Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965205AbWIRNwa (ORCPT ); Mon, 18 Sep 2006 09:52:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965213AbWIRNwa (ORCPT ); Mon, 18 Sep 2006 09:52:30 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:64711 "EHLO e35.co.us.ibm.com") by vger.kernel.org with ESMTP id S965205AbWIRNw3 (ORCPT ); Mon, 18 Sep 2006 09:52:29 -0400 Date: Mon, 18 Sep 2006 19:22:08 +0530 From: Ananth N Mavinakayanahalli To: Ingo Molnar Cc: Andrew Morton , Mathieu Desnoyers , Jes Sorensen , Roman Zippel , tglx@linutronix.de, karim@opersys.com, Paul Mundt , linux-kernel@vger.kernel.org, Christoph Hellwig , Ingo Molnar , Greg Kroah-Hartman , Tom Zanussi , ltt-dev@shafik.org, Michel Dagenais , fche@redhat.com Subject: Re: [patch] kprobes: optimize branch placement Message-ID: <20060918135208.GA6662@in.ibm.com> Reply-To: ananth@in.ibm.com References: <450BCAF1.2030205@sgi.com> <20060916172419.GA15427@Krystal> <20060916173552.GA7362@elte.hu> <20060916175606.GA2837@Krystal> <20060916191043.GA22558@elte.hu> <20060916193745.GA29022@elte.hu> <20060916202939.GA4520@elte.hu> <20060916204342.GA5208@elte.hu> <20060916155657.a233b54d.akpm@osdl.org> <20060916233038.GC23132@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060916233038.GC23132@elte.hu> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2586 Lines: 59 On Sun, Sep 17, 2006 at 01:30:38AM +0200, Ingo Molnar wrote: > > * Andrew Morton wrote: > > > On Sat, 16 Sep 2006 22:43:42 +0200 > > Ingo Molnar wrote: > > > > > --- linux.orig/arch/i386/kernel/kprobes.c > > > +++ linux/arch/i386/kernel/kprobes.c > > > @@ -354,9 +354,8 @@ no_kprobe: > > > */ > > > fastcall void *__kprobes trampoline_handler(struct pt_regs *regs) > > > { > > > - struct kretprobe_instance *ri = NULL; > > > - struct hlist_head *head; > > > - struct hlist_node *node, *tmp; > > > + struct kretprobe_instance *ri = NULL, *tmp; > > > + struct list_head *head; > > > unsigned long flags, orig_ret_address = 0; > > > unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline; > > > > Wanna fix the whitespace wreckage while you're there?? > > will do. If you consider this for -mm then there's some djprobes noise > in the patch [djprobes isnt upstream yet] - it's not completely > sanitized yet. (but it should actually work if applied to upstream - > kprobes and djprobes are disjunct.) Also, i havent tested with > CONFIG_KPROBES turned off, etc. I'll do a clean queue. Also, the hlist->list changes need to be taken care of for the other archs too. > > i386's kprobe_handler() appears to forget to reenable preemption in > > the if (p->pre_handler && p->pre_handler(p, regs)) case? > > that portion seems a bit tricky - i think what happens is that the > pre_handler() sets stuff up for single-stepping, and then we do this > recursive single-stepping (during which preemption remains disabled), > and _then_ do we re-enable preemption. Well, that is the jprobes and return probes case. In the case of normal kprobes, p->pre_handler() should always return 0. In the case of a jprobe, the setjmp_pre_handler() resets the instruction pointer to the instrumented routine (same signature as the routine being jprobed), which later does a jprobe_return(), a placeholder for the arch-specific trap instruction. We re-enter the kprobe_handler here and then re-enable preemption via the longjmp_break_handler. As for the return probe case, since the underlying instruction originally was a nop (kretprobe_trampoline), we don't need to single-step. Yes, its a bit convoluted, but we are currently covered for all cases. Ananth - 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/