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Date:   Fri, 7 Jun 2019 10:28:51 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Nadav Amit <namit@vmware.com>
Cc:     the arch/x86 maintainers <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Andy Lutomirski <luto@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        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 Cartwright <julia@ni.com>, Jessica Yu <jeyu@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Edward Cree <ecree@solarflare.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH 10/15] static_call: Add basic static call infrastructure
Message-ID: <20190607082851.GV3419@hirez.programming.kicks-ass.net>
References: <20190605130753.327195108@infradead.org>
 <20190605131945.125037517@infradead.org>
 <DD54886F-77C6-4230-A711-BF10DD44C52C@vmware.com>
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On Thu, Jun 06, 2019 at 10:44:23PM +0000, Nadav Amit wrote:
> > + * Usage example:
> > + *
> > + *   # Start with the following functions (with identical prototypes):
> > + *   int func_a(int arg1, int arg2);
> > + *   int func_b(int arg1, int arg2);
> > + *
> > + *   # Define a 'my_key' reference, associated with func_a() by default
> > + *   DEFINE_STATIC_CALL(my_key, func_a);
> > + *
> > + *   # Call func_a()
> > + *   static_call(my_key, arg1, arg2);
> > + *
> > + *   # Update 'my_key' to point to func_b()
> > + *   static_call_update(my_key, func_b);
> > + *
> > + *   # Call func_b()
> > + *   static_call(my_key, arg1, arg2);
> 
> I think that this calling interface is not very intuitive.

Yeah, it is somewhat unfortunate..

> I understand that
> the macros/objtool cannot allow the calling interface to be completely
> transparent (as compiler plugin could). But, can the macros be used to
> paste the key with the “static_call”? I think that having something like:
> 
>   static_call__func(arg1, arg2)
> 
> Is more readable than
> 
>   static_call(func, arg1, arg2)

Doesn't really make it much better for me; I think I'd prefer to switch
to the GCC plugin scheme over this.  ISTR there being some propotypes
there, but I couldn't quickly locate them.

> > +}
> > +
> > +#define static_call_update(key, func)					\
> > +({									\
> > +	BUILD_BUG_ON(!__same_type(func, STATIC_CALL_TRAMP(key)));	\
> > +	__static_call_update(&key, func);				\
> > +})
> 
> Is this safe against concurrent module removal?

It is for CONFIG_MODULE=n :-)