COFF, Common Object File Format, is the formal definition for the structure of machine code files in the UNIX System V.3 environment. All machine-code files--fully linked executables, compiled applications, or system libraries--are COFF files. There is hardly a system-related task that does not require some knowledge of COFF, from understanding assembly source to implementing a proprietary system enhancement. This handbook explains the COFF data structure and its manipulation.Contents include: Basics of COFF. Assembly code relocation process. COFF file headers. Relocation structures. Linking. The COFF system in UNIX. Magic numbers. The COFF symbolic debug system.