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os-k/boot/loader/mem/management.inc

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;=----------------------------------------------------------------------------=;
; GNU GPL OS/K ;
; ;
; Desc: Memory management from protected mode ;
; (x86_64 architecture only) ;
; ;
; ;
; Copyright © 2018-2019 The OS/K Team ;
; ;
; This file is part of OS/K. ;
; ;
; OS/K is free software: you can redistribute it and/or modify ;
; it under the terms of the GNU General Public License as published by ;
; the Free Software Foundation, either version 3 of the License, or ;
; (at your option) any later version. ;
; ;
; OS/K is distributed in the hope that it will be useful, ;
; but WITHOUT ANY WARRANTY; without even the implied warranty of ;
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;
; GNU General Public License for more details. ;
; ;
; You should have received a copy of the GNU General Public License ;
; along with OS/K. If not, see <https://www.gnu.org/licenses/>. ;
;=----------------------------------------------------------------------------=;
[BITS 32]
; ---------------------------------------------------------------------------- ;
; Constructor for the page tables in protected mode ;
; ---------------------------------------------------------------------------- ;
Setup_paging:
;; Map the first PML4 entry to PDP table
mov eax, PDP_table
or eax, 0b11 ; present + writable
mov [PML4_table], eax
;; Map the first PDP entry to PD table
mov eax, PD_table
or eax, 0b11 ; present + writable
mov [PDP_table], eax
;; Map each PD entry to a 'huge' 2MiB page
mov ecx, 0 ; counter variable
.map_p2_table:
;; map ecx-th PD entry to a huge page that starts at address 2MiB*ecx
mov eax, 0x200000
mul ecx ; start address of ecx-th page
or eax, 0b10000011 ; present + writable + huge
mov [PD_table + ecx * 8], eax
inc ecx
cmp ecx, 512 ; if counter == 512, the whole PD table is mapped
jne .map_p2_table ; else map the next entry
ret
; ---------------------------------------------------------------------------- ;
; Enable long mode and paging ;
; ---------------------------------------------------------------------------- ;
Go64:
pusha
;; Registering paging
mov eax, PML4_table
mov cr3, eax ; Load PML4 to cr3
mov eax, cr4
or eax, 1 << 5
mov cr4, eax ; Enable PAE
;; Activate long mode
mov ecx, 0xC0000080 ; address of MSR
rdmsr ; read MSR
or eax, 1 << 8 ; LME = 1. (Long Mode Enable)
wrmsr ; write MSR
;; Enable paging
mov eax, cr0
or eax, 1 << 31 ; make MSR bit 31 (PG = Paging) to 1 :
; |1|000000000000000000000000000000
; |
; `------ Paging bit
mov cr0, eax
jmp .end
nop
nop
.end:
popa
ret
; ---------------------------------------------------------------------------- ;
; Checks if Grub has enabled A20 line ;
; ---------------------------------------------------------------------------- ;
CheckA20:
pushad
mov edi,0x112345 ;odd megabyte address.
mov esi,0x012345 ;even megabyte address.
mov [esi],esi ;making sure that both addresses contain diffrent values.
mov [edi],edi ;(if A20 line is cleared the two pointers would point to the address 0x012345 that would contain 0x112345 (edi))
cmpsd ;compare addresses to see if the're equivalent.
popad
jne .A20_on ;if not equivalent , A20 line is set.
jmp .A20_err
.A20_on:
ret
.A20_err:
mov ax, "03" ; ERROR 03 : A20 line failed
jmp Error