How to compile shared lib with clang on osx

Question

source file

rsetti::fastidio { /tmp }-> cat foo.c

    #include <stdio.h>
    void ACFunction() {
      printf("ACFunction()\n");
      AGoFunction();
    }

compilation of shared lib

rsetti::fastidio { /tmp }-> clang -shared -o libfoo.so foo.c

    foo.c:4:3: warning: implicit declaration of function 'AGoFunction' is invalid in C99 [-Wimplicit-function-declaration]
      AGoFunction();
      ^
    1 warning generated.
    Undefined symbols for architecture x86_64:
      "_AGoFunction", referenced from:
          _ACFunction in foo-lFDQ4g.o
    ld: symbol(s) not found for architecture x86_64
    clang: error: linker command failed with exit code 1 (use -v to see invocation)

rsetti::fastidio { /tmp }->

the same code on linux + gcc can be easily compiled.

Solution

By using:

-Wl,-undefined -Wl,dynamic_lookup

or

clang -shared -undefined dynamic_lookup -o libfoo.so foo.c

seems to maintain the same behaviour of GCC.

Comments

[oorst]

That did the trick. I knew it must have been something simple. Onwards!

[rgov]

.dylib is the canonical extension for a shared library on macOS, using -dynamiclib instead of -shared. See stackoverflow.com/questions/2339679/…

[ezolotko]

Please note that "-undefined dynamic_lookup" has unwanted side effects, like silencing the compiler diagnostics when you have some undefined symbols in your classes. These undefined symbols will then pop up later when trying to load your library at runtime with misleading errors, like "dlopen: image not found". See stackoverflow.com/a/30934307/71689 for details.