From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Igor Kozhukhov <ikozhukhov@gmail.com>
Cc: xen-devel@lists.xen.org
Subject: Re: ctfconvert problems with build on illumos based platform
Date: Tue, 14 Jan 2014 20:58:11 +0000 [thread overview]
Message-ID: <52D5A4E3.1080405@citrix.com> (raw)
In-Reply-To: <EE36B3F3-39A2-484E-8869-AF51C72DFBD9@gmail.com>
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On 14/01/14 20:52, Igor Kozhukhov wrote:
>
> On Jan 15, 2014, at 12:46 AM, Andrew Cooper wrote:
>
>> On 14/01/14 20:38, Igor Kozhukhov wrote:
>>> Hello All,
>>>
>>> I have problems with ctfconvert with build sources of xen-4.2 on
>>> illumos based platform:
>>> https://www.illumos.org/issues/3205
>>>
>>> could you please let me know - what the reason to have a variable in
>>> structure 'struct hvm_hw_cpu_xsave' with zero size:
>>> struct { char x[0]; } ymm; /* YMM */
>>> --
>>> Best regards,
>>> Igor Kozhukhov
>>>
>>>
>>
>> The structure is variable length depending on whether the VM has
>> enabled AVX support.
>>
>> It is rather unfortunate that we have non-complient C used to specify
>> the ABI.
>
> can we use here ?
> struct { char x[1]; } ymm;
>
> it will fix my problem.
>
> -Igor
>
No, it wont.
The 'ymm' is either not present and has a size of 0 as far as save_area
is concerned, or is present, and has a size of 16 * 256bit registers.
The content of this structure is only relevant as far as
hvm_{save,load}_cpu_xsave_states() goes, which resorts to some
pointer-trickary to move the data. Changing that char x[0] to char x[1]
will break the pointer trickary, and migration will suffer an ABI breakage.
~Andrew
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next prev parent reply other threads:[~2014-01-14 20:58 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-14 20:38 ctfconvert problems with build on illumos based platform Igor Kozhukhov
2014-01-14 20:46 ` Andrew Cooper
2014-01-14 20:52 ` Igor Kozhukhov
2014-01-14 20:58 ` Andrew Cooper [this message]
2014-01-15 9:44 ` Ian Campbell
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