label, local label and variable declaration

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pstarczewski

Joined: 19 Jun 2009
Posts: 2

pstarczewski 20 Jun 2009, 05:12

Hi,

I'm new to FASM and the last time I've used asm was about 12 years ago, so please be gentle. I'm trying to learn a little about FASM, but due to last 12 years of C++ and OOP programming I've some difficulities to switch to "asm thinking" Embarassed

As a test app I wanted to display some string using "local" data from the structure. Unfortunatly as soon as I start my app it crushes. I think it has something to do with the way I've declared my variable in the code (look at .testString declaration). My question: is it possible to do such declaration or do I have to use global data section for that? I know that it is possible to use ebp/esp for proc calls and to create local memory area for data, but does it also apply to main section/code? I have also tried to use lea, but with no effect.

Here is my example:

Code:

format PE GUI 4.0
entry AppStart

include '/asm/wininc/win.asm'
include 'dr.inc'


struc MyStruc
 {
    .s      du      'fasm test app',0
 }


section '.data' data readable writeable
 g_hInstance                             dd      ?
   msg                                             MSG
 str01                                   MyStruc


section '.text' code readable executable

AppStart:
  ;  get instance handle
        push  NULL
        call    [GetModuleHandle]
   mov             [g_hInstance],eax

       call    MainWindow.Create

    ;  main loop
    .main_loop:
            .testString             MyStruc
               push  MB_OK
                 ;push str01.s
               push  .testString.s
                 ;lea  edx,[.testString.s]
           ;push edx
           push  0
             push  NULL
                call    [MessageBox]

    ;  exit app
   push  eax
 call    [ExitProcess]


;-----------------------------------------------------
;  Main window class definition
;-----------------------------------------------------
MainWindow:
     .Create:
                push    ebp
         mov             ebp,esp

         leave
               ret

20 Jun 2009, 05:12

hopcode

Joined: 04 Mar 2008
Posts: 563
Location: Germany

hopcode 20 Jun 2009, 11:10

Hallo,pstarczewski

on http://flatassembler.net/examples.php
or compile the examples in the EXAMPLE directory of your fasm dwonloaded package

First af all,
1) set up path for fasm compiler in a batch file/win environment,
or at the prompt as follows (i have fasm.exe on J:\fasm)

path=%path%;J:\fasm

2) set up include directory in a batch file/win environment,
or at the prompt as follows (i use %fasminc%" as veriable name )

set fasminc=J:\fasm\include

Now, i will try to do my best for a Console standard app:

3) include main macros and standard includes in your code

Code:

  
 format PE CONSOLE 4.0
 entry start
   include '%fasminc%\win32a.inc'

4) global data go in a data section

Code:

 section ".data" data readable writeable
   szGlobalString     db "Hello World", 13,10,0
   szPause          db "pause",0
   szMessage      db "In the subroutine local dword is=%x",13,10,0

5)your code goes in the .code section

Code:

  section ".code" code readable executable
   start:
    cinvoke printf,szGlobalString
    cinvoke system,szPause
   ret

6) if you have sub-routines declare it as follows in this model

Code:

proc myroutine _arg1dword
   local .onstack_dword:DWORD
  
   mov eax,[.onstack_dword]
   add eax,[_arg1dword]
   cinvoke printf,szMessage,eax
  ret
endp

7) all the function you use must be imported in an import section
called .idata

Code:

 section '.idata' import data readable writeable

8 ) enable importing function from MSVCRT.DLL

Code:

  library msvcrt,"MSVCRT.DLL"

9) import explicitly function one by one,not omitting alias

Code:

     ;NOTE this functions use cinvoke convention
 import msvcrt,\
    printf,"printf",\
        _getch,"_getch",\
        system,"system"

All together

Code:

 format PE CONSOLE 4.0
 entry start
 include '%fasminc%\win32a.inc'
  
  section ".data" data readable writeable
   szGlobalString      db "Hello World", 13,10,0
   szPause          db "pause",0
   szMessage      db "In the subroutine local dword is (hexadecimal) %x",13,10,0
   szMessage1    db "You have passed (hexadecimal) %x as argument",13,10,0
   szMessage2    db "In the subroutine sum of local+passed arg is (hexadecimal) %x",13,10,0

 section ".code" code readable executable
        
 start:
   cinvoke printf,szGlobalString

   push 12345h  ; this goes in _arg1dword 
   call myroutine

   cinvoke system,szPause
  ret

 proc myroutine _arg1dword
   local .onstack_dword:DWORD

   cinvoke printf,szMessage1,[_arg1dword]
        
   ; assign an arbitary  value to .onstack_dword
   mov [.onstack_dword],56789h
   cinvoke printf,szMessage,[.onstack_dword]
      
   mov eax,[.onstack_dword]
   add eax,[_arg1dword]
   cinvoke printf,szMessage2,eax
  ret
 endp

  section '.idata' import data readable writeable
   library msvcrt,"MSVCRT.DLL"

   import msvcrt,\
  printf,"printf",\
        _getch,"_getch",\
        system,"system"

NOTE: for Windowing Example you need tutorials from Iczelion (MASM, but i cannot find at the moment the translation for Fasm, here on board ) or try
CreateWindowEx in search box on board.

NOTE2: study the use of "proc" (it is a macro) and the difference
of "struc" and "struct", searching them on FAQ or on searchbox

Ok, this is a PE console app (PE CONSOLE)
using only the printf/and system function
Try to compile it. Hope it is useful and...
happy fasming. Very Happy

Regards,
hopcode

20 Jun 2009, 11:10

pstarczewski

Joined: 19 Jun 2009
Posts: 2

pstarczewski 20 Jun 2009, 23:21

Thanks hopcode,

Looks very interesting. I did look at those examples and they look like a good start for me - total beginner at asm. Thanks for your help.

20 Jun 2009, 23:21

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