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

[Florian Weimer]

On 06/21/2016 03:20 PM, H.J. Lu wrote:
> 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?

If I'm not mistaken, m68k has fundamental alignment 2 (the alignment of 
long, double, and long double), but our malloc still aligns to 8 (2 * 
sizeof (size_t)).

Florian