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

[Florian Weimer]

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)).

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