Writing applications for KolibriOS: Difference between revisions

 

Programming for KolibriOS is easy as you first learn the basic structure of an application. At this point I assume you have some experience in assembly language. The KolibriOS API (Application Programming Interface) is a easy-to-learn set of functions with practically no hierarchial accesses.

 

The operating of an application is based on events. The application is notified by the OS with the event type and the application acts accordingly. There are three event types an application is expected to handle by default: window redraw, keypress and buttonpress.

 

 

;;;;;;;;;;;;;;;;;;;;;;;;;

;                      ;

;    HEADER DATA      ;

;                      ;

;;;;;;::;;;;;;;;;;;;;;;;;

 

START:

        call   draw_window

 

;;;;;;;;;;;;;;;;;;;;;;;;;

;                      ;

;  WAIT UNTIL EVENT    ;  <-----------------------------------------------I

;                      ;                                                  I

;;;;;;;;;;;;;;;;;;;;;;;;;                                                  I

;                                                                          I

;;;;;;;;;;;;;;;;;;;;;;;;;                                                  I

;                      ;    redraw  ->  call draw_window            -> I

;    READ EVENT TYPE    ; ->  key      ->  read keypress    -> process  -> I

;                      ;    button  ->  read buttonpress -> process  -> I

;;;;;;;;;;;;;;;;;;;;;;;;;

 

draw_window:

 

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;                            ;

;  DRAW STATIC WINDOW PARTS  ;

;                            ;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

 

        ret

 

;;;;;;;;;;;;;;;;;;;;;;;;

;                      ;

;    STATIC DATA      ;

;                      ;

;;;;;;;;;;;;;;;;;;;;;;;;

<syntaxhighlight>

db 'MENUET01'

</syntaxhighlight>

 

Since KolibriOS still is more or less API compatible with MenuetOS, it has the same header. There is also an older version of the header wich uses 'MENUET00' but it should not be used anymore.

 

<syntaxhighlight>

dd 0x01 ; header version

</syntaxhighlight>

 

 

<syntaxhighlight>

dd START ; start of execution

</syntaxhighlight>

 

START is the label in your program where kernel will jump to after loading the program. You could use another name, but it's convenient to always use the same.

 

<syntaxhighlight>

dd I_END ; size of image

</syntaxhighlight>

 

 

<syntaxhighlight>

dd 0x100000

</syntaxhighlight>

 

This is the amount of ram that will be reserved for your app. You could use a static value as shown here, or you could use I_END + xx bytes. There, I_END would be the label to the end of code + all static declarations you made after the code. The xx bytes then are the number of bytes you want to use for the stack. Also note, this value can later be changed by using system functions.

 

<syntaxhighlight>

dd 0x100000 ; stack position in memory area

</syntaxhighlight>

 

Where the end of stack is (the value of esp at start of program). Logically, this would be the same as the previous value.

 

<syntaxhighlight>

dd 0x0 ; Parameters

</syntaxhighlight>

 

If you want to use parameters, this should be a pointer to a 1024 byte buffer, in wich those parameters will be written by the kernel. If you dont want to use them, set this dword to 0.

 

<syntaxhighlight>

dd 0x0 ; Path  

</syntaxhighlight>

 

The System calls (API) are explained in various sources. There is the file syscalls.txt wich you can find in kolibrios itself, but also in the zip file of the distribution.< If you understand russian, you can also find system calls on this wiki.

 

To execute a system call, you first need to fill the registers with the correct value. Say we want to wait a couple of milliseconds, we need to use system function 5 and place the time we want to wait in ebx.

 

<syntaxhighlight>

        mov    eax, 5

        mov    ebx, 10

</syntaxhighlight>

 

Now, we need to execute the function, this can be done with int 0x40:

 

<syntaxhighlight>

        int    0x40

</syntaxhighlight>

 

But also with more modern instructions such as syscall, sysenter etc. It's convenient to use the mcall macro from macros.inc, then you can chose to use int 0x40 or another method, at compile time. This macro also accepts parameters, first is eax, second is ebx, ... Code for the above would be:

 

<syntaxhighlight>

        mcall   5, 10

</syntaxhighlight>

 

<syntaxhighlight>

 

 

org 0x0                                 ; the base address of code, always 0x0

db 'MENUET01'

dd 0x01

dd START

dd I_END

dd 0x100000

dd 0x7fff0

dd 0, 0

include 'macros.inc'

 

 

         mcall                           ; event type is returned in eax