|
 |
96a45b |
commit 0b91f8a668201fc58fa732b8acc496caedfdbae0
|
|
|
96a45b |
Author: Florian Weimer <fw@deneb.enyo.de>
|
|
|
96a45b |
Date: Sun Apr 29 12:18:33 2018 -0700
|
|
|
96a45b |
|
|
|
96a45b |
Indicate that _PyGC_Head is only 8-byte aligned. (closes bpo-33374)
|
|
|
96a45b |
|
|
|
96a45b |
By spec, the "long double" in _PyGC_Head requires the union to always be 16-byte
|
|
|
96a45b |
aligned. However, obmalloc only yields 8-byte alignment. Compilers including GCC
|
|
|
96a45b |
8 are starting to use alignment information to do store-merging. So, the "long
|
|
|
96a45b |
double" needs to be changed to a simple "double" as was long ago done in Python
|
|
|
96a45b |
3 by e348c8d154cf6342c79d627ebfe89dfe9de23817. For 2.7, we need to add some
|
|
|
96a45b |
dummy padding to make sure _PyGC_Head stays the same size.
|
|
|
96a45b |
|
|
|
96a45b |
diff --git a/Include/objimpl.h b/Include/objimpl.h
|
|
|
96a45b |
index 5f28683329..cbf6bc3f87 100644
|
|
|
96a45b |
--- Python-2.7.13/Include/objimpl.h
|
|
|
96a45b |
+++ Python-2.7.13/Include/objimpl.h
|
|
|
96a45b |
@@ -248,6 +248,20 @@ PyAPI_FUNC(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, Py_ssize_t);
|
|
|
96a45b |
/* for source compatibility with 2.2 */
|
|
|
96a45b |
#define _PyObject_GC_Del PyObject_GC_Del
|
|
|
96a45b |
|
|
|
96a45b |
+/*
|
|
|
96a45b |
+ * Former over-aligned definition of PyGC_Head, used to compute the size of the
|
|
|
96a45b |
+ * padding for the new version below.
|
|
|
96a45b |
+ */
|
|
|
96a45b |
+union _gc_head;
|
|
|
96a45b |
+union _gc_head_old {
|
|
|
96a45b |
+ struct {
|
|
|
96a45b |
+ union _gc_head_old *gc_next;
|
|
|
96a45b |
+ union _gc_head_old *gc_prev;
|
|
|
96a45b |
+ Py_ssize_t gc_refs;
|
|
|
96a45b |
+ } gc;
|
|
|
96a45b |
+ long double dummy;
|
|
|
96a45b |
+};
|
|
|
96a45b |
+
|
|
|
96a45b |
/* GC information is stored BEFORE the object structure. */
|
|
|
96a45b |
typedef union _gc_head {
|
|
|
96a45b |
struct {
|
|
|
96a45b |
@@ -255,7 +269,8 @@ typedef union _gc_head {
|
|
|
96a45b |
union _gc_head *gc_prev;
|
|
|
96a45b |
Py_ssize_t gc_refs;
|
|
|
96a45b |
} gc;
|
|
|
96a45b |
- long double dummy; /* force worst-case alignment */
|
|
|
96a45b |
+ double dummy; /* Force at least 8-byte alignment. */
|
|
|
96a45b |
+ char dummy_padding[sizeof(union _gc_head_old)];
|
|
|
96a45b |
} PyGC_Head;
|
|
|
96a45b |
|
|
|
96a45b |
extern PyGC_Head *_PyGC_generation0;
|
|
|
96a45b |
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
|
|
|
96a45b |
new file mode 100644
|
|
|
96a45b |
index 0000000000..9ec1a605c8
|
|
|
96a45b |
--- /dev/null
|
|
|
96a45b |
+++ Python-2.7.13/Misc/NEWS.d/next/Core and Builtins/2018-04-29-12-07-00.bpo-33374.-xegL6.rst
|
|
|
96a45b |
@@ -0,0 +1,3 @@
|
|
|
96a45b |
+Tweak the definition of PyGC_Head, so compilers do not believe it is always
|
|
|
96a45b |
+16-byte aligned on x86. This prevents crashes with more aggressive
|
|
|
96a45b |
+optimizations present in GCC 8.
|