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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS 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 EACC4C5CFC1 for ; Fri, 15 Jun 2018 21:14:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9FBB120896 for ; Fri, 15 Jun 2018 21:14:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="DWxHaA5q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9FBB120896 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756603AbeFOVOo (ORCPT ); Fri, 15 Jun 2018 17:14:44 -0400 Received: from mail-pl0-f47.google.com ([209.85.160.47]:45186 "EHLO mail-pl0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756413AbeFOVOn (ORCPT ); Fri, 15 Jun 2018 17:14:43 -0400 Received: by mail-pl0-f47.google.com with SMTP id c23-v6so5939157plz.12 for ; Fri, 15 Jun 2018 14:14:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:mime-version:content-disposition :user-agent; bh=nx+suhTWrHqLTNae2xA9goxO9ZBD40sNvaYA30usqxI=; b=DWxHaA5qOtXskzWbhlXcb363CTyo/jIPnWhSLXfBndAOsLrInQQXOHH+yMA8XZF9g8 ZYMC6YJcKYiZvwJk80JwoC6mu0VrM6/UB/Tp2VbeIxVBC9M3EMGJWXyDMiDaYSyqcM9T NuUXwvXp33FqYyFiYbERG8bXe40ODrhjN4Jy0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:mime-version :content-disposition:user-agent; bh=nx+suhTWrHqLTNae2xA9goxO9ZBD40sNvaYA30usqxI=; b=ImoGEwqsNNB4Y3GkqfwFM7pug1Fvgoq/BGkhIPGNMySjNBXyGiPmUZXjZtgHmtYXVe SJ0/676Vki2EVBUmwxgZL3F0aQA7sVUknZ/TmZMlev4s7kCJkhM1iQBe1GXqCz4EC4E/ sZrZ30zHL4RegYV+aEna26wGHEIInnJsagfXqeVKCu5uM8+j8QfehTXvo4FikYyU/PFO mdYlWyN4VKd34tAt0jIldISPY6V1i7K/8uzCDbLzdVhzudBUPKYLeH7C1ofu6JPDe3+T 8gJ8SEGioU0dZyrq/uLPQ73v7aF3dAeFBHz873eElMfzKbDCthM5/KtmbQ0PCy9swr1Z PXLw== X-Gm-Message-State: APt69E2uNHpx0/4qU7z/2iI2v/RqfBUUZeLC+j07v7HablnavIFDZUjT KBzzVYZ3gwzN59i6KSWkndH7qA== X-Google-Smtp-Source: ADUXVKITzgPPB/u3tfnF4wRyoMP12iuL+6Fg5QHd3mz4OZl+nt+9LWwLpX7ByuPNXGr7LLrcZNC9IQ== X-Received: by 2002:a17:902:7806:: with SMTP id p6-v6mr3821911pll.17.1529097283111; Fri, 15 Jun 2018 14:14:43 -0700 (PDT) Received: from localhost ([2620:0:1000:1501:8e2d:4727:1211:622]) by smtp.gmail.com with ESMTPSA id q8-v6sm20259044pfi.96.2018.06.15.14.14.42 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 15 Jun 2018 14:14:42 -0700 (PDT) Date: Fri, 15 Jun 2018 14:14:41 -0700 From: Matthias Kaehlcke To: Josh Poimboeuf Cc: linux-kernel@vger.kernel.org, Manoj Gupta , Nick Desaulniers Subject: clang: objtool: native_machine_emergency_restart() falls through to next function Message-ID: <20180615211441.GO88063@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Josh, with your work on objtool and the upcoming implementation of -fno-delete-null-pointer-checks (https://reviews.llvm.org/D47894, https://reviews.llvm.org/D47895) in clang most objtool warnings for clang builds will be fixed. However even with -fno-delete-null-pointer-checks we currently still get a warning about native_machine_emergency_restart(): arch/x86/kernel/reboot.o: warning: objtool: native_machine_emergency_restart() falls through to next function machine_power_off() This only occurs when building with -Oz. One of our compiler engineers looked into this, LLVM optimizes the return statement away since the function has an endless loop, and actually never returns. Is there a way to tell objtool that the function is not expected to return (I tried the attribute __noreturn, but it doesn't make a difference), or do we have to tell clang to restrain from optimizing returns out? To repro: git checkout v4.16 make CC=clang defconfig echo "CONFIG_CC_OPTIMIZE_FOR_SIZE=y" >> .config make CC=clang arch/x86/kernel/reboot.o Thanks Matthias