49 lines
1.4 KiB
C
49 lines
1.4 KiB
C
/**
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* Referenced from https://github.com/tendstofortytwo/clay
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* kernel/kernel.c
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*/
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#include <kernel/gdt.h>
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#include <stdio.h>
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#include <stdint.h>
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uint32_t TSS[32];
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gdt_entry GDT[GDT_ENTRIES];
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gdt_ptr gp;
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void gdt_fill(gdt_entry* target, gdt* source) {
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if(source->limit > 0xFFFFF) {
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printf("Invalid GDT limit %d\n", source->limit);
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for(;;);
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}
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target->limit_lo = source->limit & 0xFFFF;
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target->limit_hi_flags = (source->limit >> 16) & 0x0F;
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target->base_lo = source->base & 0xFFFF;
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target->base_mid = (source->base >> 16) & 0xFF;
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target->base_hi = (source->base >> 24) & 0xFF;
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target->access = source->access;
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target->limit_hi_flags |= (source->flags << 4);
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}
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void gdt_init(void) {
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uint32_t tssRef = (uint32_t) TSS;
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gdt rows[GDT_ENTRIES] = {
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{0, 0x00000, 0x00, 0x0}, // 0x0000 Null Descriptor
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{0, 0xFFFFF, 0x9A, 0xC}, // 0x0008 Kernel Mode Code Segment
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{0, 0xFFFFF, 0x92, 0xC}, // 0x0010 Kernel Mode Data Segment
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{0, 0xFFFFF, 0xFA, 0xC}, // 0x0018 User Mode Code Segment
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{0, 0xFFFFF, 0xF2, 0xC}, // 0x0020 User Mode Data Segment
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{tssRef, sizeof(TSS), 0x89, 0x0}, // 0x0028 Task State Segment
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};
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for(uint32_t i = 0; i < GDT_ENTRIES; ++i) {
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gdt_fill(GDT+i, rows+i);
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}
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gp.base = (void*) GDT;
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gp.limit = (GDT_ENTRIES * sizeof(gdt_entry)) - 1;
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gdt_load();
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}
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