ASM Community

All: I have run into an issue that has me slightly feeling a bit nutty; when I write a structure which has a nested struct and UNION in this manor:

_PCI_HEADER_TYPE_0 STRUCT 
  BaseAddresses	 ULONG PCI_TYPE0_ADDRESSES
  Reserved1	 ULONG 2 
  ROMBaseAddress ULONG ?
  Reserved2	 ULONG 2 
  InterruptLine	 UCHAR ?
  InterruptPin	 UCHAR ?
  MinimumGrant	 UCHAR ?
  MaximumLatency UCHAR ?
_PCI_HEADER_TYPE_0 ENDS

type0 TYPEDEF _PCI_HEADER_TYPE_0


_PCI_COMMON_CONFIG	STRUCT
  VendorID	USHORT 	?
  DeviceID	USHORT 	?
  Command	USHORT 	?
  Status	USHORT 	?
  RevisionID	UCHAR 	?
  ProgIf	UCHAR 	?
  SubClass	UCHAR 	?
  BaseClass	UCHAR 	?
  CacheLineSize	UCHAR 	?
  LatencyTimer	UCHAR 	?
  HeaderType	UCHAR 	?
  BIST		UCHAR 	?
  u	UNION
    type0 <>
  u	ENDS
  DeviceSpecific UCHAR  192d	DUP(0)
_PCI_COMMON_CONFIG	ENDS

I get this error from ML.EXE: NTPCIINFO.INC(103) : error A2008: syntax error : _u NTPCIINFO.INC(105) : fatal error A1010: unmatched block nesting : _u However, if I make the following changes:

_PCI_HEADER_TYPE_0 STRUCT 
  BaseAddresses	 ULONG PCI_TYPE0_ADDRESSES	DUP(0)
  Reserved1	 ULONG 2 			DUP(0)
  ROMBaseAddress ULONG ?
  Reserved2	 ULONG 2 			DUP(0)
  InterruptLine	 UCHAR ?
  InterruptPin	 UCHAR ?
  MinimumGrant	 UCHAR ?
  MaximumLatency UCHAR ?
_PCI_HEADER_TYPE_0 ENDS

type0 TYPEDEF _PCI_HEADER_TYPE_0

_u	UNION
    type0 <>
_u	ENDS

_PCI_COMMON_CONFIG	STRUCT
  VendorID	 USHORT ?
  DeviceID	 USHORT ?
  Command	 USHORT ?
  Status	 USHORT ?
  RevisionID	 UCHAR 	?
  ProgIf	 UCHAR 	?
  SubClass	 UCHAR 	?
  BaseClass	 UCHAR 	?
  CacheLineSize	 UCHAR 	?
  LatencyTimer	 UCHAR 	?
  HeaderType	 UCHAR 	?
  BIST		 UCHAR 	?
  _u <>
  DeviceSpecific UCHAR  192d	DUP(0)
_PCI_COMMON_CONFIG	ENDS

PCI_COMMON_CONFIG 	TYPEDEF _PCI_COMMON_CONFIG
PPCI_COMMON_CONFIG	TEXTEQU  

All is well. The reason behind this post, and my question, is why would the first form generate such an error yet the second form work just fine?