From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Inada Naoki Date: Mon, 3 Jun 2019 10:51:32 +0900 Subject: [PATCH] 00358: align allocations and PyGC_Head to 16 bytes on 64-bit platforms Upstream bug: https://bugs.python.org/issue27987 Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1923658 Combination of two upstream commits: - 1b85f4ec45a5d63188ee3866bd55eb29fdec7fbf - 8766cb74e186d3820db0a855ccd780d6d84461f7 --- Include/objimpl.h | 6 +++++- .../2019-05-15-18-28-43.bpo-27987.FaxuLy.rst | 2 ++ Objects/obmalloc.c | 6 ++++++ 3 files changed, 13 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 e7a3696d7a..90d71b87ea 100644 --- a/Include/objimpl.h +++ b/Include/objimpl.h @@ -255,7 +255,11 @@ 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..98073471ca --- /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 +ensure GC-ed objects are aligned properly. Patch by Inada Naoki. diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c index d46d149311..47283354f4 100644 --- a/Objects/obmalloc.c +++ b/Objects/obmalloc.c @@ -650,8 +650,14 @@ static int running_on_valgrind = -1; * * You shouldn't change this unless you know what you are doing. */ + +#if SIZEOF_VOID_P > 4 +#define ALIGNMENT 16 /* must be 2^N */ +#define ALIGNMENT_SHIFT 4 +#else #define ALIGNMENT 8 /* must be 2^N */ #define ALIGNMENT_SHIFT 3 +#endif /* Return the number of bytes in size class I, as a uint. */ #define INDEX2SIZE(I) (((uint)(I) + 1) << ALIGNMENT_SHIFT)