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=-22.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A,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 6AA97C433F5 for ; Tue, 7 Sep 2021 22:28:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 477C961101 for ; Tue, 7 Sep 2021 22:28:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238914AbhIGW3k (ORCPT ); Tue, 7 Sep 2021 18:29:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235945AbhIGW3j (ORCPT ); Tue, 7 Sep 2021 18:29:39 -0400 Received: from mail-ot1-x32e.google.com (mail-ot1-x32e.google.com [IPv6:2607:f8b0:4864:20::32e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE7DEC061575; Tue, 7 Sep 2021 15:28:32 -0700 (PDT) Received: by mail-ot1-x32e.google.com with SMTP id c42-20020a05683034aa00b0051f4b99c40cso361451otu.0; Tue, 07 Sep 2021 15:28:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=xFav5yETJ9K/9gFqD/ijYgX8103pj31aLaLvEUcyaqI=; b=UUk+7aIudoNWpKLQcV+/OIHzmx91LOXITjFvwY3cPpOWc5p6HZNs2vIFEzVTZbBeMg kT6H4zq7/8NfYYebeuz4YjJNUQm9w4qHBPTaHN8OrwX3pBRMOMFOBOJgXQ91XGBn/L2o hdaq9v03Lm+m7LAhMJ9wrg5kud8yvZbGHJnYtDe5PXtG2wV0yiXmkhsz+ej0w0i+5+0/ K9VzauFmM4IwJoUwWw93Jqs6YN/aEvRL6XZPrke108vi4nx0R6kTJ1XEfT726vTNZ9nA eEM5z4xVv0bWnRlqeOE+PYIzJ2aAehNilG8ozvonpWSYsY4NS9WdMOey5FjHCK4VH/6S o01A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:subject:to:cc:references:from:message-id :date:user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=xFav5yETJ9K/9gFqD/ijYgX8103pj31aLaLvEUcyaqI=; b=YYBfcE8VrOFxIEBrPcPE+A4ymzBwksLcx0qpuH0OqHMPyIKpzEXI5k6MizVtxoLDS9 bPXIWMOTc6fUYZsVfI5oEM8kfNSibbgUjnb8OefmWjusvbtVMesMU2YpwsQ0rqokcGiN dIY4+UYRaaJjhn7EZKgaXE105zbPWe8/xZbCevQ97ylaNQngSGrwXV/9JjY6Y1APuwjA EdxLv0FHKANdT/CCvOF2K2QrgFPpLyfz7ogBVRhiPW4rC4w2QhNHmIzT7W01qtBLLiQV 5q/Nf67Gv+bGJHq+7piHGL8e0WrXpR8GGOqCwAduriszAwZs/QifZP+u1mXGBQ+KtOCO BTCw== X-Gm-Message-State: AOAM5332qdEjwEJlyLjAK/rGRCWbZbTIDB7EYxXYutBXnuiq/PV/sDIC iIAiXQK3bhhBbYpcZgavFMW7UEjYIeI= X-Google-Smtp-Source: ABdhPJwb9yJ9q2Q8nm67HNml4PLnJRRt1Wg0BZ0j9YzfHjGwApNTFR8ciJkmMCjO074oQBD0Kdpohg== X-Received: by 2002:a05:6830:1443:: with SMTP id w3mr564450otp.49.1631053711952; Tue, 07 Sep 2021 15:28:31 -0700 (PDT) Received: from server.roeck-us.net ([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id p81sm78494oia.48.2021.09.07.15.28.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Sep 2021 15:28:31 -0700 (PDT) Sender: Guenter Roeck Subject: Re: [PATCH] Revert "Enable '-Werror' by default for all kernel builds" To: Marco Elver , Nick Desaulniers , Linus Torvalds Cc: llvm@lists.linux.dev, LSM List , linux-toolchains@vger.kernel.org, Arnd Bergmann , Greg Kroah-Hartman , Kees Cook , Mark Brown , Masahiro Yamada , Nathan Chancellor , Michal Marek , Andrew Morton , Vipin Sharma , Chris Down , Rasmus Villemoes , Daniel Borkmann , Vlastimil Babka , Linux Kbuild mailing list , Linux Kernel Mailing List References: <20210907183843.33028-1-ndesaulniers@google.com> From: Guenter Roeck Message-ID: Date: Tue, 7 Sep 2021 15:28:28 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: On 9/7/21 3:14 PM, Marco Elver wrote: > On Tue, Sep 07, 2021 at 01:30PM -0700, Nick Desaulniers wrote: >> On Tue, Sep 7, 2021 at 12:16 PM Linus Torvalds wrote: > [...] >>> I'm not going to revert that change. I probably will have to limit it >>> (by making that WERROR option depend on certain expectations), but >>> basically any maintainer who has code that causes warnings should >>> expect that they will have to fix those warnings. >> >> I'm not 100% against it; I think it could land in a more useful >> variation. But it would be good to discuss that on-list, and give it >> time to soak. This is a conversation we should be having with CI >> maintainers IMO, and folks that maintain the build infra, at least. >> I'm happy to kick off that discussion with this RFC. > > Here's a datapoint: I had to disable CONFIG_WERROR on a bunch of syzbot > instances which started failing because of -Werror [1], because syzbot's > time is better spent on fuzzing, and having the odd warning in some > subsystem penalize fuzzing of the entire kernel is not appropriate. > > [1] https://github.com/google/syzkaller/commit/e096c0a2a414e487412c9669426780ce5acdde9d > > Getting the kernel built is a hard requirement for any sort of runtime > testing. Once the kernel is built, runtime testing of various subsystems > can proceed in parallel. A single warning in some odd subsystem > penalizing the _entire_ kernel's testing progress is inappropriate. The > severity of a use-after-free bug found by runtime testing is orders of > magnitude more severe than some "unused variable" warning. Now such a > warning would delay finding bugs at runtime on many CI systems that > haven't yet disabled the warning. > > I'm predicting most distributions and runtime-focused CIs will disable > the warning. > > I have formulated this in the form of a patch below, that might move > this new Kconfig option towards its appropriate usecases by default. > > The intent is not to dispute the usefulness of -Werror, but select the > appropriate usecases by default, limiting friction for all those who can > do little more than say CONFIG_WERROR=n. > > Thanks, > -- Marco > > ------ >8 ------ > > From: Marco Elver > Date: Tue, 7 Sep 2021 23:12:08 +0200 > Subject: [PATCH] kbuild: Only default to -Werror if COMPILE_TEST > > The cross-product of the kernel's supported toolchains, architectures, > and configuration options is large. So large, that it's generally > accepted to be infeasible to enumerate and build+test them all > (many compile-testers rely on randomly generated configs). > > Without the possibility to enumerate all possible combinations of > toolchains, architectures, and configuration options, it is inevitable > that compiler warnings in this space exist. > > With -Werror, this means that an innumerable set of kernels are now > broken, yet had been perfectly usable before (confused compilers, code > with warnings unused, or luck). > > Distributors will necessarily pick a point in the toolchain X arch X > config space, and if unlucky, will have a broken build. Granted, those > will likely disable CONFIG_WERROR and move on. > > The kernel's default configuration is unlikely to be suitable for all > users, but it's inappropriate to force many users to set CONFIG_WERROR=n. > > This also holds for CI systems which are focused on runtime testing, > where the odd warning in some subsystem will disrupt testing of the rest > of the kernel. Many of those runtime-focused CI systems run tests or > fuzz the kernel using runtime debugging tools. Runtime testing of > different subsystems can proceed in parallel, and potentially uncover > serious bugs; halting runtime testing of the entire kernel because of > the odd warning (now error) in a subsystem or driver is simply > inappropriate. > > Therefore, runtime-focused CI systems will likely choose CONFIG_WERROR=n > as well. > > The appropriate usecase for -Werror is therefore compile-test focused > builds (often done by developers or CI systems). > > Reflect this in the Kconfig option by making the default value of WERROR > match COMPILE_TEST. > > Signed-off-by: Marco Elver I like it. Acked-by: Guenter Roeck > --- > init/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/init/Kconfig b/init/Kconfig > index 8cb97f141b70..11f8a845f259 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -139,7 +139,7 @@ config COMPILE_TEST > > config WERROR > bool "Compile the kernel with warnings as errors" > - default y > + default COMPILE_TEST > help > A kernel build should not cause any compiler warnings, and this > enables the '-Werror' flag to enforce that rule by default. >