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31 .Nd archive file format for
39 archives are created and managed by the
44 These archives are typically used during program development to
45 hold libraries of program objects.
48 archive is contained in a single operating system file.
50 This manual page documents two variants of the
52 archive format: the BSD archive format, and the SVR4/GNU archive
55 In both variants the archive file starts with an identifying byte
56 sequence of the seven ASCII characters
58 followed by a ASCII linefeed character
66 Archive members follow the initial identifying byte sequence.
67 Each archive member is prefixed by a fixed size header describing the
68 file attributes associated with the member.
70 An archive header describes the file attributes for the archive member that
74 format only supports a limited number of attributes: the file name,
75 the file creation time stamp, the uid and gid of the creator, the file
76 mode and the file size.
78 Archive headers are placed at an even byte offset in the archive file.
79 If the data for an archive member ends at an odd byte offset, then a
80 padding byte with value 0x0A is used to position the next archive
81 header on an even byte offset.
83 An archive header comprises the following fixed sized fields:
84 .Bl -tag -width "Li ar_name"
86 (16 bytes) The file name of the archive member.
87 The format of this field varies between the BSD and SVR4/GNU formats and
88 is described in more detail in the section
89 .Sx "Representing File Names"
92 (12 bytes) The file modification time for the member in seconds since the
93 epoch, encoded as a decimal number.
95 (6 bytes) The uid associated with the archive member, encoded as a
98 (6 bytes) The gid associated with the archive member, encoded as a
101 (8 bytes) The file mode for the archive member, encoded as an octal
104 (10 bytes) In the SVR4/GNU archive format this field holds the size in
105 bytes of the archive member, encoded as a decimal number.
106 In the BSD archive format, for short file names, this field
107 holds the size in bytes of the archive member, encoded as a decimal
112 .Sx "Representing File Names"
115 the field contains the combined size of the
116 archive member and its file name, encoded as a decimal number.
118 (2 bytes) This field holds 2 bytes with values 0x96 and 0x0A
119 respectively, marking the end of the header.
122 Unused bytes in the fields of an archive header are set to the value
124 .Ss "Representing File Names"
125 The BSD and SVR4/GNU variants use different schemes for encoding file
127 .Bl -tag -width "SVR4/GNU"
129 File names that are up to 16 bytes long and which do not contain
130 embedded spaces are stored directly in the
132 field of the archive header.
133 File names that are either longer than 16 bytes or which contain
134 embedded spaces are stored immediately after the archive header
137 field of the archive header is set to the string
139 followed by a decimal representation of the number of bytes needed for
143 field of the archive header is set to the decimal representation of
144 the combined sizes of the archive member and the file name.
145 The file contents of the member follows the file name without further
148 As an example, if the file name for a member was
150 and its contents was the string
154 field of the header would contain
158 field of the header would contain
160 and the bytes immediately following the header would be 0x41, 0x20,
161 0x42, 0x43, 0x20 and 0x44
167 File names that are up to 15 characters long are stored directly in the
169 field of the header, terminated by a
173 If the file name is larger than would fit in space for the
175 field, then the actual file name is kept in the archive
179 .Sx "Archive String Tables"
182 and the decimal offset of the file name in the string table is stored
189 As an example, if the real file name has been stored at offset 768 in
190 the archive string table, the
192 field of the header will contain the string
195 .Ss "Special Archive Members"
196 The following archive members are special.
197 .Bl -tag -width indent
199 In the SVR4/GNU variant of the archive format, the archive member with
202 denotes an archive symbol table.
203 If present, this member will be the very first member in the
206 In the SVR4/GNU variant of the archive format, the archive member with
209 denotes the archive string table.
210 This special member is used to hold filenames that do not fit in the
211 file name field of the header
214 .Sx "Representing File Names"
217 If present, this member immediately follows the archive symbol table
218 if an archive symbol table is present, or is the first member otherwise.
219 .It Dq Li "__.SYMDEF"
220 This special member contains the archive symbol table in the BSD
221 variant of the archive format.
222 If present, this member will be the very first member in the
225 .Ss "Archive String Tables"
226 An archive string table is used in the SVR4/GNU archive format to hold
227 file names that are too large to fit into the constraints of the
229 field of the archive header.
230 An archive string table contains a sequence of file names.
231 Each file name in the archive string table is terminated by the
232 byte sequence 0x2F, 0x0A
237 No padding is used to separate adjacent file names.
238 .Ss "Archive Symbol Tables"
239 Archive symbol tables are used to speed up link editing by providing a
240 mapping between the program symbols defined in the archive
241 and the corresponding archive members.
242 Archive symbol tables are managed by the
246 The format of archive symbol tables is as follows:
247 .Bl -tag -width "SVR4/GNU"
249 In the BSD archive format, the archive symbol table comprises
250 of two parts: a part containing an array of
252 descriptors, followed by a part containing a symbol string table.
253 The sizes and layout of the structures that make up a BSD format
254 archive symbol table are machine dependent.
258 descriptors begins with a field containing the size in bytes of the
261 descriptors encoded as a C
267 descriptors follows the size field.
270 descriptor describes one symbol.
274 descriptor comprises two fields:
275 .Bl -tag -width "Ar ran_strx" -compact
278 This field contains the zero-based offset of the symbol name in the
282 This field is the file offset to the archive header for the archive
283 member defining the symbol.
286 The part containing the symbol string table begins with a field
287 containing the size in bytes of the string table, encoded as a C
290 This string table follows the size field, and contains
291 NUL-terminated strings for the symbols in the symbol table.
293 In the SVR4/GNU archive format, the archive symbol table starts with a
294 4-byte binary value containing the number of entries contained in the
295 archive symbol table.
296 This count of entries is stored most significant byte first.
300 4-byte numbers, each stored most significant byte first.
301 Each number is a binary offset to the archive header for the member in
302 the archive file for the corresponding symbol table entry.
304 After the binary offset values, there are
306 NUL-terminated strings in sequence, holding the symbol names for
307 the corresponding symbol table entries.
309 .Sh STANDARDS COMPLIANCE
312 archive format is not currently specified by a standard.
314 This manual page documents the
316 archive formats used by the
320 operating system releases.