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 [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id A00823858436 for ; Tue, 23 Aug 2022 11:58:37 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org A00823858436 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-323-iz_t8Ht-P_G9wcxrs7hUDg-1; Tue, 23 Aug 2022 07:58:33 -0400 X-MC-Unique: iz_t8Ht-P_G9wcxrs7hUDg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id AF54F29DD98B; Tue, 23 Aug 2022 11:58:32 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.143]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CCFCD18EA8; Tue, 23 Aug 2022 11:58:31 +0000 (UTC) From: Florian Weimer To: binutils@sourceware.org Cc: gcc@gcc.gnu.org, libc-alpha@sourceware.org Subject: Counting static __cxa_atexit calls Date: Tue, 23 Aug 2022 13:58:30 +0200 Message-ID: <87fshn2mu1.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 10.11.54.5 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-5.5 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 23 Aug 2022 11:58:38 -0000 We currently have a latent bug in glibc where C++ constructor calls can fail if they have static or thread storage duration and a non-trivial destructor. The reason is that __cxa_atexit (and __cxa_thread_atexit_impl) may have to allocate memory. We can avoid that if we know how many such static calls exist in an object (for C++, the compiler will never emit these calls repeatedly in a loop). Then we can allocate the resources beforehand, either during process and thread start, or when dlopen is called and new objects are loaded. What would be the most ELF-flavored way to implement this? After the final link, I expect that the count (or counts, we need a separate counter for thread-local storage) would show up under a new dynamic tag in the dynamic segment. This is actually a very good fit because older loaders will just ignore it. But the question remains what GCC should emit into assembler & object files, so that the link editor can compute the total count from that. Thanks, Florian