Re: [PATCH v2 0/4] Static calls

Josh Poimboeuf
2018-12-05T15:04:33Z

On Tue, Dec 04, 2018 at 03:41:01PM -0800, Andy Lutomirski wrote:
>
>
> > On Dec 4, 2018, at 3:08 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> >
> > Where did this end up BTW?
> >
> > I know that there's controversy about the
> > CONFIG_HAVE_STATIC_CALL_OPTIMIZED option, but I don't think the
> > CONFIG_HAVE_STATIC_CALL_UNOPTIMIZED version was controversial. From the
> > v1 patch 0 description:
> >
> > There are three separate implementations, depending on what the arch
> > supports:
> >
> > 1) CONFIG_HAVE_STATIC_CALL_OPTIMIZED: patched call sites - requires
> > objtool and a small amount of arch code
> >
> > 2) CONFIG_HAVE_STATIC_CALL_UNOPTIMIZED: patched trampolines - requires
> > a small amount of arch code
> >
> > 3) If no arch support, fall back to regular function pointers
> >
> > My benchmarks showed the best improvements with the
> > STATIC_CALL_OPTIMIZED, but it still showed improvement with the
> > UNOPTIMIZED version as well. Can we at least apply 2 and 3 from the
> > above (which happen to be the first part of the patch set. 1 comes in
> > at the end).
>
> Sounds good to me.
>
> >
> > I would also just call it CONFIG_STATIC_CALL. If we every agree on the
> > optimized version, then we can call it CONFIG_STATIC_CALL_OPTIMIZED.
> > Have an option called UNOPTIMIZED just seems wrong.

(Poking my head up for a bit, soon to disappear again until next week)

Ard had already objected to "unoptimized", which was why for v2 I
renamed them to CONFIG_STATIC_CALL_OUTLINE and CONFIG_STATIC_CALL_INLINE.

I could rename it to CONFIG_STATIC_CALL and CONFIG_STATIC_CALL_INLINE if
you prefer. I don't have much of an opinion either way.

I'll post a v3 next week or so, with the controversial bits more fully
separated from the non-controversial bits. So at least the out-of-line
implementation can get merged.

> My objection to all the bike shed colors so far is that we *always*
> have static_call() — it’s just not always static.

Hm? Do you mean you don't like that we have a generic function pointer
implementation? or what?

> Anyway, I have a new objection to Josh’s create_gap proposal: what on
> Earth will kernel CET do to it? Maybe my longjmp-like hack is
> actually better.

Does CET even care about iret? I assumed it didn't. If it does, your
proposal would have the same problem, no?

--
Josh