mirror of
https://github.com/yourtion/30dayMakeOS.git
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68 lines
1.7 KiB
C
68 lines
1.7 KiB
C
/* GDTやIDTなどの、 descriptor table 関係 */
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struct SEGMENT_DESCRIPTOR {
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short limit_low, base_low;
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char base_mid, access_right;
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char limit_high, base_high;
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};
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struct GATE_DESCRIPTOR {
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short offset_low, selector;
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char dw_count, access_right;
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short offset_high;
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};
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void init_gdtidt(void);
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void set_segmdesc(struct SEGMENT_DESCRIPTOR *sd, unsigned int limit, int base, int ar);
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void set_gatedesc(struct GATE_DESCRIPTOR *gd, int offset, int selector, int ar);
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void load_gdtr(int limit, int addr);
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void load_idtr(int limit, int addr);
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void init_gdtidt(void)
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{
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struct SEGMENT_DESCRIPTOR *gdt = (struct SEGMENT_DESCRIPTOR *) 0x00270000;
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struct GATE_DESCRIPTOR *idt = (struct GATE_DESCRIPTOR *) 0x0026f800;
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int i;
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/* GDTの初期化 */
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for (i = 0; i < 8192; i++) {
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set_segmdesc(gdt + i, 0, 0, 0);
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}
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set_segmdesc(gdt + 1, 0xffffffff, 0x00000000, 0x4092);
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set_segmdesc(gdt + 2, 0x0007ffff, 0x00280000, 0x409a);
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load_gdtr(0xffff, 0x00270000);
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/* IDTの初期化 */
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for (i = 0; i < 256; i++) {
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set_gatedesc(idt + i, 0, 0, 0);
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}
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load_idtr(0x7ff, 0x0026f800);
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return;
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}
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void set_segmdesc(struct SEGMENT_DESCRIPTOR *sd, unsigned int limit, int base, int ar)
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{
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if (limit > 0xfffff) {
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ar |= 0x8000; /* G_bit = 1 */
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limit /= 0x1000;
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}
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sd->limit_low = limit & 0xffff;
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sd->base_low = base & 0xffff;
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sd->base_mid = (base >> 16) & 0xff;
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sd->access_right = ar & 0xff;
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sd->limit_high = ((limit >> 16) & 0x0f) | ((ar >> 8) & 0xf0);
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sd->base_high = (base >> 24) & 0xff;
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return;
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}
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void set_gatedesc(struct GATE_DESCRIPTOR *gd, int offset, int selector, int ar)
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{
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gd->offset_low = offset & 0xffff;
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gd->selector = selector;
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gd->dw_count = (ar >> 8) & 0xff;
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gd->access_right = ar & 0xff;
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gd->offset_high = (offset >> 16) & 0xffff;
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return;
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}
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