(also posted to comp.lang.lisp) Hi all: I have a lisp image that contains the following functions: (defun frgo (a) (format *debug-io* "~%~A~&" a) (values)) (cffi:defcallback frgo_helper :void ((a-cstr :string)) (frgo (cffi:foreign-string-to-lisp a-cstr))) In a C dynamic library I have: * file frgo_c.h: extern void frgo_helper( char * a ); * file frgo_c.c: void frgo( char * a ) { frgo_helper( a ); } Now, the library does not compile - undefined symbol _frgo_helper() ! How do I make functions "known" to C land that are purely defined as callbacks in Lisp land? I tried to declare the function in C land like this: extern void frgo_helper( char * a ) __attribute__((weak_import)); No luck, though. My environment is: Mac OS X Snow Leopard (10.6.8), Apple LLVM compiler 3.0. An ideas / hints / tipps? Thanks a lot! Cheers Frank