Re: [Minios-devel] [UNIKRAFT PATCHv4 15/43] uk/arch: Add necessary header files for Arm64

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

On 16.07.2018 04:41, Wei Chen wrote:
> Hi Simon,
>
> > -----Original Message-----
> > From: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
> > Sent: 2018年7月13日 18:32
> > To: Julien Grall <Julien.Grall@xxxxxxx>; Wei Chen <Wei.Chen@xxxxxxx>; minios-
> > devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: Kaly Xin <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> > Subject: Re: [Minios-devel] [UNIKRAFT PATCHv4 15/43] uk/arch: Add necessary
> > header files for Arm64
> >
> > Hi all,
> >
> > On 13.07.2018 11:36, Julien Grall wrote:
> > > Hi,
> > >
> > > On 13/07/18 10:13, Wei Chen wrote:
> > > > > > +#ifndef __UKARCH_LCPU_H__
> > > > > > +#error Do not include this header directly
> > > > > > +#endif
> > > > > > +
> > > > > > +struct __regs {
> > > > > > +    /* Generic Purpose registers, from x0 ~ x29 */
> > > > > > +    unsigned long x[30];
> > > > > > +
> > > > > > +    /* Link Register (x30) */
> > > > > > +    unsigned long lr;
> > > > > > +
> > > > > > +    /* Exception Link Register */
> > > > > > +    unsigned long elr_el1;
> > > > > > +
> > > > > > +    /* Processor State Register */
> > > > > > +    unsigned long spsr_el1;
> > > > > > +
> > > > > > +    /* Exception Status Register */
> > > > > > +    unsigned long esr_el1;
> > > > > > +
> > > > > > +    /* Stack Pointer */
> > > > > > +    unsigned long sp;
> > > > > > +};
> > > > > > +
> > > > > > +#define isb()   __asm__ __volatile("isb" ::: "memory")
> > > > > What is this intended for?
> > > > This is for instruction memory barrier.
> > > Just to clarify, isb is not a memory barrier ;). It is an instruction
> > > synchronization barrier. Any instructions in program order after the isb
> > > will only be fetched from cache/memory once the instruction has
> > > completed. This is used to ensure the effect of modification such as TLB
> > > invalidation, system registers have been taken into account.
> > >
> > > I am not aware of any equivalent on x86.
> > >
> > > Cheers,
> > Nice, now I learned something more about Arm. ;-) I like the
> > explicitness of the architecture. It is giving you much more control
> > about when and what should happen on the hardware.
> >
> > My question: Is it clear for an Arm developer what "isb()" is or should
> > we add a short comment to this definition?
> Generally speaking it's enough. As you have such concern, I will add
> Some comments for it ; )
Then this is totally fine without a comment. We also did not comment the 
memory barriers. I let it up to you. ;-)
>
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