From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757001AbaIWXFx (ORCPT ); Tue, 23 Sep 2014 19:05:53 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:39056 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753292AbaIWXFw (ORCPT ); Tue, 23 Sep 2014 19:05:52 -0400 Date: Tue, 23 Sep 2014 16:05:51 -0700 From: Andrew Morton To: Oleg Nesterov Cc: Alexander Viro , Denys Vlasenko , Jan Kratochvil , Mark Wielaard , Martin Milata , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] coredump: add %i/%I in core_pattern to report the tid of the crashed thread Message-Id: <20140923160551.8e93a39f10a818684a514cf2@linux-foundation.org> In-Reply-To: <20140922171525.GA32171@redhat.com> References: <20140921175349.GA21585@redhat.com> <20140922171525.GA32171@redhat.com> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 22 Sep 2014 19:15:25 +0200 Oleg Nesterov wrote: > format_corename() can only pass the leader's pid to the core handler, but > there is no simple way to figure out which thread originated the coredump. > > As Jan explains, this also means that there is no simple way to create the > backtrace of the crashed process: > > As programs are mostly compiled with implicit gcc -fomit-frame-pointer one > needs program's .eh_frame section (equivalently PT_GNU_EH_FRAME segment) or > .debug_frame section. .debug_frame usually is present only in separate debug > info files usually not even installed on the system. While .eh_frame is a > part of the executable/library (and it is even always mapped for C++ > exceptions unwinding) it no longer has to be present anywhere on the disk > as the program could be upgraded in the meantime and the running instance > has its executable file already unlinked from disk. > > One possibility is to echo 0x3f >/proc/*/coredump_filter and dump all the > file-backed memory including the executable's .eh_frame section. But that > can create huge core files, for example even due to mmapped data files. > > Other possibility would be to read .eh_frame from /proc/PID/mem at the > core_pattern handler time of the core dump. For the backtrace one needs to > read the register state first which can be done from core_pattern handler: > > ptrace(PTRACE_SEIZE, tid, 0, PTRACE_O_TRACEEXIT) > close(0); // close pipe fd to resume the sleeping dumper > waitpid(); // should report EXIT > PTRACE_GETREGS or other requests > > The remaining problem is how to get the 'tid' value of the crashed thread. > It could be read from the first NT_PRSTATUS note of the core file but that > makes the core_pattern handler complicated. > > Unfortunately %t is already used so this patch uses %i/%I. Is any userspace actually going to use this? If so, details? Am wondering what is driving this change...