BarinkOS/source/kernel/memory/gdt/gdtc.cpp

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#include "gdtc.h"
#include "../../terminal/kterm.h"
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#define NULL_SEGMENT 0
#define KERNEL_CODE_SEGMENT 1
#define KERNEL_DATA_SEGMENT 2
#define USER_CODE_SEGMENT 3
#define USER_DATA_SEGMENT 4
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SegmentDescriptor GlobalDescriptorTable[5];
GlobalDescriptorTableDescriptor gdtDescriptor;
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void add_descriptor(int which , unsigned long base, unsigned long limit, unsigned char access, unsigned char granularity ){
GlobalDescriptorTable[which].base_low = (base & 0xFFFF );
GlobalDescriptorTable[which].base_middle = (base >> 6) & 0xFF;
GlobalDescriptorTable[which].base_high = (base >> 24) & 0xFF;
GlobalDescriptorTable[which].limit_low = (limit & 0xFFFF);
GlobalDescriptorTable[which].granularity = ((limit >> 16) & 0x0F);
GlobalDescriptorTable[which].granularity |= (granularity & 0xF0);
GlobalDescriptorTable[which].access = access;
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}
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void initGDT(){
#ifdef __VERBOSE__
printf("Init GDT!\n");
#endif
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// NULL segment
add_descriptor(NULL_SEGMENT, 0,0,0,0);
// Kernel Code Segment
add_descriptor(KERNEL_CODE_SEGMENT, 0, 0xFFFFFFFF, 0x9A, 0xCF);
// Kernel Data Segment
add_descriptor(KERNEL_DATA_SEGMENT, 0, 0xFFFFFFFF, 0x92, 0xCF);
// User Code Segment
// TODO:
// User Data Segement
// TODO:
// init Gdt Descriptor
gdtDescriptor.limit = ((sizeof(SegmentDescriptor ) * 5 ) - 1);
gdtDescriptor.base = (unsigned int) &GlobalDescriptorTable;
printf("GDT at address 0x%x, with an size of 0x%x bytes\n" , (unsigned int)GlobalDescriptorTable, sizeof(GlobalDescriptorTable));
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LoadGlobalDescriptorTable();
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}