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OzzY



Joined: 19 Sep 2003
Posts: 1029
Location: Everywhere
OzzY
Hi guys!

I was thinking about using C function on ASM with FASM. C is so easy and asm so powerful, so libC+ASM=Great code!
I've been successful on using functions like fopen, fprintf, printf, scanf, etc...
I just import them from msvcrt.dll or crtdll.dll that MSVC++ uses and comes with Windows.

But this little proggie is working. The problem is that it should copy 1536 bytes of itself (copy it totally) to an txt file. But it does it and puts lots of trash data in there. And what should have 1536 bytes goes to 20KB.

Any helps?

Code:

format PE console
include '%fasminc%\win32a.inc'
start:
invoke GetModuleFileName,0,buf,256
invoke fopen,buf,rmode
mov [fp],eax
invoke fopen,dest,wmode
mov [fp2],eax
mov ecx,1536
next:
invoke fgetc,[fp]
invoke fputc,eax,[fp2]
loop next
done:
invoke fclose,[fp]
invoke fclose,[fp2]
ret
;data
dest db 'test.txt',0
buf rb 256
rmode db 'rb',0
wmode db 'wb',0
fp dd 0
fp2 dd 0
;idata
data import
library crt,'msvcrt.dll',\
kernel32,'kernel32.dll'
import kernel32,GetModuleFileName,\
'GetModuleFileNameA'
import crt,fopen,'fopen',\
fclose,'fclose',\
fgetc,'fgetc',\
fputc,'fputc'
end data

    


Thanks a lot!
And sorry for my bad english... although code is self-explanatory... The universal language of ASM... heheh Wink
Post 17 Mar 2005, 18:57
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OzzY



Joined: 19 Sep 2003
Posts: 1029
Location: Everywhere
OzzY
Oh sorry... I've just discovered it right now...
I just read the libC reference and realized that it returns -1 on EAX if error or EOF. Wink
So, here is the code fixed:

Code:
format PE console
include '%fasminc%\win32a.inc'
start:
invoke GetModuleFileName,0,buf,256
invoke fopen,buf,rmode
mov [fp],eax
invoke fopen,dest,wmode
mov [fp2],eax
mov ecx,1536
next:
invoke fgetc,[fp]
cmp eax,-1
jz done
invoke fputc,eax,[fp2]
loop next
done:
invoke fclose,[fp]
invoke fclose,[fp2]
ret
dest db 'test2.txt',0
buf rb 256
rmode db 'rb',0
wmode db 'wb',0
fp dd 0
fp2 dd 0
;idata
data import
library crt,'msvcrt.dll',\
kernel32,'kernel32.dll'
import kernel32,GetModuleFileName,\
'GetModuleFileNameA'
import crt,fopen,'fopen',\
fclose,'fclose',\
fgetc,'fgetc',\
fputc,'fputc'
end data
    


Anyway thanks!
And FASM is just great!
Soon I'll be writing macros that will allow people to use libC just like a normal c program, like:
printf "Hi!"
printf "What is your name?"
scanf "%s",buf
.
.
.
and so on...

Bye!
Post 17 Mar 2005, 19:15
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Nikolay Petrov



Joined: 22 Apr 2004
Posts: 101
Location: Bulgaria
Nikolay Petrov
the functions and procedures are not stdcall. That's why you MUST "invoke" with "cinvoke" to return the stack - like wsprintf.
Code:
;save as test.asm and run it...
format PE console
entry start
include '%fasminc%\win32a.inc'

proc start
enter
        invoke GetModuleFileName,0,buf,256
        cinvoke fopen,buf,rmode
        mov [fp],eax
        cinvoke fopen,dest,wmode
        mov [fp2],eax
        mov ecx,1536
next:
        cinvoke fgetc,[fp]
        cmp eax,-1
        jz done
        cinvoke fputc,eax,[fp2]
        loop next
done:
        cinvoke fclose,[fp]
        cinvoke fclose,[fp2]
        return
endp

dest db 'test2.exe',0
buf rb 256
rmode db 'rb',0
wmode db 'wb',0
fp dd ?
fp2 dd ?

data import

library crt,'msvcrt.dll',kernel32,'kernel32.dll'

import kernel32,GetModuleFileName,'GetModuleFileNameA'

import crt, fopen,'fopen',\
            fclose,'fclose',\
            fgetc,'fgetc',\
            fputc,'fputc'
end data    
Post 17 Mar 2005, 20:14
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f0dder



Joined: 19 Feb 2004
Posts: 3170
Location: Denmark
f0dder
Keep the calling convention in mind - when you call external code (libc, the API, ...) those routines are allowed to trash eax,ecx,edx and must preserve ebx,esi,edi,ebp - this means you can't depend on the values of eax,ecx,edx after a call to libc (except that eax is returncode, of course).
Post 23 Mar 2005, 10:30
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