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Mon, 28 Mar 2022 13:21:34 -0700 (PDT) Received: from treble ([2600:1700:6e32:6c00::35]) by smtp.gmail.com with ESMTPSA id g9-20020a05620a108900b0067b13036bd5sm8275335qkk.52.2022.03.28.13.21.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Mar 2022 13:21:34 -0700 (PDT) Date: Mon, 28 Mar 2022 13:21:31 -0700 From: Josh Poimboeuf To: Peter Zijlstra Subject: Re: [RFC PATCH 3/3] objtool/mcount: Add powerpc specific functions Message-ID: <20220328202131.jis7swqswm7chn6k@treble> References: <20220318105140.43914-1-sv@linux.ibm.com> <20220318105140.43914-4-sv@linux.ibm.com> <0b55f122-4760-c1ba-840a-0911cefec2ad@csgroup.eu> <20220328195920.dqlfra3lcardko6r@treble> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jpoimboe@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , "aik@ozlabs.ru" , Will Deacon , "linux-kernel@vger.kernel.org" , "rostedt@goodmis.org" , Sathvika Vasireddy , "naveen.n.rao@linux.vnet.ibm.com" , "linuxppc-dev@lists.ozlabs.org" , ardb@kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Mar 28, 2022 at 10:14:38PM +0200, Peter Zijlstra wrote: > > FWIW, there have been some objtool patches for arm64 stack validation, > > but the arm64 maintainers have been hesitant to get on board with > > objtool, as it brings a certain maintenance burden. Especially for the > > full stack validation and ORC unwinder. But if you only want inline > > static calls and/or mcount then it'd probably be much easier to > > maintain. > > IIRC the major stumbling block for arm64 is the whole jump-table thing. > Either they need to rely on compiler plugins to provide objtool that > data (yuck, since we support at least 2 different compilers), disable > jump-tables (yuck, for that limits code-gen just to please a tool) or > use DWARF (yuck, because build times). Well yeah, that was indeed the main technical issue but I seem to remember some arm64 maintainers not really being sold on the value of objtool regardless. > There was a little talk about an impromptu 'abi' to communicate > jump-table details to objtool without going full on DWARF, but that > seems to have hit a dead end again. Probably my fault, not enough hours in the day... -- Josh