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From: Ed Maste <emaste@freebsd.org>
Date: Thu, 2 Oct 2014 11:10:20 -0400
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Subject: Re: Kernel/Compiler bug
To: Konstantin Belousov <kostikbel@gmail.com>, 
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On 2 October 2014 03:55, Konstantin Belousov <kostikbel@gmail.com> wrote:
>
> The cost of the increased size for kernel stack is significant, even
> on architectures with ample KVA.  This must not be done just because
> some non-default kernel settings cause stack overflow.  If somebody
> feels himself qualified enough to tune compiler options, it must
> understand the consequences and do other required adjustments,
> including kernel stack size tuning.

I wonder if we should have a comment in kern.pre.mk, even if it's just
an explicit notice that changing -O can have adverse effects. For
better or worse it's a fairly common desire to try changing the
kernel's -O.

Of course, kern.pre.mk is not intended to accommodate user-facing
changes. I suspect it's reasonably common for developers to grep '-O2'
in sys/conf and discover where it's getting set though.