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

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Date:   Thu, 29 Nov 2018 11:24:43 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Lutomirski <luto@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, mhiramat@...nel.org,
        jbaron@...mai.com, Jiri Kosina <jkosina@...e.cz>,
        David.Laight@...lab.com, bp@...en8.de, julia@...com,
        jeyu@...nel.org, Peter Anvin <hpa@...or.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call
 implementation for x86-64

On Thu, Nov 29, 2018 at 11:16 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> But then we need to implement all numbers of parameters.

Oh, I agree, it's nasty.

But it's actually a nastiness that we've solved before. In particular,
with the system call mappings, which have pretty much the exact same
issue of "map unknown number of arguments to registers".

Yes, it's different - there you map the unknown number of arguments to
a structure access instead. And yes, the macros are unbelievably ugly.
See

    arch/x86/include/asm/syscall_wrapper.h

and the __MAP() macro from

    include/linux/syscalls.h

so it's not pretty. But it would solve all the problems.

              Linus