MdePkg/Library/BaseLib/Ia32/Thunk16.S

   1 #------------------------------------------------------------------------------
   2 #
   3 # Copyright (c) 2006, Intel Corporation
   4 # All rights reserved. This program and the accompanying materials
   5 # are licensed and made available under the terms and conditions of the BSD License
   6 # which accompanies this distribution.  The full text of the license may be found at
   7 # http://opensource.org/licenses/bsd-license.php
   8 #
   9 # THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 # WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11 #
  12 # Module Name:
  13 #
  14 #   Thunk16.S
  15 #
  16 # Abstract:
  17 #
  18 #   Real mode thunk
  19 #
  20 #------------------------------------------------------------------------------
  21
  22 .global _m16Start, _m16Size, _mThunk16Attr, _m16GdtrBase, _m16Gdt, _m16GdtrBase, _mTransition
  23 .global _InternalAsmThunk16
  24
  25 #THUNK_ATTRIBUTE_BIG_REAL_MODE               EQU 1
  26 #THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15     EQU 2
  27 #THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL   EQU 4
  28
  29    .code:
  30
  31 _m16Start:
  32
  33 SavedGdt:     .space  6
  34
  35 _BackFromUserCode:
  36     push    %ss
  37     push    %cs
  38     .byte   0x66
  39     call    @Base1                      # push eip
  40 @Base1:
  41     pushfw                              # pushfd actually
  42     cli                                 # disable interrupts
  43     push    %gs
  44     push    %fs
  45     push    %es
  46     push    %ds
  47     pushaw                              # pushad actually
  48     .byte   0x66,0xba                   # mov edx, imm32
  49 _ThunkAttr: .space  4
  50     testb   $THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15, %dl
  51     jz      @1
  52     movl    $0x15cd2401, %eax           # mov ax, 2401h & int 15h
  53     cli                                 # disable interrupts
  54     jnc     @2
  55 @1:
  56     testb   $THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL, %dl
  57     jz      @2
  58     inb     $0x92, %al
  59     orb     $2, %al
  60     outb    %al, $0x92                  # deactivate A20M#
  61 @2:
  62     movl    %ss, %eax
  63     .byte   0x67, 0x66, 0x8d, 0x6c, 0x24, 0x34, 0x66
  64     mov    %ebp,0xffffffd8(%esi)
  65     mov     0xfffffff8(%esi),%ebx
  66     shlw    $4, %ax                     # shl eax, 4
  67     addw    %ax, %bp                    # add ebp, eax
  68     .byte   0x66,0xb8                   # mov eax, imm32
  69 SavedCr4:   .space  4
  70     movl    %eax, %cr4
  71     lgdtw  %cs:0xfffffff2(%edi)
  72     .byte   0x66,0xb8                   # mov eax, imm32
  73 SavedCr0:   .space  4
  74     movl    %eax, %cr0
  75     .byte   0xb8                        # mov ax, imm16
  76 SavedSs:    .space  2
  77     movl    %eax, %ss
  78     .byte   0x66,0xbc                   # mov esp, imm32
  79 SavedEsp:   .space  4
  80     .byte   0x66
  81     lret                                # return to protected mode
  82
  83 _EntryPoint:    .long      _ToUserCode - _m16Start
  84                 .word      0x8
  85 _16Idtr:        .word      0x3ff
  86                 .long      0
  87 _16Gdtr:        .word      GdtEnd - _NullSegDesc - 1
  88 _16GdtrBase:    .long     _NullSegDesc
  89
  90 _ToUserCode:
  91     movl    %ss, %edx
  92     movl    %ecx, %ss                   # set new segment selectors
  93     movl    %ecx, %ds
  94     movl    %ecx, %es
  95     movl    %ecx, %fs
  96     movl    %ecx, %gs
  97     movl    %eax, %cr0
  98     movl    %ebp, %cr4                  # real mode starts at next instruction
  99     movl    %esi, %ss                   # set up 16-bit stack segment
 100     xchgw   %bx, %sp                    # set up 16-bit stack pointer
 101     .byte   0x66
 102     call    @Base                       # push eip
 103 @Base:
 104     popw    %bp                         # ebp <- offset @Base
 105     addr16  pushl 36(%si)
 106     .byte   0x36
 107     lea     0xc(%esi),%eax
 108     pushl   %eax
 109     lret
 110
 111 @RealMode:
 112     mov     %edx,%cs:0xffffffc5(%esi)
 113     mov     %bx,%cs:0xffffffcb(%esi)
 114     lidtw   %cs:0xffffffd7(%esi)
 115     popaw                               # popad actually
 116     popl    %ds
 117     popl    %es
 118     popl    %fs
 119     popl    %gs
 120     popfw                               # popfd
 121     lretw                               # transfer control to user code
 122
 123 _NullSegDesc:   .quad   0
 124 _16CsDesc:
 125                 .word   -1
 126                 .word   0
 127                 .byte   0
 128                 .byte   0x9b
 129                 .byte   0x8f            # 16-bit segment, 4GB limit
 130                 .byte   0
 131 _16DsDesc:
 132                 .word   -1
 133                 .word   0
 134                 .byte   0
 135                 .byte   0x93
 136                 .byte   0x8f            # 16-bit segment, 4GB limit
 137                 .byte   0
 138 GdtEnd:
 139
 140 #
 141 #   @param  RegSet  Pointer to a IA32_DWORD_REGS structure
 142 #   @param  Transition  Pointer to the transition code
 143 #   @return The address of the 16-bit stack after returning from user code
 144 #
 145 _InternalAsmThunk16:
 146     push    %ebp
 147     push    %ebx
 148     push    %esi
 149     push    %edi
 150     push    %ds
 151     push    %es
 152     push    %fs
 153     push    %gs
 154     movl    36(%esp), %esi              # esi <- RegSet
 155     movzwl  0x32(%esi),%edx
 156     mov     0xc(%esi),%edi
 157     add     $0xffffffc8,%edi
 158     movl    %edi, %ebx                  # ebx <- stack offset
 159     imul    $0x10,%edx,%eax
 160     push    $0xd
 161     addl    %eax, %edi                  # edi <- linear address of 16-bit stack
 162     popl    %ecx
 163     rep
 164     movsl                               # copy RegSet
 165     movl    40(%esp), %eax              # eax <- address of transition code
 166     movl    %edx, %esi                  # esi <- 16-bit stack segment
 167     lea     0x5e(%eax),%edx
 168     movl    %eax, %ecx
 169     andl    $0xf, %ecx
 170     shll    $12, %eax
 171     lea     0x6(%ecx),%ecx
 172     movw    %cx, %ax
 173     stosl                               # [edi] <- return address of user code
 174     sgdtl  0xffffffa2(%edx)
 175     sidtl   0x24(%esp)
 176     movl    %cr0, %eax
 177     movl    %eax, (%edx)                # save CR0 in SavedCr0
 178     andl    $0x7ffffffe, %eax           # clear PE, PG bits
 179     movl    %cr4, %ebp
 180     mov     %ebp,0xfffffff1(%edx)
 181     andl    $0x300, %ebp                # clear all but PCE and OSFXSR bits
 182     pushl   $0x10
 183     popl    %ecx                        # ecx <- selector for data segments
 184     lgdtl   0x20(%edx)
 185     pushfl
 186     lcall   *0x14(%edx)
 187     popfl
 188     lidtl   0x24(%esp)
 189     lea     0xffffffcc(%ebp),%eax
 190         pop     %gs
 191         pop     %fs
 192         pop     %es
 193         pop     %ds
 194         pop     %edi
 195         pop     %esi
 196         pop     %ebx
 197         pop     %ebp
 198     ret
 199
 200     .const:
 201
 202 _m16Size:        .word      _InternalAsmThunk16 - _m16Start
 203 _mThunk16Attr:   .word      _ThunkAttr          - _m16Start
 204 _m16Gdt:         .word      _NullSegDesc        - _m16Start
 205 _m16GdtrBase:    .word      _16GdtrBase         - _m16Start
 206 _mTransition:    .word      _EntryPoint         - _m16Start
 207