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   Invokes 16-bit code in big real mode and returns the updated register set.
  19
  20   This function transfers control to the 16-bit code specified by CS:EIP using
  21   the stack specified by SS:ESP in RegisterSet. The updated registers are saved
  22   on the real mode stack and the starting address of the save area is returned.
  23
  24   @param  RegisterSet Values of registers before invocation of 16-bit code.
  25   @param  Patch       Pointer to the area following the 16-bit code.
  26
  27   @return The pointer to a IA32_REGISTER_SET structure containing the updated
  28           register values.
  29
  30 **/
  31 IA32_REGISTER_SET *
  32 InternalAsmThunk16 (
  33   IN      IA32_REGISTER_SET         *RegisterSet,
  34   IN OUT  VOID                      *Patch
  35   );
  36
  37 /**
  38   Prepares all structures a code required to use AsmThunk16().
  39
  40   Prepares all structures and code required to use AsmThunk16().
  41
  42   If ThunkContext is NULL, then ASSERT().
  43
  44   @param  ThunkContext  A pointer to the context structure that describes the
  45                         16-bit real mode code to call.
  46
  47 **/
  48 VOID
  49 EFIAPI
  50 AsmPrepareThunk16 (
  51   OUT     THUNK_CONTEXT             *ThunkContext
  52   )
  53 {
  54   ASSERT (ThunkContext != NULL);
  55 }
  56
  57 /**
  58   Transfers control to a 16-bit real mode entry point and returns the results.
  59
  60   Transfers control to a 16-bit real mode entry point and returns the results.
  61   AsmPrepareThunk16() must be called with ThunkContext before this function is
  62   used. This function must be called with interrupts disabled.
  63
  64   If ThunkContext is NULL, then ASSERT().
  65   If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
  66
  67   @param  ThunkContext  A pointer to the context structure that describes the
  68                         16-bit real mode code to call.
  69
  70 **/
  71 VOID
  72 EFIAPI
  73 AsmThunk16 (
  74   IN OUT  THUNK_CONTEXT             *ThunkContext
  75   )
  76 {
  77   UINT16                            *Patch;
  78
  79   ASSERT (ThunkContext != NULL);
  80
  81   Patch = (UINT16*)(
  82             (UINTN)ThunkContext->RealModeCode +
  83             ThunkContext->RealModeCodeSize
  84             );
  85
  86   //
  87   // 0x9a66 is the OpCode of far call with an operand size override.
  88   //
  89   *Patch = 0x9a66;
  90
  91   //
  92   // CopyMem() here copies the updated register values back to RealModeState
  93   //
  94   CopyMem (
  95     &ThunkContext->RealModeState,
  96     InternalAsmThunk16 (&ThunkContext->RealModeState, Patch + 1),
  97     sizeof (ThunkContext->RealModeState)
  98     );
  99 }
 100
 101 /**
 102   Prepares all structures and code for a 16-bit real mode thunk, transfers
 103   control to a 16-bit real mode entry point, and returns the results.
 104
 105   Prepares all structures and code for a 16-bit real mode thunk, transfers
 106   control to a 16-bit real mode entry point, and returns the results. If the
 107   caller only need to perform a single 16-bit real mode thunk, then this
 108   service should be used. If the caller intends to make more than one 16-bit
 109   real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
 110   once and AsmThunk16() can be called for each 16-bit real mode thunk. This
 111   function must be called with interrupts disabled.
 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 AsmPrepareAndThunk16 (
 122   IN OUT  THUNK_CONTEXT             *ThunkContext
 123   )
 124 {
 125   AsmPrepareThunk16 (ThunkContext);
 126   AsmThunk16 (ThunkContext);
 127 }