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Tue, 30 Jul 2019 15:31:29 +1000 (AEST) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 45yQCH3NcVzB09ZT; Tue, 30 Jul 2019 07:31:23 +0200 (CEST) Authentication-Results: localhost; dkim=pass reason="1024-bit key; insecure key" header.d=c-s.fr header.i=@c-s.fr header.b=qyEzDSXc; dkim-adsp=pass; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id rd-v7jPqQJgu; Tue, 30 Jul 2019 07:31:23 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 45yQCH2HdXzB09ZN; Tue, 30 Jul 2019 07:31:23 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=c-s.fr; s=mail; t=1564464683; bh=ePSetGxy2Hgvqtd+MAQAGKMxy2rhqR0kq9ZlpTUXHps=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=qyEzDSXcnwLMN8hHx717ZrDE0Jv3hY6oYqpm8o29LeHg0T2Nl8V/kNdFsQgoV6CQT LbYMXDw+LGfxTyJliNgft9h1Jv2zGxQ6PnhCVndsAxlVYD749/0E2dNnzcY3frc2uu /hVX8u33apZRbxJSLbuTXC1ChrxEpO0T22sRdr/w= Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 27A588B7F1; Tue, 30 Jul 2019 07:31:24 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id 8Lk1aYWXxBaY; Tue, 30 Jul 2019 07:31:24 +0200 (CEST) Received: from [172.25.230.101] (po15451.idsi0.si.c-s.fr [172.25.230.101]) by messagerie.si.c-s.fr (Postfix) with ESMTP id F1AFC8B74F; Tue, 30 Jul 2019 07:31:23 +0200 (CEST) Subject: Re: [PATCH] powerpc: workaround clang codegen bug in dcbz To: Nathan Chancellor , Nick Desaulniers References: <20190729202542.205309-1-ndesaulniers@google.com> <20190729203246.GA117371@archlinux-threadripper> From: Christophe Leroy Message-ID: <8f2331db-151f-a481-23e0-ec6dd9ba6f1c@c-s.fr> Date: Tue, 30 Jul 2019 07:31:23 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190729203246.GA117371@archlinux-threadripper> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: arnd@arndb.de, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, Paul Mackerras , linuxppc-dev@lists.ozlabs.org, kbuild test robot Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 29/07/2019 à 22:32, Nathan Chancellor a écrit : > On Mon, Jul 29, 2019 at 01:25:41PM -0700, Nick Desaulniers wrote: >> Commit 6c5875843b87 ("powerpc: slightly improve cache helpers") exposed >> what looks like a codegen bug in Clang's handling of `%y` output >> template with `Z` constraint. This is resulting in panics during boot >> for 32b powerpc builds w/ Clang, as reported by our CI. >> >> Add back the original code that worked behind a preprocessor check for >> __clang__ until we can fix LLVM. >> >> Further, it seems that clang allnoconfig builds are unhappy with `Z`, as >> reported by 0day bot. This is likely because Clang warns about inline >> asm constraints when the constraint requires inlining to be semantically >> valid. >> >> Link: https://bugs.llvm.org/show_bug.cgi?id=42762 >> Link: https://github.com/ClangBuiltLinux/linux/issues/593 >> Link: https://lore.kernel.org/lkml/20190721075846.GA97701@archlinux-threadripper/ >> Debugged-by: Nathan Chancellor >> Reported-by: Nathan Chancellor >> Reported-by: kbuild test robot >> Suggested-by: Nathan Chancellor >> Signed-off-by: Nick Desaulniers >> --- >> Alternatively, we could just revert 6c5875843b87. It seems that GCC >> generates the same code for these functions for out of line versions. >> But I'm not sure how the inlined code generated would be affected. > > For the record: > > https://godbolt.org/z/z57VU7 > > This seems consistent with what Michael found so I don't think a revert > is entirely unreasonable. Your example functions are too simple to show anything. The functions takes only one parameter so of course GCC won't use two registers allthough given the opportunity. Christophe > > Either way: > > Reviewed-by: Nathan Chancellor >