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Re: [PATCH] libio: Add small optimization on fmemopen
* Ondřej Bílka:
> On Fri, Sep 23, 2016 at 07:34:24AM +0200, Florian Weimer wrote:
>> On 09/23/2016 07:17 AM, Ondřej Bílka wrote:
>> >> size_t clen = sizeof (fmemopen_cookie_t);
>> >> if (FLEXMEMBER_NEEDS_ALIGNMENT)
>> >> clen += _Alignof (fmemopen_cookie_t) - 1;
>> >
>> >Couldn't you just use __attribute__((aligned(16))) or is that also
>> >buggy?
>>
>> Buggy in what sense?
>>
>> malloc isn't guaranteed to provide 16-byte alignment on all glibc
>> architectures.
>>
> Buggy in sense that some gcc version would ignore it. I picked 16 to
> have same alignment as malloc does as 16 is max granularity of malloc.
malloc granularity can be as low as 2 (on m68k) without impacting C
conformance, and an interposed malloc implementation might provide
just that.
On most 32-bit platforms, glibc's own malloc provides only 8-byte
alignment.