Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754145AbYCQK7R (ORCPT ); Mon, 17 Mar 2008 06:59:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751874AbYCQK7J (ORCPT ); Mon, 17 Mar 2008 06:59:09 -0400 Received: from fk-out-0910.google.com ([209.85.128.190]:34603 "EHLO fk-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751757AbYCQK7I (ORCPT ); Mon, 17 Mar 2008 06:59:08 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=X/gCZfrDSGxa68xTkswr3N22icuVNMAxzX6srRFH9LCskVQaknYy5JBsxj0xCjoo+zf03o7bshBozP33/wlJR51LcBcycDmV+4EB75frJ29/Tp8mzJNmhihBrqds0q/XIhrvHtHaEe1AnnSycgcVB5g/rTPC66/p/rH7MwC1Lew= Message-ID: Date: Mon, 17 Mar 2008 12:59:05 +0200 From: "Yakov Lerner" To: ananth@in.ibm.com Subject: Re: [PATCH] Subject: kprobes-x86: correct post-eip value in post_hander() Cc: prasanna@in.ibm.com, anil.s.keshavamurthy@intel.com, davem@davemloft.net, linux-kernel@vger.kernel.org In-Reply-To: <20080317051956.GB7229@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080317051956.GB7229@in.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1812 Lines: 37 On Mon, Mar 17, 2008 at 7:19 AM, Ananth N Mavinakayanahalli wrote: > On Sun, Mar 16, 2008 at 03:21:21AM -0500, Yakov Lerner wrote: > > > > I was trying to get the address of instruction to be executed > > next after the kprobed instruction. But regs->eip in post_handler() > > contains value which is useless to the user. It's pre-corrected value. > > This value is difficult to use without access to resume_execution(), which > > is not exported anyway. > > I moved the invocation of post_handler() to *after* resume_execution(). > > Now regs->eip contains meaningful value in post_handler(). > > > > I do not think this change breaks any backward-compatibility. > > To make meaning of the old value, post_handler() would need access to > > resume_execution() which is not exported. I have difficulty to believe > > that previous, uncorrected, regs->eip can be meaningfully used in > > post_handler(). > > resume_execution() exists not just for the program counter fixups after > out-of-line singlestepping, but is also as an insurance to put the > program counter back to the correct address in case the user's > post_handler() mucks around with it. That isn't possible with this > change :-( I see your point. This can be prevented by saving and restoring regs->ip around the post_handler() call, no ? Current code is beautiful. Saving and restoring regs->ip would make this place look ugly. Otoh, if the post_handler() wants to crash the kernel, it can do it in thousand ways, not just by trashing regs->ip, no ? Yakov -- 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/