40 lines
882 B
C
40 lines
882 B
C
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#include <stdint.h>
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#define NUM_ENTRIES 4
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typedef struct {
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uint16_t limit_low16;
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uint16_t base_low16;
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uint8_t base_mid8;
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uint8_t access;
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uint8_t limit_flags;
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uint8_t base_high8;
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} gdt_entry;
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typedef struct {
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uint16_t size;
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uint32_t address;
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} gdt_description;
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gdt_entry gdt[NUM_ENTRIES-1];
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gdt_description gdt_desc;
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void gdt_init() {
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set_entry(0,0,0,0);
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set_entry(1,0,0xFFFFF,0x9E);
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set_entry(2,0,0xFFFFF,0x92);
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gdt_desc.size=(sizeof(gdt_entry)*NUM_ENTRIES)-1;
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gdt_desc.address=&gdt[0];
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asm volatile("lgdt gdt_desc");
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}
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void set_entry(int i,uint32_t base,uint32_t limit,uint8_t access) {
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gdt[i].limit_low16=limit&0xFFFF;
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gdt[i].base_low16=base&0xFFFFF;
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gdt[i].base_mid8=(base&0xFF0000)>>16;
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gdt[i].access=access;
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uint8_t limit_high4=(limit&0xF0000)>>16;
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gdt[i].limit_flags=0xC0&limit_high4;
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gdt[i].base_high8=(base&0xFF000000)>>24;
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}
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