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
  99   //
 100   // Extra 4 bytes for return address, and another 4 bytes for mode transition
 101   //
 102   *ExtraStackSize = sizeof (IA32_DWORD_REGS) + 8;
 103 }
 104
 105 /**
 106   Prepares all structures a code required to use AsmThunk16().
 107
 108   Prepares all structures and code required to use AsmThunk16().
 109
 110   If ThunkContext is NULL, then ASSERT().
 111
 112   @param  ThunkContext  A pointer to the context structure that describes the
 113                         16-bit real mode code to call.
 114
 115 **/
 116 VOID
 117 EFIAPI
 118 AsmPrepareThunk16 (
 119   OUT     THUNK_CONTEXT             *ThunkContext
 120   )
 121 {
 122   IA32_SEGMENT_DESCRIPTOR           *RealModeGdt;
 123
 124   ASSERT (ThunkContext != NULL);
 125   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 126   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 127   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 128
 129   CopyMem (ThunkContext->RealModeBuffer, &m16Start, m16Size);
 130
 131   //
 132   // Point RealModeGdt to the GDT to be used in transition
 133   //
 134   // RealModeGdt[0]: Reserved as NULL descriptor
 135   // RealModeGdt[1]: Code Segment
 136   // RealModeGdt[2]: Data Segment
 137   // RealModeGdt[3]: Call Gate
 138   //
 139   RealModeGdt = (IA32_SEGMENT_DESCRIPTOR*)(
 140                   (UINTN)ThunkContext->RealModeBuffer + m16Gdt);
 141
 142   //
 143   // Update Code & Data Segment Descriptor
 144   //
 145   RealModeGdt[1].Bits.BaseLow =
 146     (UINT32)(UINTN)ThunkContext->RealModeBuffer & ~0xf;
 147   RealModeGdt[1].Bits.BaseMid =
 148     (UINT32)(UINTN)ThunkContext->RealModeBuffer >> 16;
 149
 150   //
 151   // Update transition code entry point offset
 152   //
 153   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mTransition) +=
 154     (UINT32)(UINTN)ThunkContext->RealModeBuffer & 0xf;
 155
 156   //
 157   // Update Segment Limits for both Code and Data Segment Descriptors
 158   //
 159   if ((ThunkContext->ThunkAttributes & THUNK_ATTRIBUTE_BIG_REAL_MODE) == 0) {
 160     //
 161     // Set segment limits to 64KB
 162     //
 163     RealModeGdt[1].Bits.LimitHigh = 0;
 164     RealModeGdt[1].Bits.G = 0;
 165     RealModeGdt[2].Bits.LimitHigh = 0;
 166     RealModeGdt[2].Bits.G = 0;
 167   }
 168
 169   //
 170   // Update GDTBASE for this thunk context
 171   //
 172   *(VOID**)((UINTN)ThunkContext->RealModeBuffer + m16GdtrBase) = RealModeGdt;
 173
 174   //
 175   // Update Thunk Attributes
 176   //
 177   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mThunk16Attr) =
 178     ThunkContext->ThunkAttributes;
 179 }
 180
 181 /**
 182   Transfers control to a 16-bit real mode entry point and returns the results.
 183
 184   Transfers control to a 16-bit real mode entry point and returns the results.
 185   AsmPrepareThunk16() must be called with ThunkContext before this function is
 186   used. This function must be called with interrupts disabled.
 187
 188   If ThunkContext is NULL, then ASSERT().
 189   If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
 190
 191   @param  ThunkContext  A pointer to the context structure that describes the
 192                         16-bit real mode code to call.
 193
 194 **/
 195 VOID
 196 EFIAPI
 197 AsmThunk16 (
 198   IN OUT  THUNK_CONTEXT             *ThunkContext
 199   )
 200 {
 201   IA32_REGISTER_SET                 *UpdatedRegs;
 202
 203   ASSERT (ThunkContext != NULL);
 204   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 205   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 206   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 207
 208   UpdatedRegs = InternalAsmThunk16 (
 209                   ThunkContext->RealModeState,
 210                   ThunkContext->RealModeBuffer
 211                   );
 212
 213   CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));
 214 }
 215
 216 /**
 217   Prepares all structures and code for a 16-bit real mode thunk, transfers
 218   control to a 16-bit real mode entry point, and returns the results.
 219
 220   Prepares all structures and code for a 16-bit real mode thunk, transfers
 221   control to a 16-bit real mode entry point, and returns the results. If the
 222   caller only need to perform a single 16-bit real mode thunk, then this
 223   service should be used. If the caller intends to make more than one 16-bit
 224   real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
 225   once and AsmThunk16() can be called for each 16-bit real mode thunk. This
 226   function must be called with interrupts disabled.
 227
 228   If ThunkContext is NULL, then ASSERT().
 229
 230   @param  ThunkContext  A pointer to the context structure that describes the
 231                         16-bit real mode code to call.
 232
 233 **/
 234 VOID
 235 EFIAPI
 236 AsmPrepareAndThunk16 (
 237   IN OUT  THUNK_CONTEXT             *ThunkContext
 238   )
 239 {
 240   AsmPrepareThunk16 (ThunkContext);
 241   AsmThunk16 (ThunkContext);
 242 }