linux-kernel - Re: [PATCH 37/74] lto, KVM: Don't assume asm statements end up in the same assembler file

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Message-ID: <20120819152058.GU11413@one.firstfloor.org>
Date:	Sun, 19 Aug 2012 17:20:58 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org, mmarek@...e.cz, linux-kbuild@...r.kernel.org,
	JBeulich@...e.com, akpm@...ux-foundation.org,
	Andi Kleen <ak@...ux.intel.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH 37/74] lto, KVM: Don't assume asm statements end up in the same assembler file

On Sun, Aug 19, 2012 at 06:12:57PM +0300, Avi Kivity wrote:
> On 08/19/2012 06:09 PM, Andi Kleen wrote:
> >> The reason we use a local label is so that we the function isn't split
> >> into two from the profiler's point of view.  See cd2276a795b013d1.
> > 
> > Hmm that commit message is not very enlightening.
> > 
> > The goal was to force a compiler error?
> 
> No, the goal was to avoid a global label in the middle of a function.
> The profiler interprets it as a new function.  After your patch,

Ah got it now. I always used to have the same problem with sys_call_return.`

I wonder if there shouldn't be a way to tell perf to ignore a symbol.

> >> 
> >> One way to fix this is to have a .data variable initialized to point to
> >> .Lkvm_vmx_return (this can be done from the same asm statement in
> >> vmx_vcpu_run), and reference that variable in
> >> vmx_set_constant_host_state().  If no one comes up with a better idea,
> >> I'll write a patch doing this.
> > 
> > I'm not clear how that is better than my patch.
> 
> My patch will not generate the artifact with kvm_vmx_return.

Ok fine for me. I'll keep this patch for now, until you have
something better.

-Andi


-- 
ak@...ux.intel.com -- Speaking for myself only.
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