Why does gcc generates strange code without flag -fno-pie?

Question

I am trying to compile dummy function in gcc with flag -fno-pie and without.

void dummy_test_entrypoint() { }

When i compile without the flag.<

Answer 1

You disassembled the object file without the --reloc flag, so the output is misleading. With the --reloc flag, you'll see this:

   3:   e8 fc ff ff ff          call   4 
            4: R_386_PC32   __x86.get_pc_thunk.ax
   8:   05 01 00 00 00          add    $0x1,%eax
            9: R_386_GOTPC  _GLOBAL_OFFSET_TABLE_

And the subroutine looks like this:

00000000 <__x86.get_pc_thunk.ax>:
   0:   8b 04 24                mov    (%esp),%eax
   3:   c3                      ret    

This construct loads the GOT pointer into %eax, in case the function needs to reference global data. The function does not contain such a reference, but because you compiled the code without optimization, GCC did not remove the dead code.