From patchwork Fri Apr 8 16:21:56 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Josh Poimboeuf X-Patchwork-Id: 12806953 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0813C433F5 for ; Fri, 8 Apr 2022 16:23:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230263AbiDHQZJ (ORCPT ); Fri, 8 Apr 2022 12:25:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44134 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230241AbiDHQZI (ORCPT ); Fri, 8 Apr 2022 12:25:08 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E780510BBF0 for ; Fri, 8 Apr 2022 09:23:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1649434983; 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; bh=ofocLwjgfrlRUiguKE9lsikbmfnw6N1ZVOog+yoEC3o=; b=V+zdEZM3ghE3q/9vuO2IO7hz6ffSj0W6FAwVwlrMzEh1Wim8k11xNS1Tq/TJayMhaymGkM KWKnY0tyzCBmyx4ZXG+3rb7XCsnkMAT8XSv31lxg/GiOicO9Nh4Riv1+7dtFAXbmHu7Y0G 7GPlFJa1F/QW29r49I6mHDfZ1Vfuw/U= Received: from mail-qt1-f198.google.com (mail-qt1-f198.google.com [209.85.160.198]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-548-FvbM32m2NeuvlX6CLa1BFA-1; Fri, 08 Apr 2022 12:23:02 -0400 X-MC-Unique: FvbM32m2NeuvlX6CLa1BFA-1 Received: by mail-qt1-f198.google.com with SMTP id cb16-20020a05622a1f9000b002ebce74a888so4078290qtb.15 for ; Fri, 08 Apr 2022 09:23:02 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=ofocLwjgfrlRUiguKE9lsikbmfnw6N1ZVOog+yoEC3o=; b=IrabeBtKAnaTaiECTZtu6bMh2EqF8H/XNSem/Fa2v9RLDJ4hqRIqtbqLkC2m3TvKj+ 92YllxHjpMwg4MF8bvQjGvr3GIVUw5RlNPUcsZCr/gIRUEG7A09usD1URfzkvYadxMAD PfW8KJ2sgsvo36yzn+hFYKBLr+cl9vU5v3eg+asE/obz4S1xj7+WVCppmk31YhEsOuB1 c1FoG8fDuAc+4qCvvZs1jHrR4FJ20D+/wvy30J7pawblsPdqzNsKoZCnKLXmQeEfV+Yj i+4rW3Hqlfs5SvA7tDrDfmdPw24LA8r7nuaNf3icNaYfLoe9K1KZzST5IktGiYzdONWG O61Q== X-Gm-Message-State: AOAM531PofLPEMrSpXIH8j/UANmXn5VHkz0Bp1o6YFz81rOuqQJ5B8nr pO0Z9DJsr81xLFevNfRK93PbjYYWd7r+fpYy4mYTXQp3PTmk5aTmRr5oRUTOieZZE6eZXeX4Ini g7oFEyUgl3X4mcWsPXtDzn4y7 X-Received: by 2002:a05:6214:2622:b0:444:1b35:b6a5 with SMTP id gv2-20020a056214262200b004441b35b6a5mr4717030qvb.102.1649434981138; Fri, 08 Apr 2022 09:23:01 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxIM9ayM7bF8aYO2zn3Ghsa6P4/1Q2tP2xWbGcFH5vNeM8F875g1oDKNWu3MONplVRltPS00g== X-Received: by 2002:a05:6214:2622:b0:444:1b35:b6a5 with SMTP id gv2-20020a056214262200b004441b35b6a5mr4717017qvb.102.1649434980810; Fri, 08 Apr 2022 09:23:00 -0700 (PDT) Received: from treble.attlocal.net ([2600:1700:6e32:6c00::15]) by smtp.gmail.com with ESMTPSA id v7-20020ac85787000000b002e1c8376517sm17629692qta.22.2022.04.08.09.22.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Apr 2022 09:23:00 -0700 (PDT) From: Josh Poimboeuf To: Masahiro Yamada , Michal Marek , Nick Desaulniers Cc: linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, Peter Zijlstra , Sam Ravnborg , x86@kernel.org Subject: [PATCH] kbuild: Remove CONFIG_DEBUG_SECTION_MISMATCH Date: Fri, 8 Apr 2022 09:21:56 -0700 Message-Id: <7fad83ecde03540e65677959034315f8fbb3755e.1649434832.git.jpoimboe@redhat.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org Modpost's section mismatch detection warns when a non-init function references an __init function or __initdata. Those warnings are very useful, because __init memory is freed during boot, so the non-init function might end up referencing or calling into some random memory. CONFIG_DEBUG_SECTION_MISMATCH is intended to root out even more of these issues by adding the -fno-inline-functions-called-once compiler flag, which forces once-called static functions to not be inlined. As described in the option's help description: - Add the option -fno-inline-functions-called-once to gcc commands. When inlining a function annotated with __init in a non-init function, we would lose the section information and thus the analysis would not catch the illegal reference. This option tells gcc to inline less (but it does result in a larger kernel). So it's basically a debug (non-production) option, which has the goal of rooting out potential issues which might exist on *other* configs which might somehow trigger different inlining decisions, without having to build all those other configs to see the warnings directly. But with -O2, once-called static functions are almost always inlined, so its usefulness for rooting out mismatch warnings on other configs is somewhere between extremely limited and non-existent. And nowadays we have build bots everywhere doing randconfigs continuously, which are great for rooting out such edge cases. Somewhat ironically, the existence of those build bots means we get a lot of unrealistic objtool warnings being reported, due to unrealistic inlines caused by CONFIG_DEBUG_SECTION_MISMATCH, where the only way to silence the warnings is to force a single-called function to be inlined with '__always_inline'. So the limited, hypothetical benefit of "rooting out configs with section mismatches" is outweighed by the very real downside of "adding lots of unnecessary '__always_inline' annotations". In fact I suspect this option has been responsible for dozens of "convert inline to __always_inline" patches over the years. Such patches usually complain about the compiler's inlining decisions being unpredictable. It turns out this config option is the main culprit. So considering the drawbacks of this option significantly outweigh the benefits, especially now in the age of randconfig build bots, remove it. Signed-off-by: Josh Poimboeuf --- .../media/maintainer-entry-profile.rst | 2 +- Makefile | 5 ----- arch/arc/configs/tb10x_defconfig | 1 - arch/s390/configs/debug_defconfig | 1 - arch/s390/configs/defconfig | 1 - kernel/configs/debug.config | 1 - lib/Kconfig.debug | 22 ------------------- .../selftests/wireguard/qemu/debug.config | 1 - 8 files changed, 1 insertion(+), 33 deletions(-) diff --git a/Documentation/driver-api/media/maintainer-entry-profile.rst b/Documentation/driver-api/media/maintainer-entry-profile.rst index ffc712a5f632..06106d7e7fae 100644 --- a/Documentation/driver-api/media/maintainer-entry-profile.rst +++ b/Documentation/driver-api/media/maintainer-entry-profile.rst @@ -123,7 +123,7 @@ Those tests need to pass before the patches go upstream. Also, please notice that we build the Kernel with:: - make CF=-D__CHECK_ENDIAN__ CONFIG_DEBUG_SECTION_MISMATCH=y C=1 W=1 CHECK=check_script + make CF=-D__CHECK_ENDIAN__ C=1 W=1 CHECK=check_script Where the check script is:: diff --git a/Makefile b/Makefile index 8c7de9a72ea2..3d7ea1a23558 100644 --- a/Makefile +++ b/Makefile @@ -871,11 +871,6 @@ KBUILD_CFLAGS += $(CC_FLAGS_FTRACE) $(CC_FLAGS_USING) KBUILD_AFLAGS += $(CC_FLAGS_USING) endif -# We trigger additional mismatches with less inlining -ifdef CONFIG_DEBUG_SECTION_MISMATCH -KBUILD_CFLAGS += -fno-inline-functions-called-once -endif - ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION KBUILD_CFLAGS_KERNEL += -ffunction-sections -fdata-sections LDFLAGS_vmlinux += --gc-sections diff --git a/arch/arc/configs/tb10x_defconfig b/arch/arc/configs/tb10x_defconfig index a12656ec0072..5acf8cc3e7b0 100644 --- a/arch/arc/configs/tb10x_defconfig +++ b/arch/arc/configs/tb10x_defconfig @@ -96,7 +96,6 @@ CONFIG_STRIP_ASM_SYMS=y CONFIG_DEBUG_FS=y CONFIG_HEADERS_INSTALL=y CONFIG_HEADERS_CHECK=y -CONFIG_DEBUG_SECTION_MISMATCH=y CONFIG_MAGIC_SYSRQ=y CONFIG_DEBUG_MEMORY_INIT=y CONFIG_DEBUG_STACKOVERFLOW=y diff --git a/arch/s390/configs/debug_defconfig b/arch/s390/configs/debug_defconfig index 498bed9b261b..66a4c65a4bd8 100644 --- a/arch/s390/configs/debug_defconfig +++ b/arch/s390/configs/debug_defconfig @@ -791,7 +791,6 @@ CONFIG_DEBUG_INFO_DWARF4=y CONFIG_DEBUG_INFO_BTF=y CONFIG_GDB_SCRIPTS=y CONFIG_HEADERS_INSTALL=y -CONFIG_DEBUG_SECTION_MISMATCH=y CONFIG_MAGIC_SYSRQ=y CONFIG_DEBUG_PAGEALLOC=y CONFIG_PAGE_OWNER=y diff --git a/arch/s390/configs/defconfig b/arch/s390/configs/defconfig index 61e36b999f67..0e6ae36cf401 100644 --- a/arch/s390/configs/defconfig +++ b/arch/s390/configs/defconfig @@ -776,7 +776,6 @@ CONFIG_DEBUG_INFO=y CONFIG_DEBUG_INFO_DWARF4=y CONFIG_DEBUG_INFO_BTF=y CONFIG_GDB_SCRIPTS=y -CONFIG_DEBUG_SECTION_MISMATCH=y CONFIG_MAGIC_SYSRQ=y CONFIG_DEBUG_WX=y CONFIG_PTDUMP_DEBUGFS=y diff --git a/kernel/configs/debug.config b/kernel/configs/debug.config index e8db8d938661..0c1a5d64febb 100644 --- a/kernel/configs/debug.config +++ b/kernel/configs/debug.config @@ -18,7 +18,6 @@ CONFIG_SYMBOLIC_ERRNAME=y # CONFIG_DEBUG_INFO=y CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y -CONFIG_DEBUG_SECTION_MISMATCH=y CONFIG_FRAME_WARN=2048 CONFIG_SECTION_MISMATCH_WARN_ONLY=y # diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 075cd25363ac..e52f851e9e3b 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -425,28 +425,6 @@ config HEADERS_INSTALL user-space program samples. It is also needed by some features such as uapi header sanity checks. -config DEBUG_SECTION_MISMATCH - bool "Enable full Section mismatch analysis" - depends on CC_IS_GCC - help - The section mismatch analysis checks if there are illegal - references from one section to another section. - During linktime or runtime, some sections are dropped; - any use of code/data previously in these sections would - most likely result in an oops. - In the code, functions and variables are annotated with - __init,, etc. (see the full list in include/linux/init.h), - which results in the code/data being placed in specific sections. - The section mismatch analysis is always performed after a full - kernel build, and enabling this option causes the following - additional step to occur: - - Add the option -fno-inline-functions-called-once to gcc commands. - When inlining a function annotated with __init in a non-init - function, we would lose the section information and thus - the analysis would not catch the illegal reference. - This option tells gcc to inline less (but it does result in - a larger kernel). - config SECTION_MISMATCH_WARN_ONLY bool "Make section mismatch errors non-fatal" default y diff --git a/tools/testing/selftests/wireguard/qemu/debug.config b/tools/testing/selftests/wireguard/qemu/debug.config index 2b321b8a96cf..e737ce3b324e 100644 --- a/tools/testing/selftests/wireguard/qemu/debug.config +++ b/tools/testing/selftests/wireguard/qemu/debug.config @@ -57,7 +57,6 @@ CONFIG_USER_STACKTRACE_SUPPORT=y CONFIG_DEBUG_SG=y CONFIG_DEBUG_NOTIFIERS=y CONFIG_X86_DEBUG_FPU=y -CONFIG_DEBUG_SECTION_MISMATCH=y CONFIG_DEBUG_PAGEALLOC=y CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT=y CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y