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Re: [PATCH] elf: dl-minimal malloc needs to respect fundamental alignment

On Tue, Jun 21, 2016 at 6:06 AM, Florian Weimer <> wrote:
> On 06/21/2016 03:00 PM, H.J. Lu wrote:
>>> MALLOC_ALIGNMENT is potentially larger.  malloc/tst-malloc-thread-fail
>>> tests
>>> for alignment.  To my knowledge, it passes on all regularly tested
>>> architectures after commit dea39b13e2958a7f0e75b5594a06d97d61cc439f.
>> MALLOC_ALIGNMENT is kind of mapped to the malloc alignment of
>> a psABI.  Shouldn't malloc have the same alignment of libc malloc?
> I don't see why.  MALLOC_ALIGNMENT has to match both the ABI constraint and
> the malloc/malloc.c implementation constraint (which requires a minimum
> alignment of 2 * sizeof (size_t)).

My understanding is since the minimum constraint of malloc alignment
<= ABI alignment, MALLOC_ALIGNMENT == ABI alignment.  Do you
have a glibc platform where it isn't true?

> Other mallocs do not have matching implementation constraints, and it is
> standard practice (in non-glibc mallocs) to lower the alignment for
> allocations which are smaller in size than _Alignof (max_align_t), although
> this is not compliant with C11.
> Florian


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