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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 5A10BC48BD3 for ; Wed, 26 Jun 2019 09:45:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 39C0D2082F for ; Wed, 26 Jun 2019 09:45:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726839AbfFZJpo (ORCPT ); Wed, 26 Jun 2019 05:45:44 -0400 Received: from foss.arm.com ([217.140.110.172]:57510 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725379AbfFZJpo (ORCPT ); Wed, 26 Jun 2019 05:45:44 -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 E6D372B; Wed, 26 Jun 2019 02:45:43 -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 B57BF3F718; Wed, 26 Jun 2019 02:45:42 -0700 (PDT) Subject: Re: "arm64: vdso: Substitute gettimeofday() with C implementation" breaks clang build To: Will Deacon Cc: Nick Desaulniers , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , Qian Cai , Thomas Gleixner , Nathan Chancellor , Linux ARM References: <1561464964.5154.63.camel@lca.pw> <1561467369.5154.67.camel@lca.pw> <00a78980-6b9c-5d5b-ed01-b28bb34be022@arm.com> <1561470705.5154.68.camel@lca.pw> <5113362e-1256-6712-6ce8-9599b1806cf1@arm.com> <1561472887.5154.72.camel@lca.pw> <668bbe72-b32b-8cee-ccad-d1f6110c6728@arm.com> <193c179e-16ca-4b4e-2584-75e8f6c1819f@arm.com> <20190626093836.y2lofo54rhxw3xsm@willie-the-truck> From: Vincenzo Frascino Message-ID: <897bf622-0f89-14f2-d278-b22f640b78f4@arm.com> Date: Wed, 26 Jun 2019 10:45:41 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190626093836.y2lofo54rhxw3xsm@willie-the-truck> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/06/2019 10:38, Will Deacon wrote: > On Tue, Jun 25, 2019 at 06:00:27PM +0100, Vincenzo Frascino wrote: >> On 25/06/2019 17:26, Nick Desaulniers wrote: >>> On Tue, Jun 25, 2019 at 7:54 AM Vincenzo Frascino >>> wrote: >>>>> but clang 7.0 is still use in many distros by default, so maybe this commit can >>>>> be fixed by adding a conditional check to use "small" if clang version < 8.0. >>>>> >>>> >>>> Could you please verify that the patch below works for you? >>> >>> Should it be checking against CONFIG_CLANG_VERSION, or better yet be >>> using cc-option macro? >>> >> >> This is what I did in my proposed patch, but I was surprised that clang-7 >> generates relocations that clang-8 does not. >> >> LD arch/arm64/kernel/vdso/vdso.so.dbg >> VDSOCHK arch/arm64/kernel/vdso/vdso.so.dbg >> 00000000000009d0 R_AARCH64_JUMP_SLOT _mcount > > Hmm. It would be nice to understand where the reference to _mcount is coming > from, since that sounds like ftrace is getting involved where it shouldn't > be. > That's very true, it was a mistake in the Makefile change that I provided with the original iteration of this patch, that had as a side effect of having ftrace involved (_mcount is defined in entry-ftrace.c). I was overriding: CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os with: CFLAGS_REMOVE_vgettimeofday.o = -mcmodel=tiny (selected if clang is < 8) that's why I said that I missed a "+" in my previous patch. Having: CFLAGS_REMOVE_vgettimeofday.o += -mcmodel=tiny restores the wanted behavior. Sorry for not being clear in my explanation. > Will > -- Regards, Vincenzo