execshield rebase

[Roland McGrath]

> I tried back in July when I got the diff down to under a thousand lines.
> Linus wasn't really enthusiastic.

I wasn't necessarily thinking too much would go in very easy.  But cleaner
and separate patches would at least probably stay easier to rebase.

> http://www.codemonkey.org.uk/junk/linus-es.txt
> has the interesting bits..
> 
> The get_wchan bit that he mentions definitly should be factored out.
> It's completely unrelated to the NX-emulation.

Quite so.  Also I think the i386 NX-emulation bits can really be isolated
well to an x86-only config option that is clean and nonintrusive.  The mmap
layout changes are necessary for NX-emulation to be worth having at all,
but it is quite separable in the code.

I think we should also clean up the use of the exec_shield sysctl setting
for so many different magic things at once.  (In the cleaned up patches, I
doubt there would be anything called "exec-shield" left.)


Thanks,
Roland