ar(4) ar(4)
NAME
ar - archive file format
SYNOPSIS
#include <ar.h>
DESCRIPTION
The archive command ar(1) is used to combine several files into one.
Archives are used mainly as libraries to be searched by the link
editor ld(1).
Each archive begins with the archive magic string.
#define ARMAG "!<arch>\n" /* magic string */
#define SARMAG 8 /* length of magic string */
Following the archive magic string are the archive file members.
Each file member is preceded by a file member header which is of the
following format:
#define ARFMAG "`\n" /* header trailer string */
struct arhdr /* file member header */
{
char arname[16]; /* '/' terminated file member name */
char ardate[12]; /* file member date */
char aruid[6]; /* file member user identification */
char argid[6]; /* file member group identification */
char armode[8]; /* file member mode (octal) */
char arsize[10]; /* file member size */
char arfmag[2]; /* header trailer string */
};
All information in the file member headers is in printable ASCII. The
numeric information contained in the headers is stored as decimal
numbers (except for ar_mode which is in octal). Thus, if the archive
contains printable files, the archive itself is printable.
If the file member name fits, the ar_name field contains the name
directly, and is terminated by a slash (/) and padded with blanks on
the right. If the member's name does not fit, ar_name contains a
slash (/) followed by a decimal representation of the name's offset
in the archive string table described below.
The ar_date field is the modification date of the file at the time of
its insertion into the archive. Common format archives can be moved
from system to system as long as the portable archive command ar(1)
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ar(4) ar(4)
is used.
Each archive file member begins on an even byte boundary; a newline
is inserted between files if necessary. Nevertheless, the size given
reflects the actual size of the file exclusive of padding.
Notice there is no provision for empty areas in an archive file.
Each archive that contains object files [see a.out(4)] includes an
archive symbol table. This symbol table is used by the link editor
ld(1) to determine which archive members must be loaded during the
link edit process. The archive symbol table (if it exists) is always
the first file in the archive (but is never listed) and is
automatically created and/or updated by ar.
The archive symbol table has a zero length name (i.e., arname[0] is
'/'), arname[1]==' ', etc.). All ``words'' in this symbol table
have four bytes, using the machine-independent encoding shown below.
(All machines use the encoding described here for the symbol table,
even if the machine's ``natural'' byte order is different.)
____________________
|0 |1 |2 |3 |
0x01020304 01 | 02 | 03 | 04 |
| | | | |
|____|____|____|____|
The contents of this file are as follows:
1. The number of symbols. Length: 4 bytes.
2. The array of offsets into the archive file. Length: 4 bytes *
``the number of symbols''.
3. The name string table. Length: ar_size - 4 bytes * (``the
number of symbols'' + 1).
As an example, the following symbol table defines 4 symbols. The
archive member at file offset 114 defines name and object. The
archive member at file offset 426 defines function and a second
version of name.
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ar(4) ar(4)
Offset +0 +1 +2 +3
| __________________|
0 | 4 | 4 offset entries
| __________________|
4 | 114 | name
| __________________|
8 | 114 | object
| __________________|
12 | 426 | function
| __________________|
16 | 426 | name
| __________________|
20 | n | a | m | e |
| ___|____|____|____|
24 | \0| o | b | j |
| ___|____|____|____|
28 | e | c | t | \0|
| ___|____|____|____|
32 | f | u | n | c |
| ___|____|____|____|
36 | t | i | o | n |
| ___|____|____|____|
40 | \0| n | a | m |
| ___|____|____|____|
44 | e | \0| | |
| ___|____|____|____|
The number of symbols and the array of offsets are managed with sgetl
and sputl. The string table contains exactly as many null terminated
strings as there are elements in the offsets array. Each offset from
the array is associated with the corresponding name from the string
table (in order). The names in the string table are all the defined
global symbols found in the common object files in the archive. Each
offset is the location of the archive header for the associated
symbol.
If some archive member's name is more than 15 bytes long, a special
archive member contains a table of file names, each followed by a
slash and a new-line. This string table member, if present, will
precede all ``normal'' archive members. The special archive symbol
table is not a ``normal'' member, and must be first if it exists.
The ar_name entry of the string table's member header holds a zero
length name arname[0]=='/', followed by one trailing slash
(arname[1]=='/'), followed by blanks (arname[2]==' ', etc.).
Offsets into the string table begin at zero. Example ar_name values
for short and long file names appear below.
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ar(4) ar(4)
Offset +0 +1 +2 +3 +4 +5 +6 +7 +8 +9
| ______|______|______|_______|______|______|_______|______|______|_______|
0 | f | i | l | e | | n | a | m | e | |
| ______|______|______|_______|______|______|_______|______|______|_______|
10 | s | a | m | p | l | e | / | \n | l | o |
| ______|______|______|_______|______|______|_______|______|______|_______|
20 | n | g | e | r | f | i | l | e | n | a |
| ______|______|______|_______|______|______|_______|______|______|_______|
30 | m | e | x | a | m | p | l | e | / | \n |
| ______|______|______|_______|______|______|_______|______|______|_______|
Member Name ar_name Note
____________________________|_____________________|______________________________
short-name | short-name/ | Not in string table
filenamesample | /0 | Offset 0 in string table
longerfilenamexample | /18 | Offset 18 in string table
____________________________|_____________________|______________________________
SEE ALSO
ar(1), ld(1), strip(1), sputl(3X), a.out(4).
NOTES
strip(1) will remove all archive symbol entries from the header. The
archive symbol entries must be restored via the -ts options of the
ar(1) command before the archive can be used with the link editor
ld(1).
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