Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751238AbVKJHKr (ORCPT ); Thu, 10 Nov 2005 02:10:47 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751247AbVKJHKr (ORCPT ); Thu, 10 Nov 2005 02:10:47 -0500 Received: from e5.ny.us.ibm.com ([32.97.182.145]:52404 "EHLO e5.ny.us.ibm.com") by vger.kernel.org with ESMTP id S1751238AbVKJHKq (ORCPT ); Thu, 10 Nov 2005 02:10:46 -0500 Date: Thu, 10 Nov 2005 23:39:54 +0530 From: Prasanna S Panchamukhi To: Zachary Amsden Cc: Ingo Molnar , Andi Kleen , virtualization@lists.osdl.org, Andrew Morton , Chris Wright , Linus Torvalds , Linux Kernel Mailing List , "H. Peter Anvin" , Zwane Mwaikambo , Martin Bligh , Pratap Subrahmanyam , Christopher Li , "Eric W. Biederman" , ananth@in.ibm.com, anil.s.keshavamurthy@intel.com, davem@davemloft.net Subject: Re: [PATCH 19/21] i386 Kprobes semaphore fix Message-ID: <20051110180954.GD8514@in.ibm.com> Reply-To: prasanna@in.ibm.com References: <200511080439.jA84diI6009951@zach-dev.vmware.com> <200511081412.05285.ak@suse.de> <4370A9F5.4060103@vmware.com> <200511091438.11848.ak@suse.de> <437227FD.6040905@vmware.com> <20051109165804.GA15481@elte.hu> <43723768.2060103@vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <43723768.2060103@vmware.com> User-Agent: Mutt/1.4i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1983 Lines: 60 On Wed, Nov 09, 2005 at 09:52:40AM -0800, Zachary Amsden wrote: > Ingo Molnar wrote: > > >* Zachary Amsden wrote: > > > > > > > >>>I believe user space kprobes are being worked on by some IBM India folks > >>>yes. > >>> > >>> > >>I'm convinced this is pointless. What does it buy you over a ptrace > >>based debugger? Why would you want extra code running in the kernel > >>that can be done perfectly well in userspace? > >> > >> > > > >kprobes are not just for 'debuggers', they are also used for tracing and > >other dynamic instrumentation in projects like systemtap. Ptrace is way > >too slow and limited for things like that. > > > > > > Well, if there is a justification for it, that means we really should > handle all the nasty EIP conversion cases due to segmentation and v8086 > mode in the kprobes code. I was hoping that might not be the case. > As Ingo mentioned above, Systemtap uses kprobes infrastructure to provide dynamic kernel instrumentation. Using which user can add lots of probes easily, so we need to take care of this fast path. Instead of calling convert_eip_to_linear() for all cases, you can just check if it is in kernel mode and calculate the address directly if (kernel mode) addr = regs->eip - sizeof(kprobe_opcode_t); else addr = convert_eip_to_linear(..); there by avoiding call to convert_eip_to_linear () for every kernel probes. As Andi mentioned user space probes support is in progress and this address conversion will help in case of user space probes as well. Thanks Prasanna -- Prasanna S Panchamukhi Linux Technology Center India Software Labs, IBM Bangalore Ph: 91-80-25044636 - 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/