235 lines
7.4 KiB
Groff
235 lines
7.4 KiB
Groff
.\" Copyright (c) 2007 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 Joseph Koshy ``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 Joseph Koshy 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 September 07, 2007
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.Os
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.Dt AR 5
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.Sh NAME
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.Nm ar
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.Nd format of archives managed by ar(1) and 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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An archive 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 is a single file that stores the individual members of the
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archive along with metadata for each member.
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There are two major variants of the
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.Xr ar 1
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archive format, the BSD variant and the SVR4/GNU variant.
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Both variants are described by this manual page.
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.Pp
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The header file
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.In ar.h
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defines constants and structures used to describe the layout
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of these archives.
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.Ss Archive Layout
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.Xr ar 1
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archives start with a string of magic bytes
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.Qq !<arch>\en
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(constant
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.Dv ARMAG
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in header
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.In ar.h ) .
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The content of the archive follows the magic bytes.
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Each member stored in the archive is preceded by a fixed size
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archive header that stores file permissions, last modification
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time, the owner, and the group of the archived file.
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.Pp
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Archive headers start at an even byte offset in the archive
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file.
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If the length of the preceding archive member was odd, then an extra
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newline character
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.Dq "\en"
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is used as padding.
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.Pp
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The archive header comprises six fixed-size ASCII strings followed
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by a two character trailer (see
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.Vt "struct ar_hdr"
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in header file
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.In ar.h Ns ):
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.Bd -literal
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struct ar_hdr {
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char ar_name[16]; /* name */
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char ar_date[12]; /* modification time */
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char ar_uid[6]; /* user id */
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char ar_gid[6]; /* group id */
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char ar_mode[8]; /* octal file permissions */
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char ar_size[10]; /* size in bytes */
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char ar_fmag[2]; /* consistency check */
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};
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.Ed
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.Pp
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Unused characters in the header are filled with space (ASCII 20H)
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characters.
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Each field of the header abuts the next without additional padding.
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.Pp
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The members of the archive header are as follows:
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.Bl -tag -width "Va ar_name" -compact
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.It Va ar_date
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This field holds the decimal representation of the
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modification time, in seconds since the epoch, of the archive
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member.
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.It Va ar_fmag
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This trailer field holds the two characters
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.Qq `\en
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(constant
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.Dv ARFMAG
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defined in header file
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.In ar.h Ns ),
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and is used for consistency checks.
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.It Va ar_gid
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This field holds the decimal representation of the numeric
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user id of the creator of the member.
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.It Va ar_mode
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This field holds octal representation of the file permissions
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for the member.
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.It Va ar_name
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This field holds the name of an archive member.
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The usage of this field depends on the format variant:
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.Bl -tag -width "SVR4/GNU" -compact
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.It BSD
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In the BSD variant, names that are shorter than 16 characters and
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without embedded spaces are stored directly in this field.
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If a name has an embedded space, or if it is longer than 16
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characters, then the string
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.Qq "#1/"
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followed by the decimal representation of the length of the file name
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is placed in this field.
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The actual file name is stored immediately after the archive header.
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The content of the archive member follows the file name.
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The
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.Va ar_size
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field of the header (see below) will then hold the sum of the size of
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the file name and the size of the member.
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.It SVR4/GNU
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In the SVR4/GNU variant, names up to 15 characters in length are
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stored directly in this field, and are terminated by a
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.Qq /
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(ASCII 2FH) character.
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Names larger than 15 characters in length are stored in a special
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archive string table member (see
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.Sx "Archive String Table"
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below), and the
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.Va ar_name
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field holds the string
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.Qq "/"
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followed by the decimal representation of the offset in the archive
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string table of the actual name.
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.El
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.It Va ar_size
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In the SVR4/GNU variant, this field holds the decimal representation
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of actual size in bytes of the archived file.
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In the BSD variant, for member names that use the
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.Va ar_name
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field directly, this field holds the decimal representation of the
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actual size in bytes of the archived member.
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For member names that use the extension mechanism described above, the
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field will hold the sum of the sizes, in bytes, of the filename and the
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archive member.
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.It Va ar_uid
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This field holds the decimal representation of the numeric
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group id of the creator of the member.
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.El
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.Ss Archive Symbol Table
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An archive may additionally contain an archive symbol table
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used by the link editor,
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.Xr ld 1 .
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This symbol table has the member name
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.Qq __.SYMDEF
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in the BSD variant of the archive format, and the name
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.Qq /
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in the SVR4/GNU variant.
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.Pp
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The format of the symbol table depends on the format variant:
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.Bl -tag -width "SVR4/GNU" -compact
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.It BSD
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In the BSD variant, the symbol table has 4 parts encoded in
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a machine dependent manner:
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.Bl -enum -compact
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.It
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The first part is a binary value containing size in bytes of the
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second part encoded as a C
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.Dq long .
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.It
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The second part is a list of
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.Vt struct ranlib
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structures (see
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.In ranlib.h Ns ).
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Each ranlib structure describes one symbol and comprises of
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two C
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.Dq long
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values.
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The first
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.Dq long
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is a zero-based offset into the string table in the fourth part
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for the symbol's name.
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The second
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.Dq long
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is an offset from the beginning of the archive to the start
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of the archive header for the member that defines the symbol.
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.It
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The third part is a binary value denoting the length of the
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string table contained in the fourth part.
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.It
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The fourth part is a string table containing NUL-terminated
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strings.
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.El
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.It SVR4/GNU
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In the SVR4/GNU variant, the symbol table comprises of three parts
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which follow each other without padding:
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.Bl -enum -compact
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.It
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The first part comprises of a count of entries in the symbol table,
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stored a 4 byte binary value in MSB first order.
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.It
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The next part is an array of 4 byte file offsets within the archive
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to archive header for members that define the symbol in question.
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Each offset in stored in MSB first order.
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.It
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The third part is a string table, that contains NUL-terminated
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strings for the symbols in the symbol table.
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.El
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.El
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.Ss Archive String Table
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In the SVR4/GNU variant of the
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.Xr ar 1
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archive format, long file names are stored in a separate
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archive string table and referenced from the archive header
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for each member.
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Each file name is terminated by the string
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.Qq /\en .
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The string table itself has a name of
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.Qq // .
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.Sh SEE ALSO
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.Xr ar 1 ,
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.Xr ranlib 1 ,
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.Xr archive 3 ,
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.Xr elf 3 ,
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.Xr gelf 3 ,
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.Xr elf 5
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