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pini



Joined: 04 Jul 2005
Posts: 14
pini
Hi folks,

After years of silence, I'm back to fasm and it still rocks.

I'm trying to write an MBR so I need my code to relocate itself before loading the bootsector of the active partition.
Basically, I'd like to do it by having the following layout :

Code:
format binary
use16

org A
; copy MBR to whatever
; jmp to whatever:B

org B
; chainload    


As it works well, what I'd like to ask is more a feature request : as I need to pad my code until offset 0x1be (from the beginning of the file, this is where the partition table is to be located), I need to define labels at the beginning and end of the first part (because $$ refers to the second org), so that I can pad with

Code:
times 0x1be - ($ - $$) - (A.end - A.start) db 0    


Basically, I'd like to write something like

Code:
times 0x1be - ($$$) db 0    


With $$$ (or whatever) being the number of bytes written to output so far, in all address spaces.

How hard would it be to add such a special value ?
And if it's easy, could it be considered for inclusion in fasm ?

Thanks a lot.
Post 06 Sep 2011, 12:09
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Tomasz Grysztar
Assembly Artist


Joined: 16 Jun 2003
Posts: 7709
Location: Kraków, Poland
Tomasz Grysztar
Code:
format binary
use16 

_$$ = 0
_$ equ (_$$+$-$$)
macro org address { _$$ = _$
                    org address }

org A
; copy MBR to whatever 
; jmp to whatever:B 

org B 
; chainload

times 0x1be - _$ db 0
    
Post 06 Sep 2011, 12:28
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pini



Joined: 04 Jul 2005
Posts: 14
pini
Oh sweet !

Thanks.

/EDIT/ It could be a good idea to evaluate the address before updating _$$ in the macro definition just in case it's based on _$, as in
Code:
macro org address {
   local a
   a = address
   _$$ = _$
   org a
}    
Post 06 Sep 2011, 13:07
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