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/* asm.h */#ifndef _ASM_H#define _ASM_Htypedef struct{	unsigned short limit;	unsigned short base;} gdtptr;typedef struct {	unsigned short limit_low;	unsigned short base_low;	unsigned char base_middle;	unsigned char access;	unsigned char granularity;	unsigned char base_high;} gdtentry;volatile gdtptr gdtaddr;void pmode(void);#endif/* <EOF> *//* ----- protected_mode.S --- */.text.globl _pmode, pmodepmode:_pmode:		cli /* atomic */ 	lgdt gdtaddr /* point it */	mov %eax, %cr0	or %eax, 1	mov %cr0, %eax	jmp somewhere_else /* to clear out the instruction prefetch queue */	nop	somewhere_else:		sti /* end of atomic */	ret/* <EOF> *//* -- kern_main.c -- */#include <multiboot.h>#include <asm.h>void kern_main(unsigned long mbpointer){	volatile unsigned char *video;	video = (unsigned char *) 0xB8052;		*video = 0x48 & 0xFF;	*(video+2) = 0x49 & 0xFF;	gdtentry mygdt[3];		mygdt[0].limit_low = 0;	mygdt[0].base_low = 0;	mygdt[0].base_middle = 0;	mygdt[0].access = 0;	mygdt[0].granularity =  0;	mygdt[0].base_high = 0;		gdtaddr.base = &mygdt;	gdtaddr.limit = (3 * sizeof(gdtentry)) - 1;	mygdt[1].limit_low = (0xFFFFFFFF & 0xFFFF);	mygdt[1].base_low = 0;	mygdt[1].base_middle = 0;	mygdt[1].access = 0x9A;	mygdt[1].granularity =  ((0xFFFFFFFF >> 16) & 0x0F);	mygdt[1].granularity |= (0xCF & 0xF0);	mygdt[1].base_high = 0;		mygdt[2].limit_low = (0xFFFFFFFF & 0xFFFF);	mygdt[2].base_low = 0;	mygdt[2].base_middle = 0;	mygdt[2].access = 0x92;	mygdt[2].granularity =  ((0xFFFFFFFF >> 16) & 0x0F);	mygdt[2].granularity |= (0xCF & 0xF0);	mygdt[2].base_high = 0;		pmode();	*(video+8) = 0x4A & 0xFF;}/* <EOF> */