Date: Wed, 25 Mar 2009 15:00:35 +0100
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
To: Tejun Heo <tj@kernel.org>
Cc: mingo@elte.hu, rusty@rustcorp.com.au, tglx@linutronix.de, x86@kernel.org,
       linux-kernel@vger.kernel.org, hpa@zytor.com,
       Paul Mundt <lethal@linux-sh.org>, rmk@arm.linux.org.uk,
       starvik@axis.com, ralf@linux-mips.org, davem@davemloft.net,
       cooloney@kernel.org, kyle@mcmartin.ca, matthew@wil.cx,
       grundler@parisc-linux.org, takata@linux-m32r.org,
       benh@kernel.crashing.org, rth@twiddle.net, ink@jurassic.park.msu.ru,
       heiko.carstens@de.ibm.com
Subject: Re: [GIT RFC] percpu: use dynamic percpu allocator as the default
 percpu allocator
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On Wed, 25 Mar 2009 20:51:31 +0900
Tejun Heo <tj@kernel.org> wrote:

> > With your patches and a RELOC_HIDE version that uses the GOTENT
> > indirection the kernel won't compile because the "X" constraint for
> > the GOTENT access needs a symbol and there are quite a few users that
> > pass a pointer. I do not see a simple solution for that problem yet.
> 
> Ah... okay.  Now I get it.  It wasn't expecting variables there.  How
> about doing the following?
> 
>  #define SHIFT_PERCPU_PTR(ptr, offset) (({				\
> 	 if (__builtin_constant_p(ptr))					\
> 		 do GOTENT trick;					\
> 	 else								\
> 		 RELOC_HIDE();						\
>  }))

That doesn't work because __builtin_constant_p is false for variable
symbols. I would need a __builtin_symbol_p but that doesn't exist.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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