/** @file
  C based implemention of IA32 interrupt handling only
  requiring a minimal assembly interrupt entry point.

  Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
  SPDX-License-Identifier: BSD-2-Clause-Patent

**/

#include "CpuDxe.h"
#include "CpuGdt.h"

//
// Global descriptor table (GDT) Template
//
STATIC GDT_ENTRIES GdtTemplate = {
  //
  // NULL_SEL
  //
  {
    0x0,            // limit 15:0
    0x0,            // base 15:0
    0x0,            // base 23:16
    0x0,            // type
    0x0,            // limit 19:16, flags
    0x0,            // base 31:24
  },
  //
  // LINEAR_SEL
  //
  {
    0x0FFFF,        // limit 15:0
    0x0,            // base 15:0
    0x0,            // base 23:16
    0x092,          // present, ring 0, data, read/write
    0x0CF,          // page-granular, 32-bit
    0x0,
  },
  //
  // LINEAR_CODE_SEL
  //
  {
    0x0FFFF,        // limit 15:0
    0x0,            // base 15:0
    0x0,            // base 23:16
    0x09F,          // present, ring 0, code, execute/read, conforming, accessed
    0x0CF,          // page-granular, 32-bit
    0x0,
  },
  //
  // SYS_DATA_SEL
  //
  {
    0x0FFFF,        // limit 15:0
    0x0,            // base 15:0
    0x0,            // base 23:16
    0x093,          // present, ring 0, data, read/write, accessed
    0x0CF,          // page-granular, 32-bit
    0x0,
  },
  //
  // SYS_CODE_SEL
  //
  {
    0x0FFFF,        // limit 15:0
    0x0,            // base 15:0
    0x0,            // base 23:16
    0x09A,          // present, ring 0, code, execute/read
    0x0CF,          // page-granular, 32-bit
    0x0,
  },
  //
  // SPARE4_SEL
  //
  {
    0x0,            // limit 15:0
    0x0,            // base 15:0
    0x0,            // base 23:16
    0x0,            // type
    0x0,            // limit 19:16, flags
    0x0,            // base 31:24
  },
  //
  // LINEAR_DATA64_SEL
  //
  {
    0x0FFFF,        // limit 15:0
    0x0,            // base 15:0
    0x0,            // base 23:16
    0x092,          // present, ring 0, data, read/write
    0x0CF,          // page-granular, 32-bit
    0x0,
  },
  //
  // LINEAR_CODE64_SEL
  //
  {
    0x0FFFF,        // limit 15:0
    0x0,            // base 15:0
    0x0,            // base 23:16
    0x09A,          // present, ring 0, code, execute/read
    0x0AF,          // page-granular, 64-bit code
    0x0,            // base (high)
  },
  //
  // SPARE5_SEL
  //
  {
    0x0,            // limit 15:0
    0x0,            // base 15:0
    0x0,            // base 23:16
    0x0,            // type
    0x0,            // limit 19:16, flags
    0x0,            // base 31:24
  },
};

/**
  Initialize Global Descriptor Table.

**/
VOID
InitGlobalDescriptorTable (
  VOID
  )
{
  GDT_ENTRIES *gdt;
  IA32_DESCRIPTOR gdtPtr;

  //
  // Allocate Runtime Data for the GDT
  //
#ifndef VBOX
  gdt = AllocateRuntimePool (sizeof (GdtTemplate) + 8);
#else
  /*
   * Apples bootloader boot.efi for at least OS X Tiger, Leopard and Snow Leopard
   * relocates runtime regions which doesn't make sense for the GDT as the GDTR is not
   * updated and would point to invalid memory. Allocate the memory as reserved to hopefully
   * keep the bootloaders hands off of it, see also OvmfPkg/PlatformPei/Platform.c
   * (search for PeiServicesAllocatePages()) for a more detailed explanation of a
   * related bug in Apples bootloader.
   */
  gdt = AllocateReservedPool (sizeof (GdtTemplate) + 8);
#endif
  ASSERT (gdt != NULL);
  gdt = ALIGN_POINTER (gdt, 8);

  //
  // Initialize all GDT entries
  //
  CopyMem (gdt, &GdtTemplate, sizeof (GdtTemplate));

  //
  // Write GDT register
  //
  gdtPtr.Base = (UINT32)(UINTN)(VOID*) gdt;
  gdtPtr.Limit = (UINT16) (sizeof (GdtTemplate) - 1);
  AsmWriteGdtr (&gdtPtr);

  //
  // Update selector (segment) registers base on new GDT
  //
  SetCodeSelector ((UINT16)CPU_CODE_SEL);
  SetDataSelectors ((UINT16)CPU_DATA_SEL);
}

