On Mon, Nov 18, 2013 at 11:23:27AM +0000, David Vrabel wrote: > On 18/11/13 09:29, Jan Beulich wrote: > >>>> On 15.11.13 at 21:07, David Vrabel <david.vrabel at citrix.com> wrote: > >> On 15/11/13 15:56, Daniel Kiper wrote: > >>> Clear unused registers before jumping into an image. This way > >>> loaded image could not assume that any register has an specific > >>> info about earlier running Xen hypervisor. However, it also > >>> does not mean that the image may expect that a given register > >>> is zeroed. The image MUST assume that every register has a random > >>> value or in other words it is uninitialized or has undefined state. > >> > >> I think this, where the specification (registers undefined) differs from > >> the implementation (registers zeroed), is the worst option. > >> > >> I also think it is more likely for an image to inadvertently rely on a > >> zero value that whatever junk Xen has left behind. > > > > Preventing users to rely on anything would likely make it > > desirable to put some random value into all unused registers. > > I don't think we need to go that far. > > I would just like to avoid someone looking that the implementation (and > not the documentation) and concluding that zero-ing of the registers is > part of the specified behaviour, or looking at the implementation and > documentation and wondering why they don't agree. David, my comment clearly states why we are doing that and what should be expected. What is wrong with it? I could improve it but say how? Daniel
