Common Object File Format (COFF)

Summary

Windows NT uses a special format for the executable (image) files and object files. The format used in these files are referred to as Portable Executable (PE) or Common Object File Format (COFF) files. The name Portable Executable refers to the fact that executable files can run on more than one platform. This article describes in detail the internal features of PE/COFF file formats and its parameters.

More Information

The PE/COFF file headers consist of a MS-DOS stub, file signature, COFF Header, and Optional Header. An object file contains only the COFF Header, but an image file contains all the headers described above. The most important of these headers is the COFF header. The table below describes the information stored in the COFF header.



Offset Size Field Description
------ ---- ------------------- -----------------------------------------------
0 2 Machine Number identifying type of target machine.
2 2 Number of Sections Number of sections; indicates size of the
Section Table, which immediately follows
the headers.
4 4 Time/Date Stamp Time and date the file was created.
8 4 Pointer to Symbol Offset, within the COFF file, of the symbol
Table table.
12 4 Number of Symbols Number of entries in the symbol table.
This data can be used in locating the
string table, which immediately follows
the symbol table.
16 2 Optional Header Size of the optional header, which is
Size included for executable files but not
object files. An object file should have a
value of 0 here.
18 2 Characteristics Flags indicating attributes of the file.
Windows NT Software Development Kit (SDK) provides a utility called DUMPBIN. DUMPBIN is a 32-bit tool that displays information about 32-bit Common Object File Format (COFF) binary files. DUMPBIN runs only from a command prompt. You can use DUMPBIN to examine the following kinds of COFF files: object files, standard libraries of COFF objects, executable files, and dynamic-link library (DLL) files.

To run DUMPBIN, use the following syntax:
DUMPBIN [options] [files]
The following are options parameters and definitions for DUMPBIN:

/ALL
/ARCHIVEMEMBERS
/DISASM
/EXPORTS
/HEADERS
/IMPORTS
/LINENUMBERS
/LINKERMEMBER[:{1|2}]
/OUT:filename
/PDATA
/RAWDATA[:{NONE|BYTES|SHORTS|LONGS}[,#]]
/RELOCATIONS
/SECTION:name
/SUMMARY
/SYMBOLS

Options Definition
---------------- -------------------------------------------------------
/ALL Setting this option causes DUMPBIN to display all
available information except code disassembly.

/ARCHIVEMEMBERS Setting this option causes DUMPBIN to display minimal
information about member objects in a library.

/DISASM Setting this option causes DUMPBIN to show disassembly
of code sections, using symbols if present in the file.

/EXPORTS This option causes DUMPBIN to list all definitions
exported from an executable file or DLL.

/HEADERS Setting this option causes DUMPBIN to display the file
header and the header for each section. When used with a
library, displays the header for each member object.

/IMPORTS This option causes DUMPBIN to list all definitions
imported to an executable file or DLL.

/LINENUMBERS Setting this option causes DUMPBIN to show COFF line
numbers. Line numbers exist in an object file if it was
compiled with /Zi. An executable file or DLL contains
COFF line numbers if it was linked with /DEBUG and
/DEBUGTYPE:COFF option.

/LINKERMEMBER [[:{1|2}]]
Setting this option causes DUMPBIN to list public symbols
defined in a library. Specify the 1 argument to display
symbols in object order, along with their offsets. Specify
the 2 argument to display offsets and index numbers of
objects, then list the symbols in alphabetical order along
with the object index for each. To get both outputs,
specify /LINKERMEMBER without the number argument.

/OUT:<filename> This option specifies a filename for the output.

/RAWDATA [[:{BYTES|SHORTS|LONGS|NONE}[[,number]]]]
Setting this option causes DUMPBIN to display the raw
contents of each section in the file. The arguments
control the format of the display, as follows:
Argument - Result
BYTES - The default. Contents are displayed in hexadecimal bytes,
and also as ASCII if they have a printed representation.
SHORTS - Contents are displayed in hexadecimal words.
LONGS - Contents are displayed in hexadecimal longwords.
NONE - Raw data is suppressed. This is useful to control the
output of /ALL.
number - Displayed lines are set to a width that holds number
values per line.

/RELOCATIONS Setting this option causes DUMPBIN to display any
relocations in the object or image.

/SECTION: <section>
This option restricts the output to information on the
specified section.

/SUMMARY Setting this option causes DUMPBIN to display minimal
information about sections, including total size. This
option is the default if no other option is specified
in a DUMPBIN command.

/SYMBOLS Setting this option causes DUMPBIN to display the COFF symbol
table. Symbol tables exist in all object files. A COFF symbol
table appears in an image file only if it is linked with
/DEBUG /DEBUGTYPE:COFF
Properties

Article ID: 121460 - Last Review: Oct 31, 2006 - Revision: 1

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