96 lines
3.0 KiB
C
96 lines
3.0 KiB
C
#include <stdint.h>
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#include "gdt.h"
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#include "kprintf.h"
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extern void set_gdt(uint32_t gdt_ptr);
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uint8_t gdt_entries[GDT_SIZE * 8];
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struct gdt_descriptor *gdtr = (struct gdt_descriptor *)GDT_ADDRESS;
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static void set_gdt_entry_value(uint8_t *target, uint32_t base, uint32_t limit,
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uint8_t access, uint8_t granularity)
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{
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if (limit > 0xFFFFF) {
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kprintf(KERN_ERR
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"GDT cannot encode limits larger than 0xFFFFF");
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}
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// Encode the limit
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target[0] = limit & 0xFF;
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target[1] = (limit >> 8) & 0xFF;
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target[6] = (limit >> 16) & 0x0F;
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// Encode the base
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target[2] = base & 0xFF;
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target[3] = (base >> 8) & 0xFF;
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target[4] = (base >> 16) & 0xFF;
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target[7] = (base >> 24) & 0xFF;
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// Encode the access byte
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target[5] = access;
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// Encode the flags
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target[6] |= (granularity << 4);
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}
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void init_gdt(void)
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{
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gdtr->size = 8 * GDT_SIZE - 1;
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gdtr->base = (uint32_t)&gdt_entries[0];
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set_gdt_entry_value(gdt_entries + 0x00, 0, 0, 0, 0); // Null segment
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set_gdt_entry_value(
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gdt_entries + 0x08, 0, 0xFFFFF,
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GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_KERNEL_MODE |
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GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_EXECUTABLE |
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GDT_ACCESS_DC_NOT_CONFORM |
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GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
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GDT_ACCESS_A_ACCESSED,
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GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // Kernel code
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set_gdt_entry_value(
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gdt_entries + 0x10, 0, 0xFFFFF,
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GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_KERNEL_MODE |
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GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_NOT_EXECUTABLE |
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GDT_ACCESS_DC_NOT_CONFORM |
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GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
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GDT_ACCESS_A_ACCESSED,
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GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // Kernel data
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set_gdt_entry_value(
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gdt_entries + 0x18, 0, 0xFFFFF,
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GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_KERNEL_MODE |
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GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_NOT_EXECUTABLE |
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GDT_ACCESS_DC_CONFORM |
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GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
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GDT_ACCESS_A_ACCESSED,
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GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // Kernel stack
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set_gdt_entry_value(
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gdt_entries + 0x20, 0, 0xFFFFF,
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GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_USER_MODE |
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GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_EXECUTABLE |
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GDT_ACCESS_DC_CONFORM |
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GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
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GDT_ACCESS_A_ACCESSED,
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GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // User code
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set_gdt_entry_value(
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gdt_entries + 0x28, 0, 0xFFFFF,
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GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_USER_MODE |
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GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_NOT_EXECUTABLE |
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GDT_ACCESS_DC_NOT_CONFORM |
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GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
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GDT_ACCESS_A_ACCESSED,
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GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // User data
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set_gdt_entry_value(
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gdt_entries + 0x30, 0, 0xFFFFF,
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GDT_ACCESS_P_VALID | GDT_ACCESS_DPL_USER_MODE |
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GDT_ACCESS_S_CODE_OR_DATA | GDT_ACCESS_E_NOT_EXECUTABLE |
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GDT_ACCESS_DC_CONFORM |
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GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
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GDT_ACCESS_A_ACCESSED,
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GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // User stack
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set_gdt(((uint32_t)gdtr));
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}
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