Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754767Ab0AEP7c (ORCPT ); Tue, 5 Jan 2010 10:59:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754572Ab0AEP7a (ORCPT ); Tue, 5 Jan 2010 10:59:30 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41178 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754400Ab0AEP7a (ORCPT ); Tue, 5 Jan 2010 10:59:30 -0500 Date: Tue, 5 Jan 2010 16:59:13 +0100 From: Oleg Nesterov To: Martin Schwidefsky Cc: Roland McGrath , caiqian@redhat.com, Heiko Carstens , Jan Kratochvil , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, utrace-devel@redhat.com Subject: Re: s390 && user_enable_single_step() (Was: odd utrace testing results on s390x) Message-ID: <20100105155913.GA10652@redhat.com> References: <1503844142.2061111261478093776.JavaMail.root@zmail06.collab.prod.int.phx2.redhat.com> <1257887498.2061171261478252049.JavaMail.root@zmail06.collab.prod.int.phx2.redhat.com> <20100104155225.GA16650@redhat.com> <20100104171626.22ea2d9c@mschwide.boeblingen.de.ibm.com> <20100104181412.GA21146@redhat.com> <20100104211147.4CC94D532@magilla.sf.frob.com> <20100105105030.66bb8a0a@mschwide.boeblingen.de.ibm.com> <20100105153633.GA9376@redhat.com> <20100105164610.388effd3@mschwide.boeblingen.de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100105164610.388effd3@mschwide.boeblingen.de.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2001 Lines: 63 On 01/05, Martin Schwidefsky wrote: > > On Tue, 5 Jan 2010 16:36:33 +0100 > Oleg Nesterov wrote: > > > For example, why do_signal() sets TIF_SINGLE_STEP? Why can't we do > > > > --- a/arch/s390/kernel/signal.c > > +++ b/arch/s390/kernel/signal.c > > @@ -500,18 +500,10 @@ void do_signal(struct pt_regs *regs) > > clear_thread_flag(TIF_RESTORE_SIGMASK); > > > > /* > > - * If we would have taken a single-step trap > > - * for a normal instruction, act like we took > > - * one for the handler setup. > > - */ > > - if (current->thread.per_info.single_step) > > - set_thread_flag(TIF_SINGLE_STEP); > > - > > - /* > > * Let tracing know that we've done the handler setup. > > */ > > tracehook_signal_handler(signr, &info, &ka, regs, > > - test_thread_flag(TIF_SINGLE_STEP)); > > + current->thread.per_info.single_step); > > } > > return; > > } > > > > ? > > The reason why we set the TIF_SINGLE_STEP bit in do_signal is that we > want to be able to stop the debugged program before the first > instruction of the signal handler has been executed. The PER single > step causes a trap after an instruction has been executed. That first > instruction can do bad things to the arguments of the signal handler.. Yes, but afaics all we need is to pass the correct "int stepping" arg to tracehook_signal_handler(). If it is true, the tracee does ptrace_notify() before it returns to user-mode. > > dmesg shows 799 lines of > > > > XXX: 2389 0 > > > > > > The kernel is 2.6.32.2 + utrace, but CONFIG_UTRACE is not set. > > With or without my bug fix ? With, but please see another email. I'll add clear_bit(TIF_SINGLE_STEP) into do_fork() path and re-test. Oleg. -- 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/