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

[Hollis Blanchard <hollisb@xxxxxxxxxx>]

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.

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?

-- 
Hollis Blanchard
IBM Linux Technology Center

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