Re: [PATCH v3 16/34] xen/lib: introduce generic find next bit operations

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.01.2024 10:44, Oleksii wrote:
> On Tue, 2024-01-23 at 14:37 +0100, Jan Beulich wrote:
>> On 23.01.2024 13:34, Oleksii wrote:
>>> On Tue, 2024-01-23 at 12:14 +0100, Jan Beulich wrote:
>>>> On 22.12.2023 16:13, Oleksii Kurochko wrote:
>>>>> --- a/xen/common/Kconfig
>>>>> +++ b/xen/common/Kconfig
>>>>> @@ -47,6 +47,9 @@ config ARCH_MAP_DOMAIN_PAGE
>>>>>  config GENERIC_BUG_FRAME
>>>>>   bool
>>>>>  
>>>>> +config GENERIC_FIND_NEXT_BIT
>>>>> + bool
>>>>
>>>> There's no need for this, as ...
>>>>
>>>>> --- a/xen/lib/Makefile
>>>>> +++ b/xen/lib/Makefile
>>>>> @@ -3,6 +3,7 @@ obj-$(CONFIG_X86) += x86/
>>>>>  lib-y += bsearch.o
>>>>>  lib-y += ctors.o
>>>>>  lib-y += ctype.o
>>>>> +lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find-next-bit.o
>>>>
>>>> ... you're moving this to lib/. Or have you encountered any issue
>>>> with building this uniformly, and you forgot to mention this in
>>>> the description?
>>> I didn't check. My intention was to provide opportunity to check if
>>> an
>>> architecture want to use generic version or not. Otherwise, I
>>> expected
>>> that we will have multiple definiotion of the funcion.
>>>
>>> But considering that they are all defined under #ifdef...#endif we
>>> can
>>> remove the declaration of the config GENERIC_FIND_NEXT_BIT.
>>
>> What #ifdef / #endif would matter here? Whats in lib/ is intended to
>> be
>> generic anyway. And what is in the resulting lib.a won't be used by
>> an
>> arch if it has an arch-specific implementation. Problems could arise
>> if
>> an arch had an inline function colliding with the out-of-line one.
>> But
>> that's about the old case where I could see a need to make the
>> building
>> of one of the objects conditional. And you'll note that withing this
>> Makefile there are pretty few conditionals.
> We will have such issue with PPC:
> ...
> static inline unsigned long find_next_bit(const unsigned long *addr,
>                                           unsigned long size,
>                                           unsigned long offset)
> ...
> 
> It looks like an introduction of new config for find_next_bit is
> needed.
> 
> Does a better option exist? Would making find_next_bit non inline non
> inline for PPC better?

Isn't that generic code anyway? If so, that also wants replacing by
the generic library function(s). Shawn - I have to admit I have a
hard time seeing why this was introduced as inline functions in the
first place.

Jan