Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266493AbUA3Akx (ORCPT ); Thu, 29 Jan 2004 19:40:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266497AbUA3Akx (ORCPT ); Thu, 29 Jan 2004 19:40:53 -0500 Received: from cpe-24-221-190-179.ca.sprintbbd.net ([24.221.190.179]:51920 "EHLO myware.akkadia.org") by vger.kernel.org with ESMTP id S266493AbUA3Akv (ORCPT ); Thu, 29 Jan 2004 19:40:51 -0500 Message-ID: <4019A7EE.301@redhat.com> Date: Thu, 29 Jan 2004 16:40:14 -0800 From: Ulrich Drepper Organization: Red Hat, Inc. User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7a) Gecko/20040118 X-Accept-Language: en-us, en MIME-Version: 1.0 To: john stultz CC: Jamie Lokier , lkml Subject: Re: [RFC][PATCH] linux-2.6.2-rc2_vsyscall-gtod_B1.patch References: <1075344395.1592.87.camel@cog.beaverton.ibm.com> <401894DA.7000609@redhat.com> <20040129132623.GB13225@mail.shareable.org> <40194B6D.6060906@redhat.com> <20040129191500.GA1027@mail.shareable.org> <1075420794.1592.162.camel@cog.beaverton.ibm.com> In-Reply-To: <1075420794.1592.162.camel@cog.beaverton.ibm.com> X-Enigmail-Version: 0.83.0.0 X-Enigmail-Supports: pgp-inline, pgp-mime Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1340 Lines: 28 john stultz wrote: > Another issue with having a separate entry point for vgettimeofday is > that I don't quite understand how glibc detects if vsyscall is > available, and how deals with the vsyscall page moving around. Well, this is indeed a problem which needs an addition solution. If we'd look for the symbol, it's automatically handled. Likewise if the normal syscall handler does it magically. If a call to the magic address is needed we'd need from kind of version information in the vDSO to check for the existence of the extension. This check needs to be done for every call unless a new-enough kernel is assumed outright. One could add a functions to the vDSO which is called via the symbol table and which returns the necessary information to make the decision. The result would have to be stored in a local variable to avoid making that call over and over again. This all requires the PIC setup which makes the whole thing once again more expensive than the simple implicit table lookup. -- ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/