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=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 071AAC74A52 for ; Thu, 11 Jul 2019 12:14:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DC78921537 for ; Thu, 11 Jul 2019 12:14:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728489AbfGKMOo (ORCPT ); Thu, 11 Jul 2019 08:14:44 -0400 Received: from foss.arm.com ([217.140.110.172]:45358 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727974AbfGKMOo (ORCPT ); Thu, 11 Jul 2019 08:14:44 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E72F92B; Thu, 11 Jul 2019 05:14:42 -0700 (PDT) Received: from [10.1.196.72] (e119884-lin.cambridge.arm.com [10.1.196.72]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6A80C3F59C; Thu, 11 Jul 2019 05:14:40 -0700 (PDT) Subject: Re: [PATCH] vsyscall: use __iter_div_u64_rem() To: Arnd Bergmann , Andy Lutomirski , Thomas Gleixner Cc: linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, linux-kselftest@vger.kernel.org, Catalin Marinas , Will Deacon , Russell King , Ralf Baechle , Paul Burton , Daniel Lezcano , Mark Salyzyn , Peter Collingbourne , Shuah Khan , Dmitry Safonov <0x7f454c46@gmail.com>, Rasmus Villemoes , Huw Davies , linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com References: <20190710130206.1670830-1-arnd@arndb.de> From: Vincenzo Frascino Message-ID: <33511b0e-6d7b-c156-c415-7a609b049567@arm.com> Date: Thu, 11 Jul 2019 13:14:39 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190710130206.1670830-1-arnd@arndb.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Hi Arnd, On 10/07/2019 14:01, Arnd Bergmann wrote: > On 32-bit x86 when building with clang-9, the loop gets turned back into > an inefficient division that causes a link error: > > kernel/time/vsyscall.o: In function `update_vsyscall': > vsyscall.c:(.text+0xe3): undefined reference to `__udivdi3' > > Use the provided __iter_div_u64_rem() function that is meant to address > the same case in other files. > > Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation") > Signed-off-by: Arnd Bergmann > --- > kernel/time/vsyscall.c | 6 +----- > 1 file changed, 1 insertion(+), 5 deletions(-) > > diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c > index a80893180826..8cf3596a4ce6 100644 > --- a/kernel/time/vsyscall.c > +++ b/kernel/time/vsyscall.c > @@ -104,11 +104,7 @@ void update_vsyscall(struct timekeeper *tk) > vdso_ts->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec; > nsec = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift; > nsec = nsec + tk->wall_to_monotonic.tv_nsec; > - while (nsec >= NSEC_PER_SEC) { > - nsec = nsec - NSEC_PER_SEC; > - vdso_ts->sec++; > - } > - vdso_ts->nsec = nsec; > + vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec); > > if (__arch_use_vsyscall(vdata)) > update_vdso_data(vdata, tk); > I am trying to test this patch using clang-9 tip: # clang -v clang version 9.0.0 (git@github.com:llvm-mirror/clang.git 6ed0749151866894a67a3e7eefdc1f3a547daa0e) (git@github.com:llvm-mirror/llvm.git a10a70238ace1093cad3adeb94814b422bd1b5c1) but I get a lot of errors similar to the one below: In file included from ~/linux/arch/x86/events/amd/core.c:11: ~/linux/arch/x86/events/amd/../perf_event.h:824:21: error: invalid output size for constraint '=q' u64 disable_mask = __this_cpu_read(cpu_hw_events.perf_ctr_virt_mask); ^ ~/linux/include/linux/percpu-defs.h:447:2: note: expanded from macro '__this_cpu_read' raw_cpu_read(pcp); \ ^ ~/linux/include/linux/percpu-defs.h:421:28: note: expanded from macro 'raw_cpu_read' #define raw_cpu_read(pcp) __pcpu_size_call_return(raw_cpu_read_, pcp) ^ ~/linux/include/linux/percpu-defs.h:322:23: note: expanded from macro '__pcpu_size_call_return' case 1: pscr_ret__ = stem##1(variable); break; \ ^ :110:1: note: expanded from here raw_cpu_read_1 ^ ~/linux/arch/x86/include/asm/percpu.h:394:30: note: expanded from macro 'raw_cpu_read_1' #define raw_cpu_read_1(pcp) percpu_from_op(, "mov", pcp) ^ ~/linux/arch/x86/include/asm/percpu.h:189:15: note: expanded from macro 'percpu_from_op' : "=q" (pfo_ret__) \ Could you please tell me which version of the compiler did you use? My building command is: # make mrproper && make CC=clang HOSTCC=clang i386_defconfig && make ARCH=i386 CC=clang HOSTCC=clang -j56 -- Regards, Vincenzo