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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 30 Sep 2005, at 16:39, Hollis Blanchard wrote:

> And yes, pointers will need to be "fixed" into u64s.
>
> As for performance, it does take an extra memory reference on x86 when 
> assigning from a 32-bit value into a 64-bit field, but I would expect 
> that cost to be insignificant compared to the cost of a hypercall. 
> Maybe doing 64-bit math on x86 would be significantly slower, but 
> that's not what we're talking about...
Cross-architecture 'compatibility' (same binary layout) is not 
currently an aim for the Xen-public interfaces, and I don't expect it 
to become so. If we went down that road we'd have to stipulate things 
like endianess, which I think we can all agree is not the way to go.
I certainly don't want to wholesale restructure our interfaces just to 
fortuitously make things match up for 32- and 64-bit ppc (which is what 
you are actually arguing for, in the guise of more general 
cross-architecture compatibility).
 -- Keir


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