audk/UefiCpuPkg/CpuDxe/CpuGdt.c

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

  Copyright (c) 2006 - 2010, 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 "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 0xFFFFF
    0x0,            // base 0
    0x0,
    0x092,          // present, ring 0, data, expand-up, writable
    0x0CF,          // page-granular, 32-bit
    0x0,
  },
  //
  // LINEAR_CODE_SEL
  //
  {
    0x0FFFF,        // limit 0xFFFFF
    0x0,            // base 0
    0x0,
    0x09A,          // present, ring 0, data, expand-up, writable
    0x0CF,          // page-granular, 32-bit
    0x0,
  },
  //
  // SYS_DATA_SEL
  //
  {
    0x0FFFF,        // limit 0xFFFFF
    0x0,            // base 0
    0x0,
    0x092,          // present, ring 0, data, expand-up, writable
    0x0CF,          // page-granular, 32-bit
    0x0,
  },
  //
  // SYS_CODE_SEL
  //
  {
    0x0FFFF,        // limit 0xFFFFF
    0x0,            // base 0
    0x0,
    0x09A,          // present, ring 0, data, expand-up, writable
    0x0CF,          // page-granular, 32-bit
    0x0,
  },
  //
  // LINEAR_CODE64_SEL
  //
  {
    0x0FFFF,        // limit 0xFFFFF
    0x0,            // base 0
    0x0,
    0x09B,          // present, ring 0, code, expand-up, writable
    0x0AF,          // LimitHigh (CS.L=1, CS.D=0)
    0x0,            // base (high)
  },
  //
  // SPARE4_SEL
  //
  {
    0x0,            // limit 0
    0x0,            // base 0
    0x0,
    0x0,            // present, ring 0, data, expand-up, writable
    0x0,            // page-granular, 32-bit
    0x0,
  },
  //
  // SPARE5_SEL
  //
  {
    0x0,            // limit 0
    0x0,            // base 0
    0x0,
    0x0,            // present, ring 0, data, expand-up, writable
    0x0,            // page-granular, 32-bit
    0x0,
  },
};

/**
  Initialize Global Descriptor Table.

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

  //
  // Allocate Runtime Data for the GDT
  //
  gdt = AllocateRuntimePool (sizeof (GdtTemplate) + 8);
  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);
}