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 a unique string identifier called an
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 ar_hdr /* file member header */
{
char ar_name[16]; /* '/' terminated file member name */
char ar_date[12]; /* file member date */
char ar_uid[6]; /* file member user identification */
char ar_gid[6]; /* file member group identification */
char ar_mode[8]; /* file member mode (octal) */
char ar_size[10]; /* file member size */
char ar_fmag[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.
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ar(4) ar(4)
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 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 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 (that is,
ar_name[0] is '/'), ar_name[1]==' ', and so on). 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 |
0x0102030| 01 | 02 | 03 | 04 |
| | | | |
|____|____|____|____|
The contents of the symbol table are as follows:
1. The number of symbols. Length: 4 bytes.
2. The array of offsets, one per symbol, 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
Copyright 1994 Novell, Inc. Page 2
ar(4) ar(4)
second version of name.
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
ar_name[0]=='/', followed by one trailing slash
Copyright 1994 Novell, Inc. Page 3
ar(4) ar(4)
(ar_name[1]=='/'), followed by blanks (ar_name[2]==' ', and so
on). Offsets into the string table begin at zero. Example
ar_name values for short and long file names appear below.
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
file_name_sample | /0 | Offset 0 in string table
longerfilenamexample | /18 | Offset 18 in string table
_______________________________|________________________|__________________________________
REFERENCES
a.out(4), ar(1), ld(1), sputl(3X), strip(1)
NOTICES
strip will remove all archive symbol entries from the header.
The archive symbol entries must be restored via the -ts
options of the ar command before the archive can be used with
the link editor ld.
Copyright 1994 Novell, Inc. Page 4