From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v1 2/4] xen-version: Add third parameter
 (len) to the do_version hypercall.
Date: Fri, 9 Oct 2015 13:29:10 +0100
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To: Jan Beulich <JBeulich@suse.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: wei.liu2@citrix.com, ian.campbell@citrix.com, ian.jackson@eu.citrix.com, mpohlack@amazon.de, xen-devel@lists.xenproject.org, dgdegra@tycho.nsa.gov
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On 09/10/15 09:25, Jan Beulich wrote:
>>>> On 09.10.15 at 04:56, <konrad.wilk@oracle.com> 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@citrix.com>
>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> ---
>>  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
>