Common Object File Format (COFF)

The following are some key features of COFF:

• applications can add system-dependent information to the object file without causing access utilities to become obsolete

• space is provided for symbolic information used by debuggers and other applications

• programmers can modify the way the object file is constructed by providing directives at compile time

The object file supports user-defined sections and contains extensive information for symbolic software testing. An object file contains:

• a file header

• optional header information

• a table of section headers

• data corresponding to the section headers

• relocation information

• line numbers

• a symbol table

• a string table

``Object file format'' shows the overall structure.

Object file format

FILE HEADER

Optional Information

Section 1 Header

...

Section n Header

Raw Data for Section 1

...

Raw Data for Section n

Relocation Info for Sect. 1

...

Relocation Info for Sect. n

Line Numbers for Sect. 1

...

Line Numbers for Sect. n

SYMBOL TABLE

STRING TABLE

The last four sections (relocation, line numbers, symbol table, and the string table) may be missing if the program is linked with the -s option of the ld command, or if the line number information, symbol table, and string table are removed by the strip(CP) command. The line number information does not appear unless the program is compiled with cc -g. Also, if there are no unresolved external references after linking, the relocation information is no longer needed and is absent. The string table is also absent if the source file does not contain any symbols with names longer than eight characters.

An object file that contains no errors or unresolved references is considered executable.