148 lines
4.5 KiB
NASM
148 lines
4.5 KiB
NASM
global start
|
|
extern x86_start
|
|
|
|
section .text
|
|
bits 32
|
|
start:
|
|
; our stack, located in bss, linker.ld puts bss at the end of the binary
|
|
mov esp, stack_top
|
|
; multiboot information pointer
|
|
push ebx
|
|
|
|
call check_multiboot
|
|
|
|
call set_up_page_tables
|
|
call enable_pse
|
|
call enable_paging
|
|
|
|
; load the new gdt
|
|
lgdt [GDTR.ptr]
|
|
|
|
jmp GDTR.gdt_cs:x86_start
|
|
|
|
check_multiboot:
|
|
cmp eax, 0x36d76289
|
|
jne .no_multiboot
|
|
ret
|
|
.no_multiboot:
|
|
mov al, "0"
|
|
jmp error
|
|
|
|
set_up_page_tables:
|
|
; map P2 table recursively
|
|
mov eax, p2_table
|
|
or eax, 0b11 ; present + writable
|
|
mov [p2_table + 1023 * 4], eax
|
|
|
|
; map each P2 entry to a huge 4MiB page
|
|
mov ecx, 0 ; counter variable
|
|
|
|
.map_p2_table:
|
|
; map ecx-th P2 entry to a huge page that starts at address 2MiB*ecx
|
|
mov eax, 0x400000 ; 4MiB
|
|
mul ecx ; start address of ecx-th page
|
|
or eax, 0b10000011 ; huge + present + writable
|
|
mov [p2_table + ecx * 4], eax ; map ecx-th entry
|
|
|
|
inc ecx ; increase counter
|
|
cmp ecx, 20 ; if counter == 1023, the whole P2 table is mapped
|
|
jne .map_p2_table ; else map the next entry
|
|
|
|
ret
|
|
|
|
; PSE (Page Size Extension) allows huge pages to exist
|
|
enable_pse:
|
|
; enable PSE in the cr4 register
|
|
mov eax, cr4
|
|
or eax, 1 << 4
|
|
mov cr4, eax
|
|
|
|
ret
|
|
|
|
enable_paging:
|
|
; load P2 to cr3 register (cpu uses this to access the P2 table)
|
|
mov eax, p2_table
|
|
mov cr3, eax
|
|
|
|
; enable paging in the cr0 register
|
|
mov eax, cr0
|
|
or eax, 1 << 31
|
|
mov cr0, eax
|
|
|
|
ret
|
|
|
|
error:
|
|
mov dword [0xb8000], 0x4f524f45
|
|
mov dword [0xb8004], 0x4f3a4f52
|
|
mov dword [0xb8008], 0x4f204f20
|
|
mov byte [0xb800a], al
|
|
cli
|
|
HALT:
|
|
hlt
|
|
jmp HALT
|
|
|
|
section .bss
|
|
align 4096
|
|
p2_table:
|
|
resb 4096
|
|
stack_bottom:
|
|
resb 4096 * 8
|
|
stack_top:
|
|
|
|
section .gdt
|
|
GDTR:
|
|
; http://tuttlem.github.io/2014/07/11/a-gdt-primer.html
|
|
.gdt_top:
|
|
DD 0, 0
|
|
.gdt_cs: equ $ - .gdt_top; the code segment Aka KERNEL CODE
|
|
DW 0xffff ; Limit ( bits 0 -15 )
|
|
DW 0x0 ; Base ( bits 0 -15 )
|
|
DB 0x0 ; Base ( bits 16 -23 )
|
|
DB 0x9A ; [ Access Flags: 0x9A=10011010b = (present)|(Privilege Ring 0=00b)|(1)|(code => 1)|(expand down => 0)|(readable)|(0) ]
|
|
DB 0xCF ; [ Flags: C=1100b = (granularity)|(32bit)|(!64bit)|(0) ] / [ Limits: (bits 16-19): F=1111b ]
|
|
DB 0x0 ; Base ( bits 24 -31 )
|
|
|
|
.gdt_ds: equ $ - .gdt_top; the data segment Aka KERNEL DATA
|
|
DW 0xffff ; Limit ( bits 0 -15 )
|
|
DW 0x0 ; Base ( bits 0 -15 )
|
|
DB 0x0 ; Base ( bits 16 -23 )
|
|
DB 0x92 ; [ Access Flags: 0x92=10010010b = (present)|(Privilege Ring 0=00b)|(1)|(data => 0)|(expand down => 0)|(readable)|(0) ]
|
|
DB 0xCF ; [ Flags: C=1100b = (granularity)|(32bit)|(!64bit)|(0) ] / [ Limits: (bits 16-19): F=1111b ]
|
|
DB 0x0 ; Base ( bits 24 -31 )
|
|
|
|
.gdt_ss: equ $ - .gdt_top; the stack segment Aka KERNEL STACK
|
|
DW 0x0 ; Limit ( bits 0 -15 )
|
|
DW 0x0 ; Base ( bits 0 -15 )
|
|
DB 0x0 ; Base ( bits 16 -23 )
|
|
DB 0x96 ; [ Access Flags: 0x96=10010110b = (present)|(Privilege Ring 0=00b)|(1)|(data => 0)|(expand up => 1)|(readable)|(0) ]
|
|
DB 0xCF ; [ Flags: C=1100b = (granularity)|(32bit)|(!64bit)|(0) ] / [ Limits: (bits 16-19): F=1111b ]
|
|
DB 0x0 ; Base ( bits 24 -31 )
|
|
|
|
.gdt_es: equ $ - .gdt_top; the extra segment Aka USER CODE
|
|
DW 0xffff ; Limit ( bits 0 -15 )
|
|
DW 0x0 ; Base ( bits 0 -15 )
|
|
DB 0x0 ; Base ( bits 16 -23 )
|
|
DB 0xFE ; [ Access Flags: 0x9A=11111110b = (present)|(Privilege Ring 3=11b)|(1)|(code => 1)|(expand up => 1)|(readable)|(0) ]
|
|
DB 0xCF ; [ Flags: C=1100b = (granularity)|(32bit)|(!64bit)|(0) ] / [ Limits: (bits 16-19): F=1111b ]
|
|
DB 0x0 ; Base ( bits 24 -31 )
|
|
|
|
.gdt_fs: equ $ - .gdt_top; the other segment Aka USER DATA
|
|
DW 0xffff ; Limit ( bits 0 -15 )
|
|
DW 0x0 ; Base ( bits 0 -15 )
|
|
DB 0x0 ; Base ( bits 16 -23 )
|
|
DB 0xF2 ; [ Access Flags: 0x9A=11110010b = (present)|(Privilege Ring 3=11b)|(1)|(data => 0)|(expand down => 0)|(readable)|(0) ]
|
|
DB 0xCF ; [ Flags: C=1100b = (granularity)|(32bit)|(!64bit)|(0) ] / [ Limits: (bits 16-19): F=1111b ]
|
|
DB 0x0 ; Base ( bits 24 -31 )
|
|
|
|
.gdt_gs: equ $ - .gdt_top; the other segment Aka USER STACK
|
|
DW 0x0 ; Limit ( bits 0 -15 )
|
|
DW 0x0 ; Base ( bits 0 -15 )
|
|
DB 0x0 ; Base ( bits 16 -23 )
|
|
DB 0x00 ; [ Access Flags: 0x9A=11110110b = (present)|(Privilege Ring 3=11b)|(1)|(data => 0)|(expand up => 1)|(readable)|(0) ]
|
|
DB 0x00 ; [ Flags: C=1100b = (granularity)|(32bit)|(!64bit)|(0) ] / [ Limits: (bits 16-19): F=1111b ]
|
|
DB 0x0 ; Base ( bits 24 -31 )
|
|
|
|
.gdt_bottom:
|
|
.ptr:
|
|
DW .gdt_bottom - .gdt_top - 1 ; length of the structure minus 1
|
|
DD .gdt_top ; pointer to top of gdt
|