On Wed, 2014-01-29 at 18:28 +0000, Leif Lindholm wrote:
> On Wed, Jan 22, 2014 at 11:20:55AM +0000, Will Deacon wrote:
> > > +#ifdef CONFIG_CPU_CP15
> > > +/* Macro for setting/clearing bits in sctlr */
> > > + .macro update_sctlr, set:req, clear:req, tmp:req, tmp2:req
> > > + mrc p15, 0, \tmp, c1, c0, 0
> > > + ldr \tmp2, =\set
> > > + orr \tmp, \tmp, \tmp2
> > > + ldr \tmp2, =\clear
> > > + mvn \tmp2, \tmp2
> > > + and \tmp, \tmp, \tmp2
> > > + mcr p15, 0, \tmp, c1, c0, 0
> >
> > I think this would be cleaner if you force the caller to put set and clear
> > into registers beforehand, rather than have to do the literal load every
> > time. Also, I don't think set and clear should be required (and then you can
> > lose tmp2 as well).
>
> I can't figure out how to make register-parameters non-required
> (i.e. conditionalise on whether an optional parameter was provided),
> so my attempt of refactoring actually ends up using an additional
> register:
>
Register parameters are just strings, so how about this:
.macro foo bar=, baz=
.ifnc \bar,
mov \bar,#0
.endif
.ifnc \baz,
mov \baz,#1
.endif
.endm
foo x0
foo
foo x1, x2
foo ,x3
Results in:
0000000000000000 <.text>:
0: d2800000 mov x0, #0x0 // #0
4: d2800001 mov x1, #0x0 // #0
8: d2800022 mov x2, #0x1 // #1
c: d2800023 mov x3, #0x1 // #1
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