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[2001:8b0:bf73:93f7::51bb:e332]) by smtp.gmail.com with ESMTPSA id n19-20020a05600c501300b0040e813f1f31sm766684wmr.25.2024.01.15.08.29.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jan 2024 08:29:39 -0800 (PST) Received: from jsm28 (helo=localhost) by digraph.polyomino.org.uk with local-esmtp (Exim 4.95) (envelope-from ) id 1rPPpe-001JSE-6J; Mon, 15 Jan 2024 16:29:02 +0000 Date: Mon, 15 Jan 2024 16:29:02 +0000 (UTC) From: Joseph Myers To: Florian Weimer cc: Carlos O'Donell , Adhemerval Zanella Netto , Szabolcs Nagy , gcc@gcc.gnu.org, libc-alpha@sourceware.org, Iain Sandoe , aburgess@redhat.com, lttng-dev@lists.lttng.org Subject: Re: New TLS usage in libgcc_s.so.1, compatibility impact In-Reply-To: <87jzoa6249.fsf@oldenburg.str.redhat.com> Message-ID: <7c159449-acb9-3448-1829-1cd26ec2c60@redhat.com> References: <8734v1ieke.fsf@oldenburg.str.redhat.com> <81279c5d-0b60-0e37-abe9-0936688b14fa@redhat.com> <87jzoa6249.fsf@oldenburg.str.redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Mon, 15 Jan 2024, Florian Weimer via Gcc wrote: > The change conflated multiple issues: sanitizer support, > async-signal-safe TLS access, and eager allocation of all TLS-related > memory, so that subsequent accesses cannot fail. My impression was the > main point of contention was eager allocation because it was perceived > as a breaking semantic change. Nowadays, as long as we are willing to > maintain both allocator variants, we could offer a choice between them > controlled by a tunable. For sanitizer compatibility, we could perform > eager allocation using malloc. It's probably a good idea to do it this > way anyway because a separate mmap-based allocator would increase TLB > pressure. Related to eager allocation is the question of whether libgcc_s.so.1 should be loaded unconditionally by glibc at startup - doing so has much the same motivation (avoiding subsequent failures from interfaces that don't have any good way to signal failure, when glibc currently loads libgcc_s.so.1 dynamically), but also no doubt compatibility risk. -- Joseph S. Myers josmyers@redhat.com