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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude
is it possible to do something like this

Code:
push 12345678, my_value = $-4    


in a single line?
Post 19 Jun 2015, 08:57
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17287
Location: In your JS exploiting you and your system
revolution
Only with a macro.
Post 19 Jun 2015, 09:44
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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude
thats fine, if i only knew how to make one D:
Post 19 Jun 2015, 09:47
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revolution
When all else fails, read the source


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revolution
Code:
macro push value,instr {
  push value
  instr
}    
Post 19 Jun 2015, 10:16
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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude
i think il just write it in 2 lines cause i would need to make one macro for push, other for call, jmp, jne... too many lol

i guess there is not other way to do it

thanks anyways Very Happy

edit: is it possible to get the size of an instruction or the address of the next instruction?
Post 19 Jun 2015, 12:17
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revolution
When all else fails, read the source


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Posts: 17287
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revolution
Code:
this: nop
next:
size = next-this    
Post 19 Jun 2015, 12:31
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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude
Code:
call near next_instr
my_address = $-4 
next_instr = $    


but wouldnt there be a way to make it more compact without using so many lines? Very Happy
Post 19 Jun 2015, 12:47
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17287
Location: In your JS exploiting you and your system
revolution
randomdude wrote:
Code:
call near next_instr
my_address = $-4 
next_instr = $    


but wouldnt there be a way to make it more compact without using so many lines? Very Happy
Yes, use a macro.
Post 19 Jun 2015, 12:51
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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude
but i would need to create one macro for each instruction lol fasm is driving me crazy
Post 19 Jun 2015, 12:53
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17287
Location: In your JS exploiting you and your system
revolution
I wonder if you are doing something in a terribly bad way. Perhaps if you explained what you are trying to achieve someone can help you find a better way?
Post 19 Jun 2015, 12:58
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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude
yes, i have the same feeling Very Happy

im basically making a dll for a game, that patches some addresses and/or creates some codecaves

since my dll has relocations, i cant simply put a 'jmp x' at the end of my codecaves. till now i had to use the following:

Code:
jmp dword[jump_back]
...
dd jump_back dd 0x12345678
    


but obviously 'jmp dword[pointer_to_x]' wastes more space and is slower, so im looking for a better alternative

the method im currently using, is to patch the jmp's of my own dll, but im unsure which would be most practical way to do it


Description:
Download
Filename: exdat.zip
Filesize: 885 Bytes
Downloaded: 213 Time(s)

Post 19 Jun 2015, 13:21
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17287
Location: In your JS exploiting you and your system
revolution
How do you know that "jmp dword[pointer_to_x]" is slower? Slower than what?
Post 19 Jun 2015, 13:27
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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude
pointer_to_0x12345678 dd 0x12345678
jmp dword[pointer_to_0x12345678]

slower than

jmp 0x12345678

well, at least it uses more space for sure Very Happy

something like this (but taht actually works lol) would make my sourcecode more clear

jmp absolute 0x12345678, JumpBack0 = $-4

with absolute i mean it would generate the relative opcode E9, but followed by 78 56 34 12 isntead of letting fasm calculate the relative value to address 0x12345678
Post 19 Jun 2015, 13:34
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17287
Location: In your JS exploiting you and your system
revolution
randomdude wrote:
pointer_to_0x12345678 dd 0x12345678
jmp dword[pointer_to_0x12345678]

slower than

jmp 0x12345678
This is not guaranteed.

You might be trying to solve a problem that doesn't exist.

Do you know the adage "Get it working, then get it fast"?
Post 19 Jun 2015, 13:45
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randomdude



Joined: 01 Jun 2012
Posts: 83
randomdude
how reading a value from memory can be as fast as reading it from immediate? but anyways, thats not the point. i just want to write my patches just like if i were patching them directly over the exe, but in asm, not machine code lol
Post 19 Jun 2015, 14:06
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17287
Location: In your JS exploiting you and your system
revolution
randomdude wrote:
how reading a value from memory can be as fast as reading it from immediate?
Caches, buffers, predictors, etc. The CPUs are very complex and sometimes the timing of things can be unintuitive. Only comparative testing on the target system can properly answer the "which is fastest?" question.
Post 19 Jun 2015, 14:09
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