Re: [Xen-devel] [PATCH v1 2/4] xen-version: Add third parameter (len) to the do_version hypercall.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/10/15 09:25, Jan Beulich wrote:
>>>> On 09.10.15 at 04:56, <konrad.wilk@xxxxxxxxxx> wrote:
>> All existing commands ignore the parameter so this does
>> not break the ABI.
> Does it not? What about the debug mode clobbering of hypercall
> argument registers?

That is an implementation detail of the hypervisor.  It is irrelevant to
guests whether Xen chooses to clobber the spare registers or not.

> I think such length indicators need to be part
> of the newly added sub-structures instead.

I disagree. Having this as a hypercall parameter is ABI compatible, and
avoids unnecessary copy_from_guest()

~Andrew

>
>> This paves the way for expanding the XENVER_
>> hypercall with variable size structures, such as
>> "XENVER_build_id: Provide ld-embedded build-ids"
>>
>> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>> ---
>>  xen/arch/arm/traps.c        | 2 +-
> xen/arch/x86/x86_64/entry.S
> xen/arch/x86/x86_64/compat/entry.S
>
> (but that's moot with the comment above)
>
> Jan
>


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