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Index > Main > PUSH multiple immediate trap when using unary negatives

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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17348
Location: In your JS exploiting you and your system
revolution
Be careful when using unary negatives within the PUSH immediate instruction. I got caught by an unexpexted outcome.

I started with this and all was okay:

Code:
infinity = 07fffffffh
use32
push -infinity   infinity ;this line okay, two PUSH opcodes generated
    


Later I rearranged the code to this:

Code:
infinity = 07fffffffh
use32
push  infinity  -infinity ;this line different, one "PUSH 0" instruction
    


The second push above is assembled as a binary negative.

One solution is this below:

Code:
infinity = 07fffffffh
use32
push  infinity 0-infinity ;this line okay, two PUSH opcodes generated
    
Post 28 Mar 2005, 01:42
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Madis731



Joined: 25 Sep 2003
Posts: 2140
Location: Estonia
Madis731
You can just put brackets around it, can't you?
Code:
infinity = 7FFFFFFFh
use32
push infinity (-infinity)
    
Post 28 Mar 2005, 07:31
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17348
Location: In your JS exploiting you and your system
revolution
Yep, you can also put brackets. Another solution, thanks.
Post 28 Mar 2005, 08:12
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