytes at p-[0-9] are FORBIDDENBYTE, as expected.\n"
r" The [0-9] pad bytes at tail={ptr} are not all FORBIDDENBYTE \(0x[0-9a-f]{{2}}\):\n"
r" at tail\+0: 0x78 \*\*\* OUCH\n"
r" at tail\+1: 0xfb\n"
r" at tail\+2: 0xfb\n"
r" at tail\+1: 0xfd\n"
r" at tail\+2: 0xfd\n"
r" .*\n"
r" The block was made by call #[0-9]+ to debug malloc/realloc.\n"
r" Data at p: cb cb cb .*\n"
r" Data at p: cd cd cd .*\n"
r"\n"
r"Enable tracemalloc to get the memory block allocation traceback\n"
r"\n"
@ -500,7 +500,7 @@ class PyMemDebugTests(unittest.TestCase):
r" The [0-9] pad bytes at p-[0-9] are FORBIDDENBYTE, as expected.\n"
r" The [0-9] pad bytes at tail={ptr} are FORBIDDENBYTE, as expected.\n"
r" The block was made by call #[0-9]+ to debug malloc/realloc.\n"
r" Data at p: cb cb cb .*\n"
r" Data at p: cd cd cd .*\n"
r"\n"
r"Enable tracemalloc to get the memory block allocation traceback\n"
r"\n"

5
Misc/NEWS.d/next/C API/2019-04-11-12-20-35.bpo-36389.P9QFoP.rst Normal file
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@ -0,0 +1,5 @@
Change the value of ``CLEANBYTE``, ``DEADDYTE`` and ``FORBIDDENBYTE`` internal
constants used by debug hooks on Python memory allocators
(:c:func:`PyMem_SetupDebugHooks` function). Byte patterns ``0xCB``, ``0xDB``
and ``0xFB`` have been replaced with ``0xCD``, ``0xDD`` and ``0xFD`` to use the
same values than Windows CRT debug ``malloc()`` and ``free()``.

9
Objects/object.c
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@ -415,13 +415,12 @@ _Py_BreakPoint(void)
}
/* Heuristic checking if the object memory has been deallocated.
Rely on the debug hooks on Python memory allocators which fills the memory
with DEADBYTE (0xDB) when memory is deallocated.
/* Heuristic checking if the object memory is uninitialized or deallocated.
Rely on the debug hooks on Python memory allocators:
see _PyMem_IsPtrFreed().
The function can be used to prevent segmentation fault on dereferencing
pointers like 0xdbdbdbdbdbdbdbdb. Such pointer is very unlikely to be mapped
in memory. */
pointers like 0xDDDDDDDDDDDDDDDD. */
int
_PyObject_IsFreed(PyObject *op)
{

9
Objects/obmalloc.c
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@ -1915,13 +1915,16 @@ _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. If modified, _PyMem_IsPtrFreed() should be updated as well.
*
* Byte patterns 0xCB, 0xBB and 0xFB have been replaced with 0xCD, 0xDD and
* 0xFD to use the same values than Windows CRT debug malloc() and free().
*/
#undef CLEANBYTE
#undef DEADBYTE
#undef FORBIDDENBYTE
#define CLEANBYTE 0xCB /* clean (newly allocated) memory */
#define DEADBYTE 0xDB /* dead (newly freed) memory */
#define FORBIDDENBYTE 0xFB /* untouchable bytes at each end of a block */
#define CLEANBYTE 0xCD /* clean (newly allocated) memory */
#define DEADBYTE 0xDD /* dead (newly freed) memory */
#define FORBIDDENBYTE 0xFD /* untouchable bytes at each end of a block */
static size_t serialno = 0; /* incremented on each debug {m,re}alloc */