Re: [PATCH v2 1/2] xen/arm: smccc: add support for SMCCCv1.2 extended input/output registers

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 11/06/2022 01:41, Stefano Stabellini wrote:
> On Thu, 9 Jun 2022, Jens Wiklander wrote:
> > +    /* Store the registers x0 - x17 into the result structure */
> > +    stp        x0, x1, [x19, #0]
> > +    stp        x2, x3, [x19, #16]
> > +    stp        x4, x5, [x19, #32]
> > +    stp        x6, x7, [x19, #48]
> > +    stp        x8, x9, [x19, #64]
> > +    stp        x10, x11, [x19, #80]
> > +    stp        x12, x13, [x19, #96]
> > +    stp        x14, x15, [x19, #112]
> > +    stp        x16, x17, [x19, #128]
> I noticed that in the original commit the offsets are declared as
> ARM_SMCCC_1_2_REGS_X0_OFFS, etc. In Xen we could add them to
> xen/arch/arm/arm64/asm-offsets.c given that they are only used in asm.
>
> That said, there isn't a huge value in declaring them given that they
> are always read and written in order and there is nothing else in the
> struct, so I am fine either way.
While we don't support big-endian in Xen (yet?), the offsets will be 
inverted.
Furthermore, I prefer to avoid open-coded value (in particular when they 
are related to offset). They are unlikely going to change, but at least 
we have the compiler that will compute them for us (so less chance for a 
problem).
Cheers,

--
Julien Grall