linux-kernel - Re: [patch 8/9] F00F bug fixup for i386

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Message-ID: <20070531213827.GD904@Krystal>
Date:	Thu, 31 May 2007 17:38:27 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch 8/9] F00F bug fixup for i386 - use conditional calls

* Andrew Morton (akpm@...ux-foundation.org) wrote:
> On Thu, 31 May 2007 17:07:55 -0400
> Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > * Andrew Morton (akpm@...ux-foundation.org) wrote:
> >  
> > > > Use the faster conditional calls for F00F bug handling in do_page_fault.
> > > > 
> > > 
> > > I guess this means that CONDCALL will be enabled on pretty much all i386,
> > > in which case making the whole feature Kconfigurable is starting to look
> > > marginal.
> > > 
> > > Perhaps a better approach would have to made this change dependent upon
> > > CONDCALL, rather than forcing it on.
> > > 
> > 
> > Do you mean making X86_F00F_BUG depend on COND_CALL instead of selecting
> > it ?
> 
> yup
> 
> > > > +	if (cond_call(fix_f00f, do_f00f_workaround(regs, address)))
> > > > +		return;
> > > 
> > > We do a cond_call() to an inlined function?  That's a bit weird, isn't it?
> > > 
> > 
> > Yes, but it works :) I will add this information to the documentation.
> 
> But why does it work?  Did the compiler generate an out-of-line copy
> of the function?  If so, we'll end up with multiple copies of the function if
> there are other callers.  If not, the `inline' was pointless.

Yes, it's doing an out-of-line copy. Just like the compiler would have
done if we place a call to an inline function within a if() { } block.

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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