Question

How to write this assembly code as inline assembly? Compiler: gcc(i586-elf-gcc). The GAS syntax confuses me. Please give tell me how to write this as inline assembly that works for gcc.

.set_video_mode:
    mov ah,00h
    mov al,13h
    int 10h   

.init_mouse:
    mov ax,0
    int 33h

Similar one I have in assembly. I wrote them separate as assembly routines to call them from my C program. I need to call these and some more interrupts from C itself.

Also I need to put some values in some registers depending on which interrupt routine I’m calling. Please tell me how to do it.

All that I want to do is call interrupt routines from C. It’s OK for me even to do it using int86() but i don’t have source code of that function.
I want int86() so that i can call interrupts from C.

I am developing my own tiny OS so i got no restrictions for calling interrupts or for any direct hardware access.

Answer 1

I’ve not tested this, but it should get you started:

void set_video_mode (int x, int y) {
  register int ah asm ("ah") = x;
  register int al asm ("al") = y;

  asm volatile ("int $0x10"
                : /* no outputs */
                : /* no inputs */
                : /* clobbers */ "ah", "al");
}

I’ve put in two ‘clobbers’ as an example, but you’ll need to set the correct list of clobbers so that the compiler knows you’ve overwritten register values (maybe none).