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 16:26, <julien.grall@xxxxxxx> wrote:

> 
> On 02/08/16 15:17, Jan Beulich wrote:
>>>>> 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:
>>>>>>>  #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.

arch-x86/xen-x86_32.h has

 * Hypercall interface:
 *  Input:  %ebx, %ecx, %edx, %esi, %edi, %ebp (arguments 1-6)
 *  Output: %eax

while arch-x86/xen-x86_64.h has

 * Hypercall interface:
 *  Input:  %rdi, %rsi, %rdx, %r10, %r8, %r9 (arguments 1-6)
 *  Output: %rax

Jan


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