From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: "E. Madison Bray" <erik.m.bray@gmail.com>
Cc: cygwin@cygwin.com
Subject: Re: Consider exposing mmap_is_attached_or_noreserve
Date: Thu, 28 Feb 2019 18:01:00 -0000 [thread overview]
Message-ID: <20190228131233.GI4133@calimero.vinschen.de> (raw)
In-Reply-To: <CAOTD34Y5F0cm7bVMiTYqA91tn7i9QZ_zLseMERmQnKp=MJqvqA@mail.gmail.com>
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On Feb 28 12:50, E. Madison Bray wrote:
> On Wed, Feb 27, 2019 at 5:17 PM Corinna Vinschen wrote:
> >
> > On Feb 27 16:38, E. Madison Bray wrote:
> > > In order to handle such a case it might be nice if
> > > mmap_is_attached_or_noreserve were able to be called by user code,
> > > perhaps as a new cygwin_internal(...) call. I'd happily provide a
> > > patch, but I fear this might be an X/Y problem that I'm not seeing.
> >
> > Honestly, I'm not overly keen to expose this stuff. Wouldn't it
> > make more sense to fix Cygwin's sigaltstack implementation to handle
> > these cases gracefully? You're apparently not shy working with
> > Windows exception handling. Patches more than welcome! I'm not
> > happy not having found a solution to this problem :}
>
> I can theoretically imagine a case where might be a problem totally
> outside the context of the altstack issue: e.g. maybe a cygwin
> application that has to link with a native Windows DLL that happens to
> register some vectored continue handler that does something with
> STATUS_ACCESS_VIOLATION exceptions. Of course, absent a real example
> I wouldn't push for it.
A Cygwin application creating a vectored exception handler is not really
a Cygwin application since that circumvents Cygwin's exeception and
signal handling. Even if Cygwin's handling isn't entirely foolproof,
that's a slippery slope.
> I completely agree it would be better to have a solution to the actual problem.
>
> > Oh, wait! Maybe there is a simple solution. Patch 9a5abcc896bd
> > added a single line
> >
> > exception protect;
> >
> > to the pthread::thread_init_wrapper method.
> >
> > What if adding the same line to the altstack_wrapper function
> > would help for altstack as well?
>
> You know, I actually noticed this just recently, because I noticed
> that pthreads also run on a stack allocated by Cygwin, and I wondered
> how exception handling would work in that case. I think I was looking
> at it in the context of the thread last month that resulted in that
> fix, but I forgot to ask you if this could work for the altstack issue
> as well.
No worries, we can't fix all problems at one :}
> > Can you test this?
>
> I'll give it a try and report back with a patch if it works.
That would be way cool. I'm looking forward to it.
> The biggest risk is if a stack overflow happens while running on the
> altstack--in this case even the Cygwin exception handling could fail
> and the application will just crash. But for other, less extreme
> cases having this would be better than nothing.
Stack overflow is nasty. You're aware of the special concession for
this case in altstack_wrapper(), right? It's not exacly what happens
on Linux, but it's at least some clean way out.
Corinna
--
Corinna Vinschen
Cygwin Maintainer
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prev parent reply other threads:[~2019-02-28 13:12 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-27 15:51 E. Madison Bray
2019-02-27 16:19 ` Corinna Vinschen
2019-02-27 16:32 ` Corinna Vinschen
2019-02-28 13:12 ` E. Madison Bray
2019-02-28 18:01 ` Corinna Vinschen [this message]
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