Re: [Xen-devel] [PATCHv9 0/9] Xen: extend kexec hypercall for use with pv-ops kernels

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Mon, Oct 14, 2013 at 03:14:13PM +0100, David Vrabel wrote:
> On 14/10/13 14:53, Daniel Kiper wrote:
> > On Fri, Oct 11, 2013 at 03:06:09PM +0100, David Vrabel wrote:
> >> On 11/10/13 12:15, Daniel Kiper wrote:
> >>>
> >>>> + * - Register values are undefined.
> >>>
> >>> If Linux and kexec guys state that they do not care then I do not care 
> >>> too.
> >>> Let's wait what will happen in "kexec: Clearing registers just before
> >>> jumping into purgatory" thread.
> >>
> >> How about we get the current series in as-is (plus the extra docs) and
> >> then, since you feel so strongly about this minor point, you post a
> >> follow patch to change the behaviour?
> >>
> >> Does that work for you?  If so and if you're happy with everything else,
> >> can I get your Reviewed-by on the whole series?
> >
> > What do you think about last Eric comments? Should we continue our 
> > discussion?
> > If yes I could do final tests of latest series now and put my Tested-by and
> > Reviewed-by as needed. Later we could establish details and put follow up 
> > patches
> > (one for zeroing registers and one fixing/aliging calling convention for
> > relocate_pages). It will be nice if we finish this stuff by the of this 
> > week.
>
> I think there are two[*] sensible options:
>
> A. Registers are specified as undefined, register values are not
> initialized.
>
> B. Registers are specified as zeroed (%rsp, %rax excepted), register
> values are initialized to zero.
>
> If A is merged, then Xen can move to B later.  If B is merged, Xen
> cannot go back to A.  Therefore, I think we should merge A and discuss
> moving to B (or perhaps even C) as a separate item.

OK.

> (FYI, I've already fixed up relocate_pages() to go into v10 since I need
> to post v10 with the extra docs anyway.)

Thanks.

> David
>
> [*] There is a third way:
>
> C. Registers are specified as undefined, but register values are
> initialized to zero.
>
> But I don't think the specification should diverge from the implementation.

I agree but I think that we could solve that problem by adding comment
which precisely explains what is going on and what callee should expect
(uninitialized registers). Eric comment is nice and could be used by us
as a starting point. Additionally, I think that similar comment should
be added to Linux Kernel source and purgatory entry (I could do that).

Daniel

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