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From: Richard Henderson <rth@twiddle.net>
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Date: Tue, 1 Dec 2015 09:20:41 -0800
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Subject: Re: [Qemu-devel] [for-2.6 PATCH 1/3] target-i386: Define structs
 for layout of xsave area
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, kvm@vger.kernel.org, Huaitong Han <huaitong.han@intel.com>

On 12/01/2015 09:15 AM, Eduardo Habkost wrote:
> On Tue, Dec 01, 2015 at 09:09:47AM -0800, Richard Henderson wrote:
>> On 11/30/2015 03:18 AM, Paolo Bonzini wrote:
>>> Because this is always little endian, I would write it as uint8_t[16][16].
>>
>> Maybe.  That isn't altogether handy for TCG, since we'll be wanting to bswap
>> these buffers (probably in uint64_t chunks).
>
> X86XSaveArea will be used only when loading/saving state using
> xsave, not for executing regular instructions.

... like the regular instruction xsave?

https://patchwork.ozlabs.org/patch/493318/

> In X86CPU, the
> data is already stored as XMMReg unions (the one with the
> XMM_[BWDQ] helpers).

Of course.  But those unions are arranged to be in big-endian format on 
big-endian hosts.  So we need to swap the data back to little-endian format for 
storage into guest memory.


r~