How using store ?

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Roman

Joined: 21 Apr 2012
Posts: 1823

Roman 15 Apr 2023, 09:22

Fasmw 1.73

Code:

Virtual text "a tion"
store ;I want put symbol "c" in second char. How do this ?

I try this

Code:

virtual at 0
        hex_digits::
        db 'a ction',0
    end virtual 

load a byte from hex_digits:1
;but store not work
store byte a +5 at  hex_digits:1 ;ok
store byte a "c" at  hex_digits:1 ;fasm error

Last edited by Roman on 15 Apr 2023, 09:36; edited 1 time in total

15 Apr 2023, 09:22

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 15 Apr 2023, 09:33

If the STORE is within the same addressing space (that is: before END VIRTUAL), you can do this quite directly:

Code:

virtual
        text db "a tion"
        store byte "c" at text+1
end virtual

If you plan to use STORE from somewhere else, you need to have a name for this virtual area, defined as a "::" label. It doesn't matter where in the virtual block you put it, it labels the whole area, not a specific point within.

Code:

virtual
    area::
        text db "a tion"
end virtual

store byte "c" at area:text+1

Note: these examples apply to both fasm 1 and fasmg. For fasmg this is a legacy syntax though, the new syntax would have <"c":byte> instead of <byte "c">.

15 Apr 2023, 09:33

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20424
Location: In your JS exploiting you and your system

revolution 15 Apr 2023, 09:37

You have a bad value

Quote:

store byte a "c" at hex_digits:2 ;fasm error

That needs to be a single byte value. a "c" is not a valid byte. Did you mean a + "c" or just "c"?

15 Apr 2023, 09:37

Roman

Joined: 21 Apr 2012
Posts: 1823

Roman 15 Apr 2023, 09:41

Thanks.
How put virtual text in data ?

Code:

;section data
virtual at 0
    area::
        text db "a tion",0
end virtual

textA area ;fasm error

I do this variant. Work

Code:

virtual at 0
    area::
        text db "a tion",0
end virtual

textAa:   rept 7 n:0 { load a byte from area:text+n
    store byte 'c' at  area:text+1    
    db a
         }
         db 0 
;now textAa db 'action',0 in data section.

Last edited by Roman on 15 Apr 2023, 09:55; edited 1 time in total

15 Apr 2023, 09:41

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 15 Apr 2023, 09:55

With fasmg it could go like this:

Code:

virtual at 0
    area::
        text db "a tion",0
    area_size:
end virtual

load all: area_size from area:0
textA db all

With fasm 1 a little more effort is needed, because you can only operate on small data units:

Code:

virtual at 0
    area::
        text db "a tion",0
    area_size:
end virtual

textA:
repeat area_size
  load a byte from area:%-1
  db a
end repeat

(This obviously works with fasmg too, but there simpler and faster method is available.)

15 Apr 2023, 09:55

Roman

Joined: 21 Apr 2012
Posts: 1823

Roman 15 Apr 2023, 09:57

Thanks.

rept not see area_size
repeat see area_size

15 Apr 2023, 09:57

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20424
Location: In your JS exploiting you and your system

revolution 15 Apr 2023, 16:11

With the named virtual blocks if there is a non-numeric base we have to remember the register base when it is used later. If the load/store code is in a macro and has the "area" label passed as a parameter then it might be unknown to the macro how to correctly address the bytes.

Code:

virtual at edx
    area::
        text db "a tion",0
    area_size = $-edx
end virtual

repeat area_size
  load a byte from area: edx + % - 1 ; <--- we have to know the implicit edx register base
  db a
end repeat

The named virtual blocks could be more flexible by supporting $$ and $.

Code:

virtual at edx
        area:: text db "a tion",0
end virtual

repeat area:$ - area:$$  ; <--- get start and end offsets without knowing any internal details
        load a byte from area:$$ + % - 1 ; <--- use $$ to get the base offset that may include non-numeric components
        db a
end repeat

15 Apr 2023, 16:11

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 15 Apr 2023, 17:48

fasmg allows "1 metadataof area" to get the base address of the block:

Code:

include 'cpu/x64.inc'

virtual at edx
    area::
end virtual

        mov     eax,[1 metadataof area] ; assembles to mov eax,[edx]

I was planning to make the "0 metadataof area" (equivalent to "sizeof area") to get the current length, but it's not there yet. [EDIT: And now it is.]

Last edited by Tomasz Grysztar on 16 Apr 2023, 07:20; edited 1 time in total

15 Apr 2023, 17:48

Roman

Joined: 21 Apr 2012
Posts: 1823

Roman 15 Apr 2023, 19:55

Mini c.
How convert text number to int ?

Code:

macro m1 { mov al,1  }
macro m2 { mov bl,2  }
macro ifcmd p1,p2,pp {
      load a p1 from cmdout:0
                if a = p2
                 display 13,10,'yes '#`p2
                 pp
                end if
      }
macro valCMD {
      repeat 300
  load a byte from area:cnt1+%-1+cnt0
  if a = ';'
   break
  end if
  store byte a at cmdout:cnt1+%-1
  display a
end repeat
}
macro nxtcmd { store qword '        ' at cmdout:0
               store qword '        ' at cmdout:8
               store qword '        ' at cmdout:16
repeat area_size
  load a byte from area:%-1+cnt0
  cnt2 = cnt0+%
  if a = ';'
   break
  end if
  end repeat
  cnt0 = cnt2
      }
macro fcmd {
      display 13,10
      repeat area_size
  cnt1 = %
  load a byte from area:%-1+cnt0
  if a = ' '
   break
  end if
  store byte a at cmdout:%-1
  display  a
end repeat
      }                     

virtual at 0
     area::
         text1 db 'for_ 551450022;',\
                  'next 44  ;',\
                  'deco ; ',0
     area_size:
end virtual
virtual at 0
     cmdout::
         text db 40 dup (32)
     cmdout_size:
end virtual      

;in code
cnt0 = 0
 fcmd
 valCMD
 ifcmd  dword,'for_',m1
 nxtcmd
 fcmd
 valCMD
 ifcmd  dword,'next',m1
 nxtcmd
 fcmd
 ifcmd  dword,'deco',m2

15 Apr 2023, 19:55

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