328 lines
9.7 KiB
Groff
328 lines
9.7 KiB
Groff
.\" Copyright (c) 2010 Joseph Koshy. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd November 28, 2010
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.Dt AR 5
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.Os
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.Sh NAME
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.Nm ar
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.Nd archive file format for
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.Xr ar 1
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and
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.Xr ranlib 1
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.Sh SYNOPSIS
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.In ar.h
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.Sh DESCRIPTION
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.Xr ar 1
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archives are created and managed by the
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.Xr ar 1
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and
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.Xr ranlib 1
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utilities.
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These archives are typically used during program development to
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hold libraries of program objects.
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An
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.Xr ar 1
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archive is contained in a single operating system file.
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.Pp
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This manual page documents two variants of the
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.Xr ar 1
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archive format: the BSD archive format, and the SVR4/GNU archive
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format.
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.Pp
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In both variants the archive file starts with an identifying byte
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sequence of the seven ASCII characters
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.Sq Li "!<arch>"
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followed by a ASCII linefeed character
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.Po
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see the constant
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.Dq ARMAG
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in the header file
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.In ar.h
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.Pc .
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.Pp
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Archive members follow the initial identifying byte sequence.
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Each archive member is prefixed by a fixed size header describing the
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file attributes associated with the member.
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.Ss "Archive Headers"
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An archive header describes the file attributes for the archive member that
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follows it.
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The
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.Xr ar 5
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format only supports a limited number of attributes: the file name,
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the file creation time stamp, the uid and gid of the creator, the file
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mode and the file size.
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.Pp
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Archive headers are placed at an even byte offset in the archive file.
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If the data for an archive member ends at an odd byte offset, then a
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padding byte with value 0x0A is used to position the next archive
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header on an even byte offset.
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.Pp
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An archive header comprises the following fixed sized fields:
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.Bl -tag -width "Li ar_name"
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.It Ar ar_name
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(16 bytes) The file name of the archive member.
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The format of this field varies between the BSD and SVR4/GNU formats and
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is described in more detail in the section
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.Sx "Representing File Names"
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below.
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.It Ar ar_date
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(12 bytes) The file modification time for the member in seconds since the
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epoch, encoded as a decimal number.
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.It Ar ar_uid
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(6 bytes) The uid associated with the archive member, encoded as a
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decimal number.
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.It Ar ar_gid
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(6 bytes) The gid associated with the archive member, encoded as a
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decimal number.
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.It Ar ar_mode
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(8 bytes) The file mode for the archive member, encoded as an octal
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number.
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.It Ar ar_size
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(10 bytes) In the SVR4/GNU archive format this field holds the size in
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bytes of the archive member, encoded as a decimal number.
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In the BSD archive format, for short file names, this field
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holds the size in bytes of the archive member, encoded as a decimal
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number.
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For long file names
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.Po
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see
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.Sx "Representing File Names"
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below
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.Pc ,
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the field contains the combined size of the
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archive member and its file name, encoded as a decimal number.
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.It Ar ar_fmag
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(2 bytes) This field holds 2 bytes with values 0x96 and 0x0A
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respectively, marking the end of the header.
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.El
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.Pp
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Unused bytes in the fields of an archive header are set to the value
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0x20.
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.Ss "Representing File Names"
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The BSD and SVR4/GNU variants use different schemes for encoding file
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names for members.
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.Bl -tag -width "SVR4/GNU"
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.It "BSD"
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File names that are up to 16 bytes long and which do not contain
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embedded spaces are stored directly in the
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.Ar ar_name
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field of the archive header.
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File names that are either longer than 16 bytes or which contain
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embedded spaces are stored immediately after the archive header
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and the
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.Ar ar_name
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field of the archive header is set to the string
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.Dq "#1/"
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followed by a decimal representation of the number of bytes needed for
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the file name.
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In addition, the
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.Ar ar_size
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field of the archive header is set to the decimal representation of
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the combined sizes of the archive member and the file name.
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The file contents of the member follows the file name without further
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padding.
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.Pp
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As an example, if the file name for a member was
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.Dq "A B"
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and its contents was the string
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.Dq "C D" ,
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then the
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.Ar ar_name
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field of the header would contain
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.Dq Li "#1/3" ,
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the
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.Ar ar_size
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field of the header would contain
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.Dq Li 6 ,
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and the bytes immediately following the header would be 0x41, 0x20,
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0x42, 0x43, 0x20 and 0x44
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.Po
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ASCII
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.Dq "A BC D"
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.Pc .
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.It "SVR4/GNU"
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File names that are up to 15 characters long are stored directly in the
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.Ar ar_name
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field of the header, terminated by a
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.Dq Li /
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character.
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.Pp
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If the file name is larger than would fit in space for the
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.Ar ar_name
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field, then the actual file name is kept in the archive
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string table
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.Po
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see
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.Sx "Archive String Tables"
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below
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.Pc ,
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and the decimal offset of the file name in the string table is stored
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in the
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.Ar ar_name
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field, prefixed by a
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.Dq Li /
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character.
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.Pp
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As an example, if the real file name has been stored at offset 768 in
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the archive string table, the
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.Ar ar_name
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field of the header will contain the string
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.Dq /768 .
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.El
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.Ss "Special Archive Members"
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The following archive members are special.
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.Bl -tag -width indent
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.It Dq Li /
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In the SVR4/GNU variant of the archive format, the archive member with
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name
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.Dq Li /
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denotes an archive symbol table.
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If present, this member will be the very first member in the
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archive.
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.It Dq Li //
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In the SVR4/GNU variant of the archive format, the archive member with
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name
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.Dq Li //
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denotes the archive string table.
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This special member is used to hold filenames that do not fit in the
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file name field of the header
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.Po
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see
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.Sx "Representing File Names"
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above
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.Pc .
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If present, this member immediately follows the archive symbol table
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if an archive symbol table is present, or is the first member otherwise.
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.It Dq Li "__.SYMDEF"
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This special member contains the archive symbol table in the BSD
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variant of the archive format.
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If present, this member will be the very first member in the
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archive.
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.El
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.Ss "Archive String Tables"
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An archive string table is used in the SVR4/GNU archive format to hold
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file names that are too large to fit into the constraints of the
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.Ar ar_name
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field of the archive header.
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An archive string table contains a sequence of file names.
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Each file name in the archive string table is terminated by the
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byte sequence 0x2F, 0x0A
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.Po
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the ASCII string
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.Dq "/\en"
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.Pc .
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No padding is used to separate adjacent file names.
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.Ss "Archive Symbol Tables"
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Archive symbol tables are used to speed up link editing by providing a
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mapping between the program symbols defined in the archive
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and the corresponding archive members.
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Archive symbol tables are managed by the
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.Xr ranlib 1
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utility.
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.Pp
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The format of archive symbol tables is as follows:
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.Bl -tag -width "SVR4/GNU"
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.It BSD
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In the BSD archive format, the archive symbol table comprises
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of two parts: a part containing an array of
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.Vt "struct ranlib"
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descriptors, followed by a part containing a symbol string table.
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The sizes and layout of the structures that make up a BSD format
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archive symbol table are machine dependent.
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.Pp
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The part containing
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.Vt "struct ranlib"
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descriptors begins with a field containing the size in bytes of the
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array of
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.Vt "struct ranlib"
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descriptors encoded as a C
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.Vt long
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value.
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.Pp
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The array of
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.Vt "struct ranlib"
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descriptors follows the size field.
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Each
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.Vt "struct ranlib"
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descriptor describes one symbol.
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.Pp
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A
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.Vt "struct ranlib"
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descriptor comprises two fields:
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.Bl -tag -width "Ar ran_strx" -compact
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.It Ar ran_strx
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.Pq C Vt long
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This field contains the zero-based offset of the symbol name in the
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symbol string table.
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.It Ar ran_off
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.Pq C Vt long
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This field is the file offset to the archive header for the archive
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member defining the symbol.
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.El
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.Pp
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The part containing the symbol string table begins with a field
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containing the size in bytes of the string table, encoded as a C
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.Vt long
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value.
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This string table follows the size field, and contains
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NUL-terminated strings for the symbols in the symbol table.
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.It SVR4/GNU
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In the SVR4/GNU archive format, the archive symbol table starts with a
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4-byte binary value containing the number of entries contained in the
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archive symbol table.
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This count of entries is stored most significant byte first.
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.Pp
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Next, there are
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.Ar count
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4-byte numbers, each stored most significant byte first.
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Each number is a binary offset to the archive header for the member in
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the archive file for the corresponding symbol table entry.
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.Pp
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After the binary offset values, there are
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.Ar count
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NUL-terminated strings in sequence, holding the symbol names for
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the corresponding symbol table entries.
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.El
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.Sh STANDARDS COMPLIANCE
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The
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.Xr ar 1
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archive format is not currently specified by a standard.
|
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.Pp
|
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This manual page documents the
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.Xr ar 1
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archive formats used by the
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.Bx 4.4
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and
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.Ux SVR4
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operating system releases.
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.Sh SEE ALSO
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.Xr ar 1 ,
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.Xr ld 1 ,
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.Xr ranlib 1 ,
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.Xr elf 3 ,
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.Xr elf_getarsym 3 ,
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.Xr elf_rand 3
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