I am using Green Card 2.05, but it seems to me that its support for Ptr/Addr types are not up-to-date. I then use ForeignPtr to marshall a C structure, but have some problem with pointers which is garbage collected too early. Here is a code sample: ------------------------ snip ------------------------ %fun destroyByteBuffer :: Addr -> IO () %code if (arg1) { free(arg1); } %result () data ByteBufferType = ByteBufferType type ByteBuffer = ForeignPtr ByteBufferType marshall_byteBuffer :: ByteBuffer -> IO Addr marshall_byteBuffer ptr = withForeignPtr ptr (\x -> return (ptrToAddr x)) unmarshall_byteBuffer :: Addr -> IO ByteBuffer unmarshall_byteBuffer addr = newForeignPtr (addrToPtr addr) (destroyByteBuffer addr) %fun readInt :: ByteBuffer -> IO Int %call (byteBuffer (addr bf)) %code INT32 r, v = 0; % r = bb_get_int((Byte_Buffer *) bf, &v); %fail {r != _NO_ERR} {"readInt failed"} %result (int v) ------------------------ snip ------------------------ The code would sometimes segfault in bb_get_int(..), and since it was coded in a separate C file, I was able to trace down the error in GDB, which hinted that, part of the C structure in "bf" was already freed prior to the bb_get_int(..) function call. So my guess is that "destroyByteBuffer" was invoked even when I use "withForeignPtr" to marshall the ByteBuffer type. What did I do wrong here? Is it a bug with Greencard or something I am still missing when constructing a garbage collectible ForeignPtr in FFI? Regards, .paul. On Tue, Feb 25, 2003 at 09:49:00PM +0800, paul@theV.net wrote:

I am using Green Card to make some FFI modules with GHC, but sometimes it segfaults in the middle of nowhere, leaving no sensible stack trace in gdb.

I wonder what is the proper way to debug FFI modules written in C? Trying to add a "-g" flag doesn't seem help at all...

Regards, .paul. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe