linux-kernel - Re: [PATCH v2 0/4] Static calls

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Message-Id: <EE66E7C9-5735-48B3-A001-E9FCDA46E177@amacapital.net>
Date:   Tue, 4 Dec 2018 15:41:01 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Baron <jbaron@...mai.com>, Jiri Kosina <jkosina@...e.cz>,
        David Laight <David.Laight@...LAB.COM>,
        Borislav Petkov <bp@...en8.de>,
        Julia Cartwright <julia@...com>, Jessica Yu <jeyu@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 0/4] Static calls



> On Dec 4, 2018, at 3:08 PM, Steven Rostedt <rostedt@...dmis.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.

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

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.