typedef struct _IMAGE_ROM_OPTIONAL_HEADER
{
     WORD Magic;
     UCHAR MajorLinkerVersion;
     UCHAR MinorLinkerVersion;
     ULONG SizeOfCode;
     ULONG SizeOfInitializedData;
     ULONG SizeOfUninitializedData;
     ULONG AddressOfEntryPoint;
     ULONG BaseOfCode;
     ULONG BaseOfData;
     ULONG BaseOfBss;
     ULONG GprMask;
     ULONG CprMask[4];
     ULONG GpValue;
} IMAGE_ROM_OPTIONAL_HEADER, *PIMAGE_ROM_OPTIONAL_HEADER;

Windows Vista Kernel Structures