Yes, the hs_add_root call is essential. You can see what ghc does when
compiling .c files by running it with -v; the main difference is that we
pass some extra -I options so that you can access header files that come
with GHC.
Cheers,
Simon
On 08 June 2005 19:09, Yann Morvan wrote:
> The problem disapears when I use GHC to compile the c file, this
> somehow allows the linker to find the __stginit_SortPoints3()
> function.
> I don't really understand what GHC does differently from gcc at
> compile time on c files.
> Thank you for your time.
>
> Yann Morvan
>
> Yann Morvan wrote:
>
>> Hello,
>> I am calling a Haskell function from C using foreign export, it
>> works fine on the first call, but as soon as I call it again I get:
>>
>> internal error: stg_ap_pp_ret
>>
>> and I am asked to report it as a bug.
>> I don't know how much detail I should give, so I'll just reproduce
>> the relevant code (excuse the clumsyness):
>> On the Haskell side:
>>
>> module SortPoints3 where
>> [...]
>> data Vect2D = Vect2D {xx,yy :: CFloat} deriving Show
>>
>> instance Storable Vect2D where
>> peek a = do
>> x <- peekElemOff (castPtr a) 0
>> y <- peekElemOff (castPtr a) 1
>> return (Vect2D x y)
>> poke a (Vect2D x y) = do
>> pokeElemOff (castPtr a) 0 x
>> pokeElemOff (castPtr a) 1 y
>> sizeOf a = let dummy = Vect2D 2.0 2.0 in
>> (sizeOf (xx dummy) + (sizeOf (yy dummy)))
>> alignment a = 4
>> [...]
>> foreign export ccall doIt :: (Ptr Vect2D) -> (Ptr Vect2D) -> CInt ->
>> CFloat -> IO ()
>>
>> doIt :: (Ptr Vect2D) -> (Ptr Vect2D) -> CInt -> CFloat -> IO ()
>> doIt pointsPtr projectedPtr n t = do
>> points <- peekArray (fromIntegral n) pointsPtr
>> (sortedPoints, sortedProjections ) <- sortPoints t points
>> pokeArray pointsPtr sortedPoints
>> pokeArray projectedPtr sortedProjections
>> return ()
>>
>> On the C side, the function is called from a callback function of
>> the OpenCV library. I pass it pointers to the OpenCV CvPoint2D32f
>> type, which is a simple struct with two floats for coordinates.
>>
>> I had to remove the call to hs_add_root as the linker (GHC's)
>> couldn't find __stginit_SortPoints3()
>>
>> I tried the following:
>>
>> foreign export ccall printIt :: CFloat -> IO ()
>>
>> printIt :: CFloat -> IO ()
>> printIt f = putStr $ "\nTest\n" ++ (show f) ++ "\n"
>>
>> this function has no problem when called several times from the same
>> location in the c code.
>>
>> Please tell me what to fix if the error is on my side.
>> Thank you for your time,
>>
>> Yann Morvan
>>
>>
>
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