#4059: possible error in foreign wrapper reentering Haskell
-----------------------+----------------------------------------------------
Reporter: aruiz | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (FFI)
Version: 6.12.2 | Keywords:
Os: Linux | Testcase:
Architecture: x86 | Failure: Incorrect result at runtime
-----------------------+----------------------------------------------------
The following simple code works as expected in 6.12.1, 6.10, and all
previous ghc versions:
fun.c:
{{{
double deriv(double f(double), double x, double h)
{
return (f(x+h)-f(x))/h;
}
}}}
pru.hs:
{{{
{-# LANGUAGE ForeignFunctionInterface #-}
import Foreign
d f x = unsafePerformIO $ do
g <- mkfun f
r <- deriv g x 0.01
return r
main = do
print $ d sin 0
print $ d (\x-> x * d (\y-> x+y) 1) 1
foreign import ccall safe "deriv" deriv :: FunPtr (Double->Double) ->
Double -> Double -> IO Double
foreign import ccall safe "wrapper" mkfun:: (Double -> Double) -> IO(
FunPtr (Double -> Double))
}}}
$ ghc -V
The Glorious Glasgow Haskell Compilation System, version 6.12.1
$ ghc --make pru.hs fun.c -fforce-recomp
[1 of 1] Compiling Main ( pru.hs, pru.o )
Linking pru ...
$ ./pru
0.9999833334166665
1.000000000004464
But it gives a wrong result in ghc-6.12.2:
$ ghc -V
The Glorious Glasgow Haskell Compilation System, version 6.12.2
$ ghc --make pru.hs fun.c -fforce-recomp
[1 of 1] Compiling Main ( pru.hs, pru.o )
Linking pru ...
$ ./pru
0.9999833334166665
0.0
I have discovered this problem when a similar test in my hmatrix library
failed in 6.12.2. As shown above, it seems that the wrapper only fails on
C functions which call back to Haskell.
Linux 2.6.28-17-generic #58-Ubuntu SMP
ghc-6.12.2-i386-unknown-linux-n.tar.bz2
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4059>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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