actividad_final.S

#include "common.h"
BEGIN
    CLEAR
    


    /* Must come before they are used. */
    .equ CODE_SEG, 8
    .equ DATA_SEG, gdt_data - gdt_start
    /* Tell the processor where our Global Descriptor Table is in memory. */
    lgdt gdt_descriptor
    /* Set PE (Protection Enable) bit in CR0 (Control Register 0),
     * effectively entering protected mode.
     */
    mov %cr0, %eax
    orl $0x1, %eax
    mov %eax, %cr0
    ljmp $CODE_SEG, $protected_mode
	/* Our GDT contains:
	 *
	 * * a null entry to fill the unusable entry 0:
	 * http://stackoverflow.com/questions/33198282/why-have-the-first-segment-descriptor-of-the-global-descriptor-table-contain-onl
	 * * a code and data. Both are necessary, because:
	 * +
	 * --
	 * ** it is impossible to write to the code segment
	 * ** it is impossible execute the data segment
	 * --
	 * +
	 * Both start at 0 and span the entire memory,
	 * allowing us to access anything without problems.
	 *
	 * A real OS might have 2 extra segments: user data and code.
	 *
	 * This is the case for the Linux kernel.
	 *
	 * This is better than modifying the privilege bit of the GDT
	 * as we'd have to reload it several times, losing cache.
	 */
	gdt_start:
	gdt_null:
	    .long 0x0
	    .long 0x0
	gdt_code:
	    .word 0x5000 /* Limite */
	    .word 0x0000 /* Desde donde arranca */
	    .byte 0x0
	    .byte 0b10011010
	    .byte 0b11001111
	    .byte 0x0
	gdt_data:
	    .word 0x1000 /* Limite */
	    .word 0x8000 /* Desde donde arranca */
	    .byte 0x0
	    .byte 0b10010000 /* Termina siendo read only */
	    .byte 0b11001111
	    .byte 0x0
	gdt_end:
	gdt_descriptor:
	    .word gdt_end - gdt_start
	    .long gdt_start
	vga_current_line:
	    .long 0
	.code32
	protected_mode:
	    /* Setup the other segments.
	     * Those movs are mandatory because they update the descriptor cache:
	     * http://wiki.osdev.org/Descriptor_Cache
	     */
	    mov $DATA_SEG, %ax
	    mov %ax, %ds
	    mov %ax, %es
	    mov %ax, %fs
	    mov %ax, %gs
	    mov %ax, %ss
	    /* TODO detect the last memory address available properly.
	     * It depends on how much RAM we have.
	     */
	    mov $0X7000, %ebp
	    mov %ebp, %esp




    VGA_PRINT_STRING $message

    jmp .

.data
message:
    .asciz "hello world"