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#include <kernel/string.h>
#include <stdint.h>
struct gdt_entry {
uint16_t limit_low;
uint16_t base_low;
uint8_t base_middle;
uint8_t access;
uint8_t gran;
uint8_t base_high;
} __attribute__((packed));
struct gdt_ptr {
uint16_t limit;
uint32_t base;
} __attribute__((packed));
struct tss_entry {
uint32_t link;
uint32_t esp0;
uint32_t ss0;
uint32_t esp1;
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 ldtr;
uint16_t trap;
uint16_t iomap_base;
} __attribute__((packed));
struct gdt_entry desc[6];
struct gdt_ptr gp;
struct tss_entry tss_entry;
extern void flush_gdt(void);
extern void flush_tss(void);
void gdt_set_gate(int num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran) {
desc[num].base_low = (base & 0xFFFF);
desc[num].base_middle = (base >> 16) & 0xFF;
desc[num].base_high = (base >> 24) & 0xFF;
desc[num].limit_low = (limit & 0xFFFF);
desc[num].gran = (limit >> 16) & 0x0F;
desc[num].gran |= (gran & 0xF0);
desc[num].access = access;
}
void write_tss(int num, uint16_t ss0, uint16_t esp0) {
uint32_t base = (uint32_t)&tss_entry;
uint32_t limit = base + sizeof(struct tss_entry);
gdt_set_gate(num, base, limit, 0xE9, 0x00);
memset(&tss_entry, 0x0, sizeof(tss_entry));
tss_entry.ss0 = ss0;
tss_entry.esp0 = esp0;
tss_entry.cs = 0x0B;
tss_entry.ss = 0x13;
tss_entry.ds = 0x13;
tss_entry.es = 0x13;
tss_entry.fs = 0x13;
tss_entry.gs = 0x13;
tss_entry.iomap_base = sizeof(tss_entry);
}
void gdt_install(void) {
gp.limit = (sizeof(struct gdt_entry) * 6) - 1;
gp.base = (uint32_t)&desc;
gdt_set_gate(0, 0, 0, 0, 0);
gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);
gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);
uint32_t esp;
__asm__ volatile("movl %%esp, %0" : "=r"(esp));
write_tss(5, 0x10, esp);
flush_gdt();
flush_tss();
}
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