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Re: [PATCH] elf: dl-minimal malloc needs to respect fundamental alignment
- From: Florian Weimer <fweimer at redhat dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 23 Jun 2016 17:01:08 +0200
- Subject: Re: [PATCH] elf: dl-minimal malloc needs to respect fundamental alignment
- Authentication-results: sourceware.org; auth=none
- References: <20160621111702 dot 39A5B402F6E95 at oldenburg dot str dot redhat dot com> <CAMe9rOpx1Vbr6_n8+SvGCe92TO5e+KdC3hNcNAN3LvfXhd79Ow at mail dot gmail dot com> <6ca009d9-433e-31f5-c3c0-c84ecc587059 at redhat dot com> <CAMe9rOpLkftyZ+4y=1E3pbrKRU-i0kE4bdQLGaCac_Q9v1cV6g at mail dot gmail dot com> <0ef86d34-0642-8e47-9fe4-dcd7638c6153 at redhat dot com> <CAMe9rOo5F4GXuh7HRUYeDh60wh6qafNtJH1xVXJREc6w4EPCiQ at mail dot gmail dot com>
On 06/21/2016 03:20 PM, H.J. Lu wrote:
On Tue, Jun 21, 2016 at 6:06 AM, Florian Weimer <email@example.com> wrote:
On 06/21/2016 03:00 PM, H.J. Lu wrote:
MALLOC_ALIGNMENT is potentially larger. malloc/tst-malloc-thread-fail
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 *