# 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))

    /* Framebuffer tag: type=5, prefer RGB 32 bpp */
    .align 8
    .word 5
    .word 0
    .long 32
    .quad 0
    .long 0
    .long 0
    .long 32
    .byte 1
    .byte 0
    .word 0

    .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:

.align 8
mboot_info_ptr:
    .space 8

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

    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:
    /* Load data segment registers with the data descriptor (0x10).
     * In long mode most of these are ignored for access checks, but
     * %ss must be a valid (or null) selector so that iretq from an
     * interrupt can safely reload it. */
    movw $0x10, %ax
    movw %ax, %ds
    movw %ax, %es
    movw %ax, %fs
    movw %ax, %gs
    movw %ax, %ss

    movabsq $stack_top, %rax
    movq %rax, %rsp
    /* Ensure 16-byte alignment for the System V AMD64 ABI. */
    andq $-16, %rsp

    movq mboot_info_ptr, %rdi
    call kernel_main
    cli
1:
    hlt
    jmp 1b

.code64
.global isr_keyboard
.align 16
isr_keyboard:
    /* Save all caller-saved registers used by the SysV AMD64 ABI. */
    pushq %rax
    pushq %rcx
    pushq %rdx
    pushq %rsi
    pushq %rdi
    pushq %r8
    pushq %r9
    pushq %r10
    pushq %r11
    /* On interrupt entry the CPU pushed 5 qwords (40 bytes), and we
     * pushed 9 more (72 bytes) = 112 bytes total. That leaves %rsp
     * misaligned by 8 relative to a 16-byte boundary after the
     * upcoming `call`. Push one dummy qword to realign. */
    subq $8, %rsp
    cld
    call keyboard_handler
    addq $8, %rsp
    popq %r11
    popq %r10
    popq %r9
    popq %r8
    popq %rdi
    popq %rsi
    popq %rdx
    popq %rcx
    popq %rax
    iretq

.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         /* 0x00: null descriptor         */
    .quad 0x00209A0000000000         /* 0x08: 64-bit code, DPL=0      */
    .quad 0x0000920000000000         /* 0x10: data, writable, present */
gdt64_end:
gdt64_pointer:
    .word gdt64_end - gdt64 - 1
    .quad gdt64