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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude 19 Feb 2014, 18:32
i see in some hex edited files: 90h (NOPs) and 66h

what is the instruction 66h? ida doesnt translate it
Post 19 Feb 2014, 18:32
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shutdownall



Joined: 02 Apr 2010
Posts: 517
Location: Munich
shutdownall 19 Feb 2014, 20:44
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
Post 19 Feb 2014, 20:44
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 20363
Location: In your JS exploiting you and your system
revolution 19 Feb 2014, 21:10
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.
Post 19 Feb 2014, 21:10
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shutdownall



Joined: 02 Apr 2010
Posts: 517
Location: Munich
shutdownall 20 Feb 2014, 09:58
Yes - it is simply a 16-bit or 32-bit NOP. Laughing
Post 20 Feb 2014, 09:58
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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude 20 Feb 2014, 18:39
ok thx Very Happy
Post 20 Feb 2014, 18:39
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