basic assembly question for gurus

[rmills]

Im reading thru "The Art of Exploitation" and had a quick asm question. When you grab or set data in a register like [epb-4] like when you zero it. Are you only setting a subset of the registrar? Is it just to efficiency or do I have this totally wrong.

naturally right after I post this he covers it and I was completely wrong. Thou im confused why you would want to change the address, i assume that you could overwrite data stored at that address.

[Jase21]

You can using different addressing modes. The above one is just one of them.

[fb1h2s]

Zero it in the sense u mean Xor the registers or memmory location?? well if ur are xor ing [ebx-4] onle tht data in tht location will only get zero

[b3r00tb4ck]

If you are messing with calls and the stack, then you need to manually set EBP in your shellcode, otherwise NASM or similar does this for you.