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

[Julien Grall <julien@xen.org>]

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