linux-kernel - Re: [PATCH v9 04/10] x86: refcount: prevent gcc distortions

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Date:   Thu, 4 Oct 2018 12:33:08 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Nadav Amit <namit@...are.com>, Ingo Molnar <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jan Beulich <JBeulich@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v9 04/10] x86: refcount: prevent gcc distortions

On 10/04/18 02:16, Ingo Molnar wrote:
> 
> * hpa@...or.com <hpa@...or.com> wrote:
> 
>> Ingo: I wasn't talking necessarily about the specifics of each bit, but rather the general 
>> concept about being able to use macros in inlines...
> 
> Ok, agreed about that part - and some of the patches did improve readability.
> 
> Also, the 275 lines macros.s is a lot nicer than the 4,200 lines macros.S.
> 
> Also, I'm not against using workarounds when the benefits are larger than the costs, but I am 
> against *hiding* the fact that these are workarounds and that for some of them there are costs.
> 

Agreed, of course.

>> I can send you something I have been working on in the background, but have been holding off 
>> on because of this, in the morning my time.
> 
> BTW., I have applied most of the series to tip:x86/kbuild already, and will push them out later 
> today after some testing. I didn't apply the final 3 patches as they have dependencies, but 
> applied the basics and fixed up the changelogs.
> 
> So you can rely on this.
> 

Wonderful.

Here is the horrible code I mentioned yesterday.  This is about
implementing the immediate-patching framework that Linus and others have
discussed (it helps both performance and kernel hardening):

Warning: this stuff can cause serious damage to your eyes, and this is a
just a small chunk of the whole mess; and relying on gas macros, as
brain damaged as they are, really is much, much cleaner than not:

	http://www.zytor.com/~hpa/foo.S

	-hpa