ppc64 vDSO in mainline

[Benjamin Herrenschmidt]

On Mon, 2005-03-28 at 15:59 -0800, Ulrich Drepper wrote:
> Steve Munroe wrote:
> > 3) a function which is currently
> > exported by libc , but a better optimized version (with a different
> > symbol) is also exported by the VDSO.
> 
> There is no reason to add any complications or dependency problems for
> this.  Just using a pointer in libc itself, a test for NULL and if not,
> jump to the function is enough.  The penalty for this extra indication
> if minimal compared to all the other work involved.

I agree that this is the best solution at first. We can always
investigate more fancy stuffs later (function pointer calls _are_
expensive) but let's get it working with the non-optimal case first as
Roland suggested. Also, since we don't need the TOC load/reload, it's
actually a bit less expensive than a real function pointer call,
provided we use an appropriate asm inline to do the call on ppc64.

Ben.