# Multiboot2 header and x86_64 long-mode bootstrap

.section .multiboot2, "a"
.align 8
multiboot_header:
    .long 0xe85250d6
    .long 0
    .long multiboot_header_end - multiboot_header
    .long -(0xe85250d6 + 0 + (multiboot_header_end - multiboot_header))

    .align 8
    .word 0
    .word 0
    .long 8
multiboot_header_end:

.section .bss, "aw", @nobits
.align 4096
pml4:
    .space 4096
pdpt:
    .space 4096
pd:
    .space 4096

.align 16
stack_bottom:
    .space 16384
stack_top:

.section .text
.code32
.global _start
.type _start, @function
_start:
    movl $stack_top, %esp

    cld
    movl $__bss_start, %edi
    movl $__bss_end, %ecx
    subl %edi, %ecx
    xorl %eax, %eax
    rep stosb

    movl $pdpt, %eax
    orl $0x03, %eax
    movl %eax, pml4

    movl $pd, %eax
    orl $0x03, %eax
    movl %eax, pdpt

    movl $0x00000083, %eax
    movl $pd, %edi
    movl $512, %ecx
1:
    movl %eax, (%edi)
    addl $0x200000, %eax
    addl $8, %edi
    loop 1b

    movl $pml4, %eax
    movl %eax, %cr3

    movl %cr4, %eax
    orl $0x20, %eax
    movl %eax, %cr4

    movl $0xC0000080, %ecx
    rdmsr
    orl $0x100, %eax
    wrmsr

    movl %cr0, %eax
    orl $0x80000000, %eax
    movl %eax, %cr0

    lgdt gdt64_pointer
    ljmp $0x08, $long_mode_start

.code64
long_mode_start:
    movabsq $stack_top, %rax
    movq %rax, %rsp

    movabsq $__bss_start, %rdi
    movabsq $__bss_end, %rcx
    subq %rdi, %rcx
    xorq %rax, %rax
    rep stosb

    call kernel_main
    cli
1:
    hlt
    jmp 1b

.section .note.Xen, "a", @note
.align 4
.long 4
.long 4
.long 18
.asciz "Xen"
.align 4
.long _start

.section .rodata
.align 8
gdt64:
    .quad 0x0000000000000000
    .quad 0x00209A0000000000
gdt64_pointer:
    .word gdt64_pointer - gdt64 - 1
    .quad gdt64