From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Mon, 14 Sep 2009 00:01:03 +0100
Subject: 'bx lr' vs 'mov pc,lr'
In-Reply-To: <94a0d4530909131556j49824b84ubddc13237f2d0bdd@mail.gmail.com>
References: <94a0d4530909131455x7a33cbaaw402642fb2e63c6d6@mail.gmail.com>
	<20090913221500.GB5398@digital-scurf.org>
	<94a0d4530909131556j49824b84ubddc13237f2d0bdd@mail.gmail.com>
Message-ID: <20090913230103.GD30169@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Mon, Sep 14, 2009 at 01:56:16AM +0300, Felipe Contreras wrote:
> On Mon, Sep 14, 2009 at 1:15 AM, Daniel Silverstone
> <dsilvers@simtec.co.uk> wrote:
> > On Mon, Sep 14, 2009 at 12:55:24AM +0300, Felipe Contreras wrote:
> >> I noticed that in 'arch/arm/lib/delay.S' we are using 'mov pc, lr'
> >> instead of 'bx lr'. Why? It looks like 'mov pc, lr' is used all over
> >> the place, but I can't find out what's the reason.
> >
> > I'd guess at the reason being that not all ARM processors whose ports use
> > arch/arm/lib/delay.S support the bx instruction, whereas the 'mov pc, lr'
> > instruction is universally supported.
> 
> Are there really processors that don't support 'bx'? Can you give some examples?

Any ARMv3 CPU and any ARMv4 which doesn't support Thumb.  Eg, StrongARM.