linux-kernel - Re: [RFC] arm: use built-in byte swap function

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Message-ID: <20130201011712.GF23505@n2100.arm.linux.org.uk>
Date:	Fri, 1 Feb 2013 01:17:12 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Kim Phillips <kim.phillips@...escale.com>
Cc:	"Woodhouse, David" <david.woodhouse@...el.com>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Santos <daniel.santos@...ox.com>,
	David Rientjes <rientjes@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robherring2@...il.com>
Subject: Re: [RFC] arm: use built-in byte swap function

On Thu, Jan 31, 2013 at 02:59:47PM -0600, Kim Phillips wrote:
> On Thu, 31 Jan 2013 09:28:01 +0000
> Russell King - ARM Linux <linux@....linux.org.uk> wrote:
> 
> > On Wed, Jan 30, 2013 at 08:09:00PM -0600, Kim Phillips wrote:
> > > v2:
> > > - at91 and lpd270 builds fixed by limiting to ARMv6 and above
> > >   (i.e., ARM cores that have support for the 'rev' instruction).
> > >   Otherwise, the compiler emits calls to libgcc's __bswapsi2 on
> > >   these ARMv4/v5 builds (and arch ARM doesn't link with libgcc).
> > 
> > Which compiler version?  gcc 4.5.4 doesn't do this, except for the 16-bit
> > swap, so I doubt that any later compiler does.
> 
> I've tried both gcc 4.6.3 [1] and 4.6.4 [2].  If you can point me to
> a 4.5.x, I'll try that, too, but as it stands now, if one moves the
> code added to swab.h below outside of its armv6 protection,
> gcc adds calls to __bswapsi2.

Take a look at the message I sent on the 29th towards the beginning of
this thread for details of gcc 4.5.4 behaviour.
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