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Index > Compiler Internals > [FIXED] Mixing 'virtual' with 'if' corrupts structure store

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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17492
Location: In your JS exploiting you and your system
revolution
Here are two situations that expose the bug:

1) The first virtual block has the restore state corrupted by the 'end if'
Code:
VAR = 0

org '0'
display $             ;<--- '0'

if VAR = VAR
  virtual at '1'
    display $       ;<--- '1'
      virtual at '2'
    display $       ;<--- '2'
end if                        ;return state of first virtual is corrupted here
if VAR = VAR
    display $       ;<--- '2'
      end virtual
 display $       ;<--- '1'
      end virtual     ;wrong state is restored here
end if

display $                ;<--- '1'    
2) The IF state is corrupted by the 'end virtual'
Code:
VAR = 0

org '0'
virtual at '1'
display $               ;<--- '1'

if VAR = VAR
    if VAR <> VAR
    else
   display $       ;<--- '1'
      end virtual     ;state of first 'if' block is corrupted here
      display $       ;<--- '0'
    end if
else                    ;<--- error: unexpected instruction.
end if    
This can be fixed by the addition of four instruction to do a top-down memory copy. In ASSEMBLE.INC around line 980:
Code:
      remove_structure_data:
    push    esi edi
     mov     esi,[structures_buffer]
     mov     ecx,ebx
     sub     ecx,esi
     lea     edi,[esi+20h]
       mov     [structures_buffer],edi
     shr     ecx,2
                       lea esi,[esi+ecx*4-4]   ;<--- add
                        lea edi,[edi+ecx*4-4]   ;<--- add
                        std                     ;<--- add
        rep     movs dword [edi],[esi]
                      cld                     ;<--- add
        pop     edi esi
     ret    


Last edited by revolution on 27 Apr 2010, 01:58; edited 3 times in total
Post 26 Apr 2010, 13:11
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7756
Location: Kraków, Poland
Tomasz Grysztar
Nice catch; thanks for the report.
Post 26 Apr 2010, 13:36
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17492
Location: In your JS exploiting you and your system
revolution
This bug is now fixed in version 1.69.14
Post 27 Apr 2010, 01:58
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