banan-os/kernel/arch/x86_64/boot.S

# Declare constants for the multiboot header
.set ALIGN,			1<<0						# align loaded modules on page boundaries
.set MEMINFO,		1<<1						# provide memory map
.set VIDEOINFO,		1<<2						# provide video info
.set MB_FLAGS,		ALIGN | MEMINFO | VIDEOINFO # this is the Multiboot 'flag' field
.set MB_MAGIC,		0x1BADB002					# 'magic number' lets bootloader find the header
.set MB_CHECKSUM,	-(MB_MAGIC + MB_FLAGS)		#checksum of above, to prove we are multiboot

.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

# Multiboot header
.section .multiboot, "aw"
	.align 4
	.long MB_MAGIC
	.long MB_FLAGS
	.long MB_CHECKSUM
	.skip 20

	.long 0
	.long 800
	.long 600
	.long 32

.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_multiboot_info
	g_multiboot_info:
		.skip 8
	.global g_multiboot_magic
	g_multiboot_magic:
		.skip 8

.section .text

# Identity map first GiB
.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: # 1 GiB
	.set i, 0
	.rept 512
		.quad i + (PG_PAGE_SIZE | PG_READ_WRITE | PG_PRESENT)
		.set i, i + 0x00200000
	.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)

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

copy_kernel_commandline:
	pushl %esi
	pushl %edi
	movl V2P(g_multiboot_info), %esi
	addl $16, %esi
	movl (%esi), %esi
	movl $1024, %ecx
	movl $V2P(g_kernel_cmdline), %edi
	rep movsl
	popl %edi
	popl %esi
	ret

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_multiboot_magic)
	movl %ebx, V2P(g_multiboot_info)

	call copy_kernel_commandline
	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:
	addq $KERNEL_OFFSET, g_multiboot_info

	# 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