From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_PASS autolearn=ham autolearn_force=no version=3.4.2 Received: (qmail 18145 invoked from network); 20 Apr 2020 01:29:18 -0000 Received-SPF: pass (mother.openwall.net: domain of lists.openwall.com designates 195.42.179.200 as permitted sender) receiver=inbox.vuxu.org; client-ip=195.42.179.200 envelope-from= Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with UTF8ESMTPZ; 20 Apr 2020 01:29:18 -0000 Received: (qmail 3367 invoked by uid 550); 20 Apr 2020 01:29:17 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 3349 invoked from network); 20 Apr 2020 01:29:16 -0000 Date: Sun, 19 Apr 2020 21:29:04 -0400 From: Rich Felker To: Nicholas Piggin Cc: Nicholas Piggin via Libc-alpha , Szabolcs Nagy , libc-dev@lists.llvm.org, linuxppc-dev@lists.ozlabs.org, musl@lists.openwall.com Message-ID: <20200420012904.GY11469@brightrain.aerifal.cx> References: <1586931450.ub4c8cq8dj.astroid@bobo.none> <20200415225539.GL11469@brightrain.aerifal.cx> <1586994952.nnxigedbu2.astroid@bobo.none> <20200416095800.GC23945@port70.net> <1587341904.1r83vbudyf.astroid@bobo.none> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1587341904.1r83vbudyf.astroid@bobo.none> User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] Powerpc Linux 'scv' system call ABI proposal take 2 On Mon, Apr 20, 2020 at 10:27:58AM +1000, Nicholas Piggin wrote: > Excerpts from Szabolcs Nagy's message of April 16, 2020 7:58 pm: > > * Nicholas Piggin via Libc-alpha [2020-04-16 10:16:54 +1000]: > >> Well it would have to test HWCAP and patch in or branch to two > >> completely different sequences including register save/restores yes. > >> You could have the same asm and matching clobbers to put the sequence > >> inline and then you could patch the one sc/scv instruction I suppose. > > > > how would that 'patch' work? > > > > there are many reasons why you don't > > want libc to write its .text > > I guess I don't know what I'm talking about when it comes to libraries. > Shame if there is no good way to load-time patch libc. It's orthogonal > to the scv selection though -- if you don't patch you have to > conditional or indirect branch however you implement it. Patched pages cannot be shared. The whole design of PIC and shared libraries is that the code("text")/rodata is immutable and shared and that only a minimal amount of data, packed tightly together (the GOT) has to exist per-instance. Also, allowing patching of executable pages is generally frowned upon these days because W^X is a desirable hardening property. Rich