Re: [Xen-devel] [PATCH 1/9] x86/hypercall: Move some of the hvm hypercall infrastructure into hypercall.h

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.08.16 at 16:04, <julien.grall@xxxxxxx> wrote:
> On 02/08/16 14:28, Jan Beulich wrote:
>>>>> On 02.08.16 at 15:14, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 02/08/16 13:50, Jan Beulich wrote:
>>>>>>> On 18.07.16 at 11:51, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>>> --- a/xen/include/asm-x86/hypercall.h
>>>>> +++ b/xen/include/asm-x86/hypercall.h
>>>>> @@ -5,9 +5,21 @@
>>>>>  #ifndef __ASM_X86_HYPERCALL_H__
>>>>>  #define __ASM_X86_HYPERCALL_H__
>>>>>
>>>>> +#include <xen/types.h>
>>>>>  #include <public/physdev.h>
>>>>> +#include <public/event_channel.h>
>>>> Why?
>>>
>>> You snipped the commit message, which justifies why.  This header file
>>> cannot currently be included in isolation, and I need it to be.
>>
>> Ah, that sentence there also relates to this addition.
>>
>>>>>  #include <public/arch-x86/xen-mca.h> /* for do_mca */
>>>>> -#include <xen/types.h>
>>>>> +
>>>>> +typedef unsigned long hypercall_fn_t(
>>>>> +    unsigned long, unsigned long, unsigned long,
>>>>> +    unsigned long, unsigned long, unsigned long);
>>>> Wouldn't this better go into xen/hypercall.h?
>>>
>>> It is architecture specific.
>>>
>>> ARM's version is
>>>
>>> typedef register_t (*arm_hypercall_fn_t)(
>>>     register_t, register_t, register_t, register_t, register_t);
>>
>> Which is bogus - they're lucky we so far don't have any 6-argument
>> hypercalls. Or the other way around - we could limit hypercalls to
>> just five arguments (for now) on x86 too, allowing things to get
>> unified. Anyway - that probably goes too far right now, so feel free
>> to add my ack to the patch.
> 
> I am not sure why you think we are lucky on ARM. The hypercall has been 
> defined on ARM to support up to 5 arguments (public/arch-arm.h):
> 
> "A hypercall can take up to 5 arguments. These are passed in
> registers, the first argument in x0/r0 (for arm64/arm32 guests
> respectively irrespective of whether the underlying hypervisor is
> 32- or 64-bit), the second argument in x1/r1, the third in x2/r2,
> the forth in x3/r3 and the fifth in x4/r4."
> 
> So the prototype matches the ABI.

Well, I find it quite odd for hypercall argument counts to differ
between arches. I.e. I'd conclude the ABI was mis-specified.

Jan


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