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;------------------------------------------------------------------------------
; @file
; Transition from 16 bit real mode into 32 bit flat protected mode
;
; Copyright (c) 2008 - 2022, Intel Corporation. All rights reserved.<BR>
; SPDX-License-Identifier: BSD-2-Clause-Patent
;
;------------------------------------------------------------------------------
%define SEC_DEFAULT_CR0 0x40000023
%define SEC_DEFAULT_CR4 0x640
BITS 16
;
; Modified: EAX, EBX
;
; @param[out] DS Selector allowing flat access to all addresses
; @param[out] ES Selector allowing flat access to all addresses
; @param[out] FS Selector allowing flat access to all addresses
; @param[out] GS Selector allowing flat access to all addresses
; @param[out] SS Selector allowing flat access to all addresses
;
TransitionFromReal16To32BitFlat:
debugShowPostCode POSTCODE_16BIT_MODE
cli
mov bx, 0xf000
mov ds, bx
mov bx, ADDR16_OF(gdtr)
o32 lgdt [cs:bx]
mov eax, SEC_DEFAULT_CR0
mov cr0, eax
jmp LINEAR_CODE_SEL:dword ADDR_OF(jumpTo32BitAndLandHere)
BITS 32
jumpTo32BitAndLandHere:
mov eax, SEC_DEFAULT_CR4
mov cr4, eax
debugShowPostCode POSTCODE_32BIT_MODE
mov ax, LINEAR_SEL
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
OneTimeCallRet TransitionFromReal16To32BitFlat
ALIGN 2
gdtr:
dw GDT_END - GDT_BASE - 1 ; GDT limit
dd ADDR_OF(GDT_BASE)
ALIGN 16
;
; Macros for GDT entries
;
%define PRESENT_FLAG(p) (p << 7)
%define DPL(dpl) (dpl << 5)
%define SYSTEM_FLAG(s) (s << 4)
%define DESC_TYPE(t) (t)
; Type: data, expand-up, writable, accessed
%define DATA32_TYPE 3
; Type: execute, readable, expand-up, accessed
%define CODE32_TYPE 0xb
; Type: execute, readable, expand-up, accessed
%define CODE64_TYPE 0xb
%define GRANULARITY_FLAG(g) (g << 7)
%define DEFAULT_SIZE32(d) (d << 6)
%define CODE64_FLAG(l) (l << 5)
%define UPPER_LIMIT(l) (l)
;
; The Global Descriptor Table (GDT)
;
GDT_BASE:
; null descriptor
NULL_SEL equ $-GDT_BASE ; Selector [0x0]
DW 0 ; limit 15:0
DW 0 ; base 15:0
DB 0 ; base 23:16
DB 0 ; sys flag, dpl, type
DB 0 ; limit 19:16, flags
DB 0 ; base 31:24
; Spare segment descriptor
SPARE1_SEL equ $-GDT_BASE ; Selector [0x8]
DW 0 ; limit 15:0
DW 0 ; base 15:0
DB 0 ; base 23:16
DB 0 ; sys flag, dpl, type
DB 0 ; limit 19:16, flags
DB 0 ; base 31:24
; linear code segment descriptor
LINEAR_CODE_SEL equ $-GDT_BASE ; Selector [0x10]
DW 0xffff ; limit 15:0
DW 0 ; base 15:0
DB 0 ; base 23:16
DB PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(CODE32_TYPE) ; 09Bh
DB GRANULARITY_FLAG(1)|DEFAULT_SIZE32(1)|CODE64_FLAG(0)|UPPER_LIMIT(0xf) ; 0CFh
DB 0 ; base 31:24
; linear data segment descriptor
LINEAR_SEL equ $-GDT_BASE ; Selector [0x18]
DW 0xffff ; limit 15:0
DW 0 ; base 15:0
DB 0 ; base 23:16
DB PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(DATA32_TYPE) ; 093h
DB GRANULARITY_FLAG(1)|DEFAULT_SIZE32(1)|CODE64_FLAG(0)|UPPER_LIMIT(0xf) ; 0CFh
DB 0 ; base 31:24
; Spare segment descriptor
SPARE2_SEL equ $-GDT_BASE ; Selector [0x20]
DW 0 ; limit 15:0
DW 0 ; base 15:0
DB 0 ; base 23:16
DB 0 ; sys flag, dpl, type
DB 0 ; limit 19:16, flags
DB 0 ; base 31:24
; linear code (16-bit) segment descriptor
LINEAR_CODE16_SEL equ $-GDT_BASE ; Selector [0x28]
DW 0xffff ; limit 15:0
DW 0 ; base 15:0
DB 0 ; base 23:16
DB PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(CODE32_TYPE) ; 09Bh
DB GRANULARITY_FLAG(1)|DEFAULT_SIZE32(0)|CODE64_FLAG(0)|UPPER_LIMIT(0xf) ; 08Fh
DB 0 ; base 31:24
; linear data (16-bit) segment descriptor
LINEAR_DATA16_SEL equ $-GDT_BASE ; Selector [0x30]
DW 0xffff ; limit 15:0
DW 0 ; base 15:0
DB 0 ; base 23:16
DB PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(DATA32_TYPE) ; 093h
DB 0
DB 0 ; base 31:24
; linear code (64-bit) segment descriptor
LINEAR_CODE64_SEL equ $-GDT_BASE ; Selector [0x38]
DW 0xffff ; limit 15:0
DW 0 ; base 15:0
DB 0 ; base 23:16
DB PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(CODE64_TYPE) ; 09Bh
DB GRANULARITY_FLAG(1)|DEFAULT_SIZE32(0)|CODE64_FLAG(1)|UPPER_LIMIT(0xf) ; 0AFh
DB 0 ; base 31:24
GDT_END:
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