Re: [PATCH v2] arm: Added support for getcpu() vDSO using TPIDRURW

[Fredrik MarkstrÃm]

On Wed, Oct 5, 2016 at 10:44 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> On Wed, Oct 05, 2016 at 08:00:38PM +0000, Fredrik MarkstrÃm wrote:
>> On Wed, Oct 5, 2016 at 7:48 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
>> As far as I understand TPIDRURW isn't anything else then an architecture
>> specific piece of tls since the last patch, possibly slightly faster then a
>> "__thread u32 x;"
>>
>> The irony is that the two different ways it was handled earlier (not context
>> switched or always set to zero on swap in) would have made it useful for this
>> purpose.
>
> The "not context switched" case was also arbitrarily corrupted, and could not
> have been relied upon.

Ok, I missed that, sorry !

>
> The zeroing case is similar to the restartable sequences design. So that's
> probably worth looking into.

Ok, I'm starting to believe my best bet is to hope that those make it
into the kernel
eventually, until then I'll probably just go with a local solution.

/Fredrik

>
> Thanks,
> Mark.