/*++
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.
--*/

#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
--*/
{
    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);
        }
    }
}


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;
}