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.globl _start
.globl kernel_pml4
.globl kernel_pdpt_0
.globl kernel_pd_0
.globl kernel_pt_0
.globl paging_pt
.globl bootstrap_pt
.extern main
.extern GDT
.section .multiboot
.align 8
# multiboot header
mb_start:
# magic
.long 0xe85250d6
.long 0
.long mb_end - mb_start
.long 0x100000000 - (0xe85250d6 + (mb_end - mb_start))
# null
.short 0
.short 0
.long 8
mb_end:
.section .bss
# kernel page tables
.align 4096
kernel_pml4: # reserve memory for initial 512 pml4 entires
.skip 4096
kernel_pdpt_0: # reserve memory for initial 512 pdpt entires
.skip 4096
kernel_pd_0: # reserve memory for initial 512 pd entries
.skip 4096
kernel_pt_0: # reserve memory for initial 512 pt entries
.skip 4096
paging_pt: # reserve pages for pager mappings
.skip 4096
bootstrap_pt: # reserve pages to bootstrap pager
.skip 4096
# kernel stack
.align 16
kern_stack_start:
.skip 8192
kern_stack_end:
.section .data
.align 16
# access bits
.set PRESENT, 1 << 7
.set NOT_SYS, 1 << 4
.set EXEC, 1 << 3
.set DC, 1 << 2
.set RW, 1 << 1
.set ACCESSED, 1 << 0
# privlage level (access bit)
.set RING0, 0 << 5
.set RING1, 1 << 5
.set RING2, 2 << 5
.set RING3, 3 << 5
# flag bits
.set GRAN_4K, 1 << 7
.set SZ_32, 1 << 6
.set LONG_MODE, 1 << 5
# kernel gdt (long mode)
GDT:
# Null Segment (0x00)
.equ GDT.Null, . - GDT
.quad 0
# Kernel Code segment (0x08)
.equ GDT.Code, . - GDT
.long 0xFFFF
.byte 0
.byte PRESENT | NOT_SYS | EXEC | RW | RING0
.byte GRAN_4K | LONG_MODE | 0xF
.byte 0
# Kernel Data segment (0x10)
.equ GDT.Data, . - GDT
.long 0xFFFF
.byte 0
.byte PRESENT | NOT_SYS | RW | RING0
.byte GRAN_4K | SZ_32 | 0xF
.byte 0
# User Code Segment (0x18)
.equ GDT.UserCode, . - GDT
.long 0xFFFF
.byte 0
.byte PRESENT | NOT_SYS | EXEC | RW | RING3
.byte GRAN_4K | LONG_MODE | 0xF
.byte 0
# User Data Segment (0x20)
.equ GDT.UserData, . - GDT
.long 0xFFFF
.byte 0
.byte PRESENT | NOT_SYS | RW | RING3
.byte GRAN_4K | SZ_32 | 0xF
.byte 0
# TSS segment (0x28)
.equ GDT.TSS, . - GDT
.quad 0 # to be modified in kernel
# GDT Pointer
.equ GDT.Pointer, .
.word . - GDT - 1
.quad GDT
.section .text
.code32
_start:
# enable interrupts
cli
# setup stack
movl $kern_stack_end, %esp
movl $kern_stack_end, %ebp
# save multiboot (if using multiboot)
pushl $0
push %ebx
pushl $0
push %eax
# zero out kernel page table
movl $0x1000, %edi # pml4 located at 0x1000
movl %edi, %cr3
xorl %eax, %eax
movl $4096, %ecx # zero 4096 pages
rep stosl
movl %cr3, %edi
# identity map kernel
movl $kernel_pdpt_0 + 3, (%edi) # Set the uint32_t at the desination index to 0x2003.
movl $kernel_pdpt_0, %edi # Add 0x1000 to the desination index.
movl $kernel_pd_0 + 3, (%edi) # Set the uint32_t at the desination index to 0x3003.
movl $kernel_pd_0, %edi # Add 0x1000 to the desination index.
movl $kernel_pt_0 + 3, (%edi) # Set the uint32_t at the desination index to 0x4003.
movl $kernel_pt_0, %edi # Add 0x1000 to the desination index.
movl $0x03, %ebx # Entry value to set
movl $512, %ecx # Loop count
_start.SetEntry:
# set entires in mapping
movl %ebx, (%edi) # Set the uint32_t at the desination index to the B-register
addl $0x1000, %ebx # Add 0x1000 to the B-register
addl $8, %edi # Add eight to the desination index
loop _start.SetEntry
# enable page address extension
movl %cr4, %eax
orl $(1 << 5), %eax
movl %eax, %cr4
# enable long mode
movl $0xC0000080, %ecx
rdmsr
orl $(1 << 8), %eax
wrmsr
# enable paging
movl %cr0, %eax
orl $(1 << 31), %eax
movl %eax, %cr0
# load gdt
lgdt GDT.Pointer
ljmp $GDT.Code, $code64
.code64
code64:
movw $GDT.Data, %dx # set segment registers
movw %dx, %ds
movw %dx, %ss
xorq %rbp, %rbp # set ebp to 0 so we know where to end stack traces
pop %rdi # pop possible multiboot header
pop %rsi
call main
cli
halt:
hlt
jmp halt
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