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   This interface is limited to be used in either physical mode or virtual modes with paging enabled where the
 114   virtual to physical mappings for ThunkContext.RealModeBuffer is mapped 1:1.
 115
 116   If ThunkContext is NULL, then ASSERT().
 117
 118   @param  ThunkContext  A pointer to the context structure that describes the
 119                         16-bit real mode code to call.
 120
 121 **/
 122 VOID
 123 EFIAPI
 124 AsmPrepareThunk16 (
 125   OUT     THUNK_CONTEXT             *ThunkContext
 126   )
 127 {
 128   IA32_SEGMENT_DESCRIPTOR           *RealModeGdt;
 129
 130   ASSERT (ThunkContext != NULL);
 131   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 132   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 133   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 134
 135   CopyMem (ThunkContext->RealModeBuffer, &m16Start, m16Size);
 136
 137   //
 138   // Point RealModeGdt to the GDT to be used in transition
 139   //
 140   // RealModeGdt[0]: Reserved as NULL descriptor
 141   // RealModeGdt[1]: Code Segment
 142   // RealModeGdt[2]: Data Segment
 143   // RealModeGdt[3]: Call Gate
 144   //
 145   RealModeGdt = (IA32_SEGMENT_DESCRIPTOR*)(
 146                   (UINTN)ThunkContext->RealModeBuffer + m16Gdt);
 147
 148   //
 149   // Update Code & Data Segment Descriptor
 150   //
 151   RealModeGdt[1].Bits.BaseLow =
 152     (UINT32)(UINTN)ThunkContext->RealModeBuffer & ~0xf;
 153   RealModeGdt[1].Bits.BaseMid =
 154     (UINT32)(UINTN)ThunkContext->RealModeBuffer >> 16;
 155
 156   //
 157   // Update transition code entry point offset
 158   //
 159   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mTransition) +=
 160     (UINT32)(UINTN)ThunkContext->RealModeBuffer & 0xf;
 161
 162   //
 163   // Update Segment Limits for both Code and Data Segment Descriptors
 164   //
 165   if ((ThunkContext->ThunkAttributes & THUNK_ATTRIBUTE_BIG_REAL_MODE) == 0) {
 166     //
 167     // Set segment limits to 64KB
 168     //
 169     RealModeGdt[1].Bits.LimitHigh = 0;
 170     RealModeGdt[1].Bits.G = 0;
 171     RealModeGdt[2].Bits.LimitHigh = 0;
 172     RealModeGdt[2].Bits.G = 0;
 173   }
 174
 175   //
 176   // Update GDTBASE for this thunk context
 177   //
 178   *(VOID**)((UINTN)ThunkContext->RealModeBuffer + m16GdtrBase) = RealModeGdt;
 179
 180   //
 181   // Update Thunk Attributes
 182   //
 183   *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mThunk16Attr) =
 184     ThunkContext->ThunkAttributes;
 185 }
 186
 187 /**
 188   Transfers control to a 16-bit real mode entry point and returns the results.
 189
 190   Transfers control to a 16-bit real mode entry point and returns the results.
 191   AsmPrepareThunk16() must be called with ThunkContext before this function is used.
 192   This function must be called with interrupts disabled.
 193
 194   The register state from the RealModeState field of ThunkContext is restored just prior
 195   to calling the 16-bit real mode entry point.  This includes the EFLAGS field of RealModeState,
 196   which is used to set the interrupt state when a 16-bit real mode entry point is called.
 197   Control is transferred to the 16-bit real mode entry point specified by the CS and Eip fields of RealModeState.
 198   The stack is initialized to the SS and ESP fields of RealModeState.  Any parameters passed to
 199   the 16-bit real mode code must be populated by the caller at SS:ESP prior to calling this function.
 200   The 16-bit real mode entry point is invoked with a 16-bit CALL FAR instruction,
 201   so when accessing stack contents, the 16-bit real mode code must account for the 16-bit segment
 202   and 16-bit offset of the return address that were pushed onto the stack. The 16-bit real mode entry
 203   point must exit with a RETF instruction. The register state is captured into RealModeState immediately
 204   after the RETF instruction is executed.
 205
 206   If EFLAGS specifies interrupts enabled, or any of the 16-bit real mode code enables interrupts,
 207   or any of the 16-bit real mode code makes a SW interrupt, then the caller is responsible for making sure
 208   the IDT at address 0 is initialized to handle any HW or SW interrupts that may occur while in 16-bit real mode.
 209
 210   If EFLAGS specifies interrupts enabled, or any of the 16-bit real mode code enables interrupts,
 211   then the caller is responsible for making sure the 8259 PIC is in a state compatible with 16-bit real mode.
 212   This includes the base vectors, the interrupt masks, and the edge/level trigger mode.
 213
 214   If THUNK_ATTRIBUTE_BIG_REAL_MODE is set in the ThunkAttributes field of ThunkContext, then the user code
 215   is invoked in big real mode.  Otherwise, the user code is invoked in 16-bit real mode with 64KB segment limits.
 216
 217   If neither THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 nor THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL are set in
 218   ThunkAttributes, then it is assumed that the user code did not enable the A20 mask, and no attempt is made to
 219   disable the A20 mask.
 220
 221   If THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 is set and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL is clear in
 222   ThunkAttributes, then attempt to use the INT 15 service to disable the A20 mask.  If this INT 15 call fails,
 223   then attempt to disable the A20 mask by directly accessing the 8042 keyboard controller I/O ports.
 224
 225   If THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 is clear and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL is set in
 226   ThunkAttributes, then attempt to disable the A20 mask by directly accessing the 8042 keyboard controller I/O ports.
 227
 228   If ThunkContext is NULL, then ASSERT().
 229   If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
 230   If both THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL are set in
 231   ThunkAttributes, then ASSERT().
 232
 233   This interface is limited to be used in either physical mode or virtual modes with paging enabled where the
 234   virtual to physical mappings for ThunkContext.RealModeBuffer is mapped 1:1.
 235
 236   @param  ThunkContext  A pointer to the context structure that describes the
 237                         16-bit real mode code to call.
 238
 239 **/
 240 VOID
 241 EFIAPI
 242 AsmThunk16 (
 243   IN OUT  THUNK_CONTEXT             *ThunkContext
 244   )
 245 {
 246   IA32_REGISTER_SET                 *UpdatedRegs;
 247
 248   ASSERT (ThunkContext != NULL);
 249   ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
 250   ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
 251   ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 252   ASSERT (((ThunkContext->ThunkAttributes & (THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 | THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL)) != \
 253            (THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 | THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL)));
 254
 255   UpdatedRegs = InternalAsmThunk16 (
 256                   ThunkContext->RealModeState,
 257                   ThunkContext->RealModeBuffer
 258                   );
 259
 260   CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));
 261 }
 262
 263 /**
 264   Prepares all structures and code for a 16-bit real mode thunk, transfers
 265   control to a 16-bit real mode entry point, and returns the results.
 266
 267   Prepares all structures and code for a 16-bit real mode thunk, transfers
 268   control to a 16-bit real mode entry point, and returns the results. If the
 269   caller only need to perform a single 16-bit real mode thunk, then this
 270   service should be used. If the caller intends to make more than one 16-bit
 271   real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
 272   once and AsmThunk16() can be called for each 16-bit real mode thunk.
 273
 274   This interface is limited to be used in either physical mode or virtual modes with paging enabled where the
 275   virtual to physical mappings for ThunkContext.RealModeBuffer is mapped 1:1.
 276
 277   See AsmPrepareThunk16() and AsmThunk16() for the detailed description and ASSERT() conditions.
 278
 279   @param  ThunkContext  A pointer to the context structure that describes the
 280                         16-bit real mode code to call.
 281
 282 **/
 283 VOID
 284 EFIAPI
 285 AsmPrepareAndThunk16 (
 286   IN OUT  THUNK_CONTEXT             *ThunkContext
 287   )
 288 {
 289   AsmPrepareThunk16 (ThunkContext);
 290   AsmThunk16 (ThunkContext);
 291 }