Re: [Qemu-devel] [for-2.6 PATCH 1/3] target-i386: Define structs for layout of xsave area

From: Paolo Bonzini <pbonzini@redhat.com>
To: Richard Henderson <rth@twiddle.net>,
	Eduardo Habkost <ehabkost@redhat.com>
Cc: qemu-devel@nongnu.org, Huaitong Han <huaitong.han@intel.com>,
	kvm@vger.kernel.org
Subject: Re: [Qemu-devel] [for-2.6 PATCH 1/3] target-i386: Define structs for layout of xsave area
Date: Tue, 1 Dec 2015 18:27:17 +0100	[thread overview]
Message-ID: <565DD875.7090108@redhat.com> (raw)
In-Reply-To: <565DD6E9.1040906@twiddle.net>

On 01/12/2015 18:20, Richard Henderson wrote:
>>
>> 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/

Right, but that's a helper anyway.

>> 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.

Yes, you can use byte moves with XMM_B (more obvious), or stq_le_p with
XMM_Q (faster I guess---though the compiler might optimize the former on
little-endian hosts).  Either works with an uint8_t[] destination.

Paolo