wiki:WikiStart

Version 5 (modified by lorenzo, 15 years ago) ( diff )

--

Laboratorio di Sistemi Operativi

TOC(noheading)

Lezione 1: Introduzione

Slide

Programmi

  • Accesso diretto alla macchina fisica mioboot-nobios-simple.asm 
    bits 16                         ; 16 bit real mode
org 0x7C00                      ; origine indirizzo 0000:7C00

start:	
 mov ax, 0xb800	 ; text video memory
 mov ds, ax
 mov eax, 10
write:
 cmp eax, 0
 jz end
 mov byte [eax], 'm'
 mov byte [eax+1], 0x0F    ; attrib = white on black
 sub eax, 2
 jmp write
end:
 hlt

times 510-($-$$) db 0 ; 0-padding 
dw 0xAA55

    nasm -l mioboot-nobios-simple.lst -o mioboot-nobios-simple.img mioboot-nobios-simple.asm
qemu mioboot-nobios-simple.img
  • Uso dei servizi del BIOS mioboot.asm 
    bits 16                         ; 16 bit real mode
org 0x7C00                      ; origine indirizzo 0000:7C00
        
start:
        cld                     ; clears direction flag (index regs incremented)
        mov si, boot
        call message
working:
        mov si, work
        call message

        call waitenter
        jmp working

message:
        lodsb                   ; carica un byte da [DS:SI] in AL e inc SI
        cmp al, 0
        jz done
        mov ah, 0x0E            ; write char to screen in text mode
        mov bx, 0               ; BH page number BL foreground color
        int 0x10                ; write AL to screen (BIOS)
        jmp message
done:   ret

boot: db "Loading unuseful system...." , 10, 13, 0
work: db "I've done my unuseful stuff!" , 10, 13, 0 
cont: db "Hit ENTER to continue...", 10, 13, 0
wow: db "Great! Hello world!" , 10, 13, 0
        
waitenter: mov si, cont
           call message
           mov ah, 0
           int 0x16                ; Wait for keypress (BIOS)
           cmp al, 'm'
           jz egg
           cmp al, 'b'
           jz basic
           cmp al, 13
           jnz waitenter
           ret
egg:       mov si, wow
           call message
           jmp waitenter
basic:     int 0x18		; basic (BIOS)
           hlt

        times 510-($-$$) db 0
        dw 0xAA55

    nasm -l mioboot.lst -o mioboot.img mioboot.asm
qemu mioboot.img
  • Programma che esegue il codice letto da standard input exec.c 
    #include <stdio.h>

int main() {
  unsigned char buf[1024];
  void (*ptr)();
  int n;
  unsigned int eax;

  n = read(0, buf, 1024);
  buf[n] = '\xc3';

  ptr = (void(*)()) buf;
  ptr();

  __asm__("mov %%eax, %0" : "=m"(eax));

  printf("EAX: %.8x\n", eax);

  return 0;
}

    gcc -o exec exec.c
echo -ne "\xB8\x11\x22\x33\x44" | ./exec
echo -n "ciao" | ./exec
...

Lezione 2

Note: See TracWiki for help on using the wiki.