From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Alan Mackenzie Newsgroups: gmane.emacs.devel Subject: Re: gdb doesn't print Lisp backtrace in some circumstances. Date: Fri, 12 Apr 2024 11:29:29 +0000 Message-ID: References: <86pluusunr.fsf@gnu.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="9416"; mail-complaints-to="usenet@ciao.gmane.io" Cc: emacs-devel@gnu.org To: Eli Zaretskii Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Fri Apr 12 13:30:50 2024 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1rvF7K-0002GI-Dq for ged-emacs-devel@m.gmane-mx.org; Fri, 12 Apr 2024 13:30:50 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rvF6M-0006xU-MR; Fri, 12 Apr 2024 07:29:50 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rvF6L-0006xM-If for emacs-devel@gnu.org; Fri, 12 Apr 2024 07:29:49 -0400 Original-Received: from mail.muc.de ([193.149.48.3]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rvF69-0000w8-D4 for emacs-devel@gnu.org; Fri, 12 Apr 2024 07:29:49 -0400 Original-Received: (qmail 10903 invoked by uid 3782); 12 Apr 2024 13:29:33 +0200 Original-Received: from muc.de (pd953ac5b.dip0.t-ipconnect.de [217.83.172.91]) (using STARTTLS) by colin.muc.de (tmda-ofmipd) with ESMTP; Fri, 12 Apr 2024 13:29:32 +0200 Original-Received: (qmail 32720 invoked by uid 1000); 12 Apr 2024 11:29:29 -0000 Content-Disposition: inline In-Reply-To: <86pluusunr.fsf@gnu.org> X-Submission-Agent: TMDA/1.3.x (Ph3nix) X-Primary-Address: acm@muc.de Received-SPF: pass client-ip=193.149.48.3; envelope-from=acm@muc.de; helo=mail.muc.de X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_PASS=-0.001, T_SPF_HELO_TEMPERROR=0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 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-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:317690 Archived-At: Hello, Eli. On Fri, Apr 12, 2024 at 14:11:04 +0300, Eli Zaretskii wrote: > > Date: Fri, 12 Apr 2024 10:31:53 +0000 > > From: Alan Mackenzie > > Yesterday I got a core dump from a segmentation fault in Emacs (my > > development version, not master). I loaded this into gdb inside Emacs > > to have a look at it. > > The backtrace command output the C data as it should, but on coming to > > the Lisp backtrace gave an error message about there needing to be a > > process running to "do this". (I don't have the exact message any > > more.) It would seem these fancy Lisp facilities only work when the > > process that produced them is still running. > Yes, because they call functions inside Emacs to format Lisp objects. > > All the information required to produce this Lisp backtrace is present > > in the core dump. Would it be possible, perhaps, to modify our .gdbinit > > to use the running Emacs to process the core dump, or something like > > that? > I don't think so, no. That's what I feared. > But you can reproduce the Lisp backtrace manually (albeit tediously, > by going over all the calls to Ffuncall, eval_sub and suchlikes, and > displaying their arg[0]. If it's a symbol, typing xsymbol should show > you the Lisp function being called. If it is not a symbol, you could > use xcar/xcdr etc., but that is much more tedious, and I usually give > up on those frames in the stack. I spent a large part of yesterday on this dump. It ends up with a call (apply apply ...) which goes into an infinite recursion with the number of arguments increasing by 1 at each stage. I've found the point in the backtrace where the recursion starts, but it's tedious indeed getting information out of it. I think I'll have to, though, since I can't see any other way of debugging this at the moment. -- Alan Mackenzie (Nuremberg, Germany).