From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from brightrain.aerifal.cx (216-12-86-13.cv.mvl.ntelos.net [216.12.86.13]) by sourceware.org (Postfix) with ESMTPS id CF2C3385C426 for ; Thu, 16 Apr 2020 15:35:11 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org CF2C3385C426 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=libc.org Authentication-Results: sourceware.org; spf=none smtp.mailfrom=dalias@libc.org Date: Thu, 16 Apr 2020 11:35:09 -0400 From: Rich Felker To: Florian Weimer Cc: Nicholas Piggin , libc-alpha@sourceware.org, musl@lists.openwall.com, linuxppc-dev@lists.ozlabs.org, libc-dev@lists.llvm.org Subject: Re: [musl] Powerpc Linux 'scv' system call ABI proposal take 2 Message-ID: <20200416153509.GT11469@brightrain.aerifal.cx> References: <1586931450.ub4c8cq8dj.astroid@bobo.none> <20200415225539.GL11469@brightrain.aerifal.cx> <87k12gf32r.fsf@mid.deneb.enyo.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87k12gf32r.fsf@mid.deneb.enyo.de> User-Agent: Mutt/1.5.21 (2010-09-15) X-Spam-Status: No, score=0.9 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS, KAM_LAZY_DOMAIN_SECURITY, KAM_NUMSUBJECT, KHOP_HELO_FCRDNS, RDNS_DYNAMIC, SPF_HELO_NONE, SPF_NONE autolearn=no autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) 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: Thu, 16 Apr 2020 15:35:13 -0000 On Thu, Apr 16, 2020 at 06:48:44AM +0200, Florian Weimer wrote: > * Rich Felker: > > > My preference would be that it work just like the i386 AT_SYSINFO > > where you just replace "int $128" with "call *%%gs:16" and the kernel > > provides a stub in the vdso that performs either scv or the old > > mechanism with the same calling convention. > > The i386 mechanism has received some criticism because it provides an > effective means to redirect execution flow to anyone who can write to > the TCB. I am not sure if it makes sense to copy it. Indeed that's a good point. Do you have ideas for making it equally efficient without use of a function pointer in the TCB? Rich