Re: [Xen-devel] [PATCH 18/18] x86: add multiboot2 protocol support for EFI platforms

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Fri, Mar 27, 2015 at 03:06:43PM +0000, Jan Beulich wrote:
> >>> On 27.03.15 at 15:57, <daniel.kiper@xxxxxxxxxx> wrote:
> > On Fri, Mar 27, 2015 at 02:34:19PM +0000, Jan Beulich wrote:
> >> >>> On 27.03.15 at 15:26, <daniel.kiper@xxxxxxxxxx> wrote:
> >> > On Fri, Mar 27, 2015 at 01:36:32PM +0000, Jan Beulich wrote:
> >> >> >>> On 27.03.15 at 14:06, <daniel.kiper@xxxxxxxxxx> wrote:
> >> >> > On Tue, Mar 17, 2015 at 10:32:01AM +0000, Jan Beulich wrote:
> >> >> >> >>> On 30.01.15 at 18:54, <daniel.kiper@xxxxxxxxxx> wrote:
> >> >> >> > +        /* Skip Multiboot2 information fixed part */
> >> >> >> > +        lea     MB2_fixed_sizeof(%ebx),%ecx
> >> >> >>
> >> >> >> Let's please not add more assumptions than necessary about stuff
> >> >> >> being below 4G.
> >> >> >
> >> >> > I am not sure what do you mean by that.
> >> >>
> >> >> See the 32-bit register used for addressing here (and in many more
> >> >> places)?
> >> >
> >> > This is what I expected but I was confused because you were referring 
> >> > only
> >> > here to this problem. Anyway, is it possible to do this in different way?
> >> > Should we care if image is always loaded at 0x100000 right now? Even with
> >> > Xen early boot code being relocatable loader could not load image higher
> >> > than 0xffffffff - 14 MiB.
> >>
> >> I don't understand what you're alluding to. Just use 64-bit registers
> >> for memory accesses and LEAs, and be done. This will result in smaller
> >> code as a benefit.
> >
> > Well... How can I do that here if processor is in 32-bit mode? Maybe,
> > we could that things after switching to 64-bit mode. However, I think
> > this requires separate patch to do these changes.
>
> No, if the processor is in 32-bit mode, then using 32-bit registers is
> fine of course. But I'm pretty certain I spotted at least some cases
> where it looked like you used 32-bit registers in 64-bit mode.

OK, I will double check. If I find something then I will fix it.

Daniel

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