LIB file format: OMF library

Introduction

Compilers and assemblers for 16-bit DOS and Windows kept their runtime libraries in .lib files of this format: a collection of OMF object modules, with a dictionary that lets a linker find the module defining a name without reading them all.

Structure

0library header, a record of type 0xF0, padded to the page size1 page
…modules, each an OMF object module starting on a page boundaryvaries
…end record of type 0xF1, padded to a 512-byte boundaryvaries
…dictionary blocks512 bytes each

An OMF library, in file order.

The library header

Offset	Size	Field	Meaning
0	1	Type	`0xF0`
1	2	Record length	The bytes after this field; the page size minus 3. The page size is a power of two, usually 16 or 512.
3	4	Dictionary offset	The file offset of the dictionary
7	2	Dictionary size	The number of 512-byte blocks
9	1	Flags	Bit 0 set: the names are case-sensitive
10	to the page	Padding	Up to the page size

Modules

Each module is an OMF object module, from THEADR or LHEADR to MODEND, and starts at a multiple of the page size. A module is named by its offset divided by the page size: its page number. Padding fills up to the next multiple of the page size. The dictionary uses these page numbers to find a symbol’s module.

The end record

After the last module comes a record of type 0xF1, with a length and a run of padding that brings the file to the next 512-byte boundary, where the dictionary starts.

Variants

Windows COFF library – a Windows static or import library in the ar archive format
Short import object – one member of an import library: a header and two strings
OMF library – a library of OMF object modules from 16-bit compilers

.LIB File Format

Introduction

Structure

The library header

Modules

The end record

Variants

Links

Software

Reference