source: vbox/trunk/src/VBox/Devices/EFI/FirmwareNew/MdePkg/Library/UefiBootServicesTableLib/UefiBootServicesTableLib.c

/** @file
  This library retrieve the EFI_BOOT_SERVICES pointer from EFI system table in
  library's constructor.

  Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
  SPDX-License-Identifier: BSD-2-Clause-Patent

**/

#include <Uefi.h>

#include <Library/UefiBootServicesTableLib.h>
#include <Library/DebugLib.h>

EFI_HANDLE         gImageHandle = NULL;
EFI_SYSTEM_TABLE   *gST         = NULL;
EFI_BOOT_SERVICES  *gBS         = NULL;

/**
  The constructor function caches the pointer of Boot Services Table.

  The constructor function caches the pointer of Boot Services Table through System Table.
  It will ASSERT() if the pointer of System Table is NULL.
  It will ASSERT() if the pointer of Boot Services Table is NULL.
  It will always return EFI_SUCCESS.

  @param  ImageHandle   The firmware allocated handle for the EFI image.
  @param  SystemTable   A pointer to the EFI System Table.

  @retval EFI_SUCCESS   The constructor always returns EFI_SUCCESS.

**/
EFI_STATUS
EFIAPI
UefiBootServicesTableLibConstructor (
  IN EFI_HANDLE        ImageHandle,
  IN EFI_SYSTEM_TABLE  *SystemTable
  )
{
  //
  // Cache the Image Handle
  //
  gImageHandle = ImageHandle;
  ASSERT (gImageHandle != NULL);

  //
  // Cache pointer to the EFI System Table
  //
  gST = SystemTable;
  ASSERT (gST != NULL);

  //
  // Cache pointer to the EFI Boot Services Table
  //
  gBS = SystemTable->BootServices;
  ASSERT (gBS != NULL);

  return EFI_SUCCESS;
}