Compile a shared library statically

Question

I've got a shared library with some homemade functions, which I compile into my other programs, but I have to link the end program with all the libraries I have used to compile the static library. Here is an example:

I have function foo in the library which requires a function from another library libbar.so.

In my main program to use function foo I have to compile it with the -lbar flag. Is there a way I can compile my library statically so it includes all the required code from the other libraries, and I can compile my end program without needing the -lbar flag?

Answer 1

Shared objects (.so) aren't libraries, they are objects. You can't extract part of them and insert it in other libraries.

What you can do if build a shared object which references the other -- but the other will be needed at run time. Just add the -lbar when linking libfoo.

If you are able to build libbar, you can obviously make a library which is the combination of libfoo and libbar. IIRC, you can also make the linker build a library which is libfoo and the needed part of libbar by linking a .a with the .o meant to go in libbar. Example:

gcc -fPIC -c lib1.c     # define foofn(), reference barfn1()
gcc -fPIC -c lib2a.c    # define barfn1(), reference barfn2()
gcc -fPIC -c lib2b.c    # define barfn2()
gcc -fPIC -c lib2c.c    # define barfn3()
gcc -c main.c           # reference foofn()
ar -cru libbar.a lib2*.o
gcc -shared -o libfoo.so lib1.o -L. -lbar
nm libfoo.so | grep barfn2()    # ok, not here
gcc -o prog main.o -L. -lfoo
env LD_LIBRARY_PATH=. ./prog    # works, so foofn(), barfn1() and barfn2() are found

Answer 2

Step 1 (Create object file):

gcc -c your.c -o your.o

Step 2 (Create static library):

ar rcs libyour.a your.o

Step 3 (Link against static library):

gcc -static main.c -L. -lyour -o statically_linked

Answer 3

You can get this sort of thing working by using libtool, see the libtool manual on Inter library dependencies for an example of how that works

Answer 4

Basically, if you have the statically-linked libraries of the system libraries that your static library depends on, you can statically-link in all the code from them.

I'm not sure why, though. *NIX platforms' handling of shared libraries is a work of genius, and severely cuts down on compiled program size. If you're worried about not being able to run code on a different computer due to missing libraries, then you can always take the path of most closed-source programs compiled for Linux libraries: just compile them with -Wl,--rpath -Wl,. options to GCC and distribute the library alongside the binary.