enabling paging leads to triple fault

Question

In case this helps somebody in the future:

• check if the global descriptor table is working
• check if the elements of page table entry struct are ordered correctly

This code worked for me:

gdt.s

section .data
gdt:
    .null:
        dq 0
    .code:
        dw 0xFFFF
        dw 0x0000
        db 0x00
        db 0x9A
        db 0xCF
        db 0x00
    .data:
        dw 0xFFFF
        dw 0x0000
        db 0x00
        db 0x92
        db 0xCF
        db 0x00

gdtr:
    dw $-gdt-1
    dd gdt

section .text

global init_global_descriptor_table
init_global_descriptor_table:
    lgdt [gdtr]
    jmp 0x08:.reload_cs

.reload_cs:
    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
    ret

paging.c

enum flags {
    Present = 1 << 0,
    ReadWrite = 1 << 1,
    AccessAll = 1 << 2,
    WriteThroughCashing = 1 << 3,
    DisableCashing = 1 << 4,
    Accessed = 1 << 5,
    Dirty = 1 << 6,     // only for page-table-entries
    MPages = 1 << 7,
    Global = 1 << 8,    // only for page-table-entries
};

struct entry {
    unsigned int flags : 9;
    unsigned int available : 3;
    unsigned int addr : 20;
};

extern void load_paging_directory(int *ptr);

void init_paging() {
    struct entry *dir = (struct entry *)0x00105000;
    struct entry *t1 = (struct entry *)0x00106000;      

    for (int i = 0; i < 1024; i++) {
        dir[i] = (struct entry){0};
        if (i <= 262) t1[i] = (struct entry){Present | ReadWrite, 0, i};
    }

    dir[0] = (struct entry){Present, 0, (int)t1 >> 12};
    load_paging_directory((int *)dir);
}

paging_asm.s

global load_paging_directory
load_paging_directory:
    push ebp,
    mov ebp, esp
    mov eax, [ebp + 8]
    mov cr3, eax
    mov eax, cr0
    or eax, 0x80000001
    mov cr0, eax   
    mov esp, ebp
    pop ebp
    ret

Answer 1

The question has been solved using this struct:

struct entry {
    unsigned int flags : 9;
    unsigned int available : 3;
    unsigned int addr : 20;
};