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bpo-27987: pymalloc: align by 16bytes on 64bit platform #12850

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merged 3 commits into from
May 14, 2019
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bpo-27987: pymalloc: align by 16bytes on 64bit platform #12850

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bpo-27987: pymalloc: align by 16bytes on 64bit platform
methane Apr 16, 2019
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add news entry
methane Apr 16, 2019
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Update 2019-04-16-11-52-21.bpo-27987.n2_DcQ.rst
methane Apr 16, 2019
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-04-16-11-52-21.bpo-27987.n2_DcQ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
pymalloc returns memory blocks aligned by 16 bytes, instead of 8 bytes, on
64-bit platforms to conform x86-64 ABI. Recent compilers assume this alignment
more often. Patch by Inada Naoki.
6 changes: 6 additions & 0 deletions Objects/obmalloc.c
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Expand Up @@ -795,8 +795,14 @@ 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)
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