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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 688A3C433E0 for ; Mon, 18 May 2020 17:57:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D492207C4 for ; Mon, 18 May 2020 17:57:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589824647; bh=n7/Jy8yngkl5+iE5tSrau/6Npt5wz5PgvgKrbzn52bo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=jefYZTrD/2RH6a38mN7BJ/cFvCy5SOErn3vT7G4kzxMg8bgzqPGYGr9qkoa9qh2Rb cuwbNKYuGiVM27VOuAmQ/7FT0nes/Egf8t05NtIsRM1xBAUOv/qeaWUO/fCnDw9Tch lIEpoev5suha1ghb9AIOjaIUXDdGDrwb1GFn9GDM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730769AbgERR50 (ORCPT ); Mon, 18 May 2020 13:57:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:36010 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731257AbgERR5Z (ORCPT ); Mon, 18 May 2020 13:57:25 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B1033207C4; Mon, 18 May 2020 17:57:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589824645; bh=n7/Jy8yngkl5+iE5tSrau/6Npt5wz5PgvgKrbzn52bo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2EgJnq1z/WDBwN3giTr/Z/wXwp31Qab+HjCbTiy/6eAbdwqm6J9DiOmH6G3oxof1F x6yDKefDTDuTqrHKQ8+SPaODLf8Lk/MwYBPRmSzDwikNaVNewbL44UWR8EW8YEWLBE P3kex+cM/e2Psjyg00hpfLZX5sDYTFy0WCPxOy6w= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Linus Torvalds Subject: [PATCH 5.4 095/147] Stop the ad-hoc games with -Wno-maybe-initialized Date: Mon, 18 May 2020 19:36:58 +0200 Message-Id: <20200518173525.364053200@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200518173513.009514388@linuxfoundation.org> References: <20200518173513.009514388@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Linus Torvalds commit 78a5255ffb6a1af189a83e493d916ba1c54d8c75 upstream. We have some rather random rules about when we accept the "maybe-initialized" warnings, and when we don't. For example, we consider it unreliable for gcc versions < 4.9, but also if -O3 is enabled, or if optimizing for size. And then various kernel config options disabled it, because they know that they trigger that warning by confusing gcc sufficiently (ie PROFILE_ALL_BRANCHES). And now gcc-10 seems to be introducing a lot of those warnings too, so it falls under the same heading as 4.9 did. At the same time, we have a very straightforward way to _enable_ that warning when wanted: use "W=2" to enable more warnings. So stop playing these ad-hoc games, and just disable that warning by default, with the known and straight-forward "if you want to work on the extra compiler warnings, use W=123". Would it be great to have code that is always so obvious that it never confuses the compiler whether a variable is used initialized or not? Yes, it would. In a perfect world, the compilers would be smarter, and our source code would be simpler. That's currently not the world we live in, though. Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- Makefile | 7 +++---- init/Kconfig | 18 ------------------ kernel/trace/Kconfig | 1 - 3 files changed, 3 insertions(+), 23 deletions(-) --- a/Makefile +++ b/Makefile @@ -707,10 +707,6 @@ else ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os endif -ifdef CONFIG_CC_DISABLE_WARN_MAYBE_UNINITIALIZED -KBUILD_CFLAGS += -Wno-maybe-uninitialized -endif - # Tell gcc to never replace conditional load with a non-conditional one KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0) @@ -860,6 +856,9 @@ KBUILD_CFLAGS += -Wno-pointer-sign # disable stringop warnings in gcc 8+ KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation) +# Enabled with W=2, disabled by default as noisy +KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized) + # disable invalid "can't wrap" optimizations for signed / pointers KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow) --- a/init/Kconfig +++ b/init/Kconfig @@ -36,22 +36,6 @@ config TOOLS_SUPPORT_RELR config CC_HAS_ASM_INLINE def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null) -config CC_HAS_WARN_MAYBE_UNINITIALIZED - def_bool $(cc-option,-Wmaybe-uninitialized) - help - GCC >= 4.7 supports this option. - -config CC_DISABLE_WARN_MAYBE_UNINITIALIZED - bool - depends on CC_HAS_WARN_MAYBE_UNINITIALIZED - default CC_IS_GCC && GCC_VERSION < 40900 # unreliable for GCC < 4.9 - help - GCC's -Wmaybe-uninitialized is not reliable by definition. - Lots of false positive warnings are produced in some cases. - - If this option is enabled, -Wno-maybe-uninitialzed is passed - to the compiler to suppress maybe-uninitialized warnings. - config CONSTRUCTORS bool depends on !UML @@ -1226,14 +1210,12 @@ config CC_OPTIMIZE_FOR_PERFORMANCE config CC_OPTIMIZE_FOR_PERFORMANCE_O3 bool "Optimize more for performance (-O3)" depends on ARC - imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives help Choosing this option will pass "-O3" to your compiler to optimize the kernel yet more for performance. config CC_OPTIMIZE_FOR_SIZE bool "Optimize for size (-Os)" - imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives help Choosing this option will pass "-Os" to your compiler resulting in a smaller kernel. --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -371,7 +371,6 @@ config PROFILE_ANNOTATED_BRANCHES config PROFILE_ALL_BRANCHES bool "Profile all if conditionals" if !FORTIFY_SOURCE select TRACE_BRANCH_PROFILING - imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives help This tracer profiles all branch conditions. Every if () taken in the kernel is recorded whether it hit or miss.