45 lines
1.1 KiB
C
45 lines
1.1 KiB
C
// Global descriptor table setup
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// Author: xamidev
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// Licensed under the Unlicense. See the repo below.
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// https://github.com/xamidev/blankos
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#include "gdt.h"
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#include "../libc/stdio.h"
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struct gdt_entry gdt[3];
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struct gdt_ptr gp;
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extern void gdt_flush();
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void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char 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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void gdt_install()
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{
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gp.limit = (sizeof(struct gdt_entry)*3) - 1;
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gp.base = (unsigned int)&gdt;
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gdt_set_gate(0, 0, 0, 0, 0);
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// Ring 0 code + data
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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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// Ring 3
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gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);
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gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);
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gdt_flush();
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printf("[kernel] GDT gates set (ring 0 and 3), gdt=0x%x\n", &gdt);
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}
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