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#include <gdt/gdt.h>
#include <lib/lib.h>
#include <memory/alloc.h>
#include <stdint.h>
#include <system.h>
struct gdt_entry {
u16 limit_low;
u16 base_low;
u8 base_middle;
u8 access;
u8 granularity;
u8 base_high;
} __attribute__((packed));
struct gdt_ptr {
u16 limit;
void *base;
} __attribute__((packed));
struct gdt_entry gdt[6];
struct gdt_ptr gp;
struct tss_entry_struct {
u32 prev_tss;
u32 esp0;
u32 ss0;
u32 esp1;
u32 ss1;
u32 esp2;
u32 ss2;
u32 cr3;
u32 eip;
u32 eflags;
u32 eax;
u32 ecx;
u32 edx;
u32 ebx;
u32 esp;
u32 ebp;
u32 esi;
u32 edi;
u32 es;
u32 cs;
u32 ss;
u32 ds;
u32 fs;
u32 gs;
u32 ldt;
u16 trap;
u16 iomap_base;
} __attribute__((packed));
struct tss_entry_struct tss_entry;
extern void gdt_flush();
void gdt_set_gate(s32 num, u32 base, u32 limit, u8 access, u8 gran)
{
// Set descriptor base address
gdt[num].base_low = (u16)(base & 0xFFFF);
gdt[num].base_middle = (u8)((base >> 16) & 0xFF);
gdt[num].base_high = (u8)((base >> 24) & 0xFF);
gdt[num].limit_low = (u16)(limit & 0xFFFF);
// Set granularity and access flags
gdt[num].granularity = (u8)((limit >> 16) & 0x0F);
gdt[num].granularity |= (gran & 0xF0);
gdt[num].access = access;
}
extern u32 stack_hold;
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, stack_hold);
// Remove old GDT and install the new changes!
gdt_flush();
tss_flush();
info("Installed Global Descriptor Table");
}
void tss_write(s32 num, u16 ss0, u32 esp0)
{
u32 base = (u32)&tss_entry;
u32 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(u32 stack)
{
tss_entry.esp0 = stack;
}
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