From patchwork Thu Nov 10 16:44:44 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Arnd Bergmann X-Patchwork-Id: 9421497 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 9682460720 for ; Thu, 10 Nov 2016 16:47:27 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 93F5F294FE for ; Thu, 10 Nov 2016 16:47:27 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 87D80295EA; Thu, 10 Nov 2016 16:47:27 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1FD7729505 for ; Thu, 10 Nov 2016 16:47:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964817AbcKJQrH (ORCPT ); Thu, 10 Nov 2016 11:47:07 -0500 Received: from mout.kundenserver.de ([212.227.126.131]:53337 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935157AbcKJQrF (ORCPT ); Thu, 10 Nov 2016 11:47:05 -0500 Received: from wuerfel.lan ([78.43.20.153]) by mrelayeu.kundenserver.de (mreue002 [212.227.15.129]) with ESMTPA (Nemesis) id 0M5lI9-1d2VXk3pwP-00xrUU; Thu, 10 Nov 2016 17:45:38 +0100 From: Arnd Bergmann To: Linus Torvalds Cc: Andrew Morton , Arnd Bergmann , Anna Schumaker , "David S. Miller" , Herbert Xu , Ilya Dryomov , Javier Martinez Canillas , Jiri Kosina , Jonathan Cameron , Ley Foon Tan , "Luis R . Rodriguez" , Martin Schwidefsky , Mauro Carvalho Chehab , Michal Marek , Russell King , Sean Young , Sebastian Ott , Trond Myklebust , x86@kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, nios2-dev@lists.rocketboards.org, linux-s390@vger.kernel.org, linux-crypto@vger.kernel.org, linux-media@vger.kernel.org, linux-nfs@vger.kernel.org Subject: [PATCH v2 01/11] Kbuild: enable -Wmaybe-uninitialized warning for "make W=1" Date: Thu, 10 Nov 2016 17:44:44 +0100 Message-Id: <20161110164454.293477-2-arnd@arndb.de> X-Mailer: git-send-email 2.9.0 In-Reply-To: <20161110164454.293477-1-arnd@arndb.de> References: <20161110164454.293477-1-arnd@arndb.de> X-Provags-ID: V03:K0:DAXk2Yxa67fKjwVk4DeXKToDkZ5sDxWPsZAvlZpQTKdNYJXUp0F mVVlzky4AH6Sq3clApz9B1jUxra6p0Gt007J8G5MPb86yl5RgPDo3BZxGoV5eVFvp9/HUpL Vjrx7B7Ox98X9RYAt4VAtf1sGqJ3cl16xDWbSw25mwWm7W6ofo81W40uYdYTyap39pTAecQ 3sMhwOWsbOM6TY4CLwcKA== X-UI-Out-Filterresults: notjunk:1; V01:K0:AKftQSy/FBI=:VHnh/LT69UYVkOIfZE/SL7 JgORH64wCohJllpLcr1KYHWSbOtbB7JdVl1v0w2bXB03wzD7+lzmVOWo9GS3SymtYebjF7hDu JHoAZ1I6/Z3ETGh9419hqaeWpovuUe8bPysQPXQ2aVu5wYR6kxJMZe5G7RhXcUeLlLFvOjELO E8rfhVMWDujd5CyVSKsXhoL1Pbc3DsVgxtlLcHsAktC+l5Tk7RdgAPm8xchpwba5aHejJTJiW FBztfn2haRUTZ4PK4tpyORyg27efR+w014esNF6tqufoCHj2rg1U6o57w3SrKM8mQXkCJKB1O Ic4+MpKvyipG0PiJPd657LJEaSVWzeB8oSjfO5cWE3SCfIRSgsP5O5BFNKaqVKZPQ+RUa1RaS PQDo4QgStIwO/jlRP4aksTor5MC/jS7OIQP9J2tdx6MKpx9FfMqMs+D8GiP1Rtdl0ePhoy/x6 +ckB63djF/sFyVu8ZigMv+QzApQxDTkiPD/PGdgP45aEx+JhwYLP2TCKYGBAIjmKhW1YDEeWe sXURoeLmTECikfD8Y+0jY3pXO8/lE3fweM/D92mmeo51pKQnFMbsjYIyiQaH0EmiNnyf7nfp6 R6rrSeASOlto0Je+JWYfHSiBkiHlhTOX0RoBQFCB7mvbGc9HDZ/LELyxpAiocddtaNUaKkPt7 bxWDXq0bCDZLdOK1sGL7ogXhBApaaFOQNeU4HdtR0Ny20rYo7Zo7V+PnQwXOT2hVZKTI= Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Traditionally, we have always had warnings about uninitialized variables enabled, as this is part of -Wall, and generally a good idea [1], but it also always produced false positives, mainly because this is a variation of the halting problem and provably impossible to get right in all cases [2]. Various people have identified cases that are particularly bad for false positives, and in commit e74fc973b6e5 ("Turn off -Wmaybe-uninitialized when building with -Os"), I turned off the warning for any build that was done with CC_OPTIMIZE_FOR_SIZE. This drastically reduced the number of false positive warnings in the default build but unfortunately had the side effect of turning the warning off completely in 'allmodconfig' builds, which in turn led to a lot of warnings (both actual bugs, and remaining false positives) to go in unnoticed. With commit 877417e6ffb9 ("Kbuild: change CC_OPTIMIZE_FOR_SIZE definition") enabled the warning again for allmodconfig builds in v4.7 and in v4.8-rc1, I had finally managed to address all warnings I get in an ARM allmodconfig build and most other maybe-uninitialized warnings for ARM randconfig builds. However, commit 6e8d666e9253 ("Disable "maybe-uninitialized" warning globally") was merged at the same time and disabled it completely for all configurations, because of false-positive warnings on x86 that I had not addressed until then. This caused a lot of actual bugs to get merged into mainline, and I sent several dozen patches for these during the v4.9 development cycle. Most of these are actual bugs, some are for correct code that is safe because it is only called under external constraints that make it impossible to run into the case that gcc sees, and in a few cases gcc is just stupid and finds something that can obviously never happen. I have now done a few thousand randconfig builds on x86 and collected all patches that I needed to address every single warning I got (I can provide the combined patch for the other warnings if anyone is interested), so I hope we can get the warning back and let people catch the actual bugs earlier. This reverts the change to disable the warning completely and for now brings it back at the "make W=1" level, so we can get it merged into mainline without introducing false positives. A follow-up patch enables it on all levels unless some configuration option turns it off because of false-positives. Link: https://rusty.ozlabs.org/?p=232 [1] Link: https://gcc.gnu.org/wiki/Better_Uninitialized_Warnings [2] Signed-off-by: Arnd Bergmann --- Makefile | 10 ++++++---- arch/arc/Makefile | 4 +++- scripts/Makefile.extrawarn | 3 +++ scripts/Makefile.ubsan | 4 ++++ 4 files changed, 16 insertions(+), 5 deletions(-) diff --git a/Makefile b/Makefile index f97f786..06e2b73 100644 --- a/Makefile +++ b/Makefile @@ -370,7 +370,7 @@ LDFLAGS_MODULE = CFLAGS_KERNEL = AFLAGS_KERNEL = LDFLAGS_vmlinux = -CFLAGS_GCOV = -fprofile-arcs -ftest-coverage -fno-tree-loop-im +CFLAGS_GCOV = -fprofile-arcs -ftest-coverage -fno-tree-loop-im -Wno-maybe-uninitialized CFLAGS_KCOV := $(call cc-option,-fsanitize-coverage=trace-pc,) @@ -620,7 +620,6 @@ ARCH_CFLAGS := include arch/$(SRCARCH)/Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) -KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,) KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,) ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION @@ -629,15 +628,18 @@ KBUILD_CFLAGS += $(call cc-option,-fdata-sections,) endif ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE -KBUILD_CFLAGS += -Os +KBUILD_CFLAGS += -Os $(call cc-disable-warning,maybe-uninitialized,) else ifdef CONFIG_PROFILE_ALL_BRANCHES -KBUILD_CFLAGS += -O2 +KBUILD_CFLAGS += -O2 $(call cc-disable-warning,maybe-uninitialized,) else KBUILD_CFLAGS += -O2 endif endif +KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0409, \ + $(call cc-disable-warning,maybe-uninitialized,)) + # Tell gcc to never replace conditional load with a non-conditional one KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0) diff --git a/arch/arc/Makefile b/arch/arc/Makefile index 864adad..25f81a1 100644 --- a/arch/arc/Makefile +++ b/arch/arc/Makefile @@ -68,7 +68,9 @@ cflags-$(CONFIG_ARC_DW2_UNWIND) += -fasynchronous-unwind-tables $(cfi) ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE # Generic build system uses -O2, we want -O3 # Note: No need to add to cflags-y as that happens anyways -ARCH_CFLAGS += -O3 +# +# Disable the false maybe-uninitialized warings gcc spits out at -O3 +ARCH_CFLAGS += -O3 $(call cc-disable-warning,maybe-uninitialized,) endif # small data is default for elf32 tool-chain. If not usable, disable it diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 53449a6..7fc2c5a 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -36,6 +36,7 @@ warning-2 += -Wshadow warning-2 += $(call cc-option, -Wlogical-op) warning-2 += $(call cc-option, -Wmissing-field-initializers) warning-2 += $(call cc-option, -Wsign-compare) +warning-2 += $(call cc-option, -Wmaybe-uninitialized) warning-3 := -Wbad-function-cast warning-3 += -Wcast-qual @@ -59,6 +60,8 @@ endif KBUILD_CFLAGS += $(warning) else +KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized) + ifeq ($(cc-name),clang) KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides) KBUILD_CFLAGS += $(call cc-disable-warning, unused-value) diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan index dd779c4..3b1b138 100644 --- a/scripts/Makefile.ubsan +++ b/scripts/Makefile.ubsan @@ -17,4 +17,8 @@ endif ifdef CONFIG_UBSAN_NULL CFLAGS_UBSAN += $(call cc-option, -fsanitize=null) endif + + # -fsanitize=* options makes GCC less smart than usual and + # increase number of 'maybe-uninitialized false-positives + CFLAGS_UBSAN += $(call cc-option, -Wno-maybe-uninitialized) endif