Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753503Ab0APKET (ORCPT ); Sat, 16 Jan 2010 05:04:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752212Ab0APKET (ORCPT ); Sat, 16 Jan 2010 05:04:19 -0500 Received: from casper.infradead.org ([85.118.1.10]:52040 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751822Ab0APKES (ORCPT ); Sat, 16 Jan 2010 05:04:18 -0500 Subject: Re: [RFC] [PATCH 4/7] Uprobes Implementation From: Peter Zijlstra To: Jim Keniston Cc: maneesh@in.ibm.com, Srikar Dronamraju , Ingo Molnar , Arnaldo Carvalho de Melo , Ananth N Mavinakayanahalli , utrace-devel , Mark Wielaard , Frederic Weisbecker , Masami Hiramatsu , LKML In-Reply-To: <1263599085.5007.88.camel@localhost.localdomain> References: <20100111122521.22050.3654.sendpatchset@srikar.in.ibm.com> <20100111122553.22050.46895.sendpatchset@srikar.in.ibm.com> <1263467394.4244.291.camel@laptop> <1263509380.4875.35.camel@localhost.localdomain> <1263546632.4244.352.camel@laptop> <20100115102645.GA22640@linux.vnet.ibm.com> <1263551607.4244.379.camel@laptop> <20100115110547.GB3660@in.ibm.com> <1263553955.4244.393.camel@laptop> <1263599085.5007.88.camel@localhost.localdomain> Content-Type: text/plain; charset="UTF-8" Date: Sat, 16 Jan 2010 11:04:09 +0100 Message-ID: <1263636249.4244.525.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2010-01-15 at 15:44 -0800, Jim Keniston wrote: > On Fri, 2010-01-15 at 12:12 +0100, Peter Zijlstra wrote: > .... > > > > Adding the probe uses the fact that (most) executable mappings are > > MAP_PRIVATE and CoWs a private copy of the page with the modified ins, > > right? > > > > What does it do for MAP_SHARED|MAP_EXECUTABLE sections -- simply fail to > > add the probe? > > If the vma containing the instruction to be probed has the VM_EXEC flag > set (and it's not in the XOL area) we go ahead and try to probe it. I'm > not familar with the implications of MAP_SHARED|MAP_EXECUTABLE -- how > you would get such a combo, or what access_process_vm() would do with > it. I'm not sure how you'd get one, the user has to explicitly create one I think, regular loaders don't create such things, but maybe JITs do. The problem is that for MAP_SHARED you cannot CoW the page, you have to modify the original page, which might get written back into a file if its file based, not something you'd want to have happen I guess. -- 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/