[mirror_edk2.git] / EmbeddedPkg / GdbStub / Arm / Processor.c

/** @file\r
  Processor specific parts of the GDB stub\r
\r
  Copyright (c) 2008 - 2009, Apple Inc. All rights reserved.<BR>\r
\r
  SPDX-License-Identifier: BSD-2-Clause-Patent\r
\r
**/\r
\r
#include <GdbStubInternal.h>\r
#include <Library/CacheMaintenanceLib.h>\r
#include <Library/PrintLib.h>\r
\r
//\r
// Array of exception types that need to be hooked by the debugger\r
// (efi, gdb) //efi number\r
//\r
EFI_EXCEPTION_TYPE_ENTRY  gExceptionType[] = {\r
  { EXCEPT_ARM_SOFTWARE_INTERRUPT, GDB_SIGTRAP }\r
  //  { EXCEPT_ARM_UNDEFINED_INSTRUCTION, GDB_SIGTRAP },\r
  //  { EXCEPT_ARM_PREFETCH_ABORT,        GDB_SIGTRAP },\r
  //  { EXCEPT_ARM_DATA_ABORT,            GDB_SIGEMT  },\r
  //  { EXCEPT_ARM_RESERVED,              GDB_SIGILL  }\r
};\r
\r
UINTN  gRegisterOffsets[] = {\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R0),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R1),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R2),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R3),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R4),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R5),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R6),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R7),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R8),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R9),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R10),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R11),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, R12),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, SP),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, LR),\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, PC),\r
  0x00000F01,                        // f0\r
  0x00000F02,\r
  0x00000F03,\r
  0x00000F11,                        // f1\r
  0x00000F12,\r
  0x00000F13,\r
  0x00000F21,                        // f2\r
  0x00000F22,\r
  0x00000F23,\r
  0x00000F31,                        // f3\r
  0x00000F32,\r
  0x00000F33,\r
  0x00000F41,                        // f4\r
  0x00000F42,\r
  0x00000F43,\r
  0x00000F51,                        // f5\r
  0x00000F52,\r
  0x00000F53,\r
  0x00000F61,                        // f6\r
  0x00000F62,\r
  0x00000F63,\r
  0x00000F71,                        // f7\r
  0x00000F72,\r
  0x00000F73,\r
  0x00000FFF,                        // fps\r
  OFFSET_OF (EFI_SYSTEM_CONTEXT_ARM, CPSR)\r
};\r
\r
/**\r
 Return the number of entries in the gExceptionType[]\r
\r
 @retval  UINTN, the number of entries in the gExceptionType[] array.\r
 **/\r
UINTN\r
MaxEfiException (\r
  VOID\r
  )\r
{\r
  return sizeof (gExceptionType) / sizeof (EFI_EXCEPTION_TYPE_ENTRY);\r
}\r
\r
/**\r
 Return the number of entries in the gRegisters[]\r
\r
 @retval  UINTN, the number of entries (registers) in the gRegisters[] array.\r
 **/\r
UINTN\r
MaxRegisterCount (\r
  VOID\r
  )\r
{\r
  return sizeof (gRegisterOffsets) / sizeof (UINTN);\r
}\r
\r
/**\r
 Check to see if the ISA is supported.\r
 ISA = Instruction Set Architecture\r
\r
 @retval TRUE if Isa is supported\r
\r
**/\r
BOOLEAN\r
CheckIsa (\r
  IN  EFI_INSTRUCTION_SET_ARCHITECTURE  Isa\r
  )\r
{\r
  if (Isa == IsaArm) {\r
    return TRUE;\r
  } else {\r
    return FALSE;\r
  }\r
}\r
\r
/**\r
 This takes in the register number and the System Context, and returns a pointer to the RegNumber-th register in gdb ordering\r
 It is, by default, set to find the register pointer of the ARM member\r
 @param   SystemContext     Register content at time of the exception\r
 @param   RegNumber       The register to which we want to find a pointer\r
 @retval  the pointer to the RegNumber-th pointer\r
 **/\r
UINTN *\r
FindPointerToRegister (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  UINTN               RegNumber\r
  )\r
{\r
  UINT8  *TempPtr;\r
\r
  ASSERT (gRegisterOffsets[RegNumber] < 0xF00);\r
  TempPtr = ((UINT8 *)SystemContext.SystemContextArm) + gRegisterOffsets[RegNumber];\r
  return (UINT32 *)TempPtr;\r
}\r
\r
/**\r
 Adds the RegNumber-th register's value to the output buffer, starting at the given OutBufPtr\r
 @param SystemContext     Register content at time of the exception\r
 @param   RegNumber       the number of the register that we want to read\r
 @param   OutBufPtr       pointer to the output buffer's end. the new data will be added from this point on.\r
 @retval  the pointer to the next character of the output buffer that is available to be written on.\r
 **/\r
CHAR8 *\r
BasicReadRegister (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  UINTN               RegNumber,\r
  IN  CHAR8               *OutBufPtr\r
  )\r
{\r
  UINTN  RegSize;\r
  CHAR8  Char;\r
\r
  if (gRegisterOffsets[RegNumber] > 0xF00) {\r
    AsciiSPrint (OutBufPtr, 9, "00000000");\r
    OutBufPtr += 8;\r
    return OutBufPtr;\r
  }\r
\r
  RegSize = 0;\r
  while (RegSize < 32) {\r
    Char = mHexToStr[(UINT8)((*FindPointerToRegister (SystemContext, RegNumber) >> (RegSize+4)) & 0xf)];\r
    if ((Char >= 'A') && (Char <= 'F')) {\r
      Char = Char - 'A' + 'a';\r
    }\r
\r
    *OutBufPtr++ = Char;\r
\r
    Char = mHexToStr[(UINT8)((*FindPointerToRegister (SystemContext, RegNumber) >> RegSize) & 0xf)];\r
    if ((Char >= 'A') && (Char <= 'F')) {\r
      Char = Char - 'A' + 'a';\r
    }\r
\r
    *OutBufPtr++ = Char;\r
\r
    RegSize = RegSize + 8;\r
  }\r
\r
  return OutBufPtr;\r
}\r
\r
/**\r
 Reads the n-th register's value into an output buffer and sends it as a packet\r
 @param   SystemContext   Register content at time of the exception\r
 @param   InBuffer      Pointer to the input buffer received from gdb server\r
 **/\r
VOID\r
ReadNthRegister (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  CHAR8               *InBuffer\r
  )\r
{\r
  UINTN  RegNumber;\r
  CHAR8  OutBuffer[9]; // 1 reg=8 hex chars, and the end '\0' (escape seq)\r
  CHAR8  *OutBufPtr;   // pointer to the output buffer\r
\r
  RegNumber = AsciiStrHexToUintn (&InBuffer[1]);\r
\r
  if (RegNumber >= MaxRegisterCount ()) {\r
    SendError (GDB_EINVALIDREGNUM);\r
    return;\r
  }\r
\r
  OutBufPtr = OutBuffer;\r
  OutBufPtr = BasicReadRegister (SystemContext, RegNumber, OutBufPtr);\r
\r
  *OutBufPtr = '\0';  // the end of the buffer\r
  SendPacket (OutBuffer);\r
}\r
\r
/**\r
 Reads the general registers into an output buffer  and sends it as a packet\r
 @param   SystemContext     Register content at time of the exception\r
 **/\r
VOID\r
EFIAPI\r
ReadGeneralRegisters (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext\r
  )\r
{\r
  UINTN  Index;\r
  CHAR8  *OutBuffer;\r
  CHAR8  *OutBufPtr;\r
  UINTN  RegisterCount = MaxRegisterCount ();\r
\r
  // It is not safe to allocate pool here....\r
  OutBuffer = AllocatePool ((RegisterCount * 8) + 1); // 8 bytes per register in string format plus a null to terminate\r
  OutBufPtr = OutBuffer;\r
  for (Index = 0; Index < RegisterCount; Index++) {\r
    OutBufPtr = BasicReadRegister (SystemContext, Index, OutBufPtr);\r
  }\r
\r
  *OutBufPtr = '\0';\r
  SendPacket (OutBuffer);\r
  FreePool (OutBuffer);\r
}\r
\r
/**\r
 Adds the RegNumber-th register's value to the output buffer, starting at the given OutBufPtr\r
 @param   SystemContext       Register content at time of the exception\r
 @param   RegNumber         the number of the register that we want to write\r
 @param   InBufPtr          pointer to the output buffer. the new data will be extracted from the input buffer from this point on.\r
 @retval  the pointer to the next character of the input buffer that can be used\r
 **/\r
CHAR8\r
*\r
BasicWriteRegister (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  UINTN               RegNumber,\r
  IN  CHAR8               *InBufPtr\r
  )\r
{\r
  UINTN   RegSize;\r
  UINTN   TempValue; // the value transferred from a hex char\r
  UINT32  NewValue;  // the new value of the RegNumber-th Register\r
\r
  if (gRegisterOffsets[RegNumber] > 0xF00) {\r
    return InBufPtr + 8;\r
  }\r
\r
  NewValue = 0;\r
  RegSize  = 0;\r
  while (RegSize < 32) {\r
    TempValue = HexCharToInt (*InBufPtr++);\r
\r
    if ((INTN)TempValue < 0) {\r
      SendError (GDB_EBADMEMDATA);\r
      return NULL;\r
    }\r
\r
    NewValue += (TempValue << (RegSize+4));\r
    TempValue = HexCharToInt (*InBufPtr++);\r
\r
    if ((INTN)TempValue < 0) {\r
      SendError (GDB_EBADMEMDATA);\r
      return NULL;\r
    }\r
\r
    NewValue += (TempValue << RegSize);\r
    RegSize   = RegSize + 8;\r
  }\r
\r
  *(FindPointerToRegister (SystemContext, RegNumber)) = NewValue;\r
  return InBufPtr;\r
}\r
\r
/** ‘P n...=r...’\r
 Writes the new value of n-th register received into the input buffer to the n-th register\r
 @param   SystemContext   Register content at time of the exception\r
 @param   InBuffer      Pointer to the input buffer received from gdb server\r
 **/\r
VOID\r
WriteNthRegister (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  CHAR8               *InBuffer\r
  )\r
{\r
  UINTN  RegNumber;\r
  CHAR8  RegNumBuffer[MAX_REG_NUM_BUF_SIZE]; // put the 'n..' part of the message into this array\r
  CHAR8  *RegNumBufPtr;\r
  CHAR8  *InBufPtr; // pointer to the input buffer\r
\r
  // find the register number to write\r
  InBufPtr     = &InBuffer[1];\r
  RegNumBufPtr = RegNumBuffer;\r
  while (*InBufPtr != '=') {\r
    *RegNumBufPtr++ = *InBufPtr++;\r
  }\r
\r
  *RegNumBufPtr = '\0';\r
  RegNumber     = AsciiStrHexToUintn (RegNumBuffer);\r
\r
  // check if this is a valid Register Number\r
  if (RegNumber >= MaxRegisterCount ()) {\r
    SendError (GDB_EINVALIDREGNUM);\r
    return;\r
  }\r
\r
  InBufPtr++;  // skips the '=' character\r
  BasicWriteRegister (SystemContext, RegNumber, InBufPtr);\r
  SendSuccess ();\r
}\r
\r
/** ‘G XX...’\r
 Writes the new values received into the input buffer to the general registers\r
 @param   SystemContext       Register content at time of the exception\r
 @param   InBuffer          Pointer to the input buffer received from gdb server\r
 **/\r
VOID\r
EFIAPI\r
WriteGeneralRegisters (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  CHAR8               *InBuffer\r
  )\r
{\r
  UINTN  i;\r
  CHAR8  *InBufPtr; /// pointer to the input buffer\r
  UINTN  MinLength;\r
  UINTN  RegisterCount = MaxRegisterCount ();\r
\r
  MinLength = (RegisterCount * 8) + 1;  // 'G' plus the registers in ASCII format\r
\r
  if (AsciiStrLen (InBuffer) < MinLength) {\r
    // Bad message. Message is not the right length\r
    SendError (GDB_EBADBUFSIZE);\r
    return;\r
  }\r
\r
  InBufPtr = &InBuffer[1];\r
\r
  // Read the new values for the registers from the input buffer to an array, NewValueArray.\r
  // The values in the array are in the gdb ordering\r
  for (i = 0; i < RegisterCount; i++) {\r
    InBufPtr = BasicWriteRegister (SystemContext, i, InBufPtr);\r
  }\r
\r
  SendSuccess ();\r
}\r
\r
// What about Thumb?\r
// Use SWI 0xdbdbdb as the debug instruction\r
#define GDB_ARM_BKPT  0xefdbdbdb\r
\r
BOOLEAN  mSingleStepActive = FALSE;\r
UINT32   mSingleStepPC;\r
UINT32   mSingleStepData;\r
UINTN    mSingleStepDataSize;\r
\r
typedef struct {\r
  LIST_ENTRY    Link;\r
  UINT64        Signature;\r
  UINT32        Address;\r
  UINT32        Instruction;\r
} ARM_SOFTWARE_BREAKPOINT;\r
\r
#define ARM_SOFTWARE_BREAKPOINT_SIGNATURE  SIGNATURE_64('A', 'R', 'M', 'B', 'R', 'K', 'P', 'T')\r
#define ARM_SOFTWARE_BREAKPOINT_FROM_LINK(a)  CR(a, ARM_SOFTWARE_BREAKPOINT, Link, ARM_SOFTWARE_BREAKPOINT_SIGNATURE)\r
\r
LIST_ENTRY  BreakpointList;\r
\r
/**\r
 Insert Single Step in the SystemContext\r
\r
 @param SystemContext  Register content at time of the exception\r
 **/\r
VOID\r
AddSingleStep (\r
  IN EFI_SYSTEM_CONTEXT  SystemContext\r
  )\r
{\r
  if (mSingleStepActive) {\r
    // Currently don't support nesting\r
    return;\r
  }\r
\r
  mSingleStepActive = TRUE;\r
\r
  mSingleStepPC = SystemContext.SystemContextArm->PC;\r
\r
  mSingleStepDataSize      = sizeof (UINT32);\r
  mSingleStepData          = (*(UINT32 *)mSingleStepPC);\r
  *(UINT32 *)mSingleStepPC = GDB_ARM_BKPT;\r
  if (*(UINT32 *)mSingleStepPC != GDB_ARM_BKPT) {\r
    // For some reason our breakpoint did not take\r
    mSingleStepActive = FALSE;\r
  }\r
\r
  InvalidateInstructionCacheRange ((VOID *)mSingleStepPC, mSingleStepDataSize);\r
  // DEBUG((DEBUG_ERROR, "AddSingleStep at 0x%08x (was: 0x%08x is:0x%08x)\n", SystemContext.SystemContextArm->PC, mSingleStepData, *(UINT32 *)mSingleStepPC));\r
}\r
\r
/**\r
 Remove Single Step in the SystemContext\r
\r
 @param SystemContext  Register content at time of the exception\r
 **/\r
VOID\r
RemoveSingleStep (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext\r
  )\r
{\r
  if (!mSingleStepActive) {\r
    return;\r
  }\r
\r
  if (mSingleStepDataSize == sizeof (UINT16)) {\r
    *(UINT16 *)mSingleStepPC = (UINT16)mSingleStepData;\r
  } else {\r
    // DEBUG((DEBUG_ERROR, "RemoveSingleStep at 0x%08x (was: 0x%08x is:0x%08x)\n", SystemContext.SystemContextArm->PC, *(UINT32 *)mSingleStepPC, mSingleStepData));\r
    *(UINT32 *)mSingleStepPC = mSingleStepData;\r
  }\r
\r
  InvalidateInstructionCacheRange ((VOID *)mSingleStepPC, mSingleStepDataSize);\r
  mSingleStepActive = FALSE;\r
}\r
\r
/**\r
 Continue. addr is Address to resume. If addr is omitted, resume at current\r
 Address.\r
\r
 @param   SystemContext     Register content at time of the exception\r
 **/\r
VOID\r
EFIAPI\r
ContinueAtAddress (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN    CHAR8             *PacketData\r
  )\r
{\r
  if (PacketData[1] != '\0') {\r
    SystemContext.SystemContextArm->PC = AsciiStrHexToUintn (&PacketData[1]);\r
  }\r
}\r
\r
/** ‘s [addr ]’\r
 Single step. addr is the Address at which to resume. If addr is omitted, resume\r
 at same Address.\r
\r
 @param   SystemContext     Register content at time of the exception\r
 **/\r
VOID\r
EFIAPI\r
SingleStep (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN    CHAR8             *PacketData\r
  )\r
{\r
  SendNotSupported ();\r
}\r
\r
UINTN\r
GetBreakpointDataAddress (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  UINTN               BreakpointNumber\r
  )\r
{\r
  return 0;\r
}\r
\r
UINTN\r
GetBreakpointDetected (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext\r
  )\r
{\r
  return 0;\r
}\r
\r
BREAK_TYPE\r
GetBreakpointType (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  UINTN               BreakpointNumber\r
  )\r
{\r
  return NotSupported;\r
}\r
\r
ARM_SOFTWARE_BREAKPOINT *\r
SearchBreakpointList (\r
  IN  UINT32  Address\r
  )\r
{\r
  LIST_ENTRY               *Current;\r
  ARM_SOFTWARE_BREAKPOINT  *Breakpoint;\r
\r
  Current = GetFirstNode (&BreakpointList);\r
  while (!IsNull (&BreakpointList, Current)) {\r
    Breakpoint = ARM_SOFTWARE_BREAKPOINT_FROM_LINK (Current);\r
\r
    if (Address == Breakpoint->Address) {\r
      return Breakpoint;\r
    }\r
\r
    Current = GetNextNode (&BreakpointList, Current);\r
  }\r
\r
  return NULL;\r
}\r
\r
VOID\r
SetBreakpoint (\r
  IN UINT32  Address\r
  )\r
{\r
  ARM_SOFTWARE_BREAKPOINT  *Breakpoint;\r
\r
  Breakpoint = SearchBreakpointList (Address);\r
\r
  if (Breakpoint != NULL) {\r
    return;\r
  }\r
\r
  // create and fill breakpoint structure\r
  Breakpoint = AllocatePool (sizeof (ARM_SOFTWARE_BREAKPOINT));\r
\r
  Breakpoint->Signature   = ARM_SOFTWARE_BREAKPOINT_SIGNATURE;\r
  Breakpoint->Address     = Address;\r
  Breakpoint->Instruction = *(UINT32 *)Address;\r
\r
  // Add it to the list\r
  InsertTailList (&BreakpointList, &Breakpoint->Link);\r
\r
  // Insert the software breakpoint\r
  *(UINT32 *)Address = GDB_ARM_BKPT;\r
  InvalidateInstructionCacheRange ((VOID *)Address, 4);\r
\r
  // DEBUG((DEBUG_ERROR, "SetBreakpoint at 0x%08x (was: 0x%08x is:0x%08x)\n", Address, Breakpoint->Instruction, *(UINT32 *)Address));\r
}\r
\r
VOID\r
ClearBreakpoint (\r
  IN UINT32  Address\r
  )\r
{\r
  ARM_SOFTWARE_BREAKPOINT  *Breakpoint;\r
\r
  Breakpoint = SearchBreakpointList (Address);\r
\r
  if (Breakpoint == NULL) {\r
    return;\r
  }\r
\r
  // Add it to the list\r
  RemoveEntryList (&Breakpoint->Link);\r
\r
  // Restore the original instruction\r
  *(UINT32 *)Address = Breakpoint->Instruction;\r
  InvalidateInstructionCacheRange ((VOID *)Address, 4);\r
\r
  // DEBUG((DEBUG_ERROR, "ClearBreakpoint at 0x%08x (was: 0x%08x is:0x%08x)\n", Address, GDB_ARM_BKPT, *(UINT32 *)Address));\r
\r
  FreePool (Breakpoint);\r
}\r
\r
VOID\r
EFIAPI\r
InsertBreakPoint (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  CHAR8               *PacketData\r
  )\r
{\r
  UINTN  Type;\r
  UINTN  Address;\r
  UINTN  Length;\r
  UINTN  ErrorCode;\r
\r
  ErrorCode = ParseBreakpointPacket (PacketData, &Type, &Address, &Length);\r
  if (ErrorCode > 0) {\r
    SendError ((UINT8)ErrorCode);\r
    return;\r
  }\r
\r
  switch (Type) {\r
    case 0:   // Software breakpoint\r
      break;\r
\r
    default:\r
      DEBUG ((DEBUG_ERROR, "Insert breakpoint default: %x\n", Type));\r
      SendError (GDB_EINVALIDBRKPOINTTYPE);\r
      return;\r
  }\r
\r
  SetBreakpoint (Address);\r
\r
  SendSuccess ();\r
}\r
\r
VOID\r
EFIAPI\r
RemoveBreakPoint (\r
  IN  EFI_SYSTEM_CONTEXT  SystemContext,\r
  IN  CHAR8               *PacketData\r
  )\r
{\r
  UINTN  Type;\r
  UINTN  Address;\r
  UINTN  Length;\r
  UINTN  ErrorCode;\r
\r
  // Parse breakpoint packet data\r
  ErrorCode = ParseBreakpointPacket (PacketData, &Type, &Address, &Length);\r
  if (ErrorCode > 0) {\r
    SendError ((UINT8)ErrorCode);\r
    return;\r
  }\r
\r
  switch (Type) {\r
    case 0:   // Software breakpoint\r
      break;\r
\r
    default:\r
      SendError (GDB_EINVALIDBRKPOINTTYPE);\r
      return;\r
  }\r
\r
  ClearBreakpoint (Address);\r
\r
  SendSuccess ();\r
}\r
\r
VOID\r
InitializeProcessor (\r
  VOID\r
  )\r
{\r
  // Initialize breakpoint list\r
  InitializeListHead (&BreakpointList);\r
}\r
\r
BOOLEAN\r
ValidateAddress (\r
  IN  VOID  *Address\r
  )\r
{\r
  if ((UINT32)Address < 0x80000000) {\r
    return FALSE;\r
  } else {\r
    return TRUE;\r
  }\r
}\r
\r
BOOLEAN\r
ValidateException (\r
  IN  EFI_EXCEPTION_TYPE     ExceptionType,\r
  IN OUT EFI_SYSTEM_CONTEXT  SystemContext\r
  )\r
{\r
  UINT32  ExceptionAddress;\r
  UINT32  Instruction;\r
\r
  // Is it a debugger SWI?\r
  ExceptionAddress = SystemContext.SystemContextArm->PC -= 4;\r
  Instruction      = *(UINT32 *)ExceptionAddress;\r
  if (Instruction != GDB_ARM_BKPT) {\r
    return FALSE;\r
  }\r
\r
  // Special for SWI-based exception handling.  SWI sets up the context\r
  // to return to the instruction following the SWI instruction - NOT what we want\r
  // for a debugger!\r
  SystemContext.SystemContextArm->PC = ExceptionAddress;\r
\r
  return TRUE;\r
}\r