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

[Julien Grall <julien.grall@arm.com>]

On 02/08/16 15:17, Jan Beulich wrote:
>>>> On 02.08.16 at 16:04, <julien.grall@arm.com> wrote:
>> On 02/08/16 14:28, Jan Beulich wrote:
>>>>>> On 02.08.16 at 15:14, <andrew.cooper3@citrix.com> wrote:
>>>> On 02/08/16 13:50, Jan Beulich wrote:
>>>>>>>> On 18.07.16 at 11:51, <andrew.cooper3@citrix.com> 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.

Is it documented somewhere for the x86 code? Looking at Linux, the 
privcmd call is only passing 5 arguments on both ARM and x86.

Regards,

-- 
Julien Grall

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