gdtsup.c

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/*++

Copyright (c) 1991  Microsoft Corporation

Module Name:

    gdtsup.c

Abstract:

    This module implements interfaces that support manipulation of i386 Gdts.
    These entry points only exist on i386 machines.

Author:

    Dave Hastings (daveh) 28 May 1991

Environment:

    Kernel mode only.

Revision History:

--*/

#include "ki.h"

#ifdef ALLOC_PRAGMA
#pragma alloc_text(PAGE,KeI386SetGdtSelector)
#endif

VOID
Ke386GetGdtEntryThread(
    IN PKTHREAD Thread,
    IN ULONG Offset,
    IN PKGDTENTRY Descriptor
    )
/*++

Routine Description:

    This routine returns the contents of an entry in the Gdt.  If the
    entry is thread specific, the entry for the specified thread is
    created and returned (KGDT_LDT, and KGDT_R3_TEB).  If the selector
    is processor dependent, the entry for the current processor is
    returned (KGDT_R0_PCR).

Arguments:

    Thread -- Supplies a pointer to the thread to return the entry for.

    Offset -- Supplies the offset in the Gdt.  This value must be 0
        mod 8.

    Descriptor -- Returns the contents of the Gdt descriptor

Return Value:

    None.

--*/

{
    PKGDTENTRY Gdt;
    PKPROCESS Process;

    //
    // If the entry is out of range, don't return anything
    //

    if (Offset >= KGDT_NUMBER * sizeof(KGDTENTRY)) {
        return ;
    }

    if (Offset == KGDT_LDT) {

        //
        // Materialize Ldt selector
        //

        Process = Thread->ApcState.Process;
        RtlMoveMemory( Descriptor,
            &(Process->LdtDescriptor),
            sizeof(KGDTENTRY)
            );

    } else {

        //
        // Copy Selector from Ldt
        //
        // N.B. We will change the base later, if it is KGDT_R3_TEB
        //


        Gdt = KiPcr()->GDT;

        RtlMoveMemory(Descriptor, (PCHAR)Gdt + Offset, sizeof(KGDTENTRY));

        //
        // if it is the TEB selector, fix the base
        //

        if (Offset == KGDT_R3_TEB) {
            Descriptor->BaseLow = (USHORT)((ULONG)(Thread->Teb) & 0xFFFF);
            Descriptor->HighWord.Bytes.BaseMid =
                (UCHAR) ( ( (ULONG)(Thread->Teb) & 0xFF0000L) >> 16);
            Descriptor->HighWord.Bytes.BaseHi =
                (CHAR)  ( ( (ULONG)(Thread->Teb) & 0xFF000000L) >> 24);
        }
    }

    return ;
}

NTSTATUS
KeI386SetGdtSelector (
    ULONG       Selector,
    PKGDTENTRY  GdtValue
    )
/*++

Routine Description:

    Sets a GDTs returned via KeI386AllocateGdtSelectors to the supplied
    GdtValue.

Arguments:

    Selector - Which GDT to set
    GdtValue - GDT value to set into GDT

Return Value:

    status code

--*/
{
    KAFFINITY       TargetSet;
    PKPRCB          Prcb;
    PKPCR           Pcr;
    PKGDTENTRY      GdtEntry;
    ULONG           GdtIndex, BitNumber;

    PAGED_CODE ();

    //
    // Verify GDT entry passed, and it's above the kernel GDT values
    //

    GdtIndex = Selector >> 3;
    if ((Selector & 0x7) != 0  || GdtIndex < KGDT_NUMBER) {
        return STATUS_UNSUCCESSFUL;
    }

    //
    // Set gdt entry in each processors GDT
    //

    TargetSet = KeActiveProcessors;
    while (TargetSet != 0) {
        BitNumber = KeFindFirstSetRightMember(TargetSet);
        ClearMember(BitNumber, TargetSet);

        Prcb = KiProcessorBlock[BitNumber];
        Pcr  = CONTAINING_RECORD (Prcb, KPCR, PrcbData);
        GdtEntry = Pcr->GDT + GdtIndex;

        // set it
        *GdtEntry = *GdtValue;
    }

    return STATUS_SUCCESS;
}

---