47 lines
1.6 KiB
C
47 lines
1.6 KiB
C
#include <kernel/gdt.h>
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#include <stdio.h>
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#include <stdint.h>
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static uint32_t tss[32];
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static gdt_entry_t gdt[GDT_ENTRIES];
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static gdtr_t gdtptr;
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void gdt_set_descriptor(uint8_t vector, uint32_t base, uint32_t limit, uint8_t access, uint8_t flags) {
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gdt[vector].base_low = base & 0xFFFF;
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gdt[vector].base_mid = (base >> 16) & 0xFF;
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gdt[vector].base_high = (base >> 24) & 0xFF;
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gdt[vector].limit_low = limit & 0xFFFF;
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gdt[vector].limit_hi_flags = (limit >> 16) & 0x0F;
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gdt[vector].limit_hi_flags |= flags << 4;
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gdt[vector].access = access;
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}
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void gdt_init(void) {
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gdt_set_descriptor(0, 0, 0, 0, 0); // 0x0000 Null Descriptor
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gdt_set_descriptor(1, 0, 0xFFFFF, 0x9A, 0xC); // 0x0008 Kernel Mode Code Segment
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gdt_set_descriptor(2, 0, 0xFFFFF, 0x92, 0xC); // 0x0010 Kernel Mode Data Segment
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gdt_set_descriptor(3, 0, 0xFFFFF, 0xFA, 0xC); // 0x0018 User Mode Code Segment
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gdt_set_descriptor(4, 0, 0xFFFFF, 0xF2, 0xC); // 0x0020 User Mode Data Segment
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gdt_set_descriptor(5, (uintptr_t)&tss[0], sizeof(tss), 0x89, 0); // 0x0028 Task State Segment
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gdtptr.base = (uintptr_t)&gdt[0];
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gdtptr.limit = sizeof(gdt_entry_t) * GDT_ENTRIES - 1;
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__asm__ volatile("lgdt %0" : : "m"(gdtptr)); // Load new GDT
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__asm__ volatile(
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"mov %cr0, %eax\n"
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"or $1, %al\n" // set PE (Protection Enable) bit in CR0 (Control Register 0)
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"mov %eax, %cr0\n"
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"jmp $0x0008, $fix_cs\n"
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"fix_cs:\n"
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"mov $0x0010, %ax\n"
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"mov %ax, %ds\n"
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"mov %ax, %es\n"
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"mov %ax, %fs\n"
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"mov %ax, %gs\n"
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"mov %ax, %ss"
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);
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}
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