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ar.h(3head)
ar.h(3HEAD) Headers ar.h(3HEAD)
NAME
ar.h, ar - archive file format
SYNOPSIS
#include <ar.h>
DESCRIPTION
The archive command ar is used to combine several files into one. Ar‐
chives are used mainly as libraries to be searched by the link editor
ld.
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 follow‐
ing 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 num‐
bers (except for ar_mode which is in octal). Thus, if the archive con‐
tains only printable files, the archive itself is printable.
If the file member name is 15 or fewer characters, 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 is longer than 15 char‐
acters, ar_name contains a slash (/) followed by a decimal representa‐
tion 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 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.
There is no provision for empty areas in an archive file.
Each archive that contains object files (see a.out(5)) includes an ar‐
chive 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 comes in 32 and 64-bit formats. These formats
differ only in the width of the integer word used to represent the num‐
ber of symbols and offsets into the archive. The 32-bit format can be
used with archives smaller than 4GB, while the 64-bit format is
required for larger archives. The ar command selects the symbol table
format to used based on the size of the archive it is creating, and
will use the smaller format when possible.
A 32-bit archive symbol table has a zero length name, so ar_name con‐
tains the string "/" padded with 15 blank characters on the right. A
64-bit archive symbol table sets ar_name to the string "/SYM64/",
padded with 9 blank characters to the right.
All integer words in a 32-bit symbol table have four bytes, while all
integer words in a 64-bit symbol table have eight bytes. Both formats
use 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
0 1 2 3 4 5 6 7
0x0102030405060708 01 02 03 04 05 06 07 08
The contents of an archive symbol table file are as follows, where
wordsize is 4 bytes for a 32-bit symbol table and 8 bytes for a 64-bit
symbol table.
1. The number of symbols. Length: wordsize bytes.
2. The array of offsets into the archive file. Length: wordsize
bytes * "the number of symbols".
3. The symbol name string table. Length: ar_size - wordsize
bytes * ("the number of symbols" + 1).
As an example, the following 32-bit symbol table defines 4 symbols. The
archive member at file offset 114 defines name. The archive member at
file offset 122 defines object. The archive member at file offset 426
defines function and the archive member at file offset 434 defines
name2.
Example Symbol Table
Offset +0 +1 +2 +3
___________________
0 | 4 | 4 offset entries
|___________________|
4 | 114 | name
|___________________|
8 | 122 | object
|___________________|
12 | 426 | function
|___________________|
16 | 434 | name2
|___________________|
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 | 2 | \0 | |
|____|____|____|____|
The same example, using a 64-bit symbol table would be rendered as fol‐
lows. The archive member at file offset 134 defines name. The archive
member at file offset 142 defines object. The archive member at file
offset 446 defines function and the archive member at file offset 454
defines name2.
Offset +0 +1 +2 +3 +4 +5 +6 +7
_______________________________________
0 | 4 | 4 offset entries
|_______________________________________|
8 | 134 | name
|_______________________________________|
16 | 142 | object
|_______________________________________|
24 | 446 | function
|_______________________________________|
32 | 454 | name2
|_______________________________________|
40 | n | a | m | e | \0 | o | b | j |
|____|____|____|____|___________________|
48 | e | c | t | \0 | f | u | n | c |
|____|____|____|____|___________________|
56 | t | i | o | n | \0 | n | a | m |
|____|____|____|____|___________________|
64 | e | 2 | \0 | |
|____|____|____|____|
The symbol 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 ta‐
ble (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 ar‐
chive 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 (ar_name[1]=='/'), fol‐
lowed by blanks (ar_name[2]==' ', etc.). 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
_______________________________________________________________
short-name | short-name/ | Not in string table
| |
file_name_sample | /0 | Offset 0 in string table
| |
longerfilenamexample | /18 | Offset 18 in string table
_____________________|______________|___________________________
SEE ALSO
ar(1), ld(1), strip(1), a.out(5)
NOTES
The strip utility will remove all archive symbol entries from the
header. The archive symbol entries must be restored with the -ts
options of the ar command before the archive can be used with the link
editor ld.
The maximum size of a single file within an archive is limited to 4GB
by the size of the ar_size field in the archive member structure. An
archive can therefore exceed 4GB in size, but no single member within
the archive can be larger than 4GB.
The maximum user ID for an individual file within an archive is limited
to 6 characters by the ar_uid field of the archive member header. Any
file with a user ID greater than 999999 is set to user ID "nobody"
(60001).
The maximum group ID for an individual file within an archive is lim‐
ited to 6 characters by the ar_gid field of the archive member header.
Any file with a group ID greater than 999999 is set to group ID
"nobody" (60001).
Oracle Solaris 11.4 22 Jun 2010 ar.h(3HEAD)