OSDev.org

Posted: **Sun Oct 13, 2024 9:01 am**

After creating a idt for my hobby os then right after calling sti i get a interrupt 32 (GPF) and i have absolutely no idea why i went over my PIC remmaping logic and it looks good also have no idea why a Protection Fault is happening as the sti correctly displays interrupts. Anyways here are the code parts for analysing:

idt_load:

Code: Select all

global idt_load
global enable_interrupts
section .text

idt_load:
    cli
    lidt [rdi]       
    ret           

enable_interrupts:
    sti                   
    ret

idt.c

Code: Select all

#define PIC1_COMMAND 0x20
#define PIC1_DATA 0x21
#define PIC2_COMMAND 0xA0
#define PIC2_DATA 0xA1
#define PIC_EOI 0x20

#define ICW1_INIT 0x10
#define ICW1_ICW4 0x01
#define ICW4_8086 0x01

struct idt_entry idt[IDT_ENTRIES];
struct idt_ptr idtp;

extern void load_segment_selectors();
extern void idt_load(uint64_t);

static void idt_set_gate(int num, uint64_t base, uint16_t sel, uint8_t flags) {
    idt[num].base_low = base & 0xFFFF;
    idt[num].base_mid = (base >> 16) & 0xFFFF;
    idt[num].base_high = (base >> 32) & 0xFFFFFFFF;
    idt[num].sel = sel;
    idt[num].always0 = 0;
    idt[num].flags = flags;
    idt[num].reserved = 0;
}

static void pic_remap(int offset1, int offset2) {
    uint8_t a1, a2;

    a1 = inb(PIC1_DATA);
    a2 = inb(PIC2_DATA);

    outb(PIC1_COMMAND, ICW1_INIT | ICW1_ICW4); 
    outb(PIC2_COMMAND, ICW1_INIT | ICW1_ICW4);
    outb(PIC1_DATA, offset1);
    outb(PIC2_DATA, offset2); 
    outb(PIC1_DATA, 4); 
    outb(PIC2_DATA, 2);

    outb(PIC1_DATA, ICW4_8086);
    outb(PIC2_DATA, ICW4_8086);

    outb(PIC1_DATA, a1); // Restore saved masks
    outb(PIC2_DATA, a2);

}

void init_idt() {
    idtp.limit = (sizeof(struct idt_entry) * IDT_ENTRIES) - 1;
    idtp.base = (uint64_t)&idt;

    for (int i = 0; i < IDT_ENTRIES; i++) {
        idt_set_gate(i, 0, 0, 0);
    }

    idt_set_gate(0, (uint64_t)isr0, 0x08, 0x8E); 
    idt_set_gate(1, (uint64_t)isr1, 0x08, 0x8E); 
    idt_set_gate(8, (uint64_t)isr8, 0x08, 0x8E);  
    idt_set_gate(13, (uint64_t)isr13, 0x08, 0x8E);
    idt_set_gate(14, (uint64_t)isr14, 0x08, 0x8E);
    idt_set_gate(32, (uint64_t)isr32, 0x08, 0x8E); 

    idt_load((uint64_t)&idtp);

    pic_remap(0x20, 0x28); 

    load_segment_selectors(); 

    enable_interrupts();

and struct

Code: Select all

#define IDT_ENTRIES 256

struct idt_entry {
    uint16_t base_low;
    uint16_t sel;
    uint8_t always0;
    uint8_t flags;
    uint16_t base_mid;
    uint32_t base_high;
    uint32_t reserved;
} __attribute__((packed));

struct idt_ptr {
    uint16_t limit;
    uint64_t base;
} __attribute__((packed));

Posted: **Sun Oct 13, 2024 11:55 am**

I helped this person on Stackoverflow. After returning from their `kernel_main` function with interrupts on they reached a single `hlt` instruction. With no code after the `hlt`, the CPU ended up calling whatever happened to be in memory and then it faulted. I recommended putting the `hlt` in an infinite loop. That resolved their issue.

Posted: **Sun Oct 13, 2024 1:09 pm**

There is nothing obviously wrong in the code you posted, so we can only guess at the problem. Might I suggest you publish all of your code on something like github? Then we can take a look at all of it. Oh, and GPF is not interrupt 32.

OSDev.org

General Protection Fault after setting up IDT then calling sti.

General Protection Fault after setting up IDT then calling sti.

Re: General Protection Fault after setting up IDT then calling sti.

Re: General Protection Fault after setting up IDT then calling sti.