Question

I disassembled simple program written in C++ and there is a function:

080486a8 <_GLOBAL__I_main>:
 80486a8:   55                      push   %ebp
 80486a9:   89 e5                   mov    %esp,%ebp
 80486ab:   83 ec 18                sub    $0x18,%esp
 80486ae:   c7 44 24 04 ff ff 00    movl   $0xffff,0x4(%esp)
 80486b5:   00 
 80486b6:   c7 04 24 01 00 00 00    movl   $0x1,(%esp)
 80486bd:   e8 a6 ff ff ff          call   8048668 <_Z41__static_initialization_and_destruction_0ii>
 80486c2:   c9                      leave  
 80486c3:   c3                      ret    
 80486c4:   90                      nop
 80486c5:   90                      nop
 80486c6:   90                      nop
 80486c7:   90                      nop
 80486c8:   90                      nop
 80486c9:   90                      nop
 80486ca:   90                      nop
 80486cb:   90                      nop
 80486cc:   90                      nop
 80486cd:   90                      nop
 80486ce:   90                      nop
 80486cf:   90                      nop 

What does this function? And why are there so many NOP operations after RET instruction?

Answer 1

As netrom mentioned, __static_initialization_and_destruction_0(int, int) arranges for global constructors and destructors to be called.

Many compilers add nop instructions after functions to enable incremental relinking. If you change the function a bit and it grows, the linker doesn’t have to move all functions that follow. Instead, the growth overwrites some of the former nop’s.