; Calcite, src/kernel/paging.asm
 ; Copyright 2025 Benji Dial
 ;
 ; This program 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.
 ;
 ; This program 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 this program. If not, see <https://www.gnu.org/licenses/>.


bits 64
default rel

;both defined in paging.c
extern kernel_p4_physical_address
extern init_stack

init_stack_length equ 16384

section .text

;referenced in paging.c
extern invlpg
invlpg:
  invlpg byte [rdi]
  ret

extern switch_to_kernel_page_tables
switch_to_kernel_page_tables:

  ;switch the page table
  mov rax, qword [kernel_p4_physical_address]
  mov cr3, rax

  ;set the stack
  mov rsp, init_stack + init_stack_length

  ;push 0 before jumping to continuation so that if the continuation
  ;does return (which it shouldn't), it returns to null instead of
  ;popping garbage and returning there
  push qword 0
  jmp rdi