49 lines
1.2 KiB
C
49 lines
1.2 KiB
C
#include <stdio.h>
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#include <stdint.h>
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struct gdt_entry_struct {
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uint16_t limit_low;
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uint16_t base_low;
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uint8_t base_middle;
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uint8_t access;
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uint8_t granularity;
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uint8_t base_high;
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}__attribute__((packed));
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typedef struct gdt_entry_struct gdt_entry_t;
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struct gdt_ptr_struct {
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uint16_t limit;
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uint32_t base;
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}__attribute__((packed));
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typedef struct gdt_ptr_struct gdt_ptr_t;
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gdt_entry_t gdt_entries[5];
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gdt_ptr_t gdt_ptr;
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extern void gdt_flush(uint32_t);
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static void gdt_set_gate(int32_t num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran)
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{
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gdt_entries[num].base_low = (base & 0xFFFF);
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gdt_entries[num].base_middle = (base >> 16) & 0xFF;
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gdt_entries[num].base_high = (base >> 24) & 0xFF;
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gdt_entries[num].limit_low = (limit & 0xFFFF);
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gdt_entries[num].granularity = (limit >> 16) & 0x0F;
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gdt_entries[num].granularity |= gran & 0xF0;
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gdt_entries[num].access = access;
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}
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void gdt_init() {
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gdt_ptr.limit = (sizeof(gdt_entry_t) * 5) - 1;
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gdt_ptr.base = (uint32_t)&gdt_entries;
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gdt_set_gate(0, 0, 0, 0, 0);
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gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
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gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
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gdt_flush((uint32_t)&gdt_ptr);
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}
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