What does NOPL do in x86 system?

Question

what is the function of NOPL in x86 machine? It feels like it doesn\'t do anything, but why is it always in the assembly code?

Answer 1

NOP is a one-byte "do nothing" operation, quite literally "no operation". NOPW, NOPL, etc.. are the equivalent do-nothings, but take up word and long-sized bytes.

e.g.

NOP // 1byte opcode
NOP // 1byte opcode

is equivalent to doing

NOPW // 2byte opcode.

They're very handy for padding things out so a code sequence begins on a particular memory boundary, by taking up a few bytes of instruction space, yet not actually doing anything.

NOP's sole effect on the CPU is to increment IP/EIP by 1. The NOPx equivalents will do so by 2, 4, etc...