IntelFspPkg/Library/SecFspSecPlatformLibNull/Ia32/Flat32.asm

   1 ;; @file
   2 ;  This is the code that goes from real-mode to protected mode.
   3 ;  It consumes the reset vector, configures the stack.
   4 ;
   5 ; Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>
   6 ; SPDX-License-Identifier: BSD-2-Clause-Patent
   7 ;;
   8
   9 ;
  10 ; Define assembler characteristics
  11 ;
  12 .586p
  13 .xmm
  14 .model flat, c
  15
  16 EXTRN   TempRamInitApi:NEAR
  17 EXTRN   FspInitApi:NEAR
  18
  19 ;
  20 ; Contrary to the name, this file contains 16 bit code as well.
  21 ;
  22 _TEXT_REALMODE      SEGMENT PARA PUBLIC USE16 'CODE'
  23                     ASSUME  CS:_TEXT_REALMODE, DS:_TEXT_REALMODE
  24
  25 ;----------------------------------------------------------------------------
  26 ;
  27 ; Procedure:    _ModuleEntryPoint
  28 ;
  29 ; Input:        None
  30 ;
  31 ; Output:       None
  32 ;
  33 ; Destroys:     Assume all registers
  34 ;
  35 ; Description:
  36 ;
  37 ;   Transition to non-paged flat-model protected mode from a
  38 ;   hard-coded GDT that provides exactly two descriptors.
  39 ;   This is a bare bones transition to protected mode only
  40 ;   used for a while in PEI and possibly DXE.
  41 ;
  42 ;   After enabling protected mode, a far jump is executed to
  43 ;   transfer to PEI using the newly loaded GDT.
  44 ;
  45 ; Return:       None
  46 ;
  47 ;----------------------------------------------------------------------------
  48 align 16
  49 _ModuleEntryPoint      PROC C PUBLIC
  50   ;
  51   ; Load the GDT table in GdtDesc
  52   ;
  53   mov     esi, OFFSET GdtDesc
  54   db      66h
  55   lgdt    fword ptr cs:[si]
  56
  57   ;
  58   ; Transition to 16 bit protected mode
  59   ;
  60   mov     eax, cr0                   ; Get control register 0
  61   or      eax, 00000003h             ; Set PE bit (bit #0) & MP bit (bit #1)
  62   mov     cr0, eax                   ; Activate protected mode
  63
  64   ;
  65   ; Now we're in 16 bit protected mode
  66   ; Set up the selectors for 32 bit protected mode entry
  67   ;
  68   mov     ax, SYS_DATA_SEL
  69   mov     ds, ax
  70   mov     es, ax
  71   mov     fs, ax
  72   mov     gs, ax
  73   mov     ss, ax
  74
  75   ;
  76   ; Transition to Flat 32 bit protected mode
  77   ; The jump to a far pointer causes the transition to 32 bit mode
  78   ;
  79   mov esi, offset ProtectedModeEntryLinearAddress
  80   jmp     fword ptr cs:[si]
  81
  82 _ModuleEntryPoint   ENDP
  83
  84 _TEXT_REALMODE      ENDS
  85
  86 .code
  87 ;
  88 ; Protected mode portion initializes stack, configures cache, and calls C entry point
  89 ;
  90
  91 ;----------------------------------------------------------------------------
  92 ;
  93 ; Procedure:    ProtectedModeEntryPoint
  94 ;
  95 ; Input:        Executing in 32 Bit Protected (flat) mode
  96 ;               cs: 0-4GB
  97 ;               ds: 0-4GB
  98 ;               es: 0-4GB
  99 ;               fs: 0-4GB
 100 ;               gs: 0-4GB
 101 ;               ss: 0-4GB
 102 ;
 103 ; Output:       This function never returns
 104 ;
 105 ; Destroys:
 106 ;               ecx
 107 ;               edi
 108 ;               esi
 109 ;               esp
 110 ;
 111 ; Description:
 112 ;               Perform any essential early platform initilaisation
 113 ;               Setup a stack
 114 ;
 115 ;----------------------------------------------------------------------------
 116
 117 ProtectedModeEntryPoint PROC NEAR C PUBLIC
 118   ;
 119   ; Dummy function. Consume 2 API to make sure they can be linked.
 120   ;
 121   mov  eax, TempRamInitApi
 122   mov  eax, FspInitApi
 123
 124   ; Should never return
 125   jmp  $
 126
 127 ProtectedModeEntryPoint ENDP
 128
 129 ;
 130 ; ROM-based Global-Descriptor Table for the PEI Phase
 131 ;
 132 align 16
 133 PUBLIC  BootGdtTable
 134
 135 ;
 136 ; GDT[0]: 0x00: Null entry, never used.
 137 ;
 138 NULL_SEL        equ     $ - GDT_BASE        ; Selector [0]
 139 GDT_BASE:
 140 BootGdtTable    DD      0
 141                 DD      0
 142 ;
 143 ; Linear code segment descriptor
 144 ;
 145 LINEAR_CODE_SEL equ     $ - GDT_BASE        ; Selector [0x8]
 146         DW      0FFFFh                      ; limit 0xFFFF
 147         DW      0                           ; base 0
 148         DB      0
 149         DB      09Bh                        ; present, ring 0, data, expand-up, not-writable
 150         DB      0CFh                        ; page-granular, 32-bit
 151         DB      0
 152 ;
 153 ; System data segment descriptor
 154 ;
 155 SYS_DATA_SEL    equ     $ - GDT_BASE        ; Selector [0x10]
 156         DW      0FFFFh                      ; limit 0xFFFF
 157         DW      0                           ; base 0
 158         DB      0
 159         DB      093h                        ; present, ring 0, data, expand-up, not-writable
 160         DB      0CFh                        ; page-granular, 32-bit
 161         DB      0
 162
 163 GDT_SIZE        EQU     $ - BootGDTtable    ; Size, in bytes
 164
 165 ;
 166 ; GDT Descriptor
 167 ;
 168 GdtDesc:                                    ; GDT descriptor
 169         DW      GDT_SIZE - 1                ; GDT limit
 170         DD      OFFSET BootGdtTable         ; GDT base address
 171
 172 ProtectedModeEntryLinearAddress   LABEL   FWORD
 173 ProtectedModeEntryLinearOffset    LABEL   DWORD
 174   DD      OFFSET ProtectedModeEntryPoint  ; Offset of our 32 bit code
 175   DW      LINEAR_CODE_SEL
 176
 177 END