a super skill to help you understand .init and .fini, just do “LD_DEBUG=libs ./a.out”, read detail http://www.bnikolic.co.uk/blog/linux-ld-debug.html One thing need to remind you, loader pass control to a.out *BEFORE* it calls the fini.

discovered something about .init and .fini sections, if you compile your source file into .o, no .init and .fini sections exist. But if you compile your code into target exe, .init and .fini are there. My question is: where does those .init and .fini come from the .o?