Re: [ros-dev] [ros-diffs] [tkreuzer] 60701: [NTOSKRNL] - Introduce a new and faster way to return to kernel mode from traps by using a ret 8 instruction instead of an iret. - Make use of KiUserTrap where appropriate - Remov...

[Alex Ionescu]

Wait, are you suggesting that "doing things better than Microsoft" and
"those idiots have no idea what they're doing" and "we shouldn't
just
be copying the instructions they use".... doesn't work? :O


Best regards,
Alex Ionescu


On Thu, Apr 14, 2016 at 8:09 AM, Thomas Faber <thomas.faber(a)reactos.org> wrote:
>   Looks like we've encountered an issue with this
>  KiTrapReturnNoSegmentsRet8 approach. As seen in
>  https://jira.reactos.org/browse/CORE-11115, when a large number of
>  interrupts happen, this will cause us to run out of kernel stack.
>
>  Since the popfd / ret 8 steps do not happen atomically, interrupts will
>  be re-enabled before those 12 bytes of stack are freed, thus many of
>  them happening in a row will cause us to run out.
>
>  Thoughts?
>
>  Thanks!
>  -Thomas
>
>
>
>  On 2013-10-19 13:33, tkreuzer(a)svn.reactos.org wrote:
> >   Author: tkreuzer
> >  Date: Sat Oct 19 11:33:34 2013
> >  New Revision: 60701
> >
> >  URL: http://svn.reactos.org/svn/reactos?rev=60701&view=rev
> >  Log:
> >  [NTOSKRNL]
> >  - Introduce a new and faster way to return to kernel mode from traps by using a ret 8
> > instruction instead of an iret.
> >  - Make use of KiUserTrap where appropriate
> >  - Remove some pointless toplevel volatile
> >
> >  Modified:
> >      trunk/reactos/ntoskrnl/include/internal/i386/asmmacro.S
> >      trunk/reactos/ntoskrnl/include/internal/i386/ke.h
> >      trunk/reactos/ntoskrnl/include/internal/i386/trap_x.h
> >      trunk/reactos/ntoskrnl/ke/i386/cpu.c
> >      trunk/reactos/ntoskrnl/ke/i386/exp.c
> >      trunk/reactos/ntoskrnl/ke/i386/patpge.c
> >      trunk/reactos/ntoskrnl/ke/i386/trap.s
> >      trunk/reactos/ntoskrnl/ke/i386/traphdlr.c
> >      trunk/reactos/ntoskrnl/ke/i386/usercall.c
> >      trunk/reactos/ntoskrnl/ke/time.c
> >
> >  Modified: trunk/reactos/ntoskrnl/include/internal/i386/asmmacro.S
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/include/internal/…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/include/internal/i386/asmmacro.S   [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/include/internal/i386/asmmacro.S   [iso-8859-1] Sat Oct 19
> > 11:33:34 2013
> >  @@ -241,6 +241,7 @@
> >   #define KI_EXIT_RET           HEX(080)
> >   #define KI_EXIT_IRET          HEX(100)
> >   #define KI_EDITED_FRAME       HEX(200)
> >  +#define KI_EXIT_RET8          HEX(400)
> >   #define KI_RESTORE_VOLATILES  (KI_RESTORE_EAX OR KI_RESTORE_ECX_EDX)
> >
> >   MACRO(KiTrapExitStub, Name, Flags)
> >  @@ -248,15 +249,15 @@
> >   PUBLIC @&Name&@4
> >   @&Name&@4:
> >
> >  -    if (Flags AND KI_RESTORE_EFLAGS)
> >  +    if (Flags AND KI_EXIT_RET8) OR (Flags AND KI_EXIT_IRET)
> >  +
> >  +        /* This is the IRET frame */
> >  +        OffsetEsp = KTRAP_FRAME_EIP
> >  +
> >  +    elseif (Flags AND KI_RESTORE_EFLAGS)
> >
> >           /* We will pop EFlags off the stack */
> >           OffsetEsp = KTRAP_FRAME_EFLAGS
> >  -
> >  -    elseif (Flags AND KI_EXIT_IRET)
> >  -
> >  -        /* This is the IRET frame */
> >  -        OffsetEsp = KTRAP_FRAME_EIP
> >
> >       else
> >
> >  @@ -335,6 +336,13 @@
> >
> >       if (Flags AND KI_RESTORE_EFLAGS)
> >
> >  +        if (Flags AND KI_EXIT_RET8)
> >  +
> >  +            /* We are at the IRET frame, so push EFLAGS first */
> >  +            push dword ptr [esp + 8]
> >  +
> >  +        endif
> >  +
> >           /* Restore EFLAGS */
> >           popfd
> >
> >  @@ -357,6 +365,11 @@
> >           /* Return to kernel mode with a jmp */
> >           jmp edx
> >
> >  +    elseif (Flags AND KI_EXIT_RET8)
> >  +
> >  +        /* Return to kernel mode with a ret 8 */
> >  +        ret 8
> >  +
> >       elseif (Flags AND KI_EXIT_RET)
> >
> >           /* Return to kernel mode with a ret */
> >
> >  Modified: trunk/reactos/ntoskrnl/include/internal/i386/ke.h
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/include/internal/…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/include/internal/i386/ke.h [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/include/internal/i386/ke.h [iso-8859-1] Sat Oct 19 11:33:34
> > 2013
> >  @@ -383,13 +383,13 @@
> >   ULONG_PTR
> >   NTAPI
> >   Ki386EnableGlobalPage(
> >  -    IN volatile ULONG_PTR Context
> >  +    IN ULONG_PTR Context
> >   );
> >
> >   ULONG_PTR
> >   NTAPI
> >   Ki386EnableTargetLargePage(
> >  -    IN volatile ULONG_PTR Context
> >  +    IN ULONG_PTR Context
> >   );
> >
> >   BOOLEAN
> >
> >  Modified: trunk/reactos/ntoskrnl/include/internal/i386/trap_x.h
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/include/internal/…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/include/internal/i386/trap_x.h     [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/include/internal/i386/trap_x.h     [iso-8859-1] Sat Oct 19
> > 11:33:34 2013
> >  @@ -163,7 +163,7 @@
> >       }
> >
> >       /* Check DR values */
> >  -    if (TrapFrame->SegCs & MODE_MASK)
> >  +    if (KiUserTrap(TrapFrame)
> >       {
> >           /* Check for active debugging */
> >           if (KeGetCurrentThread()->Header.DebugActive)
> >  @@ -244,6 +244,7 @@
> >   DECLSPEC_NORETURN VOID FASTCALL KiEditedTrapReturn(IN PKTRAP_FRAME TrapFrame);
> >   DECLSPEC_NORETURN VOID FASTCALL KiTrapReturn(IN PKTRAP_FRAME TrapFrame);
> >   DECLSPEC_NORETURN VOID FASTCALL KiTrapReturnNoSegments(IN PKTRAP_FRAME TrapFrame);
> >  +DECLSPEC_NORETURN VOID FASTCALL KiTrapReturnNoSegmentsRet8(IN PKTRAP_FRAME TrapFrame);
> >
> >   typedef
> >   ATTRIB_NORETURN
> >  @@ -382,7 +383,7 @@
> >       TrapFrame->Dr7 = 0;
> >
> >       /* Check if the frame was from user mode or v86 mode */
> >  -    if ((TrapFrame->SegCs & MODE_MASK) ||
> >  +    if (KiUserTrap(TrapFrame) ||
> >           (TrapFrame->EFlags & EFLAGS_V86_MASK))
> >       {
> >           /* Check for active debugging */
> >  @@ -411,7 +412,7 @@
> >       TrapFrame->Dr7 = 0;
> >
> >       /* Check if the frame was from user mode or v86 mode */
> >  -    if ((TrapFrame->SegCs & MODE_MASK) ||
> >  +    if (KiUserTrap(TrapFrame) ||
> >           (TrapFrame->EFlags & EFLAGS_V86_MASK))
> >       {
> >           /* Check for active debugging */
> >
> >  Modified: trunk/reactos/ntoskrnl/ke/i386/cpu.c
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/i386/cpu.c?rev…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/ke/i386/cpu.c      [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/ke/i386/cpu.c      [iso-8859-1] Sat Oct 19 11:33:34 2013
> >  @@ -1535,7 +1535,7 @@
> >       if (TargetAffinity)
> >       {
> >           /* Sanity check */
> >  -        ASSERT(Prcb == (volatile PKPRCB)KeGetCurrentPrcb());
> >  +        ASSERT(Prcb == KeGetCurrentPrcb());
> >
> >           /* FIXME: TODO */
> >           ASSERTMSG("Not yet implemented\n", FALSE);
> >
> >  Modified: trunk/reactos/ntoskrnl/ke/i386/exp.c
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/i386/exp.c?rev…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/ke/i386/exp.c      [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/ke/i386/exp.c      [iso-8859-1] Sat Oct 19 11:33:34 2013
> >  @@ -137,7 +137,7 @@
> >   KiEspFromTrapFrame(IN PKTRAP_FRAME TrapFrame)
> >   {
> >       /* Check if this is user-mode or V86 */
> >  -    if ((TrapFrame->SegCs & MODE_MASK) ||
> >  +    if (KiUserTrap(TrapFrame) ||
> >           (TrapFrame->EFlags & EFLAGS_V86_MASK))
> >       {
> >           /* Return it directly */
> >  @@ -175,7 +175,7 @@
> >       Previous = KiEspFromTrapFrame(TrapFrame);
> >
> >       /* Check if this is user-mode or V86 */
> >  -    if ((TrapFrame->SegCs & MODE_MASK) ||
> >  +    if (KiUserTrap(TrapFrame) ||
> >           (TrapFrame->EFlags & EFLAGS_V86_MASK))
> >       {
> >           /* Write it directly */
> >  @@ -225,7 +225,7 @@
> >           /* Just return it */
> >           return TrapFrame->HardwareSegSs;
> >       }
> >  -    else if (TrapFrame->SegCs & MODE_MASK)
> >  +    else if (KiUserTrap(TrapFrame))
> >       {
> >           /* User mode, return the User SS */
> >           return TrapFrame->HardwareSegSs | RPL_MASK;
> >  @@ -251,7 +251,7 @@
> >           /* Just write it */
> >           TrapFrame->HardwareSegSs = Ss;
> >       }
> >  -    else if (TrapFrame->SegCs & MODE_MASK)
> >  +    else if (KiUserTrap(TrapFrame))
> >       {
> >           /* Usermode, save the User SS */
> >           TrapFrame->HardwareSegSs = Ss | RPL_MASK;
> >  @@ -398,7 +398,7 @@
> >               TrapFrame->V86Fs = Context->SegFs;
> >               TrapFrame->V86Gs = Context->SegGs;
> >           }
> >  -        else if (!(TrapFrame->SegCs & MODE_MASK))
> >  +        else if (!KiUserTrap(TrapFrame))
> >           {
> >               /* For kernel mode, write the standard values */
> >               TrapFrame->SegDs = KGDT_R3_DATA | RPL_MASK;
> >  @@ -429,7 +429,7 @@
> >
> >       /* Handle the extended registers */
> >       if (((ContextFlags & CONTEXT_EXTENDED_REGISTERS) ==
> >  -        CONTEXT_EXTENDED_REGISTERS) && (TrapFrame->SegCs & MODE_MASK))
> >  +        CONTEXT_EXTENDED_REGISTERS) && KiUserTrap(TrapFrame))
> >       {
> >           /* Get the FX Area */
> >           FxSaveArea = (PFX_SAVE_AREA)(TrapFrame + 1);
> >  @@ -463,7 +463,7 @@
> >
> >       /* Handle the floating point state */
> >       if (((ContextFlags & CONTEXT_FLOATING_POINT) ==
> >  -        CONTEXT_FLOATING_POINT) && (TrapFrame->SegCs & MODE_MASK))
> >  +        CONTEXT_FLOATING_POINT) && KiUserTrap(TrapFrame))
> >       {
> >           /* Get the FX Area */
> >           FxSaveArea = (PFX_SAVE_AREA)(TrapFrame + 1);
> >  @@ -692,7 +692,7 @@
> >
> >       /* Handle extended registers */
> >       if (((Context->ContextFlags & CONTEXT_EXTENDED_REGISTERS) ==
> >  -        CONTEXT_EXTENDED_REGISTERS) && (TrapFrame->SegCs & MODE_MASK))
> >  +        CONTEXT_EXTENDED_REGISTERS) && KiUserTrap(TrapFrame))
> >       {
> >           /* Get the FX Save Area */
> >           FxSaveArea = (PFX_SAVE_AREA)(TrapFrame + 1);
> >  @@ -712,7 +712,7 @@
> >
> >       /* Handle Floating Point */
> >       if (((Context->ContextFlags & CONTEXT_FLOATING_POINT) ==
> >  -        CONTEXT_FLOATING_POINT) && (TrapFrame->SegCs & MODE_MASK))
> >  +        CONTEXT_FLOATING_POINT) && KiUserTrap(TrapFrame))
> >       {
> >           /* Get the FX Save Area */
> >           FxSaveArea = (PFX_SAVE_AREA)(TrapFrame + 1);
> >  @@ -1045,6 +1045,13 @@
> >                   }
> >               }
> >               _SEH2_END;
> >  +
> >  +            DPRINT("First chance exception in %.16s, ExceptionCode: %lx,
> > ExceptionAddress: %p, P0: %lx, P1: %lx\n",
> >  +                   PsGetCurrentProcess()->ImageFileName,
> >  +                   ExceptionRecord->ExceptionCode,
> >  +                   ExceptionRecord->ExceptionAddress,
> >  +                   ExceptionRecord->ExceptionInformation[0],
> >  +                   ExceptionRecord->ExceptionInformation[1]);
> >           }
> >
> >           /* Try second chance */
> >  @@ -1060,11 +1067,13 @@
> >           }
> >
> >           /* 3rd strike, kill the process */
> >  -        DPRINT1("Kill %.16s, ExceptionCode: %lx, ExceptionAddress: %p, BaseAddress:
> > %p\n",
> >  +        DPRINT1("Kill %.16s, ExceptionCode: %lx, ExceptionAddress: %p, BaseAddress:
> > %p, P0: %lx, P1: %lx\n",
> >                   PsGetCurrentProcess()->ImageFileName,
> >                   ExceptionRecord->ExceptionCode,
> >                   ExceptionRecord->ExceptionAddress,
> >  -                PsGetCurrentProcess()->SectionBaseAddress);
> >  +                PsGetCurrentProcess()->SectionBaseAddress,
> >  +                ExceptionRecord->ExceptionInformation[0],
> >  +                ExceptionRecord->ExceptionInformation[1]);
> >
> >           ZwTerminateProcess(NtCurrentProcess(), ExceptionRecord->ExceptionCode);
> >           KeBugCheckEx(KMODE_EXCEPTION_NOT_HANDLED,
> >
> >  Modified: trunk/reactos/ntoskrnl/ke/i386/patpge.c
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/i386/patpge.c?…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/ke/i386/patpge.c   [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/ke/i386/patpge.c   [iso-8859-1] Sat Oct 19 11:33:34 2013
> >  @@ -20,9 +20,9 @@
> >   ULONG_PTR
> >   NTAPI
> >   INIT_FUNCTION
> >  -Ki386EnableGlobalPage(IN volatile ULONG_PTR Context)
> >  -{
> >  -    volatile PLONG Count = (PLONG)Context;
> >  +Ki386EnableGlobalPage(IN ULONG_PTR Context)
> >  +{
> >  +    PLONG Count = (PLONG)Context;
> >       ULONG Cr4, Cr3;
> >
> >       /* Disable interrupts */
> >  @@ -144,7 +144,7 @@
> >           if (PageTable)
> >               *PageTable = (PHARDWARE_PTE)(Pde->PageFrameNumber << PAGE_SHIFT);
> >       }
> >  -
> >  +
> >       return TRUE;
> >   }
> >
> >  @@ -172,7 +172,7 @@
> >       /* Get PTE of VirtualPtr, make it valid, and map PhysicalPtr there */
> >       Pte = &PageTable[(VirtualPtr >> 12) & ((1 << PTE_BITS) - 1)];
> >       Pte->Valid = 1;
> >  -    Pte->PageFrameNumber = PhysicalPtr.QuadPart >> PAGE_SHIFT;
> >  +    Pte->PageFrameNumber = (PFN_NUMBER)(PhysicalPtr.QuadPart >> PAGE_SHIFT);
> >
> >       return TRUE;
> >   }
> >  @@ -189,7 +189,7 @@
> >       PhysicalPtr = MmGetPhysicalAddress(VirtualPtr);
> >
> >       /* Map its physical address in the page table provided by the caller */
> >  -    Pte->PageFrameNumber = PhysicalPtr.QuadPart >> PAGE_SHIFT;
> >  +    Pte->PageFrameNumber = (PFN_NUMBER)(PhysicalPtr.QuadPart >> PAGE_SHIFT);
> >   }
> >
> >   BOOLEAN
> >
> >  Modified: trunk/reactos/ntoskrnl/ke/i386/trap.s
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/i386/trap.s?re…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/ke/i386/trap.s     [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/ke/i386/trap.s     [iso-8859-1] Sat Oct 19 11:33:34 2013
> >  @@ -166,6 +166,7 @@
> >   KiTrapExitStub KiEditedTrapReturn,        (KI_RESTORE_VOLATILES OR KI_RESTORE_EFLAGS OR
> > KI_EDITED_FRAME OR KI_EXIT_RET)
> >   KiTrapExitStub KiTrapReturn,              (KI_RESTORE_VOLATILES OR KI_RESTORE_SEGMENTS
> > OR KI_EXIT_IRET)
> >   KiTrapExitStub KiTrapReturnNoSegments,    (KI_RESTORE_VOLATILES OR KI_EXIT_IRET)
> >  +KiTrapExitStub KiTrapReturnNoSegmentsRet8,(KI_RESTORE_VOLATILES OR KI_RESTORE_EFLAGS OR
> > KI_EXIT_RET8)
> >
> >   #ifdef _MSC_VER
> >   EXTERN _PsConvertToGuiThread@0:PROC
> >
> >  Modified: trunk/reactos/ntoskrnl/ke/i386/traphdlr.c
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/i386/traphdlr.…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/ke/i386/traphdlr.c [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/ke/i386/traphdlr.c [iso-8859-1] Sat Oct 19 11:33:34 2013
> >  @@ -100,7 +100,7 @@
> >       if (__builtin_expect(TrapFrame->Dr7 & ~DR7_RESERVED_MASK, 0))
> >       {
> >           /* Check if the frame was from user mode or v86 mode */
> >  -        if ((TrapFrame->SegCs & MODE_MASK) ||
> >  +        if (KiUserTrap(TrapFrame) ||
> >               (TrapFrame->EFlags & EFLAGS_V86_MASK))
> >           {
> >               /* Handle debug registers */
> >  @@ -124,13 +124,13 @@
> >       if (TrapFrame->EFlags & EFLAGS_V86_MASK) KiTrapReturnNoSegments(TrapFrame);
> >
> >       /* Check for user mode exit */
> >  -    if (TrapFrame->SegCs & MODE_MASK) KiTrapReturn(TrapFrame);
> >  +    if (KiUserTrap(TrapFrame)) KiTrapReturn(TrapFrame);
> >
> >       /* Check for edited frame */
> >       if (KiIsFrameEdited(TrapFrame)) KiEditedTrapReturn(TrapFrame);
> >
> >       /* Exit the trap to kernel mode */
> >  -    KiTrapReturnNoSegments(TrapFrame);
> >  +    KiTrapReturnNoSegmentsRet8(TrapFrame);
> >   }
> >
> >   DECLSPEC_NORETURN
> >  @@ -152,7 +152,7 @@
> >       KeGetCurrentThread()->PreviousMode = (CCHAR)TrapFrame->PreviousPreviousMode;
> >
> >       /* Check for user mode exit */
> >  -    if (TrapFrame->SegCs & MODE_MASK)
> >  +    if (KiUserTrap(TrapFrame))
> >       {
> >           /* Check if we were single stepping */
> >           if (TrapFrame->EFlags & EFLAGS_TF)
> >  @@ -186,13 +186,13 @@
> >       if (TrapFrame->EFlags & EFLAGS_V86_MASK) KiTrapReturnNoSegments(TrapFrame);
> >
> >       /* Check for user mode exit */
> >  -    if (TrapFrame->SegCs & MODE_MASK) KiTrapReturn(TrapFrame);
> >  +    if (KiUserTrap(TrapFrame)) KiTrapReturn(TrapFrame);
> >
> >       /* Check for edited frame */
> >       if (KiIsFrameEdited(TrapFrame)) KiEditedTrapReturn(TrapFrame);
> >
> >       /* Exit the trap to kernel mode */
> >  -    KiTrapReturnNoSegments(TrapFrame);
> >  +    KiTrapReturnNoSegmentsRet8(TrapFrame);
> >   }
> >
> >
> >  @@ -1250,10 +1250,10 @@
> >       /* Call the access fault handler */
> >       Status = MmAccessFault(TrapFrame->ErrCode & 1,
> >                              (PVOID)Cr2,
> >  -                           TrapFrame->SegCs & MODE_MASK,
> >  +                           KiUserTrap(TrapFrame),
> >                              TrapFrame);
> >       if (NT_SUCCESS(Status)) KiEoiHelper(TrapFrame);
> >  -
> >  +
> >       /* Check for syscall fault */
> >   #if 0
> >       if ((TrapFrame->Eip == (ULONG_PTR)CopyParams) ||
> >  @@ -1541,7 +1541,7 @@
> >       TrapFrame->Dr7 = 0;
> >
> >       /* Check if the frame was from user mode */
> >  -    if (TrapFrame->SegCs & MODE_MASK)
> >  +    if (KiUserTrap(TrapFrame))
> >       {
> >           /* Check for active debugging */
> >           if (KeGetCurrentThread()->Header.DebugActive & 0xFF)
> >
> >  Modified: trunk/reactos/ntoskrnl/ke/i386/usercall.c
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/i386/usercall.…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/ke/i386/usercall.c [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/ke/i386/usercall.c [iso-8859-1] Sat Oct 19 11:33:34 2013
> >  @@ -67,7 +67,7 @@
> >       _SEH2_TRY
> >       {
> >           /* Sanity check */
> >  -        ASSERT((TrapFrame->SegCs & MODE_MASK) != KernelMode);
> >  +        ASSERT(KiUserTrap(TrapFrame));
> >
> >           /* Get the aligned size */
> >           AlignedEsp = Context.Esp & ~3;
> >  @@ -210,7 +210,7 @@
> >   }
> >
> >
> >  -/*
> >  +/*
> >    * Stack layout for KiUserModeCallout:
> >    * ----------------------------------
> >    * KCALLOUT_FRAME.ResultLength    <= 2nd Parameter to KiCallUserMode
> >
> >  Modified: trunk/reactos/ntoskrnl/ke/time.c
> >  URL:
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/time.c?rev=607…
> >  ==============================================================================
> >  --- trunk/reactos/ntoskrnl/ke/time.c  [iso-8859-1] (original)
> >  +++ trunk/reactos/ntoskrnl/ke/time.c  [iso-8859-1] Sat Oct 19 11:33:34 2013
> >  @@ -153,7 +153,7 @@
> >
> >       /* Check if we came from user mode */
> >   #ifndef _M_ARM
> >  -    if ((TrapFrame->SegCs & MODE_MASK) || (TrapFrame->EFlags &
> > EFLAGS_V86_MASK))
> >  +    if (KiUserTrap(TrapFrame) || (TrapFrame->EFlags & EFLAGS_V86_MASK))
> >   #else
> >       if (TrapFrame->PreviousMode == UserMode)
> >   #endif
> >
> >  
>
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