Error in compiled com image

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keyoke

Joined: 18 Jun 2003
Posts: 56
Location: London

keyoke 25 Aug 2003, 07:50

Hi Privalov,
this is a example of the code i compile.

Code:

SumProc:

some intructions

someloop:
call someotherproc
jne someloop

ret

text db "somtext",0

someotherproc:

someother instructions

ret

1

now when i debug this type of example the call to the someotherproc
function works fine but the first intructions of the someotherproc procedure are compiled incorrectly almost like the defined bytes interfere with the first instructions in the procedure.
is this a error is compiler or what?
thanks for your help in advance.

25 Aug 2003, 07:50

wanderer

Joined: 18 Jun 2003
Posts: 44
Location: Moldova, Kishinev

wanderer 25 Aug 2003, 09:30

keyoke wrote:

now when i debug this type of example the call to the someotherproc
function works fine but the first intructions of the someotherproc procedure are compiled incorrectly almost like the defined bytes interfere with the first instructions in the procedure.
is this a error is compiler or what?
thanks for your help in advance.

If you mean that a wrong offset is generated in this instruction, then it's because you didn't place org 100h in the beginning of code. As you know, com files are loaded on offset 100h from segment start. The procedure call was generated correctly as there's relative offset in it, however it won't work for global variables for example.

_________________
Best regards,
Antoch Victor

25 Aug 2003, 09:30

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 25 Aug 2003, 09:40

It's probably an error of debugger - if it treats your data string as instructions and disassemble them, it might happen (an often happens) that it'll end with treating first bytes or real instructions that you put after the data block as the additional bytes for some not-really-existing instruction discovered in your data, and so the disassembly will be wrong.

25 Aug 2003, 09:40

keyoke

Joined: 18 Jun 2003
Posts: 56
Location: London

keyoke 25 Aug 2003, 10:29

Privalov,
I do use

Code:

org 100h
use16

to debug i use the ms-dos debug command would this disassemble the code incorrectly?
i have also tried turbo debugger to debug the code...
it seems like the debugger isnt disassembling the code directly???
i dunno maybe ill try disassembling it with ida to check wat comes up..

25 Aug 2003, 10:29

Yawgmoth

Joined: 20 Aug 2003
Posts: 37

Yawgmoth 25 Aug 2003, 11:44

Speaking of debuggers, when can we expect a FASM debugger?

25 Aug 2003, 11:44

keyoke

Joined: 18 Jun 2003
Posts: 56
Location: London

keyoke 27 Aug 2003, 07:09

I think privalov has enough on his plate already.....with the fasm compiler, and all the documentation. So i think we should give him a bit of a break Wink

maybe someone else will code a debugger for fasm. would be good Smile

27 Aug 2003, 07:09

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