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.global _start
.extern long_mode_start
.section .text
.code32
// Entry point. It puts the machine into a consistent state and starts long mode.
_start:
mov $0x80000, %esp // Setup the stack.
push %ebx // Pass multiboot info structure.
push %eax // Pass multiboot magic code.
call check_multiboot
call check_cpuid
call check_long_mode
//call setup_page_tables
//call enable_paging
//lgdt [gdt64.pointer]
//jmp gdt64.code_segment:long_mode_start
call halt
halt:
hlt
check_multiboot:
cmp $0x36d76289, %eax
jne .no_multiboot
ret
.no_multiboot:
mov 'M', %al
jmp error
check_cpuid:
pushfd
pop %eax
mov %eax, %ecx
xor $(1 << 21), %eax
push %eax
popfd
pushfd
pop %eax
push %ecx
popfd
cmp %eax, %ecx
je .no_cpuid
ret
.no_cpuid:
mov 'C', %al
jmp error
check_long_mode:
mov $0x80000000, %eax
cpuid
cmp $0x80000001, %eax
jb .no_long_mode
mov $0x80000001, %eax
cpuid
test $(1 << 29), %edx
jz .no_long_mode
ret
.no_long_mode:
mov 'L', %al
jmp error
//setup_page_tables:
// mov eax, page_table_l3
// or eax, 0b11 ; present, writable
// mov [page_table_l4], eax
//
// mov eax, page_table_l2
// or eax, 0b11 ; present, writable
// mov [page_table_l3], eax
//
// mov ecx, 0 ; counter
//.loop:
//
// mov eax, 0x200000 ; 2MiB
// mul ecx
// or eax, 0b10000011 ; present, writable, huge page
// mov [page_table_l2 + ecx * 8], eax
//
// inc ecx ; increment counter
// cmp ecx, 512 ; checks if the whole table is mapped
// jne .loop ; if not, continue
//
// ret
//
//enable_paging:
// ; pass page table location to cpu
// mov eax, page_table_l4
// mov cr3, eax
//
// ; enable PAE
// mov eax, cr4
// or eax, 1 << 5
// mov cr4, eax
//
// ; enable long mode
// mov ecx, 0xC0000080
// rdmsr
// or eax, 1 << 8
// wrmsr
//
// ; enable paging
// mov eax, cr0
// or eax, 1 << 31
// mov cr0, eax
//
// ret
error:
// // print "ERR: X" where X is the error code
movl $0x4f524f45, 0xb8000
// mov dword [0xb8004], 0x4f3a4f52
// mov dword [0xb8008], 0x4f204f20
// mov byte [0xb800a], al
hlt
//section .bss
//align 4096
//page_table_l4:
// resb 4096
//page_table_l3:
// resb 4096
//page_table_l2:
// resb 4096
//stack_bottom:
// resb 4096 * 4
//stack_top:
//
//section .rodata
//gdt64:
// dq 0 ; zero entry
//.code_segment: equ $ - gdt64
// dq (1 << 43) | (1 << 44) | (1 << 47) | (1 << 53) ; code segment
//.pointer:
// dw $ - gdt64 - 1 ; length
// dq gdt64 ; address
//
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