Re: dlsym: symbols in dependencies

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

On Fri, Feb 05, 2010 at 10:14:25AM +0100, Corinna Vinschen wrote:
>On Feb  4 02:29, Yaakov S wrote:
>> Per POSIX:
>> 
>> """The dlsym() function shall search for the named symbol in all
>> objects loaded automatically as a result of loading the object
>> referenced by handle (see dlopen )."""
>> 
>> With the relevant part of dlopen() saying:
>> 
>> """Note that some implementations permit the construction of
>> dependencies between such objects that are embedded within files. In
>> such cases, a dlopen() operation shall load such dependencies in
>> addition to the object referenced by file."""
>> 
>> IOW, when the target of dlopen() has linked dependencies, not only
>> shall those dependencies must also be loaded by dlopen() but the
>> symbols therein found by dlsym().  On Cygwin, by the nature of
>> PE/COFF the dependencies are loaded, but dlsym() does not search
>> their symbols.
>
>Looks like a bug in Cygwin.  Sort of.  Or rather, nobody asked for
>this functionality yet.
>
>The dlsym function only searches all modules loaded into the process if
>the pseudo handle RTLD_DEFAULT has been specified.  If a valid module
>handle is given, it only looks in that very DLL.  The underlying Win32
>function GetProcAddress does not walk dependencies, unfortunately.
>
>The question is if EnumProcessModules returns the modules in an order,
>which allows to draw conclusions about dependencies.  If so, an
>easy solution would be to call EnumProcessModules and start the search
>at the given module handle in the returned module handle array.  This
>would also allow for an easy implementation of RTLD_NEXT.
>
>But somehow I doubt that it's so simple.  Did anybody test something
>like that already?

We have the functionality to find DLL dependencies.  It just won't be
easy to link it to dlsym.

I'll add it to my todo though.  I vaguely recall that someone else
asked for this in the past.

cgf

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