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

Hollis Blanchard wrote:
> On Monday 03 October 2005 14:11, Nakajima, Jun wrote:
>> In terms of ABI/API, since Xen needs to disiguish 32-bit or 64-bit
>> guests anyway at runtime, I don't think we don't need to change the
>> size of any types at this point (i.e. before 3.0).
> You would instead propose a compatibility layer in Xen? So when a
> hypercall from a 32-bit guest arrives at a 64-bit hypervisor, Xen
> code converts the 32-bit structure into a 64-bit one and passes that
> pointer on to the rest of Xen? And then for return values you'd
> convert the other way. Hmm, and of course you wouldn't be able to
> pass 64-bit addresses back, such as via dom0_tbufcontrol_t.

I don't think dom0_tbufcontrol_t is a good example (as dicussed). Do you
have other examples?

> As mentioned previously, this is the approach Linux uses
> (linux/fs/compat_ioctl.c), and it seems less than ideal to me. Since
> we have the ability to fix it now (i.e. make the 32-bit and 64-bit
> ABI identical), shouldn't we do that rather than this copying/munging
> layer? 

The 32-bit and 64-bit hypercall ABI cannot be identical on x86 because
of the generic ABI difference between 32-bit and 64-bit. 

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