Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266184AbUA2SIf (ORCPT ); Thu, 29 Jan 2004 13:08:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266167AbUA2SIf (ORCPT ); Thu, 29 Jan 2004 13:08:35 -0500 Received: from cpe-24-221-190-179.ca.sprintbbd.net ([24.221.190.179]:56525 "EHLO myware.akkadia.org") by vger.kernel.org with ESMTP id S266184AbUA2SII (ORCPT ); Thu, 29 Jan 2004 13:08:08 -0500 Message-ID: <40194B6D.6060906@redhat.com> Date: Thu, 29 Jan 2004 10:05:33 -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: Jamie Lokier CC: john stultz , 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> In-Reply-To: <20040129132623.GB13225@mail.shareable.org> 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: 1602 Lines: 40 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Jamie Lokier wrote: > I like the second approach more. You can change glibc to look up the > weak symbol for _all_ syscalls, then none of them are special and it > will work with future kernel optimisations. Symbol lookups are slow. And they require the syscall stubs to suddenly set up the usual PIC infrastructure since a jump through the PLT is used. This is much slower than the extra indirection the vdso could do. The vdso is just one of the DSOs in the search path and usually the very last. So there would be possible many objects which are looked at first, unsuccessfully. And another problem I should have mentioned last night: in statically linked applications the vDSO isn't used this way. Do dynamic linker functionality is available. We find the vDSO through the auxiliary vector and use the absolute address, not the symbol table of the vDSO. If the syscall entry in the vDSO would do the dispatch automatically, statically linked apps would benefit from the optimizations, too. Otherwise they are left out. - -- ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.3 (GNU/Linux) iD8DBQFAGUtt2ijCOnn/RHQRAgLwAKCcvvzg/FB8/8C+Jo1I6wfWBju25gCeKr4z kErg4cvJuxBvmRltLF4AxEE= =f2aR -----END PGP SIGNATURE----- - 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/