MdePkg/Library/BaseLib/X86Thunk.c

   1 /** @file
   2   Real Mode Thunk Functions for IA32 and x64.
   3
   4   Copyright (c) 2006 - 2008, 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 **/
  14
  15
  16 #include "BaseLibInternals.h"
  17
  18
  19 //
  20 // Byte packed structure for a segment descriptor in a GDT/LDT
  21 //
  22 typedef union {
  23   struct {
  24     UINT32  LimitLow:16;
  25     UINT32  BaseLow:16;
  26     UINT32  BaseMid:8;
  27     UINT32  Type:4;
  28     UINT32  S:1;
  29     UINT32  DPL:2;
  30     UINT32  P:1;
  31     UINT32  LimitHigh:4;
  32     UINT32  AVL:1;
  33     UINT32  L:1;
  34     UINT32  DB:1;
  35     UINT32  G:1;
  36     UINT32  BaseHigh:8;
  37   } Bits;
  38   UINT64  Uint64;
  39 } IA32_SEGMENT_DESCRIPTOR;
  40
  41 extern CONST UINT8                  m16Start;
  42 extern CONST UINT16                 m16Size;
  43 extern CONST UINT16                 mThunk16Attr;
  44 extern CONST UINT16                 m16Gdt;
  45 extern CONST UINT16                 m16GdtrBase;
  46 extern CONST UINT16                 mTransition;
  47
  48 /**
  49   Invokes 16-bit code in big real mode and returns the updated register set.
  50
  51   This function transfers control to the 16-bit code specified by CS:EIP using
  52   the stack specified by SS:ESP in RegisterSet. The updated registers are saved
  53   on the real mode stack and the starting address of the save area is returned.
  54
  55   @param  RegisterSet Values of registers before invocation of 16-bit code.
  56   @param  Transition  Pointer to the transition code under 1MB.
  57
  58   @return The pointer to a IA32_REGISTER_SET structure containing the updated
  59           register values.
  60
  61 **/
  62 IA32_REGISTER_SET *
  63 EFIAPI
  64 InternalAsmThunk16 (
  65   IN      IA32_REGISTER_SET         *RegisterSet,
  66   IN OUT  VOID                      *Transition
  67   );
  68
  69 /**
  70   Retrieves the properties for 16-bit thunk functions.
  71
  72   Computes the size of the buffer and stack below 1MB required to use the
  73   AsmPrepareThunk16(), AsmThunk16() and AsmPrepareAndThunk16() functions. This
  74   buffer size is returned in RealModeBufferSize, and the stack size is returned
  75   in ExtraStackSize. If parameters are passed to the 16-bit real mode code,
  76   then the actual minimum stack size is ExtraStackSize plus the maximum number
  77   of bytes that need to be passed to the 16-bit real mode code.
  78
  79   If RealModeBufferSize is NULL, then ASSERT().
  80   If ExtraStackSize is NULL, then ASSERT().
  81
  82   @param  RealModeBufferSize  A pointer to the size of the buffer below 1MB
  83                               required to use the 16-bit thunk functions.
  84   @param  ExtraStackSize      A pointer to the extra size of stack below 1MB
  85                               that the 16-bit thunk functions require for
  86                               temporary storage in the transition to and from
  87                               16-bit real mode.
  88
  89 **/
  90 VOID
  91 EFIAPI
  92 AsmGetThunk16Properties (
  93   OUT     UINT32                    *RealModeBufferSize,
  94   OUT     UINT32                    *ExtraStackSize
  95   )
  96 {
  97   ASSERT (RealModeBufferSize != NULL);
  98   ASSERT (ExtraStackSize != NULL);
  99
 100   *RealModeBufferSize = m16Size;
 101
 102   //
 103   // Extra 4 bytes for return address, and another 4 bytes for mode transition
 104   //
 105   *ExtraStackSize = sizeof (IA32_DWORD_REGS) + 8;
 106 }
 107
 108 /**
 109   Prepares all structures a code required to use AsmThunk16().
 110
 111   Prepares all structures and code required to use AsmThunk16().
 112
 113   If ThunkContext is NULL, then ASSERT().
 114
 115   @param  ThunkContext  A pointer to the context structure that describes the
 116                         16-bit real mode code to call.
 117
 118 **/
 119 VOID
 120 EFIAPI
 121 AsmPrepareThunk16 (
 122   OUT     THUNK_CONTEXT             *ThunkContext
 123   )
 124 {
 125   IA32_SEGMENT_DESCRIPTOR           *RealModeGdt;
 126
 127   ASSERT (ThunkContext != NULL);
 128   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 129   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 130   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 131
 132   CopyMem (ThunkContext->RealModeBuffer, &m16Start, m16Size);
 133
 134   //
 135   // Point RealModeGdt to the GDT to be used in transition
 136   //
 137   // RealModeGdt[0]: Reserved as NULL descriptor
 138   // RealModeGdt[1]: Code Segment
 139   // RealModeGdt[2]: Data Segment
 140   // RealModeGdt[3]: Call Gate
 141   //
 142   RealModeGdt = (IA32_SEGMENT_DESCRIPTOR*)(
 143                   (UINTN)ThunkContext->RealModeBuffer + m16Gdt);
 144
 145   //
 146   // Update Code & Data Segment Descriptor
 147   //
 148   RealModeGdt[1].Bits.BaseLow =
 149     (UINT32)(UINTN)ThunkContext->RealModeBuffer & ~0xf;
 150   RealModeGdt[1].Bits.BaseMid =
 151     (UINT32)(UINTN)ThunkContext->RealModeBuffer >> 16;
 152
 153   //
 154   // Update transition code entry point offset
 155   //
 156   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mTransition) +=
 157     (UINT32)(UINTN)ThunkContext->RealModeBuffer & 0xf;
 158
 159   //
 160   // Update Segment Limits for both Code and Data Segment Descriptors
 161   //
 162   if ((ThunkContext->ThunkAttributes & THUNK_ATTRIBUTE_BIG_REAL_MODE) == 0) {
 163     //
 164     // Set segment limits to 64KB
 165     //
 166     RealModeGdt[1].Bits.LimitHigh = 0;
 167     RealModeGdt[1].Bits.G = 0;
 168     RealModeGdt[2].Bits.LimitHigh = 0;
 169     RealModeGdt[2].Bits.G = 0;
 170   }
 171
 172   //
 173   // Update GDTBASE for this thunk context
 174   //
 175   *(VOID**)((UINTN)ThunkContext->RealModeBuffer + m16GdtrBase) = RealModeGdt;
 176
 177   //
 178   // Update Thunk Attributes
 179   //
 180   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mThunk16Attr) =
 181     ThunkContext->ThunkAttributes;
 182 }
 183
 184 /**
 185   Transfers control to a 16-bit real mode entry point and returns the results.
 186
 187   Transfers control to a 16-bit real mode entry point and returns the results.
 188   AsmPrepareThunk16() must be called with ThunkContext before this function is used.
 189   This function must be called with interrupts disabled.
 190
 191   The register state from the RealModeState field of ThunkContext is restored just prior
 192   to calling the 16-bit real mode entry point.  This includes the EFLAGS field of RealModeState,
 193   which is used to set the interrupt state when a 16-bit real mode entry point is called.
 194   Control is transferred to the 16-bit real mode entry point specified by the CS and Eip fields of RealModeState.
 195   The stack is initialized to the SS and ESP fields of RealModeState.  Any parameters passed to
 196   the 16-bit real mode code must be populated by the caller at SS:ESP prior to calling this function.
 197   The 16-bit real mode entry point is invoked with a 16-bit CALL FAR instruction,
 198   so when accessing stack contents, the 16-bit real mode code must account for the 16-bit segment
 199   and 16-bit offset of the return address that were pushed onto the stack. The 16-bit real mode entry
 200   point must exit with a RETF instruction. The register state is captured into RealModeState immediately
 201   after the RETF instruction is executed.
 202
 203   If EFLAGS specifies interrupts enabled, or any of the 16-bit real mode code enables interrupts,
 204   or any of the 16-bit real mode code makes a SW interrupt, then the caller is responsible for making sure
 205   the IDT at address 0 is initialized to handle any HW or SW interrupts that may occur while in 16-bit real mode.
 206
 207   If EFLAGS specifies interrupts enabled, or any of the 16-bit real mode code enables interrupts,
 208   then the caller is responsible for making sure the 8259 PIC is in a state compatible with 16-bit real mode.
 209   This includes the base vectors, the interrupt masks, and the edge/level trigger mode.
 210
 211   If THUNK_ATTRIBUTE_BIG_REAL_MODE is set in the ThunkAttributes field of ThunkContext, then the user code
 212   is invoked in big real mode.  Otherwise, the user code is invoked in 16-bit real mode with 64KB segment limits.
 213
 214   If neither THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 nor THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL are set in
 215   ThunkAttributes, then it is assumed that the user code did not enable the A20 mask, and no attempt is made to
 216   disable the A20 mask.
 217
 218   If THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 is set and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL is clear in
 219   ThunkAttributes, then attempt to use the INT 15 service to disable the A20 mask.  If this INT 15 call fails,
 220   then attempt to disable the A20 mask by directly accessing the 8042 keyboard controller I/O ports.
 221
 222   If THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 is clear and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL is set in
 223   ThunkAttributes, then attempt to disable the A20 mask by directly accessing the 8042 keyboard controller I/O ports.
 224
 225   If ThunkContext is NULL, then ASSERT().
 226   If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
 227   If both THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL are set in
 228   ThunkAttributes, 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 AsmThunk16 (
 237   IN OUT  THUNK_CONTEXT             *ThunkContext
 238   )
 239 {
 240   IA32_REGISTER_SET                 *UpdatedRegs;
 241
 242   ASSERT (ThunkContext != NULL);
 243   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 244   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 245   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 246
 247   UpdatedRegs = InternalAsmThunk16 (
 248                   ThunkContext->RealModeState,
 249                   ThunkContext->RealModeBuffer
 250                   );
 251
 252   CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));
 253 }
 254
 255 /**
 256   Prepares all structures and code for a 16-bit real mode thunk, transfers
 257   control to a 16-bit real mode entry point, and returns the results.
 258
 259   Prepares all structures and code for a 16-bit real mode thunk, transfers
 260   control to a 16-bit real mode entry point, and returns the results. If the
 261   caller only need to perform a single 16-bit real mode thunk, then this
 262   service should be used. If the caller intends to make more than one 16-bit
 263   real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
 264   once and AsmThunk16() can be called for each 16-bit real mode thunk.
 265
 266   See AsmPrepareThunk16() and AsmThunk16() for the detailed description and ASSERT() conditions.
 267
 268   @param  ThunkContext  A pointer to the context structure that describes the
 269                         16-bit real mode code to call.
 270
 271 **/
 272 VOID
 273 EFIAPI
 274 AsmPrepareAndThunk16 (
 275   IN OUT  THUNK_CONTEXT             *ThunkContext
 276   )
 277 {
 278   AsmPrepareThunk16 (ThunkContext);
 279   AsmThunk16 (ThunkContext);
 280 }