#5254: usb library fails on Windows
---------------------------------+------------------------------------------
Reporter: basvandijk | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (FFI)
Version: 7.0.3 | Keywords:
Testcase: | Blockedby:
Os: Windows | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime crash
---------------------------------+------------------------------------------
I'm trying to get my Haskell `usb` library to work on Windows. I currently
get a weird error. Please follow the steps below to reproduce the error:
* Download
[http://www.libusb.org/wiki/windows_backend#LatestBinarySnapshots libusb
for Windows] and extract it somewhere e.g. `C:\Program
Files\libusb\libusb1`.
(Important build-time files: `libusb-1.0\include\libusb.h` and
`MinGW32\dll\libusb-1.0.dll.a`)
(Important run-time files: `MinGW32\dll\libusb-1.0.dll`)
* Download, unpack and cabal install the, as of yet unreleased,
[https://bitbucket.org/mauricio/bindings-dsl/get/1.0.12.tar.gz bindings-
DSL-1.0.12]
(This version lets you use the right calling convention on Windows
(`stdcall` instead of `ccall`) by configuring cabal with
`cc-options: -DBINDINGS_STDCALLCONV`)
* Install `bindings-libusb`:
{{{
git clone git://github.com/basvandijk/bindings-libusb.git
cd bindings-libusb
}}}
Make sure to checkout the `windows` branch and let cabal know where to
find `libusb`:
{{{
git checkout windows
cabal install --extra-include-dirs="C:\Program
Files\libusb\libusb1\include\libusb-1.0"
--extra-lib-dirs="C:\Program
Files\libusb\libusb1\MinGW32\dll"
}}}
* Clone the `usb` repository:
{{{
git clone git://github.com/basvandijk/usb.git
cd usb
}}}
There's no need to install the library. I included an example program
that will demonstrate the error:
{{{
cabal configure --flags="example -library"
cabal build
}}}
The example should read some bytes of an attached USB mouse (change the
VID and PID to match your mouse). However it gives two errors:
{{{
dist\build\example\example.exe
example.exe: NotFoundException
Segmentation fault/access violation in generated code
}}}
This bug report is about the segmentation fault.
The `NotFoundException` is thrown by `c'libusb_get_config_descriptor`
which is indirectly called by `getDevices`. According to the
[http://libusb.sourceforge.net/api-1.0/group__desc.html#gaa635d9aec77de4895dd0896ccf001532
libusb docs]
this error is thrown when the specified configuration doesn't
exists. Since I only call this function on existing configurations
this seems like a bug in libusb. I will dive in the libusb source code to
see what is going on.
The `Segmentation fault/access violation in generated code` is caused
by the finalizer in `newCtx`:
{{{
newCtx ∷ IO Ctx
newCtx = newCtxNoEventManager Ctx
libusb_init ∷ IO (Ptr C'libusb_context)
libusb_init = alloca $ \ctxPtrPtr → do
handleUSBException $ c'libusb_init ctxPtrPtr
peek ctxPtrPtr
newCtxNoEventManager ∷ (ForeignPtr C'libusb_context → Ctx) → IO Ctx
newCtxNoEventManager ctx = mask_ $ do
ctxPtr ← libusb_init
ctx <$> newForeignPtr p'libusb_exit ctxPtr
}}}
When `p'libusb_exit` is called the segmentation fault occurs.
'''Note that the error disappears when I change that last line with:
`ctx <$> Foreign.Concurrent.newForeignPtr ctxPtr (c'libusb_exit
ctxPtr)`'''
I previously got the exact same segmentation fault when calling other
`bindings-libusb` functions. This was caused by using the wrong calling
convention on Windows. I used `ccall` but had to use `stdcall`. So I
assume the current segmentation fault has something to do with the calling
convention of `FunPtrs`.
Any ideas what is causing this? I would really like to solve it. It's the
last step before releasing `usb-1.0`.
Thanks!
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5254>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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