On 16/01/17 13:30, Marc Zyngier wrote:
> On 13/01/17 14:56, Suzuki K Poulose wrote:
>> On 13/01/17 13:30, Marc Zyngier wrote:
>>> [+ Suzuki, who wrote the whole cpus_have_const_cap thing]
>>>
>
> [...]
>
>>> But maybe we should have have some stronger guarantees that we'll
>>> always get things inlined, and that the "const" side is enforced:
>>
>> Agreed.
>>
>>>
>>> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
>>> index b4989df..4710469 100644
>>> --- a/arch/arm64/include/asm/cpufeature.h
>>> +++ b/arch/arm64/include/asm/cpufeature.h
>>> @@ -105,10 +105,11 @@ static inline bool cpu_have_feature(unsigned int num)
>>> }
>>>
>>> /* System capability check for constant caps */
>>> -static inline bool cpus_have_const_cap(int num)
>>> +static __always_inline bool cpus_have_const_cap(int num)
>>
>> I think we should have the above change and make it inline always.
>>
>>> {
>>> - if (num >= ARM64_NCAPS)
>>> - return false;
>>> + BUILD_BUG_ON(!__builtin_constant_p(num));
>>
>> This is not needed, as the compilation would fail if num is not a constant with
>> static key code.
I also just checked this, and it doesn't fail if the compiler doesn't
directly supports jump labels (we then fallback to the static key being
a standard memory access).
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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