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: <20120819150951.GR11413@one.firstfloor.org>
Date:	Sun, 19 Aug 2012 17:09:52 +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

> 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?

With LTO there is no way to force two functions be in the same assembler
file. The partitioner is always allowed to split.

> 
> 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.

-andi

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