tracing segfaults with FFI

[Gaal Yahas]

Hello,

I have these two functions:

    freezeNode node = do
        ptr     <- newStablePtr node
        new (castPtr $ castStablePtrToPtr ptr)

    thawNode nodePtr = do
        deRefStablePtr (castPtrToStablePtr nodePtr)

I use the first to pack a Haskell structure and hand it over to a c
library with FFI. It calls me back (traces show I do get the original
address) but deRefStablePtr causes a segfault.

What am I doing wrong? More generally, how do I approach this kind of
problem? What tools exist that can help me debug FFI code?

-- 
Gaal Yahas <gaal at forum2.org>
http://gaal.livejournal.com/