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#include <stdint.h>
#include <kernel/gdt/gdt.h>
#include <kernel/system.h>
#include <kernel/lib/lib.h>
#include <kernel/memory/alloc.h>
struct gdt_entry {
unsigned short limit_low;
unsigned short base_low;
unsigned char base_middle;
unsigned char access;
unsigned char granularity;
unsigned char base_high;
} __attribute__((packed));
struct gdt_ptr {
unsigned short limit;
void *base;
} __attribute__((packed));
struct gdt_entry gdt[6];
struct gdt_ptr gp;
struct tss_entry_struct {
uint32_t prev_tss;
uint32_t esp0;
uint32_t ss0;
uint32_t esp1;
uint32_t ss1;
uint32_t esp2;
uint32_t ss2;
uint32_t cr3;
uint32_t eip;
uint32_t eflags;
uint32_t eax;
uint32_t ecx;
uint32_t edx;
uint32_t ebx;
uint32_t esp;
uint32_t ebp;
uint32_t esi;
uint32_t edi;
uint32_t es;
uint32_t cs;
uint32_t ss;
uint32_t ds;
uint32_t fs;
uint32_t gs;
uint32_t ldt;
uint16_t trap;
uint16_t iomap_base;
} __attribute__((packed));
struct tss_entry_struct tss_entry;
extern void gdt_flush();
void gdt_set_gate(int32_t num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran)
{
// Set descriptor base address
gdt[num].base_low = (unsigned short)(base & 0xFFFF);
gdt[num].base_middle = (unsigned char)((base >> 16) & 0xFF);
gdt[num].base_high = (unsigned char)((base >> 24) & 0xFF);
// Set descriptor limits
gdt[num].limit_low = (unsigned short)(limit & 0xFFFF);
gdt[num].granularity = (unsigned char)((limit >> 16) & 0x0F);
// Set granularity and access flags
gdt[num].granularity |= (gran & 0xF0);
gdt[num].access = access;
}
void gdt_install()
{
// Set GDT pointer and limit
gp.limit = (sizeof(struct gdt_entry) * 6) - 1;
gp.base = &gdt;
// NULL descriptor
gdt_set_gate(0, 0, 0, 0, 0);
// Code segment
gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
// Data segment
gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
// User mode code segment
gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);
// User mode data segment
gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);
// Write TSS
tss_write(5, 0x10, 0x0);
// Remove old GDT and install the new changes!
gdt_flush();
tss_flush();
vga_log("Installed Global Descriptor Table");
}
void tss_write(int32_t num, uint16_t ss0, uint32_t esp0)
{
uint32_t base = (uint32_t)&tss_entry;
uint32_t limit = base + sizeof(tss_entry);
gdt_set_gate(num, base, limit, 0xE9, 0x00);
memset(&tss_entry, 0, sizeof(tss_entry));
tss_entry.ss0 = ss0;
tss_entry.esp0 = esp0;
tss_entry.cs = 0x0b;
tss_entry.ss = tss_entry.ds = tss_entry.es = tss_entry.fs = tss_entry.gs = 0x13;
}
void tss_flush()
{
asm volatile("ltr %%ax" : : "a"(0x2B));
}
void set_kernel_stack(uintptr_t stack)
{
tss_entry.esp0 = stack;
}
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