From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751854AbcCWVLI (ORCPT ); Wed, 23 Mar 2016 17:11:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56202 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751447AbcCWVLG (ORCPT ); Wed, 23 Mar 2016 17:11:06 -0400 Date: Wed, 23 Mar 2016 16:11:04 -0500 From: Josh Poimboeuf To: kbuild test robot Cc: kbuild-all@01.org, linux-kernel@vger.kernel.org, Ingo Molnar Subject: Re: drivers/target/iscsi/iscsi_target.o: warning: objtool: iscsit_handle_task_mgt_cmd()+0xbcb: function has unreachable instruction Message-ID: <20160323211104.akrzp4n2a32anfc3@treble.redhat.com> References: <201603231906.LWcVUpxm%fengguang.wu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <201603231906.LWcVUpxm%fengguang.wu@intel.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 23, 2016 at 07:15:08PM +0800, kbuild test robot wrote: > tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > head: a24e3d414e59ac76566dedcad1ed1d319a93ec14 > commit: d4883d5d6b146fd65f762c462b2c6d4a327c7d50 objtool: Enable stack metadata validation on 64-bit x86 > date: 3 weeks ago > config: x86_64-randconfig-x014-03231738 (attached as .config) > reproduce: > git checkout d4883d5d6b146fd65f762c462b2c6d4a327c7d50 > # save the attached .config to linux build tree > make ARCH=x86_64 > > All warnings (new ones prefixed by >>): > > >> drivers/target/iscsi/iscsi_target.o: warning: objtool: iscsit_handle_task_mgt_cmd()+0xbcb: function has unreachable instruction Ingo, FYI, I'm aware of this issue but I'm not yet sure about the best way to fix it. I'll be on vacation next week but will try to get to it in a couple of weeks. It only seems to manifest itself in certain randconfigs which include CONFIG_PROFILE_ALL_BRANCHES=y. more details: The issue is caused by a sloppy gcc optimization. It looks like gcc created a jump table for a switch statement, but then decided not to use it, and failed to clean up its mess. So it 10094: ff 25 00 00 00 00 jmpq *0x0(%rip) # 1009a 10096: R_X86_64_PC32 .rodata+0x3c There's no -- Josh