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Index > Compiler Internals > wrong addres of label

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Kicer



Joined: 30 Apr 2005
Posts: 34
Location: Poland
Kicer
look just at this code:

Code:
console_begin:
    inc byte [ds:0b8000h+79*2+23*160]
    jmp console_begin
console_data:
console_stack: times 128 db 0                             ;segment stosu
console_end:

t_begin:
    nop
    jmp t_begin
t_stack: times 128 db 0
t_end:
    


when i jumped to t_begin the program crashed,
so i pushed nop between console_end and t_begin and everything is ok
here are listings of code with nop and without nop:

Code:
                                                console_begin:
00000BC5: FE 05 FE 8E 0B 00                         inc byte [ds:0b8000h+79*2+23*160]
00000BCB: EB F8                                     jmp console_begin
                                                console_data:
00000BCD: 00 00 00 00 00 00 00 00 00 00 00 00   console_stack: times 128 db 0                             ;segment stosu
          00 00 00 00 00 00 00 00 00 00 00 00   console_end:
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   t_begin:
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00               
00000C4D: 90                                        nop
00000C4E: EB FD                                     jmp t_begin
00000C50: 00 00 00 00 00 00 00 00 00 00 00 00   t_stack: times 128 db 0
          00 00 00 00 00 00 00 00 00 00 00 00   t_end:
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   begin:
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00               
    


and the 2nd:

Code:
                                                console_begin:
00000BC5: FE 05 FE 8E 0B 00                         inc byte [ds:0b8000h+79*2+23*160]
00000BCB: EB F8                                     jmp console_begin
                                                console_data:
00000BCD: 00 00 00 00 00 00 00 00 00 00 00 00   console_stack: times 128 db 0                             ;segment stosu
          00 00 00 00 00 00 00 00 00 00 00 00   console_end:
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00               
00000C4D: 90                                    nop
                                                t_begin:
00000C4E: 90                                        nop
00000C4F: EB FD                                     jmp t_begin
00000C51: 00 00 00 00 00 00 00 00 00 00 00 00   t_stack: times 128 db 0
          00 00 00 00 00 00 00 00 00 00 00 00   t_end:
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   begin:
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00 00 00 00 00   
          00 00 00 00 00 00 00 00               
            
    


as You see in the 1st example t_begin is in a wrong place...
Post 13 May 2005, 06:42
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7796
Location: Kraków, Poland
Tomasz Grysztar
The assembly is OK (look at it with disassembler), it's just the problem of listing extension (it is still likely to have a lots of them since it's a kind of "hack" over the fasm internals that were not initially designed to support such feature). I will try to fix it later.


Last edited by Tomasz Grysztar on 13 May 2005, 08:27; edited 2 times in total
Post 13 May 2005, 08:10
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17664
Location: In your JS exploiting you and your system
revolution
This is just an artifact of the listing output. The generated code is correct.

The line "t_begin:" has no code output directly associated with it. The listing will use lines like this for padding when it needs to print more outout data.

The binary "EB FD" is correct in both cases.
Post 13 May 2005, 08:13
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Kicer



Joined: 30 Apr 2005
Posts: 34
Location: Poland
Kicer
maybe but why my program without nop is crashing ?:/
Post 13 May 2005, 09:37
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Kicer



Joined: 30 Apr 2005
Posts: 34
Location: Poland
Kicer
ok nevermind, my fault :/
Post 13 May 2005, 09:50
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