db 66h?

flat assembler
Message board for the users of flat assembler.

Index > Main > db 66h?

Author

Thread

randomdude

Joined: 01 Jun 2012
Posts: 83

randomdude

i see in some hex edited files: 90h (NOPs) and 66h

what is the instruction 66h? ida doesnt translate it

19 Feb 2014, 18:32

shutdownall

Joined: 02 Apr 2010
Posts: 517
Location: Munich

shutdownall

66h is an operand size override (16/32 bit) to change default operand size for single instructions.

http://pdos.csail.mit.edu/6.893/2009/readings/i386/s17_01.htm

19 Feb 2014, 20:44

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 18622
Location: In your JS exploiting you and your system

revolution

AMD used to promote alignment code that was db 0x66,0x90 with varying amounts of the 0x66's from zero to three times.

It is basically a do-nothing space filler when used in that combination.

19 Feb 2014, 21:10

shutdownall

Joined: 02 Apr 2010
Posts: 517
Location: Munich

shutdownall

Yes - it is simply a 16-bit or 32-bit NOP. Laughing

20 Feb 2014, 09:58

randomdude

Joined: 01 Jun 2012
Posts: 83

randomdude

ok thx

20 Feb 2014, 18:39

< Last Thread | Next Thread >

Forum Rules:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum