/*
 * This program is boot to kernel.
 * Change mode to 64bit mode and go to CbC kernel.  */

.file "bootstrap.S"

#include "multiboot2.h"
#include "boot_header.h"

.code32
.text

    /* Align 64 bit boundly. */
    .align 8
multiboot_header:
    .quad MULTIBOOT2_HEADER_MAGIC
    .quad MULTIBOOT_ARCHITECTURE_I386
    .quad multiboot_header_end - multiboot_header
    .quad -(MULTIBOOT2_HEADER_MAGIC + MULTIBOOT_ARCHITECTURE_I386 + (multiboot_header_end - multiboot_header))
    .short MULTIBOOT_HEADER_TAG_END
    .short 0
    .long 8
multiboot_header_end:


/*
 * Prepare for entering 64bit-mode.
 */

.globl _start

_start:
    jmp move_longmode

move_longmode:
    /* load new GDT */
    leal gdt(%ebp), %eax
    movl %eax, gdt+2(%ebp)
    lgdt gdt(%ebp)

    /* 
     * PAE mode ON.
     * Physical Address Extension
     * You can use capacity of memory more than 4GiB on 32 bit CPU.
     */

    movl $0x00000020, %eax
    movl %eax, %cr4

    /* 
     * create 64bit page table
     */
    
    /* 
     * Initialize page tables to 0 
     * 6144 = 512*8*6/4 
     */

    movl $0x01fe9000, %ebx
    leal pgtable(%ebx), %edi
    xorl %eax, %eax
    movl $6144, %ecx
    rep stosl

    /* Build Level 4 */
    leal pgtable + 0(%ebx), %edi
    leal 0x1007(%edi), %eax
    movl %eax, 0(%edi)

    /* Build Level 3 */
    leal pgtable + 0x1000(%ebx), %edi
    leal 0x1007(%edi), %eax
    movl $4, %ecx
1:  movl %eax, 0x00(%edi)
    addl $0x00001000, %eax
    addl $8, %edi
    decl %ecx
    jnz 1b

    /* Build level 2 */
    leal pgtable + 0x2000(%ebx), %edi
    movl $0x00000183, %eax
    movl $2048, %ecx
1:  movl %eax, 0(%edi)
    addl $0x00200000, %eax
    addl $8, %edi
    decl %ecx
    jnz 1b

    /* Enable the boot page talbes */
    leal pgtable(%ebx), %eax
    movl %eax, %cr3
    
    /* Enable Long mode */
    movl $MSR_EFER, %ecx
    rdmsr
    btsl $EFER_LME, %eax 
    wrmsr
    
    pushl $(12*8)
    leal start_kernel(%ebp), %eax
    pushl %eax

    /* activating Long Mode */
    movl %eax, %cr0
    
    jmp start_kernel


/* 
 * jump to kernel.
 * push ebx and eax send argument to kernel.
 */
.code64

start_kernel:
    pushq %rbx
    pushq %rax
    call kmain 

.data
gdt:
    .word gdt_end - gdt
    .long gdt
    .word 0
    .quad 0x0000000000000000  /* NULL descriptor */
    .quad 0x00af9a000000ffff  /* __KERNEL_CS */
    .quad 0x00cf92000000ffff  /* __KERNEL_DS */
    .quad 0x0080890000000000  /* TS descriptor */
    .quad 0x0000000000000000  /* TS continued */
gdt_end:


/*
 * Space for page tables.
 * a : section is allocatable.
 * @nobits : section does not contain data.
 */
.section ".pgtable", "a", @nobits
.balign 4096
pgtable:
    .fill 6*4096, 1, 0