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Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code
From: David Miller <davem@davemloft.net>
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From: Scott Wood <scottwood@freescale.com>
Date: Tue, 20 May 2008 17:43:58 -0500

> David Miller wrote:
> > The __volatile__ in the asm construct disallows movement of the
> > inline asm relative to statements surrounding it.
> > 
> > The only reason barrier() in kernel.h needs a memory clobber is
> > because of a bug in ancient versions of gcc.  In fact, I think
> > that memory clobber might even be removable.
> 
> Current versions of GCC seem quite happy to move non-asm memory accesses 
> around a volatile asm without a memory clobber; see the test Trent posted.

Indeed, and even the GCC manual is clear about this.