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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 30 Sep 2005, at 01:54, Andrei Petrov wrote:

> > How about writing a script that converts the Xen public headers into a
> > set that, when compiled on 32-bit ppc, match the 64-bit ppc layout?
> > That might be saner than trying to manually finesse our headers around
> > the ppc abi so that building in 32-bit or 64-bit environment both
> > happen to give same binary layout.
> If this type of ABI compatibility is needed, interface data structures 
> should be declared
> platform-independantly, i.e using 'sized' types (yeah, field alignment 
> should be taken care of too).
> That'll guarantee 32/64 bit independance and that's good thing to 
> have. Once defined it can be
> managed in controlled way. There could be penalty involved for using 
> larger data types than neccessary,
> but that can be resolved having 32-bit(or 64-bit, depending whichever 
> is attractive as basic)
> hypercall subset.
When we previously had this, by defining packed structs, there were 
plenty of screams that it wasn't ANSI compliant, and that performance 
sucks on some architectures. At the time there seemed no good reason 
for cross-ABI compatibility (we don't plan to stuff these structs into 
network packets, for example).
 -- Keir


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