i686/lidt.c


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#include "idt.h"
#include <stdint.h>

struct __attribute__((packed)) Pointer {
  uint16_t limit;
  uint32_t base;
};

enum Type {
  Null = 0,
  Intr = 0b10001110, // 32-bit interrupt
};

struct __attribute__((packed)) Gate_t {
  uint16_t offset_15_0;  // segment offset low
  uint16_t selector;     // code segment selector
  uint8_t __unused;      // unused in protected mode
  uint8_t type;          // interrupt type
  uint16_t offset_31_16; // segment offset high
};
_Static_assert(sizeof(struct Gate_t) == 8);

void
Gate(struct Gate_t *entry, void *f, uint16_t selector)
{
  uint32_t f_addr = (uint32_t)f;
  entry->offset_15_0 = f_addr & 0xffff;
  entry->offset_31_16 = (f_addr >> 16) & 0xffff;
  entry->selector = selector;
  entry->__unused = 0;
  entry->type = Intr;
}

static struct Gate_t interrupt_table[256] __attribute((aligned(4096)));

void
idt_install()
{
  for (int i = 0; i <= 0x2f; ++i) Gate(&interrupt_table[i], &interrupt_handler, 0x10);
  Gate(&interrupt_table[0x80], &abort_handler, 0x10);

  const struct Pointer ptr = {.limit = sizeof(interrupt_table) - 1, .base = (unsigned)&interrupt_table};
  asm volatile("lidt (%0)" : : "a"(&ptr));

  asm volatile("sti");
}