From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Pip Cet Newsgroups: gmane.emacs.devel Subject: Re: Conservative GC isn't safe Date: Sat, 26 Nov 2016 19:08:44 +0000 Message-ID: References: NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: blaine.gmane.org 1480187375 26777 195.159.176.226 (26 Nov 2016 19:09:35 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 26 Nov 2016 19:09:35 +0000 (UTC) Cc: Emacs developers To: Daniel Colascione Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Sat Nov 26 20:09:32 2016 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cAiLq-00069t-7M for ged-emacs-devel@m.gmane.org; Sat, 26 Nov 2016 20:09:30 +0100 Original-Received: from localhost ([::1]:51520 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cAiLt-00075b-Rj for ged-emacs-devel@m.gmane.org; Sat, 26 Nov 2016 14:09:33 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:42110) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cAiLn-00075I-FN for emacs-devel@gnu.org; Sat, 26 Nov 2016 14:09:28 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cAiLm-0008F8-DS for emacs-devel@gnu.org; Sat, 26 Nov 2016 14:09:27 -0500 Original-Received: from mail-wm0-x233.google.com ([2a00:1450:400c:c09::233]:37308) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1cAiLm-0008Ex-6I for emacs-devel@gnu.org; Sat, 26 Nov 2016 14:09:26 -0500 Original-Received: by mail-wm0-x233.google.com with SMTP id t79so118842386wmt.0 for ; Sat, 26 Nov 2016 11:09:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=QHk5It2o8gOYdaeepD1Rb9s5eectOdhGpccBqBjLVyQ=; b=PMNg4X3l2MazqEfpMV18/AZ6sk/JgXpCyhZhFWPw4dOZssNePfubTTrSXP3c/W58zo OmT5wCJuRPhOy2Bk7no6L+mVDM6SbjERVE8vtJVaC4JZcnYIckqDyDcgmXaXAmFw6h9x w57ajTQG9mBXAgsI4axGln1UFeSb5+2EThQ4S9nyhIgKGRsPH+EXDl9MIwUJdptjVogh E7a4fdvU5lUgMZrKaPHnYJWlwqovToQ0KDOWS6vixwUcRI0ijS367rzMuF3dkl2fhNqL llCs5vLxeUT5FHcY/AMngnjI0LF4uPdegx2fpzwKZyxEs6vk1auMMU/ZnmXVtDuHTjbs OVbQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=QHk5It2o8gOYdaeepD1Rb9s5eectOdhGpccBqBjLVyQ=; b=OX6KFyh9gnozdx4sroyEoRp3neRvEKav4YZ6wAJc6Pddn1WaloyAiehStPLh1Fhgtv YoVgYZTasotAVAZKAZbLP38LMCOLmsoQk8lUpHBTJOhF95BAdTGK01jgNyy8PIvxk9c+ tc5bRF5SD3lMFpXVBRZaTtZruXWjxw5RvR6IK9OBuWe5vixr81J+q2GbmEm3RoxjPyzd tYQKd4TXXKdfywJ8jTu4aV7+SvPCZbaa4udcPNVv6sxJG5KgdYqbTMzyh0Ajgao0TKRf /GU83K7pbG3/6/QDOmapk4UcBdsdPizh1sc3C0ZQS0bdW/ZNB8URM3bo1XiS1W6IF3y6 s5Zw== X-Gm-Message-State: AKaTC03nBgHjLDH86o3xcNM/OjbcXRJeD8xivqiUmq5zwX/GUyEZuY9Pde+je3cV/CmzUTmeIBoV4wF0bynAlw== X-Received: by 10.28.234.201 with SMTP id g70mr11990697wmi.104.1480187364684; Sat, 26 Nov 2016 11:09:24 -0800 (PST) Original-Received: by 10.80.182.13 with HTTP; Sat, 26 Nov 2016 11:08:44 -0800 (PST) In-Reply-To: X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2a00:1450:400c:c09::233 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:209624 Archived-At: On Sat, Nov 26, 2016 at 8:11 AM, Daniel Colascione wrote: > 1) mark_maybe_pointer looks only for exact matches on object start. It's > perfectly legal for the compiler to keep an interior object pointer and > discard the pointer to the object start. There's a new, currently undocumented, GCC option called -fkeep-gc-roots-live, which I think addresses this problem. My understanding is previous versions of GCC did not in practice break conservative GC (except for strings, which we handle specially for this reason).