113 lines
2.1 KiB
C++
113 lines
2.1 KiB
C++
#include <kernel/GDT.h>
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#include <stdint.h>
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namespace GDT
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{
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union SegmentDesriptor
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{
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struct
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{
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uint16_t limit_lo;
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uint16_t base_lo;
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uint8_t base_hi1;
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uint8_t type : 4;
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uint8_t system : 1;
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uint8_t DPL : 2;
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uint8_t present : 1;
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uint8_t limit_hi : 4;
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uint8_t flags : 4;
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uint8_t base_hi2;
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} __attribute__((packed));
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struct
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{
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uint32_t low;
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uint32_t high;
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} __attribute__((packed));
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SegmentDesriptor() : low(0), high(0) {}
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SegmentDesriptor(uint32_t base, uint32_t limit, uint8_t access, uint8_t _flags)
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: low(0), high(0)
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{
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set_base(base);
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set_limit(limit);
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high |= ((uint16_t)access) << 8;
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flags = _flags;
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}
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void set_base(uint32_t base)
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{
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base_lo = base & 0xFFFF;
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base_hi1 = (base >> 16) & 0x00FF;
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base_hi2 = (base >> 24) & 0x00FF;
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}
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void set_limit(uint32_t limit)
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{
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limit_lo = limit & 0xFFFF;
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limit_hi = (limit >> 16) & 0x00FF;
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}
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} __attribute__((packed));
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struct GDTR
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{
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uint16_t size;
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void* address;
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} __attribute__((packed));
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static GDTR s_gdtr;
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static SegmentDesriptor s_gdt[5];
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extern "C" void load_gdt(void* gdt_ptr);
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asm(
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".global load_gdt;"
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"load_gdt:"
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"movl 4(%esp),%eax;"
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"lgdt (%eax);"
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"movw $0x10, %ax;"
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"movw %ax, %ds;"
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"movw %ax, %es;"
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"movw %ax, %fs;"
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"movw %ax, %gs;"
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"movw %ax, %ss;"
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"jmp $0x08,$flush;"
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"flush:"
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"ret;"
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);
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void write_entry_raw(uint8_t segment, uint32_t low, uint32_t high)
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{
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uint8_t index = segment >> 3;
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s_gdt[index].low = low;
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s_gdt[index].high = high;
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}
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void write_entry(uint8_t segment, SegmentDesriptor descriptor)
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{
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write_entry_raw(segment, descriptor.low, descriptor.high);
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}
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void initialize()
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{
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s_gdtr.address = s_gdt;
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s_gdtr.size = sizeof(s_gdt) - 1;
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write_entry(0x00, { 0, 0x00000, 0x00, 0x0 }); // null
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write_entry(0x08, { 0, 0xFFFFF, 0x9A, 0xC }); // kernel code
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write_entry(0x10, { 0, 0xFFFFF, 0x92, 0xC }); // kernel data
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write_entry(0x18, { 0, 0xFFFFF, 0xFA, 0xC }); // user code
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write_entry(0x20, { 0, 0xFFFFF, 0xF2, 0xC }); // user data
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load_gdt(&s_gdtr);
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}
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} |