kdb.c

Go to the documentation of this file.

/*
 * COPYRIGHT:       See COPYING in the top level directory
 * PROJECT:         ReactOS kernel
 * FILE:            ntoskrnl/kdbg/kdb.c
 * PURPOSE:         Kernel Debugger
 *
 * PROGRAMMERS:     Gregor Anich
 */

/* INCLUDES ******************************************************************/

#include <ntoskrnl.h>
#define NDEBUG
#include <debug.h>

/* TYPES *********************************************************************/

/* DEFINES *******************************************************************/

#define KDB_STACK_SIZE                   (4096*3)
#define KDB_MAXIMUM_BREAKPOINT_COUNT     256
#define KDB_MAXIMUM_HW_BREAKPOINT_COUNT  4
#define KDB_MAXIMUM_SW_BREAKPOINT_COUNT  256

#define __STRING(x) #x
#define _STRING(x) __STRING(x)

/* GLOBALS *******************************************************************/

static LONG KdbEntryCount = 0;
static CHAR KdbStack[KDB_STACK_SIZE];

static ULONG KdbBreakPointCount = 0;  /* Number of used breakpoints in the array */
static KDB_BREAKPOINT KdbBreakPoints[KDB_MAXIMUM_BREAKPOINT_COUNT] = {{0}};  /* Breakpoint array */
static ULONG KdbSwBreakPointCount = 0;  /* Number of enabled software breakpoints */
static ULONG KdbHwBreakPointCount = 0;  /* Number of enabled hardware breakpoints */
static PKDB_BREAKPOINT KdbSwBreakPoints[KDB_MAXIMUM_SW_BREAKPOINT_COUNT]; /* Enabled software breakpoints, orderless */
static PKDB_BREAKPOINT KdbHwBreakPoints[KDB_MAXIMUM_HW_BREAKPOINT_COUNT]; /* Enabled hardware breakpoints, orderless */
static PKDB_BREAKPOINT KdbBreakPointToReenable = NULL; /* Set to a breakpoint struct when single stepping after
                                                          a software breakpoint was hit, to reenable it */
LONG KdbLastBreakPointNr = -1;  /* Index of the breakpoint which cause KDB to be entered */
ULONG KdbNumSingleSteps = 0; /* How many single steps to do */
BOOLEAN KdbSingleStepOver = FALSE; /* Whether to step over calls/reps. */
ULONG KdbDebugState = 0; /* KDBG Settings (NOECHO, KDSERIAL) */
static BOOLEAN KdbEnteredOnSingleStep = FALSE; /* Set to true when KDB was entered because of single step */
PEPROCESS KdbCurrentProcess = NULL;  /* The current process context in which KDB runs */
PEPROCESS KdbOriginalProcess = NULL; /* The process in whichs context KDB was intered */
PETHREAD KdbCurrentThread = NULL;  /* The current thread context in which KDB runs */
PETHREAD KdbOriginalThread = NULL; /* The thread in whichs context KDB was entered */
PKDB_KTRAP_FRAME KdbCurrentTrapFrame = NULL; /* Pointer to the current trapframe */
static KDB_KTRAP_FRAME KdbTrapFrame = { { 0 } };  /* The trapframe which was passed to KdbEnterDebuggerException */
static KDB_KTRAP_FRAME KdbThreadTrapFrame = { { 0 } }; /* The trapframe of the current thread (KdbCurrentThread) */
static KAPC_STATE KdbApcState;
extern BOOLEAN KdbpBugCheckRequested;

/* Array of conditions when to enter KDB */
static KDB_ENTER_CONDITION KdbEnterConditions[][2] =
{
    /* First chance       Last chance */
    { KdbDoNotEnter,      KdbEnterFromKmode },   /* Zero devide */
    { KdbEnterFromKmode,  KdbDoNotEnter },       /* Debug trap */
    { KdbDoNotEnter,      KdbEnterAlways },      /* NMI */
    { KdbEnterFromKmode,  KdbDoNotEnter },       /* INT3 */
    { KdbDoNotEnter,      KdbEnterFromKmode },   /* Overflow */
    { KdbDoNotEnter,      KdbEnterFromKmode },
    { KdbDoNotEnter,      KdbEnterFromKmode },   /* Invalid opcode */
    { KdbDoNotEnter,      KdbEnterFromKmode },   /* No math coprocessor fault */
    { KdbEnterAlways,     KdbEnterAlways },
    { KdbEnterAlways,     KdbEnterAlways },
    { KdbDoNotEnter,      KdbEnterFromKmode },
    { KdbDoNotEnter,      KdbEnterFromKmode },
    { KdbDoNotEnter,      KdbEnterFromKmode },   /* Stack fault */
    { KdbDoNotEnter,      KdbEnterFromKmode },   /* General protection fault */
    { KdbDoNotEnter,      KdbEnterFromKmode },   /* Page fault */
    { KdbEnterAlways,     KdbEnterAlways },      /* Reserved (15) */
    { KdbDoNotEnter,      KdbEnterFromKmode },   /* FPU fault */
    { KdbDoNotEnter,      KdbEnterFromKmode },
    { KdbDoNotEnter,      KdbEnterFromKmode },
    { KdbDoNotEnter,      KdbEnterFromKmode },   /* SIMD fault */
    { KdbDoNotEnter,      KdbEnterFromKmode }    /* Last entry: used for unknown exceptions */
};

/* Exception descriptions */
static const CHAR *ExceptionNrToString[] =
{
    "Divide Error",
    "Debug Trap",
    "NMI",
    "Breakpoint",
    "Overflow",
    "BOUND range exceeded",
    "Invalid Opcode",
    "No Math Coprocessor",
    "Double Fault",
    "Unknown(9)",
    "Invalid TSS",
    "Segment Not Present",
    "Stack Segment Fault",
    "General Protection",
    "Page Fault",
    "Reserved(15)",
    "Math Fault",
    "Alignment Check",
    "Machine Check",
    "SIMD Fault"
};

ULONG
NTAPI
KiSsFromTrapFrame(
    IN PKTRAP_FRAME TrapFrame);

ULONG
NTAPI
KiEspFromTrapFrame(
    IN PKTRAP_FRAME TrapFrame);

VOID
NTAPI
KiSsToTrapFrame(
    IN PKTRAP_FRAME TrapFrame,
    IN ULONG Ss);

VOID
NTAPI
KiEspToTrapFrame(
    IN PKTRAP_FRAME TrapFrame,
    IN ULONG Esp);

/* FUNCTIONS *****************************************************************/

static VOID
KdbpTrapFrameToKdbTrapFrame(
    PKTRAP_FRAME TrapFrame,
    PKDB_KTRAP_FRAME KdbTrapFrame)
{
    ULONG TrapCr0, TrapCr2, TrapCr3, TrapCr4;

    /* Copy the TrapFrame only up to Eflags and zero the rest*/
    RtlCopyMemory(&KdbTrapFrame->Tf, TrapFrame, FIELD_OFFSET(KTRAP_FRAME, HardwareEsp));
    RtlZeroMemory((PVOID)((ULONG_PTR)&KdbTrapFrame->Tf + FIELD_OFFSET(KTRAP_FRAME, HardwareEsp)),
                  sizeof(KTRAP_FRAME) - FIELD_OFFSET(KTRAP_FRAME, HardwareEsp));

#ifndef _MSC_VER
   asm volatile(
      "movl %%cr0, %0"    "\n\t"
      "movl %%cr2, %1"    "\n\t"
      "movl %%cr3, %2"    "\n\t"
      "movl %%cr4, %3"    "\n\t"
      : "=r"(TrapCr0), "=r"(TrapCr2),
        "=r"(TrapCr3), "=r"(TrapCr4));
#else
   __asm
   {
       mov eax, cr0;
       mov TrapCr0, eax;

       mov eax, cr2;
       mov TrapCr2, eax;

       mov eax, cr3;
       mov TrapCr3, eax;
/* FIXME: What's the problem with cr4? */
       //mov eax, cr4;
       //mov TrapCr4, eax;
   }
#endif

    KdbTrapFrame->Cr0 = TrapCr0;
    KdbTrapFrame->Cr2 = TrapCr2;
    KdbTrapFrame->Cr3 = TrapCr3;
    KdbTrapFrame->Cr4 = TrapCr4;

    KdbTrapFrame->Tf.HardwareEsp = KiEspFromTrapFrame(TrapFrame);
    KdbTrapFrame->Tf.HardwareSegSs = (USHORT)(KiSsFromTrapFrame(TrapFrame) & 0xFFFF);


    /* FIXME: copy v86 registers if TrapFrame is a V86 trapframe */
}

static VOID
KdbpKdbTrapFrameToTrapFrame(
    PKDB_KTRAP_FRAME KdbTrapFrame,
    PKTRAP_FRAME TrapFrame)
{
    /* Copy the TrapFrame only up to Eflags and zero the rest*/
    RtlCopyMemory(TrapFrame, &KdbTrapFrame->Tf, FIELD_OFFSET(KTRAP_FRAME, HardwareEsp));

    /* FIXME: write cr0, cr2, cr3 and cr4 (not needed atm) */

    KiSsToTrapFrame(TrapFrame, KdbTrapFrame->Tf.HardwareSegSs);
    KiEspToTrapFrame(TrapFrame, KdbTrapFrame->Tf.HardwareEsp);

    /* FIXME: copy v86 registers if TrapFrame is a V86 trapframe */
}

static VOID
KdbpKdbTrapFrameFromKernelStack(
    PVOID KernelStack,
    PKDB_KTRAP_FRAME KdbTrapFrame)
{
    ULONG_PTR *StackPtr;

    RtlZeroMemory(KdbTrapFrame, sizeof(KDB_KTRAP_FRAME));
    StackPtr = (ULONG_PTR *) KernelStack;
#ifdef _M_IX86
    KdbTrapFrame->Tf.Ebp = StackPtr[3];
    KdbTrapFrame->Tf.Edi = StackPtr[4];
    KdbTrapFrame->Tf.Esi = StackPtr[5];
    KdbTrapFrame->Tf.Ebx = StackPtr[6];
    KdbTrapFrame->Tf.Eip = StackPtr[7];
    KdbTrapFrame->Tf.HardwareEsp = (ULONG) (StackPtr + 8);
    KdbTrapFrame->Tf.HardwareSegSs = KGDT_R0_DATA;
    KdbTrapFrame->Tf.SegCs = KGDT_R0_CODE;
    KdbTrapFrame->Tf.SegDs = KGDT_R0_DATA;
    KdbTrapFrame->Tf.SegEs = KGDT_R0_DATA;
    KdbTrapFrame->Tf.SegGs = KGDT_R0_DATA;
#endif

    /* FIXME: what about the other registers??? */
}

static NTSTATUS
KdbpOverwriteInstruction(
    IN  PEPROCESS Process,
    IN  ULONG_PTR Address,
    IN  UCHAR NewInst,
    OUT PUCHAR OldInst  OPTIONAL)
{
    NTSTATUS Status;
    ULONG Protect;
    PEPROCESS CurrentProcess = PsGetCurrentProcess();
    KAPC_STATE ApcState;

    /* Get the protection for the address. */
    Protect = MmGetPageProtect(Process, (PVOID)PAGE_ROUND_DOWN(Address));

    /* Return if that page isn't present. */
    if (Protect & PAGE_NOACCESS)
    {
        return STATUS_MEMORY_NOT_ALLOCATED;
    }

    /* Attach to the process */
    if (CurrentProcess != Process)
    {
        KeStackAttachProcess(&Process->Pcb, &ApcState);
    }

    /* Make the page writeable if it is read only. */
    if (Protect & (PAGE_READONLY|PAGE_EXECUTE|PAGE_EXECUTE_READ))
    {
        MmSetPageProtect(Process, (PVOID)PAGE_ROUND_DOWN(Address),
                         (Protect & ~(PAGE_READONLY|PAGE_EXECUTE|PAGE_EXECUTE_READ)) | PAGE_READWRITE);
    }

    /* Copy the old instruction back to the caller. */
    if (OldInst)
    {
        Status = KdbpSafeReadMemory(OldInst, (PUCHAR)Address, 1);
        if (!NT_SUCCESS(Status))
        {
            if (Protect & (PAGE_READONLY|PAGE_EXECUTE|PAGE_EXECUTE_READ))
            {
                MmSetPageProtect(Process, (PVOID)PAGE_ROUND_DOWN(Address), Protect);
            }

            /* Detach from process */
            if (CurrentProcess != Process)
            {
                KeDetachProcess();
            }

            return Status;
        }
    }

    /* Copy the new instruction in its place. */
    Status = KdbpSafeWriteMemory((PUCHAR)Address, &NewInst, 1);

    /* Restore the page protection. */
    if (Protect & (PAGE_READONLY|PAGE_EXECUTE|PAGE_EXECUTE_READ))
    {
        MmSetPageProtect(Process, (PVOID)PAGE_ROUND_DOWN(Address), Protect);
    }

    /* Detach from process */
    if (CurrentProcess != Process)
    {
        KeUnstackDetachProcess(&ApcState);
    }

    return Status;
}

BOOLEAN
KdbpShouldStepOverInstruction(
    ULONG_PTR Eip)
{
    UCHAR Mem[3];
    ULONG i = 0;

    if (!NT_SUCCESS(KdbpSafeReadMemory(Mem, (PVOID)Eip, sizeof (Mem))))
    {
        KdbpPrint("Couldn't access memory at 0x%p\n", Eip);
        return FALSE;
    }

    /* Check if the current instruction is a call. */
    while ((i < sizeof (Mem)) && (Mem[i] == 0x66 || Mem[i] == 0x67))
        i++;

    if (i == sizeof (Mem))
        return FALSE;

    if (Mem[i] == 0xE8 || Mem[i] == 0x9A || Mem[i] == 0xF2 || Mem[i] == 0xF3 ||
        (((i + 1) < sizeof (Mem)) && Mem[i] == 0xFF && (Mem[i+1] & 0x38) == 0x10))
    {
        return TRUE;
    }

    return FALSE;
}

BOOLEAN
KdbpStepOverInstruction(
    ULONG_PTR Eip)
{
    LONG InstLen;

    if (!KdbpShouldStepOverInstruction(Eip))
        return FALSE;

    InstLen = KdbpGetInstLength(Eip);
    if (InstLen < 1)
        return FALSE;

    if (!NT_SUCCESS(KdbpInsertBreakPoint(Eip + InstLen, KdbBreakPointTemporary, 0, 0, NULL, FALSE, NULL)))
        return FALSE;

    return TRUE;
}

BOOLEAN
KdbpStepIntoInstruction(
    ULONG_PTR Eip)
{
    KDESCRIPTOR Idtr = {0};
    UCHAR Mem[2];
    INT IntVect;
    ULONG IntDesc[2];
    ULONG_PTR TargetEip;

    /* Read memory */
    if (!NT_SUCCESS(KdbpSafeReadMemory(Mem, (PVOID)Eip, sizeof (Mem))))
    {
        /*KdbpPrint("Couldn't access memory at 0x%p\n", Eip);*/
        return FALSE;
    }

    /* Check for INT instruction */
    /* FIXME: Check for iret */
    if (Mem[0] == 0xcc)
        IntVect = 3;
    else if (Mem[0] == 0xcd)
        IntVect = Mem[1];
    else if (Mem[0] == 0xce && KdbCurrentTrapFrame->Tf.EFlags & (1<<11)) /* 1 << 11 is the overflow flag */
        IntVect = 4;
    else
        return FALSE;

    if (IntVect < 32) /* We should be informed about interrupts < 32 by the kernel, no need to breakpoint them */
    {
        return FALSE;
    }

    /* Read the interrupt descriptor table register  */
    __sidt(&Idtr.Limit);
    if (IntVect >= (Idtr.Limit + 1) / 8)
    {
        /*KdbpPrint("IDT does not contain interrupt vector %d\n.", IntVect);*/
        return TRUE;
    }

    /* Get the interrupt descriptor */
    if (!NT_SUCCESS(KdbpSafeReadMemory(IntDesc, (PVOID)(ULONG_PTR)(Idtr.Base + (IntVect * 8)), sizeof (IntDesc))))
    {
        /*KdbpPrint("Couldn't access memory at 0x%p\n", (ULONG_PTR)Idtr.Base + (IntVect * 8));*/
        return FALSE;
    }

    /* Check descriptor and get target eip (16 bit interrupt/trap gates not supported) */
    if ((IntDesc[1] & (1 << 15)) == 0) /* not present */
    {
        return FALSE;
    }
    if ((IntDesc[1] & 0x1f00) == 0x0500) /* Task gate */
    {
        /* FIXME: Task gates not supported */
        return FALSE;
    }
    else if (((IntDesc[1] & 0x1fe0) == 0x0e00) || /* 32 bit Interrupt gate */
             ((IntDesc[1] & 0x1fe0) == 0x0f00))   /* 32 bit Trap gate */
    {
        /* FIXME: Should the segment selector of the interrupt gate be checked? */
        TargetEip = (IntDesc[1] & 0xffff0000) | (IntDesc[0] & 0x0000ffff);
    }
    else
    {
        return FALSE;
    }

    /* Insert breakpoint */
    if (!NT_SUCCESS(KdbpInsertBreakPoint(TargetEip, KdbBreakPointTemporary, 0, 0, NULL, FALSE, NULL)))
        return FALSE;

    return TRUE;
}

LONG
KdbpGetNextBreakPointNr(
    IN ULONG Start  OPTIONAL)
{
    for (; Start < RTL_NUMBER_OF(KdbBreakPoints); Start++)
    {
        if (KdbBreakPoints[Start].Type != KdbBreakPointNone)
            return Start;
    }

    return -1;
}

BOOLEAN
KdbpGetBreakPointInfo(
    IN  ULONG BreakPointNr,
    OUT ULONG_PTR *Address  OPTIONAL,
    OUT KDB_BREAKPOINT_TYPE *Type  OPTIONAL,
    OUT UCHAR *Size  OPTIONAL,
    OUT KDB_ACCESS_TYPE *AccessType  OPTIONAL,
    OUT UCHAR *DebugReg  OPTIONAL,
    OUT BOOLEAN *Enabled  OPTIONAL,
    OUT BOOLEAN *Global  OPTIONAL,
    OUT PEPROCESS *Process  OPTIONAL,
    OUT PCHAR *ConditionExpression  OPTIONAL)
{
    PKDB_BREAKPOINT bp;

    if (BreakPointNr >= RTL_NUMBER_OF(KdbBreakPoints) ||
        KdbBreakPoints[BreakPointNr].Type == KdbBreakPointNone)
    {
        return FALSE;
    }

    bp = KdbBreakPoints + BreakPointNr;
    if (Address)
        *Address = bp->Address;

    if (Type)
        *Type = bp->Type;

    if (bp->Type == KdbBreakPointHardware)
    {
        if (Size)
            *Size = bp->Data.Hw.Size;

        if (AccessType)
            *AccessType = bp->Data.Hw.AccessType;

        if (DebugReg && bp->Enabled)
            *DebugReg = bp->Data.Hw.DebugReg;
    }

    if (Enabled)
        *Enabled = bp->Enabled;

    if (Global)
        *Global = bp->Global;

    if (Process)
        *Process = bp->Process;

    if (ConditionExpression)
        *ConditionExpression = bp->ConditionExpression;

    return TRUE;
}

NTSTATUS
KdbpInsertBreakPoint(
    IN  ULONG_PTR Address,
    IN  KDB_BREAKPOINT_TYPE Type,
    IN  UCHAR Size  OPTIONAL,
    IN  KDB_ACCESS_TYPE AccessType  OPTIONAL,
    IN  PCHAR ConditionExpression  OPTIONAL,
    IN  BOOLEAN Global,
    OUT PLONG BreakPointNr  OPTIONAL)
{
    LONG i;
    PVOID Condition;
    PCHAR ConditionExpressionDup;
    LONG ErrOffset;
    CHAR ErrMsg[128];

    ASSERT(Type != KdbBreakPointNone);

    if (Type == KdbBreakPointHardware)
    {
        if ((Address % Size) != 0)
        {
            KdbpPrint("Address (0x%p) must be aligned to a multiple of the size (%d)\n", Address, Size);
            return STATUS_UNSUCCESSFUL;
        }

        if (AccessType == KdbAccessExec && Size != 1)
        {
            KdbpPrint("Size must be 1 for execution breakpoints.\n");
            return STATUS_UNSUCCESSFUL;
        }
    }

    if (KdbBreakPointCount == KDB_MAXIMUM_BREAKPOINT_COUNT)
    {
        return STATUS_UNSUCCESSFUL;
    }

    /* Parse conditon expression string and duplicate it */
    if (ConditionExpression)
    {
        Condition = KdbpRpnParseExpression(ConditionExpression, &ErrOffset, ErrMsg);
        if (!Condition)
        {
            if (ErrOffset >= 0)
                KdbpPrint("Couldn't parse expression: %s at character %d\n", ErrMsg, ErrOffset);
            else
                KdbpPrint("Couldn't parse expression: %s", ErrMsg);

            return STATUS_UNSUCCESSFUL;
        }

        i = strlen(ConditionExpression) + 1;
        ConditionExpressionDup = ExAllocatePoolWithTag(NonPagedPool, i, TAG_KDBG);
        RtlCopyMemory(ConditionExpressionDup, ConditionExpression, i);
    }
    else
    {
        Condition = NULL;
        ConditionExpressionDup = NULL;
    }

    /* Find unused breakpoint */
    if (Type == KdbBreakPointTemporary)
    {
        for (i = RTL_NUMBER_OF(KdbBreakPoints) - 1; i >= 0; i--)
        {
            if (KdbBreakPoints[i].Type == KdbBreakPointNone)
                break;
        }
    }
    else
    {
        for (i = 0; i < (LONG)RTL_NUMBER_OF(KdbBreakPoints); i++)
        {
            if (KdbBreakPoints[i].Type == KdbBreakPointNone)
                break;
        }
    }

    ASSERT(i < (LONG)RTL_NUMBER_OF(KdbBreakPoints));

    /* Set the breakpoint */
    ASSERT(KdbCurrentProcess);
    KdbBreakPoints[i].Type = Type;
    KdbBreakPoints[i].Address = Address;
    KdbBreakPoints[i].Enabled = FALSE;
    KdbBreakPoints[i].Global = Global;
    KdbBreakPoints[i].Process = KdbCurrentProcess;
    KdbBreakPoints[i].ConditionExpression = ConditionExpressionDup;
    KdbBreakPoints[i].Condition = Condition;

    if (Type == KdbBreakPointHardware)
    {
        KdbBreakPoints[i].Data.Hw.Size = Size;
        KdbBreakPoints[i].Data.Hw.AccessType = AccessType;
    }

    KdbBreakPointCount++;

    if (Type != KdbBreakPointTemporary)
        KdbpPrint("Breakpoint %d inserted.\n", i);

    /* Try to enable the breakpoint */
    KdbpEnableBreakPoint(i, NULL);

    /* Return the breakpoint number */
    if (BreakPointNr)
        *BreakPointNr = i;

    return STATUS_SUCCESS;
}

BOOLEAN
KdbpDeleteBreakPoint(
    IN LONG BreakPointNr  OPTIONAL,
    IN OUT PKDB_BREAKPOINT BreakPoint  OPTIONAL)
{
    if (BreakPointNr < 0)
    {
        ASSERT(BreakPoint);
        BreakPointNr = BreakPoint - KdbBreakPoints;
    }

    if (BreakPointNr < 0 || BreakPointNr >= KDB_MAXIMUM_BREAKPOINT_COUNT)
    {
        KdbpPrint("Invalid breakpoint: %d\n", BreakPointNr);
        return FALSE;
    }

    if (!BreakPoint)
    {
        BreakPoint = KdbBreakPoints + BreakPointNr;
    }

    if (BreakPoint->Type == KdbBreakPointNone)
    {
        KdbpPrint("Invalid breakpoint: %d\n", BreakPointNr);
        return FALSE;
    }

    if (BreakPoint->Enabled && !KdbpDisableBreakPoint(-1, BreakPoint))
        return FALSE;

    if (BreakPoint->Type != KdbBreakPointTemporary)
        KdbpPrint("Breakpoint %d deleted.\n", BreakPointNr);

    BreakPoint->Type = KdbBreakPointNone;
    KdbBreakPointCount--;

    return TRUE;
}

static LONG
KdbpIsBreakPointOurs(
    IN NTSTATUS ExceptionCode,
    IN PKTRAP_FRAME TrapFrame)
{
    ULONG i;
    ASSERT(ExceptionCode == STATUS_SINGLE_STEP || ExceptionCode == STATUS_BREAKPOINT);

    if (ExceptionCode == STATUS_BREAKPOINT) /* Software interrupt */
    {
        ULONG_PTR BpEip = (ULONG_PTR)TrapFrame->Eip - 1; /* Get EIP of INT3 instruction */
        for (i = 0; i < KdbSwBreakPointCount; i++)
        {
            ASSERT((KdbSwBreakPoints[i]->Type == KdbBreakPointSoftware ||
                   KdbSwBreakPoints[i]->Type == KdbBreakPointTemporary));
            ASSERT(KdbSwBreakPoints[i]->Enabled);

            if (KdbSwBreakPoints[i]->Address == BpEip)
            {
                return KdbSwBreakPoints[i] - KdbBreakPoints;
            }
        }
    }
    else if (ExceptionCode == STATUS_SINGLE_STEP) /* Hardware interrupt */
    {
        UCHAR DebugReg;

        for (i = 0; i < KdbHwBreakPointCount; i++)
        {
            ASSERT(KdbHwBreakPoints[i]->Type == KdbBreakPointHardware &&
                   KdbHwBreakPoints[i]->Enabled);
            DebugReg = KdbHwBreakPoints[i]->Data.Hw.DebugReg;

            if ((TrapFrame->Dr6 & (1 << DebugReg)) != 0)
            {
                return KdbHwBreakPoints[i] - KdbBreakPoints;
            }
        }
    }

    return -1;
}

BOOLEAN
KdbpEnableBreakPoint(
    IN LONG BreakPointNr  OPTIONAL,
    IN OUT PKDB_BREAKPOINT BreakPoint  OPTIONAL)
{
    NTSTATUS Status;
    INT i;
    ULONG ul;

    if (BreakPointNr < 0)
    {
        ASSERT(BreakPoint);
        BreakPointNr = BreakPoint - KdbBreakPoints;
    }

    if (BreakPointNr < 0 || BreakPointNr >= KDB_MAXIMUM_BREAKPOINT_COUNT)
    {
        KdbpPrint("Invalid breakpoint: %d\n", BreakPointNr);
        return FALSE;
    }

    if (!BreakPoint)
    {
        BreakPoint = KdbBreakPoints + BreakPointNr;
    }

    if (BreakPoint->Type == KdbBreakPointNone)
    {
        KdbpPrint("Invalid breakpoint: %d\n", BreakPointNr);
        return FALSE;
    }

    if (BreakPoint->Enabled)
    {
        KdbpPrint("Breakpoint %d is already enabled.\n", BreakPointNr);
        return TRUE;
    }

    if (BreakPoint->Type == KdbBreakPointSoftware ||
        BreakPoint->Type == KdbBreakPointTemporary)
    {
        if (KdbSwBreakPointCount >= KDB_MAXIMUM_SW_BREAKPOINT_COUNT)
        {
            KdbpPrint("Maximum number of SW breakpoints (%d) used. "
                      "Disable another breakpoint in order to enable this one.\n",
                      KDB_MAXIMUM_SW_BREAKPOINT_COUNT);
            return FALSE;
        }

        Status = KdbpOverwriteInstruction(BreakPoint->Process, BreakPoint->Address,
                                          0xCC, &BreakPoint->Data.SavedInstruction);
        if (!NT_SUCCESS(Status))
        {
            KdbpPrint("Couldn't access memory at 0x%p\n", BreakPoint->Address);
            return FALSE;
        }

        KdbSwBreakPoints[KdbSwBreakPointCount++] = BreakPoint;
    }
    else
    {
        if (BreakPoint->Data.Hw.AccessType == KdbAccessExec)
            ASSERT(BreakPoint->Data.Hw.Size == 1);

        ASSERT((BreakPoint->Address % BreakPoint->Data.Hw.Size) == 0);

        if (KdbHwBreakPointCount >= KDB_MAXIMUM_HW_BREAKPOINT_COUNT)
        {
            KdbpPrint("Maximum number of HW breakpoints (%d) already used. "
                      "Disable another breakpoint in order to enable this one.\n",
                      KDB_MAXIMUM_HW_BREAKPOINT_COUNT);

            return FALSE;
        }

        /* Find unused hw breakpoint */
        ASSERT(KDB_MAXIMUM_HW_BREAKPOINT_COUNT == 4);
        for (i = 0; i < KDB_MAXIMUM_HW_BREAKPOINT_COUNT; i++)
        {
            if ((KdbTrapFrame.Tf.Dr7 & (0x3 << (i * 2))) == 0)
                break;
        }

        ASSERT(i < KDB_MAXIMUM_HW_BREAKPOINT_COUNT);

        /* Set the breakpoint address. */
        switch (i)
        {
            case 0:
                KdbTrapFrame.Tf.Dr0 = BreakPoint->Address;
                break;
            case 1:
                KdbTrapFrame.Tf.Dr1 = BreakPoint->Address;
                break;
            case 2:
                KdbTrapFrame.Tf.Dr2 = BreakPoint->Address;
                break;
            case 3:
                KdbTrapFrame.Tf.Dr3 = BreakPoint->Address;
                break;
        }

        /* Enable the global breakpoint */
        KdbTrapFrame.Tf.Dr7 |= (0x2 << (i * 2));

        /* Enable the exact match bits. */
        KdbTrapFrame.Tf.Dr7 |= 0x00000300;

        /* Clear existing state. */
        KdbTrapFrame.Tf.Dr7 &= ~(0xF << (16 + (i * 4)));

        /* Set the breakpoint type. */
        switch (BreakPoint->Data.Hw.AccessType)
        {
            case KdbAccessExec:
                ul = 0;
                break;
            case KdbAccessWrite:
                ul = 1;
                break;
            case KdbAccessRead:
            case KdbAccessReadWrite:
                ul = 3;
                break;
            default:
                ASSERT(0);
                return TRUE;
                break;
        }

        KdbTrapFrame.Tf.Dr7 |= (ul << (16 + (i * 4)));

        /* Set the breakpoint length. */
        KdbTrapFrame.Tf.Dr7 |= ((BreakPoint->Data.Hw.Size - 1) << (18 + (i * 4)));

        /* Update KdbCurrentTrapFrame - values are taken from there by the CLI */
        if (&KdbTrapFrame != KdbCurrentTrapFrame)
        {
            KdbCurrentTrapFrame->Tf.Dr0 = KdbTrapFrame.Tf.Dr0;
            KdbCurrentTrapFrame->Tf.Dr1 = KdbTrapFrame.Tf.Dr1;
            KdbCurrentTrapFrame->Tf.Dr2 = KdbTrapFrame.Tf.Dr2;
            KdbCurrentTrapFrame->Tf.Dr3 = KdbTrapFrame.Tf.Dr3;
            KdbCurrentTrapFrame->Tf.Dr6 = KdbTrapFrame.Tf.Dr6;
            KdbCurrentTrapFrame->Tf.Dr7 = KdbTrapFrame.Tf.Dr7;
        }

        BreakPoint->Data.Hw.DebugReg = i;
        KdbHwBreakPoints[KdbHwBreakPointCount++] = BreakPoint;
    }

    BreakPoint->Enabled = TRUE;
    if (BreakPoint->Type != KdbBreakPointTemporary)
        KdbpPrint("Breakpoint %d enabled.\n", BreakPointNr);

    return TRUE;
}

BOOLEAN
KdbpDisableBreakPoint(
    IN LONG BreakPointNr  OPTIONAL,
    IN OUT PKDB_BREAKPOINT BreakPoint  OPTIONAL)
{
    ULONG i;
    NTSTATUS Status;

    if (BreakPointNr < 0)
    {
        ASSERT(BreakPoint);
        BreakPointNr = BreakPoint - KdbBreakPoints;
    }

    if (BreakPointNr < 0 || BreakPointNr >= KDB_MAXIMUM_BREAKPOINT_COUNT)
    {
        KdbpPrint("Invalid breakpoint: %d\n", BreakPointNr);
        return FALSE;
    }

    if (!BreakPoint)
    {
        BreakPoint = KdbBreakPoints + BreakPointNr;
    }

    if (BreakPoint->Type == KdbBreakPointNone)
    {
        KdbpPrint("Invalid breakpoint: %d\n", BreakPointNr);
        return FALSE;
    }

    if (BreakPoint->Enabled == FALSE)
    {
        KdbpPrint("Breakpoint %d is not enabled.\n", BreakPointNr);
        return TRUE;
    }

    if (BreakPoint->Type == KdbBreakPointSoftware ||
        BreakPoint->Type == KdbBreakPointTemporary)
    {
        ASSERT(KdbSwBreakPointCount > 0);
        Status = KdbpOverwriteInstruction(BreakPoint->Process, BreakPoint->Address,
                                          BreakPoint->Data.SavedInstruction, NULL);

        if (!NT_SUCCESS(Status))
        {
            KdbpPrint("Couldn't restore original instruction.\n");
            return FALSE;
        }

        for (i = 0; i < KdbSwBreakPointCount; i++)
        {
            if (KdbSwBreakPoints[i] == BreakPoint)
            {
                KdbSwBreakPoints[i] = KdbSwBreakPoints[--KdbSwBreakPointCount];
                i = -1; /* if the last breakpoint is disabled dont break with i >= KdbSwBreakPointCount */
                break;
            }
        }

        if (i != MAXULONG) /* not found */
            ASSERT(0);
    }
    else
    {
        ASSERT(BreakPoint->Type == KdbBreakPointHardware);

        /* Clear the breakpoint. */
        KdbTrapFrame.Tf.Dr7 &= ~(0x3 << (BreakPoint->Data.Hw.DebugReg * 2));
        if ((KdbTrapFrame.Tf.Dr7 & 0xFF) == 0)
        {
            /* If no breakpoints are enabled then clear the exact match flags. */
            KdbTrapFrame.Tf.Dr7 &= 0xFFFFFCFF;
        }

        for (i = 0; i < KdbHwBreakPointCount; i++)
        {
            if (KdbHwBreakPoints[i] == BreakPoint)
            {
                KdbHwBreakPoints[i] = KdbHwBreakPoints[--KdbHwBreakPointCount];
                i = -1; /* if the last breakpoint is disabled dont break with i >= KdbHwBreakPointCount */
                break;
            }
        }

        if (i != MAXULONG) /* not found */
            ASSERT(0);
    }

    BreakPoint->Enabled = FALSE;
    if (BreakPoint->Type != KdbBreakPointTemporary)
        KdbpPrint("Breakpoint %d disabled.\n", BreakPointNr);

    return TRUE;
}

BOOLEAN
KdbpGetEnterCondition(
    IN LONG ExceptionNr,
    IN BOOLEAN FirstChance,
    OUT KDB_ENTER_CONDITION *Condition)
{
    if (ExceptionNr >= (LONG)RTL_NUMBER_OF(KdbEnterConditions))
        return FALSE;

    *Condition = KdbEnterConditions[ExceptionNr][FirstChance ? 0 : 1];
    return TRUE;
}

BOOLEAN
KdbpSetEnterCondition(
    IN LONG ExceptionNr,
    IN BOOLEAN FirstChance,
    IN KDB_ENTER_CONDITION Condition)
{
    if (ExceptionNr < 0)
    {
        for (ExceptionNr = 0; ExceptionNr < (LONG)RTL_NUMBER_OF(KdbEnterConditions); ExceptionNr++)
        {
            if (ExceptionNr == 1 || ExceptionNr == 8 ||
                ExceptionNr == 9 || ExceptionNr == 15) /* Reserved exceptions */
            {
                continue;
            }

            KdbEnterConditions[ExceptionNr][FirstChance ? 0 : 1] = Condition;
        }
    }
    else
    {
        if (ExceptionNr >= (LONG)RTL_NUMBER_OF(KdbEnterConditions) ||
            ExceptionNr == 1 || ExceptionNr == 8 || /* Do not allow changing of the debug */
            ExceptionNr == 9 || ExceptionNr == 15)  /* trap or reserved exceptions */
        {
            return FALSE;
        }

        KdbEnterConditions[ExceptionNr][FirstChance ? 0 : 1] = Condition;
    }

    return TRUE;
}

BOOLEAN
KdbpAttachToThread(
    PVOID ThreadId)
{
    PETHREAD Thread = NULL;
    PEPROCESS Process;

    /* Get a pointer to the thread */
    if (!NT_SUCCESS(PsLookupThreadByThreadId(ThreadId, &Thread)))
    {
        KdbpPrint("Invalid thread id: 0x%08x\n", (ULONG_PTR)ThreadId);
        return FALSE;
    }
    Process = Thread->ThreadsProcess;

    if (KeIsExecutingDpc() && Process != KdbCurrentProcess)
    {
        KdbpPrint("Cannot attach to thread within another process while executing a DPC.\n");
        ObDereferenceObject(Thread);
        return FALSE;
    }

    /* Save the current thread's context (if we previously attached to a thread) */
    if (KdbCurrentThread != KdbOriginalThread)
    {
        ASSERT(KdbCurrentTrapFrame == &KdbThreadTrapFrame);
        /* Actually, we can't save the context, there's no guarantee that there was a trap frame */
    }
    else
    {
        ASSERT(KdbCurrentTrapFrame == &KdbTrapFrame);
    }

    /* Switch to the thread's context */
    if (Thread != KdbOriginalThread)
    {
        /* The thread we're attaching to isn't the thread on which we entered
         * kdb and so the thread we're attaching to is not running. There
         * is no guarantee that it actually has a trap frame. So we have to
         * peek directly at the registers which were saved on the stack when the
         * thread was preempted in the scheduler */
        KdbpKdbTrapFrameFromKernelStack(Thread->Tcb.KernelStack,
                                        &KdbThreadTrapFrame);
        KdbCurrentTrapFrame = &KdbThreadTrapFrame;
    }
    else /* Switching back to original thread */
    {
        KdbCurrentTrapFrame = &KdbTrapFrame;
    }
    KdbCurrentThread = Thread;

    /* Attach to the thread's process */
    ASSERT(KdbCurrentProcess == PsGetCurrentProcess());
    if (KdbCurrentProcess != Process)
    {
        if (KdbCurrentProcess != KdbOriginalProcess) /* detach from previously attached process */
        {
            KeUnstackDetachProcess(&KdbApcState);
        }

        if (KdbOriginalProcess != Process)
        {
            KeStackAttachProcess(&Process->Pcb, &KdbApcState);
        }

        KdbCurrentProcess = Process;
    }

    ObDereferenceObject(Thread);
    return TRUE;
}

BOOLEAN
KdbpAttachToProcess(
    PVOID ProcessId)
{
    PEPROCESS Process = NULL;
    PETHREAD Thread;
    PLIST_ENTRY Entry;

    /* Get a pointer to the process */
    if (!NT_SUCCESS(PsLookupProcessByProcessId(ProcessId, &Process)))
    {
        KdbpPrint("Invalid process id: 0x%08x\n", (ULONG_PTR)ProcessId);
        return FALSE;
    }

    Entry = Process->ThreadListHead.Flink;
    ObDereferenceObject(Process);
    if (Entry == &KdbCurrentProcess->ThreadListHead)
    {
        KdbpPrint("No threads in process 0x%p, cannot attach to process!\n", ProcessId);
        return FALSE;
    }

    Thread = CONTAINING_RECORD(Entry, ETHREAD, ThreadListEntry);

    return KdbpAttachToThread(Thread->Cid.UniqueThread);
}

static VOID
KdbpCallMainLoop(VOID)
{
    KdbpCliMainLoop(KdbEnteredOnSingleStep);
}

static VOID
KdbpInternalEnter()
{
    PETHREAD Thread;
    PVOID SavedInitialStack, SavedStackBase, SavedKernelStack;
    ULONG SavedStackLimit;

    KbdDisableMouse();

    if (KdpDebugMode.Screen &&
        InbvIsBootDriverInstalled() &&
        !InbvCheckDisplayOwnership())
    {
        /* Acquire ownership and reset the display */
        InbvAcquireDisplayOwnership();
        InbvResetDisplay();

        /* Display debugger prompt */
        InbvSolidColorFill(0, 0, 639, 479, 0);
        InbvSetTextColor(15);
        InbvInstallDisplayStringFilter(NULL);
        InbvEnableDisplayString(TRUE);
        InbvSetScrollRegion(0, 0, 639, 479);
    }

    /* Call the interface's main loop on a different stack */
    Thread = PsGetCurrentThread();
    SavedInitialStack = Thread->Tcb.InitialStack;
    SavedStackBase = Thread->Tcb.StackBase;
    SavedStackLimit = Thread->Tcb.StackLimit;
    SavedKernelStack = Thread->Tcb.KernelStack;
    Thread->Tcb.InitialStack = Thread->Tcb.StackBase = (char*)KdbStack + KDB_STACK_SIZE;
    Thread->Tcb.StackLimit = (ULONG_PTR)KdbStack;
    Thread->Tcb.KernelStack = (char*)KdbStack + KDB_STACK_SIZE;

    /*KdbpPrint("Switching to KDB stack 0x%08x-0x%08x (Current Stack is 0x%08x)\n", Thread->Tcb.StackLimit, Thread->Tcb.StackBase, Esp);*/

    KdbpStackSwitchAndCall(KdbStack + KDB_STACK_SIZE - sizeof(ULONG), KdbpCallMainLoop);

    Thread->Tcb.InitialStack = SavedInitialStack;
    Thread->Tcb.StackBase = SavedStackBase;
    Thread->Tcb.StackLimit = SavedStackLimit;
    Thread->Tcb.KernelStack = SavedKernelStack;
    KbdEnableMouse();
}

static ULONG
KdbpGetExceptionNumberFromStatus(
    IN NTSTATUS ExceptionCode)
{
    ULONG Ret;

    switch (ExceptionCode)
    {
        case STATUS_INTEGER_DIVIDE_BY_ZERO:
            Ret = 0;
            break;
        case STATUS_SINGLE_STEP:
            Ret = 1;
            break;
        case STATUS_BREAKPOINT:
            Ret = 3;
            break;
        case STATUS_INTEGER_OVERFLOW:
            Ret = 4;
            break;
        case STATUS_ARRAY_BOUNDS_EXCEEDED:
            Ret = 5;
            break;
        case STATUS_ILLEGAL_INSTRUCTION:
            Ret = 6;
            break;
        case STATUS_FLOAT_INVALID_OPERATION:
            Ret = 7;
            break;
        case STATUS_STACK_OVERFLOW:
            Ret = 12;
            break;
        case STATUS_ACCESS_VIOLATION:
            Ret = 14;
            break;
        case STATUS_DATATYPE_MISALIGNMENT:
            Ret = 17;
            break;
        case STATUS_FLOAT_MULTIPLE_TRAPS:
            Ret = 18;
            break;

        default:
            Ret = RTL_NUMBER_OF(KdbEnterConditions) - 1;
            break;
    }

    return Ret;
}

KD_CONTINUE_TYPE
KdbEnterDebuggerException(
    IN PEXCEPTION_RECORD ExceptionRecord  OPTIONAL,
    IN KPROCESSOR_MODE PreviousMode,
    IN PCONTEXT Context,
    IN OUT PKTRAP_FRAME TrapFrame,
    IN BOOLEAN FirstChance)
{
    KDB_ENTER_CONDITION EnterCondition;
    KD_CONTINUE_TYPE ContinueType = kdHandleException;
    PKDB_BREAKPOINT BreakPoint;
    ULONG ExpNr;
    ULONGLONG ull;
    BOOLEAN Resume = FALSE;
    BOOLEAN EnterConditionMet = TRUE;
    ULONG OldEflags;
    KIRQL OldIrql;
    NTSTATUS ExceptionCode;

    ExceptionCode = (ExceptionRecord ? ExceptionRecord->ExceptionCode : STATUS_BREAKPOINT);

    KdbCurrentProcess = PsGetCurrentProcess();

    /* Set continue type to kdContinue for single steps and breakpoints */
    if (ExceptionCode == STATUS_SINGLE_STEP || ExceptionCode == STATUS_BREAKPOINT)
        ContinueType = kdContinue;

    /* Check if we should handle the exception. */
    /* FIXME - won't get all exceptions here :( */
    ExpNr = KdbpGetExceptionNumberFromStatus(ExceptionCode);
    EnterCondition = KdbEnterConditions[ExpNr][FirstChance ? 0 : 1];
    if (EnterCondition == KdbDoNotEnter ||
        (EnterCondition == KdbEnterFromUmode && PreviousMode == KernelMode) ||
        (EnterCondition == KdbEnterFromKmode && PreviousMode != KernelMode))
    {
        EnterConditionMet = FALSE;
    }

    /* If we stopped on one of our breakpoints then let the user know. */
    KdbLastBreakPointNr = -1;
    KdbEnteredOnSingleStep = FALSE;

    if (FirstChance && (ExceptionCode == STATUS_SINGLE_STEP || ExceptionCode == STATUS_BREAKPOINT) &&
        (KdbLastBreakPointNr = KdbpIsBreakPointOurs(ExceptionCode, TrapFrame)) >= 0)
    {
        BreakPoint = KdbBreakPoints + KdbLastBreakPointNr;

        if (ExceptionCode == STATUS_BREAKPOINT)
        {
            /* ... and restore the original instruction. */
            if (!NT_SUCCESS(KdbpOverwriteInstruction(KdbCurrentProcess, BreakPoint->Address,
                                                     BreakPoint->Data.SavedInstruction, NULL)))
            {
                KdbpPrint("Couldn't restore original instruction after INT3! Cannot continue execution.\n");
                KeBugCheck(0); // FIXME: Proper bugcode!
            }
        }

        if ((BreakPoint->Type == KdbBreakPointHardware) &&
            (BreakPoint->Data.Hw.AccessType == KdbAccessExec))
        {
            Resume = TRUE; /* Set the resume flag when continuing execution */
        }

        /*
         * When a temporary breakpoint is hit we have to make sure that we are
         * in the same context in which it was set, otherwise it could happen
         * that another process/thread hits it before and it gets deleted.
         */
        else if (BreakPoint->Type == KdbBreakPointTemporary &&
                 BreakPoint->Process == KdbCurrentProcess)
        {
            ASSERT((TrapFrame->EFlags & EFLAGS_TF) == 0);

            /* Delete the temporary breakpoint which was used to step over or into the instruction. */
            KdbpDeleteBreakPoint(-1, BreakPoint);

            TrapFrame->Eip--;

            if (--KdbNumSingleSteps > 0)
            {
                if ((KdbSingleStepOver && !KdbpStepOverInstruction(TrapFrame->Eip)) ||
                    (!KdbSingleStepOver && !KdbpStepIntoInstruction(TrapFrame->Eip)))
                {
                    Context->EFlags |= EFLAGS_TF;
                }

                goto continue_execution; /* return */
            }

            KdbEnteredOnSingleStep = TRUE;
        }

        /*
         * If we hit a breakpoint set by the debugger we set the single step flag,
         * ignore the next single step and reenable the breakpoint.
         */
        else if (BreakPoint->Type == KdbBreakPointSoftware ||
                 BreakPoint->Type == KdbBreakPointTemporary)
        {
            ASSERT(ExceptionCode == STATUS_BREAKPOINT);
            Context->EFlags |= EFLAGS_TF;
            KdbBreakPointToReenable = BreakPoint;
        }

        /* Make sure that the breakpoint should be triggered in this context */
        if (!BreakPoint->Global && BreakPoint->Process != KdbCurrentProcess)
        {
            goto continue_execution; /* return */
        }

        /* Check if the condition for the breakpoint is met. */
        if (BreakPoint->Condition)
        {
            /* Setup the KDB trap frame */
            KdbpTrapFrameToKdbTrapFrame(TrapFrame, &KdbTrapFrame);

            ull = 0;
            if (!KdbpRpnEvaluateParsedExpression(BreakPoint->Condition, &KdbTrapFrame, &ull, NULL, NULL))
            {
                /* FIXME: Print warning? */
            }
            else if (ull == 0) /* condition is not met */
            {
                goto continue_execution; /* return */
            }
        }

        if (BreakPoint->Type == KdbBreakPointSoftware)
        {
            KdbpPrint("Entered debugger on breakpoint #%d: EXEC 0x%04x:0x%08x\n",
                      KdbLastBreakPointNr, TrapFrame->SegCs & 0xffff, TrapFrame->Eip);
        }
        else if (BreakPoint->Type == KdbBreakPointHardware)
        {
            KdbpPrint("Entered debugger on breakpoint #%d: %s 0x%08x\n",
                      KdbLastBreakPointNr,
                     (BreakPoint->Data.Hw.AccessType == KdbAccessRead) ? "READ" :
                     ((BreakPoint->Data.Hw.AccessType == KdbAccessWrite) ? "WRITE" :
                     ((BreakPoint->Data.Hw.AccessType == KdbAccessReadWrite) ? "RDWR" : "EXEC")),
                     BreakPoint->Address);
        }
    }
    else if (ExceptionCode == STATUS_SINGLE_STEP)
    {
        /* Silently ignore a debugger initiated single step. */
        if ((TrapFrame->Dr6 & 0xf) == 0 && KdbBreakPointToReenable)
        {
            /* FIXME: Make sure that the breakpoint was really hit (check bp->Address vs. tf->Eip) */
            BreakPoint = KdbBreakPointToReenable;
            KdbBreakPointToReenable = NULL;
            ASSERT(BreakPoint->Type == KdbBreakPointSoftware ||
                   BreakPoint->Type == KdbBreakPointTemporary);

            /*
             * Reenable the breakpoint we disabled to execute the breakpointed
             * instruction.
             */
            if (!NT_SUCCESS(KdbpOverwriteInstruction(KdbCurrentProcess, BreakPoint->Address, 0xCC,
                                                     &BreakPoint->Data.SavedInstruction)))
            {
                KdbpPrint("Warning: Couldn't reenable breakpoint %d\n",
                          BreakPoint - KdbBreakPoints);
            }

            /* Unset TF if we are no longer single stepping. */
            if (KdbNumSingleSteps == 0)
                Context->EFlags &= ~EFLAGS_TF;

            goto continue_execution; /* return */
        }

        /* Check if we expect a single step */
        if ((TrapFrame->Dr6 & 0xf) == 0 && KdbNumSingleSteps > 0)
        {
            /*ASSERT((Context->Eflags & EFLAGS_TF) != 0);*/
            if (--KdbNumSingleSteps > 0)
            {
                if ((KdbSingleStepOver && KdbpStepOverInstruction(TrapFrame->Eip)) ||
                    (!KdbSingleStepOver && KdbpStepIntoInstruction(TrapFrame->Eip)))
                {
                    Context->EFlags &= ~EFLAGS_TF;
                }
                else
                {
                    Context->EFlags |= EFLAGS_TF;
                }

                goto continue_execution; /* return */
            }
            else
            {
                Context->EFlags &= ~EFLAGS_TF;
                KdbEnteredOnSingleStep = TRUE;
            }
        }
        else
        {
            if (!EnterConditionMet)
            {
                return kdHandleException;
            }

            KdbpPrint("Entered debugger on unexpected debug trap!\n");
        }
    }
    else if (ExceptionCode == STATUS_BREAKPOINT)
    {
        if (KdbInitFileBuffer)
        {
            KdbpCliInterpretInitFile();
            EnterConditionMet = FALSE;
        }
        if (!EnterConditionMet)
        {
            return kdHandleException;
        }

        KdbpPrint("Entered debugger on embedded INT3 at 0x%04x:0x%08x.\n",
                  TrapFrame->SegCs & 0xffff, TrapFrame->Eip - 1);
    }
    else
    {
        const CHAR *ExceptionString = (ExpNr < RTL_NUMBER_OF(ExceptionNrToString)) ?
                                      (ExceptionNrToString[ExpNr]) :
                                      ("Unknown/User defined exception");

        if (!EnterConditionMet)
        {
            return ContinueType;
        }

        KdbpPrint("Entered debugger on %s-chance exception (Exception Code: 0x%x) (%s)\n",
                  FirstChance ? "first" : "last", ExceptionCode, ExceptionString);

        if (ExceptionCode == STATUS_ACCESS_VIOLATION &&
            ExceptionRecord && ExceptionRecord->NumberParameters != 0)
        {
            /* FIXME: Add noexec memory stuff */
            ULONG_PTR TrapCr2;
            ULONG Err;

            TrapCr2 = __readcr2();

            Err = TrapFrame->ErrCode;
            KdbpPrint("Memory at 0x%p could not be %s: ", TrapCr2, (Err & (1 << 1)) ? "written" : "read");

            if ((Err & (1 << 0)) == 0)
            {
                KdbpPrint("Page not present.\n");
            }
            else
            {
                if ((Err & (1 << 3)) != 0)
                    KdbpPrint("Reserved bits in page directory set.\n");
                else
                    KdbpPrint("Page protection violation.\n");
            }
        }
    }

    /* Once we enter the debugger we do not expect any more single steps to happen */
    KdbNumSingleSteps = 0;

    /* Update the current process pointer */
    KdbCurrentProcess = KdbOriginalProcess = PsGetCurrentProcess();
    KdbCurrentThread = KdbOriginalThread = PsGetCurrentThread();
    KdbCurrentTrapFrame = &KdbTrapFrame;

    /* Setup the KDB trap frame */
    KdbpTrapFrameToKdbTrapFrame(TrapFrame, &KdbTrapFrame);

    /* Enter critical section */
    OldEflags = __readeflags();
    _disable();

    /* HACK: Save the current IRQL and pretend we are at passive level,
     * although interrupts are off. Needed because KDBG calls pageable code. */
    OldIrql = KeGetCurrentIrql();
    KeLowerIrql(PASSIVE_LEVEL);

    /* Exception inside the debugger? Game over. */
    if (InterlockedIncrement(&KdbEntryCount) > 1)
    {
        __writeeflags(OldEflags);
        return kdHandleException;
    }

    /* Call the main loop. */
    KdbpInternalEnter();

    /* Check if we should single step */
    if (KdbNumSingleSteps > 0)
    {
        if ((KdbSingleStepOver && KdbpStepOverInstruction(KdbCurrentTrapFrame->Tf.Eip)) ||
            (!KdbSingleStepOver && KdbpStepIntoInstruction(KdbCurrentTrapFrame->Tf.Eip)))
        {
            ASSERT((KdbCurrentTrapFrame->Tf.EFlags & EFLAGS_TF) == 0);
            /*KdbCurrentTrapFrame->Tf.EFlags &= ~EFLAGS_TF;*/
        }
        else
        {
            Context->EFlags |= EFLAGS_TF;
        }
    }

    /* We can't update the current thread's trapframe 'cause it might not have one */

    /* Detach from attached process */
    if (KdbCurrentProcess != KdbOriginalProcess)
    {
        KeUnstackDetachProcess(&KdbApcState);
    }

    /* Update the exception TrapFrame */
    KdbpKdbTrapFrameToTrapFrame(&KdbTrapFrame, TrapFrame);

    /* Decrement the entry count */
    InterlockedDecrement(&KdbEntryCount);

    /* HACK: Raise back to old IRWL */
    KeRaiseIrql(OldIrql, &OldIrql);

    /* Leave critical section */
    __writeeflags(OldEflags);

    /* Check if user requested a bugcheck */
    if (KdbpBugCheckRequested)
    {
        /* Clear the flag and bugcheck the system */
        KdbpBugCheckRequested = FALSE;
        KeBugCheck(MANUALLY_INITIATED_CRASH);
    }

continue_execution:
    /* Clear debug status */
    if (ExceptionCode == STATUS_BREAKPOINT) /* FIXME: Why clear DR6 on INT3? */
    {
        /* Set the RF flag so we don't trigger the same breakpoint again. */
        if (Resume)
        {
            TrapFrame->EFlags |= EFLAGS_RF;
        }

        /* Clear dr6 status flags. */
        TrapFrame->Dr6 &= ~0x0000e00f;

        if (!(KdbEnteredOnSingleStep && KdbSingleStepOver))
        {
            /* Skip the current instruction */
            Context->Eip++;
        }
    }

    return ContinueType;
}

VOID
NTAPI
INIT_FUNCTION
KdbpGetCommandLineSettings(
    PCHAR p1)
{
    PCHAR p2;

    while (p1 && (p2 = strchr(p1, ' ')))
    {
        p2 += 2;

        if (!_strnicmp(p2, "KDSERIAL", 8))
        {
            p2 += 8;
            KdbDebugState |= KD_DEBUG_KDSERIAL;
            KdpDebugMode.Serial = TRUE;
        }
        else if (!_strnicmp(p2, "KDNOECHO", 8))
        {
            p2 += 8;
            KdbDebugState |= KD_DEBUG_KDNOECHO;
        }
        else if (!_strnicmp(p2, "FIRSTCHANCE", 11))
        {
            p2 += 11;
            KdbpSetEnterCondition(-1, TRUE, KdbEnterAlways);
        }

        p1 = p2;
    }
}

NTSTATUS
KdbpSafeReadMemory(
    OUT PVOID Dest,
    IN PVOID Src,
    IN ULONG Bytes)
{
    BOOLEAN Result = TRUE;

    switch (Bytes)
    {
        case 1:
        case 2:
        case 4:
        case 8:
            Result = KdpSafeReadMemory((ULONG_PTR)Src, Bytes, Dest);
            break;

        default:
        {
            ULONG_PTR Start, End, Write;

            for (Start = (ULONG_PTR)Src,
                    End = Start + Bytes,
                    Write = (ULONG_PTR)Dest;
                 Result && (Start < End);
                 Start++, Write++)
                if (!KdpSafeReadMemory(Start, 1, (PVOID)Write))
                    Result = FALSE;

            break;
        }
    }

    return Result ? STATUS_SUCCESS : STATUS_ACCESS_VIOLATION;
}

NTSTATUS
KdbpSafeWriteMemory(
    OUT PVOID Dest,
    IN PVOID Src,
    IN ULONG Bytes)
{
    BOOLEAN Result = TRUE;
    ULONG_PTR Start, End, Write;

    for (Start = (ULONG_PTR)Src,
            End = Start + Bytes,
            Write = (ULONG_PTR)Dest;
         Result && (Start < End);
         Start++, Write++)
        if (!KdpSafeWriteMemory(Write, 1, *((PCHAR)Start)))
            Result = FALSE;

    return Result ? STATUS_SUCCESS : STATUS_ACCESS_VIOLATION;
}