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

[Hollis Blanchard <hollisb@xxxxxxxxxx>]

On Sep 30, 2005, at 10:45 AM, Keir Fraser wrote:
> 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).
Yes, I'm not trying to be sneaky about this: this is a problem for 
ppc64. It could also be a problem for x86-64, except that x86-32 is so 
limited compared to x86-64 that apparently nobody wants to do this.
I think the Linux kernel folks learned the "unsigned long" lesson too 
late, and now there is quite a lot of fixup code to convert 32-bit 
userspace structs to 64-bit kernel structs (have a look at 
linux/fs/compat_ioctl.c and compat.c). It seems a shame to repeat the 
same mistakes in Xen...
--
Hollis Blanchard
IBM Linux Technology Center


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