From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Alan Mackenzie Newsgroups: gmane.emacs.devel Subject: Help please! To track down GC trying to free an already freed object. Date: Tue, 2 Apr 2019 11:25:37 +0000 Message-ID: <20190402112537.GA6212@ACM> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="87223"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Mutt/1.10.1 (2018-07-13) To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Tue Apr 02 13:25:52 2019 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:256) (Exim 4.89) (envelope-from ) id 1hBHY8-000MZV-2n for ged-emacs-devel@m.gmane.org; Tue, 02 Apr 2019 13:25:52 +0200 Original-Received: from localhost ([127.0.0.1]:52854 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hBHY7-000752-3m for ged-emacs-devel@m.gmane.org; Tue, 02 Apr 2019 07:25:51 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:37469) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hBHY0-00074i-NB for emacs-devel@gnu.org; Tue, 02 Apr 2019 07:25:45 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hBHXz-0001Ip-NF for emacs-devel@gnu.org; Tue, 02 Apr 2019 07:25:44 -0400 Original-Received: from colin.muc.de ([193.149.48.1]:64244 helo=mail.muc.de) by eggs.gnu.org with smtp (Exim 4.71) (envelope-from ) id 1hBHXz-0001Hk-Bs for emacs-devel@gnu.org; Tue, 02 Apr 2019 07:25:43 -0400 Original-Received: (qmail 84139 invoked by uid 3782); 2 Apr 2019 11:25:38 -0000 Original-Received: from acm.muc.de (p4FE15EFB.dip0.t-ipconnect.de [79.225.94.251]) by colin.muc.de (tmda-ofmipd) with ESMTP; Tue, 02 Apr 2019 13:25:37 +0200 Original-Received: (qmail 6311 invoked by uid 1000); 2 Apr 2019 11:25:37 -0000 Content-Disposition: inline X-Delivery-Agent: TMDA/1.1.12 (Macallan) X-Primary-Address: acm@muc.de X-detected-operating-system: by eggs.gnu.org: FreeBSD 9.x [fuzzy] X-Received-From: 193.149.48.1 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:234861 Archived-At: Hello, Emacs. I get this problem after a recent merge of master into /scratch/accurate-warning-pos (my branch where I'm trying to implement correct source positions in the byte compiler's warning messages). This was a large merge, including bringing in the portable dumper. Emacs aborts at mark_object L+179 (in alloc.c), because a pseudovector being freed already has type PVEC_FREE, i.e. has been freed already. This object is a "symbol with position", a type of pseudovector which doesn't yet exist outside of this scratch branch. At a guess, I'm setting some data structure in the C code to a Lisp structure containing this object, but failing to apply static protection to this C variable. Or something like that. This failure occurs during the byte compilation of .../lisp/registry.el in a make or make bootstrap. The failure only occurs when this byte compilation is started as -batch from the command line. So my use of GDB is from the command line, not within a running Emacs. With GDB, I can break at the creation of this symbol-with-position object and again at its (first) freeing with this breakpoint: break setup_on_free_list if (v == 0x5555561d0450) . However, this isn't helping me to track down the Lisp object which still references this symbol-with-position. I've tried to find the address of Emacs's data segment, so as to be able to search through it for 0x5555561d0455 in GDB, but this doesn't feel like a very useful thing to do. Could somebody who has experience in this sort of thing please suggest how I might proceed with the debugging, or possibly offer me some other sort of help or hints. Thanks in advance! -- Alan Mackenzie (Nuremberg, Germany).