X-Recipient: archive-cygwin AT delorie DOT com
X-SWARE-Spam-Status: No, hits=-2.5 required=5.0 	tests=AWL,BAYES_00,SPF_PASS
X-Spam-Check-By: sourceware.org
Message-ID: <4A607EE5.5050306@gmail.com>
Date: Fri, 17 Jul 2009 14:38:45 +0100
From: Dave Korn <dave DOT korn DOT cygwin AT googlemail DOT com>
User-Agent: Thunderbird 2.0.0.17 (Windows/20080914)
MIME-Version: 1.0
To: cygwin AT cygwin DOT com
Subject: Re: perl threads on 2008 R2 64bit = crash ( was: perl 5.10 threads  	on 1.5.25 = instant crash )
References: <20090715162243 DOT GL14502 AT ednor DOT casa DOT cgf DOT cx> <4A5E0AB1 DOT 9020201 AT gmail DOT com> <20090715185636 DOT GA16211 AT ednor DOT casa DOT cgf DOT cx> <4A5E2ED6 DOT 3070502 AT gmail DOT com> <20090715194539 DOT GZ27613 AT calimero DOT vinschen DOT de> <4A5E3F1F DOT 9040103 AT gmail DOT com> <20090716161219 DOT GP27613 AT calimero DOT vinschen DOT de> <4A5F59A1 DOT 1060902 AT gmail DOT com> <20090716195552 DOT GU27613 AT calimero DOT vinschen DOT de> <20090716211823 DOT GC22617 AT ednor DOT casa DOT cgf DOT cx> <20090717085727 DOT GW27613 AT calimero DOT vinschen DOT de>
In-Reply-To: <20090717085727.GW27613@calimero.vinschen.de>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id: <cygwin.cygwin.com>
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sourceware.org/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com

Corinna Vinschen wrote:

> AFAICS, the problem is that _my_tls.el is not the active SEH handler at
> this point, but it is already part of the chain,
> _cygtls::init_exception_handler doesn't check for validity and just
> overwrites the entry in an invalid way.

  Argh.  Yes, there's no way we can repeatedly enter the same registration
record into the chain.  I see this has already been anticipated:

  /* Windows apparently installs a bunch of exception handlers prior to
     this function getting called and one of them may trip before cygwin
     gets to it.  So, install our own exception handler only.
     FIXME: It is possible that we may have to save state of the
     previous exception handler chain and restore it, if problems
     are noted. */

  Time to fix the fixme, I guess.

> If it's not correct to just skip the OS handlers, we would have to
> invent a new SEH entry at a lower stack address, rather than reusing
> the _my_tls entry, which is already in use.
> 
> Assuming that skipping the OS handlers is OK, 

  What if they are try....finally handlers rather than try....except?  Bad
things might happen?  It might be useful to know what those functions are
(lookup in windbg?), but then again it might be fragile if we devised a
solution that relied on that knowledge.  I guess the answer is that if we only
want a last-chance exception handler we should just make
_my_tls.init_exception_handler() idempotent so it only installs one handler at
the start of the chain, but if we want to intercept exceptions ahead of those
OS handlers (as I think is the intent of the code here) then we need to set up
and tear down a new SEH record.  The SEH chain has to be a strict stack, with
entries unlinked in the reverse order to when they're linked; we can't go
re-ordering it when there are foreign handlers in the mix.


    cheers,
      DaveK

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple