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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Inada Naoki <songofacandy@gmail.com>
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Date: Mon, 3 Jun 2019 10:51:32 +0900
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Subject: [PATCH] 00358: align allocations and PyGC_Head to 16 bytes on 64-bit
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platforms
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Upstream bug: https://bugs.python.org/issue27987
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Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1923658
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Combination of two upstream commits:
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- 1b85f4ec45a5d63188ee3866bd55eb29fdec7fbf
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- 8766cb74e186d3820db0a855ccd780d6d84461f7
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---
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Include/objimpl.h | 6 +++++-
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.../2019-05-15-18-28-43.bpo-27987.FaxuLy.rst | 2 ++
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Objects/obmalloc.c | 6 ++++++
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3 files changed, 13 insertions(+), 1 deletion(-)
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create mode 100644 Misc/NEWS.d/next/Core and Builtins/2019-05-15-18-28-43.bpo-27987.FaxuLy.rst
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diff --git a/Include/objimpl.h b/Include/objimpl.h
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index e7a3696d7a..90d71b87ea 100644
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--- a/Include/objimpl.h
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+++ b/Include/objimpl.h
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@@ -255,7 +255,11 @@ typedef union _gc_head {
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union _gc_head *gc_prev;
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Py_ssize_t gc_refs;
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} gc;
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- double dummy; /* force worst-case alignment */
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+ long double dummy; /* force worst-case alignment */
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+ // malloc returns memory block aligned for any built-in types and
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+ // long double is the largest standard C type.
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+ // On amd64 linux, long double requires 16 byte alignment.
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+ // See bpo-27987 for more discussion.
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} PyGC_Head;
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extern PyGC_Head *_PyGC_generation0;
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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
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new file mode 100644
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index 0000000000..98073471ca
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--- /dev/null
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+++ b/Misc/NEWS.d/next/Core and Builtins/2019-05-15-18-28-43.bpo-27987.FaxuLy.rst
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@@ -0,0 +1,2 @@
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+``PyGC_Head`` structure is aligned to ``long double``. This is needed to
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+ensure GC-ed objects are aligned properly. Patch by Inada Naoki.
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diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
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index d46d149311..47283354f4 100644
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--- a/Objects/obmalloc.c
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+++ b/Objects/obmalloc.c
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@@ -650,8 +650,14 @@ static int running_on_valgrind = -1;
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*
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* You shouldn't change this unless you know what you are doing.
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*/
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+
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+#if SIZEOF_VOID_P > 4
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+#define ALIGNMENT 16 /* must be 2^N */
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+#define ALIGNMENT_SHIFT 4
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+#else
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#define ALIGNMENT 8 /* must be 2^N */
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#define ALIGNMENT_SHIFT 3
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+#endif
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/* Return the number of bytes in size class I, as a uint. */
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#define INDEX2SIZE(I) (((uint)(I) + 1) << ALIGNMENT_SHIFT)
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