Structure defining a page directory (PD) entry in IA-32e paging.

pde.c

typedef struct _PDE
{
    union
    {
        struct
        {
            ULONG64 Present : 1;              // Must be 1, region invalid if 0.
            ULONG64 ReadWrite : 1;            // If 0, writes not allowed.
            ULONG64 UserSupervisor : 1;       // If 0, user-mode accesses not allowed.
            ULONG64 PageWriteThrough : 1;     // Determines the memory type used to access PT.
            ULONG64 PageCacheDisable : 1;     // Determines the memory type used to access PT.
            ULONG64 Accessed : 1;             // If 0, this entry has not been used for translation.
            ULONG64 Ignored1 : 1;
            ULONG64 PageSize : 1;             // If 1, this entry maps a 2MB page.
            ULONG64 Ignored2 : 4;
            ULONG64 PageFrameNumber : 36;     // The page frame number of the PT of this PDE.
            ULONG64 Reserved : 4;
            ULONG64 Ignored3 : 11;
            ULONG64 ExecuteDisable : 1;       // If 1, instruction fetches not allowed.
        };
        ULONG64 Value;
    };
} PDE, *PPDE;
static_assert(sizeof(PDE) == sizeof(PVOID), "Size mismatch, only 64-bit supported.");