64 lines
1.5 KiB
C
64 lines
1.5 KiB
C
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#include "gdt.h"
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#include "string.h"
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#define GDT_ENTRY 6
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Gdt_entry gdt[GDT_ENTRY];
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Gdt_ptr gdtp;
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extern void gdt_flush(uint32_t);
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Tss_entry tss;
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extern void tss_flush(void);
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static void gdt_set_gate(uint8_t num, uint32_t base, uint32_t limit, uint8_t access, uint8_t granularity)
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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) & 0xF;
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gdt[num].granularity |= (granularity & 0xF0);
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gdt[num].access = access;
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}
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static void tss_install(uint8_t num, uint16_t kernel_ss, uint16_t kernel_esp)
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{
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uint32_t base = (uint32_t)&tss;
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uint32_t limit = base + sizeof(Tss_entry);
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gdt_set_gate(num, base, limit, 0xE9, 0x0);
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memset(&tss, 0, sizeof(Tss_entry));
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tss.ss0 = kernel_ss;
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tss.esp0 = kernel_esp;
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tss.cs = 0x1B;
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tss.ss = 0x23;
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tss.es = 0x23;
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tss.ds = 0x23;
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tss.fs = 0x23;
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tss.gs = 0x23;
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}
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void gdt_install()
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{
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gdt_set_gate(0, 0x0, 0x0, 0x0, 0x0); // Null segment
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gdt_set_gate(1, 0x0, 0xFFFFFFFF, 0x9A, 0xCF); // Kernel code segment
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gdt_set_gate(2, 0x0, 0xFFFFFFFF, 0x92, 0xCF); // Data segment
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gdt_set_gate(3, 0x0, 0xFFFFFFFF, 0xFA, 0xCF); // User code segment
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gdt_set_gate(4, 0x0, 0xFFFFFFFF, 0xF2, 0xCF); // User data segment
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tss_install(5, 0x10, stack_top);
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gdtp.limit = (sizeof(Gdt_entry) * GDT_ENTRY) - 1;
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gdtp.base = (uint32_t)&gdt;
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gdt_flush((uint32_t)&gdtp);
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tss_flush();
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}
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