Re: [PATCH] xen/arm64: sysreg.h: Fix MISRA C 2012 Rule 20.7 violation

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 28/07/2022 15:17, Jan Beulich wrote:
> On 28.07.2022 15:49, Xenia Ragiadakou wrote:
> > --- a/xen/arch/arm/include/asm/arm64/sysregs.h
> > +++ b/xen/arch/arm/include/asm/arm64/sysregs.h
> > @@ -461,7 +461,7 @@
> >   /* Access to system registers */
> >   
> >   #define WRITE_SYSREG64(v, name) do {                    \
> > -    uint64_t _r = v;                                    \
> > +    uint64_t _r = (v);                                              \
> >       asm volatile("msr "__stringify(name)", %0" : : "r" (_r));       \
> Out of curiosity - why is the intermediate variable necessary?
> Can't v be used directly in the asm(), possibly with a suitable
> modifier added to %0 such that it'll always be x<N> (and not
> w<N>) which is used as the operand to "msr"?
It should be possible to use %x0. However, We may need to use (uint64_t)(v).

Linux seems to be use it, but IIRC they are not supported GCC versions 
as old as ours. So we would want to check when %x0 was introduced.
Cheers,

--
Julien Grall