Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

Josh Poimboeuf
2018-11-29T18:37:20Z

On Thu, Nov 29, 2018 at 06:15:39PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 29, 2018 at 08:59:31AM -0800, Andy Lutomirski wrote:
>
> > If you make it conditional on CPL, do it for 32-bit as well, add
> > comments,
>
> > and convince yourself that there isn’t a better solution
> > (like pointing IP at a stub that retpolines to the target by reading
> > the function pointer, a la the unoptimizable version), then okay, I
> > guess, with only a small amount of grumbling.
>
> Right; so we _could_ grow the trampoline with a retpoline indirect call
> and ret. It just makes the trampoline a whole lot bigger, but it could
> work.

I'm trying to envision how this would work. How would the function (or
stub) know how to return back to the call site?

--
Josh