Re: [PATCH v3 1/4] xen: introduce CONFIG_GENERIC_BUG_FRAME

[Julien Grall <julien@xxxxxxx>]

On 28/02/2023 17:21, Oleksii wrote:
> Hi Julien,
Hi Oleksii,
> > > +
> > > +            for ( i = 0, b = region->frame[id].bugs;
> > > +                  i < region->frame[id].n_bugs; b++, i++ )
> > > +            {
> > > +                if ( bug_loc(b) == pc )
> > > +                {
> > > +                    bug = b;
> > > +                    goto found;
> > > +                }
> > > +            }
> > > +        }
> > > +    }
> > > +
> > > + found:
> > > +    if ( !bug )
> > > +        return -EINVAL;
> > > +
> > > +    if ( id == BUGFRAME_run_fn )
> > > +    {
> > > +#ifdef BUG_FN_REG
> > > +        void (*fn)(const struct cpu_user_regs *) = (void *)regs-
> > > > BUG_FN_REG;
> > AFAIU, this is necessary so Arm can use the generic do_bug_frame().
> >
> > I was under the impression that RISC-V and Arm had the similar issue
> > with %c. It seems like you managed to resolve it on RISC-V, so can we
> > fully switch Arm to the generic implementation of bug?
> I tried to switch ARM to generic implementation.
>
> Here is the patch: [1]
I have replied on the other thread.
> > > +#ifndef BUG_ASM_CONST
> > > +#define BUG_ASM_CONST ""
> > > +#endif
> > This line is a bit misterious to me. Would you be able to outline why
> > an
> > architecture would override this?
> It is needed in case if compiler for an architecture doesn't have
> proper support of '%c' ( it is so for ARM & RISC-V )
Hmmm.... Why can't x86 use the same version? IOW what's the benefits to 
differ on x86?
Anyway, documentation is always good to have because it helps the 
reader/reviewer to understand how such decision was made.
Cheers,

--
Julien Grall