/** @file
  Execute 32-bit code in Long Mode.
  Provide a thunk function to transition from long mode to compatibility mode to execute 32-bit code and then transit
  back to long mode.

  Copyright (c) 2014 - 2015, Intel Corporation. All rights reserved.<BR>
  This program and the accompanying materials
  are licensed and made available under the terms and conditions of the BSD License
  which accompanies this distribution.  The full text of the license may be found at
  http://opensource.org/licenses/bsd-license.php.

  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/

#include <Uefi.h>
#include <Library/BaseLib.h>
#include <FspApi.h>

#pragma pack(1)
typedef union {
  struct {
    UINT32  LimitLow    : 16;
    UINT32  BaseLow     : 16;
    UINT32  BaseMid     : 8;
    UINT32  Type        : 4;
    UINT32  System      : 1;
    UINT32  Dpl         : 2;
    UINT32  Present     : 1;
    UINT32  LimitHigh   : 4;
    UINT32  Software    : 1;
    UINT32  Reserved    : 1;
    UINT32  DefaultSize : 1;
    UINT32  Granularity : 1;
    UINT32  BaseHigh    : 8;
  } Bits;
  UINT64  Uint64;
} IA32_GDT;
#pragma pack()

GLOBAL_REMOVE_IF_UNREFERENCED IA32_GDT mGdtEntries[] = {
  {{0,      0,  0,  0,    0,  0,  0,  0,    0,  0, 0,  0,  0}}, /* 0x0:  reserve */
  {{0xFFFF, 0,  0,  0xB,  1,  0,  1,  0xF,  0,  0, 1,  1,  0}}, /* 0x8:  compatibility mode */
  {{0xFFFF, 0,  0,  0xB,  1,  0,  1,  0xF,  0,  1, 0,  1,  0}}, /* 0x10: for long mode */
  {{0xFFFF, 0,  0,  0x3,  1,  0,  1,  0xF,  0,  0, 1,  1,  0}}, /* 0x18: data */
  {{0,      0,  0,  0,    0,  0,  0,  0,    0,  0, 0,  0,  0}}, /* 0x20: reserve */
};

//
// IA32 Gdt register
//
GLOBAL_REMOVE_IF_UNREFERENCED IA32_DESCRIPTOR mGdt = {
  sizeof (mGdtEntries) - 1,
  (UINTN) mGdtEntries
  };

/**
  Assembly function to transition from long mode to compatibility mode to execute 32-bit code and then transit back to
  long mode.

  @param[in] Function     The 32bit code entry to be executed.
  @param[in] Param1       The first parameter to pass to 32bit code
  @param[in] Param2       The second parameter to pass to 32bit code
  @param[in] InternalGdtr The GDT and GDT descriptor used by this library

  @return status.
**/
UINT32
AsmExecute32BitCode (
  IN UINT64           Function,
  IN UINT64           Param1,
  IN UINT64           Param2,
  IN IA32_DESCRIPTOR  *InternalGdtr
  );

/**
  Wrapper for a thunk  to transition from long mode to compatibility mode to execute 32-bit code and then transit back to
  long mode.

  @param[in] Function     The 32bit code entry to be executed.
  @param[in] Param1       The first parameter to pass to 32bit code.

  @return EFI_STATUS.
**/
EFI_STATUS
Execute32BitCode (
  IN UINT64      Function,
  IN UINT64      Param1
  )
{
  EFI_STATUS       Status;
  IA32_DESCRIPTOR  Idtr;

  //
  // Idtr might be changed inside of FSP. 32bit FSP only knows the <4G address.
  // If IDTR.Base is >4G, FSP can not handle. So we need save/restore IDTR here for X64 only.
  // Interrupt is already disabled here, so it is safety to update IDTR.
  //
  AsmReadIdtr (&Idtr);
  Status = AsmExecute32BitCode (Function, Param1, 0, &mGdt);
  AsmWriteIdtr (&Idtr);

  return Status;
}