01   .386
02   .model flat
03      extrn ExitProcess:proc
04      extrn MessageBoxA:proc
05      extrn CreateFileA:proc
;
07      generic_read   equ  80000000h
08      generic_write  equ  40000000h
09      mb_ok          equ  0
10      hwnd           equ  0
11      open_existing  equ  3
12      normal         equ  80h
;
14   .data
15      capError    db "Error",0
16      bodyerror   db "file to open not found ",0
17      capSuccess  db "Success",0
18      bodySuccess db "file to open found ",0
19      filName     db "bbb.exe",0
20      fhandle     dd  ?
;
22   .code
23      start:
23      push  0
25      push  normal
26      push  open_existing
27      push  0
28      push  0
29      push  generic_read + generic_write
30      push  offset filName

32      Call CreateFileA

34      mov fhandle,eax
35      cmp eax,0ffffffffh
36      jz notFound


CreateFile Function opens a file and returns a handle to the register eax. Using td32, i executed the code line by line but, i was not able to find any value change in eax, even though the createFile function has executed successfully.
How does one view the returned value ?

i have attached the source.
thank you.
Attachments:
Posted on 2009-07-10 03:43:10 by hell0
First, you could use something more advanced like Ollydbg. And the only thing that matters is the value that EAX has after the call. It doesn't matter if it doesn't change.

Compare the return value with the RETURN values in the CreateFile MSDN documentation and you'll know if there's a problem or not.
http://msdn.microsoft.com/en-us/library/aa363858(VS.85).aspx
Posted on 2009-07-10 04:34:58 by ChaperonNoir
Thank you ChaperonNoir..

i tried to open the exe in Ollydbg. (though, iam not very familiar with Olly). Here again the Eax maintains the same unconcerned stance.

Anyway, with the 2 files (aaa.exe and bbb.exe) in the same directory,
when aaa.exe is run, i get the expected message ‘file found’ and if the bbb.exe is removed from the directory, the likely ‘file not found’ message is received.

So, can i assume that createFile function is successful in finding and opening the specific file (bbb.exe)?

Another uncertainty,
Without closing an opened file, if the ExitProcess is called. i suppose there is a possibility of process freezing. if my view is correct, how does one explain the result that followed (no freezing) relevant to aaa.exe?

regards.
Attachments:
Posted on 2009-07-10 05:57:05 by hell0
ExitProcess doesn't freeze when you have open handles (not only handles to files but any handles). On NT it closes all handles for you but it's generally a good habit to close them yourself before you exit.
Posted on 2009-07-10 18:57:56 by ti_mo_n
Well!

On NT it closes all handles for you but it's generally a good habit to close them yourself before you exit.


It’s really instructive; i had put up with this uncertainty for quite some time.
thank you for showing the right course of action.

regards!
Posted on 2009-07-10 22:28:13 by hell0