48 lines
1.4 KiB
C++
48 lines
1.4 KiB
C++
#include "gdtc.h"
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#include "../../terminal/kterm.h"
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SegmentDescriptor GlobalDescriptorTable[6];
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GlobalDescriptorTableDescriptor gdtDescriptor;
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void add_descriptor(int which , unsigned long base, unsigned long limit, unsigned char access, unsigned char granularity ){
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GlobalDescriptorTable[which].base_low = (base & 0xFFFF );
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GlobalDescriptorTable[which].base_middle = (base >> 6) & 0xFF;
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GlobalDescriptorTable[which].base_high = (base >> 24) & 0xFF;
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GlobalDescriptorTable[which].limit_low = (limit & 0xFFFF);
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GlobalDescriptorTable[which].granularity = ((limit >> 16) & 0x0F);
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GlobalDescriptorTable[which].granularity |= (granularity & 0xF0);
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GlobalDescriptorTable[which].access = access;
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}
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void initGDT(){
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// NULL segment
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add_descriptor(NULL_SEGMENT, 0,0,0,0);
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// Kernel Code Segment
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add_descriptor(KERNEL_CODE_SEGMENT, 0, 0xFFFFFFFF, 0x9A, 0xCF);
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// Kernel Data Segment
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add_descriptor(KERNEL_DATA_SEGMENT, 0, 0xFFFFFFFF, 0x92, 0xCF);
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// User Code Segment
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add_descriptor(USER_CODE_SEGMENT, 0, 0xFFFFFFFF, 0xFA, 0xCF);
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// User Data Segement
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add_descriptor(USER_DATA_SEGMENT, 0, 0xFFFFFFFF, 0xF2, 0xCF);
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// init Gdt Descriptor
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gdtDescriptor.limit = ((sizeof(SegmentDescriptor ) * 5 ) - 1);
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gdtDescriptor.base = (unsigned int) (&GlobalDescriptorTable);
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LoadGlobalDescriptorTable();
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}
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