Re: [Mingw-users] Re: Generic DLL questions

[Brian D. <br...@de...>]

Stefan Bellon wrote:

> Yes, I pretty much understand all of that. But in your example you
> assume the DLL "foo.dll" to exist. My question is: How do I _create_

There are three scenarios that I can think of.

A) The .exe links directly against the .dll, and the .dll uses
GetProcAddress to access the symbols in the .exe.  From the standpoint
of the linker this is bog standard - creating the .dll does not depend
on the .exe at all.

gcc -shared foo.o -o foo.dll -Wl,--out-implib,libfoo.dll.a
gcc main.o -o main.exe -lfoo

B) The .exe uses LoadLibrary and GetProcAddress to load and access the
.dll (such as in the case of a plugin that can be dynamically
added/removed as necessary) and the .dll links directly against the .exe
without using GetProcAddress.  This is just the converse of the above,
except that now creating the .exe does not depend on the .dll existing
at all.

gcc main.o -o main.exe -Wl,--out-implib,libmain.a
gcc -shared foo.o -o foo.dll -lmain

C) Both the .exe and the .dll link directly against each other; neither
uses GetProcAddress.  Here there is a circular dependency that you have
to break by creating a .def file by hand and then using dlltool to turn
that into an import library.  You can create the .def file for either
the .exe or the .dll - it really just depends on which has the more
complex set of exports, and how your build is structured.  Let's assume
for the example you choose to write the .exe's .def file by hand, but
you can just as well do it the opposite way.

# create main.def
dlltool --input-def main.def --output-lib libmain.a --dllname main.exe
gcc -shared foo.o -o foo.dll -lmain -Wl,--out-implib,libfoo.dll.a
gcc main.o -o main.exe -lfoo

Note that in B) and C) you hardcode the name of the .exe into the .dll,
so it can only ever be used with that .exe and not as a general purpose
library.  In all three cases you need __declspec(dllexport) on the
symbols in main.

Brian