Re: [Xen-devel] VM System Calls

[Frederic Beck <frederic.beck@xxxxxxxx>]

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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