Relocatable Object Module Format (OMF) Specification

Relocatable Object Module Format
A0 OMF extensions This class consists of a set of records, identified by
subtype (first byte of commentary string). Values
supported by some linkers are:
01 IMPDEF Import definition record. See the IMPDEF section for a
complete description.
02 EXPDEF Export definition record. See the EXPDEF section for a
complete description.
03 INCDEF Incremental compilation record. See the INCDEF section
for a complete description.
04 Protected
memory
library
32-bit linkers only; relevant only to 32-bit dynamic-link
libraries (DLLs). This comment record is inserted in an
object module by the compiler when it encounters the
_loadds construct in the source code for a DLL. The linker
then sets a flag in the header of the executable file (DLL)
to indicate that the DLL should be loaded in such a way
that its shared data is protected from corruption. The
_loadds keyword tells the compiler to emit modified
function prolog code, which loads the DS segment
register. (Normal functions don't need this.)
When the flag is set in the .EXE header, the loader loads
the selector of a protected memory area into DS while
performing run-time fixups (relocations). All other DLLs
and applications get the regular DGROUP selector, which
doesn't allow access to the protected memory area set up
by the operating system.
05 LNKDIR Microsoft C++ linker directives record. See the LNKDIR
section for a complete description.
06 Big-endian The target for this OMF is a big-endian machine, as
opposed to little-endian. "Big-endian" describes an
architecture for which the most significant byte of a
multibyte value has the smallest address. "Little-endian"
describes an architecture for which the least significant
byte of a multibyte value has the smallest address.
07 PRECOMP When the Microsoft symbol and type information for this
object file is emitted, the directory entry for $$TYPES is to
be emitted as sstPreComp instead of sstTypes.
08-
FF
Reserved.
Note: The presence of any unrecognized subtype causes the linker to
generate a fatal error.
Tool Interface Standards (TIS) OMF Specification, Version 1.1 11