Re: [Xen-devel] 32/64-bit hypercall interface - padding

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 3 Oct 2005, at 20:16, Hollis Blanchard wrote:

> > However, since we're not actually changing the size of any types, this
> > change isn't essential to rush through before 3.0, though it might be
> > nice as it should be very low risk.
> I'm working on this patch now.
>
> However, ureg_t alone will not alleviate the padding issues that the 
> dom0_ops
> structures have. Since we're insisting on using types that change size 
> (and
> alignment requirements), only reordering the fields will help there. 
> Poor
> structure layout impacts memory usage and cache footprint, as you 
> mention
> above.
Well, at least this patch will be benign, but on its own it is also 
*totally* pointless. You can't use it to get 64-bit struct arrangement 
on 32-bit builds because it will leave pointers as 32-bit aligned and 
sized fields. We could macro up pointer fields I suppose:
#define XENIF_PTR(type, name) type name
So that macro can be overridden to get 64-bit sized and aligned pointer 
fields?
And ureg_t is a name that's bound to clash with something down the 
road. Maybe xenreg_t, or even just be explicit about what it is and 
call it xenif_ulong_t?
 -- Keir


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