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


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


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