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Date: Wed, 23 Mar 2011 16:44:21 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
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Subject: Re: Broken autoconf mmap test
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On Mar 23 10:08, Ken Brown wrote:
> On 3/23/2011 9:26 AM, Corinna Vinschen wrote:
> >Btw., I just experimented with another flag which has not been exposed
> >to the Win32 API, and which is not officially documented.  It's called
> >AT_EXTENDABLE_FILE and allows to specify a view which is bigger than
> >the filesize.  I tried this on W7-64, and it works.  Just not exactly
> >as we need it.  The trailing pages are not commited but only reserved,
> >so accessing them still results in a SEGV.  And while commiting them
> >allows to run the autoconf testcase, it also changes the filesize of
> >the file on disk.  Oh well.
> 
> Is the scenario in which the autoconf test fails likely to occur in
> practice?  I wonder if it could be responsible for some of the
> mysterious crashes that people have reported on 64-bit systems.

Usually it shouldn't.  While you can write into a mmaped area beyond
EOF up to the end of the last page, it doesn't make a lot of sense.
The data will never show up in the mapped file.

I have no idea if there are applications out there which rely on this
crude behaviour.


Corinna

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

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