unwind.c

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/*
 * COPYRIGHT:       See COPYING in the top level directory
 * PROJECT:         ReactOS system libraries
 * PURPOSE:         Unwinding related functions
 * PROGRAMMER:      Timo Kreuzer (timo.kreuzer@reactos.org)
 */
 
/* INCLUDES *****************************************************************/
 
#include <rtl.h>
 
#define NDEBUG
#include <debug.h>
 
#define UNWIND_HISTORY_TABLE_NONE 0
#define UNWIND_HISTORY_TABLE_GLOBAL 1
#define UNWIND_HISTORY_TABLE_LOCAL 2
 
#define UWOP_PUSH_NONVOL 0
#define UWOP_ALLOC_LARGE 1
#define UWOP_ALLOC_SMALL 2
#define UWOP_SET_FPREG 3
#define UWOP_SAVE_NONVOL 4
#define UWOP_SAVE_NONVOL_FAR 5
#if 0 // These are deprecated / not for x64
#define UWOP_SAVE_XMM 6
#define UWOP_SAVE_XMM_FAR 7
#else
#define UWOP_EPILOG 6
#define UWOP_SPARE_CODE 7
#endif
#define UWOP_SAVE_XMM128 8
#define UWOP_SAVE_XMM128_FAR 9
#define UWOP_PUSH_MACHFRAME 10
 
 
typedef unsigned char UBYTE;
 
typedef union _UNWIND_CODE
{
    struct
    {
        UBYTE CodeOffset;
        UBYTE UnwindOp:4;
        UBYTE OpInfo:4;
    };
    USHORT FrameOffset;
} UNWIND_CODE, *PUNWIND_CODE;
 
typedef struct _UNWIND_INFO
{
    UBYTE Version:3;
    UBYTE Flags:5;
    UBYTE SizeOfProlog;
    UBYTE CountOfCodes;
    UBYTE FrameRegister:4;
    UBYTE FrameOffset:4;
    UNWIND_CODE UnwindCode[1];
/*    union {
        OPTIONAL ULONG ExceptionHandler;
        OPTIONAL ULONG FunctionEntry;
    };
    OPTIONAL ULONG ExceptionData[];
*/
} UNWIND_INFO, *PUNWIND_INFO;
 
/* FUNCTIONS *****************************************************************/
 
PRUNTIME_FUNCTION
NTAPI
RtlLookupFunctionTable(
    IN DWORD64 ControlPc,
    OUT PDWORD64 ImageBase,
    OUT PULONG Length)
{
    PVOID Table;
    ULONG Size;
 
    /* Find corresponding file header from code address */
    if (!RtlPcToFileHeader((PVOID)ControlPc, (PVOID*)ImageBase))
    {
        /* Nothing found */
        return NULL;
    }
 
    /* Locate the exception directory */
    Table = RtlImageDirectoryEntryToData((PVOID)*ImageBase,
                                         TRUE,
                                         IMAGE_DIRECTORY_ENTRY_EXCEPTION,
                                         &Size);
 
    /* Return the number of entries */
    *Length = Size / sizeof(RUNTIME_FUNCTION);
 
    /* Return the address of the table */
    return Table;
}
 
PRUNTIME_FUNCTION
NTAPI
RtlpLookupDynamicFunctionEntry(
    _In_ DWORD64 ControlPc,
    _Out_ PDWORD64 ImageBase,
    _In_ PUNWIND_HISTORY_TABLE HistoryTable);
 
PRUNTIME_FUNCTION
NTAPI
RtlLookupFunctionEntry(
    IN DWORD64 ControlPc,
    OUT PDWORD64 ImageBase,
    OUT PUNWIND_HISTORY_TABLE HistoryTable)
{
    PRUNTIME_FUNCTION FunctionTable, FunctionEntry;
    ULONG TableLength;
    ULONG IndexLo, IndexHi, IndexMid;
 
    /* Find the corresponding table */
    FunctionTable = RtlLookupFunctionTable(ControlPc, ImageBase, &TableLength);
 
    /* If no table is found, try dynamic function tables */
    if (!FunctionTable)
    {
        return RtlpLookupDynamicFunctionEntry(ControlPc, ImageBase, HistoryTable);
    }
 
    /* Use relative virtual address */
    ControlPc -= *ImageBase;
 
    /* Do a binary search */
    IndexLo = 0;
    IndexHi = TableLength;
    while (IndexHi > IndexLo)
    {
        IndexMid = (IndexLo + IndexHi) / 2;
        FunctionEntry = &FunctionTable[IndexMid];
 
        if (ControlPc < FunctionEntry->BeginAddress)
        {
            /* Continue search in lower half */
            IndexHi = IndexMid;
        }
        else if (ControlPc >= FunctionEntry->EndAddress)
        {
            /* Continue search in upper half */
            IndexLo = IndexMid + 1;
        }
        else
        {
            /* ControlPc is within limits, return entry */
            return FunctionEntry;
        }
    }
 
    /* Nothing found, return NULL */
    return NULL;
}
 
static
__inline
ULONG
UnwindOpSlots(
    _In_ UNWIND_CODE UnwindCode)
{
    static const UCHAR UnwindOpExtraSlotTable[] =
    {
        0, // UWOP_PUSH_NONVOL
        1, // UWOP_ALLOC_LARGE (or 3, special cased in lookup code)
        0, // UWOP_ALLOC_SMALL
        0, // UWOP_SET_FPREG
        1, // UWOP_SAVE_NONVOL
        2, // UWOP_SAVE_NONVOL_FAR
        1, // UWOP_EPILOG // previously UWOP_SAVE_XMM
        2, // UWOP_SPARE_CODE // previously UWOP_SAVE_XMM_FAR
        1, // UWOP_SAVE_XMM128
        2, // UWOP_SAVE_XMM128_FAR
        0, // UWOP_PUSH_MACHFRAME
        2, // UWOP_SET_FPREG_LARGE
    };
 
    if ((UnwindCode.UnwindOp == UWOP_ALLOC_LARGE) &&
        (UnwindCode.OpInfo != 0))
    {
        return 3;
    }
    else
    {
        return UnwindOpExtraSlotTable[UnwindCode.UnwindOp] + 1;
    }
}
 
static
__inline
void
SetReg(
    _Inout_ PCONTEXT Context,
    _In_ BYTE Reg,
    _In_ DWORD64 Value)
{
    ((DWORD64*)(&Context->Rax))[Reg] = Value;
}
 
static
__inline
void
SetRegFromStackValue(
    _Inout_ PCONTEXT Context,
    _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS ContextPointers,
    _In_ BYTE Reg,
    _In_ PDWORD64 ValuePointer)
{
    SetReg(Context, Reg, *ValuePointer);
    if (ContextPointers != NULL)
    {
        ContextPointers->IntegerContext[Reg] = ValuePointer;
    }
}
 
static
__inline
DWORD64
GetReg(
    _In_ PCONTEXT Context,
    _In_ BYTE Reg)
{
    return ((DWORD64*)(&Context->Rax))[Reg];
}
 
static
__inline
void
PopReg(
    _Inout_ PCONTEXT Context,
    _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS ContextPointers,
    _In_ BYTE Reg)
{
    SetRegFromStackValue(Context, ContextPointers, Reg, (PDWORD64)Context->Rsp);
    Context->Rsp += sizeof(DWORD64);
}
 
static
__inline
void
SetXmmReg(
    _Inout_ PCONTEXT Context,
    _In_ BYTE Reg,
    _In_ M128A Value)
{
    ((M128A*)(&Context->Xmm0))[Reg] = Value;
}
 
static
__inline
void
SetXmmRegFromStackValue(
    _Out_ PCONTEXT Context,
    _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS ContextPointers,
    _In_ BYTE Reg,
    _In_ M128A *ValuePointer)
{
    SetXmmReg(Context, Reg, *ValuePointer);
    if (ContextPointers != NULL)
    {
        ContextPointers->FloatingContext[Reg] = ValuePointer;
    }
}
 
static
__inline
M128A
GetXmmReg(PCONTEXT Context, BYTE Reg)
{
    return ((M128A*)(&Context->Xmm0))[Reg];
}
 
static
__inline
BOOLEAN
RtlpTryToUnwindEpilog(
    _Inout_ PCONTEXT Context,
    _In_ ULONG64 ControlPc,
    _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS ContextPointers,
    _In_ ULONG64 ImageBase,
    _In_ PRUNTIME_FUNCTION FunctionEntry)
{
    CONTEXT LocalContext;
    BYTE *InstrPtr;
    DWORD Instr;
    BYTE Reg, Mod;
    ULONG64 EndAddress;
 
    /* Make a local copy of the context */
    LocalContext = *Context;
 
    InstrPtr = (BYTE*)ControlPc;
 
    /* Check if first instruction of epilog is "add rsp, x" */
    Instr = *(DWORD*)InstrPtr;
    if ( (Instr & 0x00fffdff) == 0x00c48148 )
    {
        if ( (Instr & 0x0000ff00) == 0x8300 )
        {
            /* This is "add rsp, 0x??" */
            LocalContext.Rsp += Instr >> 24;
            InstrPtr += 4;
        }
        else
        {
            /* This is "add rsp, 0x???????? */
            LocalContext.Rsp += *(DWORD*)(InstrPtr + 3);
            InstrPtr += 7;
        }
    }
    /* Check if first instruction of epilog is "lea rsp, ..." */
    else if ( (Instr & 0x38fffe) == 0x208d48 )
    {
        /* Get the register */
        Reg = (Instr >> 16) & 0x7;
 
        /* REX.R */
        Reg += (Instr & 1) * 8;
 
        LocalContext.Rsp = GetReg(&LocalContext, Reg);
 
        /* Get addressing mode */
        Mod = (Instr >> 22) & 0x3;
        if (Mod == 0)
        {
            /* No displacement */
            InstrPtr += 3;
        }
        else if (Mod == 1)
        {
            /* 1 byte displacement */
            LocalContext.Rsp += (LONG)(CHAR)(Instr >> 24);
            InstrPtr += 4;
        }
        else if (Mod == 2)
        {
            /* 4 bytes displacement */
            LocalContext.Rsp += *(LONG*)(InstrPtr + 3);
            InstrPtr += 7;
        }
    }
 
    /* Loop the following instructions before the ret */
    EndAddress = FunctionEntry->EndAddress + ImageBase - 1;
    while ((DWORD64)InstrPtr < EndAddress)
    {
        Instr = *(DWORD*)InstrPtr;
 
        /* Check for a simple pop */
        if ( (Instr & 0xf8) == 0x58 )
        {
            /* Opcode pops a basic register from stack */
            Reg = Instr & 0x7;
            PopReg(&LocalContext, ContextPointers, Reg);
            InstrPtr++;
            continue;
        }
 
        /* Check for REX + pop */
        if ( (Instr & 0xf8fb) == 0x5841 )
        {
            /* Opcode is pop r8 .. r15 */
            Reg = ((Instr >> 8) & 0x7) + 8;
            PopReg(&LocalContext, ContextPointers, Reg);
            InstrPtr += 2;
            continue;
        }
 
        /* Opcode not allowed for Epilog */
        return FALSE;
    }
 
    // check for popfq
 
    // also allow end with jmp imm, jmp [target], iretq
 
    /* Check if we are at the ret instruction */
    if ((DWORD64)InstrPtr != EndAddress)
    {
        /* If we went past the end of the function, something is broken! */
        ASSERT((DWORD64)InstrPtr <= EndAddress);
        return FALSE;
    }
 
    /* Make sure this is really a ret instruction */
    if (*InstrPtr != 0xc3)
    {
        return FALSE;
    }
 
    /* Unwind is finished, pop new Rip from Stack */
    LocalContext.Rip = *(DWORD64*)LocalContext.Rsp;
    LocalContext.Rsp += sizeof(DWORD64);
 
    *Context = LocalContext;
    return TRUE;
}
 
static
ULONG64
GetEstablisherFrame(
    _In_ PCONTEXT Context,
    _In_ PUNWIND_INFO UnwindInfo,
    _In_ ULONG_PTR CodeOffset)
{
    ULONG i;
 
    /* Check if we have a frame register */
    if (UnwindInfo->FrameRegister == 0)
    {
        /* No frame register means we use Rsp */
        return Context->Rsp;
    }
 
    if ((CodeOffset >= UnwindInfo->SizeOfProlog) ||
        ((UnwindInfo->Flags & UNW_FLAG_CHAININFO) != 0))
    {
        return GetReg(Context, UnwindInfo->FrameRegister) -
               UnwindInfo->FrameOffset * 16;
    }
 
    /* Loop all unwind ops */
    for (i = 0;
         i < UnwindInfo->CountOfCodes;
         i += UnwindOpSlots(UnwindInfo->UnwindCode[i]))
    {
        /* Skip codes past our code offset */
        if (UnwindInfo->UnwindCode[i].CodeOffset > CodeOffset)
        {
            continue;
        }
 
        /* Check for SET_FPREG */
        if (UnwindInfo->UnwindCode[i].UnwindOp == UWOP_SET_FPREG)
        {
            return GetReg(Context, UnwindInfo->FrameRegister) -
                       UnwindInfo->FrameOffset * 16;
        }
    }
 
    return Context->Rsp;
}
 
PEXCEPTION_ROUTINE
NTAPI
RtlVirtualUnwind(
    _In_ ULONG HandlerType,
    _In_ ULONG64 ImageBase,
    _In_ ULONG64 ControlPc,
    _In_ PRUNTIME_FUNCTION FunctionEntry,
    _Inout_ PCONTEXT Context,
    _Outptr_ PVOID *HandlerData,
    _Out_ PULONG64 EstablisherFrame,
    _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS ContextPointers)
{
    PUNWIND_INFO UnwindInfo;
    ULONG_PTR ControlRva, CodeOffset;
    ULONG i, Offset;
    UNWIND_CODE UnwindCode;
    BYTE Reg;
    PULONG LanguageHandler;
 
    /* Get relative virtual address */
    ControlRva = ControlPc - ImageBase;
 
    /* Sanity checks */
    if ( (ControlRva < FunctionEntry->BeginAddress) ||
         (ControlRva >= FunctionEntry->EndAddress) )
    {
        return NULL;
    }
 
    /* Get a pointer to the unwind info */
    UnwindInfo = RVA(ImageBase, FunctionEntry->UnwindData);
 
    /* The language specific handler data follows the unwind info */
    LanguageHandler = ALIGN_UP_POINTER_BY(&UnwindInfo->UnwindCode[UnwindInfo->CountOfCodes], sizeof(ULONG));
 
    /* Calculate relative offset to function start */
    CodeOffset = ControlRva - FunctionEntry->BeginAddress;
 
    *EstablisherFrame = GetEstablisherFrame(Context, UnwindInfo, CodeOffset);
 
    /* Check if we are in the function epilog and try to finish it */
    if ((CodeOffset > UnwindInfo->SizeOfProlog) && (UnwindInfo->CountOfCodes > 0))
    {
        if (RtlpTryToUnwindEpilog(Context, ControlPc, ContextPointers, ImageBase, FunctionEntry))
        {
            /* There's no exception routine */
            return NULL;
        }
    }
 
    /* Skip all Ops with an offset greater than the current Offset */
    i = 0;
    while ((i < UnwindInfo->CountOfCodes) &&
           (UnwindInfo->UnwindCode[i].CodeOffset > CodeOffset))
    {
        i += UnwindOpSlots(UnwindInfo->UnwindCode[i]);
    }
 
RepeatChainedInfo:
 
    /* Process the remaining unwind ops */
    while (i < UnwindInfo->CountOfCodes)
    {
        UnwindCode = UnwindInfo->UnwindCode[i];
        switch (UnwindCode.UnwindOp)
        {
            case UWOP_PUSH_NONVOL:
                Reg = UnwindCode.OpInfo;
                PopReg(Context, ContextPointers, Reg);
                i++;
                break;
 
            case UWOP_ALLOC_LARGE:
                if (UnwindCode.OpInfo)
                {
                    Offset = *(ULONG*)(&UnwindInfo->UnwindCode[i+1]);
                    Context->Rsp += Offset;
                    i += 3;
                }
                else
                {
                    Offset = UnwindInfo->UnwindCode[i+1].FrameOffset;
                    Context->Rsp += Offset * 8;
                    i += 2;
                }
                break;
 
            case UWOP_ALLOC_SMALL:
                Context->Rsp += (UnwindCode.OpInfo + 1) * 8;
                i++;
                break;
 
            case UWOP_SET_FPREG:
                Reg = UnwindInfo->FrameRegister;
                Context->Rsp = GetReg(Context, Reg) - UnwindInfo->FrameOffset * 16;
                i++;
                break;
 
            case UWOP_SAVE_NONVOL:
                Reg = UnwindCode.OpInfo;
                Offset = UnwindInfo->UnwindCode[i + 1].FrameOffset;
                SetRegFromStackValue(Context, ContextPointers, Reg, (DWORD64*)Context->Rsp + Offset);
                i += 2;
                break;
 
            case UWOP_SAVE_NONVOL_FAR:
                Reg = UnwindCode.OpInfo;
                Offset = *(ULONG*)(&UnwindInfo->UnwindCode[i + 1]);
                SetRegFromStackValue(Context, ContextPointers, Reg, (DWORD64*)Context->Rsp + Offset);
                i += 3;
                break;
 
            case UWOP_EPILOG:
                i += 1;
                break;
 
            case UWOP_SPARE_CODE:
                ASSERT(FALSE);
                i += 2;
                break;
 
            case UWOP_SAVE_XMM128:
                Reg = UnwindCode.OpInfo;
                Offset = UnwindInfo->UnwindCode[i + 1].FrameOffset;
                SetXmmRegFromStackValue(Context, ContextPointers, Reg, (M128A*)Context->Rsp + Offset);
                i += 2;
                break;
 
            case UWOP_SAVE_XMM128_FAR:
                Reg = UnwindCode.OpInfo;
                Offset = *(ULONG*)(&UnwindInfo->UnwindCode[i + 1]);
                SetXmmRegFromStackValue(Context, ContextPointers, Reg, (M128A*)Context->Rsp + Offset);
                i += 3;
                break;
 
            case UWOP_PUSH_MACHFRAME:
                /* OpInfo is 1, when an error code was pushed, otherwise 0. */
                Context->Rsp += UnwindCode.OpInfo * sizeof(DWORD64);
 
                /* Now pop the MACHINE_FRAME (RIP/RSP only. And yes, "magic numbers", deal with it) */
                Context->Rip = *(PDWORD64)(Context->Rsp + 0x00);
                Context->Rsp = *(PDWORD64)(Context->Rsp + 0x18);
                ASSERT((i + 1) == UnwindInfo->CountOfCodes);
                goto Exit;
        }
    }
 
    /* Check for chained info */
    if (UnwindInfo->Flags & UNW_FLAG_CHAININFO)
    {
        /* See https://docs.microsoft.com/en-us/cpp/build/exception-handling-x64?view=msvc-160#chained-unwind-info-structures */
        FunctionEntry = (PRUNTIME_FUNCTION)&(UnwindInfo->UnwindCode[(UnwindInfo->CountOfCodes + 1) & ~1]);
        UnwindInfo = RVA(ImageBase, FunctionEntry->UnwindData);
        i = 0;
        goto RepeatChainedInfo;
    }
 
    /* Unwind is finished, pop new Rip from Stack */
    if (Context->Rsp != 0)
    {
        Context->Rip = *(DWORD64*)Context->Rsp;
        Context->Rsp += sizeof(DWORD64);
    }
 
Exit:
 
    /* Check if we have a handler and return it */
    if (UnwindInfo->Flags & (HandlerType & (UNW_FLAG_EHANDLER | UNW_FLAG_UHANDLER)))
    {
        *HandlerData = (LanguageHandler + 1);
        return RVA(ImageBase, *LanguageHandler);
    }
 
    return NULL;
}
 
static __inline
BOOL
RtlpIsStackPointerValid(
    _In_ ULONG64 StackPointer,
    _In_ ULONG64 LowLimit,
    _In_ ULONG64 HighLimit)
{
    return (StackPointer >= LowLimit) &&
           (StackPointer < HighLimit) &&
           ((StackPointer & 7) == 0);
}
 
BOOLEAN
NTAPI
RtlpUnwindInternal(
    _In_opt_ PVOID TargetFrame,
    _In_opt_ PVOID TargetIp,
    _In_ PEXCEPTION_RECORD ExceptionRecord,
    _In_ PVOID ReturnValue,
    _In_ PCONTEXT ContextRecord,
    _In_opt_ struct _UNWIND_HISTORY_TABLE *HistoryTable,
    _In_ ULONG HandlerType)
{
    DISPATCHER_CONTEXT DispatcherContext;
    PEXCEPTION_ROUTINE ExceptionRoutine;
    EXCEPTION_DISPOSITION Disposition;
    PRUNTIME_FUNCTION FunctionEntry;
    ULONG_PTR StackLow, StackHigh;
    ULONG64 ImageBase, EstablisherFrame;
    CONTEXT UnwindContext;
 
    /* Get the current stack limits */
    RtlpGetStackLimits(&StackLow, &StackHigh);
 
    /* If we have a target frame, then this is our high limit */
    if (TargetFrame != NULL)
    {
        StackHigh = (ULONG64)TargetFrame + 1;
    }
 
    /* Copy the context */
    UnwindContext = *ContextRecord;
 
    /* Set up the constant fields of the dispatcher context */
    DispatcherContext.ContextRecord = &UnwindContext;
    DispatcherContext.HistoryTable = HistoryTable;
    DispatcherContext.TargetIp = (ULONG64)TargetIp;
 
    /* Start looping */
    while (TRUE)
    {
        if (!RtlpIsStackPointerValid(UnwindContext.Rsp, StackLow, StackHigh))
        {
            return FALSE;
        }
 
        /* Lookup the FunctionEntry for the current RIP */
        FunctionEntry = RtlLookupFunctionEntry(UnwindContext.Rip, &ImageBase, NULL);
        if (FunctionEntry == NULL)
        {
            /* No function entry, so this must be a leaf function. Pop the return address from the stack.
               Note: this can happen after the first frame as the result of an exception */
            UnwindContext.Rip = *(DWORD64*)UnwindContext.Rsp;
            UnwindContext.Rsp += sizeof(DWORD64);
 
            if (HandlerType == UNW_FLAG_UHANDLER)
            {
                /* Copy the context back for the next iteration */
                *ContextRecord = UnwindContext;
            }
            continue;
        }
 
        /* Save Rip before the virtual unwind */
        DispatcherContext.ControlPc = UnwindContext.Rip;
 
        /* Do a virtual unwind to get the next frame */
        ExceptionRoutine = RtlVirtualUnwind(HandlerType,
                                            ImageBase,
                                            UnwindContext.Rip,
                                            FunctionEntry,
                                            &UnwindContext,
                                            &DispatcherContext.HandlerData,
                                            &EstablisherFrame,
                                            NULL);
 
        /* Check, if we are still within the stack boundaries */
        if ((EstablisherFrame < StackLow) ||
            (EstablisherFrame >= StackHigh) ||
            (EstablisherFrame & 7))
        {
 
            /* If we are handling an exception, we are done here. */
            if (HandlerType == UNW_FLAG_EHANDLER)
            {
                ExceptionRecord->ExceptionFlags |= EXCEPTION_STACK_INVALID;
                return FALSE;
            }
 
            __debugbreak();
            RtlRaiseStatus(STATUS_BAD_STACK);
        }
 
        /* Check if we have an exception routine */
        if (ExceptionRoutine != NULL)
        {
            /* Check if this is the target frame */
            if (EstablisherFrame == (ULONG64)TargetFrame)
            {
                /* Set flag to inform the language handler */
                ExceptionRecord->ExceptionFlags |= EXCEPTION_TARGET_UNWIND;
            }
 
            /* Log the exception if it's enabled */
            RtlpCheckLogException(ExceptionRecord,
                                  &UnwindContext,
                                  &DispatcherContext,
                                  sizeof(DispatcherContext));
 
            /* Set up the variable fields of the dispatcher context */
            DispatcherContext.ImageBase = ImageBase;
            DispatcherContext.FunctionEntry = FunctionEntry;
            DispatcherContext.LanguageHandler = ExceptionRoutine;
            DispatcherContext.EstablisherFrame = EstablisherFrame;
            DispatcherContext.ScopeIndex = 0;
 
            /* Store the return value in the unwind context */
            UnwindContext.Rax = (ULONG64)ReturnValue;
 
             /* Loop all nested handlers */
            do
            {
                /* Call the language specific handler */
                Disposition = ExceptionRoutine(ExceptionRecord,
                                               (PVOID)EstablisherFrame,
                                               ContextRecord,
                                               &DispatcherContext);
 
                /* Clear exception flags for the next iteration */
                ExceptionRecord->ExceptionFlags &= ~(EXCEPTION_TARGET_UNWIND |
                                                     EXCEPTION_COLLIDED_UNWIND);
 
                /* Check if we do exception handling */
                if (HandlerType == UNW_FLAG_EHANDLER)
                {
                    if (Disposition == ExceptionContinueExecution)
                    {
                        /* Check if it was non-continuable */
                        if (ExceptionRecord->ExceptionFlags & EXCEPTION_NONCONTINUABLE)
                        {
                            __debugbreak();
                            RtlRaiseStatus(EXCEPTION_NONCONTINUABLE_EXCEPTION);
                        }
 
                        /* Execution continues */
                        return TRUE;
                    }
                    else if (Disposition == ExceptionNestedException)
                    {
                        __debugbreak();
                    }
                }
 
                if (Disposition == ExceptionCollidedUnwind)
                {
                    __debugbreak();
                }
 
                /* This must be ExceptionContinueSearch now */
                if (Disposition != ExceptionContinueSearch)
                {
                    __debugbreak();
                    RtlRaiseStatus(STATUS_INVALID_DISPOSITION);
                }
            } while (ExceptionRecord->ExceptionFlags & EXCEPTION_COLLIDED_UNWIND);
        }
 
        /* Check, if we have left our stack (8.) */
        if ((EstablisherFrame < StackLow) ||
            (EstablisherFrame > StackHigh) ||
            (EstablisherFrame & 7))
        {
            __debugbreak();
 
            if (UnwindContext.Rip == ContextRecord->Rip)
            {
                RtlRaiseStatus(STATUS_BAD_FUNCTION_TABLE);
            }
            else
            {
                ZwRaiseException(ExceptionRecord, ContextRecord, FALSE);
            }
        }
 
        if (EstablisherFrame == (ULONG64)TargetFrame)
        {
            break;
        }
 
        if (HandlerType == UNW_FLAG_UHANDLER)
        {
            /* We have successfully unwound a frame. Copy the unwind context back. */
            *ContextRecord = UnwindContext;
        }
    }
 
    if (ExceptionRecord->ExceptionCode != STATUS_UNWIND_CONSOLIDATE)
    {
        ContextRecord->Rip = (ULONG64)TargetIp;
    }
 
    /* Set the return value */
    ContextRecord->Rax = (ULONG64)ReturnValue;
 
    /* Restore the context */
    RtlRestoreContext(ContextRecord, ExceptionRecord);
 
    /* Should never get here! */
    ASSERT(FALSE);
    return FALSE;
}
 
VOID
NTAPI
RtlUnwindEx(
    _In_opt_ PVOID TargetFrame,
    _In_opt_ PVOID TargetIp,
    _In_opt_ PEXCEPTION_RECORD ExceptionRecord,
    _In_ PVOID ReturnValue,
    _In_ PCONTEXT ContextRecord,
    _In_opt_ struct _UNWIND_HISTORY_TABLE *HistoryTable)
{
    EXCEPTION_RECORD LocalExceptionRecord;
 
    /* Capture the current context */
    RtlCaptureContext(ContextRecord);
 
    /* Check if we have an exception record */
    if (ExceptionRecord == NULL)
    {
        /* No exception record was passed, so set up a local one */
        LocalExceptionRecord.ExceptionCode = STATUS_UNWIND;
        LocalExceptionRecord.ExceptionAddress = (PVOID)ContextRecord->Rip;
        LocalExceptionRecord.ExceptionRecord = NULL;
        LocalExceptionRecord.NumberParameters = 0;
        ExceptionRecord = &LocalExceptionRecord;
    }
 
    /* Set unwind flags */
    ExceptionRecord->ExceptionFlags = EXCEPTION_UNWINDING;
    if (TargetFrame == NULL)
    {
        ExceptionRecord->ExceptionFlags |= EXCEPTION_EXIT_UNWIND;
    }
 
    /* Call the internal function */
    RtlpUnwindInternal(TargetFrame,
                       TargetIp,
                       ExceptionRecord,
                       ReturnValue,
                       ContextRecord,
                       HistoryTable,
                       UNW_FLAG_UHANDLER);
}
 
VOID
NTAPI
RtlUnwind(
    _In_opt_ PVOID TargetFrame,
    _In_opt_ PVOID TargetIp,
    _In_opt_ PEXCEPTION_RECORD ExceptionRecord,
    _In_ PVOID ReturnValue)
{
    CONTEXT Context;
 
    RtlUnwindEx(TargetFrame,
                TargetIp,
                ExceptionRecord,
                ReturnValue,
                &Context,
                NULL);
}
 
ULONG
NTAPI
RtlWalkFrameChain(OUT PVOID *Callers,
                  IN ULONG Count,
                  IN ULONG Flags)
{
    CONTEXT Context;
    ULONG64 ControlPc, ImageBase, EstablisherFrame;
    ULONG64 StackLow, StackHigh;
    PVOID HandlerData;
    ULONG i, FramesToSkip;
    PRUNTIME_FUNCTION FunctionEntry;
    MODE CurrentMode = RtlpGetMode();
 
    DPRINT("Enter RtlWalkFrameChain\n");
 
    /* The upper bits in Flags define how many frames to skip */
    FramesToSkip = Flags >> 8;
 
    /* Capture the current Context */
    RtlCaptureContext(&Context);
    ControlPc = Context.Rip;
 
    /* Get the stack limits */
    RtlpGetStackLimits(&StackLow, &StackHigh);
 
    _SEH2_TRY
    {
        /* Loop the frames */
        for (i = 0; i < FramesToSkip + Count; i++)
        {
            /* Lookup the FunctionEntry for the current ControlPc */
            FunctionEntry = RtlLookupFunctionEntry(ControlPc, &ImageBase, NULL);
 
            /* Is this a leaf function? */
            if (!FunctionEntry)
            {
                Context.Rip = *(DWORD64*)Context.Rsp;
                Context.Rsp += sizeof(DWORD64);
                DPRINT("leaf funtion, new Rip = %p, new Rsp = %p\n", (PVOID)Context.Rip, (PVOID)Context.Rsp);
            }
            else
            {
                RtlVirtualUnwind(UNW_FLAG_NHANDLER,
                                 ImageBase,
                                 ControlPc,
                                 FunctionEntry,
                                 &Context,
                                 &HandlerData,
                                 &EstablisherFrame,
                                 NULL);
                DPRINT("normal funtion, new Rip = %p, new Rsp = %p\n", (PVOID)Context.Rip, (PVOID)Context.Rsp);
            }
 
            /* Check if we are in kernel mode */
            if (CurrentMode == KernelMode)
            {
                /* Check if we left the kernel range */
                if (Context.Rip < 0xFFFF800000000000ULL)
                {
                    /* Bail out, unless user mode was requested */
                    if ((Flags & 1) == 0)
                    {
                        break;
                    }
 
                    /* We are in user mode now, get UM stack bounds */
                    CurrentMode = UserMode;
                    StackLow = (ULONG64)NtCurrentTeb()->NtTib.StackLimit;
                    StackHigh = (ULONG64)NtCurrentTeb()->NtTib.StackBase;
                }
            }
 
            /* Check (again) if we are in user mode now */
            if (CurrentMode == UserMode)
            {
                /* Check if we left the user range */
                if ((Context.Rip < 0x10000) ||
                    (Context.Rip > 0x000007FFFFFEFFFFULL))
                {
                    break;
                }
            }
 
            /* Check, if we have left our stack */
            if ((Context.Rsp <= StackLow) || (Context.Rsp >= StackHigh))
            {
                break;
            }
 
            /* Continue with new Rip */
            ControlPc = Context.Rip;
 
            /* Save value, if we are past the frames to skip */
            if (i >= FramesToSkip)
            {
                Callers[i - FramesToSkip] = (PVOID)ControlPc;
            }
        }
    }
    _SEH2_EXCEPT(EXCEPTION_EXECUTE_HANDLER)
    {
        DPRINT1("Exception while getting callers!\n");
        i = 0;
    }
    _SEH2_END;
 
    DPRINT("RtlWalkFrameChain returns %ld\n", i);
    return i;
}
 
#undef RtlGetCallersAddress
VOID
NTAPI
RtlGetCallersAddress(
    OUT PVOID *CallersAddress,
    OUT PVOID *CallersCaller )
{
    PVOID Callers[4];
    ULONG Number;
 
    /* Get callers:
     * RtlWalkFrameChain -> RtlGetCallersAddress -> x -> y */
    Number = RtlWalkFrameChain(Callers, 4, 0);
 
    *CallersAddress = (Number >= 3) ? Callers[2] : NULL;
    *CallersCaller = (Number == 4) ? Callers[3] : NULL;
 
    return;
}
 
static
VOID
RtlpCaptureNonVolatileContextPointers(
    _Out_ PKNONVOLATILE_CONTEXT_POINTERS NonvolatileContextPointers,
    _In_ ULONG64 TargetFrame)
{
    CONTEXT Context;
    PRUNTIME_FUNCTION FunctionEntry;
    ULONG64 ImageBase;
    PVOID HandlerData;
    ULONG64 EstablisherFrame;
 
    /* Zero out the nonvolatile context pointers */
    RtlZeroMemory(NonvolatileContextPointers, sizeof(*NonvolatileContextPointers));
 
    /* Capture the current context */
    RtlCaptureContext(&Context);
 
    do
    {
        /* Make sure nothing fishy is going on. Currently this is for kernel mode only. */
        ASSERT((LONG64)Context.Rip < 0);
        ASSERT((LONG64)Context.Rsp < 0);
 
        /* Look up the function entry */
        FunctionEntry = RtlLookupFunctionEntry(Context.Rip, &ImageBase, NULL);
        if (FunctionEntry != NULL)
        {
            /* Do a virtual unwind to the caller and capture saved non-volatiles */
            RtlVirtualUnwind(UNW_FLAG_EHANDLER,
                             ImageBase,
                             Context.Rip,
                             FunctionEntry,
                             &Context,
                             &HandlerData,
                             &EstablisherFrame,
                             NonvolatileContextPointers);
 
            ASSERT(EstablisherFrame != 0);
        }
        else
        {
            Context.Rip = *(PULONG64)Context.Rsp;
            Context.Rsp += 8;
        }
 
        /* Continue until we reach user mode */
    } while ((LONG64)Context.Rip < 0);
 
    /* If the caller did the right thing, we should get past the target frame */
    ASSERT(EstablisherFrame >= TargetFrame);
}
 
VOID
RtlSetUnwindContext(
    _In_ PCONTEXT Context,
    _In_ DWORD64 TargetFrame)
{
    KNONVOLATILE_CONTEXT_POINTERS ContextPointers;
 
    /* Capture pointers to the non-volatiles up to the target frame */
    RtlpCaptureNonVolatileContextPointers(&ContextPointers, TargetFrame);
 
    /* Copy the nonvolatiles to the captured locations */
    *ContextPointers.R12 = Context->R12;
    *ContextPointers.R13 = Context->R13;
    *ContextPointers.R14 = Context->R14;
    *ContextPointers.R15 = Context->R15;
    *ContextPointers.Xmm6 = Context->Xmm6;
    *ContextPointers.Xmm7 = Context->Xmm7;
    *ContextPointers.Xmm8 = Context->Xmm8;
    *ContextPointers.Xmm9 = Context->Xmm9;
    *ContextPointers.Xmm10 = Context->Xmm10;
    *ContextPointers.Xmm11 = Context->Xmm11;
    *ContextPointers.Xmm12 = Context->Xmm12;
    *ContextPointers.Xmm13 = Context->Xmm13;
    *ContextPointers.Xmm14 = Context->Xmm14;
    *ContextPointers.Xmm15 = Context->Xmm15;
}
 
VOID
RtlpRestoreContextInternal(
    _In_ PCONTEXT ContextRecord);
 
VOID
RtlRestoreContext(
    _In_ PCONTEXT ContextRecord,
    _In_ PEXCEPTION_RECORD ExceptionRecord)
{
    if (ExceptionRecord != NULL)
    {
        if ((ExceptionRecord->ExceptionCode == STATUS_UNWIND_CONSOLIDATE) &&
            (ExceptionRecord->NumberParameters >= 1))
        {
            PVOID (*Consolidate)(EXCEPTION_RECORD*) = (PVOID)ExceptionRecord->ExceptionInformation[0];
            // FIXME: This should be called through an asm wrapper to allow handling recursive unwinding
            ContextRecord->Rip = (ULONG64)Consolidate(ExceptionRecord);
        }
    }
 
    RtlpRestoreContextInternal(ContextRecord);
}