os/arch/i686/interrupts/idt.c

#include <kernel/gdt.h>
#include <kernel/tty.h>
#include <debugging.h>
#include "interrupt.h"
#include <stdint.h>
#include <stddef.h>
#include "../io.h"

#define IRQ0 0x20
#define IRQ1 (IRQ0 + 1)
#define IRQ2 (IRQ0 + 2)
#define IRQ3 (IRQ0 + 3)
#define IRQ4 (IRQ0 + 4)
#define IRQ5 (IRQ0 + 5)
#define IRQ6 (IRQ0 + 6)
#define IRQ7 (IRQ0 + 7)

#define IRQ8 0x28
#define IRQ9  (IRQ8 + 1)
#define IRQ10 (IRQ8 + 2)
#define IRQ11 (IRQ8 + 3)
#define IRQ12 (IRQ8 + 4)
#define IRQ13 (IRQ8 + 5)
#define IRQ14 (IRQ8 + 6)
#define IRQ15 (IRQ8 + 7)

#define NUM_ENTRIES 0x100

struct InterruptDescriptor {
    uint32_t offset;
    uint32_t selector;
    uint8_t gate_type;
    uint8_t ring;
    bool present;
};

struct IDT {
    uint16_t size;
    uint64_t* base;
} __attribute__((packed));

static uint64_t entries[NUM_ENTRIES];
struct IDT idt;

enum EntryTypes {
    DivisionByZero = 0x00,
    _Reserved0     = 0x01,
    NMIInterrupt   = 0x02,
    Breakpoint     = 0x03,
    Overflow       = 0x04,
    BoundsExceeded = 0x05,
    InvalidOpcode  = 0x06,
    DeviceNotAvail = 0x07,
    DoubleFault    = 0x08,
    CoprocSegORun  = 0x09,
    InvalidTSS     = 0x0A,
    SegNotPresent  = 0x0B,
    StackSegFault  = 0x0C,
    GenerProtFault = 0x0D,
    PageFault      = 0x0E,
    _Reserved1     = 0x0F,
    x87FPUError    = 0x10,
    AlignmentCheck = 0x11,
    MachineCheck   = 0x12,
    SIMDFloatExcep = 0x13,
};

static void encodeIdtEntry(uint8_t *target, struct InterruptDescriptor source)
{
    // Encode the present bit
    if (source.present) {
        target[5] |= 0x80;
    } else {
        // Not present, return
        return;
    }

    // Encode the offset 
    target[0] = (source.offset >> 0x00) & 0xFF;
    target[1] = (source.offset >> 0x08) & 0xFF;
    target[6] = (source.offset >> 0x10) & 0xFF;
    target[7] = (source.offset >> 0x18) & 0xFF;
    
    // Encode the base
    target[2] = (source.selector >> 0x00) & 0xFF;
    target[3] = (source.selector >> 0x08) & 0xFF;
    
    // Encode the gate type
    target[5] |= source.gate_type;
    
    // Encode the DPL
    target[5] |= (source.ring << 5);
}

static void add_entry(struct InterruptDescriptor entry, uint8_t index)
{
    uint64_t descriptor = 0;
    encodeIdtEntry((uint8_t*) &descriptor, entry);

    entries[index] = descriptor;
}

static void load_idt() 
{
    idt.size = NUM_ENTRIES * 8 - 1;
    idt.base = entries;

    asm ( "lidt %0" : : "m"(idt) );
}

static struct InterruptDescriptor generate_entry(bool present, void isr(struct interrupt_frame*), uint8_t gate_type, uint8_t ring, uint8_t selector)
{
    struct InterruptDescriptor entry;
    entry.present = present;
    entry.offset = (size_t)isr;
    entry.gate_type = gate_type;
    entry.ring = ring;
    entry.selector = selector;
    return entry;
}

static void add_exceptions() 
{
    struct InterruptDescriptor entry;

    entry = generate_entry(true, exception, 0xF, 0, 0x8);
    for (int i = 0; i < 0x20; i++)
    {
        add_entry(entry, i);
    }

    entry = generate_entry(true, divide_by_zero, 0xF, 0, 0x8);
    add_entry(entry, DivisionByZero);

    entry = generate_entry(true, general_protection_fault, 0xF, 0, 0x8);
    add_entry(entry, GenerProtFault);

    entry = generate_entry(true, double_fault, 0xF, 0, 0x8);
    add_entry(entry, DoubleFault);

}

static void add_irqs()
{
    struct InterruptDescriptor entry;
    entry = generate_entry(true, irq_1, 0xE, 0, 0x8);
    for (int i = IRQ0; i <= IRQ7; i++)
    {
        add_entry(entry, i);
    }

    entry = generate_entry(true, irq_2, 0xE, 0, 0x8);
    for (int i = IRQ8; i <= IRQ15; i++)
    {
        add_entry(entry, i);
    }

    entry = generate_entry(true, irq0, 0xE, 0, 0x8);
    add_entry(entry, IRQ0);

    entry = generate_entry(true, keyboard_interrupt, 0xE, 0, 0x8);
    add_entry(entry, IRQ1);
}

static void add_syscall()
{
    struct InterruptDescriptor syscall_entry;
    syscall_entry.present = true;
    syscall_entry.offset = (size_t)syscall;
    syscall_entry.gate_type = 0xE;
    syscall_entry.ring = 3;
    syscall_entry.selector = 0x8;

    add_entry(syscall_entry, 0x80);
}

void idt_init()
{
    add_exceptions();
    add_irqs();
    add_syscall();

    load_idt();
}