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Re: Suppressing linking errors with GCC/G++/ld under Cygwin

On Tue, 7 Dec 2004, Robert McLeay wrote:

> Hi,
> (Sorry if this is OT, I'm trying to find out the Cygwin equivalent of
> a GCC flag from other platforms.)
> I'm trying to compile a library for Qu-Prolog that will be linked at
> run-time with program internals. As it will be linked at run time, I
> would like to suppress all "undefined reference" errors somewhat
> similarly to using "-undefined suppress" under Mac OS X.
> I'm using Cygwin, and here is the error message and the g++ line that I
> am using.
> rob@ches-laptop /cygdrive/c/rand2
> $ g++ -shared -Wl,-soname,sym001476 $RAND2_LIB/rand.o  -lc -o sym001476
> ./rand.o(.text+0x24f): In function `iunif_interface':
>    /    cygdrive/c/rand2/ undefined reference to
> `Thread::unify(Object*, Object*, bool)'
> ./rand.o(.text+0x2ce): In function `iunif_interface':
>    /    cygdrive/c/qp-cygwin-withicm/src/heap_qp.h:278: undefined reference to
> `Heap::outOfSpace()'
> collect2: ld returned 1 exit status
> Is there any way to suppress these errors and let it compile under
> Cygwin the same way as using "g++ -flat_namespace -undefined suppress
> -bundle" would under Mac OS X?

This isn't OT, but I'm sorry to say that what you want to do is
non-trivial due to the way Windows linking works.  You can't have a DLL
that's statically dependent on symbols from an executable.  There are two
ways around it.  The first -- which I'm sure about, as I've used it myself
-- is to extract the symbols from the executable into a helper DLL, and
link your library DLL with the helper.  The second, which is more iffy and
will probably only work if the symbols are all functions, is to use
dlopen()/dlsym() to get the address of the functions you need from the
executable module.

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