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

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Message-id: <alpine.LFD.2.03.1302200835380.6419@syhkavp.arg>
Date:	Wed, 20 Feb 2013 08:36:25 -0500 (EST)
From:	Nicolas Pitre <nico@...xnic.net>
To:	"Woodhouse, David" <david.woodhouse@...el.com>
Cc:	Kim Phillips <kim.phillips@...escale.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	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 Wed, 20 Feb 2013, Woodhouse, David wrote:

> On Tue, 2013-02-19 at 22:17 -0500, Nicolas Pitre wrote:
> > 
> > > +$(obj)/bswapsdi2.o: $(obj)/../../../../arch/$(SRCARCH)/lib/bswapsdi2.o
> > > +     $(call cmd,shipped)
> > > +
> > 
> > I don't think you can get away with this.  The decompressor code is 
> > compiled with -fpic and the main kernel is not.  Most toolchains do mark 
> > object files with some flags to prevent the link of incompatible objects 
> > together (normally pic and non pic objects are not compatible even if in 
> > this very simple case that would not matter).  Maybe you are able to 
> > link zImage successfully simply because no references to __bswap* needed 
> > to be resolved and therefore the linker didn't need to search/include 
> > that object?
> 
> This, and the issue with -Os vs. -O2, make me inclined to suggest that
> we should just provide an asm version of these functions instead of
> using the compiler.

You'll have the same issue wrt the above whether or not the source file 
is C or assembly.


Nicolas
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