[Haskell-cafe] ffi call works fine in ghci but not as ghc compiledsegfault

[Miro Karpis]

Hi,
sorry, but not sure what you mean with 'cabalizing the code and seeing the
flags its passing'.

cabal-install version 1.16.0.2
using version 1.16.0 of the Cabal library

ghc: version 7.6.3

after looking a bit more I can see that the ffi call does what it should
do, but it crashes right after that. As mentioned before in ghci everything
runs fine.


On Sun, Mar 16, 2014 at 11:20 PM, Carter Schonwald <
carter.schonwald at gmail.com> wrote:

> what version of ghc and cabal?
>
> have you tried cabalizing the code and seeing what flags its passing? is
> it possible you're passing the wrong flags?
>
>
> On Sun, Mar 16, 2014 at 5:21 PM, Miro Karpis <miroslav.karpis at gmail.com>wrote:
>
>> thanks. Have tried with safe - still seg-fault.
>>
>>
>> On Sun, Mar 16, 2014 at 5:09 PM, Vagif Verdi <vagif.verdi at gmail.com>wrote:
>>
>>> Notice that i have "safe" in my foreign import ccall. This makes it safe
>>> to run in threaded mode. Did you try that?
>>>
>>> Are you on windows?
>>>
>>>
>>> On Sunday, March 16, 2014 1:40:48 AM UTC-7, Miro Karpis wrote:
>>>
>>>> thank you very much - I have tried also that but got the the same
>>>> behaviour (seg fault)
>>>>
>>>> cheers,
>>>> m.
>>>>
>>>>
>>>> On Sun, Mar 16, 2014 at 7:45 AM, Vagif Verdi <vagif... at gmail.com>wrote:
>>>>
>>>>> I do not think i can help you, but my FFi to functions with similar
>>>>> signature looks like this:
>>>>>
>>>>> C definition:
>>>>>
>>>>> PDFLIB_API int PDFLIB_CALL
>>>>> PDF_begin_document(PDF *p, const char *filename, int len, const char
>>>>> *optlist);
>>>>>
>>>>> haskell FFI:
>>>>>
>>>>> c_beginDocument :: Pdf -> String -> String -> IO Int
>>>>> c_beginDocument pdf a2 a3 =
>>>>>   withCString a2 $ \a2' ->
>>>>>   withCString a3 $ c_beginDocument'_ pdf a2' 0
>>>>>
>>>>> foreign import ccall safe "Pdflib.chs.h PDF_begin_document"
>>>>> c_beginDocument'_ :: Pdf -> Ptr CChar -> CInt -> Ptr CChar -> IO Int
>>>>>
>>>>> The difference as you see, i'm using withCString to convert from
>>>>> ahskell to C and i'm passing 0 as the string size.
>>>>>
>>>>>
>>>>>
>>>>> On Friday, March 14, 2014 3:24:23 PM UTC-7, Miroslav Karpis wrote:
>>>>>>
>>>>>> Hi, please can you help me with following?
>>>>>>
>>>>>> I have a call to an external dll (via ffi) which if executed from
>>>>>> ghci works fine.
>>>>>> If I compile my code with 'ghc -o fm Mycode.hs -L. -lextdll' and run
>>>>>> it I get  'Segmentation fault/access violation in generated code'.
>>>>>>
>>>>>>
>>>>>>
>>>>>> main = do
>>>>>> let param = "FilePath"
>>>>>> let value = "C:/dev/misc/haskell/services/FM"
>>>>>>  result <- liftIO $ FM.setmodulestring param value
>>>>>> return "done"
>>>>>>
>>>>>> setmodulestring :: String -> String -> IO CInt
>>>>>> setmodulestring param value = do
>>>>>> let cParamLength = fromIntegral $ length param ::CInt
>>>>>>      cValueLength = fromIntegral $ length value ::CInt
>>>>>>      setVarInArray = (-1)::CInt
>>>>>>  alloca $ \cParam -> do
>>>>>> alloca $ \cValue -> do
>>>>>>  result <- c_setmodulestring cParam cParamLength cValue cValueLength
>>>>>> setVarInArray
>>>>>>  return result
>>>>>>
>>>>>> If I try also with following, the behaviour is the same:
>>>>>>
>>>>>> setmodulestring2 :: String -> String -> IO CInt
>>>>>> setmodulestring2 param value = do
>>>>>>  cParam <- newCWString param
>>>>>> cValue <- newCWString value
>>>>>> let cParamLength = fromIntegral $ length param ::CInt
>>>>>>     cValueLength = fromIntegral $ length value ::CInt
>>>>>>     setVarInArray = (-1)::CInt
>>>>>> result <- c_setmodulestring cParam cParamLength cValue cValueLength
>>>>>> setVarInArray
>>>>>>  free cParam
>>>>>> free cValue
>>>>>> return res
>>>>>>
>>>>>>
>>>>>> Any comments/ideas more than appreciated.
>>>>>>
>>>>>> Cheers,
>>>>>> Miro
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>
>>
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>>
>
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