[Haskell-cafe] Creating DLLs with GHC

[SevenThunders]

SevenThunders wrote:
> 
> 
> 
> SevenThunders wrote:
>> 
>> I am having some difficulty with creating a dynamic link library using 
>> GHC on windows XP.
>> 
>> 
> 
> 
> I need to report some additional strange DLL behavior with ghc.exe
> unfortunately.
> 
> Although I solved my linking problems and was able to create a .dll and a
> MS VC .lib file using  a .def file.
> I get a nasty run time error when my program exits.  
> 
> Here is a snippet of the  Haskell code:
> module ExternLib where
> 
> ...
> import Foreign.C.String
> import Foreign.Ptr
> import Foreign.C.Types (CInt, CDouble )
> import Foreign.Marshal.Array
> import Foreign.Storable
> 
> foreign export stdcall initNetChan :: CString -> Ptr CInt -> IO ()
> 
> 
> -- | initialize network parameters and return an integer array containing
> -- indices to the uplink channel, downlink channel
> initNetChan :: CString -> Ptr CInt -> IO()
> initNetChan simstring cptr = do
> 
> -- some processing 
> ...
> 
> 	let hup = mkCInt $ hupchan netop
> 	let hdn = mkCInt $ hdnchan netop
> 	print $ "hup = " ++ (show hup)
> 	print $ "hdn = " ++ (show hdn)
> 	-- write results to the output array
> 	pokeElemOff cptr 0 hup
> 	pokeElemOff cptr 1 hdn
> 	peekElemOff cptr 0 >>= print
> 
> Here is the C code that calls it, (test.c)
> 
> #include <stdio.h>
> 
> extern void initNetChan(char *str, int *iout) ;
> 
> int zout[64] ;
> 
> 
> int main(int argc, char *argv[])
> {
> printf("Starting initNetChan\n") ;
> initNetChan("SimPrams.in", zout) ;
> printf("Done initNetChan.  out: %p\n", zout) ;
> printf("out[0] = %d out[1] = %d\n", zout[0], zout[1]) ;
> printf("Done") ;
> return(1) ;
> }
> 
> 
> The dll itself uses this template taken from the GHC manual on DLLs
> #include <windows.h>
> #include <Rts.h>
> 
> extern void __stginit_ExternLib(void);
> 
> static char* args[] = { "ghcDll", NULL };
>                        /* N.B. argv arrays must end with NULL */
> BOOL
> STDCALL
> DllMain
>    ( HANDLE hModule
>    , DWORD reason
>    , void* reserved
>    )
> {
>   if (reason == DLL_PROCESS_ATTACH) {
>       /* By now, the RTS DLL should have been hoisted in, but we need to
> start it up. */
>       startupHaskell(1, args, __stginit_ExternLib);
>       return TRUE;
>   }
>   return TRUE;
> }
> 
> 
> I link test.c to my dll via a call
> cl.exe test.c netsim.lib
> 
> Running test.exe yields
> Starting initNetChan
> "hup = 26"
> "hdn = 30"
> 26
> Done initNetChan.  out: 00408960
> out[0] = 26 out[1] = 30
> Done
> D:\Projects\BRPhoenix\NetworkSim\FastSim>test.exe
> Starting initNetChan
> "hup = 26"
> "hdn = 30"
> 26
> Done initNetChan.  out: 00408960
> out[0] = 26 out[1] = 30
> Done
> 
> which is correct, but then the code crashes with a run time error.  It is
> an unhandled exception: access violation.
> Is it possible that the Haskell code needs to do some kind of finalization
> process before terminating?
> I haven't seen the documentation for it yet.  Hopefully it's just
> something stupid I've done, but again I am baffled.
> 
> 
> 

Well I'm batting 1000 today.  It was my dumb fault again.  In case this
helps someone else,  I forgot to use the --stdcall prefix to the function
declaration.  Thus my stack was trashed.

I needed to use a declaration something like
__declspec(dllimport) void  __stdcall initNetChan(HsPtr a1, HsPtr a2);


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