Re: NOP instruction

[Chris Wedgwood]

On Wed, Dec 16, 1998 at 11:36:00AM +1030, Mofeed Shahin wrote:

> Ummm, I was under the impression that NOP under the intel was 0x90...

nope

> I am pretty sure the intel does have a real NOP.

don't think so:

[me:1] caffeine:~$ cat nop.S
.text

_start: .globl  _start

        nop
        cpuid
        xchg    %eax,%eax

        movl    $0x01,%eax
        movl    $0x00,%ebx
        int     $0x80
[me:1] caffeine:~$ as -Qy -o nop.o nop.S
[me:1] caffeine:~$ objdump -d -S nop.o

nop.o:     file format elf32-i386

Disassembly of section .text:

00000000 <_start>:
   0:   90              nop
   1:   0f a2           cpuid
   3:   90              nop
   4:   b8 01 00 00 00  movl   $0x1,%eax
   9:   bb 00 00 00 00  movl   $0x0,%ebx
   e:   cd 80           int    $0x80

As you can see -- gas treats nop as xchg %eax,%eax.

-cw