just to follow up:
I built a xeno-kernel for my laptop, the sep flag was on,
so it was Fedora specific. I asked on fedora-list,
got this answer:
> This is pretty obscure, and I havent seen any problems because of it,
> but it is a bit odd.
> Can someone(s)
> - confirm its absence on 2.6.16-1.2069_FC4 or other
> - check their FC-5 /proc/cpuinfo, and report back.
> - explain why this is a good thing, or how it might have happened
> accidentally ?
SEP is incompatible with segment-based NX emulation provided
by exec-shield in the Fedora kernel.
The reason for this is that a SYSRET resets the segment limits.
I presume this distinction is well hidden inside glibc etc..
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