LLVM-AR(1) LLVM LLVM-AR(1)NAME
llvm-ar - LLVM archiver
SYNOPSIS
llvm-ar [-]{dmpqrtx}[Rabfikou] [relpos] [count] <archive> [files...]
DESCRIPTION
The llvm-ar command is similar to the common Unix utility, ar. It ar‐
chives several files together into a single file. The intent for this
is to produce archive libraries by LLVM bitcode that can be linked into
an LLVM program. However, the archive can contain any kind of file. By
default, llvm-ar generates a symbol table that makes linking faster
because only the symbol table needs to be consulted, not each individ‐
ual file member of the archive.
The llvm-ar command can be used to read both SVR4 and BSD style archive
files. However, it cannot be used to write them. While the llvm-ar
command produces files that are almost identical to the format used by
other ar implementations, it has two significant departures in order to
make the archive appropriate for LLVM. The first departure is that
llvm-ar only uses BSD4.4 style long path names (stored immediately
after the header) and never contains a string table for long names. The
second departure is that the symbol table is formated for efficient
construction of an in-memory data structure that permits rapid
(red-black tree) lookups. Consequently, archives produced with llvm-ar
usually won't be readable or editable with any ar implementation or
useful for linking. Using the f modifier to flatten file names will
make the archive readable by other ar implementations but not for link‐
ing because the symbol table format for LLVM is unique. If an SVR4 or
BSD style archive is used with the r (replace) or q (quick update)
operations, the archive will be reconstructed in LLVM format. This
means that the string table will be dropped (in deference to BSD 4.4
long names) and an LLVM symbol table will be added (by default). The
system symbol table will be retained.
Here's where llvm-ar departs from previous ar implementations:
Symbol Table
Since llvm-ar is intended to archive bitcode files, the symbol table
won't make much sense to anything but LLVM. Consequently, the symbol
table's format has been simplified. It consists simply of a sequence
of pairs of a file member index number as an LSB 4byte integer and a
null-terminated string.
Long Paths
Some ar implementations (SVR4) use a separate file member to record
long path names (> 15 characters). llvm-ar takes the BSD 4.4 and Mac
OS X approach which is to simply store the full path name immedi‐
ately preceding the data for the file. The path name is null termi‐
nated and may contain the slash (/) character.
Directory Recursion
Most ar implementations do not recurse through directories but sim‐
ply ignore directories if they are presented to the program in the
files option. llvm-ar, however, can recurse through directory struc‐
tures and add all the files under a directory, if requested.
TOC Verbose Output
When llvm-ar prints out the verbose table of contents (tv option),
it precedes the usual output with a character indicating the basic
kind of content in the file. A blank means the file is a regular
file. A 'B' means the file is an LLVM bitcode file. An 'S' means the
file is the symbol table.
OPTIONS
The options to llvm-ar are compatible with other ar implementations.
However, there are a few modifiers (R) that are not found in other ar
implementations. The options to llvm-ar specify a single basic opera‐
tion to perform on the archive, a variety of modifiers for that opera‐
tion, the name of the archive file, and an optional list of file names.
These options are used to determine how llvm-ar should process the ar‐
chive file.
The Operations and Modifiers are explained in the sections below. The
minimal set of options is at least one operator and the name of the ar‐
chive. Typically archive files end with a .a suffix, but this is not
required. Following the archive-name comes a list of files that indi‐
cate the specific members of the archive to operate on. If the files
option is not specified, it generally means either "none" or "all" mem‐
bers, depending on the operation.
Operations
d
Delete files from the archive. No modifiers are applicable to this
operation. The files options specify which members should be
removed from the archive. It is not an error if a specified file
does not appear in the archive. If no files are specified, the ar‐
chive is not modified.
m[abi]
Move files from one location in the archive to another. The a, b,
and i modifiers apply to this operation. The files will all be moved
to the location given by the modifiers. If no modifiers are used,
the files will be moved to the end of the archive. If no files are
specified, the archive is not modified.
p[k]
Print files to the standard output. The k modifier applies to this
operation. This operation simply prints the files indicated to the
standard output. If no files are specified, the entire archive is
printed. Printing bitcode files is ill-advised as they might con‐
fuse your terminal settings. The p operation never modifies the ar‐
chive.
q[Rf]
Quickly append files to the end of the archive. The R, and f modi‐
fiers apply to this operation. This operation quickly adds the
files to the archive without checking for duplicates that should be
removed first. If no files are specified, the archive is not modi‐
fied. Because of the way that llvm-ar constructs the archive file,
its dubious whether the q operation is any faster than the r opera‐
tion.
r[Rabfu]
Replace or insert file members. The R, a, b, f, and u modifiers
apply to this operation. This operation will replace existing files
or insert them at the end of the archive if they do not exist. If no
files are specified, the archive is not modified.
t[v]
Print the table of contents. Without any modifiers, this operation
just prints the names of the members to the standard output. With
the v modifier, llvm-ar also prints out the file type (B=bitcode,
S=symbol table, blank=regular file), the permission mode, the owner
and group, the size, and the date. If any files are specified, the
listing is only for those files. If no files are specified, the ta‐
ble of contents for the whole archive is printed.
x[oP]
Extract archive members back to files. The o modifier applies to
this operation. This operation retrieves the indicated files from
the archive and writes them back to the operating system's file sys‐
tem. If no files are specified, the entire archive is extract.
Modifiers (operation specific)
The modifiers below are specific to certain operations. See the Opera‐
tions section (above) to determine which modifiers are applicable to
which operations.
[a]
When inserting or moving member files, this option specifies the
destination of the new files as being after the relpos member. If
relpos is not found, the files are placed at the end of the archive.
[b]
When inserting or moving member files, this option specifies the
destination of the new files as being before the relpos member. If
relpos is not found, the files are placed at the end of the archive.
This modifier is identical to the i modifier.
[f]
Normally, llvm-ar stores the full path name to a file as presented
to it on the command line. With this option, truncated (15 charac‐
ters max) names are used. This ensures name compatibility with older
versions of ar but may also thwart correct extraction of the files
(duplicates may overwrite). If used with the R option, the directory
recursion will be performed but the file names will all be flattened
to simple file names.
[i]
A synonym for the b option.
[k]
Normally, llvm-ar will not print the contents of bitcode files when
the p operation is used. This modifier defeats the default and
allows the bitcode members to be printed.
[N]
This option is ignored by llvm-ar but provided for compatibility.
[o]
When extracting files, this option will cause llvm-ar to preserve
the original modification times of the files it writes.
[P]
use full path names when matching
[R]
This modifier instructions the r option to recursively process
directories. Without R, directories are ignored and only those
files that refer to files will be added to the archive. When R is
used, any directories specified with files will be scanned (recur‐
sively) to find files to be added to the archive. Any file whose
name begins with a dot will not be added.
[u]
When replacing existing files in the archive, only replace those
files that have a time stamp than the time stamp of the member in
the archive.
Modifiers (generic)
The modifiers below may be applied to any operation.
[c]
For all operations, llvm-ar will always create the archive if it
doesn't exist. Normally, llvm-ar will print a warning message indi‐
cating that the archive is being created. Using this modifier turns
off that warning.
[s]
This modifier requests that an archive index (or symbol table) be
added to the archive. This is the default mode of operation. The
symbol table will contain all the externally visible functions and
global variables defined by all the bitcode files in the archive.
Using this modifier is more efficient that using llvm-ran‐
lib|llvm-ranlib which also creates the symbol table.
[S]
This modifier is the opposite of the s modifier. It instructs
llvm-ar to not build the symbol table. If both s and S are used, the
last modifier to occur in the options will prevail.
[v]
This modifier instructs llvm-ar to be verbose about what it is
doing. Each editing operation taken against the archive will produce
a line of output saying what is being done.
STANDARDS
The llvm-ar utility is intended to provide a superset of the IEEE Std
1003.2 (POSIX.2) functionality for ar. llvm-ar can read both SVR4 and
BSD4.4 (or Mac OS X) archives. If the f modifier is given to the x or r
operations then llvm-ar will write SVR4 compatible archives. Without
this modifier, llvm-ar will write BSD4.4 compatible archives that have
long names immediately after the header and indicated using the
"#1/ddd" notation for the name in the header.
FILE FORMAT
The file format for LLVM Archive files is similar to that of BSD 4.4 or
Mac OSX archive files. In fact, except for the symbol table, the ar
commands on those operating systems should be able to read LLVM archive
files. The details of the file format follow.
Each archive begins with the archive magic number which is the eight
printable characters "!<arch>n" where n represents the newline charac‐
ter (0x0A). Following the magic number, the file is composed of even
length members that begin with an archive header and end with a n pad‐
ding character if necessary (to make the length even). Each file member
is composed of a header (defined below), an optional newline-terminated
"long file name" and the contents of the file.
The fields of the header are described in the items below. All fields
of the header contain only ASCII characters, are left justified and are
right padded with space characters.
name - char[16]
This field of the header provides the name of the archive member. If
the name is longer than 15 characters or contains a slash (/) char‐
acter, then this field contains #1/nnn where nnn provides the length
of the name and the #1/ is literal. In this case, the actual name
of the file is provided in the nnn bytes immediately following the
header. If the name is 15 characters or less, it is contained
directly in this field and terminated with a slash (/) character.
date - char[12]
This field provides the date of modification of the file in the form
of a decimal encoded number that provides the number of seconds
since the epoch (since 00:00:00 Jan 1, 1970) per Posix specifica‐
tions.
uid - char[6]
This field provides the user id of the file encoded as a decimal
ASCII string. This field might not make much sense on non-Unix sys‐
tems. On Unix, it is the same value as the st_uid field of the stat
structure returned by the stat(2) operating system call.
gid - char[6]
This field provides the group id of the file encoded as a decimal
ASCII string. This field might not make much sense on non-Unix sys‐
tems. On Unix, it is the same value as the st_gid field of the stat
structure returned by the stat(2) operating system call.
mode - char[8]
This field provides the access mode of the file encoded as an octal
ASCII string. This field might not make much sense on non-Unix sys‐
tems. On Unix, it is the same value as the st_mode field of the stat
structure returned by the stat(2) operating system call.
size - char[10]
This field provides the size of the file, in bytes, encoded as a
decimal ASCII string.
fmag - char[2]
This field is the archive file member magic number. Its content is
always the two characters back tick (0x60) and newline (0x0A). This
provides some measure utility in identifying archive files that have
been corrupted.
The LLVM symbol table has the special name "#_LLVM_SYM_TAB_#". It is
presumed that no regular archive member file will want this name. The
LLVM symbol table is simply composed of a sequence of triplets: byte
offset, length of symbol, and the symbol itself. Symbols are not null
or newline terminated. Here are the details on each of these items:
offset - vbr encoded 32-bit integer
The offset item provides the offset into the archive file where the
bitcode member is stored that is associated with the symbol. The
offset value is 0 based at the start of the first "normal" file mem‐
ber. To derive the actual file offset of the member, you must add
the number of bytes occupied by the file signature (8 bytes) and the
symbol tables. The value of this item is encoded using variable bit
rate encoding to reduce the size of the symbol table. Variable bit
rate encoding uses the high bit (0x80) of each byte to indicate if
there are more bytes to follow. The remaining 7 bits in each byte
carry bits from the value. The final byte does not have the high bit
set.
length - vbr encoded 32-bit integer
The length item provides the length of the symbol that follows. Like
this offset item, the length is variable bit rate encoded.
symbol - character array
The symbol item provides the text of the symbol that is associated
with the offset. The symbol is not terminated by any character. Its
length is provided by the length field. Note that is allowed (but
unwise) to use non-printing characters (even 0x00) in the symbol.
This allows for multiple encodings of symbol names.
EXIT STATUS
If llvm-ar succeeds, it will exit with 0. A usage error, results in an
exit code of 1. A hard (file system typically) error results in an exit
code of 2. Miscellaneous or unknown errors result in an exit code of 3.
SEE ALSO
llvm-ranlib|llvm-ranlib, ar(1)AUTHOR
Maintained by The LLVM Team (http://llvm.org/).
COPYRIGHT
2003-2013, LLVM Project
3.3 2016-02-17 LLVM-AR(1)
