linux-kernel - Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo

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Message-ID: <20190306165831.GZ32477@hirez.programming.kicks-ass.net>
Date:   Wed, 6 Mar 2019 17:58:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Akira Yokosawa <akiyks@...il.com>
Cc:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Borislav Petkov <bp@...en8.de>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Will Deacon <will.deacon@....com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Daniel Lustig <dlustig@...dia.com>
Subject: Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo

On Thu, Mar 07, 2019 at 12:46:05AM +0900, Akira Yokosawa wrote:
> So, I'm looking at the macro RELOC_HIDE() defined in include/linux/compiler-gcc.h.

> Am I the only one who was not aware of this gcc-specific macro?

It's one I regularly see, but had forgotten about in this context.

However; you can also fix things by adding asm volatile ("":::"memory");
in places.

But that's not really the point; I would really rather have a cmdline
knob to fix things. That way we can compile the kernel with and without
and look for differences. -fno-unicorns or something :-)

While I understand some compiler people revel in UB and love to make
unicorns happen, I think in this case the produces result is utterly
insane.