X-Recipient:	archive-cygwin AT delorie DOT com
DomainKey-Signature:	a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:date:from:to:subject:message-id:reply-to
	:references:mime-version:content-type:in-reply-to; q=dns; s=
	default; b=KvO1gxG85fp3wxwZtakZYH9iBdDzlzhJzdyzp7rEkTGcDAZc91y46
	5Gl/j5be2PQYYnEVOzeAeLcFgvtuMNazjZmBc66yi0CDDvBBQ5EW1TpLyG58bN6F
	kcBRMttGqHbEEQGCM/DK40KsL92stjeGreZhOHteyJAS1+axJ+53l8=
DKIM-Signature:	v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:date:from:to:subject:message-id:reply-to
	:references:mime-version:content-type:in-reply-to; s=default;
	bh=JSIrj+zpug8k8iehOwt+SiRDvOQ=; b=nhwnn0nz8T47mIfSJvwdKifLW983
	WqaD/cA+RRM1RAJMLxeDgjl/4BLugkYOr7CER3mGOWNIG2Yqmn10P7aKmUFjJP9n
	tqhgPaWxgMgg4Sv0hvhTZocm4swlMESmsrWJXre88RAs33Vm5K7hL7w8WkN5jFM0
	EKr5aWxGicVv/rk=
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
X-Spam-SWARE-Status:	No, score=-1.8 required=5.0 tests=AWL,BAYES_00,TW_MQ autolearn=ham version=3.3.1
Date:	Tue, 9 Jul 2013 12:57:24 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: mq_open fails after upgrade from cygwin 1.7.17 with gcc 3.4.4 to cygwin 1.7.20 and gcc 4.7.3
Message-ID:	<20130709105724.GB27319@calimero.vinschen.de>
Reply-To:	cygwin AT cygwin DOT com
Mail-Followup-To:	cygwin AT cygwin DOT com
References:	<0d83fe2110ce8c3066becc6ce0f546b1 AT bouldersystemsdesign DOT com>
MIME-Version:	1.0
In-Reply-To:	<0d83fe2110ce8c3066becc6ce0f546b1@bouldersystemsdesign.com>
User-Agent:	Mutt/1.5.21 (2010-09-15)

On Jul  8 12:27, stevetarr AT bouldersystemsdesign DOT com wrote:
> The following program fails after the upgrade:
> 
> #include <stdio.h>
> #include <sys/time.h>
> #include <sys/resource.h>
> #include <errno.h>
> #include <stdlib.h>
> #include <fcntl.h>
> #include <sys/stat.h>
> #include <sys/types.h>
> #include <mqueue.h>
> 
> int main(int argc, char **argv)
> {
>     mqd_t t;
>     struct mq_attr p;
>         char *name = "/stuff";
>         if ( mq_unlink(name) < 0 ) {
>                 if ( errno != ENOENT ) {
>                         printf("Unink failed - errno = %d\n");
>                 }
>         }
>     t = mq_open(name,O_RDWR|O_CREAT,0666,NULL);
>     if ( t  < 0 ) {
          ^^^^^^^^
This is the bug.  Try

      if (t == (mqd_t) -1)

Here's why.  In mqueue.h, mqd_t is defined as follows:

  typedef intptr_t mqd_t;

The mqd_t value returned to you by mq_open is a memory address of an
internal datastructure.  If the memory address is beyond the 2 Gigs
border on 32 bit systems, the returned address is a negative 32 bit
integer value.  This is what happens when running 32 bit Cygwin under
WOW64 on 64 bit machines if the executable has the large-address
awareness bit set.  That's default when compiling with newer gcc's.

In that case, the heap is by default starting at address 0x80000000.
So, for instance, if the internal datastructure is allocated at address
0x8003a990, mq_open returns the mqd_t value -2147243632, which is a
valid return value.  The only value specified as error value is (mqd_t)
-1.  Every other value is a valid, successful return value.  So, bottom
line, don't check for < 0, check for (mqd_t) -1.


HTH,
Corinna


-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

--
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

- Raw text -