[Mono-devel-list] DllImport with multiple shared libraries

[Heribert.Schuetz.extern at HVB.de]

Yes this works. Thanks. Didn't know that shared libraries can carry
references to other shared libraries just like executables.

Just one little remark: Apparently it is not necessary (though admittedly
more conventional and thus nicer) to prepend the prefix "lib" to the
libraries. You can directly name the .so file in the link command instead of
"-L. -lnative2".

Heribert.

> -----Original Message-----
> From:	Jonathan Pryor [SMTP:jonpryor at vt.edu]
> Sent:	Friday, December 24, 2004 3:10 AM
> To:	Schütz, Heribert (ext.)
> Cc:	mono-devel-list at lists.ximian.com; hs at webxcerpt.com
> Subject:	Re: [Mono-devel-list] DllImport with multiple shared
> libraries
> 
> On Thu, 2004-12-23 at 20:51 +0100, Heribert.Schuetz.extern at HVB.de wrote:
> > I'm trying to call into native code from C# within Mono (on Linux). It
> works
> > fine as long as the native function is completely implemented in a
> single
> > shared library. If, however, this shared library requires another shared
> > library, I don't know how I should tell Mono about this other library.
> 
> Short answer: you shouldn't need to.  Mono doesn't load the library, the
> Linux Shared Library mechanism does, through dlopen(3).
> 
> The reason you shouldn't need to is because the library knows all the
> libraries it statically depends on.  How's it know this?  Because you
> provide them on the link line.
> 
> Except you're not, so everything breaks.  This is also why using
> <iostream> breaks your app, you're not linking against the appropriate
> libraries.
> 
> The fix?  This is untested, but it should get the point across:
> 
> 	all: run
> 
> 	.cpp.o:
> 		g++ -c -o $@ -fpic $<
> 
> 	libnative.so : native.o libnative2.so
> 		g++ -shared -o $@ -L. -lnative2 $^
> 
> 	libnative2.so : native2.o
> 		g++ -shared -o $@ $^
> 
> 	native.exe
> 		mcs $<
> 
> 	run: native.exe libnative2.so libnative.so
> 		LD_LIBRARY_PATH=`pwd` mono native.exe
> 
> The key points to keep in mind are:
> 
> 1.  You're using the correct convention, *lib*native.so, not native.so.
> This is Unix, not Windows, the prefix should be used (because of (2)).
> 
> 2.  The libnative.so link line explicitly links against libnative2.so
> (this is done by the -L. -- include the current directory in the link
> path -- and -lnative2, which links against libnative2.so)
> 
> 3.  You're using g++ to generate the final .so.  G++ knows to link in
> the required C++ standard libraries, libstdc++.so, which should permit
> you to #include <iostream> without having linker problems.
> 
>  - Jon
>