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=-9.7 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 C8DD5C3A5A1 for ; Wed, 28 Aug 2019 05:55:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 910E7217F5 for ; Wed, 28 Aug 2019 05:55:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nifty.com header.i=@nifty.com header.b="kIYIbU4A" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726271AbfH1Fzr (ORCPT ); Wed, 28 Aug 2019 01:55:47 -0400 Received: from conuserg-07.nifty.com ([210.131.2.74]:41721 "EHLO conuserg-07.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725959AbfH1Fzr (ORCPT ); Wed, 28 Aug 2019 01:55:47 -0400 Received: from localhost.localdomain (p14092-ipngnfx01kyoto.kyoto.ocn.ne.jp [153.142.97.92]) (authenticated) by conuserg-07.nifty.com with ESMTP id x7S5sQl2027215; Wed, 28 Aug 2019 14:54:27 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conuserg-07.nifty.com x7S5sQl2027215 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1566971668; bh=qJTg+AM4SVuAt9eaitUPepAhylXNc0xd+RxSAWBzAtU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kIYIbU4AbUD9farUf9eBzCAwYeQBzv+AHzrT/s/jZzazBkLlCimwBpkOX3TnC4FKh fIixvoywpVrCh1ZGv4x6EpYWUtm7ICQuIlvDhSRZp3SeYN824z0VVpVKNsEfjZpOnm +0O80CMd1F7YEREygkWtN+GESpCkcx6fJOxSf8JvJMG03qZORVXArkaiJW3kotqgyM ZhjtDXHNXdnw/1Z6iZKZ/0sIIosoyX+8dd2+f2KMn6Eh5pDYtYrw/albHLiC1RyoC2 VRVA6THt4ZOlOyl03q/T0xknxIjCjnz3NAROjIHB8McQbuKpgYbkE3LpxJ8bcZGAwZ HduYVIGixbcpg== X-Nifty-SrcIP: [153.142.97.92] From: Masahiro Yamada To: linux-kbuild@vger.kernel.org Cc: Nick Desaulniers , Nathan Chancellor , Miguel Ojeda , Arnd Bergmann , Masahiro Yamada , Kees Cook , Luc Van Oostenryck , Michal Marek , Sven Schnelle , Xiaozhou Liu , clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org Subject: [PATCH 2/2] kbuild: allow Clang to find unused static inline functions for W=1 build Date: Wed, 28 Aug 2019 14:54:25 +0900 Message-Id: <20190828055425.24765-2-yamada.masahiro@socionext.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190828055425.24765-1-yamada.masahiro@socionext.com> References: <20190828055425.24765-1-yamada.masahiro@socionext.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org GCC and Clang have different policy for -Wunused-function; GCC does not warn unused static inline functions at all whereas Clang does if they are defined in source files instead of included headers although it has been suppressed since commit abb2ea7dfd82 ("compiler, clang: suppress warning for unused static inline functions"). We often miss to delete unused functions where 'static inline' is used in *.c files since there is no tool to detect them. Unused code remains until somebody notices. For example, commit 075ddd75680f ("regulator: core: remove unused rdev_get_supply()"). Let's remove __maybe_unused from the inline macro to allow Clang to start finding unused static inline functions. For now, we do this only for W=1 build since it is not a good idea to sprinkle warnings for the normal build. My initial attempt was to add -Wno-unused-function for no W=1 build (https://lore.kernel.org/patchwork/patch/1120594/) Nathan Chancellor pointed out that would weaken Clang's checks since we would no longer get -Wunused-function without W=1. It is true GCC would detect unused static non-inline functions, but it would weaken Clang as a standalone compiler at least. Here is a counter implementation. The current problem is, W=... only controls compiler flags, which are globally effective. There is no way to narrow the scope to only 'static inline' functions. This commit defines KBUILD_EXTRA_WARN[123] corresponding to W=[123]. When KBUILD_EXTRA_WARN1 is defined, __maybe_unused is omitted from the 'inline' macro. This makes the code a bit uglier, so personally I do not want to carry this forever. If we can manage to fix most of the warnings, we can drop this entirely, then enable -Wunused-function all the time. If you contribute to code clean-up, please run "make CC=clang W=1" and check -Wunused-function warnings. You will find lots of unused functions. Some of them are false-positives because the call-sites are disabled by #ifdef. I do not like to abuse the inline keyword for suppressing unused-function warnings because it is intended to be a hint for the compiler optimization. I prefer #ifdef around the definition, or __maybe_unused if #ifdef would make the code too ugly. Signed-off-by: Masahiro Yamada --- include/linux/compiler_types.h | 20 ++++++++++++++------ scripts/Makefile.extrawarn | 6 ++++++ 2 files changed, 20 insertions(+), 6 deletions(-) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 599c27b56c29..b056a40116da 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -130,10 +130,6 @@ struct ftrace_likely_data { /* * Force always-inline if the user requests it so via the .config. - * GCC does not warn about unused static inline functions for - * -Wunused-function. This turns out to avoid the need for complex #ifdef - * directives. Suppress the warning in clang as well by using "unused" - * function attribute, which is redundant but not harmful for gcc. * Prefer gnu_inline, so that extern inline functions do not emit an * externally visible function. This makes extern inline behave as per gnu89 * semantics rather than c99. This prevents multiple symbol definition errors @@ -144,15 +140,27 @@ struct ftrace_likely_data { */ #if !defined(CONFIG_OPTIMIZE_INLINING) #define inline inline __attribute__((__always_inline__)) __gnu_inline \ - __maybe_unused notrace + __inline_maybe_unused notrace #else #define inline inline __gnu_inline \ - __maybe_unused notrace + __inline_maybe_unused notrace #endif #define __inline__ inline #define __inline inline +/* + * GCC does not warn about unused static inline functions for -Wunused-function. + * Suppress the warning in clang as well by using __maybe_unused, but enable it + * for W=1 build. This will allow clang to find unused functions. Remove the + * __inline_maybe_unused entirely after fixing most of -Wunused-function warnings. + */ +#ifdef KBUILD_EXTRA_WARN1 +#define __inline_maybe_unused +#else +#define __inline_maybe_unused __maybe_unused +#endif + /* * Rather then using noinline to prevent stack consumption, use * noinline_for_stack instead. For documentation reasons. diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 1fa53968e292..3af1770497fd 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -28,6 +28,8 @@ KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation) KBUILD_CFLAGS += -Wno-missing-field-initializers KBUILD_CFLAGS += -Wno-sign-compare +KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 + else # W=1 also stops suppressing some warnings @@ -56,6 +58,8 @@ KBUILD_CFLAGS += -Wsign-compare KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized) KBUILD_CFLAGS += $(call cc-option, -Wunused-macros) +KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2 + endif # @@ -73,4 +77,6 @@ KBUILD_CFLAGS += -Wredundant-decls KBUILD_CFLAGS += -Wswitch-default KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat) +KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3 + endif -- 2.17.1