> > From: Theo de Raadt <dera...@cvs.openbsd.org>
> > Date: Thu, 04 Jul 2013 09:04:54 -0600
> > 
> > I suspect the best approach would be a hybrid value.  The upper half
> > of the address should try to land in an unmapped zone, or into the zero
> > page, or into some address space hole, ir into super high memory above
> > the stack which is gauranteed unmapped.
> 
> Don't forget strict alignment architectures, where it is beneficial
> to have the lowest bit set to trigger alignment traps.

That's why I vaguely mentioned the idea of a sysctl or MD defines, which
would declare a fixed component, plus a mask on top of random.

That fixed component need not just be high bits, it can also cover the
lowest bit (or two) for instance.

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