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

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Date:	Sun, 19 Aug 2012 18:12:57 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	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 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,
profiles will show a function named kvm_vmx_return taking a few percent
cpu, although there is no such function.

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

I'm not trying to force two functions to be in the same assembler file.

> 
>> 
>> 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.

-- 
error compiling committee.c: too many arguments to function
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