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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)
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