unofficial mirror of emacs-devel@gnu.org 
 help / color / mirror / code / Atom feed
From: Philipp Stephani <p.stephani2@gmail.com>
To: Paul Eggert <eggert@cs.ucla.edu>, Eli Zaretskii <eliz@gnu.org>
Cc: aurelien.aptel+emacs@gmail.com, tzz@lifelogs.com,
	dancol@dancol.org, emacs-devel@gnu.org
Subject: Re: Dynamic modules: MODULE_HANDLE_SIGNALS etc.
Date: Mon, 21 Dec 2015 20:15:43 +0000	[thread overview]
Message-ID: <CAArVCkS6yir1Rsw7NRQKXrBnH5h2-V6nqB9H1EH3os3V6+UmXw@mail.gmail.com> (raw)
In-Reply-To: <567841A6.4090408@cs.ucla.edu>

[-- Attachment #1: Type: text/plain, Size: 4139 bytes --]

Paul Eggert <eggert@cs.ucla.edu> schrieb am Mo., 21. Dez. 2015 um 19:15 Uhr:

> Eli Zaretskii wrote:
>
> > Are you
> > now saying something different from what you said back then, i.e. that
> > we cannot rely on any function/macro from lisp.h to be signal-safe?
>
> Yes and no. As I understood it, that old conversation was about functions
> that
> explicitly signal or throw, and it's safe to assume that EQ, NILP, etc.
> won't do
> that. The new conversation is about running out of memory, which is a
> different
> form of non-local exit. There may be other forms, such as operating-system
> signals (I don't recall exactly).
>

My comment was meant to refer only to signals and throws (i.e. the
constructs described in
https://www.gnu.org/software/emacs/manual/html_node/elisp/Nonlocal-Exits.html
).


>
> > If so, we should add the necessary protection, in the form of calls to
> > MODULE_FUNCTION_BEGIN, to emacs-module.c functions that until now
> > relied on those lisp.h functions/macros to be safe.
>
> This wouldn't suffice for these other non-local exits, I think; at least,
> not as
> currently constructed.
>

I don't see how such a protection could be written at all. The stack
overflow handler seems to be fixed.


>
> > AFAIK, proper C++ exception handling
> > requires non-trivial amounts of stack space that is not available when
> > there's stack overflow, where you have at most a single guard page to
> > work with.
>
> There should be workarounds for that. Surely the C++ community has run
> into this
> problem and has solutions. If we want to support C++ modules, we need to
> employ
> them.
>

The solution in C++ is simple: don't use longjmp/setjmp, and write only
trivial signal handlers (that only set a flag), or use signal fds etc. I
don't think C++ programs regularly try to catch stack overflows; such an
attempt would almost guarantee undefined behavior, so crashing is more
appropriate.


>
> > I think there is some misunderstanding here, or some confusion,
> > perhaps mine: emacs-module.c is not supposed to deal with any C++
> > exceptions.  C++ exceptions are supposed to be caught at the C++
> > level, below emacs-module.c, and handled there.  An exception that
> > isn't caught will be recorded and will cause all the subsequent calls
> > to Lisp or to emacs-module.c function to fail,
>
> Why bother? If C++ exceptions are supposed to be caught by the C++ module
> in
> question, why does Emacs need to worry about C++ exceptions that are not
> caught?
>

It doesn't, in fact due to noexcept it is impossible to throw exceptions
across the module interface (and any C++ module had better install a
catch-all handler to avoid crashes).


>
> > What emacs-module.c does with non-local exits of _any_ kind is record
> > the first occurrence of such an exit, and silently return to the
> > caller, thus allowing the C++ objects on the stack to be destroyed
> > normally.  IOW, it defers the exit until internal--module-call is
> > about to return.  What problems do you see with that which cause you
> > to think it's error-prone, let alone dysfunctional?
>
> It uses a different model at the C level from what one sees in Elisp, or
> from
> what one normally sees in C for that matter.  I don't feel that I will
> really
> understand the model unless I see some actual modules that do function
> calls and
> exception handling; but it's hard to believe that a model that does silent
> returns and that defers returns until later and that records some returns
> but
> not others will be problem-free. Wouldn't it be simpler to have a module
> invoke
> analogs of 'condition-case' and/or 'catch', and to dispense with the
> funcall_exit stuff?
>

Please see the countless discussions on this topic, starting in February
(!) with Daniel's original design:
https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00960.html
https://lists.gnu.org/archive/html/emacs-devel/2015-09/msg00548.html
https://lists.gnu.org/archive/html/emacs-devel/2015-09/msg00545.html
https://lists.gnu.org/archive/html/emacs-devel/2015-10/msg00416.html
https://lists.gnu.org/archive/html/emacs-devel/2015-11/msg02159.html

[-- Attachment #2: Type: text/html, Size: 5865 bytes --]

  parent reply	other threads:[~2015-12-21 20:15 UTC|newest]

Thread overview: 177+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-11-25 18:39 Dynamic modules: MODULE_HANDLE_SIGNALS etc Eli Zaretskii
2015-11-25 18:50 ` Philipp Stephani
2015-11-25 19:24   ` Eli Zaretskii
2015-11-26 21:29 ` Paul Eggert
2015-11-27  7:35   ` Eli Zaretskii
2015-11-27 19:19     ` Philipp Stephani
2015-11-28 10:58       ` Philipp Stephani
2015-11-28 12:10         ` Eli Zaretskii
2015-12-19 21:03         ` Philipp Stephani
2015-12-19 22:57           ` Philipp Stephani
2015-12-20 15:47             ` Eli Zaretskii
2015-12-20 18:34               ` Philipp Stephani
2015-12-20 19:11                 ` Eli Zaretskii
2015-12-20 21:40                   ` Paul Eggert
2015-12-21  3:33                     ` Eli Zaretskii
2015-12-21 11:00                       ` Paul Eggert
2015-12-21 11:21                         ` Yuri Khan
2015-12-21 11:34                           ` Paul Eggert
2015-12-21 15:46                         ` Eli Zaretskii
2015-12-21 18:15                           ` Paul Eggert
2015-12-21 18:28                             ` Daniel Colascione
2015-12-21 19:00                               ` Eli Zaretskii
2015-12-21 20:19                                 ` Philipp Stephani
2015-12-21 19:04                               ` Eli Zaretskii
2015-12-22  4:09                               ` Paul Eggert
2015-12-22  4:38                                 ` Daniel Colascione
2015-12-22  4:48                                   ` Paul Eggert
2015-12-22  4:52                                     ` Daniel Colascione
2015-12-22  6:09                                       ` Paul Eggert
2015-12-22  6:14                                         ` Daniel Colascione
2015-12-22  6:33                                           ` Paul Eggert
2015-12-22  6:35                                             ` Daniel Colascione
2015-12-22  6:44                                               ` Paul Eggert
2015-12-22  6:53                                                 ` Daniel Colascione
2015-12-22 16:13                                                   ` Eli Zaretskii
2015-12-22 16:12                                           ` Eli Zaretskii
2015-12-22 17:26                                             ` Philipp Stephani
2015-12-22 17:51                                               ` Eli Zaretskii
2015-12-22 16:03                                     ` Eli Zaretskii
2015-12-22 16:39                                       ` Paul Eggert
2015-12-22 17:46                                         ` Eli Zaretskii
2015-12-22 23:28                                           ` Paul Eggert
2015-12-23 16:10                                             ` Eli Zaretskii
2015-12-23 16:20                                               ` Philipp Stephani
2015-12-23 16:46                                                 ` Eli Zaretskii
2015-12-23 17:09                                                 ` Paul Eggert
2015-12-23 17:18                                                   ` Daniel Colascione
2015-12-24  2:51                                                     ` Paul Eggert
2015-12-24  3:11                                                       ` Daniel Colascione
2015-12-24 16:10                                                       ` Eli Zaretskii
2015-12-24 17:04                                                         ` Daniel Colascione
2015-12-24 17:17                                                           ` John Wiegley
2016-01-03 14:27                                                             ` Daniel Colascione
2016-01-03 15:46                                                               ` Eli Zaretskii
2016-01-03 15:49                                                                 ` Daniel Colascione
2016-01-03 16:40                                                                   ` Eli Zaretskii
2016-01-03 16:50                                                                     ` Daniel Colascione
2016-01-03 17:20                                                                       ` Eli Zaretskii
2016-01-03 16:31                                                               ` Paul Eggert
2016-01-03 16:48                                                                 ` Daniel Colascione
2016-01-03 18:07                                                                   ` Paul Eggert
2016-01-03 18:22                                                                     ` Daniel Colascione
2016-01-03 21:02                                                                       ` Paul Eggert
2016-01-03 21:12                                                                         ` Daniel Colascione
2016-01-03 23:11                                                                           ` Paul Eggert
2016-01-03 23:22                                                                             ` Daniel Colascione
2016-01-03 23:29                                                                               ` John Wiegley
2016-01-04  1:05                                                                               ` Paul Eggert
2016-01-04  1:07                                                                                 ` Daniel Colascione
2016-01-04 15:38                                                                               ` Eli Zaretskii
2016-01-04 15:40                                                                                 ` Daniel Colascione
2016-01-04 16:07                                                                                   ` Eli Zaretskii
2016-01-04 20:32                                                                                     ` John Wiegley
2016-01-04 20:34                                                                                       ` Daniel Colascione
2016-01-04 20:35                                                                                         ` Daniel Colascione
2016-01-04 22:06                                                                                           ` John Wiegley
2016-01-04 15:24                                                                           ` Eli Zaretskii
2016-01-04 15:28                                                                             ` Daniel Colascione
2016-01-04 16:00                                                                               ` Eli Zaretskii
2016-01-03 17:16                                                                 ` Eli Zaretskii
2016-01-03 17:22                                                                   ` Daniel Colascione
2016-01-03 17:39                                                                     ` Eli Zaretskii
2016-01-03 17:49                                                                       ` Daniel Colascione
2016-01-03 18:08                                                                         ` Eli Zaretskii
2016-01-03 18:24                                                                           ` Daniel Colascione
2016-01-03 18:51                                                                             ` Eli Zaretskii
2016-01-03 19:04                                                                               ` Daniel Colascione
2016-01-03 19:15                                                                                 ` Eli Zaretskii
2016-01-03 19:26                                                                                   ` Daniel Colascione
2016-01-03 19:46                                                                                     ` Eli Zaretskii
2016-01-03 19:47                                                                                       ` Daniel Colascione
2016-01-03 19:49                                                                                   ` John Wiegley
2016-01-03 20:14                                                                                     ` Daniel Colascione
2016-01-04  3:17                                                                           ` Richard Stallman
2016-01-03 18:17                                                                         ` Paul Eggert
2016-01-03 17:43                                                                     ` Eli Zaretskii
2016-01-03 20:25                                                               ` John Wiegley
2016-01-03 20:47                                                                 ` Daniel Colascione
2016-01-03 21:07                                                                   ` John Wiegley
2016-01-03 21:28                                                                     ` Daniel Colascione
2016-01-03 21:31                                                                       ` Daniel Colascione
2016-01-04 15:27                                                                         ` Eli Zaretskii
2016-01-04 15:29                                                                           ` Daniel Colascione
2016-01-04 16:01                                                                             ` Eli Zaretskii
2016-01-03 21:45                                                                       ` John Wiegley
2016-01-03 22:20                                                                         ` Daniel Colascione
2016-01-03 22:43                                                                           ` Crash recovery strategies (was: Dynamic modules: MODULE_HANDLE_SIGNALS etc.) John Wiegley
2016-01-03 22:55                                                                             ` Crash recovery strategies Daniel Colascione
2016-01-03 22:59                                                                               ` John Wiegley
2016-01-03 23:04                                                                                 ` Daniel Colascione
2016-01-03 23:20                                                                                   ` John Wiegley
2016-01-03 23:47                                                                               ` John Wiegley
2016-01-03 23:51                                                                                 ` Daniel Colascione
2016-01-04  0:12                                                                                   ` John Wiegley
2016-01-04 15:40                                                                                   ` Eli Zaretskii
2016-01-04 15:44                                                                                     ` Daniel Colascione
2016-01-04 15:33                                                                               ` Eli Zaretskii
2016-01-04 15:34                                                                                 ` Daniel Colascione
2016-01-04 16:02                                                                                   ` Eli Zaretskii
2016-01-03 23:21                                                                             ` Paul Eggert
2016-01-03 23:24                                                                               ` Daniel Colascione
2016-01-03 23:28                                                                                 ` John Wiegley
2016-01-04  0:51                                                                                 ` Paul Eggert
2016-01-03 23:27                                                                               ` John Wiegley
2016-01-03 23:29                                                                                 ` Daniel Colascione
2016-01-03 23:33                                                                                   ` Sending automatic crash reports to the FSF (was: Crash recovery strategies) John Wiegley
2016-01-03 23:36                                                                                     ` Sending automatic crash reports to the FSF Daniel Colascione
2016-01-03 23:39                                                                                       ` John Wiegley
2016-01-03 23:48                                                                                         ` Daniel Colascione
2016-01-04  1:34                                                                                   ` Crash recovery strategies Drew Adams
2016-01-04 15:32                                                                             ` Crash recovery strategies (was: Dynamic modules: MODULE_HANDLE_SIGNALS etc.) Eli Zaretskii
2016-01-04 15:35                                                                               ` Crash recovery strategies Daniel Colascione
2016-01-04 16:04                                                                                 ` Eli Zaretskii
2016-01-05  4:48                                                                                 ` Richard Stallman
2016-01-05 15:52                                                                                   ` Eli Zaretskii
2016-01-05 16:37                                                                                     ` Clément Pit--Claudel
2016-01-05 17:08                                                                                       ` Eli Zaretskii
2016-01-05 17:38                                                                                         ` Clément Pit--Claudel
2016-01-04 15:31                                                                           ` Dynamic modules: MODULE_HANDLE_SIGNALS etc Eli Zaretskii
2016-01-04 15:41                                                                             ` Daniel Colascione
2016-01-04 16:13                                                                               ` Eli Zaretskii
2016-01-04 15:29                                                                         ` Eli Zaretskii
2016-01-04 15:26                                                                       ` Eli Zaretskii
2015-12-24 17:36                                                           ` Eli Zaretskii
2015-12-24 18:06                                                             ` Daniel Colascione
2015-12-24 19:15                                                               ` Eli Zaretskii
2015-12-22 16:01                                   ` Eli Zaretskii
2015-12-22 16:32                                     ` John Wiegley
2015-12-22 20:31                                     ` Daniel Colascione
2015-12-22 20:46                                       ` Eli Zaretskii
2015-12-22 20:52                                         ` Daniel Colascione
2015-12-22 21:08                                           ` Eli Zaretskii
2015-12-22 21:18                                             ` Daniel Colascione
2015-12-23 16:07                                               ` Eli Zaretskii
2015-12-23 16:25                                                 ` Crash robustness (Was: Re: Dynamic modules: MODULE_HANDLE_SIGNALS etc.) Daniel Colascione
2015-12-23 17:30                                                   ` Eli Zaretskii
2015-12-23 17:41                                                     ` Daniel Colascione
2015-12-23 17:55                                                       ` Eli Zaretskii
2015-12-23 17:56                                                         ` Daniel Colascione
2015-12-23 18:09                                                           ` Eli Zaretskii
2015-12-23 18:19                                                             ` Daniel Colascione
2015-12-23 18:45                                                               ` Eli Zaretskii
2015-12-24  3:26                                                                 ` Daniel Colascione
2015-12-21 18:57                             ` Dynamic modules: MODULE_HANDLE_SIGNALS etc Eli Zaretskii
2015-12-21 20:15                             ` Philipp Stephani [this message]
2015-12-20 15:48           ` Eli Zaretskii
2015-12-20 18:27             ` Philipp Stephani
2015-12-20 19:00               ` Eli Zaretskii
2015-12-20 21:00                 ` Philipp Stephani
2017-03-26 20:18                   ` Philipp Stephani
2016-02-29 22:48           ` Philipp Stephani
2016-03-01 16:41             ` Paul Eggert
2016-03-01 21:43               ` Philipp Stephani
2016-03-02 18:54                 ` Paul Eggert
2016-03-31 18:44                   ` Philipp Stephani
2016-04-01  8:29                     ` Paul Eggert
2015-11-28 23:20     ` Paul Eggert

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: https://www.gnu.org/software/emacs/

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAArVCkS6yir1Rsw7NRQKXrBnH5h2-V6nqB9H1EH3os3V6+UmXw@mail.gmail.com \
    --to=p.stephani2@gmail.com \
    --cc=aurelien.aptel+emacs@gmail.com \
    --cc=dancol@dancol.org \
    --cc=eggert@cs.ucla.edu \
    --cc=eliz@gnu.org \
    --cc=emacs-devel@gnu.org \
    --cc=tzz@lifelogs.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

	https://git.savannah.gnu.org/cgit/emacs.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).