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

[H.J. Lu]

On Tue, Jun 21, 2016 at 6:06 AM, Florian Weimer <fweimer@redhat.com> 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 ld.so 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



-- 
H.J.