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#include "gdt.h"
#include <stdint.h>
GDT_t *table = 0x0;
extern GDTR_t gdtr;
void get_gdtr() {
uint32_t base = 0x0000;
*table = (GDT_t){
// NULL
make_descriptor(0, 0, 0),
// Code segment, read
make_descriptor(base, 0x8FFFF, make_code(0, 0, 1)),
// Data segment, read write
make_descriptor(base, 0x8FFFF, make_data(0, 0, 1)),
};
gdtr.size = sizeof(Segment_Descriptor_t) * 3 - 1;
gdtr.offset = base;
}
uint16_t make_code(uint8_t priv, uint8_t dc, uint8_t rw) {
uint16_t access = 0;
access |= (1 << 7);
access |= (priv << 5);
access |= (0b11 << 3);
access |= (dc << 2);
access |= (rw << 1); // 10
access <<= 8;
access |= FLAG;
return access;
}
uint16_t make_data(uint8_t priv, uint8_t dc, uint8_t rw) {
uint16_t access = 0;
access |= (1 << 7);
access |= (priv << 5);
access |= (0b10 << 3);
access |= (dc << 2);
access |= (rw << 1); // 10
access <<= 8;
access |= FLAG;
return access;
}
Segment_Descriptor_t make_descriptor(uint32_t base, uint32_t limit,
uint16_t access_flag) {
uint16_t lim_low = limit;
uint16_t base_low = base;
uint8_t base_mid = (base >> 16);
uint8_t access_byte = access_flag >> 8;
uint8_t lim_flag = ((access_flag << 4) | (limit >> 16));
uint8_t base_high = (base >> 24);
return (Segment_Descriptor_t){
lim_low, base_low, base_mid, access_byte, lim_flag, base_high,
};
}
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