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Compare RAX to an existing address in ASM?

 
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Kamd
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Joined: 02 May 2018
Posts: 28

PostPosted: Sun Sep 01, 2019 4:42 am    Post subject: Compare RAX to an existing address in ASM? Reply with quote

I am pretty new to Assembly, so please try explain easily.

Basically, I am working with a shared opcode, for example, a HP damage opcode. I need to make this damage opcode to only effect things that are not writing to my player (health) address.

I already have an assembly script that locates my player structure, and +10 is the offset to my health.

To determine if the damage opcode is writing to my player's health address, I want to compare RAX (write address) to my already-found health address.

Example script:
NOTE: _player is start of player struct defined in the prior script (simplified):
Code:
...
registersymbol(_player)
...
customCode:
    ...
    mov [_player],rdx

So _player+10 is address of my health.

Code:
hpWrite:
    cmp [rax],GetAddress(_player+10) // check if write address is player health address
    jne runNormalCode // if rax != playerHpAddress we run the normal damage code

    // We didn't jump so this is our player's health. Don't do anything
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sbryzl
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Joined: 25 Jul 2016
Posts: 164

PostPosted: Sun Sep 01, 2019 4:26 pm    Post subject: Reply with quote

I'm not too certain about your situation but I think you can just preserve a register, load your address, add 10 and compare it.


Code:
push rcx
mov rcx,[_player]
add rcx,10
cmp rax,rcx
pop rcx
jne runNormalCode
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