From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: buffer.c/buffer.h: How to add new buffer-local variables? Date: Wed, 03 Apr 2019 20:43:49 +0300 Message-ID: <83zhp7c7ca.fsf@gnu.org> References: <5A3C6A89-2360-46CF-8049-828A4B955445@gnu.org> <875zrzclts.fsf@igel.home> <83imvwfkik.fsf@gnu.org> <06afad36f4467eea0bc1daea58be1281.squirrel@dancol.org> Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="9725"; mail-complaints-to="usenet@blaine.gmane.org" Cc: emacs-devel@gnu.org To: "Daniel Colascione" Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Wed Apr 03 19:44:18 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 1hBjvu-0002Pg-Hh for ged-emacs-devel@m.gmane.org; Wed, 03 Apr 2019 19:44:18 +0200 Original-Received: from localhost ([127.0.0.1]:46006 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hBjvt-0003BP-Dn for ged-emacs-devel@m.gmane.org; Wed, 03 Apr 2019 13:44:17 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:47076) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hBjvH-0003AP-OL for emacs-devel@gnu.org; Wed, 03 Apr 2019 13:43:40 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]:58293) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hBjvF-0006O8-Ew; Wed, 03 Apr 2019 13:43:39 -0400 Original-Received: from [176.228.60.248] (port=2038 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from ) id 1hBjvD-000207-5m; Wed, 03 Apr 2019 13:43:35 -0400 In-reply-to: <06afad36f4467eea0bc1daea58be1281.squirrel@dancol.org> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] 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:234925 Archived-At: > Date: Tue, 2 Apr 2019 11:46:22 -0700 > From: "Daniel Colascione" > Cc: "Daniel Colascione" , > emacs-devel@gnu.org > > > The comment says "sanity check", but I would like to understand what > > kind of sanity is being checked here, and what should be done when > > some structure we dump becomes larger than this value. E.g., is there > > some other limit that requires that offsets of dumped fields never > > exceed 1024 here? I'd like to document in comments what to do when > > the assertion is violated. > > Indeed. That comment could have been a lot better. The general idea here > is this: > > When we enter field_relpos, we're in the middle of some code that's > dumping some data structure field-by-field. The object that we're dumping > begins at in_start; and in_field is an interior pointer into that object. > We can't actually check that the two pointers refer to the same object: C > doesn't give us that level of introspection. But if the two pointers point > to addresses that differ by a lot, then the two pointers probably don't > refer to the same object, and in this case, we can fail an assertion. 1024 > is probably too conservative here. We probably want to greatly increase > this number (say, to 32k) and also to give it a named constantly, maybe > something like PDUMPER_MAXIMUM_STRUCT_SIZE. Thanks, I went with a smaller value, 2KB. It should be good enough for now, as the largest object is slightly below 1KB. > Note that this limit doesn't apply to big variable-length structures like > vectors: we dump these element-by-element instead of treating the whole > thing as one big "object" with a large and variable number of fields. Right.