linux-kernel - Re: [PATCH v2 18/18] arm64: select ARCH_SUPPORTS_LTO

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Message-Id: <20171120205350.GZ3624@linux.vnet.ibm.com>
Date:   Mon, 20 Nov 2017 12:53:50 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Will Deacon <will.deacon@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Alex Matveev <alxmtvv@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Alexander Potapenko <glider@...gle.com>,
        Stephen Hines <srhines@...gle.com>,
        Pirama Arumuga Nainar <pirama@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>
Subject: Re: [PATCH v2 18/18] arm64: select ARCH_SUPPORTS_LTO_CLANG

On Mon, Nov 20, 2017 at 08:32:56PM +0100, Peter Zijlstra wrote:
> On Mon, Nov 20, 2017 at 06:05:55PM +0000, Will Deacon wrote:
> > Although the current direction of the C++ committee is to prefer
> > that dependencies are explicitly "marked", this is not deemed to be
> > acceptable for the kernel (in other words, everything is always considered
> > "marked").
> 
> Yeah, that is an attitude not compatible with existing code. Much like
> the proposal to allow temporary/wide stores on everything not explicitly
> declared atomic. Such stuff instantly breaks all extant code that does
> multi-threading with no recourse.

If someone suggests temporary/wide stores, even on non-atomics, tell
them that the standard does not permit them to introduce data races.

							Thanx, Paul