From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1AD0DC4361A for ; Fri, 4 Dec 2020 09:37:09 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A3414225AC for ; Fri, 4 Dec 2020 09:37:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A3414225AC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=2fn+c68il+ypRamRMeZKOBBub2/KGD4awg/8WfbRV9k=; b=Slh3IQM+31hYaMAADE76aqGkz myrmR74cxoZAKuSFS9x57rerVjkZFlKfi0d4NObLkEuEQdJzoIdmxZNiIXO9DYn6Z+95YXqeXzgj6 BiPBf4/UK3jzr1TXSdIV61yyTE4CAFavyHTotUsRLfyQLEJhvJlSWzqHGkqAuomHbOQjED7eiToH2 5TOsRDkjydsFh7u4j9hhp1pbHG+SqDgNVUvy1aF42ghaOYKHy7veobEIHYZ7oDlTUvtEz3r7eXYni Rz80Nwe43wATAhLu0ttFy2xpN3q6XCQ4pyC4lDcd2VZrnTbAG6093NHPE70+osnCbSH4iHP+ni9x2 OzSqbFPIg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kl7VD-000784-UJ; Fri, 04 Dec 2020 09:35:47 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kl7VA-000778-GC for linux-arm-kernel@lists.infradead.org; Fri, 04 Dec 2020 09:35:46 +0000 Date: Fri, 4 Dec 2020 09:35:36 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1607074543; bh=KiPYOwivri/c/ItidAb+vtLMDjOCyhBGcMSitc7cncU=; h=From:To:Cc:Subject:References:In-Reply-To:From; b=GjN8UC0To43FRm/tsZr8kvb4HKDZZt6WfrVN1DsurESfPe+l2A94uzzhu1vPpsxIE SWXV209qIxN9vnROEFL2hbNTbFoFDX2aTz789bdBU7n8IEYjja66swjjuutShEenPk HdAj42XjCW4qxd/vLG1PP2j/ZzWjMZOk5uAeayL+wv+giLCOA8bxFRjVaGRHLozHTh YlQwRVBgo7c4uojoeCTTzDC1zQLC8umPbJxt9odbBalrhfUgV5LSzI9t2Ue27J/55s xclSHIhMn7kaICKKuX/AMEWHc4UQCP5TBXKhUl7az+NuJaijbxMdBxQnu8hmWKcpH/ GkZxlHDT8oL8A== From: Will Deacon To: Nick Desaulniers Subject: Re: [PATCH v8 00/16] Add support for Clang LTO Message-ID: <20201204093535.GB461@willie-the-truck> References: <20201201213707.541432-1-samitolvanen@google.com> <20201203112622.GA31188@willie-the-truck> <20201203182252.GA32011@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201204_043544_695812_6D0DD179 X-CRM114-Status: GOOD ( 21.95 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch , Kees Cook , "Paul E. McKenney" , Kernel Hardening , Peter Zijlstra , Greg Kroah-Hartman , Masahiro Yamada , linux-kbuild , PCI , LKML , Steven Rostedt , Jian Cai , clang-built-linux , Sami Tolvanen , Josh Poimboeuf , Kristof Beyls , Nathan Chancellor , linux-arm-kernel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Dec 03, 2020 at 02:32:13PM -0800, Nick Desaulniers wrote: > On Thu, Dec 3, 2020 at 10:23 AM Will Deacon wrote: > > On Thu, Dec 03, 2020 at 09:07:30AM -0800, Sami Tolvanen wrote: > > > Without LLVM_IAS=1, Clang uses two different assemblers when LTO is > > > enabled: the external GNU assembler for stand-alone assembly, and > > > LLVM's integrated assembler for inline assembly. as-instr tests the > > > external assembler and makes an admittedly reasonable assumption that > > > the test is also valid for inline assembly. > > > > > > I agree that it would reduce confusion in future if we just always > > > enabled IAS with LTO. Nick, Nathan, any thoughts about this? > > > > That works for me, although I'm happy with anything which means that the > > assembler checks via as-instr apply to the assembler which will ultimately > > be used. > > I agree with Will. [...] > So I'd recommend to Sami to simply make the Kconfig also depend on > clang's integrated assembler (not just llvm-nm and llvm-ar). If > someone cares about LTO with Clang as the compiler but GAS as the > assembler, then we can revisit supporting that combination (and the > changes to KCONFIG), but it shouldn't be something we consider Tier 1 > supported or a combination that need be supported in a minimum viable > product. And at that point we should make it avoid clang's integrated > assembler entirely (I suspect LTO won't work at all in that case, so > maybe even considering it is a waste of time). > > One question I have to Will; if for aarch64 LTO will depend on RCpc, > but RCpc is an ARMv8.3 extension, what are the implications for LTO on > pre-ARMv8.3 aarch64 processors? It doesn't depend on RCpc -- we just emit a more expensive instruction (an RCsc acquire) if the RCpc one is not supported by both the toolchain and the CPU. So the implication for those processors is that READ_ONCE() may be more expensive. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel