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Date: Wed, 01 Aug 2007 08:23:15 -0700
From: Brian Dessent <brian AT dessent DOT net>
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Subject: Re: is LD_PRELOAD available in cygwin?
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Günther Jedenastik wrote:

> using g++ to compile a dll which overload's the open(); glibc system call.
> Using preload i want to load my own dll with my open(); function. using 
> dlsym(); i try to load the glibc open(); function.

Cygwin does not use glibc.  glibc is Linux-specifc.

> Q1: is LD_PRELOAD available in cygwin? if yes, any hint's why it's not
> working? (maybe some configuration problem or so, any hint would be
> helpfull)
> Q2: are there any alternative ways to preloading causing the same result?

No, LD_PRELOAD is an aspect of ELF dynamic loaders and is not available
on Windows.  It's not something that Cygwin can provide since it is a
function provided by the program loader, i.e. the operating system.

If you have source of the target program and can modify it, then you can
dlopen() the DLL and use dlsym() to get a function pointer to the
replacement open() function, and then use that function pointer instead
of the libcall throughout.  But if you want this to be transparent, i.e.
without modifying or recompiling the target, then you'll have to use
some kind of low-level Windows-specific hackery because this is not a
feature the PE loader has.

http://research.microsoft.com/sn/detours/
http://www.internals.com/articles/apispy/apispy.htm

Brian

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