IntelFspPkg/Library/SecFspSecPlatformLibNull/Ia32/Flat32.s

   1 #------------------------------------------------------------------------------
   2 #
   3 # Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>
   4 # SPDX-License-Identifier: BSD-2-Clause-Patent
   5 #
   6 # Abstract:
   7 #
   8 #  This is the code that goes from real-mode to protected mode.
   9 #  It consumes the reset vector, configures the stack.
  10 #
  11 #------------------------------------------------------------------------------
  12
  13
  14 #
  15 # Contrary to the name, this file contains 16 bit code as well.
  16 #
  17 .text
  18 #----------------------------------------------------------------------------
  19 #
  20 # Procedure:    _ModuleEntryPoint
  21 #
  22 # Input:        None
  23 #
  24 # Output:       None
  25 #
  26 # Destroys:     Assume all registers
  27 #
  28 # Description:
  29 #
  30 #   Transition to non-paged flat-model protected mode from a
  31 #   hard-coded GDT that provides exactly two descriptors.
  32 #   This is a bare bones transition to protected mode only
  33 #   used for a while in PEI and possibly DXE.
  34 #
  35 #   After enabling protected mode, a far jump is executed to
  36 #   transfer to PEI using the newly loaded GDT.
  37 #
  38 # Return:       None
  39 #
  40 #----------------------------------------------------------------------------
  41 ASM_GLOBAL ASM_PFX(_ModuleEntryPoint)
  42 ASM_PFX(_ModuleEntryPoint):
  43
  44   #
  45   # Load the GDT table in GdtDesc
  46   #
  47   .byte   0x66,0xbe        #movl    $GdtDesc, %esi
  48   .long   GdtDesc
  49
  50   .byte   0x66,0x2e,0x0f,0x01,0x14   #lgdt    %cs:(%si)
  51
  52   #
  53   # Transition to 16 bit protected mode
  54   #
  55   .byte   0x0f,0x20,0xc0       #movl    %cr0, %eax                  # Get control register 0
  56   .byte   0x66,0x83,0xc8,0x03  #orl     $0x0000003, %eax            # Set PE bit (bit #0) & MP bit (bit #1)
  57   .byte   0x0f,0x22,0xc0       #movl    %eax, %cr0                  # Activate protected mode
  58
  59   #
  60   # Now we're in 16 bit protected mode
  61   # Set up the selectors for 32 bit protected mode entry
  62   #
  63   .byte   0xb8                 #movw    SYS_DATA_SEL, %ax
  64   .word   SYS_DATA_SEL
  65
  66   .byte   0x8e,0xd8            #movw    %ax, %ds
  67   .byte   0x8e,0xc0            #movw    %ax, %es
  68   .byte   0x8e,0xe0            #movw    %ax, %fs
  69   .byte   0x8e,0xe8            #movw    %ax, %gs
  70   .byte   0x8e,0xd0            #movw    %ax, %ss
  71
  72   #
  73   # Transition to Flat 32 bit protected mode
  74   # The jump to a far pointer causes the transition to 32 bit mode
  75   #
  76   .byte   0x66,0xbe            #movl   ProtectedModeEntryLinearAddress, %esi
  77   .long   ProtectedModeEntryLinearAddress
  78   .byte   0x66,0x2e,0xff,0x2c  #jmp    %cs:(%esi)
  79
  80 #
  81 # Protected mode portion initializes stack, configures cache, and calls C entry point
  82 #
  83
  84 #----------------------------------------------------------------------------
  85 #
  86 # Procedure:    ProtectedModeEntryPoint
  87 #
  88 # Input:        Executing in 32 Bit Protected (flat) mode
  89 #               cs: 0-4GB
  90 #               ds: 0-4GB
  91 #               es: 0-4GB
  92 #               fs: 0-4GB
  93 #               gs: 0-4GB
  94 #               ss: 0-4GB
  95 #
  96 # Output:       This function never returns
  97 #
  98 # Destroys:
  99 #               ecx
 100 #               edi
 101 #               esi
 102 #               esp
 103 #
 104 # Description:
 105 #               Perform any essential early platform initilaisation
 106 #               Setup a stack
 107 #
 108 #----------------------------------------------------------------------------
 109 ProtectedModeEntryPoint:
 110   #
 111   # Dummy function. Consume 2 API to make sure they can be linked.
 112   #
 113   movl   ASM_PFX(TempRamInitApi), %eax
 114   movl   ASM_PFX(FspInitApi), %eax
 115   #
 116   # Should never return
 117   #
 118   jmp     . #'$'
 119
 120 #
 121 # ROM-based Global-Descriptor Table for the PEI Phase
 122 #
 123 .align 16
 124 #
 125 # GDT[0]: 000h: Null entry, never used.
 126 #
 127 .equ   NULL_SEL, . - GDT_BASE         # Selector [0]
 128 GDT_BASE:
 129 BootGdtTable:
 130         .long   0
 131         .long   0
 132 #
 133 # Linear code segment descriptor
 134 #
 135 .equ     LINEAR_CODE_SEL, . - GDT_BASE         # Selector [08h]
 136         .word   0xFFFF                      # limit 0FFFFh
 137         .word   0                           # base 0
 138         .byte   0
 139         .byte   0x9B                        # present, ring 0, data, expand-up, not-writable
 140         .byte   0xCF                        # page-granular, 32-bit
 141         .byte   0
 142 #
 143 # System data segment descriptor
 144 #
 145 .equ    SYS_DATA_SEL, . - GDT_BASE         # Selector [010h]
 146         .word   0xFFFF                      # limit 0FFFFh
 147         .word   0                           # base 0
 148         .byte   0
 149         .byte   0x93                        # present, ring 0, data, expand-up, not-writable
 150         .byte   0xCF                        # page-granular, 32-bit
 151         .byte   0
 152
 153 .equ            GDT_SIZE, . - BootGdtTable  # Size, in bytes
 154
 155 #
 156 # GDT Descriptor
 157 #
 158 GdtDesc:                                     # GDT descriptor
 159        .word    GDT_SIZE - 1
 160        .long    BootGdtTable
 161
 162 ProtectedModeEntryLinearAddress:
 163 ProtectedModeEntryLinearOffset:
 164        .long    ProtectedModeEntryPoint
 165        .word    LINEAR_CODE_SEL