Intel/AMD instruction nopl

**gerard4143** · 01-24-2010

Hi,

Does anyone know what the Inet/AMD instruction 'nopl' is or does anyone know where I can find a list of hex values for the Intel/AMD instructions...
Please note this question is pure curiosity...nothing important is waiting on this reply...

Code:

0000000000400478 <exit@plt-0x10>:
  400478:	ff 35 2a 05 20 00    	pushq  0x20052a(%rip)        # 6009a8 <_GLOBAL_OFFSET_TABLE_+0x8>
  40047e:	ff 25 2c 05 20 00    	jmpq   *0x20052c(%rip)        # 6009b0 <_GLOBAL_OFFSET_TABLE_+0x10>
  400484:	0f 1f 40 00          	nopl   0x0(%rax)

Processor - x86_64 AMD Athlon(tm) Processor LE-1640

**regexorcist** · 01-24-2010

Back in the day...
I used to write assembly language for specific micro-controllers
and the NOP instructins stood for (No Operation)
it was basically a 1 or 2 machine cycle delay
(a machine cycle consisted of an internal counter counting multiple clock pulses)
Many instructions had an "L" on the end indocation Long

I can't be sure, but I would guess that
NOPL probably stands for (No Operation, Long)
in other words... just a time delay

Hex codes pre-dates assembly language but the codes will
be specific to the processor/micro-controller your dealing with.
You may find a family of processors w/ the same op-codes / operands (hex codes)

Good Luck

**gerard4143** · 01-24-2010

I would agree except the objdump has the hex values

Code:

0f 1f 40 00          	nopl   0x0(%rax)

and nop is 0x90..

**jeroen_** · 03-25-2010

It could be a way to add extra padding

Code:

0f 1f 40 00          nopl   0x0(%rax)  //4byte nop
0f 1f 00                nopl   (%rax)  //3byte nop

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