1 From 0b91f8a668201fc58fa732b8acc496caedfdbae0 Mon Sep 17 00:00:00 2001
2 From: Florian Weimer <fw@deneb.enyo.de>
3 Date: Sun, 29 Apr 2018 12:18:33 -0700
4 Subject: [PATCH] Indicate that _PyGC_Head is only 8-byte aligned. (closes
7 By spec, the "long double" in _PyGC_Head requires the union to always be 16-byte
8 aligned. However, obmalloc only yields 8-byte alignment. Compilers including GCC
9 8 are starting to use alignment information to do store-merging. So, the "long
10 double" needs to be changed to a simple "double" as was long ago done in Python
11 3 by e348c8d154cf6342c79d627ebfe89dfe9de23817. For 2.7, we need to add some
12 dummy padding to make sure _PyGC_Head stays the same size.
14 Upstream: https://bugs.python.org/issue33374
15 Signed-off-by: Stefan Becker <chemobejk@gmail.com>
17 Include/objimpl.h | 17 ++++++++++++++++-
18 .../2018-04-29-12-07-00.bpo-33374.-xegL6.rst | 3 +++
19 2 files changed, 19 insertions(+), 1 deletion(-)
20 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2018-04-29-12-07-00.bpo-33374.-xegL6.rst
22 diff --git a/Include/objimpl.h b/Include/objimpl.h
23 index 5f2868332955..cbf6bc3f8763 100644
24 --- a/Include/objimpl.h
25 +++ b/Include/objimpl.h
26 @@ -248,6 +248,20 @@ PyAPI_FUNC(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, Py_ssize_t);
27 /* for source compatibility with 2.2 */
28 #define _PyObject_GC_Del PyObject_GC_Del
31 + * Former over-aligned definition of PyGC_Head, used to compute the size of the
32 + * padding for the new version below.
37 + union _gc_head_old *gc_next;
38 + union _gc_head_old *gc_prev;
44 /* GC information is stored BEFORE the object structure. */
45 typedef union _gc_head {
47 @@ -255,7 +269,8 @@ typedef union _gc_head {
48 union _gc_head *gc_prev;
51 - long double dummy; /* force worst-case alignment */
52 + double dummy; /* Force at least 8-byte alignment. */
53 + char dummy_padding[sizeof(union _gc_head_old)];
56 extern PyGC_Head *_PyGC_generation0;
57 diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-04-29-12-07-00.bpo-33374.-xegL6.rst b/Misc/NEWS.d/next/Core and Builtins/2018-04-29-12-07-00.bpo-33374.-xegL6.rst
59 index 000000000000..9ec1a605c8f2
61 +++ b/Misc/NEWS.d/next/Core and Builtins/2018-04-29-12-07-00.bpo-33374.-xegL6.rst
63 +Tweak the definition of PyGC_Head, so compilers do not believe it is always
64 +16-byte aligned on x86. This prevents crashes with more aggressive
65 +optimizations present in GCC 8.