From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by sourceware.org (Postfix) with ESMTPS id 493A83858D28 for ; Mon, 6 Dec 2021 15:27:53 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 493A83858D28 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 7E26921B3B; Mon, 6 Dec 2021 15:27:52 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 6301013C52; Mon, 6 Dec 2021 15:27:52 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id hXogF/grrmG1VgAAMHmgww (envelope-from ); Mon, 06 Dec 2021 15:27:52 +0000 Subject: Re: [PATCH] [gdb/testsuite] Fix gdb.arch/i386-avx.exp with clang To: Andrew Burgess Cc: Pedro Alves , gdb-patches@sourceware.org References: <20211104135559.5875-1-tdevries@suse.de> <20211105093300.GG918204@redhat.com> <20211105115404.GA1816063@redhat.com> <8074d4d8-fe21-bccf-3fb6-f4be2ea67f7b@palves.net> <1f6ed2db-5d31-9338-226e-3e1a5a7c225b@suse.de> <4a98d0ce-b473-7a44-f399-3a604a5b2516@suse.de> <20211105135226.GC1816063@redhat.com> From: Tom de Vries Message-ID: Date: Mon, 6 Dec 2021 16:27:52 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20211105135226.GC1816063@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-7.6 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, NICE_REPLY_A, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 06 Dec 2021 15:27:54 -0000 On 11/5/21 2:52 PM, Andrew Burgess wrote: > * Tom de Vries via Gdb-patches [2021-11-05 14:35:20 +0100]: > >> On 11/5/21 2:20 PM, Pedro Alves wrote: >>> On 2021-11-05 13:15, Tom de Vries wrote: >>>> On 11/5/21 1:55 PM, Pedro Alves wrote: >>>>> On 2021-11-05 12:23, Tom de Vries via Gdb-patches wrote: >>>>> >>>>>>> No, but in gdb/testsuite/lib/attribute.h we do setup a compatibility >>>>>>> macro for 'noclone', so there's definitely precedent for using >>>>>>> attributes that might not be supported everywhere. >>>>>>> >>>>>> >>>>>> Right, I'm aware of this, but that's a typical case where we have no >>>>>> portable alternative. >>>>> >>>>> We actually do -- _Alignas is standard C11. This fixes the test as well: >>>>> >>>>> _Alignas(32) v8sf_t data[] = >>>>> >>>> >>>> I was referring to the noclone, but ok, I was not aware of the _Alignas, >>>> good to know, thanks. >>>> >>>> Anyway, in the latest version this is not relevant anymore, since the >>>> precise alignment implementation has an extra benefit, as explained in >>>> the post. >>>> >>> >>> OOC, is that benefit important here? >>> >> >> So, this is the post I mentioned ( >> https://sourceware.org/pipermail/gdb-patches/2021-November/183183.html ). >> >> Well, the benefit is that it prevents accidental overalignment, which is >> the reason that this problem escaped detection and/or fixing for so long. >> >> Without that, I could do a thinko and specify too small an alignment and >> have the test passing accidentally, only to fail in a different setup. > > I'm still not convinced. The test doesn't appear to be about the > alignment, Correct. > but about accessing the feature specific registers, so I > don't see how making a mistake with the alignment would be different > to any other bug - eventually it gets spotted and fixed. Right, and my perception is that using precise alignment gives me confidence that I fixed it properly. Thanks, - Tom