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Re: [RFC] nptl: change default stack guard size of threads
- From: Szabolcs Nagy <szabolcs dot nagy at arm dot com>
- To: Florian Weimer <fweimer at redhat dot com>, James Greenhalgh <james dot greenhalgh at arm dot com>
- Cc: nd at arm dot com, Rich Felker <dalias at libc dot org>, GNU C Library <libc-alpha at sourceware dot org>, Jeff Law <law at redhat dot com>, Richard Earnshaw <Richard dot Earnshaw at arm dot com>, Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>
- Date: Tue, 19 Dec 2017 18:21:32 +0000
- Subject: Re: [RFC] nptl: change default stack guard size of threads
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On 19/12/17 13:06, Florian Weimer wrote:
> On 12/19/2017 01:34 PM, James Greenhalgh wrote:
>
>> Option 1: 64k guard pages for LP64 on AArch64.
>
>> Option 2: 4k guard pages for LP64 for AArch64
>
>> Our proposal then, having spoken things through with the Arm engineers
>> here, and taken in to consideration the opinions on this thread, is that
>> we move to two "blessed" configurations of the GCC support for AArch64.
>
> Are there any Arm engineers who prefer Option 2, or is that just there to accommodate feedback on libc-alpha?
>
> My main concern was the variance in configurations with Option 1 (compared to Option 2). To some extent, the
> variance with Option 1 is temporary. If both Option 1 and 2 are offered, we have permanent variance. From my
> point of view, that's worth that just going with Option 1.
>
> So if this is some sort of consensus proposal, as opposed to actual technical requirements which favor Option 2
> in some deployments, I think that's not a good idea, and we should go with Option 1 instead.
>
well glibc can pretend that only Option 1 is available,
my latest patch assumes 64k probe interval:
https://sourceware.org/ml/libc-alpha/2017-12/msg00451.html
however Option 1 requires generic code to be changed
for aarch64 only (in the libc and elsewhere) and we
cannot easily do that on all (non-glibc) systems.
it seems to me if there are systems where Option 1
may not provide guaranteed trap on stack overflow
then gcc should have Option 2 for those systems.