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 .globl ASM_PFX(m16Start), ASM_PFX(m16Size), ASM_PFX(mThunk16Attr), ASM_PFX(m16Gdt), ASM_PFX(m16GdtrBase), ASM_PFX(mTransition)
  23 .globl ASM_PFX(InternalAsmThunk16)
  24
  25 ASM_PFX(m16Start):
  26
  27 SavedGdt:     .space  6
  28
  29 ASM_PFX(BackFromUserCode):
  30     push    %ss
  31     push    %cs
  32     .byte   0x66
  33     call    L_Base1                     # push eip
  34 L_Base1:
  35     pushfw                              # pushfd actually
  36     cli                                 # disable interrupts
  37     push    %gs
  38     push    %fs
  39     push    %es
  40     push    %ds
  41     pushaw                              # pushad actually
  42     .byte   0x66, 0xba                  # mov edx, imm32
  43 ASM_PFX(ThunkAttr): .space  4
  44     testb   $THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15, %dl
  45     jz      1f
  46     movl    $0x15cd2401, %eax           # mov ax, 2401h & int 15h
  47     cli                                 # disable interrupts
  48     jnc     2f
  49 1:
  50     testb   $THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL, %dl
  51     jz      2f
  52     inb     $0x92, %al
  53     orb     $2, %al
  54     outb    %al, $0x92                  # deactivate A20M#
  55 2:
  56     movl    %ss, %eax
  57     .byte   0x67, 0x66, 0x8d, 0x6c, 0x24, 0x34, 0x66
  58     mov     %ebp, 0xffffffd8(%esi)
  59     mov     0xfffffff8(%esi), %ebx
  60     shlw    $4, %ax                     # shl eax, 4
  61     addw    %ax, %bp                    # add ebp, eax
  62     .byte   0x66, 0xb8                   # mov eax, imm32
  63 SavedCr4:   .space  4
  64     movl    %eax, %cr4
  65     lgdtw   %cs:0xfffffff2(%edi)
  66     .byte   0x66, 0xb8                   # mov eax, imm32
  67 SavedCr0:   .space  4
  68     movl    %eax, %cr0
  69     .byte   0xb8                        # mov ax, imm16
  70 SavedSs:    .space  2
  71     movl    %eax, %ss
  72     .byte   0x66, 0xbc                   # mov esp, imm32
  73 SavedEsp:   .space  4
  74     .byte   0x66
  75     lret                                # return to protected mode
  76
  77 _EntryPoint:    .long      ASM_PFX(ToUserCode) - ASM_PFX(m16Start)
  78                 .word      0x8
  79 _16Idtr:        .word      0x3ff
  80                 .long      0
  81 _16Gdtr:        .word      GdtEnd - _NullSegDesc - 1
  82 _16GdtrBase:    .long      _NullSegDesc
  83
  84 ASM_PFX(ToUserCode):
  85     movl    %ss, %edx
  86     movl    %ecx, %ss                   # set new segment selectors
  87     movl    %ecx, %ds
  88     movl    %ecx, %es
  89     movl    %ecx, %fs
  90     movl    %ecx, %gs
  91     movl    %eax, %cr0
  92     movl    %ebp, %cr4                  # real mode starts at next instruction
  93     movl    %esi, %ss                   # set up 16-bit stack segment
  94     xchgw   %bx, %sp                    # set up 16-bit stack pointer
  95     .byte   0x66
  96     call    L_Base                      # push eip
  97 L_Base:
  98     popw    %bp                         # ebp <- offset L_Base
  99     addr16  pushl 36(%si)
 100     .byte   0x36
 101     lea     0xc(%esi), %eax
 102     push    %eax
 103     lret
 104
 105 L_RealMode:
 106     mov     %edx, %cs:0xffffffc5(%esi)
 107     mov     %bx, %cs:0xffffffcb(%esi)
 108     lidtw   %cs:0xffffffd7(%esi)
 109     popaw                               # popad actually
 110     pop     %ds
 111     pop     %es
 112     pop     %fs
 113     pop     %gs
 114     popfw                               # popfd
 115     lretw                               # transfer control to user code
 116
 117 _NullSegDesc:   .quad   0
 118 _16CsDesc:
 119                 .word   -1
 120                 .word   0
 121                 .byte   0
 122                 .byte   0x9b
 123                 .byte   0x8f            # 16-bit segment, 4GB limit
 124                 .byte   0
 125 _16DsDesc:
 126                 .word   -1
 127                 .word   0
 128                 .byte   0
 129                 .byte   0x93
 130                 .byte   0x8f            # 16-bit segment, 4GB limit
 131                 .byte   0
 132 GdtEnd:
 133
 134 #
 135 #   @param  RegSet  Pointer to a IA32_DWORD_REGS structure
 136 #   @param  Transition  Pointer to the transition code
 137 #   @return The address of the 16-bit stack after returning from user code
 138 #
 139 ASM_PFX(InternalAsmThunk16):
 140     push    %ebp
 141     push    %ebx
 142     push    %esi
 143     push    %edi
 144     push    %ds
 145     push    %es
 146     push    %fs
 147     push    %gs
 148     movl    36(%esp), %esi              # esi <- RegSet
 149     movzwl  0x32(%esi), %edx
 150     mov     0xc(%esi), %edi
 151     add     $0xffffffc8, %edi
 152     movl    %edi, %ebx                  # ebx <- stack offset
 153     imul    $0x10, %edx, %eax
 154     push    $0xd
 155     addl    %eax, %edi                  # edi <- linear address of 16-bit stack
 156     pop     %ecx
 157     rep
 158     movsl                               # copy RegSet
 159     movl    40(%esp), %eax              # eax <- address of transition code
 160     movl    %edx, %esi                  # esi <- 16-bit stack segment
 161     lea     0x5e(%eax), %edx
 162     movl    %eax, %ecx
 163     andl    $0xf, %ecx
 164     shll    $12, %eax
 165     lea     0x6(%ecx), %ecx
 166     movw    %cx, %ax
 167     stosl                               # [edi] <- return address of user code
 168     sgdtl   0xffffffa2(%edx)
 169     sidtl   0x24(%esp)
 170     movl    %cr0, %eax
 171     movl    %eax, (%edx)                # save CR0 in SavedCr0
 172     andl    $0x7ffffffe, %eax           # clear PE, PG bits
 173     movl    %cr4, %ebp
 174     mov     %ebp, 0xfffffff1(%edx)
 175     andl    $0x300, %ebp                # clear all but PCE and OSFXSR bits
 176     pushl   $0x10
 177     pop     %ecx                        # ecx <- selector for data segments
 178     lgdtl   0x20(%edx)
 179     pushfl
 180     lcall   *0x14(%edx)
 181     popfl
 182     lidtl   0x24(%esp)
 183     lea     0xffffffcc(%ebp), %eax
 184         pop     %gs
 185         pop     %fs
 186         pop     %es
 187         pop     %ds
 188         pop     %edi
 189         pop     %esi
 190         pop     %ebx
 191         pop     %ebp
 192     ret
 193
 194     .const:
 195
 196 ASM_PFX(m16Size):        .word      _InternalAsmThunk16 - ASM_PFX(m16Start)
 197 ASM_PFX(mThunk16Attr):   .word      _ThunkAttr          - ASM_PFX(m16Start)
 198 ASM_PFX(m16Gdt):         .word      _NullSegDesc        - ASM_PFX(m16Start)
 199 ASM_PFX(m16GdtrBase):    .word      _16GdtrBase         - ASM_PFX(m16Start)
 200 ASM_PFX(mTransition):    .word      _EntryPoint         - ASM_PFX(m16Start)