From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by sourceware.org (Postfix) with ESMTPS id 05A5D3858C3A for ; Tue, 19 Oct 2021 19:48:55 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 05A5D3858C3A Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-489-YAIDTJ8tN9Ou8OtsvesA_Q-1; Tue, 19 Oct 2021 15:48:51 -0400 X-MC-Unique: YAIDTJ8tN9Ou8OtsvesA_Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C5AE9362FA; Tue, 19 Oct 2021 19:48:50 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.194.104]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7B7F8652AC; Tue, 19 Oct 2021 19:48:49 +0000 (UTC) From: Florian Weimer To: Joseph Myers Cc: Subject: Re: Correct access attribute on memfrob (bug 28475) References: Date: Tue, 19 Oct 2021 21:48:47 +0200 In-Reply-To: (Joseph Myers's message of "Tue, 19 Oct 2021 17:24:48 +0000") Message-ID: <87v91syew0.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.4 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, 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: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 19 Oct 2021 19:48:57 -0000 * Joseph Myers: > As noted in bug 28475, the access attribute on memfrob in > is incorrect: the function both reads and writes the memory pointed to > by its argument, so it needs to use __read_write__, not > __write_only__. This incorrect attribute results in a build failure > for accessing uninitialized memory for s390x-linux-gnu-O3 with > build-many-glibcs.py using GCC mainline. > Correct the attribute. That part looks okay. > Fixing this shows up that some calls to memfrob in elf/ tests are > reading uninitialized memory; I'm not entirely sure of the purpose of > those calls, but guess they are about ensuring that the stack space is > indeed allocated at that point in the function, and so it matters that > they are calling a function whose semantics are unknown to the > compiler. Thus, add a memset call before the memfrob call in those > tests to avoid the use of uninitialized memory. Using explicit_bzero would be more idomatic, I think. Florian