ar(4) FILE FORMATS 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
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ar(4) FILE FORMATS ar(4)
portable archive command ar(1) is used.
Each archive file member begins on an even byte boundary; a
newline is inserted between files if necessary. Neverthe-
less, 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.) center; l l
l l l l0p-2f4w(1i) | l0p-2w(.5i) | l0p-2w(.5i) | l0p-2w(.5i)
| l0p-2w(.5i)|. _ _ _ _ 0 1 2 3
l0f4w(1i) | c0w(.5i) | c0w(.5i) | c0w(.5i) | c0w(.5i)|.
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 func-
tion and a second version of name.
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ar(4) FILE FORMATS ar(4)
center; c c c c c c n | cf(CW) s s s| l.
Offset +0 +1 +2 +3 _ 0 4 4 offset
entries _ 4 114 name 8 114 object _
12 426 function 16 426 name _ n | cf(CW)
| cf(CW) | cf(CW) | cf(CW) | l. 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 ``nor-
mal'' 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. Exam-
ple ar_name values for short and long file names appear
below.
center; c c c c c c c c c c c n | cf(CW)e | cf(CW)e |
cf(CW)e | cf(CW)e | cf(CW)e | cf(CW)e | cf(CW)e | cf(CW)e |
cf(CW)e | cf(CW)e|.
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
_ _ _ _ _ _ _ _ _ _
c s s s cf2 s s c s s s lf(CW) s s s | lf(CW) s s | l s s s.
Member Name ar_name Note
_ short-name short-name/ Not in string table
file_name_sample /0 Offset 0 in string table
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ar(4) FILE FORMATS ar(4)
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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