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Index > Main > Tool to calculate relative jump/call offsets?

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Karl20001



Joined: 10 Nov 2005
Posts: 11
Karl20001
Hi Razz
Im currently trying to add functions to a program which i dont have source code off, and cant be disassembled perfectly to be changed and reassembled.
The thing is, for my asm code im partly using code caves or NOPing unused procedures. Problem here is i have to make new calls/jmp or switch old one to new locations.

I know normally a call to label is resolved by the assembler on assembling, so the offset from the call address to the label is put in hexcode.
But as here i dont assemble, i have to calculate the offsets by hand, and that is not good for many calls, considering with jmping backwards i have to think in signed offsets etc Razz
So if someone knows a tool where you can enter the call and destination address, and it gives you the offset, please tell me Razz
Post 10 Nov 2005, 22:09
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17717
Location: In your JS exploiting you and your system
revolution
Code:
call foo
bar:
;...
foo:    

becomes:
Code:
db 0xE8
dw/dd/dq (foo-bar) ;the calculated offset    
works for 16, 32 and 64 bit code.
Post 11 Nov 2005, 01:45
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