Re: [Xen-devel] VM System Calls

[Frederic Beck <frederic.beck@xxxxxxxx>]

Just another quick question.

After modifying traps.c, to recompile the hypervisor, do I need to
recompile the whole sources with a make world ? Or is it unnecessary ?

At the moment I'm running a Debian unstable with the debian packages
distribution of Xen with hypervisor 3.2 and kernel 2.6.26, and the
2.6.18 is not running on my computer.

The idea would be to compile only the hypervisor, but id did not found
yet in the documentation how to do it. I'll keep on looking, but is you
have an idea it would be welcomed :)

Thanks
Fred

Le Wed, 26 Nov 2008 09:50:32 +0100,
Frederic Beck <frederic.beck@xxxxxxxx> a Ãcrit :

> Hello
> 
> > If you're not averse to modifying the hypervisor, you should be able
> > to arrange to get what you want.
> 
> Not at all :) It's what i was planning to do in the first case.
> 
> > For 32-bit guests, we allow the system call to trap directly from
> > userspace into the PV kernel.  But that's actually an optimization;
> > it used to be the case that if you disable that direct-trap, then
> > it will trap to Xen, and Xen will forward it on to the PV kernel.
> > This will make guest system calls slightly more expensive, but it
> > will allow you to add the tracing / instrumentation you want.
> > 
> > Yes, it looks like if you comment out the following line in
> > xen/arch/x86/traps.c:do_set_trap_table():
> >        if ( cur.vector == 0x80 )
> >             init_int80_direct_trap(curr);
> > 
> > Then all guest traps, including system call, will go through
> > traps.c:do_guest_trap(), which already traces the trap number.  If
> > you want more information, you can add more trace info there.
> 
> Thanks a lot for your help, i'll give it a try. I just commented out
> that part, i'll recompile the hypervisor and play with it.
> 
> I'll let you know how it works out.
> 
> Thanks
> Fred
> 
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