为什么简单的C程序链接到libc.a，而不是libc.so？

Question

My question is, is libc.a always needed, even if I wish to link with libc.so. I searched internet and it gives 3 possible answers(conflicting)

1. c program will require to link to libc.a and crt1.o files
2. for "-l" option, ".so" is preferred against ".a"
3. There're both libc.a and libc.so

So what should be the correct answer to my question?

Answer 1

If you want to link against libc.so and not libc.a, you don't need to do anything special, this is the default.

The first answer is outdated and not applicable to most normal Linux distros. AC program by default will need libc.so but not libc.a.

The second answer is correct by default. You need to supply a linker flag like -static to change this preference. Note this answer applies to all libraries, not just libc.

The third answer is correct in most Linux distributions.

In the case of GNU libc (supplied with a majority of Linux distros), statically linking your executable against libc.a is not recommended and may not work. It is doable but you will need to know exactly what you are doing and jump through some hoops, otherwise your executable will still depend on libc.so.

Other versions of libc may be more static-linking-friendly.