From 618ef35426ecc57da1bee50f8dc5896f5fb178a9 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Sat, 25 May 2019 21:13:33 +0900
Subject: [PATCH 2/2] bpo-27987: align PyGC_Head to alignof(long double)
 (GH-13335)

---
 Include/objimpl.h                                           | 6 +++++-
 .../2019-05-15-18-28-43.bpo-27987.FaxuLy.rst                | 2 ++
 2 files changed, 7 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2019-05-15-18-28-43.bpo-27987.FaxuLy.rst

diff --git a/Include/objimpl.h b/Include/objimpl.h
index 65b6d91c36..eaf57975c8 100644
--- a/Include/objimpl.h
+++ b/Include/objimpl.h
@@ -250,7 +250,11 @@ typedef union _gc_head {
         union _gc_head *gc_prev;
         Py_ssize_t gc_refs;
     } gc;
-    double dummy;  /* force worst-case alignment */
+    long double dummy;  /* force worst-case alignment */
+    // malloc returns memory block aligned for any built-in types and
+    // long double is the largest standard C type.
+    // On amd64 linux, long double requires 16 byte alignment.
+    // See bpo-27987 for more discussion.
 } PyGC_Head;
 
 extern PyGC_Head *_PyGC_generation0;
diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-05-15-18-28-43.bpo-27987.FaxuLy.rst b/Misc/NEWS.d/next/Core and Builtins/2019-05-15-18-28-43.bpo-27987.FaxuLy.rst
new file mode 100644
index 0000000000..97ca37b262
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-05-15-18-28-43.bpo-27987.FaxuLy.rst	
@@ -0,0 +1,2 @@
+``PyGC_Head`` structure is aligned to ``long double``.  This is needed to
+GC-ed objects are aligned properly.  Patch by Inada Naoki.
-- 
2.38.4

