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[Dave P Martin]

On Tue, Apr 21, 2015 at 02:10:42PM +0100, Ard Biesheuvel wrote:
> On 21 April 2015 at 14:50, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
> > On Tue, Apr 21, 2015 at 12:24:20PM +0100, Russell King - ARM Linux wrote:
> >> We should probably create a badr macro to complement the adr pseudo-op
> >> which incorporates the BSYM thing so make this clearer - and a comment
> >> before it.  This is really the case where BSYM should be used.
> >
> > Something like this.  Note that I've also removed the BSYM() usage in
> > the KVM code.
> >
> 
> Yes, that is much better. It is a pity that we still can't use '| 1'
> but the fact that you are forced to use 'adr' now probably mostly
> eliminates the risk regarding that.
> 
> I did notice that are are 4 or 5 instances (commented inline) of an
> ARM to thumb mode switch which can just as easily be implemented as
> 'blx 1f' instead of using this badr macro (whose use we want to
> discourage, I assume, since the address arithmetic is still slightly
> dodgy). Do you think we should do something about that as well?

Err, probably.  That just looks like an oversight -- I think I'm
responsible for at least some of those.

There's no good reason not to replace adr+BSYM+bx.

For switches from ARM, this could be replaced with bx <label> which
should work just fine.  There shouldn't be any instances of this from
Thumb, because switching instruction set is the whole point here.

(Thumb doesn't have bx <label>, but blx <label> is available at the cost
of clobbering lr).

Cheers
---Dave

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