From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: Stack allocation of Lisp objects Date: Thu, 09 Oct 2014 00:09:37 -0700 Organization: UCLA Computer Science Department Message-ID: <543634B1.7000601@cs.ucla.edu> References: NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1412838620 31489 80.91.229.3 (9 Oct 2014 07:10:20 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 9 Oct 2014 07:10:20 +0000 (UTC) To: Stefan Monnier , emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Thu Oct 09 09:10:14 2014 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Xc7rZ-0002gN-FT for ged-emacs-devel@m.gmane.org; Thu, 09 Oct 2014 09:10:13 +0200 Original-Received: from localhost ([::1]:40813 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xc7rY-0006FR-Tu for ged-emacs-devel@m.gmane.org; Thu, 09 Oct 2014 03:10:12 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:47600) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xc7rI-0006EH-S1 for emacs-devel@gnu.org; Thu, 09 Oct 2014 03:10:02 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xc7rC-0001Dn-Uf for emacs-devel@gnu.org; Thu, 09 Oct 2014 03:09:56 -0400 Original-Received: from smtp.cs.ucla.edu ([131.179.128.62]:36932) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xc7rC-0001Cf-PN for emacs-devel@gnu.org; Thu, 09 Oct 2014 03:09:50 -0400 Original-Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp.cs.ucla.edu (Postfix) with ESMTP id 22FADA60009; Thu, 9 Oct 2014 00:09:42 -0700 (PDT) X-Virus-Scanned: amavisd-new at smtp.cs.ucla.edu Original-Received: from smtp.cs.ucla.edu ([127.0.0.1]) by localhost (smtp.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id KhmdZxdAvXzI; Thu, 9 Oct 2014 00:09:37 -0700 (PDT) Original-Received: from [192.168.1.9] (pool-71-177-17-123.lsanca.dsl-w.verizon.net [71.177.17.123]) by smtp.cs.ucla.edu (Postfix) with ESMTPSA id 4CFDEA60005; Thu, 9 Oct 2014 00:09:37 -0700 (PDT) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.2 In-Reply-To: X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6.x X-Received-From: 131.179.128.62 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 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-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:175166 Archived-At: Stefan Monnier wrote: > Apparently there's an AUTO_STRING somewhere which we stick into a heap > allocated cons cell. A plausible scenario is that you got bitten by a GCC bug, where GCC ignores ___attribute__ ((aligned (8))) on your platform. At least, that's how I reproduced the problem on x86. I filed a GCC bug report . If I'm right, the GCC bug cascaded into an Emacs portability bug: Emacs should use stack-based strings only if stack-base cons also works, as otherwise STACK_CONS could create a heap-based cons cell that points to a stack-based string, the symptom you observed. I fixed that bug in Emacs trunk bzr 118080. Because of this fix, Emacs no longer uses stack-based allocation on x86 + recent GCC, which is a bit of a downer. It should still work with older GCC though, and I expect the GCC folks will fix the bug in newer GCC at some point.