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[86.166.129.255]) by smtp.gmail.com with ESMTPSA id y6sm8657038wrh.18.2021.11.05.06.52.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Nov 2021 06:52:27 -0700 (PDT) Date: Fri, 5 Nov 2021 13:52:26 +0000 From: Andrew Burgess To: Tom de Vries Cc: Pedro Alves , gdb-patches@sourceware.org Subject: Re: [PATCH] [gdb/testsuite] Fix gdb.arch/i386-avx.exp with clang Message-ID: <20211105135226.GC1816063@redhat.com> 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> MIME-Version: 1.0 In-Reply-To: <4a98d0ce-b473-7a44-f399-3a604a5b2516@suse.de> X-Operating-System: Linux/5.8.18-100.fc31.x86_64 (x86_64) X-Uptime: 13:47:09 up 4 days, 4:20, X-Editor: GNU Emacs [ http://www.gnu.org/software/emacs ] X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-4.6 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_BARRACUDACENTRAL, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=no 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: Fri, 05 Nov 2021 13:52:33 -0000 * 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, 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. Thanks, Andrew