linux-kernel - Re: [PATCH 4/8] unify paravirt parts of system.h

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Date:	Tue, 4 Dec 2007 20:34:32 +0100
From:	Andi Kleen <ak@...e.de>
To:	Avi Kivity <avi@...ranet.com>
Cc:	Glauber de Oliveira Costa <gcosta@...hat.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	glommer@...il.com, tglx@...utronix.de, mingo@...e.hu,
	ehabkost@...hat.com, jeremy@...p.org, anthony@...emonkey.ws,
	virtualization@...ts.linux-foundation.org, rusty@...tcorp.com.au,
	ak@...e.de, chrisw@...s-sol.org, rostedt@...dmis.org, hpa@...or.com
Subject: Re: [PATCH 4/8] unify paravirt parts of system.h

On Tue, Dec 04, 2007 at 09:18:33PM +0200, Avi Kivity wrote:
> Glauber de Oliveira Costa wrote:
>> This patch moves the i386 control registers manipulation functions,
>> wbinvd, and clts functions to system.h. They are essentially the same
>> as in x86_64, except for the cr8 register, which we add.
>>
>> +
>> +static inline unsigned long native_read_cr8(void)
>> +{
>> +	unsigned long cr8;
>> +	asm volatile("mov %%cr8,%0" : "=r" (cr8), "=m" (__force_order));
>> +	return cr8;
>> +}
>> +
>>   
>
> There is no cr8 register on i386.  This had better be protected by an 
> #ifdef.
>
> (you're likely not getting an error since it's a static inline, so the asm 
> is never emitted)

Linux never uses that register. The only user is suspend save/restore, 
but that' bogus because it wasn't ever initialized by Linux in the first
place. It could be probably all safely removed.

-Andi

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