I am confused ! I found nop WORD PTR [rax+rax*1+0x0]

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Roman

Joined: 21 Apr 2012
Posts: 1088

Roman

I know about nop(hex op code 90).
But what this mean ?
nop WORD PTR [rax+rax*1+0x0]

hex op code: 66 0f 1f 44 00 00

24 Mar 2021, 13:47

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 18489
Location: In your JS exploiting you and your system

revolution

Multi-byte nops are also nops.

You can use them for padding. They might, or might not, be more efficient than multiple single byte nops when you execute them. Test it to see how it performs on your system running the code.

24 Mar 2021, 14:17

Roman

Joined: 21 Apr 2012
Posts: 1088

Roman

Its like rept for nop ?
I am right ?

24 Mar 2021, 14:24

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 18489
Location: In your JS exploiting you and your system

revolution

It is different. You can't arbitrarily enter the instruction at any point. You still have to begin at the proper place.

Code:

my_padding_1:
  times 6 nop
;...
my_padding_2:
  nop WORD PTR [rax+rax*1+0x0] 
;...
jmp my_padding_1 + 0 ; okay
jmp my_padding_2 + 0 ; okay
jmp my_padding_1 + 2 ; okay
jmp my_padding_2 + 2 ; FAIL

24 Mar 2021, 14:33

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