MdePkg/Library/BaseLib/Ia32/Thunk16.S

   1 //
   2 // Include common header file for this module.
   3 //
   4 #include "CommonHeader.h"
   5
   6 #------------------------------------------------------------------------------
   7 #
   8 # Copyright (c) 2006, Intel Corporation
   9 # All rights reserved. This program and the accompanying materials
  10 # are licensed and made available under the terms and conditions of the BSD License
  11 # which accompanies this distribution.  The full text of the license may be found at
  12 # http://opensource.org/licenses/bsd-license.php
  13 #
  14 # THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  15 # WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  16 #
  17 # Module Name:
  18 #
  19 #   Thunk16.S
  20 #
  21 # Abstract:
  22 #
  23 #   Real mode thunk
  24 #
  25 #------------------------------------------------------------------------------
  26
  27 .globl ASM_PFX(m16Start), ASM_PFX(m16Size), ASM_PFX(mThunk16Attr), ASM_PFX(m16Gdt), ASM_PFX(m16GdtrBase), ASM_PFX(mTransition)
  28 .globl ASM_PFX(InternalAsmThunk16)
  29
  30 ASM_PFX(m16Start):
  31
  32 SavedGdt:     .space  6
  33
  34 ASM_PFX(BackFromUserCode):
  35     push    %ss
  36     push    %cs
  37     .byte   0x66
  38     call    L_Base1                     # push eip
  39 L_Base1:
  40     pushfw                              # pushfd actually
  41     cli                                 # disable interrupts
  42     push    %gs
  43     push    %fs
  44     push    %es
  45     push    %ds
  46     pushaw                              # pushad actually
  47     .byte   0x66, 0xba                  # mov edx, imm32
  48 ASM_PFX(ThunkAttr): .space  4
  49     testb   $THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15, %dl
  50     jz      1f
  51     movl    $0x15cd2401, %eax           # mov ax, 2401h & int 15h
  52     cli                                 # disable interrupts
  53     jnc     2f
  54 1:
  55     testb   $THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL, %dl
  56     jz      2f
  57     inb     $0x92, %al
  58     orb     $2, %al
  59     outb    %al, $0x92                  # deactivate A20M#
  60 2:
  61     movl    %ss, %eax
  62     .byte   0x67, 0x66, 0x8d, 0x6c, 0x24, 0x34, 0x66
  63     mov     %ebp, 0xffffffd8(%esi)
  64     mov     0xfffffff8(%esi), %ebx
  65     shlw    $4, %ax                     # shl eax, 4
  66     addw    %ax, %bp                    # add ebp, eax
  67     .byte   0x66, 0xb8                   # mov eax, imm32
  68 SavedCr4:   .space  4
  69     movl    %eax, %cr4
  70     lgdtw   %cs:0xfffffff2(%edi)
  71     .byte   0x66, 0xb8                   # mov eax, imm32
  72 SavedCr0:   .space  4
  73     movl    %eax, %cr0
  74     .byte   0xb8                        # mov ax, imm16
  75 SavedSs:    .space  2
  76     movl    %eax, %ss
  77     .byte   0x66, 0xbc                   # mov esp, imm32
  78 SavedEsp:   .space  4
  79     .byte   0x66
  80     lret                                # return to protected mode
  81
  82 _EntryPoint:    .long      ASM_PFX(ToUserCode) - ASM_PFX(m16Start)
  83                 .word      0x8
  84 _16Idtr:        .word      0x3ff
  85                 .long      0
  86 _16Gdtr:        .word      GdtEnd - _NullSegDesc - 1
  87 _16GdtrBase:    .long      _NullSegDesc
  88
  89 ASM_PFX(ToUserCode):
  90     movl    %ss, %edx
  91     movl    %ecx, %ss                   # set new segment selectors
  92     movl    %ecx, %ds
  93     movl    %ecx, %es
  94     movl    %ecx, %fs
  95     movl    %ecx, %gs
  96     movl    %eax, %cr0
  97     movl    %ebp, %cr4                  # real mode starts at next instruction
  98     movl    %esi, %ss                   # set up 16-bit stack segment
  99     xchgw   %bx, %sp                    # set up 16-bit stack pointer
 100     .byte   0x66
 101     call    L_Base                      # push eip
 102 L_Base:
 103     popw    %bp                         # ebp <- offset L_Base
 104     addr16  pushl 36(%si)
 105     .byte   0x36
 106     lea     0xc(%esi), %eax
 107     push    %eax
 108     lret
 109
 110 L_RealMode:
 111     mov     %edx, %cs:0xffffffc5(%esi)
 112     mov     %bx, %cs:0xffffffcb(%esi)
 113     lidtw   %cs:0xffffffd7(%esi)
 114     popaw                               # popad actually
 115     pop     %ds
 116     pop     %es
 117     pop     %fs
 118     pop     %gs
 119     popfw                               # popfd
 120     lretw                               # transfer control to user code
 121
 122 _NullSegDesc:   .quad   0
 123 _16CsDesc:
 124                 .word   -1
 125                 .word   0
 126                 .byte   0
 127                 .byte   0x9b
 128                 .byte   0x8f            # 16-bit segment, 4GB limit
 129                 .byte   0
 130 _16DsDesc:
 131                 .word   -1
 132                 .word   0
 133                 .byte   0
 134                 .byte   0x93
 135                 .byte   0x8f            # 16-bit segment, 4GB limit
 136                 .byte   0
 137 GdtEnd:
 138
 139 #
 140 #   @param  RegSet  Pointer to a IA32_DWORD_REGS structure
 141 #   @param  Transition  Pointer to the transition code
 142 #   @return The address of the 16-bit stack after returning from user code
 143 #
 144 ASM_PFX(InternalAsmThunk16):
 145     push    %ebp
 146     push    %ebx
 147     push    %esi
 148     push    %edi
 149     push    %ds
 150     push    %es
 151     push    %fs
 152     push    %gs
 153     movl    36(%esp), %esi              # esi <- RegSet
 154     movzwl  0x32(%esi), %edx
 155     mov     0xc(%esi), %edi
 156     add     $0xffffffc8, %edi
 157     movl    %edi, %ebx                  # ebx <- stack offset
 158     imul    $0x10, %edx, %eax
 159     push    $0xd
 160     addl    %eax, %edi                  # edi <- linear address of 16-bit stack
 161     pop     %ecx
 162     rep
 163     movsl                               # copy RegSet
 164     movl    40(%esp), %eax              # eax <- address of transition code
 165     movl    %edx, %esi                  # esi <- 16-bit stack segment
 166     lea     0x5e(%eax), %edx
 167     movl    %eax, %ecx
 168     andl    $0xf, %ecx
 169     shll    $12, %eax
 170     lea     0x6(%ecx), %ecx
 171     movw    %cx, %ax
 172     stosl                               # [edi] <- return address of user code
 173     sgdtl   0xffffffa2(%edx)
 174     sidtl   0x24(%esp)
 175     movl    %cr0, %eax
 176     movl    %eax, (%edx)                # save CR0 in SavedCr0
 177     andl    $0x7ffffffe, %eax           # clear PE, PG bits
 178     movl    %cr4, %ebp
 179     mov     %ebp, 0xfffffff1(%edx)
 180     andl    $0x300, %ebp                # clear all but PCE and OSFXSR bits
 181     pushl   $0x10
 182     pop     %ecx                        # ecx <- selector for data segments
 183     lgdtl   0x20(%edx)
 184     pushfl
 185     lcall   *0x14(%edx)
 186     popfl
 187     lidtl   0x24(%esp)
 188     lea     0xffffffcc(%ebp), %eax
 189         pop     %gs
 190         pop     %fs
 191         pop     %es
 192         pop     %ds
 193         pop     %edi
 194         pop     %esi
 195         pop     %ebx
 196         pop     %ebp
 197     ret
 198
 199     .const:
 200
 201 ASM_PFX(m16Size):        .word      _InternalAsmThunk16 - ASM_PFX(m16Start)
 202 ASM_PFX(mThunk16Attr):   .word      _ThunkAttr          - ASM_PFX(m16Start)
 203 ASM_PFX(m16Gdt):         .word      _NullSegDesc        - ASM_PFX(m16Start)
 204 ASM_PFX(m16GdtrBase):    .word      _16GdtrBase         - ASM_PFX(m16Start)
 205 ASM_PFX(mTransition):    .word      _EntryPoint         - ASM_PFX(m16Start)