...

Thanks, looks like it's option (1) then. Could you tell me what Haskell type I have to use be able to pass a pointer to this binary to C land (genuine address, not StablePtr). I don't think the standard FFI allows this at all but, IIRC, the old ghc libraries allowed you to do this with a mutable byte array.

Does anybody know the answer to this? please.. pretty please..:-)

Sorry if this is a case of me failing to RTFM, but I don't think it is. Paragraph 8.1.1 of the users guide says..

"The types ByteArray and MutableByteArray may be used as basic foreign types (see FFI Addendum, Section 3.2). In C land, they map to (char *)."

This is still true for 5.04.x: the ByteArray and MutableArray libs in hslibs (package lang) provide these types, but they are deprecated and will be removed at some point. The functionality which allows ByteArray and MutableByteArrays to be passed to FFI functions has already been removed in CVS. In the current CVS GHC, undoubtedly the right thing to use is Foreign.mallocForeignPtr. Internally these are implemented as MutableByteArray#, so you get fast allocation and GC, but from the programmer's point of view it's a normal ForeignPtr. If you don't mind the not-so-great performance, you can use ForeignPtr with malloc/free in 5.04.x and convert to mallocForeignPtr when the next major release of GHC comes along. Or you can use ByteArray/MutableByteArray for the time being (note that you can only pass one of these to an "unsafe" FFI function, BTW). Cheers, Simon