Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753565AbdLSWio (ORCPT ); Tue, 19 Dec 2017 17:38:44 -0500 Received: from smtprelay2.synopsys.com ([198.182.60.111]:52633 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753401AbdLSWii (ORCPT ); Tue, 19 Dec 2017 17:38:38 -0500 Subject: Re: [PATCH] bug.h: Work around GCC PR82365 in BUG() To: Arnd Bergmann CC: "linux-arch@vger.kernel.org" , Andrew Morton , "linux-kbuild@vger.kernel.org" , Mikael Starvik , "Jesper Nilsson" , Tony Luck , Fenghua Yu , Geert Uytterhoeven , "David S. Miller" , "Christopher Li" , Thomas Gleixner , "Peter Zijlstra" , Kees Cook , "Ingo Molnar" , Josh Poimboeuf , Will Deacon , "Steven Rostedt (VMware)" , "Mark Rutland" , "linux-snps-arc@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-cris-kernel@axis.com" , "linux-ia64@vger.kernel.org" , "linux-m68k@lists.linux-m68k.org" , "sparclinux@vger.kernel.org" , "linux-sparse@vger.kernel.org" References: <20171219114112.939391-1-arnd@arndb.de> <8e42a1de-f619-7a4e-6d58-f90f53f5f38f@synopsys.com> From: Vineet Gupta Message-ID: Date: Tue, 19 Dec 2017 14:38:21 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [10.10.161.67] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1245 Lines: 31 On 12/19/2017 12:13 PM, Arnd Bergmann wrote: > >> I suppose BUG() implies "dead end" like semantics - which ARC was lacking >> before ? > Correct. Using __builtin_trap() here avoids the 'control reaches end of non-void > function' warnings, but then makes us run into the stack size problem that > I work around with the barrier_before_unreachable(). > > It would be good if you could give this a quick test to see if you get sensible > output from the __builtin_trap(); It does, added a BUG() arbit, hits an abort() ... ISA Extn    : atomic ll64 unalign (not used)         : mpy[opt 9] div_rem norm barrel-shift swap minmax swape BPU        : partial match, cache:2048, Predict Table:16384 BUG: failure at ../arch/arc/mm/tlb.c:827/arc_mmu_init()! Tested-by: Vineet Gupta FWIW newer ARC gcc actually implements the builtin so we get a trap 5 instruction now, vs., abort() calls before. BTW I missed reading the hunk of your changelog where this addresses the long standing mystery with ARC builds and numerous -Wreturn-type warnings. I always wondered why they were not fixed upstream already, being too lazy to investigate myself, and turns out this was due to this BUG() thingy. phew ! -Vineet