From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: Lisp object that refers to a C struct Date: Thu, 18 Oct 2012 06:50:49 +0200 Message-ID: <83391c2xjq.fsf@gnu.org> References: <83ehkz4edw.fsf@gnu.org> <83bog33wdr.fsf@gnu.org> <837gqq49j7.fsf@gnu.org> <83r4ox3frd.fsf@gnu.org> <83ipa92i95.fsf@gnu.org> <83bog03jyf.fsf@gnu.org> <507F2C74.4070107@cs.ucla.edu> Reply-To: Eli Zaretskii NNTP-Posting-Host: plane.gmane.org X-Trace: ger.gmane.org 1350535899 27149 80.91.229.3 (18 Oct 2012 04:51:39 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 18 Oct 2012 04:51:39 +0000 (UTC) Cc: emacs-devel@gnu.org To: Paul Eggert Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Thu Oct 18 06:51:46 2012 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 1TOi55-000724-Ik for ged-emacs-devel@m.gmane.org; Thu, 18 Oct 2012 06:51:39 +0200 Original-Received: from localhost ([::1]:34291 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOi4y-00082D-HN for ged-emacs-devel@m.gmane.org; Thu, 18 Oct 2012 00:51:32 -0400 Original-Received: from eggs.gnu.org ([208.118.235.92]:51107) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOi4u-000823-S0 for emacs-devel@gnu.org; Thu, 18 Oct 2012 00:51:29 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TOi4t-0002li-Bi for emacs-devel@gnu.org; Thu, 18 Oct 2012 00:51:28 -0400 Original-Received: from mtaout22.012.net.il ([80.179.55.172]:42946) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOi4t-0002lT-3L for emacs-devel@gnu.org; Thu, 18 Oct 2012 00:51:27 -0400 Original-Received: from conversion-daemon.a-mtaout22.012.net.il by a-mtaout22.012.net.il (HyperSendmail v2007.08) id <0MC200H00NT7QI00@a-mtaout22.012.net.il> for emacs-devel@gnu.org; Thu, 18 Oct 2012 06:50:34 +0200 (IST) Original-Received: from HOME-C4E4A596F7 ([87.69.4.28]) by a-mtaout22.012.net.il (HyperSendmail v2007.08) with ESMTPA id <0MC200HATO4AQ030@a-mtaout22.012.net.il>; Thu, 18 Oct 2012 06:50:34 +0200 (IST) In-reply-to: <507F2C74.4070107@cs.ucla.edu> X-012-Sender: halo1@inter.net.il X-detected-operating-system: by eggs.gnu.org: Solaris 10 (beta) X-Received-From: 80.179.55.172 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:154402 Archived-At: > Date: Wed, 17 Oct 2012 15:08:52 -0700 > From: Paul Eggert > CC: emacs-devel@gnu.org > > On 10/17/2012 01:46 PM, Eli Zaretskii wrote: > >> How do you convert the integer into the C struct pointer? > > struct foo *pwatch = (struct foo *)XLI (watch_descriptor); > > > > where watch_descriptor is a Lisp integer. > > Won't this have problems on platforms where > (EMACS_INT) pwatch < MOST_NEGATIVE_FIXNUM, > or where MOST_POSITIVE_FIXNUM < (EMACS_INT) pwatch? Given what XLI does, I don't see how this could happen, with watch_descriptor being a Lisp integer. > Also, suppose someone makes up a random integer > and then passes it as the watch descriptor -- > wouldn't Emacs dump core? No, because, like Stephen says, the descriptor is first validated against a list of known ones.