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: 20299
Location: In your JS exploiting you and your system

revolution 28 Mar 2005, 01:42

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

28 Mar 2005, 01:42

Madis731

Joined: 25 Sep 2003
Posts: 2139
Location: Estonia

Madis731 28 Mar 2005, 07:31

You can just put brackets around it, can't you?

Code:

infinity = 7FFFFFFFh
use32
push infinity (-infinity)

28 Mar 2005, 07:31

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 28 Mar 2005, 08:12

Yep, you can also put brackets. Another solution, thanks.

28 Mar 2005, 08:12

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