From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.bugs Subject: bug#34655: 26.1.92; Segfault in module with --module-assertions Date: Thu, 21 Mar 2019 22:14:46 +0200 Message-ID: <83k1gst26h.fsf@gnu.org> References: <874l8r1t3a.fsf@tcd.ie> <8336oamu3y.fsf@gnu.org> <87h8c1cv6l.fsf@tcd.ie> <83lg1dwhse.fsf@gnu.org> <87va0h12js.fsf@tcd.ie> <835zsgw3ui.fsf@gnu.org> <87ef7486h0.fsf@tcd.ie> <83r2b4ul1c.fsf@gnu.org> <831s30upqd.fsf@gnu.org> <83o964t4de.fsf@gnu.org> <83lg18t3ar.fsf@gnu.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="236190"; mail-complaints-to="usenet@blaine.gmane.org" Cc: contovob@tcd.ie, 34655@debbugs.gnu.org, monnier@iro.umontreal.ca To: Philipp Stephani Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Thu Mar 21 21:15:55 2019 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:256) (Exim 4.89) (envelope-from ) id 1h746U-000zJD-Ig for geb-bug-gnu-emacs@m.gmane.org; Thu, 21 Mar 2019 21:15:54 +0100 Original-Received: from localhost ([127.0.0.1]:46284 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h746T-0001wi-Gu for geb-bug-gnu-emacs@m.gmane.org; Thu, 21 Mar 2019 16:15:53 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:39205) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h745o-0001YG-3v for bug-gnu-emacs@gnu.org; Thu, 21 Mar 2019 16:15:13 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h745m-0007Bs-4p for bug-gnu-emacs@gnu.org; Thu, 21 Mar 2019 16:15:12 -0400 Original-Received: from debbugs.gnu.org ([209.51.188.43]:40132) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1h745i-000747-LP for bug-gnu-emacs@gnu.org; Thu, 21 Mar 2019 16:15:08 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1h745e-0008Ep-Gv for bug-gnu-emacs@gnu.org; Thu, 21 Mar 2019 16:15:06 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Eli Zaretskii Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Thu, 21 Mar 2019 20:15:02 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 34655 X-GNU-PR-Package: emacs Original-Received: via spool by 34655-submit@debbugs.gnu.org id=B34655.155319929631642 (code B ref 34655); Thu, 21 Mar 2019 20:15:02 +0000 Original-Received: (at 34655) by debbugs.gnu.org; 21 Mar 2019 20:14:56 +0000 Original-Received: from localhost ([127.0.0.1]:53676 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1h745Y-0008EI-3v for submit@debbugs.gnu.org; Thu, 21 Mar 2019 16:14:56 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:52992) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1h745V-0008E3-Vp for 34655@debbugs.gnu.org; Thu, 21 Mar 2019 16:14:55 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]:49150) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h745P-0006To-FP; Thu, 21 Mar 2019 16:14:47 -0400 Original-Received: from [176.228.60.248] (port=1589 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from ) id 1h745O-00020t-Dl; Thu, 21 Mar 2019 16:14:46 -0400 In-reply-to: (message from Philipp Stephani on Thu, 21 Mar 2019 21:01:43 +0100) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.51.188.43 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.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.org gmane.emacs.bugs:156585 Archived-At: > From: Philipp Stephani > Date: Thu, 21 Mar 2019 21:01:43 +0100 > Cc: Stefan Monnier , "Basil L. Contovounesios" , 34655@debbugs.gnu.org, > Daniel Colascione > > Am Do., 21. März 2019 um 20:50 Uhr schrieb Eli Zaretskii : > > > > > From: Philipp Stephani > > > Date: Thu, 21 Mar 2019 20:37:24 +0100 > > > Cc: Stefan Monnier , "Basil L. Contovounesios" , 34655@debbugs.gnu.org > > > > > > Let's go back to the known good state first, and then discuss how to > > > go from there. > > > > I don't see why that is better than discuss first and then go to where > > we decide to go. It's not like Emacs 27 will be released any time > > soon, so there's no rush. > > For one, it becomes harder and harder to revert commits the older they > get. Also such discussions tend to turn into endless debates about the > "perfect" solution until one side gives up, without improving > anything. I strongly prefer fixing actual bugs that affect users in > practice and then discussing (or not discussing) the gold-plating > steps later. I also prefer fixing bugs (which is why I spent several hours looking into Basil's crash, when no one else was replying to that bug report), but this is a community project, so we should discuss first and act later. Especially when controversial issues are involved. > > > We can't get stack marking to work, even theoretically. > > > > > > A module is free to do > > > > > > emacs_value x = ...; > > > uintptr_t y = ((uintrptr_t) x) ^ 0x123456u; > > > (garbage-collect) > > > emacs_value z = (emacs_value) (y ^ 0x123456u); > > > ... use z ... > > > > > > During the garbage collection, x isn't on the stack anywhere > > > > Why do you think x isn't on the stack in this case? > > Because the compiler reused the stack slot for something else? How can it? You are using the same pointer later. Garbage collection cannot happen unless you call an Emacs function, such as Ffuncall. Calling a function means that even if the pointer to a Lisp object was in a register, it will be put on the stack when calling Emacs. > Because the module is written in a language that doesn't use the stack > in a way that the garbage collector expects? Which language is that, and how can it use the emacs-module machinery? > > Moreover, emacs_value is actually a pointer to a Lisp object, so this > > object is also somewhere on the stack, right? No answer? > We do something very specific with the stack: we make sure that > Lisp_Objects are never manipulated in a way similar to the above, and > we use the C language. If worse comes to worst, we can request module writers to adhere to the same discipline. We already request them to do/not to do quite a few extraordinary things. > All regression tests still pass after reverting the commit. Didn't they also pass before?