From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.ciao.gmane.io!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.bugs Subject: bug#41321: 27.0.91; Emacs aborts due to invalid pseudovector objects Date: Sat, 30 May 2020 12:08:35 +0300 Message-ID: <83367hn624.fsf@gnu.org> References: <83zha8cgpi.fsf@gnu.org> <83imgublku.fsf@gnu.org> <831rncjuwf.fsf@gnu.org> <83h7w5xvfa.fsf@gnu.org> <83y2phwb9x.fsf@gnu.org> <83r1v9w9vi.fsf@gnu.org> <83mu5xw50d.fsf@gnu.org> <83k110wxte.fsf@gnu.org> <4bab5f55-95fe-cf34-e490-1d4319728395@cs.ucla.edu> <837dwyvi74.fsf@gnu.org> <1484f569-c260-9fb0-bfe1-67897de289d3@cs.ucla.edu> <83blm9tn4j.fsf@gnu.org> <4aeb8963-4fd1-fcd4-e6e1-be409ab54775@cs.ucla.edu> <83tuzzrk30.fsf@gnu.org> <749bc7d0-6376-ec2e-7f84-dcd3a3cea465@cs.ucla.edu> <83sgfjqn49.fsf@gnu.org> <83eer2m0b6.fsf@gnu.org> Injection-Info: ciao.gmane.io; posting-host="ciao.gmane.io:159.69.161.202"; logging-data="8156"; mail-complaints-to="usenet@ciao.gmane.io" Cc: eggert@cs.ucla.edu, 41321@debbugs.gnu.org, monnier@iro.umontreal.ca To: Pip Cet Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Sat May 30 11:09:10 2020 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jexUM-00020f-3Z for geb-bug-gnu-emacs@m.gmane-mx.org; Sat, 30 May 2020 11:09:10 +0200 Original-Received: from localhost ([::1]:44592 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jexUK-0001xc-Kn for geb-bug-gnu-emacs@m.gmane-mx.org; Sat, 30 May 2020 05:09:08 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:47306) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jexUE-0001xF-3A for bug-gnu-emacs@gnu.org; Sat, 30 May 2020 05:09:02 -0400 Original-Received: from debbugs.gnu.org ([209.51.188.43]:45403) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jexUD-0000XC-Pq for bug-gnu-emacs@gnu.org; Sat, 30 May 2020 05:09:01 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1jexUD-0001Ld-JX for bug-gnu-emacs@gnu.org; Sat, 30 May 2020 05:09:01 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Eli Zaretskii Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Sat, 30 May 2020 09:09:01 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 41321 X-GNU-PR-Package: emacs Original-Received: via spool by 41321-submit@debbugs.gnu.org id=B41321.15908297275162 (code B ref 41321); Sat, 30 May 2020 09:09:01 +0000 Original-Received: (at 41321) by debbugs.gnu.org; 30 May 2020 09:08:47 +0000 Original-Received: from localhost ([127.0.0.1]:56949 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1jexTz-0001LA-J4 for submit@debbugs.gnu.org; Sat, 30 May 2020 05:08:47 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:39832) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1jexTy-0001Kz-6Y for 41321@debbugs.gnu.org; Sat, 30 May 2020 05:08:46 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]:59349) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jexTr-0008Qi-Rv; Sat, 30 May 2020 05:08:39 -0400 Original-Received: from [176.228.60.248] (port=3517 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from ) id 1jexTr-0001Zm-Cm; Sat, 30 May 2020 05:08:39 -0400 In-Reply-To: (message from Pip Cet on Sat, 30 May 2020 07:19:18 +0000) X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.io gmane.emacs.bugs:181219 Archived-At: > From: Pip Cet > Date: Sat, 30 May 2020 07:19:18 +0000 > Cc: eggert@cs.ucla.edu, 41321@debbugs.gnu.org, > Stefan Monnier > > > Btw, can someone remind me why we started requiring non-default > > alignment from Lisp objects? > > max_align_t was changed to include a float128 type, and > alignof(float128) == 16 on x86, even though virtually all x86 systems > are configured to allow unaligned accesses. I understand that part, but my question was why, even before the change in max_align_t, did we start requiring 8-byte alignment on systems where that is not automatically guaranteed? > If I understand Paul's concerns correctly, he believes it's possible a > system will once again come into use in which atomic accesses only > work for offsets aligned to, say, 32 bytes. Since pthread variables > require atomic accesses, such a platform would see weird crashes if a > pthread inside a Lisp_Vector wasn't aligned to 32 bytes. So this alignment requirement is only due to pthreads being used? But MinGW doesn't use pthreads. > > Also, given the fact that in the crashing case the 2 32-bit parts of a > > Lisp object were pushed onto the stack non-contiguously, will fixing > > the alignment alone cause those Lisp objects to be marked? > > Yes. The lower 32-bit part was ignored because its value wasn't > 16-byte aligned, not because its stack location wasn't 8-byte aligned. Right, but I'm talking about marking. AFAIU, when scanning the stack finds a value that looks like a Lisp object, we mark that object. If the two 32-bit parts of the object are non-contiguous, will we be able to recognize such an object, and will we be able to mark it correctly, and if so, how? IOW, don't we need the upper 32-bit (which encodes the object type) for the purposes of marking it?