Arjan van de Ven wrote:

quoted

That is a really nasty problem.  You need a synchronization primitive 
which guarantees a flat stack, so you can't do it in the interrupt 
handler as I have tried to do.  I'll bang my head on it awhile.  In the 
meantime, were there ever any solutions to the syscall patching problem 
that might lend me a clue as to what to do (or not to do, or impossible?).
    

yes we just disallowed it :)
  

Ok, I just took a cold shower.  Actually, this problem is much easier to 
solve for paravirt-ops, since they are short lived operations and don't 
block.  For syscall, it is much, much harder, since you have syscalls 
that can block forever, so you can't guarantee you'll exit all instances 
of the syscall you want to patch.

I think the paravirt-ops one is doable with exports already provided by 
Linux.

Zach