[GHC] #5254: usb library fails on Windows

[GHC]

#5254: usb library fails on Windows
---------------------------------+------------------------------------------
    Reporter:  basvandijk        |       Owner:               
        Type:  bug               |      Status:  new          
    Priority:  low               |   Milestone:  7.6.1        
   Component:  Compiler (FFI)    |     Version:  7.0.3        
    Keywords:                    |          Os:  Windows      
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:                    |    Testcase:               
   Blockedby:                    |    Blocking:               
     Related:                    |  
---------------------------------+------------------------------------------

Comment(by basvandijk):

 Summarizing: executing the following isolated program with the argument
 "fp" (for !ForeignPtr) gives an error and without it I get no error:

 {{{
 {-# LANGUAGE ForeignFunctionInterface #-}

 module Main where

 import Foreign
 import Foreign.C.Types
 import Control.Concurrent
 import System.Environment

 main :: IO ()
 main = do
   ctxPtr <- alloca $ \ctxPtrPtr -> do
               _ <- c'libusb_init ctxPtrPtr
               peek ctxPtrPtr

   args <- getArgs
   case args of
     ["fp"] -> do
       fp <- newForeignPtr p'libusb_exit ctxPtr
       threadDelay 1000000
       print $ fp == fp

     _ -> c'libusb_exit ctxPtr

 data C'libusb_context = C'libusb_context

 foreign import stdcall "libusb_init" c'libusb_init
   :: Ptr (Ptr C'libusb_context) -> IO CInt

 foreign import stdcall "&libusb_exit" p'libusb_exit
   :: FunPtr (Ptr C'libusb_context -> IO ())

 foreign import stdcall "libusb_exit" c'libusb_exit
   :: Ptr C'libusb_context -> IO ()
 }}}

 Note that building the program with the new `win64_alpha1` GHC doesn't
 produce the error. I only get warnings that the `stdcall` calling
 convention is not supported. So I guess it then falls back to the `ccall`
 calling convention which does work.

 Make sure to give these flags to cabal when building the program:

  * `--extra-include-dirs="...\libusb\include\libusb-1.0"`
  * `--extra-lib-dirs="...\libusb\MinGW32\dll"` or: `--extra-lib-
 dirs="...\libusb\MinGW64\dll"` when building with the new `win64_alpha1`
 GHC.

 and make sure the `libusb-1.0.dll` is in your working directory when
 running the program.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5254#comment:4>
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