MdePkg/Library/BaseLib/x86Thunk.c

   1 /** @file
   2   Real Mode Thunk Functions for IA32 and X64.
   3
   4   Copyright (c) 2006, Intel Corporation<BR>
   5   All rights reserved. This program and the accompanying materials
   6   are licensed and made available under the terms and conditions of the BSD License
   7   which accompanies this distribution.  The full text of the license may be found at
   8   http://opensource.org/licenses/bsd-license.php
   9
  10   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  11   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  12
  13   Module Name:  x86Thunk.c
  14
  15 **/
  16
  17 //
  18 // Byte packed structure for a segment descriptor in a GDT/LDT
  19 //
  20 typedef union {
  21   struct {
  22     UINT32  LimitLow:16;
  23     UINT32  BaseLow:16;
  24     UINT32  BaseMid:8;
  25     UINT32  Type:4;
  26     UINT32  S:1;
  27     UINT32  DPL:2;
  28     UINT32  P:1;
  29     UINT32  LimitHigh:4;
  30     UINT32  AVL:1;
  31     UINT32  L:1;
  32     UINT32  DB:1;
  33     UINT32  G:1;
  34     UINT32  BaseHigh:8;
  35   } Bits;
  36   UINT64  Uint64;
  37 } IA32_SEGMENT_DESCRIPTOR;
  38
  39 extern CONST UINT8                  m16Start;
  40 extern CONST UINT16                 m16Size;
  41 extern CONST UINT16                 mThunk16Attr;
  42 extern CONST UINT16                 m16Gdt;
  43 extern CONST UINT16                 m16GdtrBase;
  44 extern CONST UINT16                 mTransition;
  45
  46 /**
  47   Invokes 16-bit code in big real mode and returns the updated register set.
  48
  49   This function transfers control to the 16-bit code specified by CS:EIP using
  50   the stack specified by SS:ESP in RegisterSet. The updated registers are saved
  51   on the real mode stack and the starting address of the save area is returned.
  52
  53   @param  RegisterSet Values of registers before invocation of 16-bit code.
  54   @param  Transition  Pointer to the transition code under 1MB.
  55
  56   @return The pointer to a IA32_REGISTER_SET structure containing the updated
  57           register values.
  58
  59 **/
  60 IA32_REGISTER_SET *
  61 InternalAsmThunk16 (
  62   IN      IA32_REGISTER_SET         *RegisterSet,
  63   IN OUT  VOID                      *Transition
  64   );
  65
  66 /**
  67   Retrieves the properties for 16-bit thunk functions.
  68
  69   Computes the size of the buffer and stack below 1MB required to use the
  70   AsmPrepareThunk16(), AsmThunk16() and AsmPrepareAndThunk16() functions. This
  71   buffer size is returned in RealModeBufferSize, and the stack size is returned
  72   in ExtraStackSize. If parameters are passed to the 16-bit real mode code,
  73   then the actual minimum stack size is ExtraStackSize plus the maximum number
  74   of bytes that need to be passed to the 16-bit real mode code.
  75
  76   If RealModeBufferSize is NULL, then ASSERT().
  77   If ExtraStackSize is NULL, then ASSERT().
  78
  79   @param  RealModeBufferSize  A pointer to the size of the buffer below 1MB
  80                               required to use the 16-bit thunk functions.
  81   @param  ExtraStackSize      A pointer to the extra size of stack below 1MB
  82                               that the 16-bit thunk functions require for
  83                               temporary storage in the transition to and from
  84                               16-bit real mode.
  85
  86 **/
  87 VOID
  88 EFIAPI
  89 AsmGetThunk16Properties (
  90   OUT     UINT32                    *RealModeBufferSize,
  91   OUT     UINT32                    *ExtraStackSize
  92   )
  93 {
  94   ASSERT (RealModeBufferSize != NULL);
  95   ASSERT (ExtraStackSize != NULL);
  96
  97   *RealModeBufferSize = m16Size;
  98   *ExtraStackSize = sizeof (IA32_DWORD_REGS) + 8;
  99 }
 100
 101 /**
 102   Prepares all structures a code required to use AsmThunk16().
 103
 104   Prepares all structures and code required to use AsmThunk16().
 105
 106   If ThunkContext is NULL, then ASSERT().
 107
 108   @param  ThunkContext  A pointer to the context structure that describes the
 109                         16-bit real mode code to call.
 110
 111 **/
 112 VOID
 113 EFIAPI
 114 AsmPrepareThunk16 (
 115   OUT     THUNK_CONTEXT             *ThunkContext
 116   )
 117 {
 118   IA32_SEGMENT_DESCRIPTOR           *RealModeGdt;
 119
 120   ASSERT (ThunkContext != NULL);
 121   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 122   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 123   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 124
 125   CopyMem (ThunkContext->RealModeBuffer, &m16Start, m16Size);
 126
 127   //
 128   // Point RealModeGdt to the GDT to be used in transition
 129   //
 130   // RealModeGdt[0]: Reserved as NULL descriptor
 131   // RealModeGdt[1]: Code Segment
 132   // RealModeGdt[2]: Data Segment
 133   // RealModeGdt[3]: Call Gate
 134   //
 135   RealModeGdt = (IA32_SEGMENT_DESCRIPTOR*)(
 136                   (UINTN)ThunkContext->RealModeBuffer + m16Gdt);
 137
 138   //
 139   // Update Code & Data Segment Descriptor
 140   //
 141   RealModeGdt[1].Bits.BaseLow =
 142     (UINT32)(UINTN)ThunkContext->RealModeBuffer & ~0xf;
 143   RealModeGdt[1].Bits.BaseMid =
 144     (UINT32)(UINTN)ThunkContext->RealModeBuffer >> 16;
 145
 146   //
 147   // Update transition code entry point offset
 148   //
 149   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mTransition) +=
 150     (UINT32)(UINTN)ThunkContext->RealModeBuffer & 0xf;
 151
 152   //
 153   // Update Segment Limits for both Code and Data Segment Descriptors
 154   //
 155   if ((ThunkContext->ThunkAttributes & THUNK_ATTRIBUTE_BIG_REAL_MODE) == 0) {
 156     //
 157     // Set segment limits to 64KB
 158     //
 159     RealModeGdt[1].Bits.LimitHigh = 0;
 160     RealModeGdt[1].Bits.G = 0;
 161     RealModeGdt[2].Bits.LimitHigh = 0;
 162     RealModeGdt[2].Bits.G = 0;
 163   }
 164
 165   //
 166   // Update GDTBASE for this thunk context
 167   //
 168   *(VOID**)((UINTN)ThunkContext->RealModeBuffer + m16GdtrBase) = RealModeGdt;
 169
 170   //
 171   // Update Thunk Attributes
 172   //
 173   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mThunk16Attr) =
 174     ThunkContext->ThunkAttributes;
 175 }
 176
 177 /**
 178   Transfers control to a 16-bit real mode entry point and returns the results.
 179
 180   Transfers control to a 16-bit real mode entry point and returns the results.
 181   AsmPrepareThunk16() must be called with ThunkContext before this function is
 182   used. This function must be called with interrupts disabled.
 183
 184   If ThunkContext is NULL, then ASSERT().
 185   If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
 186
 187   @param  ThunkContext  A pointer to the context structure that describes the
 188                         16-bit real mode code to call.
 189
 190 **/
 191 VOID
 192 EFIAPI
 193 AsmThunk16 (
 194   IN OUT  THUNK_CONTEXT             *ThunkContext
 195   )
 196 {
 197   IA32_REGISTER_SET                 *UpdatedRegs;
 198
 199   ASSERT (ThunkContext != NULL);
 200   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 201   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 202   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 203
 204   UpdatedRegs = InternalAsmThunk16 (
 205                   ThunkContext->RealModeState,
 206                   ThunkContext->RealModeBuffer
 207                   );
 208
 209   CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));
 210 }
 211
 212 /**
 213   Prepares all structures and code for a 16-bit real mode thunk, transfers
 214   control to a 16-bit real mode entry point, and returns the results.
 215
 216   Prepares all structures and code for a 16-bit real mode thunk, transfers
 217   control to a 16-bit real mode entry point, and returns the results. If the
 218   caller only need to perform a single 16-bit real mode thunk, then this
 219   service should be used. If the caller intends to make more than one 16-bit
 220   real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
 221   once and AsmThunk16() can be called for each 16-bit real mode thunk. This
 222   function must be called with interrupts disabled.
 223
 224   If ThunkContext is NULL, then ASSERT().
 225
 226   @param  ThunkContext  A pointer to the context structure that describes the
 227                         16-bit real mode code to call.
 228
 229 **/
 230 VOID
 231 EFIAPI
 232 AsmPrepareAndThunk16 (
 233   IN OUT  THUNK_CONTEXT             *ThunkContext
 234   )
 235 {
 236   AsmPrepareThunk16 (ThunkContext);
 237   AsmThunk16 (ThunkContext);
 238 }