35 lines
864 B
C
35 lines
864 B
C
#include <gdt.h>
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#define GDT_ENTRIES 3
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struct gdt_entry gdt[GDT_ENTRIES];
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struct gdt_ptr gp;
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extern void gdt_flush(uint32_t);
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void gdt_install()
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{
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gp.limit = (sizeof(struct gdt_entry) * GDT_ENTRIES) - 1;
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gp.base = (uint32_t)&gdt;
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gdt_set_entry(0, 0, 0, 0, 0); /* Null segment */
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gdt_set_entry(1, 0, 0xFFFFFFFF, 0x9A, 0xCF); /* Code segment */
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gdt_set_entry(2, 0, 0xFFFFFFFF, 0x92, 0xCF); /* Data segment */
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gdt_flush((uint32_t)&gp);
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}
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void gdt_set_entry(int num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran)
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{
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gdt[num].base_low = (base & 0xFFFF);
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gdt[num].base_middle = (base >> 16) & 0xFF;
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gdt[num].base_high = (base >> 24) & 0xFF;
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gdt[num].limit_low = (limit & 0xFFFF);
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gdt[num].granularity = (limit >> 16) & 0x0F;
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gdt[num].granularity |= (gran & 0xF0);
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gdt[num].access = access;
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}
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