Re: [PATCH 03/18] arm64: kvm: stop treating register x18 as caller save

[Sami Tolvanen]

On Tue, Oct 22, 2019 at 10:22 AM Marc Zyngier <maz@xxxxxxxxxx> wrote:
> >  .macro save_callee_saved_regs ctxt
> > +     str     x18,      [\ctxt, #CPU_XREG_OFFSET(18)]
> >       stp     x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)]
> >       stp     x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)]
> >       stp     x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)]
> > @@ -38,6 +39,7 @@
> >       ldp     x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)]
> >       ldp     x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)]
> >       ldp     x29, lr,  [\ctxt, #CPU_XREG_OFFSET(29)]
> > +     ldr     x18,      [\ctxt, #CPU_XREG_OFFSET(18)]
>
> There is now an assumption that ctxt is x18 (otherwise why would it be
> out of order?). Please add a comment to that effect.

> > -     // Restore guest regs x19-x29, lr
> > +     // Restore guest regs x18-x29, lr
> >       restore_callee_saved_regs x18
>
> Or you could elect another register such as x29 as the base, and keep
> the above in a reasonable order.

I'm fine with either option. Ard, any thoughts?

Sami