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

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# 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
.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
# Reserve memory for paging structures,
# we will identity map first 4 MiB
# 0 MiB -> 1 MiB: bootloader stuff
# 1 MiB -> 2 MiB: kernel
# 2 MiB -> 3 MiB: kmalloc
# 3 MiB -> 4 MiB: kmalloc_fixed
.align 4096
boot_pml4:
.skip 512 * 8
boot_pdpt1:
.skip 512 * 8
boot_pd1:
.skip 512 * 8
.global g_multiboot_info
g_multiboot_info:
.skip 8
.global g_multiboot_magic
g_multiboot_magic:
.skip 8
.section .text, "a"
boot_gdt:
.quad 0x0000000000000000 # null descriptor
.quad 0x00AF9A000000FFFF # kernel code
.quad 0x00AF92000000FFFF # kernel data
boot_gdtr:
.short . - boot_gdt - 1
.quad 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 g_multiboot_info, %esi
addl $16, %esi
movl (%esi), %esi
movl $1024, %ecx
movl $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:
# identity map first 4 MiB
movl $(0x00000000 + PG_PAGE_SIZE + PG_READ_WRITE + PG_PRESENT), boot_pd1 + 0
movl $(0x00200000 + PG_PAGE_SIZE + PG_READ_WRITE + PG_PRESENT), boot_pd1 + 8
# set pdpte1 and pml4e1
movl $(boot_pd1 + PG_READ_WRITE + PG_PRESENT), boot_pdpt1
movl $(boot_pdpt1 + PG_READ_WRITE + PG_PRESENT), boot_pml4
# 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 $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 $g_boot_stack_top, %esp
movl %eax, g_multiboot_magic
movl %ebx, g_multiboot_info
call copy_kernel_commandline
call check_requirements
call enable_sse
call initialize_paging
# flush gdt and jump to 64 bit
lgdt boot_gdtr
ljmpl $0x08, $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
# 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