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

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Date:   Thu, 4 Oct 2018 10:33:33 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, 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

* Ingo Molnar <mingo@...nel.org> wrote:

> I'm also somewhat annoyed at the fact that this series carries a boatload
> of reviewed-by's and acked-by's, yet none of those reviewers found it
> important to point out the large chasm that is gaping between description
> and reality.

Another problem I just realized is that we now include arch/x86/kernel/macros.S in every 
translation pass when building the kernel, right?

But arch/x86/kernel/macros.S expands to a pretty large hiearchy of header files:

  $ make arch/x86/kernel/macros.s

  $ cat $(grep include arch/x86/kernel/macros.s | cut -d\" -f2 | sort | uniq) | wc -l
  4128

That's 4,100 extra lines of code to be preprocessed for every translation unit, of
which there are tens of thousands. More if other pieces of code get macrofied in
this fasion in the future.

If we assume that a typical distribution kernel build has ~20,000 translation units
then this change adds 82,560,000 more lines to be preprocessed, just to work around
a stupid GCC bug?

I'm totally unhappy about that. Can we do this without adding macros.S?

It's also a pretty stupidly central file anyway that moves source code away
from where it's used.

Thanks,

	Ingo