On 14.03.2024 17:23, Andrew Cooper wrote:
> On 14/03/2024 2:16 pm, Jan Beulich wrote:
>> On 13.03.2024 18:27, Andrew Cooper wrote:
>>> --- a/xen/arch/arm/include/asm/bitops.h
>>> +++ b/xen/arch/arm/include/asm/bitops.h
>>> @@ -157,7 +157,7 @@ static inline int fls(unsigned int x)
>>> }
>>>
>>>
>>> -#define ffs(x) ({ unsigned int __t = (x); fls(ISOLATE_LSB(__t)); })
>>> +#define arch_ffs(x) ({ unsigned int __t = (x); fls(ISOLATE_LSB(__t)); })
>> The way the macro is invoked, I don't think the helper local variable
>> is then needed anymore?
>
> I strongly suspect It is still needed. ISOLATE_LSB() double-expands its
> parameter.
Even that double evaluation doesn't matter when the invoking entity is an
inline function, and it doesn't use any non-trivial expression as argument.
>>> --- a/xen/include/xen/bitops.h
>>> +++ b/xen/include/xen/bitops.h
>>> @@ -110,6 +110,21 @@ static inline int generic_flsl(unsigned long x)
>>>
>>> #include <asm/bitops.h>
>>>
>>> +/*
>>> + * Find First Set bit. Bits are labelled from 1.
>>> + */
>>> +static always_inline __pure unsigned int ffs(unsigned int x)
>> Why always_inline?
>
> For all the normal reasons to counter Clang and GCC doing stupid things
> with inlines that contain assembly.
Hmm, there are issues when the asm() would look "complex" to the compiler,
but that's not the case here. I was asking because, as you imply by how
you responded, we may need to gain many more always_inline when at some
time even you were arguing against overriding compiler decisions like this
(unless I'm mis-remembering).
Jan
