Jacob Sorber
https://www.youtube.com/watch?v=JbHmin2Wtmc&list=PL9IEJIKnBJjFn6zQQkJ2e8vxCVxhl2yuD&index=1
Object files are linked to get ur final binary.
.so files are share objects or shared libraries are different. .so files are separate and are designed to be loaded at runtime.
#-fPIC: Position-Independent Code - allows us to be able to run our code
# independent of where the code is loaded on to memory
#-shared: make a shared library
libmycode.so: libmycode.c mycode.h
$(CC) $(CFLAGS) -fPIC -shared -o $@ libmycode.c -lc
#-L. look for the current directory for libraries
#-lmycode link libmycode.a
runtime_librarytest: librarytest.c
$(CC) $(CFLAGS) -o $@ $^ -L. -lmycode
We can add the library path to LD_LIBRARY_PATH environment variable so our program can look for the program.
In a local system you can add it to following directories for the loader to automatically detect the libraries:
/lib
/usr/lib
/usr/local/lib
Purpose of shared library is the code size. If we use object dump to check the size of the file you can see the difference.
Section undefined because it’s defined during runtime.
#And this is the typical static library that we use in 42
#r : replace any existing file
#c : create an archive if it doesn't already exist
#s : (index) creates index
libmystaticcode.a: libmycode.o
ar rcs libmystaticcode.a libmycode.o
Static library will stuff all the code into the final binary instead of linking them in runtime.