.set PG_PRESENT,	1<<0
.set PG_READ_WRITE,	1<<1
.set PG_PAGE_SIZE,	1<<7

#define KERNEL_OFFSET 0xFFFFFFFF80000000
#define V2P(vaddr) ((vaddr) - KERNEL_OFFSET)

.code32

# multiboot2 header
.section .multiboot, "aw"
multiboot2_start:
	.align 8
	.long 0xE85250D6
	.long 0
	.long multiboot2_end - multiboot2_start
	.long -(0xE85250D6 + (multiboot2_end - multiboot2_start))

	# framebuffer tag
	.align 8
	.short 5
	.short 0
	.long 20
	.long 1920
	.long 1080
	.long 32

	# legacy start
	.align 8
	.short 3
	.short 0
	.long 12
	.long V2P(_start)

	.align 8
	.short 0
	.short 0
	.long 8
multiboot2_end:

.section .bss, "aw", @nobits
 	# Create stack
	.global g_boot_stack_bottom
	g_boot_stack_bottom:
		.skip 16384
	.global g_boot_stack_top
	g_boot_stack_top:

	.global g_kernel_cmdline
	g_kernel_cmdline:
		.skip 4096

	.global g_multiboot2_info
	g_multiboot2_info:
		.skip 8
	.global g_multiboot2_magic
	g_multiboot2_magic:
		.skip 8

.section .data

# Map first GiB to 0x00000000 and 0xFFFFFFFF80000000
.align 4096
boot_pml4:
	.quad V2P(boot_pdpt_lo) + (PG_READ_WRITE | PG_PRESENT)
	.rept 510
		.quad 0
	.endr
	.quad V2P(boot_pdpt_hi) + (PG_READ_WRITE | PG_PRESENT)
boot_pdpt_lo:
	.quad V2P(boot_pd) + (PG_READ_WRITE | PG_PRESENT)
	.rept 511
		.quad 0
	.endr
boot_pdpt_hi:
	.rept 510
		.quad 0
	.endr
	.quad V2P(boot_pd) + (PG_READ_WRITE | PG_PRESENT)
	.quad 0
boot_pd:
	.set i, 0
	.rept 512
		.quad i + (PG_PAGE_SIZE | PG_READ_WRITE | PG_PRESENT)
		.set i, i + 0x200000
	.endr

boot_gdt:
	.quad 0x0000000000000000 # null descriptor
	.quad 0x00AF9A000000FFFF # kernel code
	.quad 0x00AF92000000FFFF # kernel data
boot_gdtr:
	.short . - boot_gdt - 1
	.quad V2P(boot_gdt)

.section .text

has_cpuid:
	pushfl
	pushfl
	xorl $0x00200000, (%esp)
	popfl
	pushfl
	popl %eax
	xorl (%esp), %eax
	popfl
	testl $0x00200000, %eax
	ret

is_64_bit:
	movl $0x80000000, %eax
	cpuid
	cmpl $0x80000001, %eax
	jl .no_extension
	movl $0x80000001, %eax
	cpuid
	testl $(1 << 29), %edx
	ret
.no_extension:
	cmpl %eax, %eax
	ret

check_requirements:
	call has_cpuid
	jz .exit
	call is_64_bit
	jz .exit
	ret
.exit:
	jmp system_halt

enable_sse:
	movl %cr0, %eax
	andw $0xFFFB, %ax
	orw $0x0002, %ax
	movl %eax, %cr0
	movl %cr4, %eax
	orw $0x0600, %ax
	movl %eax, %cr4
	ret

initialize_paging:
	# enable PAE
	movl %cr4, %ecx
	orl $0x20, %ecx
	movl %ecx, %cr4

	# set long mode enable bit
	movl $0x100, %eax
	movl $0x000, %edx
	movl $0xC0000080, %ecx
	wrmsr

	# set address of paging structures
	movl $V2P(boot_pml4), %ecx
	movl %ecx, %cr3

	# enable paging
	movl %cr0, %ecx
	orl $0x80000000, %ecx
	movl %ecx, %cr0

	ret

.global _start
.type _start, @function
_start:
	# Initialize stack and multiboot info
	movl $V2P(g_boot_stack_top), %esp
	movl %eax, V2P(g_multiboot2_magic)
	movl %ebx, V2P(g_multiboot2_info)

	call check_requirements
	call enable_sse

	call initialize_paging

	# flush gdt and jump to 64 bit
	lgdt V2P(boot_gdtr)
	ljmpl $0x08, $V2P(long_mode)

.code64
long_mode:
	movw $0x10, %ax
	movw %ax, %ss

	# clear segment registers (unused in x86_64?)
	movw $0x00, %ax
	movw %ax, %ds
	movw %ax, %es
	movw %ax, %fs
	movw %ax, %gs

	# jump to higher half
	movq $g_boot_stack_top, %rsp
	movabsq $higher_half, %rcx
	jmp *%rcx

higher_half:
	# call global constuctors
	call _init

	# call to the kernel itself (clear ebp for stacktrace)
	xorq %rbp, %rbp
	call kernel_main

	# call global destructors
	call _fini

system_halt:
	xchgw %bx, %bx
	cli
1:	hlt
	jmp 1b