/*
 * PROJECT:         ReactOS Kernel
 * LICENSE:         GPL - See COPYING in the top level directory
 * FILE:            ntoskrnl/vdm/vdmexec.c
 * PURPOSE:         Support for executing VDM code and context swapping.
 * PROGRAMMERS:     Alex Ionescu (alex.ionescu@reactos.org)
 */

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

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

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

ULONG VdmBopCount;

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

NTSTATUS
NTAPI
VdmpGetVdmTib(OUT PVDM_TIB *VdmTib)
{
    PVDM_TIB Tib;
    PAGED_CODE();

    /* Assume vailure */
    *VdmTib = NULL;

    /* Get the current TIB */
    Tib = NtCurrentTeb()->Vdm;
    if (!Tib) return STATUS_INVALID_SYSTEM_SERVICE;

    /* Validate the size */
    if (Tib->Size != sizeof(VDM_TIB)) return STATUS_INVALID_SYSTEM_SERVICE;

    /* Return it */
    *VdmTib = Tib;
    return STATUS_SUCCESS;
}

VOID
NTAPI
VdmSwapContext(IN PKTRAP_FRAME TrapFrame,
               IN PCONTEXT OutContext,
               IN PCONTEXT InContext)
{
    ULONG EFlags, OldEFlags;

    /* Make sure that we're at APC_LEVEL and that this is a valid frame */
    ASSERT(KeGetCurrentIrql() == APC_LEVEL);
    ASSERT(TrapFrame->DbgArgMark == 0xBADB0D00);

    /* Check if this is a V86 frame */
    if (TrapFrame->EFlags & EFLAGS_V86_MASK)
    {
        /* Copy segment registers */
        OutContext->SegGs = TrapFrame->V86Gs;
        OutContext->SegFs = TrapFrame->V86Fs;
        OutContext->SegEs = TrapFrame->V86Es;
        OutContext->SegDs = TrapFrame->V86Ds;
    }
    else if (TrapFrame->SegCs != (KGDT_R3_CODE | RPL_MASK))
    {
        /* This was kernel mode, copy segment registers */
        OutContext->SegGs = TrapFrame->SegGs;
        OutContext->SegFs = TrapFrame->SegFs;
        OutContext->SegEs = TrapFrame->SegEs;
        OutContext->SegDs = TrapFrame->SegDs;
    }

    /* Copy CS and SS */
    OutContext->SegCs = TrapFrame->SegCs;
    OutContext->SegSs = TrapFrame->HardwareSegSs;

    /* Copy general purpose registers */
    OutContext->Eax = TrapFrame->Eax;
    OutContext->Ebx = TrapFrame->Ebx;
    OutContext->Ecx = TrapFrame->Ecx;
    OutContext->Edx = TrapFrame->Edx;
    OutContext->Esi = TrapFrame->Esi;
    OutContext->Edi = TrapFrame->Edi;

    /* Copy stack and counter */
    OutContext->Ebp = TrapFrame->Ebp;
    OutContext->Esp = TrapFrame->HardwareEsp;
    OutContext->Eip = TrapFrame->Eip;

    /* Finally the flags */
    OutContext->EFlags = TrapFrame->EFlags;

    /* Now copy from the in frame to the trap frame */
    TrapFrame->SegCs = InContext->SegCs;
    TrapFrame->HardwareSegSs = InContext->SegSs;

    /* Copy the general purpose registers */
    TrapFrame->Eax = InContext->Eax;
    TrapFrame->Ebx = InContext->Ebx;
    TrapFrame->Ecx = InContext->Ecx;
    TrapFrame->Edx = InContext->Edx;
    TrapFrame->Esi = InContext->Esi;
    TrapFrame->Edi = InContext->Edi;

    /* Copy the stack and counter */
    TrapFrame->Ebp = InContext->Ebp;
    TrapFrame->HardwareEsp = InContext->Esp;
    TrapFrame->Eip = InContext->Eip;

    /* Check if the context is from V86 */
    EFlags = InContext->EFlags;
    if (EFlags & EFLAGS_V86_MASK)
    {
        /* Sanitize the flags for V86 */
        EFlags &= KeI386EFlagsAndMaskV86;
        EFlags |= KeI386EFlagsOrMaskV86;
    }
    else
    {
        /* Add RPL_MASK to segments */
        TrapFrame->SegCs |= RPL_MASK;
        TrapFrame->HardwareSegSs |= RPL_MASK;

        /* Check for bogus CS */
        if (TrapFrame->SegCs < KGDT_R0_CODE)
        {
            /* Set user-mode */
            TrapFrame->SegCs = KGDT_R3_CODE | RPL_MASK;
        }

        /* Sanitize flags and add interrupt mask */
        EFlags &= EFLAGS_USER_SANITIZE;
        EFlags |=EFLAGS_INTERRUPT_MASK;
    }

    /* Save the new eflags */
    OldEFlags = TrapFrame->EFlags;
    TrapFrame->EFlags = EFlags;

    /* Check if we need to fixup ESP0 */
    if ((OldEFlags ^ EFlags) & EFLAGS_V86_MASK)
    {
        /* Fix it up */
        Ki386AdjustEsp0(TrapFrame);
    }

    /* Check if this is a V86 context */
    if (InContext->EFlags & EFLAGS_V86_MASK)
    {
        /* Copy VDM segments */
        TrapFrame->V86Gs = InContext->SegGs;
        TrapFrame->V86Fs = InContext->SegFs;
        TrapFrame->V86Es = InContext->SegEs;
        TrapFrame->V86Ds = InContext->SegDs;
    }
    else
    {
        /* Copy monitor segments */
        TrapFrame->SegGs = InContext->SegGs;
        TrapFrame->SegFs = InContext->SegFs;
        TrapFrame->SegEs = InContext->SegEs;
        TrapFrame->SegDs = InContext->SegDs;
    }

    /* Clear the exception list and return */
    TrapFrame->ExceptionList = EXCEPTION_CHAIN_END;
}

NTSTATUS
NTAPI
VdmpStartExecution(VOID)
{
    PETHREAD Thread = PsGetCurrentThread();
    PKTRAP_FRAME VdmFrame;
    NTSTATUS Status;
    PVDM_TIB VdmTib;
    BOOLEAN Interrupts;
    KIRQL OldIrql;
    CONTEXT VdmContext;
    PAGED_CODE();

    /* Get the thread's VDM frame and TIB */
    VdmFrame = (PVOID)((ULONG_PTR)Thread->Tcb.InitialStack -
                                  sizeof(FX_SAVE_AREA) -
                                  sizeof(KTRAP_FRAME));
    Status = VdmpGetVdmTib(&VdmTib);
    if (!NT_SUCCESS(Status)) return STATUS_INVALID_SYSTEM_SERVICE;

    /* Go to APC level */
    KeRaiseIrql(APC_LEVEL, &OldIrql);

    /* Check if interrupts are enabled */
    Interrupts = (BOOLEAN)(VdmTib->VdmContext.EFlags & EFLAGS_INTERRUPT_MASK);

    /* We don't support full VDM yet, this shouldn't happen */
    ASSERT(*VdmState == 0);
    ASSERT(VdmTib->VdmContext.EFlags & EFLAGS_V86_MASK);

    /* Check if VME is supported and V86 mode was enabled */
    if ((KeI386VirtualIntExtensions) &&
        (VdmTib->VdmContext.EFlags & EFLAGS_V86_MASK))
    {
        /* Check if interrupts are enabled */
        if (Interrupts)
        {
            /* Set fake IF flag */
            VdmTib->VdmContext.EFlags |= EFLAGS_VIF;
        }
        else
        {
            /* Remove fake IF flag, turn on real IF flag */
            VdmTib->VdmContext.EFlags &= ~EFLAGS_VIF;
            VdmTib->VdmContext.EFlags |= EFLAGS_INTERRUPT_MASK;
        }
    }
    else
    {
        /* Set interrupt state in the VDM State */
        if (VdmTib->VdmContext.EFlags & EFLAGS_INTERRUPT_MASK)
        {
            /* Enable them as well */
            InterlockedOr((PLONG)VdmState, EFLAGS_INTERRUPT_MASK);
        }
        else
        {
            /* Disable them */
            InterlockedAnd((PLONG)VdmState, ~EFLAGS_INTERRUPT_MASK);
        }

        /* Enable the interrupt flag */
        VdmTib->VdmContext.EFlags |= EFLAGS_INTERRUPT_MASK;
    }

    /*  Get the VDM context and make sure it's not an edited frame */
    VdmContext = VdmTib->VdmContext;
    if (!(VdmContext.SegCs & FRAME_EDITED))
    {
        /* Fail */
        KeLowerIrql(OldIrql);
        return STATUS_INVALID_SYSTEM_SERVICE;
    }

    /* Now do the VDM Swap */
    VdmSwapContext(VdmFrame, &VdmTib->MonitorContext, &VdmContext);

    /* Lower the IRQL and return EAX */
    KeLowerIrql(OldIrql);
    return VdmFrame->Eax;
}

VOID
NTAPI
VdmEndExecution(IN PKTRAP_FRAME TrapFrame,
                IN PVDM_TIB VdmTib)
{
    KIRQL OldIrql;
    CONTEXT Context;
    PAGED_CODE();

    /* Sanity check */
    ASSERT((TrapFrame->EFlags & EFLAGS_V86_MASK) ||
           (TrapFrame->SegCs != (KGDT_R3_CODE | RPL_MASK)));

    /* Raise to APC_LEVEL */
    KeRaiseIrql(APC_LEVEL, &OldIrql);

    /* Set success */
    VdmTib->MonitorContext.Eax = STATUS_SUCCESS;

    /* Make a copy of the monitor context */
    Context = VdmTib->MonitorContext;

    /* Check if V86 mode was enabled or the trap was edited */
    if ((Context.EFlags & EFLAGS_V86_MASK) || (Context.SegCs & FRAME_EDITED))
    {
        /* Switch contexts */
        VdmSwapContext(TrapFrame, &VdmTib->VdmContext, &Context);

        /* Check if VME is supported and V86 mode was enabled */
        if ((KeI386VirtualIntExtensions) &&
            (VdmTib->VdmContext.EFlags & EFLAGS_V86_MASK))
        {
            /* Check for VIF (virtual interrupt) flag state */
            if (VdmTib->VdmContext.EFlags & EFLAGS_VIF)
            {
                /* Set real IF flag */
                VdmTib->VdmContext.EFlags |= EFLAGS_INTERRUPT_MASK;
            }
            else
            {
                /* Remove real IF flag */
                VdmTib->VdmContext.EFlags &= ~EFLAGS_INTERRUPT_MASK;
            }

            /* Turn off VIP and VIF */
            TrapFrame->EFlags &= ~(EFLAGS_VIP | EFLAGS_VIF);
            VdmTib->VdmContext.EFlags &= ~(EFLAGS_VIP | EFLAGS_VIF);
        }
        else
        {
            /* Set the EFLAGS based on our software copy of EFLAGS */
            VdmTib->VdmContext.EFlags = (VdmTib->VdmContext.EFlags & ~EFLAGS_INTERRUPT_MASK) |
                                        (*VdmState & EFLAGS_INTERRUPT_MASK);
        }
    }

    /* Lower IRQL and reutrn */
    KeLowerIrql(OldIrql);
}

BOOLEAN
NTAPI
VdmDispatchBop(IN PKTRAP_FRAME TrapFrame)
{
    PUCHAR Eip;
    PVDM_TIB VdmTib;

    /* Check if this is from V86 mode */
    if (TrapFrame->EFlags & EFLAGS_V86_MASK)
    {
        /* Calculate flat EIP */
        Eip = (PUCHAR)((TrapFrame->Eip & 0xFFFF) +
                      ((TrapFrame->SegCs & 0xFFFF) << 4));

        /* Check if this is a BOP */
        if (*(PUSHORT)Eip == 0xC4C4)
        {
            /* Check sure its the DOS Bop */
            if (Eip[2] == 0x50)
            {
                /* FIXME: No VDM Support */
                ASSERT(FALSE);
            }

            /* Increase the number of BOP operations */
            VdmBopCount++;

            /* Get the TIB */
            VdmTib = NtCurrentTeb()->Vdm;

            /* Fill out a VDM Event */
            VdmTib->EventInfo.InstructionSize = 3;
            VdmTib->EventInfo.BopNumber = Eip[2];
            VdmTib->EventInfo.Event = VdmBop;

            /* End VDM Execution */
            VdmEndExecution(TrapFrame, VdmTib);
        }
        else
        {
            /* Not a BOP */
            return FALSE;
        }
    }
    else
    {
        /* FIXME: Shouldn't happen on ROS */
        ASSERT(FALSE);
    }

    /* Return success */
    return TRUE;
}

BOOLEAN
NTAPI
VdmDispatchPageFault(
    _In_ PKTRAP_FRAME TrapFrame)
{
    NTSTATUS Status;
    PVDM_TIB VdmTib;

    PAGED_CODE();

    /* Get the VDM TIB so we can terminate V86 execution */
    Status = VdmpGetVdmTib(&VdmTib);
    if (!NT_SUCCESS(Status))
    {
        /* Not a proper VDM fault, keep looking */
        DPRINT1("VdmDispatchPageFault: no VDM TIB, Vdm=%p\n", NtCurrentTeb()->Vdm);
        return FALSE;
    }

    /* Must be coming from V86 code */
    ASSERT(TrapFrame->EFlags & EFLAGS_V86_MASK);

    _SEH2_TRY
    {
        /* Fill out a VDM Event */
        VdmTib->EventInfo.Event = VdmMemAccess;
        VdmTib->EventInfo.InstructionSize = 0;

        /* End VDM Execution */
        VdmEndExecution(TrapFrame, VdmTib);
    }
    _SEH2_EXCEPT(EXCEPTION_EXECUTE_HANDLER)
    {
        Status = _SEH2_GetExceptionCode();
    }
    _SEH2_END;

    /* Consider the exception handled if we succeeded */
    DPRINT1("VdmDispatchPageFault EFlags %lx exit with 0x%lx\n", TrapFrame->EFlags, Status);
    return NT_SUCCESS(Status);
}