unwind.c File Reference

#include <rtl.h>
#include <debug.h>

Include dependency graph for unwind.c:

Go to the source code of this file.

Classes
union	_UNWIND_CODE
struct	_UNWIND_INFO

Macros
#define	NDEBUG
#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
#define	UWOP_EPILOG   6
#define	UWOP_SPARE_CODE   7
#define	UWOP_SAVE_XMM128   8
#define	UWOP_SAVE_XMM128_FAR   9
#define	UWOP_PUSH_MACHFRAME   10

Typedefs
typedef unsigned char	UBYTE
typedef union _UNWIND_CODE	UNWIND_CODE
typedef union _UNWIND_CODE *	PUNWIND_CODE
typedef struct _UNWIND_INFO	UNWIND_INFO
typedef struct _UNWIND_INFO *	PUNWIND_INFO

Functions
PRUNTIME_FUNCTION NTAPI	RtlLookupFunctionTable (IN DWORD64 ControlPc, OUT PDWORD64 ImageBase, OUT PULONG Length)
	Locates the table of RUNTIME_FUNCTION entries for a code address.
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)
	Locates the RUNTIME_FUNCTION entry corresponding to a code address. https://learn.microsoft.com/en-us/windows/win32/api/winnt/nf-winnt-rtllookupfunctionentry.
static __inline ULONG	UnwindOpSlots (_In_ UNWIND_CODE UnwindCode)
static __inline void	SetReg (_Inout_ PCONTEXT Context, _In_ BYTE Reg, _In_ DWORD64 Value)
static __inline void	SetRegFromStackValue (_Inout_ PCONTEXT Context, _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS ContextPointers, _In_ BYTE Reg, _In_ PDWORD64 ValuePointer)
static __inline DWORD64	GetReg (_In_ PCONTEXT Context, _In_ BYTE Reg)
static __inline void	PopReg (_Inout_ PCONTEXT Context, _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS ContextPointers, _In_ BYTE Reg)
static __inline void	SetXmmReg (_Inout_ PCONTEXT Context, _In_ BYTE Reg, _In_ M128A Value)
static __inline void	SetXmmRegFromStackValue (_Out_ PCONTEXT Context, _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS ContextPointers, _In_ BYTE Reg, _In_ M128A *ValuePointer)
static __inline M128A	GetXmmReg (PCONTEXT Context, BYTE Reg)
static __inline BOOLEAN	RtlpTryToUnwindEpilog (_Inout_ PCONTEXT Context, _In_ ULONG64 ControlPc, _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS ContextPointers, _In_ ULONG64 ImageBase, _In_ PRUNTIME_FUNCTION FunctionEntry)
	Helper function that tries to unwind epilog instructions.
static ULONG64	GetEstablisherFrame (_In_ PCONTEXT Context, _In_ PUNWIND_INFO UnwindInfo, _In_ ULONG_PTR CodeOffset)
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)
static __inline BOOL	RtlpIsStackPointerValid (_In_ ULONG64 StackPointer, _In_ ULONG64 LowLimit, _In_ ULONG64 HighLimit)
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)
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)
VOID NTAPI	RtlUnwind (_In_opt_ PVOID TargetFrame, _In_opt_ PVOID TargetIp, _In_opt_ PEXCEPTION_RECORD ExceptionRecord, _In_ PVOID ReturnValue)
ULONG NTAPI	RtlWalkFrameChain (OUT PVOID *Callers, IN ULONG Count, IN ULONG Flags)
VOID NTAPI	RtlGetCallersAddress (OUT PVOID *CallersAddress, OUT PVOID *CallersCaller)
static VOID	RtlpCaptureNonVolatileContextPointers (_Out_ PKNONVOLATILE_CONTEXT_POINTERS NonvolatileContextPointers, _In_ ULONG64 TargetFrame)
VOID	RtlSetUnwindContext (_In_ PCONTEXT Context, _In_ DWORD64 TargetFrame)
VOID	RtlpRestoreContextInternal (_In_ PCONTEXT ContextRecord)
VOID	RtlRestoreContext (_In_ PCONTEXT ContextRecord, _In_ PEXCEPTION_RECORD ExceptionRecord)

Macro Definition Documentation

NDEBUG

#define NDEBUG

Definition at line 12 of file unwind.c.

UNWIND_HISTORY_TABLE_GLOBAL

#define UNWIND_HISTORY_TABLE_GLOBAL   1

Definition at line 16 of file unwind.c.

UNWIND_HISTORY_TABLE_LOCAL

#define UNWIND_HISTORY_TABLE_LOCAL   2

Definition at line 17 of file unwind.c.

UNWIND_HISTORY_TABLE_NONE

#define UNWIND_HISTORY_TABLE_NONE   0

Definition at line 15 of file unwind.c.

UWOP_ALLOC_LARGE

#define UWOP_ALLOC_LARGE   1

Definition at line 20 of file unwind.c.

UWOP_ALLOC_SMALL

#define UWOP_ALLOC_SMALL   2

Definition at line 21 of file unwind.c.

UWOP_EPILOG

#define UWOP_EPILOG   6

Definition at line 29 of file unwind.c.

UWOP_PUSH_MACHFRAME

#define UWOP_PUSH_MACHFRAME   10

Definition at line 34 of file unwind.c.

UWOP_PUSH_NONVOL

#define UWOP_PUSH_NONVOL   0

Definition at line 19 of file unwind.c.

UWOP_SAVE_NONVOL

#define UWOP_SAVE_NONVOL   4

Definition at line 23 of file unwind.c.

UWOP_SAVE_NONVOL_FAR

#define UWOP_SAVE_NONVOL_FAR   5

Definition at line 24 of file unwind.c.

UWOP_SAVE_XMM128

#define UWOP_SAVE_XMM128   8

Definition at line 32 of file unwind.c.

UWOP_SAVE_XMM128_FAR

#define UWOP_SAVE_XMM128_FAR   9

Definition at line 33 of file unwind.c.

UWOP_SET_FPREG

#define UWOP_SET_FPREG   3

Definition at line 22 of file unwind.c.

UWOP_SPARE_CODE

#define UWOP_SPARE_CODE   7

Definition at line 30 of file unwind.c.

Typedef Documentation

PUNWIND_CODE

typedef union _UNWIND_CODE * PUNWIND_CODE

PUNWIND_INFO

typedef struct _UNWIND_INFO * PUNWIND_INFO

UBYTE

typedef unsigned char UBYTE

Definition at line 37 of file unwind.c.

UNWIND_CODE

typedef union _UNWIND_CODE UNWIND_CODE

UNWIND_INFO

typedef struct _UNWIND_INFO UNWIND_INFO

Function Documentation

GetEstablisherFrame()

static ULONG64 GetEstablisherFrame ( _In_ PCONTEXT  Context, _In_ PUNWIND_INFO  UnwindInfo, _In_ ULONG_PTR  CodeOffset  )

static

https://docs.microsoft.com/en-us/cpp/build/unwind-data-definitions-in-c

Definition at line 433 of file unwind.c.

{
    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;
}

Referenced by RtlVirtualUnwind().

GetReg()

static __inline DWORD64 GetReg ( _In_ PCONTEXT  Context, _In_ BYTE  Reg  )

static

Definition at line 237 of file unwind.c.

{
    return ((DWORD64*)(&Context->Rax))[Reg];
}

Referenced by GetEstablisherFrame(), RtlpTryToUnwindEpilog(), and RtlVirtualUnwind().

GetXmmReg()

static __inline M128A GetXmmReg ( PCONTEXT  Context, BYTE  Reg  )

static

Definition at line 286 of file unwind.c.

{
    return ((M128A*)(&Context->Xmm0))[Reg];
}

PopReg()

static __inline void PopReg ( _Inout_ PCONTEXT  Context, _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS  ContextPointers, _In_ BYTE  Reg  )

static

Definition at line 247 of file unwind.c.

{
    SetRegFromStackValue(Context, ContextPointers, Reg, (PDWORD64)Context->Rsp);
    Context->Rsp += sizeof(DWORD64);
}

Referenced by RtlpTryToUnwindEpilog(), and RtlVirtualUnwind().

RtlGetCallersAddress()

VOID NTAPI RtlGetCallersAddress	(	OUT PVOID *	CallersAddress,
		OUT PVOID *	CallersCaller
	)

RtlGetCallersAddress http://undocumented.ntinternals.net/UserMode/Undocumented%20Functions/Debug/RtlGetCallersAddress.html

Definition at line 1068 of file unwind.c.

{
    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;
}

RtlLookupFunctionEntry()

PRUNTIME_FUNCTION NTAPI RtlLookupFunctionEntry	(	IN DWORD64	ControlPc,
		OUT PDWORD64	ImageBase,
		OUT PUNWIND_HISTORY_TABLE	HistoryTable
	)

Locates the RUNTIME_FUNCTION entry corresponding to a code address. https://learn.microsoft.com/en-us/windows/win32/api/winnt/nf-winnt-rtllookupfunctionentry.

RtlLookupFunctionEntry

Todo:

Implement HistoryTable

Definition at line 124 of file unwind.c.

{
    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;
}

Referenced by RtlpCaptureNonVolatileContextPointers(), RtlpUnwindInternal(), and RtlWalkFrameChain().

RtlLookupFunctionTable()

PRUNTIME_FUNCTION NTAPI RtlLookupFunctionTable	(	IN DWORD64	ControlPc,
		OUT PDWORD64	ImageBase,
		OUT PULONG	Length
	)

Locates the table of RUNTIME_FUNCTION entries for a code address.

RtlLookupFunctionTable

Parameters

ControlPc	Address of the code, for which the table should be searched.
ImageBase	Pointer to a DWORD64 that receives the base address of the corresponding executable image.
Length	Pointer to an ULONG that receives the number of table entries present in the table.

Definition at line 82 of file unwind.c.

{
    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;
}

Referenced by RtlLookupFunctionEntry().

RtlpCaptureNonVolatileContextPointers()

static VOID RtlpCaptureNonVolatileContextPointers ( _Out_ PKNONVOLATILE_CONTEXT_POINTERS  NonvolatileContextPointers, _In_ ULONG64  TargetFrame  )

static

Definition at line 1087 of file unwind.c.

{
    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);
}

Referenced by RtlSetUnwindContext().

RtlpIsStackPointerValid()

static __inline BOOL RtlpIsStackPointerValid ( _In_ ULONG64  StackPointer, _In_ ULONG64  LowLimit, _In_ ULONG64  HighLimit  )

static

Definition at line 654 of file unwind.c.

{
    return (StackPointer >= LowLimit) &&
           (StackPointer < HighLimit) &&
           ((StackPointer & 7) == 0);
}

Referenced by RtlpUnwindInternal().

RtlpLookupDynamicFunctionEntry()

PRUNTIME_FUNCTION NTAPI RtlpLookupDynamicFunctionEntry	(	_In_ DWORD64	ControlPc,
		_Out_ PDWORD64	ImageBase,
		_In_ PUNWIND_HISTORY_TABLE	HistoryTable
	)

Definition at line 271 of file dynfntbl.c.

{
    PLIST_ENTRY listLink;
    PDYNAMIC_FUNCTION_TABLE dynamicTable;
    PRUNTIME_FUNCTION functionTable, foundEntry = NULL;
    PGET_RUNTIME_FUNCTION_CALLBACK callback;
    ULONG i;
 
    AcquireDynamicFunctionTableLockShared();
 
    /* Loop all tables to find the one matching ControlPc */
    for (listLink = RtlpDynamicFunctionTableList.Flink;
         listLink != &RtlpDynamicFunctionTableList;
         listLink = listLink->Flink)
    {
        dynamicTable = CONTAINING_RECORD(listLink, DYNAMIC_FUNCTION_TABLE, ListEntry);
 
        if ((ControlPc >= dynamicTable->MinimumAddress) &&
            (ControlPc < dynamicTable->MaximumAddress))
        {
            /* Check if there is a callback */
            callback = dynamicTable->Callback;
            if (callback != NULL)
            {
                PVOID context = dynamicTable->Context;
 
                *ImageBase = dynamicTable->BaseAddress;
                ReleaseDynamicFunctionTableLockShared();
                return callback(ControlPc, context);
            }
 
            /* Loop all entries in the function table */
            functionTable = dynamicTable->FunctionTable;
            for (i = 0; i < dynamicTable->EntryCount; i++)
            {
                /* Check if this entry contains the address */
                if ((ControlPc >= functionTable[i].BeginAddress) &&
                    (ControlPc < functionTable[i].EndAddress))
                {
                    foundEntry = &functionTable[i];
                    *ImageBase = dynamicTable->BaseAddress;
                    goto Exit;
                }
            }
        }
    }
 
Exit:
 
    ReleaseDynamicFunctionTableLockShared();
 
    return foundEntry;
}

Referenced by RtlLookupFunctionEntry().

RtlpRestoreContextInternal()

VOID RtlpRestoreContextInternal

(

_In_ PCONTEXT

ContextRecord

)

Referenced by RtlRestoreContext().

RtlpTryToUnwindEpilog()

static __inline BOOLEAN RtlpTryToUnwindEpilog ( _Inout_ PCONTEXT  Context, _In_ ULONG64  ControlPc, _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS  ContextPointers, _In_ ULONG64  ImageBase, _In_ PRUNTIME_FUNCTION  FunctionEntry  )

static

Helper function that tries to unwind epilog instructions.

RtlpTryToUnwindEpilog

Returns

TRUE if we have been in an epilog and it could be unwound. FALSE if the instructions were not allowed for an epilog. https://docs.microsoft.com/en-us/cpp/build/unwind-procedure https://docs.microsoft.com/en-us/cpp/build/prolog-and-epilog

Todo:

• Test and compare with Windows behaviour

Definition at line 304 of file unwind.c.

{
    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;
}

Referenced by RtlVirtualUnwind().

RtlpUnwindInternal()

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
	)

Remarks

The implementation is based on the description in this blog: http://www.nynaeve.net/?p=106

Differences to the desciption:
- Instead of using 2 pointers to the unwind context and previous context,
  that are being swapped and the context copied, the unwind context is
  kept in the local context and copied back into the context passed in
  by the caller.

See also

http://www.nynaeve.net/?p=106

TODO: Handle DPC stack

TODO: call RtlpExecuteHandlerForUnwind instead

TODO

TODO

TODO: Check for DPC stack

Definition at line 677 of file unwind.c.

{
    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;
}

Referenced by RtlDispatchException(), and RtlUnwindEx().

RtlRestoreContext()

VOID RtlRestoreContext	(	_In_ PCONTEXT	ContextRecord,
		_In_ PEXCEPTION_RECORD	ExceptionRecord
	)

Definition at line 1170 of file unwind.c.

{
    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);
}

Referenced by RtlpUnwindInternal().

RtlSetUnwindContext()

VOID RtlSetUnwindContext	(	_In_ PCONTEXT	Context,
		_In_ DWORD64	TargetFrame
	)

Definition at line 1139 of file unwind.c.

{
    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;
}

Referenced by KiSetTrapContextInternal().

RtlUnwind()

VOID NTAPI RtlUnwind	(	_In_opt_ PVOID TargetFrame TargetFrame	,
		_In_opt_ PVOID	TargetIp,
		_In_opt_ PEXCEPTION_RECORD	ExceptionRecord,
		_In_ PVOID	ReturnValue
	)

Definition at line 935 of file unwind.c.

{
    CONTEXT Context;
 
    RtlUnwindEx(TargetFrame,
                TargetIp,
                ExceptionRecord,
                ReturnValue,
                &Context,
                NULL);
}

Referenced by _local_unwind(), and _SEH2GlobalUnwind().

RtlUnwindEx()

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
	)

Definition at line 892 of file unwind.c.

{
    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);
}

Referenced by __C_specific_handler(), and RtlUnwind().

RtlVirtualUnwind()

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
	)

Definition at line 478 of file unwind.c.

{
    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;
}

Referenced by RtlpCaptureNonVolatileContextPointers(), RtlpUnwindInternal(), and RtlWalkFrameChain().

RtlWalkFrameChain()

ULONG NTAPI RtlWalkFrameChain	(	OUT PVOID *	Callers,
		IN ULONG	Count,
		IN ULONG	Flags
	)

Definition at line 953 of file unwind.c.

{
    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;
}

Referenced by RtlGetCallersAddress().

SetReg()

static __inline void SetReg ( _Inout_ PCONTEXT  Context, _In_ BYTE  Reg, _In_ DWORD64  Value  )

static

Definition at line 210 of file unwind.c.

{
    ((DWORD64*)(&Context->Rax))[Reg] = Value;
}

Referenced by SetRegFromStackValue().

SetRegFromStackValue()

static __inline void SetRegFromStackValue ( _Inout_ PCONTEXT  Context, _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS  ContextPointers, _In_ BYTE  Reg, _In_ PDWORD64  ValuePointer  )

static

Definition at line 221 of file unwind.c.

{
    SetReg(Context, Reg, *ValuePointer);
    if (ContextPointers != NULL)
    {
        ContextPointers->IntegerContext[Reg] = ValuePointer;
    }
}

Referenced by PopReg(), and RtlVirtualUnwind().

SetXmmReg()

static __inline void SetXmmReg ( _Inout_ PCONTEXT  Context, _In_ BYTE  Reg, _In_ M128A  Value  )

static

Definition at line 259 of file unwind.c.

{
    ((M128A*)(&Context->Xmm0))[Reg] = Value;
}

Referenced by SetXmmRegFromStackValue().

SetXmmRegFromStackValue()

static __inline void SetXmmRegFromStackValue ( _Out_ PCONTEXT  Context, _Inout_opt_ PKNONVOLATILE_CONTEXT_POINTERS  ContextPointers, _In_ BYTE  Reg, _In_ M128A *  ValuePointer  )

static

Definition at line 270 of file unwind.c.

{
    SetXmmReg(Context, Reg, *ValuePointer);
    if (ContextPointers != NULL)
    {
        ContextPointers->FloatingContext[Reg] = ValuePointer;
    }
}

Referenced by RtlVirtualUnwind().

UnwindOpSlots()

static __inline ULONG UnwindOpSlots ( _In_ UNWIND_CODE  UnwindCode )

static

Definition at line 177 of file unwind.c.

{
    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;
    }
}

Referenced by GetEstablisherFrame(), and RtlVirtualUnwind().