Re: [Xen-devel] [PATCH 8/9] x86/hypercall: Merge the hypercall arg tables

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.08.16 at 17:15, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 03/08/16 16:12, Jan Beulich wrote:
>>>>> On 18.07.16 at 11:51, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> For the same reason as c/s 33a231e3f "x86/HVM: fold hypercall tables" and
>>> (TODO - changeset) "x86/pv: Merge the pv hypercall tables", this removes the
>>> risk of accidentally updating only one of the tables.
>> Based on this argument perhaps hypercall and args tables should
>> get folded too, but I guess that's a work item for another day.
> 
> That is rather harder to do.  I thought about it, but couldn't find a
> neat way of doing it.
> 
> The call table is an array of pointers, while the args table is an array
> of bytes.  Merging them would result in excessive padding for alignment
> purposes, unless it was packed, at which point we are calling
> non-aligned function pointers, and taking that associated performance hit.

If we folded everything together (pv, hvm, args), there would be
6 bytes padding per 34 or actual data, so I wouldn't be worried
too much. But I admit that merging hvm and pv tables wouldn't be
entirely trivial.

Jan


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