Received: (at 41357) by debbugs.gnu.org; 25 May 2020 02:10:06 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 24 22:10:06 2020 Received: from localhost ([127.0.0.1]:39221 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jd2Z3-00063c-Mr for submit <at> debbugs.gnu.org; Sun, 24 May 2020 22:10:06 -0400 Received: from gateway32.websitewelcome.com ([192.185.145.119]:29693) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <tom@HIDDEN>) id 1jd2Yy-000633-C9 for 41357 <at> debbugs.gnu.org; Sun, 24 May 2020 22:10:04 -0400 Received: from cm14.websitewelcome.com (cm14.websitewelcome.com [100.42.49.7]) by gateway32.websitewelcome.com (Postfix) with ESMTP id C421D2B4243 for <41357 <at> debbugs.gnu.org>; Sun, 24 May 2020 21:09:59 -0500 (CDT) Received: from box5379.bluehost.com ([162.241.216.53]) by cmsmtp with SMTP id d2YxjCv00XVkQd2YxjFoqx; Sun, 24 May 2020 21:09:59 -0500 X-Authority-Reason: nr=8 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=tromey.com; s=default; h=Content-Type:MIME-Version:Message-ID:In-Reply-To:Date: References:Subject:Cc:To:From:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=X9iO+60VkniiP8ozUpwepW7ymY6K8/7o1cXKXi1crTE=; b=tnfQ0PHOOTbzGyG22bdlHCfM5e VA3JTDOADamXUoj96EklhWLhNos3P1LgPeQRpz+vMlcsaTwONi2GVBPEzJwDkie3Lll0odtH5fUE4 DLv4zyEhu2NOOJh7c807UJ38d; Received: from 174-16-104-48.hlrn.qwest.net ([174.16.104.48]:33322 helo=bapiya) by box5379.bluehost.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92) (envelope-from <tom@HIDDEN>) id 1jd2Yx-0014e7-DB; Sun, 24 May 2020 20:09:59 -0600 From: Tom Tromey <tom@HIDDEN> To: Andrea Corallo <akrl@HIDDEN> Subject: Re: bug#41357: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> X-Attribution: Tom Date: Sun, 24 May 2020 20:09:58 -0600 In-Reply-To: <xjfzha6ag1j.fsf@HIDDEN> (Andrea Corallo's message of "Sun, 17 May 2020 12:42:48 +0000") Message-ID: <87y2pgsr2h.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - box5379.bluehost.com X-AntiAbuse: Original Domain - debbugs.gnu.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - tromey.com X-BWhitelist: no X-Source-IP: 174.16.104.48 X-Source-L: No X-Exim-ID: 1jd2Yx-0014e7-DB X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: 174-16-104-48.hlrn.qwest.net (bapiya) [174.16.104.48]:33322 X-Source-Auth: tom+tromey.com X-Email-Count: 2 X-Source-Cap: ZWx5bnJvYmk7ZWx5bnJvYmk7Ym94NTM3OS5ibHVlaG9zdC5jb20= X-Local-Domain: yes X-Spam-Score: 0.0 (/) X-Debbugs-Envelope-To: 41357 Cc: Eli Zaretskii <eliz@HIDDEN>, 41357 <at> debbugs.gnu.org, Paul Eggert <eggert@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -0.3 (/) Andrea> For now I'm testing the simple attached patch that seams to do the job Andrea> for me. It looks like this patch was checked in, so I think this bug can be closed. I didn't want to do it without verifying with you first though. Tom
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 21:47:30 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 17:47:30 2020 Received: from localhost ([127.0.0.1]:44967 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaR86-0005Hg-7E for submit <at> debbugs.gnu.org; Sun, 17 May 2020 17:47:30 -0400 Received: from lists.gnu.org ([209.51.188.17]:34820) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <akrl@HIDDEN>) id 1jaR80-0005HV-Re for submit <at> debbugs.gnu.org; Sun, 17 May 2020 17:47:29 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60814) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <akrl@HIDDEN>) id 1jaR7v-0005Tb-O2 for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 17:47:20 -0400 Received: from mx.sdf.org ([205.166.94.20]:50028) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <akrl@HIDDEN>) id 1jaR7t-0002Xd-53; Sun, 17 May 2020 17:47:19 -0400 Received: from sdf.org (ma.sdf.org [205.166.94.33]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 04HLlC2B014694 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO); Sun, 17 May 2020 21:47:12 GMT Received: (from akrl@localhost) by sdf.org (8.15.2/8.12.8/Submit) id 04HLlCkN031467; Sun, 17 May 2020 21:47:12 GMT From: Andrea Corallo <akrl@HIDDEN> To: Paul Eggert <eggert@HIDDEN> Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> Date: Sun, 17 May 2020 21:47:12 +0000 In-Reply-To: <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> (Paul Eggert's message of "Sun, 17 May 2020 09:46:23 -0700") Message-ID: <xjfftby8c9r.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=205.166.94.20; envelope-from=akrl@HIDDEN; helo=mx.sdf.org X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/17 12:40:18 X-ACL-Warn: Detected OS = ??? 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, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-Spam-Score: -1.3 (-) X-Debbugs-Envelope-To: submit Cc: Eli Zaretskii <eliz@HIDDEN>, bug-gnu-emacs@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.3 (--) Paul Eggert <eggert@HIDDEN> writes: > On 5/17/20 9:40 AM, Andrea Corallo wrote: >> I think this is a real bug that we have in the codebase (emacs-27 >> included). > > Thanks for all the detective work! Your analysis is correct and your patch looks > good. I've always been suspicious of that code, and it looks like you've > confirmed my suspicions. > > The only question in my mind is whether to install the patch into the emacs-27 > branch or the master branch. Given Eli's problems with stability in emacs-27 > (see Bug#41321), I'm inclined to think the former, as the bug could explain the > problems Eli is observing. Hi Paul, I'm glad you liked the investigation. I've pushed the fix on master as Eli suggested, feel free to improve it in case. I hope a different agreement can be found for 27, in case I'll port it there. Thanks! Andrea -- akrl@HIDDEN
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 21:28:01 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 17:28:01 2020 Received: from localhost ([127.0.0.1]:44933 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaQpF-0004nY-JU for submit <at> debbugs.gnu.org; Sun, 17 May 2020 17:28:01 -0400 Received: from lists.gnu.org ([209.51.188.17]:57080) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eggert@HIDDEN>) id 1jaQpE-0004nS-MW for submit <at> debbugs.gnu.org; Sun, 17 May 2020 17:28:00 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58568) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eggert@HIDDEN>) id 1jaQpE-0000rT-GN for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 17:28:00 -0400 Received: from zimbra.cs.ucla.edu ([131.179.128.68]:57840) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eggert@HIDDEN>) id 1jaQpD-0007An-Lq; Sun, 17 May 2020 17:28:00 -0400 Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 385BF160052; Sun, 17 May 2020 14:27:56 -0700 (PDT) Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id N-5eeGyRC4IG; Sun, 17 May 2020 14:27:55 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 885FD1600CC; Sun, 17 May 2020 14:27:55 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 1JUqwH3zPRlz; Sun, 17 May 2020 14:27:55 -0700 (PDT) Received: from [192.168.1.9] (cpe-23-242-74-103.socal.res.rr.com [23.242.74.103]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 5D521160052; Sun, 17 May 2020 14:27:55 -0700 (PDT) Subject: Re: 28.0.50; GC may miss to mark calle safe register content To: Eli Zaretskii <eliz@HIDDEN>, Andrea Corallo <akrl@HIDDEN> References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> <83d072bihd.fsf@HIDDEN> <xjf8shqa34d.fsf@HIDDEN> <837dxabhej.fsf@HIDDEN> From: Paul Eggert <eggert@HIDDEN> Autocrypt: addr=eggert@HIDDEN; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <837dxabhej.fsf@HIDDEN> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=131.179.128.68; envelope-from=eggert@HIDDEN; helo=zimbra.cs.ucla.edu X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/17 12:21:30 X-ACL-Warn: Detected OS = Linux 3.1-3.10 X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-Spam-Score: -1.3 (-) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.3 (--) On 5/17/20 10:28 AM, Eli Zaretskii wrote: > I'm saying that we've lived with this > bug for a very long time, so if it is real, it is definitely very-very > rare. Yes, it very much has the smell of a GC bug: rare and hard to reproduce, but deadly when it occurs. I wouldn't be surprised if it's causing the rare and hard-to-reproduce crashes you reported in Bug#41321. You might try installing the patch into your copy of emacs-27 and see whether it affects Bug#41321.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 21:21:56 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 17:21:55 2020 Received: from localhost ([127.0.0.1]:44925 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaQjL-0004eg-Nx for submit <at> debbugs.gnu.org; Sun, 17 May 2020 17:21:55 -0400 Received: from lists.gnu.org ([209.51.188.17]:53378) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eggert@HIDDEN>) id 1jaQjL-0004eZ-67 for submit <at> debbugs.gnu.org; Sun, 17 May 2020 17:21:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58068) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eggert@HIDDEN>) id 1jaQjK-0007Nr-V5 for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 17:21:54 -0400 Received: from zimbra.cs.ucla.edu ([131.179.128.68]:57132) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eggert@HIDDEN>) id 1jaQjJ-0005yZ-Ga; Sun, 17 May 2020 17:21:54 -0400 Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 7947C160052; Sun, 17 May 2020 14:21:50 -0700 (PDT) Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id 7gVvAPyyDrke; Sun, 17 May 2020 14:21:49 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id C19071600CC; Sun, 17 May 2020 14:21:49 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id kO9OAON6saWw; Sun, 17 May 2020 14:21:49 -0700 (PDT) Received: from [192.168.1.9] (cpe-23-242-74-103.socal.res.rr.com [23.242.74.103]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 818A6160052; Sun, 17 May 2020 14:21:49 -0700 (PDT) Subject: Re: 28.0.50; GC may miss to mark calle safe register content To: Eli Zaretskii <eliz@HIDDEN> References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN> <92ac80b1-102b-7429-8642-d5a2e974f468@HIDDEN> <838shqbhko.fsf@HIDDEN> <ed7f81e2-faf0-e3ae-0042-0c4be32753fd@HIDDEN> <83wo5a9xd1.fsf@HIDDEN> From: Paul Eggert <eggert@HIDDEN> Autocrypt: addr=eggert@HIDDEN; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <83wo5a9xd1.fsf@HIDDEN> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=131.179.128.68; envelope-from=eggert@HIDDEN; helo=zimbra.cs.ucla.edu X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/17 12:21:30 X-ACL-Warn: Detected OS = Linux 3.1-3.10 X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-Spam-Score: -1.3 (-) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, akrl@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.3 (--) On 5/17/20 12:26 PM, Eli Zaretskii wrote: > And where's GC in this picture? If it's called directly from 'f', can > you show me such code in Emacs? Then we could disassembly it and see > what we've got. > > Usually the code that calls GC is much deeper, and thus the chance of > that temporary to stay in a register is very small, to say the least. The probability is not that small, unfortunately. Compilers often have a habit of running through the same set of callee-save registers in the same order. Let's say you're on the x86 and your compiler consumes the four callee-save registers in the order ebx, esi, edi, ebp. Then if we call f which calls g which calls h which calls the GC, it's likely that f will save just ebx, then g will save just ebx, esi, edi, then h will save just ebx and esi. Hence if the caller has assigned a local variable to ebp, the GC won't see the variable's contents. We should give Andrea a big round of applause for catching this bug.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at 41357) by debbugs.gnu.org; 17 May 2020 21:03:24 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 17:03:24 2020 Received: from localhost ([127.0.0.1]:44911 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaQRQ-0004Ef-Ax for submit <at> debbugs.gnu.org; Sun, 17 May 2020 17:03:24 -0400 Received: from zimbra.cs.ucla.edu ([131.179.128.68]:34444) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eggert@HIDDEN>) id 1jaQRP-0004ER-0p for 41357 <at> debbugs.gnu.org; Sun, 17 May 2020 17:03:23 -0400 Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 6C74D160052; Sun, 17 May 2020 14:03:17 -0700 (PDT) Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id mj-YvO_lD-5w; Sun, 17 May 2020 14:03:16 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id A594B1600CC; Sun, 17 May 2020 14:03:16 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 2nc_yWFU_pRF; Sun, 17 May 2020 14:03:16 -0700 (PDT) Received: from [192.168.1.9] (cpe-23-242-74-103.socal.res.rr.com [23.242.74.103]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 73570160052; Sun, 17 May 2020 14:03:16 -0700 (PDT) Subject: Re: bug#41357: 28.0.50; GC may miss to mark calle safe register content To: Eli Zaretskii <eliz@HIDDEN> References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> <CAOqdjBfK2h6sFhV9UgCjjM8futVCtY_rZ=6dtxdDM8LKxPwzaQ@HIDDEN> <ca688659-f490-9d85-8128-e1b16af074a9@HIDDEN> <83y2pq9xnr.fsf@HIDDEN> From: Paul Eggert <eggert@HIDDEN> Autocrypt: addr=eggert@HIDDEN; 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Q2pETDJvbXU1Y0VxNFJESE00NFFxUGs2Cmw3TzBwVXZOMW1UNEIrUzFiMDhSS3BxbS9mZjAx NUUzN0hOVi9waUl2Smx4R0FZejhQU2Z1R0NCMXRoTVlxbG0KZ2RoZDkvQmFiR0ZiR0dZSEE2 VTQvVDV6cVUrZjZ4SHkxU3NBUVoxTVNLbEx3ZWtCSVQrNC9jTFJHcUNIam5WMApxNUgvVDZh N3Q1bVBrYnpTck9MU280cHVqK0lUb05qWXlZSURCV3pobEExOWF2T2ErcnZVam1IdEQzc0ZO N2NYCld0a0dvaThidU5jYnk0VT0KPUFMNm8KLS0tLS1FTkQgUEdQIFBVQkxJQyBLRVkgQkxP Q0stLS0tLQo= Organization: UCLA Computer Science Department Message-ID: <29b1551d-1280-d358-eac8-9120ec790a3d@HIDDEN> Date: Sun, 17 May 2020 14:03:12 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <83y2pq9xnr.fsf@HIDDEN> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: 41357 Cc: 41357 <at> debbugs.gnu.org, pipcet@HIDDEN, akrl@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) >>> I don't think that platform even has callee-saved registers? >> Eli's platform is 32-bit Microsoft Windows, and W32 has four callee-save >> registers (ebx, esi, edi, ebp) not counting esp and eip which are of course >> callee-save by definition. So the problem could at least in theory be occurring >> on his platform, depending on the compiler and its options. > I've seen the same problem on 64-bit Windows as well, in Emacs > compiled with a different (newer) version of GCC. I don't think this > has anything to do with how many registers are there. You're right that the number of registers doesn't matter, in the sense that the problem can occur if any registers are callee-save. I was responding to Pip Cet's comment, where he said he thought your platform (W32 in the original bug report) had zero callee-saved registers. That would have meant the problem couldn't occur on your platform. However, because your platform does have callee-save registers the problem can occur there. 64-bit Windows also has callee-save registers (rbx, rbp, rdi, rsi, r12, r13, r14, r15) so it can also have the problem. Most platforms do have callee-save these days.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at 41357) by debbugs.gnu.org; 17 May 2020 20:23:06 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 16:23:06 2020 Received: from localhost ([127.0.0.1]:44856 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaPoQ-0003Fn-0c for submit <at> debbugs.gnu.org; Sun, 17 May 2020 16:23:06 -0400 Received: from mx.sdf.org ([205.166.94.20]:62368) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <akrl@HIDDEN>) id 1jaPoO-0003Ff-1Q for 41357 <at> debbugs.gnu.org; Sun, 17 May 2020 16:23:04 -0400 Received: from sdf.org (ma.sdf.org [205.166.94.33]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 04HKN2o1016989 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO); Sun, 17 May 2020 20:23:02 GMT Received: (from akrl@localhost) by sdf.org (8.15.2/8.12.8/Submit) id 04HKN2r4021667; Sun, 17 May 2020 20:23:02 GMT From: Andrea Corallo <akrl@HIDDEN> To: Eli Zaretskii <eliz@HIDDEN> Subject: Re: bug#41357: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> <CAOqdjBfK2h6sFhV9UgCjjM8futVCtY_rZ=6dtxdDM8LKxPwzaQ@HIDDEN> <ca688659-f490-9d85-8128-e1b16af074a9@HIDDEN> <83y2pq9xnr.fsf@HIDDEN> Date: Sun, 17 May 2020 20:23:02 +0000 In-Reply-To: <83y2pq9xnr.fsf@HIDDEN> (Eli Zaretskii's message of "Sun, 17 May 2020 22:19:52 +0300") Message-ID: <xjfo8qm8g61.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Spam-Score: 0.0 (/) X-Debbugs-Envelope-To: 41357 Cc: 41357 <at> debbugs.gnu.org, Paul Eggert <eggert@HIDDEN>, pipcet@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.0 (-) Eli Zaretskii <eliz@HIDDEN> writes: >> Eli's platform is 32-bit Microsoft Windows, and W32 has four callee-save >> registers (ebx, esi, edi, ebp) not counting esp and eip which are of course >> callee-save by definition. So the problem could at least in theory be occurring >> on his platform, depending on the compiler and its options. > > I've seen the same problem on 64-bit Windows as well, in Emacs > compiled with a different (newer) version of GCC. I don't think this > has anything to do with how many registers are there. I also never > before saw these problems, so this is most definitely due to some > recent changes, I just cannot yet figure out which ones. It's hard to say but I suspect the main gate that saved us till today is 'garbage_collect' that being quite big is likely to have calle-save regs spilled. You can disassemble your 'garbage_collect' and see if all of this regs are spilled (in my case they are at -O2). This could give an indication on the correlation of the two bugs (but nothing more). Andrea -- akrl@HIDDEN
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 19:46:43 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 15:46:43 2020 Received: from localhost ([127.0.0.1]:44809 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaPFD-0002Lk-8f for submit <at> debbugs.gnu.org; Sun, 17 May 2020 15:46:43 -0400 Received: from lists.gnu.org ([209.51.188.17]:60556) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <akrl@HIDDEN>) id 1jaPFC-0002Ld-Lh for submit <at> debbugs.gnu.org; Sun, 17 May 2020 15:46:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49508) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <akrl@HIDDEN>) id 1jaPFC-0002wT-Ds for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 15:46:42 -0400 Received: from mx.sdf.org ([205.166.94.20]:52132) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <akrl@HIDDEN>) id 1jaPFA-0007AG-O8; Sun, 17 May 2020 15:46:42 -0400 Received: from sdf.org (ma.sdf.org [205.166.94.33]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 04HJkae5005581 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO); Sun, 17 May 2020 19:46:36 GMT Received: (from akrl@localhost) by sdf.org (8.15.2/8.12.8/Submit) id 04HJkZ73001404; Sun, 17 May 2020 19:46:35 GMT From: Andrea Corallo <akrl@HIDDEN> To: Eli Zaretskii <eliz@HIDDEN> Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN> <92ac80b1-102b-7429-8642-d5a2e974f468@HIDDEN> <838shqbhko.fsf@HIDDEN> <ed7f81e2-faf0-e3ae-0042-0c4be32753fd@HIDDEN> <83wo5a9xd1.fsf@HIDDEN> Date: Sun, 17 May 2020 19:46:35 +0000 In-Reply-To: <83wo5a9xd1.fsf@HIDDEN> (Eli Zaretskii's message of "Sun, 17 May 2020 22:26:18 +0300") Message-ID: <xjfsgfy8hus.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=205.166.94.20; envelope-from=akrl@HIDDEN; helo=mx.sdf.org X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/17 12:40:18 X-ACL-Warn: Detected OS = ??? 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, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-Spam-Score: -1.3 (-) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, Paul Eggert <eggert@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.3 (--) Eli Zaretskii <eliz@HIDDEN> writes: >> Cc: akrl@HIDDEN, bug-gnu-emacs@HIDDEN >> From: Paul Eggert <eggert@HIDDEN> >> Date: Sun, 17 May 2020 12:05:25 -0700 >> >> On 5/17/20 10:24 AM, Eli Zaretskii wrote: >> > I struggle to see >> > how a Lisp object could appear in a register without leaving any trace >> > on the stack >> >> Quite easily. It happens all the time. If I do something like this: >> >> Lisp_Object a = Fcons (b, c); >> f (x, y); >> return a; > > And where's GC in this picture? GC can be triggered by f or any of his callee it does not matter. > If it's called directly from 'f', can > you show me such code in Emacs? Then we could disassembly it and see > what we've got. I'm not sure what we can prove disassembling, that would be just the result of a specific .c + toolchain + invocation. I think we want to have code that is sufficiently portable and safe because correct. > Usually the code that calls GC is much deeper, and thus the chance of > that temporary to stay in a register is very small, to say the least. Probably yes, but I don't think we want to have code that works accidentally. Andrea -- akrl@HIDDEN
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 19:26:32 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 15:26:32 2020 Received: from localhost ([127.0.0.1]:44785 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaOvg-0001p6-0p for submit <at> debbugs.gnu.org; Sun, 17 May 2020 15:26:32 -0400 Received: from lists.gnu.org ([209.51.188.17]:42692) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eliz@HIDDEN>) id 1jaOve-0001oz-Cm for submit <at> debbugs.gnu.org; Sun, 17 May 2020 15:26:30 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47680) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaOvc-0001yT-TP for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 15:26:29 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:36931) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaOvc-0002HD-DC; Sun, 17 May 2020 15:26:28 -0400 Received: from [176.228.60.248] (port=1687 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <eliz@HIDDEN>) id 1jaOvZ-0007Nz-DP; Sun, 17 May 2020 15:26:26 -0400 Date: Sun, 17 May 2020 22:26:18 +0300 Message-Id: <83wo5a9xd1.fsf@HIDDEN> From: Eli Zaretskii <eliz@HIDDEN> To: Paul Eggert <eggert@HIDDEN> In-Reply-To: <ed7f81e2-faf0-e3ae-0042-0c4be32753fd@HIDDEN> (message from Paul Eggert on Sun, 17 May 2020 12:05:25 -0700) Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN> <92ac80b1-102b-7429-8642-d5a2e974f468@HIDDEN> <838shqbhko.fsf@HIDDEN> <ed7f81e2-faf0-e3ae-0042-0c4be32753fd@HIDDEN> X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, akrl@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) > Cc: akrl@HIDDEN, bug-gnu-emacs@HIDDEN > From: Paul Eggert <eggert@HIDDEN> > Date: Sun, 17 May 2020 12:05:25 -0700 > > On 5/17/20 10:24 AM, Eli Zaretskii wrote: > > I struggle to see > > how a Lisp object could appear in a register without leaving any trace > > on the stack > > Quite easily. It happens all the time. If I do something like this: > > Lisp_Object a = Fcons (b, c); > f (x, y); > return a; And where's GC in this picture? If it's called directly from 'f', can you show me such code in Emacs? Then we could disassembly it and see what we've got. Usually the code that calls GC is much deeper, and thus the chance of that temporary to stay in a register is very small, to say the least. > The proposed fix is harmless Yeah, right. Sorry, I don't buy this. Too many gray hair from such assumptions.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at 41357) by debbugs.gnu.org; 17 May 2020 19:20:08 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 15:20:08 2020 Received: from localhost ([127.0.0.1]:44778 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaOpU-0001fl-2O for submit <at> debbugs.gnu.org; Sun, 17 May 2020 15:20:08 -0400 Received: from eggs.gnu.org ([209.51.188.92]:39554) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eliz@HIDDEN>) id 1jaOpS-0001fK-Q4 for 41357 <at> debbugs.gnu.org; Sun, 17 May 2020 15:20:07 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:36873) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaOpM-0000VP-Fn; Sun, 17 May 2020 15:20:00 -0400 Received: from [176.228.60.248] (port=1293 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <eliz@HIDDEN>) id 1jaOpL-0006Zh-UX; Sun, 17 May 2020 15:20:00 -0400 Date: Sun, 17 May 2020 22:19:52 +0300 Message-Id: <83y2pq9xnr.fsf@HIDDEN> From: Eli Zaretskii <eliz@HIDDEN> To: Paul Eggert <eggert@HIDDEN> In-Reply-To: <ca688659-f490-9d85-8128-e1b16af074a9@HIDDEN> (message from Paul Eggert on Sun, 17 May 2020 12:01:40 -0700) Subject: Re: bug#41357: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> <CAOqdjBfK2h6sFhV9UgCjjM8futVCtY_rZ=6dtxdDM8LKxPwzaQ@HIDDEN> <ca688659-f490-9d85-8128-e1b16af074a9@HIDDEN> X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: 41357 Cc: 41357 <at> debbugs.gnu.org, pipcet@HIDDEN, akrl@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) > Cc: Andrea Corallo <akrl@HIDDEN>, Eli Zaretskii <eliz@HIDDEN>, > 41357 <at> debbugs.gnu.org > From: Paul Eggert <eggert@HIDDEN> > Date: Sun, 17 May 2020 12:01:40 -0700 > > On 5/17/20 10:00 AM, Pip Cet wrote: > > I don't think that platform even has callee-saved registers? > > Eli's platform is 32-bit Microsoft Windows, and W32 has four callee-save > registers (ebx, esi, edi, ebp) not counting esp and eip which are of course > callee-save by definition. So the problem could at least in theory be occurring > on his platform, depending on the compiler and its options. I've seen the same problem on 64-bit Windows as well, in Emacs compiled with a different (newer) version of GCC. I don't think this has anything to do with how many registers are there. I also never before saw these problems, so this is most definitely due to some recent changes, I just cannot yet figure out which ones.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
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Subject: Re: 28.0.50; GC may miss to mark calle safe register content
To: Eli Zaretskii <eliz@HIDDEN>
References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN>
<xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN>
<92ac80b1-102b-7429-8642-d5a2e974f468@HIDDEN> <838shqbhko.fsf@HIDDEN>
From: Paul Eggert <eggert@HIDDEN>
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On 5/17/20 10:24 AM, Eli Zaretskii wrote:
> I struggle to see
> how a Lisp object could appear in a register without leaving any trace
> on the stack
Quite easily. It happens all the time. If I do something like this:
Lisp_Object a = Fcons (b, c);
f (x, y);
return a;
The compiler might put 'a' into a callee-save register R, which means that while
f is running there's no trace of 'a' on the stack (unless f's code itself
decides to use R for whatever reason, but let's suppose it doesn't). This
situation can persist even if f calls g which calls h which calls the garbage
collector, and the garbage collector will then think the cons is garbage even
though it's not.
The proposed fix is harmless except it may execute a handful more instructions
per GC. So the cost of applying the fix is tiny, whereas the potential
reliability benefit is large.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at 41357) by debbugs.gnu.org; 17 May 2020 19:01:53 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 15:01:53 2020 Received: from localhost ([127.0.0.1]:44746 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaOXp-0001Es-6L for submit <at> debbugs.gnu.org; Sun, 17 May 2020 15:01:53 -0400 Received: from zimbra.cs.ucla.edu ([131.179.128.68]:51270) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eggert@HIDDEN>) id 1jaOXn-0001Ee-0z for 41357 <at> debbugs.gnu.org; Sun, 17 May 2020 15:01:51 -0400 Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 83BB5160052; Sun, 17 May 2020 12:01:45 -0700 (PDT) Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id nh-maX2OCJuF; Sun, 17 May 2020 12:01:44 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id D35461600CC; Sun, 17 May 2020 12:01:44 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id c22uITxRHkyc; Sun, 17 May 2020 12:01:44 -0700 (PDT) Received: from [192.168.1.9] (cpe-23-242-74-103.socal.res.rr.com [23.242.74.103]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id A3B12160052; Sun, 17 May 2020 12:01:44 -0700 (PDT) Subject: Re: bug#41357: 28.0.50; GC may miss to mark calle safe register content To: Pip Cet <pipcet@HIDDEN> References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> <CAOqdjBfK2h6sFhV9UgCjjM8futVCtY_rZ=6dtxdDM8LKxPwzaQ@HIDDEN> From: Paul Eggert <eggert@HIDDEN> Autocrypt: addr=eggert@HIDDEN; prefer-encrypt=mutual; keydata= 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Q2pETDJvbXU1Y0VxNFJESE00NFFxUGs2Cmw3TzBwVXZOMW1UNEIrUzFiMDhSS3BxbS9mZjAx NUUzN0hOVi9waUl2Smx4R0FZejhQU2Z1R0NCMXRoTVlxbG0KZ2RoZDkvQmFiR0ZiR0dZSEE2 VTQvVDV6cVUrZjZ4SHkxU3NBUVoxTVNLbEx3ZWtCSVQrNC9jTFJHcUNIam5WMApxNUgvVDZh N3Q1bVBrYnpTck9MU280cHVqK0lUb05qWXlZSURCV3pobEExOWF2T2ErcnZVam1IdEQzc0ZO N2NYCld0a0dvaThidU5jYnk0VT0KPUFMNm8KLS0tLS1FTkQgUEdQIFBVQkxJQyBLRVkgQkxP Q0stLS0tLQo= Organization: UCLA Computer Science Department Message-ID: <ca688659-f490-9d85-8128-e1b16af074a9@HIDDEN> Date: Sun, 17 May 2020 12:01:40 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <CAOqdjBfK2h6sFhV9UgCjjM8futVCtY_rZ=6dtxdDM8LKxPwzaQ@HIDDEN> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: 41357 Cc: Eli Zaretskii <eliz@HIDDEN>, 41357 <at> debbugs.gnu.org, Andrea Corallo <akrl@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) On 5/17/20 10:00 AM, Pip Cet wrote: > I don't think that platform even has callee-saved registers? Eli's platform is 32-bit Microsoft Windows, and W32 has four callee-save registers (ebx, esi, edi, ebp) not counting esp and eip which are of course callee-save by definition. So the problem could at least in theory be occurring on his platform, depending on the compiler and its options.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
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From: Andrea Corallo <akrl@HIDDEN>
To: Eli Zaretskii <eliz@HIDDEN>
Subject: Re: 28.0.50; GC may miss to mark calle safe register content
References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN>
<xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN>
<xjfd072a3ih.fsf@HIDDEN> <83a726bhn1.fsf@HIDDEN>
<xjf4ksea213.fsf@HIDDEN> <835zcubg1j.fsf@HIDDEN>
Date: Sun, 17 May 2020 18:16:24 +0000
In-Reply-To: <835zcubg1j.fsf@HIDDEN> (Eli Zaretskii's message of "Sun, 17 May
2020 20:57:28 +0300")
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Eli Zaretskii <eliz@HIDDEN> writes:
>> From: Andrea Corallo <akrl@HIDDEN>
>> Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN
>> Date: Sun, 17 May 2020 17:45:28 +0000
>>
>> Lisp_Object
>> foo (void)
>> {
>> /* 'res' goes in a callee saved reg */
>> Lisp_Object res = build_string ("bar");
>> [...]
>> /* LTO inline the following as "flush_stack_call_func (mark_threads_callback, NULL);" */
>> mark_threads ();
>> [...]
>> gc_sweep ();
>>
>> /* The string pointed by 'res' was garbage collected. */
>> return res;
>> }
>
> But mark_threads etc. (GC in general) isn't called from functions like
> your 'foo. It is more like this:
>
> Lisp_Object
> foo (void)
> {
> /* 'res' goes in a callee saved reg */
> Lisp_Object res = build_string ("bar");
> [...]
> call_something ();
> [...]
>
> }
>
> call_something (void)
> {
> [...]
> garbage_collect ();
> [...]
> }
Yes, my example was minimal your is certanly more realistic.
But also this can be critical. We have to hope that in 'call_something'
or 'garbage_collect' there is sufficient register pressure to have the
register that is holding 'res' to be pushed.
Andrea
--
akrl@HIDDEN
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
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Date: Sun, 17 May 2020 20:57:28 +0300
Message-Id: <835zcubg1j.fsf@HIDDEN>
From: Eli Zaretskii <eliz@HIDDEN>
To: Andrea Corallo <akrl@HIDDEN>
In-Reply-To: <xjf4ksea213.fsf@HIDDEN> (message from Andrea Corallo on Sun, 17
May 2020 17:45:28 +0000)
Subject: Re: 28.0.50; GC may miss to mark calle safe register content
References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN>
<xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN>
<xjfd072a3ih.fsf@HIDDEN> <83a726bhn1.fsf@HIDDEN> <xjf4ksea213.fsf@HIDDEN>
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> From: Andrea Corallo <akrl@HIDDEN>
> Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN
> Date: Sun, 17 May 2020 17:45:28 +0000
>
> Lisp_Object
> foo (void)
> {
> /* 'res' goes in a callee saved reg */
> Lisp_Object res = build_string ("bar");
> [...]
> /* LTO inline the following as "flush_stack_call_func (mark_threads_callback, NULL);" */
> mark_threads ();
> [...]
> gc_sweep ();
>
> /* The string pointed by 'res' was garbage collected. */
> return res;
> }
But mark_threads etc. (GC in general) isn't called from functions like
your 'foo. It is more like this:
Lisp_Object
foo (void)
{
/* 'res' goes in a callee saved reg */
Lisp_Object res = build_string ("bar");
[...]
call_something ();
[...]
}
call_something (void)
{
[...]
garbage_collect ();
[...]
}
Which is quite different, AFAIU, wrt stack usage.
Or maybe I don't understand how "callee saved registers" work.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
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From: Andrea Corallo <akrl@HIDDEN>
To: Eli Zaretskii <eliz@HIDDEN>
Subject: Re: 28.0.50; GC may miss to mark calle safe register content
References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN>
<xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN>
<xjfd072a3ih.fsf@HIDDEN> <83a726bhn1.fsf@HIDDEN>
Date: Sun, 17 May 2020 17:45:28 +0000
In-Reply-To: <83a726bhn1.fsf@HIDDEN> (Eli Zaretskii's message of "Sun, 17 May
2020 20:22:58 +0300")
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Eli Zaretskii <eliz@HIDDEN> writes:
>> From: Andrea Corallo <akrl@HIDDEN>
>> Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN
>> Date: Sun, 17 May 2020 17:13:26 +0000
>>
>> If a C function caller of 'flush_stack_call_func' allocates a
>> Lisp_Object in a temp variable and the compiler decide to keep this in a
>> callee saved reg while 'flush_stack_call_func' is called this will be
>> garbage collected unexpectedly.
>
> Can you show me an example of this (as skeleton C code)?
>
> Thanks.
Sure, something like
=====
Lisp_Object
foo (void)
{
/* 'res' goes in a callee saved reg */
Lisp_Object res = build_string ("bar");
[...]
/* LTO inline the following as "flush_stack_call_func (mark_threads_callback, NULL);" */
mark_threads ();
[...]
gc_sweep ();
/* The string pointed by 'res' was garbage collected. */
return res;
}
=====
I'm not sure this is the only possible scenarion tho.
Andrea
--
akrl@HIDDEN
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 17:28:18 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 13:28:18 2020 Received: from localhost ([127.0.0.1]:44661 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaN5F-0007R7-TY for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:28:18 -0400 Received: from lists.gnu.org ([209.51.188.17]:55118) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eliz@HIDDEN>) id 1jaN5E-0007Qy-76 for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:28:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34040) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaN5C-0007Hl-QT for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 13:28:16 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:35005) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaN5B-0006Ey-7y; Sun, 17 May 2020 13:28:14 -0400 Received: from [176.228.60.248] (port=2373 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <eliz@HIDDEN>) id 1jaN59-00076T-EB; Sun, 17 May 2020 13:28:12 -0400 Date: Sun, 17 May 2020 20:28:04 +0300 Message-Id: <837dxabhej.fsf@HIDDEN> From: Eli Zaretskii <eliz@HIDDEN> To: Andrea Corallo <akrl@HIDDEN> In-Reply-To: <xjf8shqa34d.fsf@HIDDEN> (message from Andrea Corallo on Sun, 17 May 2020 17:21:54 +0000) Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> <83d072bihd.fsf@HIDDEN> <xjf8shqa34d.fsf@HIDDEN> X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) > From: Andrea Corallo <akrl@HIDDEN> > Cc: Paul Eggert <eggert@HIDDEN>, bug-gnu-emacs@HIDDEN > Date: Sun, 17 May 2020 17:21:54 +0000 > > But I just wanted to point out that I think this is clearly a bug in our > code, and it can trigger depending on decision of the tool-chain we have > no control over. I'm not saying it is not a bug. I'm saying that we've lived with this bug for a very long time, so if it is real, it is definitely very-very rare. If we put every bugfix we could think of into the release branch, we will never release Emacs 27. Never. Because there's always one more bug. > I think it should be trated as we would do if we discover and verify an > "access out of bounds" or "read after free". Depends on the circumstances.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 17:24:34 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 13:24:34 2020 Received: from localhost ([127.0.0.1]:44657 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaN1e-0007LT-Df for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:24:34 -0400 Received: from lists.gnu.org ([209.51.188.17]:52148) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eliz@HIDDEN>) id 1jaN1c-0007LM-Vl for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:24:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33596) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaN1c-0005dD-Pb for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 13:24:32 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:34942) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaN1b-0005aJ-MN; Sun, 17 May 2020 13:24:31 -0400 Received: from [176.228.60.248] (port=2147 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <eliz@HIDDEN>) id 1jaN1a-0003mZ-Sc; Sun, 17 May 2020 13:24:31 -0400 Date: Sun, 17 May 2020 20:24:23 +0300 Message-Id: <838shqbhko.fsf@HIDDEN> From: Eli Zaretskii <eliz@HIDDEN> To: Paul Eggert <eggert@HIDDEN> In-Reply-To: <92ac80b1-102b-7429-8642-d5a2e974f468@HIDDEN> (message from Paul Eggert on Sun, 17 May 2020 10:08:00 -0700) Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN> <92ac80b1-102b-7429-8642-d5a2e974f468@HIDDEN> X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, akrl@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) > Cc: bug-gnu-emacs@HIDDEN > From: Paul Eggert <eggert@HIDDEN> > Date: Sun, 17 May 2020 10:08:00 -0700 > > It's a low-level problem in which the garbage collector is not seeing some > objects that it should see, because at the machine level the object addresses > are in registers that the garbage collector hasn't saved and thus won't see when > it scans memory. Since we write in C and in Lisp, not in assembly, I struggle to see how a Lisp object could appear in a register without leaving any trace on the stack. I'm probably missing something.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 17:23:11 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 13:23:11 2020 Received: from localhost ([127.0.0.1]:44653 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaN0J-0007JP-0v for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:23:11 -0400 Received: from lists.gnu.org ([209.51.188.17]:49826) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eliz@HIDDEN>) id 1jaN0G-0007JH-SH for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:23:09 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33342) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaN0G-0004Yr-Mg for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 13:23:08 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:34913) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaN0G-0005Nk-AC; Sun, 17 May 2020 13:23:08 -0400 Received: from [176.228.60.248] (port=2056 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <eliz@HIDDEN>) id 1jaN0E-0003ba-Fg; Sun, 17 May 2020 13:23:07 -0400 Date: Sun, 17 May 2020 20:22:58 +0300 Message-Id: <83a726bhn1.fsf@HIDDEN> From: Eli Zaretskii <eliz@HIDDEN> To: Andrea Corallo <akrl@HIDDEN> In-Reply-To: <xjfd072a3ih.fsf@HIDDEN> (message from Andrea Corallo on Sun, 17 May 2020 17:13:26 +0000) Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN> <xjfd072a3ih.fsf@HIDDEN> X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) > From: Andrea Corallo <akrl@HIDDEN> > Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN > Date: Sun, 17 May 2020 17:13:26 +0000 > > If a C function caller of 'flush_stack_call_func' allocates a > Lisp_Object in a temp variable and the compiler decide to keep this in a > callee saved reg while 'flush_stack_call_func' is called this will be > garbage collected unexpectedly. Can you show me an example of this (as skeleton C code)? Thanks.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 17:22:03 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 13:22:02 2020 Received: from localhost ([127.0.0.1]:44649 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaMzC-0007HG-GP for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:22:02 -0400 Received: from lists.gnu.org ([209.51.188.17]:49600) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <akrl@HIDDEN>) id 1jaMzA-0007Gr-RI for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:22:01 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33230) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <akrl@HIDDEN>) id 1jaMzA-0004PU-8n for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 13:22:00 -0400 Received: from mx.sdf.org ([205.166.94.20]:56833) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <akrl@HIDDEN>) id 1jaMz8-0005H2-Gp; Sun, 17 May 2020 13:21:59 -0400 Received: from sdf.org (ma.sdf.org [205.166.94.33]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 04HHLsjo007568 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO); Sun, 17 May 2020 17:21:55 GMT Received: (from akrl@localhost) by sdf.org (8.15.2/8.12.8/Submit) id 04HHLsIQ026493; Sun, 17 May 2020 17:21:54 GMT From: Andrea Corallo <akrl@HIDDEN> To: Eli Zaretskii <eliz@HIDDEN> Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> <83d072bihd.fsf@HIDDEN> Date: Sun, 17 May 2020 17:21:54 +0000 In-Reply-To: <83d072bihd.fsf@HIDDEN> (Eli Zaretskii's message of "Sun, 17 May 2020 20:04:46 +0300") Message-ID: <xjf8shqa34d.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=205.166.94.20; envelope-from=akrl@HIDDEN; helo=mx.sdf.org X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/17 12:40:18 X-ACL-Warn: Detected OS = ??? 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, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-Spam-Score: -1.3 (-) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, Paul Eggert <eggert@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.3 (--) Eli Zaretskii <eliz@HIDDEN> writes: >> Cc: bug-gnu-emacs@HIDDEN >> From: Paul Eggert <eggert@HIDDEN> >> Date: Sun, 17 May 2020 09:46:23 -0700 >> >> The only question in my mind is whether to install the patch into the emacs-27 >> branch or the master branch. > > Definitely the master! Is not my responsability so I'll not insist. But I just wanted to point out that I think this is clearly a bug in our code, and it can trigger depending on decision of the tool-chain we have no control over. I think it should be trated as we would do if we discover and verify an "access out of bounds" or "read after free". My opinion :) Regards Andrea -- akrl@HIDDEN
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
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Sun, 17 May 2020 13:15:44 -0400 Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id EEAB41600CC; Sun, 17 May 2020 10:08:06 -0700 (PDT) Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id hMLv3FZxO7yw; Sun, 17 May 2020 10:08:01 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 4AADF1600DA; Sun, 17 May 2020 10:08:01 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 3z7idkr_73JW; Sun, 17 May 2020 10:08:01 -0700 (PDT) Received: from [192.168.1.9] (cpe-23-242-74-103.socal.res.rr.com [23.242.74.103]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 1FCE1160052; Sun, 17 May 2020 10:08:01 -0700 (PDT) Subject: Re: 28.0.50; GC may miss to mark calle safe register content To: Eli Zaretskii <eliz@HIDDEN>, Andrea Corallo <akrl@HIDDEN> References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN> From: Paul Eggert <eggert@HIDDEN> Autocrypt: addr=eggert@HIDDEN; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <83eeribiim.fsf@HIDDEN> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=131.179.128.68; envelope-from=eggert@HIDDEN; helo=zimbra.cs.ucla.edu X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/17 12:21:30 X-ACL-Warn: Detected OS = Linux 3.1-3.10 X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-Spam-Score: -1.3 (-) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.3 (--) On 5/17/20 10:04 AM, Eli Zaretskii wrote: > I cannot easily > correlate your description of using registers with what happens when > we call Lisp or bytecode. His description is generic: it applies regardless of whether the garbage collector is called from C code (in his branch, generated from Lisp code) or from the interpreter (either in his branch or in the emacs-27 branch) as it is executing Lisp code or bytecode. It's a low-level problem in which the garbage collector is not seeing some objects that it should see, because at the machine level the object addresses are in registers that the garbage collector hasn't saved and thus won't see when it scans memory. A serious and insidious bug in our existing system, in other words.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 17:13:34 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 13:13:34 2020 Received: from localhost ([127.0.0.1]:44525 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaMr0-0004mV-4z for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:13:34 -0400 Received: from lists.gnu.org ([209.51.188.17]:60926) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <akrl@HIDDEN>) id 1jaMqy-0004mO-KX for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:13:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59528) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <akrl@HIDDEN>) id 1jaMqy-0004oq-Ez for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 13:13:32 -0400 Received: from mx.sdf.org ([205.166.94.20]:57726) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <akrl@HIDDEN>) id 1jaMqw-0003CE-SX; Sun, 17 May 2020 13:13:32 -0400 Received: from sdf.org (ma.sdf.org [205.166.94.33]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 04HHDQow029956 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO); Sun, 17 May 2020 17:13:26 GMT Received: (from akrl@localhost) by sdf.org (8.15.2/8.12.8/Submit) id 04HHDQKQ021622; Sun, 17 May 2020 17:13:26 GMT From: Andrea Corallo <akrl@HIDDEN> To: Eli Zaretskii <eliz@HIDDEN> Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <83eeribiim.fsf@HIDDEN> Date: Sun, 17 May 2020 17:13:26 +0000 In-Reply-To: <83eeribiim.fsf@HIDDEN> (Eli Zaretskii's message of "Sun, 17 May 2020 20:04:01 +0300") Message-ID: <xjfd072a3ih.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=205.166.94.20; envelope-from=akrl@HIDDEN; helo=mx.sdf.org X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/17 12:40:18 X-ACL-Warn: Detected OS = ??? 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, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-Spam-Score: -1.3 (-) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.3 (--) Eli Zaretskii <eliz@HIDDEN> writes: >> From: Andrea Corallo <akrl@HIDDEN> >> Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN >> Date: Sun, 17 May 2020 16:40:09 +0000 >> >> I think this is a real bug that we have in the codebase (emacs-27 >> included). > > Maybe it's so, but your explanation makes sense only in the context of > calling a machine-language function. When we call Lisp or bytecode, > the machine-level operation is very different, and I cannot easily > correlate your description of using registers with what happens when > we call Lisp or bytecode. Sorry for my misunderstanding. That is correct, but I don't think we need bytecode to come into play here to have the problem. If a C function caller of 'flush_stack_call_func' allocates a Lisp_Object in a temp variable and the compiler decide to keep this in a callee saved reg while 'flush_stack_call_func' is called this will be garbage collected unexpectedly. Am I wrong? Andrea -- akrl@HIDDEN
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 17:04:56 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 13:04:56 2020 Received: from localhost ([127.0.0.1]:44518 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaMie-0004a4-7n for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:04:56 -0400 Received: from lists.gnu.org ([209.51.188.17]:51160) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eliz@HIDDEN>) id 1jaMic-0004Zv-78 for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:04:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58272) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaMic-00006M-3G for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 13:04:54 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:34388) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaMib-0008KW-QW; Sun, 17 May 2020 13:04:53 -0400 Received: from [176.228.60.248] (port=4815 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <eliz@HIDDEN>) id 1jaMia-0008Rp-W6; Sun, 17 May 2020 13:04:53 -0400 Date: Sun, 17 May 2020 20:04:46 +0300 Message-Id: <83d072bihd.fsf@HIDDEN> From: Eli Zaretskii <eliz@HIDDEN> To: Paul Eggert <eggert@HIDDEN> In-Reply-To: <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> (message from Paul Eggert on Sun, 17 May 2020 09:46:23 -0700) Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, akrl@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) > Cc: bug-gnu-emacs@HIDDEN > From: Paul Eggert <eggert@HIDDEN> > Date: Sun, 17 May 2020 09:46:23 -0700 > > The only question in my mind is whether to install the patch into the emacs-27 > branch or the master branch. Definitely the master!
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 17:04:13 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 13:04:13 2020 Received: from localhost ([127.0.0.1]:44515 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaMhw-0004Yz-T2 for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:04:13 -0400 Received: from lists.gnu.org ([209.51.188.17]:51152) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eliz@HIDDEN>) id 1jaMhu-0004Yr-Ry for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:04:11 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58214) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaMhu-0008KU-Mz for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 13:04:10 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:34381) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaMhu-0008H4-BV; Sun, 17 May 2020 13:04:10 -0400 Received: from [176.228.60.248] (port=4769 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <eliz@HIDDEN>) id 1jaMht-0004d7-LL; Sun, 17 May 2020 13:04:10 -0400 Date: Sun, 17 May 2020 20:04:01 +0300 Message-Id: <83eeribiim.fsf@HIDDEN> From: Eli Zaretskii <eliz@HIDDEN> To: Andrea Corallo <akrl@HIDDEN> In-Reply-To: <xjfh7wea51y.fsf@HIDDEN> (message from Andrea Corallo on Sun, 17 May 2020 16:40:09 +0000) Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) > From: Andrea Corallo <akrl@HIDDEN> > Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN > Date: Sun, 17 May 2020 16:40:09 +0000 > > I think this is a real bug that we have in the codebase (emacs-27 > included). Maybe it's so, but your explanation makes sense only in the context of calling a machine-language function. When we call Lisp or bytecode, the machine-level operation is very different, and I cannot easily correlate your description of using registers with what happens when we call Lisp or bytecode. Sorry for my misunderstanding.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at 41357) by debbugs.gnu.org; 17 May 2020 17:01:22 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 13:01:22 2020 Received: from localhost ([127.0.0.1]:44511 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaMfC-0003Zp-9r for submit <at> debbugs.gnu.org; Sun, 17 May 2020 13:01:22 -0400 Received: from mail-oi1-f174.google.com ([209.85.167.174]:45246) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <pipcet@HIDDEN>) id 1jaMfA-0003TW-Gj for 41357 <at> debbugs.gnu.org; Sun, 17 May 2020 13:01:20 -0400 Received: by mail-oi1-f174.google.com with SMTP id d191so6965487oib.12 for <41357 <at> debbugs.gnu.org>; Sun, 17 May 2020 10:01:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=aP23GjOmNbKxN6cYRsmnvx+TBeH0xG26Cxanqz9BthQ=; b=qohbNBiOnmKzHS3mTAA5gQw5cztFBW1E82fjBtOhO4zd66uDs532Lqen9zv0e+ThJt 0LKR3K8cHYxo6p3WW5TYwMX+vvioDa+1izwjBqPmR2RXge7PZKKRNf07uoXc4OvIOydD 1WZGLWYlMo4RCyt81Dgd5304R5BWG1Y+Ycyp1nj8RoOsRSVIs12V4ZYfa/ck8z7MWTXQ xlc2I82FxIpgaQByvtdmJIj+iVqYBXnpnDVCLUgjIplz5pG4leL01yO7kKa8fwA4jRIb QehCZvQBFBCsjhLV35+V3Bk3nabe9jvXx+6m/BCE6SIZROj0fu8Z+xygcSfX0XYZUBSc eLXA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=aP23GjOmNbKxN6cYRsmnvx+TBeH0xG26Cxanqz9BthQ=; b=I9q/yn1GKYuXqJ5j96iv0z+eL1pkR4xr6N4+HfFBTiY9O/DMoXpm/nShC2Hv4OXl/K qWVlWt94r/Hvnq+Y1ct5zqwrXS2e/fuJIzF7oUU7Shns+xBnVSPh+bGPo/SLpOZiS9K9 7oDPrMcWnjNYbJXVywUDxx2k3Nn6J6XqYUvH/rLRxJmmGVDCBYHBmW41z0HfIRZ8RUiV XMrSt8l9y4Jvsl2J8Z8IpIykiMhbmy00aao7FVLiv/qgWJo54g/LXa36gB8WkAvdIiGG Wph6AyJsTxAg3JIV4jfuJ/RPU/ShPVHcDjnGBn31wDt0Z+JY3NXbWOigZEgVJUr0MPiH X69w== X-Gm-Message-State: AOAM533ZRSfacZOUP/TWTODbSIJN5sfXMqmxomMhjaWldLjbmCT9r3FY I63Os4mq+eF3fg3gu/iFJl1cXEHiNZJ/rm0h5wA= X-Google-Smtp-Source: ABdhPJzLM3nIfO07TBtxZaf7Lwle3GvQswudwZqENjy5JGNs9JzecmIvM8dwCzE/0DOUh8WaARJCSf+hjLWIeRTTkGM= X-Received: by 2002:aca:ea05:: with SMTP id i5mr8792576oih.44.1589734874776; Sun, 17 May 2020 10:01:14 -0700 (PDT) MIME-Version: 1.0 References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> In-Reply-To: <8f0c7763-9210-aa29-7cee-945b8494d827@HIDDEN> From: Pip Cet <pipcet@HIDDEN> Date: Sun, 17 May 2020 17:00:38 +0000 Message-ID: <CAOqdjBfK2h6sFhV9UgCjjM8futVCtY_rZ=6dtxdDM8LKxPwzaQ@HIDDEN> Subject: Re: bug#41357: 28.0.50; GC may miss to mark calle safe register content To: Paul Eggert <eggert@HIDDEN> Content-Type: text/plain; charset="UTF-8" X-Spam-Score: 0.0 (/) X-Debbugs-Envelope-To: 41357 Cc: Eli Zaretskii <eliz@HIDDEN>, 41357 <at> debbugs.gnu.org, Andrea Corallo <akrl@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.0 (-) On Sun, May 17, 2020 at 4:47 PM Paul Eggert <eggert@HIDDEN> wrote: > On 5/17/20 9:40 AM, Andrea Corallo wrote: > > I think this is a real bug that we have in the codebase (emacs-27 > > included). > Thanks for all the detective work! Your analysis is correct and your patch looks > good. That's my impression as well. > The only question in my mind is whether to install the patch into the emacs-27 > branch or the master branch. Given Eli's problems with stability in emacs-27 > (see Bug#41321), I'm inclined to think the former, as the bug could explain the > problems Eli is observing. I don't think that platform even has callee-saved registers? But I think the fix should go on the emacs-27 branch. It's a bad bug and sheer luck that Fgarbage_collect on my platform (using this specific compiler, etc.) pushes all callee-saved registers. We shouldn't rely on such lucks on all platforms.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
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Sun, 17 May 2020 12:46:27 -0400 Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 4F7A9160052; Sun, 17 May 2020 09:46:24 -0700 (PDT) Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id qGQxvLSttYDH; Sun, 17 May 2020 09:46:23 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 9658E1600CC; Sun, 17 May 2020 09:46:23 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id MY5awj0NO-lr; Sun, 17 May 2020 09:46:23 -0700 (PDT) Received: from [192.168.1.9] (cpe-23-242-74-103.socal.res.rr.com [23.242.74.103]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 5639E160052; Sun, 17 May 2020 09:46:23 -0700 (PDT) Subject: Re: 28.0.50; GC may miss to mark calle safe register content To: Andrea Corallo <akrl@HIDDEN>, Eli Zaretskii <eliz@HIDDEN> References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN> <xjfh7wea51y.fsf@HIDDEN> From: Paul Eggert <eggert@HIDDEN> Autocrypt: addr=eggert@HIDDEN; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <xjfh7wea51y.fsf@HIDDEN> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=131.179.128.68; envelope-from=eggert@HIDDEN; helo=zimbra.cs.ucla.edu X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/17 12:21:30 X-ACL-Warn: Detected OS = Linux 3.1-3.10 X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-Spam-Score: -1.3 (-) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.3 (--) On 5/17/20 9:40 AM, Andrea Corallo wrote: > I think this is a real bug that we have in the codebase (emacs-27 > included). Thanks for all the detective work! Your analysis is correct and your patch looks good. I've always been suspicious of that code, and it looks like you've confirmed my suspicions. The only question in my mind is whether to install the patch into the emacs-27 branch or the master branch. Given Eli's problems with stability in emacs-27 (see Bug#41321), I'm inclined to think the former, as the bug could explain the problems Eli is observing.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
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From: Andrea Corallo <akrl@HIDDEN>
To: Eli Zaretskii <eliz@HIDDEN>
Subject: Re: 28.0.50; GC may miss to mark calle safe register content
References: <xjfzha6ag1j.fsf@HIDDEN> <83pnb2bmk2.fsf@HIDDEN>
Date: Sun, 17 May 2020 16:40:09 +0000
In-Reply-To: <83pnb2bmk2.fsf@HIDDEN> (Eli Zaretskii's message of "Sun, 17 May
2020 18:36:45 +0300")
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--=-=-=
Content-Type: text/plain
Eli Zaretskii <eliz@HIDDEN> writes:
>> From: Andrea Corallo <akrl@HIDDEN>
>> Cc: Paul Eggert <eggert@HIDDEN>, Eli Zaretskii <eliz@HIDDEN>
>> Date: Sun, 17 May 2020 12:42:48 +0000
>>
>> What is going on is that in a .eln in a function A a Lisp_Object is
>> hold in a register (r14). Function A is calling other functions into
>> emacs-core till Garbage Collection is triggered.
>>
>> Being emacs-core compiled with -O0 GCC is not selecting any callee safe
>> register and therefore these gets never pushed.
>
> Isn't this something for the infrastructure of calling
> natively-compiled Lisp to solve? The Emacs C code isn't prepared for
> calling optimized C code when it calls Lisp, and I don't think it's
> right for us to assume that, because it will make Emacs slower. If
> the natively-compiled Lisp needs some setup to be compatible with GC,
> I think the calling framework should set that up.
Hi Eli,
I think this is a real bug that we have in the codebase (emacs-27
included).
Usually it works because having many big functions with high register
pressure that gets activated before reaching 'flush_stack_call_func'
statistically callee saved regs are very likely to be pushed.
But nothing prevents a caller of 'flush_stack_call_func' to store a lisp
object into a callee saved regs and trigger the bug. This obviously
depends on the compiler, flags used etc, things we have no control over.
This could be also an explanation of instability for LTO configurations.
Given that callers of 'flush_stack_call_func' are more likely to be
inlined the exposed surface becomes considerably higher.
This bug should be also more likely to be observable if C files are
compiled with a mix of -O0 and -O2.
I think we should honor calling convention and make sure we garbage
collect also the content of callee saved registers, BTW I guess that's
the reason why we call '__builtin_unwind_init' isn't?
If we are concerned about performance the attached the attached patch
should be zero performance overhead.
Regards
Andrea
--
akrl@HIDDEN
--=-=-=
Content-Type: text/x-diff
Content-Disposition: attachment;
filename=0001-Fix-Garbage-Collector-for-missing-calle-safe-registe.patch
From ef923e029d5192b67ff7a0aede75a19c2c5327d4 Mon Sep 17 00:00:00 2001
From: Andrea Corallo <akrl@HIDDEN>
Date: Sun, 17 May 2020 13:23:59 +0100
Subject: [PATCH] * Fix Garbage Collector for missing calle safe registers
content
* src/alloc.c (SET_STACK_TOP_ADDRESS): Do not call
__builtin_unwind_init.
(flush_stack_call_func1): Rename from 'flush_stack_call_func'.
(flush_stack_call_func): New function to spill all registers
before calling 'flush_stack_call_func1'. This to make sure the
top of the stack identified includes those registers.
---
src/alloc.c | 4 +---
src/lisp.h | 9 ++++++++-
2 files changed, 9 insertions(+), 4 deletions(-)
diff --git a/src/alloc.c b/src/alloc.c
index f2b80fac88..d6ba4d9790 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -4952,12 +4952,10 @@ test_setjmp (void)
#ifdef HAVE___BUILTIN_UNWIND_INIT
# define SET_STACK_TOP_ADDRESS(p) \
stacktop_sentry sentry; \
- __builtin_unwind_init (); \
*(p) = NEAR_STACK_TOP (&sentry)
#else
# define SET_STACK_TOP_ADDRESS(p) \
stacktop_sentry sentry; \
- __builtin_unwind_init (); \
test_setjmp (); \
sys_setjmp (sentry.j); \
*(p) = NEAR_STACK_TOP (&sentry + (stack_bottom < &sentry.c))
@@ -5033,7 +5031,7 @@ mark_stack (char const *bottom, char const *end)
from FUNC. */
NO_INLINE void
-flush_stack_call_func (void (*func) (void *arg), void *arg)
+flush_stack_call_func1 (void (*func) (void *arg), void *arg)
{
void *end;
struct thread_state *self = current_thread;
diff --git a/src/lisp.h b/src/lisp.h
index 66a86ddadf..c7ce3918fc 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3819,7 +3819,14 @@ verify (FLT_RADIX == 2 || FLT_RADIX == 16);
extern void alloc_unexec_post (void);
extern void mark_maybe_objects (Lisp_Object const *, ptrdiff_t);
extern void mark_stack (char const *, char const *);
-extern void flush_stack_call_func (void (*func) (void *arg), void *arg);
+
+INLINE void
+flush_stack_call_func (void (*func) (void *arg), void *arg)
+{
+ __builtin_unwind_init ();
+ flush_stack_call_func1 (func, arg);
+}
+
extern void garbage_collect (void);
extern void maybe_garbage_collect (void);
extern const char *pending_malloc_warning;
--
2.17.1
--=-=-=--
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
Full text available.Received: (at submit) by debbugs.gnu.org; 17 May 2020 15:37:06 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Sun May 17 11:37:06 2020 Received: from localhost ([127.0.0.1]:44332 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1jaLLd-00053Q-OH for submit <at> debbugs.gnu.org; Sun, 17 May 2020 11:37:05 -0400 Received: from lists.gnu.org ([209.51.188.17]:35562) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <eliz@HIDDEN>) id 1jaLLZ-00053B-Rr for submit <at> debbugs.gnu.org; Sun, 17 May 2020 11:37:04 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49072) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaLLZ-0006yf-Ck for bug-gnu-emacs@HIDDEN; Sun, 17 May 2020 11:37:01 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:60780) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <eliz@HIDDEN>) id 1jaLLW-0002DO-Fi; Sun, 17 May 2020 11:36:58 -0400 Received: from [176.228.60.248] (port=3381 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <eliz@HIDDEN>) id 1jaLLS-0002mL-B1; Sun, 17 May 2020 11:36:55 -0400 Date: Sun, 17 May 2020 18:36:45 +0300 Message-Id: <83pnb2bmk2.fsf@HIDDEN> From: Eli Zaretskii <eliz@HIDDEN> To: Andrea Corallo <akrl@HIDDEN> In-Reply-To: <xjfzha6ag1j.fsf@HIDDEN> (message from Andrea Corallo on Sun, 17 May 2020 12:42:48 +0000) Subject: Re: 28.0.50; GC may miss to mark calle safe register content References: <xjfzha6ag1j.fsf@HIDDEN> X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: submit Cc: bug-gnu-emacs@HIDDEN, eggert@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -3.3 (---) > From: Andrea Corallo <akrl@HIDDEN> > Cc: Paul Eggert <eggert@HIDDEN>, Eli Zaretskii <eliz@HIDDEN> > Date: Sun, 17 May 2020 12:42:48 +0000 > > What is going on is that in a .eln in a function A a Lisp_Object is > hold in a register (r14). Function A is calling other functions into > emacs-core till Garbage Collection is triggered. > > Being emacs-core compiled with -O0 GCC is not selecting any callee safe > register and therefore these gets never pushed. Isn't this something for the infrastructure of calling natively-compiled Lisp to solve? The Emacs C code isn't prepared for calling optimized C code when it calls Lisp, and I don't think it's right for us to assume that, because it will make Emacs slower. If the natively-compiled Lisp needs some setup to be compatible with GC, I think the calling framework should set that up.
bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
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From: Andrea Corallo <akrl@HIDDEN>
To: bug-gnu-emacs@HIDDEN
Subject: 28.0.50; GC may miss to mark calle safe register content
Date: Sun, 17 May 2020 12:42:48 +0000
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Hi all,
debugging the native compiler I've been chasing a bug in a configuration
where the .eln are compiled at speed 2 (-O2) and emacs-core is compiled
at -O0.
What is going on is that in a .eln in a function A a Lisp_Object is
hold in a register (r14). Function A is calling other functions into
emacs-core till Garbage Collection is triggered.
Being emacs-core compiled with -O0 GCC is not selecting any callee safe
register and therefore these gets never pushed. The value stays in r14
till we enter into 'flush_stack_call_func' where we have to push all
registers and identify the end of the stack for mark.
We correctly push callee safe register with __builtin_unwind_init () and
we identify the top (end) of the stack on my machine using
__builtin_frame_address (0).
Here I think raise the issue, __builtin_frame_address on GCC 7 and 10
for X86_64 is returning the base pointer and not the stack pointer [1].
As a consequence this is not including the callee safe registers that we
have just pushed.
In my case r14 gets pushed at address 0x7ffc47b95fa0 but in mark_stack
we are scanning the interval 0x7ffc47b95fb0 (end) 0x7ffc47b9a150
(bottom). This because __builtin_frame_address returned ebp
(0x7ffc47b95fb0 in this case).
The consequence is that the object originally referenced by r14 is never
marked and this leads to have it freed and to a crash.
I think we would be interested into obtaining the stack pointer and not
the base pointer, unfortunately what __builtin_frame_address does is
appears not really portable:
https://gcc.gnu.org/onlinedocs/gcc/Return-Address.html
This bug is easy to observe in the native compiler with configurations
like this (speed2 for eln -O0 for core) but I believe can affect stock
Emacs too if any caller of flush_stack_call_func has a callee safe
register holding a reference to a live object not present into the
stack. This can get trickier especially with LTO enabled.
For now I'm testing the simple attached patch that seams to do the job
for me. It pushes the registers in 'flush_stack_call_func' and then
call 'flush_stack_call_func1' where now ebp must include the address
where those register got pushed.
I hope I'm not catastrophically wrong in this analysis, in case
I apologize for the noise.
Thanks
Andrea
[1] Reduced example. GCC7 -O0
void *
foo (void)
{
__builtin_unwind_init ();
return __builtin_frame_address (0);
}
foo:
push rbp
mov rbp, rsp
push r15
push r14
push r13
push r12
push rbx
mov rax, rbp
pop rbx
pop r12
pop r13
pop r14
pop r15
pop rbp
ret
--=-=-=
Content-Type: text/x-diff
Content-Disposition: attachment;
filename=0001-Fix-Garbage-Collector-for-missing-calle-safe-registe.patch
From f8a5d8a4a95182e91037d444d6d1f51f7dc7e467 Mon Sep 17 00:00:00 2001
From: Andrea Corallo <akrl@HIDDEN>
Date: Sun, 17 May 2020 13:23:59 +0100
Subject: [PATCH] * Fix Garbage Collector for missing calle safe registers
content
* src/alloc.c (SET_STACK_TOP_ADDRESS): Do not call
__builtin_unwind_init.
(flush_stack_call_func1): Rename from 'flush_stack_call_func'.
(flush_stack_call_func): New function to spill all registers
before calling 'flush_stack_call_func1'. This to make sure the
top of the stack identified includes those registers.
---
src/alloc.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/src/alloc.c b/src/alloc.c
index f2b80fac88..1d2ee05481 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -4952,12 +4952,10 @@ test_setjmp (void)
#ifdef HAVE___BUILTIN_UNWIND_INIT
# define SET_STACK_TOP_ADDRESS(p) \
stacktop_sentry sentry; \
- __builtin_unwind_init (); \
*(p) = NEAR_STACK_TOP (&sentry)
#else
# define SET_STACK_TOP_ADDRESS(p) \
stacktop_sentry sentry; \
- __builtin_unwind_init (); \
test_setjmp (); \
sys_setjmp (sentry.j); \
*(p) = NEAR_STACK_TOP (&sentry + (stack_bottom < &sentry.c))
@@ -5033,7 +5031,7 @@ mark_stack (char const *bottom, char const *end)
from FUNC. */
NO_INLINE void
-flush_stack_call_func (void (*func) (void *arg), void *arg)
+flush_stack_call_func1 (void (*func) (void *arg), void *arg)
{
void *end;
struct thread_state *self = current_thread;
@@ -5043,6 +5041,13 @@ flush_stack_call_func (void (*func) (void *arg), void *arg)
eassert (current_thread == self);
}
+void
+flush_stack_call_func (void (*func) (void *arg), void *arg)
+{
+ __builtin_unwind_init ();
+ flush_stack_call_func1 (func, arg);
+}
+
/* Determine whether it is safe to access memory at address P. */
static int
valid_pointer_p (void *p)
--
2.17.1
--=-=-=--
Andrea Corallo <akrl@HIDDEN>:bug-gnu-emacs@HIDDEN.
Full text available.bug-gnu-emacs@HIDDEN:bug#41357; Package emacs.
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