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=-11.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 3FEA1C3A59F for ; Thu, 29 Aug 2019 20:21:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0C35222CF5 for ; Thu, 29 Aug 2019 20:21:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=agner.ch header.i=@agner.ch header.b="HtB7SUmG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728146AbfH2UV3 (ORCPT ); Thu, 29 Aug 2019 16:21:29 -0400 Received: from mail.kmu-office.ch ([178.209.48.109]:50950 "EHLO mail.kmu-office.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726935AbfH2UV2 (ORCPT ); Thu, 29 Aug 2019 16:21:28 -0400 Received: from webmail.kmu-office.ch (unknown [IPv6:2a02:418:6a02::a3]) by mail.kmu-office.ch (Postfix) with ESMTPSA id 233B95C1F7F; Thu, 29 Aug 2019 22:21:25 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=agner.ch; s=dkim; t=1567110085; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fg2GaVUio75ldsR6EagWHhcxkRR/eMtIgg94UgACpuA=; b=HtB7SUmGK/K5TFjhNhc+4bTcQoRjeLOroIk030NC86YCFXQ+4vB4qO4OrPZwIpszip7xEx xumoIuQ4y9uB7RjeyOzU+rjc9EQWwJSy7myjs5QK6ZewmBa5CZHZT/GTpmlAiT1DT29zK7 HMINqyQgaRR1pOJr4p5WFGfDwegd8x8= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Date: Thu, 29 Aug 2019 22:21:25 +0200 From: Stefan Agner To: Nathan Chancellor Cc: Nick Desaulniers , Russell King , Arnd Bergmann , Matthias Kaehlcke , Linux ARM , LKML , clang-built-linux Subject: Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer In-Reply-To: <20190829193432.GA10138@archlinux-threadripper> References: <20190829062635.45609-1-natechancellor@gmail.com> <20190829193432.GA10138@archlinux-threadripper> Message-ID: <885bb20c11f0cb004e5eeda7b0ca6d16@agner.ch> X-Sender: stefan@agner.ch User-Agent: Roundcube Webmail/1.3.9 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-08-29 21:34, Nathan Chancellor wrote: > On Thu, Aug 29, 2019 at 10:55:28AM -0700, Nick Desaulniers wrote: >> On Wed, Aug 28, 2019 at 11:27 PM Nathan Chancellor >> wrote: >> > >> > Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build >> > with clang: >> > >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable': >> > softirq.c:(.text+0x504): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `__local_bh_enable_ip': >> > softirq.c:(.text+0x58c): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq': >> > softirq.c:(.text+0x6c8): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter': >> > softirq.c:(.text+0x75c): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit': >> > softirq.c:(.text+0x840): undefined reference to `mcount' >> > arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more undefined references to `mcount' follow >> > >> > clang can emit a working mcount symbol, __gnu_mcount_nc, when >> > '-meabi gnu' is passed to it. Until r369147 in LLVM, this was >> > broken and caused the kernel not to boot because the calling >> > convention was not correct. Now that it is fixed, add this to >> > the command line when clang is 10.0.0 or newer so everything >> > works properly. >> > >> > Link: https://github.com/ClangBuiltLinux/linux/issues/35 >> > Link: https://bugs.llvm.org/show_bug.cgi?id=33845 >> > Link: https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60 >> > Signed-off-by: Nathan Chancellor >> > --- >> > arch/arm/Makefile | 6 ++++++ >> > 1 file changed, 6 insertions(+) >> > >> > diff --git a/arch/arm/Makefile b/arch/arm/Makefile >> > index c3624ca6c0bc..7b5a26a866fc 100644 >> > --- a/arch/arm/Makefile >> > +++ b/arch/arm/Makefile >> > @@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) >> > CFLAGS_ABI +=-funwind-tables >> > endif >> > >> > +ifeq ($(CONFIG_CC_IS_CLANG),y) >> > +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 100000; echo $$?),0) >> > +CFLAGS_ABI +=-meabi gnu >> > +endif >> > +endif >> > + >> >> Thanks for the patch! I think this is one of the final issues w/ 32b >> ARM configs when building w/ Clang. >> >> I'm not super enthused about the version check. The flag is indeed >> not recognized by GCC, but I think it would actually be more concise >> with $(cc-option) and no compiler or version check. >> >> Further, I think that the working __gnu_mcount_nc in Clang would >> better be represented as marking the arch/arm/KConfig option for >> CONFIG_FUNCTION_TRACER for dependent on a version of Clang greater >> than or equal to Clang 10, not conditionally adding this flag. (We >> should always add the flag when supported, IMO. __gnu_mcount_nc's >> calling convention being broken is orthogonal to the choice of >> __gnu_mcount_nc vs mcount, and it's the former's that should be >> checked, not the latter as in this patch. > > I will test with or without CONFIG_AEABI like Matthias asked and I will > implement your Kconfig suggestion if it passes all of my tests. The > reason that I did it this way is because I didn't want a user to end up > with a non-booting kernel since -meabi gnu works with older versions of > clang at build time, the issue happens at boot time but the Kconfig > suggestion + cc-option should fix that. I agree with Nathan here, I'd rather prefer the build system to fail building rather than runtime error. If we decide we want to have it building despite it not building a functional kernel, we should at least add a #warning... -- Stefan > > I should have a v2 out this evening. > > Cheers, > Nathan