System.Posix

dlsym returns the address binding of the symbol described in symbol, as it occurs in the shared object identified by source.

undl obtains the raw handle. You mustn't do something like withDL mod flags $ liftM undl >>= p -> use p

Flags for System.Posix.DynamicLinker.dlsym. Notice that Next might not be available on your particular platform! Use haveRtldNext.

If RTLD_DEFAULT is not defined on your platform, packDL Default reduces to nullPtr.

Flags for dlopen.

On some hosts (e.g. SuSe and Ubuntu Linux) RTLD_NEXT (and RTLD_DEFAULT) are not visible without setting the macro _GNU_SOURCE. Since we don't want to define this macro, you can use the function haveRtldNext to check whether the flag Next is available. Ideally, this will be optimized by the compiler so that it should be as efficient as an #ifdef.

If you fail to test the flag and use it although it is undefined, packDL will throw an error.