SourceLevelDebugPkg/Library/DebugAgent/DebugAgentCommon/Ia32/ArchDebugSupport.c

/** @file
  Supporting functions for IA32 architecture.

  Copyright (c) 2010 - 2018, Intel Corporation. All rights reserved.<BR>
  SPDX-License-Identifier: BSD-2-Clause-Patent

**/

#include "DebugAgent.h"

/**
  Initialize IDT entries to support source level debug.

**/
VOID
InitializeDebugIdt (
  VOID
  )
{
  IA32_IDT_GATE_DESCRIPTOR  *IdtEntry;
  UINTN                     InterruptHandler;
  IA32_DESCRIPTOR           IdtDescriptor;
  UINTN                     Index;
  UINT16                    CodeSegment;
  UINT32                    RegEdx;

  AsmReadIdtr (&IdtDescriptor);

  //
  // Use current CS as the segment selector of interrupt gate in IDT
  //
  CodeSegment = AsmReadCs ();

  IdtEntry = (IA32_IDT_GATE_DESCRIPTOR *)IdtDescriptor.Base;

  for (Index = 0; Index < 20; Index++) {
    if (((PcdGet32 (PcdExceptionsIgnoredByDebugger) & ~(BIT1 | BIT3)) & (1 << Index)) != 0) {
      //
      // If the exception is masked to be reserved except for INT1 and INT3, skip it
      //
      continue;
    }

    InterruptHandler                = (UINTN)&Exception0Handle + Index * ExceptionStubHeaderSize;
    IdtEntry[Index].Bits.OffsetLow  = (UINT16)(UINTN)InterruptHandler;
    IdtEntry[Index].Bits.OffsetHigh = (UINT16)((UINTN)InterruptHandler >> 16);
    IdtEntry[Index].Bits.Selector   = CodeSegment;
    IdtEntry[Index].Bits.GateType   = IA32_IDT_GATE_TYPE_INTERRUPT_32;
  }

  InterruptHandler                             = (UINTN)&TimerInterruptHandle;
  IdtEntry[DEBUG_TIMER_VECTOR].Bits.OffsetLow  = (UINT16)(UINTN)InterruptHandler;
  IdtEntry[DEBUG_TIMER_VECTOR].Bits.OffsetHigh = (UINT16)((UINTN)InterruptHandler >> 16);
  IdtEntry[DEBUG_TIMER_VECTOR].Bits.Selector   = CodeSegment;
  IdtEntry[DEBUG_TIMER_VECTOR].Bits.GateType   = IA32_IDT_GATE_TYPE_INTERRUPT_32;

  //
  // If the CPU supports Debug Extensions(CPUID:01 EDX:BIT2), then
  // Set DE flag in CR4 to enable IO breakpoint
  //
  AsmCpuid (1, NULL, NULL, NULL, &RegEdx);
  if ((RegEdx & BIT2) != 0) {
    AsmWriteCr4 (AsmReadCr4 () | BIT3);
  }
}

/**
  Retrieve exception handler from IDT table by ExceptionNum.

  @param[in]  ExceptionNum    Exception number

  @return Exception handler

**/
VOID *
GetExceptionHandlerInIdtEntry (
  IN UINTN  ExceptionNum
  )
{
  IA32_IDT_GATE_DESCRIPTOR  *IdtEntry;
  IA32_DESCRIPTOR           IdtDescriptor;

  AsmReadIdtr (&IdtDescriptor);
  IdtEntry = (IA32_IDT_GATE_DESCRIPTOR *)IdtDescriptor.Base;

  return (VOID *)(((UINTN)IdtEntry[ExceptionNum].Bits.OffsetLow) |
                  (((UINTN)IdtEntry[ExceptionNum].Bits.OffsetHigh) << 16));
}

/**
  Set exception handler in IDT table by ExceptionNum.

  @param[in]  ExceptionNum      Exception number
  @param[in]  ExceptionHandler  Exception Handler to be set

**/
VOID
SetExceptionHandlerInIdtEntry (
  IN UINTN  ExceptionNum,
  IN VOID   *ExceptionHandler
  )
{
  IA32_IDT_GATE_DESCRIPTOR  *IdtEntry;
  IA32_DESCRIPTOR           IdtDescriptor;

  AsmReadIdtr (&IdtDescriptor);
  IdtEntry = (IA32_IDT_GATE_DESCRIPTOR *)IdtDescriptor.Base;

  IdtEntry[ExceptionNum].Bits.OffsetLow  = (UINT16)(UINTN)ExceptionHandler;
  IdtEntry[ExceptionNum].Bits.OffsetHigh = (UINT16)((UINTN)ExceptionHandler >> 16);
}