From mboxrd@z Thu Jan 1 00:00:00 1970 From: David.Laight@ACULAB.COM (David Laight) Date: Tue, 21 Nov 2017 17:23:52 +0000 Subject: [PATCH v2 18/18] arm64: select ARCH_SUPPORTS_LTO_CLANG In-Reply-To: <20171120205350.GZ3624@linux.vnet.ibm.com> References: <20171116173417.nqsh5dpu65uj7b5s@hirez.programming.kicks-ass.net> <20171116174830.GX3624@linux.vnet.ibm.com> <20171116183950.GA3624@linux.vnet.ibm.com> <20171116184508.GC21898@arm.com> <20171116191307.GC3624@linux.vnet.ibm.com> <20171116201701.GA143965@samitolvanen.mtv.corp.google.com> <20171120180554.GM32488@arm.com> <20171120193256.e6fnn2arwqc5wqkp@hirez.programming.kicks-ass.net> <20171120205350.GZ3624@linux.vnet.ibm.com> Message-ID: <1f19a8816278495f997f4331ef0e015e@AcuMS.aculab.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Paul E. McKenney > Sent: 20 November 2017 20:54 > > 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. The C standard doesn't say anything about multi-threading. The x86 bis (bit set) family are well known for being problematic because they always do a 32bit wide rmw cycle. David