On Wed, Nov 01, 2017 at 08:54:44PM +0800, gengdongjiu wrote:
> On 2017/11/1 19:24, Robin Murphy wrote:
> >> + esb
> >> +alternative_else_nop_endif
> >> +1:
> >> + .endm
> > Having a branch in here is pretty horrible, and furthermore using label
> > number 1 has a pretty high chance of subtly breaking code where this
> > macro is inserted.
> >
> > Can we not somehow nest or combine the alternative conditions here?
>
> I found it will report error if combine the alternative conditions here.
>
> For example:
>
> + .macro error_synchronize
> +alternative_if ARM64_HAS_IESB
> +alternative_if ARM64_HAS_RAS_EXTN
> + esb
> +alternative_else_nop_endif
> +alternative_else_nop_endif
> + .endm
>
> And even using b.eq/cbz instruction in the alternative instruction in
> arch/arm64/kernel/entry.S,
> it will report Error.
Alternatives cannot be nested. You need to define a cap like:
ARM64_HAS_RAS_NOT_IESB
... which is set when ARM64_HAS_RAS_EXTN && !ARM64_HAS_IESB.
Then you can do:
alternative_if ARM64_HAS_RAS_NOT_IESB
esb
alternative_else_nop_endif
See ARM64_ALT_PAN_NOT_UAO for an example.
That said, as Robin points out we may not even need the alternative.
Thanks,
Mark.
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