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Date: Tue, 27 Nov 2001 17:43:20 -0800 (PST)
From: Rock Gordon <rockgordon@yahoo.com>
Subject: Re: Executing binaries on new filesystem
To: Terje Eggestad <terje.eggestad@scali.no>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
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Oh yes, I've implemented a feeble mmap, but it never
get's to the point where it calls f_op->mmap:
It actually issues a read, starts the program with
start_thread, and it gets a segfault !

All this without calling a single line of code that
I've written that could be the cause of the segfault.
If it had page faulted, it would have been ok, since
readpage would have taken care of it ...

--- Terje Eggestad <terje.eggestad@scali.no> wrote:
> man, 2001-11-19 kl. 17:34 skrev Rock Gordon:
> > All said and done, the file is with correct
> > permissions (for that matter any binary that I
> execute
> > on my filesystem has correct permissions). The
> only
> > thing strace tells me is "bad file format". The
> same
> > binary works perfectly elsewhere.
> > 
> > I don't think mmap is the problem; you don't need
> it
> > in order to run binaries ...
> > 
> 
> Yes you do. See load_elf_binary in fs/binfmt_elf.c,
> or
> load_aout_binary in fs/binfmt_aout.c.....
> 
> 
> > --- Terje Eggestad <terje.eggestad@scali.no>
> wrote:
> > > On Sat, 17 Nov 2001, Rock Gordon wrote:
> > > 
> > > > Hi,
> > > >
> > > > I've written a modest filesystem for fun, it
> works
> > > > pretty ok, but when I try to execute binaries
> from
> > > it,
> > > > bash says "cannot execute binary file" ... If
> I
> > > copy
> > > > the same binary elsewhere, it executes
> perfectly.
> > > >
> > > > Does anybody have any clue ?
> > > 
> > > Yes
> > > 
> > > keep in mind taht the kernel do demand paging of
> the
> > > text (code) in our
> > > executable, meaning that a page of code is not
> > > loaded into the procs
> > > memory spce (and thus phys mem) until the proc
> > > actually tries to exec the
> > > code page. This is one manifestation of the
> funny
> > > term "page fault"!
> > > 
> > > I do belive that the current kernel uses mmap to
> map
> > > in the exec file text
> > > segment. (Even if I can hear the ice cracking
> under
> > > my feet, never
> > > actually looked at the code handling execs) but
> if
> > > you strace anexec that
> > > uses shared libs you'll note that the sh.libs
> are
> > > mmaped into the process
> > > space. (also note the MMAP_EXEC flag in the
> mmap(2)
> > > man page).
> > > 
> > > 
> > > TJ
> > > 
> > > >
> > > > Regards,
> > > > Rock
> > > >
> > > >
> __________________________________________________
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> > > 
> > > -- 
> > >
> >
>
_________________________________________________________________________
> > > 
> > > Terje Eggestad                 
> > > terje.eggestad@scali.no
> > > Scali Scalable Linux Systems   
> http://www.scali.com
> > > 
> > > Olaf Helsets Vei 6              tel:    +47 22
> 62 89
> > > 61 (OFFICE)
> > > P.O.Box 70 Bogerud                      +47 975
> 31
> > > 574  (MOBILE)
> > > N-0621 Oslo                     fax:    +47 22
> 62 89
> > > 51
> > > NORWAY
> > >
> >
>
_________________________________________________________________________
> > > 
> > 
> > 
> > __________________________________________________
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> -- 
>
_________________________________________________________________________
> 
> Terje Eggestad                 
> terje.eggestad@scali.no
> Scali Scalable Linux Systems    http://www.scali.com
> 
> Olaf Helsets Vei 6              tel:    +47 22 62 89
> 61 (OFFICE)
> P.O.Box 70 Bogerud                      +47 975 31
> 574  (MOBILE)
> N-0621 Oslo                     fax:    +47 22 62 89
> 51
> NORWAY            
>
_________________________________________________________________________
> 


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