luxos/Kernel/hal/cpu/gdt.h

/******************************************************************
 *    gdt.h  -  GLOBAL DESCRIPTOR TABLE                           *
 *      Contains structures and function declarations for GDT     *
 ******************************************************************/

#ifndef __GDT_H
#define __GDT_H

/* Defines a GDT entry. We say packed, because it prevents the
*  compiler from doing things that it thinks is best: Prevent
*  compiler "optimization" by packing */
struct GdtEntry
{
    unsigned short limit_low;
    unsigned short base_low;
    unsigned char base_middle;
    unsigned char access;
    unsigned char granularity;
    unsigned char base_high;
} __attribute__((packed));

/* Special pointer which includes the limit: The max bytes
*  taken up by the GDT, minus 1. Again, this NEEDS to be packed */
struct GdtPointer
{
    unsigned short limit;
    unsigned int base;
} __attribute__((packed));


/* This will be a function in start.asm. We use this to properly
*  reload the new segment registers */
extern void GdtInstall();
extern void GdtFlush();
extern void GdtSetGate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran);
extern struct GdtEntry* GdtGetGate(int num);

#endif