From patchwork Wed Mar 30 23:45:27 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nathan Chancellor X-Patchwork-Id: 12796521 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 13CF8C433FE for ; Wed, 30 Mar 2022 23:46:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233332AbiC3Xr4 (ORCPT ); Wed, 30 Mar 2022 19:47:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57712 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351881AbiC3Xrx (ORCPT ); Wed, 30 Mar 2022 19:47:53 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4BCB962A38; Wed, 30 Mar 2022 16:46:07 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E703C61835; Wed, 30 Mar 2022 23:46:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B30F2C340EC; Wed, 30 Mar 2022 23:46:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648683966; bh=uKYOWCNiJwOEjCoRKb6g6YV42LmzgDRTIg6qPpnEHkY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=I3vHdiBi0jcpYheTDatiqR+gw+80pR/T/bIjzUWsbIFZfntE99R4wqw+EEkey6SLh eS/Rv6beB7qtmqyZIspDp/SaXLgZCKWuK5U48fuhITXQtARsGCjfOzfkfl9V2wIIp8 fFROFTaPbz6m/pZaall+y5vz3kKlCc+OIDYFgxUtKmqyHlLW1XwEFNaM44q698VXVe nkXFaIqTJnmoNavy1ooUs/oXG899cpFcrn0Mei8mT8QUknWX0zA8lXW4y5DK242prO ZmVQVzyaeugF0wsxdMn9DCVfqvGl0mPOpA9iC8j6NT5nawL3yr2zMU5ytyml7l0P8B ItO1C8b5uu5yA== From: Nathan Chancellor To: Masahiro Yamada , Nick Desaulniers , Richard Weinberger , Anton Ivanov , Johannes Berg , Kees Cook Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-um@lists.infradead.org, llvm@lists.linux.dev, patches@lists.linux.dev, Nathan Chancellor Subject: [PATCH 1/2] kbuild: Remove '-mno-global-merge' Date: Wed, 30 Mar 2022 16:45:27 -0700 Message-Id: <20220330234528.1426991-2-nathan@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220330234528.1426991-1-nathan@kernel.org> References: <20220330234528.1426991-1-nathan@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org This flag is specific to clang, where it is only used by the 32-bit and 64-bit ARM backends. In certain situations, the presence of this flag will cause a warning, as shown by commit 6580c5c18fb3 ("um: clang: Strip out -mno-global-merge from USER_CFLAGS"). Since commit 61163efae020 ("kbuild: LLVMLinux: Add Kbuild support for building kernel with Clang") that added this flag back in 2014, there have been quite a few changes to the GlobalMerge pass in LLVM. Building several different ARCH=arm and ARCH=arm64 configurations with LLVM 11 (minimum) and 15 (current main version) with this flag removed (i.e., with the default of '-mglobal-merge') reveals no modpost warnings, so it is likely that the issue noted in the comment is no longer relevant due to changes in LLVM or modpost, meaning this flag can be removed. If any new warnings show up that are a result of the removal of this flag, it can be added back under arch/arm{,64}/Makefile to avoid warnings on other architectures. Signed-off-by: Nathan Chancellor Tested-by: David Gow Reviewed-by: Kees Cook Tested-by: Sedat Dilek Reviewed-by: Sedat Dilek --- Makefile | 4 ---- 1 file changed, 4 deletions(-) diff --git a/Makefile b/Makefile index daeb5c88b50b..f2723d9bfca4 100644 --- a/Makefile +++ b/Makefile @@ -784,10 +784,6 @@ ifdef CONFIG_CC_IS_CLANG KBUILD_CPPFLAGS += -Qunused-arguments # The kernel builds with '-std=gnu89' so use of GNU extensions is acceptable. KBUILD_CFLAGS += -Wno-gnu -# CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the -# source of a reference will be _MergedGlobals and not on of the whitelisted names. -# See modpost pattern 2 -KBUILD_CFLAGS += -mno-global-merge else # gcc inanely warns about local variables called 'main'