Fixed GDT load issue in some cases after a reset. Only CS should be used to access...

[mirror_edk2.git] / OvmfPkg / ResetVector / Ia16 / 16RealTo32Flat.asm

;------------------------------------------------------------------------------\r
; @file\r
; Transition from 16 bit real mode into 32 bit flat protected mode\r
;\r
; Copyright (c) 2008 - 2010, Intel Corporation\r
; All rights reserved. This program and the accompanying materials\r
; are licensed and made available under the terms and conditions of the BSD License\r
; which accompanies this distribution.  The full text of the license may be found at\r
; http://opensource.org/licenses/bsd-license.php\r
;\r
; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
;\r
;------------------------------------------------------------------------------\r
\r
%define SEC_DEFAULT_CR0  0x40000023\r
%define SEC_DEFAULT_CR4  0x640\r
\r
BITS    16\r
\r
;\r
; Modified:  EAX, EBX\r
;\r
TransitionFromReal16To32BitFlat:\r
\r
    debugShowPostCode POSTCODE_16BIT_MODE\r
\r
    cli\r
\r
    mov     bx, 0xf000\r
    mov     ds, bx\r
\r
    mov     bx, ADDR16_OF(gdtr)\r
\r
o32 lgdt    [cs:bx]\r
\r
    mov     eax, SEC_DEFAULT_CR0\r
    mov     cr0, eax\r
\r
    jmp     LINEAR_CODE_SEL:dword ADDR_OF(jumpTo32BitAndLandHere)\r
BITS    32\r
jumpTo32BitAndLandHere:\r
\r
    mov     eax, SEC_DEFAULT_CR4\r
    mov     cr4, eax\r
\r
    debugShowPostCode POSTCODE_32BIT_MODE\r
\r
    mov     ax, LINEAR_SEL\r
    mov     ds, ax\r
    mov     es, ax\r
    mov     fs, ax\r
    mov     gs, ax\r
    mov     ss, ax\r
\r
    OneTimeCallRet TransitionFromReal16To32BitFlat\r
\r
ALIGN   2\r
\r
gdtr:\r
    dw      GDT_END - GDT_BASE - 1   ; GDT limit\r
    dd      ADDR_OF(GDT_BASE)\r
\r
ALIGN   16\r
\r
;\r
; Macros for GDT entries\r
;\r
\r
%define  PRESENT_FLAG(p) (p << 7)\r
%define  DPL(dpl) (dpl << 5)\r
%define  SYSTEM_FLAG(s) (s << 4)\r
%define  DESC_TYPE(t) (t)\r
\r
; Type: data, expand-up, writable, accessed\r
%define  DATA32_TYPE 3\r
\r
; Type: execute, readable, expand-up, accessed\r
%define  CODE32_TYPE 0xb\r
\r
; Type: execute, readable, expand-up, accessed\r
%define  CODE64_TYPE 0xb\r
\r
%define  GRANULARITY_FLAG(g) (g << 7)\r
%define  DEFAULT_SIZE32(d) (d << 6)\r
%define  CODE64_FLAG(l) (l << 5)\r
%define  UPPER_LIMIT(l) (l)\r
\r
;\r
; The Global Descriptor Table (GDT)\r
;\r
\r
GDT_BASE:\r
; null descriptor\r
NULL_SEL            equ $-GDT_BASE\r
    DW      0            ; limit 15:0\r
    DW      0            ; base 15:0\r
    DB      0            ; base 23:16\r
    DB      0            ; sys flag, dpl, type\r
    DB      0            ; limit 19:16, flags\r
    DB      0            ; base 31:24\r
\r
; linear data segment descriptor\r
LINEAR_SEL          equ $-GDT_BASE\r
    DW      0xffff       ; limit 15:0\r
    DW      0            ; base 15:0\r
    DB      0            ; base 23:16\r
    DB      PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(DATA32_TYPE)\r
    DB      GRANULARITY_FLAG(1)|DEFAULT_SIZE32(1)|CODE64_FLAG(0)|UPPER_LIMIT(0xf)\r
    DB      0            ; base 31:24\r
\r
; linear code segment descriptor\r
LINEAR_CODE_SEL     equ $-GDT_BASE\r
    DW      0xffff       ; limit 15:0\r
    DW      0            ; base 15:0\r
    DB      0            ; base 23:16\r
    DB      PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(CODE32_TYPE)\r
    DB      GRANULARITY_FLAG(1)|DEFAULT_SIZE32(1)|CODE64_FLAG(0)|UPPER_LIMIT(0xf)\r
    DB      0            ; base 31:24\r
\r
%ifdef ARCH_X64\r
; linear code (64-bit) segment descriptor\r
LINEAR_CODE64_SEL   equ $-GDT_BASE\r
    DW      0xffff       ; limit 15:0\r
    DW      0            ; base 15:0\r
    DB      0            ; base 23:16\r
    DB      PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(CODE64_TYPE)\r
    DB      GRANULARITY_FLAG(1)|DEFAULT_SIZE32(0)|CODE64_FLAG(1)|UPPER_LIMIT(0xf)\r
    DB      0            ; base 31:24\r
%endif\r
\r
GDT_END:\r
\r