56 lines
1.6 KiB
C++
56 lines
1.6 KiB
C++
#include "gdt.h"
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#include <kernel/kernio.h>
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#include <lib/std/memory.h>
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struct SegmentDescriptor_t {
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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 granularity0:4;
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uint8_t granularity1:4;
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uint8_t base_high;
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} __attribute__((packed));
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struct GDT_t {
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uint16_t limit;
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uint32_t base;
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} __attribute__((packed));
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SegmentDescriptor_t _GDT[5];
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GDT_t _GDTptr;
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void lgdt(GDT_t GDT) {
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asm ("lgdt %0" : : "m"(GDT));
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}
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void GDT_Init() {
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_GDTptr.limit = (sizeof(SegmentDescriptor_t) * 5) - 1;
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_GDTptr.base = (uint32_t)&_GDT;
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// Null segment
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GDT_Set_Gate(0, 0, 0, 0, 0);
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// Code Base 0 limit 32 Access EXEC + RW
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GDT_Set_Gate(1, 0x00000000, 0xFFFFFFFF, GDT_ACCESS_PRESENT | GDT_ACCESS_EXEC | GDT_ACCESS_RW, GDT_FLAG_GR_PAGE | GDT_FLAG_SZ_32B);
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// Data Base 0 Limit 32 Access RW
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GDT_Set_Gate(2, 0x00000000, 0xFFFFFFFF, GDT_ACCESS_PRESENT | GDT_ACCESS_RW, GDT_FLAG_GR_PAGE | GDT_FLAG_SZ_32B);
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lgdt(_GDTptr);
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SEGMENTS_RELOAD();
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}
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void GDT_Set_Gate(uint32_t index, uint32_t baseAddr, uint32_t limitAddr, uint8_t accessLvl, uint8_t flags) {
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if (index > 5) return;
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_GDT[index].base_low = (baseAddr & 0xFFFF);
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_GDT[index].base_middle = (baseAddr >> 16) & 0xFF;
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_GDT[index].base_high = (baseAddr >> 24) & 0xFF;
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_GDT[index].limit_low = (limitAddr >> 0) & 0xFFFF;
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_GDT[index].granularity0 = (limitAddr >> 16) & 0x0F;
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_GDT[index].granularity1 = flags & 0x0F;
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_GDT[index].access = accessLvl;
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}
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