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Index > Windows > Why doesn't "mov eax,EBP+8" assemble?

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Ben321



Joined: 07 Dec 2017
Posts: 70
Ben321 05 Apr 2018, 23:52
When my processess is defined as
Code:
proc MyProc FirstArg:DWORD,SecondArg:DWORD
mov eax,FirstArg
mov edx,SecondArg
endp    

why do I keep getting an error when compiling? I've already included the needed .inc files to enable the "proc" and "endp" macros.


The error it gives is
Quote:
mov eax,..arg?TS


I don't even known what ..arg?TS is. I assume it is the output of one of the macros. I was expecting the first arg to be translated by the macro to EBP+8 and the second arg to be translated EBP+12. EBP+8 is valid, and would work, but ...arg?TS is not valid, so it obviously doesn't work.

When the macro is finished working the above line of code should look like:
Code:
mov eax,EBP+8
mov edx,EBP+12    


These are valid. It means "Move the sum of EBP and 8 to the EAX register" and then "Move the sum of EBP and 12 to the EAX register". Why isn't the macro doing this?
Post 05 Apr 2018, 23:52
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 20451
Location: In your JS exploiting you and your system
revolution 06 Apr 2018, 00:50
You have to include the square brackets if you want to read the value. Or alternatively, you can use LEA if you want the address of the arg (unlikely to be useful)
Code:
mov eax,[FirstArg] ;read the value of FirstArg
lea eax,[FirstArg] ;probably not useful    
Ben321 wrote:
When the macro is finished working the above line of code should look like:
Code:
mov eax,EBP+8
mov edx,EBP+12    


These are valid. It means "Move the sum of EBP and 8 to the EAX register" and then "Move the sum of EBP and 12 to the EAX register". Why isn't the macro doing this?
Actually, no, that is not a valid way to encode an add in Intel syntax. But LEA will do it. "lea eax,[ebp+8]"
Post 06 Apr 2018, 00:50
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