Add an interrupt descriptor table.

Set up a very basic handler for divide by zero and
general protection faults.

zion/interrupt/interrupt.cpp

@@ -0,0 +1,55 @@
+#include "interrupt/interrupt.h"
+
+#include <stdint.h>
+
+#include "debug/debug.h"
+
+#define IDT_INTERRUPT_GATE 0x8E
+
+#define KERNEL_CS 0x8
+
+struct InterruptDescriptorTablePointer {
+  uint16_t size;
+  uint64_t base;
+} __attribute__((packed));
+
+struct InterruptDescriptor {
+  uint16_t offset_low;
+  uint16_t selector;
+  uint8_t ist;
+  uint8_t flags;
+  uint16_t offset_medium;
+  uint32_t offset_high;
+  uint32_t zero;
+} __attribute__((packed));
+
+static InterruptDescriptor gIdt[256];
+
+InterruptDescriptor CreateDescriptor(void isr(void)) {
+  uint64_t offset = reinterpret_cast<uint64_t>(isr);
+  return InterruptDescriptor{
+      .offset_low = static_cast<uint16_t>(offset),
+      .selector = KERNEL_CS,
+      .ist = 0,
+      .flags = IDT_INTERRUPT_GATE,
+      .offset_medium = static_cast<uint16_t>(offset >> 16),
+      .offset_high = static_cast<uint32_t>(offset >> 32),
+      .zero = 0x0,
+  };
+}
+
+extern "C" void isr_divide_by_zero();
+extern "C" void interrupt_divide_by_zero(void* frame) { panic("DIV0"); }
+
+extern "C" void isr_protection_fault();
+extern "C" void interrupt_protection_fault(void* frame) { panic("GP"); }
+
+void InitIdt() {
+  gIdt[0] = CreateDescriptor(isr_divide_by_zero);
+  gIdt[13] = CreateDescriptor(isr_protection_fault);
+  InterruptDescriptorTablePointer idtp{
+      .size = sizeof(gIdt),
+      .base = reinterpret_cast<uint64_t>(gIdt),
+  };
+  asm volatile("lidt %0" ::"m"(idtp));
+}