Hi, Dan:
 I am talking about the "real hypercall" like IA32/XEN did for
the para-virtualization. For the EFI/SAL/PAL calls, maybe it is better
to be implemented in guest BIOS.
Eddie
> Re hypercalls. Actually there are hypercalls already in Xen/ia64
> and they do use the break instruction. It's just that the domain
> calls them indirectly so perhaps they are better called "hyperthunks"
> ("Thunk" is a rarely used compiler term which originated in Algol 60
> that means: "code that is used to convert calls to one interface
> into calls to another"):
>
> When a domain is created, fake EFI/SAL/PAL (firmware) calls are
> created 
> that contain the hypercalls. Thus when domain0 invokes an EFI/SAL/PAL
> call, it calls a "stub" routine that invokes a break instruction/fault
> that is recognized in Xen/ia64 as a hypercall, with arguments passed
> in general registers (unlike Xen/x86 which passes hypercall arguments
> in memory).
>
> You may want to step through a domain0 firmware call to see this work.
> If I recall correctly, the code that creates the hyperthunks is
> in arch/ia64/dom_fw.c
>
> While my intent is to use the same mechanism (breaks) for "real"
> hypercalls, 
> I also want to explore the use of fast system calls (recently added
> in Linux/ia64 by David Mosberger) using the epc instruction in certain
> cases.
>
> Dan
>
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