Re: [Xen-devel] [RFC PATCH] Adding support for coverage informations

[Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>]

On Wed, 2013-01-30 at 16:34 -0500, Konrad Rzeszutek Wilk wrote:
> On Tue, Jan 29, 2013 at 12:02:55PM +0000, Frediano Ziglio wrote:
> > On Tue, 2013-01-29 at 10:56 +0000, Ian Campbell wrote:
> > > On Mon, 2013-01-28 at 21:16 +0000, Frediano Ziglio wrote:
> > > > From: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
> > > > 
> > > > This patch introduce coverage support to Xen.
> > > > Currently it allows to compile Xen with coverage support but there is 
> > > > no way
> > > > to extract them.
> > > > 
> > > > The declarations came from Linux source files (as you can see from file
> > > > headers).
> > > > 
> > > > It also add a new hypercall (can somebody reserve a number for this 
> > > > stuff?).
> > > 
> > > You can simply patch xen/include/public/xen.h to declare the new
> > > __HYPERVISOR_foo_op. (which I now see you have done in this patch!). If
> > > you just want to reserve the number it is also allowed to send just that
> > > hunk to reserve a number pending the implementation.
> > > 
> > > BTW I'd suggest leaving the stub implementation out of the patch until
> > > you've decided what it will look like, so it returns ENOSYS instead of
> > > EINVAL (or change your stub to return ENOSYS).
> > > 
> > 
> > Easy to change. Actually I discovered that my patch does not even
> > compile if you disable TEST_COVERAGE (and it should be disabled by
> > default too). EINVAL say that the hypercall is present but the value
> > passed in invalid.
> > 
> > The reason why adding a new hypercall instead of a new sysctl is simply
> > because is easier to have a zero cost if you disable coverage
> > informations. The best thing would be redirect do_coverage_op to
> > do_ni_hypercall using linker options but even two small stub would do
> > (these stubs will return ENOSYS instead).
> 
> I am not sure I follow. Is the sysctl hypercall code path "longer" than
> the hypercall path you are introducing? What is the zero cost?

Require more changes to code already present and more compiled in code.
Yes, perhaps I'm too paranoid, I'm talking about a bunch of bytes never
executed.

Frediano

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel