NAME
llvm-ar - LLVM archiver
SYNOPSIS
llvm-ar [-]{dmpqrtx}[Rabfikouz] [relpos] [count] <archive> [files...]
DESCRIPTION
The llvm-ar command is similar to the common Unix utility, "ar". It
archives 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
individual 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
linking 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
immediately preceding the data for the file. The path name is null
terminated and may contain the slash (/) character.
Compression
llvm-ar can compress the members of an archive to save space. The
compression used depends on what's available on the platform and
what choices the LLVM Compressor utility makes. It generally favors
bzip2 but will select between "no compression" or bzip2 depending
on what makes sense for the file's content.
Directory Recursion
Most "ar" implementations do not recurse through directories but
simply ignore directories if they are presented to the program in
the files option. llvm-ar, however, can recurse through directory
structures 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 'Z' means the file is compressed. 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 (zR) that are not found in other
"ar"s. The options to llvm-ar specify a single basic operation to
perform on the archive, a variety of modifiers for that operation, 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 archive
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
archive. Typically archive files end with a ".a" suffix, but this is
not required. Following the archive-name comes a list of files that
indicate the specific members of the archive to operate on. If the
files option is not specified, it generally means either "none" or
"all" members, 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
archive 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
confuse your terminal settings. The p operation never modifies the
archive.
q[Rfz]
Quickly append files to the end of the archive. The R, f, and z
modifiers 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
modified. Because of the way that llvm-ar constructs the archive
file, its dubious whether the q operation is any faster than the r
operation.
r[Rabfuz]
Replace or insert file members. The R, a, b, f, u, and z 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,
Z=compressed, 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 table 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
system. If no files are specified, the entire archive is extract.
Modifiers (operation specific)
The modifiers below are specific to certain operations. See the
Operations 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 "a"fter 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 "b"efore the relpos member.
If relpos is not found, the files are placed at the end of the
archive. This modifier is identical to the 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
characters 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 "f"lattened 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
(recursively) 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.
[z] When inserting or replacing any file in the archive, compress the
file first. This modifier is safe to use when (previously)
compressed bitcode files are added to the archive; the compressed
bitcode files will not be doubly compressed.
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
indicating 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-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
character (0x0A). Following the magic number, the file is composed of
even length members that begin with an archive header and end with a \n
padding 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 (/)
character, 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
specifications.
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
systems. 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
systems. 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
systems. 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. If the size field is negative (starts with a
minus sign, 0x02D), then the archive member is stored in compressed
form. The first byte of the archive member's data indicates the
compression type used. A value of 0 (0x30) indicates that no
compression was used. A value of 2 (0x32) indicates that bzip2
compression was used.
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
member. 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, ar(1)
AUTHORS
Maintained by the LLVM Team (<http://llvm.org>).