OSDev

desc CETSS,TSS_SIZE-1,DF_TSS32A

desc 0,0FFFFFh,DF_CODE32

desc KCODE,sys_service,DF_TRAP32+DF_APL

desc CETSS_SEL,?,DF_TASK32

; This program is free software. It comes without any warranty, to
; the extent permitted by applicable law. You can redistribute it
; and/or modify it under the terms of the Do What The Fuck You Want
; To Public License, Version 2, as published by Sam Hocevar. See
; http://sam.zoy.org/wtfpl/COPYING for more details.

;--------------------------------------------------------------
;-----------------------README---------------------------------
;
;Use GDT_descr (base, limit, access, options) to create a GDT descriptor.
;
;Use GDT_descr (base, limit, access options, options) to create a IDT descriptor (gate).
;
;Use EnterPM (GDT,IDT,entery segment:entery point) to enter Protected Mode.
;
;Use EnterURM to get an unreal segment inside fs.
;
;(C) 418ImATeapot
;Sorry for my English!
;--------------------------------------------------------------


if ~(defined INC_protected)
INC_protected equ
include 'PIC.inc'
;protected.inc

;------------------------------------------------
;Privilegion levels
PL_CORE equ 00000000b
PL_DRV0 equ 00100000b
PL_DRV1 equ 01000000b
PL_USER equ 01100000b
;------------------------------------------------
;macro for a usual GDT element
 macro GDT_descr base,limit,access,options
  {
   dw limit and 000FFFFh  ;First 16 bits of the limit
   dw base and 0000FFFFh  ;First 16 bits of the base
   db (base and 00FF0000h) /10000h ;Bits 16:23 of the base
   db access ;access bits
   db (limit and 00F0000h)/10000h + options ;Bites 16:23 of the limit + options
   db (base and 0FF000000h)/1000000h ;Bits 23:31 of the base
  }

    ;GDT segment options
      GDT_OPT_AVL equ 10h;This option is at your option :-)
      GDT_OPT_I_WANT_TO_HANG_MY_COMPUTER equ 20h; Bit 5 is reserved and must be 0 in IA-32.
      GDT_OPT_32 equ 40h;If this option is on, the segment will use 32-bit code as default.
      GDT_OPT_PG equ 80h;Page granularity.

    ;GDT access options
      GDT_A_PRESENTED equ 80h
      ;Flags for nonsystem segments
       GDT_A_NONSYSTEM equ 10h;Must be on!!!
       GDT_ANS_AC equ 01h;This flag may be changed CPU as "durty" sign. Just don't set it.
       GDT_ANS_RW equ 02h;In code segments this flag will enabled reading, in data segments this flag will enabled writing.
       GTD_ANS_DC equ 04h;In code segments this flag will let low-privilegged code run it, in data segments this flag will change grow direction.
       GDT_ANS_EXEC equ 08h;Code segment.
      ;Types of system segments
       GDT_SYS_FREETSS16 equ 01
       GDT_SYS_LDT equ 02
       GDT_SYS_BISSYTSS16 equ 03
       GDT_SYS_CALLGATE16 equ 04
       GDT_SYS_TASKGATE equ 05
       GDT_SYS_INTGATE16 equ 06
       GDT_SYS_TRAPGATE16 equ 07
       GDT_SYS_FREETSS32 equ 09
       GDT_SYS_BISSYTSS32 equ 11
       GDT_SYS_CALLGATE32 equ 12
       GDT_SYS_INTGATE32 equ 14
       GDT_SYS_TRAPGATE32 equ 15

;------------------------------------------------
;macro for a IDT element

    ;IDT descriptor options
     IDT_PRESENTED equ 10000000b
     IDT_STORAGE_SEGMENT equ 00010000b;(Me.RTFM)
    ;IDT TYPES
     IDT_TASK  equ 0x5
     IDT_INTG16  equ 0x6
     IDT_TRAP16  equ 0x7
     IDT_INTG32  equ 0xE
     IDT_TRAPG32  equ 0xF

 macro IDT_descr segment,offset,options
  {
   dw offset and 000FFFFh  ;First 16 bits of offset
   dw segment ;Segment
   db 0
   db options ;Options
   dw (offset and 0FFFF0000h) /10000h
  }
;------------------------------------------------
;protected mode entery

 macro EnterPM GDT,IDT, start_seg, PMstart;Entering fully protected mode.
  {
   lgdt [GDT];Loading GDT
   lidt [IDT]

   ;Setup bit 0 in cr0 (X-TIME!!!)
   mov eax,cr0
   or al,1
   mov cr0,eax

   ;Jumping to the PM-code segment.
   db 66h
   use32
   jmp start_seg:PMstart
  }

 macro EnterURM;Entering UnReal mode.
  {

  MaskNMI;Masking NMI

   jmp @f
   ;URM GDT
    .gdtr: dw 16
      dd .gdt
    .gdt:
     dd 0,0;Z-segment
     GDT_descr 0,0FFFFFFh,GDT_A_PRESENTED or GDT_A_NONSYSTEM or  GDT_ANS_RW , GDT_OPT_PG;Data segment
   @@:

   ;Computing GDT adress
   push cs
   pop ds
   xor eax,eax
   mov ax,cs
   shl eax,4
   add dword [.gdtr+2],eax

   ;X-TIME
   lgdt [.gdtr]
   mov eax,cr0
   or al,1
   mov cr0,eax

   ;Loading URM segment
   mov ax,8
   mov fs,ax

   ;Going back to real mode, but with a change of dark of FS segment.
   mov eax,cr0
   and al,0FFh
   mov cr0,eax

   ;Unmasking NMI
   UMaskNMI
;   hlt
  }

end if