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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 4AEAEC5B57D for ; Wed, 3 Jul 2019 01:00:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A1532089C for ; Wed, 3 Jul 2019 01:00:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727452AbfGCBAg (ORCPT ); Tue, 2 Jul 2019 21:00:36 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:49758 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726635AbfGCBAd (ORCPT ); Tue, 2 Jul 2019 21:00:33 -0400 Received: from pd9ef1cb8.dip0.t-ipconnect.de ([217.239.28.184] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hiQnE-0008F2-DZ; Tue, 02 Jul 2019 23:58:28 +0200 Date: Tue, 2 Jul 2019 23:58:27 +0200 (CEST) From: Thomas Gleixner To: Nick Desaulniers cc: Peter Zijlstra , Josh Poimboeuf , clang-built-linux , Kees Cook , LKML , Craig Topper , Alexander Potapenko , Bill Wendling , Stephen Hines Subject: Re: objtool warnings in prerelease clang-9 In-Reply-To: Message-ID: References: User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Nick, On Tue, 2 Jul 2019, Nick Desaulniers wrote: > TL;DR > LLVM currently has a bug when unrolling loops containing asm goto and > we have a fix in hand. > > Conservatively, we can block loop unrolling when we see asm goto in a loop: Makes sense in order to make progress. > This causes objtool to not find any issues in > arch/x86/kernel/cpu/mtrr/generic.o. I don't observe any duplication > in the __jump_table section of the resulting .o file. It also cuts > down the objtool warnings I observe in a defconfig (listed at the > beginning of the email) from 4 to 2. (platform-quirks.o predates asm > goto, It does not have asm goto inside :) > i915_gem_execbuffer.o is likely a separate bug). platform-quirks.o: if (x86_platform.set_legacy_features) 74: 4c 8b 1d 00 00 00 00 mov 0x0(%rip),%r11 # 7b 7b: 4d 85 db test %r11,%r11 7e: 0f 85 00 00 00 00 jne 84 x86_platform.set_legacy_features(); } 84: c3 retq That jne jumps to __x86_indirect_thunk_r11, aka. ratpoutine. No idea why objtool thinks that the instruction at 0x84 is not reachable. Josh? Thanks, tglx