Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261191AbVARIsc (ORCPT ); Tue, 18 Jan 2005 03:48:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261189AbVARIsc (ORCPT ); Tue, 18 Jan 2005 03:48:32 -0500 Received: from e6.ny.us.ibm.com ([32.97.182.146]:4740 "EHLO e6.ny.us.ibm.com") by vger.kernel.org with ESMTP id S261200AbVARIsV (ORCPT ); Tue, 18 Jan 2005 03:48:21 -0500 Date: Tue, 18 Jan 2005 14:19:15 +0530 From: Prasanna S Panchamukhi To: Andi Kleen Cc: Juho Snellman , linux-kernel@vger.kernel.org Subject: Re: x86-64: int3 no longer causes SIGTRAP in 2.6.10 Message-ID: <20050118084915.GA1321@in.ibm.com> Reply-To: prasanna@in.ibm.com References: <20050118011244.GA23256@iki.fi> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2960 Lines: 81 On Tue, Jan 18, 2005 at 02:47:08AM +0100, Andi Kleen wrote: > Juho Snellman writes: > > > 2.6.10 changed the behaviour of the int3 instruction on x86-64. It > > used to result in a SIGTRAP, now it's a SIGSEGV in both native and > > 32-bit legacy modes. This was apparently caused by the kprobe port, > > specifically this part: > > > > --- a/arch/x86_64/kernel/traps.c 2004-12-24 13:36:17 -08:00 > > +++ b/arch/x86_64/kernel/traps.c 2004-12-24 13:36:17 -08:00 > > @@ -862,8 +910,8 @@ > > set_intr_gate(0,÷_error); > > set_intr_gate_ist(1,&debug,DEBUG_STACK); > > set_intr_gate_ist(2,&nmi,NMI_STACK); > > - set_system_gate(3,&int3); /* int3-5 can be called from all */ > > - set_system_gate(4,&overflow); > > + set_intr_gate(3,&int3); > > + set_system_gate(4,&overflow); /* int4-5 can be called from all */ > > > > Was effectively disabling int3 a conscious decision, or just an > > unintended side-effect? This breaks at least Steel Bank Common Lisp > > It's a bug. Thanks for the report. > > I'm not sure why it was even changed. Prasanna? > > I think it should be just changed back. If kprobes cannot > deal with traps for user space it needs to be fixed. e.g. > by adding a user space check in kprobe_handler(). > Yes its a bug, we turn trap 3 into interrupt gates to ensure that it is not preemtable. Thanks Prasanna > -Andi > > Like this patch. > > Index: linux/arch/x86_64/kernel/traps.c > =================================================================== > --- linux.orig/arch/x86_64/kernel/traps.c 2005-01-17 10:34:24.%N +0100 > +++ linux/arch/x86_64/kernel/traps.c 2005-01-18 02:42:02.%N +0100 > @@ -908,7 +908,7 @@ > set_intr_gate(0,÷_error); > set_intr_gate_ist(1,&debug,DEBUG_STACK); > set_intr_gate_ist(2,&nmi,NMI_STACK); > - set_intr_gate(3,&int3); > + set_system_gate(3,&int3); > set_system_gate(4,&overflow); /* int4-5 can be called from all */ > set_system_gate(5,&bounds); > set_intr_gate(6,&invalid_op); > Index: linux/arch/x86_64/kernel/kprobes.c > =================================================================== > --- linux.orig/arch/x86_64/kernel/kprobes.c 2005-01-04 12:12:39.%N +0100 > +++ linux/arch/x86_64/kernel/kprobes.c 2005-01-18 02:46:05.%N +0100 > @@ -297,6 +297,8 @@ > struct die_args *args = (struct die_args *)data; > switch (val) { > case DIE_INT3: > + if (args->regs->cs & 3) > + return NOTIFY_DONE; > if (kprobe_handler(args->regs)) > return NOTIFY_STOP; > break; > > -- Have a Nice Day! Thanks & Regards 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/