Haskell ghc visual studio DLL weird behaviour
I am trying to call a C DLL built with visual studio (2015 community edition) from GHC (version 7.8.3) on windows.
C code: (myDLL.cpp)
extern "C" {
__declspec(dllexport) int someFn() {
return 42;
}
}
Haskell code: (Main.hs)
module Main where
import Foreign.Ptr
import Foreign.C.Types
import Data.Int
foreign import ccall unsafe "someFn" c_someFn :: CInt
mySomeFn = c_someFn
main :: IO ()
main = do let z = mySomeFn
print z
after copying the generated x64 .dll and .lib and .hs file to the same folder, and running
ghci -L. -lmyDLL Main.hs
...
>main
It prints '42' as expected.
Running
ghc -L. -lmyDLL Main.hs
compiles and links fine, but after executing main.exe, no output is printed. Not even an error message. Why does this happen?
EDIT: Here's what I did to fix it. Install latest Haskell Platform, then download and copy the latest copy of binutils to the mingw folder of haskell platform. (D:Program FilesHaskell Platform7.10.2-amingw for me). Next, it started complaining about zlib1.dll, so I also downloaded that from MSYS2 and pasted it in the mingwbin folder. After that, it worked.
Seems similar to this issue. Basically, ghc-7.8 distribution contains buggy binutils, they don't handle Visual Studio .lib files properly. The workaround is to upgrade mingw distribution or regenerate the .lib file. See the ticket (and also #10726) for details.
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