.OBJ File Format – COMENT records

OMF object file

A COMENT record (0x88) carries notes and extensions. Tools ignore classes they don’t know, which made it the natural place to extend the format.

The record

  1. +0Comment type: bit 7 NP (no purge), bit 6 NL (no list)1 byte
  2. +1Comment class1 byte
  3. +2Comment bytes, by classvaries
The contents of COMENT.

Classes

ClassNameHolds
0x00TranslatorThe name of the compiler or assembler, as text
0x01Intel copyrightText
0x81Library specifierObsolete; as 0x9F
0x9CMS-DOS versionA version word; obsolete
0x9DMemory modelLetters such as s, l or f
0x9EDOSSEGNo contents: use the standard DOS segment order
0x9FDefault libraryA library name the linker should also search
0xA0OMF extensionsSee below
0xA1New OMF extensionA version byte and a two-letter style, such as CV for CodeView
0xA2Link pass separatorMarks the end of what the linker needs in its first pass
0xA3LIBMODA library module’s name
0xA4EXESTRText to copy into the program
0xA6INCERRAn incremental compile error
0xA7NOPADSegments not to pad
0xA8WKEXTPairs of external indexes: a weak name and its default
0xA9LZEXTPairs of external indexes: a lazy name and its default
0xAAEasy OMF-386Phar Lap’s marker, text 80386: this module has 32-bit fields even in records with even types
0xDA–0xDFComment, Compiler, Date, Timestamp, UserText notes
0xE9Dependency fileBorland: a source file’s date, time and name
0xFELinker directiveWatcom: a letter and its data
0xFFCommand lineMicrosoft QuickC: the compiler’s command line

Other classes in real files, such as Borland’s debug classes, are not described here.

Class 0xA0: OMF extensions

The first byte after the class is a subtype:

SubtypeNameHolds
1IMPDEFAn import: an ordinal flag byte, the internal name, the DLL’s name, and an ordinal word or an entry name
2EXPDEFAn export: a flag byte, the exported name, the internal name, and an ordinal word if bit 7 of the flag byte is set
3INCDEFIncremental compile information
4Protected memory libraryMarks a library for protected mode
5LNKDIRLinker directives
6Big-endianThe module’s data is big-endian
7PRECOMPPrecompiled type information