GCC outputs an executable ELF file when I want a shared library

Question

I'm trying to build a shared library in Cygwin using an i686-elf cross-compiler. The code is very simple:

int add(int a, int b) {
    return a + b;
}

void _init() {
    add(3, 4);
}

I'm compiling with the following command:

i686-elf-gcc -fPIC -shared -nostdlib core.c -o libcore.so

This should be producing a shared object, right? But GCC outputs a warning about not being able to find the _start symbol, which is the entry point for executables, not shared objects. Furthermore, readelf says the following:

$ readelf -a libcore.so
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
  ...
  Type:                              EXEC (Executable file)
  ...

What's going wrong here?

Answer 1

What's going wrong is essentially that you're targeting i686-elf, and nobody builds shared libraries for that target. -Wl,-shared will give you something which is marked as a shared library, but how exactly do you plan to load a shared library on a bare-metal target?