78 lines
1.4 KiB
C
78 lines
1.4 KiB
C
#include <system.h>
|
|
|
|
/*
|
|
* Global Descriptor Table Entry
|
|
*/
|
|
struct gdt_entry {
|
|
/* Limits */
|
|
unsigned short limit_low;
|
|
/* Segment address */
|
|
unsigned short base_low;
|
|
unsigned char base_middle;
|
|
/* Access modes */
|
|
unsigned char access;
|
|
unsigned char granularity;
|
|
unsigned char base_high;
|
|
} __attribute__((packed));
|
|
|
|
/*
|
|
* GDT pointer
|
|
*/
|
|
struct gdt_ptr {
|
|
unsigned short limit;
|
|
unsigned int base;
|
|
} __attribute__((packed));
|
|
|
|
struct gdt_entry gdt[3];
|
|
struct gdt_ptr gp;
|
|
|
|
/*
|
|
* (ASM) gdt_flush
|
|
* Reloads the segment registers
|
|
*/
|
|
extern void gdt_flush();
|
|
|
|
/*
|
|
* gdt_set_gate
|
|
* Set a GDT descriptor
|
|
*/
|
|
void
|
|
gdt_set_gate(
|
|
int num,
|
|
unsigned long base,
|
|
unsigned long limit,
|
|
unsigned char access,
|
|
unsigned char gran
|
|
) {
|
|
/* Base Address */
|
|
gdt[num].base_low = (base & 0xFFFF);
|
|
gdt[num].base_middle = (base >> 16) & 0xFF;
|
|
gdt[num].base_high = (base >> 24) & 0xFF;
|
|
/* Limits */
|
|
gdt[num].limit_low = (limit & 0xFFFF);
|
|
gdt[num].granularity = (limit >> 16) & 0X0F;
|
|
/* Granularity */
|
|
gdt[num].granularity |= (gran & 0xF0);
|
|
/* Access flags */
|
|
gdt[num].access = access;
|
|
}
|
|
|
|
/*
|
|
* gdt_install
|
|
* Install the kernel's GDTs
|
|
*/
|
|
void
|
|
gdt_install() {
|
|
/* GDT pointer and limits */
|
|
gp.limit = (sizeof(struct gdt_entry) * 3) - 1;
|
|
gp.base = (unsigned int)&gdt;
|
|
/* NULL */
|
|
gdt_set_gate(0, 0, 0, 0, 0);
|
|
/* Code segment */
|
|
gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
|
|
/* Data segment */
|
|
gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
|
|
/* Go go go */
|
|
gdt_flush();
|
|
}
|