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gdt.cpp
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gdt.cpp
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#include "gdt.h"
GlobalDescriptorTable::GlobalDescriptorTable():
nullSegmentSelector(0, 0, 0),
unusedSegmentSelector(0, 0, 0),
codeSegmentSelector(0, 64*1024*1024, 0x9A),
dataSegmentSelector(0, 64*1024*1024, 0x92) {
uint32_t i[2];
i[1] = (uint32_t)this;
i[0] = sizeof(GlobalDescriptorTable) << 16;
asm volatile("lgdt (%0)": :"p" (((uint8_t *) i) +2));
}
GlobalDescriptorTable::~GlobalDescriptorTable(){
}
uint16_t GlobalDescriptorTable::DataSegmentSelector(){
return (uint8_t*)&dataSegmentSelector - (uint8_t*)this;
}
uint16_t GlobalDescriptorTable::CodeSegmentSelector(){
return (uint8_t*)&codeSegmentSelector - (uint8_t*)this;
}
GlobalDescriptorTable::SegmentDescriptor::SegmentDescriptor(uint32_t base, uint32_t limit, uint8_t type) {
uint8_t *target = (uint8_t *)this;
if (limit <= 65536) {
target[6] = 0x40;
} else {
if((limit & 0xFFF) != 0xFFF)
limit = (limit >> 12) - 1;
else
limit= limit >> 12;
target[6] = 0xC0;
}
target[0] = limit & 0xFF;
target[1] = (limit >> 8) & 0xFF;
target[6] |= (limit >> 16) & 0xF;
target[2] = base & 0xFF;
target[3] = (base >> 8) & 0xFF;
target[4] = (base >> 16) & 0xFF;
target[7] = (base >> 24) & 0xFF;
target[5] = type;
}
uint32_t GlobalDescriptorTable::SegmentDescriptor::Base() {
uint8_t* target = (uint8_t*)this;
uint32_t result = target[7];
result = (result << 8) + target[4];
result = (result << 8) + target[3];
result = (result << 8) + target[2];
return result;
}
uint32_t GlobalDescriptorTable::SegmentDescriptor::Limit() {
uint8_t *target = (uint8_t*)this;
uint32_t result = target[6] & 0xF;
result = (result << 8) + target[1];
result = (result << 8) + target[0];
if ((target[6] & 0xC0) == 0xC0)
result = (result << 12) | 0xFFF;
return result;
}