RE: MMap offset parameter failing with ENOMEM error

["Shane Mann" <shane dot mann at leadup dot com dot au>]

Hi,

Has this issue been confirmed as a bug? Is it being looked into?

Cheers,
Shane

Shane Mann
Software Engineer          Phone: +61-7-3259-2223
LeadUp Software Pty Ltd    Fax:   +61-7-3259-2259
339 Coronation Drive,      Email: shane.mann@leadup.com.au
Milton, QLD, 4064          Web:   http://www.leadup.com.au


> -----Original Message-----
> From: cygwin-owner@cygwin.com [mailto:cygwin-owner@cygwin.com]On Behalf
> Of Shane Mann
> Sent: Friday, 20 September 2002 9:38
> To: cygwin@cygwin.com
> Subject: RE: MMap offset parameter failing with ENOMEM error
>
>
> Corinna,
>
> I noticed this while I continued testing last night.
> Interestingly Linux and
> SunOS don't seem to be bothered by this, however, if you read the IEEE
> standard:
> http://www.opengroup.org/onlinepubs/007904975/functions/mmap.html
> there is the following quote: "The range of bytes starting at off and
> continuing for len bytes shall be legitimate for the possible (not
> necessarily current) offsets in the file, shared memory object, or [TYM]
> typed memory object  represented by fildes." Linux and Sun seem
> to allow it
> and return '0' if you access memory beyond the EOF, go figure.
>
> Perhaps the wrong error is being returned for this case - I would have
> thought the following error code would be more appropriate:
>
> [ENXIO]
> Addresses in the range [off,off+len) are invalid for the object
> specified by
> fildes.
>
> I have since amended the code by replacing the following line:
>
> size = finfo.st_size;
>
> with
>
> size = finfo.st_size - foff;
>
> and I still get the same error. There is some example output below:
>
> Note: index.idx is a file with a size of 557592 bytes. In the output below
> it worked for an offset of 400000 and created a map of 157592 bytes - but
> failed for the same file with an offset of 300000 and a potential map of
> 257592 bytes.
>
> Run 1)
> ~/c>./a.exe 400000 index.idx
> Offset is 400000
> File index.idx opened on descriptor 3.  It is 157592 bytes long
> --- Syspagesize 4096, pagemask FFFFF000, offmask FFF
> foff is 400000
> --- Syspagesize 4096, pagemask FFFFF000, offmask FFF
> pfoff is 397312
> **** Vars just before mmap call ****
> psyz = 163840
> prot = 1
> fd = 3
> pfoff = 397312
>    Mapping 163840 at 2A231000 <---> 397312 (mapping fh
> Result from femmap is 2A231A80
> Byte is 127
>
>
> Run 2)
> ~/c>./a.exe 300000 index.idx
> Offset is 300000
> File index.idx opened on descriptor 3.  It is 257592 bytes long
> --- Syspagesize 4096, pagemask FFFFF000, offmask FFF
> foff is 300000
> --- Syspagesize 4096, pagemask FFFFF000, offmask FFF
> pfoff is 299008
> **** Vars just before mmap call ****
> psyz = 262144
> prot = 1
> fd = 3
> pfoff = 299008
> perror reports errno of 12
>    Mapping 262144 at FFFFFFFF <---> 299008 (mapping fh
>
> Any ideas?
>
> Cheers,
> Shane
>
> Shane Mann
> Software Engineer          Phone: +61-7-3259-2223
> LeadUp Software Pty Ltd    Fax:   +61-7-3259-2259
> 339 Coronation Drive,      Email: shane.mann@leadup.com.au
> Milton, QLD, 4064          Web:   http://www.leadup.com.au
>
>
> > -----Original Message-----
> > From: cygwin-owner@cygwin.com [mailto:cygwin-owner@cygwin.com]On Behalf
> > Of Corinna Vinschen
> > Sent: Thursday, 19 September 2002 17:33
> > To: Cygwin@Cygwin. Com
> > Subject: Re: MMap offset parameter failing with ENOMEM error
> >
> >
> > On Thu, Sep 19, 2002 at 12:19:06PM +1000, Shane Mann wrote:
> > > Hi,
> > >
> > > I am having trouble with mmap using the last 'offset'
> parameter. I have
> > > attached a small piece of code (and sample file) which
> demonstrates the
> > > problem. Basically if the offset parameter is passed as a
> > variable to mmap
> > > then the call fails with an ENOMEM error. But if you pass 0 as
> > the parameter
> > > and then access the return address from mmap + offset - it is fine. My
> > > question: is mmap handling the offset parameter correctly?
> > >
> > > Usage for the program:
> > >
> > > ./a.exe <offset> <file> eg: ./a.exe 11200 index.idx
> > >
> > > To see the address + offset work, comment out the first mmap
> > call and return
> > > statement and uncomment the lines below each one.
> > >
> > > Any help appreciated.
> >
> > Your application tries to mmap over EOF.
> >
> > Corinna
> >
> > --
> > Corinna Vinschen                  Please, send mails regarding Cygwin to
> > Cygwin Developer                                mailto:cygwin@cygwin.com
> > Red Hat, Inc.
> >
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>
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