From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754696AbaEOOhJ (ORCPT ); Thu, 15 May 2014 10:37:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15077 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752793AbaEOOhH (ORCPT ); Thu, 15 May 2014 10:37:07 -0400 Message-ID: <5374D10A.1060905@redhat.com> Date: Thu, 15 May 2014 16:36:58 +0200 From: Denys Vlasenko User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Pedro Alves , Oleg Nesterov , Sergio Durigan Junior CC: LKML , Roland McGrath , Tom Tromey , Jan Kratochvil , Tejun Heo , Linus Torvalds Subject: Re: [RFC/PATCH] Implement new PTRACE_EVENT_SYSCALL_{ENTER,EXIT} References: <20140107153036.GA4749@redhat.com> <52CEEF1F.90803@redhat.com> <20140110135802.GA26953@redhat.com> <20140119152922.GA13689@redhat.com> <5373BACB.9090807@redhat.com> In-Reply-To: <5373BACB.9090807@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/14/2014 08:49 PM, Pedro Alves wrote: > I realized now that I responded to this. Sorry about that. > > On 01/19/2014 03:29 PM, Oleg Nesterov wrote: >> On 01/19, Sergio Durigan Junior wrote: >>> >>> On Friday, January 10 2014, Oleg Nesterov wrote: >>> >>>> So suppose that gdb does ptrace(PTRACE_SINGLESTEP) and the tracee >>>> executes the "syscall" insn. What it should report? >>> [...] >>>> But what should syscall-exit do? Should it still report SIGSEGV as >>>> it currently does, or should it report _SYSCALL_EXIT instead (if >>>> PTRACE_O_SYSCALL_EXIT of course), or should it report both? >>> >>> Both only if _SYSCALL_EXIT is set. Otherwise, stick to the current >>> behavior, I guess. >> >> OK, both. In which order? Probably _EXIT first. But this looks a bit >> strange. Suppose that the tracee reports _EXIT, then debugger does >> ptrace(PTRACE_CONT), should the tracee report SIGTRAP? > > Seems to me that this should be very much the same as fork/vfork/clone > event handling. Those are triggered by a syscall anyway. So, say: > > - ptrace(PTRACE_SINGLESTEP) > - the tracee executes the "syscall" insn, and the syscall is "clone". > - PTRACE_EVENT_FORK is reported. > - The debugger does ptrace(PTRACE_CONT). > > What should be reported? What is reported now? Yes, PTRACE_SINGLESTEP looks ambiguous. Just like PTRACE_SYSCALL is. I think we can take it further and add PTRACE_EVENT_SINGLESTEP too, like the patches under discussing which add PTRACE_EVENT_SYSCALL_ENTER,EXIT and therefore do away with the need to use ambiguous PTRACE_SYSCALL. Such API is clearer (I hope) - as long as option is on, user wants to get single-stepping SIGTRAPs after each insn, including syscall insn (in this case, after we return to userspace).