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 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 SVR4, GNU and BSD style archive files. However, right now it can only write in the GNU format. If an SVR4 or BSD style archive is used with the r (replace) or q (quick update) operations, the archive will be reconstructed in GNU format.

Here’s where llvm-ar departs from previous ar implementations:

Symbol Table

Since llvm-ar supports bitcode files. The symbol table it creates is in GNU format and includes both native and bitcode files.

Long Paths

Currently llvm-ar can read GNU and BSD long file names, but only writes archives with the GNU format.

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 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¶

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.

Print files to the standard output. 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.

Quickly append files to the end of the archive. 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[abu]

Replace or insert file members. The a, b, 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 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 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.

[i]

A synonym for the b option.

[o]

When extracting files, this option will cause llvm-ar to preserve the original modification times of the files it writes.

[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 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.

[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 macOS) 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 macOS 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.

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.

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.