Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20181126160217.GR2113@hirez.programming.kicks-ass.net>
 <CALCETrXam8JBtXE3S97Vyb_=+pmjgr23SoZ-Dm5pmYtwZYA+7Q@mail.gmail.com>
 <20181129094210.GC2131@hirez.programming.kicks-ass.net> <ECF632D9-581B-40B7-9F0A-6B5607A4D0E3@amacapital.net>
 <20181129143853.GO2131@hirez.programming.kicks-ass.net> <20181129163342.tp5wlfcyiazwwyoh@treble>
 <CAHk-=wg5wUXJX5mF+22WXWM_vPESb+p6-z-ZrG7rC1k2O7u=NQ@mail.gmail.com>
 <0A629D30-ADCF-4159-9443-E5727146F65F@amacapital.net> <20181129121307.12393c57@gandalf.local.home>
 <CAHk-=wik5AfDs7qqjGHQ5vRBYkV8K6tFmPna3PdbwdzVwPGTsg@mail.gmail.com>
 <20181129124404.2fe55dd0@gandalf.local.home> <CAHk-=wgnZobye-KNaBVO-SdqX-5Xkz+i=aJ_kOFZ4RpZFT0HqQ@mail.gmail.com>
 <20181129125857.75c55b96@gandalf.local.home> <CAHk-=wigLUgxDM6Dq2aS7efduffratP976Ggmpv4Ev4EOrJxyA@mail.gmail.com>
 <20181129134725.6d86ade6@gandalf.local.home> <CAHk-=wgbnQs4fpuHqT1jLkDnKcvTGS5EN8m=qy7oUE5n_fhOig@mail.gmail.com>
 <20181129141648.6ef944a9@gandalf.local.home> <CAHk-=whBuSXe1+8HGT23FWDypkAP7TPun3te=fw2aLx+F6WVig@mail.gmail.com>
In-Reply-To: <CAHk-=whBuSXe1+8HGT23FWDypkAP7TPun3te=fw2aLx+F6WVig@mail.gmail.com>
From:   Andy Lutomirski <luto@amacapital.net>
Date:   Thu, 29 Nov 2018 11:28:07 -0800
Message-ID: <CALCETrU5cORg237=XvT332se8YPLq78zNPM+OsFTorXqLc05SQ@mail.gmail.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call
 implementation for x86-64
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
        David Laight <David.Laight@aculab.com>,
        Borislav Petkov <bp@alien8.de>, julia@ni.com, jeyu@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Nov 29, 2018 at 11:25 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Thu, Nov 29, 2018 at 11:16 AM Steven Rostedt <rostedt@goodmis.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.
>

Until someone does:

struct foo foo;
static_call(thingy, foo);

For syscalls, we know better than to do that.  For static calls, I'm
less confident.