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

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Date:	Tue, 4 Dec 2007 14:14:13 -0800
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	"Glauber de Oliveira Costa" <glommer@...il.com>
Cc:	"Avi Kivity" <avi@...ranet.com>,
	"Glauber de Oliveira Costa" <gcosta@...hat.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	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 Tuesday 04 December 2007 11:41, Glauber de Oliveira Costa wrote:
> On Dec 4, 2007 5:18 PM, Avi Kivity <avi@...ranet.com> wrote:
> > There is no cr8 register on i386.  This had better be protected by an
> > #ifdef.
>
> Sure. I mentioned it in the changelog. I, however, am not sure If I
> agree it should be enclosed
> in ifdefs. Me and Jeremy discussed it a while ago, and we seem to
> agree that for those functions
> that are exclusive of one architecture, there were no need for ifdefs.
> Any usage by the other arch
> is a bug.
>
> But I admit that I'm not particularly biased here, and I can change
> it, if there's agreement that
> an ifdef here is the way to go.
>
> > (you're likely not getting an error since it's a static inline, so the
> > asm is never emitted)
>
> Which also means it does not affect the binary in anyway. No bigger
> code, no nothing.

If future changes will mistakenly make 32-bit x86 call native_read_cr8(),
you will get no warning. (Hmmm. Maybe as will complain, I'm not sure).
If it explicitly ifdefed out for 32 bits, it's easier to detect misuse.
--
vda
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