Building and using Win32 DLLs
Dynamic link libraries, Win32DLLs, Win32
On Win32 platforms, the compiler is capable of both producing and using
dynamic link libraries (DLLs) containing ghc-compiled code. This
section shows you how to make use of this facility.
Linking with DLLs
The default on Win32 platforms is to link applications in such a way
that the executables will use the Prelude and system libraries DLLs,
rather than contain (large chunks of) them. This is transparent at the
command-line, so
sh$ cat main.hs
module Main where
main = putStrLn "hello, world!"
sh$ ghc -o main main.hs
ghc: module version changed to 1; reason: no old .hi file
sh$ strip main.exe
sh$ ls -l main.exe
-rwxr-xr-x 1 544 everyone 6144 May 3 17:11 main.exe*
sh$ ./main
hello, world!
sh$
will give you a binary as before, but the main.exe generated will use the Prelude and RTS DLLs instead.
6K for a "hello, world" application---not bad, huh? :-)
Not linking with DLLs
-static option (Win32)
If you want to build an executable that doesn't depend on any
ghc-compiled DLLs, use the option to link in
the code statically.
Notice that you cannot mix code that has been compiled with
and not, so you have to use the
option on all the Haskell modules that make up your application.
Creating a DLL
Creating a Win32 DLL--mk-dll
Sealing up your Haskell library inside a DLL is quite straightforward;
compile up the object files that make up the library, and then build
the DLL by issuing the following command:
ghc --mk-dll -o HSsuper.dll A.o Super.o B.o libmine.a -lgdi32
By feeding the ghc compiler driver the option , it
will build a DLL rather than produce an executable. The DLL will
consist of all the object files and archives given on the command
line.
A couple of things to notice:
Since DLLs correspond to packages (see ) you need
to use when compiling modules that
belong to a DLL. If you don't, Haskell code that calls entry points in that
DLL will do so incorrectly, and a crash will result.
By default, the entry points of all the object files will
be exported from the DLL when using . Should you want to constrain this, you can specify the module definition file to use on the command line as follows:
ghc --mk-dll -o .... -optdll--def -optdllMyDef.def
See Microsoft documentation for details, but a module definition file
simply lists what entry points you want to export. Here's one that's
suitable when building a Haskell COM server DLL:
EXPORTS
DllCanUnloadNow = DllCanUnloadNow@0
DllGetClassObject = DllGetClassObject@12
DllRegisterServer = DllRegisterServer@0
DllUnregisterServer = DllUnregisterServer@0
In addition to creating a DLL, the option will also
create an import library. The import library name is derived from the
name of the DLL, as follows:
DLL: HScool.dll ==> import lib: libHScool_imp.a
The naming scheme may look a bit weird, but it has the purpose of
allowing the co-existence of import libraries with ordinary static
libraries (e.g., libHSfoo.a and libHSfoo_imp.a.
Additionally, when the compiler driver is linking in non-static mode,
it will rewrite occurrence of on the command line to
. By doing this for you, switching from non-static
to static linking is simply a question of adding to
your command line.