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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8EB2AC43334 for ; Thu, 30 Jun 2022 16:07:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235827AbiF3QHc (ORCPT ); Thu, 30 Jun 2022 12:07:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44314 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235595AbiF3QHX (ORCPT ); Thu, 30 Jun 2022 12:07:23 -0400 Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id D5A7D1AF0F for ; Thu, 30 Jun 2022 09:07:18 -0700 (PDT) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 25UFwEc4007186; Thu, 30 Jun 2022 10:58:14 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 25UFwBWR007180; Thu, 30 Jun 2022 10:58:11 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Thu, 30 Jun 2022 10:58:11 -0500 From: Segher Boessenkool To: "Naveen N. Rao" Cc: Christophe Leroy , "linuxppc-dev@lists.ozlabs.org" , Sathvika Vasireddy , Sathvika Vasireddy , Marc Zyngier , "aik@ozlabs.ru" , "linux-kernel@vger.kernel.org" , "rostedt@goodmis.org" , "peterz@infradead.org" , "mingo@redhat.com" , "paulus@samba.org" , "jpoimboe@redhat.com" , "mbenes@suse.cz" , Chen Zhongjin , Linux ARM Subject: Re: [RFC PATCH v3 11/12] powerpc: Remove unreachable() from WARN_ON() Message-ID: <20220630155811.GK25951@gate.crashing.org> References: <20220624183238.388144-1-sv@linux.ibm.com> <20220624183238.388144-12-sv@linux.ibm.com> <70b6d08d-aced-7f4e-b958-a3c7ae1a9319@csgroup.eu> <92eae2ef-f9b6-019a-5a8e-728cdd9bbbc0@linux.vnet.ibm.com> <1656572413.pbaqjnrrcl.naveen@linux.ibm.com> <1656583960.0nqsj977sr.naveen@linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1656583960.0nqsj977sr.naveen@linux.ibm.com> User-Agent: Mutt/1.4.2.3i Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 30, 2022 at 04:07:47PM +0530, Naveen N. Rao wrote: > Objtool classifies 'ud2' as INSN_BUG, and 'int3' as INSN_TRAP. In x86 > BUG(), there is no need for an annotation since objtool assumes that > 'ud2' terminates control flow. But, for __WARN_FLAGS(), since 'ud2' is > used, an explicit annotate_reachable() is needed. That's _reachable_, to > indicate that the control flow can continue with the next instruction. > > On powerpc, we should (eventually) classify all trap variants as > INSN_TRAP. Even in the absence of that classification today, objtool > assumes that control flow continues with the next instruction. With your > work to utilize asm goto for __WARN_FLAGS(), with no extra instructions > being generated, I think it is appropriate to just use > __builtin_unreachable() and to not use the annotation. > > In any case, we are only hitting this since gcc is generating a 'bl' due > to that annotation. We are not yet enabling full objtool validation on > powerpc, so I think we can revisit this at that point. See also that asks for a __builtin_trap() variant that does not terminate control flow ("that is recoverable"). Segher