mov rax,[rip-7] means what?

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system error

Joined: 01 Sep 2013
Posts: 670

system error 16 Jun 2015, 00:35

The instruction size itself is 7 bytes. So does that mean that RAX contains its own encoding or am I getting this wrong? I am a bit confused.

16 Jun 2015, 00:35

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20451
Location: In your JS exploiting you and your system

revolution 16 Jun 2015, 01:33

RIP points to the beginning of the next instruction. So your code will load RAX with the highest byte (the MSB) being the first byte of the next instruction, and the lower seven bytes being that instruction.

16 Jun 2015, 01:33

system error

Joined: 01 Sep 2013
Posts: 670

system error 16 Jun 2015, 04:10

ok got it. kinda self-pointing instruction. Any chance I can use variable instead of constant? Like manipulating $, $$? It threw me an error, that $ thingy.

16 Jun 2015, 04:10

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20451
Location: In your JS exploiting you and your system

revolution 16 Jun 2015, 05:17

Code:

mov rax,[$]

16 Jun 2015, 05:17

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