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#include "GDT.ns.h"
extern "C" void gdt_flush(u32int);
extern "C" void tss_flush();
using namespace CMem; //For memset
#define GDT_ENTRIES 6
namespace GDT {
gdt_entry_t gdt_entries[GDT_ENTRIES];
gdt_ptr_t gdt_ptr;
tss_entry_t tss_entry;
void setGate(s32int num, u32int base, u32int limit, u8int access, u8int gran) {
gdt_entries[num].base_low = (base & 0xFFFF);
gdt_entries[num].base_middle = (base >> 16) & 0xFF;
gdt_entries[num].base_high = (base >> 24) & 0xFF;
gdt_entries[num].limit_low = (limit & 0xFFFF);
gdt_entries[num].granularity = (limit >> 16) & 0x0F;
gdt_entries[num].granularity |= gran & 0xF0;
gdt_entries[num].access = access;
}
void writeTSS(s32int num, u16int ss0, u32int esp0) {
u32int base = (u32int)&tss_entry;
u32int limit = base + sizeof(tss_entry);
setGate(num, base, limit, 0xE9, 0x00);
memset((u8int*)&tss_entry, 0, sizeof(tss_entry_t));
tss_entry.ss0 = ss0;
tss_entry.esp0 = esp0;
tss_entry.iomap_base = sizeof(tss_entry_t) - 8192;
tss_entry.cs = 0x0B; //0x0B = Kernel code segment + RPL=3 (meaning it is supposed to be called from user mode)
//0x13 = Kernel data segment + RPL=3 (meaning to be called from ring3)
tss_entry.ss = tss_entry.ds = tss_entry.es = tss_entry.fs = tss_entry.gs = 0x13;
}
void init() {
gdt_ptr.limit = (sizeof(gdt_entry_t) * GDT_ENTRIES) - 1;
gdt_ptr.base = (u32int)&gdt_entries;
setGate(0, 0, 0, 0, 0); //Null segment
setGate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF); //Kernel code segment
setGate(2, 0, 0xFFFFFFFF, 0x92, 0xCF); //Kernel data segment
setGate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF); //User code segment
setGate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF); //User data segment
writeTSS(5, 0x10, 0x0);
gdt_flush((u32int)&gdt_ptr);
tss_flush();
}
}
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