mbr_asm/idt.c

#include "idt.h"
static struct idtEntry idt[IDT_NUM];

int idtSetup()
{
    struct idtRegister idtr;

    for (int i = 0; i < IDT_NUM; i++) {
        struct idtEntry *idte = idt + i;

        /* Setup an empty IDTE interrupt gate, see figure 5-2 in Intel
           x86 doc, vol 3 */
        idte->seg_sel  = BUILD_SEGMENT_SELECTOR(RING_0, 0, SEGMENT_IDX_CODE);
        idte->reserved = 0;
        idte->flags    = 0;
        idte->type     = 0x6; /* Interrupt gate (110b) */
        idte->op_size  = 1;   /* 32bits instructions */

        /* Disabled it for now */
        idte->zero        = 0;
        idte->offset_low  = 0;
        idte->offset_high = 0;
        idte->dpl         = 0;
        idte->present     = 0;
    }

    /*
     * Setup the IDT register, see Intel x86 doc vol 3, section 5.8.
     */

    /* Address of the IDT */
    idtr.base_addr = (uint32_t)idt;

    /* The limit is the maximum offset in bytes from the base address of
       the IDT */
    idtr.limit = sizeof(idt) - 1;

    /* Commit the IDT into the CPU */
    asm volatile("lidt %0\n" ::"m"(idtr) : "memory");

    return 0;
}

int idt_set_handler(int index, unsigned int addr, int priviledge)
{
    struct idtEntry *idte;

    if (index < 0 || index >= IDT_NUM)
        return -1;
    if ((priviledge < 0) || priviledge > 3)
        return -1;

    idte = idt + index;

    if (addr != (unsigned int)NULL) {
        idte->offset_low  = addr & 0xffff;
        idte->offset_high = (addr >> 16) & 0xffff;
        idte->dpl         = priviledge;
        idte->present     = 1;
    } else {
        idte->offset_low  = 0;
        idte->offset_high = 0;
        idte->dpl         = 0;
        idte->present     = 0;
    }

    return 0;
}